Follistatin
Follistatin (myostatin/activin antagonist)
Also known as: FST-344
A natural protein that blocks myostatin and activin, studied largely through gene therapy for muscle growth and muscular dystrophy.
Overview
Follistatin is a naturally occurring protein that binds and inhibits myostatin and activin, powerful brakes on muscle growth. Blocking them increases muscle mass in animal models, which has driven follistatin gene-therapy trials for muscular dystrophies. Direct peptide use is not an approved therapy, and the human evidence remains preliminary.
Mechanism of action
Sequesters myostatin and activin, releasing their inhibition of muscle growth and promoting muscle fiber size.
Key studies & citations
- Animal2001
Regulation of myostatin activity and muscle growth
Follistatin blocks myostatin binding to ActRIIB; transgenic mice overexpressing follistatin in muscle showed dramatic increases in muscle mass.
Proceedings of the National Academy of Sciences - Animal2007
Quadrupling muscle mass in mice by targeting TGF-beta signaling pathways
A follistatin transgene in myostatin-null mice produced about four times normal muscle mass, showing follistatin also blocks regulators beyond myostatin (activins).
PLoS One - Human2015
A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy
AAV1-delivered FS344 injected into the quadriceps of six patients: four improved six-minute walk distance (29 to 125 m), no adverse effects, reduced fibrosis on biopsy.
Molecular Therapy - Human2017
Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes
Six treated patients gained a median 56 m/year on six-minute walk versus a 26 m/year decline in matched untreated controls; small, non-randomized.
Molecular Therapy
Frequently asked questions
Does follistatin build muscle in humans?
Myostatin inhibition increases muscle in animals, and early gene-therapy trials are underway, but follistatin is not an approved muscle-building treatment and human evidence is preliminary.