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• W1832018093 abstract "It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates preβ1-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 μg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased (∼50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native preβ1-LpA-I and preβ1-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither preβ1-LpA-I nor free cholesterol efflux.These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from α-HDL to preβ-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma preβ1-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease. It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates preβ1-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 μg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased (∼50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native preβ1-LpA-I and preβ1-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither preβ1-LpA-I nor free cholesterol efflux. These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from α-HDL to preβ-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma preβ1-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease. HDL is believed to be a potent physiological protective system against atherosclerotic vascular disease. Although it has become generally accepted that this protective effect of HDL is attributable to its pivotal role in the reverse cholesterol transport (RCT) process (1Brewer Jr., H.B. Santamarina-Fojo S. New insights into the role of the adenosine triphosphate-binding cassette transporters in high-density lipoprotein metabolism and reverse cholesterol transport.Am. J. Cardiol. 2003; 91: 3E-11EGoogle Scholar, 2Tall A.R. Plasma cholesteryl ester transfer protein.J. Lipid Res. 1993; 34: 1255-1274Google Scholar), structural determinants of molecular interactions between circulating HDL particles and key cell proteins governing the RCT process are complex and not well understood. A growing body of evidence indicates that ABCA1 is a critical cell surface protein required for the transfer of cellular lipid and the maintenance of HDL levels in plasma and is likely important for the first step of RCT from peripheral tissues, including macrophages in the vessel wall (3Joyce C.W. Amar M.J. Lambert G. Vaisman B.L. Paigen B. Najib-Fruchart J. Hoyt Jr., R.F. Neufeld E.D. Remaley A.T. Fredrickson D.S. et al.The ATP binding cassette transporter A1 (ABCA1) modulates the development of aortic atherosclerosis in C57BL/6 and apoE-knockout mice.Proc. Natl. Acad. Sci. USA. 2002; 99: 407-412Google Scholar, 4Marcil M. Bissonnette R. Vincent J. Krimbou L. Genest J. Cellular phospholipid and cholesterol efflux in high-density lipoprotein deficiency.Circulation. 2003; 107: 1366-1371Google Scholar). Furthermore, Brewer and colleagues (5Basso F. Freeman L. Knapper C.L. Remaley A. Stonik J. Neufeld E.B. Tansey T. Amar M.J. Fruchart-Najib J. Duverger N. et al.Role of the hepatic ABCA1 transporter in modulating intrahepatic cholesterol and plasma HDL cholesterol concentrations.J. Lipid Res. 2003; 44: 296-302Google Scholar) have documented that hepatic ABCA1 is a key protein for the formation and maintenance of plasma HDL levels. Moreover, the importance of ABCA1 in the lipidation of apolipoprotein A-I (apoA-I) is highlighted by the finding that >50 mutations in the ABCA1 gene have been associated with a variety of clinically distinct HDL deficiency diseases, including Tangier disease (TD) and familial HDL deficiency (6Marcil M. Brooks-Wilson A. Clee S.M. Roomp K. Zhang L.H. Yu L. Collins J.A. Dam M. van Molhuizen H.O. Loubster O. et al.Mutations in the ABC1 gene in familial HDL deficiency with defective cholesterol efflux.Lancet. 