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.     

PPARγ overexpression regulates cholesterol metabolism in human L02 hepatocytes

Peroxisome proliferator-activator receptor (PPAR) γ is a nuclear hormone receptor that regulates glucose homeostasis, lipid metabolism, and adipocyte function. It has been shown that activation of PPARγ can reduce the incidence of gallstone. Herein we aimed to clarify the role of PPARγ in the reduction of gallstones. The plasmid containing the coding sequence of PPARγ was constructed and transfected in the human liver cell line (L02 cells). Western blot and RT-PCR were used to detect hydroxyl-methyl-glutaryl-CoA reductase (HMGCR), sterol regulatory element-binding proteins 2 (SREBP2), 7α-hydroxylase (CYP7A1), adenosine triphosphate-binding cassette (ABC) sterol transporters G5 and G8 (ABCG5, ABCG8) and liver X receptor α (LXRα). The Amplex Red cholesterol assay kit was used to detect the intracellular or extracellular cholesterol level. Our data showed that PPARγ overexpression caused significant decreases in both extracellular and intracellular cholesterol in the L02 cells. The further studies indicated PPARγ overexpression substantially decreased expression of HMGCR and SREBP-2, increased expression of CYP7A1, ABCG5, ABCG8 and LXRα. These results indicated that upregulation of PPARγ may reduce cholesterol levels through multiple-pathways including HMGCR/SREBP2-mediated biosynthesis, CYP7A1-mediated transformation, and ABCG5/ABCG8-mediated efflux. We thus suggest that PPARγ might have beneficial effects for cholesterol gallstones diseases.     

载脂蛋白嵌合模拟肽对巨噬细胞胆固醇流出的影响

目的观察载脂蛋白嵌合模拟肽Ac-hE-18A-NH2对RAW264.7巨噬细胞胆固醇流出的影响,并探讨其机制。方法 RAW264.7巨噬细胞种植于24孔板,用0.5μCi/孔3H-胆固醇和含50mg·mL-1氧化低密度脂蛋白共同孵育24h之后,给予不同浓度的Ac-hE-18A-NH2(0～100mg·mL-1)干预24h,收集细胞用液体闪烁计数法检测胆固醇流出。采用ELISA测定细胞内cAMP含量,采用实时荧光定量PCR及Westernblot检测ABCA1、LXRα和PPARγ的mRNA及蛋白表达。结果 Ac-hE-18A-NH2以浓度依赖方式介导胆固醇流出;50mg·mL-1Ac-hE-18A-NH2干预不同时间,其介导的胆固醇流出率分别为(10.86±1.46)%(6h),(13.43±1.55)%(12h),(20.58±1.34)%(18h),和(26.93±4.37)%(24h)。同时,Ac-hE-18A-NH2还以浓度依赖方式增加细胞内cAMP水平,上调ABCA1、LXRα和PPARγmR-NA和蛋白表达。加用cAMP刺激剂8-Br-cAMP,Ac-hE-18A-NH2介导的胆固醇流出率由26.93±4.37增加至35.81±2.73,ABCA1mRNA表达增加了66.67%。而加用PPARγ特异性抑制剂预处理细胞后,PPARγ的表达几乎完全抑制,ABCA1和LXRα的表达也受到一定程度抑制,Ac-hE-18A-NH2介导的胆固醇流出率明显减少。结论模拟肽Ac-hE-18A-NH2可以明显促进巨噬细胞胆固醇流出,其机制可能与cAMP-ABCA1和PPARγ-LXRα-ABCA1两种途径有关。     

Valsartan and telmisartan abrogate angiotensin II-induced downregulation of ABCA1 expression via AT1 receptor, rather than AT2 receptor or PPARγ activation

