A deregulated cytokine balance is involved in triggering the sequence from steatosis to nonalcoholic steatohepatitis, ultimately leading to liver fibrosis and cancer. To better define the role of proinflammatory interleukin-6 (IL-6)-type cytokines in hepatocytes we investigated the role of IL-6 and its shared receptor, glycoprotein 130 (gp130), in a mouse model of steatohepatitis. IL-6 ؊/؊ mice were fed a choline-deficient, ethionine-supplemented (CDE) diet. Conditional gp130 knockout and knockin mice were used to achieve hepatocytespecific deletion of gp130 (gp130 ⌬hepa ), gp130-dependent rat sarcoma (Ras)-(gp130 ⌬hepaRas ), and signal transducers and activators of transcription (STAT)-(gp130 ⌬hepaSTAT ) activation. CDE-treated IL-6 ؊/؊ mice showed a significant hepatic steatosis at 2 weeks after feeding. The mice rapidly developed elevated fasting blood glucose, insulin serum levels, and transaminases. To better define IL-6-dependent intracellular pathways, specifically in hepatocytes, we next treated gp130 ⌬hepa mice with a CDE diet. These animals also developed a marked steatosis with hyperglycemia and displayed elevated insulin serum levels. Additionally, gp130 ⌬hepa animals showed an imbalanced inflammatory response with increased hepatic tumor necrosis factor-alpha and decreased adiponectin messenger RNA levels. Dissecting the hepatocyte-specific gp130-dependent pathways revealed a similar disease phenotype in gp130 ⌬hepaSTAT mice, whereas gp130 ⌬hepaRas animals were protected. In CDEtreated mice lack of gp130-STAT3 signaling was associated with immune-cell-infiltration, jun kinase-activation, a blunted acute-phase-response, and elevated transaminases. Furthermore, gp130 ⌬hepa and gp130 ⌬hepaSTAT mice showed beginning signs of liver fibrosis compared to gp130 ⌬hepaRas mice and controls. Conclusion: During CDE treatment mice lacking IL-6 and gp130-STAT signaling in hepatocytes are prone to hepatic metabolic changes and inflammation. This ultimately leads to progressive steatohepatitis with signs of liver remodeling. Thus, the presented model allows one to further dissect the role of IL-6/gp130-type signaling in hepatocytes during fatty liver degeneration to define new therapeutic targets in metabolic liver diseases. (HEPATOLOGY 2010;51:463-473.)

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The 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) model leads to chronic cholestatic liver injury and therefore resembles human diseases such as sclerosing cholangitis and forms of metabolic liver diseases. The role of the interleukin-6/glycoprotein 130 (gp130) system in this context is still undefined. Therefore, conditional gp130 knockout and knockin mice were used to achieve hepatocyte-specific deletions of gp130 (gp130 ⌬hepa ), gp130-dependent ras (gp130 ⌬hepaRas ), and signal transducer and activator of transcription (STAT) (gp130 ⌬hepaSTAT ) activation. These mice were treated with a DDC-containing diet and analyzed over time. Mice deficient in hepatic gp130 and STAT signaling showed increased and earlier mortality than wild-type and gp130⌬hepaRas animals. Over time, significantly more apoptosis and cholestasis became evident in gp130 ⌬hepa and gp130 ⌬hepaSTAT mice. These mice also displayed increased tumor necrosis factor-␣ expression, a diminished acute-phase response (lack of STAT3 and serum amyloid A activation), and enhanced immune cell infiltration in the liver. These were associated with stronger periportal oval cell activation. In addition, DDC treatment in gp130 ⌬hepa and gp130 Liver remodeling and fibrosis progression are often the result of an insufficient response of hepatocytes and biliary epithelial cells to different forms of chronic liver injury. A complex network of different liver and immune cells activates cytokines and growth factors, which trigger myofibroblasts to produce extracellular matrix proteins including collagen. Feeding mice 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) is a well established model to study such complex interactions in a highly relevant model of chronic cholestatic liver injury resembling certain metabolic, toxic, and cholestatic chronic liver diseases.1 Moreover, the model leads to a strong fibrotic response in the liver and can enhance the tumorigenic potential of proto-oncogenes.2 The model has also been used to study mechanisms of oval cell activation and proliferation. 3 The cholestatic phenotype of the model and its underlying pathobiology have only recently been elucidated in more detail.1 DDC feeding induces sclerosing cholangitisSupported by the Deutsche Forschungsgemeinschaft (grants 661/4-1 to K.L.S. and TRR57 to C.T.) and by the START program

