Role of Shear-Sensitive Protein HEG1 in Endothelial Biology and Atherosclerosis

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Project Summary/Abstract Atherosclerosis refers to the formation of fatty plaques in the arterial wall that underlie heart attacks and strokes, two of the deadliest medical events in the US and abroad. In general, two criteria must be met in order to develop atherosclerosis in a given artery: 1) the artery must be exposed to high levels of circulating cholesterol and lipids, and 2) the artery must typically be located in a curved or branching region of the vasculature, in which endothelial cells of the arterial wall experience low-magnitude and oscillatory shear stress from disturbed blood flow. Despite the widespread use of many different cholesterol- and lipid-lowering medications in the prevention of atherosclerosis, heart attacks and strokes have remained two of the top killers in the US. As such, it has become increasingly important to develop drugs that target different mechanisms of atherogenesis, like endothelial responses to disturbed blood flow. The current study addresses this problem by investigating the role of the flow-sensitive protein heart of glass homolog 1 (HEG1) in endothelial function and atherosclerosis. HEG1 is an endothelial-enriched single-pass transmembrane glycoprotein that has been shown to be essential for vascular development and integrity. Recently, our laboratory found that HEG1 is downregulated in endothelial cells exposed to disturbed flow and upregulated in endothelial cells exposed to stable flow. This result was confirmed at both the RNA and protein level, in vitro and in vivo, in both human and mouse endothelial cells. A recent publication demonstrated a similar result in zebrafish. Due to the clear shear- sensitivity of HEG1 and its demonstrated importance in vascular development and integrity, we hypothesize that downregulation of HEG1 in response to disturbed flow causes endothelial dysfunction, which contributes to the development of atherosclerosis. To test this hypothesis, we propose two aims: 1) to determine the role of HEG1 in endothelial dysfunction, and 2) to determine the role of HEG1 in the pathogenesis of atherosclerosis. To address Aim 1, HEG1 will be overexpressed and knocked down in human aortic endothelial cells, and these cells will be assessed in a series of experiments testing common endothelial functions such as permeability, inflammation, and migration. Mechanistic studies will subsequently be performed in order to describe exactly how HEG1 is involved in endothelial function. To address Aim 2, HEG1 will be knocked down in mice, and these mice will be subjected to our partial carotid ligation, flow-induced atherosclerosis model. Markers of endothelial dysfunction and atherosclerosis will be studied in these mice in order to assess the effects of endothelial HEG1 expression on disease pathogenesis. Addressing these aims will shed light on the effects of HEG1 downregulation in endothelial cells exposed to disturbed flow and provide a novel mechanism to target in the treatment of atherosclerosis.