Expression of interferon alfa signaling components in human alcoholic liver disease

Diammonium glycyrrhizinate ameliorates alcohol-induced liver injury by reducing oxidative stress, steatosis, and inflammation

Alcohol-induced liver injury (ALI) is a serious global health issue. Diammonium glycyrrhizinate (DG), a pharmaceutical form of glycyrrhizic acid, has been reported to have anti-inflammatory and anti-oxidative stress properties. We investigated the potential hepatoprotective effects of DG against ALI and explored the mechanisms of it. In vivo, C57BL/6J mice were used to investigate the protective effect of DG on ALI induced by chronic plus binge alcohol exposure. In vitro, AML-12 cells were applied to evaluate the role of DDX5 in the hepatic protection of DG and explore the possible mechanism of STAT1 activation regulated by DDX5. The results showed that DG significantly alleviated liver injury, inflammation, and lipid deposition in hepatocytes. It also beneficially influenced oxidative stress dysregulation. RNA-seq expression in mouse liver tissue indicated that Dead-box helicase 5 (DDX5) might be a potential target of DG. Compared with the control group, the expression of DDX5 decreased significantly in the ethanol-fed group, while DDX5 was restored in the DG treatment group. In addition, the protective effects of DG against ALI were impaired by DDX5 deficiency. DDX5 inhibited the phosphorylation of signal transducer and activator of transcription 1 (STAT1) by recruiting the protein inhibitor of activated STAT1 (PIAS1) to STAT1. The protective effect of DG against ALI associated with oxidative stress, steatosis, and inflammation was probably via regulating the DDX5/STAT1 axis.

Pharmacological inhibition of the Src homology phosphatase 2 confers partial protection in a mouse model of alcohol-associated liver disease

Alcohol-associated liver disease (ALD) is a leading factor of liver-related death worldwide. ALD has various manifestations that include steatosis, hepatitis, and cirrhosis and is currently without approved pharmacotherapies. The Src homology phosphatase 2 (Shp2) is a drug target in some cancers due to its positive regulation of Ras-mitogen-activated protein kinase signaling and cell proliferation. Shp2 pharmacological inhibition yields beneficial outcomes in animal disease models, but its impact on ALD remains unexplored. This study aims to investigate the effects of Shp2 inhibition and its validity using a preclinical mouse model of ALD. We report that the administration of SHP099, a potent and selective allosteric inhibitor of Shp2, partially ameliorated ethanol-induced hepatic injury, inflammation, and steatosis in mice. Additionally, Shp2 inhibition was associated with reduced ethanol-evoked activation of extracellular signal-regulated kinase (ERK), oxidative, and endoplasmic reticulum (ER) stress in the liver. Besides the liver, excessive alcohol consumption induces multi-organ injury and dysfunction, including the intestine. Notably, Shp2 inhibition diminished ethanol-induced intestinal inflammation and permeability, abrogated the reduction in tight junction protein expression, and the activation of ERK and stress signaling in the ileum. Collectively, Shp2 pharmacological inhibition mitigates the deleterious effects of ethanol in the liver and intestine in a mouse model of ALD. Given the multifactorial aspects underlying ALD pathogenesis, additional studies are needed to decipher the utility of Shp2 inhibition alone or as a component in a multitherapeutic regimen to combat this deadly malady.

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Hepatic protein tyrosine phosphatase Shp2 disruption mitigates the adverse effects of ethanol in the liver by modulating oxidative stress and ERK signaling

AIMS

Chronic excessive alcohol intake is a significant cause of alcohol-associated liver disease (ALD), a leading contributor to liver-related morbidity and mortality. The Src homology phosphatase 2 (Shp2; encoded by Ptpn11) is a widely expressed protein tyrosine phosphatase that modulates hepatic functions, but its role in ALD is mostly uncharted.

MAIN METHODS

Herein, we explore the effects of liver-specific Shp2 genetic disruption using the established chronic-plus-binge mouse model of ALD.

