A screen for genes involved in respiration control and longevity in Schizosaccharomyces pombe

Extension of chronological lifespan in Schizosaccharomyces pombe

There are several examples in the nature wherein the mechanism of longevity control of unicellular organisms is evolutionarily conserved with that of higher multicellular organisms. The present microreview focuses on aging and longevity studies, particularly on chronological lifespan (CLS) concerning the unicellular eukaryotic fission yeast Schizosaccharomyces pombe. In S. pombe, >30 compounds, 8 types of nutrient restriction, and >80 genes that extend CLS have been reported. Several CLS control mechanisms are known to be involved in nutritional response, energy utilization, stress responses, translation, autophagy, and sexual differentiation. In unicellular organisms, the control of CLS is directly linked to the mechanism by which cells are maintained in limited‐resource environments, and their genetic information is left to posterity. We believe that this important mechanism may have been preserved as a lifespan control mechanism for higher organisms.

Genes affecting the extension of chronological lifespan in Schizosaccharomyces pombe (fission yeast)

So far, more than 70 genes involved in the chronological lifespan (CLS) of Schizosaccharomyces pombe (fission yeast) have been reported. In this mini‐review, we arrange and summarize these genes based on the reported genetic interactions between them and the physical interactions between their products. We describe the signal transduction pathways that affect CLS in S. pombe: target of rapamycin complex 1, cAMP‐dependent protein kinase, Sty1, and Pmk1 pathways have important functions in the regulation of CLS extension. Furthermore, the Php transcription complex, Ecl1 family proteins, cyclin Clg1, and the cyclin‐dependent kinase Pef1 are important for the regulation of CLS extension in S. pombe. Most of the known genes involved in CLS extension are related to these pathways and genes. In this review, we focus on the individual genes regulating CLS extension in S. pombe and discuss the interactions among them.

Natural extract and its fractions isolated from the marine bacterium Pseudoalteromonas flavipulchra STILL-33 have antioxidant and antiaging activities in Schizosaccharomyces pombe

Investigations into the potential for pharmacological inhibition of the aging process and the onset of age-related disease are increasingly garnering attention. Here, we analyzed the antiaging properties of natural compounds derived from several marine bacteria in vitro and in vivo using the fission yeast Schizosaccharomyces pombe. The Pseudoalteromonas flavipulchra STILL-33 extract exhibited high antioxidant and antiglycation activities in vitro. We then characterized two antioxidant active fractions isolated from this extract. In addition, we showed that the P. flavipulchra STILL-33 extract or either of its two active fractions (Fractions 1 and 2) could extend the longevity of fission yeast. Moreover, the particular extract and two active fractions were found to induce mitochondrial activity and to delay the G1 phase of the fission yeast cell cycle, perhaps by improving the aging process. The P. flavipulchra STILL-33 extract and Fraction 1 also increased the expression of the catalase-encoding ctt1+ gene and thereby decreased the reactive oxygen species level. Structural analysis showed that Fraction 1 was dominated by l-arginine and ipriflavone, and we showed indeed that the two corresponding commercial products increase the fission yeast lifespan. As for Fraction 2 was identified as the putative structure of butamben. Together, these results should facilitate the discovery of additional antiaging compounds from P. flavipulchra and ultimately the development of novel antiaging compounds for pharmaceutical use.

Role of Oxidative Stress Response and Trehalose Accumulation in the Longevity of Fission Yeast

Background:

Glucose is the preferred carbon and energy source in most organisms and plays an active role in the regulation of many biological processes. However, an excess of glucose leads to such undesirable conditions as diabetes and age-related diseases. Since Schizosaccharomyces pombe homologous of many human genes, it offers several advantages for the investigation of the molecular mechanisms underlying human disease and aging studies. We have identified two glucose-repression-resistant mutants (ird5 and ird11) of S. pombe.

Objectives:

We aimed to investigate the possible relationship between lifespan extension and oxidative stress response induced by exposure to hydrogen peroxide alongside the trehalose accumulation level by using the two S. pombe mutants (i.e. ird5 and ird11), which are repressed by glucose and are resistant to oxidative stress.

Materials and Methods:

We employed trehalose accumulation measurement and colony-forming unit (CFU) counting using the ird mutants in exponential and stationary phases and compared them to the wild type grown in repressed, de-repressed, and stressed conditions to clarify the possible relationship between glucose signaling, oxidative stress response, and lifespan in S. pombe.

