MAVS Coordination of Antiviral Innate Immunity

Usutu virus NS4A suppresses the host interferon response by disrupting MAVS signaling

Usutu virus (USUV) is an emerging flavivirus that can infect birds and mammals. In humans, in severe cases, it may cause neuroinvasive disease. The innate immune system, and in particular the interferon response, functions as the important first line of defense against invading pathogens such as USUV. Many, if not all, viruses have developed mechanisms to suppress and/or evade the interferon response in order to facilitate their replication. The ability of USUV to antagonize the interferon response has so far remained largely unexplored. Using dual-luciferase reporter assays we observed that multiple of the USUV nonstructural (NS) proteins were involved in suppressing IFN-β production and signaling. In particular NS4A was very effective at suppressing IFN-β production. We found that NS4A interacted with the mitochondrial antiviral signaling protein (MAVS) and thereby blocked its interaction with melanoma differentiation-associated protein 5 (MDA5), resulting in reduced IFN-β production. The TM1 domain of NS4A was found to be essential for binding to MAVS. By screening a panel of flavivirus NS4A proteins we found that the interaction of NS4A with MAVS is conserved among flaviviruses. The increased understanding of the role of NS4A in flavivirus immune evasion could aid the development of vaccines and therapeutic strategies.

Insights into membrane interactions and their therapeutic potential

Recent research into membrane interactions has uncovered a diverse range of therapeutic opportunities through the bioengineering of human and non-human macromolecules. Although the majority of this research is focussed on fundamental developments, emerging studies are showcasing promising new technologies to combat conditions such as cancer, Alzheimer's and inflammatory and immune-based disease, utilising the alteration of bacteriophage, adenovirus, bacterial toxins, type 6 secretion systems, annexins, mitochondrial antiviral signalling proteins and bacterial nano-syringes. To advance the field further, each of these opportunities need to be better understood, and the therapeutic models need to be further optimised. Here, we summarise the knowledge and insights into several membrane interactions and detail their current and potential uses therapeutically.

PI3K/AKT mediated De novo fatty acid synthesis regulates RIG-1/MDA-5-dependent type I IFN responses in BVDV-infected CD8+T cells

Bovine viral diarrhea virus (BVDV) has caused massive economic losses in the cattle business worldwide. Fatty acid synthase (FASN), a key enzyme of the fatty acid synthesis (FAS) pathway, has been shown to support virus replication. To investigate the role of fatty acids (FAs) in BVDV infection, we infected CD8+T lymphocytes obtained from healthy cattle with BVDV in vitro. During early cytopathic (CP) and noncytopathic (NCP) BVDV infection in CD8+ T cells, there is an increase in de novo lipid biosynthesis, resulting in elevated levels of free fatty acids (FFAs) and triglycerides (TG). BVDV infection promotes de novo lipid biosynthesis in a dose-dependent manner. Treatment with the FASN inhibitor C75 significantly reduces the phosphorylation of PI3K and AKT in BVDV-infected CD8+ T cells, while inhibition of PI3K with LY294002 decreases FASN expression. Both CP and NCP BVDV strains promote de novo fatty acid synthesis by activating the PI3K/AKT pathway. Further investigation shows that pharmacological inhibitors targeting FASN and PI3K concurrently reduce FFAs, TG levels, and ATP production, effectively inhibiting BVDV replication. Conversely, the in vitro supplementation of oleic acid (OA) to replace fatty acids successfully restored BVDV replication, underscoring the impact of abnormal de novo fatty acid metabolism on BVDV replication. Intriguingly, during BVDV infection of CD8+T cells, the use of FASN inhibitors prompted the production of IFN-α and IFN-β, as well as the expression of interferon-stimulated genes (ISGs). Moreover, FASN inhibitors induce TBK-1 phosphorylation through the activation of RIG-1 and MDA-5, subsequently activating IRF-3 and ultimately enhancing the IFN-1 response. In conclusion, our study demonstrates that BVDV infection activates the PI3K/AKT pathway to boost de novo fatty acid synthesis, and inhibition of FASN suppresses BVDV replication by activating the RIG-1/MDA-5-dependent IFN response.

Prior Influenza Infection Mitigates SARS-CoV-2 Disease in Syrian Hamsters

Seasonal infection rates of individual viruses are influenced by synergistic or inhibitory interactions between coincident viruses. Endemic patterns of SARS-CoV-2 and influenza infection overlap seasonally in the Northern hemisphere and may be similarly influenced. We explored the immunopathologic basis of SARS-CoV-2 and influenza A (H1N1pdm09) interactions in Syrian hamsters. H1N1 given 48 h prior to SARS-CoV-2 profoundly mitigated weight loss and lung pathology compared to SARS-CoV-2 infection alone. This was accompanied by the normalization of granulocyte dynamics and accelerated antigen-presenting populations in bronchoalveolar lavage and blood. Using nasal transcriptomics, we identified a rapid upregulation of innate and antiviral pathways induced by H1N1 by the time of SARS-CoV-2 inoculation in 48 h dual-infected animals. The animals that were infected with both viruses also showed a notable and temporary downregulation of mitochondrial and viral replication pathways. Quantitative RT-PCR confirmed a decrease in the SARS-CoV-2 viral load and lower cytokine levels in the lungs of animals infected with both viruses throughout the course of the disease. Our data confirm that H1N1 infection induces rapid and transient gene expression that is associated with the mitigation of SARS-CoV-2 pulmonary disease. These protective responses are likely to begin in the upper respiratory tract shortly after infection. On a population level, interaction between these two viruses may influence their relative seasonal infection rates.

RNF5: inhibiting antiviral immunity and shaping virus life cycle

RNF5 is an E3 ubiquitin ligase involved in various physiological processes such as protein localization and cancer progression. Recent studies have shown that RNF5 significantly inhibits antiviral innate immunity by promoting the ubiquitination and degradation of STING and MAVS, which are essential adaptor proteins, as well as their downstream signal IRF3. The abundance of RNF5 is delicately regulated by both host factors and viruses. Host factors have been found to restrict RNF5-mediated ubiquitination, maintaining the stability of STING or MAVS through distinct mechanisms. Meanwhile, viruses have developed ingenious strategies to hijack RNF5 to ubiquitinate and degrade immune proteins. Moreover, recent studies have revealed the multifaceted roles of RNF5 in the life cycle of various viruses, including SARS-CoV-2 and KSHV. Based on these emerging discoveries, RNF5 represents a novel means of modulating antiviral immunity. In this review, we summarize the latest research on the roles of RNF5 in antiviral immunity and virus life cycle. This comprehensive understanding could offer valuable insights into exploring potential therapeutic applications focused on targeting RNF5 during viral infections.