KEY FINDINGS

We report that the hepatic Shp2 disruption had beneficial effects and partially ameliorated ethanol-induced injury, inflammation, and steatosis in the liver. Consistently, Shp2 deficiency was associated with decreased ethanol-evoked activation of extracellular signal-regulated kinase (ERK) and oxidative stress in the liver. Moreover, primary hepatocytes with Shp2 deficiency exhibited similar outcomes to those observed upon Shp2 disruption in vivo, including diminished ethanol-induced ERK activation, inflammation, and oxidative stress. Furthermore, pharmacological inhibition of ERK in primary hepatocytes mimicked the effects of Shp2 deficiency and attenuated oxidative stress caused by ethanol.

SIGNIFICANCE

Collectively, these findings highlight Shp2 as a modulator of hepatic oxidative stress upon ethanol challenge and suggest the evaluation of this phosphatase as a potential therapeutic target for ALD.

Loss of long-chain acyl-CoA synthetase 1 promotes hepatocyte death in alcohol-induced steatohepatitis

BACKGROUND

Alcohol consumption has been shown to disrupt hepatic lipid homeostasis. Long-chain acyl-CoA synthetase 1 (ACSL1) critically regulates hepatic fatty acid metabolism and lipid homeostasis by channeling fatty acids to lipid metabolic pathways. However, it remains unclear how ACSL1 contributes to the development of alcohol-associated liver disease (ALD).

METHODS

We performed chronic alcohol feeding animal studies with hepatocyte-specific ACSL1 knockout (ACSL1^Δhep) mice, hepatocyte-specific STAT5 knockout (STAT5^Δhep) mice, and ACSL1^Δhep based-STAT5B overexpression (Stat5b-OE) mice. Cell studies were conducted to define the causal role of ACSL1 deficiency in the pathogenesis of alcohol-induced liver injury. The clinical relevance of the STAT5-ACSL1 pathway was examined using liver tissues from patients with alcoholic hepatitis (AH) and normal subjects (Normal).

RESULTS

We found that chronic alcohol consumption reduced hepatic ACSL1 expression in AH patients and ALD mice. Hepatocyte-specific ACSL1 deletion exacerbated alcohol-induced liver injury by increasing free fatty acids (FFA) accumulation and cell death. Cell studies revealed that FFA elicited the translocation of BAX and p-MLKL to the lysosomal membrane, resulting in lysosomal membrane permeabilization (LMP) and thereby initiating lysosomal-mediated cell death pathway. Furthermore, we identified that the signal transducer and activator of transcription 5 (STAT5) is a novel transcriptional regulator of ACSL1. Deletion of STAT5 exacerbated alcohol-induced liver injury in association with downregulation of ACSL1, and reactivation of ACSL1 by STAT5 overexpression effectively ameliorated alcohol-induced liver injury. In addition, ACSL1 expression was positively correlated with STAT5 and negatively correlated with cell death was also validated in the liver of AH patients.

CONCLUSIONS

ACSL1 deficiency due to STAT5 inactivation critically mediates alcohol-induced lipotoxicity and cell death in the development of ALD. These findings provide insights into alcohol-induced liver injury.

High Prevalence of Pre-Existing Liver Abnormalities Identified Via Autopsies in COVID-19: Identification of a New Silent Risk Factor?

A high prevalence of hepatic pathology (in 17 of 19 cases) was reported in post-mortem (PM) examinations of COVID-19 patients, undertaken between March 2020 and February 2021 by a single autopsy pathologist in two English Coronial jurisdictions. The patients in our cohort demonstrated high levels of recognised COVID-19 risk factors, including hypertension (8/16, 50%), type 2 diabetes mellitus (8/16, 50%) and evidence of arteriopathy 6/16 (38%). Hepatic abnormalities included steatosis (12/19; 63%), moderate to severe venous congestion (5/19; 26%) and cirrhosis (4/19; 21%). A subsequent literature review indicated a significantly increased prevalence of steatosis (49%), venous congestion (34%) and cirrhosis (9.3%) in COVID-19 PM cases, compared with a pre-pandemic PM cohort (33%, 16%, and 2.6%, respectively), likely reflecting an increased mortality risk in SARS-CoV-2 infection for patients with pre-existing liver disease. To corroborate this observation, we retrospectively analysed the admission liver function test (LFT) results of 276 consecutive, anonymised COVID-19 hospital patients in our centre, for whom outcome data were available. Of these patients, 236 (85.5%) had significantly reduced albumin levels at the time of admission to hospital, which was likely indicative of pre-existing chronic liver or renal disease. There was a strong correlation between patient outcome (length of hospital admission or death) and abnormal albumin at the time of hospital admission (p = 0.000012). We discuss potential mechanisms by which our observations of hepatic dysfunction are linked to a risk of COVID-19 mortality, speculating on the importance of recently identified anti-interferon antibodies.

