Tributyltin chloride induces ABCA1 expression and apolipoprotein A-I-mediated cellular cholesterol efflux by activating LXRα/RXR

Organotins, including tri-butyltin chloride (TBTC), are widely used in agricultural and chemical industries and cause persistent and widespread pollution. TBTC has been shown to activate nuclear receptor retinoid X receptor (RXR)/PPARγ signaling by interacting with RXR to modulate adipogenesis. However, whether TBTC affects liver X receptor (LXR)/RXR activity and subsequently the expression of cholesterol mobilizing genes is not known. In this study, we evaluated the ability of TBTC to activate LXR/RXR and ABC transporter A1 (ABCA1) expression. ABCA1 plays a critical role in HDL generation, maintaining cholesterol homeostasis, and cholesterol accumulation-induced diseases, such as atherosclerosis and pancreatic islet dysfunction. In a reporter gene assay, TBTC activated LXRα/RXR but not LXRβ/RXR. In mouse macrophage RAW264 cells, TBTC activated the ABCA1 promoter in an LXR-responsive element dependent manner and increased ABCA1 mRNA expression. TBTC augmented ABCA1 protein levels and apolipoprotein A-I-dependent cellular cholesterol efflux (HDL generation). The LXR-target fatty acid synthase and Spα mRNA levels were also increased by TBTC exposure. We conclude that TBTC has the ability to activate permissive LXRα/RXR signaling and thereby modulate cellular cholesterol efflux.     

Tributyltin chloride induces ABCA1 expression and apolipoprotein A-I-mediated cellular cholesterol efflux by activating LXRalpha/RXR

Organotins, including tri-butyltin chloride (TBTC), are widely used in agricultural and chemical industries and cause persistent and widespread pollution. TBTC has been shown to activate nuclear receptor retinoid X receptor (RXR)/PPARγ signaling by interacting with RXR to modulate adipogenesis. However, whether TBTC affects liver X receptor (LXR)/RXR activity and subsequently the expression of cholesterol mobilizing genes is not known. In this study, we evaluated the ability of TBTC to activate LXR/RXR and ABC transporter A1 (ABCA1) expression. ABCA1 plays a critical role in HDL generation, maintaining cholesterol homeostasis, and cholesterol accumulation-induced diseases, such as atherosclerosis and pancreatic islet dysfunction. In a reporter gene assay, TBTC activated LXRα/RXR but not LXRβ/RXR. In mouse macrophage RAW264 cells, TBTC activated the ABCA1 promoter in an LXR-responsive element dependent manner and increased ABCA1 mRNA expression. TBTC augmented ABCA1 protein levels and apolipoprotein A-I-dependent cellular cholesterol efflux (HDL generation). The LXR-target fatty acid synthase and Spα mRNA levels were also increased by TBTC exposure. We conclude that TBTC has the ability to activate permissive LXRα/RXR signaling and thereby modulate cellular cholesterol efflux.     

Oxidized LDL upregulated ATP binding cassette transporter-1 in THP-1 macrophages

INTRODUCTIONOxidized lipid signaling in macrophages is centralto the pathogenesis of atherosclerosis[1]. Exposure ofmacrophages and other vascular cells to oxidized low-density lipoprotein (ox-LDL) leads to complex changesin gene expression that are collectively thought to influ-ence the development of the atherosclerotic lesion[2].Using two-dimensional gel electrophoresis, the overallprotein map in U937 control cells and U937 foam cellswas obtained. Compared with U937 cells, 37 spots…     

ABCA1 is Necessary for Bexarotene-Mediated Clearance of Soluble Amyloid Beta from the Hippocampus of APP/PS1 Mice

