Hepatitis B virus rigs the cellular metabolome to avoid innate immune recognition

The lncRNAs involved in regulating the RIG-I signaling pathway

Understanding the targets and interactions of long non-coding RNAs (lncRNAs) related to the retinoic acid-inducible gene-I (RIG-I) signaling pathway is essential for developing interventions, which would enable directing the host inflammatory response regulation toward protective immunity. In the RIG-I signaling pathway, lncRNAs are involved in the important processes of ubiquitination, phosphorylation, and glycolysis, thus promoting the transport of the interferon regulatory factors 3 and 7 (IRF3 and IRF7) and the nuclear factor kappa B (NF-κB) into the nucleus, and activating recruitment of type I interferons (IFN-I) and inflammatory factors to the antiviral action site. In addition, the RIG-I signaling pathway has recently been reported to contain the targets of coronavirus disease-19 (COVID-19)-related lncRNAs. The molecules in the RIG-I signaling pathway are directly regulated by the lncRNA-microRNAs (miRNAs)-messenger RNA (mRNA) axis. Therefore, targeting this axis has become a novel strategy for the diagnosis and treatment of cancer. In this paper, the studies on the regulation of the RIG-I signaling pathway by lncRNAs during viral infections and cancer are comprehensively analyzed. The aim is to provide a solid foundation of information for conducting further detailed studies on lncRNAs and RIG-I in the future and also contribute to clinical drug development.

Metabolic reprogramming as a novel therapeutic target for Coxsackievirus B3

Coxsackievirus B3 (CVB3) is a single-stranded RNA virus that belongs to the Enterovirus genus. CVB3 is a human pathogen associated with serious conditions such as myocarditis, dilated cardiomyopathy, and pancreatitis. However, there are no therapeutic interventions to treat CVB3 infections. In this study, we found that CVB3 induced metabolic alteration in host cells through increasing glycolysis level, as indicated by an increase in the extracellular acidification rate (ECAR). CVB3-mediated metabolic alteration was confirmed by metabolite change analysis using gas chromatography-mass spectrometry (GC-MS). Based on findings, a strategy to inhibit glycolysis has been proposed to treat CVB3 infection. Indeed, glycolysis inhibitors (2-Deoxy-D-glucose, sodium oxide) significantly reduced CVB3 titers after CVB3 infection, indicating that glycolysis inhibitors can be used as effective antiviral agents. Taken together, our results reveal a novel mechanism by which CVB3 infection is controlled by regulation of host cell metabolism.

Innate Immunity, Inflammation, and Intervention in HBV Infection

Hepatitis B virus (HBV) infection is still one of the most dangerous viral illnesses. HBV infects around 257 million individuals worldwide. Hepatitis B in many individuals ultimately develops hepatocellular carcinoma (HCC), which is the sixth most common cancer and the third leading cause of cancer-related deaths worldwide. The innate immunity acts as the first line of defense against HBV infection through activating antiviral genes. Along with the immune responses, pro-inflammatory cytokines are triggered to enhance the antiviral responses, but this may result in acute or chronic liver inflammation, especially when the clearance of virus is unsuccessful. To a degree, the host innate immune and inflammatory responses dominate the HBV infection and liver pathogenesis. Thus, it is crucial to figure out the signaling pathways involved in the activation of antiviral factors and inflammatory cytokines. Here, we review the interplay between HBV and the signal pathways that mediates innate immune responses and inflammation. In addition, we summarize current therapeutic strategies for HBV infection via modulating innate immunity or inflammation. Characterizing the mechanisms that underlie these HBV-host interplays might provide new approaches for the cure of chronic HBV infection.

Innate metabolic responses against viral infections

Metabolic adaptation to viral infections critically determines the course and manifestations of disease. At the systemic level, a significant feature of viral infection and inflammation that ensues is the metabolic shift from anabolic towards catabolic metabolism. Systemic metabolic sequelae such as insulin resistance and dyslipidaemia represent long-term health consequences of many infections such as human immunodeficiency virus, hepatitis C virus and severe acute respiratory syndrome coronavirus 2. The long-held presumption that peripheral and tissue-specific 'immune responses' are the chief line of defence and thus regulate viral control is incomplete. This Review focuses on the emerging paradigm shift proposing that metabolic engagements and metabolic reconfiguration of immune and non-immune cells following virus recognition modulate the natural course of viral infections. Early metabolic footprints are likely to influence longer-term disease manifestations of infection. A greater appreciation and understanding of how local biochemical adjustments in the periphery and tissues influence immunity will ultimately lead to interventions that curtail disease progression and identify new and improved prognostic biomarkers.

