Differential Anti-Influenza Activity among Allelic Variants at TheSus Scrofa Mx1Locus

Anti-Schmallenberg Virus Activities of Type I/III Interferons-Induced Mx1 GTPases from Different Mammalian Species

Mx proteins are key factors of the innate intracellular defense mechanisms that act against viruses induced by type I/III interferons. The family Peribunyaviridae includes many viruses of veterinary importance, either because infection results in clinical disease or because animals serve as reservoirs for arthropod vectors. According to the evolutionary arms race hypothesis, evolutionary pressures should have led to the selection of the most appropriate Mx1 antiviral isoforms to resist these infections. Although human, mouse, bat, rat, and cotton rat Mx isoforms have been shown to inhibit different members of the Peribunyaviridae, the possible antiviral function of the Mx isoforms from domestic animals against bunyaviral infections has, to our knowledge, never been studied. Herein, we investigated the anti-Schmallenberg virus activity of bovine, canine, equine, and porcine Mx1 proteins. We concluded that Mx1 has a strong, dose-dependent anti-Schmallenberg activity in these four mammalian species.

[Opportunities and risks of the use of genetic resistances to infectious diseases in pigs - an overview]

Demands for health, performance and welfare in pigs, as well as the desire for consumer protection and reduced antibiotic use, require optimal measures in advance of disease development. This includes, in principle, the use of genetically more resistant lines and breeding animals, whose existence has been proven for a wide range of pathogen-host interactions. In addition, attempts are being made to identify the gene variants responsible for disease resistance in order to force the selection of suitable populations, also using modern biotechnical technics. The present work is intended to provide an overview of the research status achieved in this context and to highlight opportunities and risks for the future.The evaluation of the international literature shows that genetic disease resistance exist in many areas of swine diseases. However, polygenic inheritance, lack of animal models and the influence of environmental factors during evaluation render their implementation in practical breeding programs demanding. This is where modern molecular genetic methods, such as Gene Editing, come into play. Both approaches possess their pros and cons, which are discussed in this paper. The most important infectious diseases in pigs, including general diseases and epizootics, diseases of the respiratory and digestive tract and diseases of the immune system are taken into account.

Current and prospective control strategies of influenza A virus in swine

BACKGROUND

Influenza A Viruses (IAV) are endemic pathogens of significant concern in humans and multiple keystone livestock species. Widespread morbidity in swine herds negatively impacts animal welfare standards and economic performance whilst human IAV pandemics have emerged from pigs on multiple occasions. To combat the rising prevalence of swine IAV there must be effective control strategies available.

MAIN BODY

The most basic form of IAV control on swine farms is through good animal husbandry practices and high animal welfare standards. To control inter-herd transmission, biosecurity considerations such as quarantining of pigs and implementing robust health and safety systems for workers help to reduce the likelihood of swine IAV becoming endemic. Closely complementing the physical on-farm practices are IAV surveillance programs. Epidemiological data is critical in understanding regional distribution and variation to assist in determining an appropriate response to outbreaks and understanding the nature of historical swine IAV epidemics and zoonoses. Medical intervention in pigs is restricted to vaccination, a measure fraught with the intrinsic difficulties of mounting an immune response against a highly mutable virus. It is the best available tool for controlling IAV in swine but is far from being a perfect solution due to its unreliable efficacy and association with an enhanced respiratory disease. Because IAV generally has low mortality rates there is a reticence in the uptake of vaccination. Novel genetic technologies could be a complementary strategy for IAV control in pigs that confers broad-acting resistance. Transgenic pigs with IAV resistance are useful as models, however the complexity of these reaching the consumer market limits them to research models. More promising are gene-editing approaches to prevent viral exploitation of host proteins and modern vaccine technologies that surpass those currently available.

CONCLUSION

Using the suite of IAV control measures that are available for pigs effectively we can improve the economic productivity of pig farming whilst improving on-farm animal welfare standards and avoid facing the extensive social and financial costs of a pandemic. Fighting 'Flu in pigs will help mitigate the very real threat of a human pandemic emerging, increase security of the global food system and lead to healthier pigs.

