Pseudorabies virus induces autophagy to enhance viral replication in mouse neuro-2a cells in vitro

The precise function of alphaherpesvirus tegument proteins and their interactions during the viral life cycle

Alphaherpesvirus is a widespread pathogen that causes diverse diseases in humans and animals and can severely damage host health. Alphaherpesvirus particles comprise a DNA core, capsid, tegument and envelope; the tegument is located between the nuclear capsid and envelope. According to biochemical and proteomic analyses of alphaherpesvirus particles, the tegument contains at least 24 viral proteins and plays an important role in the alphaherpesvirus life cycle. This article reviews the important role of tegument proteins and their interactions during the viral life cycle to provide a reference and inspiration for understanding alphaherpesvirus infection pathogenesis and identifying new antiviral strategies.

Carboplatin restricts peste des petits ruminants virus replication by suppressing the STING-mediated autophagy

Peste des petits ruminants virus (PPRV) is a morbillivirus that causes the acute and highly pathogenic infectious disease peste des petits ruminants (PPR) in small ruminants and poses a major threat to the goat and sheep industries. Currently, there is no effective treatment for PPRV infection. Here, we propose Carboplatin, a platinum-based regimen designed to treat a range of malignancies, as a potential antiviral agent. We showed that Carboplatin exhibits significant antiviral activity against PPRV in a cell culture model. The mechanism of action of Carboplatin against PPRV is mainly attributed to its ability to block STING mediated autophagy. Together, our study supports the discovery of Carboplatin as an antiviral against PPRV and potentially other closely related viruses, sheds light on its mode of action, and establishes STING as a valid and attractive target to counteract viral infection.

Pseudorabies virus gM and its homologous proteins in herpesviruses induce mitochondria-related apoptosis involved in viral pathogenicity

Apoptosis is a critical host antiviral defense mechanism. But many viruses have evolved multiple strategies to manipulate apoptosis and escape host antiviral immune responses. Herpesvirus infection regulated apoptosis; however, the underlying molecular mechanisms have not yet been fully elucidated. Hence, the present study aimed to study the relationship between herpesvirus infection and apoptosis in vitro and in vivo using the pseudorabies virus (PRV) as the model virus. We found that mitochondria-dependent apoptosis was induced by PRV gM, a late protein encoded by PRV UL10, a virulence-related gene involved in enhancing PRV pathogenicity. Mechanistically, gM competitively combines with BCL-XL to disrupt the BCL-XL-BAK complex, resulting in BCL-2-antagonistic killer (BAK) oligomerization and BCL-2-associated X (BAX) activation, which destroys the mitochondrial membrane potential and activates caspase-3/7 to trigger apoptosis. Interestingly, similar apoptotic mechanisms were observed in other herpesviruses (Herpes Simplex Virus-1 [HSV-1], human cytomegalovirus [HCMV], Equine herpesvirus-1 [EHV-1], and varicella-zoster virus [VZV]) driven by PRV gM homologs. Compared with their parental viruses, the pathogenicity of PRV-ΔUL10 or HSV-1-ΔUL10 in mice was reduced with lower apoptosis and viral replication, illustrating that UL10 is a key virulence-related gene in PRV and HSV-1. Consistently, caspase-3 deletion also diminished the replication and pathogenicity of PRV and HSV-1 in vitro and in mice, suggesting that caspase-3-mediated apoptosis is closely related to the replication and pathogenicity of PRV and HSV-1. Overall, our findings firstly reveal the mechanism by which PRV gM and its homologs in several herpesviruses regulate apoptosis to enhance the viral replication and pathogenicity, and the relationship between gM-mediated apoptosis and herpesvirus pathogenicity suggests a promising approach for developing attenuated live vaccines and therapy for herpesvirus-related diseases.

Regulatory Non-Coding RNAs during Porcine Viral Infections: Potential Targets for Antiviral Therapy

Pigs play important roles in agriculture and bio-medicine; however, porcine viral infections have caused huge losses to the pig industry and severely affected the animal welfare and social public safety. During viral infections, many non-coding RNAs are induced or repressed by viruses and regulate viral infection. Many viruses have, therefore, developed a number of mechanisms that use ncRNAs to evade the host immune system. Understanding how ncRNAs regulate host immunity during porcine viral infections is critical for the development of antiviral therapies. In this review, we provide a summary of the classification, production and function of ncRNAs involved in regulating porcine viral infections. Additionally, we outline pathways and modes of action by which ncRNAs regulate viral infections and highlight the therapeutic potential of artificial microRNA. Our hope is that this information will aid in the development of antiviral therapies based on ncRNAs for the pig industry.

Duck Tembusu virus induces incomplete autophagy via the ERK/mTOR and AMPK/mTOR signalling pathways to promote viral replication in neuronal cells

Duck Tembusu virus (DTMUV) is a neurotropic virus in the genus Flavivirus that causes massive economic losses to the poultry industry in China and neighbouring countries. Autophagy is pivotal in cellular responses to pathogens and in viral pathogenesis. However, little is known about the roles of autophagy in DTMUV replication and viral pathogenesis, especially in neuropathogenesis. In this study, mouse neuroblastoma cells (Neuro-2a) were used to establish a cell model of DTMUV infection. Our experiments indicated that DTMUV infection induced incomplete autophagy in Neuro-2a cells. Then, we used different autophagy regulators to alter the autophagy induced by DTMUV and found that incomplete autophagy promoted DTMUV replication. Furthermore, we showed that DTMUV infection activated the ERK and AMPK pathways, resulting in decreased phosphorylation of the autophagy repressor mTOR, subsequently leading to autophagic induction. In addition, we utilized ICR mice in an animal model of DTMUV infection to evaluate the autophagic responses in brain tissues and investigate the effects of autophagy on viral replication and tissue lesions. Our results confirmed that DTMUV induced incomplete autophagy in mouse brain tissues and that autophagy inducer treatment promoted DTMUV replication and aggravated DTMUV-induced lesions, whereas autophagy inhibitor treatment had the opposite effects. In summary, DTMUV infection induced incomplete autophagy through the ERK/mTOR and AMPK/mTOR signalling pathways to promote viral replication in mouse neuronal cells, and DTMUV-induced incomplete autophagy contributed to the neuropathogenesis of DTMUV.