Advances in Immunotherapy for Hepatitis B

Hepatitis B virus (HBV) is a hepatotropic virus with the potential to cause chronic infection, and it is one of the common causes of liver disease worldwide. Chronic HBV infection leads to liver cirrhosis and, ultimately, hepatocellular carcinoma (HCC). The persistence of covalently closed circular DNA (cccDNA) and the impaired immune response in patients with chronic hepatitis B (CHB) has been studied over the past few decades. Despite advances in the etiology of HBV and the development of potent virus-suppressing regimens, a cure for HBV has not been found. Both the innate and adaptive branches of immunity contribute to viral eradication. However, immune exhaustion and evasion have been demonstrated during CHB infection, although our understanding of the mechanism is still evolving. Recently, the successful use of an antiviral drug for hepatitis C has greatly encouraged the search for a cure for hepatitis B, which likely requires an approach focused on improving the antiviral immune response. In this review, we discuss our current knowledge of the immunopathogenic mechanisms and immunobiology of HBV infection. In addition, we touch upon why the existing therapeutic approaches may not achieve the goal of a functional cure. We also propose how combinations of new drugs, and especially novel immunotherapies, contribute to HBV clearance.

Emerging role of mitochondria in response to HBV infection

Hepatitis B is a major global health problem that potentially life‐threatening liver infection caused by the hepatitis B virus (HBV), which can lead to death due to liver cirrhosis and hepatocellular carcinoma (HCC). A considerable of research has demonstrated that mitochondrial dysfunction exists in patients with HBV infection, indicating that there is clinical relation between HBV infection and mitochondrial alterations. To explore the complex interplay between the functions of mitochondria and HBV infection in greater depth, we systematically summarized these mitochondrial alterations due to HBV infection in recent years. The liver is the central organ of metabolism that is a mitochondria‐rich tissue and represents strong defense and regeneration capabilities in the body. Infested cells and their microenvironment must upregulate energy production for proliferation, growth, and effector functions to restrain the damage imposed by HBV. The changes in metabolic pathways caused by HBV infection are nothing more than those in the cytoplasm and mitochondria. Thus, this article brings into focus the effects of novel reprogramming of inner and outer mitochondria on HBV infection and then derives novel insights and new approaches for HBV diagnosis and therapy.

Lactylation, an emerging hallmark of metabolic reprogramming: Current progress and open challenges

Lactate, the end product of glycolysis, efficiently functions as the carbon source, signaling molecules and immune regulators. Lactylation, being regulated by lactate, has recently been confirmed as a novel contributor to epigenetic landscape, not only opening a new era for in-depth exploration of lactate metabolism but also offering key breakpoints for further functional and mechanistic research. Several studies have identified the pivotal role of protein lactylation in cell fate determination, embryonic development, inflammation, cancer, and neuropsychiatric disorders. This review summarized recent advances with respect to the discovery, the derivation, the cross-species landscape, and the diverse functions of lactylation. Further, we thoroughly discussed the discrepancies and limitations in available studies, providing optimal perspectives for future research.

Mechanism of selenomethionine inhibiting of PDCoV replication in LLC-PK1 cells based on STAT3/miR-125b-5p-1/HK2 signaling

There are no licensed therapeutics or vaccines available against porcine delta coronavirus (PDCoV) to eliminate its potential for congenital disease. In the absence of effective treatments, it has led to significant economic losses in the swine industry worldwide. Similar to the current coronavirus disease 2019 (COVID-19) pandemic, PDCoV is trans-species transmissible and there is still a large desert for scientific exploration. We have reported that selenomethionine (SeMet) has potent antiviral activity against PDCoV. Here, we systematically investigated the endogenous immune mechanism of SeMet and found that STAT3/miR-125b-5p-1/HK2 signalling is essential for the exertion of SeMet anti-PDCoV replication function. Meanwhile, HK2, a key rate-limiting enzyme of the glycolytic pathway, was able to control PDCoV replication in LLC-PK1 cells, suggesting a strategy for viruses to evade innate immunity using glucose metabolism pathways. Overall, based on the ability of selenomethionine to control PDCoV infection and transmission, we provide a molecular basis for the development of new therapeutic approaches.

