![]() These neoepitopes were identified through affinity enrichments of knee joint synovial fluids from patients with acute trauma, OA, and RA followed by mass spectrometric identification and characterization of the enriched COMP fragments.īy using an in vitro model of joint disease, we have successfully demonstrated the presence of the COMP neoepitope 3 Ser 77 as a released fragment from cartilage explants. In this work, we identified 12 novel COMP neoepitopes and hereby describe the newly formed N- and C-terminal ends. Many proteases have been shown to degrade COMP, but the specific cleavage sites within COMP as well as the newly formed N and C termini have so far not been described. Each of the five globular C-terminal domains binds collagen with a K D ≃10 −9 and thereby catalyzes collagen fibril assembly ( 19). The C-terminal domain is involved in interactions with other proteins in the extracellular matrix such as collagens I, II, and IX ( 19, – 21). Each N-terminal domain is followed by four EGF repeat domains, eight thrombospondin type III domains, and a C-terminal globular domain ( 18). It is a pentameric protein of 524 kDa ( 15) in which where the monomers are joined together by a coiled coil domain in the N terminus. COMP is cleaved and released from the cartilage tissue into synovial fluid in OA, RA, and other forms of inflammatory arthritis ( 6, 10, – 13), and it is well established that COMP can be used as a marker of cartilage turnover ( 14).ĬOMP is primarily found in cartilage ( 15), but it has also been found in other tissues such as synovium and tendon ( 16, 17). Elevated serum levels of COMP are associated with ongoing joint destruction in rheumatoid arthritis ( 8, – 10). ![]() During the last decade, efforts have been made to find suitable biological markers that enable early detection of pathological cartilage degeneration ( 6, 7). In addition, the imbalance in the turnover of matrix proteins often results in increased proteolysis of molecules bound to and exposed at the surface of collagen fibers such as fibromodulin, decorin, and cartilage oligomeric matrix protein (COMP) ( 3, – 5). In progressive joint diseases, the degradation of extracellular matrix proteins and proteoglycans leads to irreversible alterations in the properties of the collagen network. To minimize permanent tissue damage caused by pathological cartilage degeneration, it is important to diagnose such conditions at an early stage ( 2). These pathological conditions resulting in tissue degradation constitute a major medical, social, and economic problem ( 1). Through neoepitope assays, tools to pinpoint disease progression, evaluation methods for therapy, and means to elucidate disease mechanisms will be provided.ĭestruction of articular cartilage and changes of the underlying bone are key characteristics of joint diseases such as osteoarthritis (OA) 2 and rheumatoid arthritis (RA). The identified neoepitopes provide a complement to the currently available commercial assays for cartilage markers. Furthermore, fragments containing the neoepitope Ser 77 were released into the culture medium of cytokine (TNF-α and IL-6/soluble IL-6 receptor)-stimulated human cartilage explants. This ELISA quantifies COMP fragments clearly distinguishable from total COMP. For one of the neoepitopes, Ser 77, an inhibition ELISA was developed. Twelve different neoepitopes were identified and characterized within the enriched COMP fragments. ![]() Using the enzymes trypsin, chymotrypsin, and Asp-N for the digestions, an extensive analysis of the enriched fragments could be accomplished. Enriched COMP fragments were separated by SDS-PAGE followed by in-gel digestion and mass spectrometric identification and characterization. Disease-specific COMP fragments were isolated by affinity chromatography of synovial fluids from patients with rheumatoid arthritis, osteoarthritis, or acute trauma. Early detection of disease and processes in the tissue as well as an understanding of the pathologic mechanisms will also open the way for novel treatment strategies. Isolation and characterization of distinct cartilage oligomeric matrix protein (COMP) fragments derived from cartilage and released into synovial fluid will allow discrimination between different pathological conditions and monitoring of disease progression. To identify patients at risk for progressive joint damage, there is a need for early diagnostic tools to detect molecular events leading to cartilage destruction.
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