Innate detection of hepatitis B and C virus and viral inhibition of the response

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

Host Innate Immunity Against Hepatitis Viruses and Viral Immune Evasion

Hepatitis viruses are primary causative agents of hepatitis and represent a major source of public health problems in the world. The host innate immune system forms the first line of defense against hepatitis viruses. Hepatitis viruses are sensed by specific pathogen recognition receptors (PRRs) that subsequently trigger the innate immune response and interferon (IFN) production. However, hepatitis viruses evade host immune surveillance via multiple strategies, which help compromise the innate immune response and create a favorable environment for viral replication. Therefore, this article reviews published findings regarding host innate immune sensing and response against hepatitis viruses. Furthermore, we also focus on how hepatitis viruses abrogate the antiviral effects of the host innate immune system.

Residues Asn118 and Glu119 of hepatitis B virus X protein are critical for HBx-mediated inhibition of RIG-I-MAVS signaling

Hepatitis B virus (HBV) X protein (HBx) has been reported to counteract the innate immune responses through interfering with the pattern recognition receptors signaling activated by retinoic acid-inducible gene-I (RIG-I)-mitochondrial antiviral signaling protein (MAVS). Here, we showed that, compared to the HBx derived from genotype (gt) A, C and D, HBx of gtB exhibited more potent inhibitory activity on the RIG-I-MAVS-mediated interferon-β promoter activation. Functional analysis of the genotype-associated differences in amino acid sequence and the reciprocal mutation experiments in transient-transfection and infection cell models revealed that HBx with asparagine (N) and glutamic acid (E) at 118-119 positions inhibited RIG-I signaling and interacted with MAVS more efficiently than that with lysine (K) and aspartic acid (D). An impaired RIG-I-induced MAVS aggregation was observed in the presence of HBx-118N119E while MAVS-TRAF3 interaction was not affected. These results implicated that HBx gene heterogeneity may affect the innate immune responses to HBV infection.

Lack of expression of hepatitis C virus core protein in human monocyte-erived dendritic cells using recombinant semliki forest virus

Hepatitis C Virus belongs to the Flaviviridae family.  One proposed mechanism of HCV persistence in the ability to infect hematopoietic cells, including Dendritic cells (DCs). HCV infection of DCs could impair their functions that represent one of the mechanisms, thus hampering viral clearance by the host immune system. Among HCV-encoded proteins, the highly conserved Core protein has been suggested to be responsible for the immunomodulatory properties of this Hepacivirus. Recombinant viral vectors expressing the HCV Core protein and allowing its transduction and therefore the expression of the protein into DCs could be useful tools for the analysis of the properties of the Core protein. Vaccinia Virus and retrovirus have been used to transduce human DCs. Likewise, gene transfer into DCs using Semliki Forest Virus has been reported. This study aimed to express the HCV Core protein in human monocyte-derived DCs using an SFV vector, in which the subgenomic RNA encoding the structural proteins was replaced by the HCV Core sequence and then analyze the effects of its expression on DCs functions.

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.

Role of miR-223 in the pathophysiology of liver diseases

MiRNAs are small, noncoding RNAs, which can regulate gene expression posttranscriptionally, and they have emerged as key factors in disease biology by aiding in disease development and progression. MiR-223 is highly conserved during evolution and it was first described as a modulator of hematopoietic lineage differentiation. MiR-223 has an essential part in inflammation by targeting the nuclear factor-κB pathway and the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome. Recent studies have shown that miR-223 expression is deregulated in various types of liver diseases, including hepatitis virus infections, alcohol-induced liver injury, drug-induced liver injury, non-alcoholic fatty liver disease, cirrhosis, and hepatocellular carcinoma. As inflammatory and immune factors are involved in the occurrence and progress of liver diseases, deregulated miR-223 may participate in the pathogenesis of these conditions by influencing neutrophil infiltration, macrophage polarization, and inflammasome activation. This review first summarizes the present understanding of the biological functions of miR-223, including its gene location and transcription regulation, as well as its physiological role in hematopoietic differentiation. This review then focuses on the role of miR-223 in liver pathophysiology and its potential applications as a diagnostic biomarker and therapeutic target in liver diseases.

