Saccharomyces Cerevisiae MPT5 and SSD1 Function in Parallel Pathways to Promote Cell Wall Integrity

Genetics. Jan, 2002  |  Pubmed ID: 11805047

Yeast MPT5 (UTH4) is a limiting component for longevity. We show here that MPT5 also functions to promote cell wall integrity. Loss of Mpt5p results in phenotypes associated with a weakened cell wall, including sorbitol-remedial temperature sensitivity and sensitivities to calcofluor white and sodium dodecyl sulfate. Additionally, we find that mutation of MPT5, in the absence of SSD1-V, is lethal in combination with loss of either Ccr4p or Swi4p. These synthetic lethal interactions are suppressed by the SSD1-V allele. Furthermore, we have provided evidence that the short life span caused by loss of Mpt5p is due to a weakened cell wall. This cell wall defect may be the result of abnormal chitin biosynthesis or accumulation. These analyses have defined three genetic pathways that function in parallel to promote cell integrity: an Mpt5p-containing pathway, an Ssd1p-containing pathway, and a Pkc1p-dependent pathway. This work also provides evidence that post-transcriptional regulation is likely to be important both for maintaining cell integrity and for promoting longevity.

Mutations in Saccharomyces Cerevisiae Gene SIR2 Can Have Differential Effects on in Vivo Silencing Phenotypes and in Vitro Histone Deacetylation Activity

Molecular Biology of the Cell. Apr, 2002  |  Pubmed ID: 11950950

The yeast SIR2 gene and many of its homologs have been identified as NAD(+)-dependent histone deacetylases. To get a broader view of the relationship between the histone deacetylase activity of Sir2p and its in vivo functions we have mutated eight highly conserved residues in the core domain of SIR2. These mutations have a range of effects on the ability of Sir2p to deacetylate histones in vitro and to silence genes at the telomeres and HM loci. Interestingly, there is not a direct correlation between the in vitro and in vivo effects in some of these mutations. We also show that the histone deacetylase activity of Sir2p is necessary for the proper localiztion of the SIR complex to the telomeres.

AGEID: a Database of Aging Genes and Interventions

Mechanisms of Ageing and Development. Apr, 2002  |  Pubmed ID: 12044961

The aging genes/interventions database (AGEID) is a database of experimental results related to aging. AGEID is available as part of the science of aging knowledge environment on the World Wide Web at http://sageke.sciencemag.org/cgi/genesdb. The goal of AGEID is to catalog, in one location, every published experiment where life span has been measured in any organism. AGEID also includes information on genes that influence the incidence of age-associated disorders such as Alzheimer's disease and Parkinson's disease. AGEID gene/intervention reports are formatted pages containing the organism and strain background in which the particular experiment was performed, the type of genetic or environmental perturbation, the effect on life span, a description of the gene function and its role in longevity, protein homologs, and references. The use of this database by researchers who study aging should facilitate easy comparison of the genes and interventions that affect life span in different organisms.

Calorie Restriction Extends Saccharomyces Cerevisiae Lifespan by Increasing Respiration

Nature. Jul, 2002  |  Pubmed ID: 12124627

Calorie restriction (CR) extends lifespan in a wide spectrum of organisms and is the only regimen known to lengthen the lifespan of mammals. We established a model of CR in budding yeast Saccharomyces cerevisiae. In this system, lifespan can be extended by limiting glucose or by reducing the activity of the glucose-sensing cyclic-AMP-dependent kinase (PKA). Lifespan extension in a mutant with reduced PKA activity requires Sir2 and NAD (nicotinamide adenine dinucleotide). In this study we explore how CR activates Sir2 to extend lifespan. Here we show that the shunting of carbon metabolism toward the mitochondrial tricarboxylic acid cycle and the concomitant increase in respiration play a central part in this process. We discuss how this metabolic strategy may apply to CR in animals.

High Osmolarity Extends Life Span in Saccharomyces Cerevisiae by a Mechanism Related to Calorie Restriction

Molecular and Cellular Biology. Nov, 2002  |  Pubmed ID: 12391171

Calorie restriction (CR) extends life span in many different organisms, including mammals. We describe here a novel pathway that extends the life span of Saccharomyces cerevisiae mother cells but does not involve a reduction in caloric content of the media, i.e., there is growth of yeast cells in the presence of a high concentration of external osmolytes. Like CR, this longevity-promoting response to high osmolarity requires SIR2, suggesting a common mechanism of life span regulation. Genetic and microarray analysis indicates that high osmolarity extends the life span by activating Hog1p, leading to an increase in the biosynthesis of glycerol from glycolytic intermediates. This metabolic shift likely increases NAD levels, thereby activating Sir2p and promoting longevity.

Saccharomyces Cerevisiae SSD1-V Confers Longevity by a Sir2p-independent Mechanism

Genetics. Apr, 2004  |  Pubmed ID: 15126388

The SSD1 gene of Saccharomyces cerevisiae is a polymorphic locus that affects diverse cellular processes including cell integrity, cell cycle progression, and growth at high temperature. We show here that the SSD1-V allele is necessary for cells to achieve extremely long life span. Furthermore, addition of SSD1-V to cells can increase longevity independently of SIR2, although SIR2 is necessary for SSD1-V cells to attain maximal life span. Past studies of yeast aging have been performed in short-lived ssd1-d strain backgrounds. We propose that SSD1-V defines a previously undescribed pathway affecting cellular longevity and suggest that future studies on longevity-promoting genes should be carried out in long-lived SSD1-V strains.

Sir2-independent Life Span Extension by Calorie Restriction in Yeast

PLoS Biology. Sep, 2004  |  Pubmed ID: 15328540

Calorie restriction slows aging and increases life span in many organisms. In yeast, a mechanistic explanation has been proposed whereby calorie restriction slows aging by activating Sir2. Here we report the identification of a Sir2-independent pathway responsible for a majority of the longevity benefit associated with calorie restriction. Deletion of FOB1 and overexpression of SIR2 have been previously found to increase life span by reducing the levels of toxic rDNA circles in aged mother cells. We find that combining calorie restriction with either of these genetic interventions dramatically enhances longevity, resulting in the longest-lived yeast strain reported thus far. Further, calorie restriction results in a greater life span extension in cells lacking both Sir2 and Fob1 than in cells where Sir2 is present. These findings indicate that Sir2 and calorie restriction act in parallel pathways to promote longevity in yeast and, perhaps, higher eukaryotes.

Aging-related Research in the "-omics" Age

Science of Aging Knowledge Environment : SAGE KE. Oct, 2004  |  Pubmed ID: 15498757

The application of high-throughput technologies to aging-related research has the potential to dramatically enhance our understanding of how longevity is determined at a molecular level. Genome-scale studies are being carried out in every major model system used for aging-related research, and new technologies are being developed to rapidly identify mutations or small-molecules that increase life span. A meta-analysis of data derived from genome-wide studies of aging in simple eukaryotes will allow the identification of conserved determinants of longevity that can be tested in mammals.

