Fibromodulin modulates myoblast differentiation by controlling calcium channel

Fibromodulin (FMOD) is a proteoglycan present in extracellular matrix (ECM). Based on our previous findings that FMOD controls myoblast differentiation by regulating the gene expressions of collagen type I alpha 1 (COL1α1) and integral membrane protein 2 A (Itm2a), we undertook this study to investigate relationships between FMOD and calcium channels and to understand further the mechanism by which they control myoblast differentiation. Gene expression studies and luciferase reporter assays showed FMOD affected calcium channel gene expressions by regulating calcium channel gene promoter, and patch-clamp experiments showed both L- and T-type calcium channel currents were almost undetectable in FMOD knocked down cells. In addition, gene knock-down studies demonstrated the COL1α1 and Itm2a genes both regulate the expressions of calcium channel genes. Studies using a cardiotoxin-induced mouse muscle injury model demonstrated calcium channels play important roles in the regeneration of muscle tissue, possibly by promoting the differentiation of muscle stem cells (MSCs). Summarizing, the study demonstrates ECM components secreted by myoblasts during differentiation provide an essential environment for muscle differentiation and regeneration.