Seneca Valley Virus Degrades STING via PERK and ATF6-Mediated Reticulophagy

Seneca Valley Virus (SVV), a member of the Picornaviridae family, is an emerging porcine virus that can cause vesicular disease in pigs. However, the immune evasion mechanism of SVV remains unclear, as does its interaction with other pathways. STING (Stimulator of interferon genes) is typically recognized as a critical factor in innate immune responses to DNA virus infection, but its role during SVV infection remains poorly understood. In the present study, we observed that STING was degraded in SVV-infected PK-15 cells, and SVV replication in the cells was affected when STING was knockdown or overexpressed. The STING degradation observed was blocked when the SVV-induced autophagy was inhibited by using autophagy inhibitors (Chloroquine, Bafilomycin A1) or knockdown of autophagy related gene 5 (ATG5), suggesting that SVV-induced autophagy is responsible for STING degradation. Furthermore, the STING degradation was inhibited when reticulophagy regulator 1 (FAM134B), a reticulophagy related receptor, was knocked down, indicating that SVV infection induces STING degradation via reticulophagy. Further study showed that in eukaryotic translation initiation factor 2 alpha kinase 3 (PERK)/activating transcription factor 6 (ATF6) deficient cells, SVV infection failed to induce reticulophagy-medaited STING degradation, indicating that SVV infection caused STING degradation via PERK/ATF6-mediated reticulophagy. Notably, blocking reticulophagy effectively hindered SVV replication. Overall, our study suggested that SVV infection resulted in STING degradation via PERK and ATF6-mediated reticulophagy, which may be an immune escape strategy of SVV. This finding improves the understanding of the intricate interplay between viruses and their hosts and provides a novel strategy for the development of novel antiviral drugs.

miR-204 suppresses porcine reproductive and respiratory syndrome virus (PRRSV) replication via inhibiting LC3B-mediated autophagy

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) has been regarded as a persistent challenge for the swine farms worldwide. microRNAs (miRNAs) play key roles in regulating almost every important biological process, including virus-host interaction. In this study, we found that miR-204 was highly expressed in cells that were not permissive to PRRSV infection compared with cells susceptible to PRRSV infection. Subsequently, we demonstrated that overexpression of miR-204 significantly inhibited PRRSV replication in porcine alveolar macrophages (PAMs). Through bioinformatic analysis, we found that there existed a potential binding site of miR-204 on the 3'UTR of microtubule associated protein 1 light chain 3B (MAP1LC3B, LC3B), a hallmark of autophagy. Applying experiments including luciferase reporter assay and UV cross-linking and immunoprecipitation (CLIP) assay, we demonstrated that miR-204 directly targeted LC3B, thereby downregulating autophagy. Meanwhile, we investigated the interplay between autophagy and PRRSV replication in PAMs, confirming that PRRSV infection induces autophagy, which in turn facilitates viral replication. Overall, we verify that miR-204 suppresses PRRSV replication via inhibiting LC3B-mediated autophagy in PAMs. These findings will provide a novel potential approach for us to develop antiviral therapeutic agents and controlling measures for future PRRSV outbreaks.

Fangchinoline inhibits the PEDV replication in intestinal epithelial cells via autophagic flux suppression

Animal and human health are severely threatened by coronaviruses. The enteropathogenic coronavirus, porcine epidemic diarrhea virus (PEDV), is highly contagious, leading to porcine epidemic diarrhea (PED), which causes large economic losses in the world's swine industry. Piglets are not protected from emerging PEDV variants; therefore, new antiviral measures for PED control are urgently required. Herein, the anti-PEDV effects and potential mechanisms of fangchinoline (Fan) were investigated. Fan dose-dependently inhibited a PEDV infection at 24 h post-infection (EC₅₀ value = 0.67 μM). We found that Fan mainly affected the PEDV replication phase but also inhibited PEDV at the attachment and internalization stages of the viral life cycle. Mechanistically, Fan blocked the autophagic flux in PEDV-infected cells by regulating the expression of autophagy-related proteins and changing PEDV virus particles. In summary, Fan inhibits PEDV infection by blocking the autophagic flux in cells. Our findings will help develop new strategies to prevent and treat PEDV infection.

Exosome-Autophagy Crosstalk in Enveloped Virus Infection

Exosomes, which are extracellular vesicles (EVs) predominantly present in bodily fluids, participate in various physiological processes. Autophagy, an intracellular degradation mechanism, eliminates proteins and damaged organelles by forming double-membrane autophagosomes. These autophagosomes subsequently merge with lysosomes for target degradation. The interaction between autophagy and endosomal/exosomal pathways can occur at different stages, exerting significant influences on normal physiology and human diseases. The interplay between exosomes and the autophagy pathway is intricate. Exosomes exhibit a cytoprotective role by inducing intracellular autophagy, while autophagy modulates the biogenesis and degradation of exosomes. Research indicates that exosomes and autophagy contribute to the infection process of numerous enveloped viruses. Enveloped viruses, comprising viral nucleic acid, proteins, or virions, can be encapsulated within exosomes and transferred between cells via exosomal transport. Consequently, exosomes play a crucial role in the infection of certain viral diseases. This review presents recent findings on the interplay between exosomes and autophagy, as well as their implications in the infection of enveloped viruses, thereby offering valuable insights into the pathogenesis and vaccine research of enveloped virus infection.

