Individuals with metabolic diseases are at a higher risk of developing atherosclerosis, a leading cause of death in the United States and worldwide. Earlier studies have linked dyslipidemia to the initiation and progression of atherosclerosis. However, recent clinical studies raised concerns about the efficacy of lowering plasma cholesterol levels in the progression of atherosclerosis. Although insulin resistance is associated with increased incidence of cardiovascular disease, whether it leads to atherosclerosis independently of its accompanying dyslipidemia remains unclear, largely because of the lack of a suitable animal model to address this question. The CarcinoEmbryonic Antigen-related Cell Adhesion Molecule-1 (CEACAM1) regulates insulin sensitivity by promoting insulin clearance in liver. Accordingly, global null deletion of Ceacam1 gene impairs hepatic insulin clearance and causes hyperinsulinemia, which in turn, results in systemic insulin resistance. Preliminary data show: (i) that global Cc1-/- null mice develop early atherosclerotic lesions and vascular dysfunction even under normal feeding conditions, and (ii) that this occurs in the absence of hyperlipidemia, despite VLDL/LDL cholesterol levels that are usually associated with atherosclerosis regression, not development. This unique animal model of atherogenesis with isolated insulin resistance in the absence of hyperlipidemia demonstrates that systemic insulin resistance resulting from hyperinsulinemia leads to vascular dysfunction and atherosclerosis in the absence of hyperlipidemia. Because phosphorylation of CEACAM1 by both insulin and VEGF receptors regulates Akt1 activation of endothelial Nitric Oxide Synthase (eNOS), an essential step in mediating endothelial function, it is reasonable to propose that CEACAM1 is the shared downstream element in VEGF and insulin signaling in endothelial cells, whose inactivation impinges upon both pathways and causes endothelial dysfunction in insulin resistance. To test this hypothesis, the regulatory effect of CEACAM1 on insulin action along the liver/endothelial cell axis will be investigated.
Aim 1 examines whether hyperinsulinemia caused by impaired hepatic insulin clearance, alters insulin action in the endothelial cell, and in this cell-nonautonomous fashion, initiates atheroma development.
Aim 2 examines whether altered signaling through CEACAM1-dependent pathways disrupts the endothelial cell's response to insulin and VEGF, and in this cell-autonomous fashion, drives endothelial dysfunction and initiates atherosclerosis. To investigate the specific role of hepatic and endothelial cell CEACAM1 in the pathogenesis of atherosclerosis and vascular dysfunction, a newly generated set of unique animal models of loss-of-function and gain-of-function will be used. Answering these questions will delineate new CEACAM1-dependent mechanisms underlying atherosclerosis along the liver/endothelial cell axis, and pinpoint sites of pharmacologic intervention.
Individuals with metabolic syndrome are at a higher risk of developing atherosclerosis, a leading cause of death in the United States. A strategy based on lowering blood cholesterol has been shown to be of limited value in stopping progression of atherosclerosis in patients with metabolic syndrome. Building on the pioneering work on the role of CEACAM1 in the regulation of insulin metabolism in liver, new compelling evidence is now presented to link its regulatory role of systemic insulin resistance to the pathogenesis of atherosclerosis. This proposal seeks to explore this mechanistic link with an eye on developing a more effective therapeutic strategy against the disease.
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