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The liver has the great ability to regenerate after partial resection or injury, and the mechanisms underlying liver regeneration have been extensively investigated. Interestingly, acute liver injuries triggered by various etiologies are associated with the formation of necrotic lesions, and such necrotic lesions are also rapidly resolved. However, how necrotic liver lesions are repaired has not been carefully investigated until recently. In this review, we briefly summarize the spatiotemporal process of necrotic liver lesion resolution in several liver injury models including immune-mediated liver injury and drug-induced liver injury. The roles of liver nonparenchymal cells and infiltrating immune cells in controlling necrotic liver lesion resolution are discussed, which may help identify potential therapies for acute liver injury and failure., Competing Interests: None declared., (Thieme. All rights reserved.)

Alcohol use disorder (AUD) affects millions of people worldwide, causing extensive morbidity and mortality with limited pharmacological treatments. The liver is considered as the principal site for the detoxification of ethanol metabolite, acetaldehyde (AcH), by aldehyde dehydrogenase 2 (ALDH2) and as a target for AUD treatment, however, our recent data indicate that the liver only plays a partial role in clearing systemic AcH. Here we show that a liver-gut axis, rather than liver alone, synergistically drives systemic AcH clearance and voluntary alcohol drinking. Mechanistically, we find that after ethanol intake, a substantial proportion of AcH generated in the liver is excreted via the bile into the gastrointestinal tract where AcH is further metabolized by gut ALDH2. Modulating bile flow significantly affects serum AcH level and drinking behaviour. Thus, combined targeting of liver and gut ALDH2, and manipulation of bile flow and secretion are potential therapeutic strategies to treat AUD., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Healthy livers contain 80% of body resident macrophages known as Kupffer cells. In diseased livers, the number of Kupffer cells usually drops but is compensated by infiltration of monocyte-derived macrophages, some of which can differentiate into Kupffer-like cells. Early studies suggest that Kupffer cells play important roles in both promoting liver injury and liver regeneration. Yet, the distinction between the functionalities of resident and infiltrating macrophages is not always made. By using more specific macrophage markers and targeted cell depletion and single-cell RNA sequencing, recent studies revealed several subsets of monocyte-derived macrophages that play important functions in inducing liver damage and inflammation as well as in liver repair and regeneration. In this review, we discuss the different roles that hepatic macrophages play in promoting necrotic liver lesion resolution and dead cell clearance, as well as the targeting of these cells as potential tools for the development of novel therapies for acute liver failure and acute-on-chronic liver failure.

Background and Aims: Aging exacerbates liver neutrophil infiltration and alcohol-associated liver disease (ALD) in mice and humans, but the underlying mechanisms remain obscure. This study aimed to examine the effect of aging and alcohol consumption on neutrophilic Sirtuin 1 (SIRT1) and microRNA-223 (miR-223), and their contribution to ALD pathogeneses., Approach and Results: Young and aged myeloid-specific Sirt1 knockout mice were subjected to chronic-plus-binge ethanol feeding. Blood samples from healthy controls and patients with chronic alcohol drinking who presented with acute intoxication were analyzed. Neutrophilic Sirt1 and miR-223 expression were down-regulated in aged mice compared with young mice. Deletion of the Sirt1 gene in myeloid cells including neutrophils exacerbated chronic-plus-binge ethanol-induced liver injury and inflammation and down-regulated neutrophilic miR-223 expression. Immunoprecipitation experiments revealed that SIRT1 promoted C/EBPα deacetylation by directly interacting with C/EBPα, a key transcription factor that controls miR-223 biogenesis, and subsequently elevated miR-223 expression in neutrophils. Importantly, down-regulation of SIRT1 and miR-223 expression was also observed in circulating neutrophils from middle-aged and elderly subjects compared with those from young individuals. Chronic alcohol users with acute intoxication had a reduction in neutrophilic SIRT1 expression in young and middle-aged patients, with a greater reduction in the latter group. The neutrophilic SIRT1 expression correlated with neutrophilic miR-223 and serum alanine transaminase levels in those patients., Conclusions: Aging increases the susceptibility of alcohol-induced liver injury in mice and humans through the down-regulation of the neutrophilic SIRT1-C/EBPα-miR-223 axis, which could be a therapeutic target for the prevention and/or treatment of ALD., (© 2021 American Association for the Study of Liver Diseases.)

Background: Hepatic platelet accumulation contributes to acetaminophen (APAP)-induced liver injury (AILI). However, little is known about the molecular pathways involved in platelet recruitment to the liver and whether targeting such pathways could attenuate AILI., Methods: Mice were fasted overnight before intraperitoneally ( i.p. ) injected with APAP at a dose of 210 mg/kg for male mice and 325 mg/kg for female mice. Platelets adherent to Kupffer cells were determined in both mice and patients overdosed with APAP. The impact of α-chitinase 3-like-1 (α-Chi3l1) on alleviation of AILI was determined in a therapeutic setting, and liver injury was analyzed., Results: The present study unveiled a critical role of Chi3l1 in hepatic platelet recruitment during AILI. Increased Chi3l1 and platelets in the liver were observed in patients and mice overdosed with APAP. Compared to wild-type (WT) mice, Chil1 -/- mice resulted in much lower numbers of hepatic platelets and liver injury than WT mice, a phenotype similar to that in Cd44 -/- mice resulted in much lower numbers of hepatic platelets and liver injury than WT mice, a phenotype similar to that in Chil1 -/- mice. Recombinant Chi3l1 could restore hepatic platelet accumulation and AILI in Chil1 -/- mice, but not in Cd44 -/- mice. Importantly, we generated anti-Chi3l1 monoclonal antibodies and demonstrated that they could effectively inhibit hepatic platelet accumulation and AILI., Conclusions: We uncovered the Chi3l1/CD44 axis as a critical pathway mediating APAP-induced hepatic platelet recruitment and tissue injury. We demonstrated the feasibility and potential of targeting Chi3l1 to treat AILI., Funding: ZS received funding from NSFC (32071129). FWL received funding from NIH (GM123261). ALFSG received funding from NIDDK (DK 058369). ZA received funding from CPRIT (RP150551 and RP190561) and the Welch Foundation (AU-0042-20030616). CJ received funding from NIH (DK122708, DK109574, DK121330, and DK122796) and support from a University of Texas System Translational STARs award. Portions of this work were supported with resources and the use of facilities of the Michael E. DeBakey VA Medical Center and funding from Department of Veterans Affairs I01 BX002551 (Equipment, Personnel, Supplies). The contents do not represent the views of the US Department of Veterans Affairs or the US Government., Competing Interests: ZS, LL, CA, MW, YW, JJ, NM, DF, XG, NZ, CL, JE, WL, BG, FL, ZA, CJ No competing interests declared

Alcoholic hepatitis (AH) is a clinical syndrome characterized by jaundice and progressive inflammatory liver injury in patients with a history of prolonged periods of excess alcohol consumption and recent heavy alcohol abuse. Severe AH is a life-threatening form of alcohol-associated liver disease with a high short-term mortality rate around 30-50% at one month from the initial presentation. A large number of pro-inflammatory mediators, metabolic pathways, transcriptional factors and epigenetic factors have been suggested to be associated with the development and progression of AH. Several factors may contribute to liver failure and mortality in patients with severe AH including hepatocyte death, inflammation, and impaired liver regeneration. Although the pathogeneses of AH have been extensively investigated and many therapeutic targets have been identified over the last five decades, no new drugs for AH have been successfully developed. In this review, we discuss interleukin-22 (IL-22) biology and its roles of anti-apoptosis, anti-fibrosis, anti-oxidation, anti-bacterial infection and regenerative stimulation in protecting against liver injury in many preclinical models including several recently developed models such as chronic-plus-binge ethanol feeding, acute-on-chronic liver failure, C-X-C motif chemokine ligand 1 plus high-fat diet-induced nonalcoholic steatohepatitis. Finally, clinical trials of IL-22 for the treatment of AH are also discussed, which showed some promising benefits for AH patients.

