Pseudorabies virus manipulates mitochondrial tryptophanyl-tRNA synthetase 2 for viral replication

The pseudorabies virus (PRV) is identified as a double-helical DNA virus responsible for causing Aujeszky's disease, which results in considerable economic impacts globally. The enzyme tryptophanyl-tRNA synthetase 2 (WARS2), a mitochondrial protein involved in protein synthesis, is recognized for its broad expression and vital role in the translation process. The findings of our study showed an increase in both mRNA and protein levels of WARS2 following PRV infection in both cell cultures and animal models. Suppressing WARS2 expression via RNA interference in PK-15 cells led to a reduction in PRV infection rates, whereas enhancing WARS2 expression resulted in increased infection rates. Furthermore, the activation of WARS2 in response to PRV was found to be reliant on the cGAS/STING/TBK1/IRF3 signaling pathway and the interferon-alpha receptor-1, highlighting its regulation via the type I interferon signaling pathway. Further analysis revealed that reducing WARS2 levels hindered PRV's ability to promote protein and lipid synthesis. Our research provides novel evidence that WARS2 facilitates PRV infection through its management of protein and lipid levels, presenting new avenues for developing preventative and therapeutic measures against PRV infections.

Improved detection sensitivity of anti-PRV variant antibodies through preparation of anti-gB and anti-gE monoclonal antibodies and development of blocking ELISAs

Since 2011, PRV has resurged in China and is characterized by a mutated strain with significant alterations in antigenicity and virulence. Therefore, we hypothesized that antibody detection kits based on classic PRV strains may have limitations in detecting PRV variants. For more sensitive antibody detection of PRV variants, two MABs targeting the gB and gE proteins were developed. IFA revealed that these MABs exhibited strong reactivity toward both classic and variant PRV strains. MAB-gE recognizes a novel conserved linear B-cell epitope (41PSAEVWD47), while MAB-gB recognizes a conformational B-cell epitope. The binding of both MABs was effectively inhibited in the PRV-positive pig blood samples. Accordingly, we established blocking-ELISAs to detect anti-PRV gB and gE antibodies, which achieved higher sensitivity than commercial kits. Moreover, the clinical serum samples results of our method and that of IFA were in high agreement, and our test results had a higher coincidence rate than that of a commercial kit. Assessing antibody levels by our methods at various times following immunization and challenge accurately reflected the trend of antibody-level changes and revealed the conversion to positive antibody status before the commercial kit. Our method is crucial for monitoring PRV infections, assessing immune responses, and controlling disease.

MicroRNA-194-5p/Heparin-binding EGF-like growth factor signaling mediates dexamethasone-induced activation of pseudorabies virus in rat pheochromocytoma cells

Pseudorabies virus (PRV) is a neurotropic virus, which infects a wide range of mammals. The activity of PRV is gradually suppressed in hosts that have tolerated the primary infection. Increased glucocorticoid levels resulting from stressful stimuli overcome repression of PRV activity. However, the host cell mechanism involved in the activation processes under stressful conditions remains unclear. In this study, infection of rat PC-12 pheochromocytoma cells with neuronal properties using PRV at a multiplicity of infection (MOI) = 1 for 24 h made the activity of PRV be the relatively repressed state, and then incubation with 0.5 μM of the corticosteroid dexamethasone (DEX) for 4 h overcomes the relative repression of PRV activity. RNA-seq deep sequencing and bioinformatics analyses revealed different microRNA and mRNA profiles of PC-12 cells with/without PRV and/or DEX treatment. qRT-PCR and western blot analyses confirmed the negative regulatory relationship of miRNA-194-5p and its target heparin-binding EGF-like growth factor (Hbegf); a dual-luciferase reporter assay revealed that Hbegf is directly targeted by miRNA-194-5p. Further, miRNA-194-5p mock transfection contributed to PRV activation, Hbegf was downregulated in DEX-treated PRV infection cells, and Hbegf overexpression contributed to returning activated PRV to the repression state. Moreover, miRNA-194-5p overexpression resulted in reduced levels of HBEGF, c-JUN, and p-EGFR, whereas Hbegf overexpression suppressed the reduction caused by miRNA-194-5p overexpression. Overall, this study is the first to report that changes in the miR-194-5p-HBEGF/EGFR pathway in neurons are involved in DEX-induced activation of PRV, laying a foundation for the clinical prevention of stress-induced PRV activation.

Intradermal vaccination with Porcilis® Begonia can clinically protect against fatal PRV challenge with the highly virulent ZJ01 field strain

Since pseudorabies (PR) re-emerged and rapidly spread in China at the end of 2011, researchers have focused on effective vaccine strategies to prevent and control pseudorabies virus (PRV) infection in pig herds. Due to the extensive application of an attenuated vaccine based on the Bartha-K61 strain isolated in Hungary in 1961 and the variation of the PRV strain, it has been suggested that traditional vaccines based on the Bartha-K61 strain offer only partial protection against variant strains. It was therefore evaluated whether the Porcilis® Begonia vaccine, which is based on the NIA-3 strain with deletions in the gE and TK genes, is efficacious against experimental infection with the virulent, contemporary Chinese PRV strain ZJ01. In this study, piglets were vaccinated with Porcilis® Begonia through either the intradermal (ID) route or the intramuscular (IM) route and subsequently challenged intranasally with strain ZJ01 at 4 weeks post-vaccination. An unvaccinated challenge group and an unvaccinated/nonchallenged group were also included in the study. All animals were monitored for 14 days after challenge. Vaccinated and negative control pigs stayed healthy during the study, while the unvaccinated control animals developed lesions associated with PRV ZJ01 challenge, and 44% of these pigs died before the end of the experiment. This study demonstrated that ID or IM vaccination of pigs with a vaccine based on the NIA-3 strain Porcilis® Begonia clinically protects against fatal PRV challenge with the ZJ01 strain.

Interference of pseudorabies virus infection on functions of porcine granulosa cells via apoptosis modulated by MAPK signaling pathways

BACKGROUND

Pseudorabies virus (PRV) is one of the major viral pathogens leading to reproductive disorders in swine. However, little is known about the effects of PRV infection on porcine reproductive system. Ovarian granulosa cells are somatic cells surrounding oocytes in ovary and required for folliculogenesis. The present study aimed to investigate the interference of PRV on functions of porcine ovarian granulosa cells in vitro.

METHODS

Primary granulosa cells were isolated from porcine ovaries. To investigate the PRV infectivity, transmission electron microscopy (TEM) was used to check the presence of viral particles, and the expression of viral gE gene was detected by quantitative real-time PCR (qPCR) in PRV-inoculated cells. After PRV infection, cell viability was detected by MTS assay, Ki67 for proliferative status was determined by immunofluorescence assay (IFA), cell cycle and apoptosis were detected by flow cytometry, and progesterone (P4) and estradiol (E2) were determined by radioimmunoassay. The checkpoint genes of cell cycle and apoptosis-related proteins were studied by qPCR and western blotting.

RESULTS

Virus particles were observed in the nucleus and cytoplasm of PRV-infected granulosa cells by TEM imaging, and the expression of viral gE gene increased in a time-dependent manner post infection. PRV infection inhibited cell viability and blocked cell cycle at S phase in porcine granulosa cells, accompanied by decreases in expression of Ki67 protein and checkpoint genes related to S phase. Radioimmunoassay revealed decreased levels in P4 and E2, and the expressions of key steroidogenic enzymes were also down-regulated post PRV-infection. In addition, PRV induced apoptosis with an increase in Bax expression and activation of caspase 9, and the phosphorylation of JNK, ERK and p38 MAPKs were significantly up-regulated in porcine ovarian granulosa cells post PRV infection.

CONCLUSIONS

The data indicate that PRV causes infection on porcine ovarian granulosa cells and interferes the cell functions through apoptosis, and the MAPK signaling pathway is involved in the viral pathogenesis.

Transcriptomic analysis reveals impact of gE/gI/TK deletions on host response to PRV infection

BACKGROUND

Pseudorabies virus (PRV) causes substantial losses in the swine industry worldwide. Attenuated PRV strains with deletions of immunomodulatory genes glycoprotein E (gE), glycoprotein I (gI) and thymidine kinase (TK) are candidate vaccines. However, the effects of gE/gI/TK deletions on PRV-host interactions are not well understood.

METHODS

To characterize the impact of gE/gI/TK deletions on host cells, we analyzed and compared the transcriptomes of PK15 cells infected with wild-type PRV (SD2017), PRV with gE/gI/TK deletions (SD2017gE/gI/TK) using RNA-sequencing.

RESULTS

The attenuated SD2017gE/gI/TK strain showed increased expression of inflammatory cytokines and pathways related to immunity compared to wild-type PRV. Cell cycle regulation and metabolic pathways were also perturbed.

