Structural Changes During Development in Bovine Fetal Epiphyseal Cartilage

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Structural changes during development have been examined in epiphyseal cartilages from bovine fetuses ranging in age from 100 to 250 days, and in proteoglycan aggregates and monomers isolated from these cartilages. The chemical composition of the whole fetal cartilage differs greatly from that of mature cartilages. The water contents of the whole fetal cartilages are higher than those of mature cartilages, and decrease progressively with increasing fetal age. The collagen contents of the whole dry fetal cartilages are much lower than those of mature cartilages, and increase progressively from approximately 14% at 100 days to 36% at 250 days. The non-collagenous matrix protein contents of the whole cartilages are higher than those of mature cartilages and, based on the yield of fraction A5A6 from associative density gradients, increase progressively with decreasing fetal age. Proteoglycan aggregates in fraction A1 from associative gradients are of much larger size than aggregates from mature cartilages and show sedimentation coefficients (S020 solvent) of approximately 150 S. The size of the proteoglycan aggregate remains constant throughout most of fetal development. In fraction Al from all but the youngest fetuses, a single proteoglycan monomer species was demonstrated. In fraction A1 from the youngest fetuses, two proteoglycan monomer species were demonstrated. The sedimentation coefficient of the single proteoglycan monomer species present in A1D1D1 of all but the youngest fetuses increased from 21.3 S to 23.5 S with decreasing fetal age. Compared with proteoglycan monomers from mature bovine articular cartilages, the fetal proteoglycan monomers showed much lower glucosamine and galactose contents, and lower glucosaminelsialate molar ratios.Associative density gradient fractions from the bovine fetal epiphyseal cartilages were examined for the presence of a dermatan sulfate-containing mesenchymal proteoglycan monomer using assays with chondroitinase AC and ABC. Little or no dermatan sulfate-containing proteoglycan was found in fraction A1, but dermatan sulfate containing-proteoglycan was consistently found in fraction A2, where dermatan sulfate accounted for 7% of the dry weight of the fraction and 25% of the total glycosaminoglycan.This description of the structural changes which occur during development in fetal epiphyseal cartilages and their proteoglycans provides an essential quantitative baseline for elucidating the structural changes which occur in growth plate cartilage and its proteoglycans during enchondral ossification.