Autophagy up-regulation upon FeHV-1 infection on permissive cells

FeHV-1 is a member of the Herpesviridae family that is distributed worldwide and causes feline viral rhinotracheitis (FVR). Since its relationship with the autophagic process has not yet been elucidated, the aim of this work was to evaluate the autophagy mediated by FeHV-1 and to determine its proviral or antiviral role. Our data showed that autophagy is induced by FeHV-1 in a viral dose and time-dependent manner. Phenotypic changes in LC3/p62 axis (increase of LC3-II and degradation of p62) were detected from 12 h post infection using western blot and immuno-fluorescence assays. In a second step, by using late autophagy inhibitors and inducers, the possible proviral role of autophagy during FeHV-1 infection was investigating by assessing the effects of each chemical in terms of viral yield, cytotoxic effects, and expression of viral glycoproteins. Our findings suggest that late-stage autophagy inhibitors (bafilomycin and chloroquine) have a negative impact on viral replication. Interestingly, we observed an accumulation of gB, a viral protein, when cells were pretreated with bafilomycin, whereas the opposite effect was observed when an autophagy inducer was used. The importance of autophagy during FeHV-1 infection was further supported by the results obtained with ATG5 siRNA. In summary, this study demonstrates FeHV-1-mediated autophagy induction, its proviral role, and the negative impact of late autophagy inhibitors on viral replication.

Membrane fusion, potential threats, and natural antiviral drugs of pseudorabies virus

Pseudorabies virus (PrV) can infect several animals and causes severe economic losses in the swine industry. Recently, human encephalitis or endophthalmitis caused by PrV infection has been frequently reported in China. Thus, PrV can infect animals and is becoming a potential threat to human health. Although vaccines and drugs are the main strategies to prevent and treat PrV outbreaks, there is no specific drug, and the emergence of new PrV variants has reduced the effectiveness of classical vaccines. Therefore, it is challenging to eradicate PrV. In the present review, the membrane fusion process of PrV entering target cells, which is conducive to revealing new therapeutic and vaccine strategies for PrV, is presented and discussed. The current and potential PrV pathways of infection in humans are analyzed, and it is hypothesized that PrV may become a zoonotic agent. The efficacy of chemically synthesized drugs for treating PrV infections in animals and humans is unsatisfactory. In contrast, multiple extracts of traditional Chinese medicine (TCM) have shown anti-PRV activity, exerting its effects in different phases of the PrV life-cycle and suggesting that TCM compounds may have great potential against PrV. Overall, this review provides insights into developing effective anti-PrV drugs and emphasizes that human PrV infection should receive more attention.

Tegument protein UL21 of alpha-herpesvirus inhibits the innate immunity by triggering CGAS degradation through TOLLIP-mediated selective autophagy

Alpha-herpesvirus causes lifelong infections and serious diseases in a wide range of hosts and has developed multiple strategies to counteract the host defense. Here, we demonstrate that the tegument protein UL21 (unique long region 21) in pseudorabies virus (PRV) dampens type I interferon signaling by triggering the degradation of CGAS (cyclic GMP-AMP synthase) through the macroautophagy/autophagy-lysosome pathway. Mechanistically, the UL21 protein scaffolds the E3 ligase UBE3C (ubiquitin protein ligase E3C) to catalyze the K27-linked ubiquitination of CGAS at Lys384, which is recognized by the cargo receptor TOLLIP (toll interacting protein) and degraded in the lysosome. Additionally, we show that the N terminus of UL21 in PRV is dominant in destabilizing CGAS-mediated innate immunity. Moreover, viral tegument protein UL21 in herpes simplex virus type 1 (HSV-1) also displays the conserved inhibitory mechanisms. Furthermore, by using PRV, we demonstrate the roles of UL21 in degrading CGAS to promote viral infection in vivo. Altogether, these findings describe a distinct pathway where alpha-herpesvirus exploits TOLLIP-mediated selective autophagy to evade host antiviral immunity, highlighting a new interface of interplay between the host and DNA virus.Abbreviations: 3-MA: 3-methyladenine; ACTB: actin beta; AHV-1: anatid herpesvirus 1; ATG7: autophagy related 7; ATG13: autophagy related 13; ATG101: autophagy related 101; BHV-1: bovine alphaherpesvirus 1; BNIP3L/Nix: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CCDC50: coiled-coil domain containing 50; CCT2: chaperonin containing TCP1 subunit 2; CGAS: cyclic GMP-AMP synthase; CHV-2: cercopithecine herpesvirus 2; co-IP: co-immunoprecipitation; CQ: chloroquine; CRISPR: clustered regulatory interspaced short palindromic repeat; Cas9: CRISPR-associated system 9; CTD: C-terminal domain; Ctrl: control; DAPI: 4',6-diamidino-2-phenylindole; DBD: N-terminal DNA binding domain; DMSO: dimethyl sulfoxide; DYNLRB1: dynein light chain roadblock-type 1; EHV-1: equine herpesvirus 1; gB: glycoprotein B; GFP: green fluorescent protein; H&E: hematoxylin and eosin; HSV-1: herpes simplex virus 1; HSV-2: herpes simplex virus 2; IB: immunoblotting; IRF3: interferon regulatory factor 3; lenti: lentivirus; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCHF9: membrane associated ring-CH-type finger 9; MG132: cbz-leu-leu-leucinal; NBR1: NBR1 autophagy cargo receptor; NC: negative control; NEDD4L: NEDD4 like E3 ubiquitin protein ligase; NH4Cl: ammonium chloride; OPTN: optineurin; p-: phosphorylated; PFU: plaque-forming unit; Poly(dA:dT): Poly(deoxyadenylic-deoxythymidylic) acid; PPP1: protein phosphatase 1; PRV: pseudorabies virus; RB1CC1/FIP200: RB1 inducible coiled-coil 1; RNF126: ring finger protein 126; RT-PCR: real-time polymerase chain reaction; sgRNA: single guide RNA; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1; TOLLIP: toll interacting protein; TRIM33: tripartite motif containing 33; UL16: unique long region 16; UL21: unique long region 21; UL54: unique long region 54; Ub: ubiquitin; UBE3C: ubiquitin protein ligase E3C; ULK1: unc-51 like autophagy activating kinase 1; Vec: vector; VSV: vesicular stomatitis virus; VZV: varicella-zoster virus; WCL: whole-cell lysate; WT: wild-type; Z-VAD: carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone.

