Liver fibrosis

Natural killer cells ameliorate liver fibrosis by killing activated stellate cells in NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent manners

BACKGROUND & AIMS

Viral hepatitis infection, which is a major cause of liver fibrosis, is associated with activation of innate immunity. However, the role of innate immunity in liver fibrosis remains obscure.

METHODS

Liver fibrosis was induced either by feeding mice with the 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet or by injecting them with carbon tetrachloride. The Toll-like receptor 3 ligand, polyinosinic-polycytidylic acid, was used to activate innate immunity cells and mediators, including natural killer cells and interferon gamma.

RESULTS

In the mouse model of DDC-induced liver fibrosis, natural killer cell activation by polyinosinic-polycytidylic acid induced cell death to activated hepatic stellate cells and attenuated the severity of liver fibrosis. Polyinosinic-polycytidylic acid treatment also ameliorated liver fibrosis induced by carbon tetrachloride. The observed protective effect of polyinosinic-polycytidylic acid on liver fibrosis was diminished through either depletion of natural killer cells or by disruption of the interferon gamma gene. Expression of retinoic acid early inducible 1, the NKG2D ligand, was undetectable on quiescent hepatic stellate cells, whereas high levels were found on activated hepatic stellate cells, which correlated with the resistance and susceptibility of quiescent hepatic stellate cells and activated hepatic stellate cells to natural killer cell lysis, respectively. Moreover, treatment with polyinosinic-polycytidylic acid or interferon gamma enhanced the cytotoxicity of natural killer cells against activated hepatic stellate cells and increased the expression of NKG2D and tumor necrosis factor-related apoptosis-inducing ligand on liver natural killer cells. Blocking NKG2D or tumor necrosis factor-related apoptosis-inducing ligand with neutralizing antibodies markedly diminished the cytotoxicity of polyinosinic-polycytidylic acid-activated natural killer cells against activated hepatic stellate cells.

CONCLUSIONS

Our findings suggest that natural killer cells kill activated hepatic stellate cells via retinoic acid early inducible 1/NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent mechanisms, thereby ameliorating liver fibrosis.

Reversal of hepatic fibrosis -- fact or fantasy?

The prospect of reversing hepatic fibrosis has generated great interest now that basic science advances are being translated into promising new antifibrotic therapies. It is appropriate to recognize both the historical advances that created the framework for these successes, and the important role that Hepatology has played in disseminating them. A sense of urgency underlies this effort as the epidemics of HCV and NASH are becoming associated with advancing fibrosis. To maintain progress and minimize confusion among investigators and clinicians it is essential to standardize terms referring to fibrosis 'reversal' and 'regression.' There must also be rapid optimization of non-invasive markers of fibrosis to relieve this current bottleneck to conducting clinical trials. Progress in identifying genetic determinants of fibrosis could further refine patient selection for clinical trials and shorten their duration, as well as unearthing new directions of scientific inquiry. Realistic expectations for successful anti-fibrotic therapies reflect solid evidence of fibrosis regression in patients treated effectively for viral liver disease, as well as growing clarity in the understanding mechanisms of extracellular matrix production and degradation. The paradigms of stellate cell activation and apoptosis remain valuable frameworks for understanding pathways of hepatic fibrogenesis and fibrosis regression, respectively. Continued progress is essential in order to identify the determinants and dynamics of fibrosis reversibility, to discover additional targets for anti-fibrotic therapy, and to develop customized multi-drug regimens. These advances are sure to be captured in the next 25 years by Hepatology , and to profoundly impact the prognosis of patients with chronic liver disease.

Molecular therapy for hepatic injury and fibrosis: Where are we?

Hepatic fibrosis is a wound healing response, involving pathways of inflammation and fibrogenesis. In response to various insults, such as alcohol, ischemia, viral agents, and medications or hepatotoxins, hepatocyte damage will cause the release of cytokines and other soluble factors by Kupffer cells and other cell types in the liver. These factors lead to activation of hepatic stellate cells, which synthesize large amounts of extracellular matrix components. With chronic injury and fibrosis, liver architecture and metabolism are disrupted, eventually manifesting as cirrhosis and its complications. In addition to eliminating etiology, such as antiviral therapy and pharmacological intervention, it is encouraging that novel strategies are being developed to directly address hepatic injury and fibrosis at the subcellular and molecular levels. With improvement in understanding these mechanisms and pathways, key steps in injury, signaling, activation, and gene expression are being targeted by molecular modalities and other molecular or gene therapy approaches. This article intends to provide an update in terms of the current status of molecular therapy for hepatic injury and fibrosis and how far we are from clinical utilization of these new therapeutic modalities.

