Are sirtuins viable targets for improving healthspan and lifespan? Nat Rev Drug Discov. 2012;11:443-461. [PMID: 22653216 DOI: 10.1038/nrd3738]

SIRT3 deficiency exacerbates ischemia-reperfusion injury: implication for aged hearts

Ischemia-reperfusion (IR) injury is significantly worse in aged hearts, but the underlying mechanisms are poorly understood. Age-related damage to mitochondria may be a critical feature, which manifests in an exacerbation of IR injury. Silent information regulator of transcription 3 (SIRT3), the major mitochondrial NAD(+)-dependent lysine deacetylase, regulates a variety of functions, and its inhibition may disrupt mitochondrial function to impact recovery from IR injury. In this study, the role of SIRT3 in mediating the response to cardiac IR injury was examined using an in vitro model of SIRT3 knockdown (SIRT3(kd)) in H9c2 cardiac-derived cells and in Langendorff preparations from adult (7 mo old) wild-type (WT) and SIRT3(+/-) hearts and aged (18 mo old) WT hearts. SIRT3(kd) cells were more vulnerable to simulated IR injury and exhibited a 46% decrease in mitochondrial complex I (Cx I) activity with low O2 consumption rates compared with controls. In the Langendorff model, SIRT3(+/-) adult hearts showed less functional recovery and greater infarct vs. WT, which recapitulates the in vitro results. In WT aged hearts, recovery from IR injury was similar to SIRT3(+/-) adult hearts. Mitochondrial protein acetylation was increased in both SIRT3(+/-) adult and WT aged hearts (relative to WT adult), suggesting similar activities of SIRT3. Also, enzymatic activities of two SIRT3 targets, Cx I and MnSOD, were similarly and significantly inhibited in SIRT3(+/-) adult and WT aged cardiac mitochondria. In conclusion, decreased SIRT3 may increase the susceptibility of cardiac-derived cells and adult hearts to IR injury and may contribute to a greater level of IR injury in the aged heart.

Emerging role of sirtuins on tumorigenesis: possible link between aging and cancer

Aging is the strongest risk factor for cancer development, suggesting that molecular crosstalks between aging and tumorigenesis exist in many cellular pathways. Recently, Sirtuins (Sirt1-7), the mammalian homologues of aging-related sir2α in yeast, have been shown to modulate several major cellular pathways, such as DNA repair, inflammation, metabolism, cell death, and proliferation in response to diverse stresses, and may serve as a possible molecular link between aging and tumorignenesis. In addition, growing evidence suggests that sirtuins are directly implicated in the development of cancer, and they can act as either a tumor suppressor or promoter, depending on the cellular context and tumor types. While the functions of Sirt1 in tumorigenesis have been reported and reviewed in many studies, the connection between sirtuins 2-7 and the development of cancer is less established. Thus, this review will present the recent updates on the emerging roles of Sirt2-7 members in carcinogenesis. [BMB Reports 2013; 46(9): 429-438]

AROS has a context-dependent effect on SIRT1

The modulation of protein deacetylase SIRT1 has a vast therapeutic potential in treatment of several aging-associated diseases. Active regulator of SIRT1 (AROS) is a small endogenous protein which was originally reported to activate SIRT1 through a direct interaction in cancer cells. We show that the interaction between the two proteins is weak and does not alter the activity of SIRT1 in non-cancerous human cells. The results of different in vitro SIRT1 activity assays disclosed AROS as an inhibitor of SIRT1. The functional relationship between AROS and SIRT1 proved to be dependent on the biological context and experimental setting.

Identification of novel SIRT2-selective inhibitors using a click chemistry approach

A series of 114 SIRT inhibitor candidates was assembled using 'click chemistry', by reacting two alkynes bearing 2-anilinobenzamide pharmacophore with 57 azide building blocks in the presence of Cu(I) catalyst. Screening identified two SIRT2-selective inhibitors, which were more SIRT2-selective than AGK2, a known SIRT2 inhibitor. These findings will be useful for further development of SIRT2-selective inhibitors.

Sirtuins' modulation of autophagy

The sirtuin family of class III histone deacetylases has been extensively implicated in modulating a myriad of cellular processes, including energy metabolism, stress response, cell/tissue survival and malignancy. Recent studies have also identified multifaceted roles for Sirt1 and Sirt2 in the regulation of autophagy. Sirt1 could influence autophagy directly via its deacetylation of key components of the autophagy induction network, such as the products of autophagy genes (Atg) 5, 7, and 8. Nucleus-localized Sirt1 is also known to induce the expression of autophagy pathway components through the activation of FoxO transcription factor family members. The perception of a linear Sirt1-FoxO axis in autophagy induction is complicated by recent findings that acetylated FoxO1 could bind to Atg7 in the cytoplasm and affect autophagy directly. This occurs with prolonged stress signaling, with FoxO1's continuous dissociation from cytoplasmic Sirt2 and its consequential hyperacetylation. FoxO-mediated nuclear transcription may induce/enhance autophagy in ways that are different compared to cytoplasmic FoxO, thereby leading to contrasting (cell survival versus cell death) outcomes. FoxO and Sirt1 are both subjected to regulation by stress signaling (e.g., through the c-Jun N-terminal kinases (JNK)) in the context of autophagy induction, which are also critical in determining between cell survival and death in a context-dependent manner. We discussed here the emerging molecular intricacies of sirtuins' connections with autophagy. A good understanding of these connections would serve to consolidate a framework of mechanisms underlying Sirt1's protective effects in multiple physiological systems.

The SIRT1 activator SRT1720 extends lifespan and improves health of mice fed a standard diet

The prevention or delay of the onset of age-related diseases prolongs survival and improves quality of life while reducing the burden on the health care system. Activation of sirtuin 1 (SIRT1), an NAD(+)-dependent deacetylase, improves metabolism and confers protection against physiological and cognitive disturbances in old age. SRT1720 is a specific SIRT1 activator that has health and lifespan benefits in adult mice fed a high-fat diet. We found extension in lifespan, delayed onset of age-related metabolic diseases, and improved general health in mice fed a standard diet after SRT1720 supplementation. Inhibition of proinflammatory gene expression in both liver and muscle of SRT1720-treated animals was noted. SRT1720 lowered the phosphorylation of NF-κB pathway regulators in vitro only when SIRT1 was functionally present. Combined with our previous work, the current study further supports the beneficial effects of SRT1720 on health across the lifespan in mice.

