Characterization of neopeptides in equine articular cartilage degradation.

Osteoarthritis is characterized by a loss of extracellular matrix that leads to cartilage degradation and joint space narrowing. Specific proteases, including the aggrecanases ADAMTS-4 and matrix metalloproteinase 3, are important in initiating and promoting cartilage degradation in osteoarthritis. This study investigated protease-specific and disease-specific cleavage patterns of particular extracellular matrix proteins by comparing new peptide fragments, neopeptides, in specific exogenous protease-driven digestion of a crude cartilage proteoglycan extract and an in-vitro model of early osteoarthritis. Additionally, equine cartilage explants were treated with interleukin-1 and the media collected. Proteolytic cleavage products following trypsin digestion were then identified using tandem mass spectrometry. Complete sequences of proteolytically cleaved neopeptides were determined for the major cartilage proteoglycans aggrecan, biglycan, decorin, fibromodulin plus cartilage oligomeric matrix protein. The generation of neopeptides varied with enzyme specificity; however, some peptides were common to all samples. Previous known and novel cleavage sites were identifies. The identification of novel peptide fragments provides a platform for the development of antibodies that could assist in the identification of biomarkers for osteoarthritis (OA), as well as the identification of basic biochemical processes underlying OA.