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Who watches the watchmen? Regulation of the expression and activity of sirtuins
The FASEB Journal
Abstract
Sirtuins (SIRT1-7) are a family of nicotine adenine dinucleotide (NAD(+))-dependent enzymes that catalyze post-translational modifications of proteins. Together, they regulate crucial cellular functions and are traditionally associated with aging and longevity. Dysregulation of sirtuins plays an important role in major diseases, including cancer and metabolic, cardiac, and neurodegerative diseases. They are extensively regulated in response to a wide range of stimuli, including nutritional and metabolic challenges, inflammatory signals or hypoxic and oxidative stress. Each sirtuin is regulated individually in a tissue- and cell-specific manner. The control of sirtuin expression involves all the major points of regulation, including transcriptional and post-translational mechanisms and microRNAs. Collectively, these mechanisms control the protein levels, localization, and enzymatic activity of sirtuins. In many cases, the regulators of sirtuin expression are also their substrates, which lead to formation of intricate regulatory networks and extensive feedback loops. In this review, we highlight the mechanisms mediating the physiologic and pathologic regulation of sirtuin expression and activity. We also discuss the consequences of this regulation on sirtuin function and cellular physiology.-Buler, M., Andersson, U., Hakkola, J. Who watches the watchmen? Regulation of the expression and activity of sirtuins.
... Lysine acetylation is a reversible post-translational modification that is determined by the relative contributions of acetylases and deacetylases (Choudhary et al., 2014). Sirtuins (Sirt1-7) are NAD + -dependent class III deacetylases that are responsive to redox ratio and utilize NAD + during deacetylation of lysine and regulate a number of cellular metabolic processes including delayed senescence (Buler et al., 2016;Choudhary et al., 2014). The seven known sirtuins have distinct and yet overlapping subcellular distribution: Sirt1 is localized to the nucleus; Sirt2 is a cytosolic protein that senses cellular redox status to initiate mitochondrial responses; Sirt3, 4 and 5 modulate mitochondrial acetylation status; while Sirt6 and 7 are primarily nuclear proteins involved in histone acetylation and transcriptional regulation (Buler et al., 2016;Choudhary et al., 2014). ...
... Sirtuins (Sirt1-7) are NAD + -dependent class III deacetylases that are responsive to redox ratio and utilize NAD + during deacetylation of lysine and regulate a number of cellular metabolic processes including delayed senescence (Buler et al., 2016;Choudhary et al., 2014). The seven known sirtuins have distinct and yet overlapping subcellular distribution: Sirt1 is localized to the nucleus; Sirt2 is a cytosolic protein that senses cellular redox status to initiate mitochondrial responses; Sirt3, 4 and 5 modulate mitochondrial acetylation status; while Sirt6 and 7 are primarily nuclear proteins involved in histone acetylation and transcriptional regulation (Buler et al., 2016;Choudhary et al., 2014). As a metabolic cofactor, redox determinant, and co-substrate for sirtuins, NAD + availability is critical for cellular functions (Canto & Auwerx, 2011). ...
... Our multiomics analyses were initiated with a layered comparative evaluation of chromosomal access, transcripts and proteins because regulation of components of the ETC, TCA cycle regulatory enzymes, NAD biosynthesis, and sirtuin signaling has been suggested to occur at multiple levels (Buler et al., 2016). There was significant but not complete concordance across layers and models, that may be due to a number of factors that include tissue and context dependent responses (Buler et al., 2016). ...
Perturbed metabolism of ammonia, an endogenous cytotoxin, causes mitochondrial dysfunction, reduced NAD+ /NADH (redox) ratio, and postmitotic senescence. Sirtuins are NAD+ -dependent deacetylases that delay senescence. In multiomics analyses, NAD metabolism and sirtuin pathways are enriched during hyperammonemia. Consistently, NAD+ -dependent Sirtuin3 (Sirt3) expression and deacetylase activity were decreased, and protein acetylation was increased in human and murine skeletal muscle/myotubes. Global acetylomics and subcellular fractions from myotubes showed hyperammonemia-induced hyperacetylation of cellular signaling and mitochondrial proteins. We dissected the mechanisms and consequences of hyperammonemia-induced NAD metabolism by complementary genetic and chemical approaches. Hyperammonemia inhibited electron transport chain components, specifically complex I that oxidizes NADH to NAD+ , that resulted in lower redox ratio. Ammonia also caused mitochondrial oxidative dysfunction, lower mitochondrial NAD+ -sensor Sirt3, protein hyperacetylation, and postmitotic senescence. Mitochondrial-targeted Lactobacillus brevis NADH oxidase (MitoLbNOX), but not NAD+ precursor nicotinamide riboside, reversed ammonia-induced oxidative dysfunction, electron transport chain supercomplex disassembly, lower ATP and NAD+ content, protein hyperacetylation, Sirt3 dysfunction and postmitotic senescence in myotubes. Even though Sirt3 overexpression reversed ammonia-induced hyperacetylation, lower redox status or mitochondrial oxidative dysfunction were not reversed. These data show that acetylation is a consequence of, but is not the mechanism of, lower redox status or oxidative dysfunction during hyperammonemia. Targeting NADH oxidation is a potential approach to reverse and potentially prevent ammonia-induced postmitotic senescence in skeletal muscle. Since dysregulated ammonia metabolism occurs with aging, and NAD+ biosynthesis is reduced in sarcopenia, our studies provide a biochemical basis for cellular senescence and have relevance in multiple tissues.
... Regarding their functions, they catalyze post-translational modifications of proteins. All of them participate in the deacetylation of histone and non-histone substrates including transcriptional factors, enzymes, and other proteins [11,19]. However, some members, like SIRT4 and SIRT6, are also ADP-ribosyl transferases [19][20][21]. ...
... All of them participate in the deacetylation of histone and non-histone substrates including transcriptional factors, enzymes, and other proteins [11,19]. However, some members, like SIRT4 and SIRT6, are also ADP-ribosyl transferases [19][20][21]. The SIRT members are ubiquitously distributed in all subcellular compartments. ...
... The SIRT members are ubiquitously distributed in all subcellular compartments. Specifically, SIRT1, SIRT6, and SIRT7 are mainly located in the nucleus, while SIRT3, SIRT4, and SIRT5 are mitochondrial enzymes [16,19,22]. Noteworthy, SIRT2 is the only member of the family found predominantly in the cytoplasm with the additional ability to translocate to the nucleus and also found in the mitochondria [23]. ...
Sirtuin 2 (SIRT2) has been associated to aging and age-related pathologies. Specifically, an age-dependent accumulation of isoform 3 of SIRT2 in the CNS has been demonstrated; however, no study has addressed the behavioral or molecular consequences that this could have on aging. In the present study, we have designed an adeno-associated virus vector (AAV-CAG-Sirt2.3-eGFP) for the overexpression of SIRT2.3 in the hippocampus of 2 month-old SAMR1 and SAMP8 mice. Our results show that the specific overexpression of this isoform does not induce significant behavioral or molecular effects at short or long term in the control strain. Only a tendency towards a worsening in the performance in acquisition phase of the Morris Water Maze was found in SAMP8 mice, together with a significant increase in the pro-inflammatory cytokine Il-1β. These results suggest that the age-related increase of SIRT2.3 found in the brain is not responsible for induction or prevention of senescence. Nevertheless, in combination with other risk factors, it could contribute to the progression of age-related processes. Understanding the specific role of SIRT2 on aging and the underlying molecular mechanisms is essential to design new and more successful therapies for the treatment of age-related diseases.
... 6 Proteins with ADP-ribosyltransferase activity catalyze the transfer of adenosine diphosphate ribose (ADPribose) from NAD þ onto specific target proteins. 7 Sirtuins are also classified as class III histone deacetylases, and, according to phylogenetic analysis, are grouped into 4 main classes (I-IV) of protein deacetylases, which include the human isotypes as well as at least 1 more class containing enzymes found in archaea and bacteria (class U). 8 In this classification, SIRT1-SIRT3 belong to class I, SIRT4 to class II, SIRT5 to class III, and SIRT6 and SIRT7 to class IV. 1 Different sirtuins also have different subcellular localizations: SIRT1, SIRT6, and SIRT7 have nuclear localization, SIRT2 has mainly cytosolic localization but can also shuttle to the nucleus during mitosis, while SIRT3, SIRT4, and SIRT5 have mitochondrial localization. In addition, some isoforms of SIRT1 and SIRT5 have been found in the cytoplasm. ...
... 9 Of the 7 human sirtuins, SIRT1 is studied most widely. This sirtuin deacetylates target proteins, such as transcription factors and histones, 8 mainly those involved in the regulation of energy metabolism, stress, and inflammatory responses. 10 For example, activated SIRT1 upregulates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1a) by deacetylation, leading to an increase in mitochondrial biogenesis and, consequently, the expression of PGC-1a target genes linked to fatty acid oxidation pathways. ...
... SIRT1 is involved in the regulation of multiple essential cellular functions, such as mitochondrial biogenesis, glucose and lipid metabolism, DNA repair, apoptosis, stress resistance, and inflammation. 8,[42][43][44][45] Consequently, alterations in SIRT1 expression or function have been associated with several chronic conditions, including cancer, diabetes, cardiovascular disease, insulin resistance, and metabolic syndrome. 26,46-48 SIRT3 is a major regulator of mitochondrial function. ...
Context:
The sirtuins (SIRT1 to SIRT7) constitute a family of highly conserved nicotinamide adenine dinucleotide-dependent proteins. When activated, sirtuins control essential cellular processes to maintain metabolic homeostasis, while lack of expression of sirtuins has been related to chronic disease.
Objective:
The aim of this systematic review is to analyze the role of fat consumption as a modulator of human sirtuins.
Data sources:
This review was conducted according to PRISMA guidelines. Studies were identified by searches of the electronic databases PubMed/MEDLINE, Scopus, and Web of Science.
Study selection:
Randomized clinical trials assessing the effect of fatty acid consumption on sirtuin mRNA expression, sirtuin protein expression, or sirtuin protein activity were eligible for inclusion.
Data extraction:
Two authors screened and determined the quality of the studies; disagreements were resolved by the third author. All authors compared the compiled data.
Results:
Seven clinical studies with 3 different types of interventions involving healthy and nonhealthy participants were selected. Only SIRT1 and SIRT3 were evaluated. Overall, the evidence from clinical studies to date is insufficient to understand how lipid consumption modulates sirtuins in humans. The best-characterized mechanism highlights oleic acid as a natural activator of SIRT1.
Conclusion:
These results draw attention to a new field of interest in nutrition science. The possible activation of sirtuins by dietary fat manipulation may represent an important nutritional strategy for management of chronic and metabolic disease.
Systematic review registration:
PROSPERO registration number CRD42018114456.
... Nevertheless, the adaptive response orchestrated at molecular level to cope with glycation injury in female reproductive cells and ovaries has been poorly investigated. Glycation-related oxidative challenge may result in altered activity of sirtuins, NAD + -dependent enzymes with deacetylase and/or mono-ADP-ribosyltransferase activity [21,22]. SIRT1, one of the seven members of the mammalian sirtuin family, plays a key role during different stages of folliculogenesis by regulating energy homoeostasis, mitochondrial biogenesis, chromatin remodelling and protection against oxidative stress [23,24]. ...
... This points to the notion that MG perturbed ovarian homeostasis by generating a condition of redox imbalance. Indeed increased expression of sirtuins is considered an adaptive response to mild oxidative stress, whereas severe oxidant conditions determined posttranslational modifications resulting in sirtuin degradation [21]. Previous studies by our group have reported that SIRT1 mRNA and protein increase in oocytes, granulosa cells and ovary in response to pro-oxidant stimuli. ...
... In these systems changes in SIRT1 expression have been linked to the mRNA binding protein HuR and the micro-RNA miR-132 [35,40]. Since oxidative conditions are known to reduce the interaction of SIRT1 with its enzymatic inhibitor DBC1, it is likely that the increased SIRT1 expression observed in this study is associated with increased SIRT1 activity [21]. ...
Methylglyoxal (MG), a highly reactive dicarbonyl derived from metabolic processes, is the most powerful precursor of advanced glycation end products (AGEs). Glycative stress has been recently associated with ovarian dysfunctions in aging and PCOS syndrome. We have investigated the role of the NAD ⁺ -dependent Class III deacetylase SIRT1 in the adaptive response to MG in mouse oocytes and ovary. In mouse oocytes, MG induced up-expression of glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) genes, components of the main MG detoxification system, whereas inhibition of SIRT1 by Ex527 or sirtinol reduced this response. In addition, the inhibition of SIRT1 worsened the effects of MG on oocyte maturation rates, while SIRT1 activation by resveratrol counteracted MG insult. Ovaries from female mice receiving 100 mg/kg MG by gastric administration for 28 days (MG mice) exhibited increased levels of SIRT1 along with over-expression of catalase, superoxide dismutase 2, SIRT3, PGC1α and mtTFA. Similar levels of MG-derived AGEs were observed in the ovaries from MG and control groups, along with enhanced protein expression of glyoxalase 1 in MG mice. Oocytes ovulated by MG mice exhibited atypical meiotic spindles, a condition predisposing to embryo aneuploidy. Our results from mouse oocytes revealed for the first time that SIRT1 could modulate MG scavenging by promoting expression of glyoxalases. The finding that up-regulation of glyoxalase 1 is associated with that of components of a SIRT1 functional network in the ovaries of MG mice provides strong evidence that SIRT1 participates in the response to methylglyoxal-dependent glycative stress in the female gonad.
... HP and I/V exposure led to a significant loss of SIRT1 expression in MMA-uria cells, while control cells were able to maintain SIRT1 levels. SIRT1 plays an important role in the governance of lipid and glucose turn over and nutrient deprivation induces SIRT1 activation 38,39 . Besides other modifiers, SIRT1 can be down-regulated by activation of autophagy, a pathway which is highly active in our system 38 . ...
... SIRT1 plays an important role in the governance of lipid and glucose turn over and nutrient deprivation induces SIRT1 activation 38,39 . Besides other modifiers, SIRT1 can be down-regulated by activation of autophagy, a pathway which is highly active in our system 38 . Increased mitochondrial fission has been associated with increased acylation of sterol regulatory element-binding protein 1 (SREBP1) suppressing SIRT1 signaling 40 . ...
Methylmalonic aciduria (MMA-uria) is caused by deficiency of the mitochondrial enzyme methylmalonyl-CoA mutase (MUT). MUT deficiency hampers energy generation from specific amino acids, odd-chain fatty acids and cholesterol. Chronic kidney disease (CKD) is a well-known long-term complication. We exposed human renal epithelial cells from healthy controls and MMA-uria patients to different culture conditions (normal treatment (NT), high protein (HP) and isoleucine/valine (I/V)) to test the effect of metabolic stressors on renal mitochondrial energy metabolism. Creatinine levels were increased and antioxidant stress defense was severely comprised in MMA-uria cells. Alterations in mitochondrial homeostasis were observed. Changes in tricarboxylic acid cycle metabolites and impaired energy generation from fatty acid oxidation were detected. Methylcitrate as potentially toxic, disease-specific metabolite was increased by HP and I/V load. Mitophagy was disabled in MMA-uria cells, while autophagy was highly active particularly under HP and I/V conditions. Mitochondrial dynamics were shifted towards fission. Sirtuin1, a stress-resistance protein, was down-regulated by HP and I/V exposure in MMA-uria cells. Taken together, both interventions aggravated metabolic fingerprints observed in MMA-uria cells at baseline. The results point to protein toxicity in MMA-uria and lead to a better understanding, how the accumulating, potentially toxic organic acids might trigger CKD.
... Dysregulation of SIRTs plays an important role in major diseases, including cancer and metabolic, cardiac and neurodegenerative diseases. 35 Sulphated metabolites accumulate in the gut following oral ingestion of resveratrol where they promote the growth of beneficial bacteria such as Lactobacillus reuteri and up-regulate the expression of tight junction and mucin-related proteins. 36 Perturbation of the gut microbiome by Rifaximin, an antibiotic which does not cross the gut-blood barrier, has a profound effect on the expression of reproductive and brain TRH and TRH-like peptides. ...
... HPLC and RIA procedures, peak identification, and quantitation by co-chromatography with synthetic TRH and TRH-like peptides, relative potency analysis of multiple antibodies to TRH and TRHlike peptides, and mass spectrometry for comparing peak areas have been previously reported in detail. [32][33][34][35][36][37][38][39][40][41][42][43][44][45] Briefly, after boiling, tissues were dried, re-extracted with methanol, dried and defatted by water-ethyl ether partitioning. Dried samples were dissolved in 0.1%trifluroacetic acid (TFA) and loaded onto reverse phaseC18 Sep-Pak cartridges (Water). ...
Introduction:
Resveratrol and related polyphenols have therapeutic effects ranging from treatment of depression, Alzheimer's and Parkinson's disease, obesity, diabetes, neurodegeneration and ageing. TRH and TRH-like peptides, with the structure pGlu-X-Pro-NH2 , where 'X can be any amino acid reside, have reproductive, caloric-restriction-like, anti-ageing, pancreatic-β cell-enhancing, cardiovascular and neuroprotective effects. We hypothesize that TRH and TRH-like peptides are mediators of the therapeutic actions of the resveratrol derivative pterostilbene (PT).
Methods:
Sixteen young adult male Sprague-Dawley rats were divided into four groups. Control group remained on ad libitum chow and water for 10 days. Acute group received ad libitum chow and water for 9 days and then 0.9 g PT/250 g rat chow for 24 h. Chronic animals received PT in chow for 10 days. Withdrawal rats received PT chow for 8 days and then normal chow for 2 days. TRH and TRH-like peptide levels were measured in medulla oblongata (MED), frontal cortex (FCX), hypothalamus (HY), amygdala (AY), hippocampus (HC), piriform cortex (PIR), nucleus accumbens (NA), entorhinal cortex (ENT), striatum (STR), cerebellum (CBL), anterior cingulate (ACNG), posterior cingulate (PCNG), prostate (PR), liver (L), testis (T), heart (H), pancreas (PAN), adrenals (AD) and epididymis (EP).
Results:
Significant changes in the levels of TRH and TRH-like peptides occurred throughout the brain and peripheral tissues in response to PT treatment.
Conclusion:
The high responsiveness of PIR, CBL, HY, STR, PCNG, MED, FCX, NA, ACNG and AY in brain and EP and PR is consistent with TRH and TRH-like peptides participating in the therapeutic effects of PT.
... Par exemple, SIRT1 peut augmenter sa propre expression en désacétylant FOXO1 et en augmentant sa transactivation (Daitoku, et al., 2004). SIRT1 peut également désacétyler p53 et BMAL1 et augmenter son expression, ce qui constitue une boucle de régulation positive (Buler, et al., 2016). Enfin, il a été montré que le stress RE pouvait augmenter l'expression de SIRT1 par un mécanisme impliquant la voie PI3K-AKT-GSK3β même si le mécanisme n'a pas été clairement identifié (Koga, et al., 2015). ...