Development of a lozenge for oral transmucosal delivery of trans-resveratrol in humans: proof of concept

Resveratrol provides multiple physiologic benefits which promote healthspan in various model species and clinical trials support continued exploration of resveratrol treatment in humans. However, there remains concern regarding low bioavailability and wide inter-individual differences in absorption and metabolism in humans, which suggests a great need to develop novel methods for resveratrol delivery. We hypothesized that oral transmucosal delivery, using a lozenge composed of a resveratrol-excipient matrix, would allow resveratrol to be absorbed rapidly into the bloodstream. We pursued proof of concept through two experiments. In the first experiment, the solubility of trans-resveratrol (tRES) in water and 2.0 M solutions of dextrose, fructose, ribose, sucrose, and xylitol was determined using HPLC. Independent t-tests with a Bonferroni correction were used to compare the solubility of tRES in each of the solutions to that in water. tRES was significantly more soluble in the ribose solution (p = 0.0013) than in the other four solutions. Given the enhanced solubility of tRES in a ribose solution, a resveratrol-ribose matrix was developed into a lozenge suitable for human consumption. Lozenges were prepared, each containing 146±5.5 mg tRES per 2000 mg of lozenge mass. Two healthy human participants consumed one of the prepared lozenges following an overnight fast. Venipuncture was performed immediately before and 15, 30, 45, and 60 minutes following lozenge administration. Maximal plasma concentrations (C_max) for tRES alone (i.e., resveratrol metabolites not included) were 325 and 332 ng⋅mL⁻¹ for the two participants at 15 minute post-administration for both individuals. These results suggest a resveratrol-ribose matrix lozenge can achieve greater C_max and enter the bloodstream faster than previously reported dosage forms for gastrointestinal absorption. While this study is limited by small sample size and only one method of resveratrol delivery, it does provide proof of concept to support further exploration of novel delivery methods for resveratrol administration.

Inhibition of NAD+-dependent histone deacetylases (sirtuins) causes growth arrest and activates both apoptosis and autophagy in the pathogenic protozoan Trypanosoma cruzi

Chagas disease, which is caused by the parasite Trypanosoma cruzi, affects approximately 7-8 million people in Latin America. The drugs available to treat this disease are ineffective against chronic phase disease and are associated with toxic side effects. Therefore, the development of new compounds that can kill T. cruzi at low concentrations is critically important. Herein, we report the effects of a novel 3-arylideneindolin-2-one that inhibits sirtuins, which are highly conserved proteins that are involved in a variety of physiological processes. The compound KH-TFMDI was tested against the epimastigote, trypomastigote and amastigote forms of T. cruzi, and its effects were evaluated using flow cytometry, light and electron microscopy. KH-TFMDI inhibited the replication of T. cruzi intracellular amastigotes with an IC50 of 0.5 ± 0.2 μM, which is significantly lower than the IC50 of benznidazole. The compound also lysed the highly infectious bloodstream trypomastigotes (BST) with LC50 values of 0.8 ± 0.3 μM at 4 °C and 2.5 ± 1.1 μM at 37 °C. KH-TFMDI inhibited cytokinesis and induced several morphological changes in the parasite, leading to its death by apoptosis and autophagy. This study highlights sirtuins as a potential new target for Chagas disease therapy.

SIRT1 but not its increased expression is essential for lifespan extension in caloric-restricted mice

The SIRT1 deacetylase is one of the best-studied putative mediators of some of the anti-aging effects of calorie restriction (CR), but its role in CR-dependent lifespan extension has not been demonstrated. We previously found that mice lacking both copies of SIRT1 displayed a shorter median lifespan than wild-type mice on an ad libitum diet. Here, we report that median lifespan extension in CR heterozygote SIRT1^+/− mice was identical (51%) to that observed in wild-type mice, but SIRT1^+/− mice displayed a higher frequency of certain pathologies. Although larger studies in additional genetic backgrounds are needed, these results provide strong initial evidence for the requirement of SIRT1 for the lifespan extension effects of CR, but suggest that its high expression is not required for CR-induced lifespan extension.

New and emerging regulators of intestinal lipoprotein secretion

Overproduction of hepatic apoB100-containing VLDL particles has been well documented in animal models and in humans with insulin resistance such as the metabolic syndrome and type 2 diabetes, and contributes to the typical dyslipidemia of these conditions. In addition, postprandial hyperlipidemia and elevated plasma concentrations of intestinal apoB48-containing chylomicron and chylomicron remnant particles have been demonstrated in insulin resistant states. Intestinal lipoprotein production is primarily determined by the amount of fat ingested and absorbed. Until approximately 10 years ago, however, relatively little attention was paid to the role of the intestine itself in regulating the production of triglyceride-rich lipoproteins (TRL) and its dysregulation in pathological states such as insulin resistance. We and others have shown that insulin resistant animal models and humans are characterized by overproduction of intestinal apoB48-containing lipoproteins. Whereas various factors are known to regulate hepatic lipoprotein particle production, less is known about factors that regulate the production of intestinal lipoprotein particles. Monosacharides, plasma free fatty acids (FFA), resveratrol, intestinal peptides (e.g. GLP-1 and GLP-2), and pancreatic hormones (e.g. insulin) have recently been shown to be important regulators of intestinal lipoprotein secretion. Available evidence in humans and animal models strongly supports the concept that the small intestine is not merely an absorptive organ but rather plays an active role in regulating the rate of production of chylomicrons in fed and fasting states. Metabolic signals in insulin resistance and type 2 diabetes and in some cases an aberrant intestinal response to these factors contribute to the enhanced formation and secretion of TRL. Understanding the regulation of intestinal lipoprotein production is imperative for the development of new therapeutic strategies for the prevention and treatment of dyslipidemia. Here we review recent developments in this field and present evidence that intestinal lipoprotein production is a process with metabolic plasticity and that modulation of intestinal lipoprotein secretion may be a feasible therapeutic strategy in the treatment of dyslipidemia and possibly prevention of atherosclerosis.

