THE EFFECTS OF LOADING ON THE SYNTHESIS OF BIGLYCAN AND DECORIN IN INTACT MATURE ARTICULAR-CARTILAGE IN-VITRO

Sesamoid bone cartilage from the metacarpophalangeal joints of 5-year-old cows was cultured intact on its bone support. The incorporation of sulfate increased similarly in experimental cartilage that was subjected to cyclic loading (0.2 MPa, 0.2 Hz) for a week and in control cartilage that was cultured without loading. The synthesis of a population of small macromolecules decreased in the cultured controls, but was maintained at a constant level in the experimental samples. This population was isolated through Sepharose CL-2B chromatography. Subsequent application to Sepharose CL-4B yielded two distinct peaks. One contained protein-free chondroitin sulfate, keratan sulfate, and possibly some dermatan sulfate glycosaminoglycans. The other, more prominent, peak consisted of dermatan sulfate proteoglycans. This peak material was pooled, and applied to a 4-15% SDS-gel. The material was separated into two major bands, which represented biglycan and decorin. They decreased to less than half their day-0 value, in the cultured control. In the loaded cartilage, biglycan synthesis remained constant while decorin synthesis increased. These findings suggest that biglycan and decorin are involved in the adaptation of articular cartilage to variations in loading regime.