The scavenger receptor BI and its ligand, HDL: partners in crime against HCV neutralizing antibodies

Summary.  Better knowledge of the viral and host factors that determine HCV clearance vs . persistence at the acute stage of infection is needed in order to improve antiviral therapy and develop efficient vaccines. Spontaneous HCV clearance is associated with a strong, early and broad cellular immune response. Yet, several observations suggest that antibody-mediated neutralisation occurs during HCV infection in vivo and that polyclonal antibodies to HCV can be protective. The recent development of HCV infection assays has confirmed that sera from HCV-infected patients neutralise infection in vitro . Recent studies have demonstrated that Nt-antibodies, of narrow specificity, are induced during the early phase of infection and could play a role in controlling viral infection or clearance. Yet, high-titre, broadly cross-reacting Nt-antibodies are readily detected in chronically infected patients, suggesting that their effectiveness is limited in patients who do not resolve the disease. The factors that mitigate the impact of the Nt-antibody response need to be clarified. Here we review some essential features of the Nt-antibody responses to HCV. We then discuss an original mechanism that HCV may use in vivo to attenuate Nt-antibodies, which involves the hyper-variable region-1 of the HCV-E2 glycoprotein, high-density lipoprotein (HDL) and the physiologic activity of the scavenger receptor BI, a receptor shared by both HCV and HDL.     

Probucol markedly reduces HDL phospholipids and elevated prebeta1-HDL without delayed conversion into alpha-migrating HDL: putative role of angiopoietin-like protein 3 in probucol-induced HDL remodeling

Probucol is a unique hypolipidemic agent that increases cholesteryl ester transfer protein (CETP) activity. Enhanced CETP-mediated conversion of high-density lipoprotein (HDL) partly explains the probucol-induced decrease in HDL cholesterol and increase in plasma preβ1-HDL (native lipid-poor HDL) concentrations. However, HDL cholesterol is reduced in patients that are completely deficient in CETP. Angiopoietin-like protein 3 (ANGPTL3) is an endogenous suppressor of endothelial lipase that promotes the hydrolysis of HDL phospholipids and may generate preβ1-HDL. To determine whether probucol decreases ANGPTL3 and HDL phospholipids while increasing preβ1-HDL, we measured these parameters before and after a 4-week probucol treatment in 39 hypercholesterolemic patients and age- and sex-matched controls. The median ANGPTL3 had decreased from 143 to 113 μg/L by week 4 (p < 0.05). High-performance liquid chromatography revealed that probucol decreased the phospholipid content of very large (13.5–15 nm) and large (12.1 nm) HDL particles predominantly by 65% (p < 0.01) and 53% (p < 0.001), respectively. The change in ANGPTL3, but not CETP mass, was positively correlated with that in large HDL phospholipids (r = 0.455, p < 0.05). The absolute and relative concentrations of preβ1-HDL increased by 14% (p < 0.01) and 60% (p < 0.001), respectively. The conversion rate of preβ1-HDL into α-migrating HDL by lecithin-cholesterol acyltransferase did not change significantly. In conclusion, probucol decreases plasma ANGPTL3 and HDL phospholipids while increasing preβ1-HDL. We speculate that probucol induces HDL remodeling via an endothelial lipase-mediated pathway.     

