👤 N Duverger

The apolipoprotein (apo)A-I/C-III/A-IV gene cluster is involved in lipid metabolism and atherosclerosis. Overexpression of apoC-III in mice causes hypertriglyceridemia and induces atherogenesis, whereas overexpression of apoA-I or apoA-IV increases cholesterol in plasma high density lipoprotein (HDL) and protects against atherosclerosis. Each gene has been studied alone in transgenic mice but not in combination as the entire cluster. To determine which phenotype is produced by the expression of the entire gene cluster, transgenic mice were generated with a 33-kb human DNA fragment. The results showed that the transgene contained the necessary elements to direct hepatic and intestinal expression of the 3 genes. In the pooled data, plasma concentrations were 257+/-9, 7.1+/-0.5, and 1.0+/-0.2 mg/dL for human apoA-I, apoC-III, and apoA-IV, respectively (mean+/-SEM). Concentrations of these apolipoproteins were higher in males than in females. Human apoA-I and apoC-III concentrations were positively correlated, suggesting that they are coregulated. Transgenic mice exhibited gross hypertriglyceridemia and accumulation of apoB(48)-containing triglyceride-rich lipoproteins. Plasma triglyceride and cholesterol concentrations were correlated positively with human apoC-III concentration, and HDL cholesterol was correlated with apoA-I concentration. In an apoE-deficient background, despite being markedly hypertriglyceridemic, cluster transgenic animals compared with nontransgenic animals showed a 61% reduction in atherosclerosis. This suggests that apoA-I and/or apoA-IV can protect against atherosclerosis even in the presence of severe hyperlipidemia. These mice provide a new model for studies of the regulation of the 3 human genes in combination. Show less

The role of apolipoprotein A-IV (apoA-IV) in lipoprotein metabolism has not been established. The aim of the present study was to investigate the role of apoA-IV in reverse cholesterol transport by comparing cellular cholesterol efflux to serum or serum fractions from control mice and from mice transgenic for human apoA-IV (HuA-IVTg mice). When Fu5AH hepatoma cells were used, the cholesterol efflux to serum from either control or transgenic mice was similar. When control J774 macrophage cells were used, a comparison of efflux to serum or lipoprotein-deficient serum (LPDS) failed to demonstrate any differences between control and transgenic mice. In contrast, when the J774 cells were pretreated with cAMP, there was a stimulation of efflux to whole serum or LPDS from HuA-IVTg mice. cAMP treatment had no effect on efflux to serum or LPDS from control mice. Pretreatment of the cells with cAMP did not enhance the efflux response to high density lipoprotein isolated from HuA-IVTg mouse serum. Our results suggest that apoA-IV, unassociated with high density lipoprotein particles, is responsible for enhanced cholesterol efflux. This study illustrates the role of lipid-free apolipoproteins in mediating cellular cholesterol efflux with use of a biological fluid and is potentially of physiological relevance, especially in apolipoprotein-rich extravascular fluids. Show less

Human apolipoprotein A-IV (apoA-IV) transgenic mice fed an atherogenic diet were shown previously to develop less atherosclerosis than control mice. The question arose whether the antiatherogenic effect of human apoA-IV is due to enhancement of reverse cholesterol transport despite no increase in plasma high-density lipoprotein (HDL) cholesterol. We studied male and female mice overexpressing human apoA-IV and their wild-type (WT) controls, all of which were fed a chow diet. Plasma total and HDL cholesterol and total phospholipids were not increased in the transgenic mice, and regression analysis showed no correlation between plasma levels of cholesterol or phospholipids and plasma human apoA-IV. To study reverse cholesterol transport in vivo, the disappearance of cholesterol from a depot of [(3)H]cholesterol-labeled cationized low-density lipoprotein injected into the rectus femoris muscle was compared in high expressers of human apoA-IV and WT controls. The loss of radioactivity and the diminution of the exogenous cholesterol mass were determined on days 8 and 12 after injection. No enhanced loss of radioactivity or cholesterol mass was seen in the transgenic mice even at levels of 2500 mg/dL of human apoA-IV. In some instances, there was even slower loss of exogenous cholesterol (radioactivity and mass) in the transgenic mice. Although [(3)H]cholesterol efflux from cultured human skin fibroblasts and mouse peritoneal macrophages was only approximately 30% higher in the presence of sera from high expressers of human apoA-IV, addition of phosphatidylcholine liposomes enhanced the efflux in both groups to the same extent. Another paradoxical finding was that the cholesterol esterification rate in plasma was 34% to 36% lower in human apoA-IV mice than in WT controls. In conclusion, even though apoA-IV was found previously to be atheroprotective under hypercholesterolemic conditions, high plasma levels of human apoA-IV did not enhance cholesterol mobilization in vivo in normocholesterolemic mice. Show less