Effect of myostatin on chemokine expression in regenerating skeletal muscle cells

Transforming growth factor-β (TGF-β) is implicated in the regulatory expression of chemokines that control multiple steps in myogenesis. However, it remains to be established whether myostatin, a member of the TGF-β superfamily, affects chemokine expression in skeletal muscle. We investigated the effects of myostatin on the expression of mRNAs and proteins for 4 chemokines (CXCL1, CXCL2, CXCL6, CCL2) in intact and regenerating musculus longissimus thoracis from normal-muscled (NM) and double-muscled (DM) cattle. These chemokines were expressed in regenerating muscle, and their expression was always lower in DM than in NM cattle. Immunohistochemistry revealed that CXCL1 and CXCL6 were detected in the regenerating areas of myoblasts and myotubes in both NM and DM cattle. In cultures of myoblasts isolated from the regenerating muscles, significantly less CXCL1, CXCL2 and CCL2 mRNA was expressed in DM myoblasts than in NM myoblasts during the proliferating stage (P-stage). The expression of CXCL1, CXCL2 and CCL2 mRNAs in NM myoblasts and CXCL1, CXCL2 and CXCL6 mRNAs in DM myoblasts decreased upon switching from P-stage to fusion stage (F-stage). Also, the expression of CXCL1, CXCL2 and CXCL6 mRNAs was significantly lower in DM than in NM myoblasts during the F-stage. The addition of 100 ng/ml myostatin during the F-stage attenuated the expression of CXCL1 and CXCL2 mRNAs and augmented that of CCL2. These results show for the first time that myostatin regulates the differential expression of chemokines in skeletal muscle cells.