Autophagy and amino acid homeostasis are required for chronological longevity in Saccharomyces cerevisiae

Potassium restriction boosts vacuolar acidity and extends lifespan in yeast

Lysosome function is compromised during aging and in many disease states. Interventions that promote lysosomal activity and acidification are thus of prime interest as treatments for longevity and health. Intracellular pH can be controlled by the exchange of protons for inorganic ions, and in cells from microbes to man, when potassium is restricted in the growth medium, the cytoplasm becomes acidified. Here we use a yeast model to show that potassium limited-cells exhibit hallmarks of increased acidity in the vacuole, the analog of the lysosome, and live long by a mechanism that requires the vacuolar machinery. The emerging picture is one in which potassium restriction shores up vacuolar acidity and function, conferring health benefits early in life and extending viability into old age. Against the backdrop of well-studied protein and carbohydrate restrictions that extend lifespan and healthspan, our work establishes a novel pro-longevity paradigm of inorganic nutrient limitation.

Metabolic regulatory mechanisms and physiological roles of functional amino acids and their applications in yeast

In yeast, amino acid metabolism and its regulatory mechanisms vary under different growth environments by regulating anabolic and catabolic processes, including uptake and export, and the metabolic styles form a complicated but robust network. There is also crosstalk with various metabolic pathways, products and signal molecules. The elucidation of metabolic regulatory mechanisms and physiological roles is important fundamental research for understanding life phenomenon. In terms of industrial application, the control of amino acid composition and content is expected to contribute to an improvement in productivity, and to add to the value of fermented foods, alcoholic beverages, bioethanol, and other valuable compounds (proteins and amino acids, etc.). This review article mainly describes our research in constructing yeast strains with high functionality, focused on the metabolic regulatory mechanisms and physiological roles of "functional amino acids", such as l-proline, l-arginine, l-leucine, l-valine, l-cysteine, and l-methionine, found in yeast.

Autophagy and aging: Maintaining the proteome through exercise and caloric restriction

Accumulation of dysfunctional and damaged cellular proteins and organelles occurs during aging, resulting in a disruption of cellular homeostasis and progressive degeneration and increases the risk of cell death. Moderating the accrual of these defunct components is likely a key in the promotion of longevity. While exercise is known to promote healthy aging and mitigate age‐related pathologies, the molecular underpinnings of this phenomenon remain largely unclear. However, recent evidences suggest that exercise modulates the proteome. Similarly, caloric restriction (CR), a known promoter of lifespan, is understood to augment intracellular protein quality. Autophagy is an evolutionary conserved recycling pathway responsible for the degradation, then turnover of cellular proteins and organelles. This housekeeping system has been reliably linked to the aging process. Moreover, autophagic activity declines during aging. The target of rapamycin complex 1 (TORC1), a central kinase involved in protein translation, is a negative regulator of autophagy, and inhibition of TORC1 enhances lifespan. Inhibition of TORC1 may reduce the production of cellular proteins which may otherwise contribute to the deleterious accumulation observed in aging. TORC1 may also exert its effects in an autophagy‐dependent manner. Exercise and CR result in a concomitant downregulation of TORC1 activity and upregulation of autophagy in a number of tissues. Moreover, exercise‐induced TORC1 and autophagy signaling share common pathways with that of CR. Therefore, the longevity effects of exercise and CR may stem from the maintenance of the proteome by balancing the synthesis and recycling of intracellular proteins and thus may represent practical means to promote longevity.

Yeast at the Forefront of Research on Ageing and Age-Related Diseases

Ageing is a complex and multifactorial process driven by genetic, environmental and stochastic factors that lead to the progressive decline of biological systems. Mechanisms of ageing have been extensively investigated in various model organisms and systems generating fundamental advances. Notably, studies on yeast ageing models have made numerous and relevant contributions to the progress in the field. Different longevity factors and pathways identified in yeast have then been shown to regulate molecular ageing in invertebrate and mammalian models. Currently the best candidates for anti-ageing drugs such as spermidine and resveratrol or anti-ageing interventions such as caloric restriction were first identified and explored in yeast. Yeasts have also been instrumental as models to study the cellular and molecular effects of proteins associated with age-related diseases such as Parkinson's, Huntington's or Alzheimer's diseases. In this chapter, a review of the advances on ageing and age-related diseases research in yeast models will be made. Particular focus will be placed on key longevity factors, ageing hallmarks and interventions that slow ageing, both yeast-specific and those that seem to be conserved in multicellular organisms. Their impact on the pathogenesis of age-related diseases will be also discussed.

Regulation of metabolic health by essential dietary amino acids

Although the beneficial effects of calorie restriction (CR) on health and aging were first observed a century ago, the specific macronutrients and molecular processes that mediate the effect of CR have been heavily debated. Recently, it has become clear that dietary protein plays a key role in regulating both metabolic health and longevity, and that both the quantity and quality - the specific amino acid composition - of dietary protein mediates metabolic health. Here, we discuss recent findings in model organisms ranging from yeast to mice and humans regarding the influence of dietary protein as well as specific amino acids on metabolic health, and the physiological and molecular mechanisms which may mediate these effects. We then discuss recent findings which suggest that the restriction of specific dietary amino acids may be a potent therapy to treat or prevent metabolic syndrome. Finally, we discuss the potential for dietary restriction of specific amino acids - or pharmaceuticals which harness these same mechanisms - to promote healthy aging.

Mitochondrial Metabolism and Aging in Yeast

Mitochondrial functionality is one of the main factors involved in cell survival, and mitochondrial dysfunctions have been identified as an aging hallmark. In particular, the insurgence of mitochondrial dysfunctions is tightly connected to mitochondrial metabolism. During aging, both mitochondrial oxidative and biosynthetic metabolisms are progressively altered, with the development of malfunctions, in turn affecting mitochondrial functionality. In this context, the relation between mitochondrial pathways and aging is evolutionarily conserved from single-celled organisms, such as yeasts, to complex multicellular organisms, such as humans. Useful information has been provided by the yeast Saccharomyces cerevisiae, which is being increasingly acknowledged as a valuable model system to uncover mechanisms underlying cellular longevity in humans. On this basis, we review the impact of specific aspects of mitochondrial metabolism on aging supported by the contributions brought by numerous studies performed employing yeast. Initially, we will focus on the tricarboxylic acid cycle and oxidative phosphorylation, describing how their modulation has consequences on cellular longevity. Afterward, we will report information regarding the importance of nicotinamide adenine dinucleotide (NAD) metabolism during aging, highlighting its relation with mitochondrial functionality. The comprehension of these key points regarding mitochondrial metabolism and their physiological importance is an essential first step for the development of therapeutic interventions that point to increase life quality during aging, therefore promoting "healthy aging," as well as lifespan itself.

