瘦素在肝脏疾病中的作用和分子机制

瘦素是由ob基因编码产生的分子量为 16ku的物质 ,以游离或结合形式存在于血浆中。瘦素在多种肝脏疾病的病理机制中发挥重要的作用 ,其通过与细胞表面的瘦素受体(leptinreceptor,OB R)结合而激活肝星状细胞及Kuffer细胞 ,从而调节脂肪肝、酒精性及非酒精性肝硬化中炎症因子及纤维化因子的表达。该文就瘦素的生物学活性 ,瘦素在脂肪肝、肝炎、肝硬化等多种肝脏疾病中的作用及其可能的分子机制作一综述     

瘦素对肝星状细胞活化的调控及其在肝纤维化进展中的作用

摘要：瘦素是一种主要由白色脂肪组织产生的激素,与肝星状细胞活化有着密切联系。瘦素与其功能性受体结合后可以通过JAK2/STAT3、PI3K/Akt、MAPK等信号通路及相关分子对肝星状细胞的活化产生影响;而肝星状细胞活化是肝纤维化发生发展的关键环节。该文就瘦素与肝星状细胞活化的相关信号通路及分子在肝纤维化发生发展中的作用进行综述,为肝纤维化的治疗提供依据。     

胆道闭锁肝纤维化研究进展

胆道闭锁（BA）是严重危及婴幼儿生命健康的消化系统疾病之一,晚期肝脏纤维化是导致患儿死亡的主要原因。在胆道闭锁发病过程中,病毒感染可诱导一系列免疫和炎症反应,导致调节性T细胞（Treg细胞）减少,CD14表达增高,多种炎症通路以及转化生长因子-β（TGF-β）/Smad2/3促纤维化通路被激活。激活的通路产生大量炎性介质损伤肝细胞和胆管细胞,释放各种促炎因子、氧代谢产物和细胞因子,进一步加重肝、胆系统损伤造成肝细胞内环境失衡,失衡的内环境伴随肝实质细胞、肝巨噬细胞、肝内聚集的炎性细胞等发生适应性变性、坏死、增生,导致肝星形细胞（HSCs）激活,HSCs转化为成纤维细胞,促进肝纤维化进程。免疫、炎症损伤、促纤维化通路是导致胆道闭锁肝纤维化肝硬化的三大重要因素。     

Hh信号通路在慢性肝脏损伤修复中的作用

Hh信号通路最早是在果蝇体内发现的一条高度保守的信号通路[1],随着研究的深入,目前发现该信号通路在脊椎动物体内也相当重要,它能够调节胚胎时期组织、器官的形成以及多种成人组织损伤修复反应,其中也包括肝脏[21.近年来,大量的研究证实在正常的肝脏中Hh信号通路保持抑制状态[ 3],而当受到病毒、药物、酒精等损伤因素持续作用后,产生大量的Hh配体蛋白并激活Hh信号通路H,而激活的Hh信号通路则参与肝脏损伤修复过程中的多个方面,包括各种类型细胞的增殖及凋亡、肌成纤维细胞的转换和聚集、与修复相关的炎症反应以及肝内血管的新生、改建,甚至肝纤维化、肝硬化的形成.     

LPS/TLR4 信号通路在肝纤维化中的作用及临床意义

肝纤维化是多种慢性肝脏疾病共有的病理过程,表现为细胞外基质合成增多,降解减少。肝星形细胞（HSC）活化并分泌大量细胞外基质是肝纤维化发生的重要机制。脂多糖（LPS）刺激细胞使细胞表面的多种LPS识别受体（包括LBP、CD14、MD2和TLR4）表达增加,通过细胞内信号传递级联使基因表达发生变化,引起细胞反应。LPS／TLR4信号通路在肝纤维化形成过程中起关键作用。     

肝窦内皮细胞在肝脏疾病中的作用

肝窦内皮细胞(liver sinusoidal endothelial cells,LSECs)作为肝脏中比例最高的非实质细胞,其窗孔结构和高内吞清除能力在肝脏生理病理过程中发挥不可或缺的作用。LSECs主要通过发挥抗炎、内吞、分泌促血管生成信号分子和维持HSCs表型等作用,参与调控非酒精性脂肪肝病(nonalcoholic fatty liver disease,NAFLD)、酒精性脂肪肝(alcoholic fatty liver,AFL)、肝细胞性肝癌(hepatocellular carcinoma,HCC)、肝再生、肝纤维化等肝脏病理过程。该文就LSECs正常生理功能及其在各种病理状态下发挥的不同作用作一综述,旨在通过靶向LSECs为治疗肝脏疾病提供新的观点。     