Mitochondrial Dysfunction and Coenzyme Q10 Supplementation in Post-Viral Fatigue Syndrome: An Overview

Post-viral fatigue syndrome (PVFS) encompasses a wide range of complex neuroimmune disorders of unknown causes characterised by disabling post-exertional fatigue, myalgia and joint pain, cognitive impairments, unrefreshing sleep, autonomic dysfunction, and neuropsychiatric symptoms. It includes myalgic encephalomyelitis, also known as chronic fatigue syndrome (ME/CFS); fibromyalgia (FM); and more recently post-COVID-19 condition (long COVID). To date, there are no definitive clinical case criteria and no FDA-approved pharmacological therapies for PVFS. Given the current lack of effective treatments, there is a need to develop novel therapeutic strategies for these disorders. Mitochondria, the cellular organelles responsible for tissue energy production, have recently garnered attention in research into PVFS due to their crucial role in cellular bioenergetic metabolism in these conditions. The accumulating literature has identified a link between mitochondrial dysfunction and low-grade systemic inflammation in ME/CFS, FM, and long COVID. To address this issue, this article aims to critically review the evidence relating to mitochondrial dysfunction in the pathogenesis of these disorders; in particular, it aims to evaluate the effectiveness of coenzyme Q10 supplementation on chronic fatigue and pain symptoms as a novel therapeutic strategy for the treatment of PVFS.

Mitochondrial Reactive Oxygen Species in TRIF-Dependent Toll-like Receptor 3 Signaling in Bronchial Epithelial Cells against Viral Infection

Toll-like receptor 3 (TLR3) plays an important role in double-stranded RNA recognition and triggers the innate immune response by acting as a key receptor against viral infections. Intracellular reactive oxygen species (ROS) are involved in TLR3-induced inflammatory responses during viral infections; however, their relationship with mitochondrial ROS (mtROS) remains largely unknown. In this study, we show that polyinosinic-polycytidylic acid (poly(I:C)), a mimic of viral RNA, induced TLR3-mediated nuclear factor-kappa B (NF-κB) signaling pathway activation and enhanced mtROS generation, leading to inflammatory cytokine production. TLR3-targeted small interfering RNA (siRNA) and Mito-TEMPO inhibited inflammatory cytokine production in poly(I:C)-treated BEAS-2B cells. Poly(I:C) recruited the TLR3 adaptor molecule Toll/IL-1R domain-containing adaptor, inducing IFN (TRIF) and activated NF-κB signaling. Additionally, TLR3-induced mtROS generation suppression and siRNA-mediated TRIF downregulation attenuated mitochondrial antiviral signaling protein (MAVS) degradation. Our findings provide insights into the TLR3-TRIF signaling pathway and MAVS in viral infections, and suggest TLR3-mtROS as a therapeutic target for the treatment of airway inflammatory and viral infectious diseases.

3β-hydroxysteroid-Δ24 reductase dampens anti-viral innate immune responses by targeting K27 ubiquitination of MAVS and STING

IMPORTANCE

The precise regulation of the innate immune response is essential for the maintenance of homeostasis. MAVS and STING play key roles in immune signaling pathways activated by RNA and DNA viruses, respectively. Here, we showed that DHCR24 impaired the antiviral response by targeting MAVS and STING. Notably, DHCR24 interacts with MAVS and STING and inhibits TRIM21-triggered K27-linked ubiquitination of MAVS and AMFR-triggered K27-linked ubiquitination of STING, restraining the activation of MAVS and STING, respectively. Together, this study elucidates how one cholesterol key enzyme orchestrates two antiviral signal transduction pathways.

The crucial regulatory role of type I interferon in inflammatory diseases

Type I interferon (IFN-I) plays crucial roles in the regulation of inflammation and it is associated with various inflammatory diseases including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and periodontitis, impacting people's health and quality of life. It is well-established that IFN-Is affect immune responses and inflammatory factors by regulating some signaling. However, currently, there is no comprehensive overview of the crucial regulatory role of IFN-I in distinctive pathways as well as associated inflammatory diseases. This review aims to provide a narrative of the involvement of IFN-I in different signaling pathways, mainly mediating the related key factors with specific targets in the pathways and signaling cascades to influence the progression of inflammatory diseases. As such, we suggested that IFN-Is induce inflammatory regulation through the stimulation of certain factors in signaling pathways, which displays possible efficient treatment methods and provides a reference for the precise control of inflammatory diseases.

Suppression of Innate Immunity by the Hepatitis C Virus (HCV): Revisiting the Specificity of Host-Virus Interactive Pathways

The hepatitis C virus (HCV) is a major causative agent of hepatitis that may also lead to liver cancer and lymphomas. Chronic hepatitis C affects an estimated 2.4 million people in the USA alone. As the sole member of the genus Hepacivirus within the Flaviviridae family, HCV encodes a single-stranded positive-sense RNA genome that is translated into a single large polypeptide, which is then proteolytically processed to yield the individual viral proteins, all of which are necessary for optimal viral infection. However, cellular innate immunity, such as type-I interferon (IFN), promptly thwarts the replication of viruses and other pathogens, which forms the basis of the use of conjugated IFN-alpha in chronic hepatitis C management. As a countermeasure, HCV suppresses this form of immunity by enlisting diverse gene products, such as HCV protease(s), whose primary role is to process the large viral polyprotein into individual proteins of specific function. The exact number of HCV immune suppressors and the specificity and molecular mechanism of their action have remained unclear. Nonetheless, the evasion of host immunity promotes HCV pathogenesis, chronic infection, and carcinogenesis. Here, the known and putative HCV-encoded suppressors of innate immunity have been reviewed and analyzed, with a predominant emphasis on the molecular mechanisms. Clinically, the knowledge should aid in rational interventions and the management of HCV infection, particularly in chronic hepatitis.

Immune escape of bovine parvovirus by VP1 inhibiting IFN-β production through the RIG-I-like receptor pathway

OBJECTIVE

The present study aimed to explore if bovine parvovirus (BPV) impacts beta interferon (IFN-β) production and to reveal further molecular mechanism of BPV immune escape.

METHOD

The pCMV-Myc-BPV-VP1 recombinant plasmid was verified with both double-enzyme digestion and sequence. HEK 293 T cells were transfected with this recombinant protein and then infected with the vesicular stomatitis virus (VSV). Expression levels of IFN-β mRNA were detected using qPCR.

RESULTS

The expression level of BPV VP1 mRNA in the pCMV-Myc-BPV-VP1 group was significantly higher than those of the untreated group (UT) and pCMV-Myc vector group. BPV virus copies in bovine turbinate (BT) cells of the BPV-VP1 group were raised (P < 0.05) with an increment of 5.8 × 104. Expression levels of IFN-β mRNA of the BPV VP1 group in HEK 293 T cells were decreased (P < 0.01). Following treatment of TBK1 and IRF3(5D), IFN-β expression levels in HEK 293 T cells were depressed. Additionally, expression levels of TBK1, IRF3(5D), MDA5, and MAVS were less than those of the flag empty vector, respectively.

CONCLUSION

pCMV-Myc-BPV-VP1 could heighten transcription levels of VP1 protein in BT cells, promote BPV proliferation, and ascend the production of IFN-β. Overexpression of pCMV-Myc-BPV-VP decreased IFN-β mRNA expression in HEK 293 T cells and inhibited IFN-β production induced by TBK1 and IRF3(5D). Furthermore, BPV VP1 obviously declined expression levels of TBK1, IRF3(5D), MDA5, and MAVS in the RIG-I-like receptor (RLR) pathway. Our findings revealed a novel mechanism evolved by BPV VP1 to inhibit type I IFN production and provided a solid scientific basis into the immunosuppression of BPV.

