The epigenetic landscape of skeletal muscle in response to exercise and aging

Skeletal muscle exhibits a remarkable level of plasticity that enables it to adapt to exercise training, as well as the deleterious effects of aging. Fundamental to this malleability are epigenetic processes, which collectively enhance chromatin remodeling and subsequently alter DNA availability for gene expression. A growing body of evidence has demonstrated that acute exercise is a powerful inducer of epigenetic remodeling, capable of stimulating gene-specific alterations, which transcriptionally activate exercise-responsive genes. These epigenetic processes, including DNA methylation and various histone modifications, are highly responsive to exercise-induced signaling cascades and mitochondrially-related metabolites, together indicating that exercise can modulate the nuclear and mitochondrial epigenome as a mechanism to regulate gene expression. However, aging is characterized by a unique epigenetic signature, which likely supports the alterations in gene expression observed with age. Yet, the effects of exercise on epigenetic regulation with age remain underexplored. To investigate the intersectionality of these two phenotypes and highlight significant gaps within the literature, this review aimed to discuss the different types of epigenetic modifications that have been reported within skeletal muscle and how they are altered with acute and chronic exercise. Furthermore, we aimed to analyze mitochondrial epigenetics and their role in mediating alterations in mitochondrial-nuclear crosstalk observed with exercise and age. Elucidating age-dependent adaptations in the epigenome and the differential effects of exercise in these populations will help uncover the complexity of gene regulation with age, and importantly, reveal how exercise can regulate many of these processes to improve muscle health.