酒精性脂肪肝脂质代谢研究进展

酒精性脂肪肝(AFL)是长期大量饮用酒精引发的肝脏损害性病变,可逆转也可进一步发展为肝纤维化和肝硬化。众多的脂肪细胞因子如瘦素(Leptin)、抵抗素(Resistin)和肿瘤坏死因子-α(TNF-α)在脂肪肝的发病中起到一定的促进作用,脂联素(Adiponectin)能改善脂质代谢,延缓脂肪肝的发生;脂联素通过腺苷酸活化蛋白激酶(AMPK)调节糖脂代谢、改善胰岛素敏感性。脂联素/AMPK信号通路是酒精在肝脏的作用靶点、也是调节PPARγ作用的重要信号通路;脂肪分化相关蛋白(ADRP)调节脂质代谢、促进酒精性脂肪肝的形成;过氧化物酶增殖体激活受体γ(PPARγ)参与机体脂质稳态的调节,脂肪肝时PPARγ表达增高,肝纤维化时PPARγ表达减少。对酒精性脂肪肝脂质代谢的深入研究,有助于阐明酒精性脂肪肝发病机制并为临床防治ALD及脂质代谢相关疾病提供新策略。     

枯否细胞在非酒精性脂肪肝炎中的发病机制

非酒精性脂肪肝炎(NASH)是一种代谢综合性肝病,是在肝脏细胞脂肪变性基础上进一步诱发炎性反应及纤维化.枯否细胞(KCs)是一种肝巨噬细胞,NASH进展过程中,KCs能够在脂质、内毒素、氧化应激等刺激作用下分泌炎性因子,引发肝细胞炎性反应,损伤肝脏.该文就KCs激活分泌的炎症因子在NASH发病机制中的作用进行详细论述.     

肝脏细胞自噬在肝纤维化中的作用研究进展

肝纤维化是由于各种致病因子引起的肝脏结缔组织的异常增生。肝星状细胞的活化被普遍认为肝纤维化的中心环节,在肝纤维化过程中,自噬在不同的肝脏细胞中发挥着不同作用。一方面,在肝巨噬细胞、肝内皮细胞和肝实质细胞中,自噬可影响肝细胞炎症损伤反应抑制肝纤维化的发生;另一方面,在肝星状细胞中,自噬可影响氧化应激、内质网应激和脂质代谢等促进肝纤维化的发生。本文对肝脏不同细胞自噬在肝纤维化中的作用进行综述,为开发延缓和逆转肝纤维化的药物提供更完善的理论基础。     

细胞因子信号转导抑制分子-3在肝纤维化中的作用及研究进展

肝纤维化是继发于各种慢性肝损伤之后组织修复过程中的代偿反应,其发病实质是肝内细胞外基质(extracellular matrix,ECM)合成与降解动态平衡发生紊乱,最终导致ECM过度沉积。肝纤维化的发生与发展受到多种细胞因子及细胞内多种信号转导通路网络的调控,其中很多靶点在肝纤维化中的作用尚没有完全定论。近年来越来越多的研究证实细胞因子信号转导抑制分子-3(suppressor of cytokine signaling,SOCS-3)在肝纤维化的发生与发展过程中扮演着重要角色。SOCS-3可通过调控肝脏内炎症反应、细胞增殖活化、胰岛素抵抗、瘦素抵抗等影响肝脏疾病的发展进程。许多学者认为SOCS-3可作为肝纤维化疾病诊断、预测预后的生物分子指标以及治疗靶标。该文从SOCS-3系统概述、SOCS-3与肝纤维化关系、SOCS-3在防治肝纤维化中的作用等方面综述了SOCS-3在防治肝纤维化中的作用及研究进展。     

