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Mitochondria—A Nexus for Aging, Calorie Restriction, and Sirtuins?
Abstract
Recent studies of calorie restriction in several organisms demonstrate an increase in mitochondrial activity that is associated with the salutary effects of this dietary restriction regimen. In this Essay, I speculate on how an increase in mitochondrial activity might provide benefit and discuss how diet, mitochondria, and sirtuins might interact in a pathway to slow aging and associated diseases.
... By contrast, dietary restriction (DR) and a reduction in insulin signaling have been demonstrated to have anti-aging effects (Guarente, 2008). DR causes circulating glucose concentrations to fall (Guarente, 2008). ...
... By contrast, dietary restriction (DR) and a reduction in insulin signaling have been demonstrated to have anti-aging effects (Guarente, 2008). DR causes circulating glucose concentrations to fall (Guarente, 2008). Thus, the pro-aging effects of reductions in brain glucose metabolism and the anti-aging effects of reducing insulin-stimulated glucose uptake are apparently contradictory. ...
... DR has been reported to extend the life span in most species, including Drosophila (Bauer et al., 2005). Since DR causes circulating glucose concentrations to fall (Guarente, 2008), the anti-aging effects of DR and increasing in glucose uptake into neurons might be independent and additive. To determine the relationship between neuronal uptake of glucose and DR in aging, we analyzed the effects of neuronal expression of hGlut3 on life span under various dietary conditions. ...
Brain neurons play a central role in organismal aging, but there is conflicting evidence about the role of neuronal glucose availability because glucose uptake and metabolism are associated with both aging and extended life span. Here, we analyzed metabolic changes in the brain neurons of Drosophila during aging. Using a genetically encoded fluorescent adenosine triphosphate (ATP) biosensor, we found decreased ATP concentration in the neuronal somata of aged flies, correlated with decreased glucose content, expression of glucose transporter and glycolytic enzymes and mitochondrial quality. The age-associated reduction in ATP concentration did not occur in brain neurons with suppressed glycolysis or enhanced glucose uptake, suggesting these pathways contribute to ATP reductions. Despite age-associated mitochondrial damage, increasing glucose uptake maintained ATP levels, suppressed locomotor deficits, and extended the life span. Increasing neuronal glucose uptake during dietary restriction resulted in the longest life spans, suggesting an additive effect of enhancing glucose availability during a bioenergetic challenge on aging.
... Sirtuins were first discovered as regulators of longevity by silencing transcription in budding yeast cells (Kaeberlein et al., 1999;Imai et al., 2000) and are hypothesized to be one mechanism linking reductions in metabolic rate and increased longevity (Guarente, 2000;Mair and Dillin, 2008) through increased mitochondrial activity (Guarente, 2008). Since their discovery, their role in metabolism and calorie restriction has been studied in numerous animal groups (reviewed by Guarente, 2013;Vasquez and Tomanek, 2019) and it is well documented that decreased dietary intake can activate sirtuins via a reduction of the TCA cycle and a concomitant increase in NAD + (Houtkooper et al., 2012;Watroba and Szukiewicz, 2021). ...
... While it is difficult to assess what qualifies as caloric restriction in mussels as food availability can be sporadic in the intertidal zone (Dowd et al., 2013), it is likely mussels in our low food treatment received quantities of algae similar to what they would experience in nature (Blanchette et al., 2007), as opposed to mussels in the high food treatment which were relatively well fed, similar to what they would be provided in an aquaculture setting. These findings indicate that activation of sirtuins in Mytilids is linked to metabolic state, as has been reported in numerous other species (Guarente, 2008;Shinmura, 2013). This observation was less apparent at our earlier sampling point, as Fig. 3. Total SIRT activity, measured as the ng of deacylated product, for mussels sampled 5 h following treatment (n = 6). ...
Sirtuins are a class of NAD+-dependent deacylases, with known regulatory roles in energy metabolism and cellular stress responses in vertebrates. Previous work using marine mussels have suggested a similar role in invertebrates, providing a potential mechanism linking food availability and thermal sensitivity in Mytilids. Sirtuin inhibitors affect mussels' recovery from environmental stressors, including acute heat shock and well-fed mussels exposed to sirtuin inhibitors and/or acute heat shock respond differently than poorly fed mussels, at the protein and whole-organism levels. While this implies a relationship between sirtuins, food availability, and temperature, the direct effects of sirtuin inhibitors (nicotinamide and suramin) on sirtuin activity or their putative effectors have not been explicitly tested. In this study, adult Mytilus californianus were acclimated to a low or high food availability and exposed to one of the following treatments: control, acute heat shock, sirtuin inhibitors, or acute heat shock and sirtuin inhibitors. Mussels increased sirtuin activity during early recovery (5 h) from sirtuin inhibition and acute heat shock, but only if acclimated to a high food availability. Redox balance was also impacted in mussels acclimated to high food availability and exposed to sirtuin inhibitors, signifying interactions between ration, acute heat shock, and sirtuin inhibitors. Additionally, we found a correlation between sirtuin and superoxide dismutase activities, suggesting a potential regulatory role of oxidative stress by sirtuins. Following prolonged recovery (17 h), we found increased sirtuin activity in mussels acclimated to low food availability, indicating that endogenous sirtuin activity may be related to food availability in mussels.
... Our finding of the green predominant mitochondrial state in the low glucose culture medium indicated a role of the nutrient sensing and the Sirtuin pathway in regulating mitoproteolysis. As a cofactor for Sirtuin activity, NAD + and its metabolism links cell metabolic state to cellular defense against oxidative stress [45]. Interestingly, Nicotinamide Riboside (NR), a precursor for NAD + synthesis, also promoted a rapid increase in mitochondrial ATP generation (Fig. 6A) and a shift to a green predominant MitoTimer fluorescence spectrum (Fig. 6B-D). ...
... The nutrient and metabolic sensing mechanisms by Sirtuin, AMPK, mTOR and others play prominent roles in controlling organismal health and longevity [45,64]. The convergence of these pathways with mitoproteostasis and oxidative metabolism in mammalian systems as revealed in this study should have broad implications in understanding and treating ageing and ageing associated diseases. ...
The regulation of mitochondria function and health is a central node in tissue maintenance, ageing as well as the pathogenesis of various diseases. However, the maintenance of an active mitochondrial functional state and its quality control mechanisms remain incompletely understood. By studying mice with a mitochondria-targeted reporter that shifts its fluorescence from “green” to “red” with time (MitoTimer), we found MitoTimer fluorescence spectrum was heavily dependent on the oxidative metabolic state in the skeletal muscle fibers. The mitoproteolytic activity was enhanced in an energy dependent manner, and accelerated the turnover of MitoTimer protein and respiratory chain substrate, responsible for a green predominant MitoTimer fluorescence spectrum under the oxidative conditions. PGC1α, as well as anti-ageing regents promoted enhanced mitoproteolysis. In addition, cells with the green predominant mitochondria exhibited lower levels of MitoSox and protein carbonylation, indicating a favorable redox state. Thus, we identified MitoTimer as a probe for mitoproteolytic activity in vivo and found a heightened control of mitoproteolysis in the oxidative metabolic state, providing a framework for understanding the maintenance of active oxidative metabolism while limiting oxidative damages.
... (88,(189)(190)(191) In muscle and white fat tissues, CR promotes mitochondrial biogenesis. (192) Resveratrol supplementation increases the amount of mitochondria in muscle, increases physical activity, and increases the average longevity of mice.(78) Reprogramming mitochondria restores them to a condition similar in Figure 7. ...
... TCA cycle's metabolic intermediates and byproducts function as cofactors and substrates for a variety of epigenetic enzymes. (64,88,91,192,195) NAD + , the cofactor for sirtuins, is another critical molecule that connects epigenetic control to mitochondria. (189) Increased NAD + levels increase mitochondrial function, replenish stem cell pools, and prolong the lives of mice. ...
BACKGROUND: Aging is an unavoidable part of life, defined by a gradual loss in tissue and organ function and an increasing chance of death. Current studies of aging connected the genetic and epigenetic changes to cause this process.
CONTENT: When the aging-related epigenetic alterations is accumulated, it may result in irregulated gene expression, metabolic instability, stem cell senescence and exhaustion, and imbalance of tissue homeostasis, which all accelerate the aging process. Altered epigenetic gene regulatory mechanisms such as DNA methylation, histone modification and chromatin remodeling, and non-coding RNAs can induce aging process, thus manipulating these processes give a chance for the success of age-delaying interventions.
SUMMARY: Given updated tools and technologies to investigate the epigenetic regulation affecting aging processes, new therapeutic strategies to delay this process can be developed to increase longevity and improve quality of life.
KEYWORDS: aging, epigenetic, senescence, autophagy, mitochondria, metabolism, rejuvenation
... Knockout of SIRT-3 in mice led to mitochondrial dysfunction in the heart with cardiac hypertrophy [118]. Additionally, SIRT-3 interacts with the transcription factor forkhead box-O3-a and appears to regulate intracellular processes like cellular resistance to oxidative stress and general metabolism [119]. Interestingly, SIRT-7-catalysed H3K122 is significantly implicated in DNA-damage response and cell survival, suggesting its implication in cellular function during aging [120]. ...
... By targeting mRNA transcription and translation, the exosome 's cargo is presumably related to and impacted by the status of the parent cell and its microenvironment. Despite exosomes containing several proteins, lipids, and DNA, among other compounds, mi-RNAs have attracted more attention because of their implication and interconnection with biological mechanisms; their expression is considered the main reflection of the responses induced by exosomes [55,84,119,144]. It is largely accepted that exosomes act through their mi-RNAs in paracrine and autocrine pathways to modulate their micro-environment and induce cell senescence [28,36,41,107,[145][146][147][148]. ...
Exosomes are the main actors of intercellular communications and have gained great interest in the new cell-free regenerative medicine. These nanoparticles are secreted by almost all cell types and contain lipids, cytokines, growth factors, messenger RNA, and different non-coding RNA, especially micro-RNAs (mi-RNAs). Exosomes’ cargo is released in the neighboring microenvironment but is also expected to act on distant tissues or organs. Different biological processes such as cell development, growth and repair, senescence, migration, immunomodulation, and aging, among others, are mediated by exosomes and principally exosome-derived mi-RNAs. Moreover, their therapeutic potential has been proved and reinforced by their use as biomarkers for disease diagnostics and progression. Evidence has increasingly shown that exosome-derived mi-RNAs are key regulators of age-related diseases, and their involvement in longevity is becoming a promising issue. For instance, mi-RNAs such as mi-RNA-21, mi-RNA-29, and mi-RNA-34 modulate tissue functionality and regeneration by targeting different tissues and involving different pathways but might also interfere with long life expectancy. Human mi-RNAs profiling is effectively related to the biological fluids that are reported differently between young and old individuals. However, their underlying mechanisms modulating cell senescence and aging are still not fully understood, and little was reported on the involvement of mi-RNAs in cell or tissue longevity. In this review, we summarize exosome biogenesis and mi-RNA synthesis and loading mechanism into exosomes’ cargo. Additionally, we highlight the molecular mechanisms of exosomes and exosome-derived mi-RNA regulation in the different aging processes.
... Reproduction can be affected by nutrition and by metabolic state. Calorie restriction (CR), which retards aging-associated functional declines in many experimental models (Benayoun et al., 2015;Guarente, 2008;Zhang et al., 2020), prevents aging-associated increases in egg aneuploidy in mouse oocytes (Selesniemi et al., 2011). ...
... Mouse oocytes have a functional insulin signaling cascade (Acevedo et al., 2007), which may be involved in the transcriptional response to CR. Insulin signaling is a key regulator of the function of mitochondria, which are the primary source of reactive oxygen species (ROS) (Guarente, 2008). In Drosophila, levels of the ROS scavenger superoxide dismutase (SOD) are critical for the long-term maintenance of chromosome cohesion in oocytes (Marquardt et al., 2016;Perkins et al., 2016). ...
Chromosome segregation errors in oocytes lead to the production of aneuploid eggs, which are the leading cause of pregnancy loss and of several congenital diseases such as Down syndrome. The frequency of chromosome segregation errors in oocytes increases with maternal age, especially at a late stage of reproductive life. How aging at various life stages affects oocytes differently remains poorly understood. In this study, we describe aging‐associated changes in the transcriptome profile of mouse oocytes throughout reproductive life. Our single‐oocyte comprehensive RNA sequencing using RamDA‐seq revealed that oocytes undergo transcriptome changes at a late reproductive stage, whereas their surrounding cumulus cells exhibit transcriptome changes at an earlier stage. Calorie restriction, a paradigm that reportedly prevents aging‐associated egg aneuploidy, promotes a transcriptome shift in oocytes with the up‐regulation of genes involved in chromosome segregation. This shift is accompanied by the improved maintenance of chromosomal cohesin, the loss of which is a hallmark of oocyte aging and causes chromosome segregation errors. These findings have implications for understanding how oocytes undergo aging‐associated functional decline throughout their reproductive life in a context‐dependent manner. This study reports single‐oocyte transcriptome analysis with RamDA‐seq during aging and calorie restriction in mice. Oocytes undergo aging‐associated transcriptome changes at a late reproductive stage, when chromosome segregation errors are pronouncedly increased, while their surrounding cumulus cells exhibit gradual transcriptome changes even at earlier life stages. Calorie restriction promotes a transcriptome shift in oocytes, accompanied with improved maintenance of chromosomal cohesin.
... Calorie restriction (CR), or more generally dietary restriction (DR), is the most robust and conserved intervention to extend lifespan in organisms from yeast to primates, suggesting the existence of evolutionarily conserved mechanisms regulating lifespan [32]. Studies in model organisms have suggested the involvement of multiple pathways in mediating longevity and health benefits from DR, including reduced insulin-like growth factor (IGF) signaling [32], elevated sirtuin activity [11], downregulated TOR signaling and ribosome abundance [33,34], reduced oxidative stress [11], and improved DNA damage repair [35]. For replicative aging of the budding yeast Saccharomyces cerevisiae, various CR conditions have been proposed to mediate lifespan extension: enhancing Sir2 function through increased NAD/NADH ratio [36,37], repressing ribosome biogenesis through downregulation of TOR signaling kinases Tor1 and Sch9 [33,34], and increasing mitochondria function and oxidative stress response [38][39][40]. ...