Dietary restriction and the pursuit of effective mimetics

Dietary restriction (DR) has been shown to extend both median and maximum lifespan in a range of animals, although recent findings suggest that these effects are not universally enjoyed across all animals. In particular, the lifespan effect following DR in mice is highly strain-specific and there is little current evidence that DR induces a positive effect on all-cause mortality in non-human primates. However, the positive effects of DR on health appear to be highly conserved across the vast majority of species, including human subjects. Despite these effects on health, it is highly unlikely that DR will become a realistic or popular life choice for most human subjects given the level of restraint required. Consequently significant research is focusing on identifying compounds that will bestow the benefits of DR without the obligation to adhere to stringent reductions in daily food intake. Several such compounds, including rapamycin, metformin and resveratrol, have been identified as potential DR mimetics. Although these compounds show significant promise, there is a need to properly understand the mechanisms through which these drugs act. This review will discuss the importance in understanding the role that genetic background and heterogeneity play in mediating the lifespan and healthspan effects of DR. It will also provide an overview of the most promising current DR mimetics and their effects on healthy lifespan.

Resveratrol induces vascular smooth muscle cell differentiation through stimulation of SirT1 and AMPK

Phenotypic plasticity in vascular smooth muscle cells (VSMC) is necessary for vessel maintenance, repair and adaptation to vascular changes associated with aging. De-differentiated VSMC contribute to pathologies including atherosclerosis and intimal hyperplasia. As resveratrol has been reported to have cardio- protective effects, we investigated its role in VSMC phenotypic modulation. We demonstrated the novel finding that resveratrol promoted VSMC differentiation as measured by contractile protein expression, contractile morphology and contraction in collagen gels. Resveratrol induced VSMC differentiation through stimulation of SirT1 and AMPK. We made the novel finding that low or high dose resveratrol had an initially different mechanism on induction of differentiation. We found that low dose resveratrol stimulated differentiation through SirT1-mediated activation of AKT, whereas high dose resveratrol stimulated differentiation through AMPK-mediated inhibition of the mTORC1 pathway, allowing activation of AKT. The health effects of resveratrol in cardiovascular diseases, cancer and longevity are an area of active research. We have demonstrated a supplemental avenue where-by resveratrol may promote health by maintaining and enhancing plasticity of the vasculature.

Structural basis for potent inhibition of SIRT2 deacetylase by a macrocyclic peptide inducing dynamic structural change

SIRT2 deacetylates specific acetyllysine residues in diverse proteins and is implicated in a variety of cellular processes. SIRT2 inhibition thus has potentials to treat human diseases such as cancers and neurodegenerative disorders. We have recently developed a series of ε-trifluoroacetyllysine-containing macrocyclic peptides, which inhibit the SIRT2 activity more potently than most other known inhibitors. Here, we report the crystal structure of human SIRT2 in complex with a macrocyclic peptide inhibitor, S2iL5, at 2.5 Å resolution. The structure revealed that S2iL5 binds to the active site of SIRT2 through extensive interactions. A structural comparison of the SIRT2-S2iL5 complex with SIRT2 in the free form, and in complex with ADP-ribose, revealed that S2iL5 induces an open-to-closed domain movement and an unexpected helix-to-coil transition in a SIRT2-specific region. Our findings unveil the potential of macrocyclic peptides to bind target proteins by inducing dynamic structural changes.

A succinyl lysine-based photo-cross-linking peptide probe for Sirtuin 5

A succinylation-specific photo-cross-linking peptide probe has been developed for the NAD⁺-dependent hydrolase Sirtuin 5.

Sirtuin 6 nuclear localization at cortical brain level of young diabetic mice: an immunohistochemical study

A study was conducted to assess the physiopathological significance of sirtuin 6 (SIRT6) at the brain cortical level. We analyzed the specific expression and subcellular localization of SIRT6 in young db/db mice, an experimental animal model of type II Diabetes mellitus. We analyzed the cytoarchitecture of the brain cortex, evaluated SIRT6 expression and its localization by immunohistochemistry comparing db/db mice to lean control mice, examining the six cortical layers and the motor and somatosensory cortex. Finally, we calculated a SIRT6 labeling index. We observed the absence of significant morphological differences between lean and db/db mice, indicating that young db/db mice showed a neuronal morphology and distribution similar to that of lean mice and also normal brain tissue architecture with intact cortical layers. Moreover, sirtuin 6 is mainly localized in the nucleus of both lean and db/db mice. In particular, the db/db mice showed few positive cells compared to lean control mice in all cortical layers. We found a lower sirtuin 6 labeling index without significant differences between the motor and somatosensory cortex. Our findings contribute to further understanding the sirtuin 6 immunohistochemical changes in the early stages of type II Diabetes mellitus and propose its possible implication in the pathogenic processes associated with Diabetes mellitus and diabetes-induced neurodegeneration.

Non-alcoholic steatohepatitis and hepatocellular carcinoma: implications for lycopene intervention

Increased prevalence of non-alcoholic fatty liver disease (NAFLD) is one of the consequences of the current obesity epidemic. NAFLD is a major form of chronic liver disease that is highly prevalent in obese and overweight adults and children. Nonalcoholic steatohepatitis (NASH) is the severe form of NAFLD, and uncontrolled inflammation as displayed in NASH has been identified as one of the key events in enhancing hepatic carcinogenesis. Lycopene is a non-provitamin A carotenoid and the pigment principally responsible for the characteristic deep-red color of ripe tomato and tomato products, as well as some fruits and vegetables. Lycopene's innate antioxidant and anti-inflammatory properties have generated research interests on its capacity to protect against human diseases that are associated with oxidative stress and inflammation. In addition, differential mechanisms of lycopene metabolism including endogenous cleavage by carotenoid cleavage oxygenases (BCOs), generate lycopene metabolites that may also have significant impact on human disease development. However, it remains to be elucidated as to whether lycopene or its metabolites apolycopenoids have protective effects against obesity-related complications including inflammation and tumorigenesis. This article summarizes the in vivo experiments that elucidated molecular mechanisms associated with obesity-related hepatic inflammation and carcinogenesis. This review also provides an overview of lycopene metabolism, and the molecular pathways involved in the potential beneficial properties of lycopene and apolycopenoids. More research is clearly needed to fully unravel the importance of BCOs in tomato carotenoid metabolism and the consequence on human health and diseases.