Relaxin receptors in hepatic stellate cells and cirrhotic liver

The polypeptide hormone relaxin has antifibrotic effects on a number of tissues, including the liver. Central to the progression of hepatic fibrosis is the transdifferentiation of hepatic stellate cells (HSC) from a quiescent state to an activated, myofibroblastic phenotype that secretes fibrillar collagen. Relaxin inhibits markers of HSC activation, but relaxin receptor expression in the liver is unclear. The purpose of this study was to determine the expression of the relaxin receptors LGR7 and LGR8 in activated HSC. Production of cAMP was induced by treatment of HSC with relaxin, or the relaxin-related peptides InsL3 or relaxin-3, selective activators of LGR8 and LGR7, respectively. Quiescent HSC expressed low levels of LGR7 but not LGR8. During progression to the activated phenotype, expression of both receptors increased markedly. Immunocytochemistry confirmed the presence of both receptors in activated HSC. In normal rat liver, LGR7, but not LGR8, was expressed at low levels. In cirrhotic liver, expression of both receptors significantly increased. Neither receptor was detectable in normal liver by immunohistochemistry, but both LGR7 and LGR8 were readily detectable in cirrhosis. These results were confirmed in human cirrhotic tissue, with the additional finding of occasional perisinusoidal LGR7 immunoreactivity in non-cirrhotic tissue. In conclusion, the expression of LGR7 and LGR8 is increased with activation of HSC in culture. Cirrhosis also caused increased expression of both receptors. Therefore, agents that stimulate LGR8 and LGR7 may be therapeutically useful to limit the activation of hepatic stellate cells in liver injury.     

Leptin and the cardiovascular system: a review

Obesity is an increasing health problem not only in the industrialized western countries but, also in the developing countries like India. The adipose tissue specific obese (ob) gene and its peptide product leptin were discovered in 1994. Leptin binding to specific receptors in the hypothalamus results in altered expression of orexigenic and anorexigenic neuropeptides that regulate neuroendocrine functions and energy homeostasis. Recent patents and experimental evidence suggest that leptin plays an important role in the pathogenesis of obesity and eating disorders. Central leptin action also includes regulation of blood pressure, bone mass, and immune function. Peripherally also, leptin plays an important role in direct regulation of immune cells, pancreatic beta cells, adipocytes and muscle cells. Leptin receptors are present on human endothelial cells, and it has been shown to induce angiogenesis both in vitro and in vivo. Further, leptin appears to be a potential pressure and volume regulating factor and may function pathophysiologically as a common link to obesity and hypertension. Obesity is also a risk factor for several other cardiovascular diseases like myocardial hypertrophy, myocardial infarction, coronary atherosclerosis and increased cardiovascular morbidity and mortality. Recent progress in understanding central and peripheral leptin receptor signaling pathways may provide potential new targets to combat obesity, hypertension etc.     

Prediction of drug-induced liver injury in humans by using in vitro methods: the case of ximelagatran.

OBJECTIVE: To investigate the possible mechanisms underlying the liver enzyme elevations seen during clinical studies of long-term treatment (>35 days) with ximelagatran, and investigate the usefulness of pre-clinical in vitro systems to predict drug-induced liver effects. METHODS: Ximelagatran and its metabolites were tested for effects on cell viability, mitochondrial function, formation of reactive metabolites and reactive oxygen species, protein binding, and induction of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) gene expression or nuclear orphan receptors. Experimental systems included fresh and cryopreserved hepatocytes, human hepatoma cell lines (HepG2 and HuH-7) and subcellular human liver fractions. RESULTS: Loss of cell viability was only seen in HepG2 cells at ximelagatran concentrations 100 microM and in cryopreserved human hepatocytes at 300 microM, while HuH-7 cells were not affected by 24 h exposure at up to 300 microM ximelagatran. Calcium homeostasis was not affected in HepG2 cells exposed to ximelagatran up to 300 microM for 15 min. There was no evidence for the formation of reactive metabolites when cell systems were exposed to ximelagatran. ALT and AST expression in human hepatoma cell lines were also unchanged by ximelagatran. Mitochondrial functions such as respiration, opening of the transition pore, mitochondrial membrane depolarization and beta-oxidation were not affected by ximelagatran or its metabolites. CONCLUSION: Ximelagatran at concentrations considerably higher than that found in plasma following therapeutic dosing had little or no effect on cellular functions studied in vitro. The in vitro studies therefore did not elucidate the mechanism by which ximelagatran induces liver effects in humans, possibly because of limitations in the experimental systems not reflecting characteristics of the human hepatocyte, restricted exposure time, or because the primary mechanism for the observed clinical liver effects is not on the parenchymal liver cell.     