Effects and mechanisms of crude astragalosides fraction on liver fibrosis in rats

Astragalosides is the major active constituent of Radix Astragali. The present study was carried out to investigate the effect of crude astragalosides fraction (CAF) on rats liver fibrosis and its possible mechanisms. Hepatic fibrosis was induced by subcutaneous injection with 50% CCl(4) in Sprague-Dawley rats. The amount of CCl(4) administered was 1 mg kg(-1). The alanine aminotransferase (ALT), aspartate aminotransferase (AST) levels in plasma and hydroxyproline (Hyp), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) contents in liver tissue were assayed by spectrophotometry. The hyaluronic acid (HA) and procollagen III (PC III) were assessed by radioimmunoassay. Tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) levels in culture supernatants of Kupffer cells (KCs) were determined with ELISA. Liver samples collected after 8 weeks of CCl(4) treatment were stained with hematoxylin-eosin (HE) and massion, and scored. Intragastric administration of CAF (10, 20 and 40 mg kg(-1)) significantly decreased indices of liver and spleen, the serum transaminase activities, HA and PC III levels, and Hyp and MDA contents in liver tissue in rats of hepatic fibrosis. Decreased SOD and GSH-px levels were reversed after administration of CAF. Histopathological scores showed CAF had inhibitory effect on the progression of hepatic fibrosis. In the in vitro experiments, CAF significantly reduced TNF-alpha and TGF-beta1 levels in culture supernatants of KCs. The results showed CAF significantly inhibited the progression of hepatic fibrosis induced by CCl(4), and the inhibitory effect of CAF on hepatic fibrosis might be associated with its ability to scavenge free radical and inhibit the production of TNF-alpha and TGF-beta1 from activated KCs.

Regulation of Fibrosis by the Immune System

Inflammation and fibrosis are two inter-related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro-fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived.

[Ca2+]i-independent contractile force generation by rat hepatic stellate cells in response to endothelin-1

The contractile force generated by hepatic stellate cells in response to endothelin-1 contributes to sinusoidal blood flow regulation and hepatic fibrosis. This study's aim was to directly test the widely held view that changes in cytosolic Ca2+ concentration ([Ca2+]i) mediate stellate cell force generation. Contractile force generation by primary cultures of rat hepatic stellate cells grown in three-dimensional collagen gels was directly and quantitatively measured using a force transducer. Stellate cell [Ca2+]i, myosin activation, and migration were quantified using standard techniques. [Ca2+]i was modulated using ionomycin, BAPTA, KCl, and removal of extracellular Ca2+. Removal of extracellular Ca2+ did not alter endothelin-1-stimulated force development or [Ca2+]i. Ionomycin, a Ca2+ ionophore, triggered an increase in [Ca2+]i that was three times greater than that stimulated by endothelin-1, but only induced 16% of the force and 38% of the myosin regulatory light chain (MLC) phosphorylation induced by endothelin-1. Physiological increases in [Ca2+]i induced by hyperkalemia had no effect on contractile force. Loading BAPTA, a Ca2+ chelator, in stellate cells completely blocked endothelin-1-induced increases in [Ca2+]i but had no effect on endothelin-1-stimulated force generation or MLC phosphorylation. In contrast, Y-27632, a selective rho-associated kinase inhibitor, inhibited endothelin-1-stimulated force generation by at least 70% and MLC phosphorylation by at least 80%. Taken together, these observations indicate that changes in [Ca2+]i are neither necessary nor sufficient for contractile force generation by rat stellate cells. Our results challenge the current model of contractile regulation in hepatic stellate cells and have important implications for our understanding of hepatic pathophysiology.

The hepatoprotective activity of kinsenoside fromAnoectochilus formosanus

Carbon tetrachloride (CCl(4)) causes chronic hepatitis, featuring an increase in hepatic hydroxyproline, spleen weight and serum GPT levels and a decrease in plasma albumin levels. Crude extracts of fresh whole plants of Anoectochilus formosanus showed inhibition of chronic hepatitis induced by CCl(4) in mice. Bioactivity-guided fractionation and spectroscopic analysis revealed that kinsenoside was the most active compound. In an in vitro study, the LD(50) values for H(2)O(2)-induced cytotoxicity in BALB/c normal liver cells were significantly higher after kinsenoside pretreatment than after vehicle alone, further confirming that kinsenoside shows significant antihepatotoxic activity.

