TOOLS AND RESOURCES A physicochemical perspective of aging from single-cell analysis of pH, macromolecular and organellar crowding in yeast Sara N Mouton1, David J Thaller2, Matthew M Crane3, Irina L Rempel1, Owen T Terpstra1, Anton Steen1, Matt Kaeberlein3, C Patrick Lusk2, Arnold J Boersma4*, Liesbeth M Veenhoff1* 1European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, Netherlands; 2Department of Cell Biology, Yale School of Medicine, New Haven, United States; 3Department of Pathology, School of Medicine, University of Washington, Seattle, United States; 4DWI-Leibniz Institute for Interactive Materials, Aachen, Germany Abstract Cellular aging is a multifactorial process that is characterized by a decline in homeostatic capacity, best described at the molecular level. Physicochemical properties such as pH and macromolecular crowding are essential to all molecular processes in cells and require maintenance. Whether a drift in physicochemical properties contributes to the overall decline of homeostasis in aging is not known. Here, we show that the cytosol of yeast cells acidifies modestly in early aging and sharply after senescence. Using a macromolecular crowding sensor optimized for long-term FRET measurements, we show that crowding is rather stable and that the stability of crowding is a stronger predictor for lifespan than the absolute crowding levels. Additionally, in aged cells, we observe drastic changes in organellar volume, leading to crowding on the *For correspondence: micrometer scale, which we term organellar crowding. Our measurements provide an initial
[email protected] framework of physicochemical parameters of replicatively aged yeast cells. (AJB);
[email protected] (LMV) Competing interest: See Introduction page 19 Cellular aging is a process of progressive decline in homeostatic capacity (Gems and Partridge, Funding: See page 19 2013; Kirkwood, 2005).