Mitochondrial antiviral signaling protein: a potential therapeutic target in renal disease

Mitochondrial antiviral signaling protein (MAVS) is a key innate immune adaptor on the outer mitochondrial membrane that acts as a switch in the immune signal transduction response to viral infections. Some studies have reported that MAVS mediates NF-κB and type I interferon signaling during viral infection and is also required for optimal NLRP3 inflammasome activity. Recent studies have reported that MAVS is involved in various cancers, systemic lupus erythematosus, kidney diseases, and cardiovascular diseases. Herein, we summarize the structure, activation, pathophysiological roles, and MAVS-based therapies for renal diseases. This review provides novel insights into MAVS's role and therapeutic potential in the pathogenesis of renal diseases.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

CELLULAR RNA INTERACTS WITH MAVS TO PROMOTE ANTIVIRAL SIGNALING

Immune signaling needs to be well-regulated to promote clearance of pathogens, while preventing aberrant inflammation. Interferons (IFNs) and antiviral genes are activated by the detection of viral RNA by RIG-I-like receptors (RLRs). Signal transduction downstream of RLRs proceeds through a multi-protein complex organized around the central adaptor protein MAVS. Recent work has shown that protein complex function can be modulated by RNA molecules providing allosteric regulation or acting as molecular guides or scaffolds. Thus, we hypothesized that RNA plays a role in organizing MAVS signaling platforms. Here, we show that MAVS, through its central intrinsically disordered domain, directly interacts with the 3' untranslated regions of cellular mRNAs. Importantly, elimination of RNA by RNase treatment disrupts the MAVS signalosome, including newly identified regulators of RLR signaling, and inhibits phosphorylation of the transcription factor IRF3. This supports the hypothesis that RNA molecules scaffold proteins in the MAVS signalosome to induce IFNs. Together, this work uncovers a function for cellular RNA in promoting signaling through MAVS and highlights a generalizable principle of RNA regulatory control of cytoplasmic immune signaling complexes.

Overexpression of the mitochondrial anti-viral signaling protein, MAVS, in cancers is associated with cell survival and inflammation

Mitochondrial anti-viral signaling protein (MAVS) plays an important role in host defense against viral infection via coordinating the activation of NF-κB and interferon regulatory factors. The mitochondrial-bound form of MAVS is essential for its anti-viral innate immunity. Recently, tumor cells were proposed to mimic a viral infection by activating RNA-sensing pattern recognition receptors. Here, we demonstrate that MAVS is overexpressed in a panel of viral non-infected cancer cell lines and patient-derived tumors, including lung, liver, bladder, and cervical cancers, and we studied its role in cancer. Silencing MAVS expression reduced cell proliferation and the expression and nuclear translocation of proteins associated with transcriptional regulation, inflammation, and immunity. MAVS depletion reduced expression of the inflammasome components and inhibited its activation/assembly. Moreover, MAVS directly interacts with the mitochondrial protein VDAC1, decreasing its conductance, and we identified the VDAC1 binding site in MAVS. Our findings suggest that MAVS depletion, by reducing cancer cell proliferation and inflammation, represents a new target for cancer therapy.

COVID-19 mRNA vaccines as hypothetical epigenetic players: Results from an in silico analysis, considerations and perspectives

OBJECTIVES

To investigate in silico the occurrence of epigenetic crosstalk by nucleotide sequence complementarity between the BNT162b2 mRNA vaccine and whole human genome, including coding and noncoding (nc)RNA genes. To correlate these results with those obtained with the original spike (S) gene of Severe Acute Respiratory Syndrome CoronaVirus-2 (SARS-CoV-2).

METHODS

The publicly available FASTA sequence of the BNT162b2 mRNA vaccine and the SARS-CoV-2 isolate Wuhan-Hu-1 S gene (NC_045512.2) were used separately as key input to the Ensembl.org library to evaluate base pair match to human GRCh38 genome. Human coding and noncoding genes harboring hits were assessed for functional activity and health effects using bioinformatics tools and GWAS databases.

RESULTS

The BLAT analysis against the human GRCh38 genome revealed a total of 37 hits for BNT162b2 mRNA and no hits for the SARS-CoV-2 S gene. More specifically, BNT162b2 mRNA matched 19 human genes whose protein products are variously involved in enzyme reactions, nucleotide or cation binding, signaling, and carrier functions. In BLASTN analysis of ncRNA genes, BNT162b2 mRNA and SARS-CoV-2 S gene matched 17 and 24 different human genomic regions, respectively. Overall, characterization of the matched noncoding sequences revealed stronger interference with epigenetic pathways for BNT162b2 mRNA compared with the original S gene.

CONCLUSION

This pivotal in silico analysis shows that SARS-CoV-2 S gene and the BNT162b2 mRNA vaccine exhibit Watson-Crick nucleotide complementarity with human coding or noncoding genes. Although they do not share the same complementarity pattern, both may disrupt epigenetic mechanisms in target cells, potentially leading to long-term complications.

MAVS Antagonizes Human Stem Cell Senescence as a Mitochondrial Stabilizer

Mitochondrial dysfunction is a hallmark feature of cellular senescence and organ aging. Here, we asked whether the mitochondrial antiviral signaling protein (MAVS), which is essential for driving antiviral response, also regulates human stem cell senescence. To answer this question, we used CRISPR/Cas9-mediated gene editing and directed differentiation techniques to generate various MAVS-knockout human stem cell models. We found that human mesenchymal stem cells (hMSCs) were sensitive to MAVS deficiency, as manifested by accelerated senescence phenotypes. We uncovered that the role of MAVS in maintaining mitochondrial structural integrity and functional homeostasis depends on its interaction with the guanosine triphosphatase optic atrophy type 1 (OPA1). Depletion of MAVS or OPA1 led to the dysfunction of mitochondria and cellular senescence, whereas replenishment of MAVS or OPA1 in MAVS-knockout hMSCs alleviated mitochondrial defects and premature senescence phenotypes. Taken together, our data underscore an uncanonical role of MAVS in safeguarding mitochondrial homeostasis and antagonizing human stem cell senescence.

Role of mitochondria in regulating immune response during bacterial infection

Mitochondria are dynamic organelles of eukaryotes involved in energy production and fatty acid oxidation. Besides maintaining ATP production, calcium signaling, cellular apoptosis, and fatty acid synthesis, mitochondria are also known as the central hub of the immune system as it regulates the innate immune pathway during infection. Mitochondria mediated immune functions mainly involve regulation of reactive oxygen species production, inflammasome activation, cytokine secretion, and apoptosis of infected cells. Recent findings indicate that cellular mitochondria undergo constant biogenesis, fission, fusion and degradation, and these dynamics regulate cellular immuno-metabolism. Several intracellular pathogens target and modulate these normal functions of mitochondria to facilitate their own survival and growth. De-regulation of mitochondrial functions and dynamics favors bacterial infection and pathogens are able to protect themselves from mitochondria mediated immune responses. Here, we will discuss how mitochondria mediated anti-bacterial immune pathways help the host to evade pathogenic insult. In addition, examples of bacterial pathogens modulating mitochondrial metabolism and dynamics will also be elaborated. Study of these interactions between the mitochondria and bacterial pathogens during infection will lead to a better understanding of the mitochondrial metabolism pathways and dynamics important for the establishment of bacterial diseases. In conclusion, detailed studies on how mitochondria regulate the immune response during bacterial infection can open up new avenues to develop mitochondria centric anti-bacterial therapeutics.