... Carcinome cervical ↑ Augmente l'expression de SIRT1 en réponse à la restriction calorique NFκB Cancer rénal ↑ Protège de l'apoptose en réponse à l'inflammation (Katto, et al., 2013) Nkx2.5 Cardiomyocytes ↑ Protège de l'apoptose en réponse à un traitement à la Doxorubicine (Zheng, et al., 2013) p53 Cellules d'estomac de singe ↑ Protège de l'apoptose et des dommages à l'ADN (Chen, et al., 2005) PPARα/β/σ Hépatocytes ↑ Augmente l'expression de SIRT1 favorisant les effets bénéfiques de la restriction calorique sur la longévité (Hayashida, et al., 2010;Okazaki, et al., 2010) PPARγ (Buler, et al., 2016) ( Figure 18). Introduction . ...
Le réticulum endoplasmique rugueux (RE) assure la synthèse et le repliement des protéines de la voie de sécrétion. Les perturbations du fonctionnment du RE entraînent l’accumulation de protéines mal repliées, une condition appelée stress RE. En réponse au stress RE, un mécanisme adaptatif connu sous le terme Unfolded Protein Response (UPR) est activé afin de rétablir l’homéostasie du RE. Néanmoins, si le stress RE est sévère ou prolongé et que l’homéostasie du RE ne peut pas être rétablie, l’hyperactivation de l’UPR entraîne l’apoptose des cellules défectueuses. Dans le coeur, il a été montré que le stress RE est impliqué dans le développement de la majorité des pathologies cardiaques et il est aujourd’hui admis qu’un stress RE modéré est bénéfique en permettant de restaurer l’homéostasie du RE et en favorisant la survie du cardiomyocyte, tandis qu’un stress RE sévère ou chronique est délétère car il provoque l’élimination des cardiomyocytes par apoptose, ce qui contribue au développement des pathologies cardiaques. Le but des recherches actuelles sur le stress RE en physiopathologie cardiaque n’est donc pas d’inhiber complètement la réponse au stress RE mais plutôt de la moduler afin de permettre l’activation des réponses adaptatives tout en limitant l’apoptose délétère des cardiomyocytes. Des études menées récemment dans notre équipe ont montré que la Sirtuine 1 (SIRT1), une désacétylase dépendante du NAD+, protège le coeur du stress RE sévère en diminuant l’apoptose. Le but de mes recherches a donc été d’identifier de nouvelles molécules et voies de signalisation activatrices de SIRT1 pour permettre de protéger le coeur des dommages induits par le stress RE sévère. Nous avons mis en évidence que l’acide férulique, le ptérostilbène et le tyrosol, trois composés phénoliques naturels présents dans notre alimentation, protègent le coeur du stress RE sévère en activant SIRT1. De plus, nous avons montré que l’inhibition de la kinase ATM par le KU-60019 diminue l’apoptose des cardiomyocytes induite par un stress RE sévère en diminuant la phosphorylation de DBC1, ce qui diminue son interaction avec SIRT1, et favorise ainsi l’activation de cette désacétylase. Un fois activée, SIRT1 regule la voie PERK de la réponse UPR via la désacétylation du facteur eIF2α. Ces résultats suggèrent que l’activation de SIRT1 via l’acide férulique, le ptérostilbène ou le tyrosol, ou via la modulation de son interaction avec la protéine inhibitrice DBC1, pourrait constituer une approche thérapeutique complémentaire pour limiter le développement des pathologies cardiaques associées au stress RE.
... Aging is associated with changes in human energy and cell metabolism, which may result in metabolic dysfunction (e.g., diabetes mellitus), increased inflammation or the accumulation of senescent cells [1,2]. One modulator of metabolic pathways and cellular stress response are sirtuins. ...
... Sirtuins are a family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases of which seven have been identified in mammals (SIRT1-SIRT7). While SIRT1, SIRT6 and SIRT7 are primarily localized within the nucleus, SIRT3-SIRT5 are found in the mitochondria and SIRT2 in the cytosol [1]. At the molecular level, the main function of sirtuins is the modification of proteins at their lysine residues [2]. ...
Sirtuins are nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases that regulate numerous pathways such as mitochondrial energy metabolism in the human body. Lower levels of these enzymes were linked to diseases such as diabetes mellitus and were also described as a result of aging. Sirtuins were previously shown to be under the control of exercise and diet, which are modifiable lifestyle factors. In this study, we analyzed SIRT1, SIRT3 and SIRT5 in blood from a subset of healthy elderly participants who took part in a 12-week randomized, controlled trial during which they performed, twice-weekly, resistance and aerobic training only (EX), the exercise routine combined with dietary counseling in accordance with the guidelines of the German Nutrition Society (EXDC), the exercise routine combined with intake of 2 g/day oil from Calanus finmarchicus (EXCO), or received no treatment and served as the control group (CON). In all study groups performing exercise, a significant increase in activities of SIRT1 (EX: +0.15 U/mg (+0.56/−[−0.16]), EXDC: +0.25 U/mg (+0.52/−0.06), EXCO: +0.40 U/mg (+0.88/−[−0.12])) and SIRT3 (EX: +0.80 U/mg (+3.18/−0.05), EXDC: 0.95 U/mg (+3.88/−0.55), EXCO: 1.60 U/mg (+2.85/−0.70)) was detected. Group comparisons revealed that differences in SIRT1 activity in EXCO and EXDC differed significantly from CON (CON vs. EXCO, p = 0.003; CON vs. EXDC, p = 0.010). For SIRT3, increases in all three intervention groups were significantly different from CON (CON vs. EX, p = 0.007; CON vs. EXDC, p < 0.001, CON vs. EXCO, p = 0.004). In contrast, differences in SIRT5-activities were less pronounced. Altogether, the analyses showed that the activity of SIRT1 and SIRT3 increased in response to the exercise intervention and that this increase may potentially be enhanced by additional dietary modifications.
... In contrast, SIRT3, SIRT4 and SIRT5 localize to the mitochondria (Houtkooper, Pirinen, & Auwerx, 2012). SIRTUINS are widely expressed and each member is regulated in a tissue-and cell-specific manner (Buler, Andersson, & Hakkola, 2016). Of note, SIRT5 might have no or very weak deacetylase activity and rather removes acyl groups (Du et al., 2011;Sabari et al., 2017). ...
... Most HDACs interact with hundreds of proteins, which is likely to affect the activity, specificity, stability and recruitment of individual HDAC members ( Joshi et al., 2013) and several deacetylases are part of multiprotein transcriptional co-repressor complexes (Kelly & Cowley, 2013;Millard et al., 2017). Moreover, HDACs are also the target of several PTMs that are likely to control their activity (Buler et al., 2016;Segr e & Chiocca, 2011). Thus, the regulation of the composition of the various HDAC-containing multiprotein complexes as well as the interplay of various PTMs on HDACs offers multiple levels to fine-tune target gene loci recruitment and activity of HDAC members in different mammalian tissues, cell types and cell lineages. ...
Natural killer (NK) cells are innate immune cells critically involved in the control of cancer. Their important role in cancer immunity reflects the ability of NK cells to recognize malignant cells through an array of germline-encoded receptors expressed on their surface, enabling NK cells to detect and rapidly kill tumor cells through targeted cytotoxicity. In addition to their cytotoxic activity, NK cells fulfill a fundamental and often underappreciated role in the local orchestration of cancer immunity through their ability to communicate with innate and adaptive immune cells within the tumor microenvironment (TME), which is achieved through the secretion of multiple chemokines, cytokines, and growth factors. Within tumor tissue, NK cells regulate the recruitment, survival and functional activity of various immune cells including monocytes, granulocytes, dendritic cells and T cells, thereby shaping intratumoral immune cell composition and functionality. Emerging evidence further suggest a role of NK cells in the regulation of stromal cells within the TME. Here, we discuss key aspects of NK cell communication with other intratumoral cell types and its role for cancer immunity. Strategies aimed at boosting anti-cancer immunity by enhancing NK cell communication and functionality within tumor tissue provide attractive new ways for treatment of cancer patients.
... Of note, the recognized top TFBSs for human SIRT1 (C/EBPα, MYOD and MYC) and SIRT3 (AML1, CREB, HTF, NRF2, PBX1, and TBP) [47] were also retrieved at the predicted promoter regions of GSB sirt1 and sirt3. Furthermore, in different human and rodent metabolic situations, it has been proven that SIRT1 deacetylase activity modulates the function of most transcriptional regulators (e.g., NF-κB, p53, FOXO1, PPARγ, CHREBP, HIF1 and C/EBP-α) forming negative feedback loops [48], which probably also occurs in fish. ...
... This metabolic feature was illustrated herein by increased expression in young fish of markers of fatty acid β-oxidation (cpt1a) and muscle respiration uncoupling (ucp3), which evolved to protect mitochondria against oxidative stress in a highly oxidative cellular milieu [74,75]. Certainly, SIRT1 acts as a major repressor of UCP3 in muscle tissues of rodents [76], also inhibiting the progression of different antioxidant responses mediated by NF-κB and NRF2 [48]. Conversely, the downregulation of SIRT1 enhances the myogenic gene program to adjust it to energetic demands driven by changing growth, nutrient availability or increased muscle activity [77]. ...
Background:
Sirtuins (SIRTs) are master regulators of metabolism, and their expression patterns in gilthead sea bream (GSB) reveal different tissue metabolic capabilities and changes in energy status. Since little is known about their transcriptional regulation, the aim of this work was to study for the first time in fish the effect of age and season on sirt gene expression, correlating expression patterns with local changes in DNA methylation in liver and white skeletal muscle (WSM).
Methods:
Gene organization of the seven sirts was analyzed by BLAT searches in the IATS-CSIC genomic database (www.nutrigroup-iats.org/seabreamdb/). The presence of CpG islands (CGIs) was mapped by means of MethPrimer software. DNA methylation analyses were performed by bisulfite pyrosequencing. A PCR array was designed for the simultaneous gene expression profiling of sirts and related markers (cs, cpt1a, pgc1α, ucp1, and ucp3) in the liver and WSM of one- and three-year-old fish during winter and summer.
Results:
The occurrence of CGIs was evidenced in the sirt1 and sirt3 promoters. This latter CGI remained hypomethylated regardless of tissue, age and season. Conversely, DNA methylation of sirt1 at certain CpG positions within the promoter varied with age and season in the WSM. Among them, changes at several SP1 binding sites were negatively correlated with the decrease in sirt1 expression in summer and in younger fish. Changes in sirt1 regulation match well with variations in feed intake and energy metabolism, as judged by the concurrent changes in the analyzed markers. This was supported by discriminant analyses, which identified sirt1 as a highly responsive element to age- and season-mediated changes in energy metabolism in WSM.
Conclusions:
The gene organization of SIRTs is highly conserved in vertebrates. GSB sirt family members have CGI- and non-CGI promoters, and the presence of CGIs at the sirt1 promoter agrees with its ubiquitous expression. Gene expression analyses support that sirts, especially sirt1, are reliable markers of age- and season-dependent changes in energy metabolism. Correlation analyses suggest the involvement of DNA methylation in the regulation of sirt1 expression, but the low methylation levels suggest the contribution of other putative mechanisms in the transcriptional regulation of sirt1.
... However, the exact SIRT2-inducing factors in HCC livers remain unidentified. SIRTs are extensively regulated in response to a wide range of stimuli, including nutritional and metabolic challenges, inflammatory signals or hypoxic and oxidative stress [21]. SIRT2 expression is shown to be dependent on p53 due to the binding of p53 to the SIRT2 promoter [22]. ...
... SIRT2 might activate Erk1/2 and p38 signaling to both and promote the tumoricidal effect of NK cells. SIRT2 can act as an ADP-ribosyltransferase, deacetylase, and demyristoylase [21]. These enzymic activities might result in MAPK activation. ...
Hepatocellular carcinoma (HCC) is the third most lethal cancer in the world. Natural killer (NK) cell-mediated immunity is crucial for tumor surveillance and therapy. Characterization of the regulatory mechanisms of NK cell function is important for developing novel immunotherapies against HCC. In this study, we used a chemical-induced mouse HCC model to identify the upregulation of Sirtuin2 (SIRT2) in liver NK cells. In particular, SIRT2 was predominantly expressed in liver CD94⁺ NK cells. The HCC liver microenvironment induced SIRT2 expression in NK cells. In addition, overexpression of exogenous SIRT2 significantly upregulated the production of cytokines and cytotoxic mediators in activated NK cells. Consistently, SIRT2-overexpressing NK cells showed a stronger tumoricidal effect on hepatoma cells. Moreover, SIRT2 remarkably promoted the phosphorylation of Extracellular-signal-regulated kinase 1/2 (Erk1/2) and p38 Mitogen-activated protein kinases (MAPK) in activated NK cells. SIRT2 knockdown in liver CD94⁺ NK cells impaired their cytotoxic effect on hepatoma cells. Our study indicates that SIRT2 enhances the tumoricidal activity of liver NK cells in HCC.
... Through the hydrolysis of NAD + and the concurrent transfer of the acetyl group from the acetylated lysine residue of target proteins to the 2 ′ -OH position of adenosine diphosphate (ADP)-ribose, SIRT1 catalyzes the deacetylation process, resulting in the formation of nicotinamide and 2 ′ -O-acetyl-ADP-ribose. The activity of SIRT1 is modulated by several factors including the NAD + /NADH ratio, interactions with binding partners, and post-translational modifications [44]. ...
Chronic kidney disease (CKD) is a major global health concern. Renal fibrosis, a prevalent outcome regardless of the initial cause, ultimately leads to end-stage renal disease. Glomerulosclerosis and renal interstitial fibrosis are the primary pathological features. Preventing and slowing renal fibrosis are considered effective strategies for delaying CKD progression. However, effective treatments are lacking. Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase belonging to class III histone deacetylases, is implicated in the physiological regulation and protection of the kidney and is susceptible to a diverse array of pathological influences, as demonstrated in previous studies. Interestingly, controversial conclusions have emerged as research has progressed. This review provides a comprehensive summary of the current understanding and advancements in the field; specifically, the biological roles and mechanisms of SIRT1 in regulating renal fibrosis progression. These include aspects such as lipid metabolism, epithelial-mesenchymal transition, oxidative stress, aging, inflammation, and autophagy. This manuscript explores the potential of SIRT1 as a therapeutic target for renal fibrosis and offers new perspectives on treatment approaches and prognostic assessments.
... To our knowledge, it is unknown whether alteration of SIRT1 protein expression in the liver or kidney cells could lead to mitochondrial malfunction. In many cases, SIRT expressions are affected by the availability of substrates, which may also involve an intricate regulatory network and extensive feedback loop [60]. In this study, we showed that BZD9L1 modulates mitochondrial response toward oxidative stress in human-derived kidney cells by regulating SIRT1 and SIRT3 protein levels, which may then impact secondary mechanisms. ...
Growing evidence has highlighted that mitochondrial dysfunction contributes to drug-induced toxicities and leads to drug attrition and post-market withdrawals. The acetylation or deacetylation of mitochondrial proteins can affect mitochondrial functions as the cells adapt to various cellular stresses and other metabolic challenges. SIRTs act as critical deacetylases in modulating mitochondrial function in response to drug toxicity, oxidative stress, reactive oxygen species (ROS), and energy metabolism. We previously showed that a recently characterised SIRT inhibitor (BZD9L1) is non-toxic in rodents in a short-term toxicity evaluation. However, the impact of BZD9L1 on mito-chondrial function is unknown. This work aims to determine the effects of BZD9L1 on mitochondrial function in human normal liver and kidney-derived cell lines using the Agilent Seahorse Cell Mito Stress Test to complement our short-term toxicity evaluations in vivo. The Mito Stress assay revealed that BZD9L1 could potentially trigger oxidative stress by inducing ROS, which promotes proton leak and reduces coupling efficiency in liver-derived THLE cells. However, the same was not observed in human kidney-derived HEK293 cells. Interestingly, BZD9L1 had no impact on SIRT3 protein expression in both cell lines but affected SOD2 and its acetylated form at 72 h in THLE cells, indicating that BZD9L1 exerted its effect through SIRT3 activity rather than protein expression. In contrast, BZD9L1 reduced SIRT1 protein expression and impacted the p53 protein differently in both cell lines. Although BZD9L1 did not affect the spare respiratory capacity in vitro, these findings call for further validation of mitochondrial function through assessment of other mitochondrial parameters to evaluate the safety of BZD9L1.
... In mammals, the plethora of SIRT2 substrates identified reflect cell and tissue-specific functions of SIRT2. Regulation of SIRT2 expression is complex and exists at multiple levels, including at the translational level (Buler et al., 2016;Li et al., 2007;Maxwell et al., 2011). ...
We previously demonstrated that Aedes aegypti pyruvate kinase (AaPK) plays a key role in the regulation of both carbon and nitrogen metabolism in mosquitoes. To further elucidate whether AaPK can be post-translationally regulated by Ae. aegypti sirtuin 2 (AaSirt2), an NAD⁺-dependent deacetylase that catalyzes the removal of acetyl groups from acetylated lysine residues, we conducted a series of analysis in non-starved and starved female mosquitoes. Transcriptional and protein profiles of AaSirt2, analyzed by qPCR and western blots, indicated that the AaSirt2 is differentially modulated in response to sugar or blood feeding in mosquito tissues dissected at different times during the first gonotrophic cycle. We also found that AaSirt2 is localized in both cytosolic and mitochondrial cellular compartments of fat body and thorax. Multiple lysine-acetylated proteins were detected by western blotting in both cellular compartments. Furthermore, western blotting of immunoprecipitated proteins provided evidence that AaPK is lysine-acetylated and bound with AaSirt2 in the cytosolic fractions of fat body and thorax from non-starved and starved females. In correlation with these results, we also discovered that RNAi-mediated knockdown of AaSirt2 in the fat body of starved females significantly decreased AaPK protein abundance. Notably, survivorship of AaSirt2-deficient females maintained under four different nutritional regimens was not significantly affected. Taken together, our data reveal that AaPK is post-translationally regulated by AaSirt2.
... Although our data align with these results, the association between SIRT1 and placental developmental insufficiency causing FGR remains unclear. The downstream targets of SIRT1 and many other related genes and signaling pathways have been investigated [35,36]. Among these targets, the serine/threonine kinase LKB1 (liver kinase B1; also known as serine/threonine kinase 11 [STK11]) tumor suppressor gene has been reported to be negatively regulated by SIRT1 in osteosarcoma and endothelial cells [37,38], and its expression is negatively correlated with placental weight [39]. ...
Objective
Insufficient placental development causes various obstetric complications, including fetal growth restriction (FGR). The Sirtuin 1 (SIRT1) and insulin-like 4 (INSL4) protein-coding genes have been demonstrated to play an important role in placental development. However, no treatment for FGR is available due to placental dysfunction. Therefore, this study aimed to examine the potential of the SIRT1–INSL4 axis as a treatment candidate for FGR caused by insufficient placental development.