1999; 354: 1341-1346Google Scholar, 7Singaraja R.R. Brunham L.R. Visscher H. Kastelein J.J. Hayden M.R. Efflux and atherosclerosis: the clinical and biochemical impact of variations in the ABCA1 gene.Arterioscler. Thromb. Vasc. Biol. 2003; 23: 1322-1332Google Scholar). These patients are characterized by extremely low HDL-cholesterol levels, caused by defective transport of cellular cholesterol and phospholipids to the extracellular space, leading to hypercatabolism of lipid-poor nascent HDL particles (8Batal R. Tremblay M. Krimbou L. Mamer O. Davignon J. Genest Jr., J. Cohn J.S. Familial HDL deficiency characterized by hypercatabolism of mature apoA-I but not proapoA-I.Arterioscler. Thromb. Vasc. Biol. 1998; 18: 655-664Google Scholar). Earlier studies by Fielding and colleagues (9Castro G.R. Fielding C.J. Early incorporation of cell-derived cholesterol into pre-beta-migrating high-density lipoprotein.Biochemistry. 1988; 27: 25-29Google Scholar, 10Kawano M. Miida T. Fielding C.J. Fielding P.E. Quantitation of pre beta-HDL-dependent and nonspecific components of the total efflux of cellular cholesterol and phospholipid.Biochemistry. 1993; 32: 5025-5028Google Scholar) have documented that a minor subspecies of human HDL that migrates with preβ mobility on agarose gels can remove free cholesterol from cultured fibroblasts at a faster rate than α-migrating HDL, which constitutes the bulk of plasma HDL. Furthermore, it was documented that preβ-HDL particles were present in the peripheral lymph of dogs (11Lefevre M. Sloop C.H. Roheim P.S. Characterization of dog prenodal peripheral lymph lipoproteins. Evidence for the peripheral formation of lipoprotein-unassociated apoA-I with slow pre-beta electrophoretic mobility.J. Lipid Res. 1988; 29: 1139-1148Google Scholar), suggesting a key role for these particles in the initial removal of cholesterol. This is consistent with the concept of Hara and Yokoyama (12Hara H. Yokoyama S. Interaction of free apolipoproteins with macrophages. Formation of high density lipoprotein-like lipoproteins and reduction of cellular cholesterol.J. Biol. Chem. 1991; 266: 3080-3086Google Scholar) that lipid-free or lipid-poor apoA-I interacts with a site on the cell membrane, removes cellular lipids, and generates nascent preβ-HDL particles. Subsequently, preβ-HDL particles become mature, spherical, and α-migrating HDL by the action of LCAT, which converts free cholesterol to cholesteryl ester. Moreover, this concept is supported by studies demonstrating that preβ-HDL particles act as an initial acceptor of cellular cholesterol and shuttle it into a series of larger preβ particles and ultimately to α-migrating particles (13Francone O.L. Gurakar A. Fielding C. Distribution and functions of lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein in plasma lipoproteins. Evidence for a functional unit containing these activities together with apolipoproteins A-I and D that catalyzes the esterification and transfer of cell-derived cholesterol.J. Biol. Chem. 1989; 264: 7066-7072Google Scholar, 14Huang Y. Eckardstein A. von Assmann G. Cell-derived unesterified cholesterol cycles between different HDLs and LDL for its effective esterification in plasma.Arterioscler. Thromb. 1993; 13: 445-458Google Scholar). In spite of the importance of preβ1-apoA-I-containing lipoproteins (LpA-I) particles in RCT, very little is known about their contribution to the human plasma ABCA1-dependent cholesterol efflux pathway. This is likely because of the low amount of these particles and the difficulty of isolating them. These problems were circumvented in the present study by increasing the plasma level of preβ1-LpA-I using dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles (MLVs). Therefore, our experiments were directed at determining the affinity of these newly formed preβ1-LpA-I-like particles for ABCA1 and monitoring their ability to promote cholesterol efflux from a macrophage cell culture model. Blood samples were obtained from normolipidemic male subjects with apoE3/3 phenotype after an overnight fast. Blood was drawn from the antecubital vein into tubes containing EDTA (final concentration, 1.5 mg/ml). Collection tubes were immediately placed on ice before being centrifuged (3,000 rpm, 15 min, 4°C). For experiments in which plasma was incubated with cells, streptokinase was