单核细胞株THP-1分化为泡沫细胞过程中清道夫受体A变化及阿托伐他汀的干预作用

目的 研究单核细胞株THP-1分化为巨噬细胞、泡沫细胞过程中细胞清道夫受体A（SRA）表达、单核细胞趋化蛋白-1（MCP-1）分泌及应用阿托伐他汀干预的情况。方法 佛波醇酯诱导THP-1细胞分化为巨噬细胞,将其分为对照组、OX-LDL组（泡沫细胞组）、OX-LDL＋阿托伐他汀组（再分为低、中、高浓度3组）。用ELISA法,测定细胞培养液中MCP-1浓度。将SRA特异性结合配体DiI-Ac-LDL与细胞孵育,应用荧光显微镜观察各组细胞SRA蛋白表达及活性情况。并将MCP-1浓度与SRA蛋白活性进行相关性分析。结果400倍光镜下观察到细胞株THP-1在佛波醇酯诱导下转变为泡沫细胞。与对照组相比,OX-LDL组MCP-1表达升高,6h后升高明显（P〈0．05）,12h达高峰（P〈0．01）,24h后逐渐下降（P〈0．01）。阿托伐他汀药物干预,呈剂量依赖性降低MCP．1水平。OX-LDL组SRA蛋白活性水平明显高于对照组（P〈0．01）。阿托伐他汀干预,呈剂量依赖性下调SRA蛋白活性水平。各组细胞12hMCP．1浓度与SRA蛋白活性水平呈明显正相关（r=0．683,P〈0．01）。结论SRA、炎症因子MCP-1在THP-1细胞分化为泡沫细胞过程中发挥重要作用,阿托伐他汀抑制MCP-1与SRA表达,可能是其抗动脉粥样硬化形成的重要机制。     

MicroRNA-19b promotes macrophage cholesterol accumulation and aortic atherosclerosis by targeting ATP-binding cassette transporter A1

Rationale

Macrophage accumulation of cholesterol leads to foam cell formation which is a major pathological event of atherosclerosis. Recent studies have shown that microRNA (miR)-19b might play an important role in cholesterol metabolism and atherosclerotic diseases. Here, we have identified miR-19b binding to the 3′UTR of ATP-binding cassette transporter A1 (ABCA1) transporters, and further determined the potential roles of this novel interaction in atherogenesis.

Objective

To investigate the molecular mechanisms involved in a miR-19b promotion of macrophage cholesterol accumulation and the development of aortic atherosclerosis.

Methods and results

We performed bioinformatics analysis using online websites, and found that miR-19b was highly conserved during evolution and directly bound to ABCA1 mRNA with very low binding free energy. Luciferase reporter assay confirmed that miR-19b bound to 3110-3116 sites within ABCA1 3′UTR. MiR-19b directly regulated the expression levels of endogenous ABCA1 in foam cells derived from human THP-1 macrophages and mouse peritoneal macrophages (MPMs) as determined by qRT-PCR and western blot. Cholesterol transport assays revealed that miR-19b dramatically suppressed apolipoprotein AI-mediated ABCA1-dependent cholesterol efflux, resulting in the increased levels of total cholesterol (TC), free cholesterol (FC) and cholesterol ester (CE) as revealed by HPLC. The excretion of ³H-cholesterol originating from cholesterol-laden MPMs into feces was decreased in mice overexpressing miR-19b. Finally, we evaluated the proatherosclerotic role of miR-19b in apolipoprotein E deficient (apoE^−/−) mice. Treatment with miR-19b precursor reduced plasma high-density lipoprotein (HDL) levels, but increased plasma low-density lipoprotein (LDL) levels. Consistently, miR-19b precursor treatment increased aortic plaque size and lipid content, but reduced collagen content and ABCA1 expression. In contrast, treatment with the inhibitory miR-19b antisense oligonucleotides (ASO) prevented or reversed these effects.

Conclusion

MiR-19b promotes macrophage cholesterol accumulation, foam cell formation and aortic atherosclerotic development by targeting ABCA1.     