... Calorie restriction (CR), or more generally dietary restriction (DR), is the most robust and conserved intervention to extend lifespan in organisms from yeast to primates, suggesting the existence of evolutionarily conserved mechanisms regulating lifespan [32]. Studies in model organisms have suggested the involvement of multiple pathways in mediating longevity and health benefits from DR, including reduced insulin-like growth factor (IGF) signaling [32], elevated sirtuin activity [11], downregulated TOR signaling and ribosome abundance [33,34], reduced oxidative stress [11], and improved DNA damage repair [35]. For replicative aging of the budding yeast Saccharomyces cerevisiae, various CR conditions have been proposed to mediate lifespan extension: enhancing Sir2 function through increased NAD/NADH ratio [36,37], repressing ribosome biogenesis through downregulation of TOR signaling kinases Tor1 and Sch9 [33,34], and increasing mitochondria function and oxidative stress response [38][39][40]. ...
Calorie restriction (CR) is the most robust longevity intervention, extending lifespan from yeast to mammals. Numerous conserved pathways regulating aging and mediating CR have been identified; however, the overall proteomic changes during these conditions remain largely unexplored. We compared proteomes between young and replicatively aged yeast cells under normal and CR conditions using the Stable-Isotope Labeling by Amino acids in Cell culture (SILAC) quantitative proteomics and discovered distinct signatures in the aging proteome. We found remarkable proteomic similarities between aged and CR cells, including induction of stress response pathways, providing evidence that CR pathways are engaged in aged cells. These observations also uncovered aberrant changes in mitochondria membrane proteins as well as a proteolytic cellular state in old cells. These proteomics analyses help identify potential genes and pathways that have causal effects on longevity.
... Calorie restriction (CR), a low-calorie dietary regimen without malnutrition, decreases the incidence of several age-associated disorders and is considered the gold-standard, nongenetic approach for life span extension. 7 A growing body of evidence in several organisms demonstrates that an increase in mitochondrial activity, together with activation of the ROS defense system, is associated with the health effects of the CR regimen. 7,8 Previous observations in yeast suggested that the branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, might be potential candidates in promoting life span extension. ...
... 7 A growing body of evidence in several organisms demonstrates that an increase in mitochondrial activity, together with activation of the ROS defense system, is associated with the health effects of the CR regimen. 7,8 Previous observations in yeast suggested that the branched-chain amino acids (BCAAs), including leucine, isoleucine, and valine, might be potential candidates in promoting life span extension. 9 We have demonstrated that long-term dietary supplementation with a specific BCAA-enriched amino acid mixture (BCAAem) increased the average life span of male mice. ...
Proper maintenance of mitochondrial homeostasis is essential for cell health, and mitochondrial dysfunction underlies several metabolic and heart diseases. Stimulation of mitochondrial biogenesis represents a valuable therapeutic tool for the prevention and treatment of disorders characterized by a deficit in energy metabolism. The present study aimed to potentiate the mitochondrial biogenetic efficacy of an amino acid (AA) mixture, enriched in branched-chain amino acids (BCAAs), which we previously showed to boost mitochondrial biogenesis, leading to life span extension and reducing of muscle and liver damage. Hence, we designed and studied several innovative mixtures. Here, we report on two new AA formulas, α5 and E7, created on the BCAA-enriched amino acid mixture (BCAAem) template and enriched with Krebs cycle substrates, including succinate, malate, and citrate. Cardiomyocytes in culture exposed to either mixture showed increased mitochondrial DNA amount, mitochondrial biogenesis markers, and oxygen consump-tion. Furthermore, α5 and E7 also increased the expression of BCAA catabolic genes. Most importantly, all of these effects of α5 and E7 were more pronounced than those observed with BCAAem, confirming the higher mitochondrial biogenesis potential of these new formulas. Therefore, α5 and E7 could represent a more efficient tool for the nutritional treatment of diseases in which energy production is defective.
... Studies in guinea pig models of NIHL have shown that combination therapy with magnesium and antioxidants, such as vitamins A, C, and E, may have a protective effect, suggesting potential synergy [171]. Notably, calorie restriction remains the only reliable method for slowing aging in mammals, with numerous reports demonstrating its effectiveness in suppressing age-related diseases and extending lifespan [172,173]. Someya et al. reported that SIRT3, a member of the mammalian sirtuin family localized in the mitochondria, is essential for the suppression of ARHL in mice by calorie restriction [174]. These results suggest that mitochondria-localized mammalian sirtuins play an important role in the suppression of age-related cochlear cell death and ARHL induced by calorie restriction. ...
Hearing is essential for communication, and its loss can cause a serious disruption to one’s social life. Hearing loss is also recognized as a major risk factor for dementia; therefore, addressing hearing loss is a pressing global issue. Sensorineural hearing loss, the predominant type of hearing loss, is mainly due to damage to the inner ear along with a variety of pathologies including ischemia, noise, trauma, aging, and ototoxic drugs. In addition to genetic factors, oxidative stress has been identified as a common mechanism underlying several cochlear pathologies. The cochlea, which plays a major role in auditory function, requires high-energy metabolism and is, therefore, highly susceptible to oxidative stress, particularly in the mitochondria. Based on these pathological findings, the potential of antioxidants for the treatment of hearing loss has been demonstrated in several animal studies. However, results from human studies are insufficient, and future clinical trials are required. This review discusses the relationship between sensorineural hearing loss and reactive oxidative species (ROS), with particular emphasis on age-related hearing loss, noise-induced hearing loss, and ischemia–reperfusion injury. Based on these mechanisms, the current status and future perspectives of ROS-targeted therapy for sensorineural hearing loss are described.
... Over time, the structure and function of the IVD can become damaged due to a variety of molecular or cellular damage. The accumulation of proteins, telomere damage, mitochondrial or DNA damage may lead to cellular senescence (Finkel and Holbrook, 2000;Hasty et al., 2003;Guarente, 2008;Niedernhofer and Robbins, 2008). Cellular senescence is a cellular state, a stagnation of cellular proliferation caused by some stimuli, a loss of proliferative capacity of normal cells (Campisi, 2005). ...
Intervertebral disc (IVD) degeneration (IDD) is a worldwide spinal degenerative disease. Low back pain (LBP) is frequently caused by a variety of conditions brought on by IDD, including IVD herniation and spinal stenosis, etc. These conditions bring substantial physical and psychological pressure and economic burden to patients. IDD is closely tied with the structural or functional changes of the IVD tissue and can be caused by various complex factors like senescence, genetics, and trauma. The IVD dysfunction and structural changes can result from extracellular matrix (ECM) degradation, differentiation, inflammation, oxidative stress, mechanical stress, and senescence of IVD cells. At present, the treatment of IDD is basically to alleviate the symptoms, but not from the pathophysiological changes of IVD. Interestingly, the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway is involved in many processes of IDD, including inflammation, ECM degradation, apoptosis, senescence, proliferation, oxidative stress, and autophagy. These activities in degenerated IVD tissue are closely relevant to the development trend of IDD. Hence, the p38 MAPK signaling pathway may be a fitting curative target for IDD. In order to better understand the pathophysiological alterations of the intervertebral disc tissue during IDD and offer potential paths for targeted treatments for intervertebral disc degeneration, this article reviews the purpose of the p38 MAPK signaling pathway in IDD.
... The simplest way to view this is that initial interaction with the cell would activate xenobiotic sensor pathways that would activate mitochondrial function by increasing calcium flux into it. However, as levels rose, mitochondrial function would become inhibited, depolarising it and decreasing levels of acetyl CoA, ATP and NADH, and might therefore induce mild ROS production, all of which would activate sirtuins and AMPK-the sirtuins are an ancient group of proteins involved in stress resistance [212]. The depolarisation would also reduce calcium uptake. ...
Before the late 1980s, ideas around how the lipophilic phytocannabinoids might be working involved membranes and bioenergetics as these disciplines were “in vogue”. However, as interest in genetics and pharmacology grew, interest in mitochondria (and membranes) waned. The discovery of the cognate receptor for tetrahydrocannabinol (THC) led to the classification of the endocannabinoid system (ECS) and the conjecture that phytocannabinoids might be “working” through this system. However, the how and the “why” they might be beneficial, especially for compounds like CBD, remains unclear. Given the centrality of membranes and mitochondria in complex organisms, and their evolutionary heritage from the beginnings of life, revisiting phytocannabinoid action in this light could be enlightening. For example, life can be described as a self-organising and replicating far from equilibrium dissipating system, which is defined by the movement of charge across a membrane. Hence the building evidence, at least in animals, that THC and CBD modulate mitochondrial function could be highly informative. In this paper, we offer a unique perspective to the question, why and how do compounds like CBD potentially work as medicines in so many different conditions? The answer, we suggest, is that they can modulate membrane fluidity in a number of ways and thus dissipation and engender homeostasis, particularly under stress. To understand this, we need to embrace origins of life theories, the role of mitochondria in plants and explanations of disease and ageing from an adaptive thermodynamic perspective, as well as quantum mechanics.
... In agreement, classic ER stress inhibitors reduced aortic diameter and the incidence and severity of experimental aneurysms, attenuating inflammation and vascular remodelling [139,269,270]. Further, it should be highlighted that under pathological conditions the cross-talk between mitochondria and the ER promotes mitochondrial ROS generation and mitochondrial dysfunction [271,272]. It has been described that the expression of transcription factors that activate mitochondrial biogenesis and regulate mitochondrial function (PGC1α, NRF1 and TFAM), as well as that of Cyt B and Cyt C oxidase, are decreased in human aneurysmal specimens, accompanied by a reduction in the mitochondrial mass [261]. ...
Abdominal aortic aneurysm (AAA) is a severe vascular disease and a major public health issue with an unmet medical need for therapy. This disease is featured by a progressive dilation of the abdominal aorta, boosted by atherosclerosis, ageing, and smoking as major risk factors. Aneurysm growth increases the risk of aortic rupture, a life-threatening emergency with high mortality rates. Despite the increasing progress in our knowledge about the etiopathology of AAA, an effective pharmacological treatment against this disorder remains elusive and surgical repair is still the unique available therapeutic approach for high-risk patients. Meanwhile, there is no medical alternative for patients with small aneurysms but close surveillance. Clinical trials assessing the efficacy of antihypertensive agents, statins, doxy-cycline, or anti-platelet drugs, among others, failed to demonstrate a clear benefit limiting AAA growth, while data from ongoing clinical trials addressing the benefit of metformin on aneurysm progression are eagerly awaited. Recent preclinical studies have postulated new therapeutic targets and pharmacological strategies paving the way for the implementation of future clinical studies exploring these novel therapeutic strategies. This review summarises some of the most relevant clinical and preclinical studies in search of new therapeutic approaches for AAA.
... Mitochondrial dysfunction contributes to oxidative stress and systemic inflammation, which are critical in obesity-related diseases [13]. In contrast, DR improves mitochondrial bioenergetics and dynamics by increasing efficiency, decreasing oxidant production, and increasing mitochondrial turnover [14][15][16]. However, mitochondrial mechanisms underlying DR remain unclear and require further investigation. ...
Diet restriction (DR) ameliorates obesity by regulating mitochondrial function. Cardiolipin (CL), a mitochondrial phospholipid, is closely associated with mitochondrial function. This study aimed to evaluate the anti-obesity effects of graded levels of DR based on mitochondrial CL levels in the liver. Obese mice were treated with 0%, 20%, 40%, and 60% reductions in the normal diet compared to normal animals (0 DR, 20 DR, 40 DR, and 60 DR groups, respectively). Biochemical and histopathological analyses were performed to evaluate the ameliorative effects of DR on obese mice. The altered profile of mitochondrial CL in the liver was explored using a targeted metabolomics strategy by ultra-high-pressure liquid chromatography MS/MS coupled with quadrupole time-of-flight mass spectrometry. Finally, gene expression associated with CL biosynthesis and remodeling was quantified. Tissue histopathology and biochemical index evaluations revealed significant improvements in the liver after DR, except for the 60 DR group. The variation in mitochondrial CL distribution and DR levels showed an inverted U-shape, and the CL content in the 40 DR group was the most upregulated. This result is consistent with the results of the target metabolomic analysis, which showed that 40 DR presented more variation. Furthermore, DR led to increased gene expression associated with CL biosynthesis and remodeling. This study provides new insights into the mitochondrial mechanisms underlying DR intervention in obesity.
... Lipid homeostasis refers to the relatively stable state of lipid content and metabolic activities in blood and tissues, which have a significant influence on lipid metabolism under different physiological conditions. It is the basis for normal physiological functions in organisms affected by dietary fat and organ function [12,13]. It provides essential nutrients for the human body, such as fatty acids and fat-soluble vitamins; the type and quantity of lipids present also affect lipid homeostasis. ...
Cactus is a tropical fruit with a high nutritional value; however, little information is available regarding the comprehensive utilization of its byproducts. This study aimed to explore the composition and nutritional value of cactus fruit seed oil (CFO) and reveal the effects of ultrasound-assisted extraction and traditional solvent extraction on oil quality. Foodomics analysis showed that CFO extracted using a traditional solvent is rich in linolenic acid (9c12cC18:2, 57.46 ± 0.84 %), α-tocopherol (20.01 ± 1.86 mg/100 g oil), and canolol (200.10 ± 1.21 μg/g). Compared to traditional solvent extraction, ultrasound-assisted extraction can significantly increase the content of lipid concomitants in CFO, whereas excessive ultrasound intensity may lead to the oxidation of oils and the formation of free radicals. Analysis of the thermal properties showed that ultrasound had no effect on the crystallization or melting behavior of CFO. To further demonstrate the nutritional value of CFO, a lipopolysaccharide (LPS)-induced lipid metabolism imbalance model was used. Lipidomics analysis showed that CFO significantly reduced the content of oxidized phospholipids stimulated by LPS and increased the content of highly bioactive metabolites such as ceramides, thus alleviating LPS-induced damage in C. elegans. Hence, CFO is a functional oil with high value, and ultrasound-assisted extraction is advocated. These findings provide new insights into the comprehensive utilization of cactus fruits.
... A decline in mitochondrial activity and quality is associated with aging and a wide range of age-related disorders (Wallace, 2005;Guarente, 2008;Cho et al, 2011;Sun et al, 2016). Along with loss of proteostasis, cellular senescence, deregulated nutrient sensing, stem cell exhaustion, epigenetic alteration, genome instability, telomere attrition, and altered intercellular communication, mitochondrial dysfunction is considered as one of the hallmarks of aging (Lopez-Otin et al, 2013). ...
