固醇调节元件结合蛋白2信号通路与非酒精性脂肪性肝病北大核心CSCD

非酒精性脂肪性肝病(non-alcoholic fatty liver disease,NAFLD)是以肝细胞内甘油三酯和胆固醇等脂毒性脂肪过度沉积为主要特征的一种临床获得性代谢综合征。最新研究表明,NAFLD向非酒精性脂肪肝炎(NASH)进展时,肝内胆固醇积累可能较甘油三酯更具有细胞毒性风险。固醇调节元件结合蛋白2(sterol regulatory element-binding protein 2,SREBP2)是脂质代谢重要的核转录因子之一,主要调控胆固醇的生物合成和体内平衡。SREBP2及其靶基因调控的胆固醇异常是引起非酒精性脂肪肝病发生发展的重要因素之一。因此,认识SREBP2信号通路中,上下游各因素的表达调控作用与NAFLD发病机制之间关系,就显得非常重要。本文总结了受SREBP2调控表达的靶基因的特点,着重介绍SREBP2调控胆固醇体内合成与平衡的信号通路与NAFLD发病机制之间关系,为研究和指导治疗NAFLD及其代谢性疾病提供新的思路。     

固醇调节元件结合蛋白-1信号通路研究进展

固醇调节元件结合蛋白-1(sterol regulatory element-binding protein-1,SREBP-1)是脂质代谢重要的核转录因子之一,主要调控脂肪酸、甘油三酯和胆固醇的生物合成。SREBP-1及其靶基因的异常表达能够引起胰岛素抵抗、糖尿病和脂肪肝等一系列代谢性疾病。因此,认识SREBP-1信号通路上下游各因素的表达调控作用就显得非常重要。该文总结了受SREBP-1调控表达的靶基因的特点,着重介绍了胰岛素等上游因子在SREBP-1调控过程中的作用,为指导治疗各类代谢性疾病提供新的思路。     

SREBP介导的基因表达的调控(英文)

SREBP转录因子是脂类代谢的重要调节者。当细胞有脂类需求时,在内质网膜上的SREBP前体通过蛋白水解被激活。然后,氨基端的SREBP片段被运到细胞核内激活靶基因的转录。细胞培养和转基因小鼠模型的研究已经证明,SREBP的主要靶基因包括负责脂肪和胆固醇合成的酶,以及低密度脂蛋白受体。早期对SREBP的研究相当完善地揭示了其前体被激活的机理。最近的研究又使我们认识了细胞核内SREBP的调控机理。在细胞核中,SREBP会结合特定的转录辅助因子,刺激或抑制其靶基因的转录,这些转录辅助因子包括CBP/p300和Mediator蛋白复合体。此外,细胞核内SREBP的稳定性受磷酸化和乙酰化的调节。细胞核内SREBP的这种蛋白质相互作用和修饰,使细胞内外信号(如胰岛素或氧化应激)更好地控制脂类合成。在正常生理状态下,脂质动态平衡是严格保持着的,然而,在有些病理条件下,如肥胖、二型糖尿病、心血管疾病和脂肪肝,SREBP往往会失调。因此,SREBP的新调控机制可能对治疗代谢性疾病提供新的机遇。     

高脂饮食性非酒精性脂肪性肝病小鼠肝脏脂代谢相关基因的改变

目的:分析非酒精性脂肪性肝病(NAFLD)小鼠肝脏中脂代谢相关基因的表达变化。方法:12周龄成年雄性C57BL/J6小鼠,随机分为对照组及NAFLD组。对照组予以普通饲料,NAFLD组予以高脂饮食喂养8周。分别测定两组小鼠肝功能、血脂及肝脂的变化,苏木精-伊红(HE)及油红O染色后光学显微镜下观察肝脏的形态结构和脂肪变性情况,并用实时荧光定量PCR(qPCR)法检测肝脏脂代谢重要基因的变化。结果:与对照组比较,NAFLD组小鼠的血清总甘油三酯(TG)、总胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)及肝脏TG、肝脏TC水平均显著升高(P0.05)。HE和油红O染色显示NAFLD组小鼠发生了显著的肝脏脂质沉积。此外,NAFLD组小鼠肝脏中脂肪酸转位酶(CD36)表达水平显著高于对照组,而硬脂酰辅酶A去饱和酶1(SCD1)、固醇调控元件结合蛋白(SREBP1c)表达水平在两组小鼠中无统计学差异。结论:高脂饮食诱导的脂肪肝中CD36表达上调,可能参与了NAFLD的发病机制。     