Low doses of DNA damaging agents extend Saccharomyces cerevisiae chronological lifespan by promoting entry into quiescence

A variety of mild stresses have been shown to extend lifespan in diverse species through hormesis, which is a beneficial response to a stress or toxin that would cause a negative response at a higher exposure. Whether particular stresses induce hormesis can vary with genotype for a given species, and the underlying mechanisms of lifespan extension are only partly understood in most cases. We show that low doses of the DNA damaging or replication stress agents hydroxyurea, methyl methanesulfonate, 4-nitroquinoline 1-oxide, or Zeocin (a phleomycin derivative) lengthened chronological lifespan in Saccharomyces cerevisiae if cells were exposed during growth, but not if they were exposed during stationary phase. Treatment with these agents did not change mitochondrial activity, increase resistance to acetic acid, ethanol, or heat stress, and three of four treatments did not increase resistance to hydrogen peroxide. Stationary phase yeast populations consist of both quiescent and nonquiescent cells, and all four treatments increased the proportion of quiescent cells. Several mutant strains with deletions in genes that influence quiescence prevented Zeocin treatment from extending lifespan and from increasing the proportion of quiescent stationary phase cells. These data indicate that mild DNA damage stress can extend lifespan by promoting quiescence in the absence of mitohormesis or improved general stress responses that have been frequently associated with improved longevity in other cases of hormesis. Further study of the underlying mechanism may yield new insights into quiescence regulation that will be relevant to healthy aging.

Natural variation of chronological aging in the Saccharomyces cerevisiae species reveals diet-dependent mechanisms of life span control

Aging is a complex trait of broad scientific interest, especially because of its intrinsic link with common human diseases. Pioneering work on aging-related mechanisms has been made in Saccharomyces cerevisiae, mainly through the use of deletion collections isogenic to the S288c reference strain. In this study, using a recently published high-throughput approach, we quantified chronological life span (CLS) within a collection of 58 natural strains across seven different conditions. We observed a broad aging variability suggesting the implication of diverse genetic and environmental factors in chronological aging control. Two major Quantitative Trait Loci (QTLs) were identified within a biparental population obtained by crossing two natural isolates with contrasting aging behavior. Detection of these QTLs was dependent upon the nature and concentration of the carbon sources available for growth. In the first QTL, the RIM15 gene was identified as major regulator of aging under low glucose condition, lending further support to the importance of nutrient-sensing pathways in longevity control under calorie restriction. In the second QTL, we could show that the SER1 gene, encoding a conserved aminotransferase of the serine synthesis pathway not previously linked to aging, is causally associated with CLS regulation, especially under high glucose condition. These findings hint toward a new mechanism of life span control involving a trade-off between serine synthesis and aging, most likely through modulation of acetate and trehalose metabolism. More generally it shows that genetic linkage studies across natural strains represent a promising strategy to further unravel the molecular basis of aging.

A Sake yeast strain deficient in producing the protein building block serine lives longer than other yeast strains, especially when exposed to high glucose. A team led by Carole Linster at the University of Luxembourg found a broad variability of lifespan when analyzing more than fifty Saccharomyces cerevisiae strains isolated from around the world. Combining hundreds of lifespan measurements with genotype data from a progeny obtained by crossing the long-lived Sake strain and a short-lived collection strain, they identified two genes playing a pivotal role in causing the contrasting aging behavior of the parents: RIM15, when glucose was limiting and SER1, when glucose was plenty. RIM15 is part of a signaling cascade also regulating aging in mammals; SER1 revealed that a blockage in serine synthesis reprograms metabolism to favor glucose storage and long life.

Autophagy and Longevity

Autophagy is an evolutionally conserved cytoplasmic degradation system in which varieties of materials are sequestered by a double membrane structure, autophagosome, and delivered to the lysosomes for the degradation. Due to the wide varieties of targets, autophagic activity is essential for cellular homeostasis. Recent genetic evidence indicates that autophagy has a crucial role in the regulation of animal lifespan. Basal level of autophagic activity is elevated in many longevity paradigms and the activity is required for lifespan extension. In most cases, genes involved in autophagy and lysosomal function are induced by several transcription factors including HLH-30/TFEB, PHA-4/FOXA and MML-1/Mondo in long-lived animals. Pharmacological treatments have been shown to extend lifespan through activation of autophagy, indicating autophagy could be a potential and promising target to modulate animal lifespan. Here we summarize recent progress regarding the role of autophagy in lifespan regulation.

Six plant extracts delay yeast chronological aging through different signaling pathways

Our recent study has revealed six plant extracts that slow yeast chronological aging more efficiently than any chemical compound yet described. The rate of aging in yeast is controlled by an evolutionarily conserved network of integrated signaling pathways and protein kinases. Here, we assessed how single-gene-deletion mutations eliminating each of these pathways and kinases affect the aging-delaying efficiencies of the six plant extracts. Our findings imply that these extracts slow aging in the following ways: 1) plant extract 4 decreases the efficiency with which the pro-aging TORC1 pathway inhibits the anti-aging SNF1 pathway; 2) plant extract 5 mitigates two different branches of the pro-aging PKA pathway; 3) plant extract 6 coordinates processes that are not assimilated into the network of presently known signaling pathways/protein kinases; 4) plant extract 8 diminishes the inhibitory action of PKA on SNF1; 5) plant extract 12 intensifies the anti-aging protein kinase Rim15; and 6) plant extract 21 inhibits a form of the pro-aging protein kinase Sch9 that is activated by the pro-aging PKH1/2 pathway.

The role of autophagy in the regulation of yeast life span

The goal of the aging field is to develop novel therapeutic interventions that extend human health span and reduce the burden of age-related disease. While organismal aging is a complex, multifactorial process, a popular theory is that cellular aging is a significant contributor to the progressive decline inherent to all multicellular organisms. To explore the molecular determinants that drive cellular aging, as well as how to retard them, researchers have utilized the highly genetically tractable budding yeast Saccharomyces cerevisiae. Indeed, every intervention known to extend both cellular and organismal health span was identified in yeast, underlining the power of this approach. Importantly, a growing body of work has implicated the process of autophagy as playing a critical role in the delay of aging. This review summarizes recent reports that have identified a role for autophagy, or autophagy factors in the extension of yeast life span. These studies demonstrate (1) that yeast remains an invaluable tool for the identification and characterization of conserved mechanisms that promote cellular longevity and are likely to be relevant to humans, and (2) that the process of autophagy has been implicated in nearly all known longevity-promoting manipulations and thus represents an ideal target for interventions aimed at improving human health span.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research.

Culture degeneration in conidia of Beauveria bassiana and virulence determinants by proteomics

The quality of Beauveria bassiana conidia directly affects the virulence against insects. In this study, continuous subculturing of B. bassiana on both rice grains and potato dextrose agar (PDA) resulted in 55 and 49 % conidial yield reduction after 12 passages and 68 and 60 % virulence reduction after 20 and 12 passages at four d post-inoculation, respectively. The passage through Tenebrio molitor and Spodoptera exigua restored the virulence of rice and PDA subcultures, respectively. To explore the molecular mechanisms underlying the conidial quality and the decline of virulence after multiple subculturing, we investigated the conidial proteomic changes. Successive subculturing markedly increased the protein levels in oxidative stress response, autophagy, amino acid homeostasis, and apoptosis, but decreased the protein levels in DNA repair, ribosome biogenesis, energy metabolism, and virulence. The nitro blue tetrazolium assay verified that the late subculture's colony and conidia had a higher oxidative stress level than the early subculture. A 2A-type protein phosphatase and a Pleckstrin homology domain protein Slm1, effector proteins of the target of rapamycin (TOR) complex 1 and 2, respectively, were dramatically increased in the late subculture. These results suggest that TOR signalling might be associated with ageing in B. bassiana late subculture, in turn affecting its physiological characteristics and virulence.

