Characterization of the extracellular matrix of baboon temporomandibular joint
The extracellular matrix (ECM) is a complex network of biomolecules that support and surround cells and regulate cellular activities. The ECM proteins are categorized as glycoproteins, proteoglycans and structural proteins like collagens and elastin. Collagen occurs in a number of forms, but type I collagen is the major protein present in the human body, and it helps strengthen and organize the matrix. Proteoglycans help in stabilizing the matrix within its aqueous environment. Our primary focus in the laboratory is on the Proteoglycan 4 (PRG4) protein. PRG4 is a secreted glycoprotein, known to be a critical component of the lubrication system in articular joints, yet its presence and function in the Temporomandibular Joint (TMJ) has not been characterized. Immunohistochemical studies indicate that PRG4 is shown to be expressed in the articular disc of the TMJ, which is also rich in type I collagen. Interestingly, PRG4 expression in the disc appears to correspond with collagen fiber patterns suggesting an association between collagen I and PRG4. Collagen-proteoglycan interactions are well described in the literature however further studies are needed to establish the exact nature of this observation.
A common disorder of the TMJ results from displacement of the articular disc (TMJ derangement) leading to degenerative joint disease. Recent evidence suggests that a defect in the lubricating system of the joint may be responsible for the development of TMJ derangement and subsequent degenerative TMJ disease (TMD). Unfortunately, the mechanisms underlying TMDs are not well understood. Attempts to localize major ECM components, including collagens, proteoglycans have provided some insight into the distribution of these molecules within the TMJ. The purpose of this study was to characterize the baboon TMJ with respect to the distribution of its major ECM components in an effort to identify the causative factors responsible for common TMJ disorders and identifying possible treatment options.