Abstract 5481: Expression of Human ABCA1 in Endothelium Protects Against Diet-Induced Atherosclerosis in Mice

Abstract

Cholesterol homeostasis in endothelium plays significant role in protecting against development of atherosclerosis and in supporting normal function of the vasculature. ABCA1 transporter is one of major players in reverse cholesterol transport responsible for biogenesis of HDL and cholesterol efflux from cells to lipid-poor apoA1 particles. To evaluate the contribution of endothelial-expressed ABCA1 in HDL generation and in processes of diet induced atherosclerosis, we expressed hABCA1 in endothelial cells with the endothelial specific Tie2 promoter. In isolated lung endothelial cells Tie2hABCA1 was expressed at the level 10+/−3% of expression of mouse ABCA1. No hABCA1 was found to be expressed in peritoneal macrophages. Expression of hABCA1 did not alter the pattern of expression of mouse ABCA1, SR-B1 and ABCG1 in aorta, heart, kidney, liver, lung, muscle, spleen and testis. Despite the modest level of expression of hABCA1 in endothelium, it had a significant impact on plasma levels of total cholesterol (TC) and HDL-C. In females, TC was increased in comparison with normal siblings from 85±3 to 101±3; HDL-C - from 57±2 to 68±2 (all values in mg/dl, p<0.001); in males TC was changed from 100±4 to 127±5 (p<0.001), HDL-C - from 73.5±2.6 to 84±3.5 (p<0.03). This effect of hABCA1 was found only on normal C57Bl background. When Tie2hABCA1 was transferred to ABC1-K/O or apoE-K/O backgrounds no effect of hABCA1 on plasma lipids was revealed. Experiments on cultivated in Transwells polarized lung endothelial cells isolated from Tie2hABCA1 mice on ABCA1-K/O background revealed that Tie2hABCA1 was able to promote cholesterol efflux to apoA1 directed mostly to apical side of the cells. Expression of Tie2hABCA1 in C57Bl mice protected them against diet-induced atherosclerosis. After 6 months on Cocoa Butter Diet (TD90221) control females had 6.5±0.8% of en face aorta lesions, whereas transgenic animals had 4±0.5% of the lesions (p<0.02). HDL-C after 6 months on diet was higher in transgenic vs control females (56±3 vs 40.5±3.5, p<0.003). There was no protection if hABCA1 was on ABCA1-K/O or apoE -K/O backgrounds. In summary, the results support a role of endothelial ABCA1 expression in the generation of HDL and in the protection of diet induced atherosclerosis.