Caloric Restriction and Rapamycin Differentially Alter Energy Metabolism in Yeast

Rapamycin (RM), a drug that inhibits the mechanistic target of rapamycin (mTOR) pathway and responds to nutrient availability, seemingly mimics the effects of caloric restriction (CR) on healthy life span. However, the extent of the mechanistic overlap between RM and CR remains incompletely understood. Here, we compared the impact of CR and RM on cellular metabolic status. Both regimens maintained intracellular ATP through the chronological aging process and showed enhanced mitochondrial capacity. Comparative transcriptome analysis showed that CR had a stronger impact on global gene expression than RM. We observed a like impact on the metabolome and identified distinct metabolites affected by CR and RM. CR severely reduced the level of energy storage molecules including glycogen and lipid droplets, whereas RM did not. RM boosted the production of enzymes responsible for the breakdown of glycogen and lipid droplets. Collectively, these results provide insights into the distinct energy metabolism mechanisms induced by CR and RM, suggesting that these two anti-aging regimens might extend life span through distinctive pathways.

Effects of Long-Term Cultivation on Medium with Alpha-Ketoglutarate Supplementation on Metabolic Processes of Saccharomyces cerevisiae

During last years, alpha-ketoglutarate (AKG), an important intermediate in the Krebs cycle, has been intensively studied as a dietary supplement with stress-protective and potential antiaging effects. Here, we examined the effects of exogenous AKG on metabolic processes and survival of yeast Saccharomyces cerevisiae during long-term cultivation. Growth on AKG had no effect on the total cell number but increased the number of reproductively active cells at the late days of cultivation (from day 7 to day 15). A gradual increase in levels of total protein, glycogen, and trehalose was found over 7-day cultivation with more pronounced effects in AKG-grown cells. In control cells, metabolic activity and the activities of superoxide dismutase and catalase decreased, whereas levels of carbonyl proteins and low-molecular-mass thiols increased during 7-day cultivation. This suggests development of oxidative stress in stationary phase cells. Meanwhile, stationary phase cells cultured on AKG possessed higher levels of low-molecular-mass thiols and lower levels of carbonyl proteins and α-dicarbonyl compounds when compared to control ones. Collectively, higher levels of storage carbohydrates and an activation of antioxidant defense with diminishing oxidative protein damage can prevent a loss of reproductive ability in yeast cells during long-term cultivation on AKG-supplemented medium.

The integrated stress response in budding yeast lifespan extension

Aging is a complex, multi-factorial biological process shared by all living organisms. It is manifested by a gradual accumulation of molecular alterations that lead to the decline of normal physiological functions in a time-dependent fashion. The ultimate goal of aging research is to develop therapeutic means to extend human lifespan, while reducing susceptibility to many age-related diseases including cancer, as well as metabolic, cardiovascular and neurodegenerative disorders. However, this first requires elucidation of the causes of aging, which has been greatly facilitated by the use of model organisms. In particular, the budding yeast Saccharomyces cerevisiae has been invaluable in the identification of conserved molecular and cellular determinants of aging and for the development of approaches to manipulate these aging determinants to extend lifespan. Strikingly, where examined, virtually all means to experimentally extend lifespan result in the induction of cellular stress responses. This review describes growing evidence in yeast that activation of the integrated stress response contributes significantly to lifespan extension. These findings demonstrate that yeast remains a powerful model system for elucidating conserved mechanisms to achieve lifespan extension that are likely to drive therapeutic approaches to extend human lifespan and healthspan.

Association of circulating branched-chain amino acids with cardiometabolic traits differs between adults and the oldest-old

Branched-chain amino acids (BCAAs) are promising for their potential anti-aging effects. However, findings in adults suggest that circulating BCAAs are associated with cardiometabolic risk. Moreover, little information is available about how BCAAs influence clustered cardiometabolic traits in the oldest-old (>85 years), which are the fastest-growing segment of the population in developed countries. Here, we applied a targeted metabolomics approach to measure serum BCAAs in Chinese participants (aged 21-110 years) based on a longevity cohort. The differences of quantitative and dichotomous cardiometabolic traits were compared across BCAAs tertiles. A generalized additive model (GAM) was used to explore the dose-response relationship between BCAAs and the risk of metabolic syndrome (MetS). Overall, BCAAs were correlated with most of the examined cardiometabolic traits. The odds ratios for MetS across the increasing BCAA tertiles were 3.22 (1.70 - 6.12) and 5.27 (2.88 - 9.94, referenced to tertile 1) after adjusting for age and gender (P_trend < 0.001). The association still existed after further controlling for lifestyle factors and inflammation factors. However, the correlations between circulating BCAAs and quantitative traits were weakened in the oldest-old, except for lipids, the levels of which were distinctly different from those in adults. The stratified analysis also suggested that the risky BCAAs-MetS association was more pronounced in adults than in the oldest-old. Moreover, generalized additive model (GAM)-based curve-fitting suggested that only when BCAAs exceeded a threshold (approximately 450 μmol/L) was the BCAAs-MetS association significant. The relationship might be aging-dependent and was more pronounced in adults than in the oldest-old.

Akt2 ablation prolongs life span and improves myocardial contractile function with adaptive cardiac remodeling: role of Sirt1-mediated autophagy regulation

Aging is accompanied with unfavorable geometric and functional changes in the heart involving dysregulation of Akt and autophagy. This study examined the impact of Akt2 ablation on life span and cardiac aging as well as the mechanisms involved with a focus on autophagy and mitochondrial integrity. Cardiac geometry, contractile, and intracellular Ca2+ properties were evaluated using echocardiography, IonOptix® edge-detection and fura-2 techniques. Levels of Sirt1, mitochondrial integrity, autophagy, and mitophagy markers were evaluated using Western blot. Our results revealed that Akt2 ablation prolonged life span (by 9.1%) and alleviated aging (24 months)-induced unfavorable changes in myocardial function and intracellular Ca2+ handling (SERCA2a oxidation) albeit with more pronounced cardiac hypertrophy (58.1%, 47.8%, and 14.5% rises in heart weight, wall thickness, and cardiomyocyte cross-sectional area). Aging downregulated levels of Sirt1, increased phosphorylation of Akt, and the nuclear transcriptional factor Foxo1, as well as facilitated acetylation of Foxo1, the effects of which (except Sirt1 and Foxo1 acetylation) were significantly attenuated or negated by Akt2 ablation. Advanced aging disturbed autophagy, mitophagy, and mitochondrial integrity as evidenced by increased p62, decreased levels of beclin-1, Atg7, LC3B, BNIP3, PTEN-induced putative kinase 1 (PINK1), Parkin, UCP-2, PGC-1α, and aconitase activity, the effects of which were reversed by Akt2 ablation. Aging-induced cardiomyocyte contractile dysfunction and loss of mitophagy were improved by rapamycin and the Sirt1 activator SRT1720. Activation of Akt using insulin or Parkin deficiency prevented SRT1720-induced beneficial effects against aging. In conclusion, our data indicate that Akt2 ablation protects against cardiac aging through restored Foxo1-related autophagy and mitochondrial integrity.

