Aggrecan degradation in human cartilage. Evidence for both matrix metalloproteinase and aggrecanase activity in normal, osteoarthritic, and rheumatoid joints.

Abstract

To examine the activity of matrix metalloproteinases (MMPs) and aggrecanase in control and diseased human articular cartilage, metabolic fragments of aggrecan were detected with monospecific antipeptide antibodies. The distribution and quantity of MMP-generated aggrecan G1 fragments terminating in VDIPEN 341 were compared with the distribution of aggrecanase-generated G1 fragments terminating in NITEGE 373 . Both types of G1 fragments were isolated from osteoarthritic cartilage. The sizes were consistent with a single enzymatic cleavage in the interglobular domain region, with no further proteolytic processing of these fragments. Both neoepitopes were also detected by immunohistochemistry in articular cartilage from patients undergoing joint replacement for osteoarthritis (OA), rheumatoid arthritis (RA), and in cartilage from adults with no known joint disease.In control specimens, the staining intensity 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 relation to both aggrecan and collagen content, confirming the immunohistochemical 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 often noted in adult cartilage lacking overt histological damage . Intense staining for both neoepitopes appeared in the more severely fibrillated, superficial region of the tissue.Intense immunostaining for both VDIPEN-and NITEGEneoepitopes was also detected in joint cartilage from patients with OA or RA. Cartilage in these specimens was significantly more degraded and high levels of staining for both epitopes was always seen in areas with extensive cartilage damage. The levels of extracted VDIPEN neoepitope relative to collagen or aggrecan in both OA and RA samples were similar to those seen in age-matched control specimens.Immunostaining for both types of aggrecan fragments was seen surrounding the cells but also further removed in the interterritorial matrix. In some regions of the tissue, both neoepitopes were found while in others only one was detected. Thus, generation and/or turnover of these specific catabolic aggrecan fragments is not necessarily coordinated. Our results are consistent with the presence in both normal and arthritic joint cartilage of proteolytic activity against aggrecan based on both classical MMPs and "aggrecanase.

Aggrecanase versus matrix metalloproteinases in the catabolism of the interglobular domain of aggrecan in vitro

“…The detection of … DIPEN-terminating aggrecan metabolites in the direct extract of porcine cartilage is consistent with reports in other species and indicates an accumulation of this neoepitope in the cartilage over the life of the animals [14][15][16][17][18][19]. However, it is not clear whether these … DIPEN metabolites detected in articular cartilage are generated by the action of MMPs on intact aggrecan or the aggrecanase-generated G1 metabolite.…”

“…Studies utilizing antibodies to the C-terminal neoepitopes on aggrecan catabolites retained within the cartilage matrix have confirmed the presence of G1-bearing fragments resulting from cleavage at both the aggrecanase and MMP sites [14][15][16][17][18][19]. The presence of these different aggrecan catabolites in the synovial fluid and cartilage matrix may be explained by a number of possible catabolic pathways, as suggested by Lark et al [16] ; i.e. (i) primary cleavage at the aggrecanase site followed by secondary MMP catabolism of the G1-bearing fragment ; (ii) primary cleavage at the MMP-site followed by secondary cleavage of the released GAG-bearing catabolite by aggrecanase ; or (iii) independent cleavage of separate aggrecan molecules by the two enzyme activities.…”

The release of crosslinked peptides from type II collagen into human synovial fluid is increased soon after joint injury and in osteoarthritis

“…Higher synovial concentrations of matrix metalloproteinases (MMPs), such as MMP-1 and MMP-3, and proteinase activity after joint injury and in OA are consistent with the observed expression of these proteases in cartilage and synovium in these conditions (13)(14)(15)(16)(17). Good evidence exists for proteolytic de-gradation of joint cartilage aggrecan (3,(18)(19)(20). For example, high concentrations of aggrecan fragments and other matrix molecules are found in SF (15,(21)(22)(23)(24).…”

Fibroblast growth factor 2 is an intrinsic chondroprotective agent that suppresses ADAMTS‐5 and delays cartilage degradation in murine osteoarthritis

“…This antibody crossreacts with the cleaved epitope of murine aggrecan (NVTEGE) that is retained in cartilage following ADAMTS-mediated cleavage (15). Staining of the NVTEGE epitope was apparent in the superficial layer of articular cartilage in both Fgf2 ϩ/ϩ and Fgf2 -/-mouse cartilage 2 weeks following DMM surgery, but was significantly reduced in tissue from sham-operated animals.…”