Viral protease cleavage of MAVS in genetically modified mice with hepatitis A virus infection

BACKGROUND & AIMS

Consistent with its relatively narrow host species range, hepatitis A virus (HAV) cannot infect C57BL/6 mice. However, in Mavs-/- mice with genetic deficiency of the innate immune signaling adaptor MAVS, HAV replicates robustly in the absence of disease. The HAV 3ABC protease cleaves MAVS in human cells, thereby disrupting virus-induced IFN responses, but it cannot cleave murine MAVS (mMAVS) due to sequence differences at the site of scission. Here, we sought to elucidate the role of 3ABC MAVS cleavage in determining HAV pathogenesis and host species range.

METHODS

Using CRISPR/Cas9 gene editing, we established two independent lineages of C57BL/6 mice with knock-in mutations altering two amino acids in mMAVS ('mMAVS-VS'), rendering it susceptible to 3ABC cleavage without loss of signaling function. We challenged homozygous Mavsvs/vs mice with HAV, and compared infection outcomes with C57BL/6 and genetically deficient Mavs-/- mice.

RESULTS

The humanized murine mMAVS-VS protein was cleaved as efficiently as human MAVS when co-expressed with 3ABC in Huh-7 cells. In embyronic fibroblasts from Mavsvs/vs mice, mMAVS-VS was cleaved by ectopically expressed 3ABC, significantly disrupting Sendai virus-induced IFN responses. However, in contrast to Mavs-/- mice with genetic MAVS deficiency, HAV failed to establish infection in Mavsvs/vs mice, even with additional genetic knockout of Trif or Irf1. Nonetheless, when crossed with permissive Ifnar1-/- mice lacking type I IFN receptors, Mavsvs/vsIfnar1-/- mice demonstrated enhanced viral replication coupled with significant reductions in serum alanine aminotransferase, hepatocellular apoptosis, and intrahepatic inflammatory cell infiltrates compared with Ifnar1-/- mice.

CONCLUSIONS

MAVS cleavage by 3ABC boosts viral replication and disrupts disease pathogenesis, but it is not by itself sufficient to break the host-species barrier to HAV infection in mice.

IMPACT AND IMPLICATIONS

The limited host range of human hepatitis viruses could be explained by species-specific viral strategies that disrupt innate immune responses. Both hepatitis A virus (HAV) and hepatitis C virus express viral proteases that cleave the innate immune adaptor protein MAVS, in human but not mouse cells. However, the impact of this immune evasion strategy has never been assessed in vivo. Here we show that HAV 3ABC protease cleavage of MAVS enhances viral replication and lessens liver inflammation in mice lacking interferon receptors, but that it is insufficient by itself to overcome the cross-species barrier to infection in mice. These results enhance our understanding of how hepatitis viruses interact with the host and their impact on innate immune responses.

Non-coding RNAs targeting NF-κB pathways in aquatic animals: A review

Nuclear factor-kappa B (NF-κB) pathways have a close relationship with many diseases, especially in terms of the regulation of inflammation and the immune response. Non-coding RNAs (ncRNAs) are a heterogeneous subset of endogenous RNAs that directly affect cellular function in the absence of proteins or peptide products; these include microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), etc. Studies on the roles of ncRNAs in targeting the NF-κB pathways in aquatic animals are scarce. A few research studies have confirmed detailed regulatory mechanisms among ncRNAs and the NF-κB pathways in aquatic animals. This comprehensive review is presented concerning ncRNAs targeting the NF-κB pathway in aquatic animals and provides new insights into NF-κB pathways regulatory mechanisms of aquatic animals. The review discusses new possibilities for developing non-coding-RNA-based antiviral applications in fisheries.

Application of Bioinformatics Tools for the Prediction of Helper MicroRNAs for Improvement of Oncolytic Virus Efficacy

Purpose. Oncolytic Reoviruses, as a self-limiting virus, can be used in cancer treatment, because they have the ability to replicate in tumor cells selectively and destroy them. Studies show that some immune response proteins may interfere with the virus life cycle. So, the main aim of this bioinformatic study is to check which microRNA is able to target some reovirus inhibitory proteins. Experimental Design. By use of online bioinformatics software, the microRNAs that could target inhibitory genes were selected. Then, other features like content ++ score and cell type were checked and finally the eligible microRNAs were determined. Results. After choosing 15 inhibitory proteins, analysis was performed and finally 37 microRNAs which could target inhibitory proteins in colorectal cell lines were selected. In the end, by investigation of web-based tools, just two microRNAs were finalized. Conclusions and Clinical Relevance. This bioinformatic study shows that microRNA-140 and microRNA-92a have the potential to target some inhibitory proteins which interfere with oncolytic Reovirus replication and it may help in the optimal use of this virus as a cancer treatment. Because selective reproduction of Reovirus in tumor cells, as a nonchemical therapy, can be a good way to overcome this disease with broad advantages.

Activated Platelets and Platelet-Derived Extracellular Vesicles Mediate COVID-19-Associated Immunothrombosis

Activated platelets and platelet-derived extracellular vesicles (EVs) have emerged as central players in thromboembolic complications associated with severe coronavirus disease 2019 (COVID-19). Platelets bridge hemostatic, inflammatory, and immune responses by their ability to sense pathogens via various pattern recognition receptors, and they respond to infection through a diverse repertoire of mechanisms. Dysregulated platelet activation, however, can lead to immunothrombosis, a simultaneous overactivation of blood coagulation and the innate immune response. Mediators released by activated platelets in response to infection, such as antimicrobial peptides, high mobility group box 1 protein, platelet factor 4 (PF4), and PF4⁺ extracellular vesicles promote neutrophil activation, resulting in the release of neutrophil extracellular traps and histones. Many of the factors released during platelet and neutrophil activation are positively charged and interact with endogenous heparan sulfate or exogenously administered heparin via electrostatic interactions or via specific binding sites. Here, we review the current state of knowledge regarding the involvement of platelets and platelet-derived EVs in the pathogenesis of immunothrombosis, and we discuss the potential of extracorporeal therapies using adsorbents functionalized with heparin to deplete platelet-derived and neutrophil-derived mediators of immunothrombosis.

Discovery Proteomics Analysis Determines That Driver Oncogenes Suppress Antiviral Defense Pathways Through Reduction in Interferon-β Autocrine Stimulation

Since the discovery of oncogenes, there has been tremendous interest to understand their mechanistic basis and to develop broadly actionable therapeutics. Some of the most frequently activated oncogenes driving diverse cancers are c-MYC, EGFR, HER2, AKT, KRAS, BRAF, and MEK. Using a reductionist approach, we explored how cellular proteomes are remodeled in isogenic cell lines engineered with or without these driver oncogenes. The most striking discovery for all oncogenic models was the systematic downregulation of scores of antiviral proteins regulated by type 1 interferon. These findings extended to cancer cell lines and patient-derived xenograft models of highly refractory pancreatic cancer and osteosarcoma driven by KRAS and MYC oncogenes. The oncogenes reduced basal expression of and autocrine stimulation by type 1 interferon causing remarkable convergence on common phenotypic and functional profiles. In particular, there was dramatically lower expression of dsRNA sensors including DDX58 (RIG-I) and OAS proteins, which resulted in attenuated functional responses when the oncogenic cells were treated with the dsRNA mimetic, polyI:C, and increased susceptibility to infection with an RNA virus shown using SARS-CoV-2. Our reductionist approach provides molecular and functional insights connected to immune evasion hallmarks in cancers and suggests therapeutic opportunities.

