Abstract 183: Oxidized LDL Cholesterol Induces Endothelial Dysfunction in the Aorta and Lox-1 Expression in Macrophages

Elevated plasma cholesterol is one of the major risk factors in the development of atherosclerotic lesions. Oxidation of native LDL cholesterol (nLDL) by reactive oxygen species leads to the formation of oxidized LDL (oxLDL). An important receptor for the cellular uptake of oxLDL is the lectin-like oxidized low-density lipoprotein receptor-1 (Lox-1). Lox-1 is highly expressed on macrophages, but also present on arterial endothelial and vascular smooth muscle cells. Especially the uptake by macrophages leads to the formation of foam cells in atherosclerotic lesions. Aim of the present study was to analyze the impact of oxLDL on endothelial function in murine aortas and on Lox-1 expression in human macrophages. In addition, we analyzed the effect of a high-fat diet on vascular function in mice with an endothelial Lox-1 overexpression. First, we incubated aortic rings of wild-type mice for 2 h with 100 μg/mL oxLDL and analyzed the endothelial function using a Mulvany myograph. Compared to basal conditions, oxLDL significantly impaired endothelium-dependent vasodilation. Next, we fed mice with an endothelial overexpression of Lox-1 for 20 weeks a high-fat diet and analyzed the endothelial function in the thoracic aorta. Interestingly, these mice had no impaired endothelium-dependent relaxation after high-fat diet feeding. To get further insight into Lox-1 regulation by oxLDL, we analyzed the impact of oxLDL on Lox-1 expression in human macrophages. Monocytic THP-1 cells were differentiated with phorbol myristate acetate into macrophages and stimulated for 24 h with nLDL or oxLDL. We found a significant induction of Lox-1 mRNA expression after oxLDL incubation, whereas nLDL had no effect. Our data suggest an increased oxLDL uptake in oxLDL-treated macrophages by increased Lox-1 receptor expression. In conclusion, our data support an important role of oxLDL as a proatherosclerotic risk factor by its ability to induce endothelial dysfunction and Lox-1 expression in macrophages. Both processes may be involved in the development of atherosclerotic lesions but the physiological significance and functional role of Lox-1 in contributing to the human disease warrants further investigations.