Follistatin 344

Overview

Follistatin 344 is a recombinant form of the naturally occurring glycoprotein that potently inhibits activin and myostatin signaling. Studied in gene therapy and protein-based research models for muscle growth regulation and fibrosis pathways.

Mechanism of Action

The 344-amino-acid isoform binds and neutralizes activin A, activin B, and myostatin (GDF-8), preventing ActRIIB activation and downstream Smad2/3 phosphorylation. This removes the myostatin brake on satellite cell proliferation and myofiber hypertrophy. The C-terminal acidic tail confers broader tissue distribution than FS-288/FS-303 isoforms.

Research Summary

AAV1-FS344 gene therapy Phase I/II in Becker muscular dystrophy showed improved 6-minute walk test and quadriceps volume increases at 24 months (Mendell et al., Molecular Therapy, 2015). Preclinical mdx mice and primate studies showed 15-30% muscle mass increases (Kota et al., Science Translational Medicine, 2009).

Dosing Information

Reported Side Effects

• Injection site reactions (erythema, swelling)
• Transient elevation of liver enzymes
• Muscle soreness or myalgia
• Potential suppression of FSH with systemic exposure

Research References

• A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy (2015)
• Follistatin gene delivery enhances muscle growth and strength in nonhuman primates (2009)