How is Follistatin 315 different from Follistatin 344?

FST-315 is the circulating isoform with weaker cell-surface binding and a more systemic distribution, whereas FST-344 is the full-length precursor that binds tissue more tightly.

Why is follistatin linked to muscle growth?

It binds and neutralizes myostatin, the protein that limits muscle growth, so blocking myostatin can disinhibit muscle hypertrophy in research models.

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Muscle Growth

Preclinical

Follistatin 315

Also known as: Follistatin 315, Follistatin-315

Follistatin 315 is the circulating isoform of follistatin, a myostatin-binding protein studied for promoting muscle growth by removing the brake on muscle development.

Mechanism of Action

Follistatin 315 is the longer, soluble isoform of follistatin that binds and neutralizes members of the TGF-beta superfamily, most importantly myostatin (GDF-8) and activin A. By sequestering myostatin it blocks activation of the ActRIIB receptor and downstream SMAD2/3 signaling that normally restrains skeletal muscle growth. The net effect in models is disinhibition of muscle protein synthesis and satellite cell activity, favoring muscle hypertrophy; the 315 isoform has lower heparin/cell-surface affinity than FST-288, giving it a more systemic distribution.

Half-life: Relatively short in circulation; cleared within hours
Administration Routes: subcutaneous, intramuscular
Research Status: Preclinical