Results:

The lifespan of the ird5 mutant was significantly longer that of either the ird11 mutant or the wild type cells. Under repressed condition, the trehalose content was increased remarkably on the 3rd day of the study in the ird11 mutant and the wild type. Under de-repressed condition, the level of intracellular trehalose was notably increased on the 3rd day in ird11. Under stressed condition, the trehalose level in ird11 was increased on the 3rd day as a pattern similar to that observed in the wild type.

Conclusions:

Our results demonstrated no significant correlation between the ird5 lifespan and the trehalose concentration. Likewise, the correlation between lifespan extension, trehalose accumulation, and cellular resistance to hydrogen peroxide was not significant.

A metabolic strategy to enhance long-term survival by Phx1 through stationary phase-specific pyruvate decarboxylases in fission yeast

In the fission yeast Schizosaccharomyces pombe, the stationary phase-specific transcription factor Phx1 contributes to long-term survival, stress tolerance, and meiosis. We identified Phx1-dependent genes through transcriptome analysis, and further analyzed those related with carbohydrate and thiamine metabolism, whose expression decreased in Δphx1. Consistent with mRNA changes, the level of thiamine pyrophosphate (TPP) and TPP-utilizing pyruvate decarboxylase activity that converts pyruvate to acetaldehyde were also reduced in the mutant. Therefore, Phx1 appears to shift metabolic flux by diverting pyruvate from the TCA cycle and respiration to ethanol fermentation. Among the four predicted genes for pyruvate decarboxylase, only the Phx1-dependent genes (pdc201⁺ and pdc202⁺) contributed to long-term survival as judged by mutation and overexpression studies. These findings indicate that the Phx1-mediated long-term survival is achieved primarily through increasing the synthesis and activity of pyruvate decarboxylase. Consistent with this hypothesis, we observed that Phx1 curtailed respiration when cells entered stationary phase. Introduction of Δphx1 mutation compromised the long-lived phenotypes of Δpka1 and Δsck2 mutants that are devoid of pro-aging kinases of nutrient-signalling pathways, and of the Δpyp1 mutant with constitutively activated stress-responsive kinase Sty1. Therefore, achievement of long-term viability through both nutrient limitation and anti-stress response appears to be dependent on Phx1.

Parallel profiling of fission yeast deletion mutants for proliferation and for lifespan during long-term quiescence

Genetic factors underlying aging are remarkably conserved from yeast to human. The fission yeast Schizosaccharomyces pombe is an emerging genetic model to analyze cellular aging. Chronological lifespan (CLS) has been studied in stationary-phase yeast cells depleted for glucose, which only survive for a few days. Here, we analyzed CLS in quiescent S. pombe cells deprived of nitrogen, which arrest in a differentiated, G0-like state and survive for more than 2 months. We applied parallel mutant phenotyping by barcode sequencing (Bar-seq) to assay pooled haploid deletion mutants as they aged together during long-term quiescence. As expected, mutants with defects in autophagy or quiescence were under-represented or not detected. Lifespan scores could be calculated for 1199 mutants. We focus the discussion on the 48 most long-lived mutants, including both known aging genes in other model systems and genes not previously implicated in aging. Genes encoding membrane proteins were particularly prominent as pro-aging factors. We independently verified the extended CLS in individual assays for 30 selected mutants, showing the efficacy of the screen. We also applied Bar-seq to profile all pooled deletion mutants for proliferation under a standard growth condition. Unlike for stationary-phase cells, no inverse correlation between growth and CLS of quiescent cells was evident. These screens provide a rich resource for further studies, and they suggest that the quiescence model can provide unique, complementary insights into cellular aging.

Aging as an emergent factor that contributes to phenotypic variation in Cryptococcus neoformans

Cryptococcus neoformans, similar to other eukaryotes, undergoes replicative aging. Replicative life spans have been determined for clinical C. neoformans strains, and although they are a reproducible trait, life spans vary considerably among strains. C. neoformans has been proposed as an ideal model organism to investigate the contribution of replicative aging in a fungal pathogen population to emerging phenotypic variation during chronic cryptococcal infections. C. neoformans cells of advanced generational age manifest a distinct phenotype; specifically, a larger cell size, a thicker cell wall, drug resistance, as well as resistance to hydrogen peroxide-mediated killing. Consequently, old cells are selected in the host environment during chronic infection and aging could be an unanticipated mechanism of pathogen adaptation that contributes to persistent disease. Aging as a natural process of phenotypic variation should be further studied as it likely is also relevant for other eukaryotic pathogen populations that undergo asymmetric replicative aging.

