Viperin restricts chikungunya virus replication and pathology

Advances in antiviral strategies targeting mosquito-borne viruses: cellular, viral, and immune-related approaches

Mosquito-borne viruses (MBVs) are a major global health threat, causing significant morbidity and mortality. MBVs belong to several distinct viral families, each with unique characteristics. The primary families include Flaviviridae (e.g., Dengue, Zika, West Nile, Yellow Fever, Japanese Encephalitis), transmitted predominantly by Aedes and Culex mosquitoes; Togaviridae, which consists of the genus Alphavirus (e.g., Chikungunya, Eastern and Western Equine Encephalitis viruses), also transmitted by Aedes and Culex; Bunyaviridae (recently reorganized), containing viruses like Rift Valley Fever and Oropouche virus, transmitted by mosquitoes and sometimes sandflies; and Reoviridae, which includes the genus Orbivirus (e.g., West Nile and Bluetongue viruses), primarily affecting animals and transmitted by mosquitoes and sandflies. Despite extensive research, effective antiviral treatments for MBVs remain scarce, and current therapies mainly provide symptomatic relief and supportive care. This review examines the viral components and cellular and immune factors involved in the life cycle of MBVs. It also highlights recent advances in antiviral strategies targeting host factors such as lipid metabolism, ion channels, and proteasomes, as well as viral targets like NS2B-NS3 proteases and nonstructural proteins. Additionally, it explores immunomodulatory therapies to enhance antiviral responses and emphasizes the potential of drug repurposing, bioinformatics, artificial intelligence, and deep learning in identifying novel antiviral candidates. Continued research is crucial in mitigating MBVs' impact and preventing future outbreaks.

Pathogenicity and virulence of O'nyong-nyong virus: A less studied Togaviridae with pandemic potential

O'nyong-nyong virus (ONNV) is a neglected mosquito-borne alphavirus belonging to the Togaviridae family. ONNV is known to be responsible for sporadic outbreaks of acute febrile disease and polyarthralgia in Africa. As climate change increases the geographical range of known and potential new vectors, recent data indicate a possibility for ONNV to spread outside of the African continent and grow into a greater public health concern. In this review, we summarise the current knowledge on ONNV epidemiology, host-pathogen interactions, vector-virus responses, and insights into possible avenues to control risk of further epidemics. In this review, the limited ONNV literature is compared and correlated to other findings on mainly Old World alphaviruses. We highlight and discuss studies that investigate viral and host factors that determine viral-vector specificity, along with important mechanisms that determine severity and disease outcome of ONNV infection.

Unraveling the Complexity of Chikungunya Virus Infection Immunological and Genetic Insights in Acute and Chronic Patients

Background: The chikungunya virus (CHIKV), transmitted by infected Aedes mosquitoes, has caused a significant number of infections worldwide. In Brazil, the emergence of the CHIKV-ECSA genotype in 2014 posed a major public health challenge due to its association with more severe symptoms. Objectives/Methods: This study aimed to shed new light on the host immune response by examining the whole-blood transcriptomic profile of both CHIKV-acute and chronically infected individuals from Feira de Santana, Bahia, Brazil, a region heavily affected by CHIKV, Dengue, and Zika virus epidemics. Results: Our data reveal complex symptomatology characterized by arthralgia and post-chikungunya neuropathy in individuals with chronic sequelae, particularly affecting women living in socially vulnerable situations. Analysis of gene modules suggests heightened metabolic processes, represented by an increase in NADH, COX5A, COA3, CYC1, and cap methylation in patients with acute disease. In contrast, individuals with chronic manifestations exhibit a distinct pattern of histone methylation, probably mediated by NCOA3 in the coactivation of different nuclear receptors, KMT2 genes, KDM3B and TET2, and with alterations in the immunological response, majorly led by IL-17RA, IL-6R, and STAT3 Th17 genes. Conclusion: Our results emphasize the complexity of CHIKV disease progression, demonstrating the heterogeneous gene expression and symptomatologic scenario across both acute and chronic phases. Moreover, the identification of specific gene modules associated with viral pathogenesis provides critical insights into the molecular mechanisms underlying these distinct clinical manifestations.

HIV-induced RSAD2/Viperin supports sustained infection of monocyte-derived macrophages

HIV establishes long-term latent infection in memory CD4+ T cells and also establishes sustained long-term productive infection in macrophages, especially in the central nervous system (CNS). To better understand how HIV sustains infection in macrophages, we performed RNAseq analysis after infection of human monocyte-derived macrophages (MDMs) with the brain-derived HIV-1 strain YU2 and compared this with acute infection of CD4+ T cells. HIV infection in MDM and CD4+ T cells altered many gene transcripts, but with few overlaps between these different cell types. We found interferon pathways upregulated in both MDM and CD4+ T cells, but with different gene signatures. The interferon-stimulated gene RSAD2/Viperin was among the most upregulated genes following HIV infection in MDMs, but not in CD4+ T cells. RSAD2/Viperin was induced early after infection with various HIV strains, was sustained over time, and remained elevated in established MDM infection even if new rounds of infection were blocked by antiretroviral treatment. Immunofluorescence microscopy revealed that RSAD2/Viperin was induced in HIV-infected cells, as well as in some uninfected neighboring cells. Knockdown of RSAD2/Viperin following the establishment of infection in MDMs reduced the production of HIV transcripts and viral p24 antigen. This correlated with the reduction in the number of multinucleated giant cells, and changes in the HIV DNA and chromatin structure, including an increased DNA copy number and loss of nucleosomes and histone modifications at the long terminal repeat (LTR). RNAseq transcriptomic analysis of RSAD2/Viperin knockdown during HIV infection of MDMs revealed the activation of interferon alpha/beta and gamma pathways and the inactivation of Rho GTPase pathways. Taken together, these results suggest that RSAD2/Viperin supports the sustained infection in macrophages, potentially through mechanisms involving the alteration of the LTR chromatin structure and the interferon response.

IMPORTANCE

HIV infection of macrophages is a barrier to HIV cure and a source of neurocognitive pathology. We found that HIV induces RSAD2/Viperin during sustained infection of macrophages. While RSAD2/Viperin is an interferon-stimulated gene with known antiviral activity, we find RSAD2/Viperin promotes HIV infection in macrophages through multiple mechanisms, including interferon signaling. Therefore, RSAD2/Viperin may be a therapeutic target for the treatment of HIV-infected macrophages.

RSAD2 suppresses viral replication by interacting with the Senecavirus A 2 C protein

Senecavirus A (SVA), an emerging virus that causes blisters on the nose and hooves, reduces the production performance of pigs. RSAD2 is a radical S-adenosylmethionine (SAM) enzyme, and its expression can suppress various viruses due to its broad antiviral activity. However, the regulatory relationship between SVA and RSAD2 and the mechanism of action remain unclear. Here, we demonstrated that SVA infection increased RSAD2 mRNA levels, whereas RSAD2 expression negatively regulated viral replication, as evidenced by decreased viral VP1 protein expression, viral titres, and infected cell numbers. Viral proteins that interact with RSAD2 were screened, and the interaction between the 2 C protein and RSAD2 was found to be stronger than that between other proteins. Additionally, amino acids (aa) 43-70 of RSAD2 were crucial for interacting with the 2 C protein and played an important role in its anti-SVA activity. RSAD2 was induced by type I interferon (IFN-I) via Janus kinase signal transducer and activator of transcription (JAK-STAT), and had antiviral activity. Ruxolitinib, a JAK-STAT pathway inhibitor, and the knockdown of JAK1 expression substantially reduced RSAD2 expression levels and antiviral activity. Taken together, these results revealed that RSAD2 blocked SVA infection by interacting with the viral 2 C protein and provide a strategy for preventing and controlling SVA infection.

Helminth induced monocytosis conveys protection from respiratory syncytial virus infection in mice

BACKGROUND

Respiratory syncytial virus (RSV) infection in infants is a major cause of viral bronchiolitis and hospitalisation. We have previously shown in a murine model that ongoing infection with the gut helminth Heligmosomoides polygyrus protects against RSV infection through type I interferon (IFN-I) dependent reduction of viral load. Yet, the cellular basis for this protection has remained elusive. Given that recruitment of mononuclear phagocytes to the lung is critical for early RSV infection control, we assessed their role in this coinfection model.