Large-scale Identification in Yeast of Conserved Ageing Genes

Mechanisms of Ageing and Development. Jan, 2005  |  Pubmed ID: 15610758

Recent advances have suggested the existence of phylogenetically conserved pathways regulating ageing in eukaryotes. At least two of these "public" longevity-determining pathways appear to have been evolutionarily conserved from yeast through mammals. We have developed a high-throughput, genome-wide approach to identify a large fraction of the non-essential, single-gene deletion mutations that confer increased longevity in yeast. The identification and characterization of conserved genes that regulate the ageing process across eukaryotic species is likely to result in an improved understanding of the causes of human ageing and provide potential therapeutic targets for drug discovery.

Substrate-specific Activation of Sirtuins by Resveratrol

The Journal of Biological Chemistry. Apr, 2005  |  Pubmed ID: 15684413

Resveratrol, a small molecule found in red wine, is reported to slow aging in simple eukaryotes and has been suggested as a potential calorie restriction mimetic. Resveratrol has also been reported to act as a sirtuin activator, and this property has been proposed to account for its anti-aging effects. We show here that resveratrol is a substrate-specific activator of yeast Sir2 and human SirT1. In particular, we observed that, in vitro, resveratrol enhances binding and deacetylation of peptide substrates that contain Fluor de Lys, a non-physiological fluorescent moiety, but has no effect on binding and deacetylation of acetylated peptides lacking the fluorophore. Consistent with these biochemical data we found that in three different yeast strain backgrounds, resveratrol has no detectable effect on Sir2 activity in vivo, as measured by rDNA recombination, transcriptional silencing near telomeres, and life span. In light of these findings, the mechanism accounting for putative longevity effects of resveratrol should be reexamined.

Genes Determining Yeast Replicative Life Span in a Long-lived Genetic Background

Mechanisms of Ageing and Development. Apr, 2005  |  Pubmed ID: 15722108

Here we describe the replicative life spans of more than 50 congenic Saccharomyces cerevisiae strains, each carrying a mutation previously implicated in yeast aging. This analysis provides a direct comparison, in a single, long-lived strain background, of a majority of reported yeast aging genes. Of the eleven deletion mutations previously reported to increase yeast life span, we find that deletion of FOB1, deletion of SCH9, and deletion of GPA2, GPR1, or HXK2 (three genetic models of calorie restriction) significantly enhanced longevity. In addition, over-expression of SIR2 or growth on low glucose increased life span. These results define a limited number of genes likely to regulate replicative life span in a strain-independent manner, and create a basis for future epistasis analysis to determine genetic pathways of aging.

The Enigmatic Role of Sir2 in Aging

Cell. Nov, 2005  |  Pubmed ID: 16286003

In this issue of Cell, Longo and colleagues (Fabrizio et al., 2005) examine the role of Sir2, a histone deacetylase, in chronological aging in yeast by measuring the long-term survival of nondividing cells. In contrast to measurements of aging for mitotic cells, cell survival in the nonmitotic state is decreased by Sir2 activity under conditions that mimic calorie restriction.

Regulation of Yeast Replicative Life Span by TOR and Sch9 in Response to Nutrients

Science (New York, N.Y.). Nov, 2005  |  Pubmed ID: 16293764

Calorie restriction increases life span in many organisms, including the budding yeast Saccharomyces cerevisiae. From a large-scale analysis of 564 single-gene-deletion strains of yeast, we identified 10 gene deletions that increase replicative life span. Six of these correspond to genes encoding components of the nutrient-responsive TOR and Sch9 pathways. Calorie restriction of tor1D or sch9D cells failed to further increase life span and, like calorie restriction, deletion of either SCH9 or TOR1 increased life span independent of the Sir2 histone deacetylase. We propose that the TOR and Sch9 kinases define a primary conduit through which excess nutrient intake limits longevity in yeast.

Increased Life Span Due to Calorie Restriction in Respiratory-deficient Yeast

PLoS Genetics. Nov, 2005  |  Pubmed ID: 16311627

A model for replicative life span extension by calorie restriction (CR) in yeast has been proposed whereby reduced glucose in the growth medium leads to activation of the NAD+-dependent histone deacetylase Sir2. One mechanism proposed for this putative activation of Sir2 is that CR enhances the rate of respiration, in turn leading to altered levels of NAD+ or NADH, and ultimately resulting in enhanced Sir2 activity. An alternative mechanism has been proposed in which CR decreases levels of the Sir2 inhibitor nicotinamide through increased expression of the gene coding for nicotinamidase, PNC1. We have previously reported that life span extension by CR is not dependent on Sir2 in the long-lived BY4742 strain background. Here we have determined the requirement for respiration and the effect of nicotinamide levels on life span extension by CR. We find that CR confers robust life span extension in respiratory-deficient cells independent of strain background, and moreover, suppresses the premature mortality associated with loss of mitochondrial DNA in the short-lived PSY316 strain. Addition of nicotinamide to the medium dramatically shortens the life span of wild type cells, due to inhibition of Sir2. However, even in cells lacking both Sir2 and the replication fork block protein Fob1, nicotinamide partially prevents life span extension by CR. These findings (1) demonstrate that respiration is not required for the longevity benefits of CR in yeast, (2) show that nicotinamide inhibits life span extension by CR through a Sir2-independent mechanism, and (3) suggest that CR acts through a conserved, Sir2-independent mechanism in both PSY316 and BY4742.

Extension of Chronological Life Span in Yeast by Decreased TOR Pathway Signaling

Genes & Development. Jan, 2006  |  Pubmed ID: 16418483

Chronological life span (CLS) in Saccharomyces cerevisiae, defined as the time cells in a stationary phase culture remain viable, has been proposed as a model for the aging of post-mitotic tissues in mammals. We developed a high-throughput assay to determine CLS for approximately 4800 single-gene deletion strains of yeast, and identified long-lived strains carrying mutations in the conserved TOR pathway. TOR signaling regulates multiple cellular processes in response to nutrients, especially amino acids, raising the possibility that decreased TOR signaling mediates life span extension by calorie restriction. In support of this possibility, removal of either asparagine or glutamate from the media significantly increased stationary phase survival. Pharmacological inhibition of TOR signaling by methionine sulfoximine or rapamycin also increased CLS. Decreased TOR activity also promoted increased accumulation of storage carbohydrates and enhanced stress resistance and nuclear relocalization of the stress-related transcription factor Msn2. We propose that up-regulation of a highly conserved response to starvation-induced stress is important for life span extension by decreased TOR signaling in yeast and higher eukaryotes.

Comment on "HST2 Mediates SIR2-independent Life-span Extension by Calorie Restriction"

Science (New York, N.Y.). Jun, 2006  |  Pubmed ID: 16741098

Calorie restriction (CR) increases life span in yeast independently of Sir2. Lamming et al. (Reports, 16 September 2005, p. 1861) recently proposed that Sir2-independent life-span extension by CR is mediated by the Sir2 paralogs Hst1 and Hst2. Contradictory to this, we find that CR greatly increases life span in cells lacking Sir2, Hst1, and Hst2, which suggests that CR is not mediated by Sir2, Hst2, or Hst1.

