Effect of TGF-β1 on Osteoclast Precursors in the Bone Microenvironment

Objectives: Osteoclasts (OC) are differentiated from monocyte/macrophage-lineage hematopoietic precursor cells which were termed OC precursors (OCPs). Many studies of chemotaxis cell migration in the bone microenvironment have researched. However, OCPs migration in the bone microenvironment during osteoclastogenesis has not been studied. The aim of this study was to determine the effects of TGF-β1 on migration of OCPs in the bone microenvironment.
Methods: We cultured the pre-osteoclastic RAW264.7 (RAW) cells with or without TGF-β1, RANKL, and the potent and specific inhibitor of the kinase activity of TGF-β1 receptor, SB431542. TRAP activity was determined by TRAP solution assay. Cell motility was measured using cell motility assay. Rho, Rac1 and Cdc42 were detected by Western blot analysis
Results: RAW cells were differentiated into OC-like cells in the presence of RANKL. Treatment with TGF-β1 alone did not induce formation of OC-like cells, but TGF-β1 increased the number of OC-like cells induced by RANKL. When RAW cells were treated with SB431542, osteoclastogenesis was strongly suppressed. Cell migration was significantly increased by treatment of TGF-β1 on 24 h, but was decreased on 72 h. The expression of RhoA, Rac1 increased on 24 hours after treatment of TGF-β1 and were strikingly reduced on 72 hours after treatment of TGF-β1.
Conclusions: These results suggest that TGF-β1 is released from the bone matrix induce motile OCPs to quiescent OCPs. TGF-β1 controls motility of OCPs and may induce their localization in bone microenvironment.