Binge Alcohol Is More Injurious to Liver in Female than in Male Rats: Histopathological, Pharmacologic, and Epigenetic Profiles

Binge alcohol consumption is a health problem, but differences between the sexes remain poorly defined. We have examined the in vivo effects of three acute, repeat binge alcohol administration on the liver in male and female rats. Sprague-Dawley rats were gavaged with alcohol (5 g/kg body weight) three times at 12-hour intervals. Blood and liver tissues were collected 4 hours after the last binge ethanol. Subsequently, several variables were analyzed. Compared with male rats, females had higher levels of blood alcohol, alanine aminotransferase, and triglycerides. Liver histology showed increased lipid vesicles that were larger in females. Protein levels of liver cytochrome P4502E1 were higher in the liver of females than in the liver of males after binge. Hepatic phospho-extracellular signal-regulated kinase 1/2 and phosph-p38 mitogen-activated protein kinase levels were lower in females compared with males after binge alcohol, but no differences were found in the phospho-C-jun N-terminal kinase levels. Peroxisome proliferator-activated receptor γ-coactivator 1α and cyclic AMP response element binding (CREB) protein levels increased more in female than in male livers; however, increases in phospho-CREB levels were lower in females. Remarkably, c-fos was reduced substantially in the livers of females, but no differences in c-myc protein were found. Binge ethanol caused elevation in acetylated (H3AcK9) and phosphoacetylated (H3AcK9PS10) histone H3 in both sexes but without any difference. Binge alcohol caused differential alterations in the levels of various species of phosphatidylethanol and a larger increase in the diacylglycerol kinase-α protein levels in the liver of female rats compared with male rats. These data demonstrate, for the first time, similarities and differences in the sex-specific responses to repeat binge alcohol leading to an increased susceptibility of female rats to have liver injury in vivo. SIGNIFICANCE STATEMENT: This study examines the molecular responses of male and female rat livers to acute binge alcohol in vivo and demonstrates significant differences in the susceptibility between sexes.

Acute and Chronic Ethanol Administration Differentially Modulate Hepatic Autophagy and Transcription Factor EB

BACKGROUND

Chronic ethanol (EtOH) consumption decelerates the catabolism of long-lived proteins, indicating that it slows hepatic macroautophagy (hereafter called autophagy) a crucial lysosomal catabolic pathway in most eukaryotic cells. Autophagy and lysosome biogenesis are linked. Both are regulated by the transcription factor EB (TFEB). Here, we tested whether TFEB can be used as a singular indicator of autophagic activity, by quantifying its nuclear content in livers of mice subjected to acute and chronic EtOH administration. We correlated nuclear TFEB to specific indices of autophagy.

METHODS

In acute experiments, we gavaged GFP-LC3(tg) mice with a single dose of EtOH or with phosphate buffered saline (PBS). We fed mice chronically by feeding them control or EtOH liquid diets.

RESULTS

Compared with PBS-gavaged controls, livers of EtOH-gavaged mice exhibited greater autophagosome (AV) numbers, a higher incidence of AV-lysosome co-localization, and elevated levels of free GFP, all indicating enhanced autophagy, which correlated with a higher nuclear content of TFEB. Compared with pair-fed controls, livers of EtOH-fed mice exhibited higher AV numbers, but had lower lysosome numbers, lower AV-lysosome co-localization, higher P62/SQSTM1 levels, and lower free GFP levels. The latter findings correlated with lower nuclear TFEB levels in EtOH-fed mice. Thus, enhanced autophagy after acute EtOH gavage correlated with a higher nuclear TFEB content. Conversely, chronic EtOH feeding inhibited hepatic autophagy, associated with a lower nuclear TFEB content.

CONCLUSIONS

Our findings suggest that the effect of acute EtOH gavage on hepatic autophagy differs significantly from that after chronic EtOH feeding. Each regimen distinctly affects TFEB localization, which in turn, regulates hepatic autophagy and lysosome biogenesis.

