Truncation of the NS1 protein converts a low pathogenic avian influenza virus into a strong interferon inducer in duck cells

The NS1 protein of influenza A viruses is known as a nonessential virulence factor inhibiting type I interferon (IFN) production in mammals and in chicken cells. Whether NS1 inhibits the induction of type I IFNs in duck cells is currently unknown. In order to investigate this issue, we used reverse genetics to generate a virus expressing a truncated NS1 protein. Using the low pathogenic avian influenza virus A/turkey/Italy/977/1999 (H7N1) as a backbone, we were able to rescue a virus expressing a truncated NS1 protein of 99 amino acids in length. The truncated virus replicated poorly in duck embryonic fibroblasts, but reached high titers in the mammalian IFN-deficient Vero cell line. Using a gene reporter system to measure duck type I IFN production, we showed that the truncated virus is a potent inducer of type I IFN in cell culture. These results show that the NS1 protein functions to prevent the induction of IFN in duck cells and underline the need for a functional NS1 protein in order for the virus to express its full virulence

Lipid-dependent regulation of the unfolded protein response.

Protein folding homeostasis in the lumen of the endoplasmic reticulum is defended by signal transduction pathways that are activated by an imbalance between unfolded proteins and chaperones (so called ER stress). Collectively referred to as the unfolded protein response (UPR) this homeostatic response is initiated by three known ER stress transducers: IRE1, PERK and ATF6. These ER-localised transmembrane (TM) proteins posses lumenal stress sensing domains and cytosolic effector domains that collectively activate a gene expression programme regulating the production of proteins involved in the processing and maturation of secreted proteins that enter the ER. However, beyond limiting unfolded protein stress in the ER the UPR has important connections to lipid metabolism that are the subject of this review.This work was supported by a Wellcome Trust Intermediate Clinical Fellowship (to R.V.), a Wellcome Trust Principal Research Fellowship (to D.R.), and European Union Seventh Framework Programme Grant (Beta Bat, 277713).This is the final published version. It first appeared at: http://www.sciencedirect.com/science/article/pii/S0955067414001434#

Nucleolar localization of influenza A NS1: striking differences between mammalian and avian cells

In mammalian cells, nucleolar localization of influenza A NS1 requires the presence of a C-terminal nucleolar localization signal. This nucleolar localization signal is present only in certain strains of influenza A viruses. Therefore, only certain NS1 accumulate in the nucleolus of mammalian cells. In contrast, we show that all NS1 tested in this study accumulated in the nucleolus of avian cells even in the absence of the above described C-terminal nucleolar localization signal. Thus, nucleolar localization of NS1 in avian cells appears to rely on a different nucleolar localization signal that is more conserved among influenza virus strains

Borna Disease Virus Blocks Potentiation of Presynaptic Activity through Inhibition of Protein Kinase C Signaling

Infection by Borna disease virus (BDV) enables the study of the molecular mechanisms whereby a virus can persist in the central nervous system and lead to altered brain function in the absence of overt cytolysis and inflammation. This neurotropic virus infects a wide variety of vertebrates and causes behavioral diseases. The basis of BDV-induced behavioral impairment remains largely unknown. Here, we investigated whether BDV infection of neurons affected synaptic activity, by studying the rate of synaptic vesicle (SV) recycling, a good indicator of synaptic activity. Vesicular cycling was visualized in cultured hippocampal neurons synapses, using an assay based on the uptake of an antibody directed against the luminal domain of synaptotagmin I. BDV infection did not affect elementary presynaptic functioning, such as spontaneous or depolarization-induced vesicular cycling. In contrast, infection of neurons with BDV specifically blocked the enhancement of SV recycling that is observed in response to stimuli-induced synaptic potentiation, suggesting defects in long-term potentiation. Studies of signaling pathways involved in synaptic potentiation revealed that this blockade was due to a reduction of the phosphorylation by protein kinase C (PKC) of proteins that regulate SV recycling, such as myristoylated alanine-rich C kinase substrate (MARCKS) and Munc18–1/nSec1. Moreover, BDV interference with PKC-dependent phosphorylation was identified downstream of PKC activation. We also provide evidence suggesting that the BDV phosphoprotein interferes with PKC-dependent phosphorylation. Altogether, our results reveal a new mechanism by which a virus can cause synaptic dysfunction and contribute to neurobehavioral disorders

Modulation of Innate Immune Signalling by Lipid-Mediated MAVS Transmembrane Domain Oligomerization.

RIG-I-like receptors detect viral RNA in infected cells and promote oligomerization of the outer mitochondrial membrane protein MAVS to induce innate immunity to viral infection through type I interferon production. Mitochondrial reactive oxygen species (mROS) have been shown to enhance anti-viral MAVS signalling, but the mechanisms have remained obscure. Using a biochemical oligomerization-reporter fused to the transmembrane domain of MAVS, we found that mROS inducers promoted lipid-dependent MAVS transmembrane domain oligomerization in the plane of the outer mitochondrial membrane. These events were mirrored by Sendai virus infection, which similarly induced lipid peroxidation and promoted lipid-dependent MAVS transmembrane domain oligomerization. Our observations point to a role for mROS-induced changes in lipid bilayer properties in modulating antiviral innate signalling by favouring the oligomerization of MAVS transmembrane domain in the outer-mitochondrial membrane.This work was supported by a Wellcome Trust Intermediate Clinical Fellowship (093764 o RV), a Wellcome Trust Principal Research Fellowship (084812 to DR), a Wellcome Trust Strategic Award for core facilities to the Cambridge Institute for Medical Research (100140) and European Union Seventh Framework Programme Grant (Beta Bat, 277713).

