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Mechanical loading affects the synthesis of decorin and biglycan in intact immature articular cartilage in vitro.

Sesamoid bone cartilage from the metacarpophalangeal (MCP) joints of six-month-old calves was cultured intact on its bone support. The sesamoid bones for the experiment were subjected to loading with 0.2 MPa at 0.2 Hz for a week. Controls were cultured for 0 or 7 days, labelled with [35S] sulfate for 17 h, harvested, and extracted in 4 M guanidine HCI with proteinase inhibitors, for analysis on Sepharose CL-2B columns under dissociative conditions. It was found that the population of labelled small proteoglycans was significantly larger in the loaded cartilage than in the cultured controls. This population was pooled and further purified on dissociative Sepharose CL-4B columns. The resulting profiles showed two peaks. The material eluting at Kav 0.80 contained only chondroitin sulfate and keratan sulfate chains. The peak at Kav 0.48 was analysed by SDS-polyacrylamide gel electrophoresis. It consisted of the dermatan sulfate proteoglycans decorin and biglycan. The amounts of newly synthesized decorin and biglycan in the cultured control cartilage were lower than in the control cartilage that had been labelled on day 0. The synthesis of decorin, but not of biglycan, was significantly higher in the loaded cartilage than in the cultured control cartilage. Through its interaction with collagen type II, decorin may aid the adaptation of articular cartilage to increased loading.