used as the anticoagulant at a final concentration of 150 U/ml blood. Plasma was separated from red blood cells by aspiration and was kept on ice until treatment with phospholipids or electrophoretic separation of apoA-I-containing particles. This study was approved by the ethics committees of the institutions involved. Plasma from TD subjects was provided by Dr. Arnold von Eckardstein from the Institute of Clinical Chemistry, University Hospital Zurich, Switzerland. Phospholipid MLVs containing DMPC, palmitoyloleoyl phosphatidylcholine (POPC), or bovine brain sphingomyelin (BBSM) were prepared as described previously (15Jian B. Llera-Moya M. Royer L. Rothblat G. Francone O. Swaney J.B. Modification of the cholesterol efflux properties of human serum by enrichment with phospholipid.J. Lipid Res. 1997; 38: 734-744Google Scholar). Plasma from each of either three normolipidemic or three TD subjects (Table 1) was incubated with phospholipids at their phase transition temperature for 1 h in the presence of 2 mM DTNB to inhibit LCAT activity. After incubation, the samples were separated by agarose gel electrophoresis or two-dimensional polyacrylamide nondenaturing gradient gel electrophoresis (2D-PAGGE). At the same time, DMPC-treated plasma samples were depleted from apoB-containing lipoprotein by precipitation with polyethylene glycol (PEG) 6000, as described previously (16Krimbou L. Marcil M. Chiba H. Genest Jr, J. Structural and functional properties of human plasma high density-sized lipoprotein containing only apoE particles.J. Lipid Res. 2003; 44: 884-892Google Scholar), before phospholipid and free cholesterol efflux experiments.TABLE 1Levels of cholesterol, triglyceride, and apolipoprotein in normolipidemic and ABCA1-deficient subjectsPlasma ConcentrationSubjectsCholesterolTriglyceridesHDL-CholesterolApoBApoA-IApoEmmol/lmg/dlControls13.411.121.3590140 4.1423.970.701.5285138 3.6034.300.901.6588153 3.90ABCA1-deficientTD14.142.540.111776 2.9TD23.502.100.09873 2.4TD33.201.670.10795 2.7apoA-I, apolipoprotein A-I; TD, Tangier disease. Open table in a new tab apoA-I, apolipoprotein A-I; TD, Tangier disease. ApoA-I-containing particles were separated by 2D-PAGGE as described previously (17Krimbou L. Marcil M. Davignon J. Genest Jr, J. Interaction of lecithin:cholesterol acyltransferase (LCAT).alpha 2-macroglobulin complex with low density lipoprotein receptor-related protein (LRP). Evidence for an alpha 2-macroglobulin/LRP receptor-mediated system participating in LCAT clearance.J. Biol. Chem. 2001; 276: 33241-33248Google Scholar). Briefly, samples (30–100 μl) were separated in the first dimension (according to their charge) by 0.75% agarose gel electrophoresis (100 V, 3 h, 4°C) and in the second dimension (according to the size) by 5–23% polyacrylamide concave gradient gel electrophoresis (125 V, 24 h, 4°C). Iodinated high molecular weight protein mixture (7.1–17.0 nm; Pharmacia) was run as a standard on each gel. Electrophoretically separated samples were electrotransferred (30 V, 24 h, 4°C) onto nitrocellulose membranes (Hybond ECL; Amersham). ApoA-I-containing particles were detected by incubating the membranes with immunopurified polyclonal anti-apoA-I antibody (Biodesign). Either native plasma preβ1-LpA-I or preβ1-LpA-I-like particles were isolated from freshly normolipidemic plasma treated or not with DMPC under nondenaturing conditions, as described previously (18Denis M. Haidar B. Marcil M. Bouvier M. Krimbou L. Genest Jr, J. Molecular and cellular physiology of apolipoprotein A-I lipidation by the ATP-binding cassette transporter A1 (ABCA1).J. Biol. Chem. 2004; 279: 7384-7394Google Scholar), with the following modifications. Plasma samples were incubated or not with DMPC (2 mg/ml plasma) for 1 h at 24°C in the presence of 2 mM DTNB. DMPC-treated plasma or untreated plasma was subjected to a human immunopurified anti-apoA-I antibody (12171-21A; Genzyme Corp.)