Mechanisms Underlying Sympathetic Activation-dependent Endothelial Cell Activation by Chronic Intermittent Hypoxia

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Project Summary- Project 3 Patients with sleep apnea (SA) and rodents exposed to intermittent hypoxia (IH), a hallmark of SA, exhibit endothelial cell (EC) activation, which is an early pathologic event in the development of cardiovascular disease. When activated, ECs express increased levels of pro-inflammatory cytokines and cell adhesion molecules leading to leukocyte adhesion to EC. The overall goal of Project 3 is to determine the mechanisms underlying EC activation caused by SA/IH. Our preliminary data from IH-exposed mice and aortic ECs suggest that SA/IH-induced EC activation is not caused directly by IH but secondarily by IH-induced sympathetic activation-derived epinephrine (not by norepinephrine). Furthermore, we found that treating ECs with epinephrine activates hypoxia-inducible factor (HIF)-1, and increases glycolysis, both of which we recently found to be required for EC activation under abnormal blood flow. Based on the preliminary data, Project 3 will test the hypothesis that SA/IH causes EC activation indirectly via sympathetic activation-derived epinephrine, which through β2-adrenergic receptors activates HIF-1α leading to upregulation of glycolysis, which is required for EC activation. We will test our hypothesis in three specific aims in two models of SA/IH: (1) experimental exposure of IH and (2) mice with spontaneous SA. In Aim 1, we will determine whether sympathetic activation- derived epinephrine mediates IH-induced EC activation and macrophage adhesion. In Aim 2, we will determine whether β2-adrenergic receptors are required for IH-induced EC activation. In Aim 3, we will determine whether IH-induced epinephrine causes EC activation through HIF-1-dependent manner and further assess the mechanism(s) by which HIF-1 is activated by IH-induced epinephrine. In Aim 4, we will determine whether increased glycolysis by HIF-1 is required for IH-induced EC activation. Project 3 has tight thematic linkages to Projects 1, 2, and 4 and utilizes Core B facilities for: a) exposing mice to IH, b) maintenance and genotyping of genetically engineered mice; c) quantitative real-time-PCR analysis. Members of the investigative team have long-standing experience and expertise with the proposed approaches and excellent track record of working together for number of years as evidenced by joint publications. The proposed studies will provide a framework for understanding the specific role of CIH-induced sympathetic activation in causing EC inflammation. Findings from the proposed studies will allow us to determine whether epinephrine/β2-adrenergic receptor signaling can be targeted to alleviate SA/IH-induced EC activation and the resulting cardiovascular disease.