Increased global DNA methylation by Dnmt3a disrupts skeletal muscle homeostasis, promotes age-related muscle atrophy, and reduces muscle metabolic elasticity

Loss of muscle mass and function—a hallmark of skeletal muscle aging—is known as sarcopenia. Moreover, mammalian aging is reportedly driven by loss of epigenetic information. However, the effect of epigenetic alterations on skeletal muscle homeostasis is unknown. In this study, we show that chronic elevation of global DNA methylation results in a myopathy-like phenotype and age-related changes in skeletal muscle. Overexpression of muscle de novo methyltransferase 3a (Dnmt3a) increased central nucleus-positive myofibers, predominantly in fast-twitch myofibers, and shifted muscle fiber type to stress-resistant slow-twitch myofibers, accompanied by increased inflammatory and senescent signatures, decreased mitochondrial OXPHOS complex I protein level, and reduced basal autophagy in skeletal muscle. Chronic Dnmt3a overexpression decreased muscle mass and strength, and impaired tolerance to endurance exercise with age. This age-related decline in endurance exercise capacity was accompanied by an augmented inflammatory signature in a manner that is enhanced with age and promoted muscle atrophy. Network analysis identified Akt1 as a potential hub gene. Dnmt3a expression not only reduced sensitivity to starvation-induced muscle atrophy by suppressing the FoxO-regulated autophagy and ubiquitin–proteasome systems, but also reduced the restorability from starvation-induced muscle atrophy. These data suggest that increased global DNA methylation disrupts skeletal muscle homeostasis, promotes age-related muscle atrophy, and reduces muscle metabolic elasticity. Overall design: Genomic DNAs were extracted from skeletal muscle (gastrocnemius) of Dnmt3a-Tg and age-matched WT mice. Libraries for whole-genome bisulfite sequencing was prepared as described in Miura F et al (2019), NAR, 47, e85.