Augmented Atherogenesis in LDL Receptor Deficient Mice Lacking Both Macrophage ABCA1 and ApoE (original) (raw)
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Biochemical and Biophysical Research Communications, 2010
Objectives: To determine the role of macrophage ATP-binding cassette transporter A5 (ABCA5) in cellular cholesterol homeostasis and atherosclerotic lesion development. Methods and results: Chimeras with dysfunctional macrophage ABCA5 (ABCA5 ÀM/ÀM ) were generated by transplantation of bone marrow from ABCA5 knockout (ABCA5 À/À ) mice into irradiated LDLr À/À mice. In vitro, bone marrow-derived macrophages from ABCA5 ÀM/ÀM chimeras exhibited a 29% (P < 0.001) decrease in cholesterol efflux to HDL, whereas a 21% (P = 0.07) increase in cholesterol efflux to apoA-I was observed. Interestingly, expression of ABCA1, but not ABCG1, was up-regulated in absence of functional ABCA5 in macrophages. To induce atherosclerosis, the transplanted LDLr À/À mice were fed a highcholesterol Western-type diet (WTD) for 6, 10, or 18 weeks, allowing analysis of effects on initial as well as advanced lesion development. Atherosclerosis development was not affected in male ABCA5 ÀM/ÀM chimeras after 6, 10, and 18 weeks WTD feeding. However, female ABCA5 ÀM/ÀM chimeras did develop significantly (P < 0.05) larger aortic root lesions as compared with female controls after 6 and 10 weeks WTD feeding. Conclusions: ABCA5 influences macrophage cholesterol efflux, and selective disruption of ABCA5 in macrophages leads to increased atherosclerotic lesion development in female LDLr À/À mice.
Atherosclerosis, 2012
Objective: The ABCA2 transporter shares high structural homology to ABCA1, which is crucial for the removal of excess cholesterol from macrophages and, by extension, in atherosclerosis. It has been suggested that ABCA2 sequesters cholesterol inside the lysosomes, however, little is known of the macrophage-specific role of ABCA2 in regulating lipid homeostasis in vivo and in modulating susceptibility to atherosclerosis. Methods: Chimeras with dysfunctional macrophage ABCA2 were generated by transplantation of bone marrow from ABCA2 knockout (KO) mice into irradiated LDL receptor (LDLr) KO mice. Results: Interestingly, lack of ABCA2 in macrophages resulted in a diminished lesion size in the aortic root (À24.5%) and descending thoracic aorta (À36.6%) associated with a 3-fold increase in apoptotic cells, as measured by both caspase 3 and TUNEL. Upon oxidized LDL exposure, macrophages from wildtype (WT) transplanted animals developed filipin-positive droplets in lysosomal-like compartments, corresponding to free cholesterol (FC) accumulation. In contrast, ABCA2-deficient macrophages displayed an abnormal diffuse distribution of FC over peripheral regions. The accumulation of neutral sterols in lipid droplets was increased in ABCA2-deficient macrophages, but primarily in cytoplasmic clusters and not in lysosomes. Importantly, apoptosis of oxLDL loaded macrophages lacking ABCA2 was increased 2.7-fold, probably as a consequence of the broad cellular distribution of FC. Conclusions: Lack of functional ABCA2 generates abnormalities in intracellular lipid distribution/trafficking in macrophages consistent with its lysosomal sequestering role, leading to an increased susceptibility to apoptosis in response to oxidized lipids and reduced atherosclerotic lesion development.
