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Development of a cleavage-site-specific monoclonal antibody for detecting metalloproteinase-derived aggrecan fragments: detection of fragments in human synovial fluids.

ABSTRACT: We have developed a monoclonal antibody AF-28 that specifically recognizes a neo-epitope on polypeptides with N-terminal FFGVG ... sequences. This sequence is found at the N-terminus of aggrecan fragments that have been digested with matrix metalloproteinases (MMPs). By immunoblotting, monoclonal antibody AF-28 specifically detected G2 fragments derived from an aggrecan G1-G2 substrate digested with stromelysin, collagenase, gelatinase and matrilysin, but failed to detect G2 fragments obtained from elastase, trypsin or cathepsin B digests. Undigested G1-G2 was not detected. In addition, AF-28 antibody detected fragments derived from whole aggrecan and this detection did not require prior treatment with chondroitinase or keratanase. Competition experiments confirmed that peptides containing internal ... FFGVG ... sequences were not detected by the antibody, while native MMP-digested aggrecan fragments and a synthetic 32-mer peptide with FFGVG ... N-termini were equally competitive on a molar basis. An FFGVG 5-mer, and an FGVGGEEDI9-mer which lacked the N-terminal phenylalanine residue, were 50 times and 230 times respectively less competitive than the FFGVG ... 32-mer. Two fragments from the interglobular domain, F342-F373 and F342-D441, that are predicted products of G1-G2 digestion by neutrophil collagenase but have not previously been detected, could be detected with AF-28. The epitope recognized by AF-28 was also detected in human synovial fluids by Western blot analysis. A broad band of 100-200 kDa was detected in some patients and a dominant band of 40-60 kDa was found in two patients. The size of this small fragment corresponds with that seen for the porcine F342-E373 product and may represent the natural physiological product of aggrecan cleaved in vivo at both the MMP site (... DIPEN341 decreases F342FGVG ...) and the aggrecanase site (... ITEGE373 decreases A374RGSVI ...).

SUBMITTER: Fosang AJ

PROVIDER: S-EPMC1135893 | biostudies-other | 1995 Aug

REPOSITORIES: biostudies-other

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Project description:IntroductionAggrecanase cleavage at the 392Glu-393Ala bond in the interglobular domain (IGD) of aggrecan, releasing N-terminal 393ARGS fragments, is an early key event in arthritis and joint injuries. Here, we use a quantitative immunoassay of aggrecan ARGS neoepitope fragments in human synovial fluid to determine if this cleavage-site specific method better identifies joint pathology than previously available less specific aggrecan assays.MethodsSynovial fluid (SF) from 26 people with healthy knees (reference) and 269 patients were analyzed in a cross-sectional study. Patient groups were acute inflammatory arthritis, acute knee injury, chronic knee injury and knee osteoarthritis (OA). Aggrecan ARGS fragments were assayed by ELISA using the monoclonal antibody OA-1. Total aggrecan content was analyzed by an ELISA using the monoclonal antibody 1-F21, and sulfated glycosaminoglycan by Alcian blue precipitation.ResultsAggrecan ARGS fragment concentrations in all groups differed from the reference group (P < 0.001). The acute inflammatory arthritis group had the highest median level, 177-fold greater than that of the reference group. Median levels (in pmol ARGS/ml SF) were: reference 0.5, acute inflammatory arthritis 88.5, acute knee injury 53.9, chronic knee injury 0.5 and OA 4.6. In contrast, aggrecan and sulfated glycosaminoglycan concentrations varied much less between groups, and only acute inflammatory arthritis and acute knee injury were found to have a two-fold increase in median levels compared to the reference.ConclusionsLevels of aggrecan ARGS fragments in human synovial fluid are increased in human arthritis, OA and after knee injury, likely reflecting an enhanced cleavage at the 392Glu-393Ala bond in the IGD by aggrecanase. An assay that specifically quantified these fragments better distinguished samples from joints with pathology than assays monitoring aggrecan or glycosaminoglycan concentrations. The newly developed ARGS fragment assay can be used to monitor aggrecanase activity in human joint disease and experimental models.

Project description:Monoclonal antibodies have been prepared that react specifically with the neoepitopes present on proteoglycan degradation products generated from the proteolytic cleavage of aggrecan in the interglobular domain. Antibody BC-3 recognizes the new N-terminus (ARGSV...) on aggrecan degradation products produced by the action of the as yet uncharacterized proteolytic activity, 'aggrecanase', and antibody BC-4 recognizes the new C-terminus (...DIPEN) generated by the proteolytic action of matrix metalloproteinases. Specificity for these neoepitope sequences was determined in competitive e.l.i.s.a. using synthetic peptide antigens as inhibitors. Antibody BC-3 was used in the detection of aggrecan degradation products in the culture medium obtained from two different in vitro culture systems: bovine cartilage explants treated with either retinoic acid or interleukin-1, and secondly, rat chondrosarcoma cells treated with retinoic acid. Both interleukin-1 and retinoic acid treatment caused an increase in aggrecan catabolism resulting in an increased release to the medium of specific aggrecan degradation products containing the BC-3 neoepitope generated by the action of 'aggrecanase'. However, several additional aggrecan catabolites were present that were not immunoreactive with antibody BC-3. In addition, under control conditions, in the bovine cartilage cultures the BC-3 epitope was found on some of these aggrecan catabolites. In contrast, no immune-reactive material was found in the aggrecan degradation products present in control media of rat chondrosarcoma cells cultured in the absence of retinoic acid. Collectively, these results demonstrate that 'aggrecanase' activity is not a constitutive event in all cartilage culture systems and also suggest that proteolytic agents other than 'aggrecanase' are involved in aggrecan catabolism in normal turnover compared with pathological conditions. Antibody BC-4 was used to demonstrate the identity of the G1 domain of aggrecan following proteolytic cleavage of a purified G1-G2 preparation with collagenase, gelatinase A or stromelysin. The G2 product of this cleavage did not react with antibody BC-3, indicating that, under the experimental conditions used, none of these enzymes exhibited 'aggrecanase' activity. It is expected that both of these antibodies will play a pivotal role in detailed studies elucidating molecular mechanisms of aggrecan degradation and they will be particularly useful for the sensitive monitoring of aggrecan degradation products in tissue extracts and body fluids.

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Development of a cleavage-site-specific monoclonal antibody for detecting metalloproteinase-derived aggrecan fragments: detection of fragments in human synovial fluids.

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