Retinoid regulation of antiviral innate immunity in hepatocytes

N-Acetyl Cysteine Restores the Diminished Activity of the Antioxidant Enzymatic System Caused by SARS-CoV-2 Infection: Preliminary Findings

SARS-CoV-2 infects type II pneumocytes and disrupts redox homeostasis by overproducing reactive oxygen species (ROS). N-acetyl cysteine (NAC) is a precursor of the synthesis of glutathione (GSH) and it restores the loss of redox homeostasis associated to viral infections. The aim of the study is to evaluate the effect of the treatment with NAC on the enzymatic antioxidant system in serum from patients infected by SARS-CoV-2. We evaluated the enzymatic activities of thioredoxin reductase (TrxR), glutathione peroxidase (GPx), -S-transferase (GST), and reductase (GR) by spectrophotometry and the concentrations of the glutathione (GSH), total antioxidant capacity (TAC), thiols, nitrites (NO₂^-), and lipid peroxidation (LPO) in serum. The activity of the extracellular super oxide dismutase (ecSOD) was determined by native polyacrylamide gels, and 3-nitrotyrosine (3-NT) was measured by ELISA. A decrease in the activities of the ecSOD, TrxR, GPx, GST GR, (p = 0 ≤ 0.1), and the GSH, TAC, thiols, and NO₂^- (p ≤ 0.001) concentrations and an increase in LPO and 3-NT (p = 0.001) concentrations were found in COVID-19 patients vs. healthy subjects. The treatment with NAC as an adjuvant therapy may contribute to a reduction in the OS associated to the infection by SARS-CoV-2 through the generation of GSH. GSH promotes the metabolic pathways that depend on it, thus contributing to an increase in TAC and to restore redox homeostasis.

Long-term cell fate and functional maintenance of human hepatocyte through stepwise culture configuration

Human hepatocyte culture system represents by far the most physiologically relevant model for our understanding of liver biology and diseases; however, its versatility has been limited due to the rapid and progressive loss of genuine characteristics, indicating the inadequacy of in vitro milieu for fate maintenance. This study, therefore, is designed to define environmental requirements necessary to sustain the homeostasis of terminally differentiated hepatocytes. Our study reveals that the supplementation of dimethyl sulfoxide (DMSO) is indispensable in mitigating fate deterioration and promoting adaptation to the in vitro environment, resulting in the restoration of tight cell-cell contact, cellular architecture, and polarity. The morphological recovery was overall accompanied by the restoration of hepatocyte marker gene expression, highlighting the interdependence between the cellular architecture and the maintenance of cell fate. However, beyond the recovery phase culture, DMSO supplementation is deemed detrimental due to the potent inhibitory effect on a multitude of hepatocyte functionalities while its withdrawal results in the loss of cell fate. In search of DMSO substitute, our screening of organic substances led to the identification of dimethyl sulfone (DMSO2), which supports the long-term maintenance of proper morphology, marker gene expression, and hepatocytic functions. Moreover, hepatocytes maintained DMSO2 exhibited clinically relevant toxicity in response to prolonged exposure to xenobiotics as well as alcohol. These observations suggest that the stepwise culture configuration consisting of the consecutive supplementation of DMSO and DMSO2 confers the microenvironment essential for the fate and functional maintenance of terminally differentiated human hepatocytes.

The role of acetaldehyde dehydrogenase 2 in the pathogenesis of liver diseases

Common liver tissue damage is mainly due to the accumulation of toxic aldehydes in lipid peroxidation under oxidative stress. Cumulative toxic aldehydes in the liver can be effectively metabolized by acetaldehyde dehydrogenase 2 (ALDH2), thereby alleviating various liver diseases. Notably, gene mutation of ALDH2 leads to impaired ALDH2 enzyme activity, thus aggravating the progress of liver diseases. However, the relationship and specific mechanism between ALDH2 and liver diseases are not clear. Consequently, the review explains the relationship between ALDH2 and liver diseases such as alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis and hepatocellular carcinoma (HCC). In addition, this review also discusses ALDH2 as a potential therapeutic target for various liver diseases,and focuses on summarizing the regulatory mechanism of ALDH2 in these liver diseases.