Expression of activation-induced cytidine deaminase in human hepatocytes during hepatocarcinogenesis

Activation-induced cytidine deaminase (AID) plays a role as a genome mutator in activated B cells, and inappropriate expression of AID has been implicated in the immunopathological phenotype of human B-cell malignancies. Notably, we found that the transgenic mice overexpressing AID developed lung adenocarcinoma and hepatocellular carcinoma (HCC), suggesting that ectopic expression of AID can lead to tumorigenesis in epithelial tissues as well. To examine the involvement of AID in the development of human HCC, we analyzed the AID expression and its correlation with mutation frequencies of the p53 gene in liver tissues from 51 patients who underwent resection of primary HCCs. The specific expression, inducibility by cytokine stimulation and mutagenic activity of AID were investigated in cultured human hepatocytes. Only trace amounts of AID transcripts were detected in the normal liver; however, endogenous AID was significantly upregulated in both HCC and surrounding noncancerous liver tissues with underlying chronic hepatitis or liver cirrhosis (p < 0.05). Most liver tissues with underlying chronic inflammation with endogenous AID upregulation already contained multiple genetic changes in the p53 gene. In both hepatoma cell lines and cultured human primary hepatocytes, the expression of AID was substantially induced by TGF-beta stimulation. Aberrant activation of AID in hepatocytes resulted in accumulation of multiple genetic alterations in the p53 gene. Our findings suggest that the aberrant expression of AID is observed in human hepatocytes with several pathological settings, including chronic liver disease and HCC, which might enhance the genetic susceptibility to mutagenesis leading to hepatocarcinogenesis.

Global gene expression profiling of dimethylnitrosamine-induced liver fibrosis: from pathological and biochemical data to microarray analysis

The development of hepatocellular carcinoma (HCC) is generally preceded by cirrhosis, which occurs at the end stage of fibrosis. This is a common and potentially lethal problem of chronic liver disease in Asia. The development of microarrays permits us to monitor transcriptomes on a genome-wide scale; this has dramatically speeded up a comprehensive understanding of the disease process. Here we used dimethylnitrosamine (DMN), a nongenotoxic hepatotoxin, to induce rat necroinflammatory and hepatic fibrosis. During the 6-week time course, histopathological, biochemical, and quantitative RT-PCR analyses confirmed the incidence of necroinflammatory and hepatic fibrosis in this established rat model system. Using the Affymetrix microarray chip, 256 differentially expressed genes were identified from the liver injury samples. Hierarchical clustering of gene expression using a gene ontology database allowed the identification of several stage-specific characters and functionally related clusters that encode proteins related to metabolism, cell growth/maintenance, and response to external challenge. Among these genes, we classified 44 potential necroinflammatory-related genes and 62 potential fibrosis-related markers or drug targets based on histopathological scores. We also compared the results with other data on well-known markers and various other microarray datasets that are available. In conclusion, we believe that the molecular picture of necroinflammatory and hepatic fibrosis from this study may provide novel biological insights into the development of early liver damage molecular classifiers than can be used for basic research and in clinical applications. A public accessible website is available at http://LiverFibrosis.nchc.org.tw:8080/LF.

Inducible nitric oxide synthase is not essential for the development of fibrosis and liver damage induced by CCl4 in mice

The aim of the present work was to investigate the role of inducible nitric oxide (NO) synthase (iNOS) in CCl(4)-induced cirrhosis by utilizing iNOS knock out mice (iNOS(-/-)). Cirrhosis was produced by i.p. administration of CCl(4) (1 ml kg(-1) of body weight) dissolved in olive oil three times a week for 3 months to iNOS(-/-) or iNOS(+/+) (wild type) mice; appropriate olive oil controls were performed. Nitrite plus nitrate levels were lower in iNOS(-/-) compared with iNOS(+/+) mice, but CCl(4) did not produce a significant effect in any mice. Reduced (GSH) glutathione was increased in iNOS(-/-) mice receiving vehicle and in both groups receiving CCl(4); lipid peroxidation increased significantly in iNOS(+/+) but not in iNOS(-/-) mice. Bilirubins, alanine aminotransferase and collagen (measured as the hepatic hydroxyproline content) were increased significantly by the chronic intoxication with CCl(4) in both iNOS(-/-) and iNOS(+/+) mice; importantly there was no difference between these groups. This study clearly suggests that NO derived from iNOS does not participate in cholestasis, necrosis or fibrosis induced by CCl(4) in the mice. The present results are in disagreement with several studies indicating a beneficial or detrimental effect of this molecule utilizing different experimental approaches and in agreement with some studies indicating that NO does not affect liver damage in some models. It must be pointed out that this is the first report in iNOS knock out mice utilizing the chronic model of intoxication with CCl(4); thus, comparisons with other models or approaches are difficult to reconcile.

