Effect of Macrophage Overexpression of Murine Liver X Receptor-α (LXR-α) on Atherosclerosis in LDL-Receptor Deficient Mice

Background-The nuclear liver X receptor-alpha (LXR-alpha) has been implicated in the regulation of intracellular cholesterol homeostasis, inflammatory response, and atherosclerosis susceptibility. The aim of the present study was to test whether transgenic expression of LXR-alpha might affect these mechanisms and result in a reduction of atherosclerosis. Methods and Results-We generated mice with macrophage overexpression of mouse LXR-alpha, evidenced by significantly elevated expression levels of LXR-target genes (ABCA1, ABCG1) in these cells. For atherosclerosis studies, mice were crossed onto the LDL-receptor deficient background. Plasma lipids and lipoproteins as well as liver triglycerides were not significantly different between transgenic animals and nontransgenic controls. However, lesion area at the brachiocephalic artery (BCA) was significantly reduced (-83%, P = 0.02) in male LXR-alpha transgenic mice. This was associated with a significantly increased cholesterol efflux to acceptor-free media (-24%, P = 0.002) and ApoA1 containing media (+20%, P < 0.0001) as well as reduced lipopolysaccharide (LPS)-induced NO-release from macrophages of transgenic animals, providing a potential mechanism for the reduction of atherosclerosis. Conclusion-Our data show for the first time that transgenic overexpression of LXR-alpha in macrophages has significant antiatherogenic properties. We conclude that overexpression of LXR-alpha in macrophages might be useful as a therapeutic principle for the prevention of atherosclerosis. (Arterioscler Thromb Vasc Biol. 2008;28:2009-2015)