Pathobiology of highly pathogenic H5 avian influenza viruses in naturally infected Galliformes and Anseriformes in France during winter 2015-2016

In late 2015, an epizootic of Highly Pathogenic Avian Influenza (H5Nx) was registered in Southwestern France, including more than 70 outbreaks in commercial poultry flocks. Phylogenetic analyses suggested local emergence of H5 viruses which differed from A/goose/Guangdong/1/1996 clade 2.3.4.4b lineage and shared a unique polybasic cleavage site in their hemagglutinin protein. The present work provides an overview of the pathobiological picture associated with this epizootic in naturally infected chickens, guinea fowls and ducks. Upon necropsy examination, selected tissues were sampled for histopathology, immunohistochemistry and quantitative Real Time Polymerase Chain Reaction. In Galliformes, HPAIVs infection manifested as severe acute systemic vasculitis and parenchymal necrosis and was associated with endothelial expression of viral antigen. In ducks, lesions were mild and infrequent, with sparse antigenic detection in respiratory and digestive mucosae and leukocytes. Tissue quantifications of viral antigen and RNA were higher in chickens and guinea fowls compared to duck. Subsequently, recombinant HA (rHA) was generated from a H5 HPAIV isolated from an infected duck to investigate its glycan-binding affinity for avian mucosae. Glycan-binding analysis revealed strong affinity of rHA for 3'Sialyl-LacNAc and low affinity for Sialyl-LewisX, consistent with a duck-adapted virus similar to A/Duck/Mongolia/54/2001 (H5N2). K222R and S227R mutations on rHA sequence shifted affinity towards Sialyl-LewisX and led to an increased affinity for chicken mucosa, confirming the involvement of these two mutations in the glycan-binding specificity of the HA. Interestingly, the rHA glycan binding pattern of guinea fowl appeared intermediate between duck and chicken. The present study presents a unique pathobiological description of the H5 HPAIVs outbreaks that occurred in 2015-2016 in Southwestern France

From one to many: The within-host rise of viral variants

International audienceOver the course of a viral infection, a tremendous number of virions are produced: up to 10 14-more than there are stars in the Milky Way [1]. These viruses do not exist as a genetically identical population. Genetic changes are constantly occurring, especially for RNA viruses, creating a cloud of genetically related variants [2]. Viral evolution within the infected host is shaped by host and viral factors. Repeatedly, in the history of viral diseases, new strains have emerged with selective advantages, such as drug resistance or enhanced transmissibility. For example, a few months after the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) emergence, variants with enhanced infectivity have spread worldwide [3]. At the origin of each of these emergences, at least one infected host has been the scene of a competition between the newly arisen variant and its progenitors. Viral populations face bottlenecks (events reducing the population size, and, therefore, its genetic diversity) that can be divided into 2 categories: transmission bottlenecks and withinhost bottlenecks, which we will discuss here [4]. We propose that, in order to emerge, a variant has to overcome the within-host bottlenecks by winning the competition against its progenitors, allowing it to be transmitted and selected

Le virus H5N1 dans l'eau de surface au Cambodge (évaluation et application d'une technique de détection)

Pour détecter le virus H5N1 responsable de l'Influenza Aviaire Hautement Pathogène, une méthode de concentration dans de grands volumes d'eau de surface est testée ici dans les conditions rencontrées au Cambodge. La technique repose sur un principe d'adsorption-élution sur laine de verre suivie d'une concentration secondaire par précipitation sur polyéthylène glycol. Le seuil de détection déterminé dans cette étude permet de mettre en évidence la présence d'une quantité de virus avoisinant la dose infectante pour un canard. Les rendements déterminés avec différents types d'eau combinés à la valeur seuil permettront d'interpréter les futurs résultats avec précision. Enfin, les virus sont toujours infections en fin de processus, ce qui permettra de conclure sur le caractère infections des échantillons analysés.TOULOUSE-EN Vétérinaire (315552301) / SudocSudocFranceF

L'influenza chez les chevaux (étude de l'épidémie de 2007 au Québec)

La grippe équine est une maladie respiratoire aiguë, causée principalement par deux sous-types distincts du virus Influenza de type A : le H7N7 et le H3N8. Il s agit de la maladie des voies respiratoires la plus pénalisante sur le plan économique pour la filière équine (courses, compétitions, ventes, ). Le travail accompli dans cette étude a pour but de présenter les caractéristiques de l épizootie de grippe équine ayant eu lieu durant l été et l automne 2007 au Québec, d analyser et discuter de l originalité de cette épizootie et enfin, de présenter les moyens de prévention de cette maladie.TOULOUSE-EN Vétérinaire (315552301) / SudocSudocFranceF