Bone Morphogenetic Protein-2 Promotes Osteoclasts-mediated Osteolysis via Smad1 and p65 Signaling Pathways

Study Design. An in vitro biological study. Objective. The aim of this study was to explore the role of bone morphogenetic protein-2 (BMP-2) in the regulation of osteoclast-mediated osteolysis, and the possible mechanism involving BMP-2 and nuclear factor-kappa B (NF-kappa B) signaling pathways. Summary of Background Data. Recombinant human BMP-2 (rhBMP-2) has been approved as a therapeutic agent in spinal fusion and bone defect repair. However, its efficacy and clinical application are limited by associated complications including osteoclast-mediated bone resorption. The mechanism of BMP-2-induced osteolysis remains unknown. Methods. Bone marrow-derived macrophages (BMMs) were isolated from C57BL/6J mice and cultured with macrophage colony-stimulating factor (M-CSF) and receptor activator for nuclear factor-kappa B Ligand (RANKL) to induce osteoclast differentiation. An in vitro bone resorption assay was performed by co-culturing BMMs and bone slides. The expression of BMP canonical and NF-kappa B signaling factors and their interaction during signal transduction were quantitated by reverse transcription polymerase chain reaction, Western blot analysis, confocal microscopy, and co-immunoprecipitation. Results. BMP-2 enhanced osteoclast-mediated bone resorption via inducing osteoclast differentiation in a concentration-dependent manner. In addition, a high concentration of BMP-2 significant upregulated phosphorylation of BMP signaling factors p-Smad1/5/8 and NF-kappa B downstream factor p65, and promoted the degeneration of I kappa B alpha. In addition, BMP-2 induced osteoclast differentiation through coupling between BMP receptor II and RANK. Conclusion. High concentrations of BMP-2 enhanced osteoclast-mediated bone resorption by promoting RANKL-induced pre-osteoclast differentiation, probably by mediating the cross-talk between BMP canonical and NF-kappa B signaling pathways.