Alzheimer’s disease (AD) is characterized by impaired clearance of amyloid beta (Aβ) peptides, leading to the accumulation of Aβ in the brain and subsequent neurodegeneration and cognitive impairment. ApoE plays a critical role in the proteolytic degradation of soluble forms of Aβ. This effect is dependent upon lipidation of ApoE by ABCA1-mediated transfer of phospholipids and cholesterol. ApoE and ABCA1 are induced by the action of the RXR agonist, bexarotene. We have previously shown that bexarotene reduces Aβ levels in AD mouse models and we have hypothesized that this effect requires ABCA1-mediated lipidation of ApoE. To test this hypothesis, we crossed ABCA1-deficient (ABCA1 KO) mice with the APP/PS1 model of AD. Aged ABCA1 WT and ABCA1 KO APP/PS1 mice were treated for 7 days with vehicle or bexarotene (100 mg/kg/day). Bexarotene reduced levels of soluble Aβ 1–40 and 1–42 in the hippocampus of ABCA1 WT but not ABCA1 KO APP/PS1 mice. In contrast, insoluble levels of Aβ, and plaque loads were unaffected by bexarotene in this study. ABCA1 KO mice had increased levels of inflammation compared with ABCA1 WT mice. Bexarotene also increased most inflammatory gene markers evaluated. The effect of bexarotene on microglial inflammatory profiles, however, was independent of ABCA1 genotype. Importantly, bexarotene ameliorated deficits in novel object recognition in ABCA1 WT but not ABCA1 KO APP/PS1 mice. These data indicate that ABCA1-induced lipidation of ApoE is necessary for the ability of bexarotene to clear hippocampal soluble Aβ and ameliorate cognitive deficits.     

Novel approaches to treating cardiovascular disease: lessons from Tangier disease

Atherosclerotic cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in Western societies. Although cholesterol is a major CVD risk factor, therapeutic interventions to lower plasma cholesterol levels have had limited success in reducing coronary events. Thus, novel approaches are needed to reduce or eliminate CVD. A potential therapeutic target is a newly discovered ATP binding cassette transporter called ABCA1, a cell membrane protein that is the gateway for secretion of excess cholesterol from macrophages into the high density lipoprotein (HDL) metabolic pathway. Mutations in ABCA1 cause Tangier disease, a severe HDL deficiency syndrome characterised by accumulation of cholesterol in tissue macrophages and prevalent atherosclerosis. Studies of Tangier disease heterozygotes revealed that the relative activity of ABCA1 determines plasma HDL levels and susceptibility to CVD. Drugs that induce ABCA1 in mice increase clearance of cholesterol from tissues and inhibit intestinal absorption of dietary cholesterol. Thus, ABCA1-stimulating drugs have the potential to both mobilise cholesterol from atherosclerotic lesions and eliminate cholesterol from the body. By reducing plaque formation and rupture independently of the atherogenic factors involved, these drugs would be powerful agents for treating CVD.     

ATP-binding cassette transporters A1 and G1, HDL metabolism, cholesterol efflux, and inflammation: important targets for the treatment of atherosclerosis

Atherosclerosis has been characterized as a chronic inflammatory response to cholesterol deposition in arteries. Plasma high density lipoprotein (HDL) levels bear a strong independent inverse relationship with atherosclerotic cardiovascular disease. One central antiatherogenic role of HDL is believed to be its ability to remove excessive peripheral cholesterol back to the liver for subsequent catabolism and excretion, a physiologic process termed reverse cholesterol transport (RCT). Cholesterol efflux from macrophage foam cells, the initial step of RCT is the most relevant step with respect to atherosclerosis. The ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 play crucial roles in the efflux of cellular cholesterol to HDL and its apolipoproteins. Moreover, ABCA1 and ABCG1 affect cellular inflammatory cytokine secretion by modulating cholesterol content in the plasma membrane and within intracellular compartments. In humans, ABCA1 mutations can cause a severe HDL-deficiency syndrome characterized by cholesterol deposition in tissue macrophages and prevalent atherosclerosis. Disrupting Abca1 or Abcg1 in mice promotes accumulation of excessive cholesterol in macrophages, and physiological manipulation of ABCA1 expression affects atherogenesis. Here we review recent advances in the role of ABCA1 and ABCG1 in HDL metabolism, macrophage cholesterol efflux, inflammation, and atherogenesis. Next, we summarize the structure, expression, and regulation of ABCA1 and ABCG1. Finally, we give an update on the progress and pitfalls of therapeutic approaches that target ABCA1 and ABCG1 to stimulate the flux of lipids through the RCT pathway.     

