Follistatin is a protein that plays a crucial role in regulating muscle growth and other cellular processes. It acts as a myostatin inhibitor, meaning it can promote muscle growth by blocking the effects of myostatin, a protein that limits muscle development. Follistatin also binds to and neutralizes members of the TGF-β superfamily, such as activin and BMPs, which are involved in various cellular functions including cell growth, differentiation, and tissue repair