What Is YK-11?
YK-11 is a synthetic steroidal compound first described by Kanno et al. (2011) at Tokai University in Japan. It is classified as a SARM (selective androgen receptor modulator) based on its AR binding and tissue-selective activity, but unlike the non-steroidal SARMs (RAD-140, LGD-4033, Ostarine), YK-11 has a steroidal scaffold structurally analogous to dihydrotestosterone (DHT).
YK-11's most notable research finding is its apparent ability to induce follistatin (FST) expression in skeletal muscle cells — a mechanism that inhibits myostatin (GDF-8), the negative regulator of muscle growth. This dual AR agonism + myostatin pathway inhibition is unique in the SARM literature.
Myostatin Biology: Why It Matters
Myostatin (growth differentiation factor 8, GDF-8) is a TGF-β superfamily member secreted primarily by skeletal muscle that acts as a negative regulator of muscle mass. Its physiological role is to limit muscle hypertrophy — effectively setting an upper ceiling on muscle growth.
Research context: natural myostatin loss-of-function mutations cause extreme muscle hypertrophy in cattle, mice, dogs, and humans. Myostatin inhibition is therefore a research target for muscle wasting diseases (DMD, cachexia, sarcopenia).
Follistatin is an endogenous myostatin antagonist — it binds and neutralizes myostatin, reducing its inhibitory effect on muscle growth. YK-11's proposed mechanism is that AR activation by YK-11 specifically upregulates follistatin gene expression in myocytes, thereby reducing myostatin activity.
Published Research: Kanno et al.
- Kanno et al. (2011): First description of YK-11 as a SARM. Characterized partial agonism at AR in HepG2 cells; showed anabolic gene expression in C2C12 myoblasts.
- Kanno et al. (2013): Key follistatin paper. YK-11 at 500 nM significantly increased follistatin mRNA expression in C2C12 myoblasts. Western blot confirmed follistatin protein elevation. Effect was AR-dependent (blocked by AR antagonist flutamide). Downstream: reduced SMAD2/3 phosphorylation (myostatin signalling cascade) in treated cells.
Important limitation: Both key papers are in vitro (C2C12 cell culture). There is no published in vivo rodent data or human clinical data for YK-11. The translational relevance is therefore lower than for non-steroidal SARMs with animal model or clinical data.
Steroidal vs Non-Steroidal: Research Implications
| Property | YK-11 (Steroidal) | RAD-140/LGD-4033 (Non-Steroidal) |
|---|---|---|
| Chemical backbone | Steroidal (DHT-like) | Non-steroidal small molecule |
| 5α-reduction | Possible (poorly characterized) | None |
| Aromatization | Possible (poorly characterized) | None |
| Myostatin inhibition | Yes (via follistatin — in vitro) | Not described |
| In vivo rodent data | Very limited | Extensive |
| Human clinical data | None | Phase I–III available |
Research Applications
- Myostatin pathway research: YK-11 is currently the only SARM documented to induce follistatin in muscle cells — useful for myostatin biology studies
- Comparative SARM mechanism studies: Steroidal vs non-steroidal AR agonism and downstream coactivator recruitment
- Muscle hypertrophy signalling: Combined AR + follistatin/myostatin pathway activation in cell culture models