INSIGHTS INTO THE DEVELOPMENT OF ATHEROSCLEROSIS AND CORONARY ARTERY DISEASE: STUDIES FROM GENE TARGETED MICE LACKING THE HIGH DENSITY LIPOPROTEIN RECEPTOR, SR-BI

Abstract

<p>High density lipoprotein (HDL) is an independent risk factor for thedevelopment of coronary heart disease. HDL mediated reverse cholesterol transport is a key element responsible for the cardioprotective effects of HDL. In addition HDL exerts other atheroprotective effects in vascular cells. The HDL receptor, scavenger receptor class I type B (SR-BI) derives the process of reverse cholesterol transport, mediates HDL signaling in the vasculature and protects against atherosclerosis. However, the exact atheroprotective mechanisms of HDL and SR-BI are not clearly understood.This thesis starts by characterizing a model of occlusive coronary arteryatherosclerosis, the SR-BI/apolipoprotein E double knockout mice and tests the effectsof phenolic rich pomegranate extract on disease progression. Coronary artery disease in these mice starts at three weeks of age and progresses rapidly leading to sudden death within three to five weeks. The administration of pomegranate extract reduced the extent of coronary artery atherosclerosis possibly via mechanisms that involved alterations in lipid metabolism and reduced inflammation and oxidative stress.The next two chapters aimed to gain better understanding of the atheroprotectiveactions of HDL and SR-BI. Increased macrophage apoptosis is a key event in the development of atherosclerotic plaques. HDL signaling via SR-BI reduced macrophage apoptosis while the lack of macrophage SR-BI was associated with increased macrophage apoptosis and necrotic core areas, features of plaque instability. Next HDL and SR-BI effects on macrophage migration, a key event in atherosclerotic plaque regression, are described. HDL stimulated the migration of macrophages in a manner that was dependent on SR-BI, its adaptor protein, PDZK1, and the G-protein coupled receptor, sphingosine-1-phosphate receptor 1. SR-BI mediated macrophage migration may suggest a potential role of SR-BI in atherosclerotic plaque regression.To expand our view of HDL effects on macrophages we have used proteomics as an approach. HDL treatment of macrophages altered the expression of multiple proteins.Validation experiment confirmed changes in interesting and particularly relevant protein targets in HDL mediated protection against macrophage apoptosis and inflammation and in HDL induced macrophage migration. Follow up experiments will determine their involvement in HDL and SR-BI mediated signaling. Overall this work represents a milestone in understanding the atheroprotective effects of HDL and SR-BI in macrophages.</p>