Follistatin 344

A naturally occurring glycoprotein that acts as a potent inhibitor of myostatin and other TGF-beta superfamily members such as activin. The 344 isoform is the full-length precursor that is processed into shorter circulating forms. By neutralizing myostatin, Follistatin 344 removes the endogenous brake on skeletal muscle growth, enabling significant hypertrophy beyond normal physiological limits.

• Binds and neutralizes myostatin (GDF-8), the primary negative regulator of muscle mass
• Also sequesters activin A and B, removing additional inhibitory signals from muscle growth pathways
• Downstream activation of Akt/mTOR signaling promotes protein synthesis
• Shifts satellite cell differentiation toward myogenic lineage

• Active malignancy (growth factor modulation risk)
• Pregnancy or breastfeeding (activin is critical for reproductive function)
• History of hormone-sensitive cancers
• Pre-existing liver or kidney disease

Store at 2–8°C (36–46°F) for up to 3 months. For long-term storage, keep at -20°C (-4°F). Once reconstituted, refrigerate and use within 14 days. Extremely sensitive to heat and agitation.

Animal studies have demonstrated dramatic increases in muscle mass (up to 100-200% in myostatin-knockout models). A gene therapy trial using AAV-delivered follistatin (NCT01519349) showed increased distance walked in Becker muscular dystrophy patients. The injectable peptide form has limited human clinical data but extensive preclinical evidence supporting its myostatin-inhibiting properties.