| Research Abstract |
This project was undertaken to elucidate the mechanism for regulation of osteoclast function at molecular level. To address the aim, we first needed a pure population of functional osteoclasts, and succeeded in developing a new method for isolation of mature osteoclasts. Using the isolated osteoclasts, we focused on elucidating the roles of receptor tyrosine kinases in the regulation of osteoclastic function. In this study, we cloned eight receptor tyrosine kinases, including fibroblast growth factor receptor-1(FGFR-1),Tyro3, vascular epithelial growth factor receptors(Fit-1 and Flk-1), insulin receptor, c-fms, and c-met, expressed on mature osteoclasts. Besides these receptor tyrosine kinases, we also detected some receptor serine/threonine kinases such as a subtype of prostaglandin (PG) E2 receptor, EP4 and Bone morphogenetic receptors (BMPR-IA and BMPR-II) in osteoclasts. We found the signaling through FGFR-1,Tyro3, and VEGF receptors stimulated the osteoclastic bone resorption and/or the osteoclast survival. These receptors associated with c-src, FAK, P13K, and 42/44p MAPKs to express the stimulatory effects. On the other hand, PGE2 inhibited the osteoclastic bone-resorbing activity through the EP4 receptor coupled with Gs-protein, whereas BMP-2 stimulated the activity through its receptors/Smads. Thus, mature osteoclasts express many receptor tyrosine kinases as well as serine/threonine kinase receptors on their plasma membranes to regulate their functions, and these results provide us a lot of insights to understand the regulatory mechanism for osteoclast.
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