ZBTB7A promotes virus-host homeostasis during human coronavirus 229E infection

The cellular fate after infection with human coronaviruses (HCoVs) is typically death. Previous data suggest, however, that the transcriptional state of an individual cell may sometimes allow additional outcomes of infection. Here, to probe the range of interactions a permissive cell type can have with a HCoV, we perform a CRISPR activation screen with HCoV-229E. The screen identified the transcription factor ZBTB7A, which strongly promotes cell survival after infection. Rather than suppressing viral infection, ZBTB7A upregulation allows the virus to induce a persistent infection and homeostatic state with the cell. We also find that control of oxidative stress is a primary driver of cellular survival during HCoV-229E infection. These data illustrate that, in addition to the nature of the infecting virus and the type of cell that it encounters, the cellular gene expression profile prior to infection can affect the eventual fate.

Role of ALDH2 in Hepatic Disorders: Gene Polymorphism and Disease Pathogenesis

Aldehyde dehydrogenase 2 (ALDH2) is a key enzyme of alcohol metabolism and it is involved in the cellular mechanism of alcohol liver disease. ALDH2 gene mutations exist in about 8% of the world's population, with the incidence reaching 45% in East Asia. The mutations will result in impairment of enzyme activity and accumulation of acetaldehyde, facilitating the progression of other liver diseases, including non-alcoholic fatty liver diseases, viral hepatitis and hepatocellular carcinoma, through adduct formation and inflammatory responses. In this review, we seek to summarize recent research progress on the correlation between ALDH2 gene polymorphism and multiple liver diseases, with an attempt to provide clues for better understanding of the disease mechanism and for strategy making.

Art of Making Artificial Liver: Depicting Human Liver Biology and Diseases in Mice

Advancement in both bioengineering and cell biology of the liver led to the establishment of the first-generation humanized liver chimeric mouse (HLCM) model in 2001. The HLCM system was initially developed to satisfy the necessity for a convenient and physiologically representative small animal model for studies of hepatitis B virus and hepatitis C virus infection. Over the last two decades, the HLCM system has substantially evolved in quality, production capacity, and utility, thereby growing its versatility beyond the study of viral hepatitis. Hence, it has been increasingly employed for a variety of applications including, but not limited to, the investigation of drug metabolism and pharmacokinetics and stem cell biology. To date, more than a dozen distinctive HLCM systems have been established, and each model system has similarities as well as unique characteristics, which are often perplexing for end-users. Thus, this review aims to summarize the history, evolution, advantages, and pitfalls of each model system with the goal of providing comprehensive information that is necessary for researchers to implement the ideal HLCM system for their purposes. Furthermore, this review article summarizes the contribution of HLCM and its derivatives to our mechanistic understanding of various human liver diseases, its potential for novel applications, and its current limitations.

Seasonal Variability and Shared Molecular Signatures of Inactivated Influenza Vaccination in Young and Older Adults

The seasonal influenza vaccine is an important public health tool but is only effective in a subset of individuals. The identification of molecular signatures provides a mechanism to understand the drivers of vaccine-induced immunity. Most previously reported molecular signatures of human influenza vaccination were derived from a single age group or season, ignoring the effects of immunosenescence or vaccine composition. Thus, it remains unclear how immune signatures of vaccine response change with age across multiple seasons. In this study we profile the transcriptional landscape of young and older adults over five consecutive vaccination seasons to identify shared signatures of vaccine response as well as marked seasonal differences. Along with substantial variability in vaccine-induced signatures across seasons, we uncovered a common transcriptional signature 28 days postvaccination in both young and older adults. However, gene expression patterns associated with vaccine-induced Ab responses were distinct in young and older adults; for example, increased expression of killer cell lectin-like receptor B1 (KLRB1; CD161) 28 days postvaccination positively and negatively predicted vaccine-induced Ab responses in young and older adults, respectively. These findings contribute new insights for developing more effective influenza vaccines, particularly in older adults.