Methods
Twenty patients were enrolled, including 10 with FGR and 10 full-term controls. FGR and control placental samples were collected. Quantitative real-time polymerase chain reaction, immunohistochemical analysis, and western blotting were used to analyze INSL4 and SIRT1 expression. An in-vitro loss-of-function approach with the human choriocarcinoma cell line BeWo was applied for functional analyses of SIRT1 in placental development. BeWo cells were differentiated into syncytiotrophoblasts by silencing SIRT1 using small interfering RNA. SIRT1 activator was added during differentiation of SIRT1-knockdown BeWo cells into syncytiotrophoblasts.
Results
The FGR samples had lower INSL4 and SIRT1 mRNA and protein expression levels than the control samples. Immunohistochemistry showed that both SIRT1 and INSL4 were expressed mainly in syncytiotrophoblasts. In-vitro analyses showed that SIRT1 knockdown decreased INSL4 expression; however, SIRT1 activator restored SIRT1 expression in SIRT1-silenced BeWo cells.
Conclusions
SIRT1 and INSL4 are downregulated in the placenta of FGR, and INSL4 is regulated by SIRT1. These findings indicate that the SIRT1–INSL4 axis may be a potential therapeutic target for FGR.
... Crosstalk between ROS production and SIRT1 activity plays a crucial role in the regulation of the aging process [170]. A variety of miRNAs regulate SIRT1 expression [171]. For instance, miR-34a is known to target SIRT1 and promote cellular senescence in different tissues [172,173]. ...
Aging is associated with the accumulation of damaged and misfolded proteins through a decline in the protein homeostasis (proteostasis) machinery, leading to various age-associated protein misfolding diseases such as Huntington’s or Parkinson’s. The efficiency of cellular stress response pathways also weakens with age, further contributing to the failure to maintain proteostasis. MicroRNAs (miRNAs or miRs) are a class of small, non-coding RNAs (ncRNAs) that bind target messenger RNAs at their 3′UTR, resulting in the post-transcriptional repression of gene expression. From the discovery of aging roles for lin-4 in C. elegans, the role of numerous miRNAs in controlling the aging process has been uncovered in different organisms. Recent studies have also shown that miRNAs regulate different components of proteostasis machinery as well as cellular response pathways to proteotoxic stress, some of which are very important during aging or in age-related pathologies. Here, we present a review of these findings, highlighting the role of individual miRNAs in age-associated protein folding and degradation across different organisms. We also broadly summarize the relationships between miRNAs and organelle-specific stress response pathways during aging and in various age-associated diseases.
... 35,36 Additionally, the localization and subcellular shuttling of SIRTs depend on different kinds of cell types and cell cycle oscillation. 37 For example, SIRT1 could be primarily located in the cytosol in some subsets of neurons, as well as expressed in both nucleus and cytosol in ependymal cells. 30 Moreover, SIRT2 is in the cytosol during most phases of cell cycle, while SIRT2 is expressed in nucleus and associates with chromatin and deacetylates the histone H4K16 during G2/M transition and mitosis. ...
Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.
... Interestingly, p66Shc is negatively regulated by sirtuin1 (SIRT1) [200]. SIRT1 belongs to the family of nicotine adenine dinucleotide (NAD+)-dependent histone deacetylase proteins, enzymes that catalyze post-translational modifications of many proteins [201]. SIRT1 acts on multiple targets, such as p53, FOXO3, and eNOS, and exhibits diverse biological activities, including negative regulation of oxidative stress (antioxidant properties) [197]. ...
Hydrogen sulfide (H 2 S) has been known for years as a poisoning gas and until recently evoked mostly negative associations. However, the discovery of its gasotransmitter functions suggested its contribution to various physiological and pathological processes. Although H 2 S has been found to exert cytoprotective effects through modulation of antioxidant, anti-inflammatory, anti-apoptotic, and pro-angiogenic responses in a variety of conditions, its role in the pathophysiology of skeletal muscles has not been broadly elucidated so far. The classical example of muscle-related disorders is Duchenne muscular dystrophy (DMD), the most common and severe type of muscular dystrophy. Mutations in the DMD gene that encodes dystrophin, a cytoskeletal protein that protects muscle fibers from contraction-induced damage, lead to prominent dysfunctions in the structure and functions of the skeletal muscle. However, the main cause of death is associated with cardiorespiratory failure, and DMD remains an incurable disease. Taking into account a wide range of physiological functions of H 2 S and recent literature data on its possible protective role in DMD, we focused on the description of the ‘old’ and ‘new’ functions of H 2 S, especially in muscle pathophysiology. Although the number of studies showing its essential regulatory action in dystrophic muscles is still limited, we propose that H 2 S-based therapy has the potential to attenuate the progression of DMD and other muscle-related disorders.
... Sumoylation increases sirt1 activity while the removal of this modification (i.e., desumoylation) in response to oxidative stress inactivates sirt1 and promotes cell apoptosis. [72] Yet another post-translational means of regulating sirtuin activities is through the formation of complexes of sirtuins with regulatory proteins. For instance, the complex of sirt1 with AROS (Active Regulator of Sirt1) leads to the activation of sirt1 and the suppression of p53 with the overall effect of reducing cell apoptosis in response to DNA damage. ...
The sirtuins constitute a family of proteins with broad enzymatic activities that have an absolute requirement for nicotinamide adenine dinucleotide (NAD+) as a cosubstrate. Evidence has been mounting over the past 15 years or so that implicates the sirtuins in a vast array of critical cellular functions. In addition to transcription silencing and DNA repair, these functions include the regulation of ion channels, neuronal functions, cell growth, circadian rhythm, inflammatory response, mitochondrial biogenesis, insulin secretion, fat oxidation, and glucose metabolism. The sirtuins are critical for maintaining mitochondrial health, energy homeostasis, and redox balance. The sirtuins are widely believed to be behind the extension of lifespan brought about by calorie restriction and fasting. Changes in sirtuins activities have been linked to most age-related pathologies including cardiovascular disease, cancer, and Alzheimer's disease (AD). NAD+ is familiar to students of biological chemistry as an enzyme cofactor whose presence is essential for the progress of hundreds of vital biochemical reactions. This compound is present in virtually all living organisms. Simply put, without NAD+, life as we know it would not exist. The progress of these reactions requires the cleavage of NAD+, whose intracellular levels are known to decline steadily with age. This decline and its negative impact on the activities of these enzymes and on metabolism in general are implicated in the development of metabolic and age-linked diseases. Therefore, maintaining high intracellular NAD+ levels throughout life may not only extend the lifespan but is likely to extend the health span as well. In this paper I review how the intracellular pool of NAD+ is maintained and summarize the functions and regulation of sirtuins activities.
... SIRT1 is the founding and most well-studied member of the class III histone deacetylase family of enzymes that are dependent on nicotinamide adenine dinucleotide (NAD + ) for their activity [23]. The control of SIRT1 expression involves all the major points of regulation, including transcriptional and post-translational mechanisms and microRNAs [24]. SIRT1 is a stress-responsive enzyme that orchestrates cellular adaptations by altering the acetylome. ...
Purpose
Although oncological advances have improved survival rates of female cancer patients, they often suffer a reduced fertility due to treatment side effects. In the present study, we evaluated the potential fertoprotective effects of the specific inhibitor of SIRT1, EX-527, on the gonadotoxic action exerted by cyclophosphamide (CPM) on loss of primordial follicles (PFs).
Methods
The effects of the CPM metabolite phosphoramide mustard (PM) on follicle activation, growth and viability and the protective action of EX-527 against PM effects were evaluated on bovine ovarian cortical strips in vitro cultured for 1 or 6 days. To understand whether PFs exposed to PM plus EX-527 were able to activate and grow to the secondary stage after suspension of the treatment, strips cultured for 3 days in PM plus EX-527 for 3 days were transferred to plain medium until day 6. Follicle growth and health were evaluated through histology and viability assay at a confocal microscope. In order to investigate the molecular pathways underlying the ovarian response to PM in the presence of EX-527, we analysed the protein level of SIRT1, HuR, PARP1 and SOD2 after 1 day of in vitro culture.
Results
We found that (1) PM, the main CPM active metabolite, promotes PF activation; (2) the ovarian stress response induced by PM includes a SIRT1-dependent pathway; and (3) EX-527 reduces PF activation and growth induced by PM.
Conclusion
SIRT1 can represent a candidate molecule to be targeted to protect ovarian follicles from alkylating agents and EX-527 could represent a potential fertoprotective agent for cancer patients.
... Sirtuins are a subject of increasing attention due to their protective roles in various pathophysiological processes, including aging, neurodegeneration, obesity, heart disease, inflammation and cancer [6]. These class III NAD + -dependent histone/protein deacetylases include seven subtypes in mammals; among them are SIRT1 and SIRT3, which have the strongest deacetylase activity. ...
The activity of sirtuin 1 (SIRT1), a class III histone deacetylase with a critical role in several biological functions, decreases with age and its deficiency is associated with many inflammatory and age-related diseases. It also regulates the chronic immune activation and viral latency during an HIV infection. The life-span and particularly the health span of HIV patients are substantially shortened; however, the participation of SIRT1 in these effects is not clear. We performed a prospective cross-sectional monocentric study that included 70 HIV-infected patients and 43 BMI-, age- and sex-matched uninfected individuals. We found that in the PBMCs of the HIV patients, SIRT1 mRNA levels were significantly lower (p < 0.0001). This decrease, which was corroborated at the protein level, occurred irrespectively of the antiretroviral regimen these patients received and was not significantly related to the general, HIV-related or comorbidity-related parameters. The levels of the major mitochondrial sirtuin SIRT3 were not altered. Moreover, the strong correlations of SIRT1 with the leukocyte markers CD8A and CD19 present in the uninfected individuals were absent in the HIV patients. In conclusion, this study showed that the PBMCs of the HIV patients displayed diminished SIRT1 levels and altered correlations of SIRT1 with markers of CD8⁺ T cells and B cells, findings which may be relevant for understanding the complex pathogenic milieu in HIV patients.
... 19 In addition to claudin-5, brain endothelial cell surface expression of claudin-1 has been found to increase in response to injury, resulting in increased leakiness of the BBB. 20 Furthermore, claudin-1 is transcriptionally regulated by Sirt1, 21 where age-associated reductions in expression are observed, 22 which would be expected to increase expression of claudin-1, and may play a causative role in BBB hyperpermeability in aging and disease. 23−25 In addition, inflammatory stimuli such as those observed during normal aging 26,27 have been shown to increase expression of claudin-1 in astrocytes, which play a major protective role in the BBB. ...
... Correspondingly, the concentration of lactate and alanine did not differ between the WT and SIRT3 KO brains, suggesting that the glycolytic pathway was not significantly affected in Sirt3 KO brain. This is in agreement with reports showing no effect of SIRT3 on cytosolic enzymes or SIRT1 and SIRT2 expression levels or activity [52]. ...
Acetylation is a post-translational modification that regulates the activity of enzymes fundamentally involved in cellular and mitochondrial bioenergetic metabolism. NAD⁺ dependent deacetylase sirtuin 3 (SIRT3) is localized to mitochondria where it plays a key role in regulating acetylation of TCA cycle enzymes and the mitochondrial respiratory complexes. Although the SIRT3 target proteins in mitochondria have been identified, the effect of SIRT3 activity on mitochondrial glucose metabolism in the brain remains elusive. The impact of abolished SIRT3 activity on glucose metabolism was determined in SIRT3 knockout (KO) and wild type (WT) mice injected with [1,6-¹³C]glucose using ex vivo ¹³C-NMR spectroscopy. The ¹H-NMR spectra and amino acid analysis showed no differences in the concentration of lactate, glutamate, alanine, succinate, or aspartate between SIRT3 KO and WT mice. However, glutamine, total creatine (Cr), and GABA were lower in SIRT3 KO brain. Incorporation of label from [1,6-¹³C]glucose metabolism into lactate or alanine was not affected in SIRT3 KO brain. However, the incorporation of the label into all isotopomers of glutamate, glutamine, GABA and aspartate was lower in SIRT3 KO brain, reflecting decreased activity of mitochondrial and TCA cycle metabolism in both neurons and astrocytes. This is most likely due to hyperacetylation of mitochondrial enzymes due to suppressed SIRT3 activity in the brain of SIRT3 KO mice. Thus, the absence of Sirt3 results in impaired mitochondrial oxidative energy metabolism and neurotransmitter synthesis in the brain. Since the SIRT3 activity is NAD⁺ dependent, these results might parallel changes in glucose metabolism under pathologic reduction in mitochondrial NAD⁺ pools.
... Indeed, each sirtuin is specifically regulated by a rich array of factors in a cell-and tissue-specific manner. Sirtuins are extensively controlled at multiple levels and have been extensively discussed previously [138]. A recent study shows that CDA1 is a negative regulator of SIRT1. ...
Diabetes is a noncommunicable disease and arguably represents the greatest pandemic in human history. Diabetic kidney disease (DKD) is seen in both type 1 and type 2 diabetes and can be detected in up to 30–50% of diabetic subjects. DKD is a progressive chronic kidney disease (CKD) and is a leading cause of mortality and morbidity in patients with diabetes. Renal fibrosis and inflammation are the major pathological features of DKD. There are a large number of independent and overlapping profibrotic and pro-inflammatory pathways involved in the pathogenesis and progression of DKD. Among these pathways, the transforming growth factor-β (TGF-β) pathway plays a key pathological role by promoting fibrosis. Sirtuin-1 (SIRT1) is a protein deacetylase that has been shown to be renoprotective with an anti-inflammatory effect. It is postulated that a reduction in renal SIRT1 levels could play a key role in the pathogenesis of DKD and that restoration of SIRT1 will attenuate DKD. Cell division autoantigen 1 (CDA1) synergistically enhances the profibrotic effect of TGF-β in DKD by regulating the expression of the TGF-β type I receptor (TβRI). CDA1 has also been found to be an inhibitor of SIRT1 in the DNA damage response. Indeed, targeting CDA1 in experimental DKD not only attenuates diabetes-associated renal fibrosis but also attenuates the expression of key pro-inflammatory genes such as tumor necrosis factor-α (TNF-α) and Monocyte Che moattractant Protein-1 (MCP-1). In conclusion, there is a large body of experimental data to support the view that targeting CDA1 is a superior approach to directly targeting TGF-β in DKD since it is not only safe but also efficacious in retarding both fibrosis and inflammation.
... The targets of SIRT1 and the related signaling pathways in tumors have also been investigated in-depth. SIRT1 has been reported to regulate apoptotic, inflammatory, and oxidative stress-related processes in ischemia/hypoxia through the deacetylation of its downstream targets, including P53, nuclear factor-kappa B (NF-kB), PGC-1a, forkhead box Os (FOXOs), and PPARs (71,72). The overexpression of SIRT1 can inhibit P53-regulated cell cycle arrest under conditions of DNA damage and oxidative stress (73). ...
Resistance is the major cause of treatment failure and disease progression in non-small cell lung cancer (NSCLC). There is evidence that hypoxia is a key microenvironmental stress associated with resistance to cisplatin, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), and immunotherapy in solid NSCLCs. Numerous studies have contributed to delineating the mechanisms underlying drug resistance in NSCLC; nevertheless, the mechanisms involved in the resistance associated with hypoxia-induced molecular metabolic adaptations in the microenvironment of NSCLC remain unclear. Studies have highlighted the importance of posttranslational regulation of molecular mediators in the control of mitochondrial function in response to hypoxia-induced metabolic adaptations. Hypoxia can upregulate the expression of sirtuin 1 (SIRT1) in a hypoxia-inducible factor (HIF)-dependent manner. SIRT1 is a stress-dependent metabolic sensor that can deacetylate some key transcriptional factors in both metabolism dependent and independent metabolic pathways such as HIF-1α, peroxisome proliferator-activated receptor gamma (PPAR-γ), and PPAR-gamma coactivator 1-alpha (PGC-1α) to affect mitochondrial function and biogenesis, which has a role in hypoxia-induced chemoresistance in NSCLC. Moreover, SIRT1 and HIF-1α can regulate both innate and adaptive immune responses through metabolism-dependent and -independent ways. The objective of this review is to delineate a possible SIRT1/PGC-1α/PPAR-γ signaling-related molecular metabolic mechanism underlying hypoxia-induced chemotherapy resistance in the NSCLC microenvironment. Targeting hypoxia-related metabolic adaptation may be an attractive therapeutic strategy for overcoming chemoresistance in NSCLC.
... The downregulation of Pgc1a gene may be related to complex and still not fully recognized role of sirtuins activity in PGC1α expression. Sirtuins activity is one of the possible way how the transcriptional pathway of Pgc1a can be regulated because sirtuins (SIRT1) are able to form a negative-feedback loop with PPARγ-related pathway [36]. In our studies, the sirtuins activity decreased after the treatment with amorfrutin B in hypoxic condition. ...
In this study, we demonstrate for the first time that amorfrutin B, a selective modulator of peroxisome proliferator-activated receptor gamma—PPARγ, can protect brain neurons from hypoxia- and ischemia-induced degeneration when applied at 6 h post-treatment in primary cultures. The neuroprotective effect of amorfrutin B suggests that it promotes mitochondrial integrity and is capable of inhibiting reactive oxygen species—ROS activity and ROS-mediated DNA damage. PPARγ antagonist and Pparg mRNA silencing abolished the neuroprotective effect of amorfrutin B, which points to agonistic action of the compound on the respective receptor. Interestingly, amorfrutin B stimulated the methylation of the Pparg gene, both during hypoxia and ischemia. Amorfrutin B also increased the protein level of PPARγ during hypoxia but decreased the mRNA and protein levels of PPARγ during ischemia. Under ischemic conditions, amorfrutin B-evoked hypermethylation of the Pparg gene is in line with the decrease in the mRNA and protein expression of PPARγ. However, under hypoxic conditions, amorfrutin B-dependent hypermethylation of the Pparg gene does not explain the amorfrutin B-dependent increase in receptor protein expression, which suggests other regulatory mechanisms. Other epigenetic parameters, such as HAT and/or sirtuins activities, were affected by amorfrutin B under hypoxic and ischemic conditions. These properties position the compound among the most promising anti-stroke and wide-window therapeutics.
... mtSIRTs crosstalk appears to be essential to define a molecular landscape in physiology and organize a coordinated stress response [17][18][19][20]. Until 2007, little was known about the biological functions of mtSIRTs [21], however, today we know that mtSIRTs are regulators of metabolic homeostasis by promoting PTMs of many protein targets [14,22]. Interestingly, the activity and expression of mtSIRTs are regulated by transcriptional and post-transcriptional mechanisms, including miRNAs [23]. ...
Mitochondria act as hubs of numerous metabolic pathways. Mitochondrial dysfunctions contribute to altering the redox balance and predispose to aging and metabolic alterations. The sirtuin family is composed of seven members and three of them, SIRT3-5, are housed in mitochondria. They catalyze NAD+-dependent deacylation and the ADP-ribosylation of mitochondrial proteins, thereby modulating gene expression and activities of enzymes involved in oxidative metabolism and stress responses. In this context, mitochondrial sirtuins (mtSIRTs) act in synergistic or antagonistic manners to protect from aging and aging-related metabolic abnormalities. In this review, we focus on the role of mtSIRTs in the biological competence of reproductive cells, organs, and embryos. Most studies are focused on SIRT3 in female reproduction, providing evidence that SIRT3 improves the competence of oocytes in humans and animal models. Moreover, SIRT3 protects oocytes, early embryos, and ovaries against stress conditions. The relationship between derangement of SIRT3 signaling and the imbalance of ROS and antioxidant defenses in testes has also been demonstrated. Very little is known about SIRT4 and SIRT5 functions in the reproductive system. The final goal of this work is to understand whether sirtuin-based signaling may be taken into account as potential targets for therapeutic applications in female and male infertility.
