Hypertrophy, replicative ageing and the ageing process

Cellular enlargement - A new hallmark of aging?

Years of important research has revealed that cells heavily invest in regulating their size. Nevertheless, it has remained unclear why accurate size control is so important. Our recent study using hematopoietic stem cells (HSCs) in vivo indicates that cellular enlargement is causally associated with aging. Here, we present an overview of these findings and their implications. Furthermore, we performed a broad literature analysis to evaluate the potential of cellular enlargement as a new aging hallmark and to examine its connection to previously described aging hallmarks. Finally, we highlight interesting work presenting a correlation between cell size and age-related diseases. Taken together, we found mounting evidence linking cellular enlargement to aging and age-related diseases. Therefore, we encourage researchers from seemingly unrelated areas to take a fresh look at their data from the perspective of cell size.

Consequences of calorie restriction and calorie excess for the physiological parameters of the yeast Saccharomyces cerevisiae cells

Glucose plays an important role in cell metabolism and has an impact on cellular physiology. Changes in glucose availability may strongly influence growth rate of the cell size, cell metabolism and the rate of generation of cellular by-products, such as reactive oxygen species. The positive effect of low glucose concentration conditions-calorie restriction is observed in a wide range of species, including the Saccharomyces cerevisiae yeast, yet little is known about the effect of high glucose concentrations-calorie excess. Such analysis seems to be particularly important due to recently common problem of diabetes and obesity. The effect of glucose on morphological and physiological parameters of the yeast cell was conducted using genetic alteration (disruption of genes involved in glucose signalling) and calorie restriction and calorie excess conditions. The results show a significant relationship among extracellular glucose concentration, cell size and reactive oxygen species generation in yeast cells. Furthermore, the results obtained through the use of mutant strains with disorders in glucose signalling pathways suggest that the intracellular level of glucose is more important than its extracellular concentration. These data also suggest that the calorie excess as a factor, which has a significant impact on cell physiology, requires further comprehensive analyses.

Cell Size Influences the Reproductive Potential and Total Lifespan of the Saccharomyces cerevisiae Yeast as Revealed by the Analysis of Polyploid Strains

The total lifespan of the yeast Saccharomyces cerevisiae may be divided into two phases: the reproductive phase, during which the cell undergoes mitosis cycles to produce successive buds, and the postreproductive phase, which extends from the last division to cell death. These phases may be regulated by a common mechanism or by distinct ones. In this paper, we proposed a more comprehensive approach to reveal the mechanisms that regulate both reproductive potential and total lifespan in cell size context. Our study was based on yeast cells, whose size was determined by increased genome copy number, ranging from haploid to tetraploid. Such experiments enabled us to test the hypertrophy hypothesis, which postulates that excessive size achieved by the cell-the hypertrophy state-is the reason preventing the cell from further proliferation. This hypothesis defines the reproductive potential value as the difference between the maximal size that a cell can reach and the threshold value, which allows a cell to undergo its first cell cycle and the rate of the cell size to increase per generation. Here, we showed that cell size has an important impact on not only the reproductive potential but also the total lifespan of this cell. Moreover, the maximal cell size value, which limits its reproduction capacity, can be regulated by different factors and differs depending on the strain ploidy. The achievement of excessive size by the cell (hypertrophic state) may lead to two distinct phenomena: the cessation of reproduction without "mother" cell death and the cessation of reproduction with cell death by bursting, which has not been shown before.

The rate of metabolism as a factor determining longevity of the Saccharomyces cerevisiae yeast

Despite many controversies, the yeast Saccharomyces cerevisiae continues to be used as a model organism for the study of aging. Numerous theories and hypotheses have been created for several decades, yet basic mechanisms of aging have remained unclear. Therefore, the principal aim of this work is to propose a possible mechanism leading to increased longevity in yeast. In this paper, we suggest for the first time that there is a link between decreased metabolic activity, fertility and longevity expressed as time of life in yeast. Determination of reproductive potential and total lifespan with the use of fob1Δ and sfp1Δ mutants allows us to compare the "longevity" presented as the number of produced daughters with the longevity expressed as the time of life. The results of analyses presented in this paper suggest the need for a change in the definition of longevity of yeast by taking into consideration the time parameter. The mutants that have been described as "long-lived" in the literature, such as the fob1Δ mutant, have an increased reproductive potential but live no longer than their standard counterparts. On the other hand, the sfp1Δ mutant and the wild-type strain produce a similar number of daughter cells, but the former lives much longer. Our results demonstrate a correlation between the decreased efficiency of the translational apparatus and the longevity of the sfp1Δ mutant. We suggest that a possible factor regulating the lifespan is the rate of cell metabolism. To measure the basic metabolism of the yeast cells, we used the isothermal microcalorimetry method. In the case of sfp1Δ, the flow of energy, ATP concentration, polysome profile and translational fitness are significantly lower in comparison with the wild-type strain and the fob1Δ mutant.

Quasi-programmed aging of budding yeast: a trade-off between programmed processes of cell proliferation, differentiation, stress response, survival and death defines yeast lifespan

Recent findings suggest that evolutionarily distant organisms share the key features of the aging process and exhibit similar mechanisms of its modulation by certain genetic, dietary and pharmacological interventions. The scope of this review is to analyze mechanisms that in the yeast Saccharomyces cerevisiae underlie: (1) the replicative and chronological modes of aging; (2) the convergence of these 2 modes of aging into a single aging process; (3) a programmed differentiation of aging cell communities in liquid media and on solid surfaces; and (4) longevity-defining responses of cells to some chemical compounds released to an ecosystem by other organisms populating it. Based on such analysis, we conclude that all these mechanisms are programs for upholding the long-term survival of the entire yeast population inhabiting an ecological niche; however, none of these mechanisms is a ʺprogram of agingʺ - i.e., a program for progressing through consecutive steps of the aging process.