Influenza virus not cRAFTy enough to dodge viperin

Rifaximin ameliorates influenza A virus infection-induced lung barrier damage by regulating gut microbiota

Prior research has indicated that the gut-lung-axis can be influenced by the intestinal microbiota, thereby impacting lung immunity. Rifaximin is a broad-spectrum antibacterial drug that can maintain the homeostasis of intestinal microflora. In this study, we established an influenza A virus (IAV)-infected mice model with or without rifaximin supplementation to investigate whether rifaximin could ameliorate lung injury induced by IAV and explore the molecular mechanism involved. Our results showed that IAV caused significant weight loss and disrupted the structure of the lung and intestine. The analysis results of 16S rRNA and metabolomics indicated a notable reduction in the levels of probiotics Lachnoclostridium, Ruminococcaceae_UCG-013, and tryptophan metabolites in the fecal samples of mice infected with IAV. In contrast, supplementation with 50 mg/kg rifaximin reversed these changes, including promoting the repair of the lung barrier and increasing the abundance of Muribaculum, Papillibacter and tryptophan-related metabolites content in the feces. Additionally, rifaximin treatment increased ILC3 cell numbers, IL-22 level, and the expression of RORγ and STAT-3 protein in the lung. Furthermore, our findings demonstrated that the administration of rifaximin can mitigate damage to the intestinal barrier while enhancing the expression of AHR, IDO-1, and tight junction proteins in the small intestine. Overall, our results provided that rifaximin alleviated the imbalance in gut microbiota homeostasis induced by IAV infection and promoted the production of tryptophan-related metabolites. Tryptophan functions as a signal to facilitate the activation and movement of ILC3 cells from the intestine to the lung through the AHR/STAT3/IL-22 pathway, thereby aiding in the restoration of the barrier. KEY POINTS: • Rifaximin ameliorated IAV infection-caused lung barrier injury and induced ILC3 cell activation. • Rifaximin alleviated IAV-induced gut dysbiosis and recovered tryptophan metabolism. • Tryptophan mediates rifaximin-induced ILC3 cell activation via the AHR/STAT3/IL-22 pathway.

Recombinant porcine interferon δ8 inhibited porcine deltacoronavirus infection in vitro and in vivo

Porcine deltacoronavirus (PDCoV) poses a significant threat to both the pig industry and public safety, and has recently been identified in humans. Currently, there are no commercially available vaccines or antiviral treatments for PDCoV. In this study, recombinant porcine interferon δ8 (rINF-δ8) expressed by the HEK 293F expression system was used to evaluated its antiviral activity against PDCoV both in vitro and in vivo. Results demonstrated that rIFN-δ8 displayed non-toxic to ST cells and primary PAMs, and effectively inhibited PDCoV replication in a dose-dependent manner in vitro, with complete suppression of virus replication at a concentration of 2 μg/ml. Treatment of piglets with two doses of 25 μg/kg of rIFN-δ8 reduced clinical symptoms, decreased virus shedding, alleviated intestinal damage, and lowered the viral load in the jejunum and ileum. Furthermore, the levels of interferon-stimulated genes (ISGs) such as Viper, Mx1, ISG15, IFIT1, OSA, and IFITM1 were significantly increased both in vitro and in vivo, with elevated ISG levels sustained for at least 3 days in vivo. These findings suggest that rIFN-δ8 has the potential to serve as an effective antiviral agent for preventing PDCoV in pigs in the future.

