Unlike some other compounds that directly bind to myostatin or its receptor, YK11 works through the androgen receptor (AR) to increase follistatin expression. Follistatin is a natural protein that binds to and neutralizes myostatin. By elevating follistatin levels, YK11 effectively lowers myostatin activity.
Mechanism step-by-step:
1.Androgen receptor activation – YK11 is a partial agonist of the AR, similar to but distinct from traditional anabolic steroids.
2.Upregulation of follistatin – AR activation triggers transcription of the FST gene, leading to higher follistatin production.
3.Myostatin inhibition – Follistatin binds directly to myostatin (a TGF-β family member), preventing it from signaling through the activin type II receptors (ActRIIB).
4.Result – Reduced myostatin signaling → less inhibition of muscle growth → enhanced myogenesis and satellite cell proliferation.
Evidence (mainly preclinical):
●A 2014 study by Kanno et al. (Biol. Pharm. Bull.) showed YK11 increased follistatin mRNA and protein in mouse myoblast cells (C2C12), while reducing myostatin signaling markers like Smad2/3 phosphorylation.
●YK11 also induced myotube hypertrophy even without exogenous androgens, suggesting its effects are AR-mediated but not fully dependent on high androgen levels.
Key distinction from other myostatin inhibitors:
| Compound | Mechanism |
|---|---|
| YK11 | ↑ follistatin (via AR) → indirect myostatin blockade |
| Follistatin itself | Direct myostatin binding |
| Myostatin antibody (e.g., stamulumab) | Direct neutralization |
| ACE-031 (ActRIIB decoy) | Traps myostatin & related ligands |
What this means for muscle growth:
●Because myostatin is a powerful brake on muscle mass, YK11's ability to reduce its activity contributes to its anabolic effect - but this is one of several mechanisms. YK11 also:
○Activates the Akt/mTOR pathway (promoting protein synthesis)
○May act as a selective androgen receptor modulator (SARM) with fewer peripheral side effects than steroids (though human data are lacking)
https://www.hormonerawsource.com/sarm-powders/sarms-finished/stromusc-superior-quality-yk11-10mg-for.html