miRNA在非酒精性脂肪肝病中的作用研究进展

非酒精性脂肪性肝病(nonalcoholic fatty liver disease, NAFLD)是目前临床常见的肝病之一,随着生活水平的提高,NAFLD的发病率不断升高,严重威胁了人们的健康,其发病机制尚未完全阐明。微小RNA(microRNA, miRNA)是一类广泛存在的非编码分子RNA,通过转录后水平调节基因的表达参与调控一系列的生命活动。近年来越来越多的研究发现,miRNA通过各种途径在NAFLD的发生发展中起着关键作用。本文主要对近年来miRNA在非酒精性脂肪肝病中的机制研究进展进行简单综述。     

核因子E2相关因子2在运动改善非酒精性脂肪性肝病中的作用

核因子E2相关因子2 (nuclear factor erythroid 2-related factor 2,Nrf2)信号通路在维持心血管疾病、神经系统退行性疾病以及慢性代谢性疾病中的细胞稳态方面起关键作用。研究表明,以氧化应激、炎症和线粒体功能失调为特征的慢性疾病可通过增加Nrf2表达来恢复机体氧化还原状态,治疗或预防疾病。非酒精性脂肪性肝病（nonalcoholic fatty liver disease,NAFLD）是一种由除酒精以外的其他多种因素导致的以肝脏脂肪变性为特征的慢性代谢性肝脏疾病,其患病率近年来在全球范围内逐渐增加。运动是防治NAFLD的有效手段,可通过运动方式、运动强度、运动环境和运动疲劳等因素影响Nrf2信号通路。本文通过阐述Nrf2信号通路的激活、其调控抗氧化的相关机制以及运动对Nrf2信号通路的影响,以NAFLD的发病机制为基础,探讨运动、Nrf2和NAFLD之间的关系,综述Nrf2在运动改善NAFLD中的作用及相关机制。为运动改善NAFLD的分子机制研究提供理论参考依据。     

高尔基体跨膜糖蛋白73高表达诱发脂肪肝的脂类特性分析

脂肪性肝病是最常见的慢性肝脏疾病,脂质代谢异常是脂肪性肝病发生的重要原因。为研究高尔基体糖蛋白(Golgi protein 73, GP73)对肝脏脂质代谢的影响,选用八周龄C57BL/6J小鼠通过尾静脉注射搭载GP73的腺相关病毒(AAV-GP73),构建肝脏特异性高表达GP73的小鼠,通过对肝脏进行脂质代谢组学分析发现小鼠肝脏中的脂质尤其是甘油三酯明显增加。京都基因与基因组百科全书(kyoto encyclopedia of genes and genomes, KEGG)富集分析显示,GP73通过引起脂代谢产物的改变导致诸多与细胞代谢活动相关的信号通路出现紊乱,特别是与人类密切相关的疾病如Ⅱ型糖尿病、非酒精性脂肪性肝病(NAFLD)和癌细胞胆碱代谢更可能发生失调。研究表明,GP73可能通过参与调控脂类代谢并促进肝脏内脂质积累诱发脂肪肝。     

非酒精性脂肪肝大鼠PPARα基因表达及脂代谢和胰岛素水平的变化

目的观察非酒精性脂肪肝（NAFLD）大鼠肝组织中PPARα基因的表达,并用PPARct激动剂进行干预,探讨其与胰岛素抵抗、脂代谢紊乱的关系。方法大鼠随机分为①正常对照组、②高脂模型组、③PPARα激动剂干预组,利用高脂饮食建立大鼠非酒精性脂肪肝模型。12周后,检测大鼠血脂、肝功能、血糖、胰岛素水平及胰岛素抵抗指数;RT-PCR法分析PPARα基因的表达;观察肝脏的形态学改变。结果PPARa激动剂可降低NAFLD大鼠转氨酶、血脂水平及胰岛素抵抗指数,可促进NAFLD大鼠中PPARa基因的表达;肝脏形态学明显改善。结论PPARα激动剂能改善NAFLD大鼠脂质代谢紊乱,有明显的保肝降酶作用,具有适度的胰岛素增敏作用。PPARα及其配体在NAFLD发病机制及治疗中的进一步深入研究,将为临床防治NAFLD提供新的思路。     

