Article

Spermidine may decrease ER stress in pancreatic beta cells and may reduce apoptosis via activating AMPK dependent autophagy pathway

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Abstract

The risk for diabetes increases with increasing BMI<25. Insulin resistance is the key factor for type 2 diabetes; studies revealed that endoplasmic reticulum stress is the main factor behind this disease. With increase in ER stress, pancreatic beta cells start to undergo apoptosis, leading to a decline in the pancreatic beta cell population. The ER stress arises due to unfolded protein response. Recently, spermidine get importance for increasing the longevity in most of the eukaryotes including yeast, Caenorhabditis elegans, Drosophila and human peripheral blood mononuclear cells via induction of autophagy pathway. Autophagy is also involved in regulation of scavenging of proteins. One of the major cellular pathways for scavenging the aggregated intracellular protein is autophagy. Hence spermidine can be a candidate for the treatment type 2 diabetes. Autophagy genes are regulated by mTOR (mammalian Target Of Rapamycin) dependent or independent pathway via AMPK. Hence either inhibition of mTOR or activation of AMPK by spermidine will play two crucial roles, first being the activation of autophagy and secondly the reduction of endoplasmic reticulum stress which will reduce beta cell death by apoptosis and thus can be a novel therapeutic candidate in the treatment of insulin resistance in type 2 diabetes and preserving pancreatic beta cell mass.

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... Polyamine alkaloid called as spermidine, reported in caper species, delays aging in yeast, flies, worms, and human immune cells through the induction of autophagy [43]. Pichiah et al. (2011) [44] suggested that spermidine is used for treating type 2 diabetes. Isocodonocarpine, isolated firstly from Capparis decidua (Forssk.) ...
... Polyamine alkaloid called as spermidine, reported in caper species, delays aging in yeast, flies, worms, and human immune cells through the induction of autophagy [43]. Pichiah et al. (2011) [44] suggested that spermidine is used for treating type 2 diabetes. Isocodonocarpine, isolated firstly from Capparis decidua (Forssk.) ...
... Spermidine is a natural polyamine ubiquitously highly present in all living organisms; it has been implicated in many pathophysiological processes including cellular proliferation, transformation, differentiation, apoptosis, ageing and tumorigenesis (Gerner and Meyskens 2004;Pegg 2009;Igarashi and Kashiwagi 2010;Mandal et al. 2013). The exogenous administration of spermidine promotes longevity in many model organisms including yeast, nematodes and flies, and significantly reduces age-related oxidative protein damage in mice (Eisenberg et al. 2009;Madeo et al. 2010;Morselli et al. 2011;Tirupathi et al. 2011). It has been postulated that the anti-age activity of spermidine could be related to this molecule's ability to modulate the autophagic process (Eisenberg et al. 2009). ...
... Spermidine plays an important role in ageing during which there is a decline of its levels in different mammalian organs (Scalabrino and Ferioli 1984). The exogenous administration of spermidine promotes longevity in many model organisms including yeast, nematodes and flies, and significantly reduces age-related oxidative protein damage in mice (Eisenberg et al. 2009;Madeo et al. 2010;Morselli et al. 2011;Tirupathi et al. 2011). This increase in longevity is linked to changes in the acetylation of nuclear histones and to a transcriptional increase of different autophagy-related genes (Eisenberg et al. 2009). ...
Article
The exogenous administration of spermidine promotes longevity in many model organisms. It has been proposed that this anti-age activity of spermidine is related to this polyamine's ability to promote autophagy. Since spermidine is the substrate for the eIF5A post-translational modification by hypusination, we asked ourselves whether mature eIF5A may represent the link between spermidine and autophagy induction. To test this hypothesis, we inhibited the conversion of native eIF5A by a pharmacological approach, using the N1-guanyl-1,7-diamineoheptane (GC7), a spermidine analogue which competitively and reversibly inhibits deoxyhypusine synthase (DHS). In addition, we also employed genetic approaches by ablating both the eIF5A protein itself and DHS, the rate limiting enzyme catalyzing the conversion of lysine to hypusine. Collectively the data presented in this study demonstrate that the mature eIF5A (hypusinated form) is not involved in the autophagic pathway and that the inhibitor of DHS, GC7, produces off-target effect(s) resulting in marked induction of basal autophagy. These data are relevant in light of the fact that GC7 is considered a potent and selective inhibitor of DHS and is a potential candidate drug for cancer, diabetes and HIV therapy.
... AMPK is an energy sensor that mediates autophagy (Harhaji-Trajkovic et al., 2009). Furthermore, it has been revealed that polyamines regulate autophagy through the AMPK-mTOR pathway (Pichiah et al., 2011;Liu et al., 2019c;Chen et al., 2021). To better understand the molecular mechanism of autophagy regulated by Put, we explored the possible involvement of signaling pathways. ...
Article
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The polyamine putrescine (Put) is a ubiquitous small cationic amine. It plays an essential role in controlling the innate immune response. However, little is known about its function in mollusks. In this study, the Put content was observed to increase in the serum of pearl oyster Pinctada fucata martensii after 6 and 24 h of lipopolysaccharide (LPS) stimulation. Activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) increased, and nitric oxide synthase was downregulated in the Put group (i.e., combined treatment with Put and LPS) compared with that in the LPS group (i.e., combined treatment with phosphate-buffered saline and LPS). Furthermore, activities of alkaline phosphatase and acid phosphatase were inhibited after 6 h of LPS stimulation. The expression levels of the nuclear factor kappa B, IκB kinase, Janus kinase, and signal transducer and activator of transcription proteins genes were all significantly suppressed at 12 and 24 h in the Put group. Pseudomonas aeruginosa and Bacillus subtilis grew better after being incubated with the serum from the Put group than that from the LPS group. Additionally, the Put treatment remarkably inhibited the autophagy of hemocytes mediated by the AMP-activated protein kinase-mammalian target of rapamycin-Beclin-1 pathway. This study demonstrated that Put can effectively inhibit the inflammatory response induced by LPS in pearl oysters. These results provide useful information for further exploration of the immunoregulatory functions of polyamines in bivalves and contribute to the development of immunosuppressive agents.
... AMPK is a nutrient-sensing kinase which is activated under energy-depleted conditions and is, in contrast to the mTORC1 pathway, a positive regulator of autophagy. Several hormones, natural compounds, and drugs that induce AMPK activity have increased islet -cell survival (367)(368)(369) and protected against diabetic complications (235,275,280,(370)(371)(372)(373)(374)(375)(376)(377)(378). AMPK activators also showed beneficial effects in reducing lipid accumulation in non-adipose tissues by inducing autophagy in animal models of obesity (101, 315,376,379). ...
Article
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Autophagy is a cellular quality control and energy-providing process that is under strict control by intra- and extra-cellular stimuli. Recently, there has been an exponential increase in autophagy research and its implications for mammalian physiology. Autophagy de-regulation now is being implicated in many human diseases and its modulation has shown promising results in several pre-clinical studies. However, despite its first discovery as a hormone-regulated process by de Duve in the early 1960's, endocrine regulation of autophagy still remains poorly understood. In this review, we provide a critical summary of our present understanding of the basic mechanism of autophagy, its regulation by endocrine hormones, and its contribution to endocrine and metabolic homeostasis under physiological and pathological settings. Understanding the cross-regulation of hormones and autophagy on endocrine cell signaling and function will provide new insight into mammalian physiology as well as promote the development of new therapeutic strategies involving modulation of autophagy in endocrine and metabolic disorders.