Roles of mitochondrial DNA in dynamics of the immune response to COVID-19

Mitochondria dynamics have a pivotal role in many aspects of immune function. Viral infections affect mitochondrial dynamics and trigger the release of mitochondrial DNA (mtDNA) in host cells. Released mtDNA guides the immune response towards an inflammatory response against pathogens. In addition, circulating cell-free mtDNA (ccf-mtDNA) is considered an invaluable indicator for the prognosis and severity of infectious diseases. This study provides an overview of the role of mtDNA in the dynamics of the immune response to COVID-19. We focused on the possible roles of mtDNA in inducing the signaling pathways, and the inflammasome activation and regulation in SARS-CoV-2. Targeting mtDNA-related pathways can provide critical insights into therapeutic strategies for COVID-19.

Mitochondrial antiviral-signalling protein is a client of the BAG6 protein quality control complex

The heterotrimeric BAG6 complex coordinates the direct handover of newly synthesised tail-anchored (TA) membrane proteins from an SGTA-bound preloading complex to the endoplasmic reticulum (ER) delivery component TRC40. In contrast, defective precursors, including aberrant TA proteins, form a stable complex with this cytosolic protein quality control factor, enabling such clients to be either productively re-routed or selectively degraded. We identify the mitochondrial antiviral-signalling protein (MAVS) as an endogenous TA client of both SGTA and the BAG6 complex. Our data suggest that the BAG6 complex binds to a cytosolic pool of MAVS before its misinsertion into the ER membrane, from where it can subsequently be removed via ATP13A1-mediated dislocation. This BAG6-associated fraction of MAVS is dynamic and responds to the activation of an innate immune response, suggesting that BAG6 may modulate the pool of MAVS that is available for coordinating the cellular response to viral infection.

Summary: Mitochondrial antiviral-signalling protein (MAVS) is a favoured client of the cytosolic BAG6 complex. We discuss how this dynamic interaction may modulate MAVS biogenesis at signalling membranes.

Surgical Strikes on Host Defenses: Role of the Viral Protease Activity in Innate Immune Antagonism

As a frontline defense mechanism against viral infections, the innate immune system is the primary target of viral antagonism. A number of virulence factors encoded by viruses play roles in circumventing host defenses and augmenting viral replication. Among these factors are viral proteases, which are primarily responsible for maturation of viral proteins, but in addition cause proteolytic cleavage of cellular proteins involved in innate immune signaling. The study of these viral protease-mediated host cleavages has illuminated the intricacies of innate immune networks and yielded valuable insights into viral pathogenesis. In this review, we will provide a brief summary of how proteases of positive-strand RNA viruses, mainly from the Picornaviridae, Flaviviridae and Coronaviridae families, proteolytically process innate immune components and blunt their functions.

Signaling from the RNA sensor RIG-I is regulated by ufmylation

The RNA-binding protein RIG-I is a key initiator of the antiviral innate immune response. The signaling that mediates the antiviral response downstream of RIG-I is transduced through the adaptor protein MAVS and results in the induction of type I and III interferons (IFNs). This signal transduction occurs at endoplasmic reticulum (ER)–mitochondrial contact sites, to which RIG-I and other signaling proteins are recruited following their activation. RIG-I signaling is highly regulated to prevent aberrant activation of this pathway and dysregulated induction of IFN. Previously, we identified UFL1, the E3 ligase of the ubiquitin-like modifier conjugation system called ufmylation, as one of the proteins recruited to membranes at ER–mitochondrial contact sites in response to RIG-I activation. Here, we show that UFL1, as well as the process of ufmylation, promote IFN induction in response to RIG-I activation. We found that following RNA virus infection, UFL1 is recruited to the membrane-targeting protein 14–3-3ε and that this complex is then recruited to activated RIG-I to promote downstream innate immune signaling. Importantly, we found that 14–3-3ε has an increase in UFM1 conjugation following RIG-I activation. Additionally, loss of cellular ufmylation prevents the interaction of 14–3-3ε with RIG-I, which abrogates the interaction of RIG-I with MAVS and thus the downstream signal transduction that induces IFN. Our results define ufmylation as an integral regulatory component of the RIG-I signaling pathway and as a posttranslational control for IFN induction.

Full-length MAVS, a mitochondrial antiviral-signaling protein, inhibits hepatitis E virus replication, requiring JAK-STAT signaling

Hepatitis E virus (HEV) infection is the leading cause of acute hepatitis worldwide. The mitochondrial antiviral signaling protein (MAVS)-mediated interferon (IFN) response plays a pivotal role in hepatic antiviral immunity. However, little is known about the effect of overexpression of MAVS on HEV infection. Full-length MAVS (FL-MAVS) is the main form of MAVS that increases the production of IFNs. Here, we studied the effect of FL-MAVS on HEV infection. We found that overexpression of FL-MAVS profoundly inhibited HEV replication. Furthermore, we showed that the anti-HEV effect of FL-MAVS is largely dependent on JAK-STAT signaling activation.

The Activated Macrophage - A Tough Fortress for Virus Invasion: How Viruses Strike Back

Macrophages (Mφ) are innate immune cells with a variety of functional phenotypes depending on the cytokine microenvironment they reside in. Mφ exhibit distinct activation patterns that are found within a wide array of activation states ranging from the originally discovered classical pro-inflammatory (M1) to the anti-inflammatory (M2) with their multi-facades. M1 cells are induced by IFNγ + LPS, while M2 are further subdivided into M2a (IL-4), M2b (Immune Complex) and M2c (IL-10) based on their inducing stimuli. Not surprisingly, Mφ activation influences the outcome of viral infections as they produce cytokines that in turn activate cells of the adaptive immune system. Generally, activated M1 cells tend to restrict viral replication, however, influenza and HIV exploit inflammation to support their replication. Moreover, M2a polarization inhibits HIV replication at the post-integration level, while HCMV encoded hrIL-10 suppresses inflammatory reactions by facilitating M2c formation. Additionally, viruses such as LCMV and Lassa Virus directly suppress Mφ activation leading to viral chronicity. Here we review how Mφ activation affects viral infection and the strategies by which viruses manipulate Mφ polarization to benefit their own fitness. An understanding of these mechanisms is important for the development of novel immunotherapies that can sway Mφ phenotype to inhibit viral replication.

Cell-type specific distribution and activation of type I IFN pathway molecules at the placental maternal-fetal interface in response to COVID-19 infection

BACKGROUND AND OBJECTIVE

COVID-19 infection in pregnancy significantly increases risks of adverse pregnancy outcomes. However, little is known how the innate immunity at the placental maternal-fetal interface responds to COVID-19 infection. Type I IFN cytokines are recognized as a key component of the innate immune response against viral infection. In this study, we specifically evaluated expression of IFN antiviral signaling molecules in placentas from women infected with COVID-19 during pregnancy.

