ABSTRACT
This chapter reviews the metabolism of proteoglycans, hyaluronan, and non collagen proteins by chondrocytes with an emphasis on the mechanisms and regulation of their synthesis, incorporation into, and their loss from the extracellular matrix of cartilage. There are three major types of proteoglycans that are synthesized by chondrocytes: large cartilage-specific aggregating proteoglycans, small proteoglycans, and cell-associated proteoglycans. Proteoglycans that are incorporated into the extracellular matrix of cartilage are specifically degraded and lost from the tissue. The route of link protein biosynthesis is the same as that of other glycoproteins, including proteoglycans; indeed, link proteins have been co-located with proteoglycan monomers in secretory vesicles in chondrocytes. The fate of hyaluronan as the result of the catabolism of the proteoglycan has been investigated in cartilage expiants and it appears that the hyaluronan has a similar half-life to that of aggrecan. Cartilage fibronectin binds to type II collagen and to chondroitin sulfate proteoglycans, but not to hyaluronan.
