Dual catenin loss in murine liver causes tight junctional deregulation and progressive intrahepatic cholestasis

The liver and muscle secreted HFE2-protein maintains central nervous system blood vessel integrity

Liver failure causes breakdown of the Blood CNS Barrier (BCB) leading to damages of the Central-Nervous-System (CNS), however the mechanisms whereby the liver influences BCB-integrity remain elusive. One possibility is that the liver secretes an as-yet to be identified molecule(s) that circulate in the serum to directly promote BCB-integrity. To study BCB-integrity, we developed light-sheet imaging for three-dimensional analysis. We show that liver- or muscle-specific knockout of Hfe2/Rgmc induces BCB-breakdown, leading to accumulation of toxic-blood-derived fibrinogen in the brain, lower cortical neuron numbers, and behavioral deficits in mice. Soluble HFE2 competes with its homologue RGMa for binding to Neogenin, thereby blocking RGMa-induced downregulation of PDGF-B and Claudin-5 in endothelial cells, triggering BCB-disruption. HFE2 administration in female mice with experimental autoimmune encephalomyelitis, a model for multiple sclerosis, prevented paralysis and immune cell infiltration by inhibiting RGMa-mediated BCB alteration. This study has implications for the pathogenesis and potential treatment of diseases associated with BCB-dysfunction.

Effects of acute and chronic disease on cell junctions in mouse liver

Cell junctions, including anchoring, occluding and communicating junctions, play an indispensable role in tissue architecture and homeostasis. Consequently, malfunctioning of cell junctions is linked with a wide range of disorders, including in liver. The present study was set up to investigate the effects of acute and chronic disease induced by chemical compounds on hepatic cell junctions in mice. Mice were either overdosed with paracetamol or repeatedly administered carbon tetrachloride followed by sampling at 24 hours or 8 weeks, respectively. mRNA and protein expression levels of adherens, gap and tight junction components were measured in liver using reverse transcription quantitative real-time polymerase chain reaction analysis and immunoblot techniques, respectively. It was found that protein levels of the adherens junction building blocks β-catenin and γ-catenin, the gap junction components Cx26 and Cx32, and the tight junction constituent zonula occludens 2 were decreased, while mRNA levels of the adherens junction building block E-cadherin, and the tight junction constituent zonula occludens 2 and claudin 1 were upregulated following paracetamol overdosing. Repeated administration of carbon tetrachloride increased protein levels of E-cadherin, β-catenin, Cx26, Cx32, Cx43 and claudin 1. The latter was reflected at the mRNA level. In conclusion, acute and chronic liver disease have different effects on cell junctions in liver.

[Hydroxynitone suppresses hepatic stellate cell activation by inhibiting TGF-β1 phosphorylation to alleviate CCl4-induced liver fibrosis in rats]

OBJECTIVE

To investigate the effect of hydronidone on CCl4-induced liver fibrosis in rats and explore the possible mechanism.

METHODS

Sixty-six male SD rats were randomized into 5 groups, including a control group (n=10), a liver fibrosis model group (n=20), 2 hydronidone dose groups (100 and 250 mg/kg; n=12), and a pirfenidone (250 mg/kg) treatment group (n= 12). Rat models of liver fibrosis were established by subcutaneous injection of CCl4 in all but the control group. Hydronidone and pirfenidone were given daily at the indicated doses by intragastric administration for 6 weeks. After the treatments, serum samples were collected from the rats for detecting liver function parameters, and hydroxyproline content in the liver tissue was determined. Inflammation and fibrosis in the liver tissue were observed using HE staining and Sirius Red staining. In the cell experiment, human hepatic stellate cell line LX-2 was stimulated with TGF-β1 and treated with hydronidone or pirfenidone, and the expression levels of α-SMA, collagen type I and phosphorylated Smad3, phosphorylated p38, phosphorylated ERK1/2 and phosphorylated Akt were detected with Western blotting.

RESULTS

In the rat models of liver fibrosis, treatment with hydronidone obviously improved the liver functions, reduced the content of hydroxyproline in the liver tissue, and significantly alleviated liver fibrosis (P < 0.05). In LX-2 cells, hydronidone dose-dependently decreased the expression levels of α-SMA and collagen type I. In TGF- β1-stimulated cells, the phosphorylation levels of Smad3, P38, ERK, and Akt increased progressively with the extension of the treatment time, but this effect was significantly attenuated by treatment with hydronidone (P < 0.05).

CONCLUSION

Hydronidone can inhibit the phosphorylation of the proteins in the TGF-β signaling pathway, thereby preventing TGF-β1-mediated activation of hepatic stellate cells, which may be a possible mechanism by which hydronidone alleviates CCl4-induced liver fibrosis in rats.

Emerging therapeutic potential of adeno-associated virus-mediated gene therapy in liver fibrosis

Liver fibrosis is a wound-healing response that results from various chronic damages. If the causes of damage are not removed or effective treatments are not given in a timely manner, it will progress to cirrhosis, even liver cancer. Currently, there are no specific medical therapies for liver fibrosis. Adeno-associated virus (AAV)-mediated gene therapy, one of the frontiers of modern medicine, has gained more attention in many fields due to its high safety profile, low immunogenicity, long-term efficacy in mediating gene expression, and increasingly known tropism. Notably, increasing evidence suggests a promising therapeutic potential for AAV-mediated gene therapy in different liver fibrosis models, which helps to correct abnormally changed target genes in the process of fibrosis and improve liver fibrosis at the molecular level. Moreover, the addition of cell-specific promoters to the genome of recombinant AAV helps to limit gene expression in specific cells, thereby producing better therapeutic efficacy in liver fibrosis. However, animal models are considered to be powerless predictive of tissue tropism, immunogenicity, and genotoxic risks in humans. Thus, AAV-mediated gene therapy will face many challenges. This review systemically summarizes the recent advances of AAV-mediated gene therapy in liver fibrosis, especially focusing on cellular and molecular mechanisms of transferred genes, and presents prospective challenges.