Dietary restriction and lifespan: Lessons from invertebrate models

Dietary restriction (DR) is the most robust environmental manipulation known to increase active and healthy lifespan in many species. Despite differences in the protocols and the way DR is carried out in different organisms, conserved relationships are emerging among multiple species. Elegant studies from numerous model organisms are further defining the importance of various nutrient-signaling pathways including mTOR (mechanistic target of rapamycin), insulin/IGF-1-like signaling and sirtuins in mediating the effects of DR. We here review current advances in our understanding of the molecular mechanisms altered by DR to promote lifespan in three major invertebrate models, the budding yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster.

Caloric restriction extends yeast chronological lifespan via a mechanism linking cellular aging to cell cycle regulation, maintenance of a quiescent state, entry into a non-quiescent state and survival in the non-quiescent state

A yeast culture grown in a nutrient-rich medium initially containing 2% glucose is not limited in calorie supply. When yeast cells cultured in this medium consume glucose, they undergo cell cycle arrest at a checkpoint in late G1 and differentiate into quiescent and non-quiescent cell populations. Studies of such differentiation have provided insights into mechanisms of yeast chronological aging under conditions of excessive calorie intake. Caloric restriction is an aging-delaying dietary intervention. Here, we assessed how caloric restriction influences the differentiation of chronologically aging yeast cultures into quiescent and non-quiescent cells, and how it affects their properties. We found that caloric restriction extends yeast chronological lifespan via a mechanism linking cellular aging to cell cycle regulation, maintenance of quiescence, entry into a non-quiescent state and survival in this state. Our findings suggest that caloric restriction delays yeast chronological aging by causing specific changes in the following: 1) a checkpoint in G1 for cell cycle arrest and entry into a quiescent state; 2) a growth phase in which high-density quiescent cells are committed to become low-density quiescent cells; 3) the differentiation of low-density quiescent cells into low-density non-quiescent cells; and 4) the conversion of high-density quiescent cells into high-density non-quiescent cells.

The genome-wide transcription response to telomerase deficiency in the thermotolerant yeast Hansenula polymorpha DL-1

BACKGROUND

In the course of replication of eukaryotic chromosomes, the telomere length is maintained due to activity of telomerase, the ribonucleoprotein reverse transcriptase. Abolishing telomerase function causes progressive shortening of telomeres and, ultimately, cell cycle arrest and replicative senescence. To better understand the cellular response to telomerase deficiency, we performed a transcriptomic study for the thermotolerant methylotrophic yeast Hansenula polymorpha DL-1 lacking telomerase activity.

RESULTS

Mutant strain of H. polymorpha carrying a disrupted telomerase RNA gene was produced, grown to senescence and analyzed by RNA-seq along with wild type strain. Telomere shortening induced a transcriptional response involving genes relevant to telomere structure and maintenance, DNA damage response, information processing, and some metabolic pathways. Genes involved in DNA replication and repair, response to environmental stresses and intracellular traffic were up-regulated in senescent H. polymorpha cells, while strong down-regulation was observed for genes involved in transcription and translation, as well as core histones.

CONCLUSIONS

Comparison of the telomerase deletion transcription responses by Saccharomyces cerevisiae and H. polymorpha demonstrates that senescence makes different impact on the main metabolic pathways of these yeast species but induces similar changes in processes related to nucleic acids metabolism and protein synthesis. Up-regulation of a subunit of the TORC1 complex is clearly relevant for both types of yeast.

The yeast protein kinase Sch9 adjusts V-ATPase assembly/disassembly to control pH homeostasis and longevity in response to glucose availability

The conserved protein kinase Sch9 is a central player in the nutrient-induced signaling network in yeast, although only few of its direct substrates are known. We now provide evidence that Sch9 controls the vacuolar proton pump (V-ATPase) to maintain cellular pH homeostasis and ageing. A synthetic sick phenotype arises when deletion of SCH9 is combined with a dysfunctional V-ATPase, and the lack of Sch9 has a significant impact on cytosolic pH (pHc) homeostasis. Sch9 physically interacts with, and influences glucose-dependent assembly/disassembly of the V-ATPase, thereby integrating input from TORC1. Moreover, we show that the role of Sch9 in regulating ageing is tightly connected with V-ATPase activity and vacuolar acidity. As both Sch9 and the V-ATPase are highly conserved in higher eukaryotes, it will be interesting to further clarify their cooperative action on the cellular processes that influence growth and ageing.

The evolutionary conserved TOR complex 1 controls growth in response to the quality and quantity of nutrients such as carbon and amino acids. The protein kinase Sch9 is the main TORC1 effector in yeast. However, only few of its direct targets are known. In this study, we performed a genome-wide screening looking for mutants which require Sch9 function for their survival and growth. In this way, we identified multiple components of the highly conserved vacuolar proton pump (V-ATPase) which mediates the luminal acidification of multiple biosynthetic and endocytic organelles. Besides a genetic interaction, we found Sch9 also physically interacts with the V-ATPase to regulate its assembly state in response to glucose availability and TORC1 activity. Moreover, the interaction with the V-ATPase has consequences for ageing as it allowed Sch9 to control vacuolar pH and thereby trigger either lifespan extension or lifespan shortening. Hence, our results provide insights into the signaling mechanism coupling glucose availability, TORC1 signaling, pH homeostasis and longevity. As both Sch9 and the V-ATPase are highly conserved and implicated in various pathologies, these results offer fertile ground for further research in higher eukaryotes.

Adaptive Roles of SSY1 and SIR3 During Cycles of Growth and Starvation in Saccharomyces cerevisiae Populations Enriched for Quiescent or Nonquiescent Cells

Over its evolutionary history, Saccharomyces cerevisiae has evolved to be well-adapted to fluctuating nutrient availability. In the presence of sufficient nutrients, yeast cells continue to proliferate, but upon starvation haploid yeast cells enter stationary phase and differentiate into nonquiescent (NQ) and quiescent (Q) cells. Q cells survive stress better than NQ cells and show greater viability when nutrient-rich conditions are restored. To investigate the genes that may be involved in the differentiation of Q and NQ cells, we serially propagated yeast populations that were enriched for either only Q or only NQ cell types over many repeated growth–starvation cycles. After 30 cycles (equivalent to 300 generations), each enriched population produced a higher proportion of the enriched cell type compared to the starting population, suggestive of adaptive change. We also observed differences in each population’s fitness suggesting possible tradeoffs: clones from NQ lines were better adapted to logarithmic growth, while clones from Q lines were better adapted to starvation. Whole-genome sequencing of clones from Q- and NQ-enriched lines revealed mutations in genes involved in the stress response and survival in limiting nutrients (ECM21, RSP5, MSN1, SIR4, and IRA2) in both Q and NQ lines, but also differences between the two lines: NQ line clones had recurrent independent mutations affecting the Ssy1p-Ptr3p-Ssy5p (SPS) amino acid sensing pathway, while Q line clones had recurrent, independent mutations in SIR3 and FAS1. Our results suggest that both sets of enriched-cell type lines responded to common, as well as distinct, selective pressures.

