Inhibition of ROCK2 impedes osteoclastogenesis through Src-Ca2+-NFATc1 signaling pathway and alleviates ovariectomy-induced bone loss.

Osteoporosis is a metabolic bone disease, and fractures caused by severe osteoporosis can lead to permanent disabilities. Targeting over-activated osteoclasts has become a therapeutic strategy for osteoporosis. Selective oral Rho-associated coiled-coil kinase 2 (ROCK2) inhibitor KD025 has been approved by FDA for treating chronic graft-versus-host disease (cGVHD) recently. ROCK2 inhibition by KD025 can treat collagen-induced arthritis in vivo by downregulating proinflammatory cytokine secretion, while the roles and mechanisms of ROCK2 in osteoporosis remain to be determined. Here, we found that ROCK2 expression in pre-osteoclastic cells was markedly upregulated in an OVX-induced osteoporosis mouse model. ROCK2 inhibition by its orally available selective inhibitor KD025 prevented OVX-induced bone loss in vivo. Mechanistically, ROCK2 pharmacological inhibition with KD025 or ROCK2-specific siRNA suppressed osteoclastogenesis, bone resorption and F-actin rings formation in bone marrow-derived macrophages (BMMs) via downregulating NF-κB/p38-c-Fos signaling, Src-Ca2+-NFATc1 pathway, and the expression of osteoclast-related genes such as Trap, Oscar. Meanwhile, ROCK2 inhibition by KD025 showed no significant effect on osteoblast differentiation in vitro. Furthermore, the inhibitory effect of KD025 on osteoclastogenesis and NFATc1-luc transcription in vitro was weakened after silencing ROCK2. In a translation study, KD025 remarkably inhibited pathological osteoclastogenesis and bone resorption function in CD14+ macrophages from patients with osteoporosis. Collectively, our findings identify ROCK2 as a promising target for osteoclast-mediated osteolysis and highlight the potential of KD025 as a therapeutic drug for osteoporosis and metastatic bone destruction.