Yeast stress, aging, and death

[Excerpt] Until about 15 years ago, programmed cell death (PCD), at that time mainly defined as apoptosis, was believed to be a feature occurring only in metazoans to ensure proper embryonic development, cell differentiation, and regulation of the immune response. However, the discovery that single-celled organisms, such as yeast, also undergo PCD challenged this idea. Meanwhile, several key regulators and cell death executers were shown to be highly conserved in yeast and other unicellular organisms, and it is now generally accepted that at least part of the molecular cell death machinery originated early in evolution. Approximately 31% of the yeast genes have a mammalian homologue, and an additional 30% of yeast genes show domain similarity. This, combined with the ease of manipulation of yeast and the elegance of yeast genetics, has turned this lower eukaryote into an ideal system to study more complex phenomena that occur in metazoan cells, including stress responses, mechanisms governing life span and cell death, and processes contributing to aging or human diseases like cancers and neurodegenerative disorders. In this special issue, we collected both original research and review articles, which combined give a nice overview on the current status of the field. (...

The role of Sch9 and the V-ATPase in the adaptation response to acetic acid and the consequences for growth and chronological lifespan

Studies with Saccharomyces cerevisiae indicated that non-physiologically high levels of acetic acid promote cellular acidification, chronological aging, and programmed cell death. In the current study, we compared the cellular lipid composition, acetic acid uptake, intracellular pH, growth, and chronological lifespan of wild-type cells and mutants lacking the protein kinase Sch9 and/or a functional V-ATPase when grown in medium supplemented with different acetic acid concentrations. Our data show that strains lacking the V-ATPase are especially more susceptible to growth arrest in the presence of high acetic acid concentrations, which is due to a slower adaptation to the acid stress. These V-ATPase mutants also displayed changes in lipid homeostasis, including alterations in their membrane lipid composition that influences the acetic acid diffusion rate and changes in sphingolipid metabolism and the sphingolipid rheostat, which is known to regulate stress tolerance and longevity of yeast cells. However, we provide evidence that the supplementation of 20 mM acetic acid has a cytoprotective and presumable hormesis effect that extends the longevity of all strains tested, including the V-ATPase compromised mutants. We also demonstrate that the long-lived sch9∆ strain itself secretes significant amounts of acetic acid during stationary phase, which in addition to its enhanced accumulation of storage lipids may underlie its increased lifespan

Activation State of the Ras2 Protein and Glucose-induced Signaling in Saccharomyces cerevisiae

The activity of adenylate cyclase in the yeast Saccharomyces cerevisiae is controlled by two G-protein systems, the Ras proteins and the Gα protein Gpa2. Glucose activation of cAMP synthesis is thought to be mediated by Gpa2 and its G-protein-coupled receptor Gpr1. Using a sensitive GTP-loading assay for Ras2 we demonstrate that glucose addition also triggers a fast increase in the GTP loading state of Ras2 concomitant with the glucose-induced increase in cAMP. This increase is severely delayed in a strain lacking Cdc25, the guanine nucleotide exchange factor for Ras proteins. Deletion of the Ras-GAPs IRA2 (alone or with IRA1) or the presence of RAS2Val19 allele causes constitutively high Ras GTP loading that no longer increases upon glucose addition. The glucose-induced increase in Ras2 GTP-loading is not dependent on Gpr1 or Gpa2. Deletion of these proteins causes higher GTP loading indicating that the two G-protein systems might directly or indirectly interact. Because deletion of GPR1 or GPA2 reduces the glucose-induced cAMP increase the observed enhancement of Ras2 GTP loading is not sufficient for full stimulation of cAMP synthesis. Glucose phosphorylation by glucokinase or the hexokinases is required for glucose-induced Ras2 GTP loading. These results indicate that glucose phosphorylation might sustain activation of cAWDP synthesis by enhancing Ras2 GTP loading likely through inhibition of the Ira proteins. Strains with reduced feedback inhibition on cAMP synthesis also display elevated basal and induced Ras2 GTP loading consistent with the Ras2 protein acting as a target of the feedback-inhibition mechanism

pH homeostasis links the nutrient sensing PKA/TORC1/Sch9 ménage-à-trois to stress tolerance and longevity

