Despite these findings, the underlying molecular mechanism leading to PI3K inhibitor LGMD1C/AD-RMD in caveolin-3-deficient muscle remains to be elucidated. Myostatin, a muscle-specific TGF-β superfamily member, is a therapeutic target of muscular dystrophy Myostatin is a muscle-specific transforming growth factor (TGF)-β superfamily member and negatively regulates skeletal muscle growth and skeletal muscle volume (19). Overexpression of myostatin causes severe muscle atrophy, whereas targeted disruption of myostatin increases skeletal muscle mass in mice (19, 20). Like most members of the TGF-β superfamily, Inhibitors,research,lifescience,medical myostatin is synthesized as a precursor protein

and undergoes proteolytic processing to generate an N-terminal prodomain and a biologically active, C-terminal disulfide-linked dimer (21). In the inactive state, the prodomain strongly inhibits the biological activity of the C-terminal dimer (22, 23), as do follistatin, and the

follistatin-related gene (FLRG); which are collectively called natural inhibitors for myostatin (24). The circulating Inhibitors,research,lifescience,medical active form of myostatin directly binds to and phosphorylates the type II serine/threonine kinase receptor, namely activin receptor IIB (ActRIIB) (Fig. ​(Fig.1)1) Inhibitors,research,lifescience,medical (25). This, in turn, phosphorylates the type I serine/threonine kinase receptors, namely activin receptor-like kinase 4/5 (ALK4/5) at the plasma membrane (25–27). The activation of a heteromeric receptor complex consisting of phosphorylated type II and type I serine/threonine kinase receptors induces the phosphorylation of intracellular

effectors, Inhibitors,research,lifescience,medical receptor-regulated Smads (R-Smads), namely Smad2/3 (26, 27). Phosphorylated R-Smads translocate to the nucleus from the cytoplasm, where it regulate the transcription of specific target genes inducing skeletal muscle atrophy (26–28). Figure 1 Putative scheme of the regulation of myostatin signaling by caveolin-3. Myostatin (MSTN) signaling is propagated through the myostatin receptor, a heteromeric complex consisting with transmembrane receptor serine/threonine kinases. Myostatin binds to … Notably, administration of a Inhibitors,research,lifescience,medical blocking antibody against myostatin, myostatin vaccine, and myostatin prodomain, or genetic introduction of a follistatin-derivative ameliorates the pathophysiology of dystrophin-deficient mdx mice (29–32). In addition, a blocking antibody against myostatin improves the condition of young model mice with δ-sarcoglycan-deficient tuclazepam LGMD2F (33). An adeno-associated virus (AAV)-mediated myostatin prodomain has ameliorates the pathology of calpain-3-deficient LGMD2A model mice (34). Therefore, myostatin inhibition through different strategies has recently come to be considered for a therapeutic option for muscular dystrophies. However, the precise molecular mechanism by which myostatin inhibition improves the above dystrophic skeletal muscle is not fully understood; i.e.