Antisense oligonucleotides-based inhibition of gene and protein expression of tissue inhibitor of metalloproteinase-2 on experimental liver fibrosis in rats

AIM: To investigate the inhibitory effect of tissue inhibitor of metalloproteinase-2 (TIMP-2) targeted antisense oligonucleotide (asON) on the progress of experimental liver fibrosis in rats.

METHODS: Twenty-two rats were divided into asON treatment (n = 6), model (n = 6), and normal control group (n = 10). The liver fibrosis model was induced by human serum albumin (HSA). During modeling, the rats were treated with antisense oligonucleotides via tail vein. The level of TIMP-2 expression was detected by reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization, immunohistochemical staining and enzyme linked immunosorbent assay (ELISA). The effect of asON on liver fibrosis was analyzed by histopathological exami-nation, immunohistochemical staining of collagenⅠand Ⅳ, and special staining of collagen fiber as well as electron microscopy.

RESULTS: The pathological grading was notably im-proved in asON group than that in model group (u = 2.071, P <0.05). The serum and tissue expression of TIMP-2 were lower in asON group than those in model group (T = 55, P <0.05; t = 3.332, P <0.05), but higher than those in the control (T = 55, P <0.05; t = 5.550, P <0.05). Image quantitative analysis for immunohistochemical staining of collagen Ⅳ showed that the value was significant decreased in asON group as compared with that in model group (t = 2.310, P <0.05), but still higher than that in the control (t = 3.623, P <0.05); The value for collagenⅠwas also decreased in asON group as compared with that in model group (t = 2.845, P <0.05). Less collagen deposition was found in the hepatic sinusoid of asON group, which was not significantly different from that of model group.

CONCLUSION: TIMP-2 targeted asON can inhibit the progress of experimental liver fibrosis in rats.

Somatostatin at nanomolar concentration reduces collagen I and III synthesis by, but not proliferation of activated rat hepatic stellate cells

Previous studies have shown antifibrotic effects of somatostatin. Since hepatic stellate cells (HSC) express somatostatin receptors and play a key role in hepatic fibrogenesis, we investigated the in vitro antifibrotic effect of somatostatin on rat HSC. At day 12 after isolation, cells were exposed to different concentrations of somatostatin (10(-6)-10(-9) mol l(-1)). mRNA expression of collagen types I and III, and of smooth muscle alpha-actin (alpha-SMA) was analysed by Northern blotting. At 10(-9) mol l(-1), somatostatin significantly reduced mRNA expression of collagen I (72.3 +/- 10.7%; 95% confidence interval (95% CI): 45.5-99.0), collagen III (79.0 +/- 4.5%; 95% CI: 67.6-90.4) and alpha-SMA (65.7 +/- 5.9%; 95% CI: 51.1-80.2), as compared to control normalized at 100%. These results were confirmed by quantitative RT-PCR. Cycloheximide experiments indicated that somatostatin has no direct transcriptional effect.Using immunoprecipitation, we demonstrated that somatostatin also decreased de novo synthesis of collagen I (73 +/-10%; 95% CI: 48-98%), collagen III (65 +/- 13%; 95% CI: 33-97%) and alpha-SMA (47 +/- 9%; 95% CI: 25-69%). Remarkably, at higher concentrations, somatostatin did not suppress collagen mRNA expression nor de novo protein synthesis. We ascribe this observation to desensitization of the cells for somatostatin. Cell proliferation, as measured by 5-bromo-2'-deoxyuridine labelling, was not altered by somatostatin. No significant effect on the intermediate and actin cytoskeleton were detected by immunohistochemistry and Western blotting. Our findings imply that in vivo antifibrotic effects of somatostatin could result partially from a direct action of somatostatin on HSC, but other, in vivo effects are probably also involved.