The possible pharmacological mechanism by which partial PPARγ-activating angiotensin II (Ang II) type 1 receptor blocker (ARB) telmisartan and non-PPARγ-activating ARB valsartan reverse Ang II-suppressed ABCA1 expression is still unclear. In this study, human monocyte-derived THP-1 cells were differentiated into macrophages. Cells were treated with various concentrations of Ang II alone or with Ang II and various drugs including highly selective ARB valsartan, partial PPARγ-activating ARB telmisartan, angiotensin II type 2 (AT2) receptor blocker PD123319, full PPARγ agonist pioglitazone, and PPARγ antagonist GW9662, respectively. After treatment, messenger RNA and protein expressions of ABCA1 and ABCG1 were analyzed by real-time polymerase chain reaction and Western blotting, respectively. ABCA1 expression was remarkably suppressed by Ang II at both messenger RNA and protein levels in a dose-dependent manner in THP-1-derived macrophages, whereas ABCG1 expression was not affected. Valsartan and telmisartan could both reverse the downregulation of Ang II on ABCA1 expression. Such effects were not affected by either AT2 receptor blocker PD123319 or PPARγ antagonist GW9662. Our findings suggest that the effect of Ang II on ABCA1 expression should be mediated by the AT1 receptor. Both valsartan and telmisartan abrogate Ang II-induced downregulation of ABCA1 expression mainly through AT1 receptor rather than through AT2 receptor or PPARγ-dependent pathway.     

Tanshinone IIA attenuates atherosclerosis in ApoE mice through down-regulation of scavenger receptor expression

This study is designed to investigate the protection of tanshinone IIA (TSIIA) against atherosclerosis in apolipoprotein E deficient (ApoE^−/−) mice and to explore the mechanisms by focusing on the expressions of scavenger receptors, scavenger receptor-A (SR-A) and CD36. The in vivo study demonstrated that TSIIA (10–90 mg/kg) inhibited the atherosclerotic lesions, down-regulated the CD68 protein expression in lesion and decreased the contents of cholesterol in aortas of ApoE^−/− mice. In addition, TSIIA reduced the serum levels of oxidized LDL (oxLDL) and down-regulated the mRNA expression of CD36, SR-A and peroxisome proliferator-activated receptor gamma (PPARγ) in aortas. The in vitro study showed that TSIIA (0.1–10 μM) decreased cholesterol level and DiI-oxLDL uptake in mouse peritoneal macrophages treated with oxLDL (50 μg/ml). In addition, TSIIA down-regulated the mRNA and protein expression of CD36 but not that of SR-A in oxLDL treated macrophages. TSIIA also down-regulated the mRNA expression of PPARγ in oxLDL treated macrophages. Furthermore, TSIIA reduced the mRNA expression of CD36 in macrophages treated with PPARγ agonist 15d-PGJ₂ (2 μM) or troglitazone (50 μM), whereas both 15d-PGJ₂ (0.5–1.5 μM) and troglitazone (5–20 μM) dose-dependently abolished the down-regulation of CD36 expression by TSIIA in oxLDL treated macrophages. These results suggest that TSIIA attenuates the atherosclerotic lesion in ApoE^−/− mice, which might be attributed to the properties of both anti-oxidation and down-regulation of scavenger receptors. Furthermore, antagonism of PPARγ might be involved in the down-regulation of CD36 by TSIIA.     

A role of peroxisome proliferator‐activated receptor γ in non‐alcoholic fatty liver disease

Non‐alcoholic fatty liver disease is becoming a major health burden, as prevalence increases and there are no approved treatment options. Thiazolidinediones target the nuclear receptor peroxisome proliferator‐activated receptor γ (PPARγ) and have been investigated in several clinical trials for their potential in treating non‐alcoholic fatty liver disease (NAFLD) and non‐alcoholic steatohepatitis (NASH). PPARγ has specialized roles in distinct tissues and cell types, and although the primary function of PPARγ is in adipose tissue, where the highest expression levels are observed, hepatic expression levels of PPARγ are significantly increased in patients with NAFLD. Thus, NAFLD patients receiving treatment with PPARγ agonists might have a liver response apart from the one in adipose tissue. Owing to the different roles of PPARγ, new treatment strategies include development of compounds harnessing the beneficial effects of PPARγ while restricting PPARγ unwanted effects such as adipogenesis resulting in weight gain. Furthermore, dual or pan agonists targeting two or more of the PPARs have shown promising results in pre‐clinical research and some are currently proceeding to clinical trials. This MiniReview explores adipose‐ and liver‐specific actions of PPARγ, and how this knowledge may contribute in the search for new treatment modalities in NAFLD/NASH.     