AMPK and vacuole-associated Atg14p orchestrate μ-lipophagy for energy production and long-term survival under glucose starvation

Dietary restriction increases the longevity of many organisms, but the cell signaling and organellar mechanisms underlying this capability are unclear. We demonstrate that to permit long-term survival in response to sudden glucose depletion, yeast cells activate lipid-droplet (LD) consumption through micro-lipophagy (µ-lipophagy), in which fat is metabolized as an alternative energy source. AMP-activated protein kinase (AMPK) activation triggered this pathway, which required Atg14p. More gradual glucose starvation, amino acid deprivation or rapamycin did not trigger µ-lipophagy and failed to provide the needed substitute energy source for long-term survival. During acute glucose restriction, activated AMPK was stabilized from degradation and interacted with Atg14p. This prompted Atg14p redistribution from ER exit sites onto liquid-ordered vacuole membrane domains, initiating µ-lipophagy. Our findings that activated AMPK and Atg14p are required to orchestrate µ-lipophagy for energy production in starved cells is relevant for studies on aging and evolutionary survival strategies of different organisms.

DOI:http://dx.doi.org/10.7554/eLife.21690.001

The frequency of yeast [PSI+] prion formation is increased during chronological ageing

Ageing involves a time-dependent decline in a variety of intracellular mechanisms and is associated with cellular senescence. This can be exacerbated by prion diseases which can occur in a sporadic manner, predominantly during the later stages of life. Prions are infectious, self-templating proteins responsible for several neurodegenerative diseases in mammals and several prion-forming proteins have been found in yeast. We show here that the frequency of formation of the yeast [PSI⁺ ] prion, which is the altered form of the Sup35 translation termination factor, is increased during chronological ageing. This increase is exacerbated in an atg1 mutant suggesting that autophagy normally acts to suppress age-related prion formation. We further show that cells which have switched to [PSI⁺ ] have improved viability during chronological ageing which requires active autophagy. [PSI⁺ ] stains show increased autophagic flux which correlates with increased viability and decreased levels of cellular protein aggregation. Taken together, our data indicate that the frequency of [PSI⁺ ] prion formation increases during yeast chronological ageing, and switching to the [PSI⁺ ] form can exert beneficial effects via the promotion of autophagic flux.

Methods to Assess Autophagy and Chronological Aging in Yeast

Autophagy is a catabolic process that is crucial for cellular homeostasis and adaptive response to changing environments. Importantly, autophagy has been shown to be induced in many longevity-associated scenarios and to be required to maintain lifespan extension. Notably, autophagy is a highly conserved cellular process among eukaryotes, and the yeast Saccharomyces cerevisiae has become a universal model system for unraveling the molecular machinery underlying autophagic mechanisms. Here, we discuss different protocols to monitor survival and autophagy of yeast cells upon chronological aging. These include the use of propidium iodide to assess the loss of cell membrane integrity, as well as clonogenic assays to directly determine survival rates. Additionally, we describe methods to quantify autophagic flux, including the alkaline phosphatase activity or the GFP liberation assays, which measure the delivery of autophagosomal cargo to the vacuole. In sum, we have recapped established protocols used to evaluate a link between lifespan extension and autophagy in yeast.

Revealing oxidative damage to enzymes of carbohydrate metabolism in yeast: An integration of 2D DIGE, quantitative proteomics, and bioinformatics

Clinical usage of lidocaine, a pro-oxidant has been linked with severe, mostly neurological complications. The mechanism(s) causing these complications is independent of the blockade of voltage-gated sodium channels. The budding yeast Saccharomyces cerevisiae lacks voltage-gated sodium channels, thus provides an ideal system to investigate lidocaine-induced protein and pathway alterations. Whole-proteome alterations leading to these complications have not been identified. To address this, S. cerevisiae was grown to stationary phase and exposed to an LC50 dose of lidocaine. The differential proteomes of lidocaine treatment and control were resolved 6 h post exposure using 2D DIGE. Amine reactive dyes and carbonyl reactive dyes were used to assess protein abundance and protein oxidation, respectively. Quantitative analysis of these dyes (⩾ 1.5-fold alteration, p ⩽ 0.05) revealed a total of 33 proteoforms identified by MS differing in abundance and/or oxidation upon lidocaine exposure. Network analysis showed enrichment of apoptotic proteins and cell wall maintenance proteins, while the abundance of proteins central to carbohydrate metabolism, such as triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase, and redox proteins superoxide dismutase and peroxiredoxin were significantly decreased. Enzymes of carbohydrate metabolism, such as phosphoglycerate kinase and enolase, the TCA cycle enzyme aconitase, and multiple ATP synthase subunits were found to be oxidatively modified. Also, the activity of aconitase was found to be decreased. Overall, these data suggest that toxic doses of lidocaine induce significant disruption of glycolytic pathways, energy production, and redox balance, potentially leading to cell malfunction and death.

Caloric restriction alleviates alpha-synuclein toxicity in aged yeast cells by controlling the opposite roles of Tor1 and Sir2 on autophagy

Alpha-synuclein (syn) is the main component of proteinaceous inclusions known as Lewy bodies (LBs), which are implicated in the pathogenesis of the neurodegenerative diseases known as synucleinopathies, like Parkinson's disease (PD). Aging is a major risk factor for PD and thus, interventions that delay aging will have promising effects in PD and other synucleinopathies. Caloric restriction (CR) is the only non-genetic intervention shown to promote lifespan extension in several model organisms. CR has been shown to alleviate syn toxicity and herein we confirmed the same effect on the yeast model for synucleinopathies during chronological lifespan. The data gathered showed that TOR1 deletion also results in similar longevity extension and abrogation of syn toxicity. Intriguingly, these interventions were associated with decreased autophagy, which was maintained at homeostatic levels. Autophagy maintenance at homeostatic levels promoted by CR or TOR1 abrogation in syn-expressing cells was achieved by decreasing Sir2 levels and activity. Furthermore, the opposite function of Tor1 and Sir2 in autophagy is probably associated with the maintenance of autophagy activity at homeostatic levels, a central event linked to abrogation of syn toxicity promoted by CR.

