LOW-DOSE EXPRESSION OF A HUMAN APOLIPOPROTEIN-E TRANSGENE IN MACROPHAGES RESTORES CHOLESTEROL EFFLUX CAPACITY OF APOLIPOPROTEIN E-DEFICIENTMOUSE PLASMA

Apolipoprotein E- (apoE) deficient (E-/-) mice develop severe hyperlip idemia and diffuse atherosclerosis. Low-dose expression of a human apo E3 transgene in macrophages of apoE-deficient mice (E(-/-)hTgE(+/0)), which results in about 5% of wild-type apoE plasma levels, did not cor rect hyperlipidemia but significantly reduced the extent of atheroscle rotic lesions. To investigate the contribution of apoE to reverse chol esterol transport, we compared plasmas of wild-type (E+/+), E-/-, and E(-/-)hTgE(+/0) mice for the appearance of apoE-containing lipoprotein s by electrophoresis and their capacity to take up and esterify H-3-la beled cholesterol from radiolabeled fibroblasts or J774 macrophages, W ild-type plasma displayed lipoproteins containing apoE that mere the s ize of high density lipoprotein and that had either electrophoretic al pha or gamma mobilities. Similar particles were also present in E(-/-) hTgE(+/0) plasma. Depending on incubation time, E-/- plasma released 4 8-74% less H-3-labeled cholesterol from fibroblasts than E-/- plasma, whereas cholesterol efflux into E(-/-)hTgE(+/0) plasma was only 11-25% lower than into E+/+ plasma. E(-/-)hTgE(+/0) plasma also released 10% more H-3-labeled cholesterol from radiolabeled J774 macrophages than E-/- plasma. E+/+ and E(-/-)hTgE(+/0) plasma each esterified significa ntly more cell-derived H-3-labeled cholesterol than E-/- plasma, Moreo ver, E-/- plasma accumulated much smaller proportions of fibroblast-de rived H-3-labeled cholesterol in fractions with electrophoretic gamma and alpha mobility than E+/+ and E(-/-)hTgE(+/0) plasma, Thus, low-dos e expression of apoE in macrophages nearly restored the cholesterol ef flux capacity of apoE-deficient plasma through the formation of apoE-c ontaining particles, which efficiently take up cell-derived cholestero l, and through the increase of cholesterol esterification activity. Th us, macrophage-derived apoE may protect against atherosclerosis by inc reasing cholesterol efflux from arterial wall cells.