-coupled Sepharose column. ApoA-I-containing fractions were then dialyzed and concentrated. Samples were separated by agarose gel electrophoresis, and the preβ-migrating region was excised out. Agarose gel pieces containing the preβ-migrating region were placed at the top of 3–26% nondenaturing gradient gels, as described previously (19Krimbou L. Tremblay M. Jacques H. Davignon J. Cohn J.S. In vitro factors affecting the concentration of gamma-LpE (gamma-LpE) in human plasma.J. Lipid Res. 1998; 39: 861-872Google Scholar). An immunoblot of apoA-I-containing lipoproteins separated by 2D-PAGGE was used as a template to localize preβ1-LpA-I, which is recovered from the gels by electroelution. Preβ1-LpA-I particles were further concentrated by ultrafiltration (spiral ultrafiltration cartridge, molecular weight cut off 50,000; Amicon) to discard any lipid-free apoA-I or proteolytic peptides. The integrity of isolated preβ1-LpA-I and preβ1-LpA-I-like particles was verified by 2D-PAGGE. SDS-PAGE revealed the presence of a single apoA-I band free of proteolytic peptides. Typically, 2 mg/ml native preβ1-LpA-I was obtained from 100 ml of normolipidemic plasma, whereas 5 mg/ml preβ1-LpA-I-like particles was obtained from 100 ml of DMPC-treated plasma, with an overall recovery of ∼20% for both native preβ1-LpA-I and preβ1-LpA-I-like particles. Purified plasma apoA-I (Biodesign) was resolubilized in 4M guanidine-HCl and dialyzed extensively against Tris buffer (10 mM Tris and 150 mM NaCl, pH 8.2). Freshly resolubilized apoA-I was used within 48 h. Competition binding assays were performed as described previously (18Denis M. Haidar B. Marcil M. Bouvier M. Krimbou L. Genest Jr, J. Molecular and cellular physiology of apolipoprotein A-I lipidation by the ATP-binding cassette transporter A1 (ABCA1).J. Biol. Chem. 2004; 279: 7384-7394Google Scholar, 20Krimbou L. Denis M. Haidar B. Carrier M. Marcil M. Genest Jr, J. Molecular interactions between apoE and ABCA1: impact on apoE lipidation.J. Lipid Res. 2004; 45: 839-848Google Scholar). Briefly, apoA-I was iodinated with 125I by Iodo-Gen® (Pierce) to a specific activity of 800–1,500 cpm/ng apoA-I. Normal fibroblasts were grown on 24-well plates and were stimulated with 2.5 μg/ml 22-(R)-hydroxycholesterol and 10 μM 9-cis-retinoic acid for 20 h. Cells were then incubated at 37°C with 125I-apoA-I in DMEM/BSA in the presence of increasing amounts of either native preβ1-LpA-I, preβ1-LpA-I-like particles, HDL3, or unlabeled apoA-I for 2 h. The cells were then washed rapidly two times with ice-cold PBS/BSA and two times with cold PBS and lysed with 0.1 N NaOH. The amount of bound iodinated ligand was determined by γ counting. Control experiments were conducted to examine whether the apparent decrease in cell binding of the labeled apoA-I may be attributable to the 125I-apoA-I binding to different competitor particles instead of the cells. Therefore, an experiment was carried out in which either preβ1-LpA-I-like particles or HDL3 particles were incubated with 125I-apoA-I under similar conditions used for the apoA-I binding assay and then the HDL3 sample was separated by fast-protein liquid chromatography. No significant amount of 125I-apoA-I was found associated with HDL3. On the other hand, because of insufficient separation between lipid-free 125I-apoA-I and preβ1-LpA-I in our fast-protein liquid chromatography system, lipid-free 125I-apoA-I was removed from the incubation medium using a size-exclusion centrifugal filter (MWCO 50,000) combined with a dialysis membrane (MWCO 50,000). This centrifugal filtration system discriminates between lipid-free apoA-I and other lipidated LpA-I particles with molecular mass > 50 kDa. No detectable lipid-free 125I-apoA-I was found associated with preβ1-LpA-I-like particles after filtration followed by dialysis, as assessed by 2D-PAGGE. In separate experiments, we show that both the centrifugal filter and the dialysis membrane retained isolated preβ1-LpA-I with an apparent molecular mass of 67 kDa. J774 mouse macrophages were cultured in RPMI 1640 with 10% fetal calf serum. At confluence, cells were labeled with 4 μCi/ml [3H]cholesterol