Recombinant Pseudorabies Virus Usage in Vaccine Development against Swine Infectious Disease

Pseudorabies virus (PRV) is the pathogen of pseudorabies (PR), which belongs to the alpha herpesvirus subfamily with a double stranded DNA genome encoding approximately 70 proteins. PRV has many non-essential regions for replication, has a strong capacity to accommodate foreign genes, and more areas for genetic modification. PRV is an ideal vaccine vector, and multivalent live virus-vectored vaccines can be developed using the gene-deleted PRV. The immune system continues to be stimulated by the gene-deleted PRVs and maintain a long immunity lasting more than 4 months. Here, we provide a brief overview of the biology of PRV, recombinant PRV construction methodology, the technology platform for efficiently constructing recombinant PRV, and the applications of recombinant PRV in vaccine development. This review summarizes the latest information on PRV usage in vaccine development against swine infectious diseases, and it offers novel perspectives for advancing preventive medicine through vaccinology.

Modifications of the PI3K/Akt/mTOR axis during FeHV-1 infection in permissive cells

FeHV-1 is the causative agent of infectious rhinotracheitis in cats. The relationship between viral infection and the PI3K/Akt/mTOR pathway, as well as its function in crucial physiological processes like as autophagy, apoptosis or the IFN induction cascade is known for other varicelloviruses. However, there is no information on whether autophagy is activated during FeHV-1 infection nor on how this infection modifies PI3K/Akt/mTOR pathway. In this work, we aim to elucidate the involvement of this pathway during cytolytic infection by FeHV-1 in permissive cell lines. Using a phenotypic approach, the expression of proteins involved in the PI3K/Akt/mTOR pathway was examined by Western blot analysis. The findings demonstrated the lack of modifications in relation to viral dose (except for phospho-mTOR), whereas there were changes in the expression of several markers in relation to time as well as a mismatch in the time of activation of this axis. These results suggest that FeHV-1 may interact independently with different autophagic signaling pathways. In addition, we found an early phosphorylation of Akt, approximately 3 h after infection, without a concomitant decrease in constitutive Akt. This result suggests a possible role for this axis in viral entry. In a second phase, the use of early autophagy inhibitors was examined for viral yield, cytotoxic effects, viral glycoprotein expression, and autophagy markers and resulted in inefficient inhibition of viral replication (12 h post-infection for LY294002 and 48 h post-infection for 3-methyladenine). The same markers were examined during Akt knockdown, and we observed no differences in viral replication. This result could be explained by the presence of a protein kinase in the FeHV-1 genome (encoded by the Us3 gene) that can phosphorylate various Akt substrates as an Akt surrogate, as has already been demonstrated in genetically related viruses (HSV-1, PRV, etc.). For the same reasons, the use of LY294002 at the beginning of infection did not affect FeHV-1-mediated Akt phosphorylation. Our findings highlight changes in the PI3K/Akt/mTOR pathway during FeHV-1 infection, although further research is needed to understand the importance of these changes and how they affect cellular processes and viral propagation.

Progress on innate immune evasion and live attenuated vaccine of pseudorabies virus

Pseudorabies virus (PRV) is a highly infectious disease that can infect most mammals, with pigs as the only natural host, has caused considerable economic losses to the pig husbandry of the world. Innate immunity is the first defense line of the host against the attack of pathogens and is essential for the proper establishment of adaptive immunity. The host uses the innate immune response to against the invasion of PRV; however PRV makes use of various strategies to inhibit the innate immunity to promote the virus replication. Currently, live attenuated vaccine is used to prevent pig from infection with the PRV worldwide, such as Bartha K61. However, a growing number of data indicates that these vaccines do not provide complete protection against new PRV variants that have emerged since late 2011. Here we summarized the interactions between PRV and host innate immunity and the current status of live attenuated PRV vaccines to promote the development of novel and more effective PRV vaccines.

The canonical Wnt/β-catenin signaling pathway facilitates pseudorabies virus proliferation and enhances virus-induced autophagy

Pseudorabies virus (PRV) is a swine herpesvirus with a broad host range that causes significant economic losses worldwide. The Wnt/β-catenin signaling pathway is reportedly involved in multiple viruses' proliferation. In this study, we demonstrated that PRV infection significantly activated the Wnt/β-catenin signaling and promoted the nuclear translocation of β-catenin. Applying specific chemical inhibitors (FH535 and iCRT14) caused a remarkable decrease in PRV titers in various cell lines. Knockdown of β-catenin by siRNA also reduced the proliferation of PRV. On the contrary, treatment with lithium chloride (LiCl), an inhibitor of GSK3β, stimulated the Wnt/β-catenin signaling pathway and enhanced the PRV proliferation. Similarly, overexpression of β-catenin promoted PRV proliferation and reversed the antiviral effect of FH535. Moreover, LiCl promoted PRV-induced autophagy, whereas FH535 and iCRT14 showed converse effects. These findings suggest that PRV infection stimulates the canonical Wnt/β-catenin signaling pathway, facilitating PRV proliferation and regulating virus-induced autophagy. These data also provide potential targets for developing antiviral agents against PRV.

