Follistatin-344
FS-344 / Follistatin
Follistatin-344 is a recombinant protein corresponding to the full-length FS344 isoform of human follistatin, a naturally occurring glycoprotein that binds and neutralizes myostatin and other TGF-beta superfamily members including activins. By inhibiting myostatin, it removes the primary negative regulator of skeletal muscle growth, potentially allowing significant muscle hypertrophy. It is a research compound investigated in gene therapy and recombinant protein contexts for muscular dystrophy, age-related sarcopenia, and muscle wasting conditions.
Mechanism of Action
Activin-binding protein that potently inhibits myostatin, a negative regulator of muscle growth. Blocking myostatin removes the genetic brake on muscle hypertrophy. Also inhibits FSH (follicle-stimulating hormone) as activin is required for FSH release.
Research Protocols
For research purposes only. Not medical advice.
Research protocols use 100-200mcg daily via subcutaneous injection for 10-30 days. Short cycles due to potential FSH suppression. Some protocols use 50mcg daily for extended periods.
Research Notes
Clinical Research Status
Follistatin-344 gene therapy (AAV-delivered) has been evaluated in Phase 1/2 clinical trials for inclusion body myositis and Becker muscular dystrophy at Nationwide Children's Hospital. Recombinant protein administration remains purely experimental with no formal clinical trials for the injectable form. The gene therapy approach (delivering the follistatin gene via adeno-associated virus) has shown more clinical progress than exogenous protein administration due to delivery challenges.
Key Published Findings
Animal studies demonstrate that follistatin overexpression produces dramatic muscle hypertrophy (up to 100% increase in muscle mass in mice) by antagonizing myostatin and activin A signaling. Gene therapy trials in humans showed modest improvements in muscle function and walking distance in inclusion body myositis patients. Recombinant follistatin protein has limited bioavailability due to rapid clearance, proteolytic degradation, and challenges in achieving sustained tissue-level concentrations sufficient for myostatin neutralization.
Safety Profile
Gene therapy approaches carry standard AAV-associated risks including immune responses to the viral vector and potential insertional mutagenesis. For recombinant protein, theoretical concerns include effects on reproductive function (activins regulate FSH secretion) and potential tumor promotion through TGF-beta pathway inhibition. No systematic human safety data exists for subcutaneous or intramuscular injection of recombinant follistatin-344 protein outside of gene therapy trials.
Comparison to Related Compounds
Unlike ACE-031 (a soluble activin receptor decoy) which was discontinued due to safety concerns, follistatin is an endogenous protein with a natural role in myostatin regulation. Compared to direct myostatin antibodies (stamulumab/MYO-029), follistatin has broader activity by also neutralizing activins and other TGF-beta ligands. The FS344 isoform is processed into FS315 and FS303 forms with different tissue distributions and binding protein interactions.
Community Observations
The research community notes significant skepticism about the efficacy of subcutaneously injected recombinant follistatin-344 reaching muscle tissue at concentrations sufficient to meaningfully inhibit myostatin. Most experts consider the gene therapy approach far more promising than protein injection for achieving sustained myostatin inhibition. Quality control of commercially available recombinant follistatin is a major concern, as proper protein folding is critical for bioactivity.
Half-Life
~Unknown (protein)
Reconstitution
Bacteriostatic water (BAC)
Storage
Lyophilized
Store at -20C for long term. Refrigerate 2-8C for short term.
Reconstituted
Refrigerate 2-8C. Use within 7 days.
US Legal Status
Also Known As
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