CONCLUSIONS

Deletion of immunomodulatory genes altered PRV interactions with host cells and immune responses. This study provides insights into PRV vaccine design.

Suppression of NF-κB signaling by Pseudorabies virus DNA polymerase processivity factor UL42 via recruiting SOCS1 to promote the ubiquitination degradation of p65

The NF-κB pathway is a critical signaling involved in the regulation of the inflammatory and innate immune responses. Previous studies have shown that Pseudorabies Virus (PRV), a porcine alpha herpesvirus, could lead to the phosphorylation and nucleus translocation of p65 while inhibiting the expression of NF-κB-dependent inflammatory cytokines, which indicated that there may be unknown mechanisms downstream of p65 that downregulate the activation of NF-κB signaling. Here, we found that PRV DNA polymerase factor UL42 inhibited TNFα-, LPS-, IKKα-, IKKβ-, and p65-mediated transactivation of NF-κB signaling, which demonstrated UL42 worked either at or downstream of p65. In addition, it was found that the DNA-binding activity of UL42 was required for inhibition of NF-κB signaling. Importantly, it was revealed that UL42 could induce the ubiquitination degradation of p65 by upregulating the suppressor of cytokine signaling 1 (SOCS1). Additionally, it was found that UL42 could promote the K6/K29-linked ubiquitination of p65. Finally, knockdown of SOCS1 attenuated the replication of PRV and led to a significant increase of the inflammatory cytokines. Taken together, our findings uncovered a novel mechanism that PRV-UL42 could upregulated SOCS1 to promote the ubiquitination degradation of p65 to prevent excessive inflammatory response during PRV infection.

A novel viral vaccine platform based on engineered transfer RNA

In recent years, an increasing number of emerging and remerging virus outbreaks have occurred and the rapid development of vaccines against these viruses has been crucial. Controlling the replication of premature termination codon (PTC)-containing viruses is a promising approach to generate live but replication-defective viruses that can be used for potent vaccines. Here, we used anticodon-engineered transfer RNAs (ACE-tRNAs) as powerful precision switches to control the replication of PTC-containing viruses. We showed that ACE-tRNAs display higher potency of reading through PTCs than genetic code expansion (GCE) technology. Interestingly, ACE-tRNA has a site preference that may influence its read-through efficacy. We further attempted to use ACE-tRNAs as a novel viral vaccine platform. Using a human immunodeficiency virus type 1 (HIV-1) pseudotyped virus as an RNA virus model, we found that ACE-tRNAs display high potency for read-through viral PTCs and precisely control their production. Pseudorabies virus (PRV), a herpesvirus, was used as a DNA virus model. We found that ACE-tRNAs display high potency for reading through viral PTCs and precisely controlling PTC-containing virus replication. In addition, PTC-engineered PRV completely attenuated and lost virulence in mice in vivo, and immunization with PRV containing a PTC elicited a robust immune response and provided complete protection against wild-type PRV challenge. Overall, replication-controllable PTC-containing viruses based on ACE-tRNAs provide a new strategy to rapidly attenuate virus infection and prime robust immune responses. This technology can be used as a platform for rapidly developing viral vaccines in the future.

RhoA suppresses pseudorabies virus replication in vitro

The porcine pseudorabies virus (PRV) is one of the most devastating pathogens and brings great economic losses to the swine industry worldwide. Viruses are intracellular parasites that have evolved numerous strategies to subvert and utilize different host processes for their life cycle. Among the different systems of the host cell, the cytoskeleton is one of the most important which not only facilitate viral invasion and spread into neighboring cells, but also help viruses to evade the host immune system. RhoA is a key regulator of cytoskeleton system that may participate in virus infection. In this study, we characterized the function of RhoA in the PRV replication by chemical drugs treatment, gene knockdown and gene over-expression strategy. Inhibition of RhoA by specific inhibitor and gene knockdown promoted PRV proliferation. On the contrary, overexpression of RhoA or activation of RhoA by chemical drug inhibited PRV infection. Besides, our data demonstrated that PRV infection induced the disruption of actin stress fiber, which was consistent with previous report. In turn, the actin specific inhibitor cytochalasin D markedly disrupted the normal fibrous structure of intracellular actin cytoskeleton and decreased the PRV replication, suggesting that actin cytoskeleton polymerization contributed to PRV replication in vitro. In summary, our data displayed that RhoA was a host restriction factor that inhibited PRV replication, which may deepen our understanding the pathogenesis of PRV and provide further insight into the prevention of PRV infection and the development of anti-viral drugs.

Ginkgolic acid inhibits the replication of pseudorabies virus in vitro and in vivo by suppressing the transcription of viral late genes

Pseudorabies virus (PRV) belongs to the species of alphaherpesvirus that can cause substantial economic losses to the world swine industry. Therefore, research on anti-PRV compounds is of great value. In this study, it was found that ginkgolic acid could efficiently inhibit the replication of PRV, and the IC50 and CC50 were 3.407 μM and 102.3 μM, respectively. Moreover, it was discovered that ginkgolic acid had no effect on the adsorption, entry, and release stages of the PRV replication cycle. Importantly, it was found that ginkgolic acid could significantly suppress the transcription of PRV late genes, while the transcription of viral immediate early and early genes was not affected. Finally, in vivo experiments showed that ginkgolic acid could significantly reduce the viral load of PRV in multiple tissues and increase 30% survival rate of mice upon the challenge of PRV. Taken together, a novel PRV replication inhibitor, ginkgolic acid, which worked through suppressing the transcription of the late genes, was found in this study. This study provides a potential therapy method for the infection of PRV.

The potential of swine pseudorabies virus attenuated vaccine for oncolytic therapy against malignant tumors

BACKGROUND

Oncolytic viruses are now well recognized as potential immunotherapeutic agents against cancer. However, the first FDA-approved oncolytic herpes simplex virus 1 (HSV-1), T-VEC, showed limited benefits in some patients in clinical trials. Thus, the identification of novel oncolytic viruses that can strengthen oncolytic virus therapy is warranted. Here, we identified a live-attenuated swine pseudorabies virus (PRV-LAV) as a promising oncolytic agent with broad-spectrum antitumor activity in vitro and in vivo.

METHODS

PRV cytotoxicity against tumor cells and normal cells was tested in vitro using a CCK8 cell viability assay. A cell kinase inhibitor library was used to screen for key targets that affect the proliferation of PRV-LAV. The potential therapeutic efficacy of PRV-LAV was tested against syngeneic tumors in immunocompetent mice, and against subcutaneous xenografts of human cancer cell lines in nude mice. Cytometry by time of flight (CyTOF) and flow cytometry were used to uncover the immunological mechanism of PRV-LAV treatment in regulating the tumor immune microenvironment.

RESULTS

Through various tumor-specific analyses, we show that PRV-LAV infects cancer cells via the NRP1/EGFR signaling pathway, which is commonly overexpressed in cancer. Further, we show that PRV-LAV kills cancer cells by inducing endoplasmic reticulum (ER) stress. Moreover, PRV-LAV is responsible for reprogramming the tumor microenvironment from immunologically naïve ("cold") to inflamed ("hot"), thereby increasing immune cell infiltration and restoring CD8+ T cell function against cancer. When delivered in combination with immune checkpoint inhibitors (ICIs), the anti-tumor response is augmented, suggestive of synergistic activity.

CONCLUSIONS

PRV-LAV can infect cancer cells via NRP1/EGFR signaling and induce cancer cells apoptosis via ER stress. PRV-LAV treatment also restores CD8+ T cell function against cancer. The combination of PRV-LAV and immune checkpoint inhibitors has a significant synergistic effect. Overall, these findings point to PRV-LAV as a serious potential candidate for the treatment of NRP1/EGFR pathway-associated tumors.

