Multiple factors lead to proteostatic perturbations, often resulting in the aberrant accumulation of toxic misfolded proteins. Cells, from yeast to humans, can respond to sudden accumulation of secretory proteins within the endoplasmic reticulum (ER) through pathways such as the Unfolded Protein Response (UPR). The ability of cells to adapt the ER folding environment to the misfolded protein burden ultimately dictates cell fate. The aging process is a particularly important modifier of the proteostasis network; as cells age, both their ability to maintain this balance in protein folding/degradation and their ability to respond to insults in these pathways can break down, a common element of age-related diseases (including neurodegenerative diseases). ER stress coping mechanisms are central to lifespan regulation under both normal and disease states. In this review, we give a brief overview of the role of ER stress response pathways in age-dependent neurodegeneration.

No abstract

Saccharomyces cerevisiae is a well-established model organism to study the mechanisms of longevity. One of the two aging paradigms studied in yeast is termed chronological lifespan (CLS). CLS is defined by the amount of time non-dividing yeast cells can survive at stationary phase. Here, we propose new approaches that allow rapid and efficient quantification of survival rates in aging yeast cultures using either a fluorescent cell counter or microplate imaging. We have generated a software called ANALYSR (Analytical Algorithm for Yeast Survival Rates) that allows automated and highly reproducible analysis of cell survival in aging yeast cultures using fluorescent data. To demonstrate the efficiency of our new experimental tools, we tested the previously characterized ability of caloric restriction to extend lifespan. Interestingly, we found that this process is independent of the expression of three central yeast heat shock proteins (Hsp26, Hsp42, Hsp104). Finally, our new assay is easily adaptable to other types of toxicity studies. Here, we assessed the toxicity of various concentrations of acetic acid, a known contributor of yeast chronological aging. These assays provide researchers with cost-effective, low-and high-content assays that can serve as an efficient complement to the time-consuming colony forming unit assay usually used in CLS studies.

No abstract

The regulation of cellular volume in response to osmotic change has largely been studied at the whole cell level. Such regulation occurs by the inhibition or activation of ionic and organic solute transport pathways at the cell surface and is coincident with remodelling of the plasma membrane. However, it is only in rare instances that osmotic insults are experienced by cells and tissues. By contrast, the relatively minute luminal volumes of membrane-bound organelles are constantly subject to shifts in their solute concentrations as exemplified in the endocytic pathway where these evolve alongside with maturation. In this review, we summarize recent evidence that suggests trafficking events are in fact orchestrated by the solute fluxes of organelles that briefly impose osmotic gradients. We first describe how hydrostatic pressure and the resultant tension on endomembranes can be readily dissipated by controlled solute efflux since water is obliged to exit. In such cases, the relief of tension on the limiting membrane of the organelle can promote its remodelling by coat proteins, ESCRT machinery, and motors. Second, and reciprocally, we propose that osmotic gradients between organellar lumens and the cytosol may persist or be created. Such gradients impose osmotic pressure and tension on the endomembrane that prevent its remodelling. The control of endomembrane tension is dysregulated in lysosomal storage disorders and can be usurped by pathogens in endolysosomes. Since trafficking and signaling pathways conceivably sense and respond to endomembrane tension, we anticipate that understanding how cells control organellar volumes and the movement of endocytic fluid in particular will be an exciting new area of research.