Molecular Mechanism of Porcine Epidemic Diarrhea Virus Cell Tropism

Epidemiological surveillance of avian coronavirus in China in 2024

To expand our understanding of the epidemiology of avian coronavirus (ACoV) in China, the risk-based active surveillance was carried out in China in 2024. A total of 7,699 avian swab samples were collected from 153 sampling sites in 13 provinces. One thousand fifty hundred and eighty-six ACoVs were detected and identified by RT-PCR and sequencing with a positive rate of 20.60 %, including 1,125 strains of avian infectious bronchitis virus (IBV), 278 strains of duck coronavirus (DuCoV), 182 strains of pigeon coronavirus (PiCoV), and 1 strain of deltacoronavirus. Most ACoVs were detected from chickens, followed by pigeons, while others were collected from ducks and geese. The positivity rates for ACoV in poultry ranged from 2.91 % to 32.27 %. The viruses were detected from 86 sampling sites (56.21 %) in all 13 provinces surveyed. The positivity rates of ACoV in retail markets (98.08 %) and wholesale markets (100 %) were much higher than those in slaughterhouses (80.00 %) and poultry farms (20.25 %). 231 representative IBV strains from different regions were selected for S1 gene sequencing and genetic evolution analysis. The results revealed that the prevalent IBV in China comprised ten genotypes, meanwhile the recombinant variants were also detected. The viruses in GI-19 (35.06 %) and GVI-1 (33.77 %) were the predominant strains in China. Importantly, no cases of SARS-CoV-2 were found in the detected poultry samples. This study reveals the prevalence, distribution, genetic and phylogenetic characteristics of ACoV in China, and extends our understanding of the epidemiological context of ACoV in China.

Procyanidins inhibit alphacoronavirus infection by reducing interferon antagonism

BACKGROUND

The development of coronavirus drugs has primarily focused on targeting viral components, such as RNA-dependent RNA polymerase (RdRP), with relatively little attention given to enhancing host antiviral defenses. α-Coronaviruses, including human-infecting HCoV-NL63 and HCoV-229E, utilize immune evasion strategies such as suppressing host interferon production to establish infection. Procyanidins (PC), oligomeric compounds composed of catechin and epicatechin, have demonstrated the ability to stimulate host interferon synthesis, potentially counteracting this immune evasion. Exploring the inhibitory effects of PC specifically on α-coronaviruses offers a promising avenue for developing novel therapeutic strategies that bolster host immunity against these pathogens.

PURPOSE

This study aims to evaluate the inhibitory effects of PC on α-coronaviruses using different cell models and investigate whether its antiviral activity is linked to enhanced interferon production. By examining PC's effects on selected α-coronaviruses, this research explores its potential as a therapeutic strategy against human-infecting HCoV-NL63 and HCoV-229E, which evade innate immunity.

METHODS

Vero cells, human embryonic kidney 293T (HEK-293T) cells, and intestinal porcine epithelial-J2 (IPEC-J2) cells were used as cell models, with porcine epidemic diarrhea virus (PEDV) serving as the α-coronavirus infection model. The inhibitory effects of PC on the α-coronaviruses and its activation of interferon were evaluated using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot (WB). Co-immunoprecipitation (co-IP) was used to assess how PC impacts the degradation of Retinoic acid-inducible gene I (RIG-I) and TANK-binding kinase 1 (TBK1) by coronavirus N protein. Confocal microscopy was utilized to observe the recovery of mitochondrial morphology disrupted by coronavirus, and flow cytometry analyses were conducted.

RESULTS

Viral cycle and time-of-addition analyses showed that PC inhibited PEDV infection during both the replication and release stages of the virus. Simultaneously, in the early stages of infection, PC countered PEDV's evasion of interferon by elevating host interferon levels. Co-immunoprecipitation experiments confirmed that this effect was achieved by reducing the binding of coronavirus N protein to key proteins in the interferon synthesis pathway, RIG-I and TBK1, a mechanism previously identified as one of the main reasons for interferon evasion by α-coronavirus N protein. Additionally, intriguingly, we observed that PC has the ability to restore excessive mitochondrial fission induced by coronaviruses, an effect achieved by reducing the binding of coronavirus N protein to mitochondrial fusion protein 1 (MFN1). This observation suggests potential mechanistic pathways through which PC impacts mitochondrial antiviral-related proteins. These results suggest that PC may also inhibit human α-coronaviruses, such as HCoV-NL63 and HCoV-229E, by utilizing similar antiviral mechanisms. This provides valuable insights into potential therapeutic strategies for treating human coronaviruses.

CONCLUSIONS

These results suggest that PC may inhibit α-coronavirus infection by reversing the virus's antagonistic effects on interferon. These findings provide a new perspective for exploring therapeutic mechanisms against coronaviruses like HCoV-NL63, HCoV-229E, SARS-CoV-2, SARS-CoV, and MERS-CoV, which can evade host innate immunity, including the identification of new drug targets.

