P1940Reciprocal regulation of Endothelial-Mesenchymal Transition by MAPK7 and EZH2 activity in Intimal Hyperplasia and Coronary Artery Disease

Abstract

Introduction Endothelial cells play a pivotal role in the formation of neointimal lesions by the acquisition of a fibro-proliferative phenotype through endothelial-to-mesenchymal transition (EndMT). Uniform laminar shear stress activates the mitogen-activated protein kinase 7 (MAPK7) which suppresses EndMT. It is elusive how MAPK7 activity is regulated in fibroproliferative disease. We recently found in intimal hyperplasia the signaling activity of MAPK7 is rapidly lost through the activation microRNA-374b. The histone methyltransferase Enhancer of Zeste Homolog 2 (EZH2), which is the catalytic subunit of the Polycomb Repressive Complex 2, plays a pivotal role in endothelial dysfunction. EZH2 trimethylates lysine 27 on histone 3, which silences gene expression and is elevated in endothelial cells in atherosclerotic lesions. Here, we found the reciprocity that exists between MAPK7 and EZH2 in the regulation of EndMT and in human coronary artery stenosis. Materials and results In endothelial cells, activation of MAPK7 increases the expression of microRNA-101, which represses the expression of EZH2. Reciprocally, the loss of EZH2 coincides with a decreased expression of the Dual Specificity Phosphatase (DUSP)-1 and DUSP-6 – the phosphatases responsible for the dephosphorylation of MAPK7 - which facilitates the activation of MAPK7. H3K27Me3, the repressive histone mark placed by EZH2, is abundantly present in the promoter regions of the miR-200b/a/429 and miR-200c/141 gene clusters, which are responsible for the loss of DUSP-1 and DUSP-6 expression. Endothelial cells deficient in EZH2 have reduced levels of H3K27Me3 at these gene promoters, which associates with the increased expression of miR-200b and miR-200c and concurrent increased MAPK7 activation. In endothelial cells with constitutively active MAPK7 signaling (MEK5D), the enrichment of H3K27Me3 at the promoter regions of miR-200b/a/429 (1.6-fold, p=0.034) and miR-200c/141 (1.9-fold, p=0.035) is decreased, suggesting that MAPK7 activation results in a decreased EZH2 activity. Disbalances in this reciprocal signaling circuit culminate in the induction of EndMT and associate to the severity of human coronary artery stenosis. Conclusion In summary, we show that in endothelial cells there is reciprocity between MAPK7 signaling and EZH2 expression and that disturbances in this reciprocal signaling circuit associate with the induction of EndMT and severity of human coronary artery stenosis. The reciprocity between MAPK7 and EZH2 is governed by a complex mechanism involving microRNAs and the phosphatases DUSP-1 and DUSP-6. Our study contributes to a better understanding of the molecular and epigenetic cascades that underlie EndMT during coronary artery stenosis and might identify novel targets for therapy. Acknowledgement/Funding Mongolian Government Scholarship #621