Effect Of Disc Displacement On MRNA Expression Of Urokinase Plasminogen Activator And Its Inhibitor-1 In Synovium Of TMJ

The articular disc and synovial membrane are main parts in the TMJ. The former plays an important biomechanical role in the articular movement, and the latter is closely related with normal metabolism and functions of the articular cartilage. Anterior disc displacement (ADD) of TMJ is the most common TMD. Many studies have indicated that the displacement of disc could cause some pathological changes in the articular cartilage and the synovial membrane. However, the relationship between the molecular mechanism of synovial membrane change and the pathological transform of joint cartilage lead by the disc displacement is still not clear. At present, some studies found that the urokinaseplasminogen activator (uPA) takes part in some physiological or pathological processes such as the fibronolysis, inflammation and cell migration. Plasminogen activator inhibitor-1 (PAI-1) can rapidly inhibit the fibronolysis activity of uPA. However, up to now, there are only a few studies focused on the TMJ are reported. This study is to investigate the effect of ADD on the expression of uPA / PAI-1 system in the rabbit synovial tissues by using the Situ Hybridization technology.Forty Japanese white rabbits were used in this study. Twenty-four of them underwent the operation to establish ADD animal models on the right side without open the articular capsule, and twelve rabbits underwent the same operation without the disc anterior displacement. The rest without any treatment were used as the control group.In Situ Hybridization technology was applied to detect the expression of uPA/PAI-1 mRN A in the synovial membrane of all the specimens.At 1 week after operation, the cells in the inferior layers of synovial membrane were increased. At 2 weeks after operation, the synovial cells in the bilaminar zone decreased rapidly or even disappeared. In the other areas of the synovial membrane the cells have the tendency to be concentrated. Some cartilage-like cells were also found scattered in collagenous fibre.At 8 and 12 weeks, some areas of the synovialmembrane seemed to be villiform. In the bilaminar zone, both fibroblast cells and cartilage-like cells increased distinguished, and rich cartilage cells appeared in the surface of the synovial layer. In the normal synovial membrane, a few endosynovial cells and fibroblast cells have weak uPA and PAI-1 positive expression. These cells, which have strong positive expression of uPA and PAI-1 genes, began to increase at one week after operation until the 12 weeks after operation.This study suggests that some normal tissues at bilaminar zone could remodel to the fiborcartiage-like tissues and act as the role of disc after ADD. Similarly, the changes of synovial membrane are close related with its function. In conclusion, this study indicates that the uPA/PAI-1 system exists in the TMJ disc and plays an important adjustive role in the histological changes caused by ADD.