Generation and characterization of UL41 null pseudorabies virus variant in vitro and in vivo

Genome-wide CRISPR screens identify CLC-2 as a drug target for anti-herpesvirus therapy: tackling herpesvirus drug resistance

The emergence of drug resistance to virus (i.e., acyclovir (ACV) to herpesviruses) has been termed one of the common clinical issues, emphasizing the discovery of new antiviral agents. To address it, a genome-wide clustered regularly interspaced short palindromic repeats (CRISPR) screening was performed in mouse haploid embryonic stem cells infected with pseudorabies virus (PRV), an α-herpesvirus causing human and pig diseases. The results demonstrated that type 2 voltage-gated chloride channels (CLC-2) encoded by one of the identified genes, CLCN2, is a potential drug target for anti-herpesvirus therapy. CLC-2 inhibitors, omeprazole (OME) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), can efficiently inhibit infection of multiple herpesviruses in cellulo (i.e., PRV, HSV and EBV), and effectively treat murine herpes simplex encephalitis (HSE). Additionally, DIDS was found to inhibit HSV-1 replication by blocking the PI3K/Akt pathway. Most importantly, both DIDS and OME were able to inhibit ACV-resistant HSV-1 strain infection. The study's findings suggest that targeting host-cell factors such as CLC-2 may be a promising approach to tackling herpesvirus drug resistance. The discovery of CLC-2 as a potential drug target for anti-herpesvirus therapy provides a new direction for the development of novel antiviral agents.

Genome editing of pseudorabies virus in the CRISPR/Cas9 era: a mini-review

Pseudorabies virus (PRV) is an important swine virus that has a significant impact on the global swine industry. PRV is a member of the herpesvirus family, specifically the alphaherpesvirus subfamily, and has been extensively utilized as a prototype herpesvirus. Notably, recent studies have reported that PRV sporadically spills over into humans. The PRV genome is approximately 150 kb in size and is difficult to manipulate at the genomic level. The development of clustered regularly interspaced short palindromic repeat-associated protein (CRISPR/Cas9) technology has revolutionized PRV genome editing. CRISPR/Cas9 has been widely used in the construction of reporter viruses, knock-out/knock-in of genes of interest, single virus tracking and antiviral strategies. Most importantly, for vaccine development, virulence gene knockout PRV vaccine candidates can be obtained within 2 weeks using CRISPR/Cas9. In this mini-review, we provide a concise overview of the application of CRISPR/Cas9 in PRV research and mainly share our experience with methods for efficiently editing the PRV genome. Through this review, we hope to give researchers better insight into the genome editing of pseudorabies virus.

Duck Enteritis Virus Inhibits the cGAS-STING DNA-Sensing Pathway To Evade the Innate Immune Response

Cyclic GMP-AMP synthase (cGAS), a key DNA sensor, detects cytosolic viral DNA and activates the adaptor protein stimulator of interferon genes (STING) to initiate interferon (IFN) production and host innate antiviral responses. Duck enteritis virus (DEV) is a duck alphaherpesvirus that causes an acute and contagious disease with high mortality in waterfowl. In the present study, we found that DEV inhibits host innate immune responses during the late phase of viral infection. Furthermore, we screened DEV proteins for their ability to inhibit the cGAS-STING DNA-sensing pathway and identified multiple viral proteins, including UL41, US3, UL28, UL53, and UL24, which block IFN-β activation through this pathway. The DEV tegument protein UL41, which exhibited the strongest inhibitory effect, selectively downregulated the expression of interferon regulatory factor 7 (IRF7) by reducing its mRNA accumulation, thereby inhibiting the DNA-sensing pathway. Ectopic expression of UL41 markedly reduced viral DNA-triggered IFN-β production and promoted viral replication, whereas deficiency of UL41 in the context of DEV infection increased the IFN-β response to DEV and suppressed viral replication. In addition, ectopic expression of IRF7 inhibited the replication of the UL41-deficient virus, whereas IRF7 knockdown facilitated its replication. This study is the first report identifying multiple viral proteins encoded by a duck DNA virus, which inhibit the cGAS-STING DNA-sensing pathway. These findings expand our knowledge of DNA sensing in ducks and reveal a mechanism through which DEV antagonizes the host innate immune response. IMPORTANCE Duck enteritis virus (DEV) is a duck alphaherpesvirus that causes an acute and contagious disease with high mortality, resulting in substantial economic losses in the commercial waterfowl industry. The evasion of DNA-sensing pathway-mediated antiviral innate immunity is essential for the persistent infection and replication of many DNA viruses. However, the mechanisms used by DEV to modulate the DNA-sensing pathway remain poorly understood. In the present study, we found that DEV encodes multiple viral proteins to inhibit the cGAS-STING DNA-sensing pathway. The DEV tegument protein UL41 selectively diminished the accumulation of interferon regulatory factor 7 (IRF7) mRNA, thereby inhibiting the DNA-sensing pathway. Loss of UL41 potently enhanced the IFN-β response to DEV and impaired viral replication in ducks. These findings provide insights into the host-virus interaction during DEV infection and help develop new live attenuated vaccines against DEV.