Carbopol dispersed PAA-modified UIO-66 with high colloidal stability as a combination nano-adjuvant boosts immune response and protection against pseudorabies virus in mice and pigs

Although inactivated vaccines have higher safety than live-attenuated vaccines in the control of pseudorabies virus (PRV), their protection efficacy is limited due to insufficient immunogenicity when used alone. High-performance adjuvants that can potentiate immune responses are highly desirable to improve the protection efficacy of inactivated vaccines. In this work, we have developed U@PAA-Car, a Carbopol dispersed zirconium-based metal-organic framework UIO-66 modified by polyacrylic acid (PAA), as a promising adjuvant for inactivated PRV vaccines. The U@PAA-Car has good biocompatibility, high colloidal stability, and antigen (vaccine) loading capacity. It significantly potentiates humoral and cellular immune responses over either U@PAA, Carbopol, or commercial adjuvants such as Alum and biphasic 201 by inducing a higher specific antibody titer, IgG2a/IgG1 ratio, cell cytokine secretion, and splenocyte proliferation. A protection rate of over 90% was observed in challenge tests in the model animal mice and the host animal pigs, which is much higher than that observed with commercial adjuvants. The high performance of the U@PAA-Car is attributed to antigen sustainable release at the injection site and highly efficient antigen internalization and presentation. In conclusion, this work not only demonstrates a great potential of the developed U@PAA-Car nano-adjuvant for the inactivated PRV vaccine but also gives a preliminary explanation of its action mechanism. STATEMENT OF SIGNIFICANCE: We have developed a Carbopol dispersed PAA-modified zirconium-based metal-organic framework UIO-66 (U@PAA-Car) as a promising combination nano-adjuvant for the inactivated PRV vaccine. The U@PAA-Car induced higher specific antibody titers and IgG2a/IgG1 ratio, increased cell cytokines secretion, and better splenocyte proliferation than U@PAA, Carbopol, and the commercial adjuvants Alum and biphasic 201, indicating that it induces a significant potentiation of humoral and cellular immune response. In addition, much higher protection rates were achieved with the U@PAA-Car-adjuvanted PRV vaccine in mice and pigs challenge than those observed from the commercial adjuvant groups. This work not only demonstrates the great potential of the U@PAA-Car nano-adjuvant in an inactivated PRV vaccine but also gives a preliminary explanation of its action mechanism.

Genome-wide analysis of long noncoding RNA profiles in pseudorabies-virus-infected PK15 cells

Recently, an increasing number of studies have shown that long noncoding RNAs (lncRNAs) are involved in host metabolism after infection with pseudorabies virus (PRV). In our study, via RNA sequencing analysis, a total of 418 mRNAs, 137 annotated lncRNAs, and 312 new lncRNAs were found to be differentially expressed. These lncRNAs were closely associated with metabolic regulation and immunity-related signalling pathways, including the T-cell receptor signalling pathway, chemokine signalling pathway, mitogen-activated protein kinase (MAPK) signalling pathway, TNF signalling pathway, Ras signalling pathway, calcium signalling pathway, and phosphatidylinositol signalling system. Real-time PCR indicated that several mRNAs and lncRNAs involved in the regulation of the immune effector process, T-cell receptor signalling pathway, TNF signalling pathway, MAPK signalling pathway, and chemokine signalling pathways were significantly expressed. These mRNAs and lncRNAs might play a role in PRV infection.

Pseudorabies virus infection activates the NLRP3 and IFI16 inflammasomes to trigger pyroptosis

Pseudorabies virus (PRV) preferably invades neural tissue and various organs, whereupon may result in multisystemic lesions. Pyroptosis mediated by proteolytic cleavage of gasdermin D (GSDMD) by inflammatory caspases (caspase-1/4/5/11), is closely associated with the activation of inflammasomes, a multiprotein proinflammatory complex. However, further studies on the mechanisms regarding PRV-induced pyroptosis in its natural host are required. Herein, it is demonstrated that PRV infection triggered GSDMD- not GSDME-mediated pyroptosis in porcine alveolar macrophage cells, resulting in increased secretion of IL-1β and LDH. During this process, caspase-1 was activated and participated in the cleaving of GSDMD. Interestingly, we found that the viral replication process or protein production is required to induce pyroptotic cell death. Also, our findings showed that PRV triggered NLRP3 inflammasome activation, which was associated with the production of reactive oxygen species (ROS) and potassium efflux. In addition to the NLRP3 inflammasome, the IFI16 inflammasome was also activated. Importantly, the NLRP3- and IFI16- inflammasomes were both involved in pyroptosis during PRV infection. Finally, we observed that the cleaved GSDMD, activated caspase-1, increased IFI16 levels, and elevated NLRP3 protein in PRV-infected tissues (brain and lung), supporting the occurrence of pyroptosis and the activation of NLRP3- and IFI16- inflammasome in PRV-infected pigs. This research advances our understanding of the PRV-mediated inflammatory response and cell death pathways, providing a deeper knowledge of effective treatments for pseudorabies.

A self-assembled nanoparticle vaccine based on pseudorabies virus glycoprotein D induces potent protective immunity against pseudorabies virus infection

Pseudorabies virus (PRV) mainly causes pseudorabies (PR) or Aujeszky's disease in pigs and can infect humans, raising public health concerns about zoonotic and interspecies transmission of PR. With the emergence of PRV variants in 2011, the classic attenuated PRV vaccine strains have failed to protect many swine herds against PR. Herein, we developed a self-assembled nanoparticle vaccine that induces potent protective immunity against PRV infection. PRV glycoprotein D (gD) was expressed using the baculovirus expression system and further presented on the lumazine synthase (LS) 60-meric protein scaffolds via the SpyTag003/SpyCatcher003 covalent coupling system. In mouse and piglet models, LSgD nanoparticles emulsified with the ISA 201VG adjuvant elicited robust humoral and cellular immune responses. Furthermore, LSgD nanoparticles provided effective protection against PRV infection and eliminated pathological symptoms in the brain and lungs. Collectively, the gD-based nanoparticle vaccine design appears to be a promising candidate for potent protection against PRV infection.

Protective effect of Platycodon grandiflorus polysaccharide on apoptosis and mitochondrial damage induced by pseudorabies virus in PK-15 cells

Previous studies have confirmed that Platycodon grandiflorus polysaccharide (PGPSt) has the effects of regulating immunity and anti-apoptosis, but its effect on mitochondrial damage and apoptosis caused by PRV infection is still unclear. In this research, the effects of PGPSt on the cell viability, mitochondria morphology, mitochondrial membrane potential and apoptosis caused by PRV based on PK-15 cells were respectively examined by CCK-F assay, Mito-Tracker Red CMXRos, JC-1 staining method and Western blot etc. CCK-F test results showed that PGPSt had a protective effect on the decrease of cell viability caused by PRV. The results of morphological observation found that PGPSt can improve mitochondrial morphology damage, mitochondrial swelling and thickening, and cristae fracture. Fluorescence staining test results showed that PGPSt alleviated the decrease of mitochondrial membrane potential and apoptosis in infected cells. The expression of apoptosis-related proteins showed that PGPSt down-regulated the expression of the pro-apoptotic protein Bax and up-regulated the expression of the anti-apoptotic protein Bcl-2 in infected cells. These results indicated that PGPSt protected against PRV-induced PK-15 cell apoptosis by inhibiting mitochondrial damage.

Immunogenic response of recombinant pseudorabies virus carrying B646L and B602L genes of African swine fever virus in mice

African swine fever (ASF) is an acute infectious disease that poses a high lethality risk to domestic pigs and wild boars, causing substantial economic losses to the global pig industry. The prevention and control of ASF remain challenging, necessitating the urgent development of a safe and effective vaccine. This study focused on the essential structural protein p72 of ASFV (encoded by the B646L gene) and its chaperone protein pB602L (encoded by the B602L gene) as the target antigenic proteins. Based on CRISPR/Cas9 gene-editing technology, we constructed a live attenuated recombinant pseudorabies virus vector expressing the p72 and pB602L proteins (designated as rPRVXJ-EGFP/B602L/B646L), and assessed its immunization effect in mice. The recombinant virus rPRVXJ-EGFP/B602L/B646L successfully proliferated and demonstrated stable expression of the p72 and pB602L proteins in BHK-21 cells. Moreover, it exhibited excellent safety when used in mice and induced specific humoral and cellular immune responses targeting p72 and pB602L. In addition, it provided complete protection (100%) against the virulent PRV strain (PRV-XJ). These results indicate that the recombinant virus rPRVXJ-EGFP/B602L/B646L possesses robust immunogenicity and safety in mice. In conclusion, PRV represents a promising viral vector for expressing ASFV gene, and our study serves as an essential reference for the development of viral vector vaccines against ASFV.

Microglia play an important role in PRV infection-induced immune responses of the central nervous system

Pseudorabies virus (PRV) can infect multiple hosts and lead to fatal encephalitis. There is a significant increase in the number of microglia in the brain of animals infected with PRV. However, whether and how microglia contribute to central nervous system damage in PRV infection remain unknown. In the present study, we elucidated that PRV infection can cause more severe inflammatory cell infiltration, thicker and more numerous vessel sleeve walls, and more severe inflammatory responses in the brains of natural hosts (pigs) than in those of nonnatural hosts (mice). In a mice infection model, activated microglia restricted viral replication in the early stage of infection. Acute neuroinflammation caused by microglia hyperactivation at late-stage of infection. Furthermore, in vitro experiments revealed that microglia restricted viral replication and decreased viral infectivity. This may be associated with the phagocytic ability of microglia because we observed a significant increase in the expression of the membrane receptor TREM2 in microglia, which is closely related to phagocytosis, we observed that depletion of microglia exacerbated neurological symptoms, blood-brain barrier breakdown, and peripheral lymphocyte infiltration. Taken together, we revealed the dual role of microglia in protecting the host and neurons from PRV infection.