Dysregulation of the Hedgehog pathway in human hepatocarcinogenesis

Hedgehog (Hh) pathway activation promotes tumors in several endodermally derived tissues, but its role in the pathogenesis of hepatocellular carcinoma (HCC) is unknown. Although normal hepatocytes lack Hh signaling, activation of the Hh pathway in endodermal progenitors is required for liver development. Thus, we hypothesized that hepatocarcinogenesis may involve regulation of Hh signaling. This pathway is activated when Hh ligand binds to its receptor, Patched (PTC). In an unoccupied state, PTC normally functions as a tumor suppressor that inhibits Smoothened (SMO), a proto-oncoprotein, from activating downstream components and transcription of target genes. Here we show that in HCCs, overexpression of the Smo proto-oncogene, as well as an increase in the stoichiometric ratio of Smo to Ptc mRNA levels, correlated with tumor size, a prognostic indicator in HCC biology. In one tumor we identified a novel Smo mutation in an evolutionarily conserved residue. We also demonstrated that HCC cell lines (HepG2 and Hep3B) expressed Hh pathway components and activated Hh transcriptional targets. In Hep3B cells, cyclopamine, an inhibitor of wild-type SMO, had no effect, but KAAD-cyclopamine, a blocker of oncogenic SMO, inhibited Hh signaling activity by 50%, decreased expression of the hepatocarcinogenic oncogene, c-myc, by 8-fold, and inhibited the growth rate of Hep3B cells by 94%. These data support our hypothesis that Hh signaling is dysregulated in human hepatocarcinogenesis. We demonstrate that overexpression and/or tumorigenic activation of the Smo proto-oncogene mediates c-myc overexpression which plays a critical role in hepatocarcinogenesis and suggests that Smo is a prognostic factor in HCC tumorigenesis.

High preoperative recipient plasma 7beta-hydroxycholesterol is associated with initial poor graft function after liver transplantation

Oxidative stress is implicated in the pathogenesis of hepatic ischemia-reperfusion injury, a major determinant of initial poor graft function (IPGF) after orthotopic liver transplantation (OLT). We prospectively investigated the association between the recipient plasma preoperative oxidative stress and the occurrence of IPGF after deceased-donor OLT and indirectly studied the source-hepatic or extra-hepatic-of systemic oxidative stress in vivo in cirrhosis. We used a recently developed specific and sensitive mass spectrometry assay to measure 7beta-hydroxycholesterol and 7-ketocholesterol (oxysterols), markers of oxidative stress, in biological matrices. At univariate analysis, preoperative recipient 7beta-hydroxycholesterol plasma concentration was significantly higher in transplants with subsequent IPGF (n = 9) compared with those with initial good graft function (IGGF; n = 23) [mean +/- SD: 30.63 +/- 26.42 and 11.57 +/- 15.76 ng/mL, respectively] (P = 0.017). In a logistic regression model, which included also the Model for End-Stage Liver Disease (MELD) score, 7beta-hydroxycholesterol plasma concentration was an independent predictor of IPGF with an odds ratio of 1.17 (95% CI, 1.02-1.33, P = 0.028). Patients with cirrhosis (n = 32) had increased oxysterol plasma levels compared with healthy controls (n = 49); livers with cirrhosis (n = 21), however, had oxysterol content comparable with normal livers obtained from organ donors (n = 19). Oxysterols persisted elevated in plasma 1 month after OLT (n = 23). In conclusion, cirrhosis presents upregulated systemic oxidative stress likely of extrahepatic source that is associated with graft failure after OLT.

Smad3 mediates TGF-beta1-induced collagen gel contraction by human lung fibroblasts

Transforming growth factor-beta1 (TGF-beta1) is a key mediator in tissue repair and fibrosis. Using small interference RNA (siRNA), the role of Smad2 and Smad3 in TGF-beta stimulation of human lung fibroblast contraction of collagenous matrix and induction of alpha-SMA and the role of alpha-SMA in contraction were assessed. HFL-1 cells were transfected with Smad2, Smad3 or control-siRNA, and cultured in floating Type I collagen gels +/- -TGF-beta1. TGF-beta1 augmented gel contraction in Smad2-siRNA- and control-siRNA-treated cells, but had no effect in Smad3-siRNA-treated cells. Similarly, TGF-beta1 upregulated alpha-SMA in Smad2-siRNA- and control-siRNA-treated cells, but had no effect on Smad3-siRNA-treated cells. Alpha-SMA-siRNA-treated cells did not contact the collagen gels with or without TGF-beta1, suggesting alpha-SMA is required for gel contraction. Thus, Smad3 mediates TGF-beta1-induced contraction and alpha-SMA induction in human lung fibroblasts. Smad3, therefore, could be a target for blocking contraction of human fibrotic tissue induced by TGF-beta1.