A tiny RNA molecule involved with gene regulation may offer an appealing target for diagnosing and treating various liver diseases. MicroRNA-223 (miR-223) was first identified as controlling gene activity in a wide variety of immune cells. A review from researchers led by Yanning Liu at China’s Zhejiang University in Hangzhou details how abnormal miR-223 also contributes to liver damage in a variety of conditions, although questions still remain about how it functions in different liver disorders. The authors highlight studies linking miR-223 with the development of fibrosis and cirrhosis, and with the inflammatory response to injury from drugs, alcohol, or infection. This could make this microRNA a useful diagnostic biomarker. The authors also identify therapeutic opportunities to modulate this molecule, referring to several studies on the manipulation of miR-223 to treat hepatitis.

Hepatitis C Virus-Associated Cancers

Most hepatitis C virus (HCV) infection results in persistent infection. Significant portion of chronic HCV-infected patients develop hepatocellular carcinoma (HCC). Chronic hepatitis C is also associated with extrahepatic manifestations, including cryoglobulinemia, lymphoma, insulin resistance, type 2 diabetes, and neurological disorders. The molecular mechanisms of how HCV infection causes liver cancer are largely unknown. HCV replication or viral proteins may perturb cellular hemostasis and induce the generation of reactive oxygen species (ROS); viral components or viral replication products act as agonist to trigger innate immune response and cause chronic inflammation. Within the liver, non-hepatocytes such as hepatic stellate cell (HSC) are activated upon HCV infection to provide the major source of extracellular proteins and play important roles in fibrogenesis. With the great achievements of HCV treatment, especially the direct-acting antivirals (DAAs) against HCV, HCV eradication is possible. However, until now there are only very limited data on the effect of DAA-based anti-HCV treatment on HCC patients.

Hepatitis B virus sensitivity to interferon-α in hepatocytes is more associated with cellular interferon response than with viral genotype

Interferon-α (IFN-α) is used to treat chronic hepatitis B virus (HBV) infection, but only 20%-40% of patients respond well. Clinical observations have suggested that HBV genotype is associated with the response to IFN therapy; however, its role in viral responsiveness to IFN in HBV-infected hepatocytes remains unclear. Here, we produced infectious virions of HBV genotypes A to D to infect three well-recognized cell-culture-based HBV infection systems, including primary human hepatocytes (PHH), differentiated HepaRG (dHepaRG), and HepG2-NTCP cells to quantitatively compare the antiviral effect of IFN-α on HBV across genotypes and cell models. The efficacy of IFN-α against HBV in hepatocytes was generally similar across genotypes A2, B5, C2, and D3; however, it was significantly different among the infection models given that the half maximal inhibitory concentration value of IFN-α for inhibition of viral DNA replication in PHH (<20 U/mL) and dHepaRG cells were much lower than that in HepG2-NTCP cells (>500 U/mL). Notably, even in PHH, IFN-α did not reduce HBV covalently closed circular DNA at the concentrations for which viral antigens and DNA replication intermediates were strongly reduced. The three cell-culture models exhibited differential cellular response to IFN-α. The genes reported to be associated with responsiveness to IFN-α in patients were robustly induced in PHH while weakly induced in HepG2-NTCP cells upon IFN-α treatment. Reduction or promotion of IFN response in PHH or HepG2-NTCP cells significantly attenuated or improved the inhibitory capacity of IFN-α on HBV replication, respectively.

CONCLUSION

In the cell-culture-based HBV infection models, the sensitivity of HBV to IFN-α in hepatocytes is determined more by the cell-intrinsic IFN response than by viral genotype, and improvement of the IFN response in HepG2-NTCP cells promotes the efficacy of IFN-α against HBV. (Hepatology 2018;67:1237-1252).