Immunohistochemical studies on early stage of hepatic damage induced by subacute inhalation of toluene vapor in rats

Toluene is one of the most widely used organic solvents and is commonly recognized as a noxious substance inducing chronically toxic damage to neural, hepatic and renal functions in the workers engaged in printing and painting. Although hepatic cells are generally considered to be vulnerable and susceptible to various organic solvents, particularly chloroform and other halogenated hydrocarbons, the hepatotoxic effects of aromatic hydrocarbons including toluene have not yet been sufficiently characterized. In particular, it still seems unclear whether toluene itself can directly act on hepatic cells, inducing toxic damage to their metabolism and function. To assess the toxic effect of toluene inhalation on rat liver, immunohistochemical analyses of the histological markers for hepatic damage were carried out in animals exposed subacutely to toluene vapor. The immunoreactivities of heat shock proteins (HSP‐70 and HSP‐90) and cytochrome P4502E1 (CYP2E1) in the liver were analyzed to assess the hepatotoxic damage induced by toluene inhalation, and the expression of these histological markers was shown to be substantially enhanced by the subacute exposure to toluene vapor. Toluene inhalation was furthermore shown to enhance the immunoreactivities of α‐smooth muscle actin (α‐SMA), collagen, glucocorticoid receptors (GR) and leptin receptors (Ob‐R) in the liver. Additional studies using human hepatoma HepG2 cells showed that toluene can directly induce toxic damage to cells. These findings suggest that toluene inhalation may primarily induce hepatic damage, which may be secondarily exacerbated by the activation of systemic processes possibly connected with glucocorticoids and leptin. Copyright © 2009 John Wiley & Sons, Ltd.     

Imbalance of NKG2D and its inhibitory counterparts: how does tumor escape from innate immunity?

NK cells form a first line of defence against pathogens or host cells that are stressed or cancerous. NK cells express surface receptors that receive signals from the environment and determine their response to foreign or malignant cells. The effector functions of NK cells are regulated by integrated signals across the array of stimulatory and inhibitory receptors engaged upon interaction with target cell surface ligands. NKG2D is a peculiar activating receptor that is expressed as a disulphide-linked homodimer by all NK cells, alphabeta CD8(+) T cells, gammadeltaT cells and murine macrophages. It not only activates NK cells but also delivers co-stimulatory signals to CD8(+) T cells and gammadeltaT cells. The ligands of NKG2D are induced by cellular stress and are specifically expressed by some tumor cells. Recent studies reveal that the expression of MIC and ULBP on human tumor cells is sufficient to overcome the inhibitory effects of MHC class I expression on NK cell killing and indicate that NKG2D provides first line surveillance against stressed or abnormal cells that have been induced to express one of its ligands. However, malignant tumors develop means to control the expression of activating versus inhibitory receptors on immune cells and their ligands on tumor cell themselves in favor of tolerance. Modulating the balance between activating and inhibitory signals through NK cell receptors on NK cells may open a new approach to NK cell-based biotherapy for cancer and infectious diseases.     

Characterization of the role of ABCG2 as a bile acid transporter in liver and placenta

ABCG2 is involved in epithelial transport/barrier functions. Here, we have investigated its ability to transport bile acids in liver and placenta. Cholylglycylamido fluorescein (CGamF) was exported by WIF-B9/R cells, which do not express the bile salt export pump (BSEP). Sensitivity to typical inhibitors suggested that CGamF export was mainly mediated by ABCG2. In Chinese hamster ovary (CHO cells), coexpression of rat Oatp1a1 and human ABCG2 enhanced the uptake and efflux, respectively, of CGamF, cholic acid (CA), glycoCA (GCA), tauroCA, and taurolithocholic acid-3-sulfate. The ability of ABCG2 to export these bile acids was confirmed by microinjecting them together with inulin in Xenopus laevis oocytes expressing this pump. ABCG2-mediated bile acid transport was inhibited by estradiol 17β-d-glucuronide and fumitremorgin C. Placental barrier for bile acids accounted for <2-fold increase in fetal cholanemia despite >14-fold increased maternal cholanemia induced by obstructive cholestasis in pregnant rats. In rat placenta, the expression of Abcg2, which was much higher than that of Bsep, was not affected by short-term cholestasis. In pregnant rats, fumitremorgin C did not affect uptake/secretion of GCA by the liver but inhibited its fetal-maternal transfer. Compared with wild-type mice, obstructive cholestasis in pregnant Abcg2(-/-) knockout mice induced similar bile acid accumulation in maternal serum but higher accumulation in placenta, fetal serum, and liver. In conclusion, ABCG2 is able to transport bile acids. The importance of this function depends on the relative expression in the same epithelium of other bile acid exporters. Thus, ABCG2 may play a key role in bile acid transport in placenta, as BSEP does in liver.     