METHODS

Expression of IFN activation signaling pathway molecules, including cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), interferon regulatory factor 3 (IRF3), Toll-like receptor 7 (TLR7), mitochondrial antiviral-signaling protein (MAVS), and IFNβ were determined in formalin-fixed paraffin embedded (FFPE) placental tissue sections (villous and fetal membrane) by immunostaining. A total of 20 placentas were examined, 12 from COVID-19 patients and 8 from non-COVID-19 controls. Patient demographics, clinical data, and placental pathology report were acquired via EPIC medical record review.

RESULTS

Except BMI and placental weight, there was no statistical difference between COVID and non-COVID groups in maternal age, gestational age at delivery, gravity/parity, delivery mode, and newborn gender and weight. In COVID-exposed group, the main pathological characteristics in the placental disc are maternal and fetal vascular malperfusion and chronic inflammation. Compared to non-COVID controls, expression of IFN activation pathway molecules were all upregulated with distinct cell-type specific distribution in COVID-exposed placentas: STING in villous and decidual stromal cells; IRF3 in cytotrophoblasts (CTs) and extra-villous trophoblasts (EVTs); and TLR7 and MAVS in syncytiotrophoblasts (STs), CTs, and EVTs. Upregulation of STING, MAVS and TLR7 was also seen in fetal endothelial cells.

CONCLUSIONS

STING, IRF3, TLR7, and MAVS are key viral sensing molecules that regulate type I IFN production. Type I IFNs are potent antiviral cytokines to impair and eradicate viral replication in infected cells. The finding of cell-type specific distribution and activation of these innate antiviral molecules at the placental maternal-fetal interface provide plausible evidence that type I IFN pathway molecules may play critical roles against SARS-CoV-2 infection in the placenta. Our findings also suggest that placental maternal-fetal interface has a well-defined antiviral defense system to protect the developing fetus from SARS-CoV-2 infection.

N4BP3 Regulates RIG-I-Like Receptor Antiviral Signaling Positively by Targeting Mitochondrial Antiviral Signaling Protein

Mitochondrial antiviral signaling protein (MAVS), an adaptor protein, is activated by RIG-I, which is critical for an effective innate immune response to infection by various RNA viruses. Viral infection causes the RIG-I-like receptor (RLR) to recognize pathogen-derived dsRNA and then becomes activated to promote prion-like aggregation and activation of MAVS. Subsequently, through the recruitment of TRAF proteins, MAVS activates two signaling pathways mediated by TBK1-IRF3 and IKK- NF-κb, respectively, and turns on type I interferon and proinflammatory cytokines. This study discovered that NEDD4 binding protein 3 (N4BP3) is a positive regulator of the RLR signaling pathway by targeting MAVS. Overexpression of N4BP3 promoted virus-induced activation of the interferon-β (IFN-β) promoter and interferon-stimulated response element (ISRE). Further experiments showed that knockdown or knockout N4BP3 impaired RIG-I-like receptor (RLR)-mediated innate immune response, induction of downstream antiviral genes, and cellular antiviral responses. We also detected that N4BP3 could accelerate the interaction between MAVS and TRAF2. Related experiments revealed that N4BP3 could facilitate the ubiquitination modification of MAVS. These findings suggest that N4BP3 is a critical component of the RIG-I-like receptor (RLR)-mediated innate immune response by targeting MAVS, which also provided insight into the mechanisms of innate antiviral responses.

SARS-CoV-2 Nsp5 Activates NF-κB Pathway by Upregulating SUMOylation of MAVS

The COVID-19 is an infectious disease caused by SARS-CoV-2 infection. A large number of clinical studies found high-level expression of pro-inflammatory cytokines in patients infected with SARS-CoV-2, which fuels the rapid development of the disease. However, the specific molecular mechanism is still unclear. In this study, we found that SARS-CoV-2 Nsp5 can induce the expression of cytokines IL-1β, IL-6, TNF-α, and IL-2 in Calu-3 and THP1 cells. Further research found that Nsp5 enhances cytokine expression through activating the NF-κB signaling pathway. Subsequently, we investigated the upstream effectors of the NF-κB signal pathway on Nsp5 overexpression and discovered that Nsp5 increases the protein level of MAVS. Moreover, Nsp5 can promote the SUMOylation of MAVS to increase its stability and lead to increasing levels of MAVS protein, finally triggering activation of NF-κB signaling. The knockdown of MAVS and the inhibitor of SUMOylation treatment can attenuate Nsp5-mediated NF-κB activation and cytokine induction. We identified a novel role of SARS-CoV-2 Nsp5 to enhance cytokine production by activating the NF-κB signaling pathway.

The MAVS Immune Recognition Pathway in Viral Infection and Sepsis

Significance: It is estimated that close to 50 million cases of sepsis result in over 11 million annual fatalities worldwide. The pathognomonic feature of sepsis is a dysregulated inflammatory response arising from viral, bacterial, or fungal infections. Immune recognition of pathogen-associated molecular patterns is a hallmark of the host immune defense to combat microbes and to prevent the progression to sepsis. Mitochondrial antiviral signaling protein (MAVS) is a ubiquitous adaptor protein located at the outer mitochondrial membrane, which is activated by the cytosolic pattern recognition receptors, retinoic acid-inducible gene I (RIG-I) and melanoma differentiation associated gene 5 (MDA5), following binding of viral RNA agonists. Recent Advances: Substantial progress has been made in deciphering the activation of the MAVS pathway with its interacting proteins, downstream signaling events (interferon [IFN] regulatory factors, nuclear factor kappa B), and context-dependent type I/III IFN response. Critical Issues: In the evolutionary race between pathogens and the host, viruses have developed immune evasion strategies for cleavage, degradation, or blockade of proteins in the MAVS pathway. For example, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) M protein and ORF9b protein antagonize MAVS signaling and a protective type I IFN response. Future Directions: The role of MAVS as a sensor for nonviral pathogens, host cell injury, and metabolic perturbations awaits better characterization in the future. New technical advances in multidimensional single-cell analysis and single-molecule methods will accelerate the rate of new discoveries. The ultimate goal is to manipulate MAVS activities in the form of immune-modulatory therapies to combat infections and sepsis. Antioxid. Redox Signal. 35, 1376-1392.

SARS-CoV-2 3C-like protease antagonizes interferon-beta production by facilitating the degradation of IRF3

The prevalence of SARS-CoV-2 is a great threat to global public health. However, the relationship between the viral pathogen SARS-CoV-2 and host innate immunity has not yet been well studied. The genome of SARS-CoV-2 encodes a viral protease called 3C-like protease. This protease is responsible for cleaving viral polyproteins during replication. In this investigation, 293T cells were transfected with SARS-CoV-2 3CL and then infected with Sendai virus (SeV) to induce the RIG-I like receptor (RLR)-based immune pathway. q-PCR, luciferase reporter assays, and western blotting were used for experimental analyses. We found that SARS-CoV-2 3CL significantly downregulated IFN-β mRNA levels. Upon SeV infection, SARS-CoV-2 3CL inhibited the nuclear translocation of IRF3 and p65 and promoted the degradation of IRF3. This effect of SARS-CoV-2 3CL on type I IFN in the RLR immune pathway opens up novel ideas for future research on SARS-CoV-2.

