Mechanisms of proteoglycan degradation in human articular cartilage

Aging of human articular cartilage is associated with proteolytic degradation of its constituent proteoglycan aggregates. Similar events are thought to be associated with proteoglycan loss in osteoarthritis. Degradative changes in link protein have been characterized and can be used as an indicator of the causative proteolytic agents. In the neonate, proteolysis results in cleavage of the N-terminal 16 amino acids, at a site characteristic for the metalloproteinase stromelysin. In the adult, further cleavage occurs in the N-terminal region and the adjacent disulfide bonded loop, indicating the action of additional proteolytic agents. In osteoarthritis, link protein cleavage occurs at sites identical to those observed in the normal adult.