Comparison of proteoglycans extracted from high and low weight-bearing human articular cartilage, with particular reference to sialic acid content.

Proteoglycan subunits extracted in the presence of proteinase inhibitors from autologous knee and shoulder cartilage were examined in different donors of various ages, in order to determine the effect of weight bearing on the age-related changes in proteoglycan structure. At each age, high density proteoglycans from the two joints of the same individual were virtually identical with respect to chemical composition, hydrodynamic size, ability to aggregate with hyaluronic acid, and chondroitin sulfate chain length. The proteoglycan content of the cartilage decreased with age, as did the size of the proteoglycan subunits. In contrast, the proportions of keratan sulfate to chondroitin sulfate, protein to glycosaminoglycan, and chondroitin 6 sulfate to chondroitin 4-sulfate all increased with age. These changes occurred to the same extent in both knee and shoulder cartilage. There was no change in the ability of the proteoglycan to aggregate with hyaluronic acid. The sialic acid profile on Bio-Gel P-10 chromatography, following alkaline borohydride degradation, showed the presence of both keratan sulfate and oligosaccharide chains. The oligosaccharide content of the core protein of the proteoglycan appeared to decrease during the aging process, but it could not be ascertained whether this was related to the increased abundance of keratan sulfate.