Myeloid cell sirtuin-1 expression does not alter host immune responses to Gram-negative endotoxemia or Gram-positive bacterial infection

The role of sirtuin-1 (SIRT1) in innate immunity, and in particular the influence of SIRT1 on antimicrobial defense against infection, has yet to be reported but is important to define since SIRT1 inhibitors are being investigated as therapeutic agents in the treatment of cancer, Huntington’s disease, and autoimmune diseases. Given the therapeutic potential of SIRT1 suppression, we sought to characterize the role of SIRT1 in host defense. Utilizing both pharmacologic methods and a genetic knockout, we demonstrate that SIRT1 expression has little influence on macrophage and neutrophil antimicrobial functions. Myeloid SIRT1 expression does not change mortality in gram-negative toxin-induced shock or gram-positive bacteremia, suggesting that therapeutic suppression of SIRT1 may be done safely without suppression of myeloid cell-specific immune responses to severe bacterial infections.

Resveratrol treatment rescues neurovascular coupling in aged mice: role of improved cerebromicrovascular endothelial function and downregulation of NADPH oxidase

Moment-to-moment adjustment of cerebral blood flow (CBF) to neuronal activity via neurovascular coupling is essential for the maintenance of normal neuronal function. Increased oxidative stress that occurs with aging was shown to impair neurovascular coupling, which likely contributes to a significant age-related decline in higher cortical function, increasing the risk for vascular cognitive impairment. Resveratrol is a polyphenolic compound that exerts significant antiaging protective effects in large vessels, but its effects on the cerebromicrovasculature remain poorly defined. The present study was undertaken to investigate the capacity of resveratrol to improve neurovascular coupling in aging. In aged (24-mo-old) C57BL/6 mice N(ω)-nitro-l-arginine methyl ester-sensitive, nitric oxide-mediated CBF responses to whisker stimulation and to the endothelium-dependent dilator acethylcholine (ACh) were impaired compared with those in young (3-mo-old) mice. Treatment of aged mice with resveratrol rescued neurovascular coupling and ACh-induced responses, which was associated with downregulation of cortical expression of NADPH oxidase and decreased levels of biomarkers of oxidative/nitrative stress (3-nitrotyrosine, 8-isoprostanes). Resveratrol also attenuated age-related increases in reactive oxygen species (ROS) production in cultured cerebromicrovascular endothelial cells (DCF fluorescence, flow cytometry). In conclusion, treatment with resveratrol rescues cortical neurovascular coupling responses to increased neuronal activity in aged mice, likely by restoring cerebromicrovascular endothelial function via downregulation of NADPH oxidase-derived ROS production. Beneficial cerebromicrovascular effects of resveratrol may contribute to its protective effects on cognitive function in aging.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Aberrant expression of SIRT3 is conversely correlated with the progression and prognosis of human gastric cancer

SIRT3 is a NAD(+)-dependent histone deacetylaseand and plays a critical role in various human carcinomas. However, its precise role in the pathogenesis of gastric cancer (GC) is still unclear. Western blot and Real-Time PCR were used to detect the protein and mRNA level of SIRT3 in freshly collected samples from GC patients. Immunohistochemistry staining was adopted to determine the expression of SIRT3 in 65 formalin-fixed, paraffin-embedded samples from GC patients. In addition, western blot was used to detect the protein levels of SIRT3 and HIF-1α in gastric cancer cells MGC-803 transfected with SIRT3 or control siRNA. Western blot analysis of 25 samples from GC patients showed that 64% (16/25) of patients exhibited decreased expression of SIRT3, whereas 4.0% (1/25) of patients displayed complete loss. In addition, Real-Time PCR analysis showed that GC patients had decreased expression of SIRT3 mRNA. Furthermore, immunohistochemistry analysis of 65 formalin-fixed, paraffin-embedded samples from GC patients showed that 67.7% (44/65) had decreased SIRT3 staining in the cancer tissues. Notably, the expression level of SIRT3 was inversely correlated with clinicopathological variable, including tumor infiltration, tumor differentiation and tumor stage and 5-year survival of these patients. In vitro experiment showed that knockdown of SIRT3 in MGC-803 gastric cancer cells significantly increased the expression of HIF-1α. Our results provide the first evidence showing that an aberrantly decreased expression of SIRT3 occurred in GC patients, suggesting that SIRT3 might function as a mitochondrial tumor suppressor in GC. Furthermore, the possible mechanism by which SIRT3 affect the progress of GC is its direct control of HIF-1α.

The therapeutic potential of skeletal muscle plasticity in Duchenne muscular dystrophy: phenotypic modifiers as pharmacologic targets

Duchenne muscular dystrophy (DMD) is a life-limiting, neuromuscular disorder that causes progressive, severe muscle wasting in boys and young men. Although there is no cure, scientists and clinicians can leverage the fact that slower, more oxidative skeletal muscle fibers possess an enhanced degree of resistance to the dystrophic pathology relative to their faster, more glycolytic counterparts, and can thus use this knowledge when investigating novel therapeutic avenues. Several factors have been identified as powerful regulators of muscle plasticity. Some proteins, such as calcineurin, peroxisome proliferator-activated receptor (PPAR) γ coactivator 1α (PGC-1α), PPARβ/δ, and AMP-activated protein kinase (AMPK), when chronically stimulated in animal models, remodel skeletal muscle toward the slow, oxidative myogenic program, whereas others, such as receptor-interacting protein 140 (RIP140) and E2F transcription factor 1 (E2F1), repress this phenotype. Recent studies demonstrating that pharmacologic and physiological activation of targets that shift dystrophic muscle toward the slow, oxidative myogenic program provide appreciable molecular and functional benefits. This review surveys the rationale behind, and evidence for, the study of skeletal muscle plasticity in preclinical models of DMD and highlights the potential therapeutic opportunities in advancing a strategy focused on remodeling skeletal muscle in patients with DMD toward the slow, oxidative phenotype.

SIRT7 represses Myc activity to suppress ER stress and prevent fatty liver disease

Nonalcoholic fatty liver disease is the most common chronic liver disorder in developed countries. Its pathogenesis is poorly understood, and therapeutic options are limited. Here, we show that SIRT7, an NAD(+)-dependent H3K18Ac deacetylase, functions at chromatin to suppress ER stress and prevent the development of fatty liver disease. SIRT7 is induced upon ER stress and is stabilized at the promoters of ribosomal proteins through its interaction with the transcription factor Myc to silence gene expression and to relieve ER stress. SIRT7-deficient mice develop chronic hepatosteatosis resembling human fatty liver disease. Myc inactivation or pharmacological suppression of ER stress alleviates fatty liver caused by SIRT7 deficiency. Importantly, SIRT7 suppresses ER stress and reverts the fatty liver disease in diet-induced obese mice. Our study identifies SIRT7 as a cofactor of Myc for transcriptional repression and delineates a druggable regulatory branch of the ER stress response that prevents and reverts fatty liver disease.

