Endothelial-Mesenchymal Transition: Mir-101 As A New Target to Treat Intimal Hyperplasia

Introduction: Endothelial-Mesenchymal Transition (EndMT) is a specific form of endothelial dysfunction wherein endothelial cells acquire a mesenchymal phenotype and lose their endothelial functions. We, and others, recently described that EndMT contributes to intimal hyperplasia and atherosclerosis. Pro-fibrotic and inflammatory cytokines, such as IL-1β and TGFβ2 induce EndMT. We found that the mitogen activated protein kinase 7 (MAPK7, also known as Erk5) inhibits EndMT. MAPK7 activation decreases the expression of the histone methyltransferase Enhancer-of-Zeste homologue 2 (Ezh2) thereby maintaining endothelial quiescence.This decrease in Ezh2 expression may therefore be responsible for the protective effects of MAPK7 activation and may thus offer new therapeutic options for the treatment of endothelial dysfunction and intimal hyperplasia. Ezh2 is the catalytic subunit of the Polycomb Repressive Complex 2 that methylates lysine 27 on histone 3 (H3K27me3). H3K27me3 is a repressive chromatin mark that inhibits gene expression. Currently, it is elusive how the crosstalk between MAPK7 and Ezh2 is regulated in the endothelium and if the balance between MAPK7 and EZH2 is disturbed during intimal hyperplasia. Methods and results: We used in silico analysis to identify miRNAs that could evoke posttranscriptional silencing of Ezh2. In Luciferase reporter assays, miR-101 efficiently inhibited expression of the luciferase reporter by interacting with the 3’UTR of EZH2. Using a uniform laminar flow setup, we revealed that MAPK7 induced miR-101 expression, which was blocked by the selective MAPK7 inhibitor BIX02189 (p<0.05). Furthermore, ectopic expression of miR-101 in endothelial cells reduced the expression of Ezh2. In samples of human coronary artery stenosis Ezh2 levels are increased, whereas MAPK7 expression is reduced. Moreover, miR-101 expression is decreased, which associated with the increase of Ezh2 (R2=0.23, p=0.051) and severity of the stenosis (Intima/Media Thickness, R2=0.45, p=0.003). Conclusion(s): Under uniform laminar flow MAPK7 inhibits Ezh2 expression via activation of miR-101. In coronary artery stenosis, endothelial cells are exposed by non-uniform shear stress which decreases MAPK7 activation, miR-101 expression and concurrently increases Ezh2 expression, which may cause EndMT and intimal hyperplasia. Therefore, the restoration of miR-101 expression or the silencing of Ezh2 in the endothelium might provide novel therapeutic approaches to treat intimal hyperplasia.