Anti-Influenza A Virus Activities of Type I/III Interferons-Induced Mx1 GTPases from Different Mammalian Species

Type I/III interferons provide powerful and universal innate intracellular defense mechanisms against viruses. Among the antiviral effectors induced, Mx proteins of some species appear as key components of defense against influenza A viruses. It is expected that such an antiviral protein must display a platform dedicated to the recognition of said viruses. In an attempt to identify such platform in human MxA, an evolution-guided approach capitalizing on the antagonistic arms race between MxA and its viral targets and the genomic signature it left on primate genomes revealed that the surface-exposed so-called "loop L4", which protrudes from the compact structure of the MxA stalk, is a hotspot of recurrent positive selection. Since MxA is archetypic of Mx1 proteins in general, we reasoned that the L4 loop also functions as a recognition platform for influenza viruses in the Mx1 proteins of other species that had been exposed to the virus for ever. In this study, the anti-influenza activity of 5 distinct mammalian Mx1 proteins was measured by comparing the number of viral nucleoprotein-positive cells 7 h after infection in a sample of 100,000 cells expected to contain both Mx1-positive and Mx1-negative cell subpopulations. The systematic depletion (P < 0.001) of virus nucleoprotein-positive cells among equine, bubaline, porcine, and bovine Mx1-expressing cell populations compared with Mx-negative cells suggests a strong anti-influenza A activity. Looking for common anti-influenza signature elements in the sequence of these Mx proteins, we found that an aromatic residue at positions 561 or 562 in the L4 loop seems critical for the anti-influenza function and/or specificity of mammalian Mx1.

Mx Is Not Responsible for the Antiviral Activity of Interferon-α against Japanese Encephalitis Virus

Mx proteins are interferon (IFN)-induced dynamin-like GTPases that are present in all vertebrates and inhibit the replication of myriad viruses. However, the role Mx proteins play in IFN-mediated suppression of Japanese encephalitis virus (JEV) infection is unknown. In this study, we set out to investigate the effects of Mx1 and Mx2 expression on the interferon-α (IFNα) restriction of JEV replication. To evaluate whether the inhibitory activity of IFNα on JEV is dependent on Mx1 or Mx2, we knocked down Mx1 or Mx2 with siRNA in IFNα-treated PK-15 cells and BHK-21 cells, then challenged them with JEV; the production of progeny virus was assessed by plaque assay, RT-qPCR, and Western blotting. Our results demonstrated that depletion of Mx1 or Mx2 did not affect JEV restriction imposed by IFNα, although these two proteins were knocked down 66% and 79%, respectively. Accordingly, expression of exogenous Mx1 or Mx2 did not change the inhibitory activity of IFNα to JEV. In addition, even though virus-induced membranes were damaged by Brefeldin A (BFA), overexpressing porcine Mx1 or Mx2 did not inhibit JEV proliferation. We found that BFA inhibited JEV replication, not maturation, suggesting that BFA could be developed into a novel antiviral reagent. Collectively, our findings demonstrate that IFNα inhibits JEV infection by Mx-independent pathways.

Porcine Mx1 fused to HIV Tat protein transduction domain (PTD) inhibits classical swine fever virus infection in vitro and in vivo

Background

Classical swine fever (CSF) caused by CSF virus (CSFV) is highly contagious andcauses significant economic losses in the pig industry throughout the world. Previously we demonstrated that porcine Mx1 (poMx1), when fused to HIV Tat protein transduction domain (PTD), inhibits CSFV propagation in PK-15 cells, but it is unknown whether PTD-poMx1 exhibits antiviral activity in other porcine lines and it is efficacious for controlling CSFV infection in pigs in China.

Methods

Two porcine cell lines, ST and 3D4/21, were used to investigate in vitro antiviral activity of PTD-poMx1 against CSFV using confocal microscopy, western blot, flow cytometry, and real-time RT-PCR. Furthermore, in vivo antiviral activity of PTD-poMx1 was assessed by means of rectal temperature, clinical score, pathological lesion, white blood cell count, viral load, etc.