The Multi-Faceted Role of Autophagy During Animal Virus Infection

Autophagy is a process of degradation to maintain cellular homeostatic by lysosomes, which ensures cellular survival under various stress conditions, including nutrient deficiency, hypoxia, high temperature, and pathogenic infection. Xenophagy, a form of selective autophagy, serves as a defense mechanism against multiple intracellular pathogen types, such as viruses, bacteria, and parasites. Recent years have seen a growing list of animal viruses with autophagy machinery. Although the relationship between autophagy and human viruses has been widely summarized, little attention has been paid to the role of this cellular function in the veterinary field, especially today, with the growth of serious zoonotic diseases. The mechanisms of the same virus inducing autophagy in different species, or different viruses inducing autophagy in the same species have not been clarified. In this review, we examine the role of autophagy in important animal viral infectious diseases and discuss the regulation mechanisms of different animal viruses to provide a potential theoretical basis for therapeutic strategies, such as targets of new vaccine development or drugs, to improve industrial production in farming.

A Tug of War: Pseudorabies Virus and Host Antiviral Innate Immunity

The non-specific innate immunity can initiate host antiviral innate immune responses within minutes to hours after the invasion of pathogenic microorganisms. Therefore, the natural immune response is the first line of defense for the host to resist the invaders, including viruses, bacteria, fungi. Host pattern recognition receptors (PRRs) in the infected cells or bystander cells recognize pathogen-associated molecular patterns (PAMPs) of invading pathogens and initiate a series of signal cascades, resulting in the expression of type I interferons (IFN-I) and inflammatory cytokines to antagonize the infection of microorganisms. In contrast, the invading pathogens take a variety of mechanisms to inhibit the induction of IFN-I production from avoiding being cleared. Pseudorabies virus (PRV) belongs to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus. PRV is the causative agent of Aujeszky’s disease (AD, pseudorabies). Although the natural host of PRV is swine, it can infect a wide variety of mammals, such as cattle, sheep, cats, and dogs. The disease is usually fatal to these hosts. PRV mainly infects the peripheral nervous system (PNS) in swine. For other species, PRV mainly invades the PNS first and then progresses to the central nervous system (CNS), which leads to acute death of the host with serious clinical and neurological symptoms. In recent years, new PRV variant strains have appeared in some areas, and sporadic cases of PRV infection in humans have also been reported, suggesting that PRV is still an important emerging and re-emerging infectious disease. This review summarizes the strategies of PRV evading host innate immunity and new targets for inhibition of PRV replication, which will provide more information for the development of effective inactivated vaccines and drugs for PRV.

The Role of Mitophagy in Viral Infection

Mitophagy, which is able to selectively clear excess or damaged mitochondria, plays a vital role in the quality control of mitochondria and the maintenance of normal mitochondrial functions in eukaryotic cells. Mitophagy is involved in many physiological and pathological processes, including apoptosis, innate immunity, inflammation, cell differentiation, signal transduction, and metabolism. Viral infections cause physical dysfunction and thus pose a significant threat to public health. An accumulating body of evidence reveals that some viruses hijack mitophagy to enable immune escape and self-replication. In this review, we systematically summarize the pathway of mitophagy initiation and discuss the functions and mechanisms of mitophagy in infection with classical swine fever virus and other specific viruses, with the aim of providing a theoretical basis for the prevention and control of related diseases.

Marek's disease virus prolongs survival of primary chicken B-cells by inducing a senescence-like phenotype

Marek’s disease virus (MDV) is an alphaherpesvirus that causes immunosuppression and deadly lymphoma in chickens. Lymphoid organs play a central role in MDV infection in animals. B-cells in the bursa of Fabricius facilitate high levels of MDV replication and contribute to dissemination at early stages of infection. Several studies investigated host responses in bursal tissue of MDV-infected chickens; however, the cellular responses specifically in bursal B-cells has never been investigated. We took advantage of our recently established in vitro infection system to decipher the cellular responses of bursal B-cells to infection with a very virulent MDV strain. Here, we demonstrate that MDV infection extends the survival of bursal B-cells in culture. Microarray analyses revealed that most cytokine/cytokine-receptor-, cell cycle- and apoptosis-associated genes are significantly down-regulated in these cells. Further functional assays validated these strong effects of MDV infections on cell cycle progression and thus, B-cell proliferation. In addition, we confirmed that MDV infections protect B-cells from apoptosis and trigger an accumulation of the autophagy marker Lc3-II. Taken together, our data indicate that MDV-infected bursal B-cells show hallmarks of a senescence-like phenotype, leading to a prolonged B-cell survival. This study provides an in-depth analysis of bursal B-cell responses to MDV infection and important insights into how the virus extends the survival of these cells.

Upon MDV entry via the respiratory tract, B-cells are among the first cells to be infected in the lung and allow an efficient amplification of the virus. B-cells ensure the transmission of the virus to activated T-cells in which it replicates and ultimately transforms CD4-positive T-cells. Although playing a pivotal role in the MDV life cycle, the response of B-cells to MDV is currently not fully understood. Here, by using an in vitro infection model of primary bursal B-cells, we show that MDV infection leads to a prolonged B-cell survival resulting from decreased cell proliferation, protection from apoptosis and activation of autophagy. Our study provides new insights into the B-cell response to MDV infection, demonstrating that MDV triggers a senescence-like phenotype in B-cells that could potentiate their role in MDV pathogenesis.