Aldehyde Dehydrogenase, Liver Disease and Cancer

Acetaldehyde dehydrogenase 2 (ALDH2) is the key enzyme responsible for metabolism of the alcohol metabolite acetaldehyde in the liver. In addition to conversion of the acetaldehyde molecule, ALDH is also involved in other cellular functions. Recently, many studies have investigated the involvement of ALDH expression in viral hepatitis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis, and liver cancer. Notably, ALDH2 expression has been linked with liver cancer risk, as well as pathogenesis and prognosis, and has emerged as a promising therapeutic target. Of note, approximately 8% of the world's population, and approximately 30-40% of the population in East Asia carry an inactive ALDH2 gene. This review summarizes new progress in understanding tissue-specific acetaldehyde metabolism by ALDH2 as well as the association of ALDH2 gene polymorphisms with liver disease and cancer. New research directions emerging in the field are also briefly discussed.

Regulation of Hepatitis C Virus Infection by Cellular Retinoic Acid Binding Proteins through the Modulation of Lipid Droplet Abundance

Retinoid (vitamin A) is an essential diet constituent that governs a broad range of biological processes. Its biologically active metabolite, all-trans retinoic acid (ATRA), exhibits a potent antiviral property by enhancing both innate and adaptive antiviral immunity against a variety of viral pathogens, such as, but not limited to, HIV, respiratory syncytial virus (RSV), herpes simplex virus (HSV), and measles. Even though the hepatocyte is highly enriched with retinoid and its metabolite ATRA, it supports the establishment of efficient hepatitis C virus (HCV) replication. Here, we demonstrate the hepatocyte-specific cell-intrinsic mechanism by which ATRA exerts either a proviral or antiviral effect, depending on how it engages cellular retinoic acid binding proteins (CRABPs). We found that the engagement of CRABP1 by ATRA potently supported viral infection by promoting the accumulation of lipid droplets (LDs), which robustly enhanced the formation of a replication complex on the LD-associated endoplasmic reticulum (ER) membrane. In contrast, ATRA binding to CRABP2 potently inhibited HCV via suppression of LD accumulation. However, this antiviral effect of CRABP2 was abrogated due to the functional and quantitative predominance of CRABP1 in the hepatocytes. In summary, our study demonstrates that CRABPs serve as an on-off switch that modulates the efficiency of the HCV life cycle and elucidates how HCV evades the antiviral properties of ATRA via the exploitation of CRABP1 functionality.IMPORTANCE ATRA, a biologically active metabolite of vitamin A, exerts pleiotropic biological effects, including the activation of both innate and adaptive immunity, thereby serving as a potent antimicrobial compound against numerous viral pathogens. Despite the enrichment of hepatocytes with vitamin A, HCV still establishes an efficient viral life cycle. Here, we discovered that the hepatocellular response to ATRA creates either a proviral or an antiviral environment depending on its engagement with CRABP1 or -2, respectively. CRABP1 supports the robust replication of HCV, while CRABP2 potently inhibits the efficiency of viral replication. Our biochemical, genetic, and microscopic analyses reveal that the pro- and antiviral effects of CRABPs are mediated by modulation of LD abundance, where HCV establishes the platform for viral replication and assembly on the LD-associated ER membrane. This study uncovered a cell-intrinsic mechanism by which HCV exploits the proviral function of CRABP1 to establish an efficient viral life cycle.

The putative tumour suppressor protein Latexin is secreted by prostate luminal cells and is downregulated in malignancy

Loss of latexin (LXN) expression negatively correlates with the prognosis of several human cancers. Despite association with numerous processes including haematopoietic stem cell (HSC) fate, inflammation and tumour suppression, a clearly defined biological role for LXN is still lacking. Therefore, we sought to understand LXN expression and function in the normal and malignant prostate to assess its potential as a therapeutic target. Our data demonstrate that LXN is highly expressed in normal prostate luminal cells but downregulated in high Gleason grade cancers. LXN protein is both cytosolic and secreted by prostate cells and expression is directly and potently upregulated by all-trans retinoic acid (atRA). Whilst overexpression of LXN in prostate epithelial basal cells did not affect cell fate, LXN overexpression in the luminal cancer line LNCaP reduced plating efficiency. Transcriptome analysis revealed that LXN overexpression had no direct effects on gene expression but had significant indirect effects on important genes involved in both retinoid metabolism and IFN-associated inflammatory responses. These data highlight a potential role for LXN in retinoid signaling and inflammatory pathways. Investigating the effects of LXN on immune cell function in the tumour microenvironment (TME) may reveal how observed intratumoural loss of LXN affects the prognosis of many adenocarcinomas.