or 4 μCi/ml [3H]choline (Perkin-Elmer) for 24 h. After a 24 h labeling period, the cells were washed and then incubated with 0.2% BSA in RPMI with or without 0.3 mM 8-bromo-cAMP for 12 h. Plasma incubated or not with DMPC was depleted of apoB-containing lipoproteins with PEG 6000 and dialyzed. Plasma samples (20 μg of apoA-I) were then incubated with cAMP-stimulated or unstimulated cells for 4 h at 37°C. In some experiments, 300 μM glyburide was added to the medium together with the acceptors. Cellular lipid efflux was determined as follow: 3H cpm in medium/(3H cpm in medium + 3H cpm in cells). The results are expressed as percentages of total radiolabeled phospholipid or cholesterol. Cholesterol and triglyceride concentrations were determined enzymatically on an autoanalyzer (Cobas Mira; Roche Molecular Biochemicals). HDL-cholesterol concentration was determined by measuring cholesterol in the supernatant after precipitation of apoB-containing lipoproteins with heparin-manganese from the d > 1.006 g/ml fraction prepared by ultracentrifugation. Plasma apoA-I and apoB concentrations were determined by nephelometry (Behring Nephelometer 100 Analyzer) or by ELISA. ApoE in total plasma was assayed by ELISA. The number of apoA-I molecules per particle was estimated by cross-linking with dithiobis(succinimidylpropionate) (21Denis M. Haidar B. Marcil M. Bouvier M. Krimbou L. Genest J. Characterization of oligomeric human ATP binding cassette transporter A1. Potential implications for determining the structure of nascent high density lipoprotein particles.J. Biol. Chem. 2004; 279: 41529-41536Google Scholar). Total phospholipid was determined in native preβ1-LpA-I or preβ1-LpA-I-like particles by the method of Sokoloff and Rothblat (22Sokoloff L. Rothblat G.H. Sterol to phospholipid molar ratios of L cells with qualitative and quantitative variations of cellular sterol.Proc. Soc. Exp. Biol. Med. 1974; 146: 1166-1172Google Scholar). Statistical analyses were performed with SigmaPlot statistical software (Jandel Corp., San Rafael, CA). Data are expressed as means ± SD. Student's t-test was used for comparisons between groups. Previous studies by Swaney and colleagues (15Jian B. Llera-Moya M. Royer L. Rothblat G. Francone O. Swaney J.B. Modification of the cholesterol efflux properties of human serum by enrichment with phospholipid.J. Lipid Res. 1997; 38: 734-744Google Scholar) and Tall et al. (23Tall A.R. Hogan V. Askinazi L. Small D.M. Interaction of plasma high density lipoproteins with dimyristoyllecithin multilamellar liposomes.Biochemistry. 1978; 17: 322-326Google Scholar) have documented that enrichment of human serum with phospholipid promotes the formation of new HDL-like complexes. To further investigate the effect of DMPC treatment on the redistribution of apoA-I within HDL subpopulations, the relative concentrations of apoA-I-containing HDL subpopulations were determined by 2D-PAGGE, as described previously by Asztalos and colleagues (24Asztalos B.F. Roheim P.S. Milani R.L. Lefevre M. McNamara J.R. Horvath K.V. Schaefer E.J. Distribution of apoA-I-containing HDL subpopulations in patients with coronary heart disease.Arterioscler. Thromb. Vasc. Biol. 2000; 20: 2670-2676Google Scholar). Plasma samples from three normolipidemic subjects (Table 1) treated or not with DMPC-MLV (2 mg/ml plasma) were separated by 2D-PAGGE, and different HDL subpopulations were quantified by densitometric scanning of radiographic films used to detect the presence of apoA-I associated with HDL subfractions. As shown in Fig. 1A, DMPC treatment of plasma significantly increased the concentrations of preβ1-LpA-I (+19%; P < 0.001), whereas the concentrations of the small LpA-I α3 particles were decreased significantly (−22%; P < 0.001). At the same time, no significant changes were observed in α1 (−4%), α2 (+7%), or preβ2-LpA-I concentrations after DMPC treatment. Interestingly, after treatment of plasma with DMPC, there was a marked shift of α-migrating HDL subpopulations toward preβ mobility. Furthermore, incubation