Enhancement of vitamin C-induced myogenesis by inhibition of extracellular signal-regulated kinase (ERK) 1/2 pathway

Myogenesis is a complex process that is regulated by a variety of factors. We have previously shown that vitamin C and mild endoplasmic reticulum stress synergistically enhance myogenesis. The present study evaluated the effects of vitamin C (ascorbic acid (AsA) and AsA 2-phosphate (AsAp)) and extracellular signal-regulated kinase (ERK) 1/2 pathway on myogenesis. Treatment with U0126, an inhibitor of MEK1/2 that phosphorylates and activates ERK1/2, during the differentiation, increased the mRNA levels of Myod and Myog with an increase in the protein level of myosin heavy chain (MYH)1/2. Treatment with AsA or AsAp alone had minimal effects on myogenesis in C2C12 cells. However, combination treatment with vitamin C and U0126 greatly enhanced myogenesis; the number of thick and long myotubes was increased, and the expression of MYH1/2 was also increased. PD98059, another MEK1/2 inhibitor, also enhanced myogenesis in combination with vitamin C. These results indicate that relief of endogenous ERK1/2 activity enhances vitamin C-mediated myogenesis, suggesting a functional interaction between endogenous ERK1/2 activity and vitamin C. In addition, inhibition of p38 mitogen-activated protein kinase repressed myogenesis in the presence of vitamin C. Thus, vitamin C is a conditional factor that modulates myogenesis.