Interleukin-10 gene therapy reverses thioacetamide-induced liver fibrosis in mice

Hepatic fibrosis represents a process of healing and scarring in response to chronic liver injury. Interleukin-10 (IL-10) is a cytokine that downregulates the proinflammatory response and has a modulatory effect on hepatic fibrogenesis. The aim of this study was to investigate whether IL-10 gene therapy possesses anti-hepatic fibrogenesis in mice. Liver fibrosis was induced by long-term thioacetamide administration in mice. Human IL-10 expression plasmid was delivered via electroporation after liver fibrosis established. IL-10 gene therapy reversed hepatic fibrosis and prevented cell apoptosis in a thioacetamide-treated liver. RT-PCR revealed IL-10 gene therapy to reduce liver transforming growth factor-beta1, tumor necrosis factor-alpha, collagen alpha1, cell adhesion molecule, and tissue inhibitors of metalloproteinase mRNA upregulation. Following gene transfer, the activation of alpha-smooth muscle actin and cyclooxygenase-2 was significantly attenuated. In brief, IL-10 gene therapy might be an effective therapeutic reagent for liver fibrosis with potential future clinical applications.

STAT3 NH2-terminal acetylation is activated by the hepatic acute-phase response and required for IL-6 induction of angiotensinogen

BACKGROUND & AIMS

The signal transducers and activators of transcription (STATs) are cytoplasmic transcription factors mediating acute-phase response (APR) of the human angiotensinogen (hAGT) gene in hepatocytes. The mechanisms of how STAT3 activates target genes are unknown. Here we analyzed the biochemistry of STAT3 activation by interleukin (IL)-6 in hepatocellular carcinoma HepG2 and Balb/C mice.

METHODS

Immunoprecipitation-Western assays and Matrix Assisted Laser Desorption-Time of Flight mass spectrometry determined sites of STAT3 acetylation by the 300-kilodalton target of E1A (p300) co-activator. The subcellular localization of acetylation-deficient STAT3 molecules were studied by microscopic imaging, effects on DNA binding measured by gel shift and chromatin immunoprecipitation (ChIP) assays, and gene transactivation by Northern blot and reporter assays.

RESULTS

Two Lys residues at amino acids 49 and 87 in the STAT3 NH2 terminus are acetylated by p300. Lys-to-Arg point mutations (STAT3 K49R/K87R) had no effect on inducible DNA binding, but blocked p300-mediated acetyl(Ac)-STAT3 formation and abrogated IL-6-induced hAGT activation. Although STAT3 K49R/K87R rapidly translocated into the nucleus, it did not bind p300 and had delayed cytoplasmic redistribution. ChIP assays show IL-6-inducible acetylated STAT3 and p300 binding to the native hAGT promoter. Activation of the APR in mice induces nuclear Tyr phosphorylated and acetylated STAT3 in hepatic nuclei. We also observed that STAT3 interacts with histone deacetylases (HDACs), specifically HDAC 1, that down-regulate IL-6-induced hAGT transactivation.

CONCLUSIONS

IL-6-induced target gene activation requires p300-mediated STAT3 acetylation, and HDACs are involved in the termination of STAT3 action. These studies indicate the acetylation-deacetylation reaction as a novel signaling mechanism controlling the IL-6-STAT3 pathway in the hepatic APR.

Role for hedgehog signaling in hepatic stellate cell activation and viability

Hepatic stellate cells (HSC) have a complex phenotype that includes both neural and myofibroblastic features. The Hedgehog (Hh) pathway has been shown to direct the fate of neural and myofibroblastic cells during embryogenesis and during tissue remodeling in adults. Therefore, we hypothesized that Hh signaling may regulate the fate of HSC in adults. In this study, we find that freshly isolated stellate cells from adult Patched-lacZ transgenic mice exhibit beta-galactosidase activity, indicating Hh pathway activity. Transcripts of Hh ligands, the Hh pathway receptor, and Hh-regulated transcription factors are expressed by stellate cells from mice, rats, and humans. Transfection experiments in a cell line using a Hh-inducible luciferase reporter demonstrate constitutive Hh pathway activity. Moreover, neutralizing antibodies to Hh increase apoptosis, while viability is restored by treatment with Hh ligand. In vitro treatment of primary stellate cells with cyclopamine (Cyc), a pharmacologic inhibitor of the Hh pathway, inhibits activation and slightly decreases cell survival, while a single injection of Cyc into healthy adult mice reduces activation of HSC by more than 50% without producing obvious liver damage. Our findings reveal a novel mechanism, namely the Hh pathway, that regulates the activation and viability of HSC.