... It is worth mentioning that spermidine is essential for hypusine modification of the translation factor eIF5A in some organisms. Spermidine performs diverse cellular functions in various other organisms (8). In the case of mammals, spermidine is involved in inhibition of neuronal nitric oxide synthase and transcription of RNA through stimulation of T4 polynucleotide kinase and T7 RNA polymerase activity (9,10). ...
Article
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Hypericin, a natural compound from Hypericum perforatum (St. John's wort), has been identified as a specific inhibitor of Leishmania donovani spermidine synthase (LdSS) using integrated computational and biochemical approaches. Hypericin showed in vitro inhibition of recombinant LdSS enzyme activity. The in vivo estimation of spermidine levels in Leishmania promastigotes after hypericin treatment showed significant decreases in the spermidine pools of the parasites, indicating target specificity of the inhibitor molecule. The inhibitor, hypericin, showed significant antileishmanial activity, and the mode of death showed necrosis-like features. Further, decreased trypanothione levels and increased glutathione levels with elevated reactive oxygen species (ROS) levels were observed after hypericin treatment. Supplementation with trypanothione in the medium with hypericin treatment restored in vivo trypanothione levels and ROS levels but could not prevent necrosis-like death of the parasites. However, supplementation with spermidine in the medium with hypericin treatment restored in vivo spermidine levels and parasite death was prevented to a large extent. The data overall suggest that the parasite death due to spermidine starvation as a result of LdSS inhibition is not related to elevated levels of reactive oxygen species. This suggests the involvement of spermidine in processes other than redox metabolism in Leishmania parasites. Moreover, the work provides a novel scaffold, i.e., hypericin, as a potent antileishmanial molecule.
... Application of spermidine treatment to other age-related conditions and diseases is also paying dividends. Spermidine provided health benefits in rodent models of diabetes (Tirupathi Pichiah et al., 2011), bone loss (Yamamoto et al., 2012), and arterial aging (LaRocca et al., 2013). Cancer is one important area of research that has seen little activity regarding spermidine treatment. ...
Article
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Strong consensus exists regarding the most robust environmental intervention for attenuating aging processes and increasing healthspan and lifespan: calorie restriction (CR). Over several decades, this paradigm has been replicated in numerous nonhuman models, and has been expanded over the last decade to formal, controlled human studies of CR. Given that long-term CR can create heavy challenges to compliance in human diets, the concept of a calorie restriction mimetic (CRM) has emerged as an active research area within gerontology. In past presentations on this subject, we have proposed that a CRM is a compound that mimics metabolic, hormonal, and physiological effects of CR, activates stress response pathways observed in CR and enhances stress protection, produces CR-like effects on longevity, reduces age-related disease, and maintains more youthful function, all without significantly reducing food intake, at least initially. Over 16 years ago, we proposed that glycolytic inhibition could be an effective strategy for developing CRM. The main argument here is that inhibiting energy utilization as far upstream as possible provides the highest chance of generating a broad spectrum of CR-like effects when compared to targeting a singular molecular target downstream. As an initial candidate CRM, 2-deoxyglucose, a known anti-glycolytic, was shown to produce a remarkable phenotype of CR, but further investigation found that this compound produced cardiotoxicity in rats at the doses we had been using. There remains interest in 2DG as a CRM but at lower doses. Beyond the proposal of 2DG as a candidate CRM, the field has grown steadily with many investigators proposing other strategies, including novel anti-glycolytics. Within the realm of upstream targeting at the level of the digestive system, research has included bariatric surgery, inhibitors of fat digestion/absorption, and inhibitors of carbohydrate digestion. Research focused on downstream sites has included insulin receptors, IGF-1 receptors, sirtuin activators, inhibitors of mTOR, and polyamines. In the current review we discuss progress made involving these various strategies and comment on the status and future for each within this exciting research field.
... An important polyamine alkaloid, spermidine, reported in these species, delays aging in yeast, flies, worms, and human immune cells through the induction of autophagy (Eisenberg et al., 2009). Pichiah et al. (2011) suggested that spermidine is helpful for treating type 2 diabetes. Another compound, isocodonocarpine, isolated for the first time from C. decidua, was found to be useful against inflammation and asthma (Yadav et al., 1997). ...
... With mild or short-lived stress, early ERSS events may provide the capacity for the cell to recover, for example by inhibiting protein translation and any further accumulation of unfolded proteins, increasing expression of chaperones, and increasing expression of ERAD components to clear the unfolded protein. Activation of autophagy allows the removal of damaged proteins or cell structures, and factors that activate autophagy can inhibit cell death upon ERSS activation (Kapuy, et al., 2014, Tirupathi Pichiah, et al., 2011. ...
Article
Oocytes and early stage embryos are highly sensitive to variation in diverse exogenous factors such as temperature, osmolarity, oxygen, nutrient restriction, pH, shear stress, toxins, amino acid availability, and lipids. It is becoming increasingly apparent that many such factors negatively affect the endoplasmic reticulum, protein synthesis and protein processing, initiating ER stress and unfolded protein responses. As a result, ER stress signaling serves as a common mediator of cellular responses to diverse stressors. In oocytes and embryos, this leads to developmental arrest and epigenetic changes. Recent studies have revealed that preventing ER stress or inhibiting ER stress signaling can preserve or even enhance oocyte and embryo developmental potential. This review examines ER stress signaling, how it arises, how it affects oocytes and embryos, and how its occurrence can be managed or prevented.
... EIF2AK4), AMPK (AMP protein kinase), and GSK3β (glycogen synthase kinase 3 beta), and these same signals can directly or indirectly modulate TOR activity, so that diverse signals may modulate the translation response to TOR signaling. AMPK can diminish ERSS downstream events ( Salvado et al., 2013;Terai et al., 2005;Tirupathi Pichiah et al., 2011) but can also activate ERSS ( Lin et al., 2014b;Yang et al., 2013). PPARβ/δ (peroxisome proliferator activated receptors) inhibit events downstream of ERSS by AMPK activation ( Salvado et al., 2014). ...
Article
Mammalian oocytes and embryos are exquisitely sensitive to a wide range of insults related to physical stress, chemical exposure, and exposures to adverse maternal nutrition or health status. Although cells manifest specific responses to various stressors, many of these stressors intersect at the endoplasmic reticulum (ER), where disruptions in protein folding and production of reactive oxygen species initiate downstream signaling events. These signals modulate mRNA translation and gene transcription, leading to recovery, activation of autophagy, or with severe and prolonged stress, apoptosis. ER stress signaling has recently come to the fore as a major contributor to embryo demise. Accordingly, agents that modulate or inhibit ER stress signaling have yielded beneficial effects on embryo survival and long-term developmental potential. We review here the mechanisms of ER stress signaling, their connections to mammalian oocytes and embryos, and the promising indications that interventions in this pathway may provide new opportunities for improving mammalian reproduction and health. Copyright © 2015 Elsevier Inc. All rights reserved.
... [30][31] Additionally, ER stress could induce autophagy in organisms ranging from yeast to mammals. 32 However, it is unclear whether disruption of autophagy or dysfunction of the ER plays a critical role in the cell death induced by Stx2. In our study, autophagy was activated by Stx2 as a cell death response in intestinal epithelial cells, and this response was mediated by ER stress. ...