Safety and Immunogenicity of SARS-CoV-2 Vaccines in Patients With Chronic Liver Diseases (CHESS-NMCID 2101): A Multicenter Study

BACKGROUND & AIMS

We aimed to assess the safety and immunogenicity of inactivated whole-virion severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with chronic liver diseases (CLD) in this study.

METHODS

This was a prospective, multi-center, open-label study. Participants aged over 18 years with confirmed CLD and healthy volunteers were enrolled. All participants received 2 doses of inactivated whole-virion SARS-CoV-2 vaccines. Adverse reactions were recorded within 14 days after any dose of SARS-CoV-2 vaccine, laboratory testing results were collected after the second dose, and serum samples of enrolled subjects were collected and tested for SARS-CoV-2 neutralizing antibodies at least 14 days after the second dose.

RESULTS

A total of 581 participants (437 patients with CLD and 144 healthy volunteers) were enrolled from 15 sites in China. Most adverse reactions were mild and transient, and injection site pain (n = 36; 8.2%) was the most frequently reported adverse event. Three participants had grade 3 aminopherase elevation (defined as alanine aminopherase >5 upper limits of normal) after the second dose of inactivated whole-virion SARS-CoV-2 vaccination, and only 1 of them was judged as severe adverse event potentially related to SARS-CoV-2 vaccination. The positive rates of SARS-CoV-2 neutralizing antibodies were 76.8% in the noncirrhotic CLD group, 78.9% in the compensated cirrhotic group, 76.7% in the decompensated cirrhotic group (P = .894 among CLD subgroups), and 90.3% in healthy controls (P = .008 vs CLD group).

CONCLUSION

Inactivated whole-virion SARS-CoV-2 vaccines are safe in patients with CLD. Patients with CLD had lower immunologic response to SARS-CoV-2 vaccines than healthy population. The immunogenicity is similarly low in noncirrhotic CLD, compensated cirrhosis, and decompensated cirrhosis.

Singapore Grouper Iridovirus Induces Glucose Metabolism in Infected Cells by Activation of Mammalian Target of Rapamycin Signaling

Singapore grouper iridovirus (SGIV), a member of the Iridoviridae family, is an important marine cultured fish pathogen worldwide. Our previous studies have demonstrated that lipid metabolism was essential for SGIV entry and replication, but the roles of glucose metabolism during SGIV infection still remains largely unknown. In this study, we found that the transcription levels of key enzymes involved in glycolysis were regulated in varying degrees during SGIV infection based on the transcriptomic analysis. Quantitative PCR and western blot analysis also indicated that the expression of both glucose transporters (GLUT1 and GLUT2) and the enzymes of glucose metabolism (hexokinase 2, HK2 and pyruvate dehydrogenase complex, PDHX) were upregulated during SGIV infection in vivo or in vitro, suggesting that glycolysis might be involved in SGIV infection. Exogenous glucose supplementation promoted the expression of viral genes and infectious virion production, while glutamine had no effect on SGIV infection, indicating that glucose was required for SGIV replication. Consistently, pharmacological inhibition of glycolysis dramatically reduced the protein synthesis of SGIV major capsid protein (MCP) and infectious virion production, and promotion of glycolysis significantly increased SGIV infection. Furthermore, knockdown of HK2, PDHX, or GLUT1 by siRNA decreased the transcription and protein synthesis of SGIV MCP and suppressed viral replication, indicating that those enzymes exerted essential roles in SGIV replication. In addition, inhibition of mTOR activity in SGIV-infected cells effectively reduced the expression of glycolysis key enzymes, including HK2, PDHX, GLUT1, and GLUT2, and finally inhibited SGIV replication, suggesting that mTOR was involved in SGIV-induced glycolysis. Thus, our results not only provided new insights into the mechanism of how SGIV infection affects host cell glycolysis, but also contributed to further understanding of the iridovirus pathogenesis.

