A role for SIR-2.1 regulation of ER stress response genes in determining C. elegans life span

Biochemical effects of SIRT1 activators

SIRT1 is the closest mammalian homologue of enzymes that extend life in lower organisms. Its role in mammals is incompletely understood, but includes modulation of at least 34 distinct targets through its nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase activity. Recent experiments using small molecule activators and genetically engineered mice have provided new insight into the role of this enzyme in mammalian biology and helped to highlight some of the potentially relevant targets. The most widely employed activator is resveratrol, a small polyphenol that improves insulin sensitivity and vascular function, boosts endurance, inhibits tumor formation, and ameliorates the early mortality associated with obesity in mice. Many of these effects are consistent with modulation of SIRT1 targets, such as PGC1alpha and NFkappaB, however, resveratrol can also activate AMPK, inhibit cyclooxygenases, and influence a variety of other enzymes. A novel activator, SRT1720, as well as various methods to manipulate NAD(+) metabolism, are emerging as alternative methods to increase SIRT1 activity, and in many cases recapitulate effects of resveratrol. At present, further studies are needed to more directly test the role of SIRT1 in mediating beneficial effects of resveratrol, to evaluate other strategies for SIRT1 activation, and to confirm the specific targets of SIRT1 that are relevant in vivo. These efforts are especially important in light of the fact that SIRT1 activators are entering clinical trials in humans, and "nutraceutical" formulations containing resveratrol are already widely available.

Cellular mechanisms of cardioprotection by calorie restriction: state of the science and future perspectives

Evidence from animal models and preliminary studies in humans indicates that calorie restriction (CR) delays cardiac aging and can prevent cardiovascular disease. These effects are mediated by a wide spectrum of biochemical and cellular adaptations, including redox homeostasis, mitochondrial function, inflammation, apoptosis, and autophagy. Despite the beneficial effects of CR, its large-scale implementation is challenged by applicability issues as well as health concerns. However, preclinical studies indicate that specific compounds, such as resveratrol, may mimic many of the effects of CR, thus potentially obviating the need for drastic food intake reductions. Results from ongoing clinical trials will reveal whether the intriguing alternative of CR mimetics represents a safe and effective strategy to promote cardiovascular health and delay cardiac aging in humans.

Caloric restriction, SIRT1 and longevity

More than 70 years after its initial report, caloric restriction stands strong as the most consistent non-pharmacological intervention increasing lifespan and protecting against metabolic disease. Among the different mechanisms by which caloric restriction might act, Sir2/SIRT1 (Silent information regulator 2/Silent information regulator T1) has been the focus of much attention because of its ability to integrate sensing of the metabolic status with adaptive transcriptional outputs. This review focuses on gathered evidence suggesting that Sir2/SIRT1 is a key mediator of the beneficial effects of caloric restriction and addresses the main questions that still need to be answered to consolidate this hypothesis.

Reduced expression of alpha-1,2-mannosidase I extends lifespan in Drosophila melanogaster and Caenorhabditis elegans

Exposure to sub-lethal levels of stress, or hormesis, was a means to induce longevity. By screening for mutations that enhance resistance to multiple stresses, we identified multiple alleles of alpha-1,2-mannosidase I (mas1) which, in addition to promoting stress resistance, also extended longevity. Longevity enhancement is also observed when mas1 expression is reduced via RNA interference in both Drosophila melanogaster and Caenorhabditis elegans. The screen also identified Edem1 (Edm1), a gene downstream of mas1, as a modulator of lifespan. As double mutants for both mas1 and Edm1 showed no additional longevity enhancement, it appeared that both mutations function within a common pathway to extend lifespan. Molecular analysis of these mutants revealed that the expression of BiP, a putative biomarker of dietary restriction (DR), is down-regulated in response to reductions in mas1 expression. These findings suggested that mutations in mas1 may extend longevity by modulating DR.

The coordination of nuclear and mitochondrial communication during aging and calorie restriction

Mitochondria are dynamic organelles that integrate environmental signals to regulate energy production, apoptosis and Ca(2+) homeostasis. Not surprisingly, mitochondrial dysfunction is associated with aging and the pathologies observed in age-related diseases. The vast majority of mitochondrial proteins are encoded in the nuclear genome, and so communication between the nucleus and mitochondria is essential for maintenance of appropriate mitochondrial function. Several proteins have emerged as major regulators of mitochondrial gene expression, capable of increasing transcription of mitochondrial genes in response to the physiological demands of the cell. In this review, we will focus on PGC-1alpha, SIRT1, AMPK and mTOR and discuss how these proteins regulate mitochondrial function and their potential involvement in aging, calorie restriction and age-related disease. We will also discuss the pathways through which mitochondria signal to the nucleus. Although such retrograde signaling is not well studied in mammals, there is growing evidence to suggest that it may be an important area for future aging research. Greater understanding of the mechanisms by which mitochondria and the nucleus communicate will facilitate efforts to slow or reverse the mitochondrial dysfunction that occurs during aging.

Catechin induced longevity in C. elegans: from key regulator genes to disposable soma

The flavanol catechin is a ubiquitous metabolite within the plant kingdom. Several health benefits have previously been reported, however, to date, most attention has been devoted to gallated forms of catechin. This study utilized the nematode Caenorhabditis elegans to assess potential life expanding effects of non-gallated catechin. Longevity was observed at three different catechin concentrations, an effect that was neither linked to a specific temperature nor to the viability of the feeding bacteria. Taken all tests into account, hormesis, calorie restriction, as well as the presence of simple antioxidative or antibacterial effects could be excluded. Likewise, the insulin/IGF-1 like signaling pathway and the calmodulin kinase II pathway were not considered to play a major mechanic role. Moreover, stress resistance was enhanced without a marked alteration in reproductive behavior. In addition, lifespan tests with various stress and lifespan relevant mutant strains revealed that the life span extending phenotype was absent in mev-1, daf-2, akt-2 and nhr-8. Finally, catechin elicited a significant reduction in body length, a finding that is in line with the "Disposable Soma Theory". It is proposed that catechin modulates an energy-intensive stress response and repair system that results in reduced body length and an enhanced lifespan.