肠道菌群影响非酒精性脂肪性肝病的机制及应对策略

非酒精性脂肪性肝病(nonalcoholic fatty liver disease,NAFLD)的发病率逐年升高,已成为最常见的肝脏疾病之一。目前其发病机制未被完全阐明,尚无有效治疗药物。肠道菌群与人体共生,作为人体的“第二基因组”,其在消化、吸收及代谢中发挥重要作用。新近研究表明,肠道菌群已成为影响NAFLD发生、进展的重要因素,肠道菌群失调和肠肝轴紊乱与非酒精性单纯性脂肪肝(nonalcoholic fatty liver,NAFL)发展为非酒精性脂肪性肝炎(nonalcoholic steatohepatitis,NASH)、肝纤维化和肝细胞癌(hepatocellular carcinoma,HCC)密切相关。因此,肠道微生态干预有望成为预防或治疗NAFLD的新手段。本综述主要探讨肠道菌群异常对NAFLD/NASH发病过程、机制的影响及干预措施。     

Effect of Bombyx mori on the Liver Protection of Non-Alcoholic Fatty Liver Disease Based on In Vitro and In Vivo Models

Edible insects, Bombyx mori (silkworm; SW), which feed on mulberry leaves, have been consumed by humans for a long time as supplements or traditional medication. Non-alcoholic fatty liver disease (NAFLD) is a liver metabolic disorder that affects many people worldwide. We examined the hepatoprotective effects of SW using in vitro and high-fat and high-fructose (HFHF) diet-induced obese in vivo model mice by real-time PCR, immunoblot analysis, and fecal microbiota analysis. SW significantly reduced lipid accumulation and expression of the lipogenic genes in HepG2 cells and the livers of HFHF-induced mice. SW caused significant reductions in triglycerides, and total cholesterol in serum and upregulation of fatty acid oxidation markers compared to the HFHF group. Besides, SW significantly induced phosphorylation of AMPK and ACC in both models, suggesting roles in AMPK activation and the ACC signaling pathway. Furthermore, the gut microbiota analysis demonstrated that SW treatment reduced Firmicutes to Bacteroidetes ratios and the relative abundance of the Lachnospiraceae family compared to HFHF-induced obese mice. These results provide a novel therapeutic agent of hepatoprotective effects of SW for non-alcoholic hepatic steatosis that targets hepatic AMPK and ACC-mediated lipid metabolism.     

Control of cholesterol biosynthesis,uptake and storage in hepatocytes by Cideb

Cideb, a member of CIDE family proteins, has emerged as an important regulator in the development of obesity and diabetes by controlling fatty acid synthesis and VLDL secretion in hepatocytes. Here, we investigated the role of Cideb in cholesterol biosynthesis, uptake and storage in the liver by using Cideb-null mice as a model system. Cideb-null mice and wild-type mice were treated with normal diet (ND) or high cholesterol diet (HCD) for one month. The metabolic parameters of cholesterol metabolism and expression profiles of genes in cholesterol biosynthesis and storage were measured. Cideb-null mice had lower levels of plasma cholesterol and LDL when fed with both ND and HCD and increased rate of cholesterol absorption. Furthermore, the liver of Cideb-null mice has lower rates of cholesterol biosynthesis and reduced expression levels of sterol response element-binding protein (SREBP) cleavage-activation protein (SCAP), and lower levels of nuclear form of SREBP2 and its downstream target genes in cholesterol biosynthesis pathway under a normal diet treatment. On the contrary, hepatic cholesterol biosynthesis rate between wild-type and Cideb-null mice was similar after high cholesterol diet treatment. Interestingly, hepatic cholesterol storage in the liver of Cideb-null mice was significantly increased due to its increased LDL receptor (LDLR) and acyl-CoA cholesterol acyltransferase (ACAT) expression. Finally, we observed drastically reduced cholesterol levels in the heart of Cideb-null mice fed with a high cholesterol diet. Overall, our data suggest that Cideb is a novel regulator in controlling cholesterol homeostasis in the liver. Therefore, Cideb could serve as an important therapeutical target for the treatment of atherosclerosis and cardiovascular diseases.     