Availability of Amino Acids Extends Chronological Lifespan by Suppressing Hyper-Acidification of the Environment in Saccharomyces cerevisiae

The chronological lifespan of Saccharomyces cerevisiae represents the duration of cell survival in the postdiauxic and stationary phases. Using a prototrophic strain derived from the standard auxotrophic laboratory strain BY4742, we showed that supplementation of non-essential amino acids to a synthetic defined (SD) medium increases maximal cell growth and extends the chronological lifespan. The positive effects of amino acids can be reproduced by modulating the medium pH, indicating that amino acids contribute to chronological longevity in a cell-extrinsic manner by alleviating medium acidification. In addition, we showed that the amino acid-mediated effects on extension of chronological longevity are independent of those achieved through a reduction in the TORC1 pathway, which is mediated in a cell-intrinsic manner. Since previous studies showed that extracellular acidification causes mitochondrial dysfunction and leads to cell death, our results provide a path to premature chronological aging caused by differences in available nitrogen sources. Moreover, acidification of culture medium is generally associated with culture duration and cell density; thus, further studies are required on cell physiology of auxotrophic yeast strains during the stationary phase because an insufficient supply of essential amino acids may cause alterations in environmental conditions.

Orchestrating the network of molecular pathways affecting aging: Role of nonselective autophagy and mitophagy

Autophagy is best known as a mechanism involved in cellular recycling of biomolecules during periods of nutritional starvation. More recently, an additional function of autophagy emerged: the selective degradation of functionally impaired or surplus proteins, organelles and invading bacteria. With this function autophagy is integrated in a network of pathways involved in molecular and cellular quality control with a key impact on development and aging. Impairments in the autophagic machinery lead to accelerated aging and the development of diseases. Here we focus on the role of nonselective autophagy and mitophagy, the selective autophagic degradation of mitochondria, on aging and lifespan of biological systems.

Ammonium is a key determinant on the dietary restriction of yeast chronological aging in culture medium

New evidences have recently emerged from studies in yeast and in higher eukaryotes showing the importance of nutrient balance in dietary regimes and its effects on longevity regulation.We have previously shown that manipulation of ammonium concentration in the culture and/or aging medium can drastically affect chronological lifespan (CLS)of Saccharomyces cerevisiae, especially in amino acid restricted cells. Here we describe that the CLS shortening under amino acid restriction can be completely reverted by removing ammonium from the culture medium. Furthermore, the absence of ammonium, and of any rich nitrogen source, was so effective in extending CLS that no beneficial effect could be observed by further imposing calorie restriction conditions. When present in the culture medium,ammonium impaired the consumption of the auxotrophy-complementing amino acids and caused in an improper cell cycle arrest of the culture.TOR1 deletion reverted ammonium effects both in amino acid restricted and non-restricted cultures, whereas, Ras2p and Sch9p seem to have only a milder effect in the mediation of ammonium toxicity under amino acid restriction and no effect on non-restricted cultures.Our studies highlight ammonium as a key effector in the nutritional equilibrium between rich and essential nitrogen sources and glucose required for longevity promotion.

Yeast MRX deletions have short chronological life span and more triacylglycerols

Saccharomyces cerevisiae is an excellent model organism for lipid research. Here, we have used yeast haploid RAdiation Damage (RAD) deletion strains to study life span and lipid storage patterns. RAD genes are mainly involved in DNA repair mechanism and hence, their deletions have resulted in shorter life span. Viable RAD mutants were screened for non-polar lipid content, and some of the mutants showed significantly high amounts of triacylglycerol (TAG) and steryl ester, besides short chronological life span. Among these, RAD50, MRE11 and XRS2 form a complex, MRX that is involved in homologous recombination that showed an increase in the amount of TAG. Microarray data of single MRX deletions revealed that besides DNA damage signature genes, lipid metabolism genes are also differentially expressed. Lipid biosynthetic genes (LPP1, SLC1) were upregulated and lipid hydrolytic gene (TGL3) was downregulated. We observed that rad50Δ, mre11Δ, xrs2Δ and mrxΔ strains have high number of lipid droplets (LDs) with fragmented mitochondria. These mutants have a short chronological life span compared to wild type. Aged wild-type cells also accumulated TAG with LDs of ∼2.0 μm in diameter. These results suggest that TAG accumulation and big size LDs could be possible markers for premature or normal aging.

β-Guanidinopropionic acid extends the lifespan of Drosophila melanogaster via an AMP-activated protein kinase-dependent increase in autophagy

Previous studies have demonstrated that AMP‐activated protein kinase (AMPK) controls autophagy through the mammalian target of rapamycin (mTOR) and Unc‐51 like kinase 1 (ULK1/Atg1) signaling, which augments the quality of cellular housekeeping, and that β‐guanidinopropionic acid (β‐GPA), a creatine analog, leads to a chronic activation of AMPK. However, the relationship between β‐GPA and aging remains elusive. In this study, we hypothesized that feeding β‐GPA to adult Drosophila produces the lifespan extension via activation of AMPK‐dependent autophagy. It was found that dietary administration of β‐GPA at a concentration higher than 900 mm induced a significant extension of the lifespan of Drosophila melanogaster in repeated experiments. Furthermore, we found that Atg8 protein, the homolog of microtubule‐associated protein 1A/1B‐light chain 3 (LC3) and a biomarker of autophagy in Drosophila, was significantly upregulated by β‐GPA treatment, indicating that autophagic activity plays a role in the effect of β‐GPA. On the other hand, when the expression of Atg5 protein, an essential protein for autophagy, was reduced by RNA interference (RNAi), the effect of β‐GPA on lifespan extension was abolished. Moreover, we found that AMPK was also involved in this process. β‐GPA treatment significantly elevated the expression of phospho‐T172‐AMPK levels, while inhibition of AMPK by either AMPK‐RNAi or compound C significantly attenuated the expression of autophagy‐related proteins and lifespan extension in Drosophila. Taken together, our results suggest that β‐GPA can induce an extension of the lifespan of Drosophila via AMPK‐Atg1‐autophagy signaling pathway.

Dietary Restriction and Nutrient Balance in Aging

Dietary regimens that favour reduced calorie intake delay aging and age-associated diseases. New evidences revealed that nutritional balance of dietary components without food restriction increases lifespan. Particular nutrients as several nitrogen sources, proteins, amino acid, and ammonium are implicated in life and healthspan regulation in different model organisms from yeast to mammals. Aging and dietary restriction interact through partially overlapping mechanisms in the activation of the conserved nutrient-signalling pathways, mainly the insulin/insulin-like growth factor (IIS) and the Target Of Rapamycin (TOR). The specific nutrients of dietary regimens, their balance, and how they interact with different genes and pathways are currently being uncovered. Taking into account that dietary regimes can largely influence overall human health and changes in risk factors such as cholesterol level and blood pressure, these new findings are of great importance to fully comprehend the interplay between diet and humans health.