Genome-wide Approaches to Understanding Human Ageing

Human Genomics. Jun, 2006  |  Pubmed ID: 16848980

The use of genomic technologies in biogerontology has the potential to greatly enhance our understanding of human ageing. High-throughput screens for alleles correlated with survival in long-lived people have uncovered novel genes involved in age-associated disease. Genome-wide longevity studies in simple eukaryotes are identifying evolutionarily conserved pathways that determine longevity. It is hoped that validation of these 'public' aspects of ageing in mice, along with analyses of variation in candidate human ageing genes, will provide targets for future interventions to slow the ageing process and retard the onset of age-associated pathologies.

Lifespan Extension in Caenorhabditis Elegans by Complete Removal of Food

Aging Cell. Dec, 2006  |  Pubmed ID: 17081160

A partial reduction in food intake has been found to increase lifespan in many different organisms. We report here a new dietary restriction regimen in the nematode Caenorhabditis elegans, based on the standard agar plate lifespan assay, in which adult worms are maintained in the absence of a bacterial food source. These findings represent the first report in any organism of lifespan extension in response to prolonged starvation. Removal of bacterial food increases lifespan to a greater extent than partial reduction of food through a mechanism that is distinct from insulin/IGF-like signaling and the Sir2-family deacetylase, SIR-2.1. Removal of bacterial food also increases lifespan when initiated in postreproductive adults, suggesting that dietary restriction started during middle age can result in a substantial longevity benefit that is independent of reproduction.

Medicine: Grapes Versus Gluttony

Nature. Nov, 2006  |  Pubmed ID: 17086197

Sirtuin-independent Effects of Nicotinamide on Lifespan Extension from Calorie Restriction in Yeast

Aging Cell. Dec, 2006  |  Pubmed ID: 17129213

Two models have been proposed for how calorie restriction (CR) enhances replicative longevity in yeast: (i) suppression of rDNA recombination through activation of the sirtuin protein deacetylase Sir2 or (ii) decreased activity of the nutrient-responsive kinases Sch9 and TOR. We report here that CR increases lifespan independently of all Sir2-family proteins in yeast. Furthermore, we demonstrate that nicotinamide, an inhibitor of Sir2-mediated deacetylation, interferes with lifespan extension from CR, but does so independent of Sir2, Hst1, Hst2, and Hst4. We also find that 5 mm nicotinamide, a concentration sufficient to inhibit other sirtuins, does not phenocopy deletion of HST3. Thus, we propose that lifespan extension by CR is independent of sirtuins and that nicotinamide has sirtuin-independent effects on lifespan extension by CR.

The Sensitivity of Yeast Mutants to Oleic Acid Implicates the Peroxisome and Other Processes in Membrane Function

Genetics. Jan, 2007  |  Pubmed ID: 17151231

The peroxisome, sole site of beta-oxidation in Saccharomyces cerevisiae, is known to be required for optimal growth in the presence of fatty acid. Screening of the haploid yeast deletion collection identified approximately 130 genes, 23 encoding peroxisomal proteins, necessary for normal growth on oleic acid. Oleate slightly enhances growth of wild-type yeast and inhibits growth of all strains identified by the screen. Nonperoxisomal processes, among them chromatin modification by H2AZ, Pol II mediator function, and cell-wall-associated activities, also prevent oleate toxicity. The most oleate-inhibited strains lack Sap190, a putative adaptor for the PP2A-type protein phosphatase Sit4 (which is also required for normal growth on oleate) and Ilm1, a protein of unknown function. Palmitoleate, the other main unsaturated fatty acid of Saccharomyces, fails to inhibit growth of the sap190delta, sit4delta, and ilm1delta strains. Data that suggest that oleate inhibition of the growth of a peroxisomal mutant is due to an increase in plasma membrane porosity are presented. We propose that yeast deficient in peroxisomal and other functions are sensitive to oleate perhaps because of an inability to effectively control the fatty acid composition of membrane phospholipids.

Sir2 and Calorie Restriction in Yeast: a Skeptical Perspective

Ageing Research Reviews. Aug, 2007  |  Pubmed ID: 17512264

Activation of Sir2-family proteins in response to calorie restriction (CR) has been proposed as an evolutionarily conserved mechanism for life span extension. This idea has been called into question with the discovery that Sir2-family proteins are not required for life span extension from CR in yeast. We present here a historical perspective and critical evaluation of the model that CR acts through Sir2 in yeast, and interpret prior reports in light of more recent discoveries. Several specific cases where the Sir2 model of CR is inconsistent with experimental data are noted. These shortcomings must be considered along with evidence supporting a role for Sir2 in CR in order to fully evaluate the validity of this model.

Recent Developments in Yeast Aging

PLoS Genetics. May, 2007  |  Pubmed ID: 17530929

In the last decade, research into the molecular determinants of aging has progressed rapidly and much of this progress can be attributed to studies in invertebrate eukaryotic model organisms. Of these, single-celled yeast is the least complicated and most amenable to genetic and molecular manipulations. Supporting the use of this organism for aging research, increasing evidence has accumulated that a subset of pathways influencing longevity in yeast are conserved in other eukaryotes, including mammals. Here we briefly outline aging in yeast and describe recent findings that continue to keep this "simple" eukaryote at the forefront of aging research.

Does Resveratrol Activate Yeast Sir2 in Vivo?

Aging Cell. Aug, 2007  |  Pubmed ID: 17635418

Molecular Basis of Ageing

EMBO Reports. Oct, 2007  |  Pubmed ID: 17823613

Protein Translation, 2007

Aging Cell. Dec, 2007  |  Pubmed ID: 17941970

Translation of RNA to protein is essential for life. It should perhaps not be surprising, therefore, that appropriate regulation of translation plays a key role in determining longevity. This Hot Topic article discusses papers published in the last year related to the importance of translation and its regulation by signaling through the target of rapamycin kinase, in modulating aging and age-associated diseases.

Genome-wide Identification of Conserved Longevity Genes in Yeast and Worms

Mechanisms of Ageing and Development. Jan, 2007  |  Pubmed ID: 17126379

Technological advancements in invertebrate model organisms have recently made it possible to survey many or all of the genes in the genome for phenotypes of interest. In both C. elegans and S. cerevisiae, genome-wide searches for hypomorphic mutations that extend life span have been performed. The results from these screens are starting to provide a more complete view of the range of life span determinants in eukaryotes. In addition, it is becoming possible to test the premise that conserved aging genes and pathways regulate aging in disparate eukaryotic species. Here we compare and contrast the results from genome-wide aging screens and assess the likelihood that there are "public" aging mechanisms.