Stat2 loss leads to cytokine-independent, cell-mediated lethality in LPS-induced sepsis

Deregulated Toll-like receptor (TLR)-triggered inflammatory responses that depend on NF-κB are detrimental to the host via excessive production of proinflammatory cytokines, including TNF-α. Stat2 is a critical component of type I IFN signaling, but it is not thought to participate in TLR signaling. Our study shows that LPS-induced lethality in Stat2(-/-) mice is accelerated as a result of increased cellular transmigration. Blocking intercellular adhesion molecule-1 prevents cellular egress and confers survival of Stat2(-/-) mice. The main determinant of cellular egress in Stat2(-/-) mice is the genotype of the host and not the circulating leukocyte. Surprisingly, lethality and cellular egress observed on Stat2(-/-) mice are not associated with excessive increases in classical sepsis cytokines or chemokines. Indeed, in the absence of Stat2, cytokine production in response to multiple TLR agonists is reduced. We find that Stat2 loss leads to reduced expression of NF-κB target genes by affecting nuclear translocation of NF-κB. Thus, our data reveal the existence of a different mechanism of LPS-induced lethality that is independent of NF-κB triggered cytokine storm but dependent on cellular egress.

Altered expression of cytokine signaling pathway genes in peripheral blood cells of alcohol dependent subjects: preliminary findings

BACKGROUND

Preclinical and clinical studies have implicated changes in cytokine and innate immune gene-expression in both the development of and end-organ damage resulting from alcohol dependence. However, these changes have not been systematically assessed on the basis of alcohol consumption in human subjects.

METHODS

Illumina Sentrix Beadchip (Human-6v2) microarrays were used to measure levels of gene-expression in peripheral blood in 3 groups of subjects: those with alcohol dependence (AD, n = 12), heavy drinkers (HD; defined as regular alcohol use over the past year of at least 8 standard drinks/wk for women and at least 15 standard drinks/wk for men, n = 13), and moderate drinkers (MD; defined as up to 7 standard drinks/wk for women and 14 standard drinks/wk for men, n = 17).

RESULTS

Four hundred and thirty-six genes were differentially expressed among the 3 groups of subjects (false discovery rate corrected p-value < 0.05). Two hundred and ninety-one genes differed between AD and MD subjects, 240 differed between AD and HD subjects, but only 6 differed between HD and MD subjects. Pathway analysis using DAVID and GeneGO Metacore(®) software showed that the most affected pathways were those related to T-cell receptor and Janus kinase-Signal transducer and activator of transcription (JAK-Stat) signaling.

CONCLUSIONS

These results suggest the transition from heavy alcohol use to dependence is accompanied by changes in the expression of genes involved in regulation of the innate immune response. Such changes may underlie some of the previously described changes in immune function associated with chronic alcohol abuse. Early detection of these changes may allow individuals at high risk for dependence to be identified.

Elevated activation of ERK1 and ERK2 accompany enhanced liver injury following alcohol binge in chronically ethanol-fed rats

BACKGROUND

Binge drinking after chronic ethanol consumption is one of the important factors contributing to the progression of steatosis to steatohepatitis. The molecular mechanisms of this effect remain poorly understood. We have therefore examined in rats the effect of single and repeat ethanol binge superimposed on chronic ethanol intake on liver injury, activation of mitogen-activated protein kinases (MAPKs), and gene expression.

METHODS

Rats were chronically treated with ethanol in liquid diet for 4 weeks followed by single ethanol binge (5 gm/kg body weight) or 3 similar repeated doses of ethanol. Serum alcohol and alanine amino transferase (ALT) levels were determined by enzymatic methods. Steatosis was assessed by histology and hepatic triglycerides. Activation of MAPK, 90S ribosomal kinase (RSK), and caspase 3 were evaluated by Western blot. Levels of mRNA for tumor necrosis factor alpha (TNFα), early growth response-1 (egr-1), and plasminogen activator inhibitor-1 (PAI-1) were measured by real-time qRT-PCR.