HIF-1 modulates dietary restriction-mediated lifespan extension via IRE-1 in Caenorhabditis elegans

Dietary restriction (DR) extends lifespan in various species and also slows the onset of age-related diseases. Previous studies from flies and yeast have demonstrated that the target of rapamycin (TOR) pathway is essential for longevity phenotypes resulting from DR. TOR is a conserved protein kinase that regulates growth and metabolism in response to nutrients and growth factors. While some of the downstream targets of TOR have been implicated in regulating lifespan, it is still unclear whether additional targets of this pathway also modulate lifespan. It has been shown that the hypoxia inducible factor-1 (HIF-1) is one of the targets of the TOR pathway in mammalian cells. HIF-1 is a transcription factor complex that plays key roles in oxygen homeostasis, tumor formation, glucose metabolism, cell survival, and inflammatory response. Here, we describe a novel role for HIF-1 in modulating lifespan extension by DR in Caenorhabditis elegans. We find that HIF-1 deficiency results in extended lifespan, which overlaps with that by inhibition of the RSKS-1/S6 kinase, a key component of the TOR pathway. Using a modified DR method based on variation of bacterial food concentrations on solid agar plates, we find that HIF-1 modulates longevity in a nutrient-dependent manner. The hif-1 loss-of-function mutant extends lifespan under rich nutrient conditions but fails to show lifespan extension under DR. Conversely, a mutation in egl-9, which increases HIF-1 activity, diminishes the lifespan extension under DR. This deficiency is rescued by tissue-specific expression of egl-9 in specific neurons and muscles. Increased lifespan by hif-1 or DR is dependent on the endoplasmic reticulum (ER) stress regulator inositol-requiring protein-1 (IRE-1) and is associated with lower levels of ER stress. Therefore, our results demonstrate a tissue-specific role for HIF-1 in the lifespan extension by DR involving the IRE-1 ER stress pathway.

Dietary restriction (DR) is one of the most robust environmental manipulations that extend lifespan in various species. DR has also been shown to slow the onset of a number of age-related diseases. Studies in model organisms like C. elegans can be used to uncover biological mechanisms that determine the beneficial effects of DR. Previous studies suggest that the nutrient-sensing target of rapamycin (TOR) pathway is required for DR-mediated lifespan extension. However, the downstream mechanisms by which TOR modulates lifespan remain unclear. In mammalian cells, TOR and the downstream S6 kinase (S6K) activate expression of the hypoxia-inducible factor-1 (HIF-1), which is frequently up-regulated in various tumors. Using C. elegans as a model system, we characterized novel functions of HIF-1 in aging. We find that inhibition of HIF-1 extends lifespan under rich nutrient conditions, whereas enhanced levels of HIF-1 only allow partial lifespan extension by DR. We also demonstrated that increased lifespan by hif-1 or DR depends on the endoplasmic reticulum (ER) stress regulator inositol-requiring protein-1 (IRE-1) and is associated with lower levels of ER stress, which is caused by overloading of misfolded/unfolded proteins to ER. Thus, our results support the idea that HIF-1–mediated changes in protein homeostasis play a key role in the lifespan extension by DR.

Different dietary restriction regimens extend lifespan by both independent and overlapping genetic pathways in C. elegans

Dietary restriction (DR) has the remarkable ability to extend lifespan and healthspan. A variety of DR regimens have been described in species ranging from yeast to mammals. However, whether different DR regimens extend lifespan via universal, distinct, or overlapping pathways is still an open question. Here we examine the genetic pathways that mediate longevity by different DR regimens in Caenorhabditis elegans. We have previously shown that the low-energy sensing AMP-activated protein kinase AMPK/aak-2 and the Forkhead transcription factor FoxO/daf-16 are necessary for longevity induced by a DR regimen that we developed (sDR). Here we find that AMPK and FoxO are necessary for longevity induced by another DR regimen, but are dispensable for the lifespan extension induced by two different DR methods. Intriguingly, AMPK is also necessary for the lifespan extension elicited by resveratrol, a natural polyphenol that mimics some aspects of DR. Conversely, we test if genes previously reported to mediate longevity by a variety of DR methods are necessary for sDR-induced longevity. Although clk-1, a gene involved in ubiquinone biosynthesis, is also required for sDR-induced lifespan extension, we find that four other genes (sir-2.1, FoxA/pha-4, skn-1, and hsf-1) are all dispensable for longevity induced by sDR. Consistent with the observation that different DR methods extend lifespan by mostly independent genetic mechanisms, we find that the effects on lifespan of two different DR regimens are additive. Understanding the genetic network by which different DR regimens extend lifespan has important implications for harnessing the full benefits of DR on lifespan and healthspan.

Elevation of oxidative-damage biomarkers during aging in F2 hybrid mice: protection by chronic oral intake of resveratrol

Resveratrol (RSV), a naturally occurring phytoalexin that can be found in red wine, berries, and peanuts, has been shown to extend both mean and maximum life span in model organisms. RSV has also been reported to shift the physiology of middle-aged mice on a high-calorie diet toward that of mice on a standard diet. These beneficial effects of RSV have been suggested to resemble caloric restriction. Our study in F2 four-way cross-hybrid mice was the first to evaluate the effects of aging and long-term RSV treatment (14.09+/-3.4 mg/L in drinking water for 6 or 12 months) on biomarkers of oxidative damage to DNA, 8-hydroxy-2'-deoxyguanosine (8OHdG); lipid, 8-iso-prostaglandin(2 alpha) (8-iso-PGF(2 alpha)); and protein, protein carbonyl content (PCC). There was a significant age-dependent accumulation of oxidative damage to DNA, lipid, and protein as well as a clear increase in urine 8-iso-PGF(2 alpha) levels in the majority of mouse tissues. Rates of age-dependent increases in damage biomarkers varied between tissues. Chronic RSV treatment elevated total RSV plasma levels and reduced the observed age-dependent accumulation of (1) 8OHdG in liver and heart, (2) 8-iso-PGF(2 alpha) in heart and urine, and (3) PCC in liver and kidney. However, a 12-month RSV intake resulted in significant elevation of 8-iso-PGF(2 alpha) and PCC in kidney. Our studies demonstrate that RSV treatment consistently attenuated oxidative damage in tissues where age-related oxidative damage accumulation was prominent, but also suggested that chronic RSV treatment may induce nephrotoxicity.