METHODS

Mice were infected by oral gavage with H. polygyrus. Myeloid immune cell populations were assessed by flow cytometry in lung, blood and bone marrow throughout infection and after secondary infection with RSV. Monocyte numbers were depleted by anti-CCR2 antibody or increased by intravenous transfer of enriched monocytes.

RESULTS

H. polygyrus infection induces bone marrow monopoiesis, increasing circulatory monocytes and lung mononuclear phagocytes in a IFN-I signalling dependent manner. This expansion causes enhanced lung mononuclear phagocyte counts early in RSV infection that may contribute to the reduction of RSV load. Depletion or supplementation of circulatory monocytes prior to RSV infection confirms that these are both necessary and sufficient for helminth induced antiviral protection.

CONCLUSIONS

H. polygyrus infection induces systemic monocytosis contributing to elevated mononuclear phagocyte numbers in the lung. These cells are central to an anti-viral effect that reduces the peak viral load in RSV infection. Treatments to promote or modulate these cells may provide novel paths to control RSV infection in high risk individuals.

Development of Proniosome Gel Formulation for CHIKV Infection

Given the increasing aging population and the rising prevalence of musculoskeletal diseases due to obesity and injury, urgent research is needed to formulate new treatment alternatives, as current options remain inadequate. Viruses can exacerbate arthritis and worsen symptoms in patients with pre-existing osteoarthritis. Over the past decade, the chikungunya virus (CHIKV) has emerged as a significant public health concern, especially in Asia and South America. Exploring natural products, such as berberine, has shown promise due to its anticatabolic, antioxidative, and anti-inflammatory effects. However, berberine's low stability and bioavailability limit its efficacy. We hypothesized that encapsulating berberine into a proniosome gel, known for its ease of preparation and stability, could enhance its bioavailability and efficacy when applied topically, potentially treating CHIKV infection. Our investigation focused on how varying berberine loads and selected excipients in the proniosome gel influenced its physical properties, stability, and skin permeability. We also examined the biological half-life of berberine in plasma upon topical administration in mice to assess the potential for controlled and sustained drug release. Additionally, we analyzed the antioxidant stress activity and cell viability of HaCaT keratinocytes and developed a lipopolysaccharide-stimulated cell culture model to evaluate anti-inflammatory effects using pro-inflammatory cytokines. Overall, the research aims to transform the treatment landscape for arthritis by leveraging berberine's therapeutic potential.

Expression analysis and antiviral activity of koi carp (Cyprinus carpio) viperin against carp edema virus (CEV)

Viperin, also known as radical S-Adenosyl methionine domain containing 2 (RSAD2), is an IFN stimulated protein that plays crucial roles in innate immunity. Here, we identified a viperin gene from the koi carp (Cyprinus carpio) (kVip). The ORF of kVip is 1047 bp in length, encoding a polypeptide of 348 amino acids with neither signal peptide nor transmembrane protein. The predicted molecular weight is 40.37 kDa and the isoelectric point is 7.7. Multiple sequence alignment indicated that putative kVip contains a radical SAM superfamily domain and a conserved C-terminal region. kVip was highly expressed in the skin and spleen of healthy koi carps, and significantly stimulated in both natural and artificial CEV-infected koi carps. In vitro immune stimulation analysis showed that both extracellular and intracellular poly (I: C) or poly (dA: dT) caused a significant increase in kVip expression of spleen cells. Furthermore, intraperitoneal injection of recombinant kVip (rkVip) not only reduced the CEV load in the gills, but also improved the survival of koi carps following CEV challenge. Additionally, rkVip administration effectively regulated inflammatory and anti-inflammatory cytokines (IL-6, IL-1β, TNF-α, IL-10) and interferon-related molecules (cGAS, STING, MyD88, IFN-γ, IFN-α, IRF3 and IRF9). Collectively, kVip effectively responded to CEV infection and exerted antiviral function against CEV partially by regulation of inflammatory and interferon responses.

Crosstalk between CD64+MHCII+ macrophages and CD4+ T cells drives joint pathology during chikungunya

Communications between immune cells are essential to ensure appropriate coordination of their activities. Here, we observed the infiltration of activated macrophages into the joint-footpads of chikungunya virus (CHIKV)-infected animals. Large numbers of CD64+MHCII+ and CD64+MHCII- macrophages were present in the joint-footpad, preceded by the recruitment of their CD11b+Ly6C+ inflammatory monocyte precursors. Recruitment and differentiation of these myeloid subsets were dependent on CD4+ T cells and GM-CSF. Transcriptomic and gene ontology analyses of CD64+MHCII+ and CD64+MHCII- macrophages revealed 89 differentially expressed genes, including genes involved in T cell proliferation and differentiation pathways. Depletion of phagocytes, including CD64+MHCII+ macrophages, from CHIKV-infected mice reduced disease pathology, demonstrating that these cells play a pro-inflammatory role in CHIKV infection. Together, these results highlight the synergistic dynamics of immune cell crosstalk in driving CHIKV immunopathogenesis. This study provides new insights in the disease mechanism and offers opportunities for development of novel anti-CHIKV therapeutics.

Human muscle cells sensitivity to chikungunya virus infection relies on their glycolysis activity and differentiation stage

Changes to our environment have led to the emergence of human pathogens such as chikungunya virus. Chikungunya virus infection is today a major public health concern. It is a debilitating chronic disease impeding patients' mobility, affecting millions of people. Disease development relies on skeletal muscle infection. The importance of skeletal muscle in chikungunya virus infection led to the hypothesis that it could serve as a viral reservoir and could participate to virus persistence. Here we questioned the interconnection between skeletal muscle cells metabolism, their differentiation stage and the infectivity of the chikungunya virus. We infected human skeletal muscle stem cells at different stages of differentiation with chikungunya virus to study the impact of their metabolism on virus production and inversely the impact of virus on cell metabolism. We observed that chikungunya virus infectivity is cell differentiation and metabolism-dependent. Chikungunya virus interferes with the cellular metabolism in quiescent undifferentiated and proliferative muscle cells. Moreover, activation of chikungunya infected quiescent muscle stem cells, induces their proliferation, increases glycolysis and amplifies virus production. Therefore, our results showed that Chikungunya virus infectivity and the antiviral response of skeletal muscle cells relies on their energetic metabolism and their differentiation stage. Then, muscle stem cells could serve as viral reservoir producing virus after their activation.

Production of polyclonal viperin antisera using N-terminal deleted recombinant bovine viperin

Viperin, also known as radical S-adenosyl methionine domain-containing protein (RSAD2) is a multifunctional interferon-stimulated gene (ISG) that is activated during the viral infections. Viperin belongs to S-adenosyl methionine (SAM) superfamily of enzymes known to catalyze radical-mediated reactions and viperin inhibits a wide range of DNA and RNA viruses through its broad range of activity. The present study reports cloning and expression of bovine viperin in a bacterial expression system. PCR-based site-directed mutagenesis was carried out for deletion of N-terminal 1-70 amino acid containing amphipathic helix of viperin that interferes in protein expression and purification. The resultant truncated viperin protein was expressed in Escherichia coli, BL-21(DE3) competent cells and purified using nickel charged affinity column. The truncated 54 kDa protein was confirmed by western blot using human RSAD2 as a probe. Further, in house, hyperimmune serum was raised against the truncated viperin in the rabbit and the reactivity was confirmed by western blot using mammalian expression vector construct of viperin transfected in Baby Hamster kidney (BHK) cells and in MDBK cells infected with Foot and Mouth disease Asia I virus.

Transcriptome screening identifies TIPARP as an antiviral host factor against the Getah virus

IMPORTANCE

Alphaviruses threaten public health continuously, and Getah virus (GETV) is a re-emerging alphavirus that can potentially infect humans. Approved antiviral drugs and vaccines against alphaviruses are few available, but several host antiviral factors have been reported. Here, we used GETV as a model of alphaviruses to screen for additional host factors. Tetrachlorodibenzo-p-dioxin-inducible poly(ADP ribose) polymerase was identified to inhibit GETV replication by inducing ubiquitination of the glycoprotein E2, causing its degradation by recruiting the E3 ubiquitin ligase membrane-associated RING-CH8 (MARCH8). Using GETV as a model virus, focusing on the relationship between viral structural proteins and host factors to screen antiviral host factors provides new insights for antiviral studies on alphaviruses.

