REGIONAL AND TEMPORAL CHANGES IN THE SYNTHESIS OF MATRIX METALLOPROTEINASES AND TIMP-1 DURING DEVELOPMENT OF THE RABBIT MANDIBULAR CONDYLE

Connective tissues synthesise and secrete a family of matrix metallopr oteinases (MMPs; collagenases, gelatinases and stromelysins) capable o f degrading all the components of connective tissue matrices at physio logical pH. We document the patterns of synthesis and distribution of MMPs and the tissue inhibitor of metalloproteinases-1 (TIMP-1) within the developing rabbit mandibular condyle using immunofluorescence micr oscopy; MMPs and TIMP-1 were detected both as bright intracellular acc umulations within Golgi vesicles and also as diffuse matrix-bound extr acellular deposits. Cells in the articular zone, proliferative zone, c ondylar cartilage and bone of the mandibular ramus were shown to produ ce all 3 classes of MMPs and TIMP-1 with the exception of stromelysin, which was not synthesised by cells of the bone of spongiosum. Tempora l synthesis of MMPs and TIMP-1 within these regions varied during the period 18 d postcoitum to 14 d postnatum. Our results document unique patterns of MMP and TIMP-1 synthesis during embryonic and early postna tal development of condylar cartilage and support the concept that cel ls synthesise and secrete MMPs and TIMP-1 before undergoing proliferat ion and hypertrophy. A comparison of these results with data in the ra bbit growth plate show many similarities, but some differences exist t hat probably reflect differences in the modes of growth of the 2 carti lages.