Molecular Therapy, 2003
The antiatherogenic effect of high-density lipoprotein (HDL) and its major protein component apolipoprotein A-I (apoA-I) has been largely attributed to their key roles in reverse cholesterol transport (RCT) and cellular cholesterol efflux. Substantial evidence shows that overexpression of human apoA-I reduces atherosclerosis in animal models. However, it is uncertain whether this protection is due to an increase in plasma HDL level or to a local effect in the artery wall. To test the hypothesis that expression of human apoA-I in macrophages can promote RCT in the artery wall, we used a retroviral construct expressing human apoA-I cDNA (MFG-HAI) to transduce ApoE ؊/؊ bone marrow cells and then transplanted these cells into ApoE ؊/؊ mice with preexisting atherosclerosis. ApoE ؊/؊ mice reconstituted with MFG-HAI marrow had a significant reduction (30%) in atherosclerotic lesions in the proximal aorta compared to control mice that received marrow expressing MFG parental virus. Peritoneal macrophages isolated from MFG-HAI mice showed a four-to fivefold increase in mRNA expression levels of both ATP-binding cassette (ABC) A1 and ABCG1 compared to controls. Our data demonstrate that gene transfer-mediated expression of human apoA-I in macrophages can compensate in part for apoE deficiency and delay the progression of atherosclerotic lesions by stimulating ABC-dependent cholesterol efflux and RCT.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2013
Objective-Hepatic ATP binding cassette transporter A1 (ABCA1) expression is critical for maintaining plasma high-density lipoprotein (HDL) concentrations, but its role in macrophage reverse cholesterol transport and atherosclerosis is not fully understood. We investigated atherosclerosis development and reverse cholesterol transport in hepatocyte-specific ABCA1 knockout HSKO) mice in the low-density lipoprotein (LDL) receptor KO (LDLrKO) C57BL/6 background. Approach and Results-Male and female LDLrKO and HSKO/LDLrKO mice were switched from chow at 8 weeks of age to an atherogenic diet (10% palm oil, 0.2% cholesterol) for 16 weeks. Chow-fed HSKO/LDLrKO mice had HDL concentrations 10% to 20% of LDLrKO mice, but similar very low-density lipoprotein and LDL concentrations. Surprisingly, HSKO/LDLrKO mice fed the atherogenic diet had significantly lower (40% to 60%) very low-density lipoprotein, LDL, and HDL concentrations (50%) compared with LDLrKO mice. Aortic surface lesion area and cholesterol content were similar for both genotypes of mice, but aortic root intimal area was significantly lower (20% to 40%) in HSKO/LDLrKO mice. Although macrophage 3 H-cholesterol efflux to apoB lipoprotein-depleted plasma was 24% lower for atherogenic diet-fed HSKO/LDLrKO versus LDLrKO mice, variation in percentage efflux among individual mice was <2-fold compared with a 10-fold variation in plasma HDL concentrations, suggesting that HDL levels, per se, were not the primary determinant of plasma efflux capacity. In vivo reverse cholesterol transport, resident peritoneal macrophage sterol content, biliary lipid composition, and fecal cholesterol mass were similar between both genotypes of mice. Conclusions-The markedly reduced plasma HDL pool in HSKO/LDLrKO mice is sufficient to maintain macrophage reverse cholesterol transport, which, along with reduced plasma very low-density lipoprotein and LDL concentrations, prevented the expected increase in atherosclerosis. (Arterioscler Thromb Vasc Biol. 2013;33:2288-2296.) The online-only Data Supplement is available with this article at http://atvb.ahajournals.org/lookup/suppl/Downloaded from I-VLDL apoB clearance from plasma, was more rapid in HSKO/LDLrKO versus LDLrKO recipient mice (area under curve; P<0.05; in the online-only Data Supplement), suggesting that the lower VLDL-C concentrations in HSKO/ by guest on March 29, 2016 http://atvb.ahajournals.org/ Downloaded from Hepatocyte ATP binding cassette transporter A1 (ABCA1) plays a pivotal role in maintaining plasma high-density lipoprotein (HDL) levels, but its impact on macrophage reverse cholesterol transport and atherogenesis is less clear. In this study, we show the importance of hepatic ABCA1 in regulating both plasma HDL and apoB lipoprotein metabolism under hyperlipidemic conditions. Despite a 50% reduction in plasma HDL cholesterol in the absence of hepatic ABCA1, atherosclerosis was not worsened, likely because of the maintenance of in vivo macrophage reverse cholesterol transport and the concomitant paradoxical 40% to 50% reduction in plasma very low-density lipoprotein and low-density lipoprotein levels. In addition, macrophage cholesterol efflux to apoB lipoprotein-depleted plasma varied <2-fold compared with a 10-fold variation in plasma HDL cholesterol concentrations, supporting the concept that steady-state HDL cholesterol concentration is not the primary determinant of plasma cholesterol efflux capacity. Therapeutic interventions targeting hepatic ABCA1 expression to alleviate cardiovascular burden should take into consideration that paradoxical effects on apoB lipoprotein metabolism may oppose atheroprotection.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2000
The effect of monocyte/macrophage-derived wild-type mouse apolipoprotein E (apoE), human apoE3-Leiden, and human apoE2 on serum cholesterol levels and the development of atherosclerosis in apoE-deficient (apoe-/-) mice was investigated by using bone marrow transplantation (BMT). At 4 weeks after BMT, murine apoeϩ/ϩ bone marrow reduced serum cholesterol levels by 87% in apoe-/-mice, whereas macrophage-derived human apoE3-Leiden and human apoE2 induced a maximal, transient reduction of 35% and 48%, respectively. At 4 months after BMT, atherosclerosis was 23-fold (PϽ0.001) reduced in apoeϩ/ϩ3apoe-/-mice, whereas no significant reduction in apoE3-Leiden.apoe-/-3apoe-/-and apoE2.apoe-/-3apoe-/-mice could be demonstrated. A highly significant decrease in serum cholesterol levels (78% reduction) and atherosclerosis (21-fold, PϽ0.001) was found in apoE3-Leiden.apoe-/-animals expressing high levels of apoE in multiple tissues, whereas apoE2 was ineffective even at high concentrations. Furthermore, in contrast to apoE-deficient macrophages, cholesterol efflux from apoE2 or apoE3-Leiden macrophages was not impaired. In conclusion, apoE3-Leiden as well as apoE2 are less effective in reducing cholesterol levels and atherosclerosis in apoe-/-animals, compared with apoeϩ/ϩ, with apoE2ϽapoE3-LeidenϽapoeϩ/ϩ, irrespective of the observed adequate efflux of cholesterol from macrophages expressing apoE2 and apoE3-Leiden, indicating that normalization of cholesterol efflux by macrophages is not accompanied by measurable effects on lesion growth.