Ferroptosis is a novel type of programmed cell death that differs from apoptosis in that it involves iron-dependent peroxidation of membrane phospholipids. Its role in a variety of human disorders, including cancer has been hypothesized in recent years. While it may function as an endogenous tumor suppressor in a variety of cancers, its role during initiation and progression of liver cancer, particularly hepatocellular carcinoma (HCC), is yet unknown. Because HCC is most commonly found in chronically injured livers, we utilized two well-established mouse models of chronic injury-dependent HCC formation: Treatment with streptozotocin and high-fat diet as metabolic injury model, as well as treatment with diethylnitrosamine and carbon tetrachloride as toxic injury model. We used mice with hepatocyte-specific deletion of Acsl4, a key mediator of ferroptosis, to explore the significance of ferroptotic cell death in hepatocytes, the cell type of origin for HCC. Surprisingly, preventing ferroptotic cell death in hepatocytes by deleting Acsl4 does not increase the formation of HCC. Furthermore, Acsl4-deficient livers display less fibrosis and proliferation, especially in the HCC model of toxic damage. Intriguingly, in this model, the absence of ACSL4-dependent processes such as ferroptosis significantly slow down the growth of HCC. These findings suggest that during HCC formation in a chronically injured liver, ferroptotic cell death is not an endogenous tumor-suppressive mechanism. Instead, we find that ACSL4-dependent processes have an unanticipated cancer-promoting effect during HCC formation, which is most likely due to aggravated liver damage as demonstrated by increased hepatic fibrosis. Previous studies suggested that ferroptosis might have beneficial effects for patients during HCC therapy. As a result, during HCC progression and therapy, ferroptosis may have both cancer-promoting and cancer-inhibitory effects, respectively.

HGF/c-Met plays a crucial role in host and donor cells of the liver for the cursiv selection of transplanted hepatocytes. Modulating HGF-dependent signalling seems a promising therapeutic option to favour expansion of transplanted hepatocytes.

Infiltrating CD4 and CD8 T cells have been shown to worsen inflammatory liver damage in non-alcoholic steatohepatitis (NASH). Inhibitory T cell receptors such as the programmed cell death protein 1 (PD1) and the natural killer cell receptor 2B4 regulate the activity of CD4 and CD8 T cells and therefore play an important role in immune tolerance required in the liver. In this study, we investigated the expression profile of inhibitory T cell receptors on CD4 and CD8 T cells in a mouse model of NASH. Male B57BL/6J mice were fed a Western diet for 24 weeks. The expression levels of inhibitory receptors on the surface of intrahepatic and peripheral T cells were measured and correlated with markers of activation (CD107a, CD69, and CD44), metabolic disorder (serum triglycerides, serum cholesterol, γ-glutamyl transferase, hepatic triglycerides), inflammation (serum alanine aminotransferase and aspartate aminotransferase) and hepatic fibrosis (collagen 1A1, α-smooth muscle actin, hydroxyproline). Under Western diet, PD1 is exclusively upregulated on intrahepatic and peripheral CD8+ T cells, whereas the expression level on CD4 T cells is unaffected. In contrast, 2B4 is upregulated liver-specifically on both CD4 and CD8 T cells and unchanged on peripheral T cells. Upregulation of PD1 on CD8 T cells is restricted to CD8 effector memory T cells and correlates with lower levels of degranulation. Similarly, the inhibitory function of PD1 on intrahepatic CD4 T cells is shown by a lower CD69 and CD44 expression on PD1-positive CD4 T cells. In murine steatohepatitis, the upregulation of PD1 on CD8 T cells and 2B4 on CD4 and CD8 T cells potentially limits T cell-mediated liver damage. Therefore, these inhibitory T cell receptors could serve as promising targets of immune-modulatory NASH therapy.

We have recently shown that hepatocyte-specific c-met deficiency accelerates the progression of nonalcoholic steatohepatitis in experimental murine models resulting in augmented production of reactive oxygen species and accelerated development of fibrosis. The aim of this study focuses on the elucidation of the underlying cellular mechanisms driven by Nrf2 overactivation in hepatocytes lacking c-met receptor characterized by a severe unbalance between pro-oxidant and antioxidant functions. Control mice (c-metfx/fx), single c-met knockouts (c-metΔhepa), and double c-met/Keap1 knockouts (met/Keap1Δhepa) were then fed a chow or a methionine-choline-deficient (MCD) diet, respectively, for 4 weeks to reproduce the features of nonalcoholic steatohepatitis. Upon MCD feeding, met/Keap1Δhepa mice displayed increased liver mass albeit decreased triglyceride accumulation. The marked increase of oxidative stress observed in c-metΔhepa was restored in the double mutants as assessed by 4-HNE immunostaining and by the expression of genes responsible for the generation of free radicals. Moreover, double knockout mice presented a reduced amount of liver-infiltrating cells and the exacerbation of fibrosis progression observed in c-metΔhepa livers was significantly inhibited in met/Keap1Δhepa. Therefore, genetic activation of the antioxidant transcription factor Nrf2 improves liver damage and repair in hepatocyte-specific c-met-deficient mice mainly through restoring a balance in the cellular redox homeostasis.

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