Composition of proteoglycans synthesized in different layers of cultured anatomically intact articular cartilage.
Calf articular cartilage was cultured anatomically intact on its natural bone-support. At day 0 and day 7, respectively, the cartilage was radiolabeled, washed and harvested in 3 successive layers parallel to the articular surface. The proteoglycans were studied after extraction by 4 M guanidine hydrochloride. In the deep layer, the endogenous proteoglycan monomers were slightly smaller, showed an increased polydispersity and the relative amount of keratan sulfate was lower. In addition, chondroitin sulfate side chains were slightly larger and the sulfation degree and proportion of 4-sulfated disaccharides was elevated. At day 0, deep layer chondrocytes incorporated about twice as much [35S]-sulfate into glycosaminoglycans as did superficial chondrocytes. The newly synthesized proteoglycan monomers were the same in all layers with respect to size, dispersity, relative amount of keratan sulfate and size of chondroitin sulfate side chains. The sulfation-pattern, however, changed with depth in the same way as noted in the endogenous proteoglycan population. Small endogenous proteoglycan was present in all layers, but its synthesis was only prominent in the upper layer and decreased with depth. After 7 days culture, the [35S]-sulfate incorporation had increased in the upper half of the cartilage. There was a strong increment in the proportion of 6-sulfated disaccharides of newly synthesized glycosaminoglycan in all layers. The synthesis of small proteoglycan was markedly reduced, especially in the upper layer.