Background and Aims: Nonalcoholic fatty liver disease encompasses a spectrum of diseases ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis, and liver cancer. At present, how simple steatosis progresses to NASH remains obscure and effective pharmacological therapies are lacking. Hepatic expression of C-X-C motif chemokine ligand 1 (CXCL1), a key chemokine for neutrophil infiltration (a hallmark of NASH), is highly elevated in NASH patients but not in fatty livers in obese individuals or in high-fat diet (HFD)-fed mice. The aim of this study was to test whether overexpression of CXCL1 itself in the liver can induce NASH in HFD-fed mice and to test the therapeutic potential of IL-22 in this new NASH model., Approach and Results: Overexpression of Cxcl1 in the liver alone promotes steatosis-to-NASH progression in HFD-fed mice by inducing neutrophil infiltration, oxidative stress, and stress kinase (such as apoptosis signal-regulating kinase 1 and p38 mitogen-activated protein kinase) activation. Myeloid cell-specific deletion of the neutrophil cytosolic factor 1 (Ncf1)/p47 phox gene, which encodes a component of the NADPH oxidase 2 complex that mediates neutrophil oxidative burst, markedly reduced CXCL1-induced NASH and stress kinase activation in HFD-fed mice. Treatment with interleukin (IL)-22, a cytokine with multiple targets, ameliorated CXCL1/HFD-induced NASH or methionine-choline deficient diet-induced NASH in mice. Mechanistically, IL-22 blocked hepatic oxidative stress and its associated stress kinases via the induction of metallothionein, one of the most potent antioxidant proteins. Moreover, although it does not target immune cells, IL-22 treatment attenuated the inflammatory functions of hepatocyte-derived, mitochondrial DNA-enriched extracellular vesicles, thereby suppressing liver inflammation in NASH., Conclusions: Hepatic overexpression of CXCL1 is sufficient to drive steatosis-to-NASH progression in HFD-fed mice through neutrophil-derived reactive oxygen species and activation of stress kinases, which can be reversed by IL-22 treatment via the induction of metallothionein., (Published 2019. This article is a U.S. Government work and is in the public domain in the USA.)

The liver is primarily thought of as a metabolic organ; however, the liver is also an important mediator of immunological functions. Key perspectives on this emerging topic were presented in a symposium at the 2018 annual meeting of the American College of Toxicology entitled "Beyond metabolism: Role of the immune system in hepatic toxicity." Viral hepatitis is an important disease of the liver for which insufficient preventive vaccines exist. Host immune responses inadequately clear these viruses and often potentiate immunological inflammation that damages the liver. In addition, the liver is a key innate immune organ against bacterial infection. Hepatocytes and immune cells cooperatively control systemic and local bacterial infections. Conversely, bacterial infection can activate multiple types of immune cells and pathways to cause hepatocyte damage and liver injury. Finally, the immune system and specifically cytokines and drugs can interact in idiosyncratic drug-induced liver injury. This rare disease can result in a disease spectrum that ranges from mild to acute liver failure. The immune system plays a role in this disease spectrum.

While liver injury is commonly associated with excessive alcohol consumption, how liver injury affects alcohol metabolism and drinking preference remains unclear. To answer these questions, we measured the expression and activity of alcohol dehydrogenase 1 (ADH1) and acetaldehyde dehydrogenase 2 (ALDH2) enzymes, ethanol and acetaldehyde levels in vivo, and binge-like and preferential drinking behaviors with drinking in the dark and two-bottle choice in animal models with liver injury. Acute and chronic carbon tetrachloride (CCl4), and acute LPS-induced liver injury repressed hepatic ALDH2 activity and expression and consequently, blood and liver acetaldehyde concentrations were increased in these models. In addition, chronic CCl4 and acute LPS treatment inhibited hepatic ADH1 expression and activity, leading to increases in blood and liver ethanol concentrations. Consistent with the increase in acetaldehyde levels, alcohol drinking behaviors were reduced in mice with acute or chronic liver injury. Furthermore, oxidative stress induced by hydrogen peroxide attenuated ADH1 and ALDH2 activity post-transcriptionally, while proinflammatory cytokines led to transcriptional repression of ADH1 and ALDH2 in cultured hepatocytes, which correlated with the repression of transcription factor HNF4α. Collectively, our data suggest that alcohol metabolism is suppressed by inflammation and oxidative stress, which is correlated with decreased drinking behavior., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Aldehyde dehydrogenase 2 (ALDH2), a key enzyme for detoxification the ethanol metabolite acetaldehyde, is recognized as a promising therapeutic target to treat alcohol use disorders (AUDs). Disulfiram, a potent ALDH2 inhibitor, is an approved drug for the treatment of AUD but has clinical limitations due to its side effects. This study aims to elucidate the relative contribution of different organs in acetaldehyde clearance through ALDH2 by using global- ( Aldh2 -/- -deficient mice, and to examine whether liver-specific ALDH2 inhibition can prevent alcohol-seeking behavior. Aldh2 -deficient mice, and to examine whether liver-specific ALDH2 inhibition can prevent alcohol-seeking behavior. Aldh2 -/- mice showed markedly higher acetaldehyde concentrations than wild-type (WT) mice after acute ethanol gavage. Acetaldehyde levels in hepatocyte-specific Aldh2 knockout ( Aldh2 Hep-/- ) mice were significantly higher than those in WT mice post gavage, but did not reach the levels observed in Aldh2 -/- mice. Energy expenditure and motility were dramatically dampened in Aldh2 deficiency did not affect voluntary alcohol consumption. Finally, specific liver -/- mice, but moderately decreased in Aldh2 markedly decreased alcohol preference. In conclusion, although the liver is the major organ responsible for acetaldehyde metabolism, a cumulative effect of ALDH2 from other organs likely also contributes to systemic acetaldehyde clearance. Liver-targeted ALDH2 inhibition can decrease heavy drinking without affecting moderate drinking, providing molecular basis for hepatic Hep-/- mice compared to controls. In the 2-bottle paradigm and the drinking-in-the-dark model, Aldh2 -/- mice drank negligible volumes from ethanol-containing bottles, whereas Aldh2 Hep-/- mice showed reduced alcohol preference at high but not low alcohol concentrations. Glial cell- or neuron-specific Aldh2 deficiency did not affect voluntary alcohol consumption. Finally, specific liver Aldh2 knockdown via injection of shAldh2 markedly decreased alcohol preference. In conclusion, although the liver is the major organ responsible for acetaldehyde metabolism, a cumulative effect of ALDH2 from other organs likely also contributes to systemic acetaldehyde clearance. Liver-targeted ALDH2 inhibition can decrease heavy drinking without affecting moderate drinking, providing molecular basis for hepatic ALDH2 targeting/editing for the treatment of AUD., Competing Interests: The authors declare no competing interest.

