Cellular Aging: A Mitochondrial Approach to Oxidative and Glucocorticoid Stress.

Abstract

cancer, arthritis, osteoporosis, type 2 diabetes, and cardiovascular disease. To meet Aging is a universal process that drives a vast number of pathologies including Alzheimer’s, cancer, arthritis, osteoporosis, type 2 diabetes, and cardiovascular disease. To meet the growing healthcare needs of an already aging human population, we need to determine the casual underlying cellular processes that promote aging and lead to increased susceptibility to disease. For over two decades evidence has accumulated from various animal models and cross sectionally in humans that mitochondria play a central role in the process of human aging. Simultaneously, we know that aging can be accelerated in human populations under chronic physical and psychological stress. Therefore, pathways whereby stress and mitochondria influence human aging must exist, but the connection between these two systems has never been studied. Here, we hypothesized that cells under chronic stress would have accelerated aging and that this effect could be mitigated by preventing mitochondrial oxidative stress. This study consisted of three parts. First, we modeled cell aging by culturing primary human fibroblasts in-vitro using both female and male participants. To map the kinetics of the aging process we tracked both replicative and molecular aging biomarkers throughout the cell’s lifespan. In parallel, we also monitored mitochondrial function using functional, genetic, and enzymatic assays. Second, we treated aging cells continually or at intervals with dexamethasone, a glucocorticoid mimetic hormone of psychological stress. Thereby we modelled both an adaptive acute stress and maladaptive chronic stress. Third, we tested if aging trajectories, and the effect of stress, could be altered through the reduction of oxidative stress by treating these groups with the mitochondrial-targeted antioxidant MitoQ or the general antioxidant N-acetyl-cysteine (NAC). Our findings show that cells aged in culture age, as measured by DNA Methylation age, at a 61 times faster rate than cells in the body. Further, cellular aging of chronically stressed cells, as measured by replicative senescence, accelerates by over 20%. Additionally, our results show that control cell’s mitochondrial bioenergetics decreases by over 50% with age but chronically stressed cells increase by over 150%. This increase of mitochondrial function was further corroborated by enzymatic, inflammatory, and genetic mitochondrial measures. These results demonstrate that the chronic stress-induced accelerated aging seen in human populations can be modelled in culture. Functionally, chronic stress caused a distinct mitochondrial signature that was not rescued by antioxidant treatment. Thus, this study offers further evidence implicating mitochondria as a central mediator between stress and human aging. Future work could use this cell-stress model for identifying biological mechanisms and therapeutic targets of the stress-aging cascade.