RESULTS

Chronic ethanol treatment resulted in mild steatosis and necrosis, whereas chronic ethanol followed by binge group exhibited marked steatosis and significant increase in necrosis. Chronic binge group also showed significant increase (compared with chronic ethanol alone) in the phosphorylation of extracellular regulated kinase 1 (ERK1), ERK2, and RSK. Phosphorylation of c-Jun N-terminal kinase (JNK) and p38 MAPK did not increase by the binge. Ethanol binge, after chronic ethanol intake, caused increase in mRNA for egr-1 and PAI-1, but not TNFα.

CONCLUSIONS

Chronic ethanol exposure increases the susceptibility of rat liver to increased injury by 1 or 3 repeat binge. Among other alterations, the activated levels of ERK1, and more so ERK2, were remarkably amplified by binge suggesting a role of these isotypes in the binge amplification of the injury. In contrast, p38 MAPK and JNK1/2 activities were not amplified. These binge-induced changes were also reflected in the increases in the RNA levels for egr-1 and PAI-1. This study offers chronic followed by repeat binge as a model for the study of progression of liver injury by ethanol and highlights the involvement of ERK1 and ERK2 isotypes in the amplification of liver injury by binge ethanol.

Different physiology of interferon-α/-γ in models of liver regeneration in the rat

Liver regeneration may take place after liver injury through replication of hepatocytes or hepatic progenitor cells called oval cells. Interferons (IFN) are natural cytokines with pleiotrophic effects including antiviral and antiproliferative actions. No data are yet available on the physiology and cellular source of natural IFNs during liver regeneration. To address this issue, we have analyzed the levels and biologic activities of IFN-α/IFN-γ in two models of partial hepatectomy. After 2/3rd partial hepatectomy (PH), hepatic levels of IFN-α and IFN-γ declined transiently in contrast to a transient increase of the IFN-γ serum level. After administration of 2-acetylaminofluorene and partial hepatectomy (AAF/PH model), however, both IFN-α and IFN-γ expression were up-regulated in regenerating livers. Again, the IFN-γ serum level was transiently increased. Whereas hepatic IFN-γ was up-regulated early (day 1–5), but not significantly, in the AAF/PH model, IFN-α was significantly up-regulated at later time points in parallel to the peak of oval cell proliferation (days 7–9). Biological activity of IFN-α was shown by activation of IFN-α-specific signal transduction and induction of IFN-α specific-gene expression. We found a significant infiltration of the liver with inflammatory monocyte-like mononuclear phagocytes (MNP) concomitant to the frequency of oval cells. We localized IFN-α production only in MNPs, but not in oval cells. These events were not observed in normal liver regeneration after standard PH. We conclude that IFN-γ functions as an acute-phase cytokine in both models of liver regeneration and may constitute a systemic component of liver regeneration. IFN-α was increased only in the AAF/PH model, and was associated with proliferation of oval cells. However, oval cells seem not to be the source of IFN-α. Instead, inflammatory MNP infiltrating AAF/PH-treated livers produce IFN-α. These inflammatory MNPs may be involved in the regulation of the oval cell compartment through local expression of cytokines, including IFN-α.

Activation of MEK 1/2 and p42/44 MAPK by angiotensin II in hepatocyte nucleus and their potentiation by ethanol

Hepato-subcellular effect of angiotensin II (Ang II) and ethanol on the p42/44 mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK 1/2) was investigated in the nucleus of rat hepatocytes. Hepatocytes were treated with ethanol (100 mM) for 24h and stimulated with Ang II (100 nM, 5 min). The levels of p42/44 MAPK and MEK 1/2 were monitored in the nuclear fraction using antibodies. Ang II itself caused significant accumulation of phosphorylated p42/44 MAPK (phospho-p42/44 MAPK) in the nucleus without any significant translocation of p42/44 MAPK protein thereby suggesting activation of p42/44 MAPK in the nucleus. Ang II caused marked accumulation of phosphorylated MEK 1/2 (phospho-MEK 1/2) in the nucleus without any significant accumulation of MEK 1/2 protein. Ratio of phospho-MEK 1/2 to MEK 1/2 protein in the nucleus after Ang II treatment was 2.4 times greater than control suggesting phosphorylation of MEK 1/2 inside the nucleus. Ethanol had no effect on the protein level or the activation of p42/44 MAPK in the nucleus. Ethanol treatment potentiated nuclear activation of p42/44 MAPK by Ang II but not translocation of p42/44 MAPK protein. This was accompanied by potentiation of Ang II-stimulated accumulation of phospho-MEK 1/2 in the nucleus by ethanol. MEK 1/2 inhibitor, U-0126 inhibited Ang II response and its potentiation by ethanol. These results suggest that Ang II-mediated accumulation of phospho-p42/44 MAPK in the hepatocyte nucleus involves MEK 1/2-dependent activation and this effect is potentiated by ethanol.