Activation of pregnane X receptor (PXR), a nuclear receptor that controls xenobiotic and endobiotic metabolism, is known to induce liver enlargement, but the molecular signals and cell types responding to PXR-induced hepatomegaly remain unknown. In this study, the effect of PXR activation on liver enlargement and cell change was evaluated in several strains of genetically modified mice and animal models. Lineage labeling using AAV-Tbg-Cre-treated Rosa26 EYFP mice or Sox9-Cre ERT , Rosa26 EYFP mice was performed and Pxr-null mice or AAV Yap short hairpin RNA (shRNA)-treated mice were used to confirm the role of PXR or yes-associated protein (YAP). Treatment with selective PXR activators induced liver enlargement and accelerated regeneration in wild-type (WT) and PXR-humanized mice, but not in Pxr-null mice, by increase of cell size, induction of a regenerative hybrid hepatocyte (HybHP) reprogramming, and promotion of hepatocyte and HybHP proliferation. Mechanistically, PXR interacted with YAP and PXR activation induced nuclear translocation of YAP. Blockade of YAP abolished PXR-induced liver enlargement in mice. Conclusion: These findings revealed a function of PXR in enlarging liver size and changing liver cell fate by activation of the YAP signaling pathway. These results have implications for understanding the physiological functions of PXR and suggest the potential for manipulation of liver size and liver cell fate., (© 2018 by the American Association for the Study of Liver Diseases.)

Alcoholic liver disease (ALD), a significant health problem, progresses through the course of several pathologies including steatosis, steatohepatitis, fibrosis, and cirrhosis. There are no effective FDA-approved medications to prevent or treat any stages of ALD, and the mechanisms involved in ALD pathogenesis are not well understood. Bioactive lipid metabolites play a crucial role in numerous pathological conditions, as well as in the induction and resolution of inflammation. Herein, a hepatic lipidomic analysis was performed on a mouse model of ALD with the objective of identifying novel metabolic pathways and lipid mediators associated with alcoholic steatohepatitis, which might be potential novel biomarkers and therapeutic targets for the disease. We found that ethanol and dietary unsaturated, but not saturated, fat caused elevated plasma ALT levels, hepatic steatosis and inflammation. These pathologies were associated with increased levels of bioactive lipid metabolites generally involved in pro-inflammatory responses, including 13-hydroxy-octadecadienoic acid, 9,10- and 12,13-dihydroxy-octadecenoic acids, 5-, 8-, 9-, 11-, 15-hydroxy-eicosatetraenoic acids, and 8,9- and 11,12-dihydroxy-eicosatrienoic acids, in parallel with an increase in pro-resolving mediators, such as lipoxin A4, 18-hydroxy-eicosapentaenoic acid, and 10S,17S-dihydroxy-docosahexaenoic acid. Elucidation of alterations in these lipid metabolites may shed new light into the molecular mechanisms underlying ALD development/progression, and be potential novel therapeutic targets., Competing Interests: The authors have declared that no competing interests exist.

Competing Interests: Competing interests: Bin Gao is a US Federal Government employee acting in the course of his employment.

Background & Aims: Short telomeres and genetic telomerase defects are risk factors for some human liver diseases, ranging from non-alcoholic fatty liver disease and non-alcoholic steatohepatitis to cirrhosis. In murine models, telomere dysfunction has been shown to metabolically compromise hematopoietic cells, liver and heart via the activation of the p53-PGC axis., Methods: Tert- and Terc-deficient mice were challenged with liquid high-fat diet. Liver metabolic contents were analysed by CE-TOFMS and liver fat content was confirmed by confocal and electronic microscopy., Results: Tert-deficient but not Terc-deficient mice develop hepatocyte injury and frank steatosis when challenged with liquid high-fat diet. Upon high-fat diet, Tert -/- hepatocytes fail to engage the citric acid cycle (TCA), with an imbalance of NADPH/NADP + and NADH/NAD + ratios and depletion of intermediates of TCA cycle, such as cis-aconitic acid. Telomerase deficiency caused an intrinsic metabolic defect unresponsive to environmental challenge. Chemical inhibition of telomerase by zidovudine recapitulated the abnormal Tert -/- metabolic phenotype in Terc -/- hepatocytes., Conclusions: Our findings indicate that in telomeropathies short telomeres are not the only molecular trigger and telomerase enzyme deficiency provokes hepatocyte metabolic dysfunction, abrogates response to environmental challenge, and causes cellular injury and steatosis, providing a mechanism for liver damage in telomere diseases., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Reactive oxygen species (ROS) contribute to the development of non-alcoholic fatty liver disease. ROS generation by infiltrating macrophages involves multiple mechanisms, including Toll-like receptor 4 (TLR4)-mediated NADPH oxidase (NOX) activation. Here, we show that palmitate-stimulated CD11b + F4/80 low hepatic infiltrating macrophages, but not CD11b + F4/80 high Kupffer cells, generate ROS via dynamin-mediated endocytosis of TLR4 and NOX2, independently from MyD88 and TRIF. We demonstrate that differently from LPS-mediated dimerization of the TLR4-MD2 complex, palmitate binds a monomeric TLR4-MD2 complex that triggers endocytosis, ROS generation and increases pro-interleukin-1β expression in macrophages. Palmitate-induced ROS generation in human CD68 low CD14 high macrophages is strongly suppressed by inhibition of dynamin. Furthermore, Nox2-deficient mice are protected against high-fat diet-induced hepatic steatosis and insulin resistance. Therefore, endocytosis of TLR4 and NOX2 into macrophages might be a novel therapeutic target for non-alcoholic fatty liver disease.

A patient with liver failure due to chronic and acute alcohol abuse under consideration for an urgent liver transplant shortly after stopping alcohol may have residual abnormalities that threaten transplant success, particularly for a small graft. To address this, we studied a model in which reduced-size (50%) Lewis rat livers are transplanted into green fluorescence protein transgenic Lewis recipients after they are fed alcohol or a control diet for 5 weeks. Here we show that normal small Lewis grafts transplanted to alcohol-fed Lewis hosts developed fibrosis, whereas no fibrosis was observed in control-fed recipients. Host-derived CD133 + 8-hydroxy-2'-deoxyguanosine (8-OHdG) cells were significantly increased in livers recovered from both alcohol-fed and control recipients, but only alcohol-fed recipients demonstrated co-staining (a marker of oxidative DNA damage). α smooth muscle actin (α-SMA) staining, a marker for myofibroblasts, also co-localized with CD133 + cells only in the livers of alcohol-fed recipients. Immunostaining and polymerase chain reaction analysis confirmed that chronic alcohol consumption decreased the proportion of bone marrow stem cells (BMSCs) expressing CD133, c-Kit, and chemokine (C-X-C motif) receptor 4 markers and caused oxidative mitochondria DNA (mtDNA) damage. Culture of CD133 + cells from normal rats with medium containing 3% ethanol for 48 hours resulted in elevated mitochondrial 8-OHdG and mtDNA deletion, and ethanol exposure diminished CD133 expression but dramatically increased α-SMA expression. In conclusion, oxidative mtDNA damage and deletions occur in BMSCs of chronic alcohol-fed recipients, and these damaged cells mobilize to the small liver grafts and become myofibroblasts where they play a key role in the subsequent development of fibrosis. Liver Transplantation 23 1564-1576 2017 AASLD., (© 2017 by the American Association for the Study of Liver Diseases.)