Evaluation of immunogenicity of gene-deleted and subunit vaccines constructed against the emerging pseudorabies virus variants

BACKGROUND

Pseudorabies (PR) (also called Aujeszky's disease, AD) is a serious infectious disease affecting pigs and other animals worldwide. The emergence of variant strains of pseudorabies virus (PRV) since 2011 has led to PR outbreaks in China and a vaccine that antigenically more closely matches these PRV variants could represent an added value to control these infections.

METHODS

The objective of this study was to develop new live attenuated and subunit vaccines against PRV variant strains. Genomic alterations of vaccine strains were based on the highly virulent SD-2017 mutant strain and gene-deleted strains SD-2017ΔgE/gI and SD-2017ΔgE/gI/TK, which constructed using homologous recombination technology. PRV gB-DCpep (Dendritic cells targeting peptide) and PorB (the outer membrane pore proteins of N. meningitidis) proteins containing gp67 protein secretion signal peptide were expressed using the baculovirus system for the preparation of subunit vaccines. We used experimental animal rabbits to test immunogenicity to evaluate the effect of the newly constructed PR vaccines.

RESULTS

Compared with the PRV-gB subunit vaccine and SD-2017ΔgE/gI inactivated vaccines, rabbits (n = 10) that were intramuscularly vaccinated with SD-2017ΔgE/gI/TK live attenuated vaccine and PRV-gB + PorB subunit vaccine showed significantly higher anti-PRV-specific antibodies as well as neutralizing antibodies and IFN-γ levels in serum. In addition, the SD-2017ΔgE/gI/TK live attenuated vaccine and PRV-gB + PorB subunit vaccine protected (90-100%) rabbits against homologous infection by the PRV variant strain. No obvious pathological damage was observed in these vaccinated rabbits.

CONCLUSIONS

The SD-2017ΔgE/gI/TK live attenuated vaccine provided 100% protection against PRV variant challenge. Interestingly, the subunit vaccines with gB protein linked to DCpep and PorB protein as adjuvant may also be a promising and effective PRV variant vaccine candidate.

A case report of long-delayed diagnosis of pseudorabies virus encephalitis with endophthalmitis: lessons from metagenomic next generation sequencing

BACKGROUND

Pseudorabies virus (PRV) was thought to only infect animals. Recent studies have shown that it can also infect human.

CASE PRESENTATION

We report a case of pseudorabies virus encephalitis and endophthalmitis, diagnosed 89 days after onset, confirmed with intraocular fluid metagenomic next generation sequencing (mNGS) after the result of two cerebrospinal fluid (CSF) mNGS tests were negative. Although treatment with intravenous acyclovir, foscarnet sodium, and methylprednisolone improved the symptoms of encephalitis, significant diagnostic delay resulted in permanent visual loss.

CONCLUSIONS

This case suggests that pseudorabies virus (PRV) DNA in the intraocular fluid may have a higher positivity than that in the CSF. PRV may persist in the intraocular fluid for an extended period and may thus require extended antiviral therapy. Patients with severe encephalitis and PRV should be examined with the focus on pupil reactivity and light reflex. A fundus examination should be performed in patients with a central nervous system infection, specifically, those in a comatose state, to help reduce eye disability.

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.

Isolation and identification of two novel pseudorabies viruses with natural recombination or TK gene deletion in China

Pseudorabies virus (PRV), the causative agent of Aujeszky's disease, has gained increased attention in China in recent years due to outbreaks of emergent pseudorabies. However, there is limited information about the evolution and pathogenicity of emergent PRV field strains in China. In this study, two PRV field strains were isolated from an intensive pig farm with suspected PRV infection. These were named the GXLB-2015 and GXGG-2016 strains and their growth characteristics together with their genome sequences and pathogenicity were determined. Nucleotide homology and phylogenetic analysis revealed the GXLB-2015 stain was relatively close to the foreign PRV isolated strains with respect to the whole genome sequence. However, it formed an independent branch between the foreign PRV isolates and the previous PRV variants isolated in China. Further recombination and genetic evolution analysis showed that the GXLB-2015 strain was a natural recombinant between the Bartha strain and PRV variants. The GXGG-2016 strain was highly homologous with the Chinese classical strains, but it has a natural deletion of 69 aa in the thymidine kinase (TK) gene. Pathogenicity analysis showed that, the GXLB-2015 strain had the strongest pathogenicity to mice with an LD50 of 103.5, while the GXGG-2016 strain with the TK gene deletion was not pathogenic to mice. Taken together, our data provide direct evidence for the genomic recombination and natural TK gene deletion of PRVs, which may provide a reference for a better understanding of PRV evolution in China and contribute to the clinical control of PRV infection in pig farms.

High expression of the classical swine fever virus (CSFV) envelope protein E2 by a single amino acid mutation and its embedded in the pseudorabies virus (PRV) vector for immunization

Pseudorabies (PR) and classical swine fever (CSF) are economically important infectious diseases in pigs. Most pig farms in China are vaccinated against these two diseases. Gene-deleted pseudorabies virus (PRV) can be used to develop promising and economical multivalent live attenuated viral vector vaccines. It has been reported that recombinant PRV can express a truncated E2 protein (1-338 aa), but it has not been reported that recombinant PRV can express a full-length E2 protein. We constructed nine groups of E2 proteins with different expression forms and found that the E2 protein could be expressed in vitro only when the transmembrane region of E2 was removed and the signal peptide was added. Analysis of the transmembrane region of E2 revealed that the high hydrophobicity of the E2 transmembrane region was the main reason for its inability to express. By mutating an amino acid to reduce the hydrophobicity of the transmembrane region, it was found that the full-length mutant of E2 (E2FL-muta3 or E2FL-muta4) could be expressed. The expressed full-length mutant E2 could also localize to the cell membrane. Mice immunized with a PRV vector vaccine expressing E2FL-muta3 or E2FL-muta4 developed specific cellular immunity to the E2 protein and stimulated higher levels of E2 antibody than mice immunized with a PRV vector expressing truncated E2. After immunizing the rabbits, the lethal challenge by PRV-ZJ2013 and the febrile response elicited by CSFV were simultaneously prevented. These results suggest that rPRV-dTK/gE-E2FL-muta4 is a promising bivalent vaccine against CSFV and PRV infections. IMPORTANCE The continuous variation of CSFV and PRV poses a serious threat to vaccination strategies. However, it is expensive to eliminate CSFV in the swine industry in China through a phase-out policy, and the existing CSFV vaccine C-Strain cannot distinguish infected from vaccinated individuals. In addition, the mutation of PRV in 2011 is also an urgent need to develop new PRV vaccine strains. In this study, we constructed a recombinant PRV strain expressing for the first time the full-length E2 protein, mice immunized with the recombinant PRV strain produced high titer antibodies against both PRV and CSFV E2 protein and showed that it could protect against both PRV variant challenge and CSFV fever response in rabbit models. It can be used to prevent two diseases with one injection.

Resveratrol alleviated neuroinflammation induced by pseudorabies virus infection through regulating microglial M1/M2 polarization

BACKGROUND

Pseudorabies virus (PRV) infections in susceptible non-porcine species trigger uncontrolled inflammations and eventually fatal encephalitis. Resveratrol (Res) has broad pharmacological functions including anti-virus, anti-inflammation, and neuroprotective.

PURPOSE

We attempted to investigate the potential of Res in ameliorating PRV infection pathology in mice and decipher the mechanism of Res in treating PRV.

METHODS

The mice were infected by PRV to investigate the protective effect of Res. Blood-brain barrier (BBB) permeability, H&E/Nissl/TUNEL staining, Real-time PCR and ELISA analyses were performed. Primary microglia and neuron were isolated from mice and cultured. The co-culture model of microglia and neuron was established by transwell. Immunofluorescence assay and flow cytometry were used.

RESULTS

In this study, we showed that Res ameliorated brain damage by reducing BBB permeability in PRV-infected mice, and diminished the expressions of MMP-2, MMP-9 and ZO-1 in the cortex. Pathological changes of neurons by H&E/Nissl/TUNEL staining suggested that Res could alleviate neuronal lesions. Moreover, Res inhibited the expressions of pro-inflammatory factors (IL-6, TNF-α) and chemokines (CCL3, CXCL10, MCP-1), but increased the expressions of anti-inflammatory factors (IL-4, IL-10) and neurotrophic factor (TGF-β, NGF and GDNF) in brain. In vitro cultured microglia cells, Res could suppress M1 microglia polarization and activate M2 microglia polarization. Co-culture of PRV-infected microglia with neuron cells by transwell system indicated that Res alleviated inflammatory response and neuronal apoptosis.

