人肝星状细胞激活和抑制及其相关分子机制的研究进展

肝纤维化是肝脏对一系列慢性刺激的损伤修复反应,以细胞外基质的过度沉积为主要特征。许多研究证明人肝星状细胞(hepatic stellate cells,HSCs)的活化与增殖是肝纤维化形成的中心环节。因此,肝星状细胞激活机制及抑制活化途径的研究和发现成为防治肝纤维化的关键。目前,国际上肝纤维化药物研发的思路之一是从肝纤维化发生的机制,即肝星状细胞激活机制中寻找分子靶点。近年来,对各种使肝星状细胞活化的信号通路及相关抑制机制的研究取得了一些进展,但由于肝星状细胞活化是多条信号通路相互协调的结果,其复杂性、未知性造成了阻断方式的特异性、多样性,使该研究还仅限于实验室阶段,要想应用于临床还需要大量实验证明。该文就最新发现的肝星状细胞激活和抑制及相关分子机制作一综述。     

活化的肝星状细胞RBP-J可诱导性基因敲除小鼠的构建及应用

目的:利用Cre-loxp可诱导系统构建活化的肝星状细胞RBP-J可诱导性基因敲除小鼠模型,以实现肝纤维化过程中活化的肝星状细胞Notch信号通路的特异性阻断。方法:将Sm22αCre ERT2和RBP-Jflox/flox转基因小鼠杂交,得到F1小鼠,将繁殖的F1小鼠继续进行交配,得到F2小鼠,通过PCR鉴定出基因型为Sm22αCre ERT2,RBP-Jflox/flox的小鼠。通过腹腔注射四氯化碳建立肝纤维化模型,检测四氯化碳注射不同时间段后肝脏纤维化进展情况和肝星状细胞活化过程中Sm22α的表达情况。注射他莫昔芬诱导活化肝星状细胞中RBP-J基因的特异性敲除。分选肝星状细胞,q-PCR和Western Blot检测活化肝星状细胞中Notch下游靶基因Hes1、Hey1表达情况以验证敲除效果。结果:通过连续交配我们获得了Sm22αCre ERT2,RBP-Jflox/flox小鼠。四氯化碳腹腔注射4周即可诱导肝脏发生较为明显的纤维化,同时肝星状细胞活化并逐渐高表达Sm22α。给予他莫昔芬诱导Cre重组酶发挥作用后,敲除了活化的肝星状细胞中的RBP-J基因,其下游基因Hes1、Hey1表达降低70%以上,阻断了Notch信号通路。结论:我们成功构建了RBP-J可诱导性条件性基因敲除小鼠模型,实现了小鼠肝纤维化过程中活化肝星状细胞Notch信号通路的阻断,为深入研究Notch信号通路在肝纤维化中的作用和机制奠定了坚实的基础。     

肝纤维化发病机制中细胞和分子机制的研究进展

关于肝纤维化形成的复杂的细胞和分子联系已经有了相当多的研究进展。最近的数据表明,纤维化进程的终止和纤维分解途径的恢复可以逆转晚期肝纤维化甚至肝硬化。因此,需要更好地阐明参与肝纤维化的细胞和分子机制。HSC(肝星状细胞)的激活是肝纤维化发生的中心事件,此外还有产生基质的其他细胞来源,包括肝门区的成纤维细胞,纤维细胞和骨髓来源的肌纤维母细胞。这些细胞与其邻近细胞通过多种联系聚集产生纤维疤痕并造成持续性损伤。阐明不同类型的细胞的相互作用,揭示细胞因子对这些细胞的影响,理清活化HSC基因表达的调控,将有助于我们探索新的肝纤维化治疗靶点。此外,不同的病因有不同的致病途径,弄清这一点有助于针对特异性疾病治疗方法的发现。本文概述了肝纤维化的细胞和分子机制的最新研究进展,可能为未来治疗方法带来新的突破。     

铁和铁调素在肝纤维化中的作用

多种慢性肝纤维化疾病均伴有肝脏过多的铁沉积,铁在肝纤维化发病中起重要作用。其机制包括:铁通过催化自由基生成和脂质过氧化反应破坏细胞生物大分子,引起细胞凋亡和坏死,激活肝星状细胞转化为肌成纤维细胞等。近来研究证实,由肝脏产生的铁调素(Hepc)表达的降低在慢性肝纤维化疾病肝脏铁沉积中起重要作用,补充外源性Hepc可以降低肝纤维化患者肝脏铁含量。因此,铁调素用于治疗铁过载疾病及肝纤维化具有重要价值。     