Longevity Genomics Across Species

Current Genomics. Apr, 2007  |  Pubmed ID: 18660849

Unbiased genome-wide studies of longevity in S. cerevisiae and C. elegans have led to the identification of more than one hundred genes that determine life span in one or both organisms. Key pathways have been uncovered linking nutrient and growth factor cues to longevity. Quantitative measures of the degree to which aging is evolutionary conserved are now possible. A major challenge for the future is determining which of these genes play a similar role in human aging and using that information to develop therapies toward age-associated diseases.

Cell Biology: A Molecular Age Barrier

Nature. Aug, 2008  |  Pubmed ID: 18685697

Protein Translation, 2008

Aging Cell. Dec, 2008  |  Pubmed ID: 18782345

The important role that regulation of protein translation plays in determining longevity in invertebrate organisms became widely appreciated in 2007, with the publication of several papers discussed in last year's review. During 2008, several studies have further strengthened the idea that regulation of translation is one component of a highly evolutionarily conserved pathway that modifies longevity. Importantly, studies published this year also began to provide insights into specific mechanisms by which altered mRNA translation does (and in some cases does not) slow aging in invertebrate model organisms.

Shortest-path Network Analysis is a Useful Approach Toward Identifying Genetic Determinants of Longevity

PloS One. 2008  |  Pubmed ID: 19030232

Identification of genes that modulate longevity is a major focus of aging-related research and an area of intense public interest. In addition to facilitating an improved understanding of the basic mechanisms of aging, such genes represent potential targets for therapeutic intervention in multiple age-associated diseases, including cancer, heart disease, diabetes, and neurodegenerative disorders. To date, however, targeted efforts at identifying longevity-associated genes have been limited by a lack of predictive power, and useful algorithms for candidate gene-identification have also been lacking.

Single-gene Deletions That Restore Mating Competence to Diploid Yeast

FEMS Yeast Research. Mar, 2008  |  Pubmed ID: 17995956

Using the Saccharomyces cerevisiae MATa/MATalpha ORF deletion collection, homozygous deletion strains were identified that undergo mating with MATa or MATalpha haploids. Seven homozygous deletions were identified that confer enhanced mating. Three of these, lacking CTF8, CTF18, and DCC1, mate at a low frequency with either MATa or MATalpha haploids. The products of these genes form a complex involved in sister chromatid cohesion. Each of these strains also exhibits increased chromosome loss rates, and mating likely occurs due to loss of one copy of chromosome III, which bears the MAT locus. Three other homozygous diploid deletion strains, ylr193cDelta/ylr193cDelta, yor305wDelta/yor305wDelta, and ypr170cDelta/ypr170cDelta, mate at very low frequencies with haploids of either or both mating types. However, an ist3Delta/ist3Delta strain mates only with MATa haploids. It is shown that IST3, previously linked to splicing, is required for efficient processing of the MATa1 message, particularly the first intron. As a result, the ist3Delta/ist3Delta strain expresses unbalanced ratios of Matalpha to Mata proteins and therefore mates with MATa haploids. Accordingly, mating in this diploid can be repressed by introduction of a MATa1 cDNA. In summary, this study underscores and elaborates upon predicted pathways by which mutations restore mating function to yeast diploids and identifies new mutants warranting further study.

Dietary Restriction by Bacterial Deprivation Increases Life Span in Wild-derived Nematodes

Experimental Gerontology. Mar, 2008  |  Pubmed ID: 18083317

Dietary restriction is known to promote longevity in a variety of eukaryotic organisms. Most studies of dietary restriction have been performed on animals bred for many generations under conditions that differ substantially from their natural environment, raising the possibility that some apparent beneficial effects of dietary restriction are due to adaptation to laboratory conditions. To address this question in an invertebrate model, we determined the effect of dietary restriction by bacterial deprivation on life span in five different wild-derived Caenorhabditis elegans strains and two strains of the related species Caenorhabditis remanei. Longevity was enhanced in each of the wild-derived C. elegans strains, in most cases to a degree similar to that observed in N2, the standard laboratory strain. Both strains of C. remanei were substantially longer lived any of the C. elegans isolates, produced larger brood sizes, and retained the ability to produce offspring for a longer period of time. Dietary restriction failed to increase mean life span in one C. remanei isolate, but significantly increased the maximum life span of both C. remanei strains. Thus, we find no evidence that adaptation to laboratory conditions has significantly altered the aging process in C. elegans under either standard or food-restricted conditions.

A Method for High-throughput Quantitative Analysis of Yeast Chronological Life Span

The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. Feb, 2008  |  Pubmed ID: 18314444

Chronological aging in yeast has been studied by maintaining cells in a quiescent-like stationary phase culture and monitoring cell survival over time. The composition of the growth medium can have a profound influence on chronological aging. For example, dietary restriction accomplished by lowering the glucose concentration of the medium significantly increases life span. Here we report a novel high-throughput method for measuring yeast chronological life span by monitoring outgrowth of aging cells using a Bioscreen C MBR machine. We show that this method provides survival data comparable to traditional methods, but with decreased variability. In addition to reducing the glucose concentration, we find that elevated amino acid levels or increased osmolarity of the growth medium is sufficient to increase chronological life span. We also report that life-span extension from dietary restriction does not require any of the five yeast sirtuins (Sir2, Hst1, Hst2, Hst3, or Hst4) either alone or in combination.

Dietary Restriction Suppresses Proteotoxicity and Enhances Longevity by an Hsf-1-dependent Mechanism in Caenorhabditis Elegans

Aging Cell. Jun, 2008  |  Pubmed ID: 18331616

Dietary restriction increases lifespan and slows the onset of age-associated disease in organisms from yeast to mammals. In humans, several age-related diseases are associated with aberrant protein folding or aggregation, including neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. We report here that dietary restriction dramatically suppresses age-associated paralysis in three nematode models of proteotoxicity. Similar to its longevity-enhancing properties, dietary restriction protects against proteotoxicity by a mechanism distinct from reduced insulin/IGF-1-like signaling. Instead, the heat shock transcription factor, hsf-1, is required for enhanced thermotolerance, suppression of proteotoxicity, and lifespan extension by dietary restriction. These findings demonstrate that dietary restriction confers a general protective effect against proteotoxicity and promotes longevity by a mechanism involving hsf-1.

Quantitative Evidence for Conserved Longevity Pathways Between Divergent Eukaryotic Species

Genome Research. Apr, 2008  |  Pubmed ID: 18340043

Studies in invertebrate model organisms have been a driving force in aging research, leading to the identification of many genes that influence life span. Few of these genes have been examined in the context of mammalian aging, however, and it remains an open question as to whether and to what extent the pathways that modulate longevity are conserved across different eukaryotic species. Using a comparative functional genomics approach, we have performed the first quantitative analysis of the degree to which longevity genes are conserved between two highly divergent eukaryotic species, the yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans. Here, we report the replicative life span phenotypes for single-gene deletions of the yeast orthologs of worm aging genes. We find that 15% of these yeast deletions are long-lived. In contrast, only 3.4% of a random set of deletion mutants are long-lived-a statistically significant difference. These data suggest that genes that modulate aging have been conserved not only in sequence, but also in function, over a billion years of evolution. Among the longevity determining ortholog pairs, we note a substantial enrichment for genes involved in an evolutionarily conserved pathway linking nutrient sensing and protein translation. In addition, we have identified several conserved aging genes that may represent novel longevity pathways. Together, these findings indicate that the genetic component of life span determination is significantly conserved between divergent eukaryotic species, and suggest pathways that are likely to play a similar role in mammalian aging.