CONCLUSION

This study provided evidence that Res could protect mice from PRV-induced encephalitis through regulation of microglia polarization and neuronal apoptosis suggesting the potential for treatment of viral encephalitis.

Recombinant porcine Interferon-α and Interleukin-2 fusion protein (rPoIFNα+IL-2) shows potent anti-pseudorabies virus activity in vitro and in vivo

Pseudorabies virus (PRV) variants have been widely prevalent since 2011, leading to substantial losses to the swine industry. Although PRV can cause cross-species transmission and induce human infection, no drugs can currently prevent PRV infection. Interferons (IFNs) and interleukin-2 (IL-2) are important cytokines that mediate several biological functions including antiviral activity and immune regulation. In this study, we expressed and purified a recombinant porcine IFN-α and IL-2 fusion protein (rPoIFNα+IL-2), which did not show a cytotoxic effect on PK-15 cells. The antiviral activity was evaluated in PK-15 cells using the cytopathic effect inhibition method, and the results indicated that rPoIFNα+IL-2 can inhibit the replication of PRV, with an antiviral activity of approximately 10⁴ U/mL. Moreover, the proliferation of peripheral blood mononuclear cells was enhanced by rPoIFNα+IL-2. Additionally, rPoIFNα+IL-2 substantially increased the expression of IFN-stimulated genes, including IFIT1, ISG15, MX1, and OAS, which are critical for antiviral activity. Furthermore, rPoIFNα+IL-2 alleviated the clinical symptoms and reduced mortality in mice infected with PRV. Simultaneously, rPoIFNα+IL-2 increased the expression levels of IFN-γ and IL-10 and inhibited the expression of IL-1β and IL-6. Additionally, the viral DNA copies in different tissues in the rPoIFNα+IL-2-treated group were lower than those in the untreated group. These findings indicate that rPoIFNα+IL-2 may serve as an antiviral agent for the prevention and treatment of PRV infection and may expand the potential function of IFN antiviral drugs in the future.

Recombinant pseudorabies virus (PRV) expressing stabilized E2 of classical swine fever virus (CSFV) protects against both PRV and CSFV

Pseudorabies (PR) and classical swine fever (CSF) are economically important infectious diseases of pigs. Most pig farms in China are immunized against these two diseases. Here, we describe a stabilized E2 protein as an immunogen inserted into the PRV genome as a bivalent live virus-vectored vaccine. The E2 protein has 48 variant sites, there are 2-5 candidate amino acids per variant site, and the relative energy contribution of each amino acid to E2 energy was calculated. Combined substitutions of amino acids at the neighbor variant site (neighbor substitution) were performed to obtain the E2 protein sequence with the lowest energy (stabilized E2). Multiple amino acid substitutions at 48 variant sites were performed, and the results were consistent with neighbor substitutions. The stabilized E2 sequence was obtained, and its energy decreased by 22 Rosetta Energy Units (REUs) compared with the original sequence. After the recombinant PRV expressing stabilized E2 of CSFV was constructed, the secretion efficiency of stabilized E2 was increased by 2.97 times, and the thermal stability was increased by 10.5 times. Immunization of mice resulted in a 2-fold increase in antibody production, and a balanced antibody level against subtype 1.1 and subtype 2.1d E2 was achieved. In rabbits immunized, the lethal challenge of PRV-ZJ and the fever response induced by CSFV could be prevented simultaneously. These findings suggest that rPRV-muta/287aaE2 is a promising bivalent vaccine against CSFV and PRV infections.

Association of THBS3 with Glycoprotein D Promotes Pseudorabies Virus Attachment, Fusion, and Entry

Pseudorabies virus (PRV) is a neurotropic virus causing obvious neurological disorders and reproductive failure in pigs. PRV entry into target cells is a complex multistep process initiated by interacting viral envelope glycoproteins with cellular receptors. In the current study, we found that thrombospondin 3 (THBS3) plays an important role in PRV entry into target cells, indicating that THBS3 is a new PRV coreceptor. To confirm this hypothesis, the knockdown of THBS3 in several permissive cells inhibited PRV primary infection, and overexpression of THBS3 in PK15 cells promoted PRV infection. CRISPR-Cas9 knockout markedly reduced PRV infection in PK15 cells. Antibodies against THBS3 blocked PRV infection in naturally permissive target cells. Moreover, soluble THBS3 protein neutralized the infectivity of PRV. Mechanistically, THBS3 interacted with the PRV gD via its N and C termini to facilitate PRV binding in permissive and nonpermissive cells. Also, in the absence of Nectin-1, THBS3 promoted cell-to-cell fusion mediated by virus glycoproteins. While THBS3 alone could not increase virus entry, overexpression of it in the presence of Nectin-1 promoted virus entry into CHO-K1 cells. Our results have identified THBS3 as a critical player in PRV binding and subsequent membrane fusion and entry. IMPORTANCE Herpesvirus entry occurs through a cascade of virus-cell interactions, and multiple surface glycoproteins play a role in virus binding and entry during the virus invasion process. Early studies showed that attachment to cells by PRV, as well as other alphaherpesviruses, is mediated by interactions between the viral glycoprotein gC and cell membrane proteoglycans carrying heparan sulfate chains (HSPGs). However, gD may also be involved in virus binding in an HSPG-independent manner. To date, the respective cellular receptors are still unknown. In this report, we identified a host molecule, THBS3, involved in gD-mediated PRV binding and subsequent membrane fusion and entry, which increases our understanding of the initial events in alpha herpesvirus infections.

Comparison of the protective efficacy between the candidate vaccine ZJ01R carrying gE/gI/TK deletion and three commercial vaccines against an emerging pseudorabies virus variant

Pseudorabies virus (PRV) is a swine alpha-herpesvirus that mainly causes reproductive disorders in sows and neurological diseases in piglets. Vaccination is the most efficient method to prevent the disease. In China, since the emergence of PRV mutant strains in late 2011, the traditional commercial vaccines have not been providing complete protection. Our previous studies have demonstrated that PRV ZJ01 is a highly virulent strain, and its derivative, ZJ01R, which carries the gE/gI/TK gene deletion, could provide protection against the variant PRV challenge. However, the difference in immune efficacy between ZJ01R and other commercial vaccines remains unclear. In this study, the immune protection efficacy between ZJ01R and three commercial PRV vaccines (Bartha-K61, HB2000, and SA215) was evaluated in piglets. The safety of ZJ01R was shown to be equivalent to that of the three commercial vaccines. The titers of the neutralizing antibodies against the PRV classical strain LA in the four vaccine groups were similar, while the anti-PRV variant neutralizing antibody titers in the ZJ01R group were significantly higher than those in the Bartha-K61, HB2000, and SA215 strain groups. After the PRV challenge, ZJ01R, HB2000, and SA215 vaccinations could provide complete protection, whereas the Bartha-K61 vaccination could only provide 60 % protection. Importantly, the rectal viral excretion and PRV DNA loads in the lung tissues in the ZJ01R group were significantly lower than those in the Bartha-K61, HB2000, and SA215 groups. Altogether, these results indicated that ZJ01R could provide higher protection efficacy against the PRV virulent ZJ01 challenge than the three commercial PRV gene-deleted live vaccines derived from the classical vaccine strains, providing the potential to develop a new PRV vaccine to control the epidemic PRV variant strains in the future.

Acute transcriptomic changes in murine RAW 264.7 cells following pseudorabies virus infection

Next-generation sequencing enables the evaluation of gene expression changes resulting from virus-host interactions at the RNA level. Pseudorabies virus (PRV) causes substantial economic loss in the swine industry. Recent research has revealed that PRV can be transmitted to and infect humans as well. To identify physiopathological and pathological responses post-PRV infection, we characterized transcriptomic changes in the murine RAW 264.7 cell line over the course of 36 h. In total, 156, 153, and 190 differentially expressed genes were identified at 2 h, 12 h, and 36 h, respectively. Seven differentially expressed genes (Trim27, Ccdc117, Mrps12, Ccl4, Cerkl, Ubald1, and Hmga1-rs1) were present across all treatment groups. Our findings expand our knowledge of gene regulation and immune response following PRV infection. These differentially expressed genes can subsequently improve our understanding of PRV pathogenesis.

