DNA demethylation enhances myoblasts hypertrophy during the late phase of myogenesis activating the IGF-I pathway

Skeletal muscle regeneration and hypertrophy are important adaptive responses to both physical activity and pathological stimuli. This research was performed to investigate DNA demethylation action on the late phase of muscle differentiation and early stage of hypertrophy. The epigenetic process involved in myogenesis was studied with the DNA-demethylating agent 5-azacytidine (AZA). We induced muscle differentiation in C2C12 mouse myoblasts in the presence of 5 μM AZA and growth or differentiation medium for 48, 72, and 96 h. To study a potential AZA hypertrophic effect, we stimulated 72 h differentiated myotubes with AZA for 24 h. Unstimulated cells were used as control. By western blot and immunofluorescence analysis, we examined AZA action on myogenic regulatory factors expression, hypertrophic signaling pathway and myotube morphology. During differentiation, protein levels of myogenic markers, Myf6 and Myosin Heavy Chain (MyHC), were higher in AZA stimulated cells compared to control. Myostatin and p21 analysis revealed morphological changes which reflect a tendency to hypertrophy in myotubes. In AZA stimulated neo formed myotubes, we observed that IGF-I pathway, kinases p70 S6, 4E-BP1, and ERK1/2 were activated. Furthermore, AZA treatment increased MyHC protein content in stimulated neo myotubes. Our work demonstrates that DNA demethylation could plays an important role in promoting the late phase of myogenesis, activating endocellular pathways involved in protein increment and stimulating the hypertrophic process.