Tumor necrosis factor (TNF) alpha increases collagen accumulation and proliferation in intestinal myofibroblasts via TNF receptor 2

Intestinal fibrosis is an incurable complication of Crohn's disease involving increased numbers of collagen-producing myofibroblasts. Tumor necrosis factor (TNF) alpha has defined proinflammatory roles in Crohn's disease but its role in fibrosis is unclear. We tested the hypothesis that TNFalpha increases collagen accumulation and proliferation in intestinal myofibroblasts and has additive effects in combination with insulin-like growth factor (IGF) I. The mechanisms, TNF receptor isoform, and downstream signaling pathways were examined. Intestinal myofibroblasts from wild-type (WT) mice or mice homozygous for disruption of genes encoding TNFR1 (TNFR1-/-), TNFR2 (TNFR2-/-), or both (TNFR1/2-/-), were treated with TNFalpha, IGF-I, or both. In WT cells, TNFalpha and IGF-I stimulated type I collagen accumulation and DNA synthesis in an additive manner. IGF-I, but not TNFalpha, stimulated type I collagen gene activation. TNFalpha, but not IGF-I, induced tissue inhibitor of metalloproteinase-1 (TIMP-1) expression and reduced matrix metalloproteinases-2 activity and collagen degradation. TNFalpha also activated ERK1/2. These responses to TNFalpha were absent in TNFR2-/- and TNFR1/2-/- myofibroblasts, whereas TNFR1-/- cells showed similar responses to WT. Inhibition of ERK1/2 diminished TNFalpha induced DNA synthesis in WT and TNFR1-/- cells. Differences in TNFalpha-induced STAT3/DNA binding activity and not NFkappaB and AP-1 transcriptional activation correlated with impaired collagen accumulation/TIMP-1 induction in TNFR2(-/-) cells. Constitutively active STAT3 rescued TIMP-1 expression in TNFR2-/- cells. We conclude that TNFalpha and IGF-I may additively contribute to fibrosis during intestinal inflammation. TNFR2 is a primary mediator of fibrogenic actions of TNFalpha acting through ERK1/2 to stimulate proliferation and through STAT3 to stimulate TIMP-1 and inhibit collagen degradation.

Liver fibrogenesis: a new role for the renin-angiotensin system

Liver fibrosis is the consequence of chronic liver injury of any etiology. When advanced, fibrosis causes portal hypertension and liver insufficiency, and is a risk factor for developing hepatocellular carcinoma. In the last decade, there have been major advances in the knowledge of the pathogenesis of hepatic fibrosis. Hepatic stellate cells (HSCs) are recognized as the main collagen-producing cells in the injured liver, and key fibrogenic factors have been identified. Among these factors, the renin-angiotensin system (RAS) appears to play a major role. Angiotensin II (Ang II) mediates key biological actions involved in hepatic tissue repair, including myofibroblast proliferation, infiltration of inflammatory cells, and collagen synthesis. Activated HSCs secrete Ang II, which induces fibrogenic actions through the activation of NADPH oxidase. Importantly, the blockade of the RAS attenuates fibrosis development in different experimental models of chronic liver injury. Based on these studies, it has been proposed that the blockade of the RAS could be effective in preventing fibrosis progression in chronic liver diseases. Although no prospective studies have evaluated the antifibrotic effect of RAS inhibitors in patients with chronic liver diseases, controlled clinical trials are under way.

Non-parenchymal liver cells support the growth advantage in the first stages of hepatocarcinogenesis