Pseudorabies virus infection induces endoplasmic reticulum stress and unfolded protein response in suspension-cultured BHK-21 cells

Viral infections cause endoplasmic reticulum (ER) stress and subsequently unfolded protein response (UPR) which restores ER homeostasis. In this study, levels of proteins or transcription of three UPR pathways were examined in suspension-cultured BHK-21 cells to investigate Pseudorabies virus (PRV) infection-induced ER stress, in which glucose-related proteins 78 kD and 94 kD (GRP78 and GRP94) were upregulated. The downstream double-stranded RNA-activated protein kinase-like ER kinase (PERK) pathway was activated with upregulation of ATF4, CHOP, and GADD34, and the inositol requiring kinase 1 (IRE1) pathway was triggered by the splicing of X box-binding protein 1 (XBP1) mRNA and the enhanced expression of p58^IPK and EDEM. Furthermore, our results showed that the ER stress, induced by 0.005 µM thapsigargin, promoted PRV replication in suspension-cultured BHK-21 cells, and that PRV glycoprotein B (gB) overexpression triggered the PERK and IRE1 pathways.

A novel Pseudorabies virus vaccine developed using HDR-CRISPR/Cas9 induces strong humoral and cellular immune response in mice

Outbreaks of Pseudorabies (PR) by numerous highly virulent and antigenic variant Pseudorabies virus (PRV) strains have been causing severe economic losses to the pig industry in China since 2011. However, current commercial vaccines are often unable to induce thorough protective immunity. In this study, a TK/gI/gE deleted recombinant PRV expressing GM-CSF was developed by using the HDR-CRISPR/Cas9 system. Here, a four-sgRNA along with the Cas9^D10A targeting system was utilized for TK/gI/gE gene deletion and GM-CSF insertion. Our study showed that the four-sgRNA targeting system appeared to have higher knock-in efficiency for PRVs editing. The replication of the recombinant PRVs were slightly lower than that of the parental strain, but they appeared to have similar properties in terms of growth curves and plaque morphology. The mice vaccinated with the recombinant PRV expressing GM-CSF via intramuscular injection showed no obvious clinical symptoms, milder pathological lesions, and were completely protected against wild-type PRV challenge. When compared to the triple gene-deleted PRV, the gB antibodies and neutralizing antibody titers were improved and the immunized mice appeared to have lower viral load and higher mRNA levels of IL-2, IL-4, IL-6, and IFN-γ in spleens. Our study offers a novel approach for recombinant PRV construction, and the triple gene-deleted PRV expressing GM-CSF could serve as a promising vaccine candidate for PR control.

Comprehensive evaluation of the safety and immunogenicity of a gene-deleted variant pseudorabies virus attenuated vaccine

Pseudorabies virus (PRV) variant infections have caused a substantial economic impact on swine production in the absence of new powerful candidate vaccines. In this study, we developed and evaluated a gene-deleted variant pseudorabies virus (PRV)-attenuated vaccine, PRV GX-ΔTK/IES, in which the genes TK, gI, gE, US9 and US2 were deleted. During a study of innocuousness, all mice inoculated with PRV GX-ΔTK/IES survived, neither clinical signs nor pathological changes were observed, and viral genomes could not be detected in the blood and tissues. All piglets inoculated with high titres of PRV GX-ΔTK/IES remained clinically healthy, and neither fever nor clinical signs were observed. Viral detection results were negative in nasal swab samples, blood and tissue samples. Moreover, none of the cohabitated piglets seroconverted during a trial on horizontal transmission. The immunogenicity was assessed through a vaccination and challenge experiment in piglets. Piglets vaccinated with PRV GX-ΔTK/IES and the commercial vaccine were completely protected from subsequent PRV infection, and the level of immunity and protection induced by PRV GX-ΔTK/IES was better than that provided by the live commercial vaccine. Thus, PRV GX-ΔTK/IES is completely safe for both nontarget and target animals and can be regarded as a novel live gene-deleted PRV vaccine candidate.

Neuropeptide S and its receptor NPSR enhance the susceptibility of hosts to pseudorabies virus infection

The neuropeptide S (NPS) and its receptor (NPSR) represent a signaling system in the brain. Increased levels of NPS and NPSR have been observed in PK15 cells and murine brains in response to pseudorabies virus (PRV) infection, but it remains unclear whether elevated levels of NPS and NPSR are involved in the pathogenic process of PRV infection. In this study, the activities of both NPS and NPSR during PRV pathogenesis were explored in vitro and in vivo by reverse transcription polymerase chain reaction (RT-PCR), PCR, real-time quantitative RT-PCR (qRT-PCR), qPCR, TCID50, and Western blotting methods. NPSR-deficient cells were less susceptible to PRV infection, as evidenced by decreased viral production and PRV-glycoprotein E (gE) expression. In vitro studies showed that exogenous NPS promoted the expression of interleukin 6 (IL-6) mRNA but inhibited interferon β (IFN-β) mRNA expression in PK15 cells after PRV infection. In vivo studies showed that NPS-treated mice were highly susceptible to PRV infection, with decreased survival rates and body weights. In addition, NPS-treated mice showed elevated levels of IL-6 mRNA and STAT3 phosphorylation. However, the expression of IFN-β mRNA was greatly decreased after virus challenge. Contrasting results were obtained from the NPSR-ir-treated groups, which further highlighted the effects of NPS. This study revealed that NPS-treated hosts are more susceptible to PRV infection than controls. Moreover, excessive IL-6/STAT3 and defective IFN-β responses in NPS-treated mice may contribute to the pathogenesis of PRV.

Specific inhibition of the interaction between pseudorabies virus DNA polymerase subunits UL30 and UL42 by a synthetic peptide

Pseudorabies virus (PRV) is a ubiquitous and economically important swine alphaherpesvirus that causes devastating swine diseases worldwide. PRV-encoded DNA-dependent DNA polymerase, comprised of the catalytic subunit UL30 and the accessory subunit UL42, is essential for viral replication. PRV UL30 and UL42 act as a heterodimer with UL30 harboring inherent DNA polymerase activity and UL42 conferring processivity on the DNA polymerase holoenzyme. The formation of PRV UL30/UL42 heterodimer holoenzyme through protein-protein interactions is indispensable for viral replication. In work described here, we defined the key domains that mediate PRV UL30/UL42 interaction, and found that the 41 carboxy-terminal amino acids region of PRV UL30 is critical for its interaction with UL42. Intriguingly, a synthetic peptide corresponding to these 41 carboxy-terminal amino acid residues efficiently disrupted PRV UL30/UL42 interaction through competitively binding to UL42. These findings suggest that the peptides from the PRV DNA polymerase UL30/UL42 subunit interface may represent potential targets for designing a novel intervention strategy against PRV infection. This work further strengthens the concept that the herpesvirus DNA polymerase catalytic subunits utilize their extreme carboxy-terminal domains as a conserved mechanism to associate with their cognate accessory subunits, providing us the opportunity of designing novel antiviral agents against herpesvirus infection through disruption of the herpesvirus DNA polymerase subunit interactions.

rhizome in mice infected with pseudorabies virus

Pseudorabies virus (PrV) is one of the most important herpesviruses which can cause severe diseases in many mammals and some avian species. In recent years, repeated outbreaks of pseudorabies worldwide indicated an urgent need for new control measures. The results described in this study demonstrated that an extract prepared from the rhizome of Kaempferia galanga L (Kge), which consisted of flavonoids (2.82%), saccharides (61.37%), phenols (1.22%) and saponins (3.10%), possessed a potent anti-PrV activity. In PK-15 cells, Kge treatment inhibited PrV-induced cell death by more than 90% at a dose of 200 μg/mL. The 50% inhibitory concentration (IC₅₀) was 55.85 μg/mL. In the PrV-infected mice treated with Kge, the survival rate was up to 60% at day 6 post-infection, while the infected mice without Kge treatment all died. The virus titers in the brains of the Kge-treated infected mice were significantly reduced. Kge treatment also alleviated the severity of the PrV-induced lesions in the heart, liver, spleen, lung and kidney. Kge exhibited immune-regulating activity through the regulation of cytokines (IFN-α, IFN-β, IL-4, IL-6 and TNF-α) in the serum of PrV-infected mice, suggesting that one possible mechanism of anti-PrV activity was through the regulation of immune function. These results suggested that Kge could be a promising drug candidate for treating PrV infections.

