Inhibitory effects of long noncoding RNA MEG3 on hepatic stellate cells activation and liver fibrogenesis

Long noncoding RNAs (lncRNAs) are being increasingly recognized as major players in governing fundamental biological processes through diverse mechanisms. Maternally expressed gene 3 (MEG3) is an imprinted gene located at 14q32 that encodes a lncRNA correlated with several human cancers. Recently, the methylation-dependent downregulation of MEG3 has been described in liver cancers. However, its biological functional role in liver fibrosis remains unknown. In our study, MEG3 levels were remarkably decreased in CCl₄-induced mouse liver fibrosis models and human fibrotic livers as demonstrated by real-time quantitative PCR. Moreover, the expression of MEG3 was downregulated in human hepatic stellate cell lines LX-2 cells in response to transforming growth factor-β1 (TGF-β1) stimulation in dose and time-dependent manner. Enforced expression of MEG3 in LX-2 cells inhibited TGF-β1-induced cell proliferation, while promoting cell apoptosis. In addition, hypermethylation of MEG3 promoter was identified by methylation-specific PCR and MEG3 expression was robustly increased by the inhibition of methylation with either 5-aza-2-deoxycytidine (5-azadC), or siRNA to DNA methyltransferase 1 (DNMT1) in TGF-β1-induced LX-2 cells. More importantly, overexpression of MEG3 could activate p53 and mediate cytochrome c release, subsequently leading to caspase-3-dependent apoptosis in TGF-β1-treated LX-2 cells. These findings suggested that MEG3 may play an important role in stellate cell activation and liver fibrosis progression and act as a novel potential therapeutic target for liver fibrosis.     

Brivanib Attenuates Hepatic Fibrosis In Vivo and Stellate Cell Activation In Vitro by Inhibition of FGF,VEGF and PDGF Signaling

MethodsIn vivo, we induced liver fibrosis by bile duct ligation (BDL), chronic carbon tetrachloride (CCl₄), and chronic thioacetamide (TAA) administration. Liver fibrosis was examined by immunohistochemistry and Western immunoblotting. In vitro, we used LX-2 human hepatic stellate cells (HSCs) to assess the effect of brivanib on stellate cell proliferation and activation.ResultsAfter in vivo induction with BDL, CCl₄, and TAA, mice treated with brivanib showed reduced liver fibrosis and decreased expression of collagen Iα1 and α-smooth muscle actin in the liver. In vitro, brivanib decreased proliferation of HSCs induced by platelet-derived growth factor (PDGF), VEGF, and FGF. Brivanib also decreased stellate cell viability and inhibited PDGFBB-induced phosphorylation of its cognate receptor.ConclusionBrivanib reduces liver fibrosis in three different animal models and decreases human hepatic stellate cell activation. Brivanib may represent a novel therapeutic approach to treatment of liver fibrosis and prevention of liver cancer.     

肝纤维化的表观遗传学研究进展

肝纤维化是常见的慢性进行性肝病,是慢性肝病发展到肝硬化阶段的必经阶段,却有逆转的可能性。肝纤维化的中心环节是肝星状细胞的激活。关于肝星状细胞的激活,除了经典的肝纤维化通路,不断有新的通路和机制出现,包括自噬、内质网应激、氧化应激、胆固醇代谢和表观遗传,这些都揭示了肝星状细胞的活化机制。表观遗传包括DNA甲基化、组蛋白修饰和调节性非编码RNAs,这些机制也参与调节肝星状细胞活化和肝纤维化发生,对表观遗传和肝纤维化治疗之间的关系研究具有重要意义。     

Inhibition of the expression of alpha-smooth muscle actin in human hepatic stellate cell line,LI90, by a selective cyclooxygenase 2 inhibitor,NS-398

Cyclooxygenase 2 (COX-2) has been thought to be associated with liver fibrosis whereas it is well known that hepatic stellate cells (HSC) play a central role in the pathogenesis of liver fibrosis. There is little evidence of how COX-2 regulates the activation of human HSC or the mechanism involved. In this study, we investigated the effect of a COX-2 inhibitor, NS-398, on a line of human HSC, LI90. Our findings demonstrated that alpha-smooth muscle actin (alpha-SMA) protein expression was inhibited in a dose-dependent manner by treatment with NS-398. Proliferation cell nuclear antigen (PCNA) expression and cell growth were partially down-regulated. The generation of PGE2, IL-8, IL-6, and hyaluronan in the cultured medium was also inhibited. In conclusion, our findings imply that a selective COX-2 inhibitor might be a potential drug for the chemoprevention and treatment of liver fibrosis by inhibiting the activation of HSC.     

