A Satellite Cell-Dependent Epigenetic Signature Of Adult Skeletal Muscle Identity After Lifelong Physical Activity

Satellite cells comprise only 2-3% of cells in adult skeletal muscle yet play a critical role in muscle plasticity, particularly during prolonged exercise training adaptation. The mechanisms by which these mononuclear cells mediate muscle fiber hypertrophy or attenuate atrophy with physical activity throughout the lifespan are still being elucidated, but epigenetic regulation may play a role. To investigate this possibility, we analyzed DNA methylation patterns in muscle tissue from female mice that engaged in lifelong voluntary unweighted wheel running with or without satellite cells; satellite cells were ablated in adulthood using the tamoxifen-inducible Pax7-DTA model. Wheel running for 13 months induced DNA methylation changes in the promoter regions of numerous muscle fiber-enriched genes - Dnm2, Mlip, Myl1, Myom2, Mstn, Tnnc1, Tnni2, Tpm1, and Ttn - only when satellite cells were present. These genes are fundamental to muscle fiber identity, cytoarchitecture, size, and function; the latter two we have shown to be compromised by the absence of satellite cells in these mice. Musk promoter methylation was altered only in the absence of satellite cells with lifelong running, which may relate to how satellite cells can influence muscle innervation status. We reveal novel epigenetic contributions from satellite cells to the myogenic identity of muscle fibers during lifelong physical activity, providing new directions for how these rare stem cells can promote muscle adaptation and function throughout the lifespan. At five months of age, mice were injected intraperitoneally with vehicle (15% ethanol in sunflower seed oil) or tamoxifen (2 mg/day, suspended in ethanol and sunflower seed oil) for five days, followed by a two-month washout period, then assignment to sedentary or wheel running groups – satellite cell replete (vehicle) or depleted (tamoxifen). Mice ran until ~20 months of age. Gastrocnemius muscles from subsets of mice (n=6/group) were used for methylation array analysis.