Yeast Life Span Extension by Depletion of 60s Ribosomal Subunits is Mediated by Gcn4

Cell. Apr, 2008  |  Pubmed ID: 18423200

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.

The Biological Sciences Section Program at the 60th Annual Meeting of the Gerontological Society of America

The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. Apr, 2008  |  Pubmed ID: 18426956

In this era of genomics and other exciting technical advances, research on the biology of aging is undergoing a renaissance. This report summarizes 10 cutting-edge areas of research covered in symposia that spanned such topics as stem cells, novel vaccine strategies, nutritional sensing, new concepts of Parkinson's disease, high throughput screening for aging interventions, manipulating telomerase in cancer and immunodeficiency, synergy between aging and HIV disease, and epigenetic influences on aging. Novel animal models, including those showing no evidence of aging, as well as ethical and political implications of embryonic stem cells and alternative medicine are also discussed.

Age- and Calorie-independent Life Span Extension from Dietary Restriction by Bacterial Deprivation in Caenorhabditis Elegans

BMC Developmental Biology. 2008  |  Pubmed ID: 18457595

Dietary restriction (DR) increases life span and delays age-associated disease in many organisms. The mechanism by which DR enhances longevity is not well understood.

The Ongoing Saga of Sirtuins and Aging

Cell Metabolism. Jul, 2008  |  Pubmed ID: 18590685

Sirtuins are known to slow aging in simple eukaryotes; however, viewing mammalian sirtuins as antiaging proteins may be overly simplistic. In this issue of Cell Metabolism, Li et al. (2008) provide evidence that SirT1 has properties consistent with both pro- and antiaging functions in mice.

A Molecular Mechanism of Chronological Aging in Yeast

Cell Cycle (Georgetown, Tex.). Apr, 2009  |  Pubmed ID: 19305133

The molecular mechanisms that cause organismal aging are a topic of intense scrutiny and debate. Dietary restriction extends the life span of many organisms, including yeast, and efforts are underway to understand the biochemical and genetic pathways that regulate this life span extension in model organisms. Here we describe the mechanism by which dietary restriction extends yeast chronological life span, defined as the length of time stationary yeast cells remain viable in a quiescent state. We find that aging under standard culture conditions is the result of a cell-extrinsic component that is linked to the pH of the culture medium. We identify acetic acid as a cell-extrinsic mediator of cell death during chronological aging, and demonstrate that dietary restriction, growth in a non-fermentable carbon source, or transferring cells to water increases chronological life span by reducing or eliminating extracellular acetic acid. Other life span extending environmental and genetic interventions, such as growth in high osmolarity media, deletion of SCH9 or RAS2, increase cellular resistance to acetic acid. We conclude that acetic acid induced mortality is the primary mechanism of chronological aging in yeast under standard conditions.

Proteasomal Regulation of the Hypoxic Response Modulates Aging in C. Elegans

Science (New York, N.Y.). May, 2009  |  Pubmed ID: 19372390

The Caenorhabditis elegans von Hippel-Lindau tumor suppressor homolog VHL-1 is a cullin E3 ubiquitin ligase that negatively regulates the hypoxic response by promoting ubiquitination and degradation of the hypoxic response transcription factor HIF-1. Here, we report that loss of VHL-1 significantly increased life span and enhanced resistance to polyglutamine and beta-amyloid toxicity. Deletion of HIF-1 was epistatic to VHL-1, indicating that HIF-1 acts downstream of VHL-1 to modulate aging and proteotoxicity. VHL-1 and HIF-1 control longevity by a mechanism distinct from both dietary restriction and insulin-like signaling. These findings define VHL-1 and the hypoxic response as an alternative longevity and protein homeostasis pathway.

Histone H4 Lysine 16 Acetylation Regulates Cellular Lifespan

Nature. Jun, 2009  |  Pubmed ID: 19516333

Cells undergoing developmental processes are characterized by persistent non-genetic alterations in chromatin, termed epigenetic changes, represented by distinct patterns of DNA methylation and histone post-translational modifications. Sirtuins, a group of conserved NAD(+)-dependent deacetylases or ADP-ribosyltransferases, promote longevity in diverse organisms; however, their molecular mechanisms in ageing regulation remain poorly understood. Yeast Sir2, the first member of the family to be found, establishes and maintains chromatin silencing by removing histone H4 lysine 16 acetylation and bringing in other silencing proteins. Here we report an age-associated decrease in Sir2 protein abundance accompanied by an increase in H4 lysine 16 acetylation and loss of histones at specific subtelomeric regions in replicatively old yeast cells, which results in compromised transcriptional silencing at these loci. Antagonizing activities of Sir2 and Sas2, a histone acetyltransferase, regulate the replicative lifespan through histone H4 lysine 16 at subtelomeric regions. This pathway, distinct from existing ageing models for yeast, may represent an evolutionarily conserved function of sirtuins in regulation of replicative ageing by maintenance of intact telomeric chromatin.

A Genomic Approach to Yeast Chronological Aging

Methods in Molecular Biology (Clifton, N.J.). 2009  |  Pubmed ID: 19521821

Yeast is a useful model organism to study the genetic and biochemical mechanisms of aging. Genomic studies of aging in yeast have been limited, however, by traditional methodologies that require a large investment of labor and resources. In this chapter, we describe a newly-developed method for quantitatively measuring the chronological life span of each strain contained in the yeast ORF deletion collection. Our approach involves determining population survival by monitoring outgrowth kinetics using a Bioscreen C MBR shaker/incubator/plate reader. This method has accuracy comparable to traditional assays, while allowing for higher throughput and decreased variability in measurement.

The TOR Pathway Comes of Age

Biochimica Et Biophysica Acta. Oct, 2009  |  Pubmed ID: 19539012

Studies in a variety of model organisms indicate that nutrient signaling is tightly coupled to longevity. In nutrient replete conditions, organisms develop, grow, and age quickly. When nutrients become sparse as with dietary restriction, growth and development decline, stress response pathways become induced and organisms live longer. Considerable effort has been devoted to understanding the molecular events mediating lifespan extension by dietary restriction. One central focus has been on nutrient-responsive signal transduction pathways including insulin/IGF-1, AMP kinase, protein kinase A and the TOR pathway. Here we describe the increasingly prominent links between TOR signaling and aging in invertebrates. Longevity studies in mammals are not published to date. Instead, we highlight studies in mouse models, which indicate that dampening the TOR pathway leads to widespread protection from an array of age-related diseases.

Ageing: A Midlife Longevity Drug?