Gene expression signatures of peripheral CD4+ T cells clearly discriminate between patients with acute and chronic hepatitis B infection

CD4+ T and regulatory T cells (Tregs) seem to play a key role in persistence of hepatitis B virus (HBV) infection. However, the molecular events by which Tregs exert their modulatory activity are largely unknown. The transcriptional profiles of CD4+ T cells of healthy controls (HCs) and patients affected by acute hepatitis B (AVH-B) or chronic hepatitis B (CHB) infection were established using a custom expression array consisting of 350 genes relevant for CD4+ T cell and Treg function. These studies were complemented by real-time reverse-transcription polymerase chain reaction. Peripheral blood mononuclear cells (PBMCs) were also analyzed for the presence of Tregs, which were more abundant in the acute stage of the disease (7%) than in HCs and CHB infection (HCs versus AVH-B, P = 0.003; AVH-B versus CHB, P = 0.04). One hundred eighteen genes (34%) intrinsically differentiate HBV-infected patients from HCs. Using gene ontology, we identified T cell receptor signaling and clusterization, mitogen-activated protein kinase kinase signaling, cell adhesion, cytokines and inflammatory responses, cell cycle/cell proliferation, and apoptosis as the most prominent affected modules. A higher expression of CCR1, CCR3, CCR4, CCR5, and CCR8 was seen in AVH-B than in CHB-infected patients and HCs. Annotation of the interconnected functional network of genes provided a unique representation of global immune activation during acute infection. Almost all genes were down-regulated in patients with CHB infection.

CONCLUSION

The fingerprints enable clear discrimination between patients suffering from AVH-B or CHB infection. The observed profiles suggest accumulation of effector T cells with a potential role in necro-inflammation during the acute stage. Subsequent down-regulated effector functions support the hypothesis of suppressed CD4+ effector T cells favoring viral persistence in the chronic infection stage.

Ethanol inhibition of angiotensin II-stimulated Tyr705 and Ser727 STAT3 phosphorylation in cultured rat hepatocytes: relevance to activation of p42/44 mitogen-activated protein kinase

Angiotensin (Ang) II-stimulated phosphorylation of signal transducer and activator transcription (STAT) 3 in rat hepatocytes and the effects of ethanol on this activation were investigated. Angiotensin II (100 nM) stimulated Tyr705 and Ser727 phosphorylation of STAT3 and formation of sis-inducing factor complexes. In the presence of U-0126 (10microM), a p42/44 mitogen-activated protein kinase (MAPK) kinase inhibitor, Ang II further increased Tyr705 phosphorylation of STAT3 but completely abrogated Ser727 phosphorylation of STAT3. Inhibition of p42/44MAPK also increased STAT3 DNA-binding activity. Pretreatment with ethanol (100mM) for 24h resulted in decrease in Tyr705 phosphorylation of STAT3 by ethanol alone and inhibition of Tyr705 phosphorylation of STAT3 stimulated by Ang II. Although ethanol potentiates Ang II stimulated p42/44 MAPK activation in hepatocytes, ethanol inhibited Ser727 phosphorylation of STAT3 stimulated by Ang II. Angiotensin II-stimulated STAT3-binding activity was not significantly affected by ethanol treatment. These results suggest a negative regulation of Ang II-stimulated STAT3 tyrosine phosphorylation and STAT3-binding activity through p42/44 MAPK activation in hepatocytes. However, ethanol modulation of Ang II-stimulated STAT3 phosphorylation occurs by MAPK independent mechanisms. Ethanol potentiation of MAPK signaling without suppression of STAT3 function may modulate the course of alcoholic liver injury.

Dynamic expression of extracellular signal-regulated kinase in rat liver tissue during hepatic fibrogenesis

AIM

To investigate whether extracellular signal-regulated kinase 1 (ERK(1)) is activated and associated with hepatic stellate cell (HSC) proliferation in fibrotic rat liver tissue.