Physiological factors affecting the expression of FMO1 and FMO3 in the rat liver and kidney

FMO1 and FMO3, the main FMOs described in the rat, are highly expressed in the liver and the kidney. The age, from 3 to 11 weeks, and gender-dependent expression of FMO1 and FMO3 in the rat liver and kidney were investigated. Based on the enzyme activities, protein levels and mRNA levels, this study demonstrates an important increase in the expression of the FMO3 in the liver of male rats during a period that corresponds to the acquisition of the sexual maturity. Rat liver FMO1 remains unchanged during this period of observation. The evolutions of both isoforms in the kidney of the male rat are similar to those observed in the liver. On the contrary, the important decrease in the total flavin-containing monooxygenase (FMO) activity observed in the liver of female rat is linked to a considerable decrease in the FMO1-dependent activity, FMO1 protein and FMO1 mRNA levels as a function of age. The expression of the FMO3 in the liver does not seem to be affected by the age of the female rat. Inversely, the expression of FMO1 in the female rat kidneys does not seem to be modified as a function of age while the expression of FMO3 is strongly increased.     

瘦素对L-02肝细胞甘油三酯沉积及乙酰辅酶A羧化酶表达的影响

目的观察瘦素对人L-02脂肪变肝细胞甘油三酯合成的影响,探讨瘦素在非酒精性脂肪性肝病发生、发展中的作用。方法人肝L-02细胞在50%胎牛血清1640培养基中造模24 h。设立正常组、模型组、处理组,处理组分为3个亚组,分别应用瘦素10-7 mol/L、10-6 mol/L、10-5 mol/L处理24 h。均行油红"O"染色,观察脂肪化情况,RT-PCR测CA羧化酶mRNA表达。结果油红"O"染色显示,50%胎牛血清的1640培养基24 h能成功制造肝细胞脂肪变性模型;加入瘦素处理后,脂肪化程度减轻,且与瘦素呈剂量依赖性关系;RT-PCR显示,肝细胞脂肪变性后,乙酰辅酶A羧化酶mRNA表达增强,加入瘦素处理后,乙酰辅酶A羧化酶mRNA表达明显减弱,与瘦素呈剂量依赖性关系。结论肝细胞脂肪变性时,瘦素能使肝细胞脂肪化程度减轻,能减少肝细胞甘油三酯的合成,对脂肪肝防治有一定的作用。     

Functional comparisons of the lysophosphatidic acid receptors, LP(A1)/VZG-1/EDG-2, LP(A2)/EDG-4, and LP(A3)/EDG-7 in neuronal cell lines using a retrovirus expression system

Lysophosphatidic acid (LPA) is a potent lipid mediator with diverse physiological actions on a wide variety of cells and tissues. Three cognate G-protein-coupled receptors have been identified as mammalian LPA receptors: LP(A1)/VZG-1/EDG-2, LP(A2)/EDG-4, and LP(A3)/EDG-7. The mouse forms of these genes were analyzed in rodent cell lines derived from nervous system cells that can express these receptors functionally. An efficient retrovirus expression system was used, and each receptor was heterologously expressed in B103 rat neuroblastoma cells that neither express these receptors nor respond to LPA in all assays tested. Comparative analyses of signaling pathways that are activated within minutes of ligand delivery were carried out. LPA induced cell rounding in LP(A1)- and LP(A2)-expressing cells. By contrast, LP(A3) expression resulted in neurite elongation in B103 cells and inhibited LPA-dependent cell rounding in TR mouse neuroblast cells that endogenously express LP(A1) and LP(A2) but not LP(A3). Each of the receptors could couple to multiple G-proteins and induced LPA-dependent inositol phosphate production, mitogen-activated protein kinase activation, and arachidonic acid release while inhibiting forskolin-induced cAMP accumulation, although the efficacy and potency of LPA varied from receptor to receptor. These results indicate both shared and distinct functions among the three mammalian LPA receptors. The retroviruses developed in this study should provide tools for addressing these functions in vivo.