The antiviral enzyme viperin inhibits cholesterol biosynthesis

Many enveloped viruses bud from cholesterol-rich lipid rafts on the cell membrane. Depleting cellular cholesterol impedes this process and results in viral particles with reduced viability. Viperin (Virus Inhibitory Protein, Endoplasmic Reticulum-associated, Interferon iNducible) is an endoplasmic reticulum membrane-associated enzyme that exerts broad-ranging antiviral effects, including inhibiting the budding of some enveloped viruses. However, the relationship between viperin expression and the retarded budding of virus particles from lipid rafts on the cell membrane is unclear. Here, we investigated the effect of viperin expression on cholesterol biosynthesis using transiently expressed genes in the human cell line human embryonic kidney 293T (HEK293T). We found that viperin expression reduces cholesterol levels by 20% to 30% in these cells. Following this observation, a proteomic screen of the viperin interactome identified several cholesterol biosynthetic enzymes among the top hits, including lanosterol synthase (LS) and squalene monooxygenase (SM), which are enzymes that catalyze key steps in establishing the sterol carbon skeleton. Coimmunoprecipitation experiments confirmed that viperin, LS, and SM form a complex at the endoplasmic reticulum membrane. While coexpression of viperin was found to significantly inhibit the specific activity of LS in HEK293T cell lysates, coexpression of viperin had no effect on the specific activity of SM, although did reduce SM protein levels by approximately 30%. Despite these inhibitory effects, the coexpression of neither LS nor SM was able to reverse the viperin-induced depletion of cellular cholesterol levels, possibly because viperin is highly expressed in transfected HEK293T cells. Our results establish a link between viperin expression and downregulation of cholesterol biosynthesis that helps explain viperin's antiviral effects against enveloped viruses.

Viperin interaction with mitochondrial antiviral signaling protein (MAVS) limits viperin-mediated inhibition of the interferon response in macrophages

Viperin is an antiviral protein that is upregulated by interferons and by ligands for a variety of innate immune receptors. It possesses diverse capabilities and functions in an array of viral infections. Studies have shown that it appears to be particularly important in defence against RNA viruses, such as West Nile, Dengue, and Chikungunya viruses, although the specific mechanisms involved are not well understood at the molecular level. Here we identify the mitochondrial antiviral signalling protein MAVS as a novel viperin interaction partner, most likely in mitochondria associated membranes, and characterize a more central, overarching role of viperin as a negative regulator of the interferon response, an ability that can be regulated by the viperin-MAVS interaction. This suggests a novel mechanism of viperin action in immune defence against RNA viruses by which it may prevent pathology from excessive immune responses.

Establishment of a Novel Primary Human Skeletal Myoblast Cellular Model for Chikungunya Virus Infection and Pathogenesis

Chikungunya virus (CHIKV) is a re-emerging arbovirus known to cause chronic myalgia and arthralgia and is now considered endemic in countries across Asia and Africa. The tissue tropism of CHIKV infection in humans remains, however, ill-defined. Due to the fact that myositis is commonly observed in most patients infected with CHIKV, we sought to develop a clinically relevant cellular model to better understand the pathogenesis of CHIKV infection. In this study, primary human skeletal muscle myoblasts (HSMM) were established as a novel human primary cell line that is highly permissive to CHIKV infection, with maximal amounts of infectious virions observed at 16 hours post infection. Genome-wide microarray profiling analyses were subsequently performed to identify and map genes that are differentially expressed upon CHIKV infection. Infection of HSMM cells with CHIKV resulted in altered expressions of host genes involved in skeletal- and muscular-associated disorders, innate immune responses, cellular growth and death, host metabolism and virus replication. Together, this study has shown the establishment of a clinically relevant primary human cell model that paves the way for the further analysis of host factors and their involvement in the various stages of CHIKV replication cycle and viral pathogenesis.

Molecular characterization and expression analysis of the duck viperin gene

Viperin is well known as one of the interferon-stimulated genes involved in innate immunity. Recent studies showed that this gene is mainly responsible for antiviral response to a large variety of viral infections. In this study, we successfully cloned and characterized the complete coding sequence of duck viperin gene. The duck viperin gene encodes 363 amino acids (aa) and is highly similar to viperins from other species. Moreover, secondary and 3D structures were predicted, and these structures showed two main domains, one signal peptide, and one radical S-adenosyl methionine (SAM) domain. Additionally, the duck viperin expression was analyzed in vitro and in vivo, and analysis results indicated that the duck viperin can be strongly up-regulated by poly(I:C) and Newcastle disease virus in primary duck embryo fibroblast cells. Results also demonstrated that Newcastle disease virus significantly induced duck viperin expression in the spleen, kidneys, liver, brain, and blood. Our findings will contribute to future studies on the detailed functions and potential underlying mechanisms of this novel protein in innate immunity.