Pathogenic Basis of Thromboinflammation and Endothelial Injury in COVID-19: Current Findings and Therapeutic Implications

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a global pandemic with a great impact on social and economic activities, as well as public health. In most patients, the symptoms of COVID-19 are a high-grade fever and a dry cough, and spontaneously resolve within ten days. However, in severe cases, COVID-19 leads to atypical bilateral interstitial pneumonia, acute respiratory distress syndrome, and systemic thromboembolism, resulting in multiple organ failure with high mortality and morbidity. SARS-CoV-2 has immune evasion mechanisms, including inhibition of interferon signaling and suppression of T cell and B cell responses. SARS-CoV-2 infection directly and indirectly causes dysregulated immune responses, platelet hyperactivation, and endothelial dysfunction, which interact with each other and are exacerbated by cardiovascular risk factors. In this review, we summarize current knowledge on the pathogenic basis of thromboinflammation and endothelial injury in COVID-19. We highlight the distinct contributions of dysregulated immune responses, platelet hyperactivation, and endothelial dysfunction to the pathogenesis of COVID-19. In addition, we discuss potential therapeutic strategies targeting these mechanisms.

Mitochondria as a Cellular Hub in Infection and Inflammation

Mitochondria are the energy center of the cell. They are found in the cell cytoplasm as dynamic networks where they adapt energy production based on the cell’s needs. They are also at the center of the proinflammatory response and have essential roles in the response against pathogenic infections. Mitochondria are a major site for production of Reactive Oxygen Species (ROS; or free radicals), which are essential to fight infection. However, excessive and uncontrolled production can become deleterious to the cell, leading to mitochondrial and tissue damage. Pathogens exploit the role of mitochondria during infection by affecting the oxidative phosphorylation mechanism (OXPHOS), mitochondrial network and disrupting the communication between the nucleus and the mitochondria. The role of mitochondria in these biological processes makes these organelle good targets for the development of therapeutic strategies. In this review, we presented a summary of the endosymbiotic origin of mitochondria and their involvement in the pathogen response, as well as the potential promising mitochondrial targets for the fight against infectious diseases and chronic inflammatory diseases.

Dengue virus is sensitive to inhibition prior to productive replication

Uncovering vulnerable steps in the life cycle of viruses supports the rational design of antiviral treatments. However, information on viral replication dynamics obtained from traditional bulk assays with host cell populations is inherently limited as the data represent averages over a multitude of unsynchronized replication cycles. Here, we use time-lapse imaging of virus replication in thousands of single cells, combined with computational inference, to identify rate-limiting steps for dengue virus (DENV), a widespread human pathogen. Comparing wild-type DENV with a vaccine candidate mutant, we show that the viral spread in the mutant is greatly attenuated by delayed onset of productive replication, whereas wild-type and mutant virus have identical replication rates. Single-cell analysis done after applying the broad-spectrum antiviral drug, ribavirin, at clinically relevant concentrations revealed the same mechanism of attenuating viral spread. We conclude that the initial steps of infection, rather than the rate of established replication, are quantitatively limiting DENV spread.

Avian Metapneumovirus Subgroup C Induces Mitochondrial Antiviral Signaling Protein Degradation through the Ubiquitin-Proteasome Pathway

The mitochondrial antiviral signaling (MAVS) protein, a critical adapter, links the upstream recognition of viral RNA to downstream antiviral signal transduction. However, the interaction mechanism between avian metapneumovirus subgroup C (aMPV/C) infection and MAVS remains unclear. Here, we confirmed that aMPV/C infection induced a reduction in MAVS expression in Vero cells in a dose-dependent manner, and active aMPV/C replication was required for MAVS decrease. We also found that the reduction in MAVS occurred at the post-translational level rather than at the transcriptional level. Different inhibitors were used to examine the effect of proteasome or autophagy on the regulation of MAVS. Treatment with a proteasome inhibitor MG132 effectively blocked MAVS degradation. Moreover, we demonstrated that MAVS mainly underwent K48-linked ubiquitination in the presence of MG132 in aMPV/C-infected cells, with amino acids 363, 462, and 501 of MAVS being pivotal sites in the formation of polyubiquitin chains. Finally, E3 ubiquitin ligases for MAVS degradation were screened and identified and RNF5 targeting MAVS at Lysine 363 and 462 was shown to involve in MAVS degradation in aMPV/C-infected Vero cells. Overall, these results reveal the molecular mechanism underlying aMPV/C infection-induced MAVS degradation by the ubiquitin-proteasome pathway.

Cellular host factors for SARS-CoV-2 infection

The coronavirus disease 2019 (COVID-19) pandemic has claimed millions of lives and caused a global economic crisis. No effective antiviral drugs are currently available to treat infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The medical need imposed by the pandemic has spurred unprecedented research efforts to study coronavirus biology. Every virus depends on cellular host factors and pathways for successful replication. These proviral host factors represent attractive targets for antiviral therapy as they are genetically more stable than viral targets and may be shared among related viruses. The application of various 'omics' technologies has led to the rapid discovery of proviral host factors that are required for the completion of the SARS-CoV-2 life cycle. In this Review, we summarize insights into the proviral host factors that are required for SARS-CoV-2 infection that were mainly obtained using functional genetic and interactome screens. We discuss cellular processes that are important for the SARS-CoV-2 life cycle, as well as parallels with non-coronaviruses. Finally, we highlight host factors that could be targeted by clinically approved molecules and molecules in clinical trials as potential antiviral therapies for COVID-19.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

Mitochondrial RNA, a new trigger of the innate immune system

Mitochondria play a pivotal role in numerous cellular processes. One of them is regulation of the innate immune pathway. In this instance, mitochondria function in two different aspects of regulatory mechanisms. First, mitochondria are part of the antiviral signaling cascade that is triggered in the cytoplasm and transmitted to effector proteins through mitochondria-localized proteins. Second, mitochondria can become an endogenous source of innate immune stimuli. Under some pathophysiological conditions, mitochondria release to the cytoplasm immunogenic factors, such as mitochondrial nucleic acids. Here, we focus on immunogenic mitochondrial double-stranded RNA (mt-dsRNA) and its origin and metabolism. We discuss factors that are responsible for regulating mt-dsRNA and its escape from mitochondria, emphasizing the contribution of polynucleotide phosphorylase (PNPase, PNPT1). Finally, we review current knowledge of the role of PNPase in human health and disease. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Inhibition of MAVS Aggregation-Mediated Type-I Interferon Signaling by Foot-and-Mouth Disease Virus VP3

As a structural protein of the Foot-and-mouth disease virus (FMDV), VP3 plays a vital role in virus assembly and inhibiting the interferon (IFN) signal transduction to promote FMDV replication. Previous studies demonstrated that FMDV VP3 blocks the type-I IFN response by inhibiting the mRNA expression of the mitochondrial antiviral-signaling protein (MAVS); however, the underlying mechanism is poorly understood. Here, we describe the specificity of FMDV VP3 interaction with the transmembrane (TM) domain of MAVS as FMDV driven type-I IFN inhibitory mechanism for its effective replication. The TM domain of MAVS governs the mitochondria localization of MAVS, and it is a key factor in type-I IFN signaling transduction via MAVS aggregation. Thereby, the interaction of FMDV VP3 with the TM domain of MAVS leads to the inhibition of MAVS mitochondria localization, self-association, and aggregation, resulting in the suppression of type-I IFN response. Collectively, these results provide a clear understanding of a key molecular mechanism used by the FMDV VP3 for the suppression of IFN responses via targeting MAVS.