Resveratrol: therapeutic potential for improving cardiometabolic health

BACKGROUND

Resveratrol, a natural polyphenol, has gained attention in recent years because of its connection with the health benefits of red wine and its anticancer activity in vitro. Studies in animal models have demonstrated beneficial effects on glucose metabolism, vascular function and anti-inflammatory and antioxidant properties. Human studies designed to understand the role of resveratrol in the prevention and treatment of age-related conditions such as diabetes, heart disease, and cancer have recently been undertaken.

METHODS

We searched PubMed for original articles that reported studies of resveratrol in humans, using search terms, including resveratrol, human studies, glucose metabolism, vascular function, and inflammation. We also searched the reference lists of identified articles for additional papers and sought expert opinion on relevant studies.

RESULTS

Resveratrol treatment has shown beneficial effects on glucose and lipid metabolism in some, but not all studies. Study population, resveratrol source, and dose have varied widely, potentially explaining inconsistent findings. Improvements were noted in endothelial function, systolic blood pressure, and markers of oxidative stress and inflammation in several studies.

CONCLUSIONS

Despite the strong preclinical evidence of positive cardiometabolic effects, studies to date have not confirmed resveratrol's benefit in humans. Study variability and methodological issues limit interpretation of available results. Additional research, focusing on subjects with defined metabolic defects and using a range of doses, is needed to advance the field.

Resveratrol in metabolic health: an overview of the current evidence and perspectives

In the search for novel preventive and therapeutic modalities in the management of metabolic diseases and obesity, resveratrol has attracted great attention over the past decades. Preclinical trials suggest that resveratrol mimics the metabolic effects of calorie restriction (CR) via activation of silent mating type information regulation 2 homolog 1 (SIRT1). In experimental animals, this potential translates into prevention or improvement of glucose metabolism, anti-inflammation, cancer, and nonalcoholic fatty liver disease. Moreover, and in accordance with CR, supplementation with resveratrol promotes longevity in several primitive species and protects against diet-induced metabolic abnormalities in rodents. Despite the substantial preclinical evidence, human clinical data are very scarce, and even though the compound is widely distributed as an over-the-counter human nutritional supplement, its therapeutic rationale has not been well characterized. In this review, we provide a brief overview of the field and discuss the future scientific directions of resveratrol research.

Unique functional roles for class I and class II histone deacetylases in central nervous system development and function

Non-specific pharmacological inhibition of the histone deacetylase (HDAC) family of enzymes has largely beneficial effects in a variety of diverse contexts including cancer, cognitive function, and neurodegeneration. This review will discuss the role of individual HDAC isoforms in brain function during development and in the adult. Importantly class I and class II HDACs exhibit distinct cellular and subcellular expression patterns and utilize different signaling pathways to influence their substrates. Moreover, dissociable phenotypic outcomes emerge following manipulation of individual HDACs in the brain. To date, pharmacological inhibitors capable of targeting individual HDACs have proven difficult to develop, an obstacle that must be overcome to unlock the substantial clinical promise of manipulating endogenous HDAC isoforms in the central nervous system.

Sirtuins in neurodegenerative diseases: an update on potential mechanisms

Silent information regulator 2 proteins (sirtuins or SIRTs) are a group of deacetylases (or deacylases) whose activities are dependent on and regulated by nicotinamide adenine dinucleotide (NAD(+)). Compelling evidence supports that sirtuins play major roles in many aspects of physiology, especially in pathways related to aging - the predominant and unifying risk factor for neurodegenerative diseases. In this review, we highlight the molecular mechanisms underlying the protective effects of sirtuins in neurodegenerative diseases, focusing on protein homeostasis, neural plasticity, mitochondrial function, and sustained chronic inflammation. We will also examine the potential and challenges of targeting sirtuin pathways to block these pathogenic pathways.

The required beta cell research for improving treatment of type 2 diabetes

In healthy individuals, insulin resistance is associated with physiological conditions such as pregnancy or body weight gain and triggers an increase in beta cell number and insulin secretion capacity to preserve normoglycaemia. Failure of this beta cell compensation capacity is a fundamental cause of diabetic hyperglycaemia. Incomplete understanding of the molecular mechanisms controlling the plasticity of adult beta cells mechanisms and how these cells fail during the pathogenesis of diabetes strongly limits the ability to develop new beta cell-specific therapies. Here, current knowledge of the signalling pathways controlling beta cell plasticity is reviewed, and possible directions for future research are discussed.

(Healthy) ageing: focus on iodothyronines

The activity of the thyroid gland diminishes during ageing, but a certain tissue reserve of T3 and its metabolites is maintained. This reserve is thought to play a regulatory role in energy homeostasis during ageing. This review critically assesses this notion. T3 was thought to act predominantly through pathways that require transcriptional regulation by thyroid hormone receptors (TRs). However, in recent years, it has emerged that T3 and its metabolites can also act through non-genomic mechanisms, including cytosolic signaling. Interestingly, differences may exist in the non-genomic pathways utilized by thyroid hormone metabolites and T3. For instance, one particular thyroid hormone metabolite, namely 3,5-diiodo-l-thyronine (T2), increases the activity of the redox-sensitive protein deacetylase SIRT1, which has been associated with improvements in healthy ageing, whereas evidence exists that T3 may have the opposite effect. Findings suggesting that T3, T2, and their signaling pathways, such as those involving SIRT1 and AMP-activated protein kinase (AMPK), are associated with improvements in diet-induced obesity and insulin resistance emphasize the potential importance of the thyroid during ageing and in ageing-associated metabolic diseases.

A healthier approach to clinical trials evaluating resveratrol for primary prevention of age‐related diseases in healthy populations

In recent years, the wealth of basic science research supporting resveratrol's potential to treat, delay, and even prevent age-related chronic diseases has led to a number of human clinical trials. While such translational research has yielded promising results in clinical populations, recently published conflicting results from studies evaluating resveratrol's potential for primary prevention of chronic disease in healthy / asymptomatic individuals have generated considerable controversy and do not initially appear consistent with findings from animal models. We argue that trials targeting healthy humans are often fundamentally flawed owing to inappropriate use of paradigms only applicable to populations with overt clinical disease and the consequent misleading (typically negative) results can severely retard advancement of drug development. To appropriately perform translational research centered on resveratrol as a primary prevention agent in non-clinical populations, it is critical to utilize study designs which can provide adequate information on clinically relevant outcome measures, avoid paradigms and assumptions from interventions which are specific to clinical populations, and maintain realistic expectations compared to interventions which provide the theoretical maximal response (e.g., caloric restriction and aerobic exercise training).