Uptake of oxidized low-density lipoprotein in a THP-1 cell line lacking scavenger receptor A

We previously isolated THP-1 subtype cells (sTHP-1), a cell line that expresses scanty amounts of scavenger receptor A (ScR-A) and does not undergo foam cell formation when incubated with acetylated low-density lipoprotein (Ac-LDL). In this study, we investigated the accumulation of esterified cholesterol in sTHP-1 cells incubated with oxidized LDL (Ox-LDL), a physiologically modified lipoprotein in human. While sTHP-1 cells incubated with Ac-LDL accumulated only small amounts of esterified cholesterol, those incubated with Ox-LDL accumulated amounts similar to those accumulated by parent THP-1 (pTHP-1) cells. sTHP-1 cells expressed CD36 in amounts similar to the amounts expressed by pTHP-1 cells, and Ox-LDL was internalized through this CD36. The amount of accumulated esterified cholesterol was 73-81% of that accumulated in pTHP-1 cells expressing ScR-A. The levels of 125I-Ox-LDL binding, association, and degradation in sTHP-1 cells were 64-70% of the corresponding levels in pTHP-1 cells. In our experiments utilizing ScR-A-deficient sTHP-1 cells and a specific antibody against human CD36, most of the Ox-LDL interacted with the CD36 receptor. In addition, a substantial amount of Ox-LDL (28-42%) was bound and degraded by sTHP-1 macrophages when both of the two major scavenger receptors, ScR-A and CD36, were deficient or blocked. These results indicate that CD36 in macrophages plays an important role in foam cell formation by Ox-LDL, while additional scavenger receptor(s) may take part in significant pathways of Ox-LDL uptake in macrophages.     

Current Diagnosis and Management of Tangier Disease

Tangier disease is a genetic disorder characterized by an absence or extremely low level of high-density lipoprotein (HDL)-cholesterol (HDL-C). It is caused by a dysfunctional mutation of the ATP-binding cassette transporter A1 ( ABCA1 ) gene, the mandatory gene for generation of HDL particles from cellular cholesterol and phospholipids, and it appears in an autosomal recessive hereditary profile. To date, 35 cases have been reported in Japan and 109 cases outside Japan. With dysfunctional mutations in both alleles (homozygotes or compound heterozygotes), the HDL-C level is mostly less than 5 mg/dL and there is 10 mg/dL or less of apolipoprotein A-I (apoA-I), the major protein component of HDL. In patients with Tangier disease, major physical findings are orange-colored pharyngeal tonsils, hepatosplenomegaly, corneal opacity, lymphadenopathy, and peripheral neuropathy. Although patients tend to have decreased low-density lipoprotein (LDL)-cholesterol (LDL-C) levels, premature coronary artery disease is frequently observed. No specific curative treatment is currently available, so early identification of patients and preventing atherosclerosis development are crucial. Management of risk factors other than low HDL-C is also important, such as LDL-C levels, hypertension and smoking. Additionally, treatment for glucose intolerance might be required because impaired insulin secretion from pancreatic beta cells has occasionally been reported.     

ATP结合盒转运蛋白A1研究进展

动脉粥样硬化是心脑血管疾病的重要基础病理改变,而胆固醇在巨噬细胞内聚集和泡沫细胞形成是动脉粥样硬化的始动环节。ATP结合盒转运蛋白Al（ABCAl）是一种重要的胆固醇流出调节蛋白,能介导细胞内胆固醇逆向转运到细胞外,使之与载脂蛋白A-Ⅰ结合并包装形成高密度脂蛋白（HDL）的膜转运蛋白。因此,ABCAl是调节血浆HDL及细胞内胆固醇水平的重要膜蛋白,ABCAl的表达水平与动脉粥样硬化的发生关系密切。同时,细胞内脂质、核受体PPAR、LXR、RXR和细胞因子等对ABCAl蛋白表达具有凋控作用。本文将ABCAl研究进展作一综述。     

