Compressive mechanical stress promotes osteoclast formation through RANKL expression on synovial cells.

Objectives: We investigated the effects of compressive mechanical stress on osteoclastogenesis of synovial cells to clarify the mechanism of osteoclast formation by those cells in temporomandibular joint (TMJ) disorders.

Study Design: Synovial cells were isolated from rat knee joints and continuously compressed using a conventional method. The expression of receptor activator nuclear factor kappaB ligand (RANKL) mRNA and protein in synovial cells was analyzed by reverse transcriptase-polymerase chain reaction, immunoblotting, and immunofluorescence staining.

Neuropeptide substance P stimulates the formation of osteoclasts via synovial fibroblastic cells.

The present study was designed to evaluate the effects of neuropeptide substance P (SP) on the formation of osteoclasts via synovial fibroblastic cells. Synovial fibroblastic cells derived from rat knee joint expressed the SP receptor, neurokinin-1 receptor (NK(1)-R). The addition of SP stimulated the proliferation of synovial fibroblastic cells and this effect was inhibited by SP or NK(1)-R antagonists.