Identification and immunolocalization of chondroitin sulfate proteoglycans in tooth cementum

Proteoglycans (PGs) display a great diversity in their core proteins as well as carbohydrate structures and are thought to be involved in many biological functions. Recently we have identified and immunolocalized two keratan sulfate PGs, fibromodulin and lumican, in bovine tooth cementum (Cheng et al., Connect. Tissue Res. 34: 87-96, 1996). The objectives of this study were to identify and characterize chondroitin sulfate (CS) PGs in cementum. In order to explore their potential association with mineral, bovine cementum matrix molecules were fractionated into mineral-unbound and -bound matrices by sequential extraction. Both fractions were subjected to DEAE anion exchange column chromatography and the eluate collected was assayed for C4S and C6S isomers by dot blot immunoassay with specific monoclonal antibodies, 2-B-6 and 3-B-3, respectively. Two families of CSPGs were identified mainly in the mineral-unbound fraction. One contained only C4S glycosaminoglycan and the other both C6S and C4S. By biochemical and immunochemical analyses, decorin and biglycan were identified in the former and versican in the latter. The ratio of C6S to C4S isomers of cementum versican was approximately 7:1. Furthermore, these PGs were immunolocalized in and around tooth cementum using antibodies generated against the respective core proteins. Intensive immunostaining for versican was found almost exclusively in the lacunae housing cementocytes in cementum and osteocytes in alveolar bone, respectively. Immunostaining for decorin was mainly associated with collagen fibers in the periodontal ligament and slightly in cementum matrix, while the one for biglycan was mainly in cementoblasts/precementum. These differential tissue distributions of the CSPGs suggest that they may play distinct roles in cementogenesis.