The ATP-binding membrane cassette transporter A1 (ABCA1) plays a protective role in the development of atherosclerosis for the reverse cholesterol transport process. Epigallocatechin-3-gallate (EGCG), which exists abundantly in green tea, exerts an anti-atherosclerotic effect via anti-inflammatory and metabolic regulation activities. Many genes and proteins related to lipid metabolism are involved in the lowering cholesterol effects of EGCG. However, effects of EGCG on ABCA1 have rarely been described. In the study presented here, we found that exposure of macrophage foam cells to TNF-α results in a downregulation of ABCA1 and a decrease in cholesterol efflux to apoA1, which is attenuated by pretreatment with EGCG. Moreover, rather than activating the Liver X receptor (LXR) pathway, inhibition of the TNF-α-induced nuclear factor-κB (NF-κB) activity is detected with EGCG treatment in cells. In order to inhibit the NF-κB activity, EGCG can promote the dissociation of the nuclear factor E2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) complex; when the released Nrf2 translocates to the nucleus and activates the transcription of genes containing an ARE element inhibition of NF-κB occurs and Keap1 is separated from the complex to directly interact with IKKβ and thus represses NF-κB function. These results provide novel insight into the anti-inflammatory effects of EGCG, as well as the identification of a novel potential therapeutic role for the prevention of atherosclerosis.

目的观察ApoAⅠ对脂多糖(LPS)诱导的THP-1巨噬细胞源性泡沫细胞炎症因子表达的影响,并从ABCA1介导激活的STAT3/TTP信号途径入手探讨其分子机制。方法采用ELISA检测炎症因子表达;构建含肿瘤坏死因子α(TNF-α)启动子的CAT报告基因,转染THP-1细胞,采用ELISA检测TNF-α启动子活性;定量PCR检测TNF-α等炎症因子mRNA表达;免疫印迹技术检测pSTAT3、TTP和HuR等蛋白表达;RNA-EMSA检测TTP与RNA复合物;构建TTP、STAT3 siRNA,转染细胞。结果用10μg/L LPS和/或10 mg/L ApoAⅠ处理THP-1源性泡沫细胞4 h,结果显示ApoAⅠ明显抑制LPS诱导的TNF-α、IL-1β和IL-6的表达;CAT报告基因显示,ApoAⅠ并不明显影响LPS诱导的TNF-α启动子活性;LPS处理细胞3 h,加入放线菌素D(Act D)终止转录,检测TNF-αmRNA表达量(0、30、60及120 min),结果显示ApoAⅠ明显增加LPS作用下TNF-α的mRNA降解;ApoAⅠ明显促进LPS作用下TTP的表达,而对HuR的表达没有明显影响,TTP siRNA处理后明显抑制ApoAⅠ促进TNF-αmRNA降解的作用;RNA-EMSA结果显示,ApoAⅠ明显促进胞内蛋白与ARE探针形成复合物,加入TTP抗体形成su-pershift;ApoAⅠ处理THP-1细胞后迅速(15 min)磷酸化STAT3,核内STAT3表达增加,STAT1和STAT6不受影响;STAT3 siR-NA处理后明显抑制TTP的表达及TNF-αmRNA的降解;采用siRNA下调ABCA1的表达,明显抑制ApoAⅠ作用下TTP的表达及TNF-αmRNA的降解。结论 ApoAⅠ通过转录后调控方式抑制LPS诱导的炎症因子表达;ApoAⅠ促进TTP表达,并通过与炎症因子3′UTR ARE序列结合促进其mRNA降解;ApoAⅠ通过激活STAT3促进TTP表达,该效应直接受ABCA1介导。

Atherosclerosis is an inflammatory disease characterized by the accumulation of macrophages in the arterial intima. The activated macrophages secreted more pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, which promote the development of the disease. Apolipoprotein A-I (apoA-I), the major component of high density lipoprotein, is involved in reverse cholesterol transport of lipid metabolism. Recently, it has been found that apoA-I suppresses inflammation via repression of inflammatory cytokine expression; the mechanisms of the apoA-I-suppressive action, however, are not yet well characterized. In this study, we have for the first time found that apoA-I suppresses the expression of some inflammatory cytokines induced by lipopolysaccharide via a specific post-transcriptional regulation process, namely mRNA destabilization, in macrophages. Our further studies have also shown that AU-rich elements in the 3′-untranslated region of TNF-α mRNA are responsive to the apoA-I-mediated mRNA destabilization. The apoA-I-induced inflammatory cytokine mRNA destabilization was associated with increased expression of mRNA-destabilizing protein tristetraprolin through a JAK2/STAT3 signaling pathway-dependent manner. When blocking interaction of apoA-I with ATP-binding membrane cassette transporter A1 (ABCA1), a major receptor for apoA-I in macrophages, it would almost totally abolish the effect of apoA-I on tristetraprolin expression. These results present not only a novel mechanism for the apoA-I-mediated inflammation suppression in macrophages but also provide new insights for developing strategies for modulating vascular inflammation and atherosclerosis.