Dietary activators of Sirt1

Calorie restriction (CR) is a non-genetic manipulation that reliably results in extended lifespan of several species ranging from yeast to dogs. The lifespan extension effect of CR has been strongly associated with an increased level and activation of the silent information regulator 2 (Sir2) histone deacetylase and its mammalian ortholog Sirt1. This association led to the search for potential Sirt1-activating, life-extending molecules. This review briefly outlines the experimental findings on resveratrol and other dietary activators of Sirt1.

The conserved NAD(H)-dependent corepressor CTBP-1 regulates Caenorhabditis elegans life span

CtBP (C-terminal binding protein) is an evolutionarily conserved NAD(H)-dependent transcriptional corepressor, whose activity has been shown to be regulated by the NAD/NADH ratio. Although recent studies have provided significant new insights into mechanisms by which CtBP regulates transcription, the biological function of CtBP remains incompletely understood. Here, we report that genetic inactivation of the Caenorhabditis elegans homolog, ctbp-1, results in life span extension, which is suppressed by reintroduction of the ctbp-1 genomic DNA encoding wild-type but not NAD(H)-binding defective CTBP-1 protein. We show that CTBP-1 possibly modulates aging through the insulin/IGF-1 signaling pathway, dependent on the forkhead transcription factor DAF-16, but independent of the NAD-dependent histone deacetylase SIR-2.1. Genome-wide microarray analysis identifies >200 potential CTBP-1 target genes. Importantly, RNAi inhibition of a putative triacylglycerol lipase gene lips-7(C09E8.2) but not another lipase suppresses the life span extension phenotype. Consistently, metabolic analysis shows that the triacylglycerol level is reduced in the ctbp-1 deletion mutant, which is restored to the wild-type level by RNAi inhibition of lips-7. Taken together, our data suggest that CTBP-1 controls life span probably through the regulation of lipid metabolism.

SIRT1 promotes differentiation of normal human keratinocytes

Sir2 regulates lifespan in model organisms, which has stimulated interest in understanding human Sir2 homolog functions. The human Sir2 gene family comprises seven members (SIRT1-SIRT7). SIRT1, the human ortholog of the yeast Sir2 by closest sequence similarity, is a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase with enzymatic properties indistinguishable from the yeast enzyme. We studied the involvement of SIRT1 in normal human keratinocyte physiology by a transcriptional microarray analysis of primary keratinocytes either overexpressing or underexpressing SIRT1. Using a systems biology analytical approach, we predicted that SIRT1 induces keratinocyte differentiation through a pathway integral to or overlapping with that of calcium-induced differentiation. We experimentally assayed this prediction and found that the SIRT1 inhibitor nicotinamide inhibited expression of keratinocyte differentiation markers, whereas a SIRT1 activator, resveratrol, enhanced expression of keratinocyte differentiation markers. Similar results were obtained in keratinocytes manipulated to overexpress or underexpress SIRT1, and modulating SIRT1 significantly affected keratinocyte proliferation rates. We conclude that SIRT1 functions in normal human keratinocytes to inhibit proliferation and to promote differentiation.

Antidepressants of the serotonin-antagonist type increase body fat and decrease lifespan of adult Caenorhabditis elegans

It was recently suggested that specific antidepressants of the serotonin-antagonist type, namely mianserin and methiothepin, may exert anti-aging properties and specifically extend lifespan of the nematode C.elegans by causing a state of perceived calorie restriction (Petrascheck M, Ye X, Buck LB: An antidepressant that extends lifespan in adult Caenorhabditis elegans; Nature, Nov 22, 2007;450(7169):553–6, PMID 18033297). Using the same model organism, we instead observe a reduction of life expectancy when employing the commonly used, standardized agar-based solid-phase assay while applying the same or lower concentrations of the same antidepressants. Consistent with a well-known side-effect of these compounds in humans, antidepressants not only reduced lifespan but also increased body fat accumulation in C. elegans reflecting the mammalian phenotype. Taken together and in conflict with previously published findings, we find that antidepressants of the serotonin-antagonist type not only promote obesity, but also decrease nematode lifespan.

Resveratrol treatment in mice does not elicit the bradycardia and hypothermia associated with calorie restriction

Dietary supplementation with resveratrol may produce calorie restriction-like effects on metabolic and longevity endpoints in mice. In this study, we sought to determine whether resveratrol treatment elicited other hallmark changes associated with calorie restriction, namely bradycardia and decreased body temperature. We found that during short-term treatment, wild-type mice on a calorie-restricted diet experienced significant decreases in both heart rate and body temperature after only 1 day whereas those receiving resveratrol exhibited no such change after 1 wk. We also used ob/ob mice to study the effects of long-term treatment because previous studies had indicated the therapeutic value of resveratrol against the linked morbidities of obesity and diabetes. After 12 wk, resveratrol treatment had produced no changes in either heart rate or body temperature. Strikingly, and in contrast to previous findings, we found that resveratrol-treated mice had significantly reduced endurance in a treadmill test. Quantitative reverse transcriptase-polymerase chain reaction suggested that a proposed target of resveratrol, Sirt1, was activated in resveratrol-treated ob/ob mice. Thus, we conclude that the bradycardia and hypothermia associated with calorie restriction occur through mechanisms unaffected by the actions of resveratrol and that further studies are needed to examine the differential effects of resveratrol in a leptin-deficient background.

