Maturation-related changes in proteoglycans of fetal articular cartilage

Abstract

Proteoglycans of the articulating and growing zones of maximum and minimum contact of bovine fetal articular cartilage were studied and compared to proteoglycans of immature calf and adult steer. During fetal maturation, localized changes were observed as early as the second trimester of fetal life but were restricted to the most superficial zones. Proteoglycans extracted from the growing zones were purified by density-gradient ultracentrifugation. The majority of proteoglycan monomers were able to interact with endogenous hyaluronate to form aggregates. Monomers had, at all fetal stages, similar elution profiles on Sepharose 2B and similar ratios of chondroitin sulfate chains/keratan sulfate chains/ O-glycosidically linked oligosaccharides. Keratan sulfate chains were of similar size at all stages, but chondroitin sulfate chain size decreased markedly with fetal maturation. In the first and second trimesters of fetal life, the proteoglycans were poorly substituted with glycosaminoglycans. A major increase in the absolute number of glycosaminoglycans and oligosaccharides attached to core protein was detected during the third trimester of fetal life. No further changes in substitution occurred in early postnatal life. Enzymatic digestion of proteoglycan monomer demonstrated that the increase in substitution with keratan sulfate occurred to the same extent in the main polysaccharide attachment region and in the keratan sulfate-rich region.