The Stationary-Phase Cells of Saccharomyces cerevisiae Display Dynamic Actin Filaments Required for Processes Extending Chronological Life Span

Stationary-growth-phase Saccharomyces cerevisiae yeast cultures consist of nondividing cells that undergo chronological aging. For their successful survival, the turnover of proteins and organelles, ensured by autophagy and the activation of mitochondria, is performed. Some of these processes are engaged in by the actin cytoskeleton. In S. cerevisiae stationary-phase cells, F actin has been shown to form static aggregates named actin bodies, subsequently cited to be markers of quiescence. Our in vivo analyses revealed that stationary-phase cultures contain cells with dynamic actin filaments, besides the cells with static actin bodies. The cells with dynamic actin displayed active endocytosis and autophagy and well-developed mitochondrial networks. Even more, stationary-phase cell cultures grown under calorie restriction predominantly contained cells with actin cables, confirming that the presence of actin cables is linked to successful adaptation to stationary phase. Cells with actin bodies were inactive in endocytosis and autophagy and displayed aberrations in mitochondrial networks. Notably, cells of the respiratory activity-deficient cox4Δ strain displayed the same mitochondrial aberrations and actin bodies only. Additionally, our results indicate that mitochondrial dysfunction precedes the formation of actin bodies and the appearance of actin bodies corresponds to decreased cell fitness. We conclude that the F-actin status reflects the extent of damage that arises from exponential growth.

Gpd1 Regulates the Activity of Tcp-1 and Heat Shock Response in Yeast Cells: Effect on Aggregation of Mutant Huntingtin

A significant correlation has been observed between the length of the polyglutamine tract in huntingtin, its aggregation and the progression of Huntington's disease (HD). The chaperonin TRiC is a potent antagonist of aggregation of mutant huntingtin. Using the well-validated Saccharomyces cerevisiae model of HD, we have investigated the role of age-related post-translational modifications of this heterooligomeric chaperonin on its ability to inhibit aggregation of the mutant protein. We show that the glycerol synthetic enzyme Gpd1 is involved in the post-translational modification of Tcp-1 (subunit of TRiC) by acetylation and glycation through the NAD(+)/NADH shuttle and the triose phosphate intermediate dihydroxyacetone phosphate, respectively. The extent of modification of Tcp-1 shows a negative correlation with the solubility of mutant huntingtin. The absence of Gpd1 also induces heat shock response in yeast cells, further inhibiting aggregation of the mutant protein. Thus, Gpd1 acts as a major regulator of the protein folding machinery in the yeast model of HD. Modification and inactivation of cellular chaperonin are accelerated in an aging cell, which has further deleterious effects for a cell harbouring misfolded/aggregated protein(s).

Functional genomic analysis reveals overlapping and distinct features of chronologically long-lived yeast populations

Yeast chronological lifespan (CLS) is extended by multiple genetic and environmental manipulations, including caloric restriction (CR). Understanding the common changes in molecular pathways induced by such manipulations could potentially reveal conserved longevity mechanisms. We therefore performed gene expression profiling on several long-lived yeast populations, including an ade4∆ mutant defective in de novo purine (AMP) biosynthesis, and a calorie restricted WT strain. CLS was also extended by isonicotinamide (INAM) or expired media derived from CR cultures. Comparisons between these diverse long-lived conditions revealed a common set of differentially regulated genes, several of which were potential longevity biomarkers. There was also enrichment for genes that function in CLS regulation, including a long-lived adenosine kinase mutant (ado1∆) that links CLS regulation to the methyl cycle and AMP. Genes co-regulated between the CR and ade4∆ conditions were dominated by GO terms related to metabolism of alternative carbon sources, consistent with chronological longevity requiring efficient acetate/acetic acid utilization. Alternatively, treating cells with isonicotinamide (INAM) or the expired CR media resulted in GO terms predominantly related to cell wall remodeling, consistent with improved stress resistance and protection against external insults like acetic acid. Acetic acid therefore has both beneficial and detrimental effects on CLS.

Branched-chain amino acids ameliorate heart failure with cardiac cachexia in rats

AIMS

Heart failure (HF) is associated with changes in energy metabolism of the heart, as well as in extra-cardiac organs such as the skeletal muscles. Cardiac cachexia is a common complication and is associated with poor prognosis. Branched-chain amino acids (BCAAs) reportedly improve sarcopenia and cancer cachexia. We tested the hypothesis that BCAA ameliorates HF with cardiac cachexia.

MAIN METHODS

We used Dahl salt-sensitive (DS) rats fed a high-salt diet as a model of HF. DS rats fed a low-salt diet were used as a control. BCAA were administered in drinking water from 11weeks of age, when cardiac hypertrophy was established but the cardiac function was preserved. Survival and the cardiac function were monitored, and animals were sacrificed at 21weeks of age and analyzed.

KEY FINDINGS

In HF rats, BCAA treatment decreased the heart rate, preserved the cardiac function, and prolonged survival. BCAA also prevented body weight loss, associated with preservation of the skeletal muscle weight. Moreover, gene expression related to mitochondrial biogenesis and function was increased with BCAA in skeletal muscles.

SIGNIFICANCE

BCAA preserved the body weight and cardiac function and prolonged survival in HF rats. The expression of genes involved in mitochondrial biogenesis and function in skeletal muscles was increased by BCAA.

Diversification of Paralogous α-Isopropylmalate Synthases by Modulation of Feedback Control and Hetero-Oligomerization in Saccharomyces cerevisiae

Production of α-isopropylmalate (α-IPM) is critical for leucine biosynthesis and for the global control of metabolism. The budding yeast Saccharomyces cerevisiae has two paralogous genes, LEU4 and LEU9, that encode α-IPM synthase (α-IPMS) isozymes. Little is known about the biochemical differences between these two α-IPMS isoenzymes. Here, we show that the Leu4 homodimer is a leucine-sensitive isoform, while the Leu9 homodimer is resistant to such feedback inhibition. The leu4Δ mutant, which expresses only the feedback-resistant Leu9 homodimer, grows slowly with either glucose or ethanol and accumulates elevated pools of leucine; this phenotype is alleviated by the addition of leucine. Transformation of the leu4Δ mutant with a centromeric plasmid carrying LEU4 restored the wild-type phenotype. Bimolecular fluorescent complementation analysis showed that Leu4-Leu9 heterodimeric isozymes are formed in vivo. Purification and kinetic analysis showed that the hetero-oligomeric isozyme has a distinct leucine sensitivity behavior. Determination of α-IPMS activity in ethanol-grown cultures showed that α-IPM biosynthesis and growth under these respiratory conditions depend on the feedback-sensitive Leu4 homodimer. We conclude that retention and further diversification of two yeast α-IPMSs have resulted in a specific regulatory system that controls the leucine-α-IPM biosynthetic pathway by selective feedback sensitivity of homomeric and heterodimeric isoforms.