Article
Shiga toxins (Stxs) are a family of cytotoxic proteins that lead to the development of bloody diarrhea, hemolytic-uremic syndrome, and central nervous system complications caused by bacteria such as S. dysenteriae, E. coli O157:H7 and E. coli O104:H4. Increasing evidence indicates that macroautophagy (autophagy) is a key factor in the cell death induced by Stxs. However, the associated mechanisms are not yet clear. This study showed that Stx2 induces autophagic cell death in Caco-2 cells, a cultured line model of human enterocytes. Inhibition of autophagy using pharmacological inhibitors, such as 3-methyladenine and bafilomycin A1, or silencing of the autophagy genes ATG12 or BECN1 decreased the Stx2-induced death in Caco-2 cells. Furthermore, there were numerous instances of dilated endoplasmic reticulum (ER) in the Stx2-treated Caco-2 cells, and repression of ER stress due to the depletion of viable candidates of DDIT3 and NUPR1. These processes led to Stx2-induced autophagy and cell death. Finally, the data showed that the pseudokinase TRIB3-mediated DDIT3 expression and AKT1 dephosphorylation upon ER stress were triggered by Stx2. Thus, the data indicate that Stx2 causes autophagic cell death via the ER stress pathway in intestinal epithelial cells.
... These compounds include spermidine and spermine, vitamin D3, and 17-beta-estradio, among others [44][45][46][47]. It was reported that spermidine and spermine can induce autophagy through inducing 5 -AMP-activated protein kinase (AMPK) and inhibiting the mTOR signaling pathway, thus spermidine and spermine both inhibited SARS-CoV-2 infection by inducing viral degradation in endolysosomes [48]. 17-beta-estradiol is the predominant estrogen during the reproductive years; it was supposed to play a major role in antiviral therapies for SARS-CoV-2, considering the effects of 17-beta-estradiol in different systems, such as repressing the transcription virus genes, inflammation modulation, inhibition of late endosome virus trafficking, and so on. ...
Article
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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters host cells mainly by the angiotensin converting enzyme 2 (ACE2) receptor, which can recognize the spike (S) protein by its extracellular domain. Previously, recombinant soluble ACE2 (sACE2) has been clinically used as a therapeutic treatment for cardiovascular diseases. Recent data demonstrated that sACE2 can also be exploited as a decoy to effectively inhibit the cell entry of SARS-CoV-2, through blocking SARS-CoV-2 binding to membrane-anchored ACE2. In this study, we summarized the current findings on the optimized sACE2-based strategies as a therapeutic agent, including Fc fusion to prolong the half-life of sACE2, deep mutagenesis to create high-affinity decoys for SARS-CoV-2, or designing the truncated functional fragments to enhance its safety, among others. Considering that COVID-19 patients are often accompanied by manifestations of cardiovascular complications, we think that administration of sACE2 in COVID-19 patients may be a promising therapeutic strategy to simultaneously treat both cardiovascular diseases and SARS-CoV-2 infection. This review would provide insights for the development of novel therapeutic agents against the COVID-19 pandemic.
... The natural polyamines spermidine, spermine and their precursor, putrescine, are the central convergence point for the multiple signaling pathways and regulate distinct cellular functions [6,7]. We [8][9][10][11] and others [12,13] have reported that cellular polyamines are implicated in the control of the apoptotic response in IECs and that polyamine depletion induces a resistance to apoptosis, at least partially, by activating Akt activity. However, the exact mechanism by which polyamine depletion activates Akt remains unknown. ...
Article
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Apoptosis plays a critical role in the maintenance of gut mucosal homeostasis and is highly regulated by numerous factors including polyamines. Decreasing cellular polyamines promotes the resistance of intestinal epithelial cells (IECs) to apoptosis by increasing Akt kinase activity, but the exact mechanisms by which polyamine depletion activates Akt remain unknown. 3-phosphoinositide-dependent protein kinase-1 (PDK1), functions as a downstream of phosphatidylinositol-3 kinase (PI3K) and upstream of Akt and serves as a major regulator of Akt activity. The current study determined if polyamines regulate Akt activity by altering PDK1. Studies were conducted in IEC-6 cells, derived from rat small intestinal crypts. Depletion of cellular polyamines induced PDK1 phosphorylation and increased its kinase activity, which were prevented by exogenous polyamine putrescine. Induced PDK1 activation following polyamine depletion was associated with an increase in phosphorylated Akt (pAkt) and Akt kinase activity. In contrast, polyamine depletion did not alter levels of total PDK1 and Akt proteins. PDK1 silencing in polyamine-deficient cells not only prevented the induced Akt activation but also blocked the increased resistance to apoptosis. These results indicate that polyamine depletion enhanced Akt phosphorylation by increasing PDK1 kinase activity, thereby protecting IECs against apoptosis.
... Moreover, spermidine has the function to induce autophagy in most eukaryotes and reduce oxidative stress. Hence, spermidine may decrease endoplasmic reticulum (ER) stress and reduce apoptosis via activating AMPK-dependent autophagy pathway [22]. ...
Article
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The quality control of skeletal muscle is a continuous requirement throughout the lifetime, although its functions and quality present as a declining trend during aging process. Dysfunctional or deficient autophagy and excessive apoptosis may contribute to the atrophy of senescent skeletal muscle. Spermidine, as a natural polyamine, can be involved in important cellular functions for lifespan extension and stress resistance in several model organisms through activating autophagy. Similarly, cellular autophagic responses to exercise have also been extensively investigated. In the present study, in order to confirm the mitigation or amelioration of skeletal muscle atrophy in aging rats through spermidine coupled with exercise intervention and explore corresponding mechanisms, the rat model with aging-related atrophy of skeletal muscle was established by intraperitoneal injection of D-galactose (D-gal) (200 mg/kgd), and model rats were subjected to the intervention with spermidine (5 mg/kgd) or swimming (60 min/d, 5 d/wk) or combination for 42 days. Spermidine coupled with exercise could attenuate D-gal-induced aging-related atrophy of skeletal muscle through induced autophagy and reduced apoptosis with characteristics of more autophagosomes, activated mitophagy, enhanced mitochondrial quality, alleviated cell shrinkage, and less swollen mitochondria under transmission scanning microscopic observation. Meanwhile, spermidine coupled with exercise could induce autophagy through activating AMPK-FOXO3a signal pathway with characterization of increased Beclin1 and LC3-II/LC3-I ratio, up-regulated anti-apoptotic Bcl-2, down-regulated pro-apoptotic Bax and caspase-3, as well as activated AMPK and FOXO3a. Therefore, spermidine combined with exercise can execute the prevention or treatment of D-gal-induced aging-related skeletal muscle atrophy through enhanced autophagy and reduced apoptosis mediated by AMPK-FOXO3a signal pathway.
... These results suggest that exercise and Spd may share mediators that act on similar pathways in varying degrees, generating a synergistic effect for delaying skeletal muscle senescence [1]. Therefore, Spd, by activating the AMPK-dependent autophagy pathway, may decrease endoplasmic reticulum stress and reduce apoptosis [62]. ...