The effect of asparagine-13 in porcine epidemic diarrhea virus envelope protein on pathogenicity

The pathogenesis of porcine epidemic diarrhea virus (PEDV) has not been fully clarified, which seriously hinders the prevention of the disease. The envelope (E) protein of PEDV induces the expression of pro-inflammatory cytokines, but the role of these inflammatory reactions in PEDV pathogenicity is still unknown. In this study, the asparagine at position 13 was found to be crucial to PEDV E protein induced inflammatory response. Exogenously expressing the parent E protein, rather than the E mutant carrying N13A, induces the activation of NF-κB and expression of inflammatory factors, including IL-6, IL-8, and TNF-α. Compared with the parental rPEDV strain, the recombinant strain rPEDV-EN13A exhibited a significantly lower infectious titer and formed smaller plaques. In addition, rPEDV-EN13A induced lower expression of inflammatory factors in vitro and in vivo. The pathogenicity assay shows that the rPEDV-EN13A strain caused diminished fecal PEDV RNA shedding, delayed death time, and milder histopathological lesions to intestinal villi. Our data provide a unique perspective for exploring the pathogenic mechanism of PEDV and a new target for the development of attenuated PEDV live vaccines.

Changes in the motifs in the D0 and SD2 domains of the S protein drive the evolution of virulence in enteric coronavirus porcine epidemic diarrhea virus

Since 2010, highly virulent mutant GII subtype porcine epidemic diarrhea virus (PEDV) strains derived from GI subtype strains have caused significant economic losses in the pig industry. However, the molecular mechanism of PEDV virulence evolution remains unclear. It has been predicted that, compared to the S proteins of GI strains, five N-linked glycosylation sites have changed in the highly virulent GII PEDV strains. To investigate how changes in these sites affect PEDV virulence, we constructed five recombinant strains harboring the above mutation sites using the GII subtype rPEDV-Swt as the backbone, among which rPEDV-Smut62, rPEDV-Smut118, rPEDV-Smut131, and rPEDV-Smut722 were successfully rescued, but rPEDV-Smut235 was not. Compared to infection with rPEDV-Swt (100%), infection with rPEDV-Smut62 and rPEDV-Smut722 resulted in lower mortality in piglets (33%), and although rPEDV-Smut118 and rPEDV-Smut131 resulted in high mortality (100%), death was delayed. All surviving piglets were challenged orally with rPEDV-Swt at 21 days post-infection. The piglets in the rPEDV-Smut62 and rPEDV-Smut722 groups produced high levels of IgG, IgA, and cross-protective neutralizing antibodies, which protected the piglets after rPEDV-Swt challenge. Furthermore, the change in the structures of the rPEDV-Smut62 and rPEDV-Smut722 S proteins predicted with high precision by AlphaFold 3 may be the cause of the attenuated virulence. Our data provide a unique perspective on the molecular mechanism of PEDV virulence evolution from the GI to the GII subtype and identify the targets of PED live attenuated vaccines.

IMPORTANCE

The continuous emergence of novel viral variants in the current landscape poses challenges for disease prevention and control. Before 2010, PED caused by GI strains was only sporadic outbreaks and not large-scale epidemics. Since 2010, highly virulent GII strains derived from GI strains have spread worldwide and caused significant economic losses. However, the molecular mechanism underlying the differences in virulence is still unclear. In this study, the differences in the predicted glycosylation sites of the S protein between the GI and GII strains were taken as the starting point to explore the key sites responsible for the variations in PEDV virulence. The results indicate that the motifs 57ENQGVNST64 and 722NSTF725 of the S protein in the GII strains are involved in the evolution of PEDV virulence. This study provides a new perspective on the molecular mechanism of PEDV virulence evolution.

The Infectivity and Pathogenicity Characteristics of a Recombinant Porcine Epidemic Diarrhea Virus, CHFJFQ

Porcine epidemic diarrhea virus (PEDV) presents a substantial challenge to the global swine industry. However, the origin, host range, and potential cross-species transmission of PEDV remain poorly understood. This study characterizes a novel PEDV strain, CHFJFQ, isolated from diarrheic piglets in Fuqing, Fujian, China. Through sequencing and phylogenetic analysis, we determined that CHFJFQ belongs to the GIIa subgroup and is a recombinant with CH/HNXX/2016 as the major parent and NW17 as the minor parent. Compared to CV777, CHFJFQ exhibits multiple base deletions and insertions across the 5'UTR, ORF1a/b, S, and ORF3 genes. Phylogenetic analysis indicates shared ancestry with bat coronaviruses, though a direct zoonotic origin remains uncertain. Interestingly, CHFJFQ demonstrated its ability to infect human and mouse cell lines in vitro and, more significantly, caused in vivo infection in both pigs and mice. The primary target organs were the intestines, lungs, and spleen, resulting in 100% mortality in suckling piglets. PEDV CHFJFQ was detected in mouse tissues, but no clinical signs were observed, indicating limited cross-species pathogenicity. Overall, these findings offer crucial insights into the epidemiology, genetics, infectivity, and pathogenicity of PEDV and provide valuable information for vaccine development.

