What it is
Follistatin 344 (FS344) is the 344-amino-acid circulating isoform of the secreted glycoprotein follistatin, alongside the shorter FS288. Both bind and inhibit TGF-β superfamily ligands.
Evidence snapshot
Category: Muscle Biology. Status: Preclinical. See the references section below for the underlying primary sources.
Mechanism
FS344 binds myostatin and activin with high affinity, preventing their interaction with activin receptors on skeletal muscle. This blocks negative regulation of muscle mass.
Key research findings
Studied in rodent models of muscle wasting, including cancer cachexia, disuse atrophy, and age-related sarcopenia. Early-phase human gene therapy work using follistatin constructs has produced muscle-growth effects in specific conditions.
Limits of the evidence
Not approved for human use. The human gene therapy work has been limited to specific disease populations. Long-term systemic myostatin inhibition carries theoretical risks for cardiac muscle and tendon integrity.