The role of the disintegrin metalloproteinase ADAM15 in the apoptosis resistance of synovial fibroblasts in rheumatoid arthritis

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Rheumatoid arthritis (RA) is the most frequent chronic inflammatory joint disease. On the background of respective genetic predispositions dysregulated immunological effector pathways fuel a chronic inflammatory process in the joints leading to the activation of proteolytic processes that represent a constant threat to the structural integrity of articular cartilage and bone. A critical effector cell population involved in the inflammatory tissue destruction is the fibroblast in the synovial membrane that exhibits a persistently activated phenotype in the RA joint and is a major source for the local liberation of matrix degrading proteinases. Characteristically the synovial fibroblast in RA (RASF) exhibits a considerably increased resistance to apoptosis induction that is so far not fully understood. In our preliminary studies we could uncover a strong upregulation of the disintegrin metalloproteinase ADAM15 in RASF. This finding is of potential relevance in the context of the increased apoptosis resistance of RASF since we could also demonstrate that the disintegrin-metalloproteinase has a protective anti-apoptotic effect upon apoptosis induction by genotoxic stress or following activation of the death receptor Fas/CD95. Aim of the project is to elucidate whether ADAM15 has a more general cytoprotective effect on RASF or if its anti-apoptotic function is more confined to few distinct death inducing stimuli. The project further aims at uncovering the signaling pathways that get activated in the RASF upon apoptosis induction in dependency on their ADAM15 expression Based on the study results we aim at elucidating possibilities to selectively block these ADAM15 dependent effector cascades in order to reestablish sensitivity to apoptosis induction in the RASF by pharmacological means. To unravel the involved molecular mechanisms we will characterize ADAM15 ligands and their potentially associated contributions to signal transduction pathways by mammalian two-hybrid-, immunoprecipitation-, protein-binding-, and phosphorylation studies in the model of the synovial fibroblast cell line K4IM. In this established cell line model the ADAM15 dependent activation of anti-apoptotic effectors upon apoptosis induction will be quantified and functionally analyzed with regard to the involved anti-apoptotic effector proteins by SILAC mass spectrometry and subsequent siRNA-transfection studies. A validation of the results will be performed on primary RASF and by immunohistology of RA synovial tissue. The elucidation of the anti-apoptotic action of ADAM15 on RASF aims at identifying new potential target structures for a therapeutic modulation of the pathogenetically crucial apoptosis resistance of this aggressive cell population.