Atherosclerosis is an inflammatory process characterized by accumulation of lipid-laden macrophages/ dendritic cells (DCs) (foam cells) in arterial walls. Hypercholesterolemia with increased levels of cholesteryl ester-rich lipoproteins (CERLs) has long been recognized as a risk factor for atherogenesis. Recent genetic and epidemiologic studies show that triglyceride-rich lipoproteins (TGRLs) also play an important role in atherosclerosis. While previous studies have focused on interactions of CERLs with tissue macrophages, infiltration of blood monocytes into tissues and differentiation to macrophages/DCs is a key step in inflammation including atherogenesis. With the recent identification of monocyte heterogeneity and plasticity, studies have shown that monocytes with different phenotypes play distinct roles in inflammation. However, effects of CERLs on blood monocyte phenotype and subsequent impacts on monocyte contribution to atherogenesis have not been well studied and effects of TGRLs on monocytes and the consequence to atherogenesis are even less well studied. We previously reported that mice with hypercholesterolemia and humans with hypertriglyceridemia had foamy monocytes, i.e., monocytes with intracellular lipid droplets, in blood. Our further preliminary studies showed that monocytes took up CERLs and TGRLs (becoming foamy monocytes) and subsequently underwent phenotypic changes, with increased expression of: 1) proinflammatory markers; 2) the adhesion molecule CD11c, which enhanced monocyte adhesion on endothelial cells (ECs); and 3) scavenger receptors that promoted further monocyte uptake of CERLs and foam cell formation. Based on these data, we formed our central hypothesis that in hyperlipidemia, blood monocytes take up TGRLs and/or CERLs and undergo phenotypic changes, with increased inflammation, enhanced adhesion to ECs and increased uptake of CERLs, which accelerate monocyte infiltration into arterial walls, differentiation into macrophages/DCs and foam cell formation, thereby contributing to atherogenesis. In this application, we will use in vitro tissue culture, in vivo mouse models and human subjects to examine how blood monocytes take up TGRLs and CERLs and change phenotypes and determine how these phenotypically changed monocytes infiltrate into arterial walls and contribute to atherogenesis. For our approach, we will use some unique protocols such as specific labeling and depletion of foamy monocytes in mouse models of atherosclerosis and microfluidic-based lab-chip assays, as well as other techniques such as flow cytometric analysis, immunofluorescent staining, Luminex technology, microarray and NanoString systems. Our approach will not only further our understanding of the mechanisms for atherogenesis but may also help identify novel therapeutic targets for atherosclerotic cardiovascular disease.
High blood levels of lipids, including cholesterol and triglyceride, increase the risk for atherosclerotic cardiovascular disease. Our project proposes to study effects of blood lipids (lipoproteins) on phenotypes and behaviors of blood monocytes, with subsequent impact on monocyte contribution to the development of atherosclerosis. Knowledge gained from our studies may help identify novel therapeutic targets to prevent cardiovascular disease.
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