Metabolic Regulation of Hepatitis B Virus Infection in HBV-Transgenic Mice

Hepatitis B virus (HBV) infection is a worldwide health burden. Metabolomics analysis has revealed HBV-induced metabolism dysregulation in liver tissues and hepatocytes. However, as an infectious disease, the tissue-specific landscape of metabolic profiles of HBV infection remains unclear. To fill this gap, we applied untargeted nuclear magnetic resonance (NMR) metabolomic analysis of the heart, liver, spleen, lung, kidney, pancreas, and intestine (duodenum, jejunum, ileum) in HBV-transgenic mice and their wild-type littermates. Strikingly, we found systemic metabolic alterations induced by HBV in liver and extrahepatic organs. Significant changes in metabolites have been observed in most tissues of HBV-transgenic mice, except for ileum. The metabolic changes may provide novel therapeutic targets for the treatment of HBV infection. Moreover, tissue-specific metabolic profiles could speed up the study of HBV induced systemic metabolic reprogramming, which could help follow the progression of HBV infection and explain the underlying pathogenesis.

RIG-I Promotes Cell Viability, Colony Formation, and Glucose Metabolism and Inhibits Cell Apoptosis in Colorectal Cancer by NF-κB Signaling Pathway

Background

Retinoic acid-inducible gene-I (RIG-I) has crucial effects on various cancers, while RIG-I's detailed roles and mechanism in colorectal cancer (CRC) are uncovered.

Methods

qRT-PCR was used to detect the expression of RIG-I in CRC, adjacent nontumor specimens, and five cell lines. CCK-8, colony formation, and flow cytometry assays were conducted to study CRC cell viabilities. Extracellular acidification rates, lactate analysis, and ATP analysis were conducted to study the cell viabilities and glucose metabolism of CRC cells. Western blot is used to determine the proteins of NF-κBp65 in the nucleus and cytoplasm.

Results

This study revealed the upregulation of RIG-I in CRC tissues and cells and that high RIG-I expression was correlated with poor prognosis of CRC patients. In addition, silencing RIG-I inhibited cell viability as well as colony formation and promoted cell apoptosis in CRC cells, while RIG-I knockdown suppressed transplanted tumor growth and facilitated apoptosis in nude mice. Moreover, silencing RIG-I inhibited glucose metabolism by decreasing extracellular acidification rate, lactate production, adenosine triphosphate, and content of hypoxia-inducible factor 1α and pyruvate kinase isoform. 2.2-Deoxy-d-glucose, a glycolysis inhibitor, reduced the growth of CRC cells and promoted apoptosis in vitro and in vivo. In addition, RIG-I knockdown decreased NF-κB nuclear translocation. Besides, inhibiting NF-κB effectively eliminated RIG-I overexpression roles in cell viability and glucose metabolism in CRC cells.

Conclusion

In summary, this study revealed that RIG-I mediated CRC cell proliferation, apoptosis, and glucose metabolism at least partly by NF-κB signaling pathway.

Ca2+/Calmodulin-Dependent Protein Kinase II Inhibits Hepatitis B Virus Replication from cccDNA via AMPK Activation and AKT/mTOR Suppression

Ca2+/calmodulin-dependent protein kinase II (CaMKII), which is involved in the calcium signaling pathway, is an important regulator of cancer cell proliferation, motility, growth, and metastasis. The effects of CaMKII on hepatitis B virus (HBV) replication have never been evaluated. Here, we found that phosphorylated, active CaMKII is reduced during HBV replication. Similar to other members of the AMPK/AKT/mTOR signaling pathway associated with HBV replication, CaMKII, which is associated with this pathway, was found to be a novel regulator of HBV replication. Overexpression of CaMKII reduced the expression of covalently closed circular DNA (cccDNA), HBV RNAs, and replicative intermediate (RI) DNAs while activating AMPK and inhibiting the AKT/mTOR signaling pathway. Findings in HBx-deficient mutant-transfected HepG2 cells showed that the CaMKII-mediated AMPK/AKT/mTOR signaling pathway was independent of HBx. Moreover, AMPK overexpression reduced HBV cccDNA, RNAs, and RI DNAs through CaMKII activation. Although AMPK acts downstream of CaMKII, AMPK overexpression altered CaMKII phosphorylation, suggesting that CaMKII and AMPK form a positive feedback loop. These results demonstrate that HBV replication suppresses CaMKII activity, and that CaMKII upregulation suppresses HBV replication from cccDNA via AMPK and the AKT/mTOR signaling pathway. Thus, activation or overexpression of CaMKII may be a new therapeutic target against HBV infection.