Trichinella spiralis excretory/secretory antigens ameliorate porcine epidemic diarrhea virus-induced mucosal damage in porcine intestinal oganoids by alleviating inflammation and promoting tight junction

Trichinella spiralis and porcine epidemic diarrhea virus (PEDV) are two infectious swine pathogens. Parasite excretory/secretory antigens play critical roles in various disease processes. To explore the coexistence mechanism of two pathogens infecting the same host, the intestinal organoid was utilized to reproduce these biological processes. In this study, we investigated the effects of T. spiralis excretory/secretory antigens (TsES) on PEDV-induced inflammatory regulation, lesion recovery, and mucosal barrier repair in porcine intestinal organoids. The results showed that PEDV effectively infected the porcine intestinal organoids. Next, TsES inhibited pro-inflammatory cytokines and increased the anti-inflammatory cytokines produced by PEDV-infected porcine intestinal organoids. Further, four-dimensional (4D) label-free quantitative proteomics and western blotting confirmed that TsES regulate the inflammation caused by PEDV infection through the nuclear factor kappa-B (NF-κB) pathway. In addition, TsES promoted cell proliferation, inhibited apoptosis, and reduced PEDV-induced lesions in intestinal organoids. The elevated secretory immunoglobulin A (sIgA) levels caused by PEDV infection were downregulated by TsES treatment in intestinal organoids. TsES treatment reversed the mucosal barrier damage caused by PEDV infection in intestinal organoids. Finally, PEDV replication increased after TsES treatment in organoids. We highlight the potential of TsES to ameliorate PEDV-induced inflammation, mucosal lesions, and barrier damage in porcine intestinal organoids. TsES also contribute to PEDV replication. This study presents a novel research model for research on host-virus-parasite interactions, while also providing a theoretical foundation to consider parasite derivatives as a potential adjunctive therapy for intestinal inflammation.

Isolation of porcine epidemic diarrhea virus strain CHCQ-2023 from Chongqing Province and analysis of S gene recombination

BACKGROUND

In recent years, the prevalence and incidence of porcine epidemic diarrhea virus (PEDV) infection have been on the rise. The occurrence of multiviral infections and recombination mutations has led to accelerated viral evolution and reduced vaccine efficacy. In the present study, a PEDV strain was isolated from a pig farm (Chongqing Province, China) with an outbreak of porcine diarrhea, and its S gene was found to be recombinant.

RESULTS

The optimal trypsin concentration for blind passage of PEDV in Vero cells was determined to be 7.5 µg/mL. Following two blind passages of the virus in Vero cells, the virus was unable to adapt to the cells. Therefore, PEDV was blindly passaged in IPEC-J2 cells using the optimal concentration of trypsin (5 µg/mL). Next, a series of characterization experiments were performed. Recombination analyses of the isolates using software revealed that the S gene of strain CHCQ-2023 was derived from the primary parent strain PEDV-1 C and secondary parent strain SQ2014, with recombination occurring at a 3152 bp breakpoint. Furthermore, a specific B-cell antigenic epitope was predicted on the S2 subunit of the S protein.

CONCLUSION

A PEDV strain was isolated and characterized, and its S gene was characterized. The findings provide a bioinformatic basis for the study of PEDV strain variation due to genetic recombination.

Host restriction factor Rab11a limits porcine epidemic diarrhea virus invasion of cells via fusion peptide-mediated membrane fusion

Porcine epidemic diarrhea virus (PEDV) causes enormous economic losses to the pork industry, and its extensive cell tropism poses a substantial challenge to public health and safety. However, the invasion mechanisms and relevant host factors of PEDV remain poorly understood. In this study, we identified 422 differentially expressed genes related to PEDV infection through transcriptome analysis. Among these, Annexin A2 (ANXA2), Prohibitin-2 (PHB2), and Caveolin-2 (CAV2) were identified through screening and verifying as having a specific interaction with the PEDV S protein, and positive regulation of PEDV internalization was validated by siRNA and overexpression tests. Subsequently, using host membrane protein interaction networks and co-immunoprecipitation analysis, we found that ANXA2 PHB2 or CAV2 directly interact with Rab11a. Next, we constructed a pseudovirus model (LV-PEDV S-GFP) to further confirm that the downregulation of Rab11a could promote PEDV invasion. In detail, ANXA2, PHB2, or CAV2 promoted PEDV invasion via downregulating Rab11a. Furthermore, we showed that the S-protein fusion peptide (FP) was sufficient for S-protein interaction with ANXA2, PHB2, CAV2, and Rab11a, and the addition of exogenous GTP could regulate the efficiency of PEDV invasion. Collectively, ANXA2, PHB2, or CAV2 influenced the membrane fusion of PEDV with host cells through the host restriction factor Rab11a. This study could be targeted for future research to develop strategies for the control of PEDV.

A novel double antibody sandwich quantitative ELISA for detecting porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea (PED), a contagious intestinal disease caused by the porcine epidemic diarrhea virus (PEDV), has caused significant economic losses to the global pig farming industry due to its rapid course and spread and its high mortality among piglets. In this study, we prepared rabbit polyclonal antibody and monoclonal antibody 6C12 against the PEDV nucleocapsid (N) protein using the conserved and antigenic PEDV N protein as an immunogen. A double-antibody sandwich quantitative enzyme-linked immunosorbent assay (DAS-qELISA) was established to detect PEDV using rabbit polyclonal antibodies as capture antibodies and horseradish peroxidase (HRP)-labeled 6C12 as the detection antibody. Using DAS-qELISA, recombinant PEDV N protein, and virus titer detection limits were approximately 0.05 ng/mL and 103.02 50% tissue culture infective dose per mL (TCID50/mL), respectively. There was no cross-reactivity with porcine reproductive and respiratory syndrome virus (PRRSV), porcine rotavirus (PoRV), porcine pseudorabies virus (PRV), porcine deltacoronavirus (PDCoV), or porcine circovirus (PCV). The reproducibility of DAS-qELISA was verified, and the coefficient of variation (CV) for intra- and inter-batch replicates was less than 10%, indicating good reproducibility. When testing anal swab samples from PEDV-infected piglets using DAS-qELISA, the coincidence rate was 92.55% with a kappa value of 0.85 when using reverse transcription-polymerase chain reaction (RT-PCR) and 94.29% with a kappa value of 0.88 when using PEDV antigen detection test strips, demonstrating the reliability of the method. These findings provide fundamental material support for both fundamental and practical studies on PEDV and offer a crucial diagnostic tool for clinical applications. KEY POINTS: • A new anti-PEDV N protein monoclonal antibody strain was prepared • Establishment of a more sensitive double antibody sandwich quantitative ELISA • DAS-qELISA was found to be useful for controlling the PEDV spread.

