Mild heat stimulation facilitates muscle hypertrophy in C2C12 and mouse satellite cells through myokine release to the culture medium.

Mild heat stimulation is defined as a stimulation that occurs several degrees above optimal cell culture or body temperatures. Muscle hypertrophy in C2C12 cells is reportedly facilitated by 39 °C mild heat stimulation. However, the underlying molecular mechanisms by which 39 °C mild heat stimulation promotes muscle hypertrophy remains elusive. In this study, we aimed at understanding the details of these mechanisms. First, we found that 39 °C mild heat stimulation has little or no effect on Myogenesis-Related Factor (MRF) expression both in C2C12 and mouse primary satellite cells. Therefore, we hypothesized that 39 °C mild heat stimulation promotes muscle hypertrophy through myokines, essential components in myogenesis. Interestingly, we observed muscle hypertrophy in the group cultured at 37 °C in conditioned medium from 39 °C compared to the group cultured at 37 °C in conditioned medium from 37 °C in the case of both C2C12 and mouse primary satellite cells. These results suggest that 39 °C mild heat stimulation promotes muscle hypertrophy through myokines, once released in the culture medium. Finally, we identified Decorin as a hypertrophy-inducing myokine candidate. Therefore, in this study, we demonstrated that 39 °C mild heat stimulation contributes to muscle hypertrophy through enhancing Decorin gene expression in C2C12 and mouse primary satellite cells.