Rapid Nuclear Exclusion of Hcm1 in AgingSaccharomyces cerevisiaeLeads to Vacuolar Alkalization and Replicative Senescence

Abstract

The yeast, Saccharomyces cerevisiae, like other higher eukaryotes, undergo a finite number of cell divisions before exiting the cell cycle due to the effects of aging. Here, we show that yeast aging begins with the nuclear exclusion of Hcm1 in young cells, resulting in loss of acidic vacuoles. Autophagy is required for healthy aging in yeast, with proteins targeted for turnover by autophagy directed to the vacuole. Consistent with this, vacuolar acidity is necessary for vacuolar function and yeast longevity. Using yeast genetics and immunofluorescence microscopy, we confirm that vacuolar acidity plays a critical role in cell health and lifespan, and is potentially maintained by a series of Forkhead Box (Fox) transcription factors. An interconnected transcriptional network involving the Fox proteins (Fkh1, Fkh2 and Hcm1) are required for transcription of v-ATPase subunits and vacuolar acidity. As cells age, Hcm1 is rapidly excluded from the nucleus in young cells, blocking the expression of Hcm1 targets (Fkh1 and Fkh2), leading to loss of v-ATPase gene expression, reduced vacuolar acidification, increased α-syn-GFP vacuolar accumulation, and finally, diminished replicative lifespan (RLS). Loss of vacuolar acidity occurs about the same time as Hcm1 nuclear exclusion and is conserved; we have recently demonstrated that lysosomal alkalization similarly contributes to aging in C. elegans following a transition from progeny producing to post-reproductive life. Our data points to a molecular mechanism regulating vacuolar acidity that signals the end of RLS when acidification is lost.

A pH probe inhibits senescence in mesenchymal stem cells

“…When viewed from this perspective, whether SGJ could exert the same effect on those BMSCs aged in vivo should be investigated further. However, many studies indicated that elements changed during aging, including autophagy, lysosomal function and activity, and v-ATPase activity, were not only found in vivo [ 1 , 15 , 38 , 44 ] but also in vitro [ 14 , 15 , 44 – 46 ]; therefore, according to our work, it is reasonable to draw a conclusion that SGJ is a potential lead compound for suppressing BMSC senescence. At least, it could be used as a powerful tool for studying and understanding the mechanism of aging.…”

Loss of vacuolar acidity results in iron sulfur cluster defects and divergent homeostatic responses during aging inSaccharomyces cerevisiae

“…The loss of vacuolar acidity is an evolutionarily conserved aging phenotype identified thus far in yeast (Ghavidel et al, 2018;Hughes and Gottschling, 2012) and worms (Baxi et al, 2017). Future studies will need to directly assess whether loss of lysosomal acidity occurs in mammalian cell types with age or age-associated diseases, which could be testable using ratiometric pH sensors.…”

“…Imaging these cells in a microfluidic device with live-cell fluorescence imaging indicated that loss of vacuolar acidity begins essentially at the start of life (Figure 3a). By comparing different genetic strains, previous studies have indicated that loss of vacuolar acidity limits lifespan (Ghavidel et al, 2018;Hughes and Gottschling, 2012). To test whether vacuolar acidity was a risk factor for early death in a wildtype isogenic population, we monitored changes in vacuolar acidity during early life (ages 0-12 divisions).…”

“…The lysosome/vacuole is maintained at an acidic pH, which is necessary for proper organelle function. Recent work has shown that the loss of lysosomal/vacuolar acidity is an evolutionarily conserved early life driver of aging and mitochondrial dysfunction (Baxi et al, 2017;Ghavidel et al, 2018;Hughes and Gottschling, 2012), and interventions that increase vacuolar acidity have been found to extend lifespan in yeast (Sasikumar et al, 2019).…”

Protein Homeostasis Networks and the Use of Yeast to Guide Interventions in Alzheimer’s Disease

“…These proton pumps maintain the acidity of the organelle by pumping the protons in the luminal part in an energy dependent manner, while its impairment has been found to increase the pH of the organelle [253]. Ageing in yeast has been found to be a major contributor of vacuolar alkalization, which is found to be caused by defective assembly of V-ATPases in lysosomal membranes [210].…”