Defenestrated endothelium delays liver-directed gene transfer in hemophilia A mice

Hemophilia A is an inherited bleeding disorder caused by defective or deficient coagulation factor VIII (FVIII) activity. Until recently, the only treatment for prevention of bleeding involved IV administration of FVIII. Gene therapy with adeno-associated vectors (AAVs) has shown some efficacy in patients with hemophilia A. However, limitations persist due to AAV-induced cellular stress, immunogenicity, and reduced durability of gene expression. Herein, we examined the efficacy of liver-directed gene transfer in FVIII knock-out mice by AAV8-GFP. Surprisingly, compared with control mice, FVIII knockout (F8TKO) mice showed significant delay in AAV8-GFP transfer in the liver. We found that the delay in liver-directed gene transfer in F8TKO mice was associated with absence of liver sinusoidal endothelial cell (LSEC) fenestration, which led to aberrant expression of several sinusoidal endothelial proteins, causing increased capillarization and decreased permeability of LSECs. This is the first study to link impaired liver-directed gene transfer to liver-endothelium maladaptive structural changes associated with FVIII deficiency in mice.

Celastrol induces ferroptosis in activated HSCs to ameliorate hepatic fibrosis via targeting peroxiredoxins and HO-1

Ferroptosis is a form of regulated cell death, characterized by excessive membrane lipid peroxidation in an iron- and ROS-dependent manner. Celastrol, a natural bioactive triterpenoid extracted from Tripterygium wilfordii, shows effective anti-fibrotic and anti-inflammatory activities in multiple hepatic diseases. However, the exact molecular mechanisms of action and the direct protein targets of celastrol in the treatment of liver fibrosis remain largely elusive. Here, we discover that celastrol exerts anti-fibrotic effects via promoting the production of reactive oxygen species (ROS) and inducing ferroptosis in activated hepatic stellate cells (HSCs). By using activity-based protein profiling (ABPP) in combination with bio-orthogonal click chemistry reaction and cellular thermal shift assay (CETSA), we show that celastrol directly binds to peroxiredoxins (PRDXs), including PRDX1, PRDX2, PRDX4 and PRDX6, through the active cysteine sites, and inhibits their anti-oxidant activities. Celastrol also targets to heme oxygenase 1 (HO-1) and upregulates its expression in activated-HSCs. Knockdown of PRDX1, PRDX2, PRDX4, PRDX6 or HO-1 in HSCs, to varying extent, elevated cellular ROS levels and induced ferroptosis. Taken together, our findings reveal the direct protein targets and molecular mechanisms via which celastrol ameliorates hepatic fibrosis, thus supporting the further development of celastrol as a promising therapeutic agent for liver fibrosis.

Astragaloside IV Alleviates Intestinal Barrier Dysfunction via the AKT-GSK3β-β-Catenin Pathway in Peritoneal Dialysis

Background and aims: Long-term peritoneal dialysis (PD) causes intestinal dysfunction, including constipation, diarrhea, or enteric peritonitis. However, the etiology and pathogenesis of these complications are still unclear and there are no specific drugs available in the clinic. This study aims to determine whether Astragaloside IV (AS IV) has therapeutic value on PD-induced intestinal epithelial barrier dysfunction in vivo and in vitro.

Methods: We established two different long-term PD treatment mice models by intraperitoneally injecting 4.25% dextrose-containing peritoneal dialysis fluid (PDF) in uremia mice and normal mice, which were served as controls. In addition, PDF was applied to T84 cells in vitro. The therapeutic effects of AS IV on PD-induced intestinal dysfunction were then examined by histopathological staining, transmission electron microscopy, western blotting, and reverse transcription polymerase chain reaction. The protein levels of protein kinase B (AKT), glycogen synthase kinase 3β (GSK-3β) and β-catenin were examined after administration of AS IV.

Results: In the present study, AS IV maintained the intestinal crypt, microvilli and desmosome structures in an orderly arrangement and improved intestinal epithelial permeability with the up-regulation of tight junction proteins in vivo. Furthermore, AS IV protected T84 cells from PD-induced damage by improving cell viability, promoting wound healing, and increasing the expression of tight junction proteins. Additionally, AS IV treatment significantly increased the levels of phosphorylation of AKT, inhibited the activity GSK-3β, and ultimately resulted in the nuclear translocation and accumulation of β-catenin.

Conclusion: These findings provide novel insight into the AS IV-mediated protection of the intestinal epithelial barrier from damage via the AKT-GSK3β-β-catenin signal axis during peritoneal dialysis.

Intravital imaging reveals inflammation as a dominant pathophysiology of age-related hepatovascular changes

Aging is the most significant risk factor for the majority of chronic diseases, including liver disease. The cellular, molecular, and pathophysiological mechanisms that promote age-induced hepatovascular changes are unknown due to our inability to visualize changes in liver pathophysiology in live mice over time. We performed quantitative liver intravital microscopy (qLIM) in live C57BL/6J mice to investigate the impact of aging on the hepatovascular system over a 24-mo period. qLIM revealed that age-related hepatic alterations include reduced liver sinusoidal blood flow, increased sinusoidal vessel diameter, and loss of small hepatic vessels. The ductular cell structure deteriorates with age, along with altered expression of hepatic junctional proteins. Furthermore, qLIM imaging revealed increased inflammation in the aged liver, which was linked to increased expression of proinflammatory macrophages, hepatic neutrophils, liver sinusoidal endothelial cells, senescent cells, and procoagulants. Finally, we detected elevated NF-κB pathway activity in aged livers. Overall, these findings emphasize the importance of inflammation in age-related hepatic vasculo-epithelial alterations and highlight the utility of qLIM in studying age-related effects in organ pathophysiology.

Human menstrual blood-derived stem cell transplantation suppresses liver injury in DDC-induced chronic cholestasis

Background

Cholestatic liver injury can lead to serious symptoms and prognoses in the clinic. Currently, an effective medical treatment is not available for cholestatic liver injury. Human menstrual blood-derived stem cells (MenSCs) are considered as an emerging treatment in various diseases. This study aimed to explore the treatment effect of MenSCs in cholestatic liver injury.

Methods

The treatment effect of MenSCs on chronic cholestatic liver injury was verified in 3,5-diethoxycarbonyl-1,4-dihydroxychollidine (DDC)-induced C57/BL6 mice. Pathological, fibrosis area in the liver tissue and serum liver enzymes were tested. Proteomics and western blot were used to explore the related targets and molecular mechanisms. Adeno-associated virus (AAV) 9-infected mice were applied for verification.

