Figure 1.

Soluble activin receptor administration increases bone volume in vivo and enhances osteoblast differentiation in vitro. ACVR2A/Fc and ACVR2B/Fc treatment demonstrates significant increases in skeletal muscle weights as compared with vehicle-treated controls (A). ACVR2A/Fc administration exhibits a near doubling in trabecular bone volume/tissue volume and a significant increase in cortical thickness (B). Similarly, ACVR2B/Fc treatment demonstrates a near tripling in trabecular bone volume/tissue volume but no significant increase in cortical thickness (C). Both ACVR2A/Fc and ACVR2B/Fc treatment demonstrate significant increases in calvarial bone volume (D). ACVR2B/Fc treatment shows a dose-dependent reduction of Smad2 phosphorylation in vitro (E). Further in vitro analysis demonstrates that ACVR2B/Fc treatment enhances alkaline phosphatase activity and mineral deposition by Alizarin Red staining in osteoblast differentiation cultures (F). *, p < 0.05.