Abstract 830: Macrophage ABCG1 Promotes Reverse Cholesterol Transport in vivo
The ATP binding cassette transporter G1 (ABCG1) mediates macrophage cholesterol efflux to high-density lipoproteins (HDL) in vitro. We performed a series of experiments to test the hypothesis that macrophage ABCG1 plays an important role in reverse cholesterol transport (RCT) from peripheral macrophages in vivo. First, using lentiviral vectors we generated stable ABCG1 knockdown (ABCG1 KD) J774 macrophages and appropriate control J774 cells. ABCG1 mRNA was reduced by more than 50% and ABCG1 protein was reduced more than 80%, whereas expression of ABCA1 and SR-BI was not changed. Cholesterol efflux to HDL3 was reduced by 33% (p<0.05) in LXR-agonist treated ABCG1 KD J774 cells. Cholesterol-loaded, [3H]-cholesterol-labeled ABCG1 KD J774 or control J774 cells were injected intraperitoneally into C57BL/6 mice (N=8) to assess RCT in vivo. Compared to mice injected with control cells, the [3H]-cholesterol in the plasma of mice injected with ABCG1 KD cells was 38%, 36%, 27% and 32% (p<0.05) lower at 2, 6, 24 and 48 hours after injection, respectively. The livers from ABCG1 KD J774 cells-injected mice at 48-hour had 45% (p<0.05) less [3H]-tracer and there was a 40% (p<0.05) decrease in [3H]-tracer level in the feces collected from mice injected with ABCG1 KD J774 cells. Three independent experiments were performed and gave similar results. Finally, we performed RCT experiments under the same conditions using bone marrow derived macrophages (BMM) from ABCG1 knock out (ABCG1 KO) mice. [3H]-cholesterol in the plasma from mice injected with ABCG1 KO BMM was about 20% (p<0.05) lower at all time points. The livers and feces from the same mice also had 20% and 25% (p<0.05) decreases in [3H]-tracer levels, respectively. These results demonstrate that reduced or ablated expression of macrophage ABCG1 significantly impairs macrophage cholesterol efflux and RCT in vivo.