肝星状细胞主要信号转导通路与肝纤维化的关系

肝纤维化是肝脏对各种急慢性炎症刺激损伤修复反应的结果,以胶原为主的细胞外基质(ECM)生成与降解之间失衡,在肝内大量沉积的病理过程。活化的肝星状细胞(HSC)是肝纤维化时产生ECM的主要细胞,是肝纤维化发生的核心环节。控制HSC的激活和增殖以逆转肝纤维化的进程是抗肝纤维化研究的重点之一。因此,了解影响HSC活化增殖的有关信号转导通路的作用机制有助于从根本上治疗肝纤维化,为肝纤维化的治疗提供更多更有效的思路和方法。目前研究较多的信号途径有TGF-β/Smad通路、MAPK通路、PPARγ通路、Leptin通路I、ntegrin通路、NF-κB通路等。     

肝星状细胞激活的细胞内信号转导

肝星状细胞(HSC)在肝纤维化形成过程中具有重要意义,当肝受到各种损伤时,HSC可被激活并向肌纤维母细胞样细胞转化,主要表现为细胞增殖、游动、收缩能力增强及生长因子、细胞因子和细胞外基质(ECM)的大量合成.参与HSC激活过程的因素主要有ECM成分和结构的变化、生长因子、细胞因子、趋化因子、氧化性应激产物及其他可溶性化学物质,它们需通过细胞内与细胞增殖及ECM合成与降解、细胞内ECM与血管活性物质等的信号转导才能发挥作用.     

肝纤维化的信号转导通路

肝纤维化是多种慢性肝病进展至肝硬化的中间过程,其特征为以胶原蛋白为主的细胞外基质(extracellular matrix,ECM)合成与降解失衡．现有的研究表明,肝星状细胞(hepatic stellate cells,HSC)是肝纤维化时过量ECM的主要来源,激活的HSC大量增殖,发生表型改变并分泌过多的ECM沉积于肝脏是肝纤维化形成的关键．这一复杂的病理过程是多条细胞信号传导通路和一系列细胞信息分子网络共同控制的结果,转化生长因子β(transforming growth factor beta,TGFβ)等细胞因子分别通过TGFβ- Smad通路、ROCK通路、MAPK(丝裂原激活的蛋白激酶,mitogen activatecl protein kinase)通路、Rho-、PI-3K通路等众多细胞信号通路网络交互影响,共同介导肝纤维化复杂的病理生理变化．现综述参与肝纤维化的主要信号转导通路及其可能的致肝纤维化机制．     

诱导活化肝星状细胞凋亡主要信号通路的研究进展

肝纤维化是各种病因引起的肝脏慢性进行性的病理过程,肝纤维化时细胞外基质(ECM)合成大于降解导致ECM在肝内大量沉积。肝星状细胞(HSC)的激活、转化并产生分泌大量ECM是肝纤维化形成的关键环节。而通过诱导活化的HSC发生凋亡是逆转肝纤维化的重要手段之一。就主要的凋亡信号通路:死亡受体通路、线粒体通路、内质网通路、神经生长因子通路进行一一阐述。指出了对活化HSC的凋亡途径进行选择性的药物干预有望发挥抗肝纤维化的作用。     

NOX介导的MAPK、PI3K/Akt信号通路与肝纤维化的研究进展

肝星状细胞(hepatic stellate cells,HSC)是肝纤维化的主要细胞,是细胞外基质(extracellular matrix,ECM)的重要来源.烟酰胺腺嘌呤二核苷酸磷酸氧化酶(NADPH oxidase,NOX)产生活性氧(reactive oxygen species,ROS),调控HSCs内信号转导,在肝纤维化发病中起关键作用.NOX产生的ROS可介导丝裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)和磷脂酰肌醇-3激酶/蛋白激酶(phosphatidylin-ositol-3 kinase/Akt,PI3K/Akt)信号通路激活,促进HSC增殖、抑制其凋亡,导致肝纤维化形成.抑制NOX产生ROS,阻断相应的信号通路可诱导HSC凋亡.因此,探索出以NOX为作用靶点的抗纤维化药物意义重大.     

