Membrane-type-1 matrix metalloproteinase is abundantly expressed in fibroblasts and osteoclasts at the bone-implant interface of aseptically loosenedjoint arthroplasties in situ

Objective. To investigate the distribution pattern of membrane-type-1 matri x metalloproteinase (MT1-MMP) within the synovial-like interface membranes of failed prosthetic joints. Methods. Interface tissue around loose arthroplasties containing both fibro us membrane and attached bone was obtained from 6 patients at revision surg ery. In situ hybridization with digoxigenin labeled RNA probes was applied to investigate MT1-MMP expression in paraffin sections of the samples. in a ddition, double labeling using immunohistochemistry was performed to charac terize MT1-MMP producing cells. Results. Apart from being present in fibroblasts, MT1-MMP was also found ex pressed in osteoclasts at sites of bone resorption. Our results revealed no expression of MT1-MMP at parts of the membrane that originally had been lo cated next to the prosthesis. Zn contrast, abundant staining for MT1-MMP wa s observed at sites attached to bone. MT1-MMP mRNA expression was more inte nse at those sites of bone resorption covered by a thicker interface membra ne. Conclusion. These results indicate a role for MT1-MMP not only in matrix de gradation by fibroblasts but also in osteoclast mediated bone resorption. G iven thr ability of MT1-MMP to activate MMP2 and MMP13, they suggest also t hat osteoclasts might contribute to matrix degradation by activating these MMP. This could be of potential interest not only for other conditions in w hich bone resorption by fibroproliferative tissue plays a role, but also to design novel strategies to prevent loosening of prosthetic joints.