Change in histone H3 phosphorylation, MAP kinase p38, SIR 2 and p53 expression by resveratrol in preventing streptozotocin induced type I diabetic nephropathy

Resveratrol has been reported to have a wide variety of biological effects. However, little is known regarding its role on phosphorylation of histone H3, MAP kinase p38, SIR2 and p53 in type I diabetic nephropathy (DN). Hence, the present study was undertaken to examine changes in the above said parameters by resveratrol treatment. Male Sprague-Dawley rats were rendered diabetic using a single dose of streptozotocin (55 mg/kg, i.p.). DN was assessed by measurements of blood urea nitrogen and creatinine levels. Phosphorylation of histone H3, SIR2, p53 and MAP kinase p38 expression were examined by western blotting. This study reports that treatment of resveratrol prevents the decrease in the expression of SIR2 in diabetic kidney. It also prevents increase in p38, p53 expression and dephosphorylation of histone H3 in diabetic kidney. This is the first report which suggests that protection against development of diabetic nephropathy by resveratrol treatment involves change in phosphorylation of histone H3, expression of Sir-2, p53 and p38 in diabetic kidney.

An elt-3/elt-5/elt-6 GATA transcription circuit guides aging in C. elegans

To define the C. elegans aging process at the molecular level, we used DNA microarray experiments to identify a set of 1294 age-regulated genes and found that the GATA transcription factors ELT-3, ELT-5, and ELT-6 are responsible for age regulation of a large fraction of these genes. Expression of elt-5 and elt-6 increases during normal aging, and both of these GATA factors repress expression of elt-3, which shows a corresponding decrease in expression in old worms. elt-3 regulates a large number of downstream genes that change expression in old age, including ugt-9, col-144, and sod-3. elt-5(RNAi) and elt-6(RNAi) worms have extended longevity, indicating that elt-3, elt-5, and elt-6 play an important functional role in the aging process. These results identify a transcriptional circuit that guides the rapid aging process in C. elegans and indicate that this circuit is driven by drift of developmental pathways rather than accumulation of damage.

Resveratrol delays age-related deterioration and mimics transcriptional aspects of dietary restriction without extending life span

A small molecule that safely mimics the ability of dietary restriction (DR) to delay age-related diseases in laboratory animals is greatly sought after. We and others have shown that resveratrol mimics effects of DR in lower organisms. In mice, we find that resveratrol induces gene expression patterns in multiple tissues that parallel those induced by DR and every-other-day feeding. Moreover, resveratrol-fed elderly mice show a marked reduction in signs of aging, including reduced albuminuria, decreased inflammation, and apoptosis in the vascular endothelium, increased aortic elasticity, greater motor coordination, reduced cataract formation, and preserved bone mineral density. However, mice fed a standard diet did not live longer when treated with resveratrol beginning at 12 months of age. Our findings indicate that resveratrol treatment has a range of beneficial effects in mice but does not increase the longevity of ad libitum-fed animals when started midlife.

Quercetin-mediated longevity in Caenorhabditis elegans: is DAF-16 involved?

The polyphenol quercetin has recently been found to extend lifespan and increase stress resistance in the nematode Caenorhabditis elegans. The forkhead transcription factor DAF-16 has previously been linked to these effects. However, by using a daf-16(mgDf50) mutant strain, we show that quercetin exposure leads to increased mean lifespans up to 15%. Furthermore, quercetin-treated daf-16(mgDf50) worms show an enhanced resistance to thermal and oxidative stress. Our data reveal that DAF-16 is not obligatorily required for quercetin-mediated longevity and stress resistance.

Unfolded protein response genes regulated by CED-1 are required for Caenorhabditis elegans innate immunity

The endoplasmic reticulum stress response, also known as the unfolded protein response (UPR), has been implicated in the normal physiology of immune defense and in several disorders, including diabetes, cancer, and neurodegenerative disease. Here, we show that the apoptotic receptor CED-1 and a network of PQN/ABU proteins involved in a noncanonical UPR response are required for proper defense to pathogen infection in Caenorhabditis elegans. A full-genome microarray analysis indicates that CED-1 functions to activate the expression of pqn/abu genes. We also show that ced-1 and pqn/abu genes are required for the survival of C. elegans exposed to live Salmonella enterica, and that overexpression of pqn/abu genes confers protection against pathogen-mediated killing. The results indicate that unfolded protein response genes, regulated in a CED-1-dependent manner, are involved in the C. elegans immune response to live bacteria.

SIRT1 and neuronal diseases

SIRT1 is the mammalian homologue of yeast silent information regulator (Sir)-2, a member of the sirtuin family of protein deacetylases which have gained much attention as mediators of lifespan extension in several model organisms. Induction of SIRT1 expression also attenuates neuronal degeneration and death in animal models of Alzheimer's disease and Huntington's disease. SIRT1 induction, either by sirtuin activators such as resveratrol, or metabolic conditioning associated with caloric restriction (CR), could be neuroprotective in several ways. It could promote the non-amyloidogenic cleavage of the amyloid precursor protein, enhance clearance of amyloid beta-peptides, and reduced neuronal damage through potential inhibition of neuroinflammatory signaling pathways. In addition, increased SIRT1 activity could alter neuronal transcription profiles to enhance anti-stress and anti-apoptotic gene activities, and has been proposed to underlie the inhibition of axonal degeneration in the Wallerian degeneration slow (Wld(s)) phenotype. As neuronal degeneration is a major pathophysiological aspect of human aging, understanding the mechanism of SIRT1 neuroprotection promises novel strategies in clinical intervention of neurodegenerative diseases.