Nature. Jul, 2009  |  Pubmed ID: 19606132

The Hypoxic Response and Aging

Cell Cycle (Georgetown, Tex.). Aug, 2009  |  Pubmed ID: 19633411

Hot Topics in Aging Research: Protein Translation, 2009

Aging Cell. Dec, 2009  |  Pubmed ID: 19747234

In the last few years, links between regulation of mRNA translation and aging have been firmly established in invertebrate model organisms. This year, a possible relationship between mRNA translation and aging in mammals has been established with the report that rapamycin increases lifespan in mice. Other significant findings have connected translation control with other known longevity pathways and provided fodder for mechanistic hypotheses. Here, we summarize advances in this emerging field and raise questions for future studies.

Attenuation of Age-related Metabolic Dysfunction in Mice with a Targeted Disruption of the Cbeta Subunit of Protein Kinase A

The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. Dec, 2009  |  Pubmed ID: 19776218

The cyclic adenosine monophosphate-dependent protein kinase A (PKA) pathway helps regulate both cell growth and division, and triglyceride storage and metabolism in response to nutrient status. Studies in yeast show that disruption of this pathway promotes longevity in a manner similar to caloric restriction. Because PKA is highly conserved, it can be studied in mammalian systems. This report describes the metabolic phenotype of mice lacking the PKA catalytic subunit Cbeta. We confirmed that Cbeta has high levels of expression in the brain but also showed moderate levels in liver. Cbeta-null animals had reduced basal PKA activity while appearing overtly normal when fed standard rodent chow. However, the absence of Cbeta protected mice from diet-induced obesity, steatosis, dyslipoproteinemia, and insulin resistance, without any differences in caloric intake or locomotor activity. These findings have relevant pharmacological implications because aging in mammals is characterized by metabolic decline associated with obesity, altered body fat distribution, and insulin resistance.

Cell Signaling. Aging is RSKy Business

Science (New York, N.Y.). Oct, 2009  |  Pubmed ID: 19797648

Spermidine Surprise for a Long Life

Nature Cell Biology. Nov, 2009  |  Pubmed ID: 19884883

Resveratrol and Rapamycin: Are They Anti-aging Drugs?

BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology. Feb, 2010  |  Pubmed ID: 20091754

Studies of the basic biology of aging have advanced to the point where anti-aging interventions, identified from experiments in model organisms, are beginning to be tested in people. Resveratrol and rapamycin, two compounds that target conserved longevity pathways and may mimic some aspects of dietary restriction, represent the first such interventions. Both compounds have been reported to slow aging in yeast and invertebrate species, and rapamycin has also recently been found to increase life span in rodents. In addition, both compounds also show impressive effects in rodent models of age-associated diseases. Clinical trials are underway to assess whether resveratrol is useful as an anti-cancer treatment, and rapamycin is already approved for use in human patients. Compounds such as these, identified from longevity studies in model organisms, hold great promise as therapies to target multiple age-related diseases by modulating the molecular causes of aging.

YODA: Software to Facilitate High-throughput Analysis of Chronological Life Span, Growth Rate, and Survival in Budding Yeast

BMC Bioinformatics. 2010  |  Pubmed ID: 20298554

The budding yeast Saccharomyces cerevisiae is one of the most widely studied model organisms in aging-related science. Although several genetic modifiers of yeast longevity have been identified, the utility of this system for longevity studies has been limited by a lack of high-throughput assays for quantitatively measuring survival of individual yeast cells during aging.

Lessons on Longevity from Budding Yeast

Nature. Mar, 2010  |  Pubmed ID: 20336133

The past decade has seen fundamental advances in our understanding of the ageing process and raised optimism that interventions to slow ageing may be on the horizon. Studies of budding yeast have made immense contributions to this progress. Yeast longevity factors have now been shown to modulate ageing in invertebrate and mammalian models, and studies of yeast have resulted in some of the best candidates for anti-ageing drugs currently in development. The first interventions to slow human ageing may spring from the humble yeast.

A Role for SIRT1 in the Hypoxic Response

Molecular Cell. Jun, 2010  |  Pubmed ID: 20620950

In this issue of Molecular Cell, Lim et al. (2010) show that SIRT1 deacetylates HIF-1alpha and regulates its ability to respond to hypoxia, revealing yet another important function of SIRT1 and suggesting a connection between HIF function in aging and sirtuin enzymes.

The Hypoxia-inducible Factor HIF-1 Functions As Both a Positive and Negative Modulator of Aging

Biological Chemistry. Oct, 2010  |  Pubmed ID: 20707608

In the past year and a half, five studies have independently established a direct connection between the hypoxic response transcription factor, HIF-1, and aging in Caenorhabditis elegans. These studies demonstrated that HIF-1 can both promote and limit longevity via pathways that are mechanistically distinct. Here, we review the current state of knowledge regarding modulation of aging by HIF-1 and speculate on potential aspects of HIF-1 function that could be relevant for mammalian longevity and healthspan.

Regulation of MRNA Translation As a Conserved Mechanism of Longevity Control

Advances in Experimental Medicine and Biology. 2010  |  Pubmed ID: 20886753

Appropriate regulation of mRNA translation is essential for growth and survival and the pathways that regulate mRNA translation have been highly conserved throughout eukaryotic evolution. Translation is controlled by a complex set of mechanisms acting at multiple levels, ranging from global protein synthesis to individual mRNAs. Recently, several mutations that perturb regulation of mRNA translation have also been found to increase longevity in three model organisms: the buddingyeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. Many of these translation control factors can be mapped to a single pathway downstream of the nutrient responsive target of rapamycin (TOR) kinase. In this chapter, we will review the data suggesting that mRNA translation is an evolutionarily conserved modifier of longevity and discuss potential mechanisms by which mRNA translation could influence aging and age-associated disease in different species.

Restoration of Senescent Human Diploid Fibroblasts by Modulation of the Extracellular Matrix

Aging Cell. Feb, 2011  |  Pubmed ID: 21108727

Human diploid fibroblasts have the capacity to complete a finite number of cell divisions before entering a state of replicative senescence characterized by growth arrest, changes in morphology, and altered gene expression. Herein, we report that interaction with extracellular matrix (ECM) from young cells is sufficient to restore aged, senescent cells to an apparently youthful state. The identity of the restored cells as having been derived from senescent cells has been confirmed by a variety of methods, including time lapse live cell imaging and DNA finger print analysis. In addition to cell morphology, phenotypic restoration was assessed by resumption of proliferative potential, growth factor responsiveness, reduction of intracellular reactive oxygen species levels, recovery of mitochondrial membrane potential, and increased telomere length. Mechanistically, we find that both Ku and SIRT1 are induced during restoration and are required for senescent cells to return to a youthful phenotype. These observations demonstrate that human cellular senescence is profoundly influenced by cues from the ECM, and that senescent cell plasticity is much greater than that was previously believed to be the case.