Platycodon grandiflorus polysaccharides inhibit Pseudorabies virus replication via downregulating virus-induced autophagy

Pseudorabies virus (PRV) is one of the common pathogens in farms. Platycodon grandiflorus polysaccharide (PGPS) has been reported with a variety of biological activities. Autophagy is one of the vital mechanisms for cells to cope with virus infection, and it may also inhibit or promote virus replication. This study was conducted to investigate the antiviral activity of total PGPS(PGPS_t) against PRV and the role of virus-induced autophagy in the anti-PRV effect of PGPS_t in PK-15 cells. First, we established an infection model and detected the autophagy induced by PRV in PK-15 cells. Then, the protective effect of PGPS_t against PRV was evaluated, and the effect of PGPS_t on PRV replication and virus-induced autophagy were analysed by quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, Western blot and confocal immunofluorescence. Results showed that PGPS_t can reduce the PRV replication. PRV infection resulted in the accumulation of autophagosomes, which were inhibited by PGPS_t. Moreover, PGPS_t upregulated the Akt/mammalian target of rapamycin (mTOR) signalling pathway repressed by PRV infection, whereas rapamycin attenuated the anti-PRV effect of PGPS_t. These findings suggest that PGPS_t possess a protective effect against PRV infection and can inhibit PRV replication through relieving PRV-induced autophagy. This article can provide ideas for the development of antiviral drugs.

Porcine circovirus 3 capsid protein induces autophagy in HEK293T cells by inhibiting phosphorylation of the mammalian target of rapamycin

Porcine circovirus 3 (PCV3) has been detected in major pig-producing countries around the world since its first report in the US in 2016. Most current studies have focused on epidemiological investigations and detection methods of PCV3 because of lack of live virus strains for research on its pathogenesis in porcine cells or even in pigs. We constructed a recombinant plasmid pCMV-Cap carrying the PCV3 orf2 gene to investigate the effects of capsid (Cap) protein expression on autophagic response in human embryonic kidney cell line 293T (HEK293T). We demonstrate that PCV3 Cap protein induced complete autophagy shown as formation of autophagosomes and autophagosome-like vesicles as well as LC3-II conversion from LC3-I via inhibiting phosphorylation of the mammalian target of rapamycin (mTOR) in HEK293T cells. The ubiquitin-proteasome pathway is also involved in the autophagy process. These findings provide insight for further exploration of PCV3 pathogenetic mechanisms in porcine cells.

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.

Curcumin protects rat hippocampal neurons against pseudorabies virus by regulating the BDNF/TrkB pathway

Pseudorabies virus (PRV) infection can elicit nervous system disorders. Curcumin has been reported to have neuroprotective effects. However, whether curcumin can protect neurons against PRV infection and the underlying mechanisms remain unclear. In the present study, for the first time, the protective effects of curcumin against PRV-induced oxidative stress, apoptosis, and mitochondrial dysfunction in rat hippocampal neurons and the brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) pathway were investigated. Results indicated that PRV with a titer of 3.06 × 10⁶ TCID50 (50% tissue culture infective dose) induced oxidative damage of hippocampal neurons 2 h post-infection and that 10 μM curcumin improved the viability of PRV-infected hippocampal neurons. Blocking the BDNF/TrkB pathway reversed the neuroprotective effects of curcumin, which were imparted by decreasing the PRV-induced upregulation of nitric oxide synthase expression, repressing the PRV-activated mitochondrial apoptotic pathway, and mitochondrial dysfunction. To conclude, curcumin exhibited a neuroprotective role against PRV infection by upregulating the BDNF/TrkB pathway. This study provides insight into the anti-PRV neuroprotective application of curcumin and the underlying mechanism in the prophylaxis and treatment of neurological disorders caused by PRV infection.

Muscovy duck reovirus promotes virus replication by inhibiting autophagy-lysosomal degradation pathway

Autophagy plays a momentous role in cellular responses against pathogens. However, the influence of the autophagy machinery on Muscovy duck reovirus (MDRV) infection is not yet confirmed. In this study, it was shown that MDRV infection significantly increased the number of autophagy-like vesicles in DF-1 cells under electron microscope and the LC3-I/LC3-II conversion, which was considered important indicators of autophagy. It was worth noting that the level of autophagy was positively correlated with MDRV replication. Further test results showed that MDRV-induced autophagy can promote virus replication in DF-1 cells, and both the envelope protein sigma A and non-structural protein sigma NS that play an important role in virus replication process can colocalize with the autophagosome marker molecule LC3-II by confocal immunofluorescence analysis. These results indicated that MDRV utilized the autophagosomes for replication. Through transfection of the dual fluorescent plasmid mcherry-EGFP-LC3 and fluorescence microscope observation, it was found that autophagosomes were more likely to fuse with lysosomes in MDRV-infected cells compared with the blank group. The phenomenon of pEGFP-LC3B fluorescent spot and LAMP1 co-localization appeared in MDRV infected cells, indicating that MDRV infection would promote the fusion of autophagosomes and the lysosomes. Conversely, accumulation of p62 was observed by immunoblotting, suggesting that autolysosomes does not exert effective degradation. MDRV infection triggered a incomplete autophagic response. Further studies found that the expression of LAMP1, a marker protein of late endosome/early lysosome, increased significantly in MDRV-infected cells, suggesting an increase in the number of immature lysosomes. In addition, the experiment detected the maturation of the lysosomal acid hydrolase Cathepsin D in the cells, and found that the expression of the 33 kDa mature form of Cathepsin D was significantly reduced after MDRV infection, indicating that MDRV inhibits the maturation of lysosomes. In general, MDRV infection induces autophagy of DF-1 cells, promotes the fusion of autophagosomes and lysosomes, inhibits autophagolysosome degradation, and promotes virus replication.

Zika virus depletes neural stem cells and evades selective autophagy by suppressing the Fanconi anemia protein FANCC

Zika virus (ZIKV) is an emerging flavivirus, which when passed through vertical transmission from mother to developing fetus can lead to developmental abnormalities, including microcephaly. While there is mounting evidence that suggests a causal relationship between ZIKV infection and microcephaly, the mechanisms by which ZIKV induces these changes remain to be elucidated. Here, we demonstrate that ZIKV infection of neural stems cells, both in vitro and in vivo, induces macroautophagy to enhance viral replication. At the same time, ZIKV downregulates a number of essential selective autophagy genes, including the Fanconi anemia (FA) pathway genes. Bioinformatics analyses indicate that the transcription factor E2F4 promotes FANCC expression and is downregulated upon ZIKV infection. Gain and loss of function assays indicate that FANCC is essential for selective autophagy and acts as a negative regulator of ZIKV replication. Finally, we show that Fancc KO mice have increased ZIKV infection and autophagy protein levels in various brain regions. Taken together, ZIKV downregulates FANCC to modulate the host antiviral response and simultaneously attenuate neuronal growth.