Interferon inhibits a model RNA virus via a limited set of inducible effector genes

Interferons control viral infection by inducing the expression of antiviral effector proteins encoded by interferon-stimulated genes (ISGs). The field has mostly focused on identifying individual antiviral ISG effectors and defining their mechanisms of action. However, fundamental gaps in knowledge about the interferon response remain. For example, it is not known how many ISGs are required to protect cells from a particular virus, though it is theorized that numerous ISGs act in concert to achieve viral inhibition. Here, we used CRISPR-based loss-of-function screens to identify a markedly limited set of ISGs that confer interferon-mediated suppression of a model alphavirus, Venezuelan equine encephalitis virus (VEEV). We show via combinatorial gene targeting that three antiviral effectors-ZAP, IFIT3, and IFIT1-together constitute the majority of interferon-mediated restriction of VEEV, while accounting for < 0.5% of the interferon-induced transcriptome. Together, our data suggest a refined model of the antiviral interferon response in which a small subset of "dominant" ISGs may confer the bulk of the inhibition of a given virus.

Host Factor Nucleophosmin 1 (NPM1/B23) Exerts Antiviral Effects against Chikungunya Virus by Its Interaction with Viral Nonstructural Protein 3

Chikungunya virus (CHIKV) hijacks host cell machinery to support its replication. Nucleophosmin 1 (NPM1/B23), a nucleolar phosphoprotein, is one of the host proteins known to restrict CHIKV infection; however, the mechanistic details of the antiviral role of NPM1 are not elucidated. It was seen in our experiments that the level of NPM1 expression affected the expression levels of interferon-stimulated genes (ISGs) that play antiviral roles in CHIKV infection, such as IRF1, IRF7, OAS3, and IFIT1, indicating that one of the antiviral mechanisms could be through modulation of interferon-mediated pathways. Our experiments also identified that for CHIKV restriction, NPM1 must move from the nucleus to the cytoplasm. A deletion of the nuclear export signal (NES), which confines NPM1 within the nucleus, abolishes its anti-CHIKV action. We observed that NPM1 binds CHIKV nonstructural protein 3 (nsP3) strongly via its macrodomain, thereby exerting a direct interaction with viral proteins to limit infection. Based on site-directed mutagenesis and coimmunoprecipitation studies, it was also observed that amino acid residues N24 and Y114 of the CHIKV nsP3 macrodomain, known to be involved in virus virulence, bind ADP-ribosylated NPM1 to inhibit infection. Overall, the results show a key role of NPM1 in CHIKV restriction and indicate it as a promising host target for developing antiviral strategies against CHIKV. IMPORTANCE Chikungunya, a recently reemerged mosquito-borne infection caused by a positive-sense, single-stranded RNA virus, has caused explosive epidemics in tropical regions. Unlike the classical symptoms of acute fever and debilitating arthralgia, incidences of neurological complications and mortality were reported. Currently there are no antivirals or commercial vaccines available against chikungunya. Like all viruses, CHIKV uses host cellular machinery for establishment of infection and successful replication. To counter this, the host cell activates several restriction factors and innate immune response mediators. Understanding these host-virus interactions helps to develop host-targeted antivirals against the disease. Here, we report the antiviral role of the multifunctional host protein NPM1 against CHIKV. The significant inhibitory effect of this protein against CHIKV involves its increased expression and movement from its natural location within the nucleus to the cytoplasm. There, it interacts with functional domains of key viral proteins. Our results support ongoing efforts toward development of host-directed antivirals against CHIKV and other alphaviruses.

Evolution and immunopathology of chikungunya virus informs therapeutic development

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, is an emerging global threat identified in more than 60 countries across continents. The risk of CHIKV transmission is rising due to increased global interactions, year-round presence of mosquito vectors, and the ability of CHIKV to produce high host viral loads and undergo mutation. Although CHIKV disease is rarely fatal, it can progress to a chronic stage, during which patients experience severe debilitating arthritis that can last from several weeks to months or years. At present, there are no licensed vaccines or antiviral drugs for CHIKV disease, and treatment is primarily symptomatic. This Review provides an overview of CHIKV pathogenesis and explores the available therapeutic options and the most recent advances in novel therapeutic strategies against CHIKV infections.

Interferon inhibits a model RNA virus via a limited set of inducible effector genes

Interferons control viral infection by inducing the expression of antiviral effector proteins encoded by interferon-stimulated genes (ISGs). The field has mostly focused on identifying individual antiviral ISG effectors and defining their mechanisms of action. However, fundamental gaps in knowledge about the interferon response remain. For example, it is not known how many ISGs are required to protect cells from a particular virus, though it is theorized that numerous ISGs act in concert to achieve viral inhibition. Here, we used CRISPR-based loss-of-function screens to identify a markedly limited set of ISGs that confer interferon-mediated suppression of a model alphavirus, Venezuelan equine encephalitis virus (VEEV). We show via combinatorial gene targeting that three antiviral effectors - ZAP, IFIT3, and IFIT1 - together constitute the majority of interferon-mediated restriction of VEEV, while accounting for less than 0.5% of the interferon-induced transcriptome. Together, our data suggests a refined model of the antiviral interferon response in which a small subset of "dominant" ISGs may confer the bulk of the inhibition of a given virus.

Interferon-induced restriction of Chikungunya virus infection

Chikungunya virus (CHIKV) is an enveloped RNA virus that causes Chikungunya fever (CHIKF), which is transmitted to humans through the bite of infected Aedes mosquitos. Although CHIKVF had been regarded as an endemic disease in limited regions of Africa and Asia, the recent global reemergence of CHIKV heightened awareness of this infectious disease, and CHIKV infection is currently considered an increasing threat to public health. However, no specific drug or licensed vaccine is available for CHIKV infection. As seen in other RNA virus infections, CHIKV triggers the interferon (IFN) response that plays a central role in host defense against pathogens. Experimental evidence has demonstrated that control of CHIVK replication by the IFN response is achieved by antiviral effector molecules called interferon-stimulated genes (ISGs), whose expressions are upregulated by IFN stimulation. This review details the molecular basis of the IFN-mediated suppression of CHIKV, particularly the ISGs restricting CHIKV replication.

Protein-Coding Region Derived Small RNA in Exosomes from Influenza A Virus-Infected Cells

Exosomes may function as multifactorial mediators of cell-to-cell communication, playing crucial roles in both physiological and pathological processes. Exosomes released from virus-infected cells may contain RNA and proteins facilitating infection spread. The purpose of our study was to analyze how the small RNA content of exosomes is affected by infection with the influenza A virus (IAV). Exosomes were isolated by ultracentrifugation after hemadsorption of virions and their small RNA content was identified using high-throughput sequencing. As compared to mock-infected controls, 856 RNA transcripts were significantly differentially expressed in exosomes from IAV-infected cells, including fragments of 458 protein-coding (pcRNA), 336 small, 28 long intergenic non-coding RNA transcripts, and 33 pseudogene transcripts. Upregulated pcRNA species corresponded mainly to proteins associated with translation and antiviral response, and the most upregulated among them were RSAD2, CCDC141 and IFIT2. Downregulated pcRNA species corresponded to proteins associated with the cell cycle and DNA packaging. Analysis of differentially expressed pseudogenes showed that in most cases, an increase in the transcription level of pseudogenes was correlated with an increase in their parental genes. Although the role of exosome RNA in IAV infection remains undefined, the biological processes identified based on the corresponding proteins may indicate the roles of some of its parts in IAV replication.

Viperin deficiency promotes dendritic cell activation and function via NF-kappaB activation during Mycobacterium tuberculosis infection

OBJECTIVES AND DESIGN

Dendritic cells (DCs) are one of the key immune cells in bridging innate and adaptive immune response against Mycobacterium tuberculosis (Mtb) infection. Interferons (IFNs) play important roles in regulating DC activation and function. Virus-inhibitory protein, endoplasmic reticulum-associated, interferon-inducible (Viperin) is one of the important IFN-stimulated genes (ISGs), and elicits host defense against infection.

METHODS

We investigated the effects and mechanisms of Viperin on DC activation and function using Viperin deficient bone marrow-derived dendritic cells (BMDCs) during Mtb infection.