Results

MenSCs markedly improved the survival rate of the DDC-treated mice (60% vs. 100%), and decreased the mouse serum aspartate aminotransferase (AST) (169.4 vs. 108.0 U/L, p < 0.001), alanine aminotransferase (ALT) (279.0 vs. 228.9 U/L, p < 0.01), alkaline phosphatase (ALP) (45.6 vs. 10.6 U/L, p < 0.0001), direct bilirubin (DBIL) (108.3 vs. 14.0 μmol/L, p < 0.0001) and total bilirubin (TBIL) (179.2 vs. 43.3 μmol/L, p < 0.0001) levels as well as intrahepatic cholestasis, bile duct dilation and fibrotic areas (16.12 vs. 6.57%, p < 0.05). The results further indicated that MenSCs repaired the DDC-induced liver tight junction (TJ) pathway and bile transporter (OATP2, BSEP and NTCP1) injury, thereby inhibiting COL1A1, α-SMA and TGF-β1 activation by upregulating liver β-catenin expression.

Conclusions

MenSC transplantation could be an effective treatment method for cholestatic liver injury in mice. MenSCs may exhibit therapeutic effects by regulating β-catenin expression.

β-Catenin-NF-κB-CFTR interactions in cholangiocytes regulate inflammation and fibrosis during ductular reaction

Expansion of biliary epithelial cells (BECs) during ductular reaction (DR) is observed in liver diseases including cystic fibrosis (CF), and associated with inflammation and fibrosis, albeit without complete understanding of underlying mechanism. Using two different genetic mouse knockouts of β-catenin, one with β-catenin loss is hepatocytes and BECs (KO1), and another with loss in only hepatocytes (KO2), we demonstrate disparate long-term repair after an initial injury by 2-week choline-deficient ethionine-supplemented diet. KO2 show gradual liver repopulation with BEC-derived β-catenin-positive hepatocytes and resolution of injury. KO1 showed persistent loss of β-catenin, NF-κB activation in BECs, progressive DR and fibrosis, reminiscent of CF histology. We identify interactions of β-catenin, NFκB, and CF transmembranous conductance regulator (CFTR) in BECs. Loss of CFTR or β-catenin led to NF-κB activation, DR, and inflammation. Thus, we report a novel β-catenin-NFκB-CFTR interactome in BECs, and its disruption may contribute to hepatic pathology of CF.

The liver has an incredible capacity to repair itself or ‘regenerate’ – that is, it has the ability to replace damaged tissue with new tissue. In order to do this, the organ relies on hepatocytes (the cells that form the liver) and bile duct cells (the cells that form the biliary ducts) dividing and transforming into each other to repair and replace damaged tissue, in case the insult is dire.

During long-lasting or chronic liver injury, bile duct cells undergo a process called ‘ductular reaction’, which causes the cells to multiply and produce proteins that stimulate inflammation, and can lead to liver scarring (fibrosis). Ductular reaction is a hallmark of severe liver disease, and different diseases exhibit ductular reactions with distinct features. For example, in cystic fibrosis, a unique type of ductular reaction occurs at late stages, accompanied by both inflammation and fibrosis. Despite the role that ductular reaction plays in liver disease, it is not well understood how it works at the molecular level.

Hu et al. set out to investigate how a protein called β-catenin – which can cause many types of cells to proliferate – is involved in ductular reaction. They used three types of mice for their experiments: wild-type mice, which were not genetically modified; and two strains of genetically modified mice. One of these mutant mice did not produce β-catenin in biliary duct cells, while the other lacked β-catenin both in biliary duct cells and in hepatocytes.

After a short liver injury – which Hu et al. caused by feeding the mice a specific diet – the wild-type mice were able to regenerate and repair the liver without exhibiting any ductular reaction. The mutant mice that lacked β-catenin in hepatocytes showed a temporary ductular reaction, and ultimately repaired their livers by turning bile duct cells into hepatocytes. On the other hand, the mutant mice lacking β-catenin in both hepatocytes and bile duct cells displayed sustained ductular reactions, inflammation and fibrosis, which looked like that seen in patients with liver disease associated to cystic fibrosis. Further probing showed that β-catenin interacts with a protein called CTFR, which is involved in cystic fibrosis. When bile duct cells lack either of these proteins, another protein called NF-B gets activated, which causes the ductular reaction, leading to inflammation and fibrosis.

The findings of Hu et al. shed light on the role of β-catenin in ductular reaction. Further, the results show a previously unknown interaction between β-catenin, CTFR and NF-B, which could lead to better treatments for cystic fibrosis in the future.

Intravital Imaging of Hepatic Blood Biliary Barrier in Live Mice

Understanding the kinetics and spatiotemporal interactions of living cells within the tissue environment requires real-time imaging. The introduction of two-photon microscopy has substantially boosted the power of live intravital imaging, making it possible to obtain information of individual cells in near-physiologic conditions within intact tissues nondestructively. Intravital imaging of the liver has proved useful in understanding its 3D structure, function, and dynamic cellular interactions. Recently we have shown that integrity of the blood-bile barrier in different physiologic and pathophysiologic conditions can be imaged in real time using intravital microscopy. Here we discuss the real-time intravital imaging method to visualize blood-bile barrier integrity in the murine liver. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Live imaging in the mouse liver Support Protocol: Monitoring vital signs of the mouse during live liver imaging Basic Protocol 2: Visualizing blood and bile transport using intravital microscopy.

Progress in research on the roles of TGR5 receptor in liver diseases

TGR5 (G protein-coupled bile acid receptor 1, GPBAR-1) is a G protein-coupled receptor with seven transmembrane domains and is widely distributed in various organs and tissues. As an important bile acid receptor, TGR5 can be activated by primary and secondary bile acids. Increased expression of TGR5 is a risk factor for polycystic liver disease and hepatobiliary cancer. However, there is evidence that the anti-inflammatory effect of the TGR5 receptor and its regulatory effect on hydrophobic bile acid confer protective effects against most liver diseases. Recent studies have shown that TGR5 receptor activation can alleviate the development of diabetic liver fibrosis, regulate the differentiation of natural killer T cells into NKT10 cells, increase the secretion of anti-inflammatory factors, inhibit the invasion of hepatitis B virus, promote white adipose tissue browning, improve arterial vascular dynamics, maintain tight junctions between bile duct cells, and protect against apoptosis. In portal hypertension, TGR5 receptor activation can inhibit the contraction of hepatic stellate cells and improve intrahepatic microcirculation. In addition, the discovery of the regulatory relationship between the TGR5 receptor and miRNA-26a provides a new direction for further studies of the molecular mechanism underlying the effects of TGR5. In this review, we describe recent findings linking TGR5 to various liver diseases, with a focus on the mechanisms underlying its effects and potential therapeutic implications.

