FIG. 1.

ATRA stimulation promotes apoA1-mediated cholesterol efflux in IRAK-1^−/− macrophages. (A) ATRA induces a significant increase in cholesterol efflux to apoA1 in IRAK-1^−/− BMDMs compared to WT. The BMDMs derived from WT and IRAK-1^−/− mice were radiolabeled with [³H]cholesterol in cell culture medium for 16 h and then treated with or without ATRA (50 nM) or TGF-β (5 ng/ml) in the presence of apoA1 (10 μg/ml). Cellular cholesterol efflux was analyzed in liquid scintillation counting assays, and the results are expressed as means ± standard deviations from three independent experiments, each performed in triplicate. *, P < 0.05. (B) Effects of ATRA on HDL-mediated cholesterol efflux. WT and IRAK-1^−/− BMDMs were radiolabeled with [³H]cholesterol for 16 h and then treated with or without ATRA (50 nM) in the presence of HDL (50 μg protein/ml). Cholesterol efflux to HDL was assayed by liquid scintillation counting as described above.