AMPK, insulin resistance, and the metabolic syndrome

Insulin resistance (IR) and hyperinsulinemia are hallmarks of the metabolic syndrome, as are central adiposity, dyslipidemia, and a predisposition to type 2 diabetes, atherosclerotic cardiovascular disease, hypertension, and certain cancers. Regular exercise and calorie restriction have long been known to increase insulin sensitivity and decrease the prevalence of these disorders. The subsequent identification of AMP-activated protein kinase (AMPK) and its activation by exercise and fuel deprivation have led to studies of the effects of AMPK on both IR and metabolic syndrome-related diseases. In this review, we evaluate this body of literature, with special emphasis on the hypothesis that dysregulation of AMPK is both a pathogenic factor for these disorders in humans and a target for their prevention and therapy.

Epigenetic modifications in the pathogenesis of diabetic nephropathy

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease. Diabetic vascular complications such as DN can progress despite subsequent glycemic control, suggesting a metabolic memory of previous exposure to hyperglycemia. Diabetes profoundly impacts transcription programs in target cells through activation of multiple signaling pathways and key transcription factors leading to aberrant expression of pathologic genes. Emerging evidence suggests that these factors associated with the pathophysiology of diabetic complications and metabolic memory also might be influenced by epigenetic mechanisms in chromatin such as DNA methylation, histone lysine acetylation, and methylation. Key histone modifications and the related histone methyltransferases and acetyltransferases have been implicated in the regulation of inflammatory and profibrotic genes in renal and vascular cells under diabetic conditions. Advances in epigenome profiling approaches have provided novel insights into the chromatin states and functional outcomes in target cells affected by diabetes. Because epigenetic changes are potentially reversible, they can provide a window of opportunity for the development of much-needed new therapies for DN in the future. In this review, we discuss recent developments in the field of epigenetics and their relevance to diabetic vascular complications and DN pathogenesis.

Dual effects of resveratrol on arterial damage induced by insulin resistance in aged mice

Aging leads to increased insulin resistance and arterial dysfunction, with oxidative stress playing an important role. This study explored the metabolic and arterial effects of a chronic treatment with resveratrol, an antioxidant polyphenol compound that has been shown to restore insulin sensitivity and decrease oxidative stress, in old mice with or without a high-protein diet renutrition care. High-protein diet tended to increase insulin resistance and atheromatous risk. Resveratrol improved insulin sensitivity in old mice fed standard diet by decreasing homeostasis model of assessment-insulin resistance and resistin levels. However, resveratrol did not improve insulin resistance status in old mice receiving the high-protein diet. In contrast, resveratrol exhibited deleterious effects by increasing inflammation state and superoxide production and diminishing aortic distensibility. In conclusion, we demonstrate that resveratrol has beneficial or deleterious effects on insulin sensitivity and arterial function, depending on nutritional status in our models.

Endothelium-dependent control of cerebrovascular functions through age: exercise for healthy cerebrovascular aging

Cognitive performances are tightly associated with the maximal aerobic exercise capacity, both of which decline with age. The benefits on mental health of regular exercise, which slows the age-dependent decline in maximal aerobic exercise capacity, have been established for centuries. In addition, the maintenance of an optimal cerebrovascular endothelial function through regular exercise, part of a healthy lifestyle, emerges as one of the key and primary elements of successful brain aging. Physical exercise requires the activation of specific brain areas that trigger a local increase in cerebral blood flow to match neuronal metabolic needs. In this review, we propose three ways by which exercise could maintain the cerebrovascular endothelial function, a premise to a healthy cerebrovascular function and an optimal regulation of cerebral blood flow. First, exercise increases blood flow locally and increases shear stress temporarily, a known stimulus for endothelial cell maintenance of Akt-dependent expression of endothelial nitric oxide synthase, nitric oxide generation, and the expression of antioxidant defenses. Second, the rise in circulating catecholamines during exercise not only facilitates adequate blood and nutrient delivery by stimulating heart function and mobilizing energy supplies but also enhances endothelial repair mechanisms and angiogenesis. Third, in the long term, regular exercise sustains a low resting heart rate that reduces the mechanical stress imposed to the endothelium of cerebral arteries by the cardiac cycle. Any chronic variation from a healthy environment will perturb metabolism and thus hasten endothelial damage, favoring hypoperfusion and neuronal stress.

Decreased levels of proapoptotic factors and increased key regulators of mitochondrial biogenesis constitute new potential beneficial features of long-lived growth hormone receptor gene-disrupted mice

Decreased somatotrophic signaling is among the most important mechanisms associated with extended longevity. Mice homozygous for the targeted disruption of the growth hormone (GH) receptor gene (GH receptor knockout; GHRKO) are obese and dwarf, are characterized by a reduced weight and body size, undetectable levels of GH receptor, high concentration of serum GH, and greatly reduced plasma levels of insulin and insulin-like growth factor-I, and are remarkably long lived. Recent results suggest new features of GHRKO mice that may positively affect longevity-decreased levels of proapoptotic factors and increased levels of key regulators of mitochondrial biogenesis. The alterations in levels of the proapoptotic factors and key regulators of mitochondrial biogenesis were not further improved by two other potential life-extending interventions-calorie restriction and visceral fat removal. This may attribute the primary role to GH resistance in the regulation of apoptosis and mitochondrial biogenesis in GHRKO mice in terms of increased life span.

Silent information regulator 1 protects the brain against cerebral ischemic damage

BACKGROUND AND PURPOSE

Sirtuin 1 (SIRT1) is a member of NAD+-dependent protein deacetylases implicated in a wide range of cellular functions and has beneficial properties in pathologies including ischemia/reperfusion processes and neurodegeneration. However, no direct evidence has been reported on the direct implication of SIRT1 in ischemic stroke. The aim of this study was to establish the role of SIRT1 in stroke using an experimental model in mice.