肝星状细胞活化相关信号通路在肝纤维化中的研究进展

肝纤维化是多种慢性肝损伤造成的细胞外基质(extracellular matrix, ECM)过度累积及降解不足的病理结果,如不加以干预会逐渐进展为肝硬化,甚至肝细胞癌。肝星状细胞(hepatic stellate cell, HSC)是ECM的主要来源,并且HSC在肝纤维化的起始、发展和消退过程中发挥关键作用。近年来,HSC活化涉及的信号传导通路成为研究热点,本文总结了HSC活化过程中的重要信号通路。     

肝星状细胞与肝纤维化研究进展

肝星状细胞(HSC)是肝脏的一种非实质细胞,HSC活化导致细胞外基质(ECM)的增加是肝纤维化形成并最终导致肝硬化、肝功能衰竭的主要原因.因此,加强对HSC激活与凋亡调控机制的研究,有助于我们对肝纤维化发生的本质的认识,从而能更有效地防治肝纤维化.     

TGFβ1信号与肝纤维化

肝星状细胞(HSC)是肝纤维化发生的关键细胞,转化生长因子β1(TGFβ1)是活化HSC、促进细胞外基质(ECM)分泌的重要细胞因子,其在肝纤维化的发生发展中有重要的调节作用,文章通过TGFβ1信号转导对HSC的作用来阐述TGFβ1信号与肝纤维化的关系.     

肝星状细胞增殖过程中的信号转导及可能的抗肝纤维化治疗靶点

如何逆转肝纤维化是临床面临的重要问题，其发病机制是一个复杂的级联反应，包括肝星状细胞（HSC）活化、增殖、表达各种信号分子及产生大量以胶原为主的细胞外间质（ECM）成分。活化HSC的增殖受一系列细胞信息分子和细胞内信号传导的调控，作用于这些信号及其转导过程或阻断这些信号转导级联反应的重要环节正成为防治肝纤维化的重要策略。本文就活化肝星状细胞增殖过程中所涉及的主要细胞内信号转导及可能的抗肝纤维化治疗靶点作一综述。     

肝星状细胞靶向导入载体的研究进展

肝星状细胞(HSC)的激活和增生是肝纤维化发生的中心环节,各种致纤维化因素共同通过这一决定性途径启动肝纤维化的过程.活化的HSC合成大量细胞外基质(ECM)沉积在肝脏,从而导致不同程度的肝纤维化.     

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.     

Signal transduction in hepatic stellate cells

ABSTRACT— Hepatic stellate cells (HSC) are presently regarded as one of the key cell types involved in the progression of liver fibrosis and in the related pathophysiological and clinical complications. Following acute or chronic liver tissue damage, HSC undergo a process of activation towards a phenotype characterised by increased proliferation, motility, contractility and synthesis of extracellular matrix (ECM) components. Several factors have been shown to play a key role in the promotion of the full-blown picture of activated HSC. These include extensive changes in the composition and organisation of the ECM, the secretion of several growth factors, cytokines, chemokines, products of oxidative stress and other soluble factors. It is evident that each cellular response to extracellular stimuli must be framed in a scenario where different forces modulate one another and result in a prevalent biological effect. Along these lines, the identification and characterisation of intracellular signalling pathways activated by different stimuli in HSC represent a mandatory step. In this review article we have made an attempt to summarise recent acquisitions to our knowledge of the involvement of different intracellular signalling pathways in key aspects of HSC biology.     

