Maturation of proteoglycan matrix in articular cartilage under increased and decreased joint loading. A study in young rabbits.

The right knees of 4-month-old NZW rabbits were splinted in extension for 1 to 8 weeks. Biochemical changes of the knee articular cartilage were noted after decreased (splinted leg) and increased loading (created by the shift of body weight onto the left, contralateral limb). Increased loading accelerated changes associated with maturation of articular cartilage, which include accumulation of hyaluronic acid (HA) and keratan sulfate-rich proteoglycans (KS, PG) that are tightly bound to the tissue. After 8-weeks of splinting the content of extractable PGs in the tibial medial condyle decreased. The lost material was apparently replaced by PGs with a higher degree of sulfation of the chondroitin sulfate (Ch-S) chains. Reduced loading disturbed normal maturation as evidenced by inhibition of the accumulation of KS-rich, non-extractable PGs. Collagen content increased in all samples of different joint sites and groups during the 8-week experiment. The content of extractable PGs decreased slightly, while the content of non-extractable, especially KS-rich PGs increased. The greatest changes occurred in the tibial medial condyle, where the KS content was highest.