Hippo-YAP/TAZ与Notch信号通路在肝纤维化中的作用

病毒性或代谢性慢性肝病引起的肝纤维化是全球健康的一大挑战。Hippo-YAP/TAZ通路与Notch信号通路在肝纤维化进展中发挥了至关重要的作用。经典的Hippo通路核心激酶级联在大量外界信号的作用下，通过磷酸化使转录共激活因子YAP/TAZ失活，从而调控细胞的生长与增殖以及干细胞再生、肿瘤形成等过程。Notch信号通路通过调控脂质代谢、IR、氧化应激、自噬、炎症与纤维化等方面参与肝病的发生与发展。该文就Hippo-YAP/TAZ与Notch信号通路在肝纤维化过程中对肝星状细胞、巨噬细胞、肝脂质代谢等方面的影响及两条通路的交互作用进行了详细地综述。概括了2条通路在肝纤维化中的研究现状，总结分析了交互作用研究中存在的问题和未来的方向，旨在为肝纤维化的防治提供新的靶点和理论依据。     

天然产物通过诱导铁死亡改善肝纤维化的研究进展

肝纤维化是多种慢性肝病发展为肝硬化和肝癌所必须经历的共同病理过程,在其发生、发展过程中受到多种细胞因子以及信号通路的调控。铁死亡是由铁过载、氧化还原稳态紊乱和脂质过氧化增加引起的一种新的细胞死亡调控模式,与肝纤维化密切相关。诱导肝星状细胞发生铁死亡可能是肝纤维化治疗的潜在靶标。许多天然产物可以诱导肝星状细胞发生铁死亡进而抑制肝纤维化的进展,因此越来越受到关注。然而,关于天然产物通过铁死亡途径调节肝纤维化的综述文章却相对较少。该文简述了天然产物通过铁死亡调控影响肝纤维化的干预机制及应用,重点探讨铁死亡与肝纤维化的关系,以及天然产物靶向铁死亡对肝纤维化的调控作用,旨在为天然产物治疗代谢性疾病和肝脏疾病的发展提供新的理论依据,也为将来的药物制取提供更多的备选策略。     

肝星状细胞中表皮形态发生素表达调控机制及其作用研究

肝星状细胞是肝脏中重要的间质细胞,是肝细胞外基质的主要来源.表皮形态发生素(epimorphin、EPM、syntaxin2)在肝脏发育、再生及癌变过程中发挥了重要的作用,目前其表达变化的调控机制及对肝星状细胞的作用还未有报道.通过对肝组织标本进行检测,发现肝纤维化过程中肝星状细胞表达EPM上调.从表观遗传学的角度对EPM表达变化调控机制进行研究,发现DNA去甲基化促进了EPM的表达.为了研究EPM对肝星状细胞的可能的调节作用,将EPM表达质粒转染肝星状细胞,之后检测了EPM对肝星状细胞增殖及迁移能力的变化.结果证明EPM能够促进肝星状细胞的增殖与迁移.本研究发现,激活的肝星状细胞高表达EPM可能是由于DNA去甲基化引起的,同时,高表达的EPM能够促进肝星状细胞的增殖与迁移,进而促进肝纤维化进展.     

三七总皂苷抗肝纤维化作用机制的研究进展

肝纤维化是各种慢性肝病共同的病理基础,是慢性肝病发展到肝硬化、肝癌的必经途径。寻找有效的抗肝纤维化药物是近年研究的热点,其中对三七的研究也取得了很大进展。现综述近几年三七皂苷在保护肝细胞、抑制肝星形细胞活化、促进肝星形细胞凋亡、抑制细胞外基质的合成及促使其降解等方面的作用及可能机制,同时也阐述了三七总皂苷在抗肝纤维化中的重要意义及应用前景。     

胰腺星状细胞活化相关的信号转导通路

胰腺纤维化是慢性胰腺炎（chronic pancreatitis,CP）和胰腺癌主要的病理学特征,活化的胰腺星状细胞（pancreatic stellate cells,PSCs）是公认的致胰腺纤维化的主要效应细胞。PSCs的活化涉及到几个重要的信号转导通路：有丝分裂原活化蛋白激酶（mitogen-activated protein kinases,MAPK）、磷酯酰肌醇3激酶（phosphatidylinositol 3-kinase,PI3K）=、Smad信号转导蛋白、过氧化物酶体增生物激活受体-γ（PPAR-γ）、Rho-ROCK等细胞内信号途径。探讨这些信号通路在胰腺纤维化中所起的作用对慢性胰腺炎、胰腺癌及糖尿病的治疗有重要意义。现就与PSCs激活有关的信号通路的研究结合最新进展作一综述。     