RESULTS

Viperin deficiency enhanced phagocytic activity and increased clearance of Mtb in DCs, produced higher abundance of NO, cytokine including interleukin-12 (IL-12), Tumor necrosis factor-α (TNF-α), IL-1β, IL-6 and chemokine including CXCL1, CXCL2 and CXCL10, elevated MHC I, MHC II and co-stimulatory molecules expression, and enhanced CD4⁺ and CD8⁺ T cell responses. Mechanistically, Viperin deficiency promoted DC activation and function through NF-κB p65 activation. NF-κB p65 inhibitor prevented cytokine and chemokine production, and co-stimulatory molecules expression promoted by Viperin deficiency.

CONCLUSIONS

These results suggest that Mtb induced Viperin expression could impair the activation of host defense function of DCs and DC-T cell cross talk during Mtb infection. This research may provide a potential target for future HDT in TB therapy.

Characterisation of key biomarkers in diabetic ulcers via systems bioinformatics

Diabetic ulcers (DUs) are characterised by a high incidence and disability rate. However, its pathogenesis remains elusive. Thus, a deep understanding of the underlying mechanisms for the pathogenesis of DUs has vital implications. The weighted gene co-expression network analysis was performed on the main data from the Gene Expression Omnibus database. Gene Ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were adopted to analyse the potential biological function of the most relevant module. Furthermore, we utilised CytoHubba and protein-protein interaction network to identify the hub genes. Finally, the hub genes were validated by animal experiments in diabetic ulcer mice models. The expression of genes from the turquoise module was found to be strongly related to DUs. GO terms, KEGG analysis showed that biological functions are closely related to immune response. The hub genes included IFI35, IFIT2, MX2, OASL, RSAD2, and XAF1, which were higher in wounds of DUs mice than that in normal lesions. Additionally, we also demonstrated that the expression of hub genes was correlated with the immune response using immune checkpoint, immune cell infiltration, and immune scores. These data suggests that IFI35, IFIT2, MX2, OASL, RSAD2, and XAF1 are crucial for DUs.

Distinct Cellular Tropism and Immune Responses to Alphavirus Infection

Alphaviruses are emerging and reemerging viruses that cause disease syndromes ranging from incapacitating arthritis to potentially fatal encephalitis. While infection by arthritogenic and encephalitic alphaviruses results in distinct clinical manifestations, both virus groups induce robust innate and adaptive immune responses. However, differences in cellular tropism, type I interferon induction, immune cell recruitment, and B and T cell responses result in differential disease progression and outcome. In this review, we discuss aspects of immune responses that contribute to protective or pathogenic outcomes after alphavirus infection. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Astrocyte Control of Zika Infection Is Independent of Interferon Type I and Type III Expression

Simple Summary

Zika virus (ZIKV) is a mosquito-borne virus first isolated from the Zika forest, Uganda, in 1947, which has been spreading across continents since then. We now know ZIKV causes both microencephaly in newborns and neurological complications in adults; however, no effective treatment options have yet been found. A more complete understanding of Zika-infection-mediated pathogenesis and host responses is required to enable the development of novel treatment strategies. In this study, efforts were made to elucidate the host responses following Zika virus infection using several astrocyte cell models, as astrocytes are a major cell type within the central nervous system (CNS) with significant antiviral ability. Our data suggest that astrocytes can resist ZIKV both in an interferon type I- and III-independent manner and suggest that an early and more diverse antiviral response may be more effective in controlling Zika infection. This study also identifies astrocyte cellular models that appear to display differential abilities in the control of viral infection, which may assist in the study of alternate neurotropic virus infections. Overall, this work adds to the growing body of knowledge surrounding ZIKV-mediated cellular host interactions and will contribute to a better understanding of ZIKV-mediated pathogenesis.

Abstract

Zika virus (ZIKV) is a pathogenic neurotropic virus that infects the central nervous system (CNS) and results in various neurological complications. Astrocytes are the dominant CNS cell producer of the antiviral cytokine IFN-β, however little is known about the factors involved in their ability to mediate viral infection control. Recent studies have displayed differential responses in astrocytes to ZIKV infection, and this study sought to elucidate astrocyte cell-specific responses to ZIKV using a variety of cell models infected with either the African (MR766) or Asian (PRVABC59) ZIKV strains. Expression levels of pro-inflammatory (TNF-α and IL-1β) and inflammatory (IL-8) cytokines following viral infection were low and mostly comparable within the ZIKV-resistant and ZIKV-susceptible astrocyte models, with better control of proinflammatory cytokines displayed in resistant astrocyte cells, synchronising with the viral infection level at specific timepoints. Astrocyte cell lines displaying ZIKV-resistance also demonstrated early upregulation of multiple antiviral genes compared with susceptible astrocytes. Interestingly, pre-stimulation of ZIKV-susceptible astrocytes with either poly(I:C) or poly(dA:dT) showed efficient protection against ZIKV compared with pre-stimulation with either recombinant IFN-β or IFN-λ, perhaps indicating that a more diverse antiviral gene expression is necessary for astrocyte control of ZIKV, and this is driven in part through interferon-independent mechanisms.

Viperin is anti-viral in vitro but is dispensable for restricting dengue virus replication or induction of innate and inflammatory responses in vivo

Viperin has antiviral function against many viruses, including dengue virus (DENV), when studied in cells in culture. Here, the antiviral actions of viperin were defined both in vitro and in a mouse in vivo model of DENV infection. Murine embryonic fibroblasts (MEFs) derived from mice lacking viperin (vip^−/−) showed enhanced DENV infection, accompanied by increased IFN-β and induction of ISGs; IFIT1 and CXCL-10 but not IRF7, when compared to wild-type (WT) MEFs. In contrast, subcutaneous challenge of immunocompetent WT and vip^−/− mice with DENV did not result in enhanced infection. Intracranial infection with DENV resulted in body weight loss and neurological disease with a moderate increase in mortality in vip^−/− compared with WT mice, although this was not accompanied by altered brain morphology, immune cell infiltration or DENV RNA level in the brain. Similarly, DENV induction of IFN-β, IFIT1, CXCL-10, IRF7 and TNF-α was not significantly different in WT and vip^−/− mouse brain, although there was a modest but significant increase in DENV induction of IL-6 and IfI27la in the absence of viperin. NanoString nCounter analysis confirmed no significant difference in induction of a panel of inflammatory genes in WT compared to vip^−/− DENV-infected mouse brains. Further, polyI:C stimulation of bone marrow-derived macrophages (BMDMs) induced TNF-α, IFN-β, IL-6 and Nos-2, but responses were not different in BMDMs generated from WT or vip^−/− mice. Thus, while there is significant evidence of anti-DENV actions of viperin in some cell types in vitro, for DENV infection in vivo a lack of viperin does not affect systemic or brain susceptibility to DENV or induction of innate and inflammatory responses.

Viperin has species-specific roles in response to herpes simplex virus infection

Viperin is a gene with a broad spectrum of antiviral functions and various mechanisms of action. The role of viperin in herpes simplex virus type 1 (HSV-1) infection is unclear, with conflicting data in the literature that is derived from a single human cell type. We have addressed this gap by investigating viperin during HSV-1 infection in several cell types, spanning species and including immortalized, non-immortalized and primary cells. We demonstrate that viperin upregulation by HSV-1 infection is cell-type-specific, with mouse cells typically showing greater increases compared with those of human origin. Further, overexpression and knockout of mouse, but not human viperin significantly impedes and increases HSV-1 replication, respectively. In primary mouse fibroblasts, viperin upregulation by infection requires viral gene transcription and occurs in a predominantly IFN-independent manner. Further we identify the N-terminal domain of viperin as being required for the anti-HSV-1 activity. Interestingly, this is the region of viperin that differs most between mouse and human, which may explain the apparent species-specific activity against HSV-1. Finally, we show that HSV-1 virion host shutoff (vhs) protein is a key viral factor that antagonises viperin in mouse cells. We conclude that viperin can be upregulated by HSV-1 in mouse and human cells, and that mouse viperin has anti-HSV-1 activity.