of plasma from a normolipidemic subject (Table 1, control 1) with DMPC generated preβ1-LpA-I particles in a dose-dependent manner, as determined by densitometric scanning of radiographic films used to detect the presence of apoA-I associated with preβ1-LpA-I separated by 2D-PAGGE (Fig. 1B, upper panel). The newly formed preβ-HDL complexes have size and charge similar to those of native plasma preβ1-LpA-I (designated preβ1-LpA-I-like particles) (Fig. 1B, lower panel). In separate experiments, we demonstrate that incubation of plasma with either POPC-MLV or BBSM-MLV did not significantly affect plasma preβ1-LpA-I levels. Analysis of isolated preβ1-LpA-I and preβ1-LpA-I-like particles by silver-stained SDS-PAGE showed a single band in the apoA-I region (28 kDa). Furthermore, cross-linking with dithiobis(succinimidylpropionate)DSP of isolated native preβ1-LpA-I and preβ1-LpA-I-like particles showed that both of these particles had one apoA-I molecule per particle (data not shown). On the other hand, the total phospholipid-to-apoA-I molar ratios of isolated native preβ1-LpA-I and preβ1-LpA-I-like particles varied with each preparation but clearly demonstrated the presence of several molecules of phospholipid in both of these particles. Native preβ1-LpA-I and preβ1-LpA-I-like particles contained approximately three and six molecules of phospholipid per molecule of apoA-I, respectively. However, both of these particles contained no detectable or background amounts of cholesterol, as assayed by enzymatic methods. Having determined that a significant proportion of apoA-I-containing particles were found as preβ1-LpA-I-like particles in DMPC-treated plasma, the question was raised whether these newly formed particles interact with the ABCA1 transporter. Competition assays were performed to determine the ability of isolated preβ1-LpA-I-like particles, as well as native preβ1-LpA-I and spherical HDL particles (HDL3), to compete for the binding of 125I-apoA-I to normal fibroblasts in which ABCA1 was induced with 22(R)-hydroxycholesterol and 9-cis-retinoic acid. As shown in Fig. 2, isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 μg/ml, respectively), whereas lipid-free apoA-I was found to have a 1.5-fold greater capacity to bind ABCA1 compared with preβ1-LpA-I- like particles (IC50 = 1.37 ± 0.48 vs. 2.20 ± 0.35 μg/ml, respectively). At the same time, no significant differences of binding to ABCA1 were observed between isolated native preβ1-LpA-I and preβ1-LpA-I- like particles (IC50 = 1.85 ± 0.50 vs. 2.20 ± 0.35 μg/ml, respectively). Control experiments were conducted to examine whether the apparent decrease in cell binding of the labeled apoA-I may be attributable to the 125I-apoA-I binding to different competitor particles instead of the cells, as described in Materials and Methods. No significant amount of 125I-apoA-I was found associated with either preβ1-LpA-I-like particles or HDL3, supporting the results shown in Fig. 2. Furthermore, we have previously documented that the specific binding of 125I-apoA-I to unstimulated fibroblasts was very low and totally absent in ABCA1 mutant (Q597R) fibroblasts (18Denis M. Haidar B. Marcil M. Bouvier M. Krimbou L. Genest Jr, J. Molecular and cellular physiology of apolipoprotein A-I lipidation by the ATP-binding cassette transporter A1 (ABCA1).J. Biol. Chem. 2004; 279: 7384-7394Google Scholar). Because native plasma preβ1-LpA-I has been proposed to be the first acceptor of cellular cholesterol (9Castro G.R. Fielding C.J. Early incorporation of cell-derived cholesterol into pre-beta-migrating high-density lipoprotein.Biochemistry. 