Activation of osteoblastic functions by a mediator of pain, bradykinin

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We investigated the effects of bradykinin (BK) on the production of interleukin (IL)-6 and prostaglandin PGE2, whose molecules are capable of stimulating the development of osteoclasts from their hematopoietic precursors as well as the signal transduction systems involved, in human osteoblasts (SaM-1 cells). BK receptors B1 (B1R) and B2 (B2R) were expressed in SaM-1 and osteosarcoma (SaOS-2, HOS, and MG-63) cells. Treatment of SaM-1 cells with BK increased the synthesis of both IL-6 and PGE2 and the increase in both was blocked by HOE140 (B2R antagonist), but not by Des-Arg9-[Leu8]-BK (B1R antagonist). U-73122, a phospholipase C (PLC) inhibitor, suppressed BK-induced IL-6 and PGE2 synthesis in SaM-1 cells. In addition, BK caused an increase in the intracellular Ca2+ concentration ([Ca2+]i), which was inhibited by pretreatment with HOE140 or 2-aminoethoxydiphenyl borate (2-APB), an inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) blocker. Furthermore, both SB203580 (an inhibitor of p38 mitogen-activated protein kinase [MAPK]) and PD98059 (an inhibitor of MEK, upstream of ERK) attenuated the BK-induced IL-6 and PGE2 synthesis. BK treatment resulted in the phosphorylation of p38 MAPK and extracellular signal-regulated kinase (ERK)1/2, and 2-APB could suppress BK-induced phosphorylation of ERK1/2. These findings suggest that BK increased both IL-6 and PGE2 synthesis in osteoblastic cells via B2R and that PLC, IP3-induced [Ca2+]i, MEK, and MAPKs were involved in the signal transduction in these cells.

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