Article
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Skeletal muscle comprises approximately 40% of the total body mass. Preserving muscle health and function is essential for the entire body in order to counteract chronic diseases such as type II diabetes, cardiovascular diseases, and cancer. Prolonged physical inactivity, particularly among the elderly, causes muscle atrophy, a pathological state with adverse outcomes such as poor quality of life, physical disability, and high mortality. In murine skeletal muscle C2C12 cells, increased expression of the spermine oxidase (SMOX) enzyme has been found during cell differentiation. Notably, SMOX overexpression increases muscle fiber size, while SMOX reduction was enough to induce muscle atrophy in multiple murine models. Of note, the SMOX reaction product spermidine appears to be involved in skeletal muscle atrophy/hypertrophy. It is effective in reactivating autophagy, ameliorating the myopathic defects of collagen VI-null mice. Moreover, spermidine treatment, if combined with exercise, can affect D-gal-induced aging-related skeletal muscle atrophy. This review hypothesizes a role for SMOX during skeletal muscle differentiation and outlines its role and that of spermidine in muscle atrophy. The identification of new molecular pathways involved in the maintenance of skeletal muscle health could be beneficial in developing novel therapeutic lead compounds to treat muscle atrophy.
... Synthesis of spermidine, a polyamine with medical and agricultural applications (Nambeesan et al., 2010;Pichiah et al., 2011;Ramot et al., 2011;Rinaldi et al., 2004), may be repressed in the presence of glucose (Kim et al., 2017b;White et al., 2001). In a case like this, the use of xylose as a carbon source allows bypassing glucose repression and may enhance production of the target molecule. ...
Article
The substantial research efforts into lignocellulosic biofuels have generated an abundance of valuable knowledge and technologies for metabolic engineering. In particular, these investments have led to a vast growth in proficiency of engineering the yeast Saccharomyces cerevisiae for consuming lignocellulosic sugars, enabling the simultaneous assimilation of multiple carbon sources, and producing a large variety of value-added products by introduction of heterologous metabolic pathways. While microbial conversion of cellulosic sugars into large-volume low-value biofuels is not currently economically feasible, there may still be opportunities to produce other value-added chemicals as regulation of cellulosic sugar metabolism is quite different from glucose metabolism. This review summarizes these recent advances with an emphasis on employing engineered yeast for the bioconversion of lignocellulosic sugars into a variety of non-ethanol value-added products.
... On this basis, it seems possible that regulation of autophagy may provide a mechanism by which the viability of β-cells can be influenced by environmental stressors and that saturated and unsaturated fatty acids may regulate autophagy differentially. In this context it is reported that additional cytoprotective agents such as spermidine and glucagonlike peptide-1 (GLP-1) can also regulate autophagy (Sharma et al. 2011, Tirupathi Pichiah et al. 2011, Zummo et al. 2017, Liu et al. 2019a. Therefore, in the present work we have studied the effects of saturated and an unsaturated fatty acids on autophagy in two clonal rat β-cell lines, BRIN-BD11 and INS-1E cells, in which FFAs are known to influence viability differentially according to their degree of saturation. ...
Article
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Long chain saturated fatty acids are lipotoxic to pancreatic β-cells whereas most unsaturates are better tolerated and some may even be cytoprotective. Fatty acids alter autophagy in β-cells and there is increasing evidence that such alterations can impact directly on the regulation of viability. Accordingly, we have compared the effects of palmitate (C16:0) and palmitoleate (C16:1) on autophagy in cultured β-cells and human islets. Treatment of BRIN-BD11 β-cells with palmitate led to enhanced autophagic activity, as judged by cleavage of microtubule-associated protein 1 light chain 3—I (LC3-I) and this correlated with a marked loss of cell viability in the cells. In addition, transfection of these cells with an mCherry-YFP-LC3 reporter construct revealed the accumulation of autophagosomes in palmitate-treated cells, indicating an impairment of autophagosome-lysosome fusion. This was also seen upon addition of the vacuolar ATPase inhibitor, bafilomycin A1. Exposure of BRIN-BD11 cells to palmitoleate (C16:1) did not lead directly to changes in autophagic activity or flux but it antagonised the actions of palmitate. In parallel, palmitoleate also improved the viability of palmitate-treated BRIN-BD11 cells. Equivalent responses were observed in INS-1E cells and in isolated human islets. Taken together, these data suggest that palmitate may cause an impairment of autophagosome-lysosome fusion. These effects were not reproduced by palmitoleate which, instead, antagonised the responses mediated by palmitate suggesting that attenuation of β-cell stress may contribute to the improvement in cell viability caused by the mono-unsaturated fatty acid.
... Moreover, spermidine has been reported to induce cell autophagy to extend life-span and reduce cardiovascular diseases-related morbidity [5][6][7][8]. In addition, spermidine also shows versatile functions such as reducing neurodegeneration, delaying senile dementia, preventing heart aging, and treating type 2 diabetes [9][10][11][12]. ...
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Background: Spermidine is a biologically active polyamine with extensive application potential in foods and pharmaceuticals. However, previously reported spermidine titers by biosynthesis methods are relatively low, which hinders the industrial fermentation of spermidine. To improve the spermidine titer, key genes affecting the spermidine production were mined to engineer the Bacillus amyloliquefaciens. Results: Genes of S-adenosylmethionine decarboxylase (speD) and spermidine synthase (speE) from different microorganisms were expressed and compared in B. amyloliquefaciens. Therein, the speD from Escherichia coli and speE from Saccharomyces cerevisiae were confirmed to be optimal for spermidine synthesis, respectively. Then, these two genes were co-expressed to generate an engineering strain B. amyloliquefaciens HSAM2(PDspeD-SspeE) with a spermidine titer of 91.31 mg/L, improving by 10.90-fold compared with the control (HSAM2). Through further optimization of fermentation medium, the spermidine titer was increased to 227.35 mg/L, which was the highest titer among present reports. Moreover, the consumption of the substrate S-adenosylmethionine was consistent with the accumulation of spermidine, which contributed to understanding the synthetic pattern of spermidine. Conclusions: Two critical genes for spermidine synthesis were obtained, and an B. amyloliquefaciens cell factory was constructed for enhanced spermidine production, which laid the foundation for further industrial production of spermidine.
... In addition, observational showed lower blood pressure and a lower incidence of cardiovascular disease in people with higher dietary consumption of spermidine. 91) While spermidine activates AMPK and inhibits mTOR, 92) its mechanism differs from that of resveratrol; thus, these two compounds could synergistically in-duce autophagy. 22) In clinical studies, spermidine was well-tolerated and improved memory performance in older adults with cognitive decline, making it a good target for cognitive aging studies. ...
Article
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Caloric restriction (CR) has been shown to extend the lifespan of many species. Research to identify compounds that imitate the results of CR has shown extensions of both lifespan and healthspan via different mechanisms. For example, mechanistic target of rapamycin (mTOR) inhibitors such as rapamycin affect nutrient-sensing pathways; phenols and flavonoids show antioxidant characteristics; aspirin has anti-inflammatory effects, while spermidine induces autophagy. Herein, we summarize research progress and proposed mechanisms for the most well-known compounds showing lifespan-extending potential for anti-aging characteristics.
... Highly conserved ability of SPD is wildly reported to extend lifespan of Saccharomyces, C. elegans, Drosophila [224], mice [225], and human cells [224]. Restoration of autophagy, improvement of mitochondrial function, and reduction of ER stress are believed to be key for SPD to improve aging impairments, especially neurodegeneration [226], metabolic diseases [227], and cardiovascular and muscle-related disorders [225,228,229]. As a stimulus of T cell protein-tyrosine phosphatase, SPD rescues intestinal epithelial barrier dysfunction disrupted by inflammatory cytokine treatment in vitro [230]. ...