Yeast life span extension by depletion of 60s ribosomal subunits is mediated by Gcn4

In nearly every organism studied, reduced caloric intake extends life span. In yeast, span extension from dietary restriction is thought to be mediated by the highly conserved, nutrient-responsive target of rapamycin (TOR), protein kinase A (PKA), and Sch9 kinases. These kinases coordinately regulate various cellular processes including stress responses, protein turnover, cell growth, and ribosome biogenesis. Here we show that a specific reduction of 60S ribosomal subunit levels slows aging in yeast. Deletion of genes encoding 60S subunit proteins or processing factors or treatment with a small molecule, which all inhibit 60S subunit biogenesis, are each sufficient to significantly increase replicative life span. One mechanism by which reduced 60S subunit levels leads to life span extension is through induction of Gcn4, a nutrient-responsive transcription factor. Genetic epistasis analyses suggest that dietary restriction, reduced 60S subunit abundance, and Gcn4 activation extend yeast life span by similar mechanisms.

C. elegans model identifies genetic modifiers of alpha-synuclein inclusion formation during aging

Inclusions in the brain containing α-synuclein are the pathological hallmark of Parkinson's disease, but how these inclusions are formed and how this links to disease is poorly understood. We have developed a C. elegans model that makes it possible to monitor, in living animals, the formation of α-synuclein inclusions. In worms of old age, inclusions contain aggregated α- synuclein, resembling a critical pathological feature. We used genome-wide RNA interference to identify processes involved in inclusion formation, and identified 80 genes that, when knocked down, resulted in a premature increase in the number of inclusions. Quality control and vesicle-trafficking genes expressed in the ER/Golgi complex and vesicular compartments were overrepresented, indicating a specific role for these processes in α-synuclein inclusion formation. Suppressors include aging-associated genes, such as sir-2.1/SIRT1 and lagr-1/LASS2. Altogether, our data suggest a link between α-synuclein inclusion formation and cellular aging, likely through an endomembrane-related mechanism. The processes and genes identified here present a framework for further study of the disease mechanism and provide candidate susceptibility genes and drug targets for Parkinson's disease and other α-synuclein related disorders.

Parkinson's disease is the second most common brain disorder of the elderly. It is thought to be caused by environmental and genetic factors. However, little is known about the genes and processes involved. Pathologically, Parkinson's disease is recognized by inclusions in the brain that contain a disease-specific protein: alpha-synuclein. We created a small animal model (C. elegans) in which we could follow the formation of alpha-synuclein inclusions in living and aging animals. With a genome-wide RNAi screen we identified 80 genes whose expression influences inclusion formation. These genes include evolutionarily conserved regulators of longevity, suggesting a link between inclusion formation and the molecular mechanism of aging. Our results offer a refined understanding of how Parkinson's disease arises during aging and we identify processes and genes that may underlie an increased susceptibility for the disease, which is important for improving diagnostics and developing strategies for therapeutic intervention.

Fibroblasts from naked mole-rats are resistant to multiple forms of cell injury, but sensitive to peroxide, ultraviolet light, and endoplasmic reticulum stress

Fibroblasts from long-lived mutant mice are resistant to many forms of lethal injury as well as to the metabolic effects of rotenone and low-glucose medium. Here we evaluated fibroblasts from young adult naked mole-rats (NMR; Heterocephalus glaber), a rodent species in which maximal longevity exceeds 28 years. Compared to mouse cells, NMR cells were resistant to cadmium, methyl methanesulfonate, paraquat, heat, and low-glucose medium, consistent with the idea that cellular resistance to stress may contribute to disease resistance and longevity. Surprisingly, NMR cells were more sensitive than mouse cells to H(2)O(2), ultraviolet (UV) light, and rotenone. NMR cells, like cells from Snell dwarf mice, were more sensitive to tunicamycin and thapsigargin, which interfere with the function of the endoplasmic reticulum (ER stress). The sensitivity of both Snell dwarf and NMR cells to ER stress suggests that alterations in the unfolded protein response might modulate cell survival and aging rate.

SIRT6 in DNA repair, metabolism and ageing

Ageing, or increased mortality with time, coupled with physiologic decline, is a nearly universal yet poorly understood biological phenomenon. Studies in model organisms suggest that two conserved pathways modulate longevity: DNA damage repair and Insulin/Igf1-like signalling. In addition, homologs of yeast Sir2--the sirtuins--regulate lifespan in diverse organisms. Here, we focus on one particular sirtuin, SIRT6. Mice lacking SIRT6 develop a degenerative disorder that in some respects mimics models of accelerated ageing [Cell (2006) 124:315]. We discuss how sirtuins in general and SIRT6 specifically relate to other evolutionarily conserved pathways affecting ageing, and how SIRT6 might function to ensure organismal homeostasis and normal lifespan.

Negative regulation of the deacetylase SIRT1 by DBC1

SIRT1 is an NAD-dependent deacetylase critically involved in stress responses, cellular metabolism and, possibly, ageing. The tumour suppressor p53 represents the first non-histone substrate functionally regulated by acetylation and deacetylation; we and others previously found that SIRT1 promotes cell survival by deacetylating p53 (refs 4-6). These results were further supported by the fact that p53 hyperacetylation and increased radiation-induced apoptosis were observed in Sirt1-deficient mice. Nevertheless, SIRT1-mediated deacetylase function is also implicated in p53-independent pathways under different cellular contexts, and its effects on transcriptional factors such as members of the FOXO family and PGC-1alpha directly modulate metabolic responses. These studies validate the importance of the deacetylase activity of SIRT1, but how SIRT1 activity is regulated in vivo is not well understood. Here we show that DBC1 (deleted in breast cancer 1) acts as a native inhibitor of SIRT1 in human cells. DBC1-mediated repression of SIRT1 leads to increasing levels of p53 acetylation and upregulation of p53-mediated function. In contrast, depletion of endogenous DBC1 by RNA interference (RNAi) stimulates SIRT1-mediated deacetylation of p53 and inhibits p53-dependent apoptosis. Notably, these effects can be reversed in cells by concomitant knockdown of endogenous SIRT1. Our study demonstrates that DBC1 promotes p53-mediated apoptosis through specific inhibition of SIRT1.

