Upregulation of C5aR Expression during TMJ Inflammation

C5a is a potent chemotactic molecule that mediates many of its effects by binding to a membrane receptor, (C5aR). Although complement activation is a hallmark event in a variety of inflammatory animal models; at this time, there are no published studies addressing its role in the context of temporomandibular (TMJ) inflammation nor the cells that express these recptors have not been identified. OBJECTIVES: In this study,our objective was to characterize the changes in C5aR expression in the joint and trigeminal ganglia. METHODS: Complete Freund's adjuvant (CFA) was injected bilaterally into the TMJ of adult female ovariectomized (OVX) Sprague Dawley rats in the absence and presence of exogenous estrogen (low and high doses). Additional OVX animals were used as saline controls. Joint tissue and trigeminal ganglia were collected after 24 or 48 hours. The samples were frozen and homogenized for Western blot analysis or processed for immunohistochemical staining. RESULTS: C5aR protein was constitutively expressed in both the TMJ and trigeminal ganglia. Upregulation of C5aR expression occurred in both tissues after CFA injection. Although C5aR expression was diffuse in the TMJ parenchymal tissue, staining was prominent on the luminal side of blood vessel endothelial cells. Addition of exogenous estrogen appeared to decrease CFA-induced increase in C5aR expression. CONCLUSIONS: The results demonstrate the presence of C5aR in theTMJ and trigeminal ganglion thus suggesting a possible role for the C5a in the development of TMJ inflammation - perhaps by recruiting macrophages and other immune cells to the area of injury. Furthermore, the ability of estrogen to modulate expression of this receptor may shed some insight into its immunoregulatory properties.

This work was supported by the Baylor Oral Health Foundation.