Article
Owing to the growing elderly population, age-related problems are gaining increasing attention from the scientific community. With senescence, the intestine undergoes a spectrum of changes and infirmities that are likely the causes of overall aging. Therefore, identification of the aged intestine and the search for novel strategies to rescue it, are required. Although progress has been made in research on some components of the aged intestine, such as intestinal stem cells, the comprehensive understanding of intestinal aging is still limited, and this restricts the in-depth search for efficient strategies. In this concise review, we discuss several aspects of intestinal aging. More emphasis is placed on the appraisal of current and potential strategies to alleviate intestinal aging, as well as future targets to rejuvenate the aged intestine.
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Insulin, as measured by C-peptide, is produced for decades after onset of type 1 diabetes, and even very low levels of C-peptide have clinical significance. In this chapter we show that two distinct pathophysiological subtypes of type 1 diabetic subjects can be distinguished. Early-onset diabetic subjects (≤20 years) have rapid loss of C-peptide, whereas late-onset diabetic subjects (>20 years) have slower C-peptide declines over decades. Early-onset diabetics have significantly lower levels of persistent autoreactive CD8+ T cells than do late-onset diabetic subjects. In late-onset disease, robust production of autoreactive T-cells occurs even in the absence of C-peptide. Metabolomics analysis reveals frequent differences between the two subtypes of subjects in the levels of amino acids, carbohydrates, cofactors, lipids, peptides, and xenobiotics. There are statistically significant differences related to protective islet functions, islet health, development, blood sugar control, and regulation of exocrine pancreas function. Taken together these findings suggest that pancreas pathobiology, as well as durability of abnormal T-cell response should be considered in immune targeting treatments. Therapies aimed at immune defects alone are likely to work best in late-onset diabetics. Therapies aimed at islet cell preservation in early-onset diabetic subjects likely have greater efficacy if administered shortly after disease onset. Here, we provide evidence that early-onset diabetics (≤20 years of age) have a significantly lower level of autoreactive T-cells than do late-onset diabetics (>20 years of age). We studied autoreactive T-cells in a subset (n = 178) of our sample (n = 1958) using a peptide-major histocompatibility complex class I (pMHC-I) multimer technique (fluorochrome-conjugated and peptide-loaded major histocompatibility complex class I multimers) in conjunction with flow cytometry. Two diabetes-specific peptides for autoreactive T-cell detection were used, i.e., peptide sequences from epitopes of pancreatic beta cells, islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) or insulin B chain (InsB) (tetramers were purchased from Beckman Coulter, Fullerton, CA, whereas dextramers were a generous gift from Immudex, Copenhagen, Denmark). For the IGRP peptide, pMHC-I was loaded with the peptide sequence for amino acids 228–236 (LNIDLLWSV). For the InsB peptide, pMHC-I was loaded with the peptide sequence corresponding to amino acids 10–18 (HLVEALYLV). For background fluorescence of T-cells, a matched negative (neg) HLA class I structure was loaded with an irrelevant peptide. The peptide sequence of the negative controls is kept proprietary by the companies but does not occur on mammalian cells (Beckman Coulter, Immudex). Using these methods, type 1 diabetics for decades after diagnosis have detectable levels of autoreactive T-cells measured with peptide-major histocompatibility complex class I (pMHC-I) multimers (Figure 2).
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Scientific understanding of the genetic components of aging has increased in recent years, with several genes being identified as playing roles in the aging process and, potentially, longevity. In particular, genes encoding components of the nuclear lamina in eukaryotes have been increasingly well characterized, owing in part to their clinical significance in age-related diseases. This review focuses on one such gene, which encodes lamin A, a key component of the nuclear lamina. Genetic variation in this gene can give rise to lethal, early-onset diseases known as laminopathies. Here, we analyze the literature and conduct computational analyses of lamin A signaling and intracellular interactions in order to examine potential mechanisms for altering or slowing down aberrant Lamin A expression and/or for restoring the ratio of normal to aberrant lamin A. The ultimate goal of such studies is to ameliorate or combat laminopathies and related diseases of aging, and we provide a discussion of current approaches in this review.
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ABSTRACT The role of autophagy in cisplatin anticancer action was investigated using human U251 glioma, rat C6 glioma and mouse L929 fibrosarcoma cell lines. A dose- and time-dependent induction of autophagy was observed in tumor cells following cisplatin treatment, as demonstrated by up-regulation of autophagy-inducing protein beclin-1 and subsequent appearance of acridine orange-stained acidic autophagic vesicles. The presence of autophagosomes in cisplatin-treated cells was also confirmed by electron microscopy. Inhibition of autophagy with lysosomal inhibitors bafilomycin A1 and chloroquine, or a PI3 kinase inhibitor wortmannin, markedly augmented cisplatin-triggered oxidative stress and caspase activation, leading to an increase in DNA fragmentation and apoptotic cell death. The mechanisms underlying the protective effect of autophagy apparently involved the interference with cisplatin-induced modulation of Bcl-2 family proteins, as inhibition of autophagy potentiated cisplatin-mediated up-regulation of proapoptotic Bax and down-regulation of antiapoptotic Bcl-2. Autophagy induction in cisplatin-treated cells was preceded by activation of adenosine monophosphate-activated protein kinase (AMPK) and concomitant down-regulation of mammalian target of rapamycin (mTOR)-mediated phosphorylation of p70S6 kinase. The ability of cisplatin to trigger autophagy was reduced by siRNA-mediated AMPK silencing, while transfection with mTOR siRNA was sufficient to trigger autophagy in tumor cells. Finally, siRNA-mediated AMPK down-regulation and AMPK inhibitor compound C increased cisplatin-induced tumor cell death, while mTOR siRNA and AMPK activator metformin protected tumor cells from cisplatin. Taken together, these data suggest that cisplatin-triggered activation of AMPK and subsequent suppression of mTOR activity can induce an autophagic response that protects tumor cells from cisplatin-mediated apoptotic death.
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Upregulation of autophagy may have therapeutic benefit in a range of diseases that includes neurodegenerative conditions caused by intracytosolic aggregate-prone proteins, such as Huntington's disease, and certain infectious diseases, such as tuberculosis. The best-characterized drug that enhances autophagy is rapamycin, an inhibitor of the TOR (target of rapamycin) proteins, which are widely conserved from yeast to man. Unfortunately, the side effects of rapamycin, especially immunosuppression, preclude its use in treating certain diseases including tuberculosis, which accounts for approximately 2 million deaths worldwide each year, spurring interest in finding novel drugs that selectively enhance autophagy. We have recently reported a novel two-step screening process for the discovery of such compounds. We first identified compounds that enhance the growth-inhibitory effects of rapamycin in the budding yeast Saccharomyces cerevisiae, which we termed small molecule enhancers of rapamycin (SMERs). Next we showed that three SMERs induced autophagy independently, or downstream of mTOR, in mammalian cells, and furthermore enhanced the clearance of a mutant huntingtin fragment in Huntington's disease cell models. These SMERs also protected against mutant huntingtin fragment toxicity in Drosophila. We have subsequently tested two of the SMERs in models of tuberculosis and both enhance the killing of mycobacteria by primary human macrophages.
