Enhanced sulfated‐proteoglycan core protein synthesis by incubation of rabbit chondrocytes with recombinant transforming growth factor‐β1

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Abstract
Rabbit articular chondrocytes were incubated with recombinant transforming‐growth‐factor‐β 1, (rhTGF‐β1) and its effect on newly synthesized proteoglycan measured. rhTGF‐β1 stimulated proteoglycan synthesis at a concentration as low as 5 ng/ml without further increase in radiosulfate incorporation up to 50 ng/ml. The quantitative increase in radiosulfate incorporation in rh‐TGF‐β1‐treated chondrocytes was greater in the cell‐associated culture compartment than in the medium compartment. rhTGF‐β1 promoted an increased proteoglycan retention in the cell‐associated compartment as evidenced by an increase in the t 1/2 retention from 8 h to 11 h. Specific enhanced synthesis of [35S]‐methionine‐labeled core proteins was seen in rh‐TGF‐β1‐treated chondrocytes. rh‐TGF‐β1 increased the synthesis of the 2 core proteins derived from hydrodynamically large proteoglycans. They possessed apparent molecular weights of > 480 kD and 390 kD after 3‐5% acrylamide gel electrophoresis. A compartmental analysis revealed that the cell‐associated culture compartment contained only the larger of the 2 core proteins derived from large proteoglycans. Two other core proteins with apparent molecular weights 52 kD and 46 kD were also stimulated by rhTGF‐β1. These results indicated that TGF‐β probably plays a significant role in stimulating proteoglycan core protein synthesis in articular chondrocytes and therefore may be an important growth factor in the restoration of cartilage extracellular matrix after injury.

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