The plasma membrane H+-ATPase Pma1 and the vacuolar V-ATPase act in close harmony to tightly control pH homeostasis, which is essential for a vast number of physiological processes. As these main two regulators of pH are responsive to the nutritional status of the cell, it seems evident that pH homeostasis acts in conjunction with nutrient-induced signalling pathways. Indeed, both PKA and the TORC1-Sch9 axis influence the proton pumping activity of the V-ATPase and possibly also of Pma1. In addition, it recently became clear that the proton acts as a second messenger to signal glucose availability via the V-ATPase to PKA and TORC1-Sch9. Given the prominent role of nutrient signalling in longevity, it is not surprising that pH homeostasis has been linked to ageing and longevity as well. A first indication is provided by acetic acid, whose uptake by the cell induces toxicity and affects longevity. Secondly, vacuolar acidity has been linked to autophagic processes, including mitophagy. In agreement with this, a decline in vacuolar acidity was shown to induce mitochondrial dysfunction and shorten lifespan. In addition, the asymmetric inheritance of Pma1 has been associated with replicative ageing and this again links to repercussions on vacuolar pH. Taken together, accumulating evidence indicates that pH homeostasis plays a prominent role in the determination of ageing and longevity, thereby providing new perspectives and avenues to explore the underlying molecular mechanisms.Support via the research grants G.0694.13, G.0A63.15 and SBO-S006617N. We also thank KU Leuven for support by granting the C14/17/063 projectinfo:eu-repo/semantics/publishedVersio

A network-based approach to identify substrate classes of bacterial glycosyltransferases

Background: Bacterial interactions with the environment-and/or host largely depend on the bacterial glycome. The specificities of a bacterial glycome are largely determined by glycosyltransferases (GTs), the enzymes involved in transferring sugar moieties from an activated donor to a specific substrate. Of these GTs their coding regions, but mainly also their substrate specificity are still largely unannotated as most sequence-based annotation flows suffer from the lack of characterized sequence motifs that can aid in the prediction of the substrate specificity. Results: In this work, we developed an analysis flow that uses sequence-based strategies to predict novel GTs, but also exploits a network-based approach to infer the putative substrate classes of these predicted GTs. Our analysis flow was benchmarked with the well-documented GT-repertoire of Campylobacter jejuni NCTC 11168 and applied to the probiotic model Lactobacillus rhamnosus GG to expand our insights in the glycosylation potential of this bacterium. In L. rhamnosus GG we could predict 48 GTs of which eight were not previously reported. For at least 20 of these GTs a substrate relation was inferred. Conclusions: We confirmed through experimental validation our prediction of WelI acting upstream of WelE in the biosynthesis of exopolysaccharides. We further hypothesize to have identified in L. rhamnosus GG the yet undiscovered genes involved in the biosynthesis of glucose-rich glycans and novel GTs involved in the glycosylation of proteins. Interestingly, we also predict GTs with well-known functions in peptidoglycan synthesis to also play a role in protein glycosylation

Enhanced end-to-end security through symmetric-key cryptography in wearable medical sensor networks

Computer Science

Yeast as a Model System to Study Tau Biology

Hyperphosphorylated and aggregated human protein tau constitutes a hallmark of a multitude of neurodegenerative diseases called tauopathies, exemplified by Alzheimer's disease. In spite of an enormous amount of research performed on tau biology, several crucial questions concerning the mechanisms of tau toxicity remain unanswered. In this paper we will highlight some of the processes involved in tau biology and pathology, focusing on tau phosphorylation and the interplay with oxidative stress. In addition, we will introduce the development of a human tau-expressing yeast model, and discuss some crucial results obtained in this model, highlighting its potential in the elucidation of cellular processes leading to tau toxicity

Sphingolipids and inositol phosphates regulate the tau protein phosphorylation status in humanized yeast

Hyperphosphorylation of protein tau is a hallmark of Alzheimer's disease (AD). Changes in energy and lipid metabolism have been correlated with the late onset of this neurological disorder. However, it is uncertain if metabolic dysregulation is a consequence of AD or one of the initiating factors of AD pathophysiology. Also, it is unclear whether variations in lipid metabolism regulate the phosphorylation state of tau. Here, we show that in humanized yeast, tau hyperphosphorylation is stimulated by glucose starvation in coincidence with the downregulation of Pho85, the yeast ortholog of CDK5. Changes in inositol phosphate (IP) signaling, which has a central role in energy metabolism, altered tau phosphorylation. Lack of inositol hexakisphosphate kinases Kcs1 and Vip1 (IP6 and IP7 kinases in mammals) increased tau hyperphosphorylation. Similar effects were found by mutation of IPK2 (inositol polyphosphate multikinase), or PLC1, the yeast phospholipase C gene. These effects may be explained by IP-mediated regulation of Pho85. Indeed, this appeared to be the case for plc1, ipk2, and kcs1. However, the effects of Vip1 on tau phosphorylation were independent of the presence of Pho85, suggesting additional mechanisms. Interestingly, kcs1 and vip1 strains, like pho85, displayed dysregulated sphingolipid (SL) metabolism. Moreover, genetic and pharmacological inhibition of SL biosynthesis stimulated the appearance of hyperphosphorylated forms of tau, while increased flux through the pathway reduced its abundance. Finally, we demonstrated that Sit4, the yeast ortholog of human PP2A protein phosphatase, is a downstream effector of SL signaling in mediating the tau phosphorylation state. Altogether, our results add new knowledge on the molecular effectors involved in tauopathies and identify new targets for pharmacological intervention

Communication and security trade-offs for battery-powered devices: a case study on wearable medical sensor systems

Computer Science