Results

PTD-poMx1 entered both cell lines within 3 h and maintained for 16 h, but did not affect CSFV binding and uptake. Viral titers and qRT-PCR data showed that PTD-poMx1 inhibited CSFV replication in both cell lines, showing significant antiviral activity after infection. Injection of PTD-poMx1 into CSFV-challenged pigs attenuated CSFV symptoms and viremia in dose-dependent manner but did not completely block virus replication within 14 days post challenge, suggesting that PTD-poMx1 confers partial protection against a lethal challenge.

Conclusion

We demonstrated the anti-CSFV activity of PTD-poMx1 in vitro and in vivo. The results have shown that treatment with PTD-poMx1 alleviated symptoms and viral load in infected pigs. The results support our previous in vitro studies and suggest that PTD-poMx1 could be promising in reducing the clinical signs caused by CSFV.

Production of transgenic pigs over-expressing the antiviral gene Mx1

The myxovirus resistance gene (Mx1) has a broad spectrum of antiviral activities. It is therefore an interesting candidate gene to improve disease resistance in farm animals. In this study, we report the use of somatic cell nuclear transfer (SCNT) to produce transgenic pigs over-expressing the Mx1 gene. These transgenic pigs express approximately 15–25 times more Mx1 mRNA than non-transgenic pigs, and the protein level of Mx1 was also markedly enhanced. We challenged fibroblast cells isolated from the ear skin of transgenic and control pigs with influenza A virus and classical swine fever virus (CFSV). Indirect immunofluorescence assay (IFA) revealed a profound decrease of influenza A proliferation in Mx1 transgenic cells. Growth kinetics showed an approximately 10-fold reduction of viral copies in the transgenic cells compared to non-transgenic controls. Additionally, we found that the Mx1 transgenic cells were more resistant to CSFV infection in comparison to non-transgenic cells. These results demonstrate that the Mx1 transgene can protect against viral infection in cells of transgenic pigs and indicate that the Mx1 transgene can be harnessed to develop disease-resistant pigs.

Evolving gene targets and technology in influenza detection

Influenza viruses cause recurring epidemic outbreaks every year associated with high morbidity and mortality. Despite extensive research and surveillance efforts to control influenza outbreaks, the primary mitigation treatment for influenza is the development of yearly vaccine mixes targeted for the most prevalent virus strains. Consequently, the focus of many detection technologies has evolved toward accurate identification of subtype and understanding the evolution and molecular determinants of novel and pathogenic forms of influenza. The recent availability of potential antiviral treatments are only effective if rapid and accurate diagnostic tests for influenza epidemic management are available; thus, early detection of influenza infection is still important for prevention, containment, patient management, and infection control. This review discusses the current and emerging technologies for detection and strain identification of influenza virus and their specific gene targets, as well as their implications in patient management.

Host genetic determinants of influenza pathogenicity

Despite effective vaccines, influenza remains a major global health threat due to the morbidity and mortality caused by seasonal epidemics, as well as the 2009 pandemic. Also of profound concern are the rare but potentially catastrophic transmissions of avian influenza to humans, highlighted by a recent H7N9 influenza outbreak. Murine and human studies reveal that the clinical course of influenza is the result of a combination of both host and viral genetic determinants. While viral pathogenicity has long been the subject of intensive efforts, research to elucidate host genetic determinants, particularly human, is now in the ascendant, and the goal of this review is to highlight these recent insights.

Pandemic influenza A viruses escape from restriction by human MxA through adaptive mutations in the nucleoprotein

The interferon-induced dynamin-like MxA GTPase restricts the replication of influenza A viruses. We identified adaptive mutations in the nucleoprotein (NP) of pandemic strains A/Brevig Mission/1/1918 (1918) and A/Hamburg/4/2009 (pH1N1) that confer MxA resistance. These resistance-associated amino acids in NP differ between the two strains but form a similar discrete surface-exposed cluster in the body domain of NP, indicating that MxA resistance evolved independently. The 1918 cluster was conserved in all descendent strains of seasonal influenza viruses. Introduction of this cluster into the NP of the MxA-sensitive influenza virus A/Thailand/1(KAN-1)/04 (H5N1) resulted in a gain of MxA resistance coupled with a decrease in viral replication fitness. Conversely, introduction of MxA-sensitive amino acids into pH1N1 NP enhanced viral growth in Mx-negative cells. We conclude that human MxA represents a barrier against zoonotic introduction of avian influenza viruses and that adaptive mutations in the viral NP should be carefully monitored.