Mechanisms underlying the depletion of NAD+ and accumulation of reactive oxygen species (ROS) in aging and age-related disorders remain poorly defined. We show that reverse electron transfer (RET) at mitochondrial complex I, which causes increased ROS production and NAD+ to NADH conversion and thus lowered NAD+ /NADH ratio, is active during aging. Genetic or pharmacological inhibition of RET decreases ROS production and increases NAD+ /NADH ratio, extending the lifespan of normal flies. The lifespan-extending effect of RET inhibition is dependent on NAD+ -dependent Sirtuin, highlighting the importance of NAD+ /NADH rebalance, and on longevity-associated Foxo and autophagy pathways. RET and RET-induced ROS and NAD+ /NADH ratio changes are prominent in human induced pluripotent stem cell (iPSC) model and fly models of Alzheimer's disease (AD). Genetic or pharmacological inhibition of RET prevents the accumulation of faulty translation products resulting from inadequate ribosome-mediated quality control, rescues relevant disease phenotypes, and extends the lifespan of Drosophila and mouse AD models. Deregulated RET is therefore a conserved feature of aging, and inhibition of RET may open new therapeutic opportunities in the context of aging and age-related diseases including AD.
... Further, melatonin increases growth hormone (GH) levels by acting at the downstream component in the GH-signaling mechanism (Nassar et al. 2007). Inhibition of the insulin growth factor-1 (IGF-1) signaling mechanism, which shares its function with insulin, through PI3K and Akt pathway, considerably extends longevity in mouse (Guarente 2008). However, the nuclear factor kappa-B (NF-κB) signaling pathway is activated by GH and IGF-1 later in life, which speeds up the aging process by inducing inflammatory responses. ...
Aging is associated with increasing impairments in brain homeostasis and represents the main risk factor across most neurodegenerative disorders. Melatonin, a neuroendocrine hormone that regulates mammalian chronobiology and endocrine functions is well known for its antioxidant potential, exhibiting both cytoprotective and chronobiotic abilities. Age-related decline of melatonin disrupting mitochondrial homeostasis and cytosolic DNA-mediated inflammatory reactions in neurons is a major contributory factor in the emergence of neurological abnormalities. There is scattered literature on the possible use of melatonin against neurodegenerative mechanisms in the aging process and its associated diseases. We have searched PUBMED with many combinations of key words for available literature spanning two decades. Based on the vast number of experimental papers, we hereby review recent advancements concerning the potential impact of melatonin on cellular redox balance and mitochondrial dynamics in the context of neurodegeneration. Next, we discuss a broader explanation of the involvement of disrupted redox homeostasis in the pathophysiology of age-related diseases and its connection to circadian mechanisms. Our effort may result in the discovery of novel therapeutic approaches. Finally, we summarize the current knowledge on molecular and circadian regulatory mechanisms of melatonin to overcome neurodegenerative diseases (NDDs) such as Alzheimer’s, Parkinson’s, Huntington’s disease, and amyotrophic lateral sclerosis, however, these findings need to be confirmed by larger, well-designed clinical trials. This review is also expected to uncover the associated molecular alterations in the aging brain and explain how melatonin-mediated circadian restoration of neuronal homeodynamics may increase healthy lifespan in age-related NDDs.
... Interestingly, BAT-specific mitochondrial adaptations closely mirror those that are believed to be a mechanism behind life extension following dietary restriction. The increased oxidation of lipids is preferential in terms of ROS production because oxidizing lipids produces a higher ratio of reduced FADH to NADH, which bypasses complex I of the ETC, and instead allows electrons to enter the ETC through complex II (Guarente 2008;Darcy & Tseng 2019). Moreover, increased metabolic rate and mitochondrial uncoupling in isolated mitochondria from myocytes have been positively associated with increased longevity in vivo (Speakman et al. 2004). ...
... Aging affects biological functions and increases vulnerability to many diseases by reducing mitochondrial biogenesis, stimulating mitochondrial malfunction, and increasing oxidative damage [32,33]. Previous studies have provided substantial evidence relating dietary BCAAs to multiple mechanisms underlying the pathogenesis of age-related loss in physical function. ...
Citation: Liao, M.; Mu, Y.; Su, X.; Zheng, L.; Zhang, S.; Chen, H.; Xu, S.; Ma, J.; Ouyang, R.; Li, W.; et al. Association between Branched-Chain Amino Acid Intake and Physical Function among Chinese Community-Dwelling Elderly Residents. Nutrients 2022, 14, 4367. https://doi.
... Aging affects biological functions and increases vulnerability to many diseases by reducing mitochondrial biogenesis, stimulating mitochondrial malfunction, and increasing oxidative damage [32,33]. Previous studies have provided substantial evidence relating dietary BCAAs to multiple mechanisms underlying the pathogenesis of age-related loss in physical function. ...
Abstract: This study aimed to evaluate the potential associations of dietary BCAAs (isoleucine, leucine, and valine) with physical function in the elderly Chinese population. A validated semiquantitative food frequency questionnaire and anthropometric and physical function measurements were used to collect data. We modeled trends in physical function indicators for BCAA quartiles using multivariate linear regression models. Among 4,336 (43.97% men) participants aged 72.73±5.48 years, a higher dietary intake of BCAAs was positively associated with increased handgrip strength (all P trends < 0.001), shorter times for 4-meter fast walking (all P trends < 0.001) and repeated chair rises (all P trends < 0.001). No linear association was found between subtypes of amino acids and any physical functions (all P trends > 0.05). Individuals in the highest quartiles of BCAA intake had a reduced risk of developing low muscle strength, and the multiadjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) for women and men were 0.50 (0.38-0.65) and 0.67 (0.50-0.91), respectively. Similarly, higher BCAA consumption was associated with a lower risk of developing low physical performance (4-m walking speed: OR=0.68 [0.50-0.93]; repeated chair rises: OR=0.66 [0.54-0.81]). Higher dietary BCAA intake might be beneficial for physical function in the elderly population.
... Moreover, gene expression profiling of CR human skeletal muscle found significant upregulation of various SIRT, FOXO, and AMPK transcripts (Mercken et al. 2013). CR also improve mitochondrial function trough Sirt1 signaling and PGC-1 alpha activation (Guarente 2008). ...
Over the past decade, extensive efforts have focused on understanding age-associated diseases and how to prolong a healthy lifespan. The induction of dietary protocols such as caloric restriction (CR) and protein restriction (PR) has positively affected a healthy lifespan. These intervention ideas (nutritional protocols) have been the subject of human cohort studies and clinical trials to evaluate their effectiveness in alleviating age-related diseases (such as type II diabetes, cardiovascular disease, obesity, and musculoskeletal fragility) and promoting human longevity. This study summarizes the literature on the nutritional protocols, emphasizing their impacts on bone and muscle biology. In addition, we analyzed several CR studies using Gene Expression Omnibus (GEO) database and identified common transcriptome changes to understand the signaling pathway involved in musculoskeletal tissue. We identified nine novel common genes, out of which five were upregulated (Emc3, Fam134b, Fbxo30, Pip5k1a, and Retsat), and four were downregulated (Gstm2, Per2, Fam78a, and Sel1l3) with CR in muscles. Gene Ontology enrichment analysis revealed that CR regulates several signaling pathways (e.g., circadian gene regulation and rhythm, energy reserve metabolic process, thermogenesis) involved in energy metabolism. In conclusion, this study summarizes the beneficiary role of CR and identifies novel genes and signaling pathways involved in musculoskeletal biology.
... Several recent studies have identified a mitochondrial nexus at the heart of the brain-body adaptation to stress, infection, injury, and mental health. 53,[65][66][67] Adaptive changes in response to exercise are set in motion by mitochondrial changes known as mitohormesis. 68,69 Broadly, the adaptive response to environmental demand is called hormesis 70,71 and is mediated in part by activation of NRF2-dependent gene expression. ...
Metabolomics has emerged as a powerful new tool in precision medicine. No studies have yet been published on the metabolomic changes in cerebrospinal fluid (CSF) produced by acute endurance exercise. CSF and plasma were collected from 19 young active adults (13 males and 6 females) before and 60 min after a 90‐min monitored outdoor run. The median age, BMI, and VO2 max of subjects was 25 years (IQR 22–31), 23.2 kg/m² (IQR 21.7–24.5), and 47 ml/kg/min (IQR 38–51), respectively. Targeted, broad‐spectrum metabolomics was performed by liquid chromatography, tandem mass spectrometry (LC–MS/MS). In the CSF, purines and pyrimidines accounted for 32% of the metabolic impact after acute endurance exercise. Branch chain amino acids, amino acid neurotransmitters, fatty acid oxidation, phospholipids, and Krebs cycle metabolites traceable to mitochondrial function accounted for another 52% of the changes. A narrow but important channel of metabolic communication was identified between the brain and body by correlation network analysis. By comparing these results to previous work in experimental animal models, we found that over 80% of the changes in the CSF correlated with a cascade of mitochondrial and metabolic changes produced by ATP signaling. ATP is released as a co‐neurotransmitter and neuromodulator at every synapse studied to date. By regulating brain mitochondrial function, ATP release was identified as an early step in the kinetic cascade of layered benefits produced by endurance exercise.
... A consequence of mitochondrial biogenesis is the inhibition of ROS production [98], despite that, in this present study male rats presented greater production of ROS, as compared to females, evaluated at the end of acrobatic training. It was reported that extent of ischemic injury is related to the mitochondrial damage to tissue and the production of mitochondria-derived reactive oxygen species [99]. ...
Chronic cerebral hypoperfusion leads to neuronal loss in the hippocampus and spatial memory impairments. Physical exercise is known to prevent cognitive deficits in animal models; and there is evidence of sex differences in behavioral neuroprotective approaches. The aim of present study was to investigate the effects of acrobatic training in male and female rats submitted to chronic cerebral hypoperfusion. Males and females rats underwent 2VO (two-vessel occlusion) surgery and were randomly allocated into 4 groups of males and 4 groups of females, as follows: 2VO acrobatic, 2VO sedentary, Sham acrobatic and Sham sedentary. The acrobatic training started 45 days after surgery and lasted 4 weeks; animals were then submitted to object recognition and water maze testing. Brain samples were collected for histological and morphological assessment and flow cytometry. 2VO causes cognitive impairments and acrobatic training prevented spatial memory deficits assessed in the water maze, mainly for females. Morphological analysis showed that 2VO animals had less NeuN labeling and acrobatic training prevented it. Increased number of GFAP positive cells was observerd in females; moreover, males had more branched astrocytes and acrobatic training prevented the branching after 2VO. Flow cytometry showed higher mitochondrial potential in trained animals and more reactive oxygen species production in males. Acrobatic training promoted neuronal survival and improved mitochondrial function in both sexes, and influenced the glial scar in a sex-dependent manner, associated to greater cognitive benefit to females after chronic cerebral hypoperfusion.
... Therefore, how to address this energy crisis plays an important role in determining healthy aging and longevity in aged people. Longevity pathways (e.g., mammalian target of rapamycin) and interventions (e.g., calorie restriction) rely on the improvement of mitochondrial activity (3,4). Notably, aging is also thought to be caused by hyperfunction, whereby the continued activity of developmental programs in late life leads to pathological issues and eventually to death (5,6). ...
Adaptation to reduced energy production during aging is a fundamental issue for maintaining healthspan or prolonging life span. Currently, however, the underlying mechanism in long-lived people remains poorly understood. Here, we analyzed transcriptomes of 193 long-lived individuals (LLIs) and 86 spouses of their children from two independent Chinese longevity cohorts and found that the ribosome pathway was significantly down-regulated in LLIs. We found that the down-regulation is likely controlled by ETS1 (ETS proto-oncogene 1), a transcription factor down-regulated in LLIs and positively coexpressed with most ribosomal protein genes (RPGs). Functional assays showed that ETS1 can bind to RPG promoters, while ETS1 knockdown reduces RPG expression and alleviates cellular senescence in human dermal fibroblast (HDF) and embryonic lung fibroblast (IMR-90) cells. As protein synthesis/turnover in ribosomes is an energy-intensive cellular process, the decline in ribosomal biogenesis governed by ETS1 in certain female LLIs may serve as an alternative mechanism to achieve energy-saving and healthy aging.
... Therefore, analysis was performed to explore the changes in aging NPCs to further understand partial reprogramming in vertebral disc. Physiological aging has similar features as RS, including high levels of DNA damage, changes in chromatin conformation, increased ROS production, decreased proliferation, activated apoptosis and initiation of senescence-associated secretory phenotype (SASP) (Boulestreau et al., 2021;Guarente, 2008;Haigis & Sinclair, 2010;Kennedy & Lamming, 2016;Soultoukis & Partridge, 2016;Steffen & Dillin, 2016). The phenotypes associated with aging achieve recovery at different degree, through short-term expression of Yamanaka factors. ...
Rejuvenation of nucleus pulposus cells (NPCs) in degenerative discs can reverse intervertebral disc degeneration (IDD). Partial reprogramming is used to rejuvenate aging cells and ameliorate progression of aging tissue to avoiding formation of tumors by classical reprogramming. Understanding the effects and potential mechanisms of partial reprogramming in degenerative discs provides insights for development of new therapies for IDD treatment. The findings of the present study show that partial reprogramming through short-term cyclic expression of Oct-3/4, Sox2, Klf4, and c-Myc (OSKM) inhibits progression of IDD, and significantly reduces senescence related phenotypes in aging NPCs. Mechanistically, short-term induction of OSKM in aging NPCs activates energy metabolism as a "energy switch" by upregulating expression of Hexokinase 2 (HK2) ultimately promoting redistribution of cytoskeleton and restoring the aging state in aging NPCs. These findings indicate that partial reprogramming through short-term induction of OSKM has high therapeutic potential in the treatment of IDD.
... In mammals and even in C. elegans, trehalose counteracts disruptions of protein homeostasis by oxidative stress, temperature variation and dessication [50][51][52] and thus leads to increasing lifespan. The absence of trehalose in long-lived queens is possibly facilitated by the protected lifestyle of reproductives in the royal cell, or by compensatory mechanisms such as the maintenance of a healthy mitochondria population producing low amounts of ROS [53][54][55][56] . We found expression patterns in trehalose pathways that were specific to physogastric queens, suggesting that the patterns of hemolymph sugars in kings might be less extreme. ...