Independent protective roles for macrophage Abcg1 and Apoe in the atherosclerotic lesion development
Atherosclerosis, 2009
Objective: ATP-binding cassette transporter G1 (Abcg1) and apolipoprotein E (Apoe) play a role in macrophage cholesterol efflux and consequently the development of atherosclerosis. A possible interaction between Abcg1 and Apoe in cholesterol efflux was postulated, but the potential combined action of these proteins on atherosclerotic lesion formation is unclear. Methods: LDL receptor knockout (KO) mice were transplanted with bone marrow from Abcg1/Apoe double KO (dKO) mice, their respective single knockouts, and wild-type (WT) controls and challenged with a high-fat/high-cholesterol diet for 6 weeks to induce atherosclerosis. Results: No differences were found in serum lipid levels. The mean atherosclerotic lesion area in dKO transplanted animals (187 ± 18 × 10 3 m 2 ) was 1.4-fold (p < 0.01) increased compared to single knockouts (Abcg1 KO: 138 ± 5 × 10 3 m 2 ; Apoe KO: 131 ± 7 × 10 3 m 2 ) and 1.9-fold (p < 0.001) as compared to WT controls (97 ± 15 × 10 3 m 2 ). In vitro cholesterol efflux experiments established that combined deletion of Abcg1 and Apoe leads to a larger attenuation of macrophage cholesterol efflux to HDL as compared to single knockouts. Conclusions: Single deletion of macrophage Abcg1 or Apoe does lead to a moderate non-significant increase in atherosclerotic lesion development as tested by ANOVA, while combined deletion of Abcg1 and Apoe induces a more dramatic and significant increase in atherosclerosis. Our results indicate an additive, independent effect for both macrophage Abcg1 and Apoe in the prevention of atherosclerosis.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2006
Objective-ABCG1 has recently been identified as a facilitator of cellular cholesterol and phospholipid efflux to high-density lipoprotein (HDL). Its expression in macrophages is induced during cholesterol uptake in macrophages and by liver X receptor (LXR). The role of macrophage ABCG1 in atherosclerotic lesion development is, however, still unknown. Methods and Results-To assess the role of macrophage ABCG1 in atherosclerosis, we generated low-density lipoprotein (LDL) receptor knockout (LDLr Ϫ/Ϫ ) mice that are selectively deficient in macrophage ABCG1 by using bone marrow transfer (ABCG1 Ϫ/Ϫ 3 LDLr Ϫ/Ϫ ). Peritoneal macrophages isolated from donor ABCG1 Ϫ/Ϫ mice exhibited a 22% (Pϭ0.0007) decrease in cholesterol efflux to HDL. To induce atherosclerosis, transplanted mice were fed a high-cholesterol diet containing 0.25% cholesterol and 15% fat for 6 and 12 weeks. Serum lipid levels and lipoprotein profiles did not differ significantly between ABCG1 Ϫ/Ϫ 3 LDLr Ϫ/Ϫ mice and controls. In lungs of ABCG1 Ϫ/Ϫ 3 LDLr Ϫ/Ϫ mice a striking accumulation of lipids was observed in macrophages localized to the subpleural region. After 6 weeks of high-cholesterol diet feeding the atherosclerotic lesion size was 49Ϯ12ϫ10 3 m 2 for ABCG1 ϩ/ϩ 3 LDLr Ϫ/Ϫ mice versus 65Ϯ15ϫ10 3 m 2 for ABCG1 Ϫ/Ϫ 3 LDLr Ϫ/Ϫ mice and after 12 weeks of high-cholesterol diet feeding 124Ϯ17ϫ10 3 m 2 for ABCG1 ϩ/ϩ 3 LDLr Ϫ/Ϫ mice versus 168Ϯ17ϫ10 3 m 2 for ABCG1 Ϫ/Ϫ 3 LDLr Ϫ/Ϫ mice. Atherosclerotic lesion size depended on both time and the macrophage ABCG1 genotype (Pϭ0.038 by 2-way ANOVA, nՆ8), indicating a moderately 33% to 36% increase in lesion formation in the absence of macrophage ABCG1.