During the process of intestinal cholesterol absorption,NPC1L1 mediated the uptake of cholesterol,and modified absorption overdose in coordination with ABCG5/g8.Cholesterol was transported to Endoplasmic Reticulum (ER),where its rate of esterification was regulated by ACAT.Then,these esterified cholesterol participated in the synthesis of chylomicrons,which,however,depended on activities of apoB,MTP and IRE1β.Chylomicrons were transported to basolateral membranes by specific vesicles for excretion.Finally,the ripe chylomicrons were transported to lymphatic system.Moreover, some unesterified cholesterols were transported back to intestine via ABCG5/G8,and others were mediated into blood from basolateral membrane by ABCA1.This review concerned relevant proteins and mechanisms of cholesterol absorption.

目的本实验通过高脂饮食建立早期高脂血症兔模型,观察普罗布考对胆固醇相关转运体以及炎症因子的影响。方法新西兰白兔36只,雄雌不拘,采用数字表法随机分为基础组(n=9)、基础+普罗布考组(每只77 mg/d,n=9)、高脂组(n=9)和高脂+普罗布考组(每只77 mg/d,n=9)。40天后观察普罗布考对血脂的影响;HE染色观察普罗布考对各组新西兰白兔腹主动脉斑块形成的影响;油红O染色观察普罗布考对各组新西兰白兔肝脏脂质蓄积的影响;定量PCR测定普罗布考对新西兰白兔腹主动脉、肝脏和小肠中胆固醇相关转运体基因表达的影响;Western blot以及免疫组化测定普罗布考对新西兰白兔腹主动脉、肝脏、小肠内胆固醇相关转运蛋白表达的影响;ELISA方法测定普罗布考对炎症因子的影响。结果与基础组相比,高脂组免血清总胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)、甘油三酯(TG)水平均明显升高;与高脂组比较,高脂+普罗布考组免血清TC、LDL-C、HDL-C、TG水平均明显下降;高脂组中有动脉斑块形成,肝脏脂质蓄积增多;高脂+普罗布考组中,普罗布考明显抑制斑块的形成,减少肝脏脂质蓄积;普罗布考促进肝脏中ABCG1和SR-BI蛋白及其mRNA的表达,抑制ABCA1蛋白及其mRNA的表达,对SR-A和CD36的表达没有影响;普罗布考抑制炎症因子如IL-6、MCP-1、MCSF、VCAM-1、TNF-α的表达。结论普罗布考抑制ABCA1和炎症因子的表达,促进ABCG1和SR-B1的表达。

Aim: To determine the effects and potential mechanisms of ibrolipim on ATP-binding membrane cassette transporter A-1 (ABCA1) and ATP-binding membrane cassette transporter G-1 (ABCG1) expression from human macrophage foam cells, which may play a critical role in atherogenesis. Methods: Human THP-1 cells pre-incubated with ox-LDL served as foam cell models. Specific mRNA was quantified using real-time RT-PCR and protein expression using Western blotting. Cellular cholesterol handling was studied using cholesterol efflux experiments and high performance liquid chromatography assays. Results: Ibrolipim 5 and 50 μmol/L significantly increased cholesterol efflux from THP-1 macrophage-derived foam cells to apoA-I or HDL. Moreover, it upregulated the expression of ABCA1 and ABCG1. In addition, LXRα was also upregulated by the ibrolipim treatment. In addition, LXRα small interfering RNA completely abolished the promotion effect that was induced by ibrolipim. Conclusion: Ibrolipim increased ABCA1 and ABCG1 expression and promoted cholesterol efflux, which was mediated by the LXRα signaling pathway.

Adenosine triphosphate-binding cassette transporter A1 (ABCA1) plays a crucial role in apolipoprotein A-I (apoA-I) binding activity and promotes cellular cholesterol efflux. ApoA-I mimetic peptide D4-F has reported to have the similar ability as apoA-I. However, the detailed mechanisms of ABCA1 regulation by D4-F are not understood. In the present study, we investigated the effects of D4-F on ABCA1 expression and ABCA1-dependent cholesterol efflux and examined the role of Cdc42/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway on the regulation of ABCA1 by D4-F in THP-1 macrophage-derived foam cells. Results showed that D4-F stabilized ABCA1 protein and enhanced ABCA1-dependent cholesterol efflux but had no effect on ABCA1 messenger RNA expression. We also revealed that D4-F enhanced cAMP level and PKA activity and ABCA1 serine phosphorylation. Short interfering RNA of PKA led to reduction of ABCA1 serine phosphorylation and ABCA1-mediated cholesterol efflux compensated by D4-F. PKA-specific activation by PKA agonist enhanced the upregulation of ABCA1 serine phosphorylation and ABCA1-mediated cholesterol efflux by D4-F. However, ABCA1 expression did not change by treatment with PKA agonist or PKA-short interfering RNA. We found that secramine B of Cdc42 inhibitor reduced the cAMP level compensated by D4-F. These results provide evidence that D4-F enhances ABCA1 serine phosphorylation and ABCA1-dependent cholesterol efflux through Cdc42/cAMP/PKA pathway in THP-1 macrophage-derived foam cells.