STRUCTURE OF CHONDROITIN SULFATE ON AGGRECAN ISOLATED FROM BOVINE TIBIAL AND COSTOCHONDRAL GROWTH PLATES

The structure of chondroitin sulfate on aggrecan isolated from the rib and proximal tibial growth plates of bovine fetuses was investigated, and the previously reported increase in the hydrodynamic size of chondroitin sulfate chains between the reserve and hypertrophic zones of the rib was confirmed in the tibial growth plate. Superose 6 gel chromatography, calibrated for chondroitin sulfate chain length by monosaccharide analysis, showed that the average molecular mass of chondroitin sulfate in the reserve and maturing zones of both growth plates was 21,600 and 30,400, respectively. Determination by capillary zone electrophoresis of the disaccharide composition of chains following chondroitinase digestion showed that Delta Di-0S, Delta Di-4S, and Delta Di-6S together accounted for more than 98% of the disaccharides in the digests from all zones of both growth plates; Delta disulfated and Delta trisulfated disaccharides were not detected. Furthermore, this analysis revealed a gradient in chondroitin sulfate composition from the reserve to the hypertrophic zone, characterized by a marked increase in the content of Delta Di-6S (from about 32% to about 52%) and a marked decrease in the content of Delta Di-4S (from about 53% to about 35%). Moreover, this altered pattern of sulfation was detected on chains of all sizes in the hypertrophic zone, suggesting that a proportion of the reserve zone aggrecan might be removed and replaced with aggrecan rich in chondroitin-6-sulfate synthesized during the proliferative and maturation stages of the resident chondrocytes. These data are discussed in relation to the biosynthetic mechanisms that control chondroitin sulfate chain length and sulfation on aggrecan and their modification during chondrocyte proliferation, maturation, and hypertrophy in the growth plate.