P-selectin-deficient mice to study pathophysiology of sickle cell disease

P-selectin–deficient SCD mice are protected from lung vaso-occlusion. P-selectin–deficient SCD mice will be useful in assessing the benefits of anti–P-selectin therapy in diverse complications of SCD.

β-Catenin Activation in Hepatocellular Cancer: Implications in Biology and Therapy

Simple Summary

Liver cancer is a dreadful tumor which has gradually increased in incidence all around the world. One major driver of liver cancer is the Wnt–β-catenin pathway which is active in a subset of these tumors. While this pathway is normally important in liver development, regeneration and homeostasis, it’s excessive activation due to mutations, is detrimental and leads to tumor cell growth, making it an important therapeutic target. There are also some unique characteristics of this pathway activation in liver cancer. It makes the tumor addicted to specific amino acids and in turn to mTOR signaling, which can be treated by certain existing therapies. In addition, activation of the Wnt–β-catenin in liver cancer appears to alter the immune cell landscape making it less likely to respond to the new immuno-oncology treatments. Thus, Wnt–β-catenin active tumors may need to be treated differently than non-Wnt–β-catenin active tumors.

Abstract

Hepatocellular cancer (HCC), the most common primary liver tumor, has been gradually growing in incidence globally. The whole-genome and whole-exome sequencing of HCC has led to an improved understanding of the molecular drivers of this tumor type. Activation of the Wnt signaling pathway, mostly due to stabilizing missense mutations in its downstream effector β-catenin (encoded by CTNNB1) or loss-of-function mutations in AXIN1 (the gene which encodes for Axin-1, an essential protein for β-catenin degradation), are seen in a major subset of HCC. Because of the important role of β-catenin in liver pathobiology, its role in HCC has been extensively investigated. In fact, CTNNB1 mutations have been shown to have a trunk role. β-Catenin has been shown to play an important role in regulating tumor cell proliferation and survival and in tumor angiogenesis, due to a host of target genes regulated by the β-catenin transactivation of its transcriptional factor TCF. Proof-of-concept preclinical studies have shown β-catenin to be a highly relevant therapeutic target in CTNNB1-mutated HCCs. More recently, studies have revealed a unique role of β-catenin activation in regulating both tumor metabolism as well as the tumor immune microenvironment. Both these roles have notable implications for the development of novel therapies for HCC. Thus, β-catenin has a pertinent role in driving HCC development and maintenance of this tumor-type, and could be a highly relevant therapeutic target in a subset of HCC cases.

Dual β-Catenin and γ-Catenin Loss in Hepatocytes Impacts Their Polarity through Altered Transforming Growth Factor-β and Hepatocyte Nuclear Factor 4α Signaling

Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Loss of β-catenin at adherens junctions is compensated by γ-catenin and dual loss of both catenins in double knockouts (DKOs) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Herein, simultaneous loss of β-catenin and γ-catenin was identified in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defects in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of transforming growth factor-β signaling and repression of hepatocyte nuclear factor 4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may play a pathogenic role in subsets of cholangiopathies. The findings also support a previously unknown role of β-catenin and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β-catenin and γ-catenin may potentially benefit development of new therapies for cholestasis.

Altered integrity of hepatocyte tight junctions in rats with triptolide-induced cholestasis

Triptolide (TP), an active component of Tripterygium wilfordiiHook. f. (TWHF), has been widely used for centuries as a traditional Chinese medicine. However, the clinical application of TP has been restricted due to multitarget toxicity, such as hepatotoxicity. In this study, 28 days of oral TP administration (100, 200, or 400 μg·kg^-1·d^-1) induced the occurrence of cholestasis in female Wistar rats, as evidenced by increased serum levels of γ-glutamyl transpeptidase (γ-GGT), alkaline phosphatase (ALP) and hepatic total bile acids (TBAs). In addition, the heptocyte polarity associated with the strcture of tight junctions (TJs) was disrupted in both rats and sandwich-cultured primary hepatocytes. Immunoblotting revealed decreased expression of the TJ-associated proteins occludin, claudin-1, and zonula occludens protein (ZO-1), and downregulated mRNA levels of these TJs was also detected by real-time PCR. An immunofluorescence analysis showed abnormal subcellular localization of occludin, claudin-1 and ZO-1, which was also confirmed by transmission electron microscopy. Moreover, the concentration of FITC-dextran, a marker of paracellular penetration, was found to increase rapidly in bile increased rapidly (within 6 minutes) after treatment with TP, which indicated the functional impairment of TJs. Taken together, these results suggest that the administration of TP for 28 consecutive days to rats could induce cholestatic injury in the liver, and the increased paracellular permeability might play an important role in these pathological changes.

Impaired Bile Secretion Promotes Hepatobiliary Injury in Sickle Cell Disease

BACKGROUND AND AIMS

Hepatic crisis is an emergent complication affecting patients with sickle cell disease (SCD); however, the molecular mechanism of sickle cell hepatobiliary injury remains poorly understood. Using the knock-in humanized mouse model of SCD and SCD patient blood, we sought to mechanistically characterize SCD-associated hepato-pathophysiology applying our recently developed quantitative liver intravital imaging, RNA sequence analysis, and biochemical approaches.

APPROACH AND RESULTS

SCD mice manifested sinusoidal ischemia, progressive hepatomegaly, liver injury, hyperbilirubinemia, and increased ductular reaction under basal conditions. Nuclear factor kappa B (NF-κB) activation in the liver of SCD mice inhibited farnesoid X receptor (FXR) signaling and its downstream targets, leading to loss of canalicular bile transport and altered bile acid pool. Intravital imaging revealed impaired bile secretion into the bile canaliculi, which was secondary to loss of canalicular bile transport and bile acid metabolism, leading to intrahepatic bile accumulation in SCD mouse liver. Blocking NF-κB activation rescued FXR signaling and partially ameliorated liver injury and sinusoidal ischemia in SCD mice.