1988; 27: 25-29Google Scholar), the question was raised whether the newly formed preβ1-LpA-I-like particles affect the cholesterol efflux properties of plasma and to what extent this effect is mediated by the ABCA1 transporter. After treatment of normolipidemic plasma (Table 1, control 2) with increasing amounts of DMPC, as described in Materials and Methods, plasma was depleted of apoB-containing lipoproteins with PEG 6000 precipitation and then dialyzed. ApoB-depleted plasma samples (20 μg of apoA-I) were incubated for 4 h with either [3H]choline- or [3H]cholesterol-labeled J774 macrophages stimulated or not with 0.3 mM cAMP. The current cell culture model has been used by many investigators to examine ABCA1-mediated lipid efflux. Indeed, it was documented that under basal conditions, J774 macrophages express low levels of ABCA1 and scavenger receptor class B type I (SR-BI) and release membrane cholesterol to extracellular acceptors by passive diffusion, whereas stimulation with cAMP upregulates ABCA1-mediated cholesterol efflux (25Favari E. Lee M. Calabresi L. Franceschini G. Zimetti F. Bernini F. Kovanen P.T. Depletion of pre-beta-high density lipoprotein by human chymase impairs ATP-binding cassette transporter A1- but not scavenger receptor class B type I-mediated lipid efflux to high density lipoprotein.J. Biol. Chem. 2004; 279: 9930-9936Google Scholar). As shown in Fig. 3, by varying the ratio of DMPC to plasma, we found that DMPC can increase the ability of plasma to promote both phospholipid and free cholesterol efflux in either stimulated or unstimulated cells in a dose-dependent manner. At 2 mg DMPC/ml plasma (saturating DMPC concentration), phospholipid efflux to DMPC-treated plasma from cAMP-stimulated cells was increased by ∼50% compared with unstimulated cells (9.60 ± 0.25% vs. 6.30 ± 0.10%, respectively; P < 0.001). Similarly, free cholesterol efflux to DMPC-treated plasma was increased significantly compared with unstimulated cells (12.30 ± 0.20% vs. 8.70 ± 0.15%, respectively; P < 0.001). Similarly, both phospholipid and free cholesterol efflux from stimulated cells to either isolated native preβ1-LpA-I or preβ1-LpA-I-like particles was increased (+48% and +45%, respectively) compared with unstimulated cells (Fig. 4). In separate experiments, we show that free cholesterol efflux to DMPC-MLV alone (2 mg/ml RPMI) represents <1% of free cholesterol efflux to DMPC-treated plasma (2 mg/ml plasma). Furthermore, there were no significant differences in free cholesterol efflux to DMPC-MLV alone between cAMP-stimulated and unstimulated cells (data not shown).Fig. 4Phospholipid and cholesterol efflux from J774 macrophages to either isolated native preβ1-apoA-I-containing lipoproteins (LpA-I) or preβ1-LpA-I-like particles. J774 cells were labeled with [3H]choline chloride or [3H]cholesterol and stimulated or not with 0.3 mM 8-Br-cAMP as described in Materials and Methods. Isolated native preβ1-LpA-I or preβ1-LpA-I-like particles (15 μg) were incubated for 8 h with J774 cells. Phospholipid and cholesterol efflux were determined as percentages of total (media plus cells) 3H measured in the medium and represent means ± SD from triplicate wells.View Large Image Figure ViewerDownload (PPT) To demonstrate further that preβ1-LpA-I-like particles present in DMPC-treated plasma were responsible for the ABCA1-mediated efflux, we examined the ability of either DMPC-treated or untreated plasma to promote phospholipid and free cholesterol efflux from cAMP-stimulated J774 cells in the absence or p" @default.
• W1832018093 created "2016-06-24" @default.
• W1832018093 creator A5011375774 @default.
• W1832018093 creator A5022102417 @default.
• W1832018093 creator A5026213968 @default.
• W1832018093 creator A5041185655 @default.
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• W1832018093 date "2005-07-01" @default.
• W1832018093 modified "2023-10-14" @default.
• W1832018093 title "Structural modification of plasma HDL by phospholipids promotes efficient ABCA1-mediated cholesterol release" @default.
• W1832018093 cites W1552121147 @default.
• W1832018093 cites W1813524107 @default.
• W1832018093 cites W1833460366 @default.
• W1832018093 cites W1947043095 @default.
• W1832018093 cites W1963889275 @default.
• W1832018093 cites W1983457976 @default.
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• W1832018093 cites W2012533363 @default.
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