Caveolin-3 regulates the activity of Ca²⁺/calmodulin-dependent protein kinase II in C2C12 cells.

Caveolins, encoded by the <i>Cav</i> gene family, are the main components of caveolae. Caveolin-3 (<i>Cav3</i>) is specifically expressed in muscle cells. Mutations in <i>Cav3</i> are responsible for a group of muscle diseases called caveolinopathies, and <i>Cav3</i> deficiency is associated with sarcolemmal membrane alterations, disorganization of T-tubules, and disruption of specific cell-signaling pathways. However, Cav3 overexpression increases the number of sarcolemmal caveolae and muscular dystrophy-like regenerating muscle fibers with central nuclei, suggesting that the alteration of Cav3 expression levels or localization influences muscle cell functions. Here, we used mouse C2C12 myoblasts in which <i>Cav3</i> expression was suppressed with short hairpin RNA and found that <i>Cav3</i> suppression impaired myotube differentiation without affecting the expression of <i>MyoD</i> and <i>Myog</i>. We also observed an increase of intracellular Ca²⁺ levels, total calpain activity, and Ca²⁺-dependent calmodulin kinase II (CaMKII) levels in <i>Cav3</i>-depleted myoblasts. Importantly, those phenotypes due to <i>Cav3</i> suppression were caused by the ryanodine receptor activation. Furthermore, pharmacological inhibition of CaMKII rescued the impairment of myoblast differentiation due to <i>Cav3</i> knockdown. Our results suggest that <i>Cav3</i> regulates intracellular Ca²⁺ concentrations by modulating ryanodine receptor activity in muscle cells and that CaMKII suppression in muscle could be a novel therapy for caveolinopathies.