Kinetics of aggrecanase- and metalloproteinase-induced neoepitopes in various stages of cartilage destruction in murine arthritis

Objective. Two major cleavage sites, one mediated by metalloproteinases (MM Ps) and the other by an as-yet unidentified enzyme termed aggrecanase, have been observed in aggrecan, To learn more about the relative contribution o f these enzymes during cartilage degradation, this study assessed the occur rence of both specific neoepitopes in cartilage during murine arthritis and examined the correlation between neoepitope formation and different aspect s of cartilage damage. Methods, Reversible cartilage damage was induced in mice in the zymosan-ind uced arthritis (ZIA) model, partly irreversible cartilage damage in the ant igen-induced arthritis (AIA) model, and irreversible, destructive cartilage damage in the collagen-induced arthritis (CIA) model. Immunolocalization t echniques were used to detect the specific C-terminal neoepitopes VDIPEN (M MPs) and NITEGE (aggrecanase). Results, In normal cartilage from young adult mice, no VDIPEN epitopes were detected, but a limited amount of NITEGE epitopes were already present. Du ring the early phase of proteoglycan (PG) depletion, NITEGE expression was raised substantially in all arthritis models. VDIPEN epitopes were not dete cted in this early phase of cartilage destruction. When PG depletion progre ssed toward advanced cartilage damage, VDIPEN epitopes were induced. During ZIA, minimal induction of VDIPEN was observed, whereas in AIA, strong, but partly reversible, VDIPEN staining was evident, and in CLA, an extensive p resence and persistence of the il MMP-induced neoepitope was seen. When VDI PEN epitopes were intensely present, NITEGE epitopes were greatly reduced a t that site in the cartilage. Conclusion, Presence of VDIPEN epitopes in cartilage correlated with severe cartilage damage, but these epitopes were not detected during early PC; de gradation. This suggests a limited role for VDIPEN-inducing MMPs in early P G degradation during murine arthritis. In contrast, aggrecanase epitopes we re induced before the appearance of VDIPEN epitopes, but they disappeared w ith progression of cartilage damage.