Antiviral RNAi response against the insect-specific Agua Salud alphavirus

Arboviruses transmitted by mosquitoes are responsible for the death of millions of people each year. In addition to arboviruses, many insect-specific viruses (ISVs) have been discovered in mosquitoes in the last decade. ISVs, in contrast to arboviruses transmitted by mosquitoes to vertebrates, cannot replicate in vertebrate cells even when they are evolutionarily closely related to arboviruses. The alphavirus genus includes many arboviruses, although only a few ISVs have been discovered from this genus so far. Here, we investigate the interactions of a recently isolated insect-specific alphavirus, Agua-Salud alphavirus (ASALV), with its mosquito host. RNAi is one of the essential antiviral responses against arboviruses, although there is little knowledge on the interactions of RNAi with ISVs. Through knock-down of transcripts of the different key RNAi pathway (siRNA, miRNA and piRNA) proteins, we show the antiviral role of Ago2 (siRNA), Ago1 (miRNA), and Piwi4 proteins against ASALV in Aedes aegypti derived cells. ASALV replication increased in Dicer2 and Ago2 knock-out cells, confirming the antiviral role of the siRNA pathway. In infected cells, mainly ASALV-specific siRNAs are produced while piRNAs, with the characteristic nucleotide bias resulting from ping-pong amplification, are only produced in Dicer2 knock-out cells. Taken together, ASALV interactions with the mosquito RNAi response differs from arthropod-borne alphaviruses in some aspects, although they also share some commonalities. Further research is needed to understand whether the identified differences can be generalised to other insect-specific alphaviruses.

The Innate Immune DNA Sensing cGAS-STING Signaling Pathway Mediates Anti-PRRSV Function

Porcine reproductive and respiratory syndrome virus (PRRSV) modulates host innate immunity which plays a key role against PRRSV infection. As a RNA virus, PRRSV is mainly sensed by innate immune RNA receptors, whereas the role of innate immune DNA sensors in the PRRSV infection has not been elucidated. Here, we investigated the roles of DNA sensing cGAS-STING pathway in both PRRSV infected Marc-145 cells and porcine macrophages. The results show that in Marc-145 cells, the stable expression of STING with or without stimulations exhibited anti-PRRSV activity, and STING knockout heightened PRRSV infection. In CD163-3D4/21 porcine macrophages, either expression of STING or stimulation of cGAS-STING signaling obviously suppressed PRRSV infection, whereas in STING knockdown macrophages, the PRRSV infection was upregulated. Our results clearly demonstrate that the host cGAS-STING signal exerts an important antiviral role in PRRSV infection.

The balance between p53 isoforms modulates the efficiency of HIV-1 infection in macrophages

Several host factors influence HIV-1 infection and replication. The p53-mediated antiviral role in monocytes-derived macrophages (MDMs) was previously highlighted. Indeed, an increase in p53 level results in a stronger restriction against HIV-1 early replication steps through SAMHD1 activity. In this study, we investigated the potential role of some p53 isoforms in HIV-1 infection. Transfection of isoform-specific siRNA induces distinctive effects on the virus life cycle. For example, in contrast to a siRNA targeting all isoforms, a knockdown of Δ133p53 transcripts reduces virus replication in MDMs that is correlated with a decrease in phosphorylated inactive SAMHD1. Combination of Δ133p53 knockdown and Nutlin-3, a pharmacological inhibitor of MDM2 that stabilizes p53, further reduces susceptibility of MDMs to HIV-1 infection, thus suggesting an inhibitory role of Δ133p53 towards p53 antiviral activity. In contrast, p53β knockdown in MDMs increases the viral production independently of SAMHD1. Moreover, experiments with a Nef-deficient virus show that this viral protein plays a protective role against the antiviral environment mediated by p53. Finally, HIV-1 infection affects the expression pattern of p53 isoforms by increasing p53β and p53γ mRNA levels while stabilizing the protein level of p53α and some isoforms from the p53β subclass. The balance between the various p53 isoforms is therefore an important factor in the overall susceptibility of macrophages to HIV-1 infection, fine-tuning the p53 response against HIV-1. This study brings a new understanding of the complex role of p53 in virus replication processes in myeloid cells. Importance As of today, HIV-1 is still considered as a global pandemic without a functional cure, partly because of the presence of stable viral reservoirs. Macrophages constitute one of these cell reservoirs, contributing to the viral persistence. Studies investigating the host factors involved in cell susceptibility to HIV-1 infection might lead to a better understanding of the reservoir formation and will eventually allow the development of an efficient cure. Our team previously showed the antiviral role of p53 in macrophages, which acts by compromising the early steps of HIV-1 replication. In this study, we demonstrate the involvement of p53 isoforms, which regulates p53 activity and define the cellular environment influencing viral replication. In addition, the results concerning the potential role of p53 in antiviral innate immunity could be transposed to other fields of virology and suggest that knowledge in oncology can be applied to HIV-1 research.