TIMP-1和肝星状细胞对肝纤维化的影响

肝纤维化是慢性肝病向肝硬化发展的必经之路,是细胞外基(Extracellular matrix,ECM)在肝内过多沉积所致。ECM主要由激活的肝星状细胞(Hepatic stellate cell,HSC)合成,同时它的降解受到基质金属蛋白酶组织抑制剂-1(Tissue inhibitor of metal protease-1,TIMP-1)的调控,因此HSC及TIMP-1对肝纤维化形成至关重要。近年来针对HSC及TIMP-1抗肝纤维化的研究已成为热点,就HSC及TIMP-1的生物学特性及其对肝纤维化的作用作一综述。     

Hepatic fibrosis--role of hepatic stellate cell activation

Hepatic fibrosis is a reversible wound healing response characterized by accumulation of extracellular matrix (ECM), or "scar," that follows chronic but not self-limited liver disease. The ECM components in fibrotic liver are similar regardless of the underlying cause. Activation of hepatic stellate cells is the central event in hepatic fibrosis. These perisinusoidal cells orchestrate an array of changes including degradation of the normal ECM of liver, deposition of scar molecules, vascular and organ contraction, and release of cytokines. Not only is hepatic fibrosis reversible, but it is also increasingly clear that cirrhosis may be reversible as well. The exact stage at which fibrosis/cirrhosis becomes truly irreversible is not known. Antifibrotic therapies will soon be a clinical reality. Emerging therapies will be targeted to those patients with reversible disease. The paradigm of stellate cell activation provides an important framework for defining therapeutic targets.     

Pathogenesis of liver fibrosis: role of oxidative stress

In the liver, the progressive accumulation of connective tissue, a complex and dynamic process termed fibrosis, represents a very frequent event following a repeated or chronic insult of sufficient intensity to trigger a "wound healing"-like reaction. The fibrotic process recognises the involvement of various cells and different factors in bringing about an excessive fibrogenesis with disruption of intercellular contacts and interactions and of extracellular matrix composition. However, Kupffer cells, together with recruited mononuclear cells, and hepatic stellate cells are by far the key-players in liver fibrosis. Their cross-talk is triggered and favoured by a series of chemical mediators, with a prominent role played by the transforming growth factor beta. Both expression and synthesis of this inflammatory and pro-fibrogenic cytokine are mainly modulated through redox-sensitive reactions. Further, involvement of reactive oxygen species and lipid peroxidation products can be clearly demonstrated in other fundamental events of hepatic fibrogenesis, like activation and effects of stellate cells, expression of metalloproteinases and of their specific inhibitors. The important outcome of such findings as regards the pathogenesis of liver fibrosis derives from the observation of a consistent and marked oxidative stress condition in many if not all chronic disease processes affecting hepatic tissue. Hence, reactive oxidant species likely contribute to both onset and progression of fibrosis as induced by alcohol, viruses, iron or copper overload, cholestasis, hepatic blood congestion.     

Different effects of rat interferon alpha, beta and gamma on rat hepatic stellate cell proliferation and activation

Background  

Liver fibrosis is the common sequel of chronic liver diseases. Recent studies have identified hepatic stellate cells as the primary cell type mediating hepatic fibrogenesis. It has been demonstrated that hepatic stellate cells undergo a process of activation during the development of liver fibrosis. During the activation process, hepatic stellate cells acquire myofibroblast-like phenotype featuring the expression of smooth muscle alpha actin. Interferons have been employed for the treatment of viral hepatitis. However, it is unclear what is the effect of interferons on the prevention and treatment of liver fibrosis. Moreover, it is not clear whether there are any differences among interferon alpha, interferon beta, and interferon gamma in the treatment of liver fibrosis. Therefore, our objective in current study is to investigate the effects of rat interferon-α, interferon-β, and interferon-γ on the proliferation and activation of rat hepatic stellate cells.     

Innate immunity in alcoholic liver disease

Excessive alcohol consumption is a leading cause of chronic liver disease in the Western world. Alcohol-induced hepatotoxicity and oxidative stress are important mechanisms contributing to the pathogenesis of alcoholic liver disease. However, emerging evidence suggests that activation of innate immunity involving TLR4 and complement also plays an important role in initiating alcoholic steatohepatitis and fibrosis, but the role of adaptive immunity in the pathogenesis of alcoholic liver disease remains obscure. Activation of a TLR4-mediated MyD88-independent (TRIF/IRF-3) signaling pathway in Kupffer cells contributes to alcoholic steatohepatitis, whereas activation of TLR4 signaling in hepatic stellate cells promotes liver fibrosis. Alcohol consumption activates the complement system in the liver by yet unidentified mechanisms, leading to alcoholic steatohepatitis. In contrast to activation of TLR4 and complement, alcohol consumption can inhibit natural killer cells, another important innate immunity component, contributing to alcohol-mediated acceleration of viral infection and liver fibrosis in patients with chronic viral hepatitis. Understanding of the role of innate immunity in the pathogenesis of alcoholic liver disease may help us identify novel therapeutic targets to treat this disease.     

