Follistatin 315
Also known as: Follistatin 315, Follistatin-315
Follistatin 315 is the circulating isoform of follistatin, a myostatin-binding protein studied for promoting muscle growth by removing the brake on muscle development.
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Mechanism of Action
Follistatin 315 is the longer, soluble isoform of follistatin that binds and neutralizes members of the TGF-beta superfamily, most importantly myostatin (GDF-8) and activin A. By sequestering myostatin it blocks activation of the ActRIIB receptor and downstream SMAD2/3 signaling that normally restrains skeletal muscle growth. The net effect in models is disinhibition of muscle protein synthesis and satellite cell activity, favoring muscle hypertrophy; the 315 isoform has lower heparin/cell-surface affinity than FST-288, giving it a more systemic distribution.
- Half-life
- Relatively short in circulation; cleared within hours
- Administration Routes
- subcutaneous, intramuscular
- Research Status
- Preclinical
Reported Benefits
- Inhibits myostatin to promote muscle hypertrophy
- May increase lean muscle mass in models
- Neutralizes activin A signaling
- Studied for muscle wasting and atrophy conditions
- More systemic distribution than the FST-288 isoform
Potential Side Effects
- Limited human safety data
- Theoretical effects on reproductive and other activin-dependent tissues
- Possible injection-site reaction
- Risk of unregulated tissue growth with chronic myostatin suppression
Common Dosing
No validated human dosing; animal and research-grade protocols reference microgram-range injections. For research use only; not personal medical advice.
The dosing information above is aggregated from research literature and anecdotal community reports for educational purposes only. It is not a recommendation, prescription, or medical advice. Peptides are sold as research chemicals only and are not intended for human use.
Contraindications
- Known hypersensitivity to the peptide
- Active or history of malignancy
- Pregnancy or breastfeeding, given activin's reproductive roles
Follistatin 344
Follistatin 344 is the full-length precursor isoform of follistatin studied for blocking myostatin and activin to drive muscle growth and tissue repair.
ACE-031
ACE-031 is a soluble decoy receptor (ActRIIB-Fc fusion) studied as a myostatin inhibitor to increase muscle mass and strength.
IGF-1 LR3
IGF-1 LR3 (Long R3 IGF-1) is an engineered, long-acting analog of insulin-like growth factor 1 studied for sustained anabolic and tissue-growth signaling. Its modifications give it a far longer half-life than native IGF-1.
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Regulation of muscle mass by follistatin and activins
2010
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Biological activity of follistatin isoforms and follistatin-like-3 is dependent on differential cell surface binding and specificity for activin, myostatin, and bone morphogenetic proteins
2006
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Differential distribution of follistatin isoforms: application of a new FS315-specific immunoassay
2004
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Difference between follistatin isoforms in the inhibition of activin signalling: activin neutralizing activity of follistatin isoforms is dependent on their affinity for activin
2000
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Follistatin complexes Myostatin and antagonises Myostatin-mediated inhibition of myogenesis
2004