New collagenolytic enzymes cascade identified at the pannus-hard tissue junction in rheumatoid arthritis: Destruction from above

Our aim was to investigate the collagenolytic potential and localization of matrix metalloproteinase-2 (MMP-2) in relation to its regulatory proteins membrane type MT1-MMP and tissue inhibitor of metalloproteinases-2; (TIMP-2 ) in rheumatoid arthritis (RA). For this purpose, we have used purification of MMP-2, MMP-8, MMP-9 and interstitial type I, II and III collagens; SDS- PAGE/densitometric collagenase activity assay; zymography; Western blotting ; reverse transcriptase polymerase chain reaction; in situ hybridization; a nd immunofluorescence, ABC, ABC-APAAP double immunostainings. MMP-2 degrade d human type II collagen almost as effectively as MMP-8, whereas MMP-9 did not cleave type II collagen. In synovial tissue, MT1-MMP, TIMP-2 and MMP-2 were found in synovial lining in fibroblast- and macrophage-like cells, in stromal cells and in vascular endothelium. MT1-MMP, TIMP-2 and MMP-2 were s trongly expressed in the pannocytes of the invasive pannus at the interface , but staining was weak and/or there were few positive cells both "above" a nd "below" the soft-to-hard tissue (cartilage and/or bone) interface. Rheum atoid synovial tissue extract contained proteolytically active 62/59 kDa MM P-2 and 43 kDa MT1-MMP, but no free TIMP-2. These results indicate that com ponents of the ternary MT1-MMP/TIMP-2/MMP-2 complex are coexpressed in the normal synovial lining and in its pathological extension on the hyaline art icular cartilage. MMP-2 may participate in the remodeling of the normal lin ing and also seems to be localized/focalized to pannocytes at a site critic al for tissue destruction in arthritis.