Novel Molecular Therapeutics Targeting Signaling Pathway to Control Hepatitis B Viral Infection

Numerous canonical cellular signaling pathways modulate hepatitis B virus (HBV) replication. HBV genome products are known to play a significant role in regulating these cellular pathways for the liver’s viral-related pathology and physiology and have been identified as the main factor in hepatocarcinogenesis. Signaling changes during viral replication ultimately affect cellular persistence, multiplication, migration, genome instability, and genome damage, leading to proliferation, evasion of apoptosis, block of differentiation, and immortality. Recent studies have documented that numerous signaling pathway agonists or inhibitors play an important role in reducing HBV replication in vitro and in vivo, and some have been used in phase I or phase II clinical trials. These optional agents as molecular therapeutics target cellular pathways that could limit the replication and transcription of HBV or inhibit the secretion of the small surface antigen of HBV in a signaling-independent manner. As principle-based available information, a combined strategy including antiviral therapy and immunomodulation will be needed to control HBV infection effectively. In this review, we summarize recent findings on interventions of molecular regulators in viral replication and the interactions of HBV proteins with the components of the various targeting cellular pathways, which may assist in designing novel agents to modulate signaling pathways to prevent HBV replication or carcinogenesis.

Interferon Alpha Induces Cellular Autophagy and Modulates Hepatitis B Virus Replication

Hepatitis B virus (HBV) infection causes acute and chronic liver diseases, including severe hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). Interferon alpha 2a (IFNα-2a) is commonly used for treating chronic HBV infection. However, its efficacy remains relatively low. Yet, the immunological and molecular mechanisms for successful IFNα-2a treatment remain elusive. One issue is whether the application of increasing IFNα doses may modulate cellular processes and HBV replication in hepatic cells. In the present study, we focused on the interaction of IFNα signaling with other cellular signaling pathways and the consequence for HBV replication. The results showed that with the concentration of 6000 U/ml IFNα-2a treatment downregulated the activity of not only the Akt/mTOR signaling but also the AMPK signaling. Additionally, IFNα-2a treatment increased the formation of the autophagosomes by blocking autophagic degradation. Furthermore, IFNα-2a treatment inhibited the Akt/mTOR signaling and initiated autophagy under low and high glucose concentrations. In reverse, inhibition of autophagy using 3-methyladenine (3-MA) and glucose concentrations influenced the expression of IFNα-2a-induced ISG15 and IFITM1. Despite of ISGs induction, HBV replication and gene expression in HepG2.2.15 cells, a cell model with continuous HBV replication, were slightly increased at high doses of IFNα-2a. In conclusion, our study indicates that IFNα-2a treatment may interfere with multiple intracellular signaling pathways, facilitate autophagy initiation, and block autophagic degradation, thereby resulting in slightly enhanced HBV replication.

Carbohydrates Metabolic Signatures in Immune Cells: Response to Infection

INTRODUCTION

Metabolic reprogramming in immune cells is diverse and distinctive in terms of complexity and flexibility in response to heterogeneous pathogenic stimuli. We studied the carbohydrate metabolic changes in immune cells in different types of infectious diseases. This could help build reasonable strategies when understanding the diagnostics, prognostics, and biological relevance of immune cells under alternative metabolic burdens.

METHODS

Search and analysis were conducted on published peer-reviewed papers on immune cell metabolism of a single pathogen infection from the four known types (bacteria, fungi, parasites, and viruses). Out of the 131 selected papers based on the PIC algorithm (pathogen type/immune cell/carbohydrate metabolism), 30 explored immune cell metabolic changes in well-studied bacterial infections, 17 were on fungal infections of known medical importance, and 12 and 57 were on parasitic and viral infections, respectively.

RESULTS AND DISCUSSION

While carbohydrate metabolism in immune cells is signaled by glycolytic shift during a bacterial or viral infection, it is widely evident that effector surface proteins are expressed on the surface of parasites and fungi to modulate metabolism in these cells.

CONCLUSIONS

Carbohydrate metabolism in immune cells can be categorized according to the pathogen or the disease type. Accordingly, this classification can be used to adopt new strategies in disease diagnosis and treatment.

