Transcriptomic Profiling Reveals Novel Shear Stress-sensitive Genes in Human Endothelial Cells.

Abstract

Atherosclerosis is recognized as the pathological basis of ischemic heart disease and stroke, two leading causes of death worldwide. Shear stress generated from blood flow plays a key role in the development of atherosclerosis. Shear stress is critical to endothelial function, maintaining the homeostasis of vasculature. Alterations in the magnitude and direction of shear stress are implicated in endothelial dysfunction, leading to atherogenesis. Unidirectional and high laminar shear stress (LS), often found in straight arterial segments, exerts strong anti-atherosclerotic effects whereas bidirectional and low oscillatory shear stress (OS), in areas of lesser curvatures and arterial bifurcations, induces atherogenesis. We hypothesize that there are novel shear stress-sensitive genes that are involved in the process of atherosclerosis, elucidating which may become the key to understanding the underlying mechanisms of atherogenesis. In my thesis work, I surveyed the shear stress-induced gene expression in ECs. I performed RNA sequencing to profile the transcriptome of primary human coronary artery ECs under LS, OS and static culture condition (ST) to understand the transcriptomic differences in ECs under different types of shear stress. Differential expression analysis provided a large number of novel shear stress sensitive genes including protein-coding genes as well as non-coding RNAs. Among all of these differentially expressed genes, I focus on the pro-inflammatory cytokine macrophage migration inhibitory factor (MIF). High levels of MIF expression were detected in atherosclerotic lesions in animal models as well as human subjects. However, the regulatory mechanism of endothelial MIF remains to be addressed. I provide evidence to show that anti-atherosclerotic LS inhibits MIF expression, whereas pro-atherosclerotic OS increases MIF expression. Mechanistically, shear stress-induced MIF regulation in ECs is governed by Krüpple like factor 2 (KLF2). Knockdown of KLF2 abolished LS-induced MIF reduction. In conclusion, my dissertation work presents a broad view of the endothelial transcriptomic profile under different types of shear stress. The revealed novel shear stress-sensitive genes inform the field of potential therapeutic targets for atherosclerosis treatment. In addition, my mechanistic study on the pro-atherosclerotic role of MIF from a biomechanical perspective, highlights the importance of shear stress in the pathogenesis of atherosclerosis.