Accelerated atherosclerosis in C57Bl/6 mice transplanted with ApoE-deficient bone marrow
Atherosclerosis, 2000
Apolipoprotein E (apoE), a high affinity ligand for lipoprotein receptors, is synthesized by the liver and extrahepatic tissues, including cells of the monocyte/macrophage cell lineage. The role of monocyte/macrophage-derived apoE in atherogenesis was assessed by transplantation of apoE-deficient (apoE −/−) bone marrow into normolipidemic C57Bl/6 mice. No significant effect could be demonstrated on serum apoE levels in C57Bl/6 mice, transplanted with apoE-deficient bone marrow compared with control transplanted mice. Furthermore, no consistent effect on serum cholesteryl esters and triglyceride concentrations could be demonstrated on either a standard chow diet or a high cholesterol diet. Quantitative analysis of atherosclerosis in mice transplanted with apoE-deficient bone marrow, after two months on a high cholesterol diet, revealed a 4-fold increase in the atherosclerotic lesion area as compared to animals transplanted with apoE +/+ bone marrow. Analysis of the ability of apoE-deficient macrophages to release cholesterol after loading with acetylated LDL revealed that the release of cholesterol from apoE-deficient macrophages was impaired as compared to wild-type macrophages in the absence and the presence of specific cholesterol acceptors. In conclusion, apoE production by macrophages retards the formation of atherosclerotic plaques, possibly by mediating cholesterol efflux. We anticipate that pharmacological approaches to increase apoE synthesis and/or secretion by macrophages might be beneficial for the treatment of atherosclerosis. : S 0 0 2 1 -9 1 5 0 ( 9 9 ) 0 0 3 7 2 -X
Dietary cholesterol-induced changes in macrophage characteristics. Relationship to atherosclerosis
The American journal of pathology, 1986
In diet-induced hypercholesterolemia, circulating monocytes adhere to the endothelium of the vessel wall and emigrate into the intima. Atherosclerotic lesions may develop, characterized by the presence of lipid-laden macrophages and proliferating smooth muscle cells recruited from the media. Using rat peritoneal macrophages, the authors examined the influence of diet-induced hypercholesterolemia on several variables of macrophage function that may contribute to lesion formation, including adhesion to bovine aortic endothelial cells (BAECs) and vascular smooth muscle cells (VSMCs), the production of chemoattractants and mitogens for VSMCs, and the release of the reactive oxygen species, superoxide. In general, a hypercholesterolemia-induced augmentation of macrophage function was observed. In comparison with macrophages from normal animals (N M phi s), macrophages from hypercholesterolemic animals (H M phi s) were 50-80% more adhesive to BAECs and VSMCs. H M phi-secreted products inc...
Increased atherosclerosis in mice reconstituted with apolipoprotein E null macrophages
Proceedings of the …, 1997
Macrophage-derived foam cells express apolipoprotein E (apoE) abundantly in atherosclerotic lesions. To examine the physiologic role of apoE secretion by the macrophage in atherogenesis, bone marrow transplantation was used to reconstitute C57BL/6 mice with macrophages that were either null or wild type for the apoE gene. After 13 weeks on an atherogenic diet, C57BL/6 mice reconstituted with apoE null marrow developed 10-fold more atherosclerosis than controls in the absence of significant differences in serum cholesterol levels or lipoprotein profiles. ApoE expression was absent in the macrophage-derived foam cells of C57BL/6 mice reconstituted with apoE null marrow. Thus, lack of apoE expression by the macrophage promotes foam cell formation. These data support a protective role for apoE expression by the macrophage in early atherogenesis. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.