African swine fever virus regulates host energy and amino acid metabolism to promote viral replication

African swine fever is one of the most serious viral diseases caused by African swine fever virus (ASFV). The metabolic changes induced by ASFV infection remain unknown. Here, PAMs infected with ASFV was analyzed by ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) in combination with multivariate statistical analysis. A total of 90 metabolites were significantly changed after ASFV infection, and most of them belong to amino acids and TCA cycle intermediates. ASFV infection induced increase of most of amino acids in host during the early stages of infection, and amino acids decreased in the late stages of infection. ASFV infection did not significantly affected glycolysis pathway, whereas it induced the increase of citrate, succinate, α-ketoglutarate, and oxaloacetate levels in the TCA cycle, suggesting that ASFV infection promoted TCA cycle. The activity of aspartate aminotransferase and glutamate production were significantly elevated in ASFV-infected cells and pigs, resulting in reversible transition between TCA cycle and amino acids synthesis. Aspartate, glutamate, and TCA cycle were essential for ASFV replication. In addition, ASFV infection induced an increase in lactate level using lactate dehydrogenase, which led to low expression of IFN-β and increased of ASFV replication. Our data, for the first time, indicated that ASFV infection controls IFN-β production through RIG-I-mediated signaling pathways. These data identified a novel mechanism evolved by ASFV to inhibit host innate immune responses, and will provide insights for development of new preventive or therapeutic strategies targeting the altered metabolic pathways. IMPORTANCE In order to promote viral replication, viruses often cause severe immunosuppression and seize organelles to synthesize a large number of metabolites required for self-replication. African swine fever virus (ASFV) has developed many strategies to evade host innate immune responses. However, the impact of ASFV infection on host cellular metabolism remains unknown. Here, for the first time, we analyzed the metabolomic profiles of ASFV-infected PAMs cells. ASFV infection increased host TCA cycle and amino acids metabolism. Aspartate, glutamate, and TCA cycle promoted ASFV replication. ASFV infection also induced the increase of lactate production to inhibit innate immune responses for self-replication. This study identified novel immune evasion mechanisms utilized by ASFV and provided viewpoints on ASFV-host interactions, which is critical for guiding the design of new prevention strategies against ASFV targeting the altered metabolic pathways.

The Triangle Relationship Between Long Noncoding RNA, RIG-I-like Receptor Signaling Pathway, and Glycolysis

Long noncoding RNA (LncRNA), a noncoding RNA over 200nt in length, can regulate glycolysis through metabolic pathways, glucose metabolizing enzymes, and epigenetic reprogramming. Upon viral infection, increased aerobic glycolysis providzes material and energy for viral replication. Mitochondrial antiviral signaling protein (MAVS) is the only protein-specified downstream of retinoic acid-inducible gene I (RIG-I) that bridges the gap between antiviral immunity and glycolysis. MAVS binding to RIG-I inhibits MAVS binding to Hexokinase (HK2), thereby impairing glycolysis, while excess lactate production inhibits MAVS and the downstream antiviral immune response, facilitating viral replication. LncRNAs can also regulate antiviral innate immunity by interacting with RIG-I and downstream signaling pathways and by regulating the expression of interferons and interferon-stimulated genes (ISGs). Altogether, we summarize the relationship between glycolysis, antiviral immunity, and lncRNAs and propose that lncRNAs interact with glycolysis and antiviral pathways, providing a new perspective for the future treatment against virus infection, including SARS-CoV-2.

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.

Influenza A induces lactate formation to inhibit type I IFN in primary human airway epithelium

Pathogenic viruses induce metabolic changes in host cells to secure the availability of biomolecules and energy to propagate. Influenza A virus (IAV) and severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) both infect the human airway epithelium and are important human pathogens. The metabolic changes induced by these viruses in a physiologically relevant human model and how this affects innate immune responses to limit viral propagation are not well known. Using an ex vivo model of pseudostratified primary human airway epithelium, we here demonstrate that infection with both IAV and SARS-CoV-2 resulted in distinct metabolic changes including increases in lactate dehydrogenase A (LDHA) expression and LDHA-mediated lactate formation. Interestingly, LDHA regulated both basal and induced mitochondrial anti-viral signaling protein (MAVS)-dependent type I interferon (IFN) responses to promote IAV, but not SARS-CoV-2, replication. Our data demonstrate that LDHA and lactate promote IAV but not SARS-CoV-2 replication by inhibiting MAVS-dependent induction of type I IFN in primary human airway epithelium.