Detection of disease resistance and susceptibility alleles in pigs using oligonucleotide microarray hybridization

A multiplex DNA microarray chip aimed at the identification of allelic polymorphisms was developed for simultaneous detection of swine disease resistance genes underlying malignant hyperthermia ( RYR), postweaning diarrhea, edema disease ( FUT1), neonatal diarrhea ( MUC4), and influenza ( MX1). The on-chip detection was performed with fragmented polymerase chain reaction (PCR)–amplified products. Particular emphasis was placed on the reduction of the number of PCR reactions required. The targets were biotin labeled during the PCR reaction, and the arrays were detected using a colorimetric methodology. Target recognition was provided by specific capture probes designed for each susceptible or resistant allelic variant. Sequencing was chosen as the gold standard to assess chip accuracy. All genotypes retrieved from the microarray (476) fit with sequencing data despite the fact that each pig was heterozygote for at least 1 target gene.

Genetic and splice variations of Bos taurus CD46 shift cell permissivity to BVDV, the bovine pestivirus

The pestivirus bovine viral diarrhea virus (BVDV) is known to bind to the CD46 molecule, which subsequently promotes entry of the virus. Mapping of the BVD-virion-binding site has shown that two peptides, 66EQIV69 and 82GQVLAL87, located on antiparallel beta sheets in the most distal complement control protein module (CCP1), provide the attachment platform. In the present study, we reveal the existence of ten distinct allelic versions of the CCP1 module, varying significantly in frequency among taurine and indicine races. A complex mRNA splicing pattern was also evidenced for bovine CD46, generating three different serine-threonine-proline segments and five different cytoplasmic domains. The four most frequent allelic variants and the six splice variants were then expressed in BVDV-nonpermissive porcine cells and the quantity of progeny virions generated by each cell preparation was measured 48 h post-infection. As expected, ectopic expression of the 10 bovine CD46 isoforms rendered the PK15 cells permissive to BVDV, as attested by the 100,000-fold greater recovery of virions from these cells than from non-transfected cells. This permissivity increase was significantly lower (-33%, P<0.001) when the canonical CCP1 was replaced with the variant most frequent in zebus, suggesting positive or negative selection of this allele in the latter and in the former, respectively. The predicted secondary structure of this variant suggests that the measured loss of function is due to the disappearance of one of the two beta sheets constituting the BVDV attachment platform. On the other hand we showed that for a given CCP1, the titer recovered at 48 hpi also depended on the nature of the CD46 cytoplasmic domain (P<0.001). This result implies that virus binding generates a cytoplasmic-tail-dependent outside-in signal that determines permissivity to BVDV.

Genetic control of host resistance to porcine reproductive and respiratory syndrome virus (PRRSV) infection

This manuscript focuses on the advances made using genomic approaches to identify biomarkers that define genes and pathways that are correlated with swine resistance to infection with porcine reproductive and respiratory syndrome virus (PRRSV), the most economically important swine viral pathogen worldwide. International efforts are underway to assess resistance and susceptibility to infectious pathogens using tools such as gene arrays, single nucleotide polymorphisms (SNPs) chips, genome-wide association studies (GWAS), proteomics, and advanced bioinformatics. These studies should identify new candidate genes and biological pathways associated with host PRRS resistance and alternate viral disease processes and mechanisms; they may unveil biomarkers that account for genetic control of PRRS or, alternately, that reveal new targets for therapeutics or vaccines. Previous genomic approaches have expanded our understanding of quantitative trait loci (QTL) controlling traits of economic importance in pig production, e.g., feed efficiency, meat production, leanness; only recently have these included health traits and disease resistance. Genomic studies should have substantial impact for the pig industry since it is now possible to include the use of biomarkers for basic health traits alongside broader set of markers utilized for selection of pigs for improved performance and reproductive traits, as well as pork quality. Additionally these studies may reveal alternate PRRS control mechanisms that can be exploited for novel drugs, biotherapeutics and vaccine designs.