METHODS

Rat hepatic fibrosis was induced by bile duct ligation (BDL). Histopathological changes were evaluated by hematoxylin and eosin staining, and Masson's trichrome method. ERK(1) mRNA in rat liver tissue was determined by reverse transcription-polymerase chain reaction, while the distribution of ERK(1) was assessed by immunohistochemistry. ERK(1) protein was detected by Western blotting analysis. The number of activated HSCs was quantified after alpha smooth muscle actin (alpha-SMA) staining.

RESULTS

With the development of hepatic fibrosis, the positive staining cells of alpha-SMA increased obviously, and mainly resided in the portal ducts. Fiber septa and perisinuses were accompanied with proliferating bile ducts. The positive staining areas of the rat livers in model groups 1-4 wk after ligation of common bile duct (12.88% +/- 2.63%, 22.65% +/- 2.16%, 27.45% +/- 1.86%, 35.25% +/- 2.34%, respectively) were significantly larger than those in the control group (5.88% +/- 1.46%, P < 0.01). With the development of hepatic fibrosis, the positive cells of ERK(1) increased a lot, and were mainly distributed in portal ducts, fiber septa around the bile ducts, vascular endothelial cells and perisinusoidal cells. Western blotting analysis displayed that the expression of ERK(1) and ERK(2) protein was up-regulated during the model course, and its level was the highest 4 wk after operation, being 3.9-fold and 7.2-fold higher in fibrotic rat liver than in controls. ERK(1) mRNA was expressed in normal rat livers as well, which was up-regulated two days after BDL and reached the highest 4 wk after BDL. The expression of ERK(1) was positively correlated with alpha-SMA expression (r = 0.958, P < 0.05).

CONCLUSION

The expression of ERK(1) protein and mRNA is greatly increased in fibrotic rat liver tissues, which may play a key role in HSC proliferation and hepatic fibrogenesis.

Mechanisms of alcohol-induced hepatic fibrosis: a summary of the Ron Thurman Symposium

This report is a summary of Ron Thurman Symposium on the Mechanisms of Alcohol-Induced Hepatic Fibrosis which was organized by The National Institutes of Health in Santa Barbara, California, June 25, 2005. The Symposium and this report highlight the unique aspects by which drinking alcoholic beverages may result in hepatic fibrosis. Acetaldehyde, the first metabolite of ethanol, can upregulate transcription of collagen I directly as well as indirectly by upregulating the synthesis of transforming growth factor-beta 1 (TGF-beta1). Reactive oxygen species (ROS) generated in hepatocytes by alcohol metabolism can activate collagen production in hepatic stellate cells (HSCs) in a paracrine manner. Alcohol-induced hepatocyte apoptotic bodies can be phagocytosed by HSCs and Kupffer cells and result in increased expression of TGF-beta1 and subsequent HSC activation. Kupffer cells may contribute to the activation of HSCs by releasing ROS and TGF- beta1. Innate immunity may suppress hepatic fibrosis by killing activated HSCs and blocking TGF-beta1 signaling. In patients infected with hepatitis C virus (HCV), alcohol may promote hepatic fibrosis by suppressing innate immunity. HCV core and non-structural proteins contribute to HCV-induced hepatic fibrosis. Alcohol and HCV together may promote hepatic fibrosis through increased oxidative stress and upregulation of fibrogenic cytokines. The inactive aldehyde dehydrogenase (ALDH2) and the super-active alcohol dehydrogenase (ADH2) alleles may promote hepatic fibrosis through increased accumulation of acetaldehyde in the liver. Hepatic fibrosis can be reversed by inducing selective apoptosis or necrosis of activated HSCs, or by reverse trans-differentiation of activated HSCs into the quiescent phenotype.

Undetectable phospho-STAT1 in peripheral blood mononuclear cells from patients with chronic hepatitis C who do not respond to interferon-alpha therapy

BACKGROUND

Recent studies have suggested that phosphorylated signal transducers and activators of transcription 1 (STAT1) plays an important role in interferon (IFN)-mediated biological functions, including antiviral activity. Moreover, it has been demonstrated that suppressors of the cytokine signal 1 (SOCS1) negatively regulates IFN activities.

