Changes in the sulfated proteoglycans synthesized by "aging" chondrocytes. I. Dispersed cultured chondrocytes and in vivo cartilages.

Structural and chemical changes in the sulfated proteoglycans synthesized by "aging" cultures of dispersed chondrocytes were compared to those synthesized by freshly excised, intact cartilage explants in organ culture from chickens of various ages. In vitro, chondrocytes isolated from embryonic chick vertebral cartilages synthesized a proteoglycan monomer characteristic of cartilage (type IV). Monomers synthesized between 3 days and 6 weeks in culture: (i) showed a decrease in average molecular size, which could be correlated, in part, with a decrease in the average size of the chondroitin sulfate chains; (ii) were able to interact with hyaluronic acid to form proteoglycan aggregates regardless of size; (iii) maintained a relatively constant 6S/4S disaccharide ratio of 2.2 for chondroitin sulfate; and (iv) maintained a constant keratan sulfate composition of 5 to 10%. Sulfated proteoglycans synthesized by freshly excised embryonic tibia cartilaginous head and by tibial articular cartilages of 1- and 6-year-old chickens were compared. With age: (i) the type IV monomer size decreased; (ii) the chondroitin sulfate chain size decreased; (iii) the type IV monomers retained their ability to interact with hyaluronic acid; (iv) the 6S/4S disaccharide ratio decreased from 1.7 to 0.6; (v) the keratan sulfate composition increased from 7 to 40%. Although monomer sizes decrease in both the culture and explant systems, in other respects the differences are considerable. These findings suggest that the changes in sulfated proteoglycans observed in subcultured monolayers of chondrocytes must be interpreted with caution when attempting to relate them to the changes that occur in aging in vivo chondrocytes.