Dynamin-like MxA GTPase: structural insights into oligomerization and implications for antiviral activity

The interferon-inducible MxA GTPase is a key mediator of cell-autonomous innate immunity against a broad range of viruses such as influenza and bunyaviruses. MxA shares a similar domain structure with the dynamin superfamily of mechanochemical enzymes, including an N-terminal GTPase domain, a central middle domain, and a C-terminal GTPase effector domain. Recently, crystal structures of a GTPase domain dimer of dynamin 1 and of the oligomerized stalk of MxA (built by the middle and GTPase effector domains) were determined. These data provide exciting insights into the architecture and antiviral function of the MxA oligomer. Moreover, the structural knowledge paves the way for the development of novel antiviral drugs against influenza and other highly pathogenic viruses.

Interferon-induced Sus scrofa Mx1 blocks endocytic traffic of incoming influenza A virus particles

The interferon-induced Mx proteins of vertebrates are dynamin-like GTPases, some isoforms of which can additionally inhibit the life cycle of certain RNA viruses. Here we show that the porcine Mx1 protein (poMx1) inhibits replication of influenza A virus and we attempt to identify the step at which the viral life cycle is blocked. In infected cells expressing poMx1, the level of transcripts encoding the viral nucleoprotein is significantly lower than normal, even when secondary transcription is prevented by exposure to cycloheximide. This reveals that a pretranscriptional block participates to the anti-influenza activity. Binding and internalization of incoming virus particles are normal in the presence of poMx1 but centripetal traffic to the late endosomes is interrupted. Surprisingly but decisively, poMx1 significantly alters binding of early endosome autoantigen 1 to early endosomes and/or early endosome size and spatial distribution. This is compatible with impairment of traffic of the endocytic vesicles to the late endosomes.

Enhanced grass carp reovirus resistance of Mx-transgenic rare minnow (Gobiocypris rarus)

In the interferon-induced antiviral mechanisms, the Mx pathway is one of the most powerful. Mx proteins have direct antiviral activity and inhibit a wide range of viruses by blocking an early stage of the viral genome replication cycle. However, antiviral activity of piscine Mx remains unclear in vivo. In the present study, an Mx-like gene was cloned, characterized and gene-transferred in rare minnow Gobiocypris rarus, and its antiviral activity was confirmed in vivo. The full length of the rare minnow Mx-like cDNA is 2241 bp in length and encodes a polypeptide of 625 amino acids with an estimated molecular mass of 70.928 kDa and a predicted isoelectric point of 7.33. Analysis of the deduced amino acid sequence indicated that the mature peptide contains an amino-terminal tripartite GTP-binding motif, a dynamin family signature sequence, a GTPase effector domain and two carboxy-terminal leucine zipper motifs, and is the most similar to the crucian carp (Carassius auratus) Mx3 sequence with an identity of 89%. Both P0 and F1 generations of Mx-transgenic rare minnow demonstrated very significantly high survival rate to GCRV infection (P<0.01). The mRNA expression of Mx gene was consistent with survival rate in F1 generation. The virus yield was also concurrent with survival time using electron microscope technology. Rare minnow has Mx gene(s) of its own but introducing more Mx gene improves their resistance to GCRV. Mx-transgenic rare minnow might contribute to control the GCRV diseases.

