Increasing evidence demonstrates that IL-6 has a protective role during liver injury. IL-6 activates intracellular pathways via the gp130 receptor. In order to identify IL-6–gp130 pathways involved in mediating liver protection, we analyzed hepatocyte-specific gp130 knockout mice in a concanavalin A–induced (Con A–induced) model of immune-mediated hepatitis. We demonstrated that IL-6–gp130–dependent pathways in hepatocytes alone are sufficient for triggering protection in Con A–induced hepatitis. gp130-STAT3 signaling in hepatocytes mediates the IL-6–triggered protective effect. This was demonstrated by analysis of IL-6–induced protection in mice selectively deficient for gp130-dependent STAT1/3 or gp130-SHP2-RAS signaling in hepatocytes. To identify IL-6–gp130–STAT1/3 dependently expressed liver-protective factors, we performed gene array analysis of hepatic gene expression in hepatocyte-specific gp130–/– mice as well as in gp130-STAT1/3– and gp130-SHP2-RAS-MAPK–deficient mice. The mouse IL-8 ortholog KC (also known as Gro-α) and serum amyloid A2 (SAA2) was identified as differentially IL-6–gp130–STAT3–regulated genes. Hepatic expression of KC and SAA2 mediate the liver-protective potential of IL-6, since treatment with recombinant KC or serum SAA2 effectively reduced liver injury during Con A–induced hepatitis. In summary, this study defines IL-6–gp130–STAT3–dependent gene expression in hepatocytes that mediates IL-6–triggered protection in immune-mediated Con A–induced hepatitis. Additionally, we identified the IL-6–gp130–STAT3–dependent proteins KC and SAA2 as new candidates for therapeutic targets in liver diseases.
Christian Klein, Torsten Wüstefeld, Ulrike Assmus, Tania Roskams, Stefan Rose-John, Michael Müller, Michael P. Manns, Mattias Ernst, Christian Trautwein
Cholecystokinin (CCK) modulates contractility of the gallbladder, the sphincter of Oddi, and the stomach. These effects are mediated through activation of gastrointestinal smooth muscle as well as enteric neuron CCK-1 receptors (CCK-1Rs). To investigate the potential physiological and pathophysiological functions linked to CCK-1R–mediated signaling, we compared male WT and CCK-1R–deficient mice (129/SvEv). After 12 weeks on either a standard mouse chow or a lithogenic diet (containing 1% cholesterol, 0.5% cholic acid, and 15% dairy fat), small-intestinal transit time, intestinal cholesterol absorption, biliary cholesterol secretion, and cholesterol gallstone prevalence were compared in knockout versus WT animals. Analysis of mice on either the chow or the lithogenic diet revealed that CCK-1R–/– animals had larger gallbladder volumes (predisposing to bile stasis), significant retardation of small-intestinal transit times (resulting in increased cholesterol absorption), and increased biliary cholesterol secretion rates. The elevation in bile cholesterol, coupled with a tendency toward gallbladder stasis (due to the absence of CCK-induced contraction), facilitates nucleation, growth, and agglomeration of cholesterol monohydrate crystals; this sequence of events in turn results in a significantly higher prevalence of cholesterol gallstones in the CCK-1R–null mice.
David Q.-H. Wang, Frank Schmitz, Alan S. Kopin, Martin C. Carey
The etiology and pathogenesis of bile duct obstruction in children with biliary atresia are largely unknown. We have previously reported that, despite phenotypic heterogeneity, genomic signatures of livers from patients display a proinflammatory phenotype. Here, we address the hypothesis that production of IFN-γ is a key pathogenic mechanism of disease using a mouse model of rotavirus-induced biliary atresia. We found that rotavirus infection of neonatal mice has a unique tropism to bile duct cells, and it triggers a hepatobiliary inflammation by IFN-γ–producing CD4+ and CD8+ lymphocytes. The inflammation is tissue specific, resulting in progressive jaundice, growth failure, and greater than 90% mortality due to obstruction of extrahepatic bile ducts. In this model, the genetic loss of IFN-γ did not alter the onset of jaundice, but it remarkably suppressed the tissue-specific targeting of T lymphocytes and completely prevented the inflammatory and fibrosing obstruction of extrahepatic bile ducts. As a consequence, jaundice resolved, and long-term survival improved to greater than 80%. Notably, administration of recombinant IFN-γ led to recurrence of bile duct obstruction following rotavirus infection of IFN-γ–deficient mice. Thus, IFN-γ–driven obstruction of bile ducts is a key pathogenic mechanism of disease and may constitute a therapeutic target to block disease progression in patients with biliary atresia.