Hepatitis C virus RNA replication in human stellate cells regulates gene expression of extracellular matrix-related molecules

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, including chronic hepatitis, fibrosis, and cirrhosis. Fibrosis often develops in HCV-infected livers and ultimately leads to cirrhosis and carcinoma. During fibrosis, hepatic stellate cells (HSC) play important roles in the control of extracellular matrix synthesis and degradation in fibrotic livers. In this study, we established a subgenomic replicon (SGR) cell line with human hepatic stellate cells to investigate the effect of HCV RNA replication on HSC. Isolated SGR clones contained HCV RNA copy numbers ranging from 10⁴ to 10⁷ per μg total RNA, and long-term culture of low-copy number SGR clones resulted in markedly increased HCV RNA copy numbers. Furthermore, HCV RNA replication affected gene expression of extracellular matrix-related molecules in both hepatic stellate cells and hepatic cells, suggesting that HCV RNA replication and/or HCV proteins directly contribute to liver fibrosis. The HCV RNA-replicating hepatic stellate cell line isolated in this study will be useful for investigating hepatic stellate cell functions and HCV replication machinery.     

Induction of cell death in activated hepatic stellate cells by targeted gene expression of the thymidine kinase/ganciclovir system

Liver fibrosis is the result from a relative imbalance between synthesis and degradation of matrix proteins. Following liver injury of any etiology, hepatic stellate cells undergo a response known as activation, which is the transition of quiescent cells into proliferative, fibrogenic, and contractile myofibroblasts. Upon this cellular transdifferentiation the effector cell becomes the major source of fibrillar and non-fibrillar matrix proteins resulting in excessive scar formation and cirrhosis, the end stage of fibrosis. Concomitant with progressive liver fibrosis, the tissue inhibitor of metalloproteinases-1 (TIMP-1) is strongly activated in hepatic stellate cells. We have developed a recombinant replication-defective adenovirus in which the TIMP-1 promoter is coupled to the herpes simplex virus thymidine kinase gene rendering activated hepatic stellate cells susceptible to ganciclovir. This novel targeted suicide gene approach was validated in a culture model considered to reflect an accelerated time course of the cellular and molecular events that occur during liver fibrosis. We demonstrate that transfer of the suicide gene to culture-activated hepatic stellate cells results in a strong expression of the respective transgene as assessed by Northern blot and Western blot analyses. The enzyme catalyzed the proper conversion of its prodrug subsequently initiating programmed cell death as estimated by caspase-3 assay and Annexin V-Fluos staining. Altogether, these results indicate that induction of programmed cell death is a promising approach to eliminate fibrogenic HSC.     

Herbal medicine Rhei rhizome prevents liver fibrosis in rat liver cirrhosis induced by a choline-deficient L-amino acid-defined diet

The aim of this study was to investigate whether herbal medicine Rhei rhizome, extract powder from herbs, has influences on the development of liver fibrosis. In in vivo studies the effects of Rhei rhizome were examined using the choline-deficient L-amino acid-defined (CDAA) diet-induced liver fibrosis model. In In vitro studies the effects of Rhei rhizome on type I procollagen mRNA expression, alpha-smooth muscle actin (alpha-SMA), metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) of isolated hepatic stellate cell were examined. In vivo Rhei rhizome prevented fibrosis in a dose-dependent manner up to 1.0% (w/w) with a reduced number of activated stellate cells. In vitro the Rhei rhizome prevented stellate cell activation resulting in reduced type I procollagen mRNA, alpha-SMA and TIMP-1, 2 expression. These results indicate that Rhei rhizome significantly reduces liver fibrosis by the direct inhibition of stellate cell activation without reducing hepatocyte cell death.     

