Follistatin 344

Follistatin-344 (FST-344)

Evidence & Status

  • Preliminary / Experimental
  • Preliminary

At a Glance

The cell-associated isoform of follistatin, a naturally occurring inhibitor of myostatin and activin that places a brake on muscle growth. Studied in muscle biology, Duchenne muscular dystrophy research, and as a scientific tool for understanding myostatin-pathway inhibition.

Plain English

Researchers study Follistatin 344 because it naturally blocks myostatin — a protein that limits how much muscle the body can grow — as well as activin, which influences muscle, bone, and reproductive biology. Scientists are interested in whether follistatin's ability to remove these inhibitory signals could be relevant to conditions characterized by severe muscle loss. It has also been explored in gene therapy research contexts for muscular dystrophy. Most available research is preclinical, and significant questions about safety, specificity, and physiological effects remain open.

Overview

A naturally occurring glycoprotein that binds and neutralizes myostatin (GDF-8) and activin A, both potent inhibitors of muscle growth. By blocking these TGF-beta family members, follistatin dramatically disinhibits muscle hypertrophy pathways. Also plays roles in fertility and follicle development. Gene therapy studies have demonstrated profound muscle mass gains.

Research Summary

Follistatin-344 evidence is largely preclinical, with dramatic muscle hypertrophy demonstrated in animal models via myostatin and activin A inhibition. One Phase 1/2a human study (Mendell et al., 2015) examined follistatin gene therapy using an AAV1.CMV.FS344 vector for Becker muscular dystrophy. This gene-therapy study is NOT evidence for injectable FST-344 peptide protocols; the delivery system, mechanism, and regulatory pathway are entirely distinct. Direct injectable FST-344 peptide has never been formally studied in controlled human trials. The previously stored PubMed identifiers (PMID 19714099 and PMID 15059942) were confirmed as entity mismatches and have been removed. Foundational preclinical evidence (Lee & McPherron, 2001) demonstrates that myostatin inhibition and follistatin overexpression produce pronounced skeletal muscle hypertrophy in animal models; this preclinical evidence is distinct from and should not be conflated with the AAV1.CMV.FS344 gene-therapy human study or injectable FST-344 peptide use. Profound anabolic effects in animals are preclinical only; oncogenic risk via activin pathway suppression remains a significant safety concern preventing clinical development of the injectable form. Evidence remains preliminary.

Research Areas

  • Muscle hypertrophy
  • Myostatin inhibition
  • Duchenne muscular dystrophy
  • Fertility & folliculogenesis
  • Sarcopenia

Safety & Risks

Serious Risks

  • Potential oncogenic risk via activin/TGF-beta pathway suppression; risk of connective tissue injury if muscle hypertrophy outpaces tendon adaptation; WADA prohibited

Reported Side Effects

  • Potential for excessive muscle growth relative to connective tissue capacity
  • Injection site reactions
  • Systemic inflammatory response (rare at research doses)
United States
Research only; WADA prohibited substance (competition)
United Kingdom
Research only; WADA prohibited
Australia
Research only; WADA prohibited
Canada
Research only; WADA prohibited

Citations & Sources