Follistatin 344

Follistatin 344 is a synthetic or full-length version of the naturally occurring glycoprotein follistatin, which is encoded by the FST gene and produced in many tissues. It consists of 344 amino acids, representing the complete precursor form of the protein found in the human body.

Follistatin 344 is believed to promote muscle growth by inhibiting myostatin, a protein that limits muscle development. It may also support tissue repair and cellular regeneration, contributing to improved muscle strength and recovery.

Follistatin-344 mainly increases skeletal muscle mass and strength by blocking TGF-β family ligands such as myostatin and activin, which normally restrain muscle growth. Animal studies show robust muscle hypertrophy and improved contractile function after FS-344 delivery; mice treated with FS-344 had larger muscles and greater strength compared with controls. Overexpression of FS-344 also promotes satellite cell activation and appears to increase muscle protein synthesis, which helps grow and repair fibers. These molecular and cellular effects together explain why FS-344 consistently produces larger, stronger muscles in preclinical models ¹

Early human translation and broader preclinical work indicate added functional and age-related benefits beyond raw size. A phase 1/2a intramuscular gene therapy trial in Becker muscular dystrophy reported improved ambulation and muscle function after follistatin gene delivery. Studies in aged mice found improvements in neuromuscular junction innervation and transmission following follistatin treatment, suggesting potential to support muscle quality and neuromuscular function as well as mass. In short, FS-344 promotes larger muscles through myostatin/activin blockade and satellite-cell mediated growth, and those gains have translated into measurable functional improvements in disease and aging models and early clinical testing ².

The main negative side-effects associated with the use of Follistatin 344 (FS 344) appear to be modest in early gene-therapy trials but include theoretical and observed risks. In a Phase 1/2a muscle‐gene therapy trial for Becker muscular dystrophy, delivery of the FS 344 cassette produced no serious adverse events, no hormone (gonadotropin/testosterone) changes, and no organ system abnormalities in the short term ³. However, animal and observational human studies highlight potential metabolic and cardiovascular associations: elevated circulating follistatin levels have been correlated with increased risk of type 2 diabetes, heart failure, and all-cause mortality in large cohorts ⁴. Also, in animal models the anabolic hypertrophy induced by follistatin gene delivery did not always translate when muscle‐nerve interaction was compromised, which may indirectly point to limits or risks of use in denervated or pathologic muscle tissue ⁵.

Follistatin‑344 functions by binding and neutralizing members of the Myostatin and Activin A ligands in the TGF-β superfamily, thereby preventing them from signaling through activin type II receptors ⁶. This inhibition lifts the suppression of the Akt/mTOR pathway in skeletal muscle and thereby increases protein synthesis, as well as reduces expression of ubiquitin ligases involved in muscle protein degradation ⁷. In animal models of muscle atrophy, overexpression of follistatin leads to muscle hypertrophy by activating satellite cells and increasing protein synthesis in innervated muscle fibers.

Follistatin-344 is not an FDA-approved drug product; it has been the subject of research and clinical trials (including AAV-based follistatin gene therapy trials and orphan-designation activity) but does not have a marketed approval ⁸. Athletic/regulatory consideration: follistatin (including FS-344) is listed by WADA under the S4 category (myostatin/activin-modulating agents) and is treated as a prohibited, performance-enhancing agent in sport. Anti-doping agencies have active detection and research programs for follistatin doping ⁹.