Follistatin-344

Follistatin-344 (FST-344) is a naturally occurring glycoprotein that functions as a potent inhibitor of several TGF-beta superfamily members, most notably myostatin (GDF-8) and activins A and B. By binding and neutralizing these growth factors, follistatin promotes muscle growth and prevents muscle wasting.

The protein contains three characteristic follistatin domains that mediate binding to target ligands, plus a heparin-binding sequence that influences tissue distribution. FST-344 is the full-length isoform that circulates systemically, while the FST-317 variant lacks the heparin-binding domain and acts more locally.

Research has demonstrated dramatic muscle hypertrophy in animal models when follistatin is overexpressed or administered exogenously. The mechanism involves both direct myostatin inhibition, which removes the brake on muscle growth, and activin inhibition, which influences muscle stem cell function and differentiation.

Beyond muscle research, follistatin plays important roles in reproductive biology (follicular development, FSH regulation), inflammation, fibrosis, and cancer. Its ability to modulate multiple TGF-beta family members makes it a broad-spectrum tool for studying this signaling pathway, though this also complicates interpretation of results.