Hepatocellular carcinoma almost always arises in chronically inflamed livers. We developed a culture model to study the role of non-parenchymal cells (NPCs) for inflammation-driven hepatocarcinogenesis. Rats were treated with the carcinogen N-nitrosomorpholine, which induced initiated hepatocytes expressing the marker placental glutathione-S-transferase (GSTp). After 21 days two preparations of hepatocytes were made: (i) conventional ones (Hep-conv) containing NPCs and (ii) hepatocytes purified of NPCs (Hep-pur). Initiated hepatocytes, being positive for GSTp (GSTp-pos) were present in both preparations and were cultured along with normal hepatocytes, being negative for GSTp (GSTp-neg). Under any culture condition DNA synthesis was approximately 4-fold higher in GSTp-pos than in GSTp-neg hepatocytes demonstrating the inherent growth advantage of the first stages of hepatocarcinogenesis. Hepatocytes showed approximately 3-fold lower rates of DNA synthesis in Hep-pur than in Hep-conv, which was elevated above Hep-conv levels by addition of NPC or NPC-supernatant. Pretreatment of NPCs with proinflammatory lipopolysaccharide (LPS) further increased DNA synthesis. Thus, NPCs release soluble growth stimulators. Next we investigated the effect of specific cytokines produced by NPCs. Tumour necrosis factor alpha and interleukin 6 barely altered DNA synthesis, whereas hepatocyte growth factor (HGF), keratinocyte growth factor (KGF) and the heparin-binding epidermal growth factor-like growth factor (HB-EGF) were potent inducers of DNA replication in both, GSTp-neg and GSTp-pos cells. In conclusion, DNA synthesis of hepatocytes is increased by factors released from NPCs, an effect augmented by LPS-stimulation. NPC-derived cytokines, such as KGF, HGF and HB-EGF, stimulate DNA synthesis preferentially in initiated hepatocytes, presumably resulting in tumour promotion. Similar mechanisms may contribute to carcinogenesis in human inflammatory liver diseases.

Alpha-crystallin is a target gene of the farnesoid X-activated receptor in human livers

Alpha-crystallins comprise 35% of soluble proteins in the ocular lens and possess chaperone-like functions. Furthermore, the alphaA subunit (alphaA-crystallin) of alpha crystallin is thought to be "lens-specific" as only very low levels of expression were detected in a few non-lenticular tissues. Here we report that human alphaA-crystallin is expressed in human livers and is regulated by farnesoid X-activated receptor (FXR) in response to FXR agonists. AlphaA-crystallin was identified in a microarray screen as one of the most highly induced genes after treatment of HepG2 cells with the synthetic FXR ligand GW4064. Northern blot and quantitative real-time PCR analyses confirmed that alphaA-crystallin expression was induced in HepG2-derived cell lines and human primary hepatocytes and hepatic stellate cells in response to either natural or synthetic FXR ligands. Transient transfection studies and electrophoretic mobility shift assays revealed a functional FXR response element located in intron 1 of the human alphaA-crystallin gene. Importantly, immunohistochemical staining of human liver sections showed increased alphaA-crystallin expression in cholangiocytes and hepatocytes. As a member of the small heat shock protein family possessing chaperone-like activity, alphaA-crystallin may be involved in protection of hepatocytes from the toxic effects of high concentrations of bile acids, as would occur in disease states such as cholestasis.

Complement factor 5 is a quantitative trait gene that modifies liver fibrogenesis in mice and humans

Fibrogenesis or scarring of the liver is a common consequence of all chronic liver diseases. Here we refine a quantitative trait locus that confers susceptibility to hepatic fibrosis by in silico mapping and show, using congenic mice and transgenesis with recombined artificial chromosomes, that the gene Hc (encoding complement factor C5) underlies this locus. Small molecule inhibitors of the C5a receptor had antifibrotic effects in vivo, and common haplotype-tagging polymorphisms of the human gene C5 were associated with advanced fibrosis in chronic hepatitis C virus infection. Thus, the mouse quantitative trait gene led to the identification of an unknown gene underlying human susceptibility to liver fibrosis, supporting the idea that C5 has a causal role in fibrogenesis across species.

Molecular mechanisms of alcohol-induced hepatic fibrosis

Alcohol abuse is a major cause of liver fibrosis and cirrhosis in developed countries. Before alcoholic liver fibrosis becomes evident, the liver undergoes several stages of alcoholic liver disease including steatosis and steatohepatitis. Although the main mechanisms of fibrogenesis are independent of the etiology of liver injury, alcoholic liver fibrosis is distinctively characterized by a pronounced inflammatory response due to elevated gut-derived endotoxin plasma levels, an augmented generation of oxidative stress with pericentral hepatic hypoxia and the formation of cell-toxic and profibrogenic ethanol metabolites (e.g. acetaldehyde or lipid oxidation products). These factors, based on a complex network of cytokine actions, together result in increased hepatocellular damage and activation of hepatic stellate cells, the key cell type of liver fibrogenesis. Although to date removal of the causative agent, i.e. alcohol, still represents the most effective intervention to prevent the manifestation of alcoholic liver disease, sophisticated molecular approaches are underway, aiming to specifically blunt profibrogenic signaling pathways in liver cells or specifically induce cell death in activated hepatic stellate cells to decrease the scarring of the liver.