CONCLUSIONS

These findings identify that NF-κB/FXR-dependent impaired bile secretion promotes intrahepatic bile accumulation, which contributes to hepatobiliary injury of SCD. Improved understanding of these processes could potentially benefit the development of therapies to treat sickle cell hepatic crisis.

Bile Acids and GPBAR-1: Dynamic Interaction Involving Genes, Environment and Gut Microbiome

Bile acids (BA) are amphiphilic molecules synthesized in the liver from cholesterol. BA undergo continuous enterohepatic recycling through intestinal biotransformation by gut microbiome and reabsorption into the portal tract for uptake by hepatocytes. BA are detergent molecules aiding the digestion and absorption of dietary fat and fat-soluble vitamins, but also act as important signaling molecules via the nuclear receptor, farnesoid X receptor (FXR), and the membrane-associated G protein-coupled bile acid receptor 1 (GPBAR-1) in the distal intestine, liver and extra hepatic tissues. The hydrophilic-hydrophobic balance of the BA pool is finely regulated to prevent BA overload and liver injury. By contrast, hydrophilic BA can be hepatoprotective. The ultimate effects of BA-mediated activation of GPBAR-1 is poorly understood, but this receptor may play a role in protecting the remnant liver and in maintaining biliary homeostasis. In addition, GPBAR-1 acts on pathways involved in inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity, and sinusoidal blood flow. Recent evidence suggests that environmental factors influence GPBAR-1 gene expression. Thus, targeting GPBAR-1 might improve liver protection, facilitating beneficial metabolic effects through primary prevention measures. Here, we discuss the complex pathways linked to BA effects, signaling properties of the GPBAR-1, mechanisms of liver damage, gene-environment interactions, and therapeutic aspects.

The zonula occludens protein family regulates the hepatic barrier system in the murine liver

The hepatic barrier is indispensable for the physiological functions of the liver and is impaired under various pathological conditions. Tight junctions reportedly play a central role in hepatic barrier regulation; however, there is limited direct evidence supporting this observation, with few in vivo models or confirmations of the implicated molecular mechanisms presented to date. We inactivated the tight junction component gene, Tjp2/ZO-2, and the related molecule, Tjp1/ZO-1, in mouse livers. In humans, TJP2/ZO-2 mutations have been implicated in the development of human progressive familial intrahepatic cholestasis 4 (PFIC4). The mice deficient in either ZO-1 or ZO-2 in the liver did not exhibit major abnormalities. However, the ablation of both molecules impaired the molecular architecture as well as the structure and function of hepatocyte tight junctions, which disrupted the hepatic barrier and was lethal to the mice by 6 weeks of age. In mutant mice, bile canaliculus formation and cellular polarity were compromised; also, transporter expression and localization were deregulated. Moreover, typical hepatic zonation and bile duct formation were inhibited, and sinusoidal vessels were disorganized. These findings clarify the role of tight junctions and polarity in the hepatic barrier as well as the effect that their disruption has on liver tissue. The observations also suggest that liver-specific ZO-1^-/- and ZO-2^-/- mice could be used as models for PFIC4, and this will provide new insights into liver pathophysiology and clinical applications.

Live Imaging of Innate and Adaptive Immune Responses in the Liver

Immune response in the liver is determined by the spatial organization and cellular dynamics of hepatic immune cells. The liver vasculature accommodates abundant tissue-resident innate immune cells, such as Kupffer cells, natural killer cells, and natural killer T cells, to ensure efficient intravascular immunosurveillance. The fenestrated sinusoids also allow direct contact between circulating T cells and non-canonical antigen-presenting cells, such as hepatocytes, to instruct adaptive immune responses. Distinct cellular behaviors are exploited by liver immune cells to exert proper functions. Intravital imaging enables real-time visualization of individual immune cell in living animals, representing a powerful tool in dissecting the spatiotemporal features of intrahepatic immune cells during steady state and liver diseases. This review summarizes current advances in liver immunology prompted by in vivo imaging, with a particular focus on liver-resident innate immune cells and hepatic T cells.

Ileal bile acid transporter inhibition as an anticholestatic therapeutic target in biliary atresia and other cholestatic disorders

Biliary atresia is a rare cholestatic liver disease that presents in infants and rapidly advances to death in the absence of intervention. As a result of blockage or destruction of the biliary tract, bile acids accumulate and drive inflammation, fibrosis, and disease progression. The standard of care, Kasai portoenterostomy (KPE), is typically performed shortly after diagnosis (currently at ~ 2 months of age) and aims to restore bile flow and relieve cholestasis. Nevertheless, most patients continue to experience liver injury from accumulation of bile acids after KPE, since there are no known effective therapeutics that may enhance survival after KPE. Improving cholestasis via interruption of the enterohepatic circulation of bile acids may directly attenuate hepatic bile acid retention and reduce the risk of early organ failure. Directly addressing intrahepatic accretion of bile acids to avoid inherent bile acid toxicities provides an attractive and plausible therapeutic target for biliary atresia. This review explores the novel therapeutic concept of inhibiting the sole ileal bile acid transporter (IBAT), also known as ASBT (apical sodium-bile acid transporter, encoded by SLC10A2), as a means to reduce hepatic bile acid concentration after KPE. By reducing return of bile acids to the cholestatic liver, IBAT inhibitors may potentially lessen or delay liver damage associated with the hepatotoxicity and cholangiopathy of bile acid accumulation. The clinical programs of 2 IBAT inhibitors in development for the treatment of pediatric cholestatic liver diseases, maralixibat and odevixibat, are highlighted.

