Comparative analysis of semaphorin 3A in soleus and EDL muscle satellite cells in vitro toward understanding its role in modulating myogenin expression

Resident myogenic stem cells, satellite cells, up-regulate a secreted multi-functional modulator, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle-crush injury and treatment with hepatocyte growth factor (HGF) or basic fibroblast growth factor (FGF2). Here, we add evidence that the Sema3A expression and secretion induced by the growth factors is significantly higher in primary cultures from adult rat soleus than from the fast-twitch extensor digitorum longus (EDL) muscle. The higher Sema3A response, revealed by quantitative PCR and Western blotting of cell lysates and conditioned media, may account for the higher myogenin expression of soleus muscle satellite cells early in differentiation since addition of recombinant Sema3A stimulates myogenin expression in cultures. These experiments also showed that mRNA expression of plexin A2, which together with neuropilins, constitutes Sema3A composite-receptors, was higher in satellite cells from soleus than EDL with no difference in plexin A1 and A3 and neuropilin-1 and 2 levels. These comparative studies, therefore, highlight a possible Sema3A-plexin A2-myogenin signaling axis that may ensure promoting early differentiation by soleus muscle satellite cells.