Inhaled Nitric Oxide for postexposure chemoprophylaxis of COVID-19

Background: Postexposure prophylaxis has been an overlooked strategy in the context of COVID-19. Inhaled Nitric Oxide offers itself as a potential tool in this context. The aim of this systematic review was to depict previous in vivo and in vitro studies demonstrating an antiviral role for NO Methodology:Embase, Medline and the Cochrane Central Register were used to search for specific keywords such as “Nitric oxide” AND “Antiviral activity” for relevant publications up to 1st of June 2021. The systematic review was performed using PRISMA protocolResults:Twenty-one studies were identified depicting an antiviral role for Nitric Oxide. Those studies involved sixteen viruses. Only four of the depicted studies were clinical trials, while three were performed on a murine model. The remainder of the studies involved in vitro experimentation of the role of NO in halting viral replication of several viruses including SARS-CoV-2Conclusion: While early reports of NO role in the treatment of COVID-19 suggested its use for the treatment of established ARDS, NO seems to have a much earlier and more efficient prophylactic role. It inhibits a protease needed for canonical viral replication of SARS-CoV-2, namely Furin, by decreasing calcium's cytosolic levels. This might add a significant tool for postexposure chemoprophylaxis in the at-risk group, especially medical personnel.

The Role of Autophagy in Varicella Zoster Virus Infection

Autophagy is an evolutionary conserved cellular process serving to degrade cytosolic organelles or foreign material to maintain cellular homeostasis. Autophagy has also emerged as an important process involved in complex interactions with viral pathogens during infection. It has become apparent that autophagy may have either proviral or antiviral roles, depending on the cellular context and the specific virus. While evidence supports an antiviral role of autophagy during certain herpesvirus infections, numerous examples illustrate how herpesviruses may also evade autophagy pathways or even utilize this process to their own advantage. Here, we review the literature on varicella zoster virus (VZV) and autophagy and describe the mechanisms by which VZV may stimulate autophagy pathways and utilize these to promote cell survival or to support viral egress from cells. We also discuss recent evidence supporting an overall antiviral role of autophagy, particularly in relation to viral infection in neurons. Collectively, these studies suggest complex and sometimes opposing effects of autophagy in the context of VZV infection. Much remains to be understood concerning these virus–host interactions and the impact of autophagy on infections caused by VZV.

Viral Infection Modulates Mitochondrial Function

Mitochondria are important organelles involved in metabolism and programmed cell death in eukaryotic cells. In addition, mitochondria are also closely related to the innate immunity of host cells against viruses. The abnormality of mitochondrial morphology and function might lead to a variety of diseases. A large number of studies have found that a variety of viral infections could change mitochondrial dynamics, mediate mitochondria-induced cell death, and alter the mitochondrial metabolic status and cellular innate immune response to maintain intracellular survival. Meanwhile, mitochondria can also play an antiviral role during viral infection, thereby protecting the host. Therefore, mitochondria play an important role in the interaction between the host and the virus. Herein, we summarize how viral infections affect microbial pathogenesis by altering mitochondrial morphology and function and how viruses escape the host immune response.