Alcoholic liver disease is a major human health problem leading to significant morbidity and mortality in the United States and worldwide. Dietary fat plays an important role in alcoholic liver disease pathogenesis. Herein, we tested the hypothesis that a combination of ethanol and a diet rich in linoleic acid (LA) leads to the increased production of oxidized LA metabolites (OXLAMs), specifically 9- and 13-hydroxyoctadecadienoic acids (HODEs), which contribute to a hepatic proinflammatory response exacerbating liver injury. Mice were fed unsaturated (with a high LA content) or saturated fat diets (USF and SF, respectively) with or without ethanol for 10 days, followed by a single binge of ethanol. Compared to SF+ethanol, mice fed USF+ethanol had elevated plasma alanine transaminase levels, enhanced hepatic steatosis, oxidative stress, and inflammation. Plasma and liver levels of 9- and 13-HODEs were increased in response to USF+ethanol feeding. We demonstrated that primarily 9-HODE, but not 13-HODE, induced the expression of several proinflammatory cytokines in vitro in RAW264.7 macrophages. Finally, deficiency of arachidonate 15-lipoxygenase, a major enzyme involved in LA oxidation and OXLAM production, attenuated liver injury and inflammation caused by USF+ethanol feeding but had no effect on hepatic steatosis. This study demonstrates that OXLAM-mediated induction of a proinflammatory response in macrophages is one of the potential mechanisms underlying the progression from alcohol-induced steatosis to alcoholic steatohepatitis., (Copyright © 2017 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Alcoholic steatohepatitis (ASH) is the progressive form of alcoholic liver disease and may lead to cirrhosis and hepatocellular carcinoma. We studied mouse models and human tissues to identify molecules associated with ASH progression and focused on the mouse fat-specific protein 27 (FSP-27)/human cell death-inducing DFF45-like effector C (CIDEC) protein, which is expressed in white adipose tissues and promotes formation of fat droplets., Methods: C57BL/6N mice or mice with hepatocyte-specific disruption of Fsp27 (Fsp27(Hep-/-) mice) were fed the Lieber-Decarli ethanol liquid diet (5% ethanol) for 10 days to 12 weeks, followed by 1 or multiple binges of ethanol (5 or 6 g/kg) during the chronic feeding. Some mice were given an inhibitor (GW9662) of peroxisome proliferator-activated receptor γ (PPARG). Adenoviral vectors were used to express transgenes or small hairpin (sh) RNAs in cultured hepatocytes and in mice. Liver tissue samples were collected from ethanol-fed mice or from 31 patients with alcoholic hepatitis (AH) with biopsy-proved ASH and analyzed histologically and immunohistochemically and by transcriptome, immunoblotting, and real-time PCR analyses., Results: Chronic-plus-binge ethanol feeding of mice, which mimics the drinking pattern of patients with AH, produced severe ASH and mild fibrosis. Microarray analyses revealed similar alterations in expression of many hepatic genes in ethanol-fed mice and humans with ASH, including up-regulation of mouse Fsp27 (also called Cidec) and human CIDEC. Fsp27(Hep-/-) mice and mice given injections of adenovirus-Fsp27shRNA had markedly reduced ASH following chronic-plus-binge ethanol feeding. Inhibition of PPARG and cyclic AMP-responsive element binding protein H (CREBH) prevented the increases in Fsp27α and FSP27β mRNAs, respectively, and reduced liver injury in this chronic-plus-binge ethanol feeding model. Overexpression of FSP27 and ethanol exposure had synergistic effects in inducing production of mitochondrial reactive oxygen species and damage to hepatocytes in mice. Hepatic CIDEC mRNA expression was increased in patients with AH and correlated with the degree of hepatic steatosis and disease severity including mortality., Conclusions: In mice, chronic-plus-binge ethanol feeding induces ASH that mimics some histological and molecular features observed in patients with AH. Hepatic expression of FSP27/CIDEC is highly up-regulated in mice following chronic-plus-binge ethanol feeding and in patients with AH; this up-regulation contributes to alcohol-induced liver damage., (Published by Elsevier Inc.)

Excessive alcohol consumption causes a wide spectrum of liver disease, ranging from simple steatosis to severe forms of liver injury such as steatohepatitis, liver fibrosis, cirrhosis, and liver cancer. Moreover, alcohol consumption also accelerates liver fibrosis in patients with other types of liver diseases such as viral hepatitis and nonalcoholic fatty liver disease. Virtually all clinical complications of alcoholic liver disease occur in patients with established fibrosis and cirrhosis, thus making fibrosis a key parameter for treatment and prognosis of patients. Here, the authors review diagnosis, management, and antifibrotic therapy of alcoholic liver fibrosis. They discuss both the unique features of alcoholic liver fibrosis and the similarities to liver fibrosis from other etiologies, and review molecular pathogenesis and animal models. Finally, future directions for basic and clinical research on alcoholic liver fibrosis are proposed., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Unlabelled: Invariant natural killer T (iNKT) cells are a major subset of lymphocytes found in the liver. These cells mediate various functions, including hepatic injury, fibrogenesis, and carcinogenesis. However, the function of iNKT cells in liver regeneration remains unclear. In the present study, partial hepatectomy (PHx) was used to study liver regeneration. α-Galactosylceramide (α-GalCer), a specific ligand for iNKT cells, was used to induce iNKT cell activation. After PHx, two strains of iNKT cell-deficient mice, CD1d(-/-) and Jα281(-/-) mice, showed normal liver regeneration. Injection of α-GalCer before or after PHx, which rapidly stimulated interferon-gamma (IFN-γ) and interleukin (IL)-4 production by iNKT cells, markedly inhibited liver regeneration. In vitro treatment with IFN-γ inhibited hepatocyte proliferation. In agreement with this in vitro finding, genetic disruption of IFN-γ or its downstream signaling molecule signal transducer and activator of transcription (STAT)1 significantly abolished the α-GalCer-mediated inhibition of liver regeneration. In vitro exposure to IL-4 did not affect hepatocyte proliferation, but surprisingly, genetic ablation of IL-4 or its downstream signaling molecule STAT6 partially eliminated the inhibitory effect of α-GalCer on liver regeneration. Further studies revealed that IL-4 contributed to α-GalCer-induced iNKT cell expansion and IFN-γ production, thereby inhibiting liver regeneration., Conclusion: iNKT cells play a minor role in controlling liver regeneration after PHx under healthy conditions. Activation of iNKT cells by α-GalCer induces the production of IFN-γ, which directly inhibits liver regeneration, and IL-4, which indirectly attenuates liver regeneration by stimulating iNKT cell expansion and IFN-γ production., (© 2014 by the American Association for the Study of Liver Diseases. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

Unlabelled: Growth arrest and DNA damage-inducible beta (GADD45b) plays an important role in many intracellular events, such as cell cycle arrest, DNA repair, cell survival, apoptosis, and senescence. However, its mechanism of transcriptional regulation remains unclear. In this study the mechanism of peroxisome proliferator-activated receptor α (PPARα) ligand induction of the Gadd45b gene in mouse liver was investigated. Gadd45b messenger RNA (mRNA) was markedly induced by the PPARα agonist Wy-14,643 in wild-type mice but not in Ppara-null mice. Signal transducer and activator of transcription 3 (STAT3) was found to be a repressor of the Gadd45b gene through binding to upstream regulatory elements. The role of STAT3 in control of Gadd45b was confirmed using liver-specific Stat3-null mice. Wy-14,643 treatment stimulated STAT3 ubiquitination leading to activation of the Gadd45b gene as a result of loss of Gadd45b repression by STAT3. STAT3 degradation was induced by forced overexpression of the PPARα target gene-encoded enzyme ACOX1, which produces increased H(2)O(2) as a byproduct of fatty acid β-oxidation. H(2)O(2) also stimulated expression of Gadd45b in cultured cells., Conclusion: PPARα indirectly induces the Gadd45b gene in liver through promoting degradation of the repressor STAT3 as a result of elevated oxidative stress., (Published 2013. This article is a U.S. Government work and is in the public domain in the USA.)

