MicroRNA-129-5p inhibits C2C12 myogenesis and represses slow fiber gene expression in vitro.

The miR-129 family is widely reported as tumor repressors, although their roles in skeletal muscle have not been fully investigated. Here, the function and mechanism of miR-129-5p in skeletal muscle, a member of the miR-129 family, were explored using C2C12 cell line. Our study showed that miR-129-5p was widely detected in mouse tissues, with the highest expression in skeletal muscle. Gain- and loss-of-function study showed that miR-129-5p could negatively regulate myogenic differentiation, indicated by reduced ratio of MyHC-positive myofibers and repressed expression of myogenic genes, such as , , and . Furthermore, miR-129-5p was more enriched in fast extensor digitorum longus (EDL) than in slow soleus (SOL). Enhanced miR-129-5p could significantly reduce the expression of mitochondrial cox family, together with that of , and knockdown of miR-129-5p conversely increased the expression of cox genes and . Mechanistically, miR-129-5p directly targeted the 3'-UTR of , which was suppressed by miR-129-5p agomir at both mRNA and protein levels in C2C12 cells. Moreover, overexpression of could rescue the inhibitory effects of miR-129-5p on the expression of myogenic factors and . Collectively, our data revealed that miR-129-5p is a negative regulator of myogenic differentiation and slow fiber gene expression, thus affecting body metabolic homeostasis.