Regulation of peroxisome proliferator-activated receptor-gamma in liver fibrosis

The peroxisome proliferator-activated receptors (PPARs) impart diverse cellular effects in biological systems. Because stellate cell activation during liver injury is associated with declining PPARgamma expression, we hypothesized that its expression is critical in stellate cell-mediated fibrogenesis. We therefore modulated its expression during liver injury in vivo. PPARgamma was depleted in rat livers by using an adenovirus-Cre recombinase system. PPARgamma was overexpressed by using an additional adenoviral vector (AdPPARgamma). Bile duct ligation was utilized to induce stellate cell activation and liver fibrosis in vivo; phenotypic effects (collagen I, smooth muscle alpha-actin, hydroxyproline content, etc.) were measured. PPARgamma mRNA levels decreased fivefold and PPARgamma protein was undetectable in stellate cells after culture-induced activation. During activation in vivo, collagen accumulation, assessed histomorphometrically and by hydroxyproline content, was significantly increased after PPARgamma depletion compared with controls (1.28 +/- 0.14 vs. 1.89 +/- 0.21 mg/g liver tissue, P < 0.03). In isolated stellate cells, AdPPARgamma overexpression resulted in significantly increased adiponectin mRNA expression and decreased collagen I and smooth muscle alpha-actin mRNA expression compared with controls. During in vivo fibrogenesis, rat livers exposed to AdPPARgamma had significantly less fibrosis than controls. Collagen I and smooth muscle alpha-actin mRNA expression were significantly reduced in AdPPARgamma-infected rats compared with controls (P < 0.05, n = 10). PPARgamma-deficient mice exhibited enhanced fibrogenesis after liver injury, whereas PPARgamma receptor overexpression in vivo attenuated stellate cell activation and fibrosis. The data highlight a critical role for PPARgamma during in vivo fibrogenesis and emphasize the importance of the PPARgamma pathway in stellate cells during liver injury.     

Byakangelicin protects against carbon tetrachloride–induced liver injury and fibrosis in mice

Liver fibrosis is a disease caused by long‐term damage that is related to a number of factors. The current research on the treatment of liver fibrosis mainly focuses on the activation of hepatic stellate cell, in addition to protecting liver cells. byakangelicin has certain anti‐inflammatory ability, but its effect on liver fibrosis is unclear. This study aims to explore whether byakangelicin plays a role in the development of liver fibrosis and to explore its mechanism. We determined that byakangelicin has a certain ability to resist fibrosis and reduce liver cell damage in a model of carbon tetrachloride–induced liver fibrosis in mice. Thereafter, we performed further verification in vitro. The signalling pathways of two important pro‐fibrotic cytokines, transforming growth factor‐β and platelet‐derived growth factor, were studied. Results showed that byakangelicin can inhibit related pathways. According to the hepatoprotective effect of byakangelicin observed in animal experiments, we studied the effect of byakangelicin on 4‐HNE–induced hepatocyte (HepG2) apoptosis and explored its related pathways. The results showed that byakangelicin could attenuate 4‐HNE–induced hepatocyte apoptosis via inhibiting ASK‐1/JNK signalling. In conclusion, byakangelicin could improve carbon tetrachloride–induced liver fibrosis and liver injury by inhibiting hepatic stellate cell proliferation and activation and suppressing hepatocyte apoptosis.     

Schistosoma japonicum soluble egg antigens induce apoptosis and inhibit activation of hepatic stellate cells: a possible molecular mechanism

Hepatic stellate cells play a key role in the development of hepatic fibrosis. Activated hepatic stellate cells can be reversed to a quiescent-like state or apoptosis can be induced to reverse fibrosis. Some studies have recently shown that Schistosoma mansoni eggs could suppress the activation of hepatic stellate cells and that soluble egg antigens from schistosome eggs could promote immunocyte apoptosis. Hence, in this study, we attempt to assess the direct effects of Schistosoma japonicum soluble egg antigens on hepatic stellate cell apoptosis, and to explore the mechanism by which the apoptosis of activated hepatic stellate cells can be induced by soluble egg antigens, as well as the mechanism by which hepatic stellate cell activation is inhibited by soluble egg antigens. Here, it was shown that S. japonicum-infected mouse livers had increased apoptosis phenomena and a variability of peroxisome proliferator-activated receptor γ expression. Soluble egg antigens induce morphological changes in the hepatic stellate cell LX-2 cell line, inhibit cell proliferation and induce cell-cycle arrest at the G₁ phase. Soluble egg antigens also induce apoptosis in hepatic stellate cells through the TNF-related apoptosis-inducing ligand/death receptor 5 and caspase-dependent pathways. Additionally, soluble egg antigens could inhibit the activation of hepatic stellate cells through peroxisome proliferator-activated receptor γ and the transforming growth factor β signalling pathways. Therefore, our study provides new insights into the anti-fibrotic effects of S. japonicum soluble egg antigens on hepatic stellate cell apoptosis and the underlying mechanism by which the liver fibrosis could be attenuated by soluble egg antigens.     

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.     

