Vascular Protective Effects of Alcohol - Role of Notch

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Abstract     Moderate consumption of alcohol (EtOH) is a negative risk factor for cardiovascular disease but the precise mechanisms involved have not been elucidated. Pivotal to the initiation of vessel disease is endothelial cell (EC) dysfunction or loss. Subsequently, the growth and migration of vascular smooth muscle cells (SMC) are key processes in atherosclerotic plaque development, contributing to intima-medial thickening and vessel stenosis. Given the key role of both EC and SMC in the pathophysiology of atherosclerosis, effects of EtOH on these vascular cells are, thus, of considerable clinical interest. In this context Notch signaling has emerged as a novel potential target for alcohol. Repression of Notch signaling in arterial EC unlocks pro-inflammatory and pro-atherogenic signals that contribute to the initiation of atherosclerosis. Moreover, Notch signaling drives the differentiation of adult SMC from a contractile to a proliferative phenotype. Studies in animal models demonstrate that Notch signaling is stimulated following experimentally induced vascular injury, and point to a preferential role for SMC Notch 1 in mediating neointimal formation. We have shown that alcohol restrains SMC proliferation in vitro by inhibiting Notch signaling. In apparent contrast, alcohol stimulates Notch signaling and angiogenic activity in EC, while inhibiting monocyte chemoattractant protein-1 expression. These data highlight a differential effect of alcohol on Notch signaling in vascular EC and SMC - stimulatory and inhibitory, respectively, and further, implicate the Notch pathway in mediating both alcohols maintenance of an anti- atherogenic EC phenotype and it's attenuation of SMC proliferation, actions that might be considered synergistically atheroprotective. Indeed, moderate alcohol consumption ameliorates remodeling and plaque formation in injured mouse arteries. Recently, in SMC, we demonstrated a novel inhibitory effect of alcohol specifically on the γ-secretase cleavage activity that is critical for Notch signaling.  Our preliminary data now indicate that EtOH enhances γ-secretase activity in EC. Therefore, the central hypothesis of our proposal is that moderate alcohol consumption protects against atherogenesis by differential yet synergistic effects on Notch signaling at the level of γ-secretase, in vascular smooth muscle and endothelial cells. To test our hypothesis, and delineate the mechanisms involved, we will use a novel in vitro `mock artery' stented and seeded with SMC cells under cyclic strain conditions, as well as endothelial cells exposed to physiologic and pathologic shear stresses in artificial capillaries, in conjunction with in vivo studies utilizing transgenic mice and a `flow-restriction' model of atherosclerosis. Deciphering the mechanisms whereby alcohol may protect against cardiovascular disease is of major clinical significance and will uncover new therapy targets for this common cause of morbidity and mortality.