METHODS

Wild-type and Sirt1-/- mice were subjected to permanent focal ischemia by permanent ligature. In another set of experiments, wild-type mice were treated intraperitoneally with vehicle, activator 3 (SIRT1 activator, 10 mg/kg), or sirtinol (SIRT1 inhibitor, 10 mg/kg) for 10 minutes, 24 hours, and 40 hours after ischemia. Brains were removed 48 hours after ischemia for determining the infarct volume. Neurological outcome was evaluated using the modified neurological severity score.

RESULTS

Exposure to middle cerebral artery occlusion increased SIRT1 expression in neurons of the ipsilesional mouse brain cortex. Treatment of mice with activator 3 reduced infarct volume, whereas sirtinol increased ischemic injury. Sirt1-/- mice displayed larger infarct volumes after ischemia than their wild-type counterparts. In addition, SIRT1 inhibition/deletion was concomitant with increased acetylation of p53 and nuclear factor κB (p65).

CONCLUSIONS

These results support the idea that SIRT1 plays an important role in neuroprotection against brain ischemia by deacetylation and subsequent inhibition of p53-induced and nuclear factor κB-induced inflammatory and apoptotic pathways.

Selective overexpression of human SIRT1 in adipose tissue enhances energy homeostasis and prevents the deterioration of insulin sensitivity with ageing in mice

SIRT1, a longevity regulator and NAD(+)-dependent deacetylase, plays a critical role in promoting metabolic fitness associated with calorie restriction and healthy ageing. Using a tissue-specific transgenic approach, the present study demonstrates that over-expression of human SIRT1 selectively in adipose tissue of mice prevents ageing-induced deterioration of insulin sensitivity and ectopic lipid distribution, reduces whole body fat mass and enhances locomotor activity. During ageing, the water-soluble vitamin biotin is progressively accumulated in adipose tissue. Over-expression of SIRT1 alleviates ageing-associated biotin accumulation and reduces the amount of biotinylated proteins, including acetyl CoA carboxylase, a major reservoir of biotin in adipose tissues. Chronic biotin supplementation increases adipose biotin contents and abolishes adipose SIRT1-mediated beneficial effects on insulin sensitivity, lipid metabolism and locomotor activity. Biochemical, spectrometric and chromatographic analysis revealed that biotin and its metabolites act as competitive inhibitors of SIRT1-mediated deacetylation. In summary, these results demonstrate that adipose SIRT1 is a key player in maintaining systemic energy homeostasis and insulin sensitivity; enhancing its activity solely in adipose tissue can prevent ageing-associated metabolic disorders.

Pharmacological approaches to restore mitochondrial function

Mitochondrial dysfunction is not only a hallmark of rare inherited mitochondrial disorders but also implicated in age-related diseases, including those that affect the metabolic and nervous system, such as type 2 diabetes and Parkinson's disease. Numerous pathways maintain and/or restore proper mitochondrial function, including mitochondrial biogenesis, mitochondrial dynamics, mitophagy and the mitochondrial unfolded protein response. New and powerful phenotypic assays in cell-based models as well as multicellular organisms have been developed to explore these different aspects of mitochondrial function. Modulating mitochondrial function has therefore emerged as an attractive therapeutic strategy for several diseases, which has spurred active drug discovery efforts in this area.

Rejuvenating SIRT1 activators

Whether the red wine component resveratrol directly activates the NAD(+)-dependent protein deacetylase SIRT1 has been debated. A recent study by Hubbard et al. (2013) strengthens the case that SIRT1-activating compounds (STACs) function as positive allosteric regulators of SIRT1 and thereby regulate mitochondrial function.

Estrogen-dependent dynamic profile of eNOS-DNA associations in prostate cancer

In previous work we have documented the nuclear translocation of endothelial NOS (eNOS) and its participation in combinatorial complexes with Estrogen Receptor Beta (ERβ) and Hypoxia Inducible Factors (HIFs) that determine localized chromatin remodeling in response to estrogen (E2) and hypoxia stimuli, resulting in transcriptional regulation of genes associated with adverse prognosis in prostate cancer (PCa). To explore the role of nuclear eNOS in the acquisition of aggressive phenotype in PCa, we performed ChIP-Sequencing on chromatin-associated eNOS from cells from a primary tumor with poor outcome and from metastatic LNCaP cells. We found that: 1. the eNOS-bound regions (peaks) are widely distributed across the genome encompassing multiple transcription factors binding sites, including Estrogen Response Elements. 2. E2 increased the number of peaks, indicating hormone-dependent eNOS re-localization. 3. Peak distribution was similar with/without E2 with ≈ 55% of them in extragenic DNA regions and an intriguing involvement of the 5′ domain of several miRs deregulated in PCa. Numerous potentially novel eNOS-targeted genes have been identified suggesting that eNOS participates in the regulation of large gene sets. The parallel finding of downregulation of a cluster of miRs, including miR-34a, in PCa cells associated with poor outcome led us to unveil a molecular link between eNOS and SIRT1, an epigenetic regulator of aging and tumorigenicity, negatively regulated by miR-34a and in turn activating eNOS. E2 potentiates miR-34a downregulation thus enhancing SIRT1 expression, depicting a novel eNOS/SIRT1 interplay fine-tuned by E2-activated ER signaling, and suggesting that eNOS may play an important role in aggressive PCa.

Targeting sirtuins for the treatment of diabetes

Sirtuins are a class of NAD⁺-dependent deacetylases, such as deacetylases, that have a wide array of biological functions. Recent studies have suggested that reduced sirtuin action is correlated with Type 2 diabetes. Both overnutrition and aging, which are two major risk factors for diabetes, lead to decreased sirtuin function and result in abnormal glucose and lipid metabolism. Therefore, restoring normal levels of sirtuin action in Type 2 diabetes may be a promising method of treating diabetes. This article reviews the biological functions of three of the seven mammalian sirtuins - SIRT1, SIRT3 and SIRT6 - that have demonstrated prominent metabolic roles and early potential for drug targeting. Clinical trials investigating the use of sirtuin activators for treating diabetes are already underway and show promise as alternatives to current diabetes therapies. Thus, further research into sirtuin activators is warranted and may lead to a new class of safe, effective diabetes treatments.

