NF-κB activation and iNOS expression in the synovial membrane of rat temporomandibular joints after induced synovitis

NF-κB plays a pivotal role in pathogenesis in general arthritis. However, the participation of NF-κB in inflammation of the temporomandibular joint (TMJ) is poorly understood. We examined NF-κB expression in rat TMJs with synovitis induced by condyle hypermobility. By immunohistochemistry, NF-κB immunoreactivity was found mainly in the cytoplasm, not the nucleus, of the synovial lining cells of induced-synovitis and control TMJs. Southwestern histochemistry, a new method for detecting transcription factors, showed greater NF-κB expression in the nucleus of the synovial lining cells in the hypertrophic synovium than in control synovium. Increased numbers of the synovial lining cells with immunoreactivity for inducible nitric oxide synthase (iNOS), which is transcriptionally regulated by NF-κB, were also seen in the inflamed synovium. These findings indicate that excess mechanical stress increases NF-κB activation in the TMJ and suggest that active NF-κB is involved in the progression of TMJ inflammation.