Resveratrol induces the heat-shock response and protects human cells from severe heat stress

Molecular chaperones play key roles in protein quality control, signal transduction, proliferation, and cell death, and confer cytoprotection and assure survival after environmental stress. The heat-shock response is implicated in a variety of conditions including ischemic diseases, infection and immunity, neurodegeneration, and aging. Physiologic and pharmacologic chaperone inducers were shown to be an efficient therapeutic approach in different acute and chronic diseases. Here we characterize resveratrol, a polyphenol from red wine, as an inducer of the heat-shock response. Resveratrol activated the heat-shock promoter and the expression of the major chaperone Hsp70 in cell lines and in human peripheral lymphocytes, comparable to moderate heat stress. This effect was not due to its antioxidant property, because 5 mM N-acetylcysteine was unable to activate the heat-shock response. Moreover, resveratrol failed to upregulate Grp78, and tunicamycin was unable to induce Hsp70, suggesting that the resveratrol-induced heat-shock response was not mediated by canonic endoplasmic reticulum stress. Resveratrol synergized with mild to moderate heat shock and conferred cytoprotection against severe heat stress. Our results reveal resveratrol as a chaperone inducer that may contribute to its pleiotropic effects in ameliorating stress and promoting longevity.

Genetic links between diet and lifespan: shared mechanisms from yeast to humans

Caloric restriction is the only known non-genetic intervention that robustly extends lifespan in mammals. This regimen also attenuates the incidence and progression of many age-dependent pathologies. Understanding the genetic mechanisms that underlie dietary-restriction-induced longevity would therefore have profound implications for future medical treatments aimed at tackling conditions that are associated with the ageing process. Until recently, however, almost nothing was known about these mechanisms in metazoans. Recent advances in our understanding of the genetic bases of energy sensing and lifespan control in yeast, invertebrates and mammals have begun to solve this puzzle. Evidence is mounting that the brain has a crucial role in sensing dietary restriction and promoting longevity in metazoans.

Models, mechanisms and clinical evidence for cancer dormancy

Patients with cancer can develop recurrent metastatic disease with latency periods that range from years even to decades. This pause can be explained by cancer dormancy, a stage in cancer progression in which residual disease is present but remains asymptomatic. Cancer dormancy is poorly understood, resulting in major shortcomings in our understanding of the full complexity of the disease. Here, I review experimental and clinical evidence that supports the existence of various mechanisms of cancer dormancy including angiogenic dormancy, cellular dormancy (G0-G1 arrest) and immunosurveillance. The advances in this field provide an emerging picture of how cancer dormancy can ensue and how it could be therapeutically targeted.

Drug targeting of dysregulated transcription in Huntington's disease

Transcriptional dysregulation in Huntington's disease (HD) is a well documented and broadly studied phenomenon. Its basis appears to be in huntingtin's aberrant protein-protein interactions with a variety of transcription factors. The development of therapeutics targeting altered transcription, however, faces serious challenges. No single transcriptional regulator has emerged as a primary actor in HD. The levels of literally hundreds of RNA transcripts are altered in affected cells and it is uncertain which are most relevant. The protein-protein interactions of mutant huntingtin with transcriptional factors do not constitute conventional and easy targets for drug molecules. Nevertheless, potential therapeutic advances, targeting transcriptional deregulation in HD, have been made in recent years. In this chapter we review current progress in this area of therapeutic development. We also discuss possible drug discovery strategies targeting altered transcriptional pathways.

Genetics of aging in Caenorhabditis elegans

A dissection of longevity in Caenorhabditis elegans reveals that animal life span is influenced by genes, environment, and stochastic factors. From molecules to physiology, a remarkable degree of evolutionary conservation is seen.

MSN2 and MSN4 link calorie restriction and TOR to sirtuin-mediated lifespan extension in Saccharomyces cerevisiae

Calorie restriction (CR) robustly extends the lifespan of numerous species. In the yeast Saccharomyces cerevisiae, CR has been proposed to extend lifespan by boosting the activity of sirtuin deacetylases, thereby suppressing the formation of toxic repetitive ribosomal DNA (rDNA) circles. An alternative theory is that CR works by suppressing the TOR (target of rapamycin) signaling pathway, which extends lifespan via mechanisms that are unknown but thought to be independent of sirtuins. Here we show that TOR inhibition extends lifespan by the same mechanism as CR: by increasing Sir2p activity and stabilizing the rDNA locus. Further, we show that rDNA stabilization and lifespan extension by both CR and TOR signaling is due to the relocalization of the transcription factors Msn2p and Msn4p from the cytoplasm to the nucleus, where they increase expression of the nicotinamidase gene PNC1. These findings suggest that TOR and sirtuins may be part of the same longevity pathway in higher organisms, and that they may promote genomic stability during aging.

Effects of resveratrol on lifespan in Drosophila melanogaster and Caenorhabditis elegans

It was recently reported that the plant polyphenol resveratrol, found, e.g., in grape berry skins, extended lifespan in the fruit fly Drosophila melanogaster and the nematode worm Caenorhabditis elegans. This lifespan extension was dependent on an NAD(+)-dependent histone deacetylase, Sir2 in Drosophila and SIR-2.1 in C. elegans. The extension of lifespan appeared to occur through a mechanism related to dietary restriction (DR), the reduction of available nutrients without causing malnutrition, an intervention that extends lifespan in diverse organisms from yeast to mammals. In Drosophila, lifespan extension by DR is associated with a reduction in fecundity. However, a slight increase in fecundity was reported upon treatment with resveratrol, suggesting a mode of action at least partially distinct from that of DR. To probe this mechanism further, we initiated a new study of the effects of resveratrol on Drosophila. We saw no significant effects on lifespan in seven independent trials. We analysed our resveratrol and found that its structure was normal, with no oxidative modifications. We therefore re-tested the effects of resveratrol in C. elegans, in both wild-type and sir-2.1 mutant worms. The results were variable, with resveratrol treatment resulting in slight increases in lifespan in some trials but not others, in both wild type and sir-2.1 mutant animals. We postulate that the effect of resveratrol upon lifespan in C. elegans could reflect induction of phase 2 drug detoxification or activation of AMP kinase.