Identification of Novel Regulatory Cholesterol Metabolite, 5-Cholesten, 3β,25-Diol,Disulfate

Oxysterol sulfation plays an important role in regulation of lipid metabolism and inflammatory responses. In the present study, we report the discovery of a novel regulatory sulfated oxysterol in nuclei of primary rat hepatocytes after overexpression of the gene encoding mitochondrial cholesterol delivery protein (StarD1). Forty-eight hours after infection of the hepatocytes with recombinant StarD1 adenovirus, a water-soluble oxysterol product was isolated and purified by chemical extraction and reverse-phase HPLC. Tandem mass spectrometry analysis identified the oxysterol as 5-cholesten-3β, 25-diol, disulfate (25HCDS), and confirmed the structure by comparing with a chemically synthesized compound. Administration of 25HCDS to human THP-1-derived macrophages or HepG2 cells significantly inhibited cholesterol synthesis and markedly decreased lipid levels in vivo in NAFLD mouse models. RT-PCR showed that 25HCDS significantly decreased SREBP-1/2 activities by suppressing expression of their responding genes, including ACC, FAS, and HMG-CoA reductase. Analysis of lipid profiles in the liver tissues showed that administration of 25HCDS significantly decreased cholesterol, free fatty acids, and triglycerides by 30, 25, and 20%, respectively. The results suggest that 25HCDS inhibits lipid biosynthesis via blocking SREBP signaling. We conclude that 25HCDS is a potent regulator of lipid metabolism and propose its biosynthetic pathway.     

Clofibrate causes an upregulation of PPAR-{alpha} target genes but does not alter expression of SREBP target genes in liver and adipose tissue of pigs

This study investigated the effect of clofibrate treatment on expression of target genes of peroxisome proliferator-activated receptor (PPAR)-alpha and various genes of the lipid metabolism in liver and adipose tissue of pigs. An experiment with 18 pigs was performed in which pigs were fed either a control diet or the same diet supplemented with 5 g clofibrate/kg for 28 days. Pigs treated with clofibrate had heavier livers, moderately increased mRNA concentrations of various PPAR-alpha target genes in liver and adipose tissue, a higher concentration of 3-hydroxybutyrate, and markedly lower concentrations of triglycerides and cholesterol in plasma and lipoproteins than control pigs (P < 0.05). mRNA concentrations of sterol regulatory element-binding proteins (SREBP)-1 and -2, insulin-induced genes (Insig)-1 and Insig-2, and the SREBP target genes acetyl-CoA carboxylase, 3-methyl-3-hydroxyglutaryl-CoA reductase, and low-density lipoprotein receptor in liver and adipose tissue and mRNA concentrations of apolipoproteins A-I, A-II, and C-III in the liver were not different between both groups of pigs. In conclusion, this study shows that clofibrate treatment activates PPAR-alpha in liver and adipose tissue and has a strong hypotriglyceridemic and hypocholesterolemic effect in pigs. The finding that mRNA concentrations of some proteins responsible for the hypolipidemic action of fibrates in humans were not altered suggests that there were certain differences in the mode of action compared with humans. It is also shown that PPAR-alpha activation by clofibrate does not affect hepatic expression of SREBP target genes involved in synthesis of triglycerides and cholesterol homeostasis in liver and adipose tissue of pigs.     

Increased Hepatic Lipogenesis Elevates Liver Cholesterol Content

Cardiovascular diseases (CVDs) are the most common cause of death in patients with nonalcoholic fatty liver disease (NAFLD) and dyslipidemia is considered at least partially responsible for the increased CVD risk in NAFLD patients. The aim of the present study is to understand how hepatic de novo lipogenesis influences hepatic cholesterol content as well as its effects on the plasma lipid levels. Hepatic lipogenesis was induced in mice by feeding a fat-free/high-sucrose (FF/HS) diet and the metabolic pathways associated with cholesterol were then analyzed. Both liver triglyceride and cholesterol contents were significantly increased in mice fed an FF/HS diet. Activation of fatty acid synthesis driven by the activation of sterol regulatory element binding protein (SREBP)-1c resulted in the increased liver triglycerides. The augmented cholesterol content in the liver could not be explained by an increased cholesterol synthesis, which was decreased by the FF/HS diet. HMG-CoA reductase protein level was decreased in mice fed an FF/HS diet. We found that the liver retained more cholesterol through a reduced excretion of bile acids, a reduced fecal cholesterol excretion, and an increased cholesterol uptake from plasma lipoproteins. Very low-density lipoprotein-triglyceride and -cholesterol secretion were increased in mice fed an FF/HS diet, which led to hypertriglyceridemia and hypercholesterolemia in Ldlr^-/- mice, a model that exhibits a more human like lipoprotein profile. These findings suggest that dietary cholesterol intake and cholesterol synthesis rates cannot only explain the hypercholesterolemia associated with NAFLD, and that the control of fatty acid synthesis should be considered for the management of dyslipidemia.