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We have earlier shown that alpha-methylated spermidine and spermine analogues rescue cells from polyamine depletion-induced growth inhibition and maintain pancreatic integrity under severe polyamine deprivation. However, because alpha-methylspermidine can serve as a precursor of hypusine, an integral part of functional eukaryotic translation initiation factor 5A required for cell proliferation, and because alpha, omega-bismethylspermine can be converted to methylspermidine, it is not entirely clear whether the restoration of cell growth is actually attributable to hypusine formed from these polyamine analogues. Here, we have used optically active isomers of methylated spermidine and spermine and show that polyamine depletion-induced acute cytostasis in cultured cells could be reversed by all the isomers of the methylpolyamines irrespective of whether they served or not as precursors of hypusine. In transgenic rats with activated polyamine catabolism, all the isomers similarly restored liver regeneration and reduced plasma alpha-amylase activity associated with induced pancreatitis. Under the above experimental conditions, the (S, S)- but not the (R, R)-isomer of bismethylspermine was converted to methylspermidine apparently through the action of spermine oxidase strongly preferring the (S, S)-isomer. Of the analogues, however, only (S)-methylspermidine sustained cell growth during prolonged (more than 1 week) inhibition of polyamine biosynthesis. It was also the only isomer efficiently converted to hypusine, indicating that deoxyhypusine synthase likewise possesses hidden stereospecificity. Taken together, the results show that growth inhibition in response to polyamine depletion involves two phases, an acute and a late hypusine-dependent phase.
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Accumulating evidence suggests that endoplasmic reticulum (ER) stress plays a role in the pathogenesis of diabetes, contributing to pancreatic beta-cell loss and insulin resistance. Components of the unfolded protein response (UPR) play a dual role in beta-cells, acting as beneficial regulators under physiological conditions or as triggers of beta-cell dysfunction and apoptosis under situations of chronic stress. Novel findings suggest that "what makes a beta-cell a beta-cell", i.e., its enormous capacity to synthesize and secrete insulin, is also its Achilles heel, rendering it vulnerable to chronic high glucose and fatty acid exposure, agents that contribute to beta-cell failure in type 2 diabetes. In this review, we address the transition from physiology to pathology, namely how and why the physiological UPR evolves to a proapoptotic ER stress response and which defenses are triggered by beta-cells against these challenges. ER stress may also link obesity and insulin resistance in type 2 diabetes. High fat feeding and obesity induce ER stress in liver, which suppresses insulin signaling via c-Jun N-terminal kinase activation. In vitro data suggest that ER stress may also contribute to cytokine-induced beta-cell death. Thus, the cytokines IL-1beta and interferon-gamma, putative mediators of beta-cell loss in type 1 diabetes, induce severe ER stress through, respectively, NO-mediated depletion of ER calcium and inhibition of ER chaperones, thus hampering beta-cell defenses and amplifying the proapoptotic pathways. A better understanding of the pathways regulating ER stress in beta-cells may be instrumental for the design of novel therapies to prevent beta-cell loss in diabetes.
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The target of rapamycin (TOR) is a conserved Ser/Thr kinase that regulates cell growth and metabolism in response to environmental cues. Here, highlighting contributions from studies in model organisms, we review mammalian TOR complexes and the signaling branches they mediate. TOR is part of two distinct multiprotein complexes, TOR complex 1 (TORC1), which is sensitive to rapamycin, and TORC2, which is not. The physiological consequences of mammalian TORC1 dysregulation suggest that inhibitors of mammalian TOR may be useful in the treatment of cancer, cardiovascular disease, autoimmunity, and metabolic disorders.
Article
Resistance to insulin-stimulated glucose uptake is present in the majority of patients with impaired glucose tolerance (IGT) or non-insulin-dependent diabetes mellitus (NIDDM) and in ∼25% of nonobese individuals with normal oral glucose tolerance. In these conditions, deterioration of glucose tolerance can only be prevented if the β-cell is able to increase its insulin secretory response and maintain a state of chronic hyperinsulinemia. When this goal cannot be achieved, gross decompensation of glucose homeostasis occurs. The relationship between insulin resistance, plasma insulin level, and glucose intolerance is mediated to a significant degree by changes in ambient plasma free-fatty acid (FFA) concentration. Patients with NIDDM are also resistant to insulin suppression of plasma FFA concentration, but plasma FFA concentrations can be reduced by relatively small increments in insulin concentration.Consequently, elevations of circulating plasma FFA concentration can be prevented if large amounts of insulin can be secreted. If hyperinsulinemia cannot be maintained, plasma FFA concentration will not be suppressed normally, and the resulting increase in plasma FFA concentration will lead to increased hepatic glucose production. Because these events take place in individuals who are quite resistant to insulinstimulated glucose uptake, it is apparent that even small increases in hepatic glucose production are likely to lead to significant fasting hyperglycemia under these conditions. Although hyperinsulinemia may prevent frank decompensation of glucose homeostasis in insulin-resistant individuals, this compensatory response of the endocrine pancreas is not without its price. Patients with hypertension, treated or untreated, are insulin resistant, hyperglycemic, and hyperinsulinemic. In addition, a direct relationship between plasma insulin concentration and blood pressure has been noted. Hypertension can also be produced in normal rats when they are fed a fructose-enriched diet, an intervention that also leads to the development of insulin resistance and hyperinsulinemia. The development of hypertension in normal rats by an experimental manipulation known to induce insulin resistance and hyperinsulinemia provides further support for the view that the relationship between the three variables may be a causal one. However, even if insulin resistance and hyperinsulinemia are not involved in the etiology of hypertension, it is likely that the increased risk of coronary artery disease (CAD) in patients with hypertension and the fact that this risk if not reduced with antihypertensive treatment are due to the clustering of risk factors for CAD, in addition to high blood pressure, associated with insulin resistance. These include hyperinsulinemia, IGT, increased plasma triglyceride concentration, and decreased high-density lipoprotein cholesterol concentration, all of which are associated with increased risk for CAD. It is likely that the same risk factors play a significant role in the genesis of CAD in the population as a whole. Based on these considerations the possibility is raised that resistance to insulin-stimulated glucose uptake and hyperinsulinemia are involved in the etiology and clinical course of three major related diseases— NIDDM, hypertension, and CAD.
Article
Organismal lifespan can be extended by genetic manipulation of cellular processes such as histone acetylation, the insulin/IGF-1 (insulin-like growth factor 1) pathway or the p53 system. Longevity-promoting regimens, including caloric restriction and inhibition of TOR with rapamycin, resveratrol or the natural polyamine spermidine, have been associated with autophagy (a cytoprotective self-digestive process) and in some cases were reported to require autophagy for their effects. We summarize recent developments that outline these links and hypothesize that clearing cellular damage by autophagy is a common denominator of many lifespan-extending manipulations.
Article
AMP-activated protein kinase (AMPK) inhibits IGF-I actions, but the mechanism by which AMPK functions is undefined. This study identified signaling events that were induced by AMPK that mediated inhibition of IGF-I-stimulated phosphoinosotide-3-kinase (PI3K) pathway activation. The AMPK activator metformin stimulated AMPK Thr172 phosphorylation and inhibited IGF-I-stimulated phosphorylation of Akt/tuberous sclerosis 2 (TSC2)/mammalian target of rapamycin (mTOR)/p70S6 kinase (p70S6K). Expression of constitutively active forms of AMPK suppressed IGF-I-stimulated activation of Akt/TSC2/mTOR/p70S6K and protein synthesis, whereas AMPK knockdown resulted in enhanced responses to IGF-I. To determine the mechanism by which AMPK inhibited IGF-I signaling, the role of insulin receptor substrate-1 (IRS-1) was examined. Both metformin and constitutively activated AMPK enhanced phosphorylation of IRS-1 Ser794, which led to decreased IRS-1 tyrosine phosphorylation and recruitment of the p85 subunit of PI3K. Overexpression of IRS-1 S794A was associated with increased IGF-I-stimulated IRS-1 tyrosine phosphorylation, p85 association, and protein synthesis. To determine whether other signaling molecules mediated the effect of AMPK, TSC2 function was examined. Cells overexpressing TSC2/S1345A (the site of AMPK phosphorylation) were less responsive to metformin-induced inhibition of p70S6 kinase. These findings are relevant to whole animal physiology because administration of metformin to mice resulted in inhibition of IGF-I-stimulated phosphorylation of Akt/mTOR/p70S6K. In conclusion, AMPK functions to inhibit IGF-I-stimulated PI3K pathway activation through stimulation of IRS-1 serine 794 phosphorylation. Because IGF-I is an important stimulant of the anabolic response, this effect of AMPK could account for part of its inhibitory effect on protein synthesis, thus allowing more efficient energy use by other cellular processes.