Hot Topics in Aging Research: Protein Translation and TOR Signaling, 2010

Aging Cell. Apr, 2011  |  Pubmed ID: 21176090

In this, the fourth installment of our annual Hot Topics review on mRNA translation and aging, we have decided to expand our scope to include recent findings related to the role of TOR signaling in aging. As new data emerge, it is clear that TOR signaling acts upstream of mRNA translation, as well as a variety of other cellular processes, to modulate longevity and healthspan in evolutionarily diverse species. This Hot Topics review will cover important new findings in this area that have occurred over the past year. These include the demonstration that the TOR substrate ribosomal S6 kinase modulates longevity in mammals, the potential for TOR inhibitors as therapeutic treatments for Alzheimer's disease, and further studies emphasizing the importance of differential translation of specific mRNAs for healthy aging and enhanced longevity.

Quantitative Evidence for Early Life Fitness Defects from 32 Longevity-associated Alleles in Yeast

Cell Cycle (Georgetown, Tex.). Jan, 2011  |  Pubmed ID: 21191185

Reduced fecundity has been associated with some alleles that enhance longevity in invertebrate and mammalian models. This observation has been suggested to support the antagonistic pleiotropy theory of aging, which predicts that alleles of some genes promoting fitness early in life have detrimental effects later in life that limit survival. In only a few cases, however, has the relative fitness of long-lived mutants been quantified through direct competition with the wild type genotype. Here we report the first comprehensive analysis of longevity/fitness trade-offs by measuring the relative fitness of 49 long-lived yeast variants in a direct competition assay with wild type cells. We find that 32 (65%) of these variants show a significant defect in fitness in this competition assay. In 26 (81%) of these cases, this reduction in fitness can be partially accounted for by reduced maximal growth rate during early life, usually resulting from a G0/G1-specific cell cycle defect. A majority of the less fit longevity-enhancing variants are associated with reduced mRNA translation. These findings are therefore consistent with the idea that enhanced longevity often comes with a fitness cost and suggest that this cost is often associated with variation in a subset of longevity factors, such as those regulating mRNA translation, growth, and reproduction.

HIF-1 Modulates Longevity and Healthspan in a Temperature-dependent Manner

Aging Cell. Apr, 2011  |  Pubmed ID: 21241450

The hypoxia-inducible factor HIF-1 has recently been identified as an important modifier of longevity in the roundworm Caenorhabditis elegans. Studies have reported that HIF-1 can function as both a positive and negative regulator of life span, and several disparate models have been proposed for the role of HIF in aging. Here, we resolve many of the apparent discrepancies between these studies. We find that stabilization of HIF-1 increases life span robustly under all conditions tested; however, deletion of hif-1 increases life span in a temperature-dependent manner. Animals lacking HIF-1 are long lived at 25°C but not at 15°C. We further report that deletion or RNAi knockdown of hif-1 impairs healthspan at lower temperatures because of an age-dependent loss of vulval integrity. Deletion of hif-1 extends life span modestly at 20°C when animals displaying the vulval integrity defect are censored from the experimental data, but fails to extend life span if these animals are included. Knockdown of hif-1 results in nuclear relocalization of the FOXO transcription factor DAF-16, and DAF-16 is required for life span extension from deletion of hif-1 at all temperatures regardless of censoring.

A Genomic Analysis of Chronological Longevity Factors in Budding Yeast

Cell Cycle (Georgetown, Tex.). May, 2011  |  Pubmed ID: 21447998

Chronological life span (CLS) has been studied as an aging paradigm in yeast. A few conserved aging genes have been identified that modulate both chronological and replicative longevity in yeast as well as longevity in the nematode Caenorhabditis elegans; however, a comprehensive analysis of the relationship between genetic control of chronological longevity and aging in other model systems has yet to be reported. To address this question, we performed a functional genomic analysis of chronological longevity for 550 single-gene deletion strains, which accounts for approximately 12% of the viable homozygous diploid deletion strains in the yeast ORF deletion collection. This study identified 33 previously unknown determinants of CLS. We found no significant enrichment for enhanced CLS among deletions corresponding to yeast orthologs of worm aging genes or among replicatively long-lived deletion strains, although a trend toward overlap was noted. In contrast, a subset of gene deletions identified from a screen for reduced acidification of culture media during growth to stationary phase was enriched for increased CLS. These results suggest that genetic control of CLS under the most commonly utilized assay conditions does not strongly overlap with longevity determinants in C. elegans, with the existing confined to a small number of genetic pathways. These data also further support the model that acidification of the culture medium plays an important role in survival during chronological aging in synthetic medium, and suggest that chronological aging studies using alternate medium conditions may be more informative with regard to aging of multicellular eukaryotes.

Trinations Aging Symposium

Mechanisms of Ageing and Development. Jun-Jul, 2011  |  Pubmed ID: 21771608

The "Trinations Aging Symposium" was held on the campus of Guangdong Medical College in Dongguan, China from April 28 to 30, 2011. The goal was to promote interaction, collaboration, and exchange of ideas between scientists in the field of aging research from Japan, South Korea, and China. Aging research is on the rise in Asia. This represents an important development, since Korea and Japan are the two longest-lived countries in the world, and life expectancy is increasing rapidly in China and other Asian countries. The world will see a greater percentage of people over age 65 in coming years than any period in human history. Developing therapeutic approaches to increase healthspan has the potential not only to enhance quality of life, but would also help stem the looming economic crisis associated with a high percentage of elderly. The focus of the Trinations Aging Symposium was on the basic biology of aging, and topics discussed included genome maintenance, metabolism and aging, longevity genes and interventions, and new therapies for age-related diseases. The meeting finished with a commitment for another symposium next year that will include additional Asian countries and the formation of a new scientific organization, the Asian Association for Aging Research.

Sir2 Deletion Prevents Lifespan Extension in 32 Long-lived Mutants

Aging Cell. Dec, 2011  |  Pubmed ID: 21902802

Activation of Sir2 orthologs is proposed to increase lifespan downstream of dietary restriction. Here, we describe an examination of the effect of 32 different lifespan-extending mutations and four methods of DR on replicative lifespan (RLS) in the short-lived sir2Δ yeast strain. In every case, deletion of SIR2 prevented RLS extension; however, RLS extension was restored when both SIR2 and FOB1 were deleted in several cases, demonstrating that SIR2 is not directly required for RLS extension. These findings indicate that suppression of the sir2Δ lifespan defect is a rare phenotype among longevity interventions and suggest that sir2Δ cells senesce rapidly by a mechanism distinct from that of wild-type cells. They also demonstrate that failure to observe lifespan extension in a short-lived background, such as cells or animals lacking sirtuins, should be interpreted with caution.