Unlabelled: Chronic plus binge ethanol feeding acts synergistically to induce liver injury in mice, but the mechanisms underlying this phenomenon remain unclear. Here, we show that chronic plus binge ethanol feeding synergistically up-regulated the hepatic expression of interleukin-1β and tumor necrosis factor alpha and induced neutrophil accumulation in the liver, compared with chronic or binge feeding alone. In vivo depletion of neutrophils through administration of an anti-Ly6G antibody markedly reduced chronic-binge ethanol feeding-induced liver injury. Real-time polymerase chain reaction analyses revealed that hepatic E-selectin expression was up-regulated 10-fold, whereas expression of other neutrophil infiltration-related adhesion molecules (e.g., P-selectin, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1) was slightly up- or down-regulated in this chronic-binge model. The genetic deletion of E-selectin prevented chronic-binge ethanol-induced hepatic neutrophil infiltration as well as elevation of serum transaminases without affecting ethanol-induced steatosis. In addition, E-selectin-deficient mice showed reduced hepatic expression of several proinflammatory cytokines, chemokines, and adhesion molecules, compared to wild-type mice, after chronic-binge ethanol feeding. Finally, the expression of E-selectin was highly up-regulated in human alcoholic fatty livers, but not in alcoholic cirrhosis., Conclusions: Chronic-binge ethanol feeding up-regulates expression of proinflammatory cytokines, followed by the induction of E-selectin. Elevated E-selectin plays an important role in hepatic neutrophil infiltration and injury induced by chronic-binge feeding in mice and may also contribute to the pathogenesis of early stages of human alcoholic liver disease., (© 2013 by the American Association for the Study of Liver Diseases.)

The liver is the largest organ in the body and is generally regarded by nonimmunologists as having little or no lymphoid function. However, such is far from accurate. This review highlights the importance of the liver as a lymphoid organ. Firstly, we discuss experimental data surrounding the role of liver as a lymphoid organ. The liver facilitates tolerance rather than immunoreactivity, which protects the host from antigenic overload of dietary components and drugs derived from the gut and it is instrumental to fetal immune tolerance. Loss of liver tolerance leads to autoaggressive phenomena, which if not controlled by regulatory lymphoid populations, may lead to the induction of autoimmune liver diseases. Liver-related lymphoid subpopulations also act as critical antigen-presenting cells. The study of the immunological properties of liver and delineation of the microenvironment of the intrahepatic milieu in normal and diseased livers provides a platform to understand the hierarchy of a series of detrimental events that lead to immune-mediated destruction of the liver and the rejection of liver allografts. The majority of emphasis within this review will be on the normal mononuclear cell composition of the liver. However, within this context, we will discuss selected, but not all, immune-mediated liver disease and attempt to place these data in the context of human autoimmunity.

The aim of the present study was to investigate the inhibitory potential of glimepiride towards important UDP-glucuronosyltransferase (UGT) isoforms in human liver, which play a key role in the elimination of drugs. The recombinant UGT enzymes were used as enzyme source, and a nonspecific substrate 4-methylumbelliferone (4-MU) was utilized as substrate. The results showed that 100 microM of glimepiride inhibited UGT1A1, UGT1A3, UGT1A6, UGT1A9, UGT2B7 and UGT2B15 by 54.7%, 43.1%, 100%, 70.5%, 32.7 and 37.2%, respectively. Given that glimepiride exhibited strong inhibition towards UGT1A6, further inhibitory kinetic behaviour was determined. Glimepiride exerted concentration-dependent inhibition towards UGT1A6. Both Dixon and Lineweaver-Burk plots demonstrated that inhibition of UGT1A6 was best fit for noncompetitive inhibition type, and the inhibition kinetic parameter (Ki) was calculated to be 59.8 microM. Given that UGT1A6 plays a key role in detoxification of many drugs, more attention should be given when glimepiride was co-administered with the drugs mainly undergoing UGT1A6-mediated metabolism.

Background & Aims: Proliferation of liver stem/progenitor cells (LPCs), which can differentiate into hepatocytes or biliary epithelial cells, is often observed in chronically inflamed regions of liver in patients. We investigated how inflammation might promote proliferation of LPCs., Methods: We examined the role of interleukin (IL)-22, a survival factor for hepatocytes, on proliferation of LPCs in patients with chronic hepatitis B virus (HBV) infection and in mice. Proliferation of LPCs in mice was induced by feeding a diet that contained 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)., Results: Hepatic expression of IL-22 was increased in patients with HBV and correlated with the grade of inflammation and proliferation of LPCs. Mice on the DDC diet that overexpressed an IL-22 transgene specifically in liver (IL-22TG), or that were infected with an IL-22-expressing adenovirus, had increased proliferation of LPCs. Signal transducer and activator of transcription (STAT) 3, a component of the IL-22 signaling pathway, was activated in LPCs isolated from DDC-fed IL-22TG mice. Deletion of STAT3 from livers of IL-22TG mice reduced proliferation of LPCs. In addition, the receptors IL-22R1 and IL-10R2 were detected on epithelial cell adhesion molecule(+)CD45(-) LPCs isolated from DDC-fed wild-type mice. Culture of these cells with IL-22 activated STAT3 and led to cell proliferation, but IL-22 had no effect on proliferation of STAT3-deficient EpCAM(+)CD45(-) LPCs. IL-22 also activated STAT3 and promoted proliferation of cultured BMOL cells (a mouse LPC line)., Conclusions: In livers of mice and patients with chronic HBV infection, inflammatory cells produce IL-22, which promotes proliferation of LPCs via STAT3. These findings link inflammation with proliferation of LPCs in patients with HBV infection., (Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.)

The activation of innate immunity by various factors (e.g. lipopolysaccharide and complements) plays an important role in initiating and promoting alcoholic liver injury via the stimulation of Kupffer cells to induce oxidative stress and to produce pro-inflammatory cytokines (e.g. tumor necrosis factor [TNF]-α) that cause hepatocellular damage. Accumulating evidence suggests that the activation of innate immunity also stimulates Kupffer cells to produce the hepatoprotective cytokine interleukin-6 (IL-6) and the anti-inflammatory cytokine IL-10 during alcoholic liver injury. IL-6 protects against alcoholic liver injury via the activation of signal transducer and activator of transcription 3 (STAT3) and the subsequent induction of a variety of hepatoprotective genes in hepatocytes. IL-10 inhibits alcoholic liver inflammation via the activation of STAT3 in Kupffer cells/macrophages and the subsequent inhibition of liver inflammation. Recent studies have suggested that IL-10 may play a dual role in controlling ethanol-induced steatosis and liver injury via the inhibition of the pro-inflammatory cytokine TNF-α, thereby ameliorating alcoholic liver injury, or via the inhibition of the hepatoprotective cytokine IL-6, thereby potentiating alcoholic liver injury. IL-22 is another important hepatoprotective cytokine that protects against acute and chronic alcoholic liver injury by binding to a receptor complex composed of IL-10R2 and IL-22R chains on the surfaces of hepatocytes. Finally, IL-22 treatment is a potential therapeutic option for treating severe forms of alcoholic liver disease because of its antioxidant, antiapoptotic, antisteatotic, proliferative, and antimicrobial effects, as well as the potential added benefit of few side effects., (Published © 2012 This article is a U.S. Government work and is in the public domain in the USA.)