... They are known to modulate metabolism, cell signaling, ageing, and longevity [11][12][13][14][15][16][17]. In particular, sirtuin 1 is known to be involved in the regulation of lipid and glucose metabolism, while sirtuin 3 regulates mitochondrial energy metabolism [18,19]. Moreover, several studies have linked sirtuins to neurodegenerative diseases, and metabolic changes such as caloric restriction trigger alterations of sirtuin 2 and sirtuin 3 [15,17]. ...
Breast feeding is regarded as the preferred nutrition modality for children during the first few months of life. It not only furthers growth and development but also is supposed to impact later life. The first 1000 days are regarded as a critical window for development, even beyond infancy. The physiological basis underlying this beneficial effect is not clear. Sirtuins are important regulatory proteins of metabolism and are supposed to play a critical role in ageing and longevity as well as in diseases. In the present study, we developed novel methods to assay sirtuin 1 and sirtuin 3 at enzyme activity (via fluorometry) and protein levels (by Western blot) in the aqueous phase and in the cell pellet of human breast milk and assessed the impact of ongoing lactation during the neonatal period. Sirtuin activities in the aqueous phase were negatively correlated with the duration of lactation in the neonatal period. There was no correlation of sirtuin activities in the cell pellet with the duration of lactation. The amounts of sirtuin 1 and sirtuin 3 measured by Western blot were negatively correlated with the lactation period.
... Besides having a negative feedback on itself [33], as detected in SIRT y/y mice (see Figure 3), SIRT1 is a key factor in the regulation of several apoptosis cascades and survival signaling pathways, particularly by repression of p53 [34]. These findings are supported by others, who have shown that histone modifications on Fas facilitate apoptosis in fibrotic-lung myofibroblasts [35]. ...
In contrast to normal regenerating tissue, resistance to Fas- and FasL-positive T cell-induced apoptosis were detected in myofibroblasts from fibrotic-lungs of humans and mice following bleomycin (BLM) exposure. In this study we show, decreased FLIP expression in lung-tissues with resolution of BLM-induced fibrosis and in isolated-lung fibroblasts, with decreased resistance to apoptosis. Using a FLIP-expression vector or a shFLIP-RNA, we further confirmed the critical need for FLIP to regain/lose susceptibility of fibrotic-lung myofibroblast to Fas-induced apoptosis. Our study further show that FLIP is regulated by SIRT1 (Sirtuin 1) deacetylase. Chimeric mice, with SIRT1-deficiency in deacetylase domain (H355Y-Sirt1y/y), specifically in mesenchymal cells, were not only protected from BLM-induced lung fibrosis but, as assessed following Ku70 immunoprecipitation, had also decreased Ku70-deacetylation, decreasedKu70/FLIP complex, and decreased FLIP levels in their lung myofibroblasts. In addition, myofibroblasts isolated from lungs of BLM-treated miR34a-knockout mice, exposed to a miR34a mimic, which we found here to downregulate SIRT1 in the luciferase assay, had a decreased Ku70-deacetylation indicating decrease in SIRT1 activity. Thus, SIRT1 may mediate, miR34a-regulated, persistent FLIP levels by deacetylation of Ku70 in lung myofibroblasts, promoting resistance to cell-death and lung fibrosis.
... Caspase-8 activation further targets effector caspase-3 and caspase-7, a parallel extrinsic pathway, caspases 6 and 9, MAPKs, and Bim phosphorylations with binding cascades to Bax, Apaf-1, and caspase-9, allowing Bax-mediated cell death to be detected as well ( Figure 3A, green arrows). Concomitantly, inhibitors of these processes, including FLIP, show negative interaction with FADD and with the inhibitors of apoptotic proteins E2F1-SIRT1 interplay bears some resemblance to that of the p53-SIRT1 axis and may be part of the mechanism controlling the fine balance between cell repair and apoptosis [38]. Of note, as detailed in our previous study [39], we did not detect the 75kDa-cleaved variant of SIRT1 in IB assays; hence, we do not expect its accumulation would affect apoptosome assembly in our cells. ...
Regenerative capacity in vital organs is limited by fibrosis propensity. Idiopathic pulmonary fibrosis (IPF), a progressive lung disease linked with aging, is a classic example. In this study, we show that in flow cytometry, immunoblots (IB) and in lung sections, FLIP levels can be regulated, in vivo and in vitro, through SIRT1 activity inhibition by CMH (4-(4-Chloro-2-methylphenoxy)-N-hydroxybutanamide), a small molecule that, as we determined here by structural biology calculations, docked into its nonhistone substrate Ku70-binding site. Ku70 immunoprecipitations and immunoblots confirmed our theory that Ku70-deacetylation, Ku70/FLIP complex, myofibroblast resistance to apoptosis, cell survival, and lung fibrosis in bleomycin-treated mice, are reduced and regulated by CMH. Thus, small molecules associated with SIRT1-mediated regulation of Ku70 deacetylation, affecting FLIP stabilization in fibrotic-lung myofibroblasts, may be a useful strategy, enabling tissue regeneration.
... Finally, miRNA deregulation occurs in different species and tissues with ageing as a result of impaired miRNA biogenesis. DNMT, DNA methyltransferase; HDAC, histone deacetylase; HAT, histone acetyltransferase; HD, histone demethylase; HMT, histone methylase McCay 1947;Fontana et al. 2010;Sierra et al. 2015;Guerra et al. 2019) and alters DNA methylation in a manner that is associated with increased SIRT1 expression (Ions et al. 2013;Buler et al. 2016;Wątroba et al. 2017). CR also delays the ageassociated pattern of methylation in genes involved in lipid metabolism, causing epigenetic reprogramming and improving metabolic control (Hahn et al. 2017). ...
As life expectancy increases worldwide, ageing and age-related diseases arise as a major issue for societies around the globe. Understanding the biological mechanisms underlying the ageing process is thus instrumental for the development of efficient interventions aimed to prevent and treat age-related conditions. Current knowledge in the biogerontology field points to epigenetics as a critical component of the ageing process, not only by serving as a bona-fide marker of biological age but also by controlling and conferring inheritability to cellular and organismal ageing. This is reflected by a myriad of evidences demonstrating the relationship between DNA methylation, histone modifications, chromatin remodeling and small non-coding RNAs and several age-related phenotypes. Given the reversibility of epigenetic alterations, epigenetic reprogramming may also be envisioned as a potential approach to treat age-related disorders. Here we review how different types of epigenetic mechanisms are involved in the ageing process. In addition, we highlight how interventions modulate epigenetics and thus promote health- and lifespan.
... SIRT1, SIRT6, and SIRT7 are nuclear enzymes; SIRT3, SIRT4, and SIRT5 are located in mitochondria; while SIRT2 is the only cytosolic sirtuin. Additionally, a subcellular shift of SIRT1 and SIRT3 into the cytosol was described under specific conditions [4]. The enzymatic reactions catalyzed by sirtuins are either a NAD+-dependent deacylation of lysine residues or a NAD+-dependent ADP (Adenosine diphosphate) -ribosylation of lysine residues [5]. ...
Both nutrition and exercise are known to affect metabolic regulation in humans. Sirtuins are essential regulators of cellular energy metabolism; SIRT1, SIRT3, and SIRT4 have a direct effect on glycolysis, oxidative phosphorylation, and fatty acid oxidation. This cross-sectional study investigates the effect of different diets on exercise-induced regulation of sirtuins. SIRT1 and SIRT3–SIRT5 were measured in blood from omnivorous, lacto-ovo vegetarian, and vegan recreational runners (21–25 subjects, respectively) before and after exercise at the transcript, protein, and enzymatic levels. SIRT1, SIRT3, and SIRT5 enzyme activities increased during exercise in omnivores and lacto-ovo vegetarians, commensurate with increased energy demand. However, activities decreased in vegans. Malondialdehyde as a surrogate marker of oxidative stress inversely correlated with sirtuin activities and was elevated in vegans after exercise compared to both other groups. A significant negative correlation of all sirtuins with the intake of the antioxidative substances, ascorbate and tocopherol, was found. In vegan participants, increased oxidative stress despite higher amounts of the antioxidative substances in the diet was observed after exercise.
... Also, the levels of total SIRT1 protein expression do not necessarily reflect the level of SIRT1 enzyme activity, which are regulated by multiple post-translational modifications of SIRT1 protein (ie, phosphorylation, ubiquitination, sumoylation, carbonylation, etc.) and the availability of critical metabolic cofactors, such as NAD + . 63 Noninvasive in vivo imaging of SIRT1 expression-activity in gliomas using PET/CT/MRI with 2-[ 18 F]BzAHA may help to resolve this controversy by providing the means for the initial molecular profiling, image guidance of biopsies, and for image-guided resection of glioma samples for further molecular genetic analyses. The role of SIRT1 expression-activity on progression and prognosis of gliomas can now be investigated more accurately using quantitative imaging of Previous studies in patient-derived glioblastoma cells demonstrated that SAHA, VPA, MS275, LBH589, and Scriptaid are effective radiosensitizers of gliomas. ...
Background
Several studies demonstrated that glioblastoma multiforme progression and recurrence is linked to epigenetic regulatory mechanisms. Sirtuin 1 (SIRT1) plays an important role in glioma progression, invasion, and treatment response, and is a potential therapeutic target. The aim of this study is to test the feasibility of 2-[18F]BzAHA for quantitative imaging of SIRT1 expression-activity and monitoring pharmacologic inhibition in a rat model of intracerebral glioma.
Methods
Sprague Dawley rats bearing 9L (N=12) intracerebral gliomas were injected with 2-[18F]BzAHA (300-500 µCi/animal i.v.) and dynamic PET imaging was performed for 60 minutes. Then, SIRT1 expression in 9L tumors (N=6) was studied by immunofluorescence microscopy (IFM). Two days later, rats with 9L gliomas were treated either with SIRT1 specific inhibitor EX-527 (5 mg/kg, i.p; N=3) or with HDACs class IIa specific inhibitor MC1568 (30 mg/kg, i.p.; N=3) and 30 minutes later were injected i.v. with 2-[18F]BzAHA. PET/CT/(MR) images acquired after EX-527 and MC1568 treatments were co-registered with baseline images.
Results
Standard uptake values (SUV) of 2-[18F]BzAHA in 9L tumors measured at 20 min post radiotracer administration were 1.11±0.058 for SUV and had an tumor-to-brainstem SUV ratio of 2.73±0.141. IFM of 9L gliomas revealed heterogeneous upregulation of SIRT1, especially in hypoxic and perinecrotic regions. Significant reduction in 2-[18F]BzAHA SUV and distribution volume in 9L tumors was observed after administration of EX-527, but not MC1568.
Conclusions
Thus, PET/CT/(MR) with 2-[18F]BzAHA can facilitate studies to elucidate the roles of SIRT1 in gliomagenesis and progression and to optimize therapeutic doses of novel SIRT1 inhibitors in gliomas.
... Here we found that DHEA mice exhibited enhanced ovarian expression of SIRT1. Indeed, increased expression of sirtuins is considered an adaptive response to mild oxidative stress, whereas severe oxidant conditions determined sirtuin degradation [55]. The recruitment of SIRT1 in DHEA ovarian response to prooxidant conditions is supported by the rise in protein levels of SIRT3 and SOD2, which are mitochondrial elements of SIRT1 functional network involved in antioxidant response. ...
Advanced glycation end-products (AGEs) are involved in the pathogenesis and consequences of polycystic ovary syndrome (PCOS), a complex metabolic disorder associated with female infertility. The most powerful AGE precursor is methylglyoxal (MG), a byproduct of glycolysis, that is detoxified by the glyoxalase system. By using a PCOS mouse model induced by administration of dehydroepiandrosterone (DHEA), we investigated whether MG-dependent glycative stress contributes to ovarian PCOS phenotype and explored changes in the Sirtuin 1 (SIRT1) functional network regulating mitochondrial functions and cell survival. In addition to anovulation and reduced oocyte quality, DHEA ovaries revealed altered collagen deposition, increased vascularization, lipid droplets accumulation and altered steroidogenesis. Here we observed increased intraovarian MG-AGE levels in association with enhanced expression of receptor for AGEs (RAGEs) and deregulation of the glyoxalase system, hallmarks of glycative stress. Moreover, DHEA mice exhibited enhanced ovarian expression of SIRT1 along with increased protein levels of SIRT3 and superoxide dismutase 2 (SOD2), and decreased peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC1α), mitochondrial transcriptional factor A (mtTFA) and translocase of outer mitochondrial membrane 20 (TOMM20). Finally, the presence of autophagy protein markers and increased AMP-activated protein kinase (AMPK) suggested the involvement of SIRT1/AMPK axis in autophagy activation. Overall, present findings demonstrate that MG-dependent glycative stress is involved in ovarian dysfunctions associated to PCOS and support the hypothesis of a SIRT1-dependent adaptive response.
... The regulation of SIRT1 in cells can be achieved at multiple levels. At transcriptional and post-transcriptional level, SIRT1 expression is modulated by the activity of related transcription factors and microRNAs (miRNAs), which have been well summarized in previous reviews (Buler et al. 2016;Revollo and Li 2013;Yamakuchi 2012 Table 1 deacetylase activity towards p53. Residues 114-217, which localize at the N-terminal of SIRT1, were responsible for their interaction. ...
Silent information regulator proteins (SIRT), or sirtuins, are evolutionarily conserved NAD⁺-dependent deacetylases and ADP-mono-ribosyltransferases. In mammalian, seven sirtuins have been identified, namely SIRT1–7, with different subcellular localization. Nuclear sirtuins, including SIRT1, SIRT6 and SIRT7, localize predominantly in the nucleus and are implicated in many vital biological processes, including stress response, transcription, genome maintenance, tumorigenesis and aging. Dysregulation of nuclear sirtuins is associated with the development of many diseases, including cancer and metabolic disorders. Therefore, the activities of nuclear sirtuins must be properly regulated. In this review, we summarize the current knowledge on the post-translational modifications of nuclear sirtuins and discuss how these modifications modulate their functions.
Oxidation-reduction (redox) reactions are central to the existence of life. Reactive species of oxygen, nitrogen and sulfur mediate redox control of a wide range of essential cellular processes. Yet, excessive levels of oxidants are associated with ageing and many diseases, including cardiological and neurodegenerative diseases, and cancer. Hence, maintaining the fine-tuned steady-state balance of reactive species production and removal is essential. Here, we discuss new insights into the dynamic maintenance of redox homeostasis (that is, redox homeodynamics) and the principles underlying biological redox organization, termed the 'redox code'. We survey how redox changes result in stress responses by hormesis mechanisms, and how the lifelong cumulative exposure to environmental agents, termed the 'exposome', is communicated to cells through redox signals. Better understanding of the molecular and cellular basis of redox biology will guide novel redox medicine approaches aimed at preventing and treating diseases associated with disturbed redox regulation.
Sirtuins (SIRTs) are stress-responsive proteins that regulate several post-translational modifications, partly by acetylation, deacetylation, and affecting DNA methylation. As a result, they significantly regulate several cellular processes. In essence, they prolong lifespan and control the occurrence of spontaneous tumor growth. Members of the SIRT family have the ability to govern embryonic, hematopoietic, and other adult stem cells in certain tissues and cell types in distinct ways. Likewise, they can have both pro-tumor and anti-tumor effects on cancer stem cells, contingent upon the specific tissue from which they originate. The impact of autophagy on cancer stem cells, which varies depending on the specific circumstances, is a very intricate phenomenon that has significant significance for clinical and therapeutic purposes. SIRTs exert an impact on the autophagy process, whereas autophagy reciprocally affects the activity of certain SIRTs. The mechanism behind this connection in cancer stem cells remains poorly understood. This review presents the latest findings that position SIRTs at the point where cancer cells and autophagy interact. Our objective is to highlight the various roles of distinct SIRTs in cancer stem cell-related functions through autophagy. This would demonstrate their significance in the genesis and recurrence of cancer and offer a more precise understanding of their treatment possibilities in relation to autophagy.
Aging is a complex biological process involving multiple interacting mechanisms and is being increasingly linked to environmental exposures such as wildfire smoke. In this review, we detail the hallmarks of aging, emphasizing the role of telomere attrition, cellular senescence, epigenetic alterations, proteostasis, genomic instability, and mitochondrial dysfunction, while also exploring integrative hallmarks - altered intercellular communication and stem cell exhaustion. Within each hallmark of aging, our review explores how environmental disasters like wildfires, and their resultant inhaled toxicants, interact with these aging mechanisms. The intersection between aging and environmental exposures, especially high-concentration insults from wildfires, remains under-studied. Preliminary evidence, from our group and others, suggests that inhaled wildfire smoke can accelerate markers of neurological aging and reduce learning capabilities. This is likely mediated by the augmentation of circulatory factors that compromise vascular and blood-brain barrier integrity, induce chronic neuroinflammation, and promote age-associated proteinopathy-related outcomes. Moreover, wildfire smoke may induce a reduced metabolic, senescent cellular phenotype. Future interventions could potentially leverage combined anti-inflammatory and NAD + boosting compounds to counter these effects. This review underscores the critical need to study the intricate interplay between environmental factors and the biological mechanisms of aging to pave the way for effective interventions.
Purpose:
Sirtuin 1 (SIRT1) comprises a major anti-aging longevity factor with multiple protective effects on chondrocyte homeostasis. Previous studies have reported that downregulation of SIRT1 is linked to osteoarthritis (OA) progression. In this study, we aimed to investigate the role of DNA methylation on SIRT1 expression regulation and deacetylase activity in human OA chondrocytes.
Materials and methods:
Methylation status of SIRT1 promoter was analyzed in normal and OA chondrocytes using bisulfite sequencing analysis. CCAAT/enhancer binding protein alpha (C/EBPα) binding to SIRT1 promoter was assessed by chromatin immunoprecipitation (ChIP) assay. Subsequently, C/EBPα's interaction with SIRT1 promoter and SIRT1 expression levels were evaluated after treatment of OA chondrocytes with 5-Aza-2'-Deoxycytidine (5-AzadC). Acetylation and nuclear levels of nuclear factor kappa-B p65 subunit (NF-κΒp65) and expression levels of selected OA-related inflammatory mediators, interleukin 1β (IL-1β) and IL-6 and catabolic genes (metalloproteinase-1 (MMP-1) and MMP-9) were evaluated in 5-AzadC-treated OA chondrocytes with or without subsequent transfection with siRNA against SIRT1.
