Cell organelles and yeast longevity: an intertwined regulation

Low-Molecular Weight Compounds that Extend the Chronological Lifespan of Yeasts, Saccharomyces cerevisiae, and Schizosaccharomyces pombe

Yeast is an excellent model organism for research for regulating aging and lifespan, and the studies have made many contributions to date, including identifying various factors and signaling pathways related to aging and lifespan. More than 20 years have passed since molecular biological perspectives are adopted in this research field, and intracellular factors and signal pathways that control aging and lifespan have evolutionarily conserved from yeast to mammals. Furthermore, these findings have been applied to control the aging and lifespan of various model organisms by adjustment of the nutritional environment, genetic manipulation, and drug treatment using low-molecular weight compounds. Among these, drug treatment is easier than the other methods, and research into drugs that regulate aging and lifespan is consequently expected to become more active. Chronological lifespan, a definition of yeast lifespan, refers to the survival period of a cell population under nondividing conditions. Herein, low-molecular weight compounds are summarized that extend the chronological lifespan of Saccharomyces cerevisiae and Schizosaccharomyces pombe, along with their intracellular functions. The low-molecular weight compounds are also discussed that extend the lifespan of other model organisms. Compounds that have so far only been studied in yeast may soon extend lifespan in other organisms.

Acyl CoA oxidase: from its expression, structure, folding, and import to its role in human health and disease

β-oxidation of fatty acids is an important metabolic pathway and is a shared function between mitochondria and peroxisomes in mammalian cells. On the other hand, peroxisomes are the sole site for the degradation of fatty acids in yeast. The first reaction of this pathway is catalyzed by the enzyme acyl CoA oxidase housed in the matrix of peroxisomes. Studies in various model organisms have reported the conserved function of the protein in fatty acid oxidation. The importance of this enzyme is highlighted by the lethal conditions caused in humans due to its altered function. In this review, we discuss various aspects ranging from gene expression, structure, folding, and import of the protein in both yeast and human cells. Further, we highlight recent findings on the role of the protein in human health and aging, and discuss the identified mutations in the protein associated with debilitating conditions in patients.

Mitochondrial networks through the lens of mathematics

Mitochondria serve a wide range of functions within cells, most notably via their production of ATP. Although their morphology is commonly described as bean-like, mitochondria often form interconnected networks within cells that exhibit dynamic restructuring through a variety of physical changes. Further, though relationships between form and function in biology are well established, the extant toolkit for understanding mitochondrial morphology is limited. Here, we emphasize new and established methods for quantitatively describing mitochondrial networks, ranging from unweighted graph-theoretic representations to multi-scale approaches from applied topology, in particular persistent homology. We also show fundamental relationships between mitochondrial networks, mathematics, and physics, using ideas of graph planarity and statistical mechanics to better understand the full possible morphological space of mitochondrial network structures. Lastly, we provide suggestions for how examination of mitochondrial network form through the language of mathematics can inform biological understanding, and vice versa.

Oxidation of biological molecules with age and induced oxidative stress in different growth phases of Saccharomyces cerevisiae

One of the mechanistic approaches for explaining ageing is the oxidative stress theory of ageing. Saccharomyces cerevisiae has been used as a model to study ageing due to many factors. We have attempted to investigate if the differential ability to withstand oxidative stress can be correlated with their lifespans. In all the four strains studied (AP22, 699, 8C, and SP4), there was no age-associated increases in lipid peroxidation levels measured as thiobarbituric acid reactive substances (TBARS). Under induced oxidative stress conditions, there was an increased TBARS level in both the ages assessed with a quantum-fold increase in the stationary phase cells of AP22. In contrast, the late stationary phase cells of 8C exhibited the least susceptibility to induced oxidative stress. The level of TBARS in both exponential and late stationary phase cells of 699 was overall more than that in the other three strains. Protein carbonylation increased with age in 8C and 699. Induced stress increased carbonylation in the exponential cells of SP4 and 699 and the stationary phase cells of all four strains. Protein carbonylation data indicate that the AP22 cells exhibit decreased protein carbonylation vis-à-vis the other strains. Induced stress data showed that while the exponential cells of 699 are susceptible, the late stationary phase cells of 699 are most resistant. Western blotting analysis using anti-HNE antibodies showed two proteins of molecular mass ~ 56 and ~ 84 kDa that were selectively modified with age in all the strains. Under induced stress conditions, an additional protein of ~ 69 kDa was oxidized. Our investigation shows that the difference in lifespan between the four strains of S. cerevisiae may be regulated by oxidative stress. Knowledge of the identity of the oxidized proteins will significantly facilitate a better understanding of the effect of oxidative stress conditions on the cells of S. cerevisiae.