Pranavkumar Shivakumar, Kathleen M. Campbell, Gregg E. Sabla, Alexander Miethke, Greg Tiao, Monica M. McNeal, Richard L. Ward, Jorge A. Bezerra
Ali Canbay, Maria Eugenia Guicciardi, Hajime Higuchi, Ariel Feldstein, Steven F. Bronk, Robert Rydzewski, Makiko Tanai, Gregory J. Gores
We recently showed that antigen-nonspecific inflammatory cells are recruited into the liver when hepatitis B virus (HBV)-specific CTLs are injected into HBV transgenic mice, and that this process amplifies the severity of liver disease. We also showed that the severity of CTL-induced liver disease is ameliorated by the depletion of Gr-1+ cells (Gr-1 is an antigen highly expressed by neutrophils), which, secondarily, abolishes the intrahepatic recruitment of all antigen-nonspecific Gr-1– mononuclear cells (NK and NKT cells, T and B lymphocytes, monocytes, macrophages, dendritic cells) despite the strong induction of chemokine gene expression. Those results suggested that in addition to chemokine expression, CTL-induced functions are necessary for mononuclear cell recruitment to occur. We now report that MMPs known to be produced by Gr-1+ cells are rapidly induced in the livers of CTL-injected mice. The inhibition of MMP activity reduced the intrahepatic recruitment of antigen-nonspecific mononuclear cells and much of the attending liver disease without affecting the migration or antiviral potential of antigen-specific CTLs. The notion that the inhibition of MMP activity is associated with maintenance of antiviral effects but diminished tissue damage may be significant for the development of immunotherapeutic approaches for the treatment of chronic HBV infection.
Giovanni Sitia, Masanori Isogawa, Matteo Iannacone, Iain L. Campbell, Francis V. Chisari, Luca G. Guidotti
Yin Zhi Huang, a decoction of Yin Chin (Artemisia capillaris) and three other herbs, is widely used in Asia to prevent and treat neonatal jaundice. We recently identified the constitutive androstane receptor (CAR, NR1I3) as a key regulator of bilirubin clearance in the liver. Here we show that treatment of WT and humanized CAR transgenic mice with Yin Zhi Huang for 3 days accelerates the clearance of intravenously infused bilirubin. This effect is absent in CAR knockout animals. Expression of bilirubin glucuronyl transferase and other components of the bilirubin metabolism pathway is induced by Yin Zhi Huang treatment of WT mice or mice expressing only human CAR, but not CAR knockout animals. 6,7-Dimethylesculetin, a compound present in Yin Chin, activates CAR in primary hepatocytes from both WT and humanized CAR mice and accelerates bilirubin clearance in vivo. We conclude that CAR mediates the effects of Yin Zhi Huang on bilirubin clearance and that 6,7-dimethylesculetin is an active component of this herbal medicine. CAR is a potential target for the development of new drugs to treat neonatal, genetic, or acquired forms of jaundice.
Wendong Huang, Jun Zhang, David D. Moore
Farnesoid X receptor (FXR) is a bile acid–activated transcription factor that is a member of the nuclear hormone receptor superfamily. Fxr-null mice exhibit a phenotype similar to Byler disease, an inherited cholestatic liver disorder. In the liver, activation of FXR induces transcription of transporter genes involved in promoting bile acid clearance and represses genes involved in bile acid biosynthesis. We investigated whether the synthetic FXR agonist GW4064 could protect against cholestatic liver damage in rat models of extrahepatic and intrahepatic cholestasis. In the bile duct–ligation and α-naphthylisothiocyanate models of cholestasis, GW4064 treatment resulted in significant reductions in serum alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase, as well as other markers of liver damage. Rats that received GW4064 treatment also had decreased incidence and extent of necrosis, decreased inflammatory cell infiltration, and decreased bile duct proliferation. Analysis of gene expression in livers from GW4064-treated cholestatic rats revealed decreased expression of bile acid biosynthetic genes and increased expression of genes involved in bile acid transport, including the phospholipid flippase MDR2. The hepatoprotection seen in these animal models by the synthetic FXR agonist suggests FXR agonists may be useful in the treatment of cholestatic liver disease.