AIMS

To investigate the involvement of phospho-STAT1 in the response to IFN-alpha therapy in patients with chronic hepatitis C and to evaluate the negative regulatory effect of SOCS1 on STAT1 activation.

METHODS

Sixty-five patients with chronic hepatitis C and 25 healthy subjects were enrolled. Twenty-five of the patients had never been treated with IFN-alpha therapy (naive), while the remaining 40 patients had. The IFN-treated patients were divided into sustained responders (SRs) or non-responders (NRs) on the basis of their response to the antiviral therapy. Peripheral blood mononuclear cells (PBMCs) were obtained from each patient and control, and were either stimulated with IFN-alpha or left unstimulated. Total STAT1, phospho-STAT1 and SOCS1 were revealed by means of Western blot.

RESULTS

Total STAT1 was equally expressed in unstimulated and stimulated PBMCs from all patients and controls. One hundred percent of the stimulated PBMCs from healthy controls and SRs, 96% from naive subjects, and 30% from NRs showed detectable phospho-STAT1. By contrast, 70% of the stimulated PBMCs from NRs showed undetectable phospho-STAT1.

CONCLUSIONS

We have demonstrated that phospho-STAT1 proteins in 70% of patients with chronic hepatitis C who do not respond to IFN treatment are undetectable, which suggests that this protein may be involved in the mediation of IFN sensitivity. The down-regulation of the Jak-STAT pathway because of SOCS1 expression may be one of the possible underlying mechanisms involved in resistance to IFN.

Interferon-gamma inhibits interferon-alpha signalling in hepatic cells: evidence for the involvement of STAT1 induction and hyperexpression of STAT1 in chronic hepatitis C

IFN-gamma (interferon-gamma) modulates IFN-alpha therapy in chronic hepatitis C infection; however, the underlying mechanism remains unclear. Here we demonstrate that long-term (3-6 days) but not short-term (up to 1 day) IFN-gamma treatment of human hepatoma Hep3B cells attenuates IFN-alpha activation of STAT1 (signal transducers and activators of transcription factor 1), STAT2 and STAT3, but enhances IFN-gamma and interleukin 6 activation of STATs. Prolonged exposure to IFN-gamma also significantly induces STAT1 protein expression without affecting STAT2, STAT3 and ERK (extracellular-signal-regulated kinase) 1/2 protein expression. To determine the role of STAT1 protein overexpression in regulation of IFN-alpha signalling, Hep3B cells were stably transfected with wild-type STAT1. Overexpression of STAT1 via stable transfection enhances IFN-gamma activation of STAT1, but surprisingly attenuates IFN-alpha activation of STAT1, STAT2 and STAT3 without affecting Janus kinase activation. This STAT1-mediated inhibition does not require STAT1 tyrosine phosphorylation because overexpression of dominant-negative STAT1 with a mutation on tyrosine residue 701 also blocks IFN-alpha activation of STAT1, STAT2 and STAT3. Moreover, overexpression of STAT1 blocks IFN-alpha-activated STAT2 translocation from IFN-alpha receptor 2 to IFN-alpha receptor 1, a critical step in IFN-alpha signalling activation. Finally, significantly higher levels of STAT1 protein expression, which is probably induced by IFN-gamma, are detected in the majority of hepatitis C virus-infected livers compared with healthy controls. In conclusion, long-term IFN-gamma treatment inhibits IFN-alpha-activated signals most probably, at least in part, through the induction of STAT1 protein expression, which could partly contribute to IFN-alpha treatment failure in hepatitis C patients.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

Host factors and failure of interferon-alpha treatment in hepatitis C virus

Failure of interferon-alpha (IFN-alpha) treatment in patients with chronic hepatitis C virus (HCV) infection is a challenging obstacle for clinical and experimental hepatology. Both viral and host factors have been implicated in reducing responsiveness to IFN-alpha therapy. The role of viral factors has been studied extensively and has been summarized in several review articles; however, much less attention has been paid to host factors. In this paper, we review evidence of host factor involvement in IFN-alpha treatment failure. We discuss possible underlying mechanisms responsible for these effects. Potential therapeutic strategies to enhance the effectiveness of IFN-alpha therapy for HCV are also proposed.