Sphingosine 1-phosphate receptor-1 specific agonist SEW2871 ameliorates ANIT-induced dysregulation of bile acid homeostasis in mice plasma and liver

Dysregulated bile acid (BA) homeostasis is an extremely significant pathological phenomenon of intrahepatic cholestasis, and the accumulated BA could further trigger hepatocyte injury. Here, we showed that the expression of sphingosine-1-phosphate receptor 1 (S1PR1) was down-regulated by α-naphthylisothiocyanate (ANIT) in vivo and in vitro. The up-regulated S1PR1 induced by SEW2871 (a specific agonist of S1PR1) could improve ANIT-induced deficiency of hepatocyte tight junctions (TJs), cholestatic liver injury and the disrupted BA homeostasis in mice. BA metabolic profiles showed that SEW2871 not only reversed the disruption of plasma BA homeostasis, but also alleviated BA accumulation in the liver of ANIT-treated mice. Further quantitative analysis of 19 BAs showed that ANIT increased almost all BAs in mice plasma and liver, all of which were restored by SEW2871. Our data demonstrated that the top performing BAs were taurine conjugated bile acids (T-), especially taurocholic acid (TCA). Molecular mechanism studies indicated that BA transporters, synthetase, and BAs nuclear receptors (NRs) might be the important factors that maintained BA homeostasis by SEW2871 in ANIT-induced cholestasis. In conclusion, these results demonstrated that S1PR1 selective agonists might be the novel and potential effective agents for the treatment of intrahepatic cholestasis by recovering dysregulated BA homeostasis.

Hepatoprotective impact of the bile acid receptor TGR5

During liver repair after injury, bile secretion has to be tightly modulated in order to preserve liver parenchyma from bile acid (BA)-induced injury. The mechanisms allowing the liver to maintain biliary homeostasis during repair after injury are not completely understood. Besides their historical role in lipid digestion, bile acids (BA) and their receptors constitute a signalling network with multiple impacts on liver repair, both stimulating regeneration and protecting the liver from BA overload. BA signal through nuclear (mainly Farnesoid X Receptor, FXR) and membrane (mainly G Protein-coupled BA Receptor 1, GPBAR-1 or TGR5) receptors to elicit a wide array of biological responses. While a great number of studies have been dedicated to the hepato-protective impact of FXR signalling, TGR5 is by far less explored in this context. Because the liver has to face massive and potentially harmful BA overload after partial ablation or destruction, BA-induced protective responses crucially contribute to spare liver repair capacities. Based on the available literature, the TGR5 BA receptor protects the remnant liver and maintains biliary homeostasis, mainly through the control of inflammation, biliary epithelial barrier permeability, BA pool hydrophobicity and sinusoidal blood flow. Mouse experimental models of liver injury reveal that in the lack of TGR5, excessive inflammation, leaky biliary epithelium and hydrophobic BA overload result in parenchymal insult and compromise optimal restoration of a functional liver mass. Translational perspectives are thus opened to target TGR5 with the aim of protecting the liver in the context of injury and BA overload.

Wnt/β-Catenin Signaling Plays a Protective Role in the Mdr2 Knockout Murine Model of Cholestatic Liver Disease

BACKGROUND AND AIMS

The Wnt/β-catenin signaling pathway has a well-described role in liver pathobiology. Its suppression was recently shown to decrease bile acid (BA) synthesis, thus preventing the development of cholestatic liver injury and fibrosis after bile duct ligation (BDL).

APPROACH AND RESULTS

To generalize these observations, we suppressed β-catenin in Mdr2 knockout (KO) mice, which develop sclerosing cholangitis due to regurgitation of BA from leaky ducts. When β-catenin was knocked down (KD) in KO for 2 weeks, hepatic and biliary injury were exacerbated in comparison to KO given placebo, as shown by serum biochemistry, ductular reaction, inflammation, and fibrosis. Simultaneously, KO/KD livers displayed increased oxidative stress and senescence and an impaired regenerative response. Although the total liver BA levels were similar between KO/KD and KO, there was significant dysregulation of BA transporters and BA detoxification/synthesis enzymes in KO/KD compared with KO alone. Multiphoton intravital microscopy revealed a mixing of blood and bile in the sinusoids, and validated the presence of increased serum BA in KO/KD mice. Although hepatocyte junctions were intact, KO/KD livers had significant canalicular defects, which resulted from loss of hepatocyte polarity. Thus, in contrast to the protective effect of β-catenin KD in BDL model, β-catenin KD in Mdr2 KO aggravated rather than alleviated injury by interfering with expression of BA transporters, hepatocyte polarity, canalicular structure, and the regenerative response.

CONCLUSIONS

The resulting imbalance between ongoing injury and restitution led to worsening of the Mdr2 KO phenotype, suggesting caution in targeting β-catenin globally for all cholestatic conditions.

The protective effect of obeticholic acid on lipopolysaccharide-induced disorder of maternal bile acid metabolism in pregnant mice

The disorder of bile acid metabolism is a common feature during pregnancy, which leads to adverse birth outcomes and maternal damage effects. However, the cause and therapy about the disorder of bile acid metabolism are still poor. Microbial infection often occurs in pregnant women, which can induce the disorder of bile acid metabolism in adult mice. Here, this study observed the acute effect of lipopolysaccharide (LPS) on maternal bile acid of pregnant mice at gestational day 17 and the protective effect of obeticholic acid (OCA) pretreatment, a potent agonist of bile acid receptor farnesoid X receptor (FXR). The results showed LPS significantly increased the level of maternal serum and disordered bile acids components of maternal serum and liver, which were ameliorated by OCA pretreatment with obviously reducing the contents of CA, TCA, DCA, TCDCA, CDCA, GCA and TDCA in maternal serum and DCA, TCA, TDCA, TUDCA, CDCA and TCDCA in maternal liver. Furthermore, we investigated the effects of OCA on LPS-disrupted bile acid metabolism in maternal liver. LPS disrupted maternal bile acid profile by decreasing transport and metabolism with hepatic tight junctions of bile acid in pregnant mice. OCA obviously increased the protein level of nuclear FXR and regulated its target genes involving in the metabolism of bile acid, which was characterized by the lower expression of bile acid synthase CYP7A1, the higher expression of CYP3A and the higher mRNA level of transporter Mdr1a/b. This study provided the evidences that LPS disrupted bile acid metabolism in the late stage of pregnant mice and OCA pretreatment played the protective role on it by activating FXR.

