Follistatin-344

Follistatin-344 (FST-344) is the predominant isoform of follistatin found in muscle tissue. It functions as a binding protein that sequesters myostatin (GDF-8) and activin A, two powerful inhibitors of muscle growth. By neutralising these signals, FST-344 allows unchecked activation of the Akt/mTOR pathway, leading to pronounced skeletal muscle hypertrophy in animal models.

Research in mice with FST-344 overexpression shows muscle mass increases of 200–300% over controls, with no observed cardiac hypertrophy. Human and primate studies remain in early phases, with gene therapy vectors currently in clinical trials for Duchenne muscular dystrophy and spinal muscular atrophy.

FST-344 binds myostatin and activin A with high affinity, preventing their interaction with activin type II receptors (ActRIIA/B). This disinhibits Smad2/3 phosphorylation suppression, allowing full Akt/mTOR/p70S6K anabolic signalling. FST-344 also upregulates satellite cell proliferation, accelerating muscle repair and regeneration.

Research-only compound. No approved human therapeutic form exists. Most studies use recombinant protein or AAV-delivered FST-344 gene constructs. Exogenous peptide administration has very short circulatory half-life due to rapid receptor binding and clearance.