Herpes Simplex Type 1 UL43 Multiple Membrane-Spanning Protein Increases Energy Metabolism in Host Cells through Interacting with ARL2

Non-essential proteins for viral replication affect host cell metabolism, while the function of the UL43 protein of herpes simplex virus 1 (HSV-1) is not clear. Herein, we performed a comprehensive microarray analysis of HUVEC cells infected with HSV-1 and its UL43-deficient mutant and found significant variation in genes associated with cellular energy metabolic pathways. The localization of UL43 protein in host cells and how it affects cellular energy metabolism pathways were further investigated. Internalization analysis showed that the UL43 protein could be endocytosis-mediated by YPLF motif (aa144-147) and localized to mitochondria. At the same time, more ATP was produced by coupling with mitochondrial small G protein ARF-like 2 (ARL2) GTPase, which triggered the phosphorylation of ANT1 (SLC25A4) to affect the opening degree of mitochondrial permeability transition pore (mPTP), and significantly promoted the aerobic oxidation and oxidative phosphorylation of glucose. Our study shows that UL43 mediates the improvement of host cell metabolism after HSV-1 infection. Additionally, UL43 protein could be a valuable ATP-stimulating factor for mammalian cells.

Interferon-Stimulated Gene 15 Knockout in Mice Impairs IFNα-Mediated Antiviral Activity

Type I interferon (IFN) plays an important role in the host defense against viral infection by inducing expression of interferon-stimulated genes (ISGs). In a previous study, we found that porcine interferon-stimulated gene 15 (ISG15) exhibited antiviral activity against PRV in vitro. To further investigate the antiviral function of ISG15 in vivo, we utilized ISG15 knockout (ISG15^-/-) mice in this study. Here, we demonstrate that ISG15^-/- mice were highly susceptible to PRV infection in vivo, as evidenced by a considerably reduced survival rate, enhanced viral replication and severe pathological lesions. However, we observed no significant difference between female and male infected WT and ISG15^-/- mice. Moreover, ISG15^-/- mice displayed attenuated antiviral protection as a result of considerably reduced expression of IFNβ and relevant ISGs during PRV replication. Furthermore, excessive production of proinflammatory cytokines may be closely related to encephalitis and pneumonia. In further studies, we found that the enhanced sensitivity to PRV infection in ISG15^-/- mice might be caused by reduced phosphorylation of STAT1 and STAT2, thereby inhibiting type I IFN-mediated antiviral activity. Based on these findings, we conclude that ISG15 is essential for host type I IFN-mediated antiviral response.

An overview: CRISPR/Cas-based gene editing for viral vaccine development

INTRODUCTION

: Gene-editing technology revolutionized vaccine manufacturing and offers a variety of benefits over traditional vaccinations, such as improved immune response, higher production rate, stability, precise immunogenic activity, and fewer adverse effects. The more recently discovered Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/associated protein 9 (Cas9) system has become the most widely utilized technology based on its efficiency, utility, flexibility, versatility, ease of use, and cheaper compared to other gene-editing techniques. Considering its wider scope for genomic modification, CRISPR/Cas9-based technology's potential is explored for vaccine development.

AREAS COVERED

: In this review, we will address the recent advances in the CRISPR/Cas system for the development of vaccines and viral vectors for delivery. In addition, we will discuss strategies for the development of the vaccine, as well as the limitations and future prospects of the CRISPR/Cas system.

EXPERT OPINION

: Human and animal viruses have been exposed to antiviral CRISPR/Cas9-based engineering to prevent infection, which uses knockout, knock-in, gene activation/deactivation, RNA targeting, and editing cell lines strategies for gene editing of viruses. Because of that CRISPR/Cas system is used to boost the vaccine production yield by removing unwanted genes that cause disease or are required for viral infection.

Application of CRISPR-Cas9 Editing for Virus Engineering and the Development of Recombinant Viral Vaccines

CRISPR-Cas technology, discovered originally as a bacterial defense system, has been extensively repurposed as a powerful tool for genome editing for multiple applications in biology. In the field of virology, CRISPR-Cas9 technology has been widely applied on genetic recombination and engineering of genomes of various viruses to ask some fundamental questions about virus-host interactions. Its high efficiency, specificity, versatility, and low cost have also provided great inspiration and hope in the field of vaccinology to solve a series of bottleneck problems in the development of recombinant viral vaccines. This review highlights the applications of CRISPR editing in the technological advances compared to the traditional approaches used for the construction of recombinant viral vaccines and vectors, the main factors affecting their application, and the challenges that need to be overcome for further streamlining their effective usage in the prevention and control of diseases. Factors affecting efficiency, target specificity, and fidelity of CRISPR-Cas editing in the context of viral genome editing and development of recombinant vaccines are also discussed.