Identification of Retinoic Acid Receptor Agonists as Potent Hepatitis B Virus Inhibitors via a Drug Repurposing Screen

Currently available therapies for chronic hepatitis B virus (HBV) infection can efficiently reduce viremia but induce hepatitis B surface antigen (HBsAg) loss in very few patients; also, these therapies do not greatly affect the viral covalently closed circular DNA (cccDNA). To discover new agents with complementary anti-HBV effects, we performed a drug repurposing screen of 1,018 Food and Drug Administration (FDA)-approved compounds using HBV-infected primary human hepatocytes (PHH). Several compounds belonging to the family of retinoic acid receptor (RAR) agonists were identified that reduced HBsAg levels in a dose-dependent manner without significant cytotoxicity. Among them, tazarotene exhibited the most potent anti-HBV effect, with a half-maximal inhibitory concentration (IC₅₀) for HBsAg of less than 30 nM in PHH. The inhibitory effect was also observed in HBV-infected differentiated HepaRG (dHepaRG) models, but not in HepG2.215 cells, and HBV genotypes A to D were similarly inhibited. Tazarotene was further demonstrated to repress HBV cccDNA transcription, as determined by the levels of HBV cccDNA and RNAs and the activation of HBV promoters. Moreover, RNA sequence analysis showed that tazarotene did not induce an interferon response but altered the expression of a number of genes associated with RAR and metabolic pathways. Inhibition of RARβ, but not RARα, by a specific antagonist significantly attenuated the anti-HBV activity of tazarotene, suggesting that tazarotene inhibits HBV in part through RARβ. Finally, a synergistic effect of tazarotene and entecavir on HBV DNA levels was observed. Therefore, RAR agonists as represented by tazarotene were identified as potential novel anti-HBV agents.

The Impact of Tumor Differentiation on the Prognosis of HBV-Associated Solitary Hepatocellular Carcinoma Following Hepatectomy: A Propensity Score Matching Analysis

AIM

The role of tumor differentiation in the prognosis of hepatocellular carcinoma (HCC) after hepatectomy remains controversial. The present study aimed to classify the impact of tumor differentiation on solitary hepatitis B viral (HBV)-associated HCC using propensity score matching analysis.

METHODS

Between January 2009 and March 2015, the data of 721 HCC patients in West China Hospital were prospectively collected and analyzed. Propensity matching analysis was applied to overcome the imbalance in baseline characteristics. Survival analysis was performed using the Kaplan-Meier method. Risk factors were identified by the Cox proportional hazards model.

RESULTS

All HCC patients were classified into the moderately well-differentiated HCCs group (group A, n = 442, 61.3%) or poorly differentiated HCCs group (group B, n = 279, 38.7%). Patients with poorly differentiated HCCs commonly had a larger tumor size, more advanced tumors, and a higher alpha-fetoprotein (AFP) level. Patients with poorly differentiated HCCs had a poorer recurrence-free survival and overall survival before and after propensity score matching analysis. Poorly differentiated tumors, positive serum hepatitis B viral e antigen, positive hepatitis B virus deoxyribonucleic acid load, tumor size, microvascular invasion, and AFP > 400 ng/ml were risk factors of a poor outcome.

CONCLUSIONS

Our propensity model provided strong evidence that a poorly differentiated tumor had a negative impact on the recurrence and long-term survival of solitary HBV-associated HCCs after curative hepatectomy. Antiviral therapy might improve their prognosis.

Demethylase JMJD6 as a New Regulator of Interferon Signaling: Effects of HCV and Ethanol Metabolism

BACKGROUND & AIMS

Alcohol-induced progression of hepatitis C virus (HCV) infection is related to dysfunction of innate immunity in hepatocytes. Endogenously produced interferon (IFN)α induces activation of interferon-stimulated genes (ISGs) via triggering of the Janus kinase-signal transducer and activator of transcription 1 (STAT1) pathway. This activation requires protein methyltransferase 1-regulated arginine methylation of STAT1. Here, we aimed to study whether STAT1 methylation also depended on the levels of demethylase jumonji domain-containing 6 protein (JMJD6) and whether ethanol and HCV affect JMJD6 expression in hepatocytes.