Autophagy in ageing and ageing-associated diseases

Autophagy is a cell self-digestion process via lysosomes that clears “cellular waste”, including aberrantly modified proteins or protein aggregates and damaged organelles. Therefore, autophagy is considered a protein and organelle quality control mechanism that maintains normal cellular homeostasis. Dysfunctional autophagy has been observed in ageing tissues and several ageing-associated diseases. Lifespan of model organisms such as yeast, worms, flies, and mice can be extended through promoting autophagy, either by genetic manipulations such as over-expression of Sirtuin 1, or by administrations of rapamycin, resveratrol or spermidine. The evidence supports that autophagy may play an important role in delaying ageing or extending lifespan. In this review, we summarize the current knowledge about autophagy and its regulation, outline recent developments ie the genetic and pharmacological manipulations of autophagy that affects the lifespan, and discuss the role of autophagy in the ageing-related diseases.

Discovery of thieno[3,2-d]pyrimidine-6-carboxamides as potent inhibitors of SIRT1, SIRT2, and SIRT3

The sirtuins SIRT1, SIRT2, and SIRT3 are NAD(+) dependent deacetylases that are considered potential targets for metabolic, inflammatory, oncologic, and neurodegenerative disorders. Encoded library technology (ELT) was used to affinity screen a 1.2 million heterocycle enriched library of DNA encoded small molecules, which identified pan-inhibitors of SIRT1/2/3 with nanomolar potency (e.g., 11c: IC50 = 3.6, 2.7, and 4.0 nM for SIRT1, SIRT2, and SIRT3, respectively). Subsequent SAR studies to improve physiochemical properties identified the potent drug like analogues 28 and 31. Crystallographic studies of 11c, 28, and 31 bound in the SIRT3 active site revealed that the common carboxamide binds in the nicotinamide C-pocket and the aliphatic portions of the inhibitors extend through the substrate channel, explaining the observable SAR. These pan SIRT1/2/3 inhibitors, representing a novel chemotype, are significantly more potent than currently available inhibitors, which makes them valuable tools for sirtuin research.

Resveratrol vs. calorie restriction: data from rodents to humans

Calorie restriction extends lifespan and confers metabolic benefits similar to the effect of lifestyle interventions. Poor compliance to long-term dietary restriction, however, hinders the success of this approach. Evidence is now persuasive for a role of resveratrol supplementation (a polyphenol in red grapes) as potential alternative to calorie restriction. This review summarizes the latest literature on the effects and the molecular mechanisms by which calorie restriction and resveratrol confer health benefits. Resveratrol activates SIRT1 and the associated improvement in energy utilization and insulin sensitivity closely resembles the benefits of calorie restriction. Current data largely support resveratrol as a potential calorie restriction mimetic to improve metabolic and probably functional health. Future studies which characterize the bioavailability and efficacy of resveratrol supplementation are critical to provide evidence for its long-term health benefits.

Role of SIRT1 and FOXO factors in eNOS transcriptional activation by resveratrol

Many of the cardiovascular protective effects of resveratrol are attributable to an enhanced production of nitric oxide (NO) by the endothelial NO synthase (eNOS). Resveratrol has been shown to enhance eNOS gene expression as well as eNOS enzymatic activity. The aim of the present study was to analyze the molecular mechanisms of eNOS transcriptional activation by resveratrol. Treatment of human EA.hy 926 endothelial cells with resveratrol led to a concentration-dependent upregulation of eNOS expression. In luciferase reporter gene assay, resveratrol enhanced the activity of human eNOS promoter fragments (3500, 1600, 633 and 263bp in length, respectively), indicating that the proximal promoter region is required for resveratrol-induced eNOS transcriptional activation. Knockdown of the NAD(+)-dependent protein deacetylase sirtuin 1 (SIRT1) by siRNA prevented the upregulation of eNOS mRNA and protein by resveratrol. Forkhead box O (FOXO) transcription factors are established downstream targets of SIRT1. siRNA-mediated knockdown of FOXO1 and FOXO3a abolished the effect of resveratrol on eNOS expression, indicating the involvement of these factors. Resveratrol treatment enhanced the expression of FOXO1 and FOXO3a in EA.hy 926 cells. Reporter gene assay using promoter containing forkhead response elements showed increased FOXO factor activity by resveratrol. In electrophoretic mobility shift assay, the enhanced binding of nuclear proteins to the eNOS promoter regions by resveratrol could be blocked by antibodies against FOXO1 and FOXO3a. In conclusion, resveratrol enhances the expression and activity of FOXO transcription factors. The SIRT1/FOXO factor axis is involved in resveratrol-induced eNOS transcriptional activation.

SIRT1 polymorphism, long-term survival and glucose tolerance in the general population

Mutations that increase activity of Sir2 (silent information regulator 2) are associated with extended lifespan of yeast, fruit flies and worms. SIRT1, the human homolog of Sir2, that controls numerous physiological processes including the glucose metabolism, is considered a candidate gene for predicting variation in human lifespan. Whereas the role of Sir2 has been extensively investigated in model organisms, less is known about the relation between SIRT1 and lifespan in humans. In the current study we included 1,390 subjects from a general population-based cohort with 18 years of follow-up to investigate associations between variation in single nucleotide polymorphisms (SNPs) in the SIRT1 gene and human survival. Additionally in 535 male subjects with available data we investigated associations between SIRT1 and glucose tolerance. Carriers of the minor allele of rs12778366 had a significantly reduced mortality risk compared to the wild types: Hazard Ratio 0.69 (95% CI 0.50 to 0.96; p = 0.025). The directions of the effect were the same in females and males, never and ever smokers and the effect was significantly protective in overweight/obese subjects. Carriers of the minor allele of SNP rs12778366 had better glucose tolerance indicated by 0.34 mmol/l lower glucose levels compared to wild type subjects (p = 0.03). This study shows that SIRT1 affects human long-term survival and therefore may be an important factor in modulating lifespan not only in lower organisms, but also in humans.

The sirtuin family's role in aging and age-associated pathologies

The 7 mammalian sirtuin proteins compose a protective cavalry of enzymes that can be invoked by cells to aid in the defense against a vast array of stressors. The pathologies associated with aging, such as metabolic syndrome, neurodegeneration, and cancer, are either caused by or exacerbated by a lifetime of chronic stress. As such, the activation of sirtuin proteins could provide a therapeutic approach to buffer against chronic stress and ameliorate age-related decline. Here we review experimental evidence both for and against this proposal, as well as the implications that isoform-specific sirtuin activation may have for healthy aging in humans.

Seven sirtuins for seven deadly diseases of aging

Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.