Aberrantly hyperactivated STAT3 has been found in human liver cancers as an oncogene; however, STAT3 has also been shown to exert hepatoprotective effects during liver injury. The balancing act that STAT3 plays between hepatoprotection and liver tumorigenesis remains poorly defined. In this study, the diethylnitrosamine (DEN)-induced liver tumor model and the chronic carbon tetrachloride (CCl(4))-induced liver fibrosis model were both used to investigate the role of STAT3 in liver tumorigenesis. Hepatocyte-specific STAT3 knockout mice were resistant to liver tumorigenesis induced by a single DEN injection, whose tumorigenesis was associated with minimal chronic liver inflammation, injury, and fibrosis. In contrast, long-term CCl(4) treatment resulted in severe hepatic oxidative damage, inflammation, and fibrosis but rarely induced liver tumor formation in wild-type mice. Despite the oncogenic function of STAT3 in DEN-induced liver tumor, hepatocyte-specific STAT3 knockout mice were more susceptible to liver tumorigenesis after 16 weeks of CCl(4) injection, which was associated with higher levels of liver injury, inflammation, fibrosis, and oxidative DNA damage compared with wild-type mice. These findings suggest that the hepatoprotective feature of STAT3 prevents hepatic damage and fibrosis under the condition of persistent inflammatory stress, consequently suppressing injury-driven liver tumor initiation. Once liver tumor cells have developed, STAT3 likely acts as an oncogenic factor to promote tumor growth., (Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Unlabelled: Interleukin-22 (IL-22), which acts as either a proinflammatory or anti-inflammatory cytokine in various disease models, is markedly up-regulated in chronic liver diseases, including hepatitis B and C. In this report, we demonstrate a strong correlation between IL-22 expression in the liver with active, inflammatory human liver disease. To clarify the role of IL-22 up-regulation in the pathogenesis of liver diseases, liver-specific IL-22 transgenic (IL-22TG) mice, under the control of albumin promoter, were developed. Despite elevated IL-22 serum levels ranging from 4,000 to 7,000 pg/mL, IL-22TG mice developed normally without obvious adverse phenotypes or evidence of chronic inflammation (except for slightly thicker epidermis and minor inflammation of the skin) compared with wild-type mice. Interestingly, IL-22TG mice were completely resistant to concanavalin A-induced T cell hepatitis with minimal effect on liver inflammation and had accelerated liver regeneration after partial hepatectomy. Although they did not spontaneously develop liver tumors, IL-22TG mice were more susceptible to diethylnitrosamine-induced liver cancer. Microarray analyses revealed that a variety of antioxidant, mitogenic, acute phase genes were up-regulated in the livers of IL-22TG mice compared with those from wild-type mice., Conclusion: These findings indicate that localized production of IL-22 in the liver promotes hepatocyte survival and proliferation but primes the liver to be more susceptible to tumor development without significantly affecting liver inflammation., (Copyright © 2011 American Association for the Study of Liver Diseases.)

The mammalian liver regenerates upon tissue loss, which induces quiescent hepatocytes to enter the cell cycle and undergo limited replication under the control of multiple hormones, growth factors, and cytokines. Endocannabinoids acting via cannabinoid type 1 receptors (CB(1)R) promote neural progenitor cell proliferation, and in the liver they promote lipogenesis. These findings suggest the involvement of CB(1)R in the control of liver regeneration. Here we report that mice lacking CB(1)R globally or in hepatocytes only and wild-type mice treated with a CB(1)R antagonist have a delayed proliferative response to two-thirds partial hepatectomy (PHX). In wild-type mice, PHX leads to increased hepatic expression of CB(1)R and hyperactivation of the biosynthesis of the endocannabinoid anandamide in the liver via an in vivo pathway involving conjugation of arachidonic acid and ethanolamine by fatty-acid amide hydrolase. In wild-type but not CB(1)R(-/-) mice, PHX induces robust up-regulation of key cell-cycle proteins involved in mitotic progression, including cyclin-dependent kinase 1 (Cdk1), cyclin B2, and their transcriptional regulator forkhead box protein M1 (FoxM1), as revealed by ultrahigh-throughput RNA sequencing and pathway analysis and confirmed by real-time PCR and Western blot analyses. Treatment of wild-type mice with anandamide induces similar changes mediated via activation of the PI3K/Akt pathway. We conclude that activation of hepatic CB(1)R by newly synthesized anandamide promotes liver regeneration by controlling the expression of cell-cycle regulators that drive M phase progression.

Excessive alcohol consumption is a leading cause of chronic liver disease in the Western world. Alcohol-induced hepatotoxicity and oxidative stress are important mechanisms contributing to the pathogenesis of alcoholic liver disease. However, emerging evidence suggests that activation of innate immunity involving TLR4 and complement also plays an important role in initiating alcoholic steatohepatitis and fibrosis, but the role of adaptive immunity in the pathogenesis of alcoholic liver disease remains obscure. Activation of a TLR4-mediated MyD88-independent (TRIF/IRF-3) signaling pathway in Kupffer cells contributes to alcoholic steatohepatitis, whereas activation of TLR4 signaling in hepatic stellate cells promotes liver fibrosis. Alcohol consumption activates the complement system in the liver by yet unidentified mechanisms, leading to alcoholic steatohepatitis. In contrast to activation of TLR4 and complement, alcohol consumption can inhibit natural killer cells, another important innate immunity component, contributing to alcohol-mediated acceleration of viral infection and liver fibrosis in patients with chronic viral hepatitis. Understanding of the role of innate immunity in the pathogenesis of alcoholic liver disease may help us identify novel therapeutic targets to treat this disease.

Unlabelled: Natural killer (NK) cells are abundant in the liver and serve as a major innate immune component against microbial infection. Although NK cells have been implicated in inducing hepatocellular damage in patients with chronic hepatitis virus infections, the roles that hepatic NK cells play in chronic hepatitis B virus (HBV) infections remain obscure. In this study, we comprehensively characterized intrahepatic and peripheral NK cells and investigated their impact on liver pathology in a cohort of HBV-infected individuals; this cohort included 51 immune-activated (IA) patients, 27 immune-tolerant (IT) carriers, and 26 healthy subjects. We found that NK cells expressing NK receptors (activation receptors) preferentially accumulated in the livers of IA patients, in which they were activated and skewed toward cytolytic activity but without a concomitant increase in interferon-γ production, in comparison with those of IT carriers and healthy subjects. Further analysis showed that the livers of IA patients, in comparison with those of IT and healthy subjects, expressed higher levels of interleukin-12 (IL-12), IL-15, and IL-18 in situ and lower levels of IL-10, which in vitro can induce the activation and degranulation of NK cells from healthy individuals. Finally, hepatic NK cells displayed more cytolytic activity than peripheral NK cells, and this was found to be positively correlated with the liver histological activity index and serum alanine aminotransferase levels in these IA patients., Conclusion: In IA patients, hepatic NK cells are activated and preferentially skew toward cytolytic activity, which depends on an imbalanced cytokine milieu and correlates with liver injury during chronic HBV infection., (Copyright © 2010 American Association for the Study of Liver Diseases.)

Under various conditions, mammals have the ability to maintain serum glucose concentration within a narrow range. SIRT1 plays an important role in regulating gluconeogenesis and fat metabolism; however, the underlying mechanisms remain elusive. Here, we show that SIRT1 forms a complex with FOXO3a and NRF1 on the SIRT6 promoter and positively regulates expression of SIRT6, which, in turn, negatively regulates glycolysis, triglyceride synthesis, and fat metabolism by deacetylating histone H3 lysine 9 in the promoter of many genes involved in these processes. Liver-specific deletion of SIRT6 in mice causes profound alterations in gene expression, leading to increased glycolysis, triglyceride synthesis, reduced beta oxidation, and fatty liver formation. Human fatty liver samples exhibited significantly lower levels of SIRT6 than did normal controls. Thus, SIRT6 plays a critical role in fat metabolism and may serve as a therapeutic target for treating fatty liver disease, the most common cause of liver dysfunction in humans., (2010 Elsevier Inc. All rights reserved.)