Inhibition of a large double-stranded DNA virus by MxA protein

Increasing evidence points to the importance of the interferon (IFN) response in determining the host range and virulence of African swine fever virus (ASFV). Infection with attenuated strains of ASFV leads to the upregulation of genes controlled by IFN pathways, including myxovirus resistance (Mx) genes that are potent effectors of the antiviral state. Mx gene products are known to inhibit the replication of many negative-sense single-stranded RNA viruses, as well as double-stranded RNA viruses, positive-sense single-stranded RNA viruses, and the reverse-transcribing DNA virus hepatitis B virus. Here, we provide data that extend the known range of viruses inhibited by Mx to include the large double-stranded DNA viruses. Stably transfected Vero cells expressing human MxA protein did not support ASFV plaque formation, and virus replication in these cells was reduced 100-fold compared with that in control cells. In contrast, ASFV replication in cells expressing MxB protein or a mutant MxA protein was similar to that in control Vero cells. There was a drastic reduction in ASFV late protein synthesis in MxA-expressing cells, correlating with the results of previous work on the effect of IFN on viral replication. Strikingly, the inhibition of ASFV replication was linked to the recruitment of MxA protein to perinuclear viral assembly sites, where the protein surrounded the virus factories. Interactions between ASFV and MxA were similar to those seen between MxA and different RNA viruses, suggesting a common inhibitory mechanism.

Genetic susceptibility and resistance to influenza infection and disease in humans and mice

Although genetic risk factors for influenza infection have not yet been defined in people, differences in genetic background and related variation in the response to infection, as well as viral virulence, are all likely to influence both the likelihood of infection and disease severity. However, apart from characterization of viral binding sites in avian and mammalian hosts, relatively little investigation has focused on host genetic determinants of susceptibility or resistance to infection, or the severity of the associated disease in humans or other species. Similarly, the role of genetic background in the generation of an efficacious immune response to either infection or vaccination has not been extensively evaluated. However, genetic influences on susceptibility and resistance to numerous infectious agents and on the resultant host inflammatory and immune responses are well established in both humans and other animals. Mouse-adapted strains of human influenza viruses and the use of inbred strains of laboratory mice have supported extensive characterization of the pathogenesis and immunology of influenza virus infections. Like individual humans, inbred strains of mice vary in their reactions to influenza infection, particularly with regard to the inflammatory response and disease severity, supporting the potential use of these mice as a valuable surrogate for human genetic variation. Relying heavily on what we have learned from mice, this overview summarizes existing animal, human and epidemiologic data suggestive of host genetic influences on influenza infection.

The Mx GTPase family of interferon-induced antiviral proteins

Mx proteins are interferon-induced members of the dynamin superfamily of large GTPases. They inhibit a wide range of viruses by blocking an early stage of the replication cycle. Studies in genetically defined mouse strains highlight their powerful action in early antiviral host defence.

Interferon-induced Mx proteins in antiviral host defense

Mx proteins are key components of the antiviral state induced by interferons in many species. They belong to the class of dynamin-like large guanosine triphosphatases (GTPases) known to be involved in intracellular vesicle trafficking and organelle homeostasis. Mx GTPases share structural and functional properties with dynamin, such as self-assembly and association with intracellular membranes. A unique property of some Mx GTPases is their antiviral activity against a wide range of RNA viruses, including influenza viruses and members of the bunyavirus family. These viruses are inhibited at an early stage in their life cycle, soon after host cell entry and before genome amplification. The mouse Mx1 GTPase accumulates in the cell nucleus where it associates with components of the PML nuclear bodies and inhibits influenza and Thogoto viruses known to replicate in the nucleus. The human MxA GTPase accumulates in the cytoplasm and is partly associated with a COP-I-positive subcompartment of the endoplasmic reticulum. This membrane compartment seems to provide an interaction platform that facilitates viral target recognition. In the case of bunyaviruses, MxA recognizes the viral nucleocapsid protein and interferes with its role in viral genome replication. In the case of Thogoto virus, MxA recognizes the viral nucleoprotein and prevents the incoming viral nucleocapsids from being transported into the nucleus, the site of viral transcription and replication. In both cases, GTP-binding and carboxy-terminal effector functions of MxA are required for target recognition. In general, Mx GTPases appear to detect viral infection by sensing nucleocapsid-like structures. As a consequence, these viral components are trapped and sorted to locations where they become unavailable for the generation of new virus particles.