Yaping Liu, Jane Binz, Mary Jo Numerick, Steve Dennis, Guizhen Luo, Bhasha Desai, Kathleen I. MacKenzie, Traci A. Mansfield, Steven A. Kliewer, Bryan Goodwin, Stacey A. Jones
Angiotensin II (Ang II) is a pro-oxidant and fibrogenic cytokine. We investigated the role of NADPH oxidase in Ang II–induced effects in hepatic stellate cells (HSCs), a fibrogenic cell type. Human HSCs express mRNAs of key components of nonphagocytic NADPH oxidase. Ang II phosphorylated p47phox, a regulatory subunit of NADPH oxidase, and induced reactive oxygen species formation via NADPH oxidase activity. Ang II phosphorylated AKT and MAPKs and increased AP-1 DNA binding in a redox-sensitive manner. Ang II stimulated DNA synthesis, cell migration, procollagen α1(I) mRNA expression, and secretion of TGF-β1 and inflammatory cytokines. These effects were attenuated by N-acetylcysteine and diphenylene iodonium, an NADPH oxidase inhibitor. Moreover, Ang II induced upregulation of genes potentially involved in hepatic wound-healing response in a redox-sensitive manner, as assessed by microarray analysis. HSCs isolated from p47phox–/– mice displayed a blunted response to Ang II compared with WT cells. We also assessed the role of NADPH oxidase in experimental liver fibrosis. After bile duct ligation, p47phox–/– mice showed attenuated liver injury and fibrosis compared with WT counterparts. Moreover, expression of smooth muscle α-actin and expression of TGF-β1 were reduced in p47phox–/– mice. Thus, NADPH oxidase mediates the actions of Ang II on HSCs and plays a critical role in liver fibrogenesis.
Ramón Bataller, Robert F. Schwabe, Youkyung H. Choi, Liu Yang, Yong Han Paik, Jeffrey Lindquist, Ting Qian, Robert Schoonhoven, Curt H. Hagedorn, John J. Lemasters, David A. Brenner
Stem cell factor (SCF) is a molecule with known proliferative effects on hematopoietic cells. More recent studies suggest that this molecule may also have effects on cellular differentiation and proliferation in other types of cells. The current investigations demonstrate that there is a large reservoir of SCF in the liver, that hepatic SCF levels change dramatically following partial hepatectomy in mice, and that SCF blockade, either by administration of anti-SCF antibodies or by using genetically altered, SCF-deficient mice, inhibits hepatocyte proliferation after partial hepatectomy; if SCF is replaced in the genetically SCF-deficient mice after partial hepatectomy, hepatocyte proliferation is restored to that seen in WT animals. Furthermore, SCF administration to IL-6 knockout mice also restores hepatocyte proliferation to normal. In vitro studies using primary mouse hepatocytes demonstrate that SCF causes hepatocyte proliferation and is induced by IL-6 and that treatment with anti-SCF antibodies inhibits IL-6–induced hepatocyte proliferation. Further in vivo studies in IL-6 knockout mice demonstrate that SCF administration to these animals increases p-stat3 levels, suggesting that the SCF-induced increase in hepatocyte proliferation in this system is stat3-mediated.
Xiaodan Ren, Cory Hogaboam, Audra Carpenter, Lisa Colletti
Although a lysosomal, cathepsin B–dependent (Ctsb-dependent) pathway of apoptosis has been described, the contribution of this pathway to tissue damage remains unclear. Our aim was to ascertain if Ctsb inactivation attenuates liver injury, inflammation, and fibrogenesis after bile duct ligation (BDL). In 3-day BDL mice, hepatocyte apoptosis, mitochondrial cytochrome c release, and serum alanine aminotransferase (ALT) values were reduced in Ctsb–/– versus Ctsb+/+ animals. Likewise, R-3032 (a Ctsb inhibitor) also reduced these parameters in BDL WT mice. Both genetic and pharmacologic inhibition of Ctsb in the BDL mouse reduced (a) hepatic inflammation, as assessed by transcripts for CXC chemokines and neutrophil infiltration, and (b) fibrogenesis, as assessed by transcripts for stellate cell activation and sirius red staining for hepatic collagen deposition. These differences could not be ascribed to alterations in cholestasis. These findings support a prominent role for the lysosomal pathway of apoptosis in tissue injury and link apoptosis to inflammation and fibrogenesis. Ctsb inhibition may be therapeutic in liver diseases.
Ali Canbay, Maria Eugenia Guicciardi, Hajime Higuchi, Ariel Feldstein, Steven F. Bronk, Robert Rydzewski, Makiko Taniai, Gregory J. Gores