Follistatin 315
Educational information only — not medical advice. Many listed compounds are not FDA-approved for human use. Consult a licensed clinician before starting, changing, or stopping any protocol.
Overview
Follistatin 315 is the mature, circulating form of follistatin — a protein that binds and inactivates myostatin and activin, both of which suppress muscle growth. Unlike the shorter, more potent FS-288 isoform, FST-315 exhibits lower affinity for cell-surface receptors and is thought to mediate systemic effects when circulating in blood.
Follistatin 315 is primarily discussed in the context of muscle research. Most evidence to date comes from preclinical studies in animals and early-phase gene therapy trials in specific disease populations. Injectable FST-315 peptide products have not been evaluated for safety or efficacy in humans and are available only for research purposes.
How it works
Follistatin 315 is a binding protein that sequesters myostatin and activin ligands, preventing them from engaging with their cognate cell-surface receptors. This blocks downstream SMAD-mediated signaling and removes inhibitory signals on myogenesis (muscle-cell differentiation) and muscle protein synthesis.
In preclinical models, follistatin-mediated myostatin and activin inhibition has been associated with rapid skeletal muscle hypertrophy, increased strength, and improvements in markers of muscle fiber integrity. The precise timing, tissue distribution, and long-term effects of injectable follistatin peptide in humans remain unstudied.
Reported benefits
- Stimulation of skeletal muscle hypertrophy (animal data)
- Increased muscle strength and force output (animal and early gene-therapy data)
- Potential support for muscle maintenance in degenerative conditions (investigational gene therapy)
These are reported effects in research settings, not guaranteed outcomes in humans.
Considerations & side effects
Because human trials using injectable follistatin peptide are absent, the safety profile in humans is not established. Reported side effects in preclinical and gene-therapy studies are generally mild and may include injection-site reactions and transient elevations in muscle-injury markers.
Product purity and composition vary widely in the research-chemical market. Follistatin is not a substitute for evaluation and treatment by a qualified clinician. Long-term systemic effects of myostatin and activin inhibition in humans are not known.
Frequently asked
What is Follistatin 315?
Follistatin 315 (FST-315) is the mature, circulating form of follistatin — a naturally occurring protein that binds and neutralizes myostatin and activin. Follistatin 315 is generated from FST-344 (a longer isoform) via proteolytic cleavage in the body.
How does Follistatin 315 differ from Follistatin 344?
FST-344 is a longer isoform that is processed in vivo to generate the shorter, more widely circulating FST-315. FS-315 has lower cell-surface affinity than FS-288, making it suited for systemic effects. FST-344 is the typical form used in research peptide products.
Is Follistatin 315 FDA-approved?
No. Follistatin 315 is not approved by the FDA or any major regulator for human therapeutic use. It is sold for research purposes only. Gene therapy variants have been studied in Phase 1/2a trials for muscular dystrophy but remain investigational.
What does it target?
Follistatin 315 binds myostatin and activin, two negative regulators of muscle growth, and prevents them from activating their cell-surface receptors. This removes a brake on muscle protein synthesis and may support hypertrophy.
Is there human evidence?
Robust preclinical data exists in rodents and nonhuman primates. Limited Phase 1/2a gene-therapy data exists for neuromuscular diseases. Injectable follistatin peptide has no established human efficacy or safety data.
References
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