Alcoholism can result in fatty liver that can progress to steatohepatitis, cirrhosis, and liver cancer. Mice fed alcohol develop fatty liver through endocannabinoid activation of hepatic CB(1) cannabinoid receptors (CB(1)R), which increases lipogenesis and decreases fatty acid oxidation. Chronic alcohol feeding also up-regulates CB(1)R in hepatocytes in vivo, which could be replicated in vitro by co-culturing control hepatocytes with hepatic stellate cells (HSC) isolated from ethanol-fed mice, implicating HSC-derived mediator(s) in the regulation of hepatic CB(1)R (Jeong, W. I., Osei-Hyiaman, D., Park, O., Liu, J., Bátkai, S., Mukhopadhyay, P., Horiguchi, N., Harvey-White, J., Marsicano, G., Lutz, B., Gao, B., and Kunos, G. (2008) Cell Metab. 7, 227-235). HSC being a rich source of retinoic acid (RA), we tested whether RA and its receptors may regulate CB(1)R expression in cultured mouse hepatocytes. Incubation of hepatocytes with RA or RA receptor (RAR) agonists increased CB(1)R mRNA and protein, the most efficacious being the RARgamma agonist CD437 and the pan-RAR agonist TTNPB. The endocannabinoid 2-arachidonoylglycerol (2-AG) also increased hepatic CB(1)R expression, which was mediated indirectly via RA, because it was absent in hepatocytes from mice lacking retinaldehyde dehydrogenase 1, the enzyme catalyzing the generation of RA from retinaldehyde. The binding of RARgamma to the CB(1)R gene 5' upstream domain in hepatocytes treated with RAR agonists or 2-AG was confirmed by chromatin immunoprecipitation and electrophoretic mobility shift and antibody supershift assays. Finally, TTNPB-induced CB(1)R expression was attenuated by small interfering RNA knockdown of RARgamma in hepatocytes. We conclude that RARgamma regulates CB(1)R expression and is thus involved in the control of hepatic fat metabolism by endocannabinoids.

Unlabelled: Liver injury is associated with inflammation, which is generally believed to accelerate the progression of liver diseases; however, clinical data show that inflammation does not always correlate with hepatocelluar damage in some patients. Investigating the cellular mechanisms underlying these events using an experimental animal model, we show that inflammation may attenuate liver necrosis induced by carbon tetrachloride (CCl(4)) in myeloid-specific signal transducer and activator of transcription 3 (STAT3) knockout mice. As an important anti-inflammatory signal, conditional deletion of STAT3 in myeloid cells results in markedly enhanced liver inflammation after CCl(4) injection. However, these effects are also accompanied by reduced liver necrosis, correlating with elevated serum interleukin-6 (IL-6) and hepatic STAT3 activation. An additional deletion of STAT3 in hepatocytes in myeloid-specific STAT3 knockout mice restored hepatic necrosis but decreased liver inflammation., Conclusion: Inflammation-mediated STAT3 activation attenuates hepatocellular injury induced by CCl(4) in myeloid-specific STAT3 knockout mice, suggesting that inflammation associated with a predominance of hepatoprotective cytokines that activate hepatic STAT3 may reduce rather than accelerate hepatocellular damage in patients with chronic liver diseases.

Control of organ size by cell proliferation and survival is a fundamental developmental process, and its deregulation leads to cancer. However, the molecular mechanism underlying organ size control remains elusive in vertebrates. In Drosophila, the Hippo (Hpo) signaling pathway controls organ size by both restricting cell growth and proliferation and promoting cell death. Here we investigated whether mammals also require the Hpo pathway to control organ size and adult tissue homeostasis. We found that Mst1 and Mst2, the two mouse homologs of the Drosophila Hpo, control the sizes of some, but not all organs, in mice, and Mst1 and Mst2 act as tumor suppressors by restricting cell proliferation and survival. We show that Mst1 and Mst2 play redundant roles, and removal of both resulted in early lethality in mouse embryos. Importantly, tumors developed in the liver with a substantial increase of the stem/progenitor cells by 6 months after removing Mst1 and Mst2 postnatally. We show that Mst1 and Mst2 were required in vivo to control Yap phosphorylation and activity. Interestingly, apoptosis induced by TNFalpha was blocked in the Mst1 and Mst2 double-mutant cells both in vivo and in vitro. As TNFalpha is a pleiotropic inflammatory cytokine affecting most organs by regulating cell proliferation and cell death, resistance to TNFalpha-induced cell death may also contribute significantly to tumor formation in the absence of Mst1 and Mst2.

Background & Aims: T cell-mediated hepatitis is a leading cause of acute liver failure; there is no effective treatment, and the mechanisms underlying its pathogenesis are obscure. The aim of this study was to investigate the immune cell-signaling pathways involved-specifically the role of signal transducer and activator of transcription 3 (STAT3)-in T cell-mediated hepatitis in mice., Methods: T cell-mediated hepatitis was induced in mice by injection of concanavalin A (Con A). Mice with myeloid cell-specific and T-cell-specific deletion of STAT3 were generated., Results: STAT3 was activated in myeloid and T cells following Con A injection. Deletion of STAT3 specifically from myeloid cells exacerbated T-cell hepatitis and induced STAT1-dependent production of a T helper cell (Th)1 cytokine (interferon [IFN]-gamma) and to a lesser extent of Th17 cytokines (interleukin [IL]-17 and IL-22) in a STAT1-independent manner. In contrast, deletion of STAT3 in T cells reduced T cell-mediated hepatitis and IL-17 production. Furthermore, deletion of IFN-gamma completely abolished Con A-induced T-cell hepatitis, whereas deletion of IL-17 slightly but significantly reduced such injury. In vitro experiments indicated that IL-17 promoted liver inflammation but inhibited hepatocyte apoptosis., Conclusions: Myeloid STAT3 activation inhibits T cell-mediated hepatitis via suppression of a Th1 cytokine (IFN-gamma) in a STAT1-dependent manner, whereas STAT3 activation in T cells promotes T-cell hepatitis to a lesser extent, via induction of IL-17. Therefore, activation of STAT3 in myeloid cells could be a novel therapeutic strategy for patients with T-cell hepatitis.

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Unlabelled: Liver fibrosis is a common scarring response to all forms of chronic liver injury and is always associated with inflammation that contributes to fibrogenesis. Although a variety of cell populations infiltrate the liver during inflammation, it is generically clear that CD8 T lymphocytes promote while natural killer (NK) cells inhibit liver fibrosis. However, the role of invariant natural killer T (iNKT) cells, which are abundant in the liver, in hepatic fibrogenesis, remains obscure. Here we show that iNKT-deficient mice are more susceptible to carbon tetrachloride (CCl(4))-induced acute liver injury and inflammation. The protective effect of naturally activated iNKT in this model is likely mediated via suppression of the proinflammatory effect of activated hepatic stellate cells. Interestingly, strong activation of iNKT through injection of iNKT activator alpha-galactosylceramide (alpha-GalCer) accelerates CCl(4)-induced acute liver injury and fibrosis. In contrast, chronic CCl(4) administration induces a similar degree of liver injury in iNKT-deficient and wild-type mice, and only a slightly higher grade of liver fibrosis in iNKT-deficient mice than wild-type mice 2 weeks but not 4 weeks after CCl(4) injection, although iNKT cells are able to kill activated stellate cells. An insignificant role of iNKT in chronic liver injury and fibrosis may be attributable to hepatic iNKT cell depletion. Finally, chronic alpha-GalCer treatment had little effect on liver injury and fibrosis, which is attributable to iNKT tolerance after alpha-GalCer injection., Conclusion: Natural activation of hepatic iNKT cells inhibits, whereas strong activation of iNKT cells by alpha-GalCer accelerates CCl(4)-induced acute liver injury, inflammation, and fibrosis. During chronic liver injury, hepatic iNKT cells are depleted and play a role in inhibiting liver fibrosis in the early stage but not the late stage of fibrosis.