不同剂量氯沙坦对氧化修饰型低密度脂蛋白诱导的人单核巨噬细胞肝X受体及小凹蛋白mRNA表达的影响

目的探讨不同剂量氯沙坦对氧化修饰型低密度脂蛋白(ox-LDL)诱导的人单核巨噬细胞肝X受体及小凹蛋白-1 mRNA表达的影响。方法采用体外密度梯度离心法分离健康人血单核细胞并培养至3⁴代,以佛波酯诱导转化为巨噬细胞,用ox-LDL干预细胞使其转化为泡沫细胞,分别用不同剂量氯沙坦(10、50、75和100μmol/L)干预泡沫细胞,实时PCR检测各组肝X受体、小凹蛋白-1 mRNA的表达情况。结果与空白对照组比较,ox-LDL组肝X受体mRNA表达(0.26±0.02比1.00±0.02)、小凹蛋白-1 mRNA表达(0.27±0.01比1.00±0.04)均下调,差异有统计学意义(均为P<0.05);与ox-LDL组比较,随着氯沙坦剂量的升高,各氯沙坦组的肝X受体、小凹蛋白-1 mRNA表达逐渐上调,且呈剂量依赖性,差异均有统计学意义(均为P<0.05);不同剂量氯沙坦组之间进行两两比较,肝X受体、小凹蛋白-1 mRNA的表达差异均有统计学意义(均为P<0.05)。结论氯沙坦可以逆转ox-LDL对人单核巨噬细胞肝X受体及小凹蛋白-1 mRNA表达的抑制,且呈一定的剂量依赖趋势。     

Increased LDL cholesterol and atherosclerosis in LDL receptor-deficient mice with attenuated expression of scavenger receptor B1

Scavenger receptor BI (SR-BI) is a multiligand cell-surface receptor that plays a central role in high density lipoprotein homeostasis in rodents. To investigate a role for SR-BI in atherosclerosis, mice with attenuated SR-BI expression were crossed with low density lipoprotein (LDL) receptor-deficient mice. Compound-homozygous mutants showed increased plasma cholesterol, surprisingly due primarily to increased LDL cholesterol and apolipoprotein B levels. LDL turnover studies showed that this resulted from increased LDL cholesterol production rather than decreased LDL catabolism. Atherosclerotic lesion size was significantly increased in male compound-mutant mice relative to LDL receptor-deficient controls (93 427+/-16 079 versus 34 448+/-5 331 microm(2), respectively; P=0.003). The proatherogenic effect of attenuated SR-BI expression may in part be due to increased LDL cholesterol levels. These findings suggest that upregulation of the receptor could have therapeutic potential for the treatment of atherosclerosis.     

Coexistence of foam cells and hypocholesterolemia in mice lacking the ABC transporters A1 and G1

The concept that macrophages can become foam cells as a result of a disturbed balance between the uptake of cholesterol from lipoproteins and cholesterol efflux is generally accepted. ABCA1 and ABCG1 are two cholesterol transporters that may act sequentially to remove cellular cholesterol, but currently their combined role in vivo is unknown. We report here that targeted disruption of both ABCA1 and ABCG1 in mice, despite severe plasma hypocholesterolemia, leads to massive lipid accumulation and foam cell formation of tissue macrophages. A complete ablation of cellular cholesterol efflux in vitro is observed, whereas in vivo macrophage-specific reverse cholesterol transport to the feces is markedly decreased. Despite the massive foam cell formation of tissue macrophages, no lipid accumulation was observed in the vascular wall, even in mice of 1 year old, indicating that the double knockout mice, possibly because of their hypocholesterolemia, lack the trigger to attract macrophages to the vessel wall. In conclusion, even under hypocholesterolemic conditions macrophages can be converted into foam cells, and ABCA1 and ABCG1 play an essential role in the prevention of foam cell formation.     

Absence of CD36 protects against atherosclerosis in ApoE knock-out mice with no additional protection provided by absence of scavenger receptor A I/II