Nutrient-sensitive mitochondrial NAD+ levels dictate cell survival

A major cause of cell death caused by genotoxic stress is thought to be due to the depletion of NAD(+) from the nucleus and the cytoplasm. Here we show that NAD(+) levels in mitochondria remain at physiological levels following genotoxic stress and can maintain cell viability even when nuclear and cytoplasmic pools of NAD(+) are depleted. Rodents fasted for 48 hr show increased levels of the NAD(+) biosynthetic enzyme Nampt and a concomitant increase in mitochondrial NAD(+). Increased Nampt provides protection against cell death and requires an intact mitochondrial NAD(+) salvage pathway as well as the mitochondrial NAD(+)-dependent deacetylases SIRT3 and SIRT4. We discuss the relevance of these findings to understanding how nutrition modulates physiology and to the evolution of apoptosis.

Nutrient-sensitive mitochondrial NAD+ levels dictate cell survival

A major cause of cell death caused by genotoxic stress is thought to be due to the depletion of NAD(+) from the nucleus and the cytoplasm. Here we show that NAD(+) levels in mitochondria remain at physiological levels following genotoxic stress and can maintain cell viability even when nuclear and cytoplasmic pools of NAD(+) are depleted. Rodents fasted for 48 hr show increased levels of the NAD(+) biosynthetic enzyme Nampt and a concomitant increase in mitochondrial NAD(+). Increased Nampt provides protection against cell death and requires an intact mitochondrial NAD(+) salvage pathway as well as the mitochondrial NAD(+)-dependent deacetylases SIRT3 and SIRT4. We discuss the relevance of these findings to understanding how nutrition modulates physiology and to the evolution of apoptosis.

Influence of lactic acid bacteria on longevity of Caenorhabditis elegans and host defense against salmonella enterica serovar enteritidis

This study aimed to develop a convenient model to investigate the senescence of host defenses and the influence of food and nutrition. A small soil nematode, Caenorhabditis elegans, was grown for 3 days from hatching on a lawn of Escherichia coli OP50 as the normal food source, and subsequently some of the nematodes were fed lactic acid bacteria (LAB). The life spans of worms fed LAB were significantly longer than the life spans of those fed OP50. To investigate the effect of age on host defenses, 3- to 7-day-old worms fed OP50 were transferred onto a lawn of Salmonella enterica serovar Enteritidis for infection. The nematodes died over the course of several days, and the accumulation of salmonella in the intestinal lumen suggested that the worms were infected. The 7-day-old worms showed a higher death rate during the 5 days after infection than nematodes infected at the age of 3 days; no clear difference was observed when the worms were exposed to OP50. We then investigated whether the LAB could exert probiotic effects on the worms' host defenses and improve life span. Seven-day-old nematodes fed LAB from the age of 3 days were more resistant to salmonella than worms fed OP50 until they were infected with salmonella. This study clearly showed that LAB can enhance the host defense of C. elegans and prolong life span. The nematode appears to be an appropriate model for screening useful probiotic strains or dietetic antiaging substances.

Effect of resveratrol on proliferation and differentiation of embryonic cardiomyoblasts

Resveratrol (trans-3,5,4'-trihydroxystilbene), a polyphenolic compound found largely in the skins of red grapes, has been used as a nutritional supplement or an investigational new drug for prevention of cardiovascular diseases. Previous reports showed that resveratrol had a protective effect against oxidative agent-induced cell injury. Our studies indicate that resveratrol plays a role in the differentiation of cardiomyoblasts. The cardiomyoblast cell line, H9c2, was exposed to 30-120 microM resveratrol for up to 5 days. Resveratrol inhibits cardiomyoblast proliferation without causing cells injury. Moreover, resveratrol treatment modulated the differentiation of morphological characteristics including elongation and cell fusion in cardiomyoblasts. Proliferation and differentiation of H9c2 cells were further revealed by measurement of the mRNA expression of a cell cycle marker (CDK2), a differentiation marker (myogenin), and a contractile apparatus protein (MLC-2). Gene expression analysis revealed that resveratrol promoted entry into cell cycle arrest but extended the myogenic differentiation progress. These results have implications for the role of resveratrol in modulating cell cycle control and differentiation in cardiomyoblasts.

Systems biology of aging in four species

Using DNA microarrays to generate transcriptional profiles of the aging process is a powerful tool for identifying biomarkers of aging. In Caenorhabditis elegans, a number of whole-genome profiling studies identified genes that change expression levels with age. High-throughput RNAi screens in worms determined a number of genes that modulate lifespan when silenced. Transcriptional profiling of the fly head identified a molecular pathway, the 'response to light' gene set, that increases expression with age and could be directly related to the tendency for a reduction in light levels to extend fly's lifespan. In mouse, comparing the gene expression profiles of several drugs to the gene expression profile of caloric restriction identified metformin as a drug whose action could potentially mimic caloric restriction in vivo. Finally, genes in the mitochondrial electron transport chain group decrease expression with age in the human, mouse, fly, and worm.

Live longer through PHAsting

Dietary restriction provides considerable health benefits and may even increase life span in humans. Panowski et al. (2007) have now identified PHA-4/FoxA as an essential and specific component of DR-induced life-span extension in C. elegans.