Exocytosis of Progeny Infectious Varicella-Zoster Virus Particles via a Mannose-6-Phosphate Receptor Pathway without Xenophagy following Secondary Envelopment

The literature on the egress of different herpesviruses after secondary envelopment is contradictory. In this report, we investigated varicella-zoster virus (VZV) egress in a cell line from a child with Pompe disease, a glycogen storage disease caused by a defect in the enzyme required for glycogen digestion. In Pompe cells, both the late autophagy pathway and the mannose-6-phosphate receptor (M6PR) pathway are interrupted. We have postulated that intact autophagic flux is required for higher recoveries of VZV infectivity. To test that hypothesis, we infected Pompe cells and then assessed the VZV infectious cycle. We discovered that the infectious cycle in Pompe cells was remarkably different from that of either fibroblasts or melanoma cells. No large late endosomes filled with VZV particles were observed in Pompe cells; only individual viral particles in small vacuoles were seen. The distribution of the M6PR pathway (trans-Golgi network to late endosomes) was constrained in infected Pompe cells. When cells were analyzed with two different anti-M6PR antibodies, extensive colocalization of the major VZV glycoprotein gE (known to contain M6P residues) and the M6P receptor (M6PR) was documented in the viral highways at the surfaces of non-Pompe cells after maximum-intensity projection of confocal z-stacks, but neither gE nor the M6PR was seen in abundance at the surfaces of infected Pompe cells. Taken together, our results suggested that (i) Pompe cells lack a VZV trafficking pathway within M6PR-positive large endosomes and (ii) most infectious VZV particles in conventional cell substrates are transported via large M6PR-positive vacuoles without degradative xenophagy to the plasma membrane.IMPORTANCE The long-term goal of this research has been to determine why VZV, when grown in cultured cells, invariably is more cell associated and has a lower titer than other alphaherpesviruses, such as herpes simplex virus 1 (HSV1) or pseudorabies virus (PRV). Data from both HSV1 and PRV laboratories have identified a Rab6 secretory pathway for the transport of single enveloped viral particles from the trans-Golgi network within small vacuoles to the plasma membrane. In contrast, after secondary envelopment in fibroblasts or melanoma cells, multiple infectious VZV particles accumulated within large M6PR-positive late endosomes that were not degraded en route to the plasma membrane. We propose that this M6PR pathway is most utilized in VZV infection and least utilized in HSV1 infection, with PRV's usage being closer to HSV1's usage. Supportive data from other VZV, PRV, and HSV1 laboratories about evidence for two egress pathways are included.

Typical gene expression profile of pseudorabies virus reactivation from latency in swine trigeminal ganglion

Pseudorabies virus (PRV) establishes a lifelong latent infection in swine trigeminal ganglion (TG) following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Muscle injection combined with intravenous deliver of the synthetic corticosteroid dexamethasone (DEX) consistently induces reactivation from latency in pigs. In this study, PRV-free piglets were infected with PRV. Viral shedding in nasal and ocular swabs demonstrated that PRV infection entered the latent period. The anti-PRV antibody was detected by enzyme-linked immunosorbent assay and the serum neutralization test, which suggested that the PRV could establish latent infection in the presence of humoral immunity. Immunohistochemistry and viral genome detection of TG neurons suggested that PRV was reactivated from latency. Viral gene expressions of IE180, EP0, VP16, and LLT-intron were readily detected at 3-h post-DEX treatment, but gB, a γ1 gene, was not detectable. The differentially expressed phosphorylated proteins of TG neurons were analyzed by ITRAQ coupled with LC-MS/MS, and p-EIF2S2 differentially expression was confirmed by western blot assay. Taken together, our study provides the evidence that typical gene expression in PRV reactivation from latency in TG is disordered compared with known lytic infection in epithelial cells.

Autophagy involved in antiviral activity of sodium tanshinone IIA sulfonate against porcine reproductive and respiratory syndrome virus infection in vitro

BACKGROUND

In previous research, we have demonstrated that sodium tanshinone IIA sulfonate (STS) has anti-porcine reproductive and respiratory syndrome virus (PRRSV) activity, but whether autophagy is involved in this process is still unknown. In this study, the autophagy effect of STS against PRRSV infection was investigated in vitro.

METHODS

Quantitative real-time PCR (qRT-PCR) and western blot was used to evaluate the inhibition ability of STS on the mRNA expression levels on cell autophagy genes, that is Beclin1, ATG5 and ATG7. Simultaneously, the effect of STS on N protein/gene expression was assessed by indirect immuno-fluorescence assay (IFA), qRT-PCR and western blot.

RESULTS

The results indicated that STS inhibits autophagy induced by PRRSV. In addition, STS effectively suppresses PRRSV's N protein replication and N gene expression in Marc-145 cells infected with PRRSV in a time-dependent manner.

CONCLUSIONS

Our results suggest that STS exhibits anti-PRRSV activity in vitro by suppressing autophagy-related genes, which may provide a theoretical basis for further pharmacological agent development regarding PRRSV infection.