AIMS: The role of scavenger receptors in atherogenesis is controversial as a result of conflicting reports and a recent hypothesis suggesting that scavenger receptor absence would enhance the pro-inflammatory, pro-atherogenic milieu. This study addresses the effect of combined absence of scavenger receptors CD36 and SRA I/II on atherosclerosis lesion development in the apolipoprotein E knock-out (apoE degrees ) model. METHODS: We created background-related strains of apoE degrees , scavenger receptor A I/II knock-out (SRA degrees )/apoE degrees , CD36 knock-out (CD36 degrees )/apoE degrees , and CD36 degrees /SRA degrees /apoE degrees mice that were >99% C57Bl/6. Four-week-old mice were fed a Western diet for 12 weeks and were assessed for lesion burden/morphology, risk factors for atherosclerosis, inflammatory mediators, and macrophage function. RESULTS: There was a 61 and 74% decrease in total aortic lesion area in CD36 degrees /apoE degrees males and females, respectively, compared with apoE degrees controls. The absence of SRA was protective (32% decrease in lesion) in female mice. The combined absence of CD36 and SRA provided no further protection in either gender. Macrophages from mice lacking CD36 had decreased pro-inflammatory characteristics and less migration to a pro-inflammatory stimulus. Plasma levels of cytokines/chemokines showed that CD36 degrees /apoE degrees and CD36 degrees /SRA degrees /apoE degrees mice had a less pro-inflammatory phenotype compared with apoE degrees and SRA degrees /apoE degrees mice. Oblivious mice in the apoE degrees background ruled out potential 'passenger gene' effects in the case of CD36. CONCLUSION: These results provide new insights into the pro-atherogenic mechanisms of CD36 by implicating processes other than modified lipoprotein uptake.     

Hyperalgesia, anxiety, and decreased hypoxic neuroprotection in mice lacking the adenosine A1 receptor

Caffeine is believed to act by blocking adenosine A(1) and A(2A) receptors (A(1)R, A(2A)R), indicating that some A(1) receptors are tonically activated. We generated mice with a targeted disruption of the second coding exon of the A(1)R (A(1)R(-/-)). These animals bred and gained weight normally and had a normal heart rate, blood pressure, and body temperature. In most behavioral tests they were similar to A(1)R(+/+) mice, but A(1)R(-/-) mice showed signs of increased anxiety. Electrophysiological recordings from hippocampal slices revealed that both adenosine-mediated inhibition and theophylline-mediated augmentation of excitatory glutamatergic neurotransmission were abolished in A(1)R(-/-) mice. In A(1)R(+/-) mice the potency of adenosine was halved, as was the number of A(1)R. In A(1)R(-/-) mice, the analgesic effect of intrathecal adenosine was lost, and thermal hyperalgesia was observed, but the analgesic effect of morphine was intact. The decrease in neuronal activity upon hypoxia was reduced both in hippocampal slices and in brainstem, and functional recovery after hypoxia was attenuated. Thus A(1)Rs do not play an essential role during development, and although they significantly influence synaptic activity, they play a nonessential role in normal physiology. However, under pathophysiological conditions, including noxious stimulation and oxygen deficiency, they are important.     

氧化低密度脂蛋白、荷叶生物碱对THP-1巨噬细胞源性泡沫细胞ABCA1表达的影响

目的：了解不同浓度氧化低密度脂蛋白（ox-LDL）及荷叶生物碱对THP-1巨噬细胞源性泡沫细胞三磷酸腺苷结合盒转运蛋白A1（ABCA1）表达的影响。方法：用佛波酯（PMA）诱导THP-1源性单核细胞分化为巨噬细胞：以不同浓度的ox-LDL孵育其24h;50mg/L的ox-LDL孵育使该细胞成为泡沫细胞,再以不同浓度荷叶生物碱对其进行干预24h。以PCR和蛋白质免疫印迹法（Western blot）分别检测不同浓度ox-LDL及荷叶生物碱干预下各组细胞ABCA1的表达。以油红O染色观察各组细胞。结果：镜下：ox-LDL处理组细胞内脂滴的大小与多少随着ox-LDL的浓度的增加而增加;随荷叶生物碱浓度的升高而减少。ABCA1mRNA表达量：ox-LDL各组的表达量均较空白对照组明显升高[25mg/L组：（1.4677±0.0907）,50mg/L组：（2.0510±0.1065）,100 mg/L组：（1.5356±0.0903）比0mg/L组：（1.00）,P均〈0.05],荷叶生物碱各组细胞的表达量[荷叶生物碱25mg/L：（1.0460±0.0580）,50mg/L：（0.8391±0.0661）,100mg/L：（1.1003±0.0752）]表达量均较单纯50mg/L ox-LDL干预组（0.5136±0.0632）明显升高（P均〈0.05）。ABCA1蛋白的表达与ABCA1mRNA表达水平改变相一致。结论：ox-LDL可上调PMA诱导的THP-1单核细胞源性巨噬细胞内ABCA1的表达,使其细胞内脂质蓄积。荷叶生物碱既使上述细胞内ABCA1表达上调,又使其细胞内脂质蓄积减少。     