Host Zinc-finger CCHC-type containing protein 3 inhibits pseudorabies virus proliferation by regulating type I interferon signaling

Zinc finger CCHC-type containing protein 3 (ZCCHC3) acts as an antiviral factor that interacts with RIG-I and cGAS to modulate innate signaling against viral infections. Here, we investigated the role of porcine ZCCHC3 during pseudorabies virus (PRV) proliferation. We found that porcine ZCCHC3 plays an inhibitory role in the proliferation of PRV by regulating cellular innate immune responses. Further, overexpression of ZCCHC3 inhibited gB protein levels and viral titers, whereas knockdown of ZCCHC3 promoted viral growth. ZCCHC3 overexpression increased IFN-β expression to upregulate downstream gene expression, thus leading to the suppression of viral replication. However, PRV infection reduced the endogenous expression of ZCCHC3 in permissive cells. Importantly, PRV-encoded UL13 and UL24 proteins were identified to inhibit the expression of ZCCHC3, thus antagonizing its antiviral effect. Collectively, our data underscore the important role of ZCCHC3 against PRV infection and promote understandings of viral proteins in PRV pathogenesis.

Peptidomic Analysis on Mouse Lung Tissue Reveals AGDP as a Potential Bioactive Peptide against Pseudorabies Virus Infection

Pseudorabies virus (PRV) infection could cause severe histopathological damage via releasing multiple factors, including cytokines, peptides, etc. Here, peptidomic results showed that 129 peptides were identified in PRV-infected mouse lungs and were highly involved in the process of PRV infection. The role of one down-regulated biological peptide (designated as AGDP) during PRV infection was investigated. To verify the expression profiles of AGDP in response to PRV infection, the expression level of the precursor protein of AGDP mRNA was significantly decreased in PRV-infected mouse lungs and cells. The synthesized AGDP-treating cells were less susceptible to PRV challenges than the controls, as demonstrated by the decreased virus production and gE expression. AGDP not only inhibited the expression of TNF-α and IL-8 but also appeared to suppress the extracellular release of high-mobility group box 1 (HMGB1) by inhibiting the output of nuclear HMGB1 in cells. AGDP could also inhibit the degradation of IκBα and the phosphorylation levels of P65 after PRV infection. In total, our results revealed many meaningful peptides involved in PRV infection, thereby enhancing the current understanding of the host response to PRV infection, and how AGDP may serve as a promising candidate for developing novel anti-PRV drugs.

Direct cloning of a herpesvirus genome for rapid generation of infectious BAC clones

INTRODUCTION

The herpesviridae are DNA viruses with large and complicated genomes. The herpesvirus bacterial artificial chromosomes (BACs) have been useful for generating recombinant viruses to study the biology and pathogenesis. However, the conventional method using homologous recombination is not only time consuming but also prone to accumulate attenuating mutations during serial passage of the virus in cells. Elimination of the BAC vector from the recombinant viral genome requires additional step for phenotypically consistence with the original strain.

OBJECTIVES

To generate a streamlined approach for generating infectious BAC clones of herpesvirus.

METHODS

The 142-kb pseudorabies virus genome was directly cloned into a bacterial artificial chromosome (BAC) in Escherichia coli by Exonuclease Combined with RecET recombination (ExoCET). Placement of the BAC vector at the terminus of the linear virus genome enabled excision of the BAC backbone from the viral genome by restriction endonuclease for delivery into mammalian cells, with the subsequent rapid rescue of virus that was genetically identical to the original strain.

RESULTS

This new approach for molecular cloning of the genome from a large DNA virus and isolation of pure virus lacking the BAC vector from transfected mammalian cells bypass the tedious and time-consuming method of multiple rounds of plaque purification. The viral BAC was stable in E. coli, allowing further mutagenesis mediated by the Red system or various site-specific recombination methods.

CONCLUSION

An efficient method for construction of infectious clones of herpesvirus was established. It is expected to be potentially useful for other viruses with large double-stranded DNA genomes.

A natural product, (S)-10-Hydroxycamptothecin inhibits pseudorabies virus proliferation through DNA damage dependent antiviral innate immunity

Pseudorabies virus (PRV), a member of the subfamily alphaherpesvirinae, is one of the most important pathogenes that cause acute death in infected pigs and leads to substantial economic losses in the global swine industry. Recently, China's emerging PRV mutant strains resulted in the traditionally commercial vaccines not providing complete protection. Some studies reported that PRV could infect humans and cause endophthalmitis and encephalitis under certain circumstances. It is necessary to develop alternative manners to control the virus infection. Here, by screening a library of natural products, (S)-10-Hydroxycamptothecin (10-HCPT) was revealed to inhibit PRV replication with a selective index of 270.04. And 10-HCPT inhibited PRV replication by blocking the viral genome replication but not inhibiting the viral attachment, internalization, and release. RNA interference assay showed that 10-HCPT inhibited PRV replication by targeting DNA topoisomerase 1 (TOP1). Meanwhile, 10-HCPT treatment induced DNA damage response and stimulated antiviral innate immunity. Animal challenge experiments showed that 10-HCPT effectively alleviated clinical signs and hispathology, and increased INF-β responses in lung and brain tissues of mice induced by PRV infection. The results demonstrate that 10-HCPT is a promising therapeutic agent to control PRV infection.

Methods and Applications of Campenot Trichamber Neuronal Cultures for the Study of Neuroinvasive Viruses

The development of compartmentalized neuron culture systems has been invaluable in the study of neuroinvasive viruses, including the alpha herpesviruses Herpes Simplex Virus 1 (HSV-1) and Pseudorabies Virus (PRV). This chapter provides updated protocols for assembling and culturing rodent embryonic superior cervical ganglion (SCG) and dorsal root ganglion (DRG) neurons in Campenot trichamber cultures. In addition, we provide several illustrative examples of the types of experiments that are enabled by Campenot cultures: (1) Using fluorescence microscopy to investigate axonal outgrowth/extension through the chambers, and alpha herpesvirus infection, intracellular trafficking, and cell-cell spread via axons. (2) Using correlative fluorescence microscopy and cryo electron tomography to investigate the ultrastructure of virus particles trafficking in axons.

Pseudorabies virus UL16 protein influences the inhibition of LRPPRC for the viral proliferation

Pseudorabies is caused by pseudorabies virus (PRV), a member of the Herpesvirus family, and has caused tremendous damage to the pig industry. Protein unique lone 16 (pUL16) is a conserved envelope protein in all herpesviruses, that is known to play an important role in several aspects, including virus diffusion in cells and virulence in mice. It has been shown that the pUL16 can interact with the virus proteins UL11, UL49, UL21, gD, and gE. However, the research to date on pUL16 has only focused on etiology, without discussing the possible cellular pathways involved in PRV infection. Leucine-rich PPR motif-containing protein (LRPPRC) is a multifunctional cellular protein that participates in various cellular processes, such as RNA processing, splicing, stabilization, editing, translation, and energy metabolism. This was the first caspase-independent apoptosis protein to be identified. In this study, immune precipitation and mass spectrometry was performed to define the function of the pUL16 in PRV infection to study the possible cellular pathways in which pUL16 may participate. It was found that LRPRRC could interact with PRV pUL16, which may indicate that UL16 is involved in a redox reaction or cellular apoptosis. This is the first study of the interaction between pUL16 and host proteins, which has positive significance to gain a further understanding of the pUL16.

Exploring propriospinal neuron-mediated neural circuit plasticity using recombinant viruses after spinal cord injury

Propriospinal neurons (PSNs) play a crucial role in motor control and sensory processing and contribute to plastic reorganization of spinal circuits responsible for recovery from spinal cord injury (SCI). Due to their scattered distribution and various intersegmental projection patterns, it is challenging to dissect the function of PSNs within the neuronal network. New genetically encoded tools, particularly cell-type-specific transgene expression methods using recombinant viral vectors combined with other genetic, pharmacologic, and optogenetic approaches, have enormous potential for visualizing PSNs in the neuronal circuits and monitoring and manipulating their activity. Furthermore, recombinant viral tools have been utilized to promote the intrinsic regenerative capacities of PSNs, towards manipulating the 'hostile' microenvironment for improving functional regeneration of PSNs. Here we summarize the latest development in this fast-moving field and provide a perspective for using this technology to dissect PSN physiological role in contributing to recovery of function after SCI.

Vitritis and retinal vasculitis caused by pseudorabies virus

Pseudorabies virus (PRV) is a herpesvirus of swine. PRV is also called suid herpesvirus 1 and is a member of the Alphaherpesvirinae subfamily within the family Herpesviridae. The number of PRV cases worldwide is small, but in susceptible individuals, infection with this virus has a poor prognosis. Therefore, it is urgent to improve our understanding of this disease in clinical practice to avoid misdiagnosis and to identify optimal treatments. We report a patient with PRV infection who was admitted to hospital with viral encephalitis and subsequently developed intraocular infection. Because to the lack of relevant clinical experience in the treatment of this disease, we carried out experimental treatment with good therapeutic effect. This case provides a basis for clinical diagnosis and treatment of patients with PRV.

