Altered DNA methylation indicates an oscillatory flow mediated epithelial-to-mesenchymal transition signature in ascending aorta of patients with bicuspid aortic valve

Hanna M Björck,Karin Lundströmer,Cecilia Österholm,Shohreh Maleki,Arturo Evangelista,Aleksandra Kostina ,Silvia Pulignani,Anna Kostareva,Anders Franco‐Cereceda ,Anna Malashicheva,Lei Du,Valentina Paloschi,Gisela Teixidó‐Turà ,Per Eriksson

doi:10.1038/s41598-018-20642-4

Abstract

Disturbed flow has been suggested to contribute to aneurysm susceptibility in bicuspid aortic valve (BAV) patients. Lately, flow has emerged as an important modulator of DNA methylation. Hear we combined global methylation analysis with in vitro studies of flow-sensitive methylation to identify biological processes associated with BAV-aortopathy and the potential contribution of flow. Biopsies from non-dilated and dilated ascending aortas were collected from BAV (n = 21) and tricuspid aortic valve (TAV) patients (n = 23). DNA methylation and gene expression was measured in aortic intima-media tissue samples, and in EA.hy926 and primary aortic endothelial cells (ECs) isolated from BAV and TAV exposed to oscillatory (±12 dynes/cm2) or laminar (12 dynes/cm2) flow. We show methylation changes related to epithelial-mesenchymal-transition (EMT) in the non-dilated BAV aorta, associated with oscillatory flow related to endocytosis. The results indicate that the flow-response in BAV ECs involves hypomethylation and increased expression of WNT/β-catenin genes, as opposed to an angiogenic profile in TAV ECs. The EMT-signature was exasperated in dilated BAV aortas. Aberrant EMT in BAV aortic walls could contribute to increased aneurysm susceptibility, and may be due to disturbed flow-exposure. Perturbations during the spatiotemporally related embryonic development of ascending aorta and semilunar valves can however not be excluded.

Highlights

Disturbed flow has been suggested to contribute to aneurysm susceptibility in bicuspid aortic valve (BAV) patients
To identify biological processes potentially contributing to the increased aneurysm susceptibility in BAV patients, we measured DNA methylation in the aortic intima-media portion of the ascending aorta of BAV and tricuspid aortic valve (TAV) patients operated due to valve disease, with normal ascending aortic dimensions
Type I diabetes was the top enriched pathway (FDR q = 2.49e-4), and when looking at specific genes covered by the ontology term (i.e. HLA-B, HLA-DMB, HLA-DPA1, GAD1 and CPE) we found that HLA genes were down-regulated in BAV-ND at mRNA level (HLA-B, P = 0.011; HLA-DMB, P = 0.033; HLA-DPA1, P = 0.010), which may be indicative of a decrease in immune reactivity

Summary

Introduction

Disturbed flow has been suggested to contribute to aneurysm susceptibility in bicuspid aortic valve (BAV) patients. Aberrant EMT in BAV aortic walls could contribute to increased aneurysm susceptibility, and may be due to disturbed flow-exposure. The importance of valve-related hemodynamics in BAV aortopathy has been addressed in a recent study in humans, showing a link between proteolytic dysregulation, elastic fiber degeneration and increased regional wall shear stress[4]. The majority of BAV patients develop ascending aortic dilatation in adulthood, and molecular and histological analysis of BAV aorta implies that aneurysm formation in BAV is a gradual process with changes accumulating over a considerable period of time[6,7]. Given the complex interaction between hemodynamics and genetic factors in the pathology of BAV aortopathy, DNA methylation may be of particular importance, mediating hemodynamic and genetic risks, thereby favoring aneurysm formation

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Results

Conclusion