Articular-cartilage proteoglycans in aging and osteoarthritis

Abstract

The composition of macroscopically normal hip articular cartilage obtained from dogs of various ages was studied. Pieces of cartilage with signs of degeneration were studied separately. In normal aging the extraction yield of proteoglycans decreased; the keratan sulfate content of extracted proteoglycans increased, and the chondroitin sulfate content decreased. The extracted proteoglycans were smaller in the older cartilage, mainly owing to a decrease in the chondroitin sulfate-rich region of the proteoglycan monomers. The hyaluronic acid-binding region and the keratan sulfate-rich region were increased and the molar concentration of proteoglycan probably increased with increasing age. The degenerated cartilage had higher water content, and the proteoglycans, as well as other tissue components, gave higher yields. The proteoglycan monomers from the degenerated cartilage were smaller than those from normal cartilage of the same age, and hence had a smaller chondroitin sulfate-rich region, and some of the molecules appeared to lack the hyaluronic acid-binding region. Increased proteolytic activity may be involved in the process of cartilage degeneration.