Kings and queens of eusocial termites can live for decades, while queens sustain a nearly maximal fertility. To investigate the molecular mechanisms underlying their long lifespan, we carried out transcriptomics, lipidomics and metabolomics in Macrotermes natalensis on sterile short-lived workers, long-lived kings and five stages spanning twenty years of adult queen maturation. Reproductives share gene expression differences from workers in agreement with a reduction of several aging-related processes, involving upregulation of DNA damage repair and mitochondrial functions. Anti-oxidant gene expression is downregulated, while peroxidability of membranes in queens decreases. Against expectations, we observed an upregulated gene expression in fat bodies of reproductives of several components of the IIS pathway, including an insulin-like peptide, Ilp9. This pattern does not lead to deleterious fat storage in physogastric queens, while simple sugars dominate in their hemolymph and large amounts of resources are allocated towards oogenesis. Our findings support the notion that all processes causing aging need to be addressed simultaneously in order to prevent it.
... Mitonuclear communication involves anterograde (nucleus-to-mitochondria) signals and retrograde (mitochondrionto-nucleus) signals (Liu and Butow 2006). As the central organelle responsible for a wealth of metabolic processes related to nutrient and oxygen flux, the combined mitonuclear genome is a nexus for epistatic (G×G) and G×E interactions (Guarente 2008). ...
Mitochondria evolved from a union of microbial cells belonging to distinct lineages that were likely anaerobic. The evolution of eukaryotes required a massive reorganization of the 2 genomes and eventual adaptation to aerobic environments. The nutrients and oxygen that sustain eukaryotic metabolism today are processed in mitochondria through coordinated expression of 37 mitochondrial genes and over 1000 nuclear genes. This puts mitochondria at the nexus of gene-by-gene (G×G) and gene-by-environment (G×E) interactions that sustain life. Here we use a Drosophila model of mitonuclear genetic interactions to explore the notion that mitochondria are environments for the nuclear genome, and vice versa. We construct factorial combinations of mtDNA and nuclear chromosomes to test for epistatic interactions (G×G), and expose these mitonuclear genotypes to altered dietary environments to examine G×E interactions. We use development time and genome-wide RNAseq analyses to assess the relative contributions of mtDNA, nuclear chromosomes, and environmental effects on these traits (mitonuclear G×G×E). We show that the nuclear transcriptional response to alternative mitochondrial "environments" (G×G) has significant overlap with the transcriptional response of mitonuclear genotypes to altered dietary environments. These analyses point to specific transcription factors (e.g., giant) that mediated these interactions, and identified coexpressed modules of genes that may account for the overlap in differentially expressed genes. Roughly 20% of the transcriptome includes G×G genes that are concordant with G×E genes, suggesting that mitonuclear interactions are part of an organism's environment.
... Due to differential entry points into the mitochondrial electron-transport system (ETS), for example, the reducing equivalents from fatty acids in beta-oxidation enter the ETS via electron transfer flavoprotein: ubiquinone oxidoreductase (ETF:QO; oxidizing FADH2) and the electrons are deposited to ubiquinone, thereby bypassing complex I, a major site of ROS production. On the other hand, under a rich diet, reducing equivalents from carbohydrates directly enter complex I, producing more ROS (Guarente, 2008). Altogether, evidence suggests that mitochondrial metabolism plays an essential role in DR-mediated longevity. ...
Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.
... Fornasiero electrons are transferred via FADH2 to complex III of the mitochondrial respiratory chain. This bypasses complex I, where electrons from carbohydrate oxidation and NADH2 are delivered and where ROS are mainly produced (Guarente, 2008;Kushnareva et al., 2002). Importantly, this switch is induced mostly in peripheral organs whereas neurons in the brain make limited use of fatty acid oxidation (Panov et al., 2014). ...
Due to the extension of human life expectancy, the prevalence of cognitive impairment is rising in the older portion of society. Developing new strategies to delay or attenuate cognitive decline is vital. For this purpose, it is imperative to understand the cellular and molecular events at the basis of brain aging. While several organs are directly accessible to molecular analysis through biopsies, the brain constitutes a notable exception. Most of the molecular studies are performed on postmortem tissues, where cell death and tissue damage have already occurred. Hence, the study of the molecular aspects of cognitive decline largely relies on animal models and in particular on small mammals such as mice. What have we learned from these models? Do these animals recapitulate the changes observed in humans? What should we expect from future mouse studies? In this review we answer these questions by summarizing the state of the research that has addressed cognitive decline in mice from several perspectives, including genetic manipulation and omics strategies. We conclude that, while extremely valuable, mouse models have limitations that can be addressed by the optimal design of future studies and by ensuring that results are cross-validated in the human context.
... Sirtuins are NAD ? -dependent protein deacetylases that stimulate mitochondrial biogenesis and promote longevity in numerous organisms (Guarente 2008). SIRT1 deacetylates and activates downstream target, forkhead box O (FoxO) transcription factor which stimulates the expression of antioxidant enzymes to enhanced cellular resistance against oxidative stress (Daitoku et al. 2004). ...
Circadian disruption due to artificial light at night (ALAN) is an alarming threat to modern society. In the present study we evaluated the protective effect of melatonin on age dependent redox insults and neurochemical deficits induced by ALAN in the brain of chronodisrupted rat model. Young (3 months) and old (22 months) male Wistar rats were exposed to ALAN along with melatonin supplementation (10 mg Kg−1, oral) for 10 days. Results demonstrated significant increment in the pro-oxidant biomarkers: reactive oxygen species, lipid hydroperoxidation, protein carbonyl, nitric oxide while suppression in the total thiol, ferric reducing antioxidant potential level, superoxide dismutase and catalase activities in the brain of ALAN exposed groups with higher amplitude in aged rats. Further these oxidative modifications were protected by subsequent administration of melatonin. Mitochondrial complexes (C-I to C-IV) activity was significantly altered in young and old ALAN exposed groups with melatonin showing protective effect. Histopathological analysis show dense cytosolic staining and neuronal degeneration in cerebral cortex and different hippocampus regions with greater extent in old ALAN rats effectively moderated by melatonin supplementation. RT-PCR data analysis revealed melatonin effectively downregulated neuroinflammatory (IL-6, TNF α) and neurodegenerative marker (Ngb) while upregulating the aging (Sirt 1) gene expression in both young and old melatonin supplemented ALAN exposed groups. Our results may help in understanding the degree of ALAN induced photo-oxidative damage in neuronal redox homeostasis during aging. We also show that melatonin supplementation might provide a basis for amelioration of oxidative disturbances to improve circadian entrainment in aged populations.
... 18 Induced mitochondrial biogenesis and content is thought to defend against increased oxidative stress by reducing ROS production due to lowered ETC activity per each mitochondrion and the increased number of entry points for electrons. 31 This will reduce the probability of electron leakage at ETC complexes known to promote partial reduction of oxygen to form superoxide in mitochondria. Previous studies investigating long-term energy deficit leading to sustained weight loss have documented increased markers of mitochondrial biogenesis 21 in subcutaneous white adipose tissue as well as both increased 32 and unchanged 22 mitochondrial biogenesis in skeletal muscle after weight loss. ...
Prolonged periods of energy deficit leading to weight loss induce metabolic adaptations resulting in reduced energy expenditure, but the mechanisms for energy conservation are incompletely understood. We examined 42 healthy athletic females (age 27.5 ± 4.0 years, body mass index 23.4 ± 1.7 kg/m²) who volunteered into either a group dieting for physique competition (n = 25) or a control group (n = 17). The diet group substantially reduced their energy intake and moderately increased exercise levels to induce loss of fat mass that was regained during a voluntary weight regain period. The control group maintained their typical lifestyle habits and body mass as instructed. From the diet group, fasting blood samples were drawn at baseline (PRE), after 4‐ to 5‐month weight loss (PRE‐MID), and after 4‐ to 5‐month weight regain (MID‐POST) as well as from the control group at similar intervals. Blood was analyzed to determine leukocyte transcriptome by RNA‐Sequencing and serum metabolome by nuclear magnetic resonance (NMR) platform. The intensive weight loss period induced several metabolic adaptations, including a prominent suppression of transcriptomic signature for mitochondrial OXPHOS and ribosome biogenesis. The upstream regulator analysis suggested that this reprogramming of cellular energy metabolism may be mediated via AMPK/PGC1‐α signaling and mTOR/eIF2 signaling‐dependent pathways. Our findings show for the first time that prolonged energy deprivation induced modulation of mitochondrial metabolism can be observed through minimally invasive measures of leukocyte transcriptome and serum metabolome at systemic level, suggesting that adaptation to energy deficit is broader in humans than previously thought.
... Mitochondrial quality, which is facilitated by coordination of degradation of defective mitochondria and their replacement by biogenesis, is one critical factor in keeping the levels of reactive oxygen species (ROS) low; therefore, it plays key roles for health and longevity of cells as well as tissues [1]. However, under oxidative stress or during senescence or aging of cells, mitochondrial autophagy (mitophagy), a major mechanism for the removal of damaged mitochondria, is frequently impaired, and therefore mitochondrial quality deteriorates [2][3][4][5][6][7]. ...
Mitochondrial autophagy (or mitophagy) is essential for mitochondrial quality control, which is critical for cellular and organismal health by attenuating reactive oxygen species generation and maintaining bioenergy homeostasis. Previously, we showed that mitophagy is activated in human cells through SIRT1 activation upon treatment of nicotinamide (NAM). Further, mitochondria are maintained as short fragments in the treated cells. In the current study, molecular pathways for NAM-induced mitochondrial fragmentation were sought. NAM treatment induced mitochondrial fission, at least in part by activating dynamin-1-like protein (Drp1), and this was through attenuation of the inhibitory phosphorylation at serine 637 (S637) of Drp1. This Drp1 hypo-phosphorylation was attributed to SIRT1-mediated activation of AMP-activated protein kinase (AMPK), which in turn induced a decrease in cellular levels of cyclic AMP (cAMP) and protein kinase A (PKA) activity, a kinase targeting S637 of Drp1. Furthermore, in NAM-treated cells, cytosolic Ca2+ was highly maintained; and, as a consequence, activity of calcineurin, a Drp1-dephosphorylating phosphatase, is expected to be elevated. These results suggest that NAD+-mediated SIRT1 activation facilitates mitochondrial fission through activation of Drp1 by suppressing its phosphorylation and accelerating its dephosphorylation. Additionally, it is suggested that there is a cycle of mitochondrial fragmentation and cytosolic Ca2+-mediated Drp1 dephosphorylation that may drive sustained mitochondrial fragmentation.
... There is also evidence that in non-hibernating mammals living in their natural environment, body temperature can exhibit wide fluctuations [66]. Pertinent to the role of energy metabolism in aging, CR activates mitochondrial pathways in adipose tissue and liver by inducing the expression of PGC-1, a key regulator of mitochondrial biogenesis [67,68]. Moreover, CR was shown to ameliorate age-related dysfunction in WAT, BAT, and beige adipose tissue [69]. ...
Since the rediscovery of brown adipose tissue (BAT) in adult humans, researchers in the metabolism field have been trying to hijack BAT to improve metabolism, decrease obesity, and decrease obesity-associated comorbidities. Intriguingly, many obesity-associated comorbidities such as cancer, dementia, diabetes, and cardiovascular disease are also age-related disease. This, of course, opens up the possibility that through obesity-dependent and -independent mechanisms, increased thermogenesis (or an overall improvement in energy metabolism) may delay age-associated diseases and possibly extend lifespan. Owing to the fact that energy utilization is deeply intertwined with all life processes, this becomes a somewhat intuitive hypothesis. Therefore this review aims to give a brief overview of thermogenic adipose tissue and thermogenesis, and delve deeper into how energy metabolism and aging are interrelated.
... RAS (Pittsburgh, PA, USA) demonstrated that ischemic neuroprotection can be achieved by dietary restriction, improving both gray and white matter outcomes and functional recovery (Zhang et al., 2018). Although the activation of sirtuins may be a potential contributor to ischemic neuroprotection (Haigis and Guarente, 2006;Guarente, 2008;Stetler et al., 2014), dietary restriction is also well known to affect the release of a variety of humoral factors, particularly from adipose tissue. Adiponectin release into the plasma occurs acutely after dietary restriction and increased levels in the serum. ...
The past decade has brought tremendous progress in diagnostic and therapeutic options for cerebrovascular diseases as exemplified by the advent of thrombectomy in ischemic stroke, benefitting a steeply increasing number of stroke patients and potentially paving the way for a renaissance of neuroprotectants. Progress in basic science has been equally impressive. Based on a deeper understanding of pathomechanisms underlying cerebrovascular diseases, new therapeutic targets have been identified and novel treatment strategies such as pre- and post-conditioning methods were developed. Moreover, translationally relevant aspects are increasingly recognized in basic science studies, which is believed to increase their predictive value and the relevance of obtained findings for clinical application.This review reports key results from some of the most remarkable and encouraging achievements in neurovascular research that have been reported at the 10th International Symposium on Neuroprotection and Neurorepair. Basic science topics discussed herein focus on aspects such as neuroinflammation, extracellular vesicles, and the role of sex and age on stroke recovery. Translational reports highlighted endovascular techniques and targeted delivery methods, neurorehabilitation, advanced functional testing approaches for experimental studies, pre-and post-conditioning approaches as well as novel imaging and treatment strategies. Beyond ischemic stroke, particular emphasis was given on activities in the fields of traumatic brain injury and cerebral hemorrhage in which promising preclinical and clinical results have been reported. Although the number of neutral outcomes in clinical trials is still remarkably high when targeting cerebrovascular diseases, we begin to evidence stepwise but continuous progress towards novel treatment options. Advances in preclinical and translational research as reported herein are believed to have formed a solid foundation for this progress.
... 56 Furthermore, the shift to FAO with efficient mitochondrial function reduces the production of reactive oxygen species (ROS), attenuating oxidative damage and maintaining the cellular redox balance. 57,58 Energy depletion is marked by the accumulation of adenosine monophosphate (AMP), an impending energy crisis activates the serine/ threonine AMP-activated protein kinase (AMPK). AMPK interrupts ATP-consuming reactions and activates ATPgenerating pathways, thereby promoting mitochondrial biogenesis. ...