Article
Selenium possesses the chemotherapeutic feature by inducing apoptosis in cancer cell with trivial side effects on normal cells. However, the mechanism in which is not clearly understood. Emerging evidence indicates the overlaps between the autophagy and the apoptosis. In this study, we have investigated the role of autophagy in selenium-induced apoptosis in NB4 cells. We find that autophagy is suppressed in NB4 cells treated by sodium selenite, as measured by electron microscope, acridine orange staining and western blot. Moreover, selenite combined with autophagy inhibitor contributes to the up-regulation of apoptosis, while the PI3K/Akt signaling pathway is down- regulated. Consistently, when the inhibitor of PI3K was applied, the autophagic level significantly decreased. In summary, sodium selenite increases NB4 cell apoptosis by autophagy inhibition through PI3K/Akt, and the inhibition of autophagy contributes to the up-regulation of apoptosis. [BMB reports 2009; 42(9): 599-604].
Article
AMP-activated protein kinase (AMPK) is an evolutionarily conserved cellular switch that activates catabolic pathways and turns off anabolic processes. In this way, AMPK activation can restore the perturbation of cellular energy levels. In physiological situations, AMPK senses energy deficiency (in the form of an increased AMP/ATP ratio), but it is also activated by metabolic insults, such as glucose or oxygen deprivation. Metformin, one of the most widely prescribed anti-diabetic drugs, exerts its actions by AMPK activation. However, while the functions of AMPK as a metabolic regulator are fairly well understood, its actions in neuronal cells only recently gained attention. This review will discuss newly emerged functions of AMPK in neuroprotection and neurodegeneration. Additionally, recent views on the role of AMPK in autophagy, an important catabolic process that is also involved in neurodegeneration and cancer, will be highlighted.
Article
The p53 family consists of three transcription factors, p53, p63 and p73 that share domain architecture and sequence identity. The mTOR (mammalian target of rapamycin) kinase responds to growth factors and nutrient levels to regulate cellular growth and autophagy. Whereas p53 acts both upstream and downstream of mTOR, gene signature-based analyses have revealed that p73 is inhibited by mTOR activity. p53 can both activate and repress autophagy levels depending on cellular context. While less is known about p73, recent studies have shown that it induces cellular autophagy and multiple autophagy-associated genes downstream of mTOR. Chromatin immunoprecipitation analyses demonstrate that endogenous p73 binds the regulatory regions of genes such as ATG5, ATG7 and UVRAG. How p73 regulates the expression levels of these genes in response to different cellular stresses remains unknown. Because p53 family members play key roles in tumor suppression, development, aging and neurodegeneration, the context and manner by which these transcription factors regulate autophagy may have implications for a wide range of human diseases.
Article
Anthocyanins extracted from the berries of Phillyrea latifolia L., Pistacia lentiscus L., and Rubia peregrina L., three evergreen shrubs widely distributed in the Mediterranean area, were examined for their antioxidant and anticancer activity. The P. lentiscus anthocyanins showed the highest H(2)O(2) and 1,1-diphenyl-2-picryl-hydrazil radical scavenging effects, indicating that these compounds can be considered as an alternative source of natural antioxidants for food and pharmaceutical products. Here, we also report a novel function of anthocyanins: the induction of autophagy, a process of subcellular turnover involved in carcinogenesis. Autophagy was characterized by the up-regulation of eIF2alpha, an autophagy inducer, and down-regulation of mTOR and Bcl-2, two autophagy inhibitors. This led to the enhanced expression of LC3-II, an autophagosome marker in mammals, and monodansylcadaverine incorporation into autolysosomes. Anthocyanin-induced autophagy switched to apoptosis, as shown by the activation of Bax, cytochrome c and caspase 3, terminal deoxynucleotide transferase-mediated dUTP nick-end labeling-positive fragmented nuclei, and cells with sub-G(1) DNA content, which were prevented by z-VAD. Inhibition of autophagy by either 3-methyladenine or Atg5 small interfering RNA enhanced anthocyanin-triggered apoptosis. This provided evidence that autophagy functions as a survival mechanism in liver cancer cells against anthocyanin-induced apoptosis and a rationale for the use of autophagy inhibitors in combination with dietary chemopreventive agents.
Article
The effect of L-arginine on the arginase activity and polyamine levels was studied in the pancreas of normal and diabetic rats (120 mg/kg alloxan, i.v.). Four groups were formed (10 male adults per group). I-Control-0.154 M NaCl. II-Diabetic-0.154 M NaCl (96 h after alloxan). III-Control plus 10 mM L-arginine IV-Diabetics plus 10 mM L-arginine. Rats were sacrificed 20 min after L-arginine injection. Glucose in serum and dry weight, proteins, arginase activity and polyamines (HPLC) in pancreas were measured. Higher ratio mg protein/mg dry weight and arginase induction was observed for groups III and IV. Putrescine was low as a consequence of diabetes but restored with L-arginine. The concentrations of spermidine and spermine were lower. These results may suggest that arginine is metabolized to putrescine in the pancreas and that polyamines may be utilized in regenerating processes or for recovering the endocrine pancreatic function.
Article
The ability of insulin to stimulate glucose uptake can vary substantially in non-obese individuals with no apparent disease (10). In addition, differences in either degree of obesity or level of habitual physical activity can also modulate in vivo insulin action (18,24). In an apparent attempt to maintain glucose homeostasis, the compensatory response to a decrease in insulin-stimulated glucose up take is an increase in plasma insulin concentration. A defect in the ability of insulin-stimulated glucose uptake has also been demonstrated (21) in patients with either impaired glucose tolerance (IGT) or non-insulin dependent diabetes mellitus (NIDDM). It has been suggested that the degree to which glucose tolerance deteriorates in these individuals is a function of the level of compensatory hyperinsulinemia that they can maintain, and the appearance of severe fasting hyperglycemia marks the failure of the pancreatic beta cell to sustain the necessary increase in insulin secretory response (21).
Article
The S/T-protein kinases activated by phosphoinositide 3-kinase (PI3K) regulate a myriad of cellular processes. Here, we show that an approach using a combination of biochemistry and bioinformatics can identify substrates of these kinases. This approach identifies the tuberous sclerosis complex-2 gene product, tuberin, as a potential target of Akt/PKB. We demonstrate that, upon activation of PI3K, tuberin is phosphorylated on consensus recognition sites for PI3K-dependent S/T kinases. Moreover, Akt/PKB can phosphorylate tuberin in vitro and in vivo. We also show that S939 and T1462 of tuberin are PI3K-regulated phosphorylation sites and that T1462 is constitutively phosphorylated in PTEN(-/-) tumor-derived cell lines. Finally, we find that a tuberin mutant lacking the major PI3K-dependent phosphorylation sites can block the activation of S6K1, suggesting a means by which the PI3K-Akt pathway regulates S6K1 activity.