Results:
Hypermethylation of specific CpG dinucleotides on SIRT1 promoter was associated with downregulation of SIRT1 expression in OA chondrocytes. Moreover, we found decreased binding affinity of C/EBPα on the hypermethylated SIRT1 promoter. 5-AzadC treatment restored C/EBPα's transcriptional activity inducing SIRT1 upregulation in OA chondrocytes. Deacetylation of NF-κΒp65 in 5-AzadC-treated OA chondrocytes was prevented by siSIRT1 transfection. Similarly, 5-AzadC-treated OA chondrocytes exhibited decreased expression of IL-1β, IL-6, MMP-1 and MMP-9 which was reversed following 5-AzadC/siSIRT1 treatment.
Conclusions:
Our results suggest the impact of DNA methylation on SIRT1 suppression in OA chondrocytes contributing to OA pathogenesis.
Poor control of metabolic diseases induces kidney injury, resulting in microalbuminuria, renal insufficiency and, ultimately, chronic kidney disease. The potential pathogenetic mechanisms of renal injury caused by metabolic diseases remain unclear. Tubular cells and podocytes of the kidney show high expression of histone deacetylases known as sirtuins (SIRT1-7). Available evidence has shown that SIRTs participate in pathogenic processes of renal disorders caused by metabolic diseases. The present review addresses the regulatory roles of SIRTs and their implications for the initiation and development of kidney damage due to metabolic diseases. SIRTs are commonly dysregulated in renal disorders induced by metabolic diseases such as hypertensive nephropathy and diabetic nephropathy. This dysregulation is associated with disease progression. Previous literature has also suggested that abnormal expression of SIRTs affects cellular biology, such as oxidative stress, metabolism, inflammation, and apoptosis of renal cells, resulting in the promotion of invasive diseases. This literature reviews the research progress made in understanding the roles of dysregulated SIRTs in the pathogenesis of metabolic disease-related kidney disorders and describes the potential of SIRTs serve as biomarkers for early screening and diagnosis of these diseases and as therapeutic targets for their treatment.
Claudin-5 has recently attracted increasing attention by its potential as a novel treatment target in the early stage of heart failure. However, whether Claudin-5 produces beneficial effects on myocardial ischemia and reperfusion (IR) injury has not been elucidated yet. In this study, we identified reduced levels of Claudin-5 in the hearts of mice subjected to acute myocardial IR injury and murine HL-1 cardiomyocytes subjected to hypoxia and reoxygenation (HR). We then constructed cardiac-specific Cldn5-overexpressing mice using an adeno-associated virus (AAV9) vector and demonstrated that Cldn5 overexpression ameliorated cardiac dysfunction and myocardial damage in mice subjected to myocardial IR injury. Moreover, Cldn5 overexpression attenuated myocardial oxidative stress (DHE and protein levels of Nrf2, HO-1, and NQO1), inflammatory response (levels of MPO, F4/80, Ly6C, and circulating inflammatory cells), mitochondrial dysfunction (protein levels of PGC-1α, NRF1, and TFAM), endoplasmic reticulum stress (protein levels of GRP78, ATF6, and CHOP and p-PERK), energy metabolism disorder (p-AMPK and ACC), and apoptosis (TUNEL assay and protein levels of Bax and Bcl2) in mice subjected to myocardial IR. Next, we generated Cldn5 knockdown cells by lentiviral shRNA and observed that Cldn5 knockdown inhibited cell viability and affected the expression or activation of these IR-related signalings in HL-1 cardiomyocytes subjected to HR. Mechanistically, SIRT1 was proved to be involved in regulating the expression of Claudin-5 by co-immunoprecipitation analysis and Sirt1 knockdown experiments. Our data demonstrated that targeting Claudin-5 may represent a promising approach for preventing and treating acute myocardial IR injury.
Among all of the new antidiabetic drugs, an increasing number of studies have evaluated the relationship between the sodium-glucose cotransporter 2 inhibitors (SGLT2i) and acute myocardial infarction (AMI). Since SGLT2i like empagliflozin, canagliflozin, and recently, dapagliflozin have shown impressive positive effects in patients with chronic heart failure with reduced ejection fraction (HFrEF), it has increased research interest to explore the cardiac molecular mechanisms underlying the clinical benefits and attracted more attention to the effects of SGLT2i on a series of cardiovascular events. Experimental and clinical data on SGLT2i treatment after AMI is limited. This is a review of the clinical and preclinical effects of SGLT2i, focusing on available data on the effects of SGLT2i in AMI patients with a brief overview of ongoing trials.
Sirtuine sind eine evolutionär hoch konservierte Familie der Histon-Deacetylasen. Sie katalysieren die Deacylierung von Acyllysinresten in Substratproteinen durch einen einzigartigen Mechanismus, der NAD+ als Cosubstrat benötigt. Dies macht Sirtuine zu metabolischen Sensoren. Diese Enzyme regulieren Stressreaktionen und Alterungsprozesse. Da sie in altersbedingten und metabolischen Erkrankungen involviert sind, ist die Regulation von Sirtuinen von medizinischem Interesse und besitzt therapeutisches Potenzial. In dieser Arbeit wurden neue Erkenntnisse zur endogenen Regulation von Sirtuinen durch das Protein AROS und zur Sirtuinmodulation durch Kleinmoleküle gewonnen. Das Pflanzenflavonoid Quercetin hat im Gegensatz zur Sirt6-spezifischen Aktvierung eine inhibitorische Wirkung auf die anderen Sirtuinisoformen. Die molekularen Grundlagen der Quercetin-vermittelten Inhibition konnte mit Hilfe einer Kristallstruktur des Sirt2/Quercetin-Komplexes aufgeklärt werden. So inhibiert der Naturstoff die Sirtuinaktivität durch Bindung am Eingang des aktiven Zentrums und daraus resultierender Kompetition mit dem acylierten Substrat. In Sirt6 wird diese Bindungsstelle durch den N-Terminus des Proteins besetzt. Die Sirt2-Quercetinbindungsstelle ist in Sirt6 nicht zugänglich. Quercetin bindet stattdessen in einer Sirt6-spezifischen Bindungstasche. Die Sirt2/Quercetin-Struktur trägt dazu bei, den Sirt6-spezifische Aktivierungseffekt von Quercetin zu erklären und liefert somit Informationen zur Weiterentwicklung von Sirt6-spezifischen, potenten Modulatoren. Die Erkenntnisse der Quercetin-Bindung in Sirt2 könnten zudem zur Entwicklung neuer Quercetin-basierender Inhibitoren beitragen. Neben der Regulation von Sirt6 und Sirt2 steht auch die Aktivierung von Sirt3 im Fokus. Als einziges Sirtuin mit robuster Deacetylaseaktivität im Mitochondrium gilt es als vielversprechendes Ziel zur pharmakologischen Modulation durch Aktivatoren. Aufgrund des Mangels an Sirt3-Aktivatoren wurde durch kristallografisches Screening einer Fragment-Bibliothek nach neuen Modulatoren für Sirt3 gesucht. Auf diese Weise konnten zwei neue Liganden sowie drei bisher unbekannte Liganden-Bindungsstellen für Sirt3 gefunden werden. Aufbauend auf diesen Fragmentgerüsten könnten Kleinmoleküle entwickelt werden, die Potential zur Modulation der Sirt3-Aktivität besitzen. Das Protein AROS wurde zunächst als bisher einziger endogener Aktivator von Sirt1 beschrieben. Dem widersprechend wurde von anderen Autoren eine inhibierende Wirkung von AROS auf die Sirt1-Deacetylaseaktivität festgestellt. Das Verständnis des Regulationsmechanismus von Sirt1 durch AROS könnte zur Entwicklung pharmakologischer Modulatoren beitragen. In dieser Arbeit konnte das Protein AROS zum ersten Mal charakterisiert werden. AROS akkumuliert exprimiert in E. coli in Einschlusskörpern. Daher wurde ein Renaturierungsprotokoll etabliert, welches in löslichem, reinem Protein resultierte. AROS konnte als ein flexibles Protein ohne stabile Tertiärstruktur aber mit Sekundärstrukturelementen wie α Helices charakterisiert werden. Zudem scheint das Protein unter stabilisierenden Bedingungen eine deutlich strukturiertere Konformation einzunehmen. Der Sirt1/AROS-Komplex musste zunächst durch Optimierung des Puffersystems stabilisiert werden. Anschließende Aktivitätstest von Sirt1 und AROS resultierten in einer Inhibition der Sirt1-Deacetylaseaktivität. Für die Isoformen 2,3 und 5 konnte ebenso eine AROS-vermittelte Inhibition gezeigt werden. Diese ist im Vergleich zu Sirt1 jedoch geringer. Als Interaktionsbereich im Sirtuin konnte der generische, katalytische Sirtuinkern identifiziert werden. Zudem lässt sich die höhere inhibitorische Wirkung von AROS auf Sirt1 durch zusätzliche Interaktionen mit der regulatorischen, N-terminalen Domäne von Sirt1 erklären. Für AROS konnte gezeigt werden, dass der mittlere Bereich des Proteins für die Inhibition verantwortlich ist. N- und C-terminale Abschnitte in AROS scheinen die Affinität zum Sirtuin durch zusätzliche Bindungsstellen zu erhöhen bzw. wichtige Bereiche für die Inhibition zu stabilisieren. Titrationen der beiden Sirt1-Substrate resultierten in einer Verringerung der Affinität des acetylierten Peptid-Substrates in Anwesenheit von AROS und liesen daher auf einen Inhibitons-Mechanismus, der auf Kompetiton mit dem acetylierten Peptid-Substrat beruht, schließen. Eine Kristallstruktur von Sirt3 konnte in Komplex mit einem AROS-Peptid gelöst werden. Im aktiven Zentrum des Sirtuins in der Bindungsstelle des acetylierten Lysins befindet sich das Lysin 65 von AROS, was den Kompetitionsmechanismus bestätigt. Unter Verwendung der strukturellen und mechanistischen Daten wurde ein Modell für den Sirt1/AROS-Komplex postuliert, in dem AROS die Bildung eines Enzym-Substrat-Komplexes durch Interaktion mit dem N-Terminus und der katalytischen Domäne von Sirt1 verhindert.
Sirtuins are Class III protein deacetylases with seven conserved isoforms. In general, Sirtuins are highly activated under cellular stress conditions in which NAD⁺ levels are increased. Nevertheless, regulation of Sirtuins extends far beyond the influences of cellular NAD⁺/NADH ratio and a rapidly expanding body of evidence currently suggests that their expression and catalytic activity are highly kept under control at multiple levels by various factors and processes. Owing to their intrinsic ability to enzymatically target various intracellular proteins, Sirtuins are prominently involved in the regulation of fundamental biological processes including inflammation, metabolism, redox homeostasis, DNA repair and cell proliferation and senescence. In fact, Sirtuins are well established to regulate and reprogram different redox and metabolic pathways under both pathological and physiological conditions. Therefore, alterations in Sirtuin levels can be a pivotal intermediary step in the pathogenesis of several disorders. This review first highlights the mechanisms involved in the regulation of Sirtuins and further summarizes the current findings on the major functions of Sirtuins in cellular redox homeostasis and bioenergetics (glucose and lipid metabolism).
Arterial stiffness, a consequence of smoking, is an underlying risk factor of cardiovascular diseases. Epoxyeicosatrienoic acids (EETs), hydrolyzed by soluble epoxide hydrolase (sEH), have beneficial effects against vascular dysfunction. However, the role of sEH knockout in nicotine-induced arterial stiffness was not characterized. We hypothesized that sEH knockout could prevent nicotine-induced arterial stiffness. In the present study, Ephx2 (the gene encodes sEH enzyme) null (Ephx2 -/- ) mice and wild-type (WT) littermate mice were infused with or without nicotine and administered with or without nicotinamide (NAM, SIRT1 inhibitor) simultaneously for four weeks. Nicotine treatment increased sEH expression and activity in the aortas of WT mice. Nicotine infusion significantly induced vascular remodeling, arterial stiffness, and SIRT1 deactivation in WT mice, which was attenuated in Ephx2 -/- mice without NAM treatment. However, the arterial protective effects were gone in Ephx2 -/- mice with NAM treatment. In vitro, 11,12-EET treatment attenuated nicotine-induced MMP2 upregulation via SIRT1-mediated YAP deacetylation. In conclusion, sEH knockout attenuated nicotine-induced arterial stiffness and vascular remodeling via SIRT1-induced YAP deacetylation.
Our study aims at developing knowledge-based strategies minimizing chronic changes in the brain after severe spinal cord injury (SCI). The SCI-induced long-term metabolic alterations and their reactivity to treatments shortly after the injury are characterized in rats. Eight weeks after severe SCI, significant mitochondrial lesions outside the injured area are demonstrated in the spinal cord and cerebral cortex. Among the six tested enzymes essential for the TCA cycle and amino acid metabolism, mitochondrial 2-oxoglutarate dehydrogenase complex (OGDHC) is the most affected one. SCI downregulates this complex by 90% in the spinal cord and 30% in the cerebral cortex. This is associated with the tissue-specific changes in other enzymes of the OGDHC network. Single administrations of a pro-activator (thiamine, or vitamin B1, 1.2 mmol/kg) or a synthetic pro-inhibitor (triethyl glutaryl phosphonate, TEGP, 0.02 mmol/kg) of OGDHC within 15–20 h after SCI are tested as protective strategies. The biochemical and physiological assessments 8 weeks after SCI reveal that thiamine, but not TEGP, alleviates the SCI-induced perturbations in the rat brain metabolism, accompanied by the decreased expression of (acetyl)p53, increased expression of sirtuin 5 and an 18% improvement in the locomotor recovery. Treatment of the non-operated rats with the OGDHC pro-inhibitor TEGP increases the p53 acetylation in the brain, approaching the brain metabolic profiles to those after SCI. Our data testify to an important contribution of the OGDHC regulation to the chronic consequences of SCI and their control by p53 and sirtuin 5.
Reversible lysine acetylation of histones is a key epigenetic regulatory process controlling gene expression. Reversible histone acetylation is mediated by two opposing enzyme families: histone acetyltransferases (HATs) and histone deacetylases (HDACs). Moreover, many non-histone targets of HATs and HDACs are known, suggesting a crucial role for lysine acetylation as a posttranslational modification on the cellular proteome and protein function far beyond chromatin-mediated gene regulation. The HDAC family consists of 18 members and pan-HDAC inhibitors (HDACi) are clinically used for the treatment of certain types of cancer. HDACi or individual HDAC member-deficient (cell lineage-specific) mice have also been tested in a large number of preclinical mouse models for several autoimmune and autoinflammatory diseases and in most cases HDACi treatment results in an attenuation of clinical disease severity. A reduction of disease severity has also been observed in mice lacking certain HDAC members. This indicates a high therapeutic potential of isoform-selective HDACi for immune-mediated diseases. Isoform-selective HDACi and thus targeted inactivation of HDAC isoforms might also overcome the adverse effects of current clinically approved pan-HDACi. This review provides a brief overview about the fundamental function of HDACs as epigenetic regulators, highlights the roles of HDACs beyond chromatin-mediated control of gene expression and summarizes the studies showing the impact of HDAC inhibitors and genetic deficiencies of HDAC members for the outcome of autoimmune and autoinflammatory diseases with a focus on rheumatoid arthritis, inflammatory bowel disease and experimental autoimmune encephalomyelitis (EAE) as an animal model of multiple sclerosis.
Schizophyllan (SPG), produced by Schizophyllum commune, is an exopolysaccharide with multiple academic and commercial uses, including in the food industry and for various medical functions. We previously demonstrated that SPG conjugated with c-Src peptide exerted a significant therapeutic effect on mouse models of the acute inflammatory diseases polymicrobial sepsis and ulcerative colitis. Here we extended these results by investigating whether SPG exerted a protective effect against mitochondrial damage in the liver via sirtuin 3 (SIRT3) induction, focusing on the deacetylation of succinate dehydrogenase A (SDHA) and superoxide dismutase 2 (SOD2). Liver damage models induced by alcohol or conjugated linoleic acid (CLA, which simulates lipodystrophy) in SIRT3−/−, SOD2−/−, and SDHA−/− mice were used. Results showed that dietary supplementation with SPG induced SIRT3 activation; this was involved in mitochondrial metabolic resuscitation that countered the adverse effects of alcoholic liver disease and CLA-induced damage. The mitochondrial SIRT3 mediated the deacetylation and activation of SOD2 in the liver and SDHA in adipose tissues, suggesting that SPG supplementation reduced ethanol-induced liver damage and CLA-induced adverse dietary effects via SIRT3–SOD2 and SIRT3–SDHA signaling, respectively. Together, these results suggest that dietary SPG has a previously unrecognized role in SIRT3-mediated mitochondrial metabolic resuscitation during mitochondria-related diseases.
Eukaryotic complexity and thus their ability to respond to diverse cues are largely driven by varying expression of gene products, qualitatively and quantitatively. Protein adducts in the form of post-translational modifications, most of which are derived from metabolic intermediates, allow fine tuning of gene expression at multiple levels. With the advent of high-throughput and high-resolution mapping technologies there has been an explosion in terms of the kind of modifications on chromatin and other factors that govern gene expression. Moreover, even the classical notion of acetylation and methylation dependent regulation of transcription is now known to be intrinsically coupled to biochemical pathways, which were otherwise regarded as ‘mundane’. Here we have not only reviewed some of the recent literature but also have highlighted the dependence of gene regulatory mechanisms on metabolic inputs, both direct and indirect. We have also tried to bring forth some of the open questions, and how our understanding of gene expression has changed dramatically over the last few years, which has largely become metabolism centric. Finally, metabolic regulation of epigenome and gene expression has gained much traction due to the increased incidence of lifestyle and age-related diseases.
Cows at the beginning of lactation often do not meet their energy needs by feeding and therefore mobilize body fat, which produces ketone bodies, including β-hydroxybutyrate (BHB). They are nevertheless usually inseminated around 60 d postpartum, when they are still in this characteristic period of energy deficit. The aim of this study was to observe the effects of negative energy balance on embryo quality and to identify ways to improve the fertility of dairy cows. Holstein cows (n = 18) grouped as high or low BHB based on blood measurement at day 45 postpartum were estrus-synchronized and treated with follicle-stimulating hormone to obtain multiple follicle development, induced to ovulate and inseminated with sexed semen around day 60 postpartum. Of the 290 embryos collected over16 mo, 159 were of quality I to IV. Based on microarray analysis of gene expression, exposure to an energy deficit metabolic environment (high BHB) during early development appeared to modify signaling by the mTOR and sirtuins pathways in the embryo, implying mitochondrial dysfunction and inhibition of transcription, leading to slower cell division, thus programming the embryo to be more energy efficient. Altered methylation markings suggested that such coping mechanisms might persist into adulthood.