A chimeric strain of porcine reproductive and respiratory syndrome virus 2 derived from HP-PRRSV and NADC30-like PRRSV confers cross-protection against both strains

Porcine reproductive and respiratory syndrome (PRRS) is one of the most significant swine viral infectious diseases worldwide. Vaccination is a key strategy for the control and prevention of PRRS. At present, the NADC30-like PRRSV strain has become the predominant epidemic strain in China, superseding the HP-PRRSV strain. The existing commercial vaccines offer substantial protection against HP-PRRSV, but their efficacy against NADC30-like PRRSV is limited. The development of a novel vaccine that can provide valuable cross-protection against both NADC30-like PRRSV and HP-PRRSV is highly important. In this study, an infectious clone of a commercial MLV vaccine strain, GD (HP-PRRSV), was first generated (named rGD). A recombinant chimeric PRRSV strain, rGD-SX-5U2, was subsequently constructed by using rGD as a backbone and embedding several dominant immune genes, including the NSP2, ORF5, ORF6, and ORF7 genes, from an NADC30-like PRRSV isolate. In vitro experiments demonstrated that chimeric PRRSV rGD-SX-5U2 exhibited high tropism for MARC-145 cells, which is of paramount importance in the production of PRRSV vaccines. Moreover, subsequent in vivo inoculation and challenge experiments demonstrated that rGD-SX-5U2 confers cross-protection against both HP-PRRSV and NADC30-like PRRSV, including an improvement in ADG levels and a reduction in viremia and lung tissue lesions. In conclusion, our research demonstrated that the chimeric PRRSV strain rGD-SX-5U2 is a novel approach that can provide broad-spectrum protection against both HP-PRRSV and NADC30-like PRRSV. This may be a significant improvement over previous MLV vaccinations.

Progress of research on coronaviruses and toroviruses in large domestic animals using reverse genetics systems

The generation of genetically engineered recombinant viruses from modified DNA/RNA is commonly referred to as reverse genetics, which allows the introduction of desired mutations into the viral genome. Reverse genetics systems (RGSs) are powerful tools for studying fundamental viral processes, mechanisms of infection, pathogenesis and vaccine development. However, establishing RGS for coronaviruses (CoVs) and toroviruses (ToVs), which have the largest genomes among vertebrate RNA viruses, is laborious and hampered by technical constraints. Hence, little research has focused on animal CoVs and ToVs using RGSs, especially in large domestic animals such as pigs and cattle. In the last decade, however, studies of porcine CoVs and bovine ToVs using RGSs have been reported. In addition, the coronavirus disease-2019 pandemic has prompted the development of new and simple CoV RGSs, which will accelerate RGS-based research on animal CoVs and ToVs. In this review, we summarise the general characteristics of CoVs and ToVs, the RGSs available for CoVs and ToVs and the progress made in the last decade in RGS-based research on porcine CoVs and bovine ToVs.

Research progress of porcine epidemic diarrhea virus S protein

Porcine epidemic diarrhea virus (PEDV) is a single-stranded RNA virus with a capsid membrane that causes acute infectious gastrointestinal disease characterized by vomiting, diarrhea, and dehydration in swine. Piglets are more susceptible to PEDV than adults, with an infection rate reaching 90% and a fatality rate as high as 100%. Moreover, PEDV has a rapid transmission rate and broad transmission range. Consequently, PEDV has caused considerable economic losses and negatively impacted the sustainability of the pig industry. The surface spike (S) glycoprotein is the largest structural protein in PEDV virions and is closely associated with host cell fusion and virus invasion. As such, the S protein is an important target for vaccine development. In this article, we review the genetic variation, immunity, apoptosis-induction function, virulence, vaccine potential, and other aspects of the PEDV S protein. This review provides a theoretical foundation for preventing and controlling PEDV infection and serves as a valuable resource for further research and development of PEDV vaccines.

Developing Next-Generation Live Attenuated Vaccines for Porcine Epidemic Diarrhea Using Reverse Genetic Techniques

Porcine epidemic diarrhea virus (PEDV) is the etiology of porcine epidemic diarrhea (PED), a highly contagious digestive disease in pigs and especially in neonatal piglets, in which a mortality rate of up to 100% will be induced. Immunizing pregnant sows remains the most promising and effective strategy for protecting their neonatal offspring from PEDV. Although half a century has passed since its first report in Europe and several prophylactic vaccines (inactivated or live attenuated) have been developed, PED still poses a significant economic concern to the swine industry worldwide. Hence, there is an urgent need for novel vaccines in clinical practice, especially live attenuated vaccines (LAVs) that can induce a strong protective lactogenic immune response in pregnant sows. Reverse genetic techniques provide a robust tool for virological research from the function of viral proteins to the generation of rationally designed vaccines. In this review, after systematically summarizing the research progress on virulence-related viral proteins, we reviewed reverse genetics techniques for PEDV and their application in the development of PED LAVs. Then, we probed into the potential methods for generating safe, effective, and genetically stable PED LAV candidates, aiming to provide new ideas for the rational design of PED LAVs.

