Specific properties of the extracellular chondroitin sulphate proteoglycans in the mandibular condylar growth centre in pigs

Abstract

The developing condylar cartilage of the temporomandibular joint responds to changes in load by adaptive growth. Because local regulatory events taking place during growth processes are not well understood, investigation of extracellular matrix composition could provide new information about which matrix molecules are involved in the regulation of growth processes in this avascular tissue. The large chondroitin sulphate-rich proteoglycans in the mandibular condyle were compared to the proteoglycans in the weight-bearing femoral condyle of juvenile domestic pigs with respect to their buoyant density, chemical composition and immunological identity after isolation by dissociative extraction and CsCl density-gradient centrifugation. The distribution of these proteoglycans was studied in cryosections of mandibular condyle by immunohistochemistry using polyclonal antibodies produced against pig large proteoglycans. In the mandibular condyle, predominantly in the articular zone, the relative amount of proteoglycans with a low glycosaminoglycan content was greater than in femoral cartilage. The large proteoglycan immunologically related to aggrecan gave a protein core of 450 kDa after enzymatic deglycosylation and clearly possessed less keratan sulphate than in femoral aggrecan. Furthermore, the mandibular tissue contained another large proteoglycan with a protein core of 550 kDa after enzymatic deglycosylation, which was immunologically related to the fibroblast-like versican. Immunohistochemistry showed aggrecan increasing in amount inferiorly. In contrast, ‘versican’ was exclusively found in the fibrous and differentiation layers. Aggrecan is mainly responsible for shock absorption and versican and its homologues may be involved in the control of cell proliferation and differentiation. Thus the matrix components of the mandibular condyle seem to be adapted to its special functional needs including parallel articulation and growth.