Viperin, an IFN-Stimulated Protein, Delays Rotavirus Release by Inhibiting Non-Structural Protein 4 (NSP4)-Induced Intrinsic Apoptosis

Viral infections lead to expeditious activation of the host's innate immune responses, most importantly the interferon (IFN) response, which manifests a network of interferon-stimulated genes (ISGs) that constrain escalating virus replication by fashioning an ill-disposed environment. Interestingly, most viruses, including rotavirus, have evolved numerous strategies to evade or subvert host immune responses to establish successful infection. Several studies have documented the induction of ISGs during rotavirus infection. In this study, we evaluated the induction and antiviral potential of viperin, an ISG, during rotavirus infection. We observed that rotavirus infection, in a stain independent manner, resulted in progressive upregulation of viperin at increasing time points post-infection. Knockdown of viperin had no significant consequence on the production of total infectious virus particles. Interestingly, substantial escalation in progeny virus release was observed upon viperin knockdown, suggesting the antagonistic role of viperin in rotavirus release. Subsequent studies unveiled that RV-NSP4 triggered relocalization of viperin from the ER, the normal residence of viperin, to mitochondria during infection. Furthermore, mitochondrial translocation of NSP4 was found to be impeded by viperin, leading to abridged cytosolic release of Cyt c and subsequent inhibition of intrinsic apoptosis. Additionally, co-immunoprecipitation studies revealed that viperin associated with NSP4 through regions including both its radical SAM domain and its C-terminal domain. Collectively, the present study demonstrated the role of viperin in restricting rotavirus egress from infected host cells by modulating NSP4 mediated apoptosis, highlighting a novel mechanism behind viperin's antiviral action in addition to the intricacy of viperin-virus interaction.

Structural Insight into the Substrate Scope of Viperin and Viperin-like Enzymes from Three Domains of Life

Viperin is a member of the radical S-adenosylmethionine superfamily and has been shown to restrict the replication of a wide range of RNA and DNA viruses. We recently demonstrated that human viperin (HsVip) catalyzes the conversion of CTP to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP or ddh-synthase), which acts as a chain terminator for virally encoded RNA-dependent RNA polymerases from several flaviviruses. Viperin homologues also exist in non-chordate eukaryotes (e.g., Cnidaria and Mollusca), numerous fungi, and members of the archaeal and eubacterial domains. Recently, it was reported that non-chordate and non-eukaryotic viperin-like homologues are also ddh-synthases and generate a diverse range of ddhNTPs, including the newly discovered ddhUTP and ddhGTP. Herein, we expand on the catalytic mechanism of mammalian, fungal, bacterial, and archaeal viperin-like enzymes with a combination of X-ray crystallography and enzymology. We demonstrate that, like mammalian viperins, these recently discovered viperin-like enzymes operate through the same mechanism and can be classified as ddh-synthases. Furthermore, we define the unique chemical and physical determinants supporting ddh-synthase activity and nucleotide selectivity, including the crystallographic characterization of a fungal viperin-like enzyme that utilizes UTP as a substrate and a cnidaria viperin-like enzyme that utilizes CTP as a substrate. Together, these results support the evolutionary conservation of the ddh-synthase activity and its broad phylogenetic role in innate antiviral immunity.

Antivirals against the Chikungunya Virus

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has re-emerged in recent decades, causing large-scale epidemics in many parts of the world. CHIKV infection leads to a febrile disease known as chikungunya fever (CHIKF), which is characterised by severe joint pain and myalgia. As many patients develop a painful chronic stage and neither antiviral drugs nor vaccines are available, the development of a potent CHIKV inhibiting drug is crucial for CHIKF treatment. A comprehensive summary of current antiviral research and development of small-molecule inhibitor against CHIKV is presented in this review. We highlight different approaches used for the identification of such compounds and further discuss the identification and application of promising viral and host targets.

Viperin interacts with PEX19 to mediate peroxisomal augmentation of the innate antiviral response

Peroxisomes are recognized as significant platforms for the activation of antiviral innate immunity where stimulation of the key adapter molecule mitochondrial antiviral signaling protein (MAVS) within the RIG-I like receptor (RLR) pathway culminates in the up-regulation of hundreds of ISGs, some of which drive augmentation of multiple innate sensing pathways. However, whether ISGs can augment peroxisome-driven RLR signaling is currently unknown. Using a proteomics-based screening approach, we identified Pex19 as a binding partner of the ISG viperin. Viperin colocalized with numerous peroxisomal proteins and its interaction with Pex19 was in close association with lipid droplets, another emerging innate signaling platform. Augmentation of the RLR pathway by viperin was lost when Pex19 expression was reduced. Expression of organelle-specific MAVS demonstrated that viperin requires both mitochondria and peroxisome MAVS for optimal induction of IFN-β. These results suggest that viperin is required to enhance the antiviral cellular response with a possible role to position the peroxisome at the mitochondrial/MAM MAVS signaling synapse, furthering our understanding of the importance of multiple organelles driving the innate immune response against viral infection.

Rediscovering the chikungunya virus

El virus de chikunguña (CHIKV) es un Alfavirus perteneciente al grupo denominado del Viejo Mundo; estos son virus artritogénicos que causan una enfermedad febril caracterizada por artralgias y mialgias. Aunque la muerte por CHIKV es poco frecuente, la enfermedad puede llegar a ser incapacitante y generar un amplio espectro de manifestaciones atípicas, como complicaciones cardiovasculares, respiratorias, oculares, renales y dérmicas, entre otras. Cuando el dolor articular persiste por tres o más meses, da lugar a la forma crónica de la enfermedad denominada reumatismo inflamatorio crónico poschikunguña, el cual es la principal secuela de la enfermedad. Se considera que este virus no es neurotrópico, sin embargo, puede afectar el sistema nervioso central y generar secuelas graves y permanentes, principalmente, en niños y ancianos.

En África, Asia y Europa se habían reportado anteriormente brotes epidémicos por CHIKV, pero solo hasta finales del 2013 se documentó la introducción del virus a las Américas; desde entonces, el virus se ha propagado a 45 países o territorios del continente y el número de casos acumulados ascendió a cerca de dos millones en dos años.

Esta revisión describe de manera general la biología molecular del virus, sus manifestaciones clínicas, su patogénesis y las principales complicaciones posteriores a la infección. Además, reúne la información de la epidemia en Colombia y el continente americano publicada entre el 2014 y el 2020.

Current Status of Chikungunya in India

Chikungunya fever (CHIKF) is an arbovirus disease caused by chikungunya virus (CHIKV), an alphavirus of Togaviridae family. Transmission follows a human-mosquito-human cycle starting with a mosquito bite. Subsequently, symptoms develop after 2-6 days of incubation, including high fever and severe arthralgia. The disease is self-limiting and usually resolve within 2 weeks. However, chronic disease can last up to several years with persistent polyarthralgia. Overlapping symptoms and common vector with dengue and malaria present many challenges for diagnosis and treatment of this disease. CHIKF was reported in India in 1963 for the first time. After a period of quiescence lasting up to 32 years, CHIKV re-emerged in India in 2005. Currently, every part of the country has become endemic for the disease with outbreaks resulting in huge economic and productivity losses. Several mutations have been identified in circulating strains of the virus resulting in better adaptations or increased fitness in the vector(s), effective transmission, and disease severity. CHIKV evolution has been a significant driver of epidemics in India, hence, the need to focus on proper surveillance, and implementation of prevention and control measure in the country. Presently, there are no licensed vaccines or antivirals available; however, India has initiated several efforts in this direction including traditional medicines. In this review, we present the current status of CHIKF in India.

Common Dysregulation of Innate Immunity Pathways in Human Primary Astrocytes Infected With Chikungunya, Mayaro, Oropouche, and Zika Viruses

Arboviruses pose a major threat throughout the world and represent a great burden in tropical countries of South America. Although generally associated with moderate febrile illness, in more severe cases they can lead to neurological outcomes, such as encephalitis, Guillain-Barré syndrome, and Congenital Syndromes. In this context astrocytes play a central role in production of inflammatory cytokines, regulation of extracellular matrix, and control of glutamate driven neurotoxicity in the central nervous system. Here, we presented a comprehensive genome-wide transcriptome analysis of human primary astrocytes infected with Chikungunya, Mayaro, Oropouche, or Zika viruses. Analyses of differentially expressed genes (DEGs), pathway enrichment, and interactomes have shown that Alphaviruses up-regulated genes related to elastic fiber formation and N-glycosylation of glycoproteins, with down-regulation of cell cycle and DNA stability and chromosome maintenance genes. In contrast, Oropouche virus up-regulated cell cycle and DNA maintenance and condensation pathways while down-regulated extracellular matrix, collagen metabolism, glutamate and ion transporters pathways. Zika virus infection only up-regulated eukaryotic translation machinery while down-regulated interferon pathways. Reactome and integration analysis revealed a common signature in down-regulation of innate immune response, antiviral response, and inflammatory cytokines associated to interferon pathway for all arboviruses tested. Validation of interferon stimulated genes by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) corroborated our transcriptome findings. Altogether, our results showed a co-evolution in the mechanisms involved in the escape of arboviruses to antiviral immune response mediated by the interferon (IFN) pathway.