Tight Junction Proteins and the Biology of Hepatobiliary Disease

Tight junctions (TJ) are intercellular adhesion complexes on epithelial cells and composed of integral membrane proteins as well as cytosolic adaptor proteins. Tight junction proteins have been recognized to play a key role in health and disease. In the liver, TJ proteins have several functions: they contribute as gatekeepers for paracellular diffusion between adherent hepatocytes or cholangiocytes to shape the blood-biliary barrier (BBIB) and maintain tissue homeostasis. At non-junctional localizations, TJ proteins are involved in key regulatory cell functions such as differentiation, proliferation, and migration by recruiting signaling proteins in response to extracellular stimuli. Moreover, TJ proteins are hepatocyte entry factors for the hepatitis C virus (HCV)—a major cause of liver disease and cancer worldwide. Perturbation of TJ protein expression has been reported in chronic HCV infection, cholestatic liver diseases as well as hepatobiliary carcinoma. Here we review the physiological function of TJ proteins in the liver and their implications in hepatobiliary diseases.

TGR5-dependent hepatoprotection through the regulation of biliary epithelium barrier function

OBJECTIVE

We explored the hypothesis that TGR5, the bile acid (BA) G-protein-coupled receptor highly expressed in biliary epithelial cells, protects the liver against BA overload through the regulation of biliary epithelium permeability.

DESIGN

Experiments were performed under basal and TGR5 agonist treatment. In vitro transepithelial electric resistance (TER) and FITC-dextran diffusion were measured in different cell lines. In vivo FITC-dextran was injected in the gallbladder (GB) lumen and traced in plasma. Tight junction proteins and TGR5-induced signalling were investigated in vitro and in vivo (wild-type [WT] and TGR5-KO livers and GB). WT and TGR5-KO mice were submitted to bile duct ligation or alpha-naphtylisothiocyanate intoxication under vehicle or TGR5 agonist treatment, and liver injury was studied.

RESULTS

In vitro TGR5 stimulation increased TER and reduced paracellular permeability for dextran. In vivo dextran diffusion after GB injection was increased in TGR5-knock-out (KO) as compared with WT mice and decreased on TGR5 stimulation. In TGR5-KO bile ducts and GB, junctional adhesion molecule A (JAM-A) was hypophosphorylated and selectively downregulated among TJP analysed. TGR5 stimulation induced JAM-A phosphorylation and stabilisation both in vitro and in vivo, associated with protein kinase C-ζ activation. TGR5 agonist-induced TER increase as well as JAM-A protein stabilisation was dependent on JAM-A Ser285 phosphorylation. TGR5 agonist-treated mice were protected from cholestasis-induced liver injury, and this protection was significantly impaired in JAM-A-KO mice.

CONCLUSION

The BA receptor TGR5 regulates biliary epithelial barrier function in vitro and in vivo through an impact on JAM-A expression and phosphorylation, thereby protecting liver parenchyma against bile leakage.

Development of the Intrahepatic and Extrahepatic Biliary Tract: A Framework for Understanding Congenital Diseases

The involvement of the biliary tract in the pathophysiology of liver diseases and the increased attention paid to bile ducts in the bioconstruction of liver tissue for regenerative therapy have fueled intense research into the fundamental mechanisms of biliary development. Here, I review the molecular, cellular and tissular mechanisms driving differentiation and morphogenesis of the intrahepatic and extrahepatic bile ducts. This review focuses on the dynamics of the transcriptional and signaling modules that promote biliary development in human and mouse liver and discusses studies in which the use of zebrafish uncovered unexplored processes in mammalian biliary development. The review concludes by providing a framework for interpreting the mechanisms that may help us understand the origin of congenital biliary diseases.

YAP, but Not RSPO-LGR4/5, Signaling in Biliary Epithelial Cells Promotes a Ductular Reaction in Response to Liver Injury

Biliary epithelial cells (BECs) form bile ducts in the liver and are facultative liver stem cells that establish a ductular reaction (DR) to support liver regeneration following injury. Liver damage induces periportal LGR5+ putative liver stem cells that can form BEC-like organoids, suggesting that RSPO-LGR4/5-mediated WNT/β-catenin activity is important for a DR. We addressed the roles of this and other signaling pathways in a DR by performing a focused CRISPR-based loss-of-function screen in BEC-like organoids, followed by in vivo validation and single-cell RNA sequencing. We found that BECs lack and do not require LGR4/5-mediated WNT/β-catenin signaling during a DR, whereas YAP and mTORC1 signaling are required for this process. Upregulation of AXIN2 and LGR5 is required in hepatocytes to enable their regenerative capacity in response to injury. Together, these data highlight heterogeneity within the BEC pool, delineate signaling pathways involved in a DR, and clarify the identity and roles of injury-induced periportal LGR5+ cells.

Blood-Bile Barrier: Morphology, Regulation, and Pathophysiology

The term blood-bile barrier (BBlB) refers to the physical structure within a hepatic lobule that compartmentalizes and hence segregates sinusoidal blood from canalicular bile. Thus, this barrier provides physiological protection in the liver, shielding the hepatocytes from bile toxicity and restricting the mixing of blood and bile. BBlB is primarily composed of tight junctions; however, adherens junction, desmosomes, gap junctions, and hepatocyte bile transporters also contribute to the barrier function of the BBlB. Recent findings also suggest that disruption of BBlB is associated with major hepatic diseases characterized by cholestasis and aberrations in BBlB thus may be a hallmark of many chronic liver diseases. Several molecular signaling pathways have now been shown to play a role in regulating the structure and function and eventually contribute to regulation of the BBlB function within the liver. In this review, we will discuss the structure and function of the BBlB, summarize the methods to assess the integrity and function of BBlB, discuss the role of BBlB in liver pathophysiology, and finally, discuss the mechanisms of BBlB regulation. Collectively, this review will demonstrate the significance of the BBlB in both liver homeostasis and hepatic dysfunction.