Hepatic stellate cells and oxidative stress]

Hepatic fibrosis is a wound-healing response that takes place during chronic liver injury and is characterized by excessive production and deposition of extracellular matrix (ECM) components, mainly collagen type I. Hepatic stellate cells (HSC) are responsible for the excessive production of scar tissue during liver fibrosis. Activation of HSC, the main step in the development of hepatic fibrosis, is mediated by cytokines and reactive oxygen species (ROS) released by damaged hepatocytes and/or activated Kupffer cells and even HSC themselves. While HSC usually remain quiescent, in response to factors promoting liver injury they undergo activation and become highly proliferative and fibrogenic. Indeed a key feature of HSC activation is uncontrolled production of collagen type I. Collagen is a heterotrimeric protein composed of two a1 chains and one a2 chain forming a triple helix structure. Initiation of HSC activation is largely due to paracrine stimulation, whereas the perpetuation of such activated state involves autocrine as well as paracrine loops. This review focuses on the role of oxidant stress on the activation of stellate cells.     

促纤维化因子在肝纤维化发生中的作用研究进展

肝纤维化是多种病因所致的慢性肝损伤的一种创伤愈合反应,持续的炎症与纤维形成最终导致肝硬化。肝星状细胞（HSC）是肝纤维化的主要生成细胞,肝脏内细胞外基质（ECM）的过度沉积是其主要功能。各种促纤维化因子如血管紧张素-II（AngII）、血小板衍生生长因子（PDGF）、血管内皮生长因子（VEGF）、转化生长因子-β（TGF-β）、瘦素、结缔组织因子等可与HSC表面上相应的受体结合,并激活相应的信号通路,进而导致HSC的激活、增殖,ECM过度沉积,引起肝纤维化形成。因此,了解各种促纤维化因子与肝纤维化的关系,可为抗纤维化的科学研究及临床治疗提供理论依据。     

Halofuginone to prevent and treat thioacetamide-induced liver fibrosis in rats

Hepatic fibrosis is associated with activation of hepatic stellate cells (HSC), the major source of the extracellular matrix (ECM) proteins. The predominant ECM protein synthesized by the HSC is collagen type I. We evaluated the effect of halofuginone-an inhibitor of collagen synthesis-on thioacetamide (TAA)-induced liver fibrosis in rats. In the control rats the HSC did not express smooth muscle actin, collagen type I gene, or tissue inhibitor of metalloproteinases-2 (TIMP-2), suggesting that they were in their quiescent state. When treated with TAA, the livers displayed large fibrous septa, which were populated by smooth muscle actin-positive cells expressing high levels of the collagen alpha1(I) gene and containing high levels of TIMP-2, all of which are characteristic of advanced fibrosis. Halofuginone given orally before fibrosis induction prevented the activation of most of the stellate cells and the remaining cells expressed low levels of collagen alpha1(I) gene, resulting in low levels of collagen. The level of TIMP-2 was almost the same as in the control livers. When given to rats with established fibrosis, halofuginone caused almost complete resolution of the fibrotic condition. The levels of collagen, collagen alpha1(I) gene expression, TIMP-2 content, and smooth muscle actin-positive cells were as in the control rats. Halofuginone inhibited the proliferation of other cell types of the fibrotic liver in vivo and inhibited collagen production and collagen alpha1(I) gene expression in the SV40-immortalized rat HSC-T6 cells in vitro. These results suggest that halofuginone may become an effective and novel mode of therapy in the treatment of liver fibrosis.     

Hepatic fibrogenesis]