In diabetes, some of the cellular changes are similar to aging. We hypothesized that hyperglycemia accelerates aging-like changes in the endothelial cells (ECs) and tissues leading to structural and functional damage. We investigated glucose-induced aging in 3 types of ECs using senescence associated b-gal (SA b-gal) staining and cell morphology. Alterations of sirtuins (SIRTs) and their downstream mediator FOXO and oxidative stress were investigated. Relationship of such alteration with histone acetylase (HAT) p300 was examined. Similar examinations were performed in tissues of diabetic animals. ECs in high glucose (HG) showed evidence of early senescence as demonstrated by increased SA b-gal positivity and reduced replicative capacities. These alterations were pronounced in microvascular ECs. They developed an irregular and hypertrophic phenotype. Such changes were associated with decreased SIRT (1-7) mRNA expressions. We also found that p300 and SIRT1 regulate each other in such process, as silencing one led to increase of the others' expression. Furthermore, HG caused reduction in FOXO1's DNA binding ability and antioxidant target gene expressions. Chemically induced increased SIRT1 activity and p300 knockdown corrected these abnormalities slowing aging-like changes. Diabetic animals showed increased cellular senescence in renal glomerulus and retinal blood vessels along with reduced SIRT1 mRNA expressions in these tissues. Data from this study demonstrated that hyperglycemia accelerates aging-like process in the vascular ECs and such process is mediated via downregulation of SIRT1, causing reduction of mitochondrial antioxidant enzyme in a p300 and FOXO1 mediated pathway.
Several members of the sirtuin family (SIRT1-7), which are a highly conserved family of NAD+-dependent enzymes, play an important role in tumor formation. Recent studies indicate that SIRT4 acts as a tumor suppressor by regulating glutamine metabolism. In the present study, we investigated the expression and activity of SIRT4 in colorectal cancer. Using a tissue microarray of 89 colorectal cancer cases, we found that SIRT4 was significantly downregulated in colorectal cancer tissues compared with that noted in the corresponding normal tissue (P<0.001). Lower SIRT4 levels were associated with worse pathological differentiation (P=0.031) and poorer post-operative overall survival rate (P=0.041). We found that SIRT4 overexpression inhibited the proliferation of colorectal cancer cells in vitro and in vivo. SIRT4 inhibited the glutamine metabolism of colorectal cancer cells and synergistically with glycolysis inhibitors induced cell death. SIRT4 also increased the sensitivity of colorectal cancer cells to chemotherapeutic drug 5-fluorouracil by inhibiting the cell cycle. Together, these results highlight the prognostic value of SIRT4 in colorectal cancer and the potential application of SIRT4 in colorectal cancer treatment.
Mammalian sirtuins are involved in the control of metabolism and life-span regulation. Here, we link the mitochondrial sirtuin SIRT4 with cellular senescence, skin aging, and mitochondrial dysfunction. SIRT4 expression significantly increased in human dermal fibroblasts undergoing replicative or stress-induced senescence triggered by UVB or gamma-irradiation. In-vivo, SIRT4 mRNA levels were upregulated in photoaged vs. non-photoaged human skin. Interestingly, in all models of cellular senescence and in photoaged skin, upregulation of SIRT4 expression was associated with decreased levels of miR-15b. The latter was causally linked to increased SIRT4 expression because miR-15b targets a functional binding site in the SIRT4 gene and transfection of oligonucleotides mimicking miR-15b function prevented SIRT4 upregulation in senescent cells. Importantly, increased SIRT4 negatively impacted on mitochondrial functions and contributed to the development of a senescent phenotype. Accordingly, we observed that inhibition of miR-15b, in a SIRT4-dependent manner, increased generation of mitochondrial reactive oxygen species, decreased mitochondrial membrane potential, and modulated mRNA levels of nuclear encoded mitochondrial genes and components of the senescence-associated secretory phenotype (SASP). Thus, miR-15b is a negative regulator of stress-induced SIRT4 expression thereby counteracting senescence associated mitochondrial dysfunction and regulating the SASP and possibly organ aging, such as photoaging of human skin.
Mitochondrial genes play important roles in cellular energy metabolism, free radical generation, and apoptosis. Dysregulation of these genes have long been suspected to contribute to the generation of reactive oxygen species (ROS), increased proliferation and progression of cancer. A family of orthologues of yeast silent information regulator 3 (SIRT3), 4 (SIRT4) and mitochondrial tumor suppressor 1 (MTUS1) are important mitochondrial tumor suppressor genes which play an important role in the progression of multiple cancers. However, their role in the development of oxidative stress, enhanced proliferation and progression of head and neck squamous cell carcinoma (HNSCC) has not yet been studied. In this study we aimed to test the association between reduced mitochondrial tumor suppressor genes' activities and enhancement in tissue oxidative stress and cell proliferation in HNSCC cases. The expression of mitochondrial tumor suppressor genes (SIRT3, SIRT4 and MTUS1), mitochondrial DNA repair gene (OGG1-2a) and a proliferation marker (Ki-67) was studied in a study cohort of 120 HNSCC patients and controls with reverse transcriptase polymerase chain reaction (RT-PCR) and real-time PCR (qPCR) in order to determine the potential prognostic significance of these genes. A statistically significant downregulation of SIRT3 (p
Mice overexpressing the longevity protein SIRT6 or deficient for the liver's most prevalent microRNA miR-122 display a similar set of phenotypes, including improved lipid profile and protection against damage linked to obesity. Here, we show that miR-122 and SIRT6 negatively regulate each other's expression. SIRT6 downregulates miR-122 by deacetylating H3K56 in the promoter region. MiR-122 binds to three sites on the SIRT6 3' UTR and reduces its levels. The interplay between SIRT6 and miR-122 is manifested in two physiologically relevant ways in the liver. First, they oppositely regulate a similar set of metabolic genes and fatty acid β-oxidation. Second, in hepatocellular carcinoma patients, loss of a negative correlation between SIRT6 and miR-122 expression is significantly associated with better prognosis. These findings show that SIRT6 and miR-122 negatively regulate each other to control various aspects of liver physiology and SIRT6-miR-122 correlation may serve as a biomarker for hepatocarcinoma prognosis.
SIRT6, a member of the mammalian sirtuins family, functions as a mono-ADP-ribosyl transferase and NAD+-dependent deacylase of both acetyl groups and long-chain fatty acyl groups. SIRT6 regulates diverse cellular functions such
as transcription, genome stability, telomere integrity, DNA repair, inflammation and metabolic related diseases such as diabetes,
obesity and cancer. In this review, we will discuss the implication of SIRT6 in the biology of cancer and the relevance to
organism homeostasis and lifespan.
Glucokinase (GK), mainly expressed in the liver and pancreatic β-cells, is critical for maintaining glucose homeostasis. GK expression and kinase activity, respectively, are both modulated at the transcriptional and post-translational levels. Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis. Although hepatic GKRP is known to be regulated by allosteric mechanisms, the precise details of modulation of GKRP activity, by post-translational modification, are not well known. Here, we demonstrate that GKRP is acetylated at Lys5 by the acetyltransferase p300. Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export. Deacetylation of GKRP is effected by the NAD+-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide. Moreover, the livers of db/db obese, diabetic mice also show elevated GKRP acetylation, suggesting a broader, critical role in regulating blood glucose. Given that acetylated GKRP may affiliate with type-2 diabetes mellitus (T2DM), understanding the mechanism of GKRP acetylation in the liver could reveal novel targets within the GK-GKRP pathway, for treating T2DM and other metabolic pathologies.
Impaired angiogenesis is a prominent risk factor that contributes to the development of diabetes-associated cardiovascular disease (CVD). MicroRNAs (miRNAs), small non-coding RNAs, are implicated as important regulators of vascular function including endothelial cell differentiation, proliferation and angiogenesis. In-silico analysis and in-vitro studies indicate that SIRT1 is a potential target for endothelial cell specific miRNAs. In this study, we investigated the molecular crosstalk between miR-34a, the protein product of SIRT1 (sirtuin1) and the antidiabetic drug, metformin, in hyperglycaemia-mediated impaired angiogenesis in mouse microvascular endothelial cells (MMECs). MMECs were cultured, transfected with either a miR-34a inhibitor or mimic in normal glucose (NG, 11 mM) or high glucose (HG, 40 mM) in the presence or absence of metformin. The expression of miR-34a, sirtuin1 and their signalling targets were evaluated. miR-34a expression is upregulated in a hyperglycaemic milieu and parallels changes in the expression of sirtuin1, post-translational modification of eNOS (phospho/acetylation) as well as an impairment in angiogenesis. The presence of metformin, or the inhibition of miR-34a using an anti-miR-34a inhibitor, increases the expression of sirtuin1 and attenuates the impairment in angiogenesis in HG-exposed MMECs. In contrast, overexpression of a miR-34a mimic prevents metformin-mediated protection. These data indicate that miR-34a, via the regulation of sirtuin1 expression, has an anti-angiogenic action in MMECs, which can be modulated by metformin. In summary, miR-34a represents both a target whereby metformin mediates its vasculoprotective actions and also a potential therapeutic target for the prevention/treatment of diabetic vascular disease.
Sirtuin 1 (SIRT1), an NAD+-dependent histone deacetylase, plays crucial roles in various biological processes including longevity, stress response,
and cell survival. Endoplasmic reticulum (ER) stress is caused by dysfunction of ER homeostasis and exacerbates various diseases
including diabetes, fatty liver, and chronic obstructive pulmonary disease. Although several reports have shown that SIRT1
negatively regulates ER stress and ER stress-induced responses in vitro and in vivo, the effect of ER stress on SIRT1 is less explored. In this study, we showed that ER stress induced SIRT1 expression in vitro and in vivo. We further determined the molecular mechanisms of how ER stress induces SIRT1 expression. Surprisingly, the conventional
ER stress-activated transcription factors XBP1, ATF4, and ATF6 seem to be dispensable for SIRT1 induction. Based on inhibitor
screening experiments with SIRT1 promoter, we found that the PI3K-Akt-GSK3β signaling pathway is required for SIRT1 induction
by ER stress. Moreover, we showed that pharmacological inhibition of SIRT1 by EX527 inhibited the ER stress-induced cellular
death in vitro and severe hepatocellular injury in vivo, indicating a detrimental role of SIRT1 in ER stress-induced damage responses. Collectively, these data suggest that SIRT1
expression is up-regulated by ER stress and contributes to ER stress-induced cellular damage.
Sexual dysfunction and cognitive deficits are markers of the aging process. Mammalian sirtuins (SIRT), encoded by sirt 1-7 genes, are known as aging molecules which are sensitive to serotonin (5-hydroxytryptamine, 5-HT). Whether the 5-HT system regulates SIRT in the preoptic area (POA), which could affect reproduction and cognition has not been examined. Therefore, this study was designed to examine the effects of citalopram (CIT, 10 mg/kg for 4 weeks), a potent selective-serotonin reuptake inhibitor and aging on SIRT expression in the POA of male mice using real-time PCR and immunocytochemistry. Age-related increases of sirt1, sirt4, sirt5, and sirt7 mRNA levels were observed in the POA of 52 weeks old mice. Furthermore, 4 weeks of chronic CIT treatment started at 8 weeks of age also increased sirt2 and sirt4 mRNA expression in the POA. Moreover, the number of SIRT4 immuno-reactive neurons increased with aging in the medial septum area (12 weeks = 1.00 ± 0.15 vs. 36 weeks = 1.68 ± 0.14 vs. 52 weeks = 1.54 ± 0.11, p < 0.05). In contrast, the number of sirt4-immunopositive cells did not show a statistically significant change with CIT treatment, suggesting that the increase in sirt4 mRNA levels may occur in cells in which sirt4 is already being expressed. Taken together, these studies suggest that CIT treatment and the process of aging utilize the serotonergic system to up-regulate SIRT4 in the POA as a common pathway to deregulate social cognitive and reproductive functions.
Among a number of non-coding RNAs, role of microRNAs (miRNAs) in cancer cell proliferation, cancer initiation, development and metastasis have been extensively studied and miRNA based therapeutic approaches are being pursued. Prostate cancer (PCa) is a major health concern and several deregulated miRNAs have been described in PCa. miR-212 is differentially modulated in multiple cancers however its function remains elusive. In this study, we found that miR-212 is downregulated in PCa tissues when compared with benign adjacent regions (n = 40). Also, we observed reduced levels of circulatory miR-212 in serum from PCa patients (n = 40) when compared with healthy controls (n = 32). Elucidating the functional role of miR-212, we demonstrate that miR-212 negatively modulates starvation induced autophagy in PCa cells by targeting sirtuin 1 (SIRT1). Overexpression of miR-212 also leads to inhibition of angiogenesis and cellular senescence. In conclusion, our study indicates a functional role of miR-212 in PCa and suggests the development of miR-212 based therapies.
Aim:
To reveal the functions of microRNAs (miRNAs) with respect to hepatic stellate cells (HSCs) in response to portal hypertension.
Methods:
Primary rat HSCs were exposed to static water pressure (10 mmHg, 1 h) and the pressure-induced miRNA expression profile was detected by next-generation sequencing. Quantitative real-time polymerase chain reaction was used to verify the expression of miRNAs. A potential target of MiR-9a-5p was measured by a luciferase reporter assay and Western blot. CCK-8 assay and Transwell assay were used to detect the proliferation and migration of HSCs under pressure.
Results:
According to the profile, the expression of miR-9a-5p was further confirmed to be significantly increased after pressure overload in HSCs (3.70 ± 0.61 vs 0.97 ± 0.15, P = 0.0226), which resulted in the proliferation, migration and activation of HSCs. In vivo, the up-regulation of miR-9a-5p (2.09 ± 0.91 vs 4.27 ± 1.74, P = 0.0025) and the down-regulation of Sirt1 (2.41 ± 0.51 vs 1.13 ± 0.11, P = 0.0006) were observed in rat fibrotic liver with portal hypertension. Sirt1 was a potential target gene of miR-9a-5p. Through restoring the expression of Sirt1 in miR-9a-5p transfected HSCs on pressure overload, we found that overexpression of Sirt1 could partially abrogate the miR-9a-5p mediated suppression of the proliferation, migration and activation of HSCs.
Conclusion:
Our results suggest that during liver fibrosis, portal hypertension may induce the proliferation, migration and activation of HSCs through the up-regulation of miR-9a-5p, which targets Sirt1.
Cyclic adenosine monophosphate (cAMP) plays an important role in many biological processes as a second messenger, and cAMP treatment has been reported to extend the lifespan of wild-type Drosophila melanogaster. Our study showed that exogenous cAMP improved ageing-related phenotypes by increasing the protein level of Sirtuins, which prevented metabolic disorders to mimic the effect of calorie restriction. Experiments in vitro showed that cAMP directly bound to SIRT1 and SIRT3 and consequently increased their activity. These findings suggest that cAMP slows the ageing process and is a good candidate to mimic calorie restriction. Our research provides a promising therapeutic strategy to target metabolic disorder-induced ageing-related diseases.
The mitochondrial deacetylase SIRT3 regulates several important metabolic processes. SIRT3 is transcriptionally upregulated in multiple tissues during nutrient stresses such as dietary restriction and fasting, but the molecular mechanism of this induction is unclear. We conducted a bioinformatic study to identify transcription factor(s) involved in SIRT3 induction. Our analysis identified an enrichment of binding sites for nuclear respiratory factor 2 (NRF-2), a transcription factor known to play a role in the expression of mitochondrial genes, in the DNA sequences of SIRT3 and genes with closely correlated expression patterns. In vitro, knockdown or overexpression of NRF-2 modulated SIRT3 levels, and the NRF-2α subunit directly bound to the SIRT3 promoter. Our results suggest that NRF-2 is a regulator of SIRT3 expression and may shed light on how SIRT3 is upregulated during nutrient stress.
© 2015 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.
SIRT4, which is localised in the mitochondria, is one of the least characterised members of the sirtuin family of nicotinamide adenine dinucleotide-dependent enzymes that play key roles in multiple cellular processes such as metabolism, stress response and longevity. There are only a few studies that have characterised its function and assessed its clinical significance in human cancers.
We established colorectal cancer cell lines (SW480, HCT116, and HT29) overexpressing SIRT4 and investigated their effects on proliferation, migration and invasion, as well as E-cadherin expression, that negatively regulates tumour invasion and metastases. The associations between SIRT4 expression in colorectal cancer specimens and clinicopathological features including prognosis were assessed by immunohistochemistry.
SIRT4 upregulated E-cadherin expression and suppressed proliferation, migration and invasion through inhibition of glutamine metabolism in colorectal cancer cells. Moreover, SIRT4 expression in colorectal cancer decreased with the progression of invasion and metastasis, and a low expression level of SIRT4 was correlated with a worse prognosis.
SIRT4 has a tumour-suppressive function and may serve as a novel therapeutic target in colorectal cancer.British Journal of Cancer advance online publication, 18 June 2015; doi:10.1038/bjc.2015.226 www.bjcancer.com.
Although there are seven mammalian sirtuins (SIRT1-7), little is known about their expression in the aging brain. To characterize the change(s) in mRNA and protein expression of SIRT1-7 and their associated proteins in the brain of "physiologically" aged Wistar rats. We tested mRNA and protein expression levels of rat SIRT1-7, and the levels of associated proteins in the brain using RT-PCR and western blotting. Our data shows that SIRT1 expression increases with age, concurrently with increased acetylated p53 levels in all brain regions investigated. SIRT2 and FOXO3a protein levels increased only in the occipital lobe. SIRT3-5 expression declined significantly in the hippocampus and frontal lobe, associated with increases in superoxide and fatty acid oxidation levels, and acetylated CPS-1 protein expression, and a reduction in MnSOD level. While SIRT6 expression declines significantly with age acetylated H3K9 protein expression is increased throughout the brain. SIRT7 and Pol I protein expression increased in the frontal lobe. This study identifies previously unknown roles for sirtuins in regulating cellular homeostasis and healthy aging.
Several members of the SIRT family (SIRT1-7), which are a highly conserved family of NAD(+)-dependent enzymes, play an important role in tumor formation. Recently, several studies have suggested that SIRT4 can regulate glutamine metabolism yet have tumor suppressor function too. However, our understanding of SIRT4 expression and its association with the clinicopathological parameters remains poor.
We evaluated SIRT4 protein expression levels in gastric adenocarcinoma and corresponding normal gastric tissue by immunohistochemical staining on a tissue microarray that included 75 gastric adenocarcinoma patients. We also determined the association between SIRT4 expression levels and selected clinicopathological parameters in gastric adenocarcinoma.
We found that the expression level of SIRT4 in gastric adenocarcinoma was significantly lower than the corresponding normal tissue levels (P=0.003). Besides, lower SIRT4 levels were observed in pathological grade (P=0.002), depth of tumor invasion (P=0.034), positive lymph node numbers (P=0.005) and UICC stage (P=0.002).
Our results support the notion that SIRT4 behaves as a tumor suppressor at the human tissue protein level. In addition, our data indicate that SIRT4 might be closely involved in the process of gastric adenocarcinoma development and it might potentially serve as a diagnostic biomarker and therapeutic target in gastric adenocarcinoma.
Copyright © 2015 Elsevier Masson SAS. All rights reserved.
The anti-tumor effects of quercetin have been reported, but the underlying molecular mechanisms remain to be elucidated. The aim of present study was to explore the role of miRNA in the anticancer effects of quercetin.