RNA regulatory mechanisms that control antiviral innate immunity

From the initial sensing of viral nucleotides by pattern recognition receptors, through the induction of type I and III interferons (IFN), upregulation of antiviral effector proteins, and resolution of the inflammatory response, each step of innate immune signaling is under tight control. Though innate immunity is often associated with broad regulation at the level of gene transcription, RNA-centric post-transcriptional processes have emerged as critical mechanisms for ensuring a proper antiviral response. Here, we explore the diverse RNA regulatory mechanisms that modulate the innate antiviral immune response, with a focus on RNA sensing by RIG-I-like receptors (RLR), interferon (IFN) and IFN signaling pathways, viral pathogenesis, and host genetic variation that contributes to these processes. We address the post-transcriptional interactions with RNA-binding proteins, non-coding RNAs, transcript elements, and modifications that control mRNA stability, as well as alternative splicing events that modulate the innate immune antiviral response.

MAVS splicing variants associated with TRAF3 and TRAF6 in NF-κB and IRF3 signaling pathway in large yellow croaker Larimichthys crocea

Mitochondrial antiviral signaling protein (MAVS) acts as an essential adaptor in host RIG-I-like receptors (RLRs) mediated antiviral signaling pathway. In the present study, two MAVS transcript variants, the typical form and a splicing variant, namely Lc-MAVS_tv1 and Lc-MAVS_tv2 were characterized in large yellow croaker (Larimichthys crocea). The putative Lc-MAVS_tv1 protein contains 512 aa, with an N-terminal CARD domain, a central proline-rich region, and a C-terminal transmembrane (TM) domain, whereas Lc-MAVS_tv2 contains 302 aa and lacks the C-terminal TM domain due to a premature stop in the 102 bp intron fragment insertion. Lc-MAVS_tv1 was identified as a mitochondrion localized protein whereas Lc-MAVS_tv2 exhibited an entire cytosolic distribution. Quantitative real-time PCR revealed that Lc-MAVS_tv1 mRNA was broadly expressed in examined organs/tissues and showed extremely higher level than that of Lc-MAVS_tv2, and both of them could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo. Interestingly, overexpression of Lc-MAVS_tv2 could induce the activation of NF-κB but not IRF3, and Lc-MAVS_tv2 co-transfected with Lc-MAVS_tv1 induced a significantly higher level of NF-κB and IRF3 promoter activity. In addition, Lc-MAVS_tv2 overexpression could enhance TRAF3 and TRAF6 mediated NF-κB activation, but suppress TRAF3 and TRAF6 mediated IRF3 activation, implying that the splicing variant Lc-MAVS_tv2 may function as an important regulator in MAVS mediated signaling pathway.

The Coronavirus Disease 2019 (COVID-19): Key Emphasis on Melatonin Safety and Therapeutic Efficacy

Viral infections constitute a tectonic convulsion in the normophysiology of the hosts. The current coronavirus disease 2019 (COVID-19) pandemic is not an exception, and therefore the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, like any other invading microbe, enacts a generalized immune response once the virus contacts the body. Melatonin is a systemic dealer that does not overlook any homeostasis disturbance, which consequently brings into play its cooperative triad, antioxidant, anti-inflammatory, and immune-stimulant backbone, to stop the infective cycle of SARS-CoV-2 or any other endogenous or exogenous threat. In COVID-19, the corporal propagation of SARS-CoV-2 involves an exacerbated oxidative activity and therefore the overproduction of great amounts of reactive oxygen and nitrogen species (RONS). The endorsement of melatonin as a possible protective agent against the current pandemic is indirectly supported by its widely demonstrated beneficial role in preclinical and clinical studies of other respiratory diseases. In addition, focusing the therapeutic action on strengthening the host protection responses in critical phases of the infective cycle makes it likely that multi-tasking melatonin will provide multi-protection, maintaining its efficacy against the virus variants that are already emerging and will emerge as long as SARS-CoV-2 continues to circulate among us.

Battle Royale: Innate Recognition of Poxviruses and Viral Immune Evasion

Host pattern recognition receptors (PRRs) sense pathogen-associated molecular patterns (PAMPs), which are molecular signatures shared by different pathogens. Recognition of PAMPs by PRRs initiate innate immune responses via diverse signaling pathways. Over recent decades, advances in our knowledge of innate immune sensing have enhanced our understanding of the host immune response to poxviruses. Multiple PRR families have been implicated in poxvirus detection, mediating the initiation of signaling cascades, activation of transcription factors, and, ultimately, the expression of antiviral effectors. To counteract the host immune defense, poxviruses have evolved a variety of immunomodulators that have diverse strategies to disrupt or circumvent host antiviral responses triggered by PRRs. These interactions influence the outcomes of poxvirus infections. This review focuses on our current knowledge of the roles of PRRs in the recognition of poxviruses, their elicited antiviral effector functions, and how poxviral immunomodulators antagonize PRR-mediated host immune responses.

HSPBP1 facilitates cellular RLR-mediated antiviral response by inhibiting the K48-linked ubiquitination of RIG-I

Retinoic acid-inducible gene I (RIG-I) plays a critical role in the recognition of intracytoplasmic viral RNA. Upon binding to the RNA of invading viruses, the activated RIG-I translocates to mitochondria, where it recruits adapter protein MAVS, causing a series of signaling cascades. In this study, we demonstrated that Hsp70 binding protein 1 (HSPBP1) promotes RIG-I-mediated signal transduction. The overexpression of HSPBP1 can increase the stability of RIG-I protein by inhibiting its K48-linked ubiquitination, and promote the activation of IRF3 and the production of IFN-β induced by Sendai virus. Knockdown and knockout of HSPBP1 leads to down-regulation of virus-induced RIG-I expression, inhibits IRF3 activation, and reduces the production of IFNB1. These results indicate that HSPBP1 positively regulates the antiviral signal pathway induced by inhibiting the K48-linked ubiquitination of RIG-I.

Coenzyme Q10 and Immune Function: An Overview

Coenzyme Q10 (CoQ10) has a number of important roles in the cell that are required for optimal functioning of the immune system. These include its essential role as an electron carrier in the mitochondrial respiratory chain, enabling the process of oxidative phosphorylation to occur with the concomitant production of ATP, together with its role as a potential lipid-soluble antioxidant, protecting the cell against free radical-induced oxidation. Furthermore, CoQ10 has also been reported to have an anti-inflammatory role via its ability to repress inflammatory gene expression. Recently, CoQ10 has also been reported to play an important function within the lysosome, an organelle central to the immune response. In view of the differing roles CoQ10 plays in the immune system, together with the reported ability of CoQ10 supplementation to improve the functioning of this system, the aim of this article is to review the current literature available on both the role of CoQ10 in human immune function and the effect of CoQ10 supplementation on this system.

Herpesvirus Regulation of Selective Autophagy

Selective autophagy has emerged as a key mechanism of quality and quantity control responsible for the autophagic degradation of specific subcellular organelles and materials. In addition, a specific type of selective autophagy (xenophagy) is also activated as a line of defense against invading intracellular pathogens, such as viruses. However, viruses have evolved strategies to counteract the host’s antiviral defense and even to activate some proviral types of selective autophagy, such as mitophagy, for their successful infection and replication. This review discusses the current knowledge on the regulation of selective autophagy by human herpesviruses.