METHODS

Huh7.5-CYP (RLW) cells and hepatocytes were exposed to acetaldehyde-generating system (AGS) and 50 mmol/L ethanol, respectively. JMJD6 messenger RNA and protein expression were measured by real-time polymerase chain reaction and Western blot. IFNα-activated cells either overexpressing JMJD6 or with knocked-down JMJD6 expression were tested for STAT1 methylation, ISG activation, and HCV RNA. In vivo studies have been performed on C57Bl/6 mice (expressing HCV structural proteins or not) or chimeric mice with humanized livers fed control or ethanol diets.

RESULTS

AGS exposure to cells up-regulated JMJD6 expression in RLW cells. These results were corroborated by ethanol treatment of primary hepatocytes. The promethylating agent betaine reversed the effects of AGS/ethanol. Similar results were obtained in vivo, when mice were fed control/ethanol with and without betaine supplementation. Overexpression of JMJD6 suppressed STAT1 methylation, IFNα-induced ISG activation, and increased HCV-RNA levels. In contrast, JMJD6 silencing enhanced STAT1 methylation, ISG stimulation by IFNα, and attenuated HCV-RNA expression in Huh7.5 cells.

CONCLUSIONS

We conclude that arginine methylation of STAT1 is suppressed by JMJD6. Both HCV and acetaldehyde increase JMJD6 levels, thereby impairing STAT1 methylation and innate immunity protection in hepatocytes exposed to the virus and/or alcohol.

Dual modulation of human hepatic zonation via canonical and non-canonical Wnt pathways

The hepatic lobule is divided into three zones along the portal-central vein axis. Hepatocytes within each zone exhibit a distinctive gene expression profile that coordinates their metabolic compartmentalization. The zone-dependent heterogeneity of hepatocytes has been hypothesized to result from the differential degree of exposure to oxygen, nutrition and gut-derived toxins. In addition, the gradient of Wnt signaling that increases towards the central vein seen in rodent models is believed to play a critical role in shaping zonation. Furthermore, hepatic zonation is coupled to the site of the homeostatic renewal of hepatocytes. Despite its critical role, the regulatory mechanisms that determine the distinctive features of zonation and its relevance to humans are not well understood. The present study first conducted a comprehensive zone-dependent transcriptome analysis of normal human liver using laser capture microdissection. Upstream pathway analysis revealed the signatures of host responses to gut-derived toxins in the periportal zone, while both the canonical Wnt pathway and the xenobiotic response pathway govern the perivenular zone. Furthermore, we found that the hypoxic environment of the perivenular zone promotes Wnt11 expression in hepatocytes, which then regulates unique gene expression via activation of the non-canonical Wnt pathway. In summary, our study reports the comprehensive zonation-dependent transcriptome of the normal human liver. Our analysis revealed that the LPS response pathway shapes the characteristics of periportal hepatocytes. By contrast, the perivenular zone is regulated by a combination of three distinct pathways: the xenobiotic response pathway, canonical Wnt signaling, and hypoxia-induced noncanonical Wnt signaling.

Dietary and metabolic modulators of hepatic immunity

The liver is the central metabolic organ of the organism and is thus constantly exposed to gut-derived dietary and microbial antigens. The liver maintains homoeostatic tolerance to these mostly harmless antigens. However, the liver also functions as a barrier organ to harmful pathogens and is thus permissive to liver inflammation. The regulation of the delicate balance between liver tolerance and liver inflammation is of vital importance for the organism. In recent years, a general role for dietary components and metabolites as immune mediators has been emerging. However, although the liver is exposed to a great deal of metabolic mediators, surprisingly, little is known about their actual role in the regulation of hepatic immune responses. Here, we will explore the possible impacts of metabolic mediators for homoeostatic and pathological immunity in the liver, by highlighting selected examples of metabolic immune regulation in the liver.