The differential miRNAs expression between the HepG2 and Huh7 cells treated by quercetin were detected by microarray. The xCELLigence, Flow cytometry, RT-PCR and Western blot were used to analyze the cell proliferation, cell apoptosis, cell cycle arrest, anti-tumor genes, and protein expression.
miR-34a was up-regulated in HepG2 cells treated by quercetin exhibiting wild-type p53. When inhibiting the miR-34a, the sensitivity of the cells to quercetin decreased and the expression of the SIRT1 was up-regulated, but the acetylation of p53 and the expression of some genes related to p53 down-regulated.
miR-34a plays an important role in the anti-tumor effects of querctin in HCC, miR-34a may be a tiemolecule between the p53 and SIRT1 and is composed of a p53/miR-34a/SIRT1 signal feedback loop, which could enhance apoptosis signal and significantly promote cell apoptosis. © 2015 S. Karger AG, Basel.
Gastric cancer is the fourth most common cancer worldwide, with a low 5-year survival rate. Epigenetic modification plays pivotal roles in gastric cancer development. However, the role of histone-modifying enzymes in gastric cancer remains largely unknown. Here we report that Sirt7, a NAD+-dependent class III histone deacetylase, is over-expressed in human gastric cancer tissues. Sirt7 level is significantly correlated with disease stage, metastasis, and survival. Knockdown of Sirt7 in gastric cancer cells inhibits cell proliferation and colony formation in vitro. In vivo subcutaneous xenograft results also show that Sirt7 knockdown can markedly repress gastric cancer cell growth. In addition, Sirt7 depletion induces apoptosis in gastric cancer cells via up-regulating expression of pro-apoptotic proteins and down-regulating anti-apoptotic proteins. Mechanically, Sirt7 binds to the promoter of miR-34a and deacetylases the H3K18ac, thus represses miR-34a expression. Reversely, depletion of miR-34a inhibits gastric cancer apoptosis induced by Sirt7 knockdown, and restores cellular capacity of proliferation and colony formation. miR-34a depletion reduces Sirt7-knockdown-induced arrest of gastric growth. Finally, miR-34a is tightly associated with survival of patients with gastric cancer.
The mitochondrial protein deacetylase sirtuin (SIRT) 3 may mediate exercise training-induced increases in mitochondrial biogenesis and improvements in reactive oxygen species (ROS) handling. We determined the requirement of AMP-activated protein kinase (AMPK) for exercise training-induced increases in skeletal muscle abundance of SIRT3 and other mitochondrial proteins. Exercise training for 6.5 weeks increased SIRT3 (p < 0.01) and superoxide dismutase 2 (MnSOD; p < 0.05) protein abundance in quadriceps muscle of wild-type (WT; n = 13–15), but not AMPK α2 kinase dead (KD; n = 12–13) mice. We also observed a strong trend for increased MnSOD abundance in exercise-trained skeletal muscle of healthy humans (p = 0.051; n = 6). To further elucidate a role for AMPK in mediating these effects, we treated WT (n = 7–8) and AMPK α2 KD (n = 7–9) mice with 5-amino-1-β-D-ribofuranosyl-imidazole-4-carboxamide (AICAR). Four weeks of daily AICAR injections (500 mg/kg) resulted in AMPK-dependent increases in SIRT3 (p < 0.05) and MnSOD (p < 0.01) in WT, but not AMPK α2 KD mice. We also tested the effect of repeated AICAR treatment on mitochondrial protein levels in mice lacking the transcriptional coactivator peroxisome proliferator-activated receptor γ-coactivator 1α (PGC-1α KO; n = 9–10). Skeletal muscle SIRT3 and MnSOD protein abundance was reduced in sedentary PGC-1α KO mice (p < 0.01) and AICAR-induced increases in SIRT3 and MnSOD protein abundance was only observed in WT mice (p < 0.05). Finally, the acetylation status of SIRT3 target lysine residues on MnSOD (K122) or oligomycin-sensitivity conferring protein (OSCP; K139) was not altered in either mouse or human skeletal muscle in response to acute exercise. We propose an important role for AMPK in regulating mitochondrial function and ROS handling in skeletal muscle in response to exercise training.
Deterioration of adult stem cells accounts for much of aging-associated compromised tissue maintenance. How stem cells maintain metabolic homeostasis remains elusive. Here, we identified a regulatory branch of the mitochondrial unfolded protein response (UPR(mt)), which is mediated by the interplay of SIRT7 and NRF1 and is coupled to cellular energy metabolism and proliferation. SIRT7 inactivation caused reduced quiescence, increased mitochondrial protein folding stress (PFS(mt)), and compromised regenerative capacity of hematopoietic stem cells (HSCs). SIRT7 expression was reduced in aged HSCs, and SIRT7 up-regulation improved the regenerative capacity of aged HSCs. These findings define the deregulation of a UPR(mt)-mediated metabolic checkpoint as a reversible contributing factor for HSC aging.
Copyright © 2015, American Association for the Advancement of Science.
A hesitant fuzzy linguistic set is an extension of both a linguistic term set and a hesitant fuzzy set. It combines a quantitative evaluation with a qualitative evaluation, which can describe the real preferences of decision makers and reflect their uncertainty, hesitancy and inconsistency. The focus of this paper is those multi-criteria decision-making (MCDM) problems in which the criteria values take the form of hesitant fuzzy linguistic numbers (HFLNs). Having reviewed the relevant literature, the Hausdorff distance for HFLNs is provided and some linguistic scale functions are applied. Subsequently, two hesitant fuzzy linguistic MCDM methods are proposed, which are based on the proposed distance measure and the TOPSIS and TODIM methods. The first of these MCDM methods is based on complete rationality, whilst the second is based on bounded rationality. Finally, an illustrative example is provided to verify the proposed methods, which are then compared to the existing approaches.
The sirtuins are NAD+-dependent protein deacetylases and/or ADP-ribosyltransferases that play roles in metabolic homeostasis, stress response and potentially aging. This enzyme family resides in different subcellular compartments, and acts on a number of different targets in the nucleus, cytoplasm and in the mitochondria. Despite their recognized ability to regulate metabolic processes, the roles played by specific sirtuins in the brain—the most energy demanding tissue in the body—remains less well investigated and understood. In the present study, we examined the regional mRNA and protein expression patterns of individual sirtuin family members in the developing, adult, and aged rat brain. Our results show that while each sirtuin is expressed in the brain at each of these different stages, they display unique spatial and temporal expression patterns within the brain. Further, for specific members of the family, the protein expression profile did not coincide with their respective mRNA expression profile. Moreover, using primary cultures enriched for neurons and astrocytes respectively, we found that specific sirtuin members display preferential neural lineage expression. Collectively, these results provide the first composite illustration that sirtuin family members display differential expression patterns in the brain, and provide evidence that specific sirtuins could potentially be targeted to achieve cell-type selective effects within the brain.
The cAMP signaling system regulates various cellular functions, including metabolism, gene expression, and death. Sirtuin 6 (SIRT6) removes acetyl groups from histones and regulates genomic stability and cell viability. We hypothesized that cAMP modulates SIRT6 activity to regulate apoptosis. Therefore, we examined the effects of cAMP signaling on SIRT6 expression and radiation-induced apoptosis in lung cancer cells. cAMP signaling in H1299 and A549 human non-small cell lung cancer cells was activated via the expression of constitutively active Gαs plus treatment with prostaglandin E2 (PGE2), isoproterenol, or forskolin. The expression of sirtuins and signaling molecules were analyzed by western blotting. Activation of cAMP signaling reduced SIRT6 protein expression in lung cancer cells. cAMP signaling increased the ubiquitination of SIRT6 protein and promoted its degradation. Treatment with MG132 and inhibiting PKA with H89 or with a dominant-negative PKA abolished the cAMP-mediated reduction in SIRT6 levels. Treatment with PGE2 inhibited c-Raf activation by increasing inhibitory phosphorylation at Ser-259 in a PKA-dependent manner, thereby inhibiting downstream MEK-ERK signaling. Inhibiting ERK with inhibitors or with dominant-negative ERKs reduced SIRT6 expression, whereas activation of ERK by constitutively active ERK abolished the SIRT6-depleting effects of PGE2. cAMP signaling also augmented radiation-induced apoptosis in lung cancer cells. This effect was abolished by exogenous expression of SIRT6. It is concluded that cAMP signaling reduces SIRT6 expression by promoting its ubiquitin-proteasome-dependent degradation, a process mediated by the PKA-dependent inhibition of the Raf-MEK-ERK pathway. Reduced SIRT6 expression mediates the augmentation of radiation-induced apoptosis by cAMP signaling in lung cancer cells.
Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
Sirtuins are a class of enzymes originally identified as nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacetylases. Among the seven mammalian sirtuins, SIRT1-7, only SIRT1-3 possess efficient deacetylase activity in vitro, whereas SIRT4-7 possess very weak in vitro deacetylase activity. Several sirtuins that exhibit weak deacetylase activity have recently been shown to possess more efficient activity for the removal other acyl lysine modifications, such as succinyl lysine and palmitoyl lysine. Here, we demonstrate that even the well-known deacetylase SIRT2 possesses efficient activity for the removal of long-chain fatty acyl groups. The catalytic efficiency (kcat/Km) for the removal of a myristoyl group is slightly higher than that for the removal of an acetyl group. The crystal structure of SIRT2 in complex with a thiomyristoyl peptide reveals that SIRT2 possesses a large hydrophobic pocket that can accommodate the myristoyl group. Comparison of the SIRT2 acyl pocket to those of SIRT1, SIRT3, and SIRT6 reveals that the acyl pockets of SIRT1-3 are highly similar, and to a lesser degree, similar to that of SIRT6. The efficient in vitro demyristoylase activity of SIRT2 suggests that this activity may be physiologically relevant and warrants future investigative studies.
Recently, we have found that a number of microRNAs (miRNAs) and proteins are involved in the response to acupuncture therapy in hypertensive rats. Our bioinformatics study suggests an association between these miRNAs and proteins, which include miR-339 and sirtuin 2 (Sirt2). In this paper, we aimed to investigate whether Sirt2 was a direct target of miR-339 in neurons. In human SH-SY5Y cells, the luciferase assay implied that Sirt2 was likely a target of miRNA-339. Overexpression of miR-339 downregulated Sirt2 expression, while knockdown of miR-339 upregulated Sirt2 expression in human SH-SY5Y cells and rat PC12 cells. In addition, overexpression of miR-399 increased the acetylation of nuclear factor-κB (NF-κB) and forkhead box protein O1 (FOXO1) in SH-SY5Y cells, which are known targets of Sirt2. Our findings demonstrate that miR-339 regulates Sirt2 in human and rat neurons. Since Sirt2 plays a critical role in multiple important cellular functions, our data imply that acupuncture may act through epigenetic changes and subsequent action on their targets, such as miRNA-339/Sirt2/NF-κB/FOXO1 axis. Some physiological level changes of neurons after altering the miR-339 levels are needed to validate the suggested therapeutic role of miR-339/Sirt2/NF-κB/FOXO1 axis in response to acupuncture therapy in the future work.
Downstream signaling of physiological and pathological cell responses depends on post-translational modification such as ubiquitination. The mechanisms regulating downstream DNA damage response (DDR) signaling are not completely elucidated. Sirtuin 1 (SIRT1), the founding member of Class III histone deacetylases, regulates multiple steps in DDR and is closely associated with many physiological and pathological processes. However, the role of post-translational modification or ubiquitination of SIRT1 during DDR is unclear. We show that SIRT1 is dynamically and distinctly ubiquitinated in response to DNA damage. SIRT1 was ubiquitinated by the MDM2 E3 ligase in vitro and in vivo. SIRT1 ubiquitination under normal conditions had no effect on its enzymatic activity or rate of degradation; hypo-ubiquitination, however, reduced SIRT1 nuclear localization. Ubiquitination of SIRT1 affected its function in cell death and survival in response to DNA damage. Our results suggest that ubiquitination is required for SIRT1 function during DDR.
Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
Increasing evidences have indicated histone posttranslational modifications (PTMs) play crucial roles in regulating a wide range of chromatin-templated nuclear processes, such as gene transcription, DNA replication and DNA damage repair [1]. PTMs on histones have been proposed to serve as histone code that provides epigenetic information from a mother cell to daughter cells [2]. Histone code is under control of opposing enzymes that ‘write’ or ‘erase’ modifications on histones [1, 3]. Meanwhile, this epigenetic code could be translated by ‘reader’ proteins, which can recognize specific histone modifications, into biological readout, without alteration of genetic information [4, 5].
Mammalian Sirtuin proteins (SIRTs) are homologs of yeast Sir2, and characterized as class III histone deacetylases of NAD(+) dependence. Unlike their lower counterparts that directly involved in the extending of lifespan, mammalian SIRTs are mainly function in metabolism and cellular homeostasis, among them, SIRT7 is the least understood. SIRT7 is localized in nucleus and rich in nucleoli associated with RNA polymerase I, and correlated with cell proliferation. In contrast, SIRT7 has recently been demonstrated to specifically deacetylate H3K18ac in the chromatin, and in most cases represses proliferation. Although MicroRNA as miR-125b has been reported to down-regulate SIRT7 by binding to its 3'UTR, however, how SIRT7 gene is regulated remains unclear. Here, we identified the transcription initiation site of human SIRT7 gene at the upstream 23(rd) A nucleotide respective to the translational codon, and the SIRT7 is a TATA-less and initiator-less gene. The sequences in the upstream region between -256 and -129bp are identical with important functions in the three species detected. A C/EBPα responding element is found that binds both C/EBPα and C/EBPβ in vitro. We showed TSA induced SIRT7 gene transcription and only the HDAC3, but not its catalytic domain depleted mutant, interacted with C/EBPα to occupy the C/EBPα element and repressed SIRT7 gene in the hepatocellular carcinoma cells. To our knowledge, this is the first report on the regulation mechanism of SIRT7 gene, in which, HDAC3 collaborated with C/EBPα to occupy its responding element in the upstream region of SIRT7 gene and repressed its expression in human cells.
Nicotinamide adenine dinucleotide (NAD+) is a coenzyme found in all living cells. It serves both as a critical coenzyme for enzymes that fuel reduction-oxidation reactions, carrying electrons from one reaction to another, and as a cosubstrate for other enzymes such as the sirtuins and poly(adenosine diphosphate-ribose) polymerases. Cellular NAD+ concentrations change during aging, and modulation of NAD+ usage or production can prolong both health span and life span. Here we review factors that regulate NAD+ and discuss how supplementation with NAD+ precursors may represent a new therapeutic opportunity for aging and its associated disorders, particularly neurodegenerative diseases.
NAD, as well as its phosphorylated form, NADP, are best known as electron carriers and co-substrates of various redox reactions. As such they participate in approximately one quarter of all reactions listed in the reaction database KEGG. In metabolic pathway analysis, the total amount of NAD is usually assumed to be constant. That means that changes in the redox state might be considered, but concentration changes of the NAD moiety are usually neglected. However, a growing number of NAD-consuming reactions have been identified, showing that this assumption does not hold true in general. NAD-consuming reactions are common characteristics of NAD+ -dependent signalling pathways and include mono- and poly-ADP-ribosylation of proteins, NAD+ -dependent deacetylation by sirtuins and the formation of messenger molecules such as cyclic ADP-ribose (cADPR) and nicotinic acid (NA)-ADP (NAADP). NAD-consuming reactions are thus involved in major signalling and gene regulation pathways such as DNA-repair or regulation of enzymes central in metabolism. All known NAD+ -dependent signalling processes include the release of nicotinamide (Nam). Thus cellular NAD pools need to be constantly replenished, mostly by recycling Nam to NAD+ . This process is, among others, regulated by the circadian clock, causing complex dynamic changes in NAD concentration. As disturbances in NAD homoeostasis are associated with a large number of diseases ranging from cancer to diabetes, it is important to better understand the dynamics of NAD metabolism to develop efficient pharmacological invention strategies to target this pathway.
Cancer cells display an altered metabolic circuitry that is directly regulated by oncogenic mutations and loss of tumor suppressors. Mounting evidence indicates that altered glutamine metabolism in cancer cells has critical roles in supporting macromolecule biosynthesis, regulating signaling pathways, and maintaining redox homeostasis, all of which contribute to cancer cell proliferation and survival. Thus, intervention in these metabolic processes could provide novel approaches to improve cancer treatment. This review summarizes current findings on the role of glutaminolytic enzymes in human cancers and provides an update on the development of small molecule inhibitors to target glutaminolysis for cancer therapy.
SIRT1, a class III histone deacetylase, exerts inhibitory effects on tumorigenesis and is downregulated in gastric cancer. However, the role of microRNAs in the regulation of SIRT1 in gastric cancer is still largely unknown. Here, we identified miR-543 as a predicted upstream regulator of SIRT1 using 3 different bioinformatics databases. Mimics of miR-543 significantly inhibited the expression of SIRT1, whereas an inhibitor of miR-543 increased SIRT1 expression. MiR-543 directly targeted the 3'-UTR of SIRT1, and both of the two binding sites contributed to the inhibitory effects. In gastric epithelium-derived cell lines, miR-543 promoted cell proliferation and cell cycle progression, and overexpression of SIRT1 rescued the above effects of miR-543. The inhibitory effects of miR-543 on SIRT1 were also validated using clinical gastric cancer samples. Moreover, we found that miR-543 expression was positively associated with tumor size, clinical grade, TNM stage and lymph node metastasis in gastric cancer patients. Our results identify a new regulatory mechanism of miR-543 on SIRT1 expression in gastric cancer, and raise the possibility that the miR-543/SIRT1 pathway may serve as a potential target for the treatment of gastric cancer.
Sirtuins are an evolutionarily conserved family of NAD(+)-dependent deacylases that display diversity in subcellular localization and function. SIRT2, the predominantly cytosolic sirtuin, is among the least understood of the seven mammalian sirtuin isoforms described (SIRT1-7). The purpose of this review is to summarize the most recent findings about the potential roles and effects of SIRT2 in mammalian metabolic homeostasis. We discuss the different functions and targets of SIRT2 in various physiological processes, including adipogenesis, fatty acid oxidation, gluconeogenesis, and insulin sensitivity. We also cover the role of SIRT2 in inflammation and oxidative stress due to the possible implications for metabolic disorders. Finally, we consider its potential as a therapeutic target for the prevention and treatment of type 2 diabetes.
Accumulating evidence demonstrates that microRNA-22 (miR-22) was deregulated in many types of cancers and was involved in various cellular processes related to carcinogenesis. However, the exact roles and mechanisms of miR-22 remain unknown in human renal cell carcinoma (RCC). Here, the relationship between miR-22 expression pattern and clinicopathological features of patients with EOC were determined by real-time quantitative RT-PCR (qRT-PCR). Furthermore, the role of miR-22 and possible molecular mechanisms in EOC were investigated by several in vitro approaches and in a nude mouse model. Results from qRT-PCR showed that miR-22 was significantly downregulated in RCC samples compared with corresponding non-cancerous tissues, which was significantly associated with tumor stage and lymph node metastasis. Functional study demonstrated that enforced overexpression of miR-22 in renal cancer cells inhibited proliferation, migration and invasion, and induced cell apoptosis in vitro, and suppressed tumor growth in vivo. In addition, SIRT1 was identified as a direct target of miR-22 by a luciferase reporter assay. Overexpression of miR-22 activated p53 and its downstream target p21 and PUMA, and the apoptosis markers cleaved CASP3 and PARP, and inhibited epithelial-mesenchymal transition (EMT). These findings showed that miR-22 functioned as tumor suppressor in RCC and blocked RCC growth and metastasis by directly targeting SIRT1 in RCC, indicating a potential novel therapeutic role in RCC treatment.