Article
Mutations in either the TSC1 or TSC2 tumor suppressor gene are responsible for Tuberous Sclerosis Complex. The gene products of TSC1 and TSC2 form a functional complex and inhibit the phosphorylation of S6K and 4EBP1, two key regulators of translation. Here, we describe that TSC2 is regulated by cellular energy levels and plays an essential role in the cellular energy response pathway. Under energy starvation conditions, the AMP-activated protein kinase (AMPK) phosphorylates TSC2 and enhances its activity. Phosphorylation of TSC2 by AMPK is required for translation regulation and cell size control in response to energy deprivation. Furthermore, TSC2 and its phosphorylation by AMPK protect cells from energy deprivation-induced apoptosis. These observations demonstrate a model where TSC2 functions as a key player in regulation of the common mTOR pathway of protein synthesis, cell growth, and viability in response to cellular energy levels.
Article
In animals, cells are dependent on extracellular signals to prevent apoptosis. However, using growth factor-dependent cells from Bax/Bak-deficient mice, we demonstrate that apoptosis is not essential to limit cell autonomous survival. Following growth factor withdrawal, Bax-/-Bak-/- cells activate autophagy, undergo progressive atrophy, and ultimately succumb to death. These effects result from loss of the ability to take up sufficient nutrients to maintain cellular bioenergetics. Despite abundant extracellular nutrients, growth factor-deprived cells maintain ATP production from catabolism of intracellular substrates through autophagy. Autophagy is essential for maintaining cell survival following growth factor withdrawal and can sustain viability for several weeks. During this time, cells respond to growth factor readdition by rapid restoration of the ability to take up and metabolize glucose and by subsequent recovery of their original size and proliferative potential. Thus, growth factor signal transduction is required to direct the utilization of sufficient exogenous nutrients to maintain cell viability.
Article
The pancreatic beta-cell senses nutrients, neurotransmitters and hormones in the circulating blood. The unique function of the cell is to integrate all these ambient signals into an appropriate insulin secretory rate in order to maintain normal glucose homeostasis. A prerequisite for adequate insulin secretion is proper biosynthesis of the hormone. The rate of biosynthesis needs to be regulated in order to compensate for rapid fluctuations in secretory rate. The synthesis of insulin includes transcription of its gene to mRNA, translation of mRNA into preproinsulin, and processing of preproinsulin via proinsulin into mature insulin. It also involves the induction of additional components of the secretory pathway to support processing, transport and exocytosis of insulin granules. The endoplasmic reticulum (ER) is the cell organelle playing a paramount role in these processes. A functional ER is crucial to all eukaryotic cells, but especially important in a professional hormone-secreting cell like the beta-cell. This essay will describe the phenomenon of ER stress in pancreatic beta-cells with special focus on its involvement in the regulation of beta-cell survival and death. The involvement of some ER stress components in the regulation of insulin biosynthesis and secretion will be discussed, along with a short description of the ER stress response (also known as the unfolded protein response).
Article
The polyamines putrescine, spermidine and spermine are organic cations shown to participate in a bewildering number of cellular reactions, yet their exact functions in intermediary metabolism and specific interactions with cellular components remain largely elusive. Pharmacological interventions have demonstrated convincingly that a steady supply of these compounds is a prerequisite for cell proliferation to occur. The last decade has witnessed the appearance of a substantial number of studies, in which genetic engineering of polyamine metabolism in transgenic rodents has been employed to unravel their cellular functions. Transgenic activation of polyamine biosynthesis through an overexpression of their biosynthetic enzymes has assigned specific roles for these compounds in spermatogenesis, skin physiology, promotion of tumorigenesis and organ hypertrophy as well as neuronal protection. Transgenic activation of polyamine catabolism not only profoundly disturbs polyamine homeostasis in most tissues, but also creates a complex phenotype affecting skin, female fertility, fat depots, pancreatic integrity and regenerative growth. Transgenic expression of ornithine decarboxylase antizyme has suggested that this unique protein may act as a general tumor suppressor. Homozygous deficiency of the key biosynthetic enzymes of the polyamines, ornithine and S-adenosylmethionine decarboxylase, as achieved through targeted disruption of their genes, is not compatible with murine embryogenesis. Finally, the first reports of human diseases apparently caused by mutations or rearrangements of the genes involved in polyamine metabolism have appeared.
Article
Stable polyamine homeostasis is important for cell survival and regeneration. Our experimental studies have shown that catabolism of spermidine and spermine to putrescine is associated with the development of pancreatitis. We investigated the pathogenetic role of polyamine catabolism by studying the effect of a methylated polyamine analog on taurodeoxycholate-induced acute experimental pancreatitis. Acute pancreatitis was induced by infusion of sodium taurodeoxycholate (2%) into the pancreatic duct. Bismethylspermine (Me(2)Spm) was administered as a pretreatment before the induction of pancreatitis or as a treatment after the induction of pancreatitis. The sham operation included laparotomy only. Pancreas tissue and blood were sampled at 24 h and 72 h after the infusion of taurodeoxycholate and studied for pancreatitis severity (serum amylase activity, pancreatic water content, and histology) and polyamine catabolism, which includes spermidine/spermine N(1)-acetyltransferase (SSAT) activity as well as spermidine, spermine, and putrescine concentrations in the pancreas. Sodium taurodeoxycholate-induced acute pancreatitis manifests as increases in serum amylase and pancreatic water content, leukocytosis, and acinar cell necrosis in the pancreas. The activity of SSAT increased significantly together with an increase in the ratios of pancreatic putrescine/spermidine and putrescine/spermine at 24 h, which indicates SSAT-induced polyamine catabolism. Pancreatic water content and necrosis were reduced significantly by the treatment with Me(2)Spm at 24 h but not at 72 h when the polyamine homeostasis had recovered, and the pancreatitis had progressed. Taurodeoxycholate-induced acute pancreatitis was associated with activation of polyamine catabolism in the pancreas. The polyamine analog Me(2)Spm ameliorated the injury in the early stage, but it did not ameliorate the late progression of the pancreatic necrosis at 72 h. Thus, besides proteolytic enzyme activation and the cascades of inflammation, polyamine catabolism may be an important pathogenetic mediator of the early stages of acute pancreatitis.
Spermidine andresveratrolinduce converging on the acetylproteome
  • E Morselli
  • G Mariño
  • Mv Bennetzen
  • T Eisenberg
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Morselli E, Mariño G, Bennetzen MV, Eisenberg T, Megalou E, Schroeder S, et al. Spermidine andresveratrolinduce converging on the acetylproteome. J Cell Biol 2011;192(4):615–29.
mTOR regulates autophagy-associated genes downstream of p53
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Rosenbluth JM, Pietenpol JM. mTOR regulates autophagy-associated genes downstream of p53 2009;5:114-6.
Expanding roles for AMP-activated protein kinase in neuronal survival and autophagy
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Poels J, Spasic MR, Callaerts P, Norga KK. Expanding roles for AMP-activated protein kinase in neuronal survival and autophagy. Bioessays 2009;31:944-52.
Autophagic cell death: the story of a misnomer
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Kroemer G, Levine B. Autophagic cell death: the story of a misnomer. Nat Rev Mol Cell Biol 2008;9:1004-10.
The mammalian unfolded protein response
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