Sanjay Kalra,1,2 Ambika Gopalakrishnan Unnikrishnan,3 Manash P Baruah,4 Rakesh Sahay,5 Ganapathi Bantwal6 1Department of Endocrinology, Bharti Hospital, Karnal, India; 2Department of Endocrinology, All India Institute of Medical Sciences, Rishikesh, Uttarakhand, India; 3Department of Endocrinology and Diabetes, Chellaram Diabetes Institute, Pune, Maharashtra, India; 4Department of Endocrinology, Excel Hospitals, Guwahati, India; 5Department of Endocrinology, Osmania Medical College, Hyderabad, Telangana, India; 6Department of Endocrinology, St. John’s Medical College and Hospital, Bangalore, Karnataka, IndiaCorrespondence: Sanjay KalraBharti Hospital, Kunjpura Road, Karnal, 132001 Haryana, IndiaTel +919896048555Email brideknl@gmail.comAbstract: Metabolic flexibility is the ability to efficiently adapt metabolism based on nutrient availability and requirement that is essential to maintain homeostasis in times of either caloric excess or restriction and during the energy-demanding state. This regulation is orchestrated in multiple organ systems by the alliance of numerous metabolic pathways under the master control of the insulin-glucagon-sympathetic neuro-endocrine axis. This, in turn, regulates key metabolic enzymes and transcription factors, many of which interact closely with and culminate in the mitochondrial energy generation machinery. Metabolic flexibility is compromised due to the continuous mismatch between availability and intake of calorie-dense foods and reduced metabolic demand due to sedentary lifestyle and age-related metabolic slowdown. The resultant nutrient overload leads to mitochondrial trafficking of substrates manifesting as mitochondrial dysfunction characterized by ineffective substrate switching and incomplete substrate utilization. At the systemic level, the manifestation of metabolic inflexibility comprises reduced skeletal muscle glucose disposal rate, impaired suppression of hepatic gluconeogenesis and adipose tissue lipolysis manifesting as insulin resistance. This is compounded by impaired β-cell function and progressively reduced β-cell mass. A consequence of insulin resistance is the upregulation of the mitogen-activated protein kinase pathway leading to a pro-hypertensive, atherogenic, and thrombogenic environment. This is further aggravated by oxidative stress, advanced glycation end products, and inflammation, which potentiates the risk of micro- and macro-vascular complications. This review aims to elucidate underlying mechanisms mediating the onset of metabolic inflexibility operating at the main target organs and to understand the progression of metabolic diseases. This could potentially translate into a pharmacological tool that can manage multiple interlinked conditions of dysglycemia, hypertension, and dyslipidemia by restoring metabolic flexibility. We discuss the breadth and depth of metabolic flexibility and its impact on health and disease.Keywords: metabolic flexibility, DBCD, insulin resistance, prediabetes, diabetes, microvascular and macrovascular complication
Calorie restriction (CR) provides anti-aging benefits through diverse processes, such as reduced metabolism and growth and increased mitochondrial activity. Although controversy still exists regarding CR-mediated lifespan effects, many researchers are seeking interventions that mimic the effects of CR. Yeast has proven to be a useful model system for aging studies, including CR effects. We report here that yeast adapted through in vitro evolution to the severe cellular stress caused by loss of the Ulp2 SUMO-specific protease exhibit both enhanced growth rates and replicative lifespan, and they have altered gene expression profiles similar to those observed in CR. Notably, in certain evolved ulp2Δ lines, a dramatic increase in the auto-sumoylation of Ubc9 E2 SUMO-conjugating enzyme results in altered regulation of multiple targets involved in energy metabolism and translation at both transcriptional and post-translational levels. This increase is essential for the survival of aged cells and CR-mediated lifespan extension. Thus, we suggest that high Ubc9 auto-sumoylation exerts potent anti-aging effects by promoting efficient energy metabolism-driven improvements in cell replication abilities. This potential could be therapeutically explored for the development of novel CR-mimetic strategies.
Mitochondria are thought to have become incorporated within the eukaryotic cell approximately 2 billion years ago and play a role in a variety of cellular processes, such as energy production, calcium buffering and homeostasis, steroid synthesis, cell growth, and apoptosis, as well as inflammation and ROS production. Considering that mitochondria are involved in a multitude of cellular processes, mitochondrial dysfunction has been shown to play a role within several age-related diseases, including cancers, diabetes (type 2), and neurodegenerative diseases, although the underlying mechanisms are not entirely understood. The significant increase in lifespan and increased incidence of age-related diseases over recent decades has confirmed the necessity to understand the mechanisms by which mitochondrial dysfunction impacts the process of aging and age-related diseases. In this review, we will offer a brief overview of mitochondria, along with structure and function of this important organelle. We will then discuss the cause and consequence of mitochondrial dysfunction in the aging process, with a particular focus on its role in inflammation, cognitive decline, and neurodegenerative diseases, such as Huntington’s disease, Parkinson’s disease, and Alzheimer’s disease. We will offer insight into therapies and interventions currently used to preserve or restore mitochondrial functioning during aging and neurodegeneration.
Dietary restriction (DR) increases lifespan in many organisms, but its underlying mechanisms are not fully understood. Mitochondria play a central role in metabolic regulation and are known to undergo changes in structure and function in response to DR. Mitochondrial membrane potential (Δψm) is the driving force for ATP production and mitochondrial outputs that integrate many cellular signals. One such signal regulated by Δψm is nutrient-status sensing. Here, we tested the hypothesis that DR promotes longevity through preserved Δψm during adulthood. Using the nematode Caenorhabditis elegans, we find that Δψm declines with age relatively early in the lifespan, and this decline is attenuated by DR. Pharmacologic depletion of Δψm blocked the longevity and health benefits of DR. Genetic perturbation of Δψm and mitochondrial ATP availability similarly prevented lifespan extension from DR. Taken together, this study provides further evidence that appropriate regulation of Δψm is a critical factor for health and longevity in response to DR.
Oxidized triglyceride monomers are the main cytotoxic products of deep-frying oil. However, its impact on the intestinal barrier, the first health guardian, remains unknown. In this study, HPLC-MS/MS analysis revealed that the epoxy group is the main oxidation product, indicating that it may be the main cytotoxic factor. Therefore, 1-9,10-epoxystearic ester, 2,3-dioleic acid (EGT) and glycerol trioleate (GT) were used to reveal the effect of the epoxy group on the intestinal barrier of dextran sulfate sodium-induced colitis. Characteristics analysis showed that EGT could aggravate intestinal damage. The relative mRNA expression analysis suggested that EGT could activate Caspase-1/NLRP3/GSDMD, thereby inducing pyroptosis. The proinflammatory cytokines activated by pyroptosis and the cGAS-STING pathway were released through the pores, thus inducing the disintegration of the tight junction between the intestinal epithelial cells and enhancing intestinal permeability. Metabonomics further confirmed that EGT can change the composition and content of phospholipids on the cell membrane, indicating the morphological changes of the intestinal epithelial cell membrane. In conclusion, this study highlights that EGT induced intestinal dysfunction via Caspase-1/NLRP3/GSDMD and cGAS-STING pathways.
Dietary restriction (DR) increases lifespan in many organisms, but its underlying mechanisms are not fully understood. Mitochondria play a central role in metabolic regulation and are known to undergo changes in structure and function in response to DR. Mitochondrial membrane potential (Δψ m ) is the driving force for ATP production and mitochondrial outputs that integrate many cellular signals. One such signal regulated by Δψ m is nutrient-status sensing. Here, we tested the hypothesis that DR promotes longevity through preserved Δψ m during adulthood. Using the nematode Caenorhabditis elegans, we find that Δψ m declines with age relatively early in the lifespan, and this decline is attenuated by DR. Pharmacologic depletion of Δψ m blocked the longevity and health benefits of DR. Genetic perturbation of Δψm and mitochondrial ATP availability similarly prevented lifespan extension from DR. Taken together, this study provides further evidence that appropriate regulation of Δψ m is a critical factor for health and longevity in response to DR.
Decreased oocyte quality and compromised embryo development are particularly prevalent in older females, but the aging-related cellular processes and effective ameliorative approaches have not been fully characterized. Intermittent fasting (IF) can help improve health and extend lifespan; nevertheless, how it regulates reproductive aging and its mechanisms remain unclear. We used naturally aged mice to investigate the role of IF in reproduction and found that just one month of every-other-day fasting was sufficient to improve oocyte quality. IF not only increased antral follicle numbers and ovulation but also enhanced oocyte meiotic competence and embryonic development by improving both nuclear and cytoplasmic maturation in maternally aged oocytes. The beneficial effects of IF manifested as alleviation of spindle structure abnormalities and chromosome segregation errors and maintenance of the correct cytoplasmic organelle reorganization. Moreover, single-cell transcriptome analysis showed that the positive impact of IF on aged oocytes was mediated by restoration of the nicotinamide adenine dinucleotide (NAD+)/Sirt1-mediated antioxidant defense system, which eliminated excessive accumulated ROS to suppress DNA damage and apoptosis. Collectively, these findings suggest that IF is a feasible approach to protect oocytes against advanced maternal age-related oxidation damage and to improve the reproductive outcomes of aged females.
Caloric restriction (CR) prevents obesity and increases resilience against pathological stimuli in laboratory rodents. At the mitochondrial level, protection promoted by CR in the brain and liver is related to higher calcium uptake rates and capacities, avoiding Ca ²⁺ -induced mitochondrial permeability transition. Dietary restriction has also been shown to increase kidney resistance against damaging stimuli, but if these effects are related to similar mitochondrial adaptations has not been uncovered. Here, we characterized changes in mitochondrial function in response to six months CR in rats, measuring bioenergetic parameters, redox balance and calcium homeostasis. CR promoted an increase in succinate-supported mitochondrial oxygen consumption rates. While CR prevents mitochondrial reactive oxygen species production in many tissues, in kidney we found that mitochondrial H 2 O 2 release was enhanced in a succinate-dependent manner. Surprisingly, and opposite to the effects observed in brain and liver, mitochondria from CR animals are more prone to Ca ²⁺ -induced mitochondrial permeability transition, in a manner reversed by antioxidant dithiothreitol. CR mitochondria also displayed higher calcium uptake rates, which were not accompanied by changes in calcium efflux rates, nor related to altered inner mitochondrial membrane potentials or amounts of the mitochondrial calcium uniporter (MCU). Instead, increased mitochondrial calcium uptake rates in CR kidneys correlate with a loss of MICU2, an MCU modulator. Interestingly, MICU2 is also modulated by CR in liver, suggesting it has a broader diet-sensitive regulatory role controlling mitochondrial calcium homeostasis. Together, our results highlight the organ-specific bioenergetic, redox, and ionic transport effects of CR, with some unexpected deleterious effects in kidney.
Mitochondria are one of the most important subcellular organelles that play important roles in cell function. They are double membrane–bound organelles responsible for many processes in eukaryotic cells, such as the production of adenosine triphosphate (ATP). Mitochondria are the main site of ROS production. They are responsible for cellular death, regulation of calcium hemostasis, and immunity. Recent researches demonstrated that mitochondria play a key role for aging. In recent years, nutritional approaches have been considered as possible alternatives to the currently existing medications to increase the response to therapy. Based on many studies, the positive effect of fasting on health and the prevention of many diseases has been confirmed. This section of the book explains the mitochondrial mechanisms of aging and the effects of diet on it.
Skeletal muscle (muscle) is essential for physical health and for metabolic integrity, with sarcopenia (progressive muscle mass loss and weakness), a precursor of aging and chronic disease. Loss of lean mass and muscle quality (force generation per unit of muscle) in the general population are associated with fatigue, weakness, and slowed walking speed, eventually interfering with the ability to maintain physical independence, and impacting participation in social roles and quality of life. Muscle mass and strength impairments are also documented during childhood cancer treatment, which often persist into adult survivorship, and contribute to an aging phenotype in this vulnerable population. Although several treatment exposures appear to confer increased risk for loss of mass and strength that persists after therapy, the pathophysiology responsible for poor muscle quantity and quality is not well understood in the childhood cancer survivor population. This is partly due to limited access to both pediatric and adult survivor muscle tissue samples, and to difficulties surrounding noninvasive investigative approaches for muscle assessment. Because muscle accounts for just under half of the body's mass and is essential for movement, metabolism, and metabolic health, understanding mechanisms of injury responsible for both initial and persistent dysfunction is important and will provide a foundation for intervention. The purpose of this review is to provide an overview of the available evidence describing associations between childhood cancer, its treatment, and muscle outcomes, identifying gaps in current knowledge.
This chapter introduces aging-related changes in various stem cell groups and discusses how these specific changes contribute to their loss of function exponentially to affect the overall longevity of the organism. The chapter begins with categorical descriptions of various types of stem cells depending on their cellular origin and different cellular and environmental factors responsible for promoting stem cell depletion and dysfunction during the progression of aging. Next, it discusses possible gender-related hormonal factors responsible for striking differences in longevity between males and females. Finally, possible therapeutic approaches to minimize these aging-related stem cell dysfunction and longevity are briefly summarized.
Sirtuins and melatonin have been discussed as agents that favor healthy aging and may, to a certain extent, prolong life. Interestingly, sirtuins and melatonin interact with each other in multiple ways. Overlapping effects have been described in the fields of metabolic regulation, mitochondrial function, protection against hypoxia/reperfusion, and circadian rhythms. In the chronobiological context, SIRT1 is capable of enhancing circadian amplitudes and assumed to increase the nocturnal secretion of melatonin by the pineal gland. However, melatonin feeds back to the circadian master clock and also modulates peripheral oscillators, which should have effects on sirtuins. In aging, which is characterized by reductions in various circadian rhythm amplitudes and in melatonin secretion, administration of melatonin has been shown to increase SIRT1 expression. A similar positive relationship has been described for inflammatory conditions. However, in cancer cells, melatonin downregulates SIRT1, an effect that is interpretable on the basis of dysregulated oscillators.
