Abstract 827: Total Body ABCG1-Deficiency Increases Atherosclerotic Lesion Development In LDL-Receptor Knockout Mice

Abstract

ATP-binding cassette transporter G1 (ABCG1) facilitates the efflux of cholesterol from macrophages to HDL. As ABCG1 plays a role in preventing cellular lipid accumulation, macrophage ABCG1 expression has been suggested to protect against atherosclerosis. In bone marrow transplantation studies, however, we and others obtained different effects of specific macrophage ABCG1-deficiency on atherosclerotic lesion development under different experimental settings. The objective of this study was to further define the effect of ABCG1-deficiency on lipid metabolism and atherosclerotic lesion development. ABCG1 knockout (KO) mice upon atherogenic diet feeding develop only modest atherosclerotic lesions, therefore, we recently cross-bred ABCG1 KO mice with LDL-receptor KO (LDLr KO) mice. LDLr KO and LDLr/ABCG1 double KO (dKO) littermates were fed a high-fat, high-cholesterol Western-type diet (WTD) containing 0.25% cholesterol and 15% fat for 10 weeks to induce atherosclerotic lesion formation. Both on chow diet and on WTD, serum lipid levels and lipoprotein profiles showed no significant differences between the LDLr KO and LDLr/ABCG1 dKO mice. However, after 10 weeks of diet feeding, a significant 1.5-fold increase in atherosclerotic lesion size was observed in the aortic root of LDLr/ABCG1 dKO mice (130 ± 12x10 3 μm 2 [n = 8] compared to 88 ± 11x10 3 μm 2 [n=7] for LDLr KO mice; p =0.026). In addition, macrophage-rich areas of the lungs and spleens of LDLr/ABCG1 dKO mice exhibited excessive lipid accumulation compared with LDLr KO mice. Furthermore, in vitro studies using bone marrow derived macrophages of LDLr KO and LDLr/ABCG1 dKO mice showed that disruption of ABCG1 results in a 15% decrease in cholesterol efflux to HDL ( p< 0.001), whereas the cholesterol efflux to ApoAI was unaffected. These studies reveal that total-body ABCG1 deficiency leads to increased atherosclerotic lesion development and massive lipid accumulation in macrophages of the lung and spleen, possibly due to impaired efflux of cholesterol from macrophages deficient in ABCG1. In conclusion, the expression of ABCG1 protects against atherosclerotic lesion development.