Prophylactic strategies to control chikungunya virus infection

Chikungunya virus (CHIKV) is a (re)emerging arbovirus and the causative agent of chikungunya fever. In recent years, CHIKV was responsible for a series of outbreaks, some of which had serious economic and public health impacts in the affected regions. So far, no CHIKV-specific antiviral therapy or vaccine has been approved. This review gives a brief summary on CHIKV epidemiology, spread, infection and diagnosis. It furthermore deals with the strategies against emerging diseases, drug development and the possibilities of testing antivirals against CHIKV in vitro and in vivo. With our review, we hope to provide the latest information on CHIKV, disease manifestation, as well as on the current state of CHIKV vaccine development and post-exposure therapy.

Current and Promising Antivirals Against Chikungunya Virus

Chikungunya virus (CHIKV) is the causative agent of chikungunya fever (CHIKF) and is categorized as a(n) (re)emerging arbovirus. CHIKV has repeatedly been responsible for outbreaks that caused serious economic and public health problems in the affected countries. To date, no vaccine or specific antiviral therapies are available. This review gives a summary on current antivirals that have been investigated as potential therapeutics against CHIKF. The mode of action as well as possible compound targets (viral and host targets) are being addressed. This review hopes to provide critical information on the in vitro efficacies of various compounds and might help researchers in their considerations for future experiments.

Viperin binds STING and enhances the type-I interferon response following dsDNA detection

Viperin is an interferon-inducible protein that is pivotal for eliciting an effective immune response against an array of diverse viral pathogens. Here we describe a mechanism of viperin's broad antiviral activity by demonstrating the protein's ability to synergistically enhance the innate immune dsDNA signaling pathway to limit viral infection. Viperin co-localized with the key signaling molecules of the innate immune dsDNA sensing pathway, STING and TBK1; binding directly to STING and inducing enhanced K63-linked polyubiquitination of TBK1. Subsequent analysis identified viperin's necessity to bind the cytosolic iron-sulfur assembly component 2A, to prolong its enhancement of the type-I interferon response to aberrant dsDNA. Here we show that viperin facilitates the formation of a signaling enhanceosome, to coordinate efficient signal transduction following activation of the dsDNA signaling pathway, which results in an enhanced antiviral state. We also provide evidence for viperin's radical SAM enzymatic activity to self-limit its immunomodulatory functions. These data further define viperin's role as a positive regulator of innate immune signaling, offering a mechanism of viperin's broad antiviral capacity.

Interleukin-17A Facilitates Chikungunya Virus Infection by Inhibiting IFN-α2 Expression

Interferons (IFNs) are the key components of innate immunity and are crucial for host defense against viral infections. Here, we report a novel role of interleukin-17A (IL-17A) in inhibiting IFN-α2 expression thus promoting chikungunya virus (CHIKV) infection. CHIKV infected IL-17A deficient (Il17a^-/- ) mice expressed a higher level of IFN-α2 and developed diminished viremia and milder footpad swelling in comparison to wild-type (WT) control mice, which was also recapitulated in IL-17A receptor-deficient (Il17ra^-/- ) mice. Interestingly, IL-17A selectively blocked IFN-α2 production during CHIKV, but not West Nile virus (WNV) or Zika virus (ZIKV), infections. Recombinant IL-17A treatment inhibited CHIKV-induced IFN-α2 expression and enhanced CHIKV replication in both human and mouse cells. We further found that IL-17A inhibited IFN-α2 production by modulating the expression of Interferon Regulatory Factor-5 (IRF-5), IRF-7, IFN-stimulated gene 49 (ISG-49), and Mx1 expression during CHIKV infection. Neutralization of IL-17A in vitro leads to the increase of the expression of these antiviral molecules and decrease of CHIKV replication. Collectively, these results suggest a novel function of IL-17A in inhibiting IFN-α2-mediated antiviral responses during CHIKV infection, which may have broad implications in viral infections and other inflammatory diseases.

Chikungunya virus infection induces differential inflammatory and antiviral responses in human monocytes and monocyte-derived macrophages

Chikungunya virus (CHIKV) is a zoonotic arthropod-borne virus that has caused several outbreaks in tropical and subtropical areas worldwide during the last 50 years. The virus is known to target different human cell types throughout the course of infection including epithelial and endothelial cells, fibroblasts, primary monocytes and monocyte-derived macrophages (MDMs). The two latter are phagocytic cell populations of the innate immune system which are involved in some aspects of CHIKV pathogenesis. However, monocytes and macrophages also potentially contribute to the control of viral replication through the expression of different pattern recognition receptors sensing viral pathogens and subsequently, inducing an type I interferone (IFN-I)-dependent antiviral immune response. The aim of this study was to determine the modulation of the expression of Toll-like receptors (TLRs), cytokine secretion capabilities and antiviral factor production in monocytes and MDMs following infection with CHIKV. Moreover, we sought to determine the replication kinetics of CHIKV in these two cell populations. We found that the maximum peak of CHIKV replication was observed between 18- and 24-hours post-infection (hpi), while after that the is strongly reduced. Furthermore, CHIKV infection induced the pro-inflammatory cytokine production starting from the first 6 hpi in both monocytes and MDMs, with similar kinetics but different protein levels. In contrast, the kinetics of transcriptional expression of some TLRs were different between both cell types. In addition, IFN-I, 2',5'-oligoadenylate synthetase 1 (OAS1), and double-stranded RNA-activated protein kinase R (PKR) mRNA levels were detected in response to CHIKV infection of monocytes and MDMs, resulting the highest expression levels at 48 hpi. In conclusion, our data provides evidence that CHIKV infection activates the TLR pathways in primary monocytes and MDMs, which play a crucial role in CHIKV pathogenesis and/or host defense, differentially. However, additional studies are required to determine the functional role of TLRs in monocytes and MDMs.

Antiviral Strategies against Arthritogenic Alphaviruses

Alphaviruses are members of the Togaviridae family that are mainly transmitted by arthropods such as mosquitoes. In the last decades, several alphaviruses have re-emerged, causing outbreaks worldwide. One example is the re-emergence of chikungunya virus (CHIKV) in 2004, which caused massive epidemics in the Indian Ocean region after which the virus dramatically spread to the Americas in late 2013. Besides CHIKV, other alphaviruses, such as the Ross River virus (RRV), Mayaro virus (MAYV), and Venezuelan equine encephalitis virus (VEEV), have emerged and have become a serious public health concern in recent years. Infections with the Old World alphaviruses (e.g., CHIKV, RRV) are primarily associated with polyarthritis and myalgia that can persist for months to years. On the other hand, New World alphaviruses such as VEEV cause mainly neurological disease. Despite the worldwide (re-)emergence of these viruses, there are no antivirals or vaccines available for the treatment or prevention of infections with alphaviruses. It is therefore of utmost importance to develop antiviral strategies against these viruses. We here provided an overview of the reported antiviral strategies against arthritogenic alphaviruses. In addition, we highlighted the future perspectives for the development and the proper use of such antivirals.

Transcriptome analysis of duck embryo fibroblasts for the dynamic response to duck tembusu virus infection and dual regulation of apoptosis genes

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that has caused enormous economic losses in Southeast Asia. However, the pathogenic mechanism and host's responses after DTMUV infection remain poorly understood. During this study, total mRNA sequencing (RNA-Seq) analysis was used to detect the global gene expression in DEFs at various time points after DTMUV infection. We identified 326 genes altered significantly at all time points, and these genes were dynamically enriched in multifarious biological processes, including apoptosis, innate immune response, DNA replication, cell cycle arrest and DNA repair. Next, the results showed that apoptosis was induced and the proportion of apoptosis increased with time, and pro-apoptotic molecules caspases were activated. The RNA-seq data analysis further revealed that most pro-apoptosis and anti-apoptosis genes were early continually responsive, and the genes involved in both intrinsic and extrinsic apoptotic pathways were initiated. Further, the considerably enriched immune-relevant pathways were involved in apoptosis process, and protein-protein interactions (PPIs) analysis showed that IL6, STAT1, TNFAIP3, CFLAR and PTGS2 may be key regulators of DEFs apoptosis. In conclusion, this study not only contributes to understanding the underlying mechanism of DEFs infection with DTMUV, but also provides new insights into targets screening for antiviral therapy.

