Follistatin-344
Follistatin-344 is the shorter of the two major human follistatin splice variants — a myostatin- and activin-binding protein studied mainly through animal and human gene-therapy research, with essentially no published data on synthetic follistatin-344 peptide administered by direct injection.
This page is a research-orientation summary, not a dosing guide. For anything beyond general background, read the primary literature or talk to a qualified clinician — specifics like amount, frequency, or administration aren't something we publish here.
What it does & how it works
Follistatin-344 (FS-344) is a naturally occurring splice isoform of the follistatin gene that binds and neutralizes myostatin (GDF-8) and activin A, both TGF-β superfamily ligands that normally signal through activin type II receptors to activate SMAD2/3 signaling and restrain skeletal muscle growth. By sequestering these ligands, follistatin prevents them from engaging their receptors, relieving the brake on satellite cell proliferation and muscle protein accretion. Unlike the longer FS-288 isoform, FS-344 diffuses more freely from the cell surface and has comparatively lower affinity for activin, a property researchers have leveraged in attempts to limit off-target endocrine effects.
Typical results seen in research
In mice, viral (AAV1) gene delivery of FS-344 produced long-term, dose-dependent increases in skeletal muscle mass and strength in both healthy animals and a dystrophic (mdx) model, with effects sustained for well over a year. In a small (n=6) Phase 1/2a human gene-therapy trial for Becker muscular dystrophy, intramuscular injection of an AAV1 vector carrying the FS-344 gene improved 6-minute walk distance in most participants with no serious treatment-related adverse events — but this delivered the FS-344 gene for sustained local protein production via a viral vector, which is pharmacologically distinct from injecting synthetic follistatin-344 peptide directly. No published studies test injectable recombinant follistatin-344 peptide on its own pharmacokinetics or muscle effects in any species.
How it’s commonly used
In published research, follistatin-344 has been delivered via localized (typically intramuscular) injection, including as the transgene payload of an AAV viral vector in the only human study conducted to date; it is not an oral compound, as it is a protein that digestion would degrade.
- Proceedings of the National Academy of Sciences · 2008 Long-term enhancement of skeletal muscle mass and strength by single gene administration of myostatin inhibitors
- Molecular Therapy · 2015 A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy
- Journal of Neuromuscular Diseases · 2015 Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy
Curated from published literature for research orientation. Not an exhaustive review, and not a substitute for reading primary sources.