In acute injury, liver recovers completely without any scarring change or complication. However, large portion of liver is changed into fibrotic state by excessive production of extracellular matrix (ECM) under chronic injury. Excessive production of ECM results in hepatic fibrosis and repeated process of hepatic fibrosis progress into liver cirrhosis. Liver cirrhosis is an irreversible and terminal state of chronic liver disease and one of the major causes of death in Korea. To block the progression to liver cirrhosis, various studies in the field of virology and immunology have been proceeded. Recently, studies on the hepatic fibrogenesis have progressed with the development of molecular biology. Hepatic stellate cells (HSC) play a key role in the pathogenesis of hepatic fibrosis by producing ECM. The degree of hepatic fibrosis depends on the proliferation and activation of HSC and increased net production of collagen. Therefore, inhibition of HSC activation is one of the main ways to block the progression of hepatic fibrosis. Many kinds of factors such as oxidative stress, acetaldehyde, ascorbic acid, transforming growth factor-beta (TGF-beta) and carbon tetrachloride (CCl4) have been reported to activate HSC and stimulate collagen gene expression. Although there are no definite and effective antifibrogenic agents, possible candidates are antioxidants, interferon, retinoids such as beta-carotene, flavonoids, renin-angiotensin system inhibitors and peroxisome proliferator activated receptor-gamma (PPAR-gamma) agonists. We tried to evaluate the charateristics of HSC in order to develop agents that inhibit hepatic fibrogenesis.     

Tetramethylpyrazine reduces glucose and insulin-induced activation of hepatic stellate cells by inhibiting insulin receptor-mediated PI3K/AKT and ERK pathways

Hepatic stellate cell (HSC) activation is the central event during liver fibrogenesis. Metabolic syndrome characterized by hyperglycemia and hyperinsulinemia contributes to nonalcoholic steatohepatitis-associated liver fibrosis. This study was to investigate the effects of tetramethylpyrazine (TMP) on HSC activation induced by glucose and insulin (Glu/Ins) and the underlying mechanisms. Results showed that Glu/Ins significantly stimulated proliferation, invasion, adhesion, and extracellular matrix (ECM) production in HSCs. TMP inhibited HSC proliferation, invasion and adhesion, and reduced the expression of marker genes related to HSC activation in Glu/Ins-activated HSCs. Mechanistic evidence revealed that TMP reduced insulin receptor (InsR) expression and blocked the downstream phosphatidylinositol-3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK) cascades, which was required for TMP attenuation of HSC activation. Moreover, TMP modulated the genes relevant to ECM homeostasis favoring ECM degradation. It could be concluded that TMP inhibited Glu/Ins-stimulated HSC activation and ECM production by inhibiting InsR-mediated PI3K/AKT and ERK pathways.     

Osteopontin is a novel downstream target of SOX9 with diagnostic implications for progression of liver fibrosis in humans

Osteopontin (OPN) is an important component of the extracellular matrix (ECM), which promotes liver fibrosis and has been described as a biomarker for its severity. Previously, we have demonstrated that Sex-determining region Y-box 9 (SOX9) is ectopically expressed during activation of hepatic stellate cells (HSC) when it is responsible for the production of type 1 collagen, which causes scar formation in liver fibrosis. Here, we demonstrate that SOX9 regulates OPN. During normal development and in the mature liver, SOX9 and OPN are coexpressed in the biliary duct. In rodent and human models of fibrosis, both proteins were increased and colocalized to fibrotic regions in vivo and in culture-activated HSCs. SOX9 bound a conserved upstream region of the OPN gene, and abrogation of Sox9 in HSCs significantly decreased OPN production. Hedgehog (Hh) signaling has previously been shown to regulate OPN expression directly by glioblastoma (GLI) 1. Our data indicate that in models of liver fibrosis, Hh signaling more likely acts through SOX9 to modulate OPN. In contrast to Gli2 and Gli3, Gli1 is sparse in HSCs and is not increased upon activation. Furthermore, reduction of GLI2, but not GLI3, decreased the expression of both SOX9 and OPN, whereas overexpressing SOX9 or constitutively active GLI2 could rescue the antagonistic effects of cyclopamine on OPN expression. Conclusion: These data reinforce SOX9, downstream of Hh signaling, as a core factor mediating the expression of ECM components involved in liver fibrosis. Understanding the role and regulation of SOX9 during liver fibrosis will provide insight into its potential modulation as an antifibrotic therapy or as a means of identifying potential ECM targets, similar to OPN, as biomarkers of fibrosis. (HEPATOLOGY 2012;56:1108-1116).