ActivinA activates Notch1-Shh signaling to regulate proliferation in C2C12 skeletal muscle cells.

The myoblast is a precursor cell that rebuilds muscle tissue after trauma in human and animal skeletal muscle tissue. Proliferation of myoblasts is important for skeletal muscle damage repair and is controlled by numerous transcription factors and signals. The regulation of these signaling pathways and their complex interactions are not fully understood. This study aims to determine the physiological functions of Activin A, Notch and Sonic Hedgehog (Shh) signaling in the proliferation of mouse C2C12 myoblasts and to explore their interactions. Activin A facilitated proliferation of C2C12 cells and promoted the conversion of G1 into S phase in cell cycle, whereas addition of the receptor inhibitor SB431542 attenuated the proliferation activity of rActA on C2C12 cells. Activin A also activated Notch and Shh signaling, while blockage of these pathways attenuated the function of Activin A in cell cycle. Inhibition of the Notch signaling by Notch response inhibitor DAPT significantly down-regulated the expression of Shh signaling molecules, whereas exogenous rShh reversed the inhibition of C2C12 cells proliferative activity induced by DAPT, indicating Notch signaling act upstream of the Shh pathway. Furthermore, inhibition of Notch signaling weakened the activation of Activin A-mediated Shh signaling. Taken together, our results provide a novel role of Activin A in regulating the proliferation of C2C12 skeletal muscle cells, which impacts ActivinA-Notch1-Shh signaling pathways.