Aging and cell death in the other yeasts, Schizosaccharomyces pombe and Candida albicans

How do cells age and die? For the past 20 years, the budding yeast, Saccharomyces cerevisiae, has been used as a model organism to uncover the genes that regulate lifespan and cell death. More recently, investigators have begun to interrogate the other yeasts, the fission yeast, Schizosaccharomyces pombe, and the human fungal pathogen, Candida albicans, to determine if similar longevity and cell death pathways exist in these organisms. After summarizing the longevity and cell death phenotypes in S. cerevisiae, this mini-review surveys the progress made in the study of both aging and programed cell death (PCD) in the yeast models, with a focus on the biology of S. pombe and C. albicans. Particular emphasis is placed on the similarities and differences between the two types of aging, replicative aging, and chronological aging, and between the three types of cell death, intrinsic apoptosis, autophagic cell death, and regulated necrosis, found in these yeasts. The development of the additional microbial models for aging and PCD in the other yeasts may help further elucidate the mechanisms of longevity and cell death regulation in eukaryotes.

Cryptococcus neoformans constitutes an ideal model organism to unravel the contribution of cellular aging to the virulence of chronic infections

Aging affects all organisms, from unicellular yeasts to multicellular humans. Studies in model organisms demonstrate that the pathways that mediate the two forms of aging, replicative and chronological, are highly conserved. Most studies are focused on the effect of aging on an individual cell rather than a whole population. Complex longevity regulation, however, makes aging a highly adaptive trait that is subject to natural selection. Recent studies have shed light on the potential relevance of aging in fungal pathogens, which undergo replicative aging when they expand in the host environment. Hence, pathogens causing chronic infections can constitute ideal model organisms in unraveling the contribution of selection to aging within a population and help elucidate the contribution of aging itself to the virulence of infections.

Investigation of the relationship between oxidative stress and glucose signaling in Schizosaccharomyces pombe

The invertase mutant defective in the glucose signaling pathway of Schizosaccharomyces pombe (ird11) is resistant to glucose repression. This mutant is able to consume sucrose alongside glucose and grows in glucose-containing media with a generation time close to that of the wild type. Intracellular oxidation, protein carbonyl, and reduced glutathione levels and catalase, superoxide dismutase, and glutathione peroxidase activity were investigated in ird11, to determine the relationship between oxidative stress response and glucose signaling. The expression profiles of some genes involved in regulation of glucose repression (fbp1, fructose-1,6-bis-phosphatase; hxk2, hexokinase) and stress response (atf1 and pap1 transcription factors; ctt1, catalase; sod1, Cu,Zn superoxide dismutase) were analyzed using the quantitative real-time PCR technique. Oxidative stress response in ird11 seems to be affected by glucose signaling in a manner different from that caused by glucose deprivation.

Genetic approaches to aging in budding and fission yeasts: new connections and new opportunities

Yeasts are powerful model systems to examine the evolutionarily conserved aspects of eukaryotic aging because they maintain many of the same core cellular signaling pathways and essential organelles as human cells. We constructed a strain of the budding yeast Saccharomyces cerevisiae that could monitor the distribution of proteins involved in heterochromatic silencing and aging, and isolated mutants that alter this distribution. The largest class of such mutants cause defects in mitochondrial function, and appear to cause changes in nuclear silencing separate from the well-known Rtg2p-dependent pathway that alters nuclear transcription in response to the loss of the mitochondrial genome. Mutants that inactivate the ATP2 gene, which encodes the ATPase subunit of the mitochondrial F(1)F(0)-ATPase, were isolated twice in our screen and identify a lifespan extending pathway in a gene that is conserved in both prokaryotes and eukaryotes. The budding yeast S. cerevisiae S. cerevisiae has been used with great success to identify other lifespan-extending pathways in screens using surrogate phenotypes such as stress resistance or silencing to identify random mutants, or in high throughput screens that utilize the deletion strain set resource. However, the direct selection of long-lived mutants from a pool of random mutants is more challenging. We have established a new chronological aging assay for the evolutionarily distant fission yeast Schizosaccharomyces pombe that recapitulates aspects of aging conserved in all eukaryotes. We have constructed a novel S. pombe S. pombe DNA insertion mutant bank, and used it to show that we can directly select for a long-lived mutant. The use of both the budding and fission yeast systems should continue to facilitate the identification and validation of lifespan extending pathways that are conserved in humans.