Engagement of alphavbeta3 integrin regulates proliferation and apoptosis of hepatic stellate cells

Hepatic stellate cells are the major source of the extracellular matrix that accumulates in fibrotic liver. During progressive liver fibrosis, hepatic stellate cells proliferate, but during resolution of fibrosis there is extensive stellate cell apoptosis that coincides with degradation of the liver scar. We have examined the possibility that the fate of stellate cells is influenced by the extracellular matrix through the intermediary of alpha(v)beta(3) integrin. alpha(v)beta(3) integrin was expressed by activated, myofibroblastic rat and human stellate cells in culture. Antagonism of this integrin using neutralizing antibodies, echistatin, or small inhibitory RNA to silence alpha(v) subunit expression inhibited stellate cell proliferation and their expression of proliferating cell nuclear antigen and activated forms of p44 and p42 MAPK. These alpha(v)beta(3) antagonists also increased apoptosis of cultured stellate cells, and this was associated with an increase in the BAX/BCL-2 protein ratio, induction of nuclear DNA fragmentation, and activation of intracellular caspase-3. Expression of tissue inhibitor of metalloproteinases-1 by activated stellate cells was reduced by the alpha(v)beta(3) antagonists, while matrix metalloproteinase-9 synthesis was enhanced. Stellate cells incubated with active recombinant matrix metalloproteinase-9 showed enhanced apoptosis, while cells treated with a synthetic inhibitor of this protease showed increased survival. Our studies suggest that alpha(v)beta(3) integrin regulates the fate of hepatic stellate cells. Degradation of alpha(v)beta(3) ligands surrounding activated stellate cells during resolution of liver fibrosis might decrease alpha(v)beta(3) integrin ligation, suppressing stellate cell proliferation and inducing a fibrolytic, matrix metalloproteinase-secreting phenotype that may prime stellate cells for apoptosis.     

PLK1 regulates hepatic stellate cell activation and liver fibrosis through Wnt/β‐catenin signalling pathway

As an outcome of chronic liver disease, liver fibrosis involves the activation of hepatic stellate cells (HSCs) caused by a variety of chronic liver injuries. It is important to explore approaches to inhibit the activation and proliferation of HSCs for the treatment of liver fibrosis. PLK1 is overexpressed in many human tumour cells and has become a popular drug target in tumour therapy. Therefore, further study of the function of PLK1 in the cell cycle is valid. In the present study, we found that PLK1 expression was elevated in primary HSCs isolated from CCl₄‐induced liver fibrosis mice and LX‐2 cells stimulated with TGF‐β1. Knockdown of PLK1 inhibited α‐SMA and Col1α1 expression and reduced the activation of HSCs in CCl₄‐induced liver fibrosis mice and LX‐2 cells stimulated with TGF‐β1. We further showed that inhibiting the expression of PLK1 reduced the proliferation of HSCs and promoted HSCs apoptosis in vivo and in vitro. Furthermore, we found that the Wnt/β‐catenin signalling pathway may be essential for PLK1‐mediated HSCs activation. Together, blocking PLK1 effectively suppressed liver fibrosis by inhibiting HSC activation, which may provide a new treatment strategy for liver fibrosis.     

Hepatoprotective effects of berberine on liver fibrosis via activation of AMP-activated protein kinase

Aims

We investigated the protective effect of berberine (BBR) on chronic liver fibrosis in mice and the potential mechanism underlying the activation of AMP-activated protein kinase (AMPK) pathway.

Main methods

CCl4-induced chronic liver fibrosis model in mice was established and activated rat hepatic stellate cell was treated with BBR. Cell viability was evaluated by SRB assay and protein expressions were detected by Western blot.

Key findings

Our results showed that BBR ameliorated the liver fibrosis in mice with CCl4-induced liver injury and inhibited the proliferation of hepatic stellate cell in dose- and time-dependent manner. BBR decreased the enzyme release of ALT, AST, and ALP in serum, elevated SOD and reduced MDA content of liver tissue in CCl4-induced liver fibrosis model. BBR delayed the formation of regenerative nodules and reduced necrotic areas compared to CCl4 group. Moreover, BBR treatment activated AMPK, decreased the protein expression of Nox4, TGF-β1 and the phosphorylated Akt. The expression of smooth muscle actin (α-SMA), the marker of activated hepatic stellate cell, was also reduced by BBR treatment.

Significance

Our studies firstly demonstrated that BBR exerted hepatoprotective effects possibly via activation of AMPK, blocking Nox4 and Akt expression. Our findings may benefit the development of new strategies in the prevention of chronic liver disease.