Sirtuins in mammals: insights into their biological function

Sirtuins are a conserved family of proteins found in all domains of life. The first known sirtuin, Sir2 (silent information regulator 2) of Saccharomyces cerevisiae, from which the family derives its name, regulates ribosomal DNA recombination, gene silencing, DNA repair, chromosomal stability and longevity. Sir2 homologues also modulate lifespan in worms and flies, and may underlie the beneficial effects of caloric restriction, the only regimen that slows aging and extends lifespan of most classes of organism, including mammals. Sirtuins have gained considerable attention for their impact on mammalian physiology, since they may provide novel targets for treating diseases associated with aging and perhaps extend human lifespan. In this review we describe our current understanding of the biological function of the seven mammalian sirtuins, SIRT1-7, and we will also discuss their potential as mediators of caloric restriction and as pharmacological targets to delay and treat human age-related diseases.

Sirtuins in mammals: insights into their biological function

Sirtuins are a conserved family of proteins found in all domains of life. The first known sirtuin, Sir2 (silent information regulator 2) of Saccharomyces cerevisiae, from which the family derives its name, regulates ribosomal DNA recombination, gene silencing, DNA repair, chromosomal stability and longevity. Sir2 homologues also modulate lifespan in worms and flies, and may underlie the beneficial effects of caloric restriction, the only regimen that slows aging and extends lifespan of most classes of organism, including mammals. Sirtuins have gained considerable attention for their impact on mammalian physiology, since they may provide novel targets for treating diseases associated with aging and perhaps extend human lifespan. In this review we describe our current understanding of the biological function of the seven mammalian sirtuins, SIRT1-7, and we will also discuss their potential as mediators of caloric restriction and as pharmacological targets to delay and treat human age-related diseases.

Molecular Chaperones and the Epigenetics of Longevity and Cancer Resistance

The inherent immortality of embryonic stem cells demonstrates that replicative senescence as possibly the aging of species are epigenetic phenomena. The cellular level of expression of the housekeeping molecular chaperones correlates with longevity and cancer resistance of species. The chaperones are cancer antagonists by acting as genetic buffers, stabilizing the normal phenotype. Probably the progressive age-related silencing of the housekeeping genes contributes to the phenotype of aging, with the associated increase in cancer incidence. The present review concerns epigenetic chemical, immunological, and hormonal mechanisms, activating chaperone- and immune-response genes, which have proved effective in increasing longevity and cancer resistance. The relation of steroid hormone levels to species longevity, the anticarcinogenic activity of pregnancy hormones, and the influence of hormones on the longevity of social insects, illustrates the importance of hormonal mechanisms for the activation of longevity genes.

The Caenorhabditis elegans nicotinamidase PNC-1 enhances survival

In yeast, increasing the copy number of the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase Sir2 extends lifespan, which can be inhibited by nicotinamide (Nam), the end-product of Sir2-mediated NAD-breakdown. Furthermore, the yeast pyrazinamidase/nicotinamidase PNC-1 can extend yeast lifespan by converting Nam. In Caenorhabditis elegans (C. elegans), increased dosage of the gene encoding SIR-2.1 also increases lifespan. Here, we report that knockdown of the C. elegans homologue of yeast PNC-1 as well as growing worms on Nam-containing medium significantly decreases adult lifespan. Accordingly, increased gene dosage of pnc-1 increases adult survival under conditions of oxidative stress. These data show for the first time the involvement of PNC-1/Nam in the survival of a multicellular organism and may also contribute to our understanding of lifespan regulation in mammals.

Design and synthesis of compounds that extend yeast replicative lifespan

This past decade has seen the identification of numerous conserved genes that extend lifespan in diverse species, yet the number of compounds that extend lifespan is relatively small. A class of compounds called STACs, which were identified as activators of Sir2/SIRT1 NAD+-dependent deacetylases, extend the lifespans of multiple species in a Sir2-dependent manner and can delay the onset of age-related diseases such as cancer, diabetes and neurodegeneration in model organisms. Plant-derived STACs such as fisetin and resveratrol have several liabilities, including poor stability and relatively low potency as SIRT1 activators. To develop improved STACs, stilbene derivatives with modifications at the 4' position of the B ring were synthesized using a Horner-Emmons-based synthetic route or by hydrolyzing deoxyrhapontin. Here, we describe synthetic STACs with lower toxicity toward human cells, and higher potency with respect to SIRT1 activation and lifespan extension in Saccharomyces cerevisiae. These studies show that it is possible to improve upon naturally occurring STACs based on a number of criteria including lifespan extension.

SIR2: a potential target for calorie restriction mimetics

Calorie restriction (CR) extends lifespan in a wide variety of species and mitigates diseases of aging in mammals. Here, we describe the evidence that the silent information regulator 2 (SIR2) gene, which encodes a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, regulates lifespan and mediates CR in lower species such as Saccharomyces cerevisiae and Caenorhabditis elegans. We discuss the emerging roles of mammalian SIR2 homologs in regulating physiological changes triggered by CR and their potential connections to diseases of aging. We conclude with the recent advances on small molecules that activate the enzymatic activity of SIR2 as potential CR mimetics. The SIR2 family represents an evolutionarily conserved lifespan regulator. Modulating the activity of SIR2 might provide effective CR mimetics to combat diseases of aging.

Sirtuins in aging and disease

Sirtuin genes function as anti-aging genes in yeast, Caenorhabditis elegans, and Drosophila. The NAD requirement for sirtuin function indicates a link between aging and metabolism, and a boost in sirtuin activity may in part explain how calorie restriction extends life span. In mammals, one of the substrates of the SIR2 ortholog, SIRT1, is a regulator of mitochondrial biogenesis, PGC-1alpha. Indeed, the putative SIRT1 activator resveratrol has been shown to stimulate mitochondrial biogenesis and deliver health benefits in treated mice. I explore here how mitochondrial biogenesis may have beneficial effects on aging and, perhaps, diseases of aging. In particular, I speculate that SIRT1-mediated mitochondrial biogenesis may reduce the production of reactive oxygen species, a possible cause of aging, and offer two possible mechanisms for this effect. An understanding of how calorie restriction works may lead to novel drugs to combat diseases of aging.