Proteoglycans are categoried depending upon the nature of their glycosaminoglycan chains (chondroitin sulfate, dermatan sulfate, heparan sulphate and keratan sullfate) as well as characterized by size.

Aggrecan is a large aggregating proteoglycan of articular cartilage. It is found also in aorta tissue, discs, tendons and in the perineuronal net. It is responsible for hydrating cartilage, giving it compressibility and resiliance during joint loading, thereby playing a major role in the normal function of cartilage. Depletion of glycosaminoglycan bearing aggrecan fragments is one of the earliest events in cartilage destruction.