Effect of exercise on skeletal muscle-derived extracellular vesicles and regulation of mitochondrial biogenesis

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Skeletal muscle (SkM) is highly adaptable and plays a critical role in determining whole-body metabolic capacity. The gold standard response to chronic exercise (CE) is an increase in mitochondrial content & activity termed mitochondrial biogenesis (MB). While mechanisms regulating MB within SkM have been studied extensively, less is known about how SkM drives systemic adaptations. The lion's share of attention has been attributed to proteins released from SkM termed myokines, that can be released directly, or packaged in carrier vehicles called extracellular vesicles (EVs) to ferry them in the circulatory system. EVs are an evolutionary conserved method of intercellular communication, are released from all cells and contain biochemical cargo that can modify function in recipient cells. Previous work has shown that CE promotes an increase in systemic EV concentration, changes EV cargo, and that these EVs evoke protective adaptations. However, these EVs were mostly obtained from serum/plasma which contain EVs from all tissues in the body. The effect of CE specifically on SkM-EVs, and their role in mediating systemic adaptations to CE e.g. MB remains unknown. This is a critical gap in knowledge, as SkM is one of the largest organ systems, performs the physical work during CE, a reservoir of myokines, and known to regulate metabolic performance. I hypothesize that CE modifies SkM-EVs and that these SkM-EVs can mediate an increase in MB. Novel and exciting pilot data from my lab support this hypothesis. My NSERC DG research program will use cutting-edge molecular biology techniques to address this gap. We will use an in vitro model of chronic contractile activity (CCA) to isolate and measure SkM-EVs using established & validated techniques. SkM-EVs will be co-cultured with other cells, and changes in MB measured. We will genetically modify SkM cells to express a specific enzyme (cre), subject them to CCA, isolate EVs and inject into a double-reporter mouse. In this model, tissues that take up SkM-EVs will switch from red to green fluorescence. Since only the SkM-EVs contain the cre enzyme, this model will allow us to quantitatively track SkM-EVs in vivo post-CCA. Metabolically-active tissues will be harvested, EV uptake confirmed and changes in MB evaluated post-chronic treatment with CCA-SkM-EVs. Thus, my HQP will determine the effect of CCA on SkM-EVs & discover whether SkM-EVs can regulate MB using innovative and mechanistic techniques. The short-term results will lead to landmark discoveries that will create new knowledge about the effects of CCA on SkM-EVs and their effect on MB. The long-term goals of my NSERC DG research program are to elucidate upstream mechanisms of SkM-EV biogenesis, release and uptake, and downstream signalling pathways that mediate MB. My program will fuel interdisciplinary research with biotechnology and applied physiology fields to advance knowledge, benefit and accelerate Canadian research and promote HQP training.