Transcriptomic Analysis and Functional Characterization Reveal the Duck Interferon Regulatory Factor 1 as an Important Restriction Factor in the Replication of Tembusu Virus

Duck Tembusu virus (DTMUV) infection has caused great economic losses to the poultry industry in China, since its first discovery in 2010. Understanding of host anti-DTMUV responses, especially the innate immunity against DTMUV infection, would be essential for the prevention and control of this viral disease. In this study, transcriptomic analysis of duck embryonic fibroblasts (DEFs) infected with DTMUV reveals that several innate immunity-related pathways, including Toll-like, NOD-like, and retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathways, are activated. Further verification by RT-qPCR confirmed that RIG-I, MAD5, TLR3, TLR7, IFN-α, IFN-β, MX, PKR, MHCI, MHCII, IL-1β, IL-6, (IFN-regulatory factor 1) IRF1, VIPERIN, IFIT5, and CMPK2 were up-regulated in cells infected with DTMUV. Through overexpression and knockdown/out of gene expression, we demonstrated that both VIPERIN and IRF1 played an important role in the regulation of DTMUV replication. Overexpression of either one significantly reduced viral replication as characterized by reduced viral RNA copy numbers and the envelope protein expression. Consistently, down-regulation of either one resulted in the enhanced replication of DTMUV in the knockdown/out cells. We further proved that IRF1 can up-regulate VIPERIN gene expression during DTMUV infection, through induction of type 1 IFNs as well as directly binding to and activation of the VIPERIN promoter. This study provides a genome-wide differential gene expression profile in cells infected with DTMUV and reveals an important function for IRF1 as well as several other interferon-stimulated genes in restricting DTMUV replication.

Viperin: An ancient radical SAM enzyme finds its place in modern cellular metabolism and innate immunity

Viperin plays an important and multifaceted role in the innate immune response to viral infection. Viperin is also notable as one of very few radical SAM-dependent enzymes present in higher animals; however, the enzyme appears broadly conserved across all kingdoms of life, which suggests that it represents an ancient defense mechanism against viral infections. Although viperin was discovered some 20 years ago, only recently was the enzyme's structure determined and its catalytic activity elucidated. The enzyme converts CTP to 3'-deoxy-3',4'-didehydro-CTP, which functions as novel chain-terminating antiviral nucleotide when misincorporated by viral RNA-dependent RNA polymerases. Moreover, in higher animals, viperin interacts with numerous other host and viral proteins, and it is apparent that this complex network of interactions constitutes another important aspect of the protein's antiviral activity. An emerging theme is that viperin appears to facilitate ubiquitin-dependent proteasomal degradation of some of the proteins it interacts with. Viperin-targeted protein degradation contributes to the antiviral response either by down-regulating various metabolic pathways important for viral replication or by directly targeting viral proteins for degradation. Here, we review recent advances in our understanding of the structure and catalytic activity of viperin, together with studies investigating the interactions between viperin and its target proteins. These studies have provided detailed insights into the biochemical processes underpinning this unusual enzyme's wide-ranging antiviral activity. We also highlight recent intriguing reports that implicate a broader role for viperin in regulating nonpathological cellular processes, including thermogenesis and protein secretion.

Viperin protein inhibits the replication of caprine parainfluenza virus type 3 (CPIV 3) by interaction with viral N protein

Caprine parainfluenza virus type3 (CPIV3) is a newly identified member of Paramyxoviridae family. CPIV3 is highly prevalence in China and showed pathogenicity to goats; in addition, CPIV3 infection causes severe clinical disease under stress and/or co-infection conditions. Viperin is one of the hundreds of interferon-stimulated genes (ISGs), and possesses a wide range of antiviral activities. The aim of this study was to systemically explore the anti-CPIV3 activity of ruminants' Viperin. CPIV3 infection up-regulated Viperin transcription but not protein expression in MDBK cells. Bovine and caprine Viperin genes (bVi and gVi) were amplified and analyzed by BLAST and multiple alignment. The obtained bVi/gVi amino acid sequences showed 99.5%-100% identity with previously submitted sequences and has variants at N-terminal domain (1-70aa) between each other. The pcDNA3.1 plasmids containing bVi and gVi genes were constructed to over-express the target proteins. CPIV3 was inoculated in MDBK cells over-expressing bVi/gVi and viral load was detected by qRT-PCR, virus titration and Western blot. Both of the bVi and gVi significantly inhibited CPIV3 genome copy numbers and viral titers at 24 and 48 hpi (P < 0.01); and viral N protein expression was also decreased, comparing with those of mock transfected group. The last 50aa C-terminal region was crucial for its anti-CPIV3 activity. In addition, the over-expression of bVi/gVi did not influence CPIV3 binding, entry and release in the cells. These results indicated the anti-CPIV3 activity occurred in viral RNA/protein synthesis progress of the viral replication cycle. The Viperin also showed similar inhibitory effect on different CPIV3 strains. The potential interaction of Viperin with viral proteins (N, P, C and V) was determined by confocal laser scanning microscopy and Co-IP assay. Co-localization of Viperin with N, P or C, but not V, was observed; while only N protein direct interacted with Viperin in Co-IP test, no matter using viral protein expressing plasmids transfected or CPIV3 infected cell samples. In conclusion, the bVi and gVi Viperin effectively inhibited CPIV3 replication potentially via the interaction of Viperin with viral N protein. The present results gave more information about antiviral activity of ruminants Viperin and provided foundation for further studies of the interaction of Viperin with CPIV3 and other related viruses.

Modelling West Nile Virus and Usutu Virus Pathogenicity in Human Neural Stem Cells

West Nile virus (WNV) and Usutu virus (USUV) are genetically related neurotropic mosquito-borne flaviviruses, which frequently co-circulate in nature. Despite USUV seeming to be less pathogenic for humans than WNV, the clinical manifestations induced by these two viruses often overlap and may evolve to produce severe neurological complications. The aim of this study was to investigate the effects of WNV and USUV infection on human induced pluripotent stem cell-derived neural stem cells (hNSCs), as a model of the neural progenitor cells in the developing fetal brain and in adult brain. Zika virus (ZIKV), a flavivirus with known tropism for NSCs, was used as the positive control. Infection of hNSCs and viral production, effects on cell viability, apoptosis, and innate antiviral responses were compared among viruses. WNV displayed the highest replication efficiency and cytopathic effects in hNSCs, followed by USUV and then ZIKV. In these cells, both WNV and USUV induced the overexpression of innate antiviral response genes at significantly higher levels than ZIKV. Expression of interferon type I, interleukin-1β and caspase-3 was significantly more elevated in WNV- than USUV-infected hNSCs, in agreement with the higher neuropathogenicity of WNV and the ability to inhibit the interferon response pathway.

Ovine viperin inhibits bluetongue virus replication

Viral infections can lead to interferon production, which achieves its antiviral function primarily by activating the JAK/STAT pathway and inducing multiple interferon-stimulated genes (ISGs). Although considerable ISGs have been identified in antiviral researches, little is known about ISGs in bluetongue virus (BTV) infection. Viperin is the most highly induced ISG following BTV infection, which suggests that it may play a critical role in the anti-BTV immune response. The aim of this study was to characterize ovine Viperin (oViperin) and explore whether it can inhibit BTV replication. We cloned the coding sequences (CDS) of sheep Viperin, and the sequence analysis showed that oViperin displayed a high similarity with other species. oViperin has a leucine zipper in the N-terminal, a CxxxCxxC motif in the SAM domain, and a conservative C-terminus. We found that oViperin mRNA expression was significantly up-regulated in a time- and multiplicity of infection (MOI)-dependent manner following BTV infection. oViperin overexpression resulted in a significant inhibition in BTV replication, whereas an oViperin knockdown in MDOK cells increased BTV replication. This study shows for the first time, that oViperin has antiviral activity towards BTV infection and provides important information to research the interaction between BTV and oViperin.