Toll-Like Receptor Response to Hepatitis B Virus Infection and Potential of TLR Agonists as Immunomodulators for Treating Chronic Hepatitis B: An Overview

Chronic hepatitis B virus (HBV) infection remains a major global health problem. The immunopathology of the disease, especially the interplay between HBV and host innate immunity, is poorly understood. Moreover, inconsistent literature on HBV and host innate immunity has led to controversies. However, recently, there has been an increase in the number of studies that have highlighted the link between innate immune responses, including Toll-like receptors (TLRs), and chronic HBV infection. TLRs are the key sensing molecules that detect pathogen-associated molecular patterns and regulate the induction of pro- and anti-inflammatory cytokines, thereby shaping the adaptive immunity. The suppression of TLR response has been reported in patients with chronic hepatitis B (CHB), as well as in other models, including tree shrews, suggesting an association of TLR response in HBV chronicity. Additionally, TLR agonists have been reported to improve the host innate immune response against HBV infection, highlighting the potential of these agonists as immunomodulators for enhancing CHB treatment. In this study, we discuss the current understanding of host innate immune responses during HBV infection, particularly focusing on the TLR response and TLR agonists as immunomodulators.

Interferon and Hepatitis B: Current and Future Perspectives

Chronic hepatitis B virus (HBV) infection remains a major health burden worldwide for which there is still no effective curative treatment. Interferon (IFN) consists of a group of cytokines with antiviral activity and immunoregulatory and antitumor effects, that play crucial roles in both innate and adaptive immune responses. IFN-α and its pegylated form have been used for over thirty years to treat chronic hepatitis B (CHB) with advantages of finite treatment duration and sustained virologic response, however, the efficacy is limited and side effects are common. Here, we summarize the status and unique advantages of IFN therapy against CHB, review the mechanisms of IFN-α action and factors affecting IFN response, and discuss the possible improvement of IFN-based therapy and the rationale of combinations with other antiviral agents in seeking an HBV cure.

MAVS: A Two-Sided CARD Mediating Antiviral Innate Immune Signaling and Regulating Immune Homeostasis

Mitochondrial antiviral signaling protein (MAVS) functions as a "switch" in the immune signal transduction against most RNA viruses. Upon viral infection, MAVS forms prion-like aggregates by receiving the cytosolic RNA sensor retinoic acid-inducible gene I-activated signaling and further activates/switches on the type I interferon signaling. While under resting state, MAVS is prevented from spontaneously aggregating to switch off the signal transduction and maintain immune homeostasis. Due to the dual role in antiviral signal transduction and immune homeostasis, MAVS has emerged as the central regulation target by both viruses and hosts. Recently, researchers show increasing interest in viral evasion strategies and immune homeostasis regulations targeting MAVS, especially focusing on the post-translational modifications of MAVS, such as ubiquitination and phosphorylation. This review summarizes the regulations of MAVS in antiviral innate immune signaling transduction and immune homeostasis maintenance.

Effects of lactate in immunosuppression and inflammation: Progress and prospects

Lactate used to be considered as a waste product of glucose metabolism. However, accumulating evidence has revealed its crucial role in regulating various biological and pathological processes. Hypoxia, inflammation, viral infection, and tumor promote the production of lactate. Then lactate activates G protein-coupled receptor 81 (GPR81) or shuttles across membranes by monocarboxylate-transporters (MCTs) to execute its intricate effects. Many studies highlighted the function of lactate in regulating dendritic cells, monocytes, natural killer cells, mast cells, T cells, tumor cells, fibroblasts, macrophages polarization, and the differentiation of Th1, Th17, MDSCs, Tregs; all of which play a role in maintaining the immune homeostasis of the host when challenged with the noxious stimuli. In this review, we summarized the influence of lactate in diverse tissue-specific cells, and discuss their effects on viral infection, acute inflammation, chronic inflammation, sepsis, and tumor immunosuppression. The goal of this review is to expose that lactate has a double-edged effect on host immunity and accompanying inflammatory reactions, which could be a potentially effective target for treating the tumor and multiple infectious diseases.

