Role of osteoclast differentiation in the occurrence of osteoarthritis of temporomandibular joint.

OBJECTIVES: This study aimed to explore the role of osteoclast differentiation in the occurrence of temporomandibular joint osteoarthritis (TMJOA). METHODS: A mouse TMJOA model was constructed. Micro-CT was used to observe the changes in condylar bone during the development of TMJOA. Hematoxylin-eosin (HE) staining was used to observe the histological structure changes of the condyle of TMJOA mice. Tartrate resistant acid phosphatase (TRAP) staining was used to observe the presence of osteoclasts in TMJOA joint tissue. The synovial fluid of patients with TMJ-OA was collected to determine the effect on osteoclast differentiation. RESULTS: Micro-CT revealed that the condyle of the TMJOA group had the most obvious damage in the second and third weeks, and the shape of the condyles also changed in a beak-like manner. HE staining showed that the condyle cartilage and subchondral bone structure of TMJOA mice were disordered in the second week. TRAP tissue staining showed that the number of osteoclasts of the TMJOA group obviously increased in the second week. Results of cell experiments showed that the number of osteoclast differentiation significantly increased after stimulation of synovial fluid from TMJOA patients, and the cell volume increased. CONCLUSIONS: TMJOA animal models and TMJOA patient synovial cell experiments could induce osteoclast differentiation, indicating that osteoclast differentiation plays an important role in TMJOA occurrence.

TLR4 contributes to the damage of cartilage and subchondral bone in discectomy-induced TMJOA mice.

The abundance of inflammatory mediators in injured joint indicates innate immune reactions activated during temporomandibular joint osteoarthritis (TMJOA) progression. Toll-like receptor 4 (TLR4) can mediate innate immune reaction. Herein, we aimed to investigate the expression profile and effect of TLR4 in the cartilage and subchondral bone of the discectomy-induced TMJOA mice. The expression of TLR4 and NFκB p65 in the synovium of TMJOA patients was measured by immunohistochemistry, Western blotting and RT-PCR. H&E and Masson staining were utilized to assess the damage of cartilage and subchondral bone of the discectomy-induced TMJOA mice. A TLR4 inhibitor, TAK-242, was used to assess the effect of TLR4 in the cartilage and subchondral bone of the discectomy-induced TMJOA mice by Safranin O, micro-CT, immunofluorescence and immunohistochemistry. Western blotting was used to quantify the expression and effect of TLR4 in IL-1ß-induced chondrocytes. The expression of TLR4 and NFκB p65 was elevated in the synovium of TMJOA patients, compared with the normal synovium. TLR4 elevated in the damaged cartilage and subchondral bone of discectomy-induced TMJOA mice, and the rate of TLR4 expressing chondrocytes positively correlated with OA score. Intraperitoneal injections of TAK-242 ameliorate the extent of TMJOA. Furthermore, TLR4 promotes the expression of MyD88/NFκB, pro-inflammatory and catabolic mediators in cartilage of discectomy-induced TMJOA. Besides, TLR4 participates in the production of MyD88/NFκB, pro-inflammatory and catabolic mediators in IL-1ß-induced chondrocytes. TLR4 contributes to the damage of cartilage and subchondral bone in discectomy-induced TMJOA mice through activation of MyD88/NFκB and release of pro-inflammatory and catabolic mediators.

Inhibition of glycolysis by targeting lactate dehydrogenase A facilitates hyaluronan synthase 2 synthesis in synovial fibroblasts of temporomandibular joint osteoarthritis.

OBJECTIVE: Although associations between dysregulated glucose metabolism and human rheumatoid arthritis have been reported, the disturbance and influence of glycolytic metabolism on temporomandibular joint osteoarthritis remains unclear. This study aimed to investigate the expression level and metabolite profile of the critical glycolytic enzyme, lactate dehydrogenase A (LDHA) in synovial fibroblasts (SFs) of TMJOA, assess the effect of glycolytic inhibition on synthesis of hyaluronan synthase 2 (HAS2) and inflammation progression in these cells. METHODS: Immunohistochemistry and western blotting were performed to detect the expression of LDHA in the lining and sub-lining layers of synovial tissue and SFs. MTT and EdU assays were used to measure the cell proliferation. The cell apoptosis were demonstrated by TUNEL staining and Annexin V/PI double staining. A potent and specific inhibitor of LDHA, GSK2837808A, was administrated to suppress the activity of LDHA and detect the potential efficacy on HAS2. RESULTS: LDHA expression was dramatically higher in the synovial tissue and SFs from TMJOA patients compared to control groups. LDHA inhibition impaired active LDHA performance, suppressed the glucose uptake and decreased lactate concentration. Furthermore, GSK2837808A reversed the occurrence of low ratio of ATP/AMP, high level of Adenosine Monophosphate-activated Protein Kinase (AMPK) activation, disturbed HAS2 synthesis and hyaluronic acid (HA) production by inhibiting LDHA. The cellular viability and cell cycle were not affected by GSK2837808A at the working concentration. CONCLUSIONS: Targeting LDHA using its specific suppressant GSK2837808A impeded lactate secretion and contributed to HAS2 and HA synthesis in TMJOA SFs, providing the vital role of LDHA associated with TMJOA pathogenesis and a novel therapeutic approach for TMJOA.