Pyrroloquinoline-Quinone Suppresses Liver Fibrogenesis in Mice

Liver fibrosis represents the consequences of a sustained wound healing response to chronic liver injuries, and its progression toward cirrhosis is the major cause of liver-related morbidity and mortality worldwide. However, anti-fibrotic treatment remains an unconquered area for drug development. Accumulating evidence indicate that oxidative stress plays a critical role in liver fibrogenesis. In this study, we found that PQQ, a natural anti-oxidant present in a wide variety of human foods, exerted potent anti-fibrotic and ROS-scavenging activity in Balb/C mouse models of liver fibrosis. The antioxidant activity of PQQ was involved in the modulation of multiple steps during liver fibrogenesis, including chronic liver injury, hepatic inflammation, as well as activation of hepatic stellate cells and production of extracellular matrix. PQQ also suppressed the up-regulation of RACK1 in activated HSCs in vivo and in vitro. Our data suggest that PQQ suppresses oxidative stress and liver fibrogenesis in mice, and provide rationale for the clinical application of PQQ in the prevention and treatment of liver fibrosis.     

The hepatic stellate cell in the post-genomic era

The draft human genome sequence was published on February 15, 2001, which will provide a huge amount of information on human genetics, human disease, and human cell biology. Now, medical scientists and cell biologists are turning their attention to illustrating gene expression pattern using gene microarray and to identifying the functions and the expression patterns of proteins encoded by the genes. Hepatic stellate cell is one of the sinusoid-constituent cells that play multiple roles in the liver pathophysiology. Transformation of stellate cells from the vitamin A-storing phenotype to the "myofibroblastic" one closely correlates to hepatic fibrosis during chronic liver trauma. Analyses of the molecular mechanisms of stellate cell activation have made a great progress, in particular, in the field of intracellular signal transduction of transforming growth factor-beta and platelet-derived growth factor, integrin signaling related to cell-adhesion, and cell motility-associated Rho and focal-adhesion kinase. Accumulation of the information on the stellate cell activation would shed light on the establishment of a novel therapeutic strategy against fibrosis of human liver disease.     

Endoplasmic reticulum stress and autophagy are involved in adipocyte-induced fibrosis in hepatic stellate cells

Liver fibrosis, with the characterization of progressive accumulation of extracellular matrix (ECM), is the common pathologic feature in the process of chronic liver disease. Hepatic stellate cells (HSCs) which are activated and differentiate into proliferative and contractile myofibroblasts are recognized as the main drivers of fibrosis. Obesity-related adipocytokine dysregulation is known to accelerate liver fibrosis progression, but the direct fibrogenic effect of mature adipocytes on HSCs has been rarely reported. Therefore, the purpose of this study was to explore the fibrogenic effect of adipocyte 3T3-L1 cells on hepatic stellate LX-2 cells. The results showed that incubating LX-2 cells with the supernatant of 3T3-L1 adipocytes triggered the expression of ECM related proteins, such as α-smooth muscle actin (α-SMA), type I collagen (CO-I), and activated TGF β/Smad2/3 signaling pathway in LX-2 cells. In addition, 3T3-L1 cells inhibited insulin sensitivity, activated endoplasmic reticulum stress and autophagy to promote the development of fibrosis. These results supported the notion that mature adipocytes can directly activate hepatic stellate cells, and the establishment of an in vitro model of adipocytes on HSCs provides an insight into screening of drugs for liver diseases, such as nonalcoholic fatty liver disease.

     

Hepatic stellate cell: A star cell in the liver

Hepatic stellate cells represent a highly versatile cytotype that plays a significant role in liver development and differentiation, regeneration, xenobiotic response, immunoregulation, control of hepatic blood flow and inflammatory reactions. Because of the wide panel of molecular intermediates they may produce and secrete, particularly after their sustained activation in a disease state, hepatic stellate cells are definitely involved in the pathogenesis of various liver pathologies, besides the well know key role in fibrosis and extracellular matrix remodelling. In particular, they can actively contribute to the progression of hepatitis and steatohepatitis of different aetiology, and of liver carcinogenesis.