Artesunate alleviates liver fibrosis by regulating ferroptosis signaling pathway

Liver fibrosis is a progression of chronic liver disease, which lacks effective therapies in the world. Attractively, more and more evidences show that natural products are safe and effective in the prevention and treatment of hepatic fibrosis. Artesunate, a water-soluble hemisuccinate derivative of artemisinin, exerts various pharmacological activities such as anti-inflammatory, anti-tumor and immunomodulating abilities. However, the effects of artesunate on hepatic fibrosis are little-known. Here our study was performed to investigate the effect of artesunate on carbon tetrachloride (CCl₄)-induced mouse liver fibrosis and elucidate whether artesunate could alleviate liver fibrosis by regulating ferritinophagy- mediated ferroptosis in hepatic stellate cells (HSCs). Firstly, our results demonstrated that artesunate treatment could induce activated HSC ferroptosis in fibrotic livers. Moreover, primary HSCs isolated from different animal groups were cultured to detect biomarkers of ferroptosis including iron, lipid peroxidation, glutathione (GSH) and prostaglandin endoperoxide synthase 2 (ptgs2) levels. The results revealed that artesunate remarkably promoted ferroptosis of activated HSCs. Furthermore, consistent with the experimental results in vivo, the data in vitro still indicated that artesunate treatment markedly induced ferroptosis in activated HSCs, which mainly embodied as declined cell vitality, increased cell death rate, accumulated iron, elevated lipid peroxides and reduced antioxidant capacity. Conversely, inhibition of ferroptosis by deferoxamine (DFO) completely abolished artesunate-induced anti-fibrosis effect. Surprisingly, artesunate also evidently triggered ferritinophagy accompanied by up-regulation of LC3 (microtubule-associated protein light chain 3), Atg3, Atg5, Atg6/beclin1, Atg12 (autophagy related genes) and down-regulation of p62, FTH1 (ferritin heavy chain), NCOA4 (nuclear receptor co-activator 4) in activated HSCs. Nevertheless, depletion of ferritinophagy by specific inhibitor lysosomal lumen alkalizer-chloroquine (CQ) inhibited artesunate-induced ferroptosis and anti-fibrosis function. These results suggested that ferritinophagy-mediated HSC ferroptosis was responsible for artesunate-induced anti-fibrosis efficacy, which provided new clues for further pharmacological study of artesunate.

Dysregulated Bile Transporters and Impaired Tight Junctions During Chronic Liver Injury in Mice

BACKGROUND & AIMS

Liver fibrosis, hepatocellular necrosis, inflammation, and proliferation of liver progenitor cells are features of chronic liver injury. Mouse models have been used to study the end-stage pathophysiology of chronic liver injury. However, little is known about differences in the mechanisms of liver injury among different mouse models because of our inability to visualize the progression of liver injury in vivo in mice. We developed a method to visualize bile transport and blood-bile barrier (BBlB) integrity in live mice.

METHODS

C57BL/6 mice were fed a choline-deficient, ethionine-supplemented (CDE) diet or a diet containing 0.1% 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) for up to 4 weeks to induce chronic liver injury. We used quantitative liver intravital microscopy (qLIM) for real-time assessment of bile transport and BBlB integrity in the intact livers of the live mice fed the CDE, DDC, or chow (control) diets. Liver tissues were collected from mice and analyzed by histology, immunohistochemistry, real-time polymerase chain reaction, and immunoblots.

RESULTS

Mice with liver injury induced by a CDE or a DDC diet had breaches in the BBlB and impaired bile secretion, observed by qLIM compared with control mice. Impaired bile secretion was associated with reduced expression of several tight-junction proteins (claudins 3, 5, and 7) and bile transporters (NTCP, OATP1, BSEP, ABCG5, and ABCG8). A prolonged (2-week) CDE, but not DDC, diet led to re-expression of tight junction proteins and bile transporters, concomitant with the reestablishment of BBlB integrity and bile secretion.

CONCLUSIONS

We used qLIM to study chronic liver injury, induced by a choline-deficient or DDC diet, in mice. Progression of chronic liver injury was accompanied by loss of bile transporters and tight junction proteins.

Dual ablation of β- and γ-catenin: Critical regulators of junctions and their functions

The duality of β- and γ–catenin during liver injury has not been defined. It’s well known that loss of β-catenin plays a critical role in overall liver health and is a major component of adherens junctions (AJ). Further, γ-catenin has been shown to regulate β-catenin and vice-versa. In this excellent manuscript, the authors investigated the effects of knocking out both β- and γ–catenin creating a β-;γ-catenin-double knockout (DKO). The result of this interbreeding revealed a model that is reminiscent of early childhood cholestatic liver diseases (CLD) like Progressive Familial Intrahepatic Cholestasis (PFIC). The authors provide both in vivo and in vitro data to demonstrate the important role of these catenin genes in the regulation of hepatocyte-junctions. The experiments show partially redundant function of catenin’s at hepatocyte AJ in regulating tight junctions (TJ) and contributing to a disrupted blood-bile barrier. Further, concomitant hepatic loss of β- and γ-catenin disrupts structural and functional integrity of AJ and TJ via transcriptional and posttranslational mechanisms. Overall, these studies shed important light on junctional protein dysregulation during CLD.

Modulation of O-GlcNAc Levels in the Liver Impacts Acetaminophen-Induced Liver Injury by Affecting Protein Adduct Formation and Glutathione Synthesis

Overdose of acetaminophen (APAP) results in acute liver failure. We have investigated the role of a posttranslational modification of proteins called O-GlcNAcylation, where the O-GlcNAc transferase (OGT) adds and O-GlcNAcase (OGA) removes a single β-D-N-acetylglucosamine (O-GlcNAc) moiety, in the pathogenesis of APAP-induced liver injury. Hepatocyte-specific OGT knockout mice (OGT KO), which have reduced O-GlcNAcylation, and wild-type (WT) controls were treated with 300 mg/kg APAP and the development of injury was studied over a time course from 0 to 24 h. OGT KO mice developed significantly lower liver injury as compared with WT mice. Hepatic CYP2E1 activity and glutathione (GSH) depletion following APAP treatment were not different between WT and OGT KO mice. However, replenishment of GSH and induction of GSH biosynthesis genes were significantly faster in the OGT KO mice. Next, male C57BL/6 J mice were treated Thiamet-G (TMG), a specific inhibitor of OGA to induce O-GlcNAcylation, 1.5 h after APAP administration and the development of liver injury was studied over a time course of 0-24 h. TMG-treated mice exhibited significantly higher APAP-induced liver injury. Treatment with TMG did not affect hepatic CYP2E1 levels, GSH depletion, APAP-protein adducts, and APAP-induced mitochondrial damage. However, GSH replenishment and GSH biosynthesis genes were lower in TMG-treated mice after APAP overdose. Taken together, these data indicate that induction in cellular O-GlcNAcylation exacerbates APAP-induced liver injury via dysregulation of hepatic GSH replenishment response.