Dengue virus infects the mouse eye following systemic or intracranial infection and induces inflammatory responses

Dengue virus (DENV) infection is associated with clinical ocular presentations and here DENV infection of the eye was assessed in mice. In an AG129 mouse model of antibody-dependent enhancement of DENV infection, DENV RNA was detected in the eye and vascular changes were present in the retinae. Intraocular CD8 and IFN-γ mRNA were increased in mice born to DENV-naïve, but not DENV-immune mothers, while TNF-α mRNA was induced and significantly higher in mice born to DENV-immune than DENV-naïve mothers. DENV RNA was detected in the eye following intracranial DENV infection and CD8 mRNA but not IFN-γ nor TNF-α were induced. In all models, viperin was increased following DENV infection. Thus, DENV in the circulation or the brain can infect the eye and stimulate innate immune responses, with induction of viperin as one response that consistently occurs in multiple DENV eye-infection models in both an IFN-dependent and independent manner.

The Intestinal Microbiome Restricts Alphavirus Infection and Dissemination through a Bile Acid-Type I IFN Signaling Axis

Chikungunya virus (CHIKV), an emerging alphavirus, has infected millions of people. However, the factors modulating disease outcome remain poorly understood. Here, we show in germ-free mice or in oral antibiotic-treated conventionally housed mice with depleted intestinal microbiomes that greater CHIKV infection and spread occurs within 1 day of virus inoculation. Alteration of the microbiome alters TLR7-MyD88 signaling in plasmacytoid dendritic cells (pDCs) and blunts systemic production of type I interferon (IFN). Consequently, circulating monocytes express fewer IFN-stimulated genes and become permissive for CHIKV infection. Reconstitution with a single bacterial species, Clostridium scindens, or its derived metabolite, the secondary bile acid deoxycholic acid, can restore pDC- and MyD88-dependent type I IFN responses to restrict systemic CHIKV infection and transmission back to vector mosquitoes. Thus, symbiotic intestinal bacteria modulate antiviral immunity and levels of circulating alphaviruses within hours of infection through a bile acid-pDC-IFN signaling axis, which affects viremia, dissemination, and potentially transmission.

Viperin Reveals Its True Function

Most cells respond to viral infections by activating innate immune pathways that lead to the induction of antiviral restriction factors. One such factor, viperin, was discovered almost two decades ago based on its induction during viral infection. Since then, viperin has been shown to possess activity against numerous viruses via multiple proposed mechanisms. Most recently, however, viperin was demonstrated to catalyze the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP), a previously unknown ribonucleotide. Incorporation of ddhCTP causes premature termination of RNA synthesis by the RNA-dependent RNA polymerase of some viruses. To date, production of ddhCTP by viperin represents the only activity of viperin that links its enzymatic activity directly to an antiviral mechanism in human cells. This review examines the multiple antiviral mechanisms and biological functions attributed to viperin.

Disease Resolution in Chikungunya-What Decides the Outcome?

Chikungunya disease (CHIKD) is a viral infection caused by an alphavirus, chikungunya virus (CHIKV), and triggers large outbreaks leading to epidemics. Despite the low mortality rate, it is a major public health concern owing to high morbidity in affected individuals. The complete spectrum of this disease can be divided into four phases based on its clinical presentation and immunopathology. When a susceptible individual is bitten by an infected mosquito, the bite triggers inflammatory responses attracting neutrophils and initiating a cascade of events, resulting in the entry of the virus into permissive cells. This phase is termed the pre-acute or the intrinsic incubation phase. The virus utilizes the cellular components of the innate immune system to enter into circulation and reach primary sites of infection such as the lymph nodes, spleen, and liver. Also, at this point, antigen-presenting cells (APCs) present the viral antigens to the T cells thereby activating and initiating adaptive immune responses. This phase is marked by the exhibition of clinical symptoms such as fever, rashes, arthralgia, and myalgia and is termed the acute phase of the disease. Viremia reaches its peak during this phase, thereby enhancing the antigen-specific host immune response. Simultaneously, T cell-mediated activation of B cells leads to the formation of CHIKV specific antibodies. Increase in titres of neutralizing IgG/IgM antibodies results in the clearance of virus from the bloodstream and marks the initiation of the post-acute phase. Immune responses mounted during this phase of the infection determine the degree of disease progression or its resolution. Some patients may progress to a chronic arthritic phase of the disease that may last from a few months to several years, owing to a compromised disease resolution. The present review discusses the immunopathology of CHIKD and the factors that dictate disease progression and its resolution.

TREM-1 activation is a potential key regulator in driving severe pathogenesis of enterovirus A71 infection

Hand, foot and mouth disease (HFMD), caused by enterovirus A71 (EV-A71), presents mild to severe disease, and sometimes fatal neurological and respiratory manifestations. However, reasons for the severe pathogenesis remain undefined. To investigate this, infection and viral kinetics of EV-A71 isolates from clinical disease (mild, moderate and severe) from Sarawak, Malaysia, were characterised in human rhabdomyosarcoma (RD), neuroblastoma (SH-SY5Y) and peripheral blood mononuclear cells (PBMCs). High resolution transcriptomics was used to decipher EV-A71-host interactions in PBMCs. Ingenuity analyses revealed similar pathways triggered by all EV-A71 isolates, although the extent of activation varied. Importantly, several pathways were found to be specific to the severe isolate, including triggering receptor expressed on myeloid cells 1 (TREM-1) signalling. Depletion of TREM-1 in EV-A71-infected PBMCs with peptide LP17 resulted in decreased levels of pro-inflammatory genes for the moderate and severe isolates. Mechanistically, this is the first report describing the transcriptome profiles during EV-A71 infections in primary human cells, and the potential involvement of TREM-1 in the severe disease pathogenesis, thus providing new insights for future treatment targets.

Pan-viral protection against arboviruses by activating skin macrophages at the inoculation site

Arthropod-borne viruses (arboviruses) are important human pathogens for which there are no specific antiviral medicines. The abundance of genetically distinct arbovirus species, coupled with the unpredictable nature of their outbreaks, has made the development of virus-specific treatments challenging. Instead, we have defined and targeted a key aspect of the host innate immune response to virus at the arthropod bite that is common to all arbovirus infections, potentially circumventing the need for virus-specific therapies. Using mouse models and human skin explants, we identify innate immune responses by dermal macrophages in the skin as a key determinant of disease severity. Post-exposure treatment of the inoculation site by a topical TLR7 agonist suppressed both the local and subsequent systemic course of infection with a variety of arboviruses from the Alphavirus, Flavivirus, and Orthobunyavirus genera. Clinical outcome was improved in mice after infection with a model alphavirus. In the absence of treatment, antiviral interferon expression to virus in the skin was restricted to dermal dendritic cells. In contrast, stimulating the more populous skin-resident macrophages with a TLR7 agonist elicited protective responses in key cellular targets of virus that otherwise proficiently replicated virus. By defining and targeting a key aspect of the innate immune response to virus at the mosquito bite site, we have identified a putative new strategy for limiting disease after infection with a variety of genetically distinct arboviruses.

Integrated Analysis of Differentially Expressed miRNAs and mRNAs in Goat Skin Fibroblast Cells in Response to Orf Virus Infection Reveals That cfa-let-7a Regulates Thrombospondin 1 Expression

Orf is a zoonotic disease that has caused huge economic losses globally. Systematical analysis of dysregulated cellular micro RNAs (miRNAs) in response to Orf virus (ORFV) infection has not been reported. In the current study, miRNA sequencing and RNA sequencing (RNA-seq) were performed in goat skin fibroblast (GSF) cells at 0, 18, and 30 h post infection (h.p.i). We identified 140 and 221 differentially expressed (DE) miRNAs at 18 and 30 h.p.i, respectively. We also identified 729 and 3961 DE genes (DEGs) at 18 and 30 h.p.i, respectively. GO enrichment analysis indicates enrichment of apoptotic regulation, defense response to virus, immune response, and inflammatory response at both time points. DE miRNAs and DEGs with reverse expression were used to construct miRNA-gene networks. Seven DE miRNAs and seven DEGs related to "negative regulation of viral genome replication" were identified. These were validated by RT-qPCR. Cfa-let-7a, a significantly upregulated miRNA, was found to repress Thrombospondin 1 (THBS1) mRNA and protein expression by directly targeting the THBS1 3' untranslated region. THBS1 has been reported to induce apoptosis; therefore, the cfa-let-7a-THBS1 axis may play an important role in cellular apoptosis during ORFV infection. This study provides new insights into ORFV and host cell interaction mechanisms.