S2 subunit plays a critical role in pathogenesis of TW-like avian coronavirus infectious bronchitis virus

To investigate the critical role of the S gene in determining pathogenesis of TW-like avian infectious bronchitis virus (IBV), we generated two recombinant IBVs (rGDaGD-S1 and rGDaGD-S2) by replacing either the S1 or S2 region of GD strain with the corresponding regions from an attenuated vaccine candidate aGD strain. The virulence and pathogenicity of these recombinant viruses was assessed both in vitro and in vivo. Our results indicated the mutations in the S2 region led to decreased virulence, as evidenced by reduced virus replication in embryonated chicken eggs and chicken embryonic kidney cells as well as observed clinical symptoms, gross lesions, microscopic lesions, tracheal ciliary activity, and viral distribution in SPF chickens challenged with recombinant IBVs. These findings highlight that the S2 subunit is a key determinant of TW-like IBV pathogenicity. Our study established a foundation for future investigations into the molecular mechanisms underlying IBV virulence.

Porcine Epidemic Diarrhea: Insights and Progress on Vaccines

Porcine epidemic diarrhea (PED) is a swine-wasting disease caused by coronavirus infection. It causes great economic damage to the swine industry worldwide. Despite the continued use of vaccines, PED outbreaks continue, highlighting the need to review the effectiveness of current vaccines and develop additional vaccines based on new platforms. Here, we review existing vaccine technologies for preventing PED and highlight promising technologies that may help control PED virus in the future.

Isolation and Identification of a Tibetan Pig Porcine Epidemic Diarrhoea Virus Strain and Its Biological Effects on IPEC-J2 Cells

Porcine epidemic diarrhoea virus (PEDV) is a coronavirus that can cause severe watery diarrhoea in piglets, with high morbidity and mortality rates, seriously hindering the healthy development of the global swine industry. In this study, we isolated a strain of PEDV from Tibetan pigs and named it CH/GS/2022. Subsequently, we screened the apoptosis signals of PEDV-infected IPEC-J2 cells and studied the correlation between apoptosis signals and cell apoptosis. The results showed that different infections of PEDV induced different degrees of apoptosis in cells, and PEDV-induced cell apoptosis was dose-dependent. We then detected the expression of the p53, p38, JNK, Bax, and Bcl-2 genes in the apoptosis signal pathway. The results showed that 24 h after PEDV infection, the expression of the p53, p38, JNK, and Bax genes in IPEC-J2 cells increased significantly, while the expression of the Bcl-2 gene decreased significantly (p < 0.05). Subsequently, we used Western blot to detect the protein levels of these five genes, and the results showed that PEDV infection upregulated the expression of p53, p38, JNK, and Bax proteins (p < 0.05) while downregulating the expression of Bcl-2 protein (p < 0.05). Thus, it was initially inferred that PEDV infection could regulate cell apoptosis by activating the p53, p38, and JNK signalling pathways. Finally, we further investigated the apoptosis of the cells through the use of inhibitors. The results indicated that the p53 inhibitor Pifithrin-α has a significant inhibitory effect on the expression of the p53 protein after PEDV infection and can reverse the expression levels of Bax and Bcl-2 proteins. This suggested that p53 is involved in PEDV-induced cell apoptosis. Similarly, the p38 MAPK inhibitor SB203580 has an inhibitory effect on the expression of the p38 protein and can reverse the expression levels of Bax and Bcl-2 proteins. This suggested that p38 is also involved in PEDV-induced cell apoptosis. On the other hand, the JNK inhibitor SP600125 has no inhibitory effect on the expression of the JNK protein after PEDV infection, but the expression levels of Bax and Bcl-2 proteins have changed. Furthermore, it is noteworthy that SP600125 can inhibit the activity of apoptotic proteins but not their levels, resulting in reduced cell apoptosis. These preliminary results indicated that JNK may be involved in PEDV-induced IPEC-J2 cell apoptosis.

The natural compound Sanggenon C inhibits PRRSV infection by regulating the TRAF2/NF-κB signalling pathway

Porcine reproductive and respiratory syndrome (PRRS) is a serious infectious disease and one of the major causes of death in the global pig industry. PRRS virus (PRRSV) strains have complex and diverse genetic characteristics and cross-protection between strains is low, which complicates vaccine selection; thus, the current vaccination strategy has been greatly compromised. Therefore, it is necessary to identify effective natural compounds for the clinical treatment of PRRS. A small molecule library composed of 720 natural compounds was screened in vitro, and we found that Sanggenon C (SC) was amongst the most effective natural compound inhibitors of PRRSV infection. Compared with ribavirin, SC more significantly inhibited PRRSV infection at both the gene and protein levels and reduced the viral titres and levels of protein expression and inflammatory cytokine secretion to more effectively protect cells from PRRSV infection and damage. Mechanistically, SC inhibits activation of the NF-κB signalling pathway by promoting TRAF2 expression, thereby reducing PRRSV replication. In conclusion, by screening natural compounds, we found that SC suppresses PRRSV infection by regulating the TRAF2/NF-κB signalling pathway. This study contributes to a deeper understanding of the therapeutic targets and pathogenesis of PRRSV infection. More importantly, our results demonstrate that SC has potential as a candidate for the treatment of PRRS.

