Follistatin-344

Follistatin-344 (FS344) is a naturally occurring peptide hormone and endogenous myostatin antagonist. It binds myostatin and related TGF-beta family ligands (notably activin A), removing the biological brake on skeletal muscle growth. In humans, FS344 has only been investigated as AAV1 gene therapy (AAV1-FS344) in Phase 1/2a trials - an injectable FS344 peptide without a viral vector has no published human data.

What is Follistatin-344 and how does it work?

Follistatin exists in several splice variants; FS344 (344 amino acids) is the form used in the clinical gene-therapy programmes. Its main binding partners are:

• Myostatin (GDF-8) - the central negative regulator of skeletal muscle mass,
• Activin A - involved in inflammation and muscle catabolism,
• other TGF-beta family members (including GDF-11, certain BMPs).

Neutralising these ligands shifts muscle turnover toward hypertrophy and regeneration.

Which clinical trials exist for Follistatin-344?

The only published human dataset comes from the programme of Jerry Mendell at Nationwide Children's Hospital (Columbus, OH):

• Becker muscular dystrophy (BMD): Phase 1/2a, intramuscular AAV1-FS344 into quadriceps and biceps, with significant improvement in the 6-minute walk test and quadriceps strength (Mendell et al., Mol Ther 2015, PMID 25322757).
• Sporadic inclusion body myositis (sIBM): Phase 1/2a with functional improvement (Mendell et al., Mol Ther 2017, PMID 28279643).
• Duchenne muscular dystrophy (DMD): Phase 1/2a, NCT02354781 - trial completed.

For injectable FS344 peptide without a viral vector there are no published human safety or pharmacokinetic data.

Which effects are being researched?

In BMD and sIBM, local muscle hypertrophy with measurable functional improvement has been demonstrated. Beyond these disease-specific indications, FS344 has been discussed for age-related sarcopenia and body composition on the basis of its dual myostatin/activin blockade - here the evidence remains purely preclinical.

How is FS344 prepared and stored?

The clinical trial products are administered intramuscularly by trained study staff. If you are working with research material, follow the peptide storage guide: powder and mixed solution (lyophilisate cool, dry, dark; reconstituted solution in the fridge at 2-8 °C). For clean reconstitution see the step-by-step reconstitution guide with BAC water; a broader look at helpful tools is in the Peptipedia tools overview.