Myostatin (GDF-8)

Myostatin, also called GDF-8, is a secreted signal that tells muscle to stop growing. It is made as a larger precursor and trimmed down to a short active form, two copies of which lock together. It docks onto receptors on the muscle cell surface and sets off an internal cascade that suppresses the production of new muscle fibres and promotes wasting. Animals and people lacking myostatin are strikingly muscular — Belgian Blue cattle, certain whippets, and one documented human case — making it among the best-validated single-gene muscle targets known. That has become commercially urgent because GLP-1 weight-loss drugs strip muscle along with fat. Trevogrumab is in trials alongside semaglutide, and in the Phase 2 EMBRAZE trial adding apitegromab to tirzepatide produced 1.9 kg less muscle loss than tirzepatide alone, retaining about 55 percent more lean mass. Bimagrumab is often grouped with these, but it blocks the receptors rather than myostatin itself, which also shuts down related signals and explains its larger effect.