Genome-scale CRISPR screen identifies TRIM2 and SLC35A1 associated with porcine epidemic diarrhoea virus infection

Porcine epidemic diarrhoea (PED) caused by the porcine epidemic diarrhoea virus (PEDV) is the most devastating disease in the global pig industry due to its high mortality rate in piglets. The host factors critical for PEDV replication are poorly understood. Here, we designed a pooled African green monkey genome-scale CRISPR/Cas9 knockout (VeroCKO) library containing 75,608 single guide RNAs targeting 18,993 protein-coding genes. Subsequently, we use the VeroCKO library to identify key host factors facilitating PEDV infection in Vero E6 cells. Several previously unreported genes associated with PEDV infection are highly enriched post-PEDV selection. We discovered that knocking out the tripartite motif 2 (TRIM2) and the solute carrier family 35 member A1 (SLC35A1) inhibited PEDV replication. Virtual screening and molecular docking approaches showed that chem-80,048,685 (M2) s ignificantly inhibited PEDV attachment and late replication by impeding SLC35A1. Furthermore, we found that knocking out SLC35A1 in Vero E6 cells upregulated a disintegrin and metalloprotease protein-17 (ADAM17) by splicing porcine aminopeptidase N (pAPN) and angiotensin-converting enzyme 2 (ACE2) ectodomains to reduce PEDV-infection in a CMP-Sialic Acid (CMP-SA) cell entry-independent manner. These findings provide a new perspective for a better understanding of host-pathogen interactions and new therapeutic targets for PEDV infection.

Deletion of a 7-amino-acid region in the porcine epidemic diarrhea virus envelope protein induces higher type I and III interferon responses and results in attenuation in vivo

Porcine epidemic diarrhea virus (PEDV) leads to enormous economic losses for the pork industry. However, the commercial vaccines failed to fully protect against the epidemic strains. Previously, the rCH/SX/2016-SHNXP strain with the entire E protein and the rCH/SX/2015 strain with the deletion of 7-amino-acid (7-aa) at positions 23-29 in E protein were constructed and rescued. The pathogenicity assay indicated that rCH/SX/2015 is an attenuated strain, but rCH/SX/2016-SHNXP belongs to the virulent strains. Then, the recombination PEDV (rPEDV-EΔaa23-aa29)strain with a 7-aa deletion in the E protein was generated, using the highly virulent rCH/SX/2016-SHNXP strain (rPEDV-Ewt) as the backbone. Compared with the rPEDV-Ewt strain, the release and infectivity of the rPEDV-EΔaa23-aa29 strain were significantly reduced in vitro, but stronger interferon (IFN) responses were triggered both in vitro and in vivo. The pathogenicity assay showed that the parental strain resulted in severe diarrhea (100%) and death (100%) in all piglets. Compared with the parental strain group, rPEDV-EΔaa23-aa29 caused lower mortality (33%) and diminished fecal PEDV RNA shedding. At 21 days, all surviving pigs were challenged orally with rPEDV-Ewt. No pigs died in the two groups. Compared with the mock group, significantly delayed and milder diarrhea and reduced fecal PEDV RNA shedding were detected in the rPEDV-EΔaa23-aa29 group. In conclusion, the deletion of a 7-aa fragment in the E protein (EΔaa23-aa29) attenuated PEDV but retained its immunogenicity, which can offer new ideas for the design of live attenuated vaccines and provide new insights into the attenuated mechanism of PEDV. IMPORTANCE Porcine epidemic diarrhea virus (PEDV) causes high mortality in neonatal piglets and remains a large challenge to the pork industry. Unfortunately, no safe and effective vaccines are available yet. The pathogenesis and molecular basis of the attenuation of PEDV remain unclear, which seriously hinders the development of PEDV vaccines. This study found that the rPEDV carrying EΔaa23-aa29 mutation in the E protein induced significantly higher IFN responses than the parental virus, partially attenuated, and remained immunogenic in piglets. For the first time, PEDV E was verified as an IFN antagonist in the infection context and identified as a virulence factor of PEDV. Our data also suggested that EΔaa23-aa29 mutation can be a good target for the development of live attenuated vaccines for PEDV and also provide new perspectives for the attenuated mechanism of PEDV.

Reverse Genetics Systems for Emerging and Re-Emerging Swine Coronaviruses and Applications

Emerging and re-emerging swine coronaviruses (CoVs), including porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), and swine acute diarrhea syndrome-CoV (SADS-CoV), cause severe diarrhea in neonatal piglets, and CoV infection is associated with significant economic losses for the swine industry worldwide. Reverse genetics systems realize the manipulation of RNA virus genome and facilitate the development of new vaccines. Thus far, five reverse genetics approaches have been successfully applied to engineer the swine CoV genome: targeted RNA recombination, in vitro ligation, bacterial artificial chromosome-based ligation, vaccinia virus -based recombination, and yeast-based method. This review summarizes the advantages and limitations of these approaches; it also discusses the latest research progress in terms of their use for virus-related pathogenesis elucidation, vaccine candidate development, antiviral drug screening, and virus replication mechanism determination.

