Myostatin (GDF8)

Myostatin, also called GDF8, is a secreted protein in the TGF-β family, and the main brake on your muscle growth. McPherron, Lawler, and Lee first characterized it in 1997. Your muscle fibers make it. It circulates in an inactive, bound form. It signals through activin type II receptors (ActRIIA/B) to activate SMAD2/3. That suppresses muscle stem-cell growth and protein-making. When it is knocked out, muscle balloons. That is seen in certain cattle and dogs. And, as large human genetic datasets confirm, in some people too, proving its inhibitory role. The protein follistatin neutralizes myostatin by binding it directly; FSTL-3 and GASP-1 add more regulation. Circulating myostatin runs 34% higher in older versus younger women (Bergen 2015), fitting a role in muscle loss (sarcopenia). In men the age trend reverses, hinting at sex-specific roles. A 2025 Phase I trial (Gonzalez Trotter et al.) is telling. Blocking both GDF8 and activin A together (but not GDF8 alone) substantially raised lean mass in postmenopausal women. That shows the two ligands cooperate. Several drugs (monoclonal antibodies and activin-receptor decoys like bimagrumab and landogrozumab) have reached Phase II/III for sarcopenia and cachexia. But none has a specific sarcopenia approval as of 2026, and functional gains have been inconsistent.

Last reviewed: June 22, 2026

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