Interactive effect of interleukin-6 and prostaglandin E₂ on osteoclastogenesis via the OPG/RANKL/RANK system

The OPG/RANKL/RANK system regulates osteoclastogenesis. Both cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2) and interleukin-6 (IL-6) are reported to induce osteoclast differentiation. The mechanisms underlying these signaling pathways on the OPG/RANKL/RANK system are not fully understood. We herein demonstrate that COX-2 and PGE2 stimulated osteoclastogenesis through inhibition of OPG secretion, stimulation of RANKL production by osteoblasts, and upregulation of RANK expression in osteoclasts. PGE2 also stimulated IL-6 production, and IL-6, in turn, increased PGE2 secretion, COX-2, and EP ₄/EP₂ expression in bone cells. These findings provide evidence of interactive effect of PGE2 and IL-6 signaling pathways in osteoclastogenesis via effect on the OPG/RANKL/RANK system.