According to the WHO, 38 million individuals were living with human immunodeficiency virus (HIV), 25.4 million of which were using antiretroviral therapy (ART) at the end of 2019. Despite ART-mediated suppression of viral replication, ART is not a cure and is associated with viral persistence, residual inflammation, and metabolic disturbances. Indeed, due to the presence of viral reservoirs, lifelong ART therapy is required to control viremia and prevent disease progression into acquired immune deficiency syndrome (AIDS). Successful ART treatment allows people living with HIV (PLHIV) to achieve a similar life expectancy to uninfected individuals. However, recent studies have illustrated the presence of increased comorbidities, such as accelerated, premature immune aging, in ART-controlled PLHIV compared to uninfected individuals. Studies suggest that both HIV-infection and ART-treatment lead to mitochondrial dysfunction, ultimately resulting in cellular exhaustion, senescence, and apoptosis. Since mitochondria are essential cellular organelles for energy homeostasis and cellular metabolism, their compromise leads to decreased oxidative phosphorylation (OXPHOS), ATP synthesis, gluconeogenesis, and beta-oxidation, abnormal cell homeostasis, increased oxidative stress, depolarization of the mitochondrial membrane potential, and upregulation of mitochondrial DNA mutations and cellular apoptosis. The progressive mitochondrial damage induced by HIV-infection and ART-treatment likely contributes to accelerated aging, senescence, and cellular dysfunction in PLHIV. This review discusses the connections between mitochondrial compromise and cellular dysfunction associated with HIV- and ART-induced toxicities, providing new insights into how HIV and current ART directly impact mitochondrial functions and contribute to cellular senescence and aging in PLHIV. Identifying this nexus and potential mechanisms may be beneficial in developing improved therapeutics for treating PLHIV.
Resveratrol (3,5,4'-trihydroxystilbene) extends the lifespan of diverse species including Saccharomyces cerevisiae, Caenorhabditis elegans and Drosophila melanogaster. In these organisms, lifespan extension is dependent on Sir2, a conserved deacetylase proposed to underlie the beneficial effects of caloric restriction. Here we show that resveratrol shifts the physiology of middle-aged mice on a high-calorie diet towards that of mice on a standard diet and significantly increases their survival. Resveratrol produces changes associated with longer lifespan, including increased insulin sensitivity, reduced insulin-like growth factor-1 (IGF-I) levels, increased AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor- coactivator 1 (PGC-1) activity, increased mitochondrial number, and improved motor function. Parametric analysis of gene set enrichment revealed that resveratrol opposed the effects of the high-calorie diet in 144 out of 153 significantly altered pathways. These data show that improving general health in mammals using small molecules is an attainable goal, and point to new approaches for treating obesity-related disorders and diseases of ageing.
Yeast Sir2 is a heterochromatin component that silences transcription at silent mating loci, telomeres and the ribosomal DNA, and that also suppresses recombination in the rDNA and extends replicative life span. Mutational studies indicate that lysine 16 in the amino-terminal tail of histone H4 and lysines 9, 14 and 18 in H3 are critically important in silencing, whereas lysines 5, 8 and 12 of H4 have more redundant functions. Lysines 9 and 14 of histone H3 and lysines 5, 8 and 16 of H4 are acetylated in active chromatin and hypoacetylated in silenced chromatin, and overexpression of Sir2 promotes global deacetylation of histones, indicating that Sir2 may be a histone deacetylase. Deacetylation of lysine 16 of H4 is necessary for binding the silencing protein, Sir3. Here we show that yeast and mouse Sir2 proteins are nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylases, which deacetylate lysines 9 and 14 of H3 and specifically lysine 16 of H4. Our analysis of two SIR2 mutations supports the idea that this deacetylase activity accounts for silencing, recombination suppression and extension of life span in vivo. These findings provide a molecular framework of NAD-dependent histone deacetylation that connects metabolism, genomic silencing and ageing in yeast and, perhaps, in higher eukaryotes.
Homologs of the chromatin-bound yeast silent information regulator 2 (SIR2) protein are found in organisms from all biological kingdoms. SIR2 itself was originally discovered to influence mating-type control in haploid cells by locus-specific transcriptional silencing. Since then, SIR2 and its homologs have been suggested to play additional roles in suppression of recombination, chromosomal stability, metabolic regulation, meiosis, and aging. Considering the far-ranging nature of these functions, a major experimental goal has been to understand the molecular mechanism(s) by which this family of proteins acts. We report here that members of the SIR2 family catalyze an NAD-nicotinamide exchange reaction that requires the presence of acetylated lysines such as those found in the N termini of histones. Significantly, these enzymes also catalyze histone deacetylation in a reaction that absolutely requires NAD, thereby distinguishing them from previously characterized deacetylases. The enzymes are active on histone substrates that have been acetylated by both chromatin assembly-linked and transcription-related acetyltransferases. Contrary to a recent report, we find no evidence that these proteins ADP-ribosylate histones. Discovery of an intrinsic deacetylation activity for the conserved SIR2 family provides a mechanism for modifying histones and other proteins to regulate transcription and diverse biological processes.
Metformin is a widely used drug for treatment of type 2 diabetes with no defined cellular mechanism of action. Its glucose-lowering effect results from decreased hepatic glucose production and increased glucose utilization. Metformin's beneficial effects on circulating lipids have been linked to reduced fatty liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of lipid and glucose metabolism. Here we report that metformin activates AMPK in hepatocytes; as a result, acetyl-CoA carboxylase (ACC) activity is reduced, fatty acid oxidation is induced, and expression of lipogenic enzymes is suppressed. Activation of AMPK by metformin or an adenosine analogue suppresses expression of SREBP-1, a key lipogenic transcription factor. In metformin-treated rats, hepatic expression of SREBP-1 (and other lipogenic) mRNAs and protein is reduced; activity of the AMPK target, ACC, is also reduced. Using a novel AMPK inhibitor, we find that AMPK activation is required for metformin's inhibitory effect on glucose production by hepatocytes. In isolated rat skeletal muscles, metformin stimulates glucose uptake coincident with AMPK activation. Activation of AMPK provides a unified explanation for the pleiotropic beneficial effects of this drug; these results also suggest that alternative means of modulating AMPK should be useful for the treatment of metabolic disorders.
Calorie restriction (CR) extends lifespan in a wide spectrum of organisms and is the only regimen known to lengthen the lifespan of mammals. We established a model of CR in budding yeast Saccharomyces cerevisiae. In this system, lifespan can be extended by limiting glucose or by reducing the activity of the glucose-sensing cyclic-AMP-dependent kinase (PKA). Lifespan extension in a mutant with reduced PKA activity requires Sir2 and NAD (nicotinamide adenine dinucleotide). In this study we explore how CR activates Sir2 to extend lifespan. Here we show that the shunting of carbon metabolism toward the mitochondrial tricarboxylic acid cycle and the concomitant increase in respiration play a central part in this process. We discuss how this metabolic strategy may apply to CR in animals.
Several lines of evidence indicate that mitochondrial reactive oxygen species (ROS) generation is the major source of oxidative stress in the cell. It has been shown that ROS production accompanies cytochrome c release in different apoptotic paradigms, but the site(s) of ROS production remain obscure. In the current study, we demonstrate that loss of cytochrome c by mitochondria oxidizing NAD(+)-linked substrates results in a dramatic increase of ROS production and respiratory inhibition. This increased ROS production can be mimicked by rotenone, a complex I inhibitor, as well as other chemical inhibitors of electron flow that act further downstream in the electron transport chain. The effects of cytochrome c depletion from mitoplasts on ROS production and respiration are reversible upon addition of exogenous cytochrome c. Thus in these models of mitochondrial injury, a primary site of ROS generation in both brain and heart mitochondria is proximal to the rotenone inhibitory site, rather than in complex III. ROS production at complex I is critically dependent upon a highly reduced state of the mitochondrial NAD(P)(+) pool and is achieved upon nearly complete inhibition of the respiratory chain. Redox clamp experiments using the acetoacetate/L-beta-hydroxybutyrate couple in the presence of a maximally inhibitory rotenone concentration suggest that the site is approx. 50 mV more electronegative than the NADH/NAD(+) couple. In the absence of inhibitors, this highly reduced state of mitochondria can be induced by reverse electron flow from succinate to NAD(+), accounting for profound ROS production in the presence of succinate. These results lead us to propose a model of thermodynamic control of mitochondrial ROS production which suggests that the ROS-generating site of complex I is the Fe-S centre N-1a.
To explore the role of mitochondrial activity in the aging process, we have lowered the activity of the electron transport
chain and adenosine 5′-triphosphate (ATP) synthase with RNA interference (RNAi) in Caenorhabditis elegans. These perturbations reduced body size and behavioral rates and extended adult life-span. Restoring messenger RNA to near-normal
levels during adulthood did not elevate ATP levels and did not correct any of these phenotypes. Conversely, inhibiting respiratory-chain
components during adulthood only did not reset behavioral rates and did not affect life-span. Thus, the developing animal
appears to contain a regulatory system that monitors mitochondrial activity early in life and, in response, establishes rates
of respiration, behavior, and aging that persist during adulthood.
Calorie restriction extends lifespan in a broad range of organisms, from yeasts to mammals. Numerous hypotheses have been proposed to explain this phenomenon, including decreased oxidative damage and altered energy metabolism. In Saccharomyces cerevisiae, lifespan extension by calorie restriction requires the NAD+-dependent histone deacetylase, Sir2 (ref. 1). We have recently shown that Sir2 and its closest human homologue SIRT1, a p53 deacetylase, are strongly inhibited by the vitamin B3 precursor nicotinamide. Here we show that increased expression of PNC1 (pyrazinamidase/nicotinamidase 1), which encodes an enzyme that deaminates nicotinamide, is both necessary and sufficient for lifespan extension by calorie restriction and low-intensity stress. We also identify PNC1 as a longevity gene that is responsive to all stimuli that extend lifespan. We provide evidence that nicotinamide depletion is sufficient to activate Sir2 and that this is the mechanism by which PNC1 regulates longevity. We conclude that yeast lifespan extension by calorie restriction is the consequence of an active cellular response to a low-intensity stress and speculate that nicotinamide might regulate critical cellular processes in higher organisms.
A major cause of aging is thought to result from the cumulative effects of cell loss over time. In yeast, caloric restriction
(CR) delays aging by activating the Sir2 deacetylase. Here we show that expression of mammalian Sir2 (SIRT1) is induced in
CR rats as well as in human cells that are treated with serum from these animals. Insulin and insulin-like growth factor 1
(IGF-1) attenuated this response. SIRT1 deacetylates the DNA repair factor Ku70, causing it to sequester the proapoptotic
factor Bax away from mitochondria, thereby inhibiting stress-induced apoptotic cell death. Thus, CR could extend life-span
by inducing SIRT1 expression and promoting the long-term survival of irreplaceable cells.
Increased replicative longevity in Saccharomyces cerevisiae because of calorie restriction has been linked to enhanced mitochondrial respiratory activity. Here we have further investigated
how mitochondrial respiration affects yeast life span. We found that calorie restriction by growth in low glucose increased
respiration but decreased mitochondrial reactive oxygen species production relative to oxygen consumption. Calorie restriction
also enhanced chronological life span. The beneficial effects of calorie restriction on mitochondrial respiration, reactive
oxygen species release, and replicative and chronological life span could be mimicked by uncoupling agents such as dinitrophenol.
Conversely, chronological life span decreased in cells treated with antimycin (which strongly increases mitochondrial reactive
oxygen species generation) or in yeast mutants null for mitochondrial superoxide dismutase (which removes superoxide radicals)
and for RTG2 (which participates in retrograde feedback signaling between mitochondria and the nucleus). These results suggest that yeast
aging is linked to changes in mitochondrial metabolism and oxidative stress and that mild mitochondrial uncoupling can increase
both chronological and replicative life span.
To determine the role of reactive oxygen species in mammalian longevity, we generated transgenic mice that overexpress human catalase localized to the peroxisome, the nucleus, or mitochondria (MCAT). Median and maximum life spans were maximally increased (averages of 5 months and 5.5 months, respectively) in MCAT animals. Cardiac pathology and cataract development were delayed, oxidative damage was reduced, H2O2 production and H2O2-induced aconitase inactivation were attenuated, and the development of mitochondrial deletions was reduced. These results support the free radical theory of aging and reinforce the importance of mitochondria as a source of these radicals.
Mutations in mitochondrial DNA (mtDNA) accumulate in tissues of mammalian species and have been hypothesized to contribute
to aging. We show that mice expressing a proofreading-deficient version of the mitochondrial DNA polymerase g (POLG) accumulate
mtDNA mutations and display features of accelerated aging. Accumulation of mtDNA mutations was not associated with increased
markers of oxidative stress or a defect in cellular proliferation, but was correlated with the induction of apoptotic markers,
particularly in tissues characterized by rapid cellular turnover. The levels of apoptotic markers were also found to increase
during aging in normal mice. Thus, accumulation of mtDNA mutations that promote apoptosis may be a central mechanism driving
mammalian aging.
Calorie restriction extends life span in organisms ranging from yeast to mammals. Here, we report that calorie restriction
for either 3 or 12 months induced endothelial nitric oxide synthase (eNOS) expression and 3′,5′-cyclic guanosine monophosphate
formation in various tissues of male mice. This was accompanied by mitochondrial biogenesis, with increased oxygen consumption
and adenosine triphosphate production, and an enhanced expression of sirtuin 1. These effects were strongly attenuated in
eNOS null-mutant mice. Thus, nitric oxide plays a fundamental role in the processes induced by calorie restriction and may
be involved in the extension of life span in mammals.
Calorie restriction increases life span in many organisms, including the budding yeast Saccharomyces cerevisiae. From a large-scale analysis of 564 single-gene–deletion strains of yeast, we identified 10 gene deletions that increase
replicative life span. Six of these correspond to genes encoding components of the nutrient-responsive TOR and Sch9 pathways.
Calorie restriction of tor1D or sch9D cells failed to further increase life span and, like calorie restriction, deletion of either SCH9 or TOR1 increased life span independent of the Sir2 histone deacetylase. We propose that the TOR and Sch9 kinases define a primary
conduit through which excess nutrient intake limits longevity in yeast.
A model for replicative life span extension by calorie restriction (CR) in yeast has been proposed whereby reduced glucose in the growth medium leads to activation of the NAD+-dependent histone deacetylase Sir2. One mechanism proposed for this putative activation of Sir2 is that CR enhances the rate of respiration, in turn leading to altered levels of NAD+ or NADH, and ultimately resulting in enhanced Sir2 activity. An alternative mechanism has been proposed in which CR decreases levels of the Sir2 inhibitor nicotinamide through increased expression of the gene coding for nicotinamidase, PNC1. We have previously reported that life span extension by CR is not dependent on Sir2 in the long-lived BY4742 strain background. Here we have determined the requirement for respiration and the effect of nicotinamide levels on life span extension by CR. We find that CR confers robust life span extension in respiratory-deficient cells independent of strain background, and moreover, suppresses the premature mortality associated with loss of mitochondrial DNA in the short-lived PSY316 strain. Addition of nicotinamide to the medium dramatically shortens the life span of wild type cells, due to inhibition of Sir2. However, even in cells lacking both Sir2 and the replication fork block protein Fob1, nicotinamide partially prevents life span extension by CR. These findings (1) demonstrate that respiration is not required for the longevity benefits of CR in yeast, (2) show that nicotinamide inhibits life span extension by CR through a Sir2-independent mechanism, and (3) suggest that CR acts through a conserved, Sir2-independent mechanism in both PSY316 and BY4742.
