AGGRECAN DEGRADATION IN HUMAN CARTILAGE - EVIDENCE FOR BOTH MATRIX METALLOPROTEINASE AND AGGRECANASE ACTIVITY IN NORMAL, OSTEOARTHRITIC, AND RHEUMATOID JOINTS

To examine the activity of matrix metalloproteinases (MMPs) and aggrec anase in control and diseased human articular cartilage, metabolic fra gments of aggrecan were detected with monospecific antipeptide antibod ies. The distribution and quantity of MMP-generated aggrecan G1 fragme nts terminating in VDIPEN341 were compared with the distribution of ag grecanase-generated G1 fragments terminating in NITEGE(373), Both type s of G1 fragments were isolated from osteoarthritic cartilage. The siz es were consistent with a single enzymatic cleavage in the interglobul ar domain region, with no further proteolytic processing of these frag ments. Both neoepitopes were also detected by immunohistochemistry in articular cartilage from patients undergoing joint replacement for ost eoarthritis (OA), rheumatoid arthritis (RA), and in cartilage from adu lts with no known joint disease, In control specimens, the staining in tensity for both G1 fragments increased with age, with little staining in cartilage from 22-wk-old fetal samples. There was also an increase with age in the extracted amount of MMP-generated neoepitope in relat ion to both aggrecan and collagen content, confirming the immunohistoc hemical results, After the age of 20-30 yr this relationship remained at a steady state, The staining for the MMP-generated epitope was most marked in control cartilage exhibiting histological signs of damage, whereas intense staining for the aggrecanase-generated fragment was of ten noted in adult cartilage lacking overt histological damage. Intens e staining for both neoepitopes appeared in the more severely fibrilla ted, superficial region of the tissue, Intense immunostaining for both VDIPEN- and NITEGE-neoepitopes was also detected in joint cartilage f rom patients with OA or RA, Cartilage in these specimens was significa ntly more degraded and high levels of staining for both epitopes was a lways seen in areas with extensive cartilage damage. The levels of ext racted VDIPEN neoepitope relative to collagen or aggrecan in both OA a nd RA samples were similar to those seen in age-matched control specim ens, Immunostaining for both types of aggrecan fragments was seen surr ounding the cells but also further removed in the interterritorial mat rix. In some regions of the tissue, both neoepitopes were found while in others only one was detected, Thus, generation and/or turnover of t hese specific catabolic aggrecan fragments is not necessarily coordina ted, Our results are consistent with the presence in both normal and a rthritic joint cartilage of proteolytic activity against aggrecan base d on both classical MMPs and ''aggrecanase.''