Follistatin is a naturally occurring glycoprotein that acts as a potent inhibitor of myostatin and other members of the TGF-β family, including activin A, activin B, and certain BMPs. By binding directly to myostatin, follistatin reduces negative regulation of muscle growth, while also promoting angiogenesis, reducing inflammation, and limiting fibrosis.

Therapeutic approaches utilize specific isoforms for improved safety and reduced endocrine disruption. Formulations include localized fusion proteins for targeted muscle therapy and systemic variants delivered via adeno-associated virus (AAV) gene therapy or recombinant proteins, enabling broader applications from neuromuscular repair to metabolic modulation. Follistatin has shown strong preclinical and early clinical evidence for enhancing muscle mass, improving function, and supporting tissue recovery.