ABC家族转运体与糖尿病

糖尿病是一种常见的全身性慢性代谢疾病,其发病过程伴随着血糖、血脂和激素水平的失调,并由此引发高血脂、动脉粥样硬化、心肌病等并发症.ABCA,ABCB,ABCC,ABCG等ABC家族转运体有可能参与糖尿病及其并发症发病机制.如ABCA1和ABCG1促使细胞内的胆固醇泵出,进入高密度脂蛋白通路,减少巨噬细胞中的胆固醇沉积,防止巨噬细胞转化为泡沫细胞;ABCG5和ABCG8抑制肠道膳食中脂类吸收,并促进胆固醇通过胆汁排泄;表达在胰岛β细胞上的ABCC8作为钾通道的调节亚基控制胰岛素的释放,维持血糖平衡;ABCB1,ABCC1-ABCC5以及ABCC2是药物转运相关的外排蛋白,影响着其底物药物的体内过程,也参与体内内源性物质的转运.上述ABC家族转运体缺失或变异有可能诱发糖尿病及其并发症;而糖尿病状态下体内环境的变化也会改变这些ABC家族转运体表达与功能,进一步加剧了病情的发展.本文讨论了糖尿病及与之相关的四类ABC家族转运体,以期深入理解两者之间的相互作用,为糖尿病研究和治疗提供新思路.     

Atorvastatin inhibits ABCA1 expression and cholesterol efflux in THP-1 macrophages by an LXR-dependent pathway

The effect of atorvastatin on adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1) expression and cholesterol efflux remains controversial. In an effort to clarify this issue, ABCA1 expression and apolipoprotein AI (apoAI)-mediated cholesterol efflux after atorvastatin treatment were investigated in THP-1 macrophages. Atorvastatin from 2 microM to 40 microM dose-dependently inhibited ABCA1 expression in human monocyte-derived macrophages and phorbol 12-myristate 13-acetate (PMA)-stimulated THP-1 monocytes. ApoAI-mediated cholesterol efflux was reduced in PMA-stimulated THP-1 cells treated with atorvastatin, this effect was abolished with acetylated low-density lipoprotein (LDL) pretreatment. Atorvastatin treatment also dose-dependently reduced liver X receptor alpha (LXRalpha) expression and Rho activation. Rho activation by farnysylpyophosphate (FPP) and lysophosphatidic acid (LPA) did not salvage, but further depressed, the cholesterol efflux and ABCA1 expression in the presence of atorvastatin. Without atorvastatin, Rho activation by mevalonate, FPP, and LPA diminished apoAI-mediated cholesterol efflux, and Rho activation by GTPgammaS also decreased ABCA1 messenger ribonucleic acid (mRNA) by 16%. Furthermore, Rho inhibition by C3 exoenzyme increased ABCA1 mRNA by 48% despite a 17% decrease in apoAI-mediated cholesterol efflux. LXRalpha agonists (T01901317 and 22(R)-hydroxycholesterol) prevented any reductions in cholesterol efflux or ABCA1 expression associated with atorvastatin treatment. Furthermore, Western blot analysis demonstrated the reciprocal inhibition of Rho and LXRalpha. In conclusion, atorvastatin decreases ABCA1 expression in noncholesterol-loaded macrophages in an LXRalpha- but not Rho-dependent pathway; this effect can be compromised after acetylated LDL cholesterol loading.     

mRNA expression of the ATP-binding cassette transporter subfamily A (ABCA) in rat and human brain capillary endothelial cells

The ATP-binding cassette transporter subfamily A (ABCA) consists of the transporters mediating cholesterol release and regulated by cholesterol. As about 25% of total body cholesterol exists in the brain, sterol homeostasis is an important issue as far as central nervous system function is concerned. The purpose of this study was to clarify the mRNA expression of ABCA subtypes at the blood-brain barrier (BBB) using cultured rat and human brain capillary endothelial cells, TR-BBB and hBME cells, respectively. mRNA expression of ABCA1, 2, 3, 4, 5, 6, 7 and 8/9 was detected in TR-BBB cells. In the brain capillary-rich fraction, mRNA expression of ABCA1, 2, 3, 4, 5, 7 and 8/9 was detected. ABCA2 and 5 mRNA were also detected in hBME cells. These results demonstrate, for the first time, that ABCA subtypes are expressed at the rat and/or human BBB. The expression of ABCA subtypes at the BBB is likely to contribute to sterol homeostasis in the central nervous system.     

ATP binding cassette transporter A1 (ABCA1) associated proteins: potential drug targets in the metabolic syndrome and atherosclerotic disease?