The serine/threonine/tyrosine kinase STY46 defends against hordeivirus infection by phosphorylating γb protein

Protein phosphorylation is a common post-translational modification that frequently occurs during plant–virus interaction. Host protein kinases often regulate virus infectivity and pathogenicity by phosphorylating viral proteins. The Barley stripe mosaic virus (BSMV) γb protein plays versatile roles in virus infection and the coevolutionary arms race between plant defense and viral counter-defense. Here, we identified that the autophosphorylated cytosolic serine/threonine/tyrosine (STY) protein kinase 46 of Nicotiana benthamiana (NbSTY46) phosphorylates and directly interacts with the basic motif domain (aa 19–47) of γb in vitro and in vivo. Overexpression of wild-type NbSTY46, either transiently or transgenically, suppresses BSMV replication and ameliorates viral symptoms, whereas silencing of NbSTY46 leads to increased viral replication and exacerbated symptom. Moreover, the antiviral role of NbSTY46 requires its kinase activity, as the NbSTY46T436A mutant, lacking kinase activity, not only loses the ability to phosphorylate and interact with γb but also fails to impair BSMV infection when expressed in plants. NbSTY46 could also inhibit the replication of Lychnis ringspot virus, another chloroplast-replicating hordeivirus. In summary, we report a function of the cytosolic kinase STY46 in defending against plant viral infection by phosphorylating a viral protein in addition to its basal function in plant growth, development, and abiotic stress responses.

Modulation of the Tissue Expression Pattern of Zebrafish CRP-Like Molecules Suggests a Relevant Antiviral Role in Fish Skin

Recent studies suggest that short pentraxins in fish might serve as biomarkers for not only bacterial infections, as in higher vertebrates including humans, but also for viral ones. These fish orthologs of mammalian short pentraxins are currently attracting interest because of their newly discovered antiviral activity. In the present work, the modulation of the gene expression of all zebrafish short pentraxins (CRP-like proteins, CRP1-7) was extensively analyzed by quantitative polymerase chain reaction. Initially, the tissue distribution of crp1-7 transcripts and how the transcripts varied in response to a bath infection with the spring viremia of carp virus, were determined. The expression of crp1-7 was widely distributed and generally increased after infection (mostly at 5 days post infection), except for crp1 (downregulated). Interestingly, several crp transcription levels significantly increased in skin. Further assays in mutant zebrafish of recombinant activation gene 1 (rag1) showed that all crps (except for crp2, downregulated) were already constitutively highly expressed in skin from rag1 knockouts and only increased moderately after viral infection. Similar results were obtained for most mx isoforms (a reporter gene of the interferon response), suggesting a general overcompensation of the innate immunity in the absence of the adaptive one.

Host Transcriptomic Response Following Administration of Rotavirus Vaccine in Infants’ Mimics Wild Type Infection

BackgroundRotavirus (RV) is an enteric pathogen that has devastating impact on childhood morbidity and mortality worldwide. The immunologic mechanism underlying the protection achieved after RV vaccination is not yet fully understood.MethodsWe compared the transcriptome of children affected by community-acquired RV infection and children immunized with a live attenuated RV vaccine (RotaTeq®).ResultsRV vaccination mimics the wild type infection causing similar changes in children’s transcriptome, including transcripts associated with cell cycle, diarrhea, nausea, vomiting, intussusception, and abnormal morphology of midgut. A machine learning approach allowed to detect a combination of nine-transcripts that differentiates vaccinated from convalescent-naturally infected children (AUC: 90%; 95%CI: 70–100) and distinguishes between acute-infected and healthy control children (in both cases, AUC: 100%; 95%CI: 100–100). We identified a miRNA hsa-mir-149 that seems to play a role in the host defense against viral pathogens and may have an antiviral role.DiscussionOur findings might shed further light in the understanding of RV infection, its functional link to intussusception causes, as well as guide development of antiviral treatments and safer and more effective vaccines. The nine-transcript signature may constitute a marker of vaccine protection and helps to differentiate vaccinated from naturally infected or susceptible children.