Age-Related Changes in the Composition of Proteoglycans in Sheep Cartilage

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Abstract
Age-related changes in the proteoglycans of costal, tracheal, nasal and xiphoid cartilages of sheep, starting at 100 days in utero to 1 year postnatally and in scapular cartilages up to 13 years of age, have been assessed. The amino acid compositions of the core proteins in the proteoglycans from one-year-old cartilages are indistinguishable on the basis of kind of cartilage or of earlier stages of development. At 13 years of age, the core protein in the proteoglycans of scapular cartilages contains less glutamic acid/glutamine and glycine and more lysine, histidine, arginine, and threonine than at one year of age. Relative to the protein, the amount of chondroitin sulfates decreases with age but the amount of keratan sulfate increases. In part, this is a reflection of a decrease in the size of the chondroitin sulfate chains and an increase in the size of the keratan sulfate chains. Up to one year of age, the ratio of chondroitin-4-sulfate to chondroitin-6-sulfate increases in the scapular cartilages. From two to nine years of age, this ratio remains relatively constant at 1.7. At 100 days in utero, about 12% of the disaccharide repeats in the chondroitin sulfate are notsulfated, and this fraction progressively decreases to about 1% by two years postnatally. After one year of age, the size of the proteoglycan monomers decreases. As indicated by sedimentation velocity analysis, the proportion of monomers in aggregate form increases up to 1–2 years of age and then decreases. At 100 days of age the “immature” core protein does not react in vitro with hyaluronan and link proteins to form aggregates discernable in the ultracentrifuge.