Molecular biological analysis of bone metabolism by compressive mechanical stress in human synovial cells of the temporomandibular joint

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1. 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. Mouse bone marrow cells were cultured with synovial cells for 7 days to detect osteoclasts. RESULTS: The expressions of RANKL mRNA and protein in synovial cells were increased with compressive force. When mouse bone marrow cells were cultured with continuously compressed synovial cells, tartrate-resistant acid phosphatase-positive multinucleated cells were formed. Osteoprotegerin completely inhibited osteoclast formation induced … More by culturing with compressed synovial cells. CONCLUSION: Our results indicated that the expression of RANKL in compressed synovial cells enhanced osteoclast formation, whereas continuous compressive force may induce osteoclastic bone destruction in the TMJ.2. OBJECTIVE: Although biochemical studies have examined the synovial fluid (SF) of patients with temporomandibular joint (TMJ) disorders (TMDs), the details of the molecular mechanism of bone destruction and remodeling remain unknown. In this study, we induced and characterized osteoclast-like cells from the SF of patients with TMD and investigated the participation of these cells in the pathogenesis of TMD. METHODS: We collected SF cells from patients with TMD after a pumping procedure, cultured osteoclast-like cells, and examined their characteristics, including osteoclast markers and bone resorption activities. In addition, we obtained fibroblastic cells from the SF of TMD patients by continuous sub-culturing. Using these fibroblastic cells, we examined fibroblast markers using immunocytochemical staining and analyzed the receptor activator of nuclear-factor-kappaB ligand (RANKL) mRNA levels. Detection of soluble form of RANKL (sRANKL) in the SF was measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: Osteoclast-like cells were induced from the SF cells of patients with TMD by adding recombinant human (rh) macrophage colony stimulating factor (M-CSF) and either 1, 25-dihydroxy vitamin D3 [1, 25 (OH) 2D3] or prostaglandin E2 (PGE2). These multinucleated giant cells were positive for tartrate-resistant acid phosphatase (TRAP) and had the ability to absorb bone. The fibroblastic cells from the SF of TMD patients were positive for fibroblast markers and RANKL mRNA was up-regulated. Detection of sRANKL in SF of patient group was significantly higher than control group. CONCLUSION: The results suggest that the joint-infiltrating SF cells from TMD patients play important roles in the pathogenesis of these disorders, which is characterized by progressive bone destruction or remodeling. Less