The metabolic syndrome is defined as a cluster of disorders including visceral obesity, insulin resistance, hypertension, hypertriglyceridemia and low HDL. Patients have an increased risk to develop atherosclerotic disease characterized by excessive macrophage cholesterol deposition in the vascular wall. HDL removes excess cellular cholesterol which is subsequently transported to the liver for biliary excretion and thereby preserves cholesterol homeostasis. Circulating HDL levels are maintained by hepatic ATP-binding cassette transporter A1 (ABCA1) which also transports peripheral cell cholesterol to extracellular lipid acceptors. Lipid export activity of ABCA1 improves pancreatic -cell function and ameliorates insulin release. ABCA1 affects plasma membrane cholesterol distribution and formation of lipid rafts representing signalling platforms for diverse receptors including toll-like receptor 4 (TLR4). Pharmacological activation of ABCA1 pathways presumably progresses metabolic diseases, and current approaches demonstrate beneficial effects of small peptides mimicking ABCA1 ligands which stabilize ABCA1 and enhance lipid efflux similar to its physiological acceptor apolipoprotein A-I. Research of the last decade has resulted in the identification of several ABCA1 binding proteins influencing ABCA1 signalling, stability and activity. In the current review the proteins suggested to form a complex with ABCA1 are summarized and their up to now characterized features towards ABCA1 functions are described.     

糖肾方抑制TGF-β1/Smad3通路促进小鼠肾小管上皮细胞胆固醇流出

目的:利用高糖诱导的小鼠肾小管上皮细胞(mouse tubular epithelial cells,mTECs)观察中药糖肾方颗粒及Smad3抑制剂SIS3对于TGF-β1/Smad3通路及细胞胆固醇流出通路的影响。方法:25 mmol/L高糖诱导mTECs细胞后,分别给予糖肾方及Smad3抑制剂SIS3干预,利用ELISA试剂盒检测细胞中脂质含量,利用Western blot和Real-time PCR检测细胞中TGF-β1/Smad3通路及过氧化物酶体增殖物激活受体γ共激活因子1α(peroxisome proliferator-activated receptorγcoactivator 1α,PGC-1α)、肝脏X受体(liver X receptor,LXR)、ATP-结合盒转运蛋白A1(ABCA1)、ATP-结合盒转运蛋白G1(ABCG1)的表达。结果:糖肾方可以降低高糖诱导mTECs细胞中总胆固醇(total cholesterol,TC)、甘油三酸酯(triglyceride,TG)、低密度脂蛋白胆固醇(low-density lipoprotein cholesterol,LDL-C)含量,上调高密度脂蛋白胆固醇(high-density lipoprotein cholesterol,HDL-C)含量(P<0.05);糖肾方及Smad3抑制剂SIS3可下调高糖诱导mTECs细胞中TGF-β1、Smad3、CollagenⅠ和Fibronectin的表达,上调PGC-1α、LXR、ABCA1、ABCG1的表达(P<0.05)。结论:糖肾方可通过抑制TGF-β1/Smad3信号通路促进细胞胆固醇流出,减轻肾损害。     

ABCA1 as a New Therapeutic Target for Treating Cardiovascular Disease

Atherosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in western societies. Although cholesterol is a major cardiovascular disease risk factor, therapeutic interventions to lower plasma cholesterol levels have had limited success in reducing coronary events, underscoring the need for other treatment strategies. A promising therapeutic target is an ATP binding cassette transporter called ABCA1, a cell membrane protein that is the gatekeeper for secretion of excess cholesterol from macrophages into the high-density lipoprotein (HDL) metabolic pathway. Mutations in ABCA1 cause Tangier disease, a severe HDL-deficiency syndrome characterized by accumulation of cholesterol in tissue macrophages and prevalent atherosclerosis. Thus, ABCA1-activating drugs have the potential to mobilize cholesterol from macrophages of atherosclerotic lesions, making them powerful agents for preventing and reversing cardiovascular disease. (c) 2002 Prous Science. All rights reserved.     

Angiotensin‐(1–7) upregulates expression of adenosine triphosphate‐binding cassette transporter A1 and adenosine triphosphate‐binding cassette transporter G1 through the Mas receptor through the liver X receptor alpha signalling pathway in THP‐1 macrophages treated with angiotensin‐II

