PROTEOGLYCAN EXPRESSION IN THE RAT TEMPOROMANDIBULAR-JOINT IN RESPONSE TO UNILATERAL BITE RAISE

The vertebrate articular tissue consists of collagen fibers embedded i n a ground substance. Collagen resists tensile forces, while proteogly cans in the ground substance provide resilience and resistance to comp ression. It was hypothesized that unilateral bite raise would induce i ncreasing expression of proteoglycans in TMJ articular tissues. As a t est of this hypothesis, six- and nine-week-old Sprague-Dawley rats rec eived unilateral bite-raising appliances bonded to their right upper m olars for 4 wks. A group of nine-week-old rats was housed for an addit ional 4 wks after removal of the appliances they had worn for 4 wks. P roteoglycans that carry abundant chondroitin sulfate and keratan sulfa te side-chains, most likely aggrecans, were detected by safranin O in the fibrocartilaginous zone of the condyle in parasagittal sections. A monoclonal antibody against a large chondroitin sulfate proteoglycan related to versican reacted strongly in the surface fibrous layer of t he mandibular condyle and moderately in the discs of the treated speci mens. Computer quantification for safranin O and anti-versican antibod y staining revealed that the average intensities of the treated specim ens were significantly higher than those of their corresponding sham-o perated controls, and the average intensities of the treatment-reversa l specimens had no significant differences from their corresponding sh am-operated controls. Thus, unilateral bite raise appeared to have ind uced an increase in the expression of aggrecan in the condylar cartila ge and a proteoglycan related to versican in the TMJ disc and the arti cular surface of the condyle. The elevated proteoglycan expression is interpreted to suggest that unilateral bite raise leads to an increase in the magnitude of compressive forces in the rat temporomandibular j oint.