Cleavage of Cartilage Oligomeric Matrix Protein (COMP) by ADAMTS4 generates a neoepitope associated with osteoarthritis and other forms of degenerative joint disease
Rens de Groot, Patricia Badía Folgado, Kazuhiro Yamamoto, Daniel R. Martin, Christopher D. Koch, Danielle A. Debruin, Sophie Blagg, Alexander F Minns, Sumit Bhutada, Josefin Ahnström, Jonathan Larkin, Anders Aspberg, Patrik Önnerfjord, Suneel Apte, Salvatore Santamaria
Abstract
• Degradation of COMP plays a role in osteoarthritis (OA) • We identified ADAMTS4 as a major COMPase • One of the COMP fragments generated by ADAMTS4 was previously detected in OA serum • Inhibition of ADAMTS4 abolished generation of COMP fragments in human OA explants • By cleaving COMP, ADAMTS4 may be implicated in OA pathogenesis Osteoarthritis (OA) is a highly prevalent joint disease, affecting millions of people worldwide and characterized by degradation of articular cartilage, subchondral bone remodeling and low-grade inflammation, leading to pain, stiffness and disability. Cartilage Oligomeric Matrix Protein (COMP) is a major structural component of cartilage and its degradation has been proposed as a marker of OA severity/progression. Several proteases cleave COMP in vitro , however, it is unclear which of these COMPase activities is prevalent in an osteoarthritic joint. Here, using purified recombinant proteins, we show that A Disintegrin And Metalloproteinase with Thrombospondin motifs 4 (ADAMTS4) is the most potent COMPase, followed by ADAMTS1. Using liquid chromatography-tandem mass spectrometry, we identified several novel cleavage sites in COMP resulting from ADAMTS4 and ADAMTS1 activity. Cleavage at S 77 -V 78 disrupted the pentameric organization of COMP and generated a neopeptide previously identified in the synovial fluid of OA patients. Immunoblots with anti-QQS 77 antibodies confirmed that ADAMTS4 efficiently cleaved this peptide bond. By analyzing five ADAMTS4 variants, we found that the C-terminal spacer domain is strictly necessary for COMPase activity and identified the specific residues involved in the interaction with COMP. An inhibitory anti-ADAMTS4 antibody significantly decreased generation of the COMP QQS 77 neoepitope in human OA cartilage explants, implicating ADAMTS4 as a key protease in generating the QQS 77 neopeptides in OA. Since another majorADAMTS4 substrate is aggrecan, the most abundant proteoglycan in cartilage, these findings highlight that, by cleaving both COMP and aggrecan, ADAMTS4 may play a crucial role in modulating the structural integrity of cartilage.