Role of TLRs and IL-6 in the outcome of chronic hepatitis C treatment in Tunisian population

OBJECTIVES

TLRs are one of the most studied families of pathogen recognition receptors (PRRs) and play a pivotal role during HCV infection. The binding of ligands to TLRs on antigen presenting cells (APCs) leads to secretion of inflammatory cytokines, such as IL6, and induction of the acquired immunity response. Therefore, it has become necessarily to harness the TLRs properties' on therapeutically tools to enhance the HCV treatment response. Herein, we investigated the association between TLR3, TLR4 variants and nine IL-6 polymorphisms, and response to anti-viral treatment during HCV infection.

METHODS

Study subjects comprised 120 patients infected with HCV-1b and treated with Peg-IFN/RBV. Genotyping of nine IL-6 variants were done by real -time PCR and genotyping of TLRs polymorphisms were done by RFLP-PCR.

RESULTS

High frequency of TLR3 rs3775290 C/C genotype and TLR4 rs4986790 A/A genotype were noticed among patients with sustained viral response compared to Non-responder patients. The genetic association of TLR3 and TLR4 variants was evidenced by the improvement in the kinetics of viral load decline, with superiority of TLR3 compared to TLR4. Among, nine polymorphisms studied on IL-6 only rs1800796, rs2069845 and rs1880242 were associated with sustained viral response. Our study reports also that the common favourable IL-28B variant is essential for TLR-activated antiviral protection.

CONCLUSION

TLR3 and TLR4 are involved in the pathogenesis of viral infections. TLR3 may be better suited than TLR4 to activate anti-viral program. Moreover, we propose that the Th2 cytokine, IL-6, constitutes a determinant of the outcome of therapy in HCV patients.

Interplay between the Hepatitis B Virus and Innate Immunity: From an Understanding to the Development of Therapeutic Concepts

The hepatitis B virus (HBV) infects hepatocytes, which are the main cell type composing a human liver. However, the liver is enriched with immune cells, particularly innate cells (e.g., myeloid cells, natural killer and natural killer T-cells (NK/NKT), dendritic cells (DCs)), in resting condition. Hence, the study of the interaction between HBV and innate immune cells is instrumental to: (1) better understand the conditions of establishment and maintenance of HBV infections in this secondary lymphoid organ; (2) define the role of these innate immune cells in treatment failure and pathogenesis; and (3) design novel immune-therapeutic concepts based on the activation/restoration of innate cell functions and/or innate effectors. This review will summarize and discuss the current knowledge we have on this interplay between HBV and liver innate immunity.

Development of mouse models for analysis of human virus infections

Viruses usually exhibit strict species-specificity as a result of co-evolution with the host. Thus, in mouse models, a great barrier exists for analysis of infections with human-tropic viruses. Mouse models are unlikely to faithfully reproduce the human immune response to viruses or viral compounds and it is difficult to evaluate human therapeutic efficacy with antiviral reagents in mouse models. Humans and mice essentially have different immune systems, which makes it difficult to extrapolate mouse results to humans. In addition, apart from immunological reasons, viruses causing human diseases do not always infect mice because of species tropism. One way to determine tropism would be a virus receptor that is expressed on affected cells. The development of gene-disrupted mice and Tg mice, which express human receptor genes, enables us to analyze several viral infections in mice. Mice are, indeed, susceptible to human viruses when artificially infected in receptor-supplemented mice. Although the mouse cells less efficiently permit viral replication than do human cells, the models for analysis of human viruses have been established in vivo as well as in vitro, and explain viral pathogenesis in the mouse systems. In most systems, however, nucleic acid sensors and type I interferon suppress viral propagation to block the appearance of infectious manifestation. We herein review recent insight into in vivo antiviral responses induced in mouse infection models for typical human viruses.