Recent studies have implicated dysregulation of the endocannabinoid system in various liver diseases and their complications (e.g., hepatitis, fibrosis, cirrhosis, cirrhotic cardiomyopathy, and ischemia-reperfusion), and demonstrated that its modulation by either cannabinoid 2 (CB(2)) receptor agonists or CB(1) antagonists may be of significant therapeutic benefits. This review is aimed to focus on the triggers and sources of endocannabinoids during liver inflammation and on the novel role of CB(2) receptors in the interplay between the activated endothelium and various inflammatory cells (leukocytes, lymphocytes, etc.), which play pivotal role in the early development and progression of inflammatory and other liver diseases.

Liver transplantation is presently the only curative treatment for patients with end-stage liver disease. However, the mechanisms underlying liver injury and hepatocyte proliferation posttransplantation remain obscure. In this investigation, liver injury and hepatocyte proliferation in syngeneic and allogeneic animal models were compared. Male Lewis and Dark Agouti (DA) rats were subjected to orthotopic liver transplantation (OLT). Rat OLT was performed in syngeneic (Lewis-Lewis) and allogeneic (Lewis-DA or DA-Lewis) animal models. Allogeneic liver grafts exhibited greater injury and cellular apoptosis than syngeneic grafts but less hepatocyte proliferation after OLT. Expression of IFN-gamma mRNA and activation of the downstream signal transducer and activator of transcription 1 (STAT1) and genes (interferon regulatory factor-1 and cyclin-dependent kinase inhibitor p21(CDKN1A)) were also greater in the allogeneic grafts compared with the syngeneic grafts. In contrast, STAT3 activation was lower in the allogeneic grafts. Furthermore, in the allogeneic grafts, depletion of natural killer (NK) cells decreased IFN-gamma/STAT1 activation but enhanced hepatocyte proliferation. These findings suggest that, compared with syngeneic transplantation, innate immunity (NK/IFN-gamma) is activated after allogeneic transplantation, which likely contributes to liver injury and inhibits hepatocyte proliferation.

Alcohol-induced fatty liver, a major cause of morbidity, has been attributed to enhanced hepatic lipogenesis and decreased fat clearance of unknown mechanism. Here we report that the steatosis induced in mice by a low-fat, liquid ethanol diet is attenuated by concurrent blockade of cannabinoid CB1 receptors. Global or hepatocyte-specific CB1 knockout mice are resistant to ethanol-induced steatosis and increases in lipogenic gene expression and have increased carnitine palmitoyltransferase 1 activity, which, unlike in controls, is not reduced by ethanol treatment. Ethanol feeding increases the hepatic expression of CB1 receptors and upregulates the endocannabinoid 2-arachidonoylglycerol (2-AG) and its biosynthetic enzyme diacylglycerol lipase beta selectively in hepatic stellate cells. In control but not CB1 receptor-deficient hepatocytes, coculture with stellate cells from ethanol-fed mice results in upregulation of CB1 receptors and lipogenic gene expression. We conclude that paracrine activation of hepatic CB1 receptors by stellate cell-derived 2-AG mediates ethanol-induced steatosis through increasing lipogenesis and decreasing fatty acid oxidation.

Unlabelled: Blood circulating from the intestines to the liver is rich in bacterial products, environmental toxins, and food antigens. To effectively and quickly defend against potentially toxic agents without launching harmful immune responses, the liver relies on its strong innate immune system. This comprises enrichment of innate immune cells (such as macrophages, natural killer, natural killer T, and gammadelta T cells) and removal of waste molecules and immunologic elimination of microorganisms by liver endothelial cells and Kupffer cells. In addition, the liver also plays an important role in controlling systemic innate immunity through the biosynthesis of numerous soluble pathogen-recognition receptors and complement components., Conclusion: The liver is an organ with predominant innate immunity, playing an important role not only in host defenses against invading microorganisms and tumor transformation but also in liver injury and repair. Recent evidence suggests that innate immunity is also involved in the pathogenesis of liver fibrosis, providing novel therapeutic targets to treat such a liver disorder.

Unlabelled: Primary biliary cirrhosis (PBC) is an organ-specific autoimmune liver disease characterized by the presence of antimitochondrial antibodies and the destruction of small intrahepatic bile ducts with portal inflammation. In previous studies, we reported that both CD1d expression and the frequency of CD1d-restricted natural killer T (NKT) cells were increased in the livers of patients with PBC. To define a specific role of CD1d-restricted NKT cells in the pathogenesis of PBC, particularly early events, we investigated the function of hepatic CD1d-restricted NKT cells in our transforming growth factor beta (TGF-beta) receptor II dominant-negative (dnTGFbetaRII) mouse model of PBC. We generated CD1d(-/-) and CD1d(+/-) dnTGFbetaRII mice and performed a comparative study of liver immunopathology. We report herein that these dnTGFbetaRII mice demonstrate a massive increase of hyperactive CD1d-restricted NKT cells within the hepatic tissues. CD1d(-/-)dnTGFbetaRII mice, which lack CD1d-restricted CD1d-restricted NKT cells, exhibit significantly decreased hepatic lymphoid cell infiltrates and milder cholangitis compared with CD1d(+/-)dnTGFbetaRII mice. Interestingly, there was a significant increase in the production of interferon-gamma in hepatic CD1d-restricted NKT cells activated by alpha-galactosylceramide in young but not older dnTGFbetaRII mice, suggesting an age-dependent role of CD1d-restricted NKT cells., Conclusion: These data demonstrate that CD1d-restricted NKT cells in dnTGFbetaRII mice are a critical factor in liver injury.

In this study, we have investigated the role of the cannabinoid CB(2) (CB(2)) receptor in an in vivo mouse model of hepatic ischemia/reperfusion (I/R) injury. In addition, we have assessed the role of the CB(2) receptor in TNF-alpha-induced ICAM-1 and VCAM-1 expression in human liver sinusoidal endothelial cells (HLSECs) and in the adhesion of human neutrophils to HLSECs in vitro. The potent CB(2) receptor agonist HU-308, given prior to the induction of I/R, significantly attenuated the extent of liver damage (measured by serum alanine aminotransferase and lactate dehydrogenase) and decreased serum and tissue TNF-alpha, MIP-1alpha, and MIP-2 levels, tissue lipid peroxidation, neutrophil infiltration, DNA fragmentation, and caspase 3 activity. The protective effect of HU-308 against liver damage was also preserved when given right after the ischemic episode. HU-308 also attenuated the TNF-alpha-induced ICAM-1 and VCAM-1 expression in HLSECs, which expressed CB(2) receptors, and the adhesion of human neutrophils to HLSECs in vitro. These findings suggest that selective CB(2) receptor agonists may represent a novel, protective strategy against I/R injury by attenuating oxidative stress, inflammatory response, and apoptosis.