Myostatin

Myostatin, also known as Growth Differentiation Factor 8 (GDF-8), is a secreted protein belonging to the transforming growth factor-beta (TGF-beta) superfamily that functions as a potent negative regulator of skeletal muscle mass. Produced primarily by skeletal muscle cells, myostatin acts in an autocrine and paracrine manner by binding to activin type II receptors (ActRIIB), which then recruit and phosphorylate ALK4/ALK5, activating Smad2/3 signalling to suppress muscle-specific gene expression and satellite cell proliferation. Natural loss-of-function mutations in the myostatin gene result in dramatic muscle hypertrophy, as famously observed in Belgian Blue cattle and certain dog breeds. In humans, myostatin levels increase with age, inactivity, and chronic disease, contributing to sarcopenia and muscle wasting. Research into myostatin inhibition has explored antibodies, soluble receptors, and follistatin-based approaches. Growth hormone secretagogues such as CJC-1295 and Ipamorelin may indirectly modulate myostatin levels through elevated GH and IGF-1 signalling, which opposes myostatin's catabolic effects on muscle tissue.