Poster 238: RAGE, Inflammation, and Temporomandibular Joint Disorders

Abstract

Temporomandibular Joint Disorders (TMDs) are a common cause of facial pain. Although the etiology of TMDs is yet to be fully elucidated, histologic and arthroscopic studies strongly suggest that the inflammatory process is similar to that seen in osteoarthritis of other synovial joints. The Receptor for Advanced Glycation Endproducts (RAGE) is a multiligand receptor that is present on cells of the monocyte/macrophage lineage, vascular cells, and many tumor cells. RAGE is expressed at low levels in most normal tissues and is upregulated where its ligands are present. This receptor binds multiple ligands including a number of Advanced Glycation Endproducts (AGEs), S100/calgranulins, proinflammatory cytokines, MAC-1, a leukocyte beta-2 integrin receptor, and amphoterin, also known as HMGB1, a DNA binding protein released during cell necrosis, resulting in activation of a number of critical cell signaling pathways as well as the generation of reactive oxygen species. It appears that RAGE is emerging as a key inflammatory mediator. In order to investigate the role that RAGE and its ligands play in TMD inflammation we have utilized a transgenic murine model that overexpressses human Tumor Necrosis Factor-alpha (tg hTNF-alpha), resulting in progressive inflammation and destruction of the synovial joints. Furthermore, to test the impact of genetic deletion of RAGE these transgenic animals were breed into the RAGE null background. Animals were sacrificed at 3, 5, and 11 months of age. The temporomandibular joints (TMJ) and knee joints were examined by H & E staining, immunocytochemistry, western blot analysis for RAGE and S100b protein, and ELISA for Interleukin-1 beta (IL-1 bet&cjs0744;a and AGEs). Age and sex-matched C57BL animals and RAGE null animals served as controls. Analysis was by ANOVA and the Tukey-Kramer poc-hoc test was performed for all pair-wise comparisons. Significance was set at p < 0.05. Transgenic animals showed progressive inflammation and joint destruction with increased age, although there were significant differences between the TMJ and knee joints. At 11 months knee joints showed a large amount of destruction and synovitis. While the TMJ had some synovitis, there was only minimal articular destruction. Histological examination showed a more aggressive disease pattern in affected females compared to males in both TMJ and knee joints. RAGE staining correlated with disease progression although there was greater intensity in the knee joints. This was confirmed by western blot analysis. A significant increase in S100b levels was found in tg hTNF-alpha mice compared to control C57B6 mice. Transgenic hTNF-alpha/RAGE null mice had baseline levels of both RAGE and S100b. TNF-alpha mice expressed significantly higher levels of AGEs than control mice. Interestingly, AGE levels were significantly increased in many of the tg hTNF-alpha/RAGE null samples compared with TNF-alpha mice. IL-1 beta ELISA results demonstrated that TNF-alpha affected samples had greater levels of IL-1 beta compared with control mice. However, TNF-alpha/RAGE null samples were comparable to controls. The tg hTNF-alpha mouse is a useful model of TMD inflammation. Affected animals showed significant inflammatory changes with more severe disease observed in the knee joints when compared to the TMJs. Furthermore, RAGE upregulation is critical in the arthritic progression as insertion of the RAGE null background into the TNF mouse decreases a number of inflammatory mediators to baseline levels. RAGE blockage may have therapeutic value in the treatment of TMDs and inflammatory arthridities.