Sirtuin 1 (SIRT1) is a prototype mammalian NAD(+)-dependent protein deacetylase that has emerged as a key metabolic sensor in various metabolic tissues. Growing evidence suggests that SIRT1 regulates glucose and lipid metabolism through its deacetylase activity. In this review, we have summarized the recent progress in SIRT1 research with a particular focus on the role of SIRT1 in insulin resistance at different metabolic tissues. Recent data indicate that activated SIRT1 improves the insulin sensitivity of liver, skeletal muscle and adipose tissues and protects the function and cell mass of pancreatic β-cells. These findings suggest that SIRT1 might be a new therapeutic target for the prevention of disease related to insulin resistance, such as metabolic syndrome and type 2 diabetes mellitus.
Sirtuins, initially described as histone deacetylases and gene silencers in yeast, are now known to have much more functions and to be much more abundant in living organisms. Sirtuins gained much attention when they were first acknowledged to be responsible for some beneficial and longevity-promoting effects of calorie restriction in many species of animals - from fruit flies to mammals. In this paper, we discuss some detailed molecular mechanisms of inducing these effects, and wonder if they could be possibly mimicked without actually applying calorie restriction, through induction of sirtuin activity. It is known now that sirtuins, when adjusting the pattern of cellular metabolism to nutrient availability, can regulate many metabolic functions significant from the standpoint of aging research - including DNA repair, genome stability, inflammatory response, apoptosis, cell cycle, and mitochondrial functions. While carrying out these regulations, sirtuins cooperate with many transcription factors, including PGC-1a, NFKB, p53 and FoxO. This paper contains some considerations about possible use of facilitating activity of the sirtuins in prevention of aging, metabolic syndrome, chronic inflammation, and other diseases.
Succinylation refers to modification of lysine residues with succinyl groups donated by succinyl-CoA. Sirtuin5 (Sirt5) is a mitochondrial NAD(+)-dependent deacylase that catalyzes the removal of succinyl groups from proteins. Sirt5 and protein succinylation are conserved across species, suggesting functional importance of the modification. Sirt5 loss impacts liver metabolism but the role of succinylation in the heart has not been explored. We combined affinity enrichment with proteomics and mass spectrometry to analyze total succinylated lysine content of mitochondria isolated from WT and Sirt5(-/-) mouse hearts. We identified 887 succinylated lysine residues in 184 proteins. 44 peptides (5 proteins) occurred uniquely in WT samples, 289 (46 proteins) in Sirt5(-/-) samples, and 554 (133 proteins) were common to both groups. The 46 unique proteins in Sirt5(-/-) heart participate in metabolic processes such as fatty acid β-oxidation (Eci2) and branched chain amino acid catabolism, and include respiratory chain proteins (Ndufa7, 12, 13, Dhsa). We performed label-free analysis of the peptides common to WT and Sirt5(-/-) hearts. 16 peptides from 9 proteins were significantly increased in Sirt5(-/-) by at least 30%. The adenine nucleotide transporter 1 showed the highest increase in succinylation in Sirt5(-/-) (108.4 fold). The data indicate that succinylation is widespread in the heart and enriched in metabolic pathways. We examined whether the loss of Sirt5 would impact ischemia-reperfusion (I/R) injury and we found an increase in infarct size in Sirt5(-/-) hearts compared to WT littermates (68.5(+)/-1.1% Sirt5(-/-) vs 39.6(+)/(-) 6.8% WT) following 20min of ischemia and 90-minute reperfusion. We further demonstrate that I/R injury in Sirt5(-/-) heart is restored to WT levels by pretreatment with dimethyl malonate, a competitive inhibitor of succinate dehydrogenase (SDH), implicating alteration in SDH activity as causative of the injury.
Sirtuins or Sir2 family of proteins are a class of NAD(+) dependent protein deacetylases which are evolutionarily conserved from bacteria to humans. Some sirtuins also exhibit mono-ADP ribosyl transferase, demalonylation and desuccinylation activities. Originally identified in the yeast, these proteins regulate key cellular processes like cell cycle, apoptosis, metabolic regulation and inflammation. Humans encode seven sirtuin isoforms SIRT1-SIRT7 with varying intracellular distribution. Apart from their classic role as histone deacetylases regulating transcription, a number of cytoplasmic and mitochondrial targets of sirtuins have also been identified. Sirtuins have been implicated in longevity and accumulating evidences indicate their role in a spectrum of diseases like cancer, diabetes, obesity and neurodegenerative diseases. A number of studies have reported profound changes in SIRT1 expression and activity linked to mitochondrial functional alterations following hypoxic-ischemic conditions and following reoxygenation injury. The SIRT1 mediated deacetylation of targets such as PGC-1α, FOXO3, p53 and NF-κb has profound effect on mitochondrial function, apoptosis and inflammation. These biological processes and functions are critical in life-span determination and outcome following injury. Aging is reported to be characterized by declining SIRT1 activity and its increased expression or activation demonstrated prolonged life-span in lower forms of animals. A pseudohypoxic state due to declining NAD+ has also been implicated in aging. In this review we provide an overview of studies on the role of sirtuins in aging and injury.
Copyright © 2015. Published by Elsevier B.V.
Modification of histones is one of the important mechanisms of epigenetics, in which genetic control is determined by factors other than an individual's DNA sequence. Sirtuin family proteins, which are class III histone deacetylases (HDACs), were originally identified as gene silencers that affect the mating type of yeast, leading to the name 'silent mating type information regulation 2 (SIR2)'. They are characterized by their requirement of nicotinamide adenine dinucleotide (NAD+) for their enzyme activity, unlike other classes of HDACs. Sirtuins have traditionally been linked to longevity and the beneficial effects of calorie restriction and DNA damage repair. Recently, sirtuins have been shown to be involved in a wide range of physiological and pathological processes, including aging, energy responses to low calorie availability, and stress resistance, as well as apoptosis and inflammation. Sirtuins can also regulate mitochondrial biogenesis and circadian clocks. Seven sirtuin family proteins (Sirt1-7) have been identified as mammalian SIR2 orthologs, localized in different subcellular compartments, namely, the cytoplasm (Sirt1, 2), the mitochondria (Sirt3, 4, 5), and the nucleus (Sirt1, 2, 6, 7). Sirt1 is evolutionarily close to yeast SIR2 and has been the most intensively investigated in the cardiovascular system. Endogenous Sirt1 plays a pivotal role in mediating the cell death/survival process and has been implicated in the pathogenesis of cardiovascular disease. Downregulation of Sirt2 is protective against ischemic/reperfusion injury. Increased Sirt3 expression has been shown to correlate with longevity in humans. In addition, Sirt3 protects cardiomyocytes from aging and oxidative stress and suppresses cardiac hypertrophy. Sirt6 has also recently been demonstrated to attenuate cardiac hypertrophy, and Sirt7 is known to regulate apoptosis and stress responses in the heart. On the other hand, the roles of Sirt4 and Sirt5 in the heart remain largely uncharacterized.
Copyright © 2014, American Journal of Physiology - Heart and Circulatory Physiology.
Mitochondrial oxidative damage is hypothesized to contribute to the pathogenesis of chronic cholestatic liver diseases. Melatonin, an indolamine synthesized in the pineal gland, shows a wide range of physiological functions, and is under clinical investigation for expanded applications. Melatonin has demonstrated efficient protective effects against various types of oxidative damage in the liver system. This study investigates the protective effects of melatonin pretreatment on glycochenodeoxycholic acid (GCDCA)-induced hepatotoxicity and elucidates the potential mechanism of melatonin-mediated protection. Melatonin markedly decreased mitochondrial ROS (mROS) production in L02 cells treated with 100 µM GCDCA, and inhibited GCDCA-stimulated cytotoxicity. Notably, melatonin exerted its hepatoprotective effects by up-regulating SIRT3 activity and its expression level, thus regulating SOD2 acetylation and inhibiting the production of mROS induced by GCDCA. Moreover, siRNA targeting SIRT3 blocked the melatonin-mediated elevation in mitochondrial function by inhibiting SIRT3/SOD2 signaling. Importantly, melatonin -activated SIRT3 activity was completely abolished by AMPK siRNA transfection. Similar results were obtained in rat with bile duct ligation (BDL). In summary, our findings indicate that melatonin is a novel hepatoprotective small molecule that functions by elevating SIRT3, stimulating SOD2 activity and suppressing mitochondrial oxidative stress at least through AMPK, and that SIRT3 may be of therapeutic value in liver cell protection for GCDCA-induced hepatotoxicity.
Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, but its underlying mechanism is poorly understood. Here we show that hepatocyte nuclear factor 4α (HNF4α), a liver-enriched nuclear hormone receptor, is markedly inhibited, whereas miR-34a is highly induced in patients with non-alcoholic steatohepatitis, diabetic mice and mice fed a high-fat diet. miR-34a is essential for HNF4α expression and regulates triglyceride accumulation in human and murine hepatocytes. miR-34a inhibits very low-density lipoprotein secretion and promotes liver steatosis and hypolipidemia in an HNF4α-dependent manner. As a result, increased miR-34a or reduced HNF4α expression in the liver attenuates the development of atherosclerosis in Apoe(-/-) or Ldlr(-/-) mice. These data indicate that the miR-34a-HNF4α pathway is activated under common conditions of metabolic stress and may have a role in the pathogenesis of NAFLD and in regulating plasma lipoprotein metabolism. Targeting this pathway may represent a novel approach for the treatment of NAFLD.
Diabetic vascular smooth muscle cells (VSMCs) exhibit significantly increased rates of proliferation and migration, which was the most common pathological change in atherosclerosis. In addition, the study about the role for miRNAs in the regulation of VSMC proliferation is just beginning to emerge and additional miRNAs involved in VSMC proliferation modulation should be identified.
The expression of miR-138 and SIRT1 were examined in SMCs separated from db/db mice and in SMC lines C-12511 exposed to high glucose with qRT-PCR and western blot. The regulation of miR-138 on the expression of SMCs was detected with luciferase report assay. VSMCs proliferation and migration assays were performed to examine the effect of miR-138 inhibitor on VSMCs proliferation and migration.
We discovered that higher mRNA level of miR-138 and reduced expression of SIRT1 were observed in SMCs separated from db/db mice and in SMC lines C-12511. Moreover, luciferase report assay showed that the activity of SIRT1 3'-UTR was highly increased by miR-138 inhibitor and reduced by miR-138 mimic. In addition, we examined that the up-regulation of NF-κB induced by high glucose in SMCs was reversed by resveratrol and miR-138 inhibitor. MTT and migration assays showed that miR-138 inhibitor attenuated the proliferation and migration of smooth muscle cells.
In this study, we revealed that miR-138 might promote proliferation and migration of SMC in db/db mice through suppressing the expression of SIRT1.
Copyright © 2015. Published by Elsevier Inc.
Protein acylation links energetic substrate flux with cellular adaptive responses. SIRT5 is a NAD(+)-dependent lysine deacylase and removes both succinyl and malonyl groups. Using affinity enrichment and label free quantitative proteomics, we characterized the SIRT5-regulated lysine malonylome in wild-type (WT) and Sirt5(-/-) mice. 1,137 malonyllysine sites were identified across 430 proteins, with 183 sites (from 120 proteins) significantly increased in Sirt5(-/-) animals. Pathway analysis identified glycolysis as the top SIRT5-regulated pathway. Importantly, glycolytic flux was diminished in primary hepatocytes from Sirt5(-/-) compared to WT mice. Substitution of malonylated lysine residue 184 in glyceraldehyde 3-phosphate dehydrogenase with glutamic acid, a malonyllysine mimic, suppressed its enzymatic activity. Comparison with our previous reports on acylation reveals that malonylation targets a different set of proteins than acetylation and succinylation. These data demonstrate that SIRT5 is a global regulator of lysine malonylation and provide a mechanism for regulation of energetic flux through glycolysis.
Copyright © 2015 Elsevier Inc. All rights reserved.
Emerging data suggests that mitochondrial dysfunction is prominently involved in Alzheimer disease (AD) progression. Sirtuin-3 (Sirt3) is a member of the sirtuin family of nicotinamide adenine dinucleotide dependent deacetylases that regulates a variety of mitochondrial functions and suppresses mitochondria-related physiology. Here, we determined sirt3 expression in a mouse model of AD. Spatial learning and memory were tested by Morris water maze in APP/PS1 double transgenic mice. The expression of sirt3 was assayed by real-time quantitative PCR and western blotting. Age-and gender-matched wild-type (WT) littermates were used as controls. Cortical sirt3 localization was assessed using immunohistochemistry. The expression of sirt3 mRNA was significantly lower in the cortex of APP/PS1 double transgenic mice than in WT littermates (0.83 ± 0.24 vs. 1.10 ± 0.21, P < 0.05). A comparable reduction was found in sirt3 protein levels using western blotting. The ratio of mean optical density (MOD) of total sirt3/β-actin in the cortex was 0.77 ± 0.11 in APP/PS1 double transgenic mice and 1.34 ± 0.17 in the WT littermates (P < 0.01). Immunohistochemistry showed the same change as western blotting. The ratio of MOD of integral optical density/total area in APP/PS1 and WT littermates was 0.58 ± 0.02 and 0.71 ± 0.05 (P < 0.01). These data show that sirt3 was depleted in APP/PS1 double transgenic mice. The results suggest that mitochondrial sirt3 might participate in the development of AD via mitochondrial dysfunction.
MicroRNAs (miRs) play crucial roles in tumorigenesis by directly suppressing the protein expression levels of their target genes. miR-204 has been suggested to act as a tumor suppressor in several types of human cancer. However, the exact role of miR-204 in osteosarcoma (OS) remains undetermined. In the present study, we aimed to investigate the effects of miR-204 on OS cell proliferation, migration and invasion, as well as the underlying molecular mechanisms. We found that the expression of miR-204 was frequently downregulated in four OS cell lines compared to the level in normal human osteoblast cells. Moreover, overexpression of miR-204 significantly inhibited the proliferation, migration and invasion of OS cells. Based on bioinformatics prediction and a luciferase reporter assay, we identified Sirtuin 1 (Sirt1) as a direct target gene of miR-204 in OS Saso-2 cells. Moreover, the protein expression of Sirt1 was negatively mediated by miR-204 in the OS cells. siRNA-mediated knockdown of Sirt1 also inhibited the proliferation, migration and invasion of the OS cells. Moreover, overexpression of Sirt1 reversed the inhibitory effect of miR-204 overexpression on the proliferation, migration and invasion of the OS cells. In addition, after miR-204 overexpression or Sirt1 knockdown in OS cells, the expression of E-cadherin was increased, while the N-cadherin protein level was reduced. Based on these findings, we suggest that miR-204 inhibits the proliferation, migration, invasion and epithelial-mesenchymal transition (EMT) of OS cells by directly targeting Sirt1.
Recent researches demonstrate that microRNAs (miRNAs) are deregulated in numerous cancers and involved in tumorigenesis, while their influences on pancreatic cancer (PC) still need further elucidation. The present research revealed that miR-494 was significantly decreased in PC cell lines and tissues. Functional study showed that overexpressed miR-494 could remarkably inhibit proliferation of PC cells both in vitro and in vivo, which was due to induction of apoptosis, G1 phase arrest and senescence. Moreover, upregulated miR-494 significantly prohibited invasion of PC cells. Meanwhile, both c-Myc and SIRT1 was identified as targets of miR-494 through dual luciferase assay and further confirmed by the reverse correlation between miR-494 and c-Myc/SIRT1 in PC samples. Furthermore, co-transfection with c-Myc-RNAi and SIRT1-RNAi synergistically reduced c-Myc and SIRT1 expression, and inhibited proliferation of PC which simulated the effects of miR-494 overexpression. On the contrary, co-overexpression of c-Myc and SIRT1 effectively rescued inhibition of overexpressed miR-494 on PC cells. The clinical characteristics further revealed that low miR-494 correlated with larger tumor size, late TNM stage, lymphatic invasion, distant metastasis and poor prognosis. In conclusion, the present study indicated that miR-494 might serve as predictor and inhibitor in PC by direct down-regulating the loop of c-Myc and SIRT1.Gene Therapy accepted article preview online, 12 May 2015. doi:10.1038/gt.2015.39.
Insulin resistance in skeletal muscle is a key feature in the pathogenesis of type 2 diabetes (T2D) that often manifests early in its development. Pharmaceutical and dietary strategies have targeted insulin resistance to control T2D, and many natural products with excellent pharmacological properties are good candidates for the control or prevention of T2D. Dihydromyricetin (DHM) is a natural flavonol which provides a wide range of health benefits including anti-inflammatory and anti-tumor effects. However, little information is available regarding the effects of DHM on skeletal muscle insulin sensitivity as well as the underlying mechanisms. In the present study, we found that DHM activated insulin signaling and increased glucose uptake in skeletal muscle in vitro and in vivo. The expression of light chain 3, the degradation of sequestosome 1, and the formation of autophagosomes were also upregulated by DHM. DHM-induced insulin sensitivity improvement was significantly abolished in the presence of 3-methyladenine, bafilomycin A1, or Atg5 siRNA in C2C12 myotubes. Furthermore, DHM increased the levels of phosphorylated AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor coactivator-1α (PGC-1α), and Sirt3 in skeletal muscle in vitro and in vivo. Autophagy was inhibited in the presence of Sirt3 siRNA in C2C12 myotubes and in skeletal muscles from Sirt3-/- mice. Additionally, PGC-1α or AMPK siRNA transfection attenuated DHM-induced Sirt3 expression, thereby abrogating DHM-induced autophagy in C2C12 myotubes. In conclusion, DHM improved skeletal muscle insulin sensitivity by partially inducing autophagy via activation of the AMPK-PGC-1α-Sirt3 signaling pathway.
In addition to its role as a redox coenzyme, NAD is a substrate of various enzymes that split the molecule to either catalyze covalent modifications of target proteins or convert NAD into biologically active metabolites. The coenzyme bioavailability may be significantly affected by these reactions, with ensuing major impact on energy metabolism, cell survival, and aging. Moreover, through the activity of the NAD-dependent deacetylases sirtuins, NAD behaves as a beacon molecule that reports the cell metabolic state, and accordingly modulates transcriptional responses and metabolic adaptations. In this view, NAD biosynthesis emerges as a highly regulated process: it enables cells to preserve NAD homeostasis in response to significant NAD-consuming events and it can be modulated by various stimuli to induce, via NAD level changes, suitable NAD-mediated metabolic responses. Here we review the current knowledge on the regulation of mammalian NAD biosynthesis, with focus on the relevant rate-limiting enzymes. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.
Copyright © 2015. Published by Elsevier B.V.