| The influence of redox homeostasis on aging and DNA stability is a complex one. To address how thiol oxidoreductases affect these processes, we analyzed the functions of methionine sulfoxide reductases (Msrs) and thiol peroxidases in Saccharomyces cerevisiae. Yeast cells deficient in Msrs did not grow on respiratory carbon sources and had low levels of cytochrome c, indicating impairment of mitochondrial function. Lifespan analyses revealed a decrease in both chronological and replicative lifespan of Msr deficient cells. The data suggested that regulation of aging by Msrs could be linked to mitochondrial function. We further analyzed how thiol peroxidases affect genome stability and aging. We developed a S. cerevisiae strain lacking all 8 thiol peroxidase genes (Δ8) and subjected its multiple independent lines to long-term experimental evolution, followed by genome sequencing. Compared to wild type cells, Δ8 lines showed a 15-fold increase in point mutations and a significant increase in indels. Further gene expression analyses revealed dysregulation of DNA replication and repair genes in Δ8 cells. These data suggested that thiol peroxidases protect genomes by both reducing hydroperoxides and regulating cellular homeostasis through control of gene expression. To determine how genomic instability is linked to aging, we took advantage of the yeast replicative aging model assessing the frequency and type of spontaneous mutations. We isolated daughter cells at different replicative age from wild type and Δ8 cells and sequenced their genomes. Mutation rate increased as a function of age and it was higher in Δ8 than in wild type cells. However, the observed low numbers of mutations were inconsistent with the idea that mutations cause or contribute to aging. Overall, we demonstrated how deficiency in non-essential, yet critical and conserved oxidoreductase functions, leads to increased mutational load and decreased cell fitness and how these features are linked to the aging process. |