The Mechanisms of HBV-Induced Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy, and the hepatitis B virus (HBV) is its major pathogenic factor. Over the past decades, it has been confirmed that HBV infection could promote disease progression through a variety of mechanisms, ultimately leading to the malignant transformation of liver cells. Many factors have been identified in the pathogenesis of HBV-associated HCC (HBV-HCC), including HBV gene integration, genomic instability caused by mutation, and activation of cancer-promoting signaling pathways. As research in the progression of HBV-HCC progresses, the role of many new mechanisms, such as epigenetics, exosomes, autophagy, metabolic regulation, and immune suppression, is also being continuously explored. The occurrence of HBV-HCC is a complex process caused by interactions across multiple genes and multiple steps, where the synergistic effects of various cancer-promoting mechanisms accelerate the process of disease evolution from inflammation to tumorigenesis. In this review, we aim to provide a brief overview of the mechanisms involved in the occurrence and development of HBV-HCC, which may contribute to a better understanding of the role of HBV in the occurrence and development of HCC.

Innate immunity and HBV persistence

Hepatitis B virus (HBV) causes chronic infections that are associated with immune dysfunction. Though T cell impairment is perhaps the most prominent immune change contributing to viral persistence, HBV interaction with the innate immune system is also likely key, as the lack of effective innate immunity has functional consequences that promote chronic infection. In addition to an intrinsic ability to fight viral infections, the innate immune system also impacts T cell responses and other adaptive immune mechanisms critical for HBV control. Therefore, it is essential to understand the relationships between HBV and innate immunity, as these interactions may be useful immunotherapeutic targets to manage the infection.

Viral Infection Modulates Mitochondrial Function

Mitochondria are important organelles involved in metabolism and programmed cell death in eukaryotic cells. In addition, mitochondria are also closely related to the innate immunity of host cells against viruses. The abnormality of mitochondrial morphology and function might lead to a variety of diseases. A large number of studies have found that a variety of viral infections could change mitochondrial dynamics, mediate mitochondria-induced cell death, and alter the mitochondrial metabolic status and cellular innate immune response to maintain intracellular survival. Meanwhile, mitochondria can also play an antiviral role during viral infection, thereby protecting the host. Therefore, mitochondria play an important role in the interaction between the host and the virus. Herein, we summarize how viral infections affect microbial pathogenesis by altering mitochondrial morphology and function and how viruses escape the host immune response.

Cellular Metabolites Regulate Central Nucleic Acid Sensing Pathways

Detection of pathogen-derived DNA or RNA species by cellular nucleic acid sensors prompts release of anti-microbial interferons and cytokines. In contrast to their protective anti-microbial functions, inappropriate or excessive activation of nucleic acid sensors can cause inflammatory diseases. Nucleic acid sensing is therefore tightly controlled by regulatory factors acting through both transcriptional and post-transcriptional mechanisms. Recently, it has become clearer that metabolic pathways-previously thought to be unconnected with immune responses-can influence nucleic acid sensing. This regulation can be observed when immune system cells undergo metabolic reprogramming in response to stimulation with pathogen-associated molecular patterns such as lipopolysaccharide from gram negative bacteria. Metabolic reprogramming leads to accumulation and secretion of metabolites, which have been mostly viewed as end-products of processes providing cellular energy and building blocks. However, metabolites have now been identified as important regulators of nucleic acid sensing. This mini-review aims to outline current knowledge on regulation of central nucleic acid sensing pathways by metabolites during metabolic reprogramming.

Metabolism and Innate Immunity Meet at the Mitochondria

Mitochondria are master regulators of metabolism and have emerged as key signalling organelles of the innate immune system. Each mitochondrion harbours potent agonists of inflammation, including mitochondrial DNA (mtDNA), which are normally shielded from the rest of the cell and extracellular environment and therefore do not elicit detrimental inflammatory cascades. Mitochondrial damage and dysfunction can lead to the cytosolic and extracellular exposure of mtDNA, which triggers inflammation in a number of diseases including autoimmune neurodegenerative disorders. However, recent research has revealed that the extra-mitochondrial exposure of mtDNA is not solely a negative consequence of mitochondrial damage and pointed to an active role of mitochondria in innate immunity. Metabolic cues including nucleotide imbalance can stimulate the release of mtDNA from mitochondria in order to drive a type I interferon response. Moreover, important effectors of the innate immune response to pathogen infection, such as the mitochondrial antiviral signalling protein (MAVS), are located at the mitochondrial surface and modulated by the cellular metabolic status and mitochondrial dynamics. In this review, we explore how and why metabolism and innate immunity converge at the mitochondria and describe how mitochondria orchestrate innate immune signalling pathways in different metabolic scenarios. Understanding how cellular metabolism and metabolic programming of mitochondria are translated into innate immune responses bears relevance to a broad range of human diseases including cancer.