The mitochondrial theory of aging proposes that reactive oxygen species (ROS) generated inside the cell will lead, with time, to increasing amounts of oxidative damage to various cell components. The main site for ROS production is the respiratory chain inside the mitochondria and accumulation of mtDNA mutations, and impaired respiratory chain function have been associated with degenerative diseases and aging. The theory predicts that impaired respiratory chain function will augment ROS production and thereby increase the rate of mtDNA mutation accumulation, which, in turn, will further compromise respiratory chain function. Previously, we reported that mice expressing an error-prone version of the catalytic subunit of mtDNA polymerase accumulate a substantial burden of somatic mtDNA mutations, associated with premature aging phenotypes and reduced lifespan. Here we show that these mtDNA mutator mice accumulate mtDNA mutations in an approximately linear manner. The amount of ROS produced was normal, and no increased sensitivity to oxidative stress-induced cell death was observed in mouse embryonic fibroblasts from mtDNA mutator mice, despite the presence of a severe respiratory chain dysfunction. Expression levels of antioxidant defense enzymes, protein carbonylation levels, and aconitase enzyme activity measurements indicated no or only minor oxidative stress in tissues from mtDNA mutator mice. The premature aging phenotypes in mtDNA mutator mice are thus not generated by a vicious cycle of massively increased oxidative stress accompanied by exponential accumulation of mtDNA mutations. We propose instead that respiratory chain dysfunction per se is the primary inducer of premature aging in mtDNA mutator mice.
• mitochondria
• mtDNA mutator mice
Sir2 (silent information regulator 2) is a nicotinamide adenine dinucleotide-dependent deacetylase required for longevity due to calorie restriction in yeast and Drosophila. In mammals, calorie restriction induces a complex pattern of physiological and behavioral changes. Here we report that the mammalian Sir2 ortholog, Sirt1, is required for the induction of a phenotype by calorie restriction in mice.
Age-related accumulation of cellular damage and death has been linked to oxidative stress. Calorie restriction (CR) is the most robust, nongenetic intervention that increases lifespan and reduces the rate of aging in a variety of species. Mechanisms responsible for the antiaging effects of CR remain uncertain, but reduction of oxidative stress within mitochondria remains a major focus of research. CR is hypothesized to decrease mitochondrial electron flow and proton leaks to attenuate damage caused by reactive oxygen species. We have focused our research on a related, but different, antiaging mechanism of CR. Specifically, using both in vivo and in vitro analyses, we report that CR reduces oxidative stress at the same time that it stimulates the proliferation of mitochondria through a peroxisome proliferation-activated receptor coactivator 1α signaling pathway. Moreover, mitochondria under CR conditions show less oxygen consumption, reduce membrane potential, and generate less reactive oxygen species than controls, but remarkably they are able to maintain their critical ATP production. In effect, CR can induce a peroxisome proliferation-activated receptor coactivator 1α-dependent increase in mitochondria capable of efficient and balanced bioenergetics to reduce oxidative stress and attenuate age-dependent endogenous oxidative damage.
• aging
• peroxisome proliferation-activated receptor coactivator 1
• reactive oxygen species
A compound found in red grapes called resveratrol improves the health and lifespan of mice on a high-calorie diet. This is potentially good news for overweight humans. Does it bode well for the rest of us too?
Caloric restriction without malnutrition extends life span in a range of organisms including insects and mammals and lowers free radical production by the mitochondria. However, the mechanism responsible for this adaptation are poorly understood.
The current study was undertaken to examine muscle mitochondrial bioenergetics in response to caloric restriction alone or in combination with exercise in 36 young (36.8 +/- 1.0 y), overweight (body mass index, 27.8 +/- 0.7 kg/m(2)) individuals randomized into one of three groups for a 6-mo intervention: Control, 100% of energy requirements; CR, 25% caloric restriction; and CREX, caloric restriction with exercise (CREX), 12.5% CR + 12.5% increased energy expenditure (EE). In the controls, 24-h EE was unchanged, but in CR and CREX it was significantly reduced from baseline even after adjustment for the loss of metabolic mass (CR, -135 +/- 42 kcal/d, p = 0.002 and CREX, -117 +/- 52 kcal/d, p = 0.008). Participants in the CR and CREX groups had increased expression of genes encoding proteins involved in mitochondrial function such as PPARGC1A, TFAM, eNOS, SIRT1, and PARL (all, p < 0.05). In parallel, mitochondrial DNA content increased by 35% +/- 5% in the CR group (p = 0.005) and 21% +/- 4% in the CREX group (p < 0.004), with no change in the control group (2% +/- 2%). However, the activity of key mitochondrial enzymes of the TCA (tricarboxylic acid) cycle (citrate synthase), beta-oxidation (beta-hydroxyacyl-CoA dehydrogenase), and electron transport chain (cytochrome C oxidase II) was unchanged. DNA damage was reduced from baseline in the CR (-0.56 +/- 0.11 arbitrary units, p = 0.003) and CREX (-0.45 +/- 0.12 arbitrary units, p = 0.011), but not in the controls. In primary cultures of human myotubes, a nitric oxide donor (mimicking eNOS signaling) induced mitochondrial biogenesis but failed to induce SIRT1 protein expression, suggesting that additional factors may regulate SIRT1 content during CR.
The observed increase in muscle mitochondrial DNA in association with a decrease in whole body oxygen consumption and DNA damage suggests that caloric restriction improves mitochondrial function in young non-obese adults.
In mammals, maintenance of energy and nutrient homeostasis during food deprivation is accomplished through an increase in mitochondrial fatty acid oxidation in peripheral tissues. An important component that drives this cellular oxidative process is the transcriptional coactivator PGC-1alpha. Here, we show that fasting induced PGC-1alpha deacetylation in skeletal muscle and that SIRT1 deacetylation of PGC-1alpha is required for activation of mitochondrial fatty acid oxidation genes. Moreover, expression of the acetyltransferase, GCN5, or the SIRT1 inhibitor, nicotinamide, induces PGC-1alpha acetylation and decreases expression of PGC-1alpha target genes in myotubes. Consistent with a switch from glucose to fatty acid oxidation that occurs in nutrient deprivation states, SIRT1 is required for induction and maintenance of fatty acid oxidation in response to low glucose concentrations. Thus, we have identified SIRT1 as a functional regulator of PGC-1alpha that induces a metabolic gene transcription program of mitochondrial fatty acid oxidation. These results have implications for understanding selective nutrient adaptation and how it might impact lifespan or metabolic diseases such as obesity and diabetes.
Reduced food intake as a result of dietary restriction increases the lifespan of a wide variety of metazoans and delays the onset of multiple age-related pathologies. Dietary restriction elicits a genetically programmed response to nutrient availability that cannot be explained by a simple reduction in metabolism or slower growth of the organism. In the nematode worm Caenorhabditis elegans, the transcription factor PHA-4 has an essential role in the embryonic development of the foregut and is orthologous to genes encoding the mammalian family of Foxa transcription factors, Foxa1, Foxa2 and Foxa3. Foxa family members have important roles during development, but also act later in life to regulate glucagon production and glucose homeostasis, particularly in response to fasting. Here we describe a newly discovered, adult-specific function for PHA-4 in the regulation of diet-restriction-mediated longevity in C. elegans. The role of PHA-4 in lifespan determination is specific for dietary restriction, because it is not required for the increased longevity caused by other genetic pathways that regulate ageing.
Reduced caloric intake decreases arterial blood pressure in healthy individuals and improves endothelium-dependent vasodilation in obese and overweight individuals. The SIRT1 protein deacetylase mediates many of the effects of calorie restriction (CR) on organismal lifespan and metabolic pathways. However, the role of SIRT1 in regulating endothelium-dependent vasomotor tone is not known. Here we show that SIRT1 promotes endothelium-dependent vasodilation by targeting endothelial nitric oxide synthase (eNOS) for deacetylation. SIRT1 and eNOS colocalize and coprecipitate in endothelial cells, and SIRT1 deacetylates eNOS, stimulating eNOS activity and increasing endothelial nitric oxide (NO). SIRT1-induced increase in endothelial NO is mediated through lysines 496 and 506 in the calmodulin-binding domain of eNOS. Inhibition of SIRT1 in the endothelium of arteries inhibits endothelium-dependent vasodilation and decreases bioavailable NO. Finally, CR of mice leads to deacetylation of eNOS. Our results demonstrate that SIRT1 plays a fundamental role in regulating endothelial NO and endothelium-dependent vascular tone by deacetylating eNOS. Furthermore, our results provide a possible molecular mechanism connecting the effects of CR on the endothelium and vascular tone to SIRT1-mediated deacetylation of eNOS.
• calorie restriction
• vasorelaxation
• silent information regulator 2
• resveratrol
• deacetylation
Dietary restriction extends life span in diverse species including Caenorhabditis elegans. However, the downstream cellular targets regulated by dietary restriction are largely unknown. Autophagy, an evolutionary conserved lysosomal degradation pathway, is induced under starvation conditions and regulates life span in insulin signaling C. elegans mutants. We now report that two essential autophagy genes (bec-1 and Ce-atg7) are required for the longevity phenotype of the C. elegans dietary restriction mutant (eat-2(ad1113) animals. Thus, we propose that autophagy mediates the effect, not only of insulin signaling, but also of dietary restriction on the regulation of C. elegans life span. Since autophagy and longevity control are highly conserved from C. elegans to mammals, a similar role for autophagy in dietary restriction-mediated life span extension may also exist in mammals.
Prior studies have shown that disruption of mitochondrial electron transport chain (ETC) function in the nematode Caenorhabditis elegans can result in life extension. Counter to these findings, many mutations that disrupt ETC function in humans are known to be pathologically life-shortening. In this study, we have undertaken the first formal investigation of the role of partial mitochondrial ETC inhibition and its contribution to the life-extension phenotype of C. elegans. We have developed a novel RNA interference (RNAi) dilution strategy to incrementally reduce the expression level of five genes encoding mitochondrial proteins in C. elegans: atp-3, nuo-2, isp-1, cco-1, and frataxin (frh-1). We observed that each RNAi treatment led to marked alterations in multiple ETC components. Using this dilution technique, we observed a consistent, three-phase lifespan response to increasingly greater inhibition by RNAi: at low levels of inhibition, there was no response, then as inhibition increased, lifespan responded by monotonically lengthening. Finally, at the highest levels of RNAi inhibition, lifespan began to shorten. Indirect measurements of whole-animal oxidative stress showed no correlation with life extension. Instead, larval development, fertility, and adult size all became coordinately affected at the same point at which lifespan began to increase. We show that a specific signal, initiated during the L3/L4 larval stage of development, is sufficient for initiating mitochondrial dysfunction-dependent life extension in C. elegans. This stage of development is characterized by the last somatic cell divisions normally undertaken by C. elegans and also by massive mitochondrial DNA expansion. The coordinate effects of mitochondrial dysfunction on several cell cycle-dependent phenotypes, coupled with recent findings directly linking cell cycle progression with mitochondrial activity in C. elegans, lead us to propose that cell cycle checkpoint control plays a key role in specifying longevity of mitochondrial mutants.
Type-2 diabetes results from the development of insulin resistance and a concomitant impairment of insulin secretion. Recent studies place altered mitochondrial oxidative phosphorylation (OxPhos) as an underlying genetic element of insulin resistance. However, the causative or compensatory nature of these OxPhos changes has yet to be proven. Here, we show that muscle- and liver-specific AIF ablation in mice initiates a pattern of OxPhos deficiency closely mimicking that of human insulin resistance, and contrary to current expectations, results in increased glucose tolerance, reduced fat mass, and increased insulin sensitivity. These results are maintained upon high-fat feeding and in both genetic mosaic and ubiquitous OxPhos-deficient mutants. Importantly, the effects of AIF on glucose metabolism are acutely inducible and reversible. These findings establish that tissue-specific as well as global OxPhos defects in mice can counteract the development of insulin resistance, diabetes, and obesity.
Although metformin is widely used for the treatment of non-insulin-dependent diabetes, its mode of action remains unclear. Here we provide evidence that its primary site of action is through a direct inhibition of complex 1 of the respiratory chain. Metformin(50 microM) inhibited mitochondrial oxidation of glutamate+malate in hepatoma cells by 13 and 30% after 24 and 60 h exposure respectively, but succinate oxidation was unaffected. Metformin also caused time-dependent inhibition of complex 1 in isolated mitochondria, whereas in sub-mitochondrial particles inhibition was immediate but required very high metformin concentrations (K(0.5),79 mM). These data are compatible with the slow membrane-potential-driven accumulation of the positively charged drug within the mitochondrial matrix leading to inhibition of complex 1. Metformin inhibition of gluconeogenesis from L-lactate in isolated rat hepatocytes was also time- and concentration-dependent, and accompanied by changes in metabolite levels similar to those induced by other inhibitors of gluconeogenesis acting on complex 1. Freeze-clamped livers from metformin-treated rats exhibited similar changes in metabolite concentrations. We conclude that the drug's pharmacological effects are mediated, at least in part, through a time-dependent, self-limiting inhibition of the respiratory chain that restrains hepatic gluconeogenesis while increasing glucose utilization in peripheral tissues. Lactic acidosis, an occasional side effect, canal so be explained in this way.
Calorie restriction (CR) extends life span in a wide variety of species. Previously, we showed that calorie restriction increases the replicative life span in yeast by activating Sir2, a highly conserved NAD-dependent deacetylase. Here we test whether CR activates Sir2 by increasing the NAD/NADH ratio or by regulating the level of nicotinamide, a known inhibitor of Sir2. We show that CR decreases NADH levels, and that NADH is a competitive inhibitor of Sir2. A genetic intervention that specifically decreases NADH levels increases life span, validating the model that NADH regulates yeast longevity in response to CR.