Adenosine triphosphate‐binding cassette transporter A1 (ABCA1) and ABCG1 play crucial roles in reverse cholesterol transport, and have anti‐atherosclerosis effects, and liver X receptor alpha (LXRα) can stimulate cholesterol efflux through these transporters. Angiotensin (Ang)‐(1–7) can protect endothelial cells, inhibit smooth muscle cell growth, ameliorate inflammation and exert anti‐atherosclerotic effects. In the present study, we attempted to clarify the effect of Ang‐(1–7) on expression of ABCA1 and ABCG1, and explored the role of LXRα in the regulation of ABCA1 and ABCG1 in THP‐1 macrophages that had been incubated with angiotensin‐II (AngII). Ang‐(1–7) increased ABCA1 and ABCG1 expression in a concentration‐dependent manner at both the mRNA and protein levels, promoted cholesterol efflux, and decreased cholesterol content in THP‐1 macrophages treated with AngII. Furthermore, Ang‐(1–7) upregulated the expression of LXRα in a concentration‐dependent manner in these cells. LXRα small interfering RNA, as well as the Mas receptor antagonist A‐779, completely abolished these effects of Ang‐(1–7). In summary, Ang‐(1–7) upregulates ABCA1 and ABCG1 expression in THP‐1 macrophages treated with AngII through the Mas receptor, via the LXRα pathway. This novel insight into the molecular mechanism underlying Ang‐(1–7) and AngII interaction could prove useful for developing new strategies for treatment of cardiovascular diseases.     

人膜转运蛋白ABCA1表达上调剂的筛选与鉴定

人ATP结合盒转运体A1(ATP-binding cassette transporter A1,ABCA1)可介导细胞内磷脂和游离胆固醇转运至贫脂或无脂的载脂蛋白A-I(apolipoprotein A-I,apoA-I),从而促进高密度脂蛋白(high density lipoprotein,HDL)生成,启动胆固醇逆转运过程,在机体清除多余脂质的过程中发挥重要作用。因此,本研究以ABCA1为靶点,前期建立了ABCA1上调剂抗动脉粥样硬化(atherosclerosis,AS)药物筛选模型,以期寻找具有新作用机制的抗AS药物。在此研究中,利用该模型对1 600个化合物进行筛选,发现2030421B上调活性大于50%,其EC50为0.50μg.mL-1。进一步研究发现,2030421B不仅能上调ABCA1的mRNA以及蛋白水平,而且能使小鼠巨噬细胞RAW264.7内胆固醇流出增加,脂滴量减少,是具有较好效果的ABCA1上调剂。     

脂联素对巨噬细胞源性泡沫细胞ABCA1及胆固醇含量的影响及机制

目的探讨脂联素对RAW264.7巨噬细胞源性泡沫细胞ABCA1及胆固醇含量的影响及其可能的机制。方法体外培养RAW264.7细胞,加入20 mg/L氧化低密度脂蛋白(ox-LDL)共同孵育48 h,将其诱导成泡沫细胞,加入不同浓度(0、1、5、10μg/mL)的脂联素干预24 h,RT-PCR测定ABCA1 mRNA的表达,高效液相色谱测定细胞内胆固醇含量。观察脂联素对泡沫细胞中ABCA1表达的影响。结果脂联素显著增加RAW264.7巨噬细胞源性泡沫细胞ABCA1 mRNA的表达(P<0.05),并增加细胞内胆固醇含量,且呈浓度依赖性(P<0.05)。结论脂联素可以增加巨噬源性泡沫细胞ABCA1转录水平,促进胆固醇流出,延缓AS的发生发展。     

ABCA1: regulation,function and relationship to atherosclerosis

Since the identification of mutations in the ATP-binding cassette transporter (ABCA1), the relationship between ABCA1 expression, cholesterol efflux, high-density lipoprotein (HDL) biosynthesis and cholesterol homeostasis has been a subject of intense investigation. Several studies have provided significant new information with regards to pathways controlling ABCA1 expression and activity and established that this transporter facilitates the efflux of cholesterol and phospholipids to apoprotein acceptors, leading to the formation of nascent HDL particles. Although ABCA1 appears to play a critical role in cholesterol flux from tissues, and despite a considerable interest in developing pharmacological agents that increase ABCA1 activity, the role of ABCA1 in preventing atherosclerosis remains unclear.     

High-density lipoproteins and ATP-binding cassette transporters as targets for cardiovascular drug therapy

The recently identified lipid-regulated group of ATP-binding cassette (ABC) transporters acts in various cells and tissues that are important for total body lipid homeostasis. ABCA1 and ABCG1 are key regulators of high-density lipoprotein (HDL) metabolism, acting as protective factors against the development of atherosclerosis. Recent data regarding how these ABC transporters control cholesterol and phospholipid homeostasis have provided valuable insights into the mechanisms of mRNA and protein expression, intracellular trafficking, surface membrane localization and interaction with binding partners and lipoproteins. These studies have identified several potential new targets, including nuclear receptors, ABCA1-interactive proteins and apolipoprotein A-I mimetics, which could be promising tools for raising HDL levels and improving the pharmacological treatment of cardiovascular disease.