Transcriptional Regulation of Antiviral Interferon-Stimulated Genes

Interferon-stimulated genes (ISGs) are a group of gene products that coordinately combat pathogen invasions, in particular viral infections. Transcription of ISGs occurs rapidly upon pathogen invasion, and this is classically provoked via activation of the Janus kinase/signal transducer and activator of transcription (JAK–STAT) pathway, mainly by interferons (IFNs). However, a plethora of recent studies have reported a variety of non-canonical mechanisms regulating ISG transcription. These new studies are extremely important for understanding the quantitative and temporal differences in ISG transcription under specific circumstances. Because these canonical and non-canonical regulatory mechanisms are essential for defining the nature of host defense and associated detrimental proinflammatory effects, we comprehensively review the state of this rapidly evolving field and the clinical implications of recently acquired knowledge in this respect.

Transcriptional regulation of ISGs defines the state of host anti-pathogen defense.

In light of the recently identified regulatory elements and mechanisms of the IFN–JAK–STAT pathway, new insights have been gained into this classical cascade in regulating ISG transcription.

A variety of non-canonical mechanisms have been recently revealed that coordinately regulate ISG transcription.

With regards to the adverse effects of IFNs in clinic, ISG-based antiviral strategy could be the next promising frontier in drug discovery.

Relationship between vitamin A deficiency and the thyroid axis in clinically stable patients with liver cirrhosis related to hepatitis C virus

Vitamin A deficiency (VAD) and altered thyroid function are commonly encountered in patients with liver cirrhosis. The link between vitamin A metabolism and thyroid function has been previously identified. The aim of this study was to explore the association between VAD and the thyroid axis in clinically stable patients with cirrhosis related to hepatitis C virus (HCV). One hundred and twelve patients with clinically stable HCV-related cirrhosis and 56 healthy controls matched for age, sex, and socioeconomic status were recruited for this study. Vitamin A status, liver function, thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), reverse triiodothyronine (rT3), anti-thyroid peroxidase antibodies (anti-TPO), and thyroid volume were evaluated. The prevalence of VAD among patients with HCV-related cirrhosis was 62.5% compared with 5.4% among controls (P < 0.001). Patients with HCV-related cirrhosis had significantly higher FT4, FT3, TSH, and thyroid volume than did healthy controls. Of the 112 patients initially recruited, 18 were excluded (patients with subclinical hypothyroidism and/or anti-TPO positive), so a total of 94 patients with HCV-related cirrhosis were divided into 2 groups according to vitamin A status: VAD and normal vitamin A. Patients with VAD had significantly lower vitamin A intake and serum albumin and higher serum bilirubin, FT4, FT3, and TSH than patients with normal vitamin A status. Multiple logistic regression analysis revealed that VAD was associated with Child-Pugh score (β = 0.11, P = 0.05) and TSH (β = -1.63, P = 0.02) independently of confounding variables. We conclude that VAD may be linked to central hyperthyroidism in patients with clinically stable HCV-related liver cirrhosis.

Organ system view of the hepatic innate immunity in HCV infection

An orchestration of innate and adaptive immunity determines the infection outcome and whether the host achieves clearance or allows the pathogen to establish persistent infection. The robust activation of the innate immune response plays the most critical role in both limiting viral replication and halting the spread of the pathogen immediately after infection. The magnitude of innate immune activation is coupled with the efficient mounting of the adaptive immunity. Although immunity against HCV infection is known to be inadequate as most cases transitions to chronicity, approximately 25% of acute infection cases result in spontaneous clearance. The exact immune mechanisms that govern the infection outcome remain largely unknown; recent discoveries suggest that the innate immune system facilitates this event. Both infected hepatocytes and local innate immune cells trigger the front line defense program of the liver as well as the recruitment of diverse adaptive immune cells to the site of infection. Although hepatocyte is the target of HCV infection, nearly all cell types that exist in the liver are involved in the innate defense and contribute to the pathophysiology of hepatic inflammation. The main focus of this comprehensive review is to discuss the current knowledge on how each hepatic cell type contributes to the organ system level innate immunity against HCV infection as well as interplays with the viral evasion program. Furthermore, this review article also aims to synchronize the observations from both molecular biological studies and clinical studies with the ultimate goal of improving our understanding of HCV mediated hepatitis. J. Med. Virol. 88:2025-2037, 2016. © 2016 Wiley Periodicals, Inc.