Cleavage of aggrecan at the Asn341–Phe342 site coincides with the initiation of collagen damage in murine antigen-induced arthritis: A pivotal role for stromelysin 1 in matrix metalloproteinase activity
✍ Scribed by Joyce Van Meurs; Peter Van Lent; Reinout Stoop; Astrid Holthuysen; Irwin Singer; Ellen Bayne; John Mudgett; Robin Poole; Clark Billinghurst; Peter Van Der Kraan; Pieter Buma; Wim Van Den Berg
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 545 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0004-3591
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✦ Synopsis
Objective. The destruction of articular cartilage during arthritis is due to proteolytic cleavage of the extracellular matrix components. This study investigates the kinetic involvement of metalloproteinases (MMPs) in the degradation of the 2 major cartilage components, aggrecan and type II collagen, during murine antigen-induced arthritis (AIA). In addition, the role of stromelysin 1 (SLN-1) induction of MMPinduced neoepitopes was studied.
Methods. VDIPEN neoepitopes in aggrecan and collagenase-induced COL2-3/4C neoepitopes in type II collagen were identified by immunolocalization. Stromelysin 1-deficient knockout (SLN1-KO) mice were used to study SLN-1 involvement.
Results. In AIA, the VDIPEN epitopes in aggrecan appeared after initial proteoglycan (PG) depletion. The collagenase-induced type II collagen neoepitopes colocalized with VDIPEN epitopes. Remarkably, cartilage from arthritic SLN1-KO mice showed neither the induction of VDIPEN nor collagen cleavage-site neoepitopes during AIA, suggesting that stromelysin is a pivotal mediator in this process. PG depletion, as measured by the loss of Safranin O staining, was similar in SLN1-KO mice and wild-type strains. Furthermore, in vitro induction of VDIPEN epitopes in aggrecan and COL2-3/4C epitopes in type II collagen, on exposure of cartilage to interleukin-1, could not be accomplished in SLN1-KO mice, whereas intense staining was achieved for both epitopes in cartilage of wild-type strains.
Conclusion. This study emphasizes that SLN-1 is essential in the induction of MMP-specific aggrecan and collagen cleavage sites during AIA. It suggests that SLN-1 is not a dominant enzyme in PG breakdown, but that it activates procollagenases and is crucial in the initiation of collagen damage.
Cartilage destruction is a major complication of chronic joint inflammation and markedly contributes to disability in patients with rheumatoid arthritis (RA). The role of matrix metalloproteinases (MMPs) in cartilage degradation is still a matter of debate. There is a large body of indirect evidence for the involvement of MMPs in cartilage degradation. They are produced in high amounts by the inflamed synovium and cartilage of RA and osteoarthritis (OA) patients (1-3). In animal models of arthritis, large quantities of these enzymes are found in extracts of synovial biopsy tissues and in synovial fluid (4-7). MMP inhibitors have been used to demonstrate the active involvement of MMPs in cartilage destruction in vitro (8), but in vivo studies are scarce.
An elegant and direct way to identify enzyme involvement in vivo is to look at specific proteasegenerated matrix-degradation products (9). Amino acid sequence analysis of cartilage proteoglycan (PG) breakdown products in the synovial fluid of RA patients has defined 2 major sites of proteolytic cleavage in aggrecan,