Small Molecules Dorsomorphin and LDN-193189 Inhibit Myostatin/GDF8 Signaling and Promote Functional Myoblast Differentiation*

Background: GDF8/myostatin suppresses myogenic differentiation. Results: The small molecule inhibitors dorsomorphin and LDN-193189 bind to and inhibit the GDF8 receptor ActRII and ALK4. Conclusion: Dorsomorphin and LDN-193189 promote myogenesis in vitro. Significance: Detailed molecular characterization of small molecule inhibitors targeting the GDF8/myostatin pathway demonstrates their potential and risk when applied to promote muscle development.
GDF8, or myostatin, is a member of the TGF-β superfamily of secreted polypeptide growth factors. GDF8 is a potent negative regulator of myogenesis both in vivo and in vitro. We found that GDF8 signaling was inhibited by the small molecule ATP competitive inhibitors dorsomorphin and LDN-193189. These compounds were previously shown to be potent inhibitors of BMP signaling by binding to the BMP type I receptors ALK1/2/3/6. We present the crystal structure of the type II receptor ActRIIA with dorsomorphin and demonstrate that dorsomorphin or LDN-193189 target GDF8 induced Smad2/3 signaling and repression of myogenic transcription factors. As a result, both inhibitors rescued myogenesis in myoblasts treated with GDF8. As revealed by quantitative live cell microscopy, treatment with dorsomorphin or LDN-193189 promoted the contractile activity of myotubular networks in vitro. We therefore suggest these inhibitors as suitable tools to promote functional myogenesis.