The role of Yes-associated protein kinase YAP1 in canonical and non-canonical Hippo pathway in the disintegrin metalloproteinase ADAM15-mediated anoikis resistance of synovial fibroblasts in rheumatoid arthritis
Final Report Abstract
Rheumatoid arthritis (RA) is the most frequent inflammatory rheumatic joint disease. Based on genetic predispositions aberrantly dysregulated immunological effector cascades lead to chronic inflammatory reactions, resulting in the proteolytic destruction of cartilage and bone, thus compromising the integrity of articular joints. A major cell population critical for these destructive processes are the synovial fibroblasts, which are activated in the inflamed synovial membrane and secrete matrix degrading enzymes. A hallmark of rheumatoid arthritis synovial fibroblasts (RASFs) is their pathophysiological increased apoptosis resistance. Also RASFs, freely swimming in inflamed synovial fluid, are vital after their loss of matrix contact, which usually induces apoptosis, thereby rendering them anoikis resistant. The underlying mechanism of their acquired anoikis resistance are poorly understood, albeit pathophysiological relevant due to their capability to expand and infiltrate into joint tissues within one affected joint, and moreover their potential to migrate into distant healthy cartilage via the circulatory system, as has been demonstrated by animal studies. Our data show that silencing of ADAM15 or YAP1 in RASFs leads to significantly increased levels of detachment-induced caspase activity. In non-silenced RASFs detachment causes simultaneous ADAM15-enhanced phosphorylation of YAP1 at S127 known for promoting its cytoplasmic localization, and Src-dependent phosphorylation at tyrosine Y357. The majority of nuclear YAP1 leaves the nucleus shortly after cell detachment, but prolonged detachment causes a marked nuclear re-entry of YAP1, resulting in significantly increased synthesis of CTGF. The newly-synthesised CTGF, however, is not detectable in the supernatant, but bound to the outside of the plasma membrane. In vitro studies demonstrated autocrine binding of CTGF to the EGF receptor and β1 integrin, with concomitant triggering of survival kinases, AKT1, ERK1/2, Src, and focal adhesion kinase. Functional studies revealed antiapoptotic effects of CTGF on detached RASFs and an enhancement of their potential for endothelial transmigration using HUVEC-coated transwells. The elucidation of a new molecular mechanism that protects RASFs in the highly proapoptotic environment of inflamed RA joints by promoting anoikis-resistance and transendothelial migration via ADAM15/YAP1-mediated CTGF upregulation uncovers potentially new targets for future therapeutic intervention. In conclusion, our results contribute to a better understanding, how mesenchymal cells from synovial tissues upon disintegration from their ECM acquire mechanisms to enter the circulation and survive in the bloodstream long enough for giving rise to bloodborne spread of pathogenicity to distant joints, thereby providing clues to potentially new treatment options.
Publications
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A Novel Pro-Inflammatory Mechanosensing Pathway Orchestrated by the Disintegrin Metalloproteinase ADAM15 in Synovial Fibroblasts. Cells, 10(10), 2705.
Janczi, Tomasz; Meier, Florian; Fehrl, Yuliya; Kinne, Raimund W.; Böhm, Beate & Burkhardt, Harald
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Detachment promotes RA synovial fibroblast survival and invasiveness. Nature Reviews Rheumatology, 18(8), 432-432.
Phillips, Robert
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The role of YAP1 target gene CTGF in the anoikis resistance of rheumatoid arthritis synovial fibroblasts. Rheumatology, 62(2), 850-860.
Janczi, Tomasz; Fehrl, Yuliya; Kinne, Raimund W.; Böhm, Beate & Burkhardt, Harald