Response of primary human airway epithelial cells to influenza infection: a quantitative proteomic study

Influenza A virus exerts a large health burden during both yearly epidemics and global pandemics. However, designing effective vaccine and treatment options has proven difficult since the virus evolves rapidly. Therefore, it may be beneficial to identify host proteins associated with viral infection and replication to establish potential new antiviral targets. We have previously measured host protein responses in continuously cultured A549 cells infected with mouse-adapted virus strain A/PR/8/34(H1N1; PR8). We here identify and measure host proteins differentially regulated in more relevant primary human bronchial airway epithelial (HBAE) cells. A total of 3740 cytosolic HBAE proteins were identified by 2D LC–MS/MS, of which 52 were up-regulated ≥2-fold and 41 were down-regulated ≥2-fold after PR8 infection. Up-regulated HBAE proteins clustered primarily into interferon signaling, other host defense processes, and molecular transport, whereas down-regulated proteins were associated with cell death signaling pathways, cell adhesion and motility, and lipid metabolism. Comparison to influenza-infected A549 cells indicated some common influenza-induced host cell alterations, including defense response, molecular transport proteins, and cell adhesion. However, HBAE-specific alterations consisted of interferon and cell death signaling. These data point to important differences between influenza replication in continuous and primary cell lines and/or alveolar and bronchial epithelial cells.

In vivo and in vitro studies on the antiviral activities of viperin against influenza H1N1 virus infection

Influenza A virus has caused a number of pandemics in past decades, including the recent H1N1-2009 pandemic. Viperin is an interferon (IFN)-inducible protein of innate immunity, and acts as a broad-spectrum antiviral protein. We explored the antiviral activities and mechanisms of viperin during influenza virus (IFV) infection in vitro and in vivo. Wild-type (WT) HeLa and viperin-expressing HeLa cells were infected with influenza A/WSN/33/H1N1 (WSN33) virus, and subjected to virological, light and electron microscopic analyses. Viperin expression reduced virus replication and titres, and restricted viral budding. Young and old viperin-knockout (KO) mice and WT control animals were challenged with influenza WSN33 at lethal doses of 103 and 104 p.f.u. via the intratracheal route. Lungs were subjected to histopathological, virological and molecular studies. Upon lethal IFV challenge, both WT and KO mice revealed similar trends of infection and recovery with similar mortality rates. Viral quantification assay and histopathological evaluation of lungs from different time points showed no significant difference in viral loads and lung damage scores between the two groups of mice. Although the in vitro studies demonstrated the ability of viperin to restrict influenza H1N1 virus replication, the viperin-deficient mouse model indicated that absence of viperin enhanced neither the viral load nor pulmonary damage in the lungs of infected mice. This may be due to the compensation of IFN-stimulated genes in the lungs and/or the influenza non-structural protein 1-mediated IFN antagonism dampening the IFN response, thereby rendering the loss of viperin insignificant. Nevertheless, further investigations that exploit the antiviral mechanisms of viperin as prophylaxis are still warranted.

The antiviral protein viperin is a radical SAM enzyme

Viperin, an interferon-inducible antiviral protein, is shown to bind an iron-sulfur cluster, based on iron analysis as well as UV-Vis and electron paramagnetic resonance spectroscopic data. The reduced protein contains a [4Fe-4S](1+) cluster whose g-values are altered upon addition of S-adenosylmethionine (SAM), consistent with SAM coordination to the cluster. Incubation of reduced viperin with SAM results in reductive cleavage of SAM to produce 5'-deoxyadenosine (5'-dAdo), a reaction characteristic of the radical SAM superfamily. The 5'-dAdo cleavage product was identified by a combination of HPLC and mass spectrometry analysis.