Elevated Proteasome Capacity Extends Replicative Lifespan in Saccharomyces Cerevisiae

PLoS Genetics. Sep, 2011  |  Pubmed ID: 21931558

Aging is characterized by the accumulation of damaged cellular macromolecules caused by declining repair and elimination pathways. An integral component employed by cells to counter toxic protein aggregates is the conserved ubiquitin/proteasome system (UPS). Previous studies have described an age-dependent decline of proteasomal function and increased longevity correlates with sustained proteasome capacity in centenarians and in naked mole rats, a long-lived rodent. Proof for a direct impact of enhanced proteasome function on longevity, however, is still lacking. To determine the importance of proteasome function in yeast aging, we established a method to modulate UPS capacity by manipulating levels of the UPS-related transcription factor Rpn4. While cells lacking RPN4 exhibit a decreased non-adaptable proteasome pool, loss of UBR2, an ubiquitin ligase that regulates Rpn4 turnover, results in elevated Rpn4 levels, which upregulates UPS components. Increased UPS capacity significantly enhances replicative lifespan (RLS) and resistance to proteotoxic stress, while reduced UPS capacity has opposing consequences. Despite tight transcriptional co-regulation of the UPS and oxidative detoxification systems, the impact of proteasome capacity on lifespan is independent of the latter, since elimination of Yap1, a key regulator of the oxidative stress response, does not affect lifespan extension of cells with higher proteasome capacity. Moreover, since elevated proteasome capacity results in improved clearance of toxic huntingtin fragments in a yeast model for neurodegenerative diseases, we speculate that the observed lifespan extension originates from prolonged elimination of damaged proteins in old mother cells. Epistasis analyses indicate that proteasome-mediated modulation of lifespan is at least partially distinct from dietary restriction, Tor1, and Sir2. These findings demonstrate that UPS capacity determines yeast RLS by a mechanism that is distinct from known longevity pathways and raise the possibility that interventions to promote enhanced proteasome function will have beneficial effects on longevity and age-related disease in humans.

Absence of Effects of Sir2 Overexpression on Lifespan in C. Elegans and Drosophila

Nature. Sep, 2011  |  Pubmed ID: 21938067

Overexpression of sirtuins (NAD(+)-dependent protein deacetylases) has been reported to increase lifespan in budding yeast (Saccharomyces cerevisiae), Caenorhabditis elegans and Drosophila melanogaster. Studies of the effects of genes on ageing are vulnerable to confounding effects of genetic background. Here we re-examined the reported effects of sirtuin overexpression on ageing and found that standardization of genetic background and the use of appropriate controls abolished the apparent effects in both C. elegans and Drosophila. In C. elegans, outcrossing of a line with high-level sir-2.1 overexpression abrogated the longevity increase, but did not abrogate sir-2.1 overexpression. Instead, longevity co-segregated with a second-site mutation affecting sensory neurons. Outcrossing of a line with low-copy-number sir-2.1 overexpression also abrogated longevity. A Drosophila strain with ubiquitous overexpression of dSir2 using the UAS-GAL4 system was long-lived relative to wild-type controls, as previously reported, but was not long-lived relative to the appropriate transgenic controls, and nor was a new line with stronger overexpression of dSir2. These findings underscore the importance of controlling for genetic background and for the mutagenic effects of transgene insertions in studies of genetic effects on lifespan. The life-extending effect of dietary restriction on ageing in Drosophila has also been reported to be dSir2 dependent. We found that dietary restriction increased fly lifespan independently of dSir2. Our findings do not rule out a role for sirtuins in determination of metazoan lifespan, but they do cast doubt on the robustness of the previously reported effects of sirtuins on lifespan in C. elegans and Drosophila.

Composition and Acidification of the Culture Medium Influences Chronological Aging Similarly in Vineyard and Laboratory Yeast

PloS One. 2011  |  Pubmed ID: 21949725

Chronological aging has been studied extensively in laboratory yeast by culturing cells into stationary phase in synthetic complete medium with 2% glucose as the carbon source. During this process, acidification of the culture medium occurs due to secretion of organic acids, including acetic acid, which limits survival of yeast cells. Dietary restriction or buffering the medium to pH 6 prevents acidification and increases chronological life span. Here we set out to determine whether these effects are specific to laboratory-derived yeast by testing the chronological aging properties of the vineyard yeast strain RM11. Similar to the laboratory strain BY4743 and its haploid derivatives, RM11 and its haploid derivatives displayed increased chronological life span from dietary restriction, buffering the pH of the culture medium, or aging in rich medium. RM11 and BY4743 also displayed generally similar aging and growth characteristics when cultured in a variety of different carbon sources. These data support the idea that mechanisms of chronological aging are similar in both the laboratory and vineyard strains.

The MDT-15 Subunit of Mediator Interacts with Dietary Restriction to Modulate Longevity and Fluoranthene Toxicity in Caenorhabditis Elegans

PloS One. 2011  |  Pubmed ID: 22132200

Dietary restriction (DR), the limitation of calorie intake while maintaining proper nutrition, has been found to extend life span and delay the onset of age-associated disease in a wide range of species. Previous studies have suggested that DR can reduce the lethality of environmental toxins. To further examine the role of DR in toxin response, we measured life spans of the nematode Caenorhabditis elegans treated with the mutagenic polyaromatic hydrocarbon, fluoranthene (FLA). FLA is a direct byproduct of combustion, and is one of U.S. Environmental Protection Agency's sixteen priority environmental toxins. Treatment with 5 µg/ml FLA shortened the life spans of ad libitum fed nematodes, and DR resulted in increased sensitivity to FLA. To determine the role of detoxifying enzymes in the toxicity of FLA, we tested nematodes with mutations in the gene encoding the MDT-15 subunit of mediator, a transcriptional coactivator that regulates genes involved in fatty acid metabolism and detoxification. Mutation of mdt-15 increased the life span of FLA treated animals compared to wild-type animals with no difference observed between DR and ad libitum fed mdt-15 animals. We also examined mutants with altered insulin-IGF-1-like signaling (IIS), which is known to modulate life span and stress resistance in C. elegans independently of DR. Mutation of the genes coding for the insulin-like receptor DAF-2 or the FOXO-family transcription factor DAF16 did not alter the animals' susceptibility to FLA compared to wild type. Taken together, our results suggest that certain compounds have increased toxicity when combined with a DR regimen through increased metabolic activation. This increased metabolic activation appears to be mediated through the MDT-15 transcription factor and is independent of the IIS pathway.

A New Chronological Survival Assay in Mammalian Cell Culture

Cell Cycle (Georgetown, Tex.). Jan, 2012  |  Pubmed ID: 22214665

Genome-wide Analysis of Yeast Aging

Sub-cellular Biochemistry. 2012  |  Pubmed ID: 22094426

In the past several decades the budding yeast Saccharomyces cerevisiae has emerged as a prominent model for aging research. The creation of a single-gene deletion collection covering the majority of open reading frames in the yeast genome and advances in genomic technologies have opened yeast research to genome-scale screens for a variety of phenotypes. A number of screens have been performed looking for genes that modify secondary age-associated phenotypes such as stress resistance or growth rate. More recently, moderate-throughput methods for measuring replicative life spanreplicative life span and high-throughput methods for measuring chronological life spanchronological life span have allowed for the first unbiased screens aimed at directly identifying genes involved in determining yeast longevity. In this chapter we discuss large-scale life span studies performed in yeast and their implications for research related to the basic biology of aging.