CER-001, a HDL-mimetic,stimulates the reverse lipid transport and atherosclerosis regression in high cholesterol diet-fed LDL-receptor deficient mice

Objective

CER-001 is a novel engineered HDL-mimetic comprised of recombinant human apoA-I and phospholipids that was designed to mimic the beneficial properties of nascent pre-β HDL. In this study, we have evaluated the capacity of CER-001 to perform reverse lipid transport in single dose studies as well as to regress atherosclerosis in LDLr^−/− mice after short-term multiple-dose infusions.

Approach and results

CER-001 induced cholesterol efflux from macrophages and exhibited anti-inflammatory response similar to natural HDL. Studies with HUVEC demonstrated CER-001 at a concentration of 500 μg/mL completely suppressed the secretion of cytokines IL-6, IL-8, GM-CSF and MCP-1. Following infusion of CER-001 (10 mg/kg) in C57Bl/6J mice, we observed a transient increase in the mobilization of unesterified cholesterol in HDL particles containing recombinant human apoA-I. Finally we show that cholesterol elimination was stimulated in CER-001 treated animals as demonstrated by the increased cholesterol concentration in liver and feces. In a familial hypercholesterolemia mouse model (LDL-receptor deficient mice), the infusion of CER-001 caused 17% and 32% reductions in plaque size, 17% and 23% reductions in lipid content after 5 and 10 doses given every 2 days, respectively. Also, there was an 80% reduction in macrophage content in the plaque following 5 doses, and decreased VCAM-1 expression by 16% and 22% in the plaque following 5 and 10 intravenous doses of CER-001, respectively.

Conclusion

These data demonstrate that CER-001 rapidly enhances reverse lipid transport in the mouse, reducing vascular inflammation and promoting regression of diet-induced atherosclerosis in LDLr^−/− mice upon a short-term multiple dose treatment.     

短时重复游泳调节SAM8鼠AMPA受体GluR1亚单位的磷酸化

目的观察短时重复游泳训练对SAM鼠AMPA受体GluR1亚单位磷酸化的影响,探讨运动改善脑功能的可能机制。方法选取3月龄SAMP8(prone/8)亚系为研究对象,运动模型采用2 w游泳方案:2次/d,每次6 min的游泳,结束后给予浴巾擦干放回鼠笼;对照组则在相同时间每天给予两次相同的浴巾安抚刺激。采用Western印迹方法,检测SAM8鼠海马和皮层AMPA受体GluR1亚单位Ser831和Ser 845位点的磷酸化水平的变化。结果 SAMP8海马、皮层中AMPA受体GluR1亚单位Ser831和Ser845磷酸化水平与对照组相比均增加(P<0.05)。结论 2 w的短时间重复游泳运动作为一种应激诱导剂促进了AMPA受体的活化,这可能是运动改善脑功能的机制之一。     