Humulus japonicus extract exhibits antioxidative and anti-aging effects via modulation of the AMPK-SIRT1 pathway

The perennial herb, Humulus japonicus, has been previously described as possessing potential antituberculosis and anti-inflammatory properties. In the present study, the anti-aging activity of ethanol extracts from the leaves of H. japonicus (HJE) was evaluated in yeast and human fibroblast cells. In addition, the antioxidant activity of HJE was analyzed using free radical scavenging assays. Furthermore, the mechanism underlying the hypothesized HJE-associated extension of lifespan was investigated, and the results indicated that HJE was able to extend the lifespan of yeast cells. Further experiments demonstrated that HJE upregulated the longevity-associated proteins, sirtuin 1 and AMP-activated protein kinase, and effectively inhibited the generation of reactive oxygen species (ROS). In addition, the antioxidative potential of the active constituents of HJE, including luteolin, luteolin 7-glycoside, quercetin and quercitrin, was evaluated and the results demonstrated that these flavonoids were able to scavenge ROS in cell-free and intracellular systems. In summary, the results revealed that HJE possessed the potential for antioxidative activity; however, further in vivo investigations are required with the aim of developing safe, high-efficacy anti-aging agents.

Interplay among Gcn5, Sch9 and mitochondria during chronological aging of wine yeast is dependent on growth conditions

Saccharomyces cerevisiae chronological life span (CLS) is determined by a wide variety of environmental and genetic factors. Nutrient limitation without malnutrition, i.e. dietary restriction, expands CLS through the control of nutrient signaling pathways, of which TOR/Sch9 has proven to be the most relevant, particularly under nitrogen deprivation. The use of prototrophic wine yeast allows a better understanding of the role of nitrogen in longevity in natural and more demanding environments, such as grape juice fermentation. We previously showed that acetyltransferase Gcn5, a member of the SAGA complex, has opposite effects on CLS under laboratory and winemaking conditions, and is detrimental under the latter. Here we demonstrate that integrity of the SAGA complex is necessary for prolonged longevity, as its dismantling by SPT20 deletion causes a drop in CLS under both laboratory and winemaking conditions. The sch9Δ mutant is long-lived in synthetic SC medium, as expected, and the combined deletion of GCN5 partially suppresses this phenotype. However it is short-lived in grape juice, likely due to its low nitrogen/carbon ratio. Therefore, unbalance of nutrients can be more relevant for life span than total amounts of them. Deletion of RTG2, which codes for a protein associated with Gcn5 and is a component of the mitochondrial retrograde signal, and which communicates mitochondrial dysfunction to the nucleus, is detrimental under laboratory, but not under winemaking conditions, where respiration seems not so relevant for longevity. Transcription factor Rgm1 was found to be a novel CLS regulator Sch9-dependently.

Mechanisms of amino acid-mediated lifespan extension in Caenorhabditis elegans

BACKGROUND

Little is known about the role of amino acids in cellular signaling pathways, especially as it pertains to pathways that regulate the rate of aging. However, it has been shown that methionine or tryptophan restriction extends lifespan in higher eukaryotes and increased proline or tryptophan levels increase longevity in C. elegans. In addition, leucine strongly activates the TOR signaling pathway, which when inhibited increases lifespan.

RESULTS

Therefore each of the 20 proteogenic amino acids was individually supplemented to C. elegans and the effects on lifespan were determined. All amino acids except phenylalanine and aspartate extended lifespan at least to a small extent at one or more of the 3 concentrations tested with serine and proline showing the largest effects. 11 of the amino acids were less potent at higher doses, while 5 even decreased lifespan. Serine, proline, or histidine-mediated lifespan extension was greatly inhibited in eat-2 worms, a model of dietary restriction, in daf-16/FOXO, sir-2.1, rsks-1 (ribosomal S6 kinase), gcn-2, and aak-2 (AMPK) longevity pathway mutants, and in bec-1 autophagy-defective knockdown worms. 8 of 10 longevity-promoting amino acids tested activated a SKN-1/Nrf2 reporter strain, while serine and histidine were the only amino acids from those to activate a hypoxia-inducible factor (HIF-1) reporter strain. Thermotolerance was increased by proline or tryptophan supplementation, while tryptophan-mediated lifespan extension was independent of DAF-16/FOXO and SKN-1/Nrf2 signaling, but tryptophan and several related pyridine-containing compounds induced the mitochondrial unfolded protein response and an ER stress response. High glucose levels or mutations affecting electron transport chain (ETC) function inhibited amino acid-mediated lifespan extension suggesting that metabolism plays an important role. Providing many other cellular metabolites to C. elegans also increased longevity suggesting that anaplerosis of tricarboxylic acid (TCA) cycle substrates likely plays a role in lifespan extension.

CONCLUSIONS

Supplementation of C. elegans with 18 of the 20 individual amino acids extended lifespan, but lifespan often decreased with increasing concentration suggesting hormesis. Lifespan extension appears to be caused by altered mitochondrial TCA cycle metabolism and respiratory substrate utilization resulting in the activation of the DAF-16/FOXO and SKN-1/Nrf2 stress response pathways.

Sub1 and Maf1, two effectors of RNA polymerase III, are involved in the yeast quiescence cycle

Sub1 and Maf1 exert an opposite effect on RNA polymerase III transcription interfering with different steps of the transcription cycle. In this study, we present evidence that Sub1 and Maf1 also exhibit an opposite role on yeast chronological life span. First, cells lacking Sub1 need more time than wild type to exit from resting and this lag in re-proliferation is correlated with a delay in transcriptional reactivation. Second, our data show that the capacity of the cells to properly establish a quiescent state is impaired in the absence of Sub1 resulting in a premature death that is dependent on the Ras/PKA and Tor1/Sch9 signalling pathways. On the other hand, we show that maf1Δ cells are long-lived mutant suggesting a connection between Pol III transcription and yeast longevity.

Investigation of Geotrichum candidum gene expression during the ripening of Reblochon-type cheese by reverse transcription-quantitative PCR

Cheese ripening involves the activity of various bacteria, yeasts or molds, which contribute to the development of the typical color, flavor and texture of the final product. In situ measurements of gene expression are increasingly being used to improve our understanding of the microbial flora activity in cheeses. The objective of the present study was to investigate the physiology and metabolic activity of Geotrichum candidum during the ripening of Reblochon-type cheeses by quantifying mRNA transcripts at various ripening times. The expression of 80 genes involved in various functions could be quantified with a correct level of biological repeatability using a set of three stable reference genes. As ripening progresses, a decrease in expression was observed for genes involved in cell wall organization, translation, vesicular mediated transport, and in cytoskeleton constituents and ribosomal protein genes. There was also a decrease in the expression of mitochondrial F1F0 ATP synthase and plasma membrane H(+) ATPase genes. Some genes involved in the catabolism of lactate, acetate and ethanol were expressed to a greater extent at the beginning of ripening. During the second part of ripening, there was an increased expression of genes involved in the transport and catabolism of amino acids, which could be attributed to a change in the energy source. There was also an increase in the expression of genes involved in autophagy and of genes possibly involved in lifespan determination. Quantification of mRNA transcripts may also be used to produce bioindicators relevant for cheesemaking, for example when considering genes encoding enzymes involved in the catabolism of amino acids.