Porcine epidemic diarrhea virus: an update overview of virus epidemiology, vaccines, and control strategies in South Korea

Porcine epidemic diarrhea virus (PEDV) has posed significant financial threats to the domestic pig industry over the last three decades in South Korea. PEDV infection will mostly result in endemic persistence in the affected farrow-to-finish (FTF) herds, leading to endemic porcine epidemic diarrhea (PED) followed by year-round recurrent outbreaks. This review aims to encourage collaboration among swine producers, veterinarians, and researchers to offer answers that strengthen our understanding of PEDV in efforts to prevent and control endemic PED and to prepare for the next epidemics or pandemics. We found that collaboratively implementing a PED risk assessment and customized four-pillar-based control measures is vital to interrupt the chain of endemic PED in affected herds: the former can identify on-farm risk factors while the latter aims to compensate for or improve weaknesses via herd immunity stabilization and virus elimination. Under endemic PED, long-term virus survival in slurry and asymptomatically infected gilts ("Trojan Pigs") that can transmit the virus to farrowing houses are key challenges for PEDV eradication in FTF farms and highlight the necessity for active monitoring and surveillance of the virus in herds and their environments. This paper underlines the current knowledge of molecular epidemiology and commercially available vaccines, as well as the risk assessment and customized strategies to control PEDV. The intervention measures for stabilizing herd immunity and eliminating virus circulation may be the cornerstone of establishing regional or national PED eradication programs.

Coronavirus Porcine Epidemic Diarrhea Virus Utilizes Chemokine Interleukin-8 to Facilitate Viral Replication by Regulating Ca2+ Flux

Chemokine production by epithelial cells is crucial for neutrophil recruitment to sites of inflammation during viral infection. However, the effect of chemokine on epithelia and how chemokine is involved in coronavirus infection remains to be fully understood. Here, we identified an inducible chemokine interleukin-8 (CXCL8/IL-8), which could promote coronavirus porcine epidemic diarrhea virus (PEDV) infection in African green monkey kidney epithelial cells (Vero) and Lilly Laboratories cell-porcine kidney 1 epithelial cells (LLC-PK1). IL-8 deletion restrained cytosolic calcium (Ca2+), whereas IL-8 stimulation improved cytosolic Ca2+. The consumption of Ca2+ restricted PEDV infection. PEDV internalization and budding were obvious reductions when cytosolic Ca2+ was abolished in the presence of Ca2+ chelators. Further study revealed that the upregulated cytosolic Ca2+ redistributes intracellular Ca2+. Finally, we identified that G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-store-operated Ca2+ (SOC) signaling was crucial for enhancive cytosolic Ca2+ and PEDV infection. To our knowledge, this study is the first to uncover the function of chemokine IL-8 during coronavirus PEDV infection in epithelia. PEDV induces IL-8 expression to elevate cytosolic Ca2+, promoting its infection. Our findings reveal a novel role of IL-8 in PEDV infection and suggest that targeting IL-8 could be a new approach to controlling PEDV infection. IMPORTANCE Coronavirus porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that caused severe economic losses worldwide, and more effort is needed to develop economical and efficient vaccines to control or eliminate this disease. The chemokine interleukin-8 (CXCL8/IL-8) is indispensable for the activation and trafficking of inflammatory mediators and tumor progression and metastasis. This study evaluated the effect of IL-8 on PEDV infection in epithelia. We found that IL-8 expression improved cytosolic Ca2+ in epithelia, facilitating PEDV rapid internalization and egress. G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-SOC signaling was activated by IL-8, releasing the intracellular Ca2+ stores from endoplasmic reticulum (ER). These findings provide a better understanding of the role of IL-8 in PEDV-induced immune responses, which will help develop small-molecule drugs for coronavirus cure.

Genomic Characterizations of Porcine Epidemic Diarrhea Viruses (PEDV) in Diarrheic Piglets and Clinically Healthy Adult Pigs from 2019 to 2022 in China

Porcine epidemic diarrhea virus (PEDV) is a major causative pathogen of diarrheic disease. In this study, the prevalence and evolution of PEDV was evaluated using intestinal samples collected from six provinces of China in 2019-2022. PEDV could not only be detected in diarrheic piglets but also in adult pigs without enteric diseases. The complete genomes of five temporal and geographical representative PEDV strains were determined. Genome-based phylogenetic analysis indicated that XJ1904-700 belongs to the G2-a subgroup, while the other strains are clustered within the S-INDEL subgroup. Recombination analyses supported that JSNJ2004-919 is an inter-subgroup recombinant from SD2014-like (G2-b), CHZ-2013-like (G2-b) and CV777-like (G1-b) isolates, while FJFZ2004-1017 is an intra-subgroup recombinant from XM1-2-like (S-INDEL) and LYG-2014-like (S-INDEL) isolates. Both JSNJ2004-919 and FJFZ2004-1017 were from adult pigs, providing evidence that adult pigs may also serve as the host of PEDV reservoirs for virus evolution. Overall, this study provides new insights into PEDV's prevalence and evolution in both diseased piglets and clinically healthy adult pigs.