三磷酸腺苷结合盒转运体A1的组织特异性功能与动脉粥样硬化

动脉粥样硬化是一种脂质沉积引发的慢性血管炎症。动脉粥样硬化的发生发展与细胞胆固醇稳态的破坏密切相关。三磷酸腺苷结合盒转运体A1(ABCA1)介导了细胞胆固醇流出至载脂蛋白AⅠ、preβ高密度脂蛋白(HDL)和HDL₃。当该通路胆固醇流出障碍可致细胞内胆固醇沉积。更重要的是,ABCA1的功能障碍还影响着动脉粥样硬化斑块的生长及临床冠心病的发生。最近研究显示ABCA1对动脉粥样硬化的调控作用具有组织特异性。本文介绍了胆固醇逆向转运与动脉粥样硬化的相关性,并着重讨论了ABCA1的组织特异性功能及其调控动脉粥样硬化的作用和机制。     

Effect of human scavenger receptor class A overexpression in bone marrow-derived cells on cholesterol levels and atherosclerosis in ApoE-deficient mice

In the arterial wall, scavenger receptor class A (SRA) is implicated in pathological lipid deposition. In contrast, in the liver, SRA is suggested to remove modified lipoproteins from the circulation, thereby protecting the body from their pathological action. The role of SRA on bone marrow-derived cells in lipid metabolism and atherogenesis was assessed in vivo by transplantation of bone marrow cells overexpressing human SRA (MSR1) to apoE-deficient mice. In vitro studies with peritoneal macrophages from the transplanted mice showed that macrophage scavenger receptor function, as measured by cell association and degradation studies with acetylated LDL, was approximately 3-fold increased on overexpression of MSR1 in bone marrow-derived cells as compared with control mice. Despite the increased macrophage scavenger receptor function in vitro, no significant effect of MSR1 overexpression in bone marrow-derived cells on the in vivo atherosclerotic lesion development was found. In addition to arterial wall macrophages, liver sinusoidal Kupffer cells also overexpress MSR1 after bone marrow transplantation, which may scavenge atherogenic particles more efficiently from the blood compartment. Introduction of bone marrow cells overexpressing human MSR1 in apoE-deficient mice induced a significant reduction in serum cholesterol levels of approximately 20% (P:<0.001, 2-way ANOVA) as the result of a decrease in VLDL cholesterol. It is suggested that the reduction in VLDL cholesterol levels is due to increased clearance of modified lipoproteins by the overexpressed MSR1 in Kupffer cells of the liver, thereby protecting the arterial wall against the proatherogenic action of modified lipoproteins.     

High density lipoprotein deficiency and foam cell accumulation in mice with targeted disruption of ATP-binding cassette transporter-1

Recently, the human ATP-binding cassette transporter-1 (ABC1) gene has been demonstrated to be mutated in patients with Tangier disease. To investigate the role of the ABC1 protein in an experimental in vivo model, we used gene targeting in DBA-1J embryonic stem cells to produce an ABC1-deficient mouse. Expression of the murine Abc1 gene was ablated by using a nonisogenic targeting construct that deletes six exons coding for the first nucleotide-binding fold. Lipid profiles from Abc1 knockout (-/-) mice revealed an approximately 70% reduction in cholesterol, markedly reduced plasma phospholipids, and an almost complete lack of high density lipoproteins (HDL) when compared with wild-type littermates (+/+). Fractionation of lipoproteins by FPLC demonstrated dramatic alterations in HDL cholesterol (HDL-C), including the near absence of apolipoprotein AI. Low density lipoprotein (LDL) cholesterol (LDL-C) and apolipoprotein B were also significantly reduced in +/- and -/- compared with their littermate controls. The inactivation of the Abc1 gene led to an increase in the absorption of cholesterol in mice fed a chow or a high-fat and -cholesterol diet. Histopathologic examination of Abc1-/- mice at ages 7, 12, and 18 mo demonstrated a striking accumulation of lipid-laden macrophages and type II pneumocytes in the lungs. Taken together, these findings demonstrate that Abc1-/- mice display pathophysiologic hallmarks similar to human Tangier disease and highlight the capacity of ABC1 transporters to participate in the regulation of dietary cholesterol absorption.