Follistatin-344

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Snapshot

Chemistry and make-up

Follistatin 344 is not a short synthetic peptide but a ~37 to 38 kDa recombinant glycoprotein, one of the natural isoforms of human follistatin (the gene produces FS-317, FS-344 and others by alternative splicing). The 344-residue form carries a 29-amino-acid signal peptide; once that is removed the mature FST-315 circulating protein remains. Structurally it has a heparin-binding N-terminal domain followed by three cysteine-rich follistatin domains (FSD1, FSD2, FSD3), and those domains form the surface that grips activin and myostatin. Because it is a folded, disulfide-rich, potentially glycosylated protein made by recombinant expression (not solid-phase synthesis), the meaningful QC questions are identity, correct folding, glycosylation state and endotoxin, not peptide sequencing or a single exact mass. The molecular formula and any PubChem/UniProt identifiers should be taken from the batch CoA and primary databases rather than assumed.

What it is studied for (evidence)

• Mechanism (well characterised [A]): follistatin is a high-affinity antagonist of the TGF-beta superfamily. By binding myostatin (GDF-8), activin A and activin B, it prevents them from signalling through their receptors. Myostatin is a natural brake on skeletal-muscle growth, so neutralising it removes that brake, the mechanism behind the dramatic muscle phenotypes seen in myostatin-null animals and in follistatin-overexpression models [A].
• Established: the myostatin/activin biology and the preclinical muscle effects are solid. Follistatin gene therapy and follistatin overexpression produce large muscle-mass increases in mice and non-human primates, and follistatin is a genuine, heavily studied node in muscle and fibrosis biology [A].
• Emerging / thin: human evidence is early and mostly gene-therapy based, not injected-protein based. Clinical work has explored follistatin gene therapy in muscular dystrophies (for example Becker and inclusion-body myositis) with mixed, early-stage results [A]. There is no established efficacy for an injected recombinant follistatin-344 protein for muscle building in healthy people, and a large protein injected peripherally faces real bioavailability and half-life problems.
• Marketing claims vs data: vendors sell “Follistatin 344” as an injectable muscle-growth and fat-loss peptide with dosing charts. This borrows from myostatin-knockout genetics and gene-therapy studies, not from trials of the injected protein, and glosses over whether a 38 kDa protein even survives and acts as claimed after peripheral injection. Treat all muscle-growth and dosing claims as marketing.
• Human clinical status: no approved follistatin product. Human activity is at the gene-therapy research stage; injected recombinant follistatin-344 is a research reagent and grey-market physique product, not a medicine.

Handling, format and stability

Supplied lyophilised; reconstituted with bacteriostatic or sterile water for research handling (no dosing guidance here). As a large, disulfide-rich, possibly glycosylated protein it is more fragile than a small peptide: sensitive to heat, surface adsorption, aggregation and repeated freeze-thaw, so the lyophilised powder is stored cold and dark, reconstituted material is treated as short-lived and cold-chain dependent, and aliquoting before freezing is preferable to repeated thaw cycles. Research-reagent grades are often supplied with a carrier protein, which a grey-market physique vial usually will not be, a difference that matters for both stability and stated content.

Regulatory and trade status

• UK/EU RUO: research use only; not an approved medicine. Muscle-growth, physique or anti-ageing framing pushes a listing toward “medicinal product by presentation”, so keep listings strictly RUO with no performance claims.
• US: no approved follistatin drug. Follistatin gene therapies are investigational (clinical-trial stage), which means the target is on regulators’ radar; an injected “follistatin-344” research protein is not an approved product.
• WADA (sport): prohibited. Agents that reduce or neutralise myostatin, and growth factors affecting muscle, are named under S2 (peptide hormones, growth factors, related substances and mimetics), “myostatin function-altering agents” / growth-factor modulators, prohibited at all times. Follistatin falls squarely here [B — confirm current-year WADA wording].
• Customs / import: a known muscle-building agent in the myostatin-inhibitor class, so elevated enforcement interest relative to a benign repair peptide.

Sources

• [A] Follistatin, myostatin (GDF-8) and activin biology; follistatin overexpression / gene therapy increases muscle mass (preclinical and early clinical) — NCBI/PMC review literature — https://www.ncbi.nlm.nih.gov/pmc/
• [A] Follistatin gene therapy in muscular dystrophy (Becker MD, inclusion-body myositis), early-stage human trials — ClinicalTrials.gov / PubMed — https://pubmed.ncbi.nlm.nih.gov/
• [B] UniProt P19883 (FST_HUMAN), follistatin isoforms and domain structure — https://www.uniprot.org/uniprotkb/P19883/
• [B] WADA Prohibited List, S2 peptide hormones / growth factors (myostatin function-altering agents, growth-factor modulators) — https://www.wada-ama.org/en/prohibited-list
• [D] Vendor/clinic pages (PeptideInsight, MedsBase, Paramount Peptides, Pep-Pedia) — commercial; publish dosing and muscle-growth claims, which we do not use.

Plain summary

Follistatin 344 is not a small peptide but a roughly 38 kDa recombinant protein that blocks myostatin, the body’s natural brake on muscle growth, along with the activins. The muscle-building science is real but comes from myostatin-knockout animals and follistatin gene therapy, not from trials of the injected protein, and there is no approved product and no solid human evidence that an injected follistatin-344 vial builds muscle. For AxYn it is a strict RUO SKU where the CoA must treat it as a folded glycoprotein (isoform stated, protein-appropriate purity methods, endotoxin note), not as a simple peptide, and every listing stays research use only, with the muscle claims left off.

For laboratory and research use only (RUO). Not for human or veterinary use, not for consumption, and not a medicine. Information is a research summary, not medical advice, and contains no dosing guidance.

For laboratory research use only. Not for human or veterinary use, not for consumption, and not a medicine. This is a research summary, not medical advice, and contains no dosing guidance.