Based on the Results of PEDV Phylogenetic Analysis of the Most Recent Isolates in China, the Occurrence of Further Mutations in the Antigenic Site S1° and COE of the S Protein Which Is the Target Protein of the Vaccine

The continuous challenge of existing vaccine systems by porcine epidemic diarrhea virus (PEDV) variant strains in recent years, it caused significant economic losses in the global swine industry. A PEDV virulent strain CH/HLJBQL/2022 was successfully isolated in China in this study. A genome-wide based phylogenetic analysis suggests that CH/HLJBQL/2022 belongs to the GII subtype, and 96.3%-99.6% homology existed in the whole genomes of other strains. For the first time, simultaneous mutations of four amino acids were found in the highly conserved membrane (M) and nucleocapsid (N) proteins, as well as five amino acid mutations that differed from the vast majority of strains in the spike (S) protein. Mutations in the M and S proteins were found to produce coils with different angles by building 2D and 3D structural models. Epitope analysis indicated that the isolates produced specific changes and that the transmembrane function of the M protein had not been affected. In addition, typing markers exist during strain evolution, but isolates are using the fusion of specific amino acids from multiple variant strains to add additional features, as also demonstrated by protein alignments and 3D models of numerous subtype strains. These results suggest that aa mutations in the M and S proteins may have changed the structure and antigenic epitope of the isolates and PEDV is evolving again on the basis of variants that have been found to counteract the immune network of the new vaccine.

Three Amino Acid Substitutions in the Spike Protein Enable the Coronavirus Porcine Epidemic Diarrhea Virus To Infect Vero Cells

Porcine epidemic diarrhea virus (PEDV), a continuously evolving pathogen, causes severe diarrhea in piglets, with high mortality rates. To prevent or mitigate the disease, it is common practice to develop live or inactivated PEDV vaccines based on cell-adapted viral variants. Propagating wild-type PEDV in cultured cells is, however, often challenging due to the lack of knowledge about the requirements for the cell adaptation of PEDV. In the present study, by using the RNA-targeted reverse genetic system for PEDV to apply S protein swapping followed by the rescue of the recombinant viruses, three key amino acid mutations in the S protein, A605E, E633Q, and R891G, were identified, which enable attenuated PEDV strain DR13 (DR13^att) to efficiently and productively infect Vero cells, in contrast to the parental DR13 strain (DR13^par). The former two key mutations reside inside and in the vicinity of the receptor binding domain (RBD), respectively, while the latter occurs at the N-terminal end of the fusion peptide (FP). Besides the three key mutations, other mutations in the S protein further enhanced the infection efficiency of the recombinant viruses. We hypothesize that the three mutations changed PEDV tropism by altering the S2' cleavage site and the RBD structure. This study provides basic molecular insight into cell adaptation by PEDV, which is also relevant for vaccine design. IMPORTANCE Porcine epidemic diarrhea virus (PEDV) is a lethal pathogen for newborn piglets, and an efficient vaccine is needed urgently. However, propagating wild-type PEDV in cultured cells for vaccine development is still challenging due to the lack of knowledge about the mechanism of the cell adaptation of PEDV. In this study, we found that three amino acid mutations, A605E, E633Q, and R891G, in the spike protein of the Vero cell-adapted PEDV strain DR13^att were critical for its cell adaptation. After analyzing the mutation sites in the spike protein, we hypothesize that the cell adaptation of DR13^att was achieved by altering the S2' cleavage site and the RBD structure. This study provides new molecular insight into the mechanism of PEDV culture adaptation and new strategies for PEDV vaccine design.

A new PEDV strain CH/HLJJS/2022 can challenge current detection methods and vaccines

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) variant strains cause great economic losses to the global swine industry. However, vaccines do not provide sufficient protection against currently circulating strains due to viral mutations. This study traced the molecular characteristics of the most recent isolates in China and aimed to provide a basis for the prevention and treatment of PEDV.

METHODS

We obtained samples from a Chinese diarrheal swine farm in 2022. Reverse transcription polymerase chain reaction and immunofluorescence were used to determine the etiology, and the full-length PEDV genome was sequenced. Nucleotide similarity was calculated using MEGA to construct a phylogenetic tree and DNASTAR. Mutant amino acids were aligned using DNAMAN and modeled by SWISS-MODEL, Phyre2 and FirstGlance in JMOL for protein tertiary structure simulation. Additionally, TMHMM was used for protein function prediction.

RESULTS

A PEDV virulent strain CH/HLJJS/2022 was successfully isolated in China. A genome-wide based phylogenetic analysis suggests that it belongs to the GII subtype, and 96.1-98.9% homology existed in the whole genomes of other strains. For the first time, simultaneous mutations of four amino acids were found in the highly conserved membrane (M) and nucleocapsid (N) proteins, as well as eight amino acid mutations that differed from the vast majority of strains in the spike (S) protein. Three of the mutations alter the S-protein spatial structure. In addition, typing markers exist during strain evolution, but isolates are using the fusion of specific amino acids from multiple variant strains to add additional features, as also demonstrated by protein alignments and 3D models of numerous subtype strains.

CONCLUSION

The newly isolated prevalent strain CH/HLJJS/2022 belonged to the GII subtype, and thirteen mutations different from other strains were found, including mutations in the highly conserved m and N proteins, and in the S1° and COE neutralizing epitopes of the S protein. PEDV is breaking through original cognitions and moving on a more complex path. Surveillance for PEDV now and in the future and improvements derived from mutant strain vaccines are highