The effect of hyaluronic acid on proteoglycan synthesis and secretion by chondrocytes of adult cartilage

The chondrocyte is a specialized cell that synthesizes proteoglycans of a type found only in cartilage and nucleus pulposus. These proteoglycans are distinct in forming multiple aggregates of unique structure in which hyaluronic acid provides a central chain to which many proteoglycan molecules are bound at one end only. Chondrocytes were isolated from adult cartilage and used in suspension culture to test the effect of compounds in the medium on the synthesis of proteoglycans. Hyaluronic acid alone, among a number of compounds extracted from or analogous to those in cartilage, reduced the incorporation of [35S] sulphate into macromolecular material. Oligosaccharides of hyaluronic acid of the size of decasaccharides and above also had this effect but hyaluronic acid already bound to proteoglycan did not. The proportion of total labelled material associated with the cells increased at the expense of that in the medium. Treatment of the cells with trypsin abolished the effect of hyaluronic acid but treatment with chondroitinase did not. It is suggested that hyaluronic acid interacts with proteoglycans at the cell surface by a specific mechanism similar to that involved in proteoglycan aggregation, as a result of which the secretion and synthesis of proteoglycans is reduced.