ACE-031
A myostatin-blocking decoy receptor that increased muscle mass in trials, then had its development halted over vascular bleeding events.
Bone & Muscle
Follistatin
The body's natural myostatin trap. Gene-therapy trials have been conducted in muscular dystrophy; injectable follistatin as sold has no human evidence at all.
Overview
Follistatin binds and neutralises activin and myostatin, the signals that hold muscle growth in check. Removing those brakes increases muscle mass — this is well established in animals and in gene-transfer studies. The important distinction is that the human work uses gene therapy, delivering the instructions for making follistatin into muscle so the tissue produces it continuously. Injecting the protein is a different proposition entirely, and it has never been tested.
A secreted glycoprotein existing in FST-288, FST-303 and FST-315 isoforms, differing in heparan sulfate affinity and tissue distribution. Binds activin A with high affinity and neutralises myostatin (GDF-8) and GDF-11, blocking their engagement of ActRIIB and downstream SMAD2/3 signalling. AAV1-mediated intramuscular delivery of FS344 has been evaluated in phase 1/2 studies in Becker muscular dystrophy and sporadic inclusion body myositis, with reported improvements in six-minute walk distance in some participants. Recombinant follistatin protein has a very short circulating half-life and has not been evaluated in registered human trials.
Research areas
Muscle wastingMuscular dystrophyMyostatin signalling
Dosing reported in the literature
Every protocol below is reproduced from a published study or approved labelling, with its source named. These are records of what was studied — not recommendations, and not a suggestion that any of them is appropriate for any person.
| Protocol as reported | Source |
|---|---|
| Bilateral intramuscular AAV1.CMV.FS344 injection into the quadriceps, with six-minute walk distance followed over yearsGene transfer, not protein injection. The two are not interchangeable. | Mendell et al., Molecular Therapy 2015 |
Trial status
Phase 1/2 AAV gene-therapy studies in Becker muscular dystrophy and inclusion body myositis. No trials of injected follistatin protein.
Reported safety signals
- Activin and myostatin signalling regulate far more than muscle — reproductive, haematopoietic and vascular tissue all depend on it.
- The ACE-031 programme, which trapped the same ligand family, was halted for vascular bleeding events; that concern is directly relevant here.
- Injectable "follistatin" sold through research channels has never been tested in humans and its content is unverified.
Common questions
Does injecting follistatin build muscle?
There is no human study that has tested it. The published human work uses gene therapy to make muscle produce follistatin continuously, which is a completely different exposure profile from injecting a protein that clears from the blood within minutes.
Primary sources
Medical disclaimer
This page is for informational and research purposes only. Nothing here constitutes medical advice. The compounds discussed are research chemicals. Consult a qualified clinician before starting any protocol.
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