Effects of Basic Fibroblast Growth Factor (FGF-2) on Osteoclastogenesis

Objectives: Bone remodeling is regulated by orchestrated cellular functions between osteoblasts and osteoclasts. Recently, RANK (Receptor Activator of Nuclear Factor kB Ligand), RANKL (Ligand of RANK; osteoclast diffentiation factor) and OPG (Osteoprotegerin; osteoclastogenesis-inhibitory factor) were identified as the crucial factors for the osteoclastogenesis. In our previous studies, we have reported that the topical application of basic fibroblast growth factor (FGF-2) into the bony defects induced the ideal periodontal regeneration without ankylosis and epithelial downgrowth. In addition we have revealed that FGF-2 is distributed on the periodontal ligamental cells, gingival fibroblasts and osteoclasts by immunohistochemical analysis. However, there is no report about the effects of FGF-2 on the osteoclast formation during process of periodontal regeneration. In this study, we examined how the expressions of OPG and RANKLin osteoclastogenesis by periodontal ligamental cells and gingival fibroblasts regulated by FGF-2 stimulation. Methods: RAW264 myelomonocytic cells was cultured with sRANKL in the presence or absence of CM (conditioned media) of the MPDL-22 stimulated with FGF-2 and assayed by TRAP (Tartrate-resistant acid phosphatase) staining. Results: Multinucleated osteoclasts were induced from RAW264 myelomonocytic cells by stimulating the cells with sRANKL for 3 days. The CM of FGF-2-stimulated MPDL-22 and MG/B6 inhibited the osteoclast formation, but did not influence the maturation of the osteoclasts. The inhibitory effects of the CM of FGF-2-stimulated MPDL-22 was blocked by anti-OPG mAb. FGF-2 upregulated the mRNA expressions of OPG and RANKL in MPDL-22 and MGB/6. Conclusions: The upregulation of the OPG induced by FGF-2-stimulated periodontal ligament cells and gingival fibroblasts may inhibit osteoclast formation by blocking RANKL-RANK dependent osteoclastogenesis pathway. These results may suggest that the topically-applied FGF-2 downregulates osteoclast formation and in turn accelerates hard tissue formation. This study was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (No.15592186).