DPV UL41 gene encoding protein induces host shutoff activity and affects viral replication

The virion host shutoff (VHS) protein, encoded by the UL41 gene of herpes simplex virus (HSV), specifically degrades mRNA and induces host shutoff. VHS and its homologs are highly conserved in the Alphaherpesvirinae subfamily. However, the role of the duck plague virus (DPV) UL41 gene is unclear. In this study, we found that the DPV UL41 gene-encoded protein (pUL41) degrades RNA polymerase (pol) II-transcribed translatable RNA and induces protein synthesis shutoff. DPV pUL41 was dispensable for viral replication, but the UL41-deleted mutant virus exhibited a significant viral growth defect and plaque size reduction in Duck embryo fibroblast (DEF) cells. Furthermore, DPV pUL41 regulated viral mRNA accumulation to affect viral DNA replication, release and cell-to-cell spread.

A Review on the Use of Antimicrobial Peptides to Combat Porcine Viruses

Viral infectious diseases pose a serious threat to animal husbandry, especially in the pig industry. With the rapid, continuous variation of viruses, a series of therapeutic measures, including vaccines, have quickly lost their efficacy, leading to great losses for animal husbandry. Therefore, it is urgent to find new drugs with more stable and effective antiviral activity. Recently, it has been reported that antimicrobial peptides (AMPs) have great potential for development and application in animal husbandry because of their significant antibacterial and antiviral activity, and the antiviral ability of AMPs has become a research hotspot. This article aims to review the research situation of AMPs used to combat viruses in swine production of animal husbandry, clarify the mechanism of action of AMPs on viruses and raise some questions, and explore the future potential of AMPs in animal husbandry.

Construction and immunogenicity of a gE/gI/TK-deleted PRV based on porcine pseudorabies virus variant

Pseudorabies (PR) caused by re-emerging pseudorabies virus (PRV) variant has outbroken among PRV vaccine-immunized swine herds on many Chinese pig farms, with severe socioeconomic consequences since late 2011. Here, a gE/gI/TK-deleted recombinant virus (rPRV NY-gE^-/gI^-/TK^-) was constructed based on PRV NY strain from 2012 through homologous DNA recombination and gene-editing technology termed clustered regularly interspaced palindromic repeats (CRISPR)/associated (Cas9) system. The rPRV NY-gE^-/gI^-/TK^- strain showed similar growth kinetics to the parental PRV NY strain in vitro, and was safe for mice. Sixty mice were injected subcutaneously (s.c.) twice with 10^6.0 TCID₅₀ of rPRV NY-gE^-/gI^-/TK^- and DMEM, respectively, with two-week interval. The levels of PRV gB antibodies and neutralizing antibodies against PRV NY in mice immunized with rPRV NY-gE^-/gI^-/TK^- were higher than those in the DMEM control group. The number of T lymphocyte subclasses CD3⁺, CD4⁺ and CD8⁺ in rPRV NY-gE^-/gI^-/TK^--immunized mice was higher than that in DMEM-injected mice. After challenge with 10^6.0 TCID₅₀ PRV NY at 42 dpi, all rPRV NY-gE^-/gI^-/TK^--immunized mice survived without exhibiting any pathological lesions in different tissues and intranuclear eosinophilic inclusions of the brain, and the viral genomic copy numbers in various organs of mice were obviously lower than DMEM group. These results showed the rPRV NY-gE^-/gI^-/TK^- could be a promising next-generation vaccine to control now epidemic PR in China.

Antiviral activity of Piscidin 1 against pseudorabies virus both in vitro and in vivo

Background

Swine-origin virus infection spreading widely could cause significant economic loss to porcine industry. Novel antiviral agents need to be developed to control this situation.

Methods

In this study, we evaluated the activities of five broad-spectrum antimicrobial peptides (AMPs) against several important swine-origin pathogenic viruses by TCID₅₀ assay. Plaque reduction assay and cell apoptosis assay were also used to test the activity of the peptides. Protection effect of piscidin against pseudorabies virus (PRV) was also examined in mouse model.

Results

Piscidin (piscidin 1), caerin (caerin 1.1) and maculatin (maculatin 1.1) could inhibit PRV by direct interaction with the virus particles in a dose-dependent manner and they could also protect the cells from PRV-induced apoptosis. Among the peptides tested, piscidin showed the strongest activity against PRV. Moreover, in vivo assay showed that piscidin can reduce the mortality of mice infected with PRV.

Conclusion

In vitro and in vivo experiments indicate that piscidin has antiviral activity against PRV.