Cultures of human skin fibroblasts were labeled to high cholesterol specific activity with [3H]cholesterol and incubated briefly (1-3 min) with normal human plasma. The plasma was fractionated by two-dimensional agarose-polyacrylamide gel electrophoresis and the early appearance of cholesterol label among plasma lipoproteins determined. A major part of the label at 1-min incubation was in a pre-beta-migrating apo A-I lipoprotein fraction with a molecular weight of ca. 70,000. Label was enriched about 30-fold in this fraction relative to its content of apo A-I (1-2% of total apo A-I). The proportion of label in this lipoprotein was strongly correlated with its concentration in plasma. Further incubation (2 min) in the presence of unlabeled cells demonstrated transfer of label from this fraction to a higher molecular weight pre-beta apo A-I species, to low-density lipoprotein, and to the alpha-migrating apo A-I that made up the bulk (96%) of total apo A-I in plasma. The data suggest that a significant part of cell-derived cholesterol is transferred specifically to a pre-beta-migrating lipoprotein A-I species as part of a cholesterol transport transfer sequence in plasma.

Apolipoproteins are protein constituents of plasma lipid transport particles. Human apolipoprotein A-IV (apoA-IV) was expressed in the liver of C57BL/6 mice and mice deficient in apoE, both of which are prone to atherosclerosis, to investigate whether apoA-IV protects against this disease. In transgenic C57BL/6 mice on an atherogenic diet, the serum concentration of high density lipoprotein (HDL) cholesterol increased by 35 percent, whereas the concentration of endogenous apoA-I decreased by 29 percent, relative to those in transgenic mice on a normal diet. Expression of human apoA-IV in apoE-deficient mice on a normal diet resulted in an even more severe atherogenic lipoprotein profile, without affecting the concentration of HDL cholesterol, than that in nontransgenic apoE-deficient mice. However, transgenic mice of both backgrounds showed a substantial reduction in the size of atherosclerotic lesions. Thus, apoA-IV appears to protect against atherosclerosis by a mechanism that does not involve an increase in HDL cholesterol concentration.

Objective-Uptake of modified low-density lipoprotein (LDL) by macrophages through scavenger receptors results in lipid droplets accumulation and foam cell formation. Excess lipid deposition in macrophages has been reported to modulate expression of several genes including adipophilin. In this study, we investigated the function of adipophilin in lipid accumulation and cholesterol efflux in THP-1 macrophages. Methods and Results-Adipophilin mRNA expression was 3.5-fold higher in human atherosclerotic plaques compared with healthy areas of the same arteries. Moreover, in the presence of acetylated LDL (AcLDL), triglycerides and cholesteryl esters were increased in macrophages overexpressing adipophilin by 40% and 67%, respectively, whereas their accumulation was reduced when endogenous cellular adipophilin was depleted using siRNA approach. In addition, neither overexpression nor downregulation of adipophilin altered expression of genes involved in lipid efflux. However, the affinity and the number of AcLDL receptors were not affected. After 24-hour incubation of lipid-loaded macrophages with apolipoprotein A-I, cholesterol efflux was reduced by 47% in adipophilin transfected cells versus control cells. Key Words: adipophilin Ⅲ macrophage Ⅲ acetylated LDL Ⅲ cholesterol efflux Ⅲ atherosclerosis A therosclerosis, a complex disease process, is initiated by an infiltration of low-density lipoproteins (LDL) into the subendothelial space where they accumulate and become modified mainly by oxidation. In parallel, chemokines elaborated by endothelial cells attract circulating monocytes into the intima, where they differentiate into macrophages. 1 Intimal macrophages contribute to the formation of arterial lesions by accumulating large amounts of cholesteryl ester (CE) through the uptake of modified lipoproteins such as oxidized LDL (oxLDL) by a variety of mechanisms, including the scavenger pathway. 2,3 Several studies indicated that oxLDL has a number of diverse effects on macrophage function including growth stimulation 4 proinflammatory effects such as expression of inflammatory cytokines, 5 increase in cytotoxicity and expression of metalloproteinases, 6 inhibition of expression of inducible nitric oxide synthase, 7 and effects on lipid metabolism and accumulation. 8,9 Using either a DNA array approach 10 or a subtractive approach, 11 numerous genes have been shown to be regulated on exposure of THP-1 cells to modified LDL. Adipophilin, or adipose differentiation-related protein (ADRP), a 50-kDa protein initially described in adipocytes, 12 which is considered a marker of lipid accumulation, is among those genes upregulated by modified LDL. Conclusion-OurAdipophilin is found associated with intracellular lipid droplets in a variety of cells and tissues that store or synthesize lipids. 13,14 In addition to oxLDL, 15 acetylated LDL (AcLDL) 11 or enzymatically modified LDL, 16 the nuclear receptor PPAR␦, is involved in lipid accumulation in human macrophages and THP-1-derived macrophages, and also increases adipophilin e...