Leptin coordinates efferent sympathetic outflow to the white adipose tissue through the midbrain centrally-projecting Edinger-Westphal nucleus in male rats

The centrally-projecting Edinger-Westphal nucleus (EWcp) hosts a large population of neurons expressing urocortin 1 (Ucn1) and about half of these neurons also express the leptin receptor (LepRb). Previously, we have shown that the peripheral adiposity hormone leptin signaling energy surfeit modulates EWcp neurons' activity. Here, we hypothesized that Ucn1/LepRb neurons in the EWcp would act as a crucial neuronal node in the brain-white adipose tissue (WAT) axis modulating efferent sympathetic outflow to the WAT. We showed that leptin bound to neurons of the EWcp stimulated STAT3 phosphorylation, and increased Ucn1-production in a time-dependent manner. Besides, retrograde transneuronal tract-tracing using pseudorabies virus (PRV) identified EWcp Ucn1 neurons connected to WAT. Interestingly, reducing EWcp Ucn1 contents by ablating EWcp LepRb-positive neurons with leptin-saporin, did not affect food intake and body weight gain, but substantially (+26%) increased WAT weight accompanied by a higher plasma leptin level and changed plasma lipid profile. We also found that ablation of EWcp Ucn1/LepRb neurons resulted in lower respiratory quotient and oxygen consumption one week after surgery, but was comparable to sham values after 3 and 5 weeks of surgery. Taken together, we report that EWcp/LepRb/Ucn1 neurons not only respond to leptin signaling but also control WAT size and fat metabolism without altering food intake. These data suggest the existence of a EWcp-WAT circuitry allowing an organism to recruit fuels without being able to eat in situations such as the fight-or-flight response.

Epidemiology of Porcine Pseudorabies from 2010 to 2018 in Tianjin, China

Pseudorabies (PR), the causative agent of Aujeszky's disease, has rapidly increased in recent years and has caused significant economic losses. To understand the seroprevalence and epidemiological characteristics of PR in Tianjin, China, a total of 23,627 blood and 1,093 tissue samples were collected from 228 pig farms during January 2010 to December 2018. The Pseudorabies virus (PRV) glycoprotein E (gE) antibody was tested by enzyme-linked immunosorbent assay (ELISA), and wild-type PRV (WT PRV) was detected by gE-polymerase chain reaction (PCR). Macroscopic and microscopic lesions were observed in tissue samples. The results showed that 46.70% of the serum samples and 49.76% of pig farms were seropositive for PRV gE antibody based on the ELISA results, and 13.54% of the tissue samples were positive for WT PRV detected by PCR. The positive rate of serum samples increased rapidly after 2011 and reached 62.40% in 2013. Although it gradually decreased from 2014 to 2018, the positive rate of serum samples remained at a high level. The positive rate of pig farms showed the same trend. Moreover, after 2011, the detection rate of WT PRV was increased rapidly and was significantly higher than in 2010 and 2011. Macroscopic and microscopic lesions were observed in various tissues during histopathological examination. Based on univariate analysis, the increased risk of seropositivity was associated with the immune status and infection in sows and fattening pigs. These findings demonstrate that PR was prevalent in the region of Tianjin, China. These epidemiological data can assist in the control of PR.

In vitro anti-PRV activity of dihydromyricetin from Ampelopsis grossedentata

Pseudorabies (PR) is an acute infectious disease caused by pseudorabies virus (PRV). There are no available drugs due to the emergence of variant of PRV. Dihydromyricetin (DMY) is a flavonoid extracted from Ampelopsis grossedentata (A. grossedentata), which has a variety of pharmacological activities. In this study, we aim to investigate the in vitro anti-PRV activity of DMY extracted from A. grossedentata. MTT assay was used to detect the cytotoxicity and antiviral activity of DMY. The results detected by flow cytometry and qRT-PCR showed that DMY played anti-PRV role mainly by interfering with the process of virus invasion into host cell and inhibiting the occurrence of pyroptosis in vitro. This suggested that anti-pyroptosis may be an important antiviral mechanism for DMY which is expected to be a potential anti-PRV drug.

Quercetin as an antiviral agent inhibits the Pseudorabies virus in vitro and in vivo

Pseudorabies virus (PRV) accounts for a critical swine disease incurring economic losses worldwide. Several PRV vaccines are commercially available but these vaccines are effective against only certain prevalent PRV strains in China. To prevent PRV-induced latent infection and decrease the pathogenicity, novel anti-PRV drugs are required to prevent PRV infection. Natural products show exceptional structural diversity representing an important source for developing novel therapeutic agents. Quercetin is a flavonoid with anti-oxidant, anti-cancer, anti-bacterial and anti-viral activities. This study involved quercetin for studying the anti-PRV function in vitro and in vivo. Quercetin was found to significantly decrease the PRV virulent strain HNX at a half-maximal inhibitory concentration (IC₅₀) of 2.618 μM and selectivity index 229. This anti-PRV activity of quercetin was found to be dose-dependent. Furthermore, quercetin also inhibited a wide the infections by a spectrum of PRV strains like HNX, Ea, Bartha and Fa strain. These virucidal effects of quercetin suggest the interaction between these molecules and viral particles, and quercetin is responsible for inhibiting the adsorption of PRV infections. The silico assays suggesting that quercetin might interact with the gD-protein on the surface of the PRV important for viral infection. Additional, the quercetin plantar injection protected the mice from the lethal challenge, decreasing the PRV-infected mice's brain viral loads and mortality. These results provides a anti-PRV strategy and contribute to drug discovery and development.

Establishment of inflammatory model induced by Pseudorabies virus infection in mice

BACKGROUND

Pseudorabies virus (PRV) infection leads to high mortality in swine. Despite extensive efforts, effective treatments against PRV infection are limited. Furthermore, the inflammatory response induced by PRV strain GXLB-2013 is unclear.

OBJECTIVES

Our study aimed to investigate the inflammatory response induced by PRV strain GXLB-2013, establish an inflammation model to elucidate the pathogenesis of PRV infection further, and develop effective drugs against PRV infection.

METHODS

Kunming mice were infected intramuscularly with medium, LPS, and different doses of PRV-GXLB-2013. Viral spread and histopathological damage to brain, spleen, and lung were determined at 7 days post-infection (dpi). Immune organ indices, levels of reactive oxygen species (ROS), nitric oxide (NO), and inflammatory cytokines, as well as levels of activity of COX-2 and iNOS were determined at 4, 7, and 14 dpi.

RESULTS

At 10⁵-10⁶ TCID₅₀ PRV produced obviously neurological symptoms and 100% mortality in mice. Viral antigens were detectable in kidney, heart, lung, liver, spleen, and brain. In addition, inflammatory injuries were apparent in brain, spleen, and lung of PRV-infected mice. Moreover, PRV induced increases in immune organ indices, ROS and NO levels, activity of COX-2 and iNOS, and the content of key pro-inflammatory cytokines, including interleukin (IL)-1β, IL-6, tumor necrosis factor-α, interferon-γ and MCP-1. Among the tested doses, 10² TCID₅₀ of PRV produced a significant inflammatory mediator increase.

CONCLUSIONS

An inflammatory model induced by PRV infection was established in mice, and 10² TCID₅₀ PRV was considered as the best concentration for the establishment of the model.

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.

A monoclonal antibody neutralizes pesudorabies virus by blocking gD binding to the receptor nectin-1

Pseudorabies virus (PRV) was isolated from some human cases recently and the infected patients manifested respiratory dysfunction and acute neurological symptoms. However, no effective drug or vaccine, preventing the progression of PRV infection, is available. Nectin-1 was the only reported receptor for PRV cell entry both swine and human origin, representing an excellent target to block PRV infection, and especially its transmission from pigs to humans. A PRV-gD specific mAbs (10B6) was isolated from hybridomas and its neutralizing activities in vitro and in vivo were determined. 10B6 exhibited effective neutralizing activities in vitro with IC₅₀ = 2.514 μg/ml and 4.297 μg/ml in the presence and absence of complement. And in vivo, 10B6 provided 100% protection against PRV lethal challenge with a dose of 15 mg/kg. Further, 10B6 could bind to a conserved epitope, ³¹⁶QPAEPFP³²², locating in gD pro-fusion domain, and finally blocks the binding of PRV-gD to nectin-1. Moreover, 10B6 showed an effective inhibition on PRV cell-attachment in a cell type-independent manner and could also block the virus spreading among cells. 10B6 exhibited effectively neutralizing activities to Chinese PRV variant strain in vitro and in vivo by blocking gD binding to nectin-1, implied both prophylactic and therapeutic interventions against PRV infections.