Point mutations and deletions of mitochondrial DNA (mtDNA) accumulate in a variety of tissues during ageing in humans, monkeys and rodents. These mutations are unevenly distributed and can accumulate clonally in certain cells, causing a mosaic pattern of respiratory chain deficiency in tissues such as heart, skeletal muscle and brain. In terms of the ageing process, their possible causative effects have been intensely debated because of their low abundance and purely correlative connection with ageing. We have now addressed this question experimentally by creating homozygous knock-in mice that express a proof-reading-deficient version of PolgA, the nucleus-encoded catalytic subunit of mtDNA polymerase. Here we show that the knock-in mice develop an mtDNA mutator phenotype with a threefold to fivefold increase in the levels of point mutations, as well as increased amounts of deleted mtDNA. This increase in somatic mtDNA mutations is associated with reduced lifespan and premature onset of ageing-related phenotypes such as weight loss, reduced subcutaneous fat, alopecia (hair loss), kyphosis (curvature of the spine), osteoporosis, anaemia, reduced fertility and heart enlargement. Our results thus provide a causative link between mtDNA mutations and ageing phenotypes in mammals.
Maintenance of normal blood glucose levels depends on a complex interplay between the insulin responsiveness of skeletal muscle
and liver and glucose-stimulated insulin secretion by pancreatic β cells. Defects in the former are responsible for insulin
resistance, and defects in the latter are responsible for progression to hyperglycemia. Emerging evidence supports the potentially
unifying hypothesis that both of these prominent features of type 2 diabetes are caused by mitochondrial dysfunction.
Mutations in genes affecting endocrine signaling, stress responses, metabolism, and telomeres can all increase the life spans of model organisms. These mutations have revealed evolutionarily conserved pathways for aging, some of which appear to extend life span in response to sensory cues, caloric restriction, or stress. Many mutations affecting longevity pathways delay age-related disease, and the molecular analysis of these pathways is leading to a mechanistic understanding of how these two processes--aging and disease susceptibility--are linked.
Homeostatic mechanisms in mammals respond to hormones and nutrients to maintain blood glucose levels within a narrow range. Caloric restriction causes many changes in glucose metabolism and extends lifespan; however, how this metabolism is connected to the ageing process is largely unknown. We show here that the Sir2 homologue, SIRT1--which modulates ageing in several species--controls the gluconeogenic/glycolytic pathways in liver in response to fasting signals through the transcriptional coactivator PGC-1alpha. A nutrient signalling response that is mediated by pyruvate induces SIRT1 protein in liver during fasting. We find that once SIRT1 is induced, it interacts with and deacetylates PGC-1alpha at specific lysine residues in an NAD(+)-dependent manner. SIRT1 induces gluconeogenic genes and hepatic glucose output through PGC-1alpha, but does not regulate the effects of PGC-1alpha on mitochondrial genes. In addition, SIRT1 modulates the effects of PGC-1alpha repression of glycolytic genes in response to fasting and pyruvate. Thus, we have identified a molecular mechanism whereby SIRT1 functions in glucose homeostasis as a modulator of PGC-1alpha. These findings have strong implications for the basic pathways of energy homeostasis, diabetes and lifespan.
Life is the interplay between structure and energy, yet the role of energy deficiency in human disease has been poorly explored by modern medicine. Since the mitochondria use oxidative phosphorylation (OXPHOS) to convert dietary calories into usable energy, generating reactive oxygen species (ROS) as a toxic by-product, I hypothesize that mitochondrial dysfunction plays a central role in a wide range of age-related disorders and various forms of cancer. Because mitochondrial DNA (mtDNA) is present in thousands of copies per cell and encodes essential genes for energy production, I propose that the delayed-onset and progressive course of the age-related diseases results from the accumulation of somatic mutations in the mtDNAs of post-mitotic tissues. The tissue-specific manifestations of these diseases may result from the varying energetic roles and needs of the different tissues. The variation in the individual and regional predisposition to degenerative diseases and cancer may result from the interaction of modern dietary caloric intake and ancient mitochondrial genetic polymorphisms. Therefore the mitochondria provide a direct link between our environment and our genes and the mtDNA variants that permitted our forbears to energetically adapt to their ancestral homes are influencing our health today.
Over 250 bacterial genome sequences are currently available in public databases, representing hundreds of species as well as multiple strains of the same species. The study of these genomes by both computational and experimental approaches has significantly advanced our understanding of the physiology and pathogenicity of many microbes and provided insights into the mechanisms and history of genome evolution. This review will discuss specific examples, with an emphasis on how “postgenomic” methods have been utilized to identify genes that are essential for bacterial growth or pathogenesis. There are two general categories of postgenomic studies—those that are based primarily on analysis of sequence information itself and those that require some use of genomic sequence information but not based on direct sequence analysis. Direct sequence analysis has the advantage of enabling genome-level analysis of pathogens that are difficult to manipulate genetically and permitting examination of small differences such as single nucleotide polymorphisms (SNPs). However, the accuracy of bioinformatic genomic annotations remains unclear since there have been no reported attempts to confirm functional assignments of genes on a genome-wide scale. It is imperative not only to improve annotation quality but also to dovetail computational approaches with empirical studies, especially those that seek to unravel the functions of the numerous hypothetical genes still found in genomes.
Skeletal muscle-mass loss with age has severe health consequences, yet the molecular basis of the loss remains obscure. Although mitochondrial DNA (mtDNA)-deletion mutations have been shown to accumulate with age, for these aberrant genomes to be physiologically relevant, they must accumulate to high levels intracellularly and be present in a significant number of cells. We examined mtDNA-deletion mutations in vastus lateralis (VL) muscle of human subjects aged 49-93 years, using both histologic and polymerase-chain-reaction (PCR) analyses, to determine the physiological and genomic integrity of mitochondria in aging human muscle. The number of VL muscle fibers exhibiting mitochondrial electron-transport-system (ETS) abnormalities increased from an estimated 6% at age 49 years to 31% at age 92 years. We analyzed the mitochondrial genotype of 48 single ETS-abnormal, cytochrome c oxidase-negative/succinate dehydrogenase-hyperreactive (COX-/SDH++) fibers from normal aging human subjects and identified mtDNA-deletion mutations in all abnormal fibers. Deletion mutations were clonal within a fiber and concomitant to the COX-/SDH++ region. Quantitative PCR analysis of wild-type and deletion-containing mtDNA genomes within ETS-abnormal regions of single fibers demonstrated that these deletion mutations accumulate to detrimental levels (>90% of the total mtDNA).
Diminished mitochondrial oxidative phosphorylation and aerobic capacity are associated with reduced longevity. We tested whether resveratrol (RSV), which is known to extend lifespan, impacts mitochondrial function and metabolic homeostasis. Treatment of mice with RSV significantly increased their aerobic capacity, as evidenced by their increased running time and consumption of oxygen in muscle fibers. RSV's effects were associated with an induction of genes for oxidative phosphorylation and mitochondrial biogenesis and were largely explained by an RSV-mediated decrease in PGC-1alpha acetylation and an increase in PGC-1alpha activity. This mechanism is consistent with RSV being a known activator of the protein deacetylase, SIRT1, and by the lack of effect of RSV in SIRT1(-/-) MEFs. Importantly, RSV treatment protected mice against diet-induced-obesity and insulin resistance. These pharmacological effects of RSV combined with the association of three Sirt1 SNPs and energy homeostasis in Finnish subjects implicates SIRT1 as a key regulator of energy and metabolic homeostasis.
Metabolic syndrome threatens health gains made during the past century. Physiological processes degraded by this syndrome are often oppositely affected by calorie restriction, which extends lifespan and prevents disease in rodents. Recent research in the field of ageing has begun to identify important mediators of calorie restriction, offering the hope of new drugs to improve healthspan. Moreover, if metabolic syndrome and calorie restriction are opposite extremes of the same metabolic spectrum, calorie restriction mimetics might provide another therapeutic approach to metabolic syndrome. Sirtuins and other important metabolic pathways that affect calorie restriction may serve as entry points for drugs to treat metabolic syndrome.
Various recent investigations relevant to the study of aging mechanisms have recently found that increases in longevity during dietary restriction can occur together with lack of decreases or even increases in O2 consumption. This is frequently interpreted as contradictory with the mitochondrial free radical theory of aging. But this is based on the erroneous assumption that increasing O2 consumption must increase the rate of mitochondrial oxygen radical generation. Here it is shown that the opposite occurs in many important situations. Strong decreases in absolute and relative (per unit of O2 consumed) mitochondrial oxygen radical production occur during aerobic exercise bouts, chronic exercise training, and hyperthyroidism, and notably, during dietary restriction. Mitochondrial oxygen radical generation is also lower in long-lived birds than in short-lived mammals of similar body size and metabolic rate. Total rates of reactive oxygen species generation can also vary between tissues in a way not linked to their differences in oxygen consumption. All this indicates that mitochondrial reactive oxygen species (ROS) production is not a simple byproduct of mitochondrial respiration. Instead, it is regulated independently of O2 consumption in many different physiologic situations, tissues, and animal species. Thus, the apparently paradoxical increases in O2 consumption observed in some models of dietary restriction do not discredit the mitochondrial free radical theory of aging, and they can further strengthen it.
Dietary restriction extends lifespan and retards age-related disease in many species and profoundly alters endocrine function in mammals. However, no causal role of any hormonal signal in diet-restricted longevity has been demonstrated. Here we show that increased longevity of diet-restricted Caenorhabditis elegans requires the transcription factor gene skn-1 acting in the ASIs, a pair of neurons in the head. Dietary restriction activates skn-1 in these two neurons, which signals peripheral tissues to increase metabolic activity. These findings demonstrate that increased lifespan in a diet-restricted metazoan depends on cell non-autonomous signalling from central neuronal cells to non-neuronal body tissues, and suggest that the ASI neurons mediate diet-restriction-induced longevity by an endocrine mechanism.
Key characteristics relating oxidative damage to aging and longevity are reviewed. Available information indicates that the specific composition of tissue macromolecules (proteins, lipids and mitochondrial DNA) in long-lived animal species gives them an intrinsically high resistance to modification that likely contributes to the superior longevity of these species. This is obtained in the case of lipids by decreasing fatty acid unsaturation, and in the proteins by lowering their methionine content. Long-lived animals also show low rates of reactive oxygen species (ROS) generation and oxidative damage at their mitochondria. On the other hand, dietary restriction decreases mitochondrial ROS production and oxidative damage to mitochondrial DNA and proteins. These changes are due to the decreased intake of dietary proteins (not of lipids or carbohydrates) of the dietary restricted animals. In turn, these effects of protein restriction seem to be specifically due to the lowered methionine intake of the protein and dietary restricted animals. It is emphasized that both a low rate of generation of endogenous damage and an intrinsically high resistance to modification of tissue macromolecules are key traits of animal longevity.
Accumulation of reactive oxygen species (ROS) is an oxidative stress to which cells respond by activating various defense mechanisms or, finally, by dying. At low levels, however, ROS act as signaling molecules in various intracellular processes. Autophagy, a process by which eukaryotic cells degrade and recycle macromolecules and organelles, has an important role in the cellular response to oxidative stress. Here, we review recent reports suggesting a regulatory role for ROS of mitochondrial origin as signaling molecules in autophagy, leading, under different circumstances, to either survival or cell death. We then discuss the relationship between mitochondria and autophagosomes and propose that mitochondria have an essential role in autophagosome biogenesis.
We generated mice that overexpress the sirtuin, SIRT1. Transgenic mice have been generated by knocking in SIRT1 cDNA into the beta-actin locus. Mice that are hemizygous for this transgene express normal levels of beta-actin and higher levels of SIRT1 protein in several tissues. Transgenic mice display some phenotypes similar to mice on a calorie-restricted diet: they are leaner than littermate controls; are more metabolically active; display reductions in blood cholesterol, adipokines, insulin and fasted glucose; and are more glucose tolerant. Furthermore, transgenic mice perform better on a rotarod challenge and also show a delay in reproduction. Our findings suggest that increased expression of SIRT1 in mice elicits beneficial phenotypes that may be relevant to human health and longevity.
A major cause of cell death caused by genotoxic stress is thought to be due to the depletion of NAD(+) from the nucleus and the cytoplasm. Here we show that NAD(+) levels in mitochondria remain at physiological levels following genotoxic stress and can maintain cell viability even when nuclear and cytoplasmic pools of NAD(+) are depleted. Rodents fasted for 48 hr show increased levels of the NAD(+) biosynthetic enzyme Nampt and a concomitant increase in mitochondrial NAD(+). Increased Nampt provides protection against cell death and requires an intact mitochondrial NAD(+) salvage pathway as well as the mitochondrial NAD(+)-dependent deacetylases SIRT3 and SIRT4. We discuss the relevance of these findings to understanding how nutrition modulates physiology and to the evolution of apoptosis.
We demonstrate a role for the NAD-dependent deacetylase Sirt1 in the regulation of autophagy. In particular, transient increased expression of Sirt1 is sufficient to stimulate basal rates of autophagy. In addition, we show that Sirt1−/− mouse embryonic fibroblasts do not fully activate autophagy under starved conditions. Reconstitution with wild-type but not a deacetylase-inactive mutant of Sirt1 restores autophagy in these cells. We further demonstrate that Sirt1 can form a molecular complex with several essential components of the autophagy machinery, including autophagy genes (Atg)5, Atg7, and Atg8. In vitro, Sirt1 can, in an NAD-dependent fashion, directly deacetylate these components. The absence of Sirt1 leads to markedly elevated acetylation of proteins known to be required for autophagy in both cultured cells and in embryonic and neonatal tissues. Finally, we show that Sirt1−/− mice partially resemble Atg5−/− mice, including the accumulation of damaged organelles, disruption of energy homeostasis, and early perinatal mortality. Furthermore, the in utero delivery of the metabolic substrate pyruvate extends the survival of Sirt1−/− pups. These results suggest that the Sirt1 deacetylase is an important in vivo regulator of autophagy and provide a link between sirtuin function and the overall cellular response to limited nutrients.
• mitochondria
• starvation
• acetylation
• aging
- H Yang
- T Yang
- Ja Baur
- E Perez
- T Matsui
- Jj Carmona
- Dw Lamming
- Nc Souza-Pinto
- Va Bohr
- A Rosenzweig
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