Dihydroartemisinin Ameliorates Learning and Memory in Alzheimer's Disease Through Promoting Autophagosome-Lysosome Fusion and Autolysosomal Degradation for Aβ Clearance

Dihydroartemisinin (DHA) is an active metabolite of sesquiterpene trioxane lactone extracted from Artemisia annua, which is used to treat malaria worldwide. DHA can activate autophagy, which is the main mechanism to remove the damaged cell components and recover the harmful or useless substances from eukaryotic cells and maintain cell viability through the autophagy lysosomal degradation system. Autophagy activation and autophagy flux correction are playing an important neuroprotective role in the central nervous system, as they accelerate the removal of toxic protein aggregates intracellularly and extracellularly to prevent neurodegenerative processes, such as Alzheimer's disease (AD). In this study, we explored whether this mechanism can mediate the neuroprotective effect of DHA on the AD model in vitro and in vivo. Three months of DHA treatment improved the memory and cognitive impairment, reduced the deposition of amyloid β plaque, reduced the levels of Aβ40 and Aβ42, and ameliorated excessive neuron apoptosis in APP/PS1 mice brain. In addition, DHA treatment increased the level of LC3 II/I and decreased the expression of p62. After Bafilomycin A1 and Chloroquine (CQ) blocked the fusion of autophagy and lysosome, as well as the degradation of autolysosomes (ALs), DHA treatment increased the level of LC3 II/I and decreased the expression of p62. These results suggest that DHA treatment can correct autophagic flux, improve autophagy dysfunction, inhibit abnormal death of neurons, promote the clearance of amyloid-β peptide (Aβ) fibrils, and have a multi-target effect on the neuropathological process, memory and cognitive deficits of AD.

Interactions between Autophagy and DNA Viruses

Autophagy is a catabolic biological process in the body. By targeting exogenous microorganisms and aged intracellular proteins and organelles and sending them to the lysosome for phagocytosis and degradation, autophagy contributes to energy recycling. When cells are stimulated by exogenous pathogenic microorganisms such as viruses, activation or inhibition of autophagy is often triggered. As autophagy has antiviral effects, many viruses may escape and resist the process by encoding viral proteins. At the same time, viruses can also use autophagy to enhance their replication or increase the persistence of latent infections. Here, we give a brief overview of autophagy and DNA viruses and comprehensively review the known interactions between human and animal DNA viruses and autophagy and the role and mechanisms of autophagy in viral DNA replication and DNA virus-induced innate and acquired immunity.

Progeny Varicella-Zoster Virus Capsids Exit the Nucleus but Never Undergo Secondary Envelopment during Autophagic Flux Inhibition by Bafilomycin A1

Varicella-zoster virus (VZV) is an alphaherpesvirus that lacks the herpesviral neurovirulence protein ICP34.5. The underlying hypothesis of this project was that inhibitors of autophagy reduce VZV infectivity. We selected the vacuolar proton ATPase inhibitor bafilomycin A1 for analysis because of its well-known antiautophagy property of impeding acidification during the late stage of autophagic flux. We documented that bafilomycin treatment from 48 to 72 h postinfection lowered VZV titers substantially (P ≤ 0.008). Because we were unable to define the site of the block in the infectious cycle by confocal microscopy, we turned to electron microscopy. Capsids were observed in the nucleus, in the perinuclear space, and in the cytoplasm adjacent to Golgi apparatus vesicles. Many of the capsids had an aberrant appearance, as has been observed previously in infections not treated with bafilomycin. In contrast to prior untreated infections, however, secondary envelopment of capsids was not seen in the trans-Golgi network, nor were prototypical enveloped particles with capsids (virions) seen in cytoplasmic vesicles after bafilomycin treatment. Instead, multiple particles with varying diameters without capsids (light particles) were seen in large virus assembly compartments near the disorganized Golgi apparatus. Bafilomycin treatment also led to increased numbers of multivesicular bodies in the cytoplasm, some of which contained remnants of the Golgi apparatus. In summary, we have defined a previously unrecognized property of bafilomycin whereby it disrupted the site of secondary envelopment of VZV capsids by altering the pH of the trans-Golgi network and thereby preventing the correct formation of virus assembly compartments.IMPORTANCE This study of VZV assembly in the presence of bafilomycin A1 emphasizes the importance of the Golgi apparatus/trans-Golgi network as a platform in the alphaherpesvirus life cycle. We have previously shown that VZV induces levels of autophagy far above the basal levels of autophagy in human skin, a major site of VZV assembly. The current study documented that bafilomycin treatment led to impaired assembly of VZV capsids after primary envelopment/de-envelopment but before secondary reenvelopment. This VZV study also complemented prior herpes simplex virus 1 and pseudorabies virus studies investigating two other inhibitors of endoplasmic reticulum (ER)/Golgi apparatus function: brefeldin A and monensin. Studies with porcine herpesvirus demonstrated that primary enveloped particles accumulated in the perinuclear space in the presence of brefeldin A, while studies with herpes simplex virus 1 documented an impaired secondary assembly of enveloped viral particles in the presence of monensin.

Autophagy Quantification and STAT3 Expression in a Human Skin Organ Culture Model for Innate Immunity to Herpes Zoster

The goal of this project was to document the autophagy response in human neonatal skin organ culture (SOC) after infection with varicella-zoster virus (VZV). The VZV-infected SOC model has attributes of herpes zoster, in that an injection of virus into the skin is analogous to exit of virus from the sensory nerve termini into skin during herpes zoster. Cultures were maintained for 28 days and periodically examined for an autophagy response by quantitation of autophagosomes with Imaris software. Expression of the STAT3 protein was plentiful in the VZV-infected SOC. Abundant autophagy was observed in VZV-infected SOC between 14 and 28 days after infection, while autophagy in mock-infected SOC was minimal (p = 0.0003). The autophagic response after infection of SOC with a recombinant VZV genome containing the herpes simplex virus ICP34.5 neurovirulence gene was similar to wild-type VZV (p = 0.3). These results suggested that the VZV-infected SOC system resembled biopsy data from herpes zoster infection of skin. An enhanced autophagy response has now been reported after infection with two additional alpha herpesviruses besides VZV, namely, pseudorabies virus and duck enteritis herpes virus; both lack the ICP34.5 protein.