The nexus between peroxisome abundance and chronological ageing in Saccharomyces cerevisiae

Ageing is characterized by changes in several cellular processes, with dysregulation of peroxisome function being one of them. Interestingly, the most conserved function of peroxisomes, ROS homeostasis, is strongly associated with ageing and age-associated pathologies. Previous studies have identified a role for peroxisomes in the regulation of chronological lifespan in yeast. In this study, we report the effect of altered peroxisome number on the chronological lifespan of yeast in two different growth media conditions. Three mutants, pex11, pex25 and pex27, defective in peroxisome fission, have been thoroughly investigated for the chronological lifespan. Reduced chronological lifespan of all the mutants was observed in peroxisome-inducing growth conditions. Furthermore, the combined deletion pex11pex25 exhibited the most prominent reduction in lifespan. Interestingly altered peroxisomal phenotype upon ageing was observed in all the cells. Increased ROS accumulation and reduced catalase activity was exhibited by chronologically aged mutant cells. Interestingly, mutants with reduced number of peroxisomes concomitantly also exhibited an accumulation of free fatty acids and increased number of lipid droplets. Taken together, our results reveal a previously unrealized effect of fission proteins in the chronological lifespan of yeast.

Response to sulfur in Schizosaccharomyces pombe

Sulfur is an essential component of various biologically important molecules, including methionine, cysteine and glutathione, and it is also involved in coping with oxidative and heavy metal stress. Studies using model organisms, including budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), have contributed not only to understanding various cellular processes but also to understanding the utilization and response mechanisms of each nutrient, including sulfur. Although fission yeast can use sulfate as a sulfur source, its sulfur metabolism pathway is slightly different from that of budding yeast because it does not have a trans-sulfuration pathway. In recent years, it has been found that sulfur starvation causes various cellular responses in S. pombe, including sporulation, cell cycle arrest at G₂, chronological lifespan extension, autophagy induction and reduced translation. This MiniReview identifies two sulfate transporters in S. pombe, Sul1 (encoded by SPBC3H7.02) and Sul2 (encoded by SPAC869.05c), and summarizes the metabolic pathways of sulfur assimilation and cellular response to sulfur starvation. Understanding these responses, including metabolism and adaptation, will contribute to a better understanding of the various stress and nutrient starvation responses and chronological lifespan regulation caused by sulfur starvation.

Understanding the Impact of Industrial Stress Conditions on Replicative Aging in Saccharomyces cerevisiae

In yeast, aging is widely understood as the decline of physiological function and the decreasing ability to adapt to environmental changes. Saccharomyces cerevisiae has become an important model organism for the investigation of these processes. Yeast is used in industrial processes (beer and wine production), and several stress conditions can influence its intracellular aging processes. The aim of this review is to summarize the current knowledge on applied stress conditions, such as osmotic pressure, primary metabolites (e.g., ethanol), low pH, oxidative stress, heat on aging indicators, age-related physiological changes, and yeast longevity. There is clear evidence that yeast cells are exposed to many stressors influencing viability and vitality, leading to an age-related shift in age distribution. Currently, there is a lack of rapid, non-invasive methods allowing the investigation of aspects of yeast aging in real time on a single-cell basis using the high-throughput approach. Methods such as micromanipulation, centrifugal elutriator, or biotinylation do not provide real-time information on age distributions in industrial processes. In contrast, innovative approaches, such as non-invasive fluorescence coupled flow cytometry intended for high-throughput measurements, could be promising for determining the replicative age of yeast cells in fermentation and its impact on industrial stress conditions.

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.

Peroxisomes of the Brain: Distribution, Functions, and Associated Diseases

Peroxisomes are versatile cell organelles that exhibit a repertoire of organism and cell-type dependent functions. The presence of oxidases and antioxidant enzymes is a characteristic feature of these organelles. The role of peroxisomes in various cell types in human health and disease is under investigation. Defects in the biogenesis of the organelle and its function lead to severe debilitating disorders. In this manuscript, we discuss the distribution and functions of peroxisomes in the nervous system and especially in the brain cells. The important peroxisomal functions in these cells and their role in the pathology of associated disorders such as neurodegeneration are highlighted in recent studies. Although the cause of the pathogenesis of these disorders is still not clearly understood, emerging evidence supports a crucial role of peroxisomes. In this review, we discuss research highlighting the role of peroxisomes in brain development and its function. We also provide an overview of the major findings in recent years that highlight the role of peroxisome dysfunction in various associated diseases.

Discovery of fifteen new geroprotective plant extracts and identification of cellular processes they affect to prolong the chronological lifespan of budding yeast

In a quest for previously unknown geroprotective natural chemicals, we used a robust cell viability assay to search for commercially available plant extracts that can substantially prolong the chronological lifespan of budding yeast. Many of these plant extracts have been used in traditional Chinese and other herbal medicines or the Mediterranean and other customary diets. Our search led to a discovery of fifteen plant extracts that significantly extend the longevity of chronologically aging yeast not limited in calorie supply. We show that each of these longevity-extending plant extracts is a geroprotector that decreases the rate of yeast chronological aging and promotes a hormetic stress response. We also show that each of the fifteen geroprotective plant extracts mimics the longevity-extending, stress-protecting, metabolic and physiological effects of a caloric restriction diet but if added to yeast cultured under non-caloric restriction conditions. We provide evidence that the fifteen geroprotective plant extracts exhibit partially overlapping effects on a distinct set of longevity-defining cellular processes. These effects include a rise in coupled mitochondrial respiration, an altered age-related chronology of changes in reactive oxygen species abundance, protection of cellular macromolecules from oxidative damage, and an age-related increase in the resistance to long-term oxidative and thermal stresses.