Effects of Exogenous TGF-β on TMJ Discal Development
The temporomandibular joint (TMJ) disc is a complex, fibrocartilaginous tissue with defined functional regions. It is an integral joint component functioning to promote smoothness of movement and absorbing shock and stresses accompanying joint function. It develops its microheterogenous structure and gross form between birth and three-months postnatal. Previous studies from our lab have indicated that transforming growth factor-beta (TGF-β), a regulator of cell growth and extracellular matrix (ECM) synthesis, is expressed during discal maturation. OBJECTIVE: This study's objective was to understand the role of TGF-β in the postnatal development of the disc. METHODS: The effects of TGF- β on discal development was studied in newborn, two week, one, two, and three month postnatal NZW rabbits. Animals were sacrificed, discs extracted and organ cultured in the presence or absence of exogenous TGF-β. Discs were then fixed, paraffin embedded and prepared for light microscopy. Changes in the character and composition of the ECM were examined using histochemical and immunohistochemical techniques and a suite of monoclonal antibodies to cartilage matrix proteins. RESULTS: This study demonstrated a common pattern throughout normal discal development; as the disc matures, cell population decreases and types I and II collagen content and organization increases, as well as an increase in keratan sulfate and decorin content. In TGF-β treated discs, cell proliferation and differentiation were stimulated in earlier stages (newborn to two weeks) while proteoglycan and type II collagen synthesis was reduced in later stages of development (two to three months). CONCLUSION: The addition of exogenous TGF-β seemed to provide both a stimulatory and inhibitory effect on discal cells during maturation. Discal maturation is a complex process of matrix synthesis and organization. TGF-β's role may be to assist in cellular differentiation associated with assembly of the disc's unique ECM architecture.