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.     

Resveratrol mediates anti-atherogenic effects on cholesterol flux in human macrophages and endothelium via PPARγ and adenosine

Resveratrol is a bioactive molecule used in dietary supplements and herbal medicines and consumed worldwide. Known cardioprotective and anti-inflammatory properties of resveratrol have spurred investigation of the mechanisms involved. The present study explored potential atheroprotective actions of resveratrol on cholesterol metabolism in cells of the arterial wall, including human macrophages and arterial endothelium. Using QRT-PCR and Western blotting techniques, we measured expression of the proteins involved in reverse cholesterol transport (ABCA1, ABCG1 and SR-B1) and the scavenger receptors responsible for uptake of modified cholesterol (CD36, SR-A1 and LOX-1). We analyzed the effect of resveratrol on apoA-1-and HDL-mediated cholesterol efflux in human THP-1 macrophages. The effect of resveratrol on oxLDL internalization and foam cell formation were evaluated using confocal and light microscopy. Our data indicate that resveratrol regulates expression of major proteins involved in cholesterol transport, promotes apoA-1 and HDL-mediated efflux, downregulates oxLDL uptake and diminishes foam cell formation. Mechanistically, resveratrol effects were dependent upon PPAR-γ and adenosine 2A receptor pathways. For the first time we demonstrate that resveratrol regulates expression of the cholesterol metabolizing enzyme cytochrome P450 27-hydroxylase, providing efficient cholesterol elimination via formation of oxysterols. This study establishes that resveratrol attenuates lipid accumulation in cultured human macrophages via effects on cholesterol transport. Further in vivo studies are needed to determine whether resveratrol may be an additional resource available to reduce lipid deposition and atherosclerosis in humans.     

Synthesis,Hypoglycaemic, Hypolipidemic and PPARγ Agonist Activities of 5‐(2‐Alkyl/aryl‐6‐Arylimidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene‐1,3‐Thiazolidinediones

A novel series of 5‐(2‐alkyl/aryl‐6‐arylimidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene‐1,3‐thiazolidinediones were synthesized as possible PPARγ agonists. The structures of these target molecules were established by spectral and analytical data. All the newly synthesized compounds were screened for their in vivo hypoglycaemic and hypolipidemic activity in male Wistar rats. Further, compounds with good activity were screened for PPARγ agonist activity. Among the screened compounds, 5‐{[2‐Cyclohexyl‐6‐(4‐methoxyphenyl)imidazo[2,1‐b] [1,3,4]thiadiazol‐5‐yl]methylene}‐1,3‐thiazolidine‐2,4‐dione (3i) exhibits promising hypoglycaemic and hypolipidemic activity via potential PPARγ agonist activity.     

The novel role and underlying mechanism of Wnt5a in regulating cellular cholesterol accumulation

Cholesterol accumulation is a critical step during the development and progression of atherosclerosis. Recently, Wnt5a expression has been found to be markedly upregulated in both murine and human atherosclerotic lesions. However, the effect and mechanism of Wnt5a in atherosclerosis is poorly understood. In the present study, we investigated the effects and potential mechanisms of Wnt5a on cholesterol accumulation during atherosclerosis. We used RAW264.7 and vascular smooth muscle cells (VSMC) treated with oxidized low‐density lipoprotein (oxLDL) as lipid‐loaded cell models. We found that expression of Wnt5a protein was increased in a concentration (25, 50, 75 and 100 μg/mL)‐ and time (24, 48 and 72 h)‐dependent manner by oxLDL treatment. To explore the underlying mechanism, we used Wnt5a short interference (si) RNA to knockdown Wnt5a expression in both RAW264.7 cells and VSMC, or applied recombinant Wnt5a (rWnt5a) to stimulate Wnt5a signalling. After Wnt5a knockdown, total cholesterol (TC) and free cholesterol (FC) content in both cell types increased significantly (P < 0.05) upon exposure to oxLDL. Conversely, the TC and FC content decreased markedly (P < 0.05) after treatment of cells with rWnt5a. More importantly, both protein and mRNA expression of Caveolin‐1 and ATP‐binding cassette transporter A1 (ABCA1) was significantly reduced after exposure of wnt5a siRNA‐treated cells to oxLDL, whereas rWnt5a treatment of cells resulted in increased Caveolin‐1 and ABCA1 protein expression after exposure of cells to oxLDL. Together, these findings demonstrate, for the first time, that Wnt5a reduces the accumulation of cholesterol in lipid‐loaded cells by regulating the mRNA expression of Caveolin‐1 and ABCA1, which are involved in reverse cholesterol transport. This may present a novel mechanism of Wnt5a‐mediated cholesterol transportation in macrophages and VSMC. Therefore, targeting the Wnt5a signalling pathway may have clinical implications in atherosclerosis.     

PPARγ activation redirects macrophage cholesterol from fecal excretion to adipose tissue uptake in mice via SR-BI

PPARγ agonists, used in the treatment of Type 2 diabetes, can raise HDL-cholesterol, therefore could potentially stimulate macrophage-to-feces reverse cholesterol transport (RCT). We aimed to test whether PPARγ activation promotes macrophage RCT in vivo. Macrophage RCT was assessed in mice using cholesterol loaded/³H-cholesterol labeled macrophages. PPARγ agonist GW7845 (20 mg/kg/day) did not change ³H-tracer plasma appearance, but surprisingly decreased fecal ³H-free sterol excretion by 43% (P < 0.01) over 48 h. Total free cholesterol efflux from macrophages to serum (collected from control and GW7845 groups) was not different, although ABCA1-mediated efflux was significantly higher with GW7845. To determine the effect of PPARγ activation on HDL cholesterol uptake by different tissues, the metabolic fate of HDL labeled with ³H-cholesteryl ether (CE) was also measured. We observed two-fold increase in HDL derived ³H-CE uptake by adipose tissue (P < 0.005) with concomitant 22% decrease in HDL derived ³H-CE uptake by the liver (P < 0.05) in GW7845 treated wild type mice. This was associated with a significant increase in SR-BI protein expression in adipose tissue, but not liver. The same experiment in SR-BI knockout mice, showed no difference in HDL derived ³H-CE uptake by adipose tissue or liver. In conclusion, PPARγ activation decreases the fecal excretion of macrophage derived cholesterol in mice. This is not due to inhibition of cholesterol efflux from macrophages, but rather involves redirection of effluxed cholesterol from liver towards adipose tissue uptake via SR-BI. This represents a novel mechanism for regulation of RCT and may extend the therapeutic implications of these ligands.     

Galectin‐3 aggravates ox‐LDL‐induced endothelial dysfunction through LOX‐1 mediated signaling pathway

Galectin‐3, a biomarker linking oxidative stress and inflammation, participates in different mechanisms related to atherothrombosis, such as inflammation, proliferation, or macrophage chemotaxis. Accumulating evidence indicates that galectin‐3 may also promote atherogenesis through inducing endothelial dysfunction. Lectin‐like oxidized low‐density lipoprotein (oxLDL) receptor‐1 (LOX‐1), a receptor for oxLDL uptake, contributes to oxLDL‐induced endothelial dysfunction. Whether galectin‐3 induces endothelial dysfunction through modulation of LOX‐1‐mediated signaling remains unclear. In the present study, we explored the mechanisms underlying galectin‐3 enhanced cytotoxicity of oxLDL in human umbilical vein endothelial cells (HUVECs) and the role of LOX‐1. Incubation of HUVECs with galectin‐3 increased the expression of LOX‐1 in RNA and protein levels. In addition, the expression of LOX‐1 induced by oxLDL was promoted by galectin‐3. However, pretreatment of LOX‐1 antibody reduced LOX‐1 mRNA expression level in cells with oxLDL plus galectin‐3 incubation. Compared to cells treated with oxLDL alone, reactive oxygen species (ROS) generation via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and subsequent activation of p38 mitogen‐activated protein kinases followed by nuclear factor kappa B (NF‐κB) activation and related inflammatory responses including adhesion molecule expression, adhesiveness of monocytic cells, and IL‐8 release were also aggravated in cells treated with galectin‐3 combined with oxLDL. Compared to cells treated with galectin‐3 plus oxLDL group. We found that LOX‐1 antibody mitigated NADPH oxidase activity, p‐38 up‐regulation, NF‐κB activation, and proinflammatory responses in cells treated with galectin‐3 combined with oxLDL. We conclude that galectin‐3 enhances endothelial LOX‐1 expression and propose a new mechanism by which galectin‐3 may promote endothelial dysfunction by inducing inflammation via LOX‐1/ROS/p38/NF‐κB‐mediated signaling pathway.     

The effect of maternal exposure to di‐(2‐ethylhexyl)‐phthalate on fetal cardiac development in mice

Accumulating evidence has suggested a link between maternal di‐(2‐ethylhexyl)‐phthalate (DEHP) exposure and various developmental abnormalities. However, the evidence regarding the effect of maternal DEHP exposure on fetal cardiac development is scarce. The present study aimed to determine the effect of maternal DEHP exposure on fetal cardiac development in mice and explore the possible involved mechanism preliminarily. The C57BL mice were randomly divided into four groups: the vehicle group (corn oil, n = 10), 250 mg kg^–1 DEHP group (n = 15), 500 mg kg^–1 DEHP group (n = 20) and 1 g kg^–1 DEHP group (n = 20). Pregnant dams in different group received respective intervention by gavage once daily from embryonic day (E)6.5 to E14.5. Maternal weights were monitored every day and samples were collected at E15.5. Hematoxylin and eosin staining was used to examine fetal cardiac malformations. Real‐time quantitative polymerase chain reaction and western blot were applied to detect peroxisome proliferator‐activated receptor (PPAR)α/PPARγ/Nkx2.5/Gata4/Tbx5/Mef2c/Chf1 mRNA and protein expression, respectively. Maternal DEHP exposure significantly decreased maternal body weight, fetal weight and placental weight, and remarkably elevated fetal cardiac malformations rate. The phenotypes of cardiac anomalies mainly include septal defects, ventricular myocardium noncompaction and cardiac hypoplasia. Higher doses DEHP (500 mg kg^–1 and 1 g kg^–1) could significantly decreased fetal cardiac Gata4/Mef2c/Chf1 expression, while PPARγ expression was upregulated. Maternal exposure to higher doses of DEHP could result in fetal cardiac development malformations in mice and it might have resulted from the inhibition of cardiac GATA4/Mef2c/Chf1 expression via PPARγ activation.     

Rate‐limiting factors of cholesterol efflux in reverse cholesterol transport: Acceptors and donors

1. Plasma levels of high‐density lipoprotein (HDL) are believed to be inversely related to coronary artery disease. High‐density lipoprotein plays a key role in the process of reverse cholesterol transport, by which HDL is able to extract excess cholesterol from peripheral tissues and transfer it to the liver for biliary excretion. 2. Efflux of lipids (cholesterol and phospholipids) is the first step in reverse cholesterol transport. Several cellular membrane transporters, including ABCA1 and ABCG1, as well as scavenger receptor (SR)‐BI receptor, are believed to facilitate the active efflux of cholesterol to lipid‐poor apolipoprotein A‐I and mature HDL, respectively. Furthermore, overexpression or deletion of one or more specific genes supports the view that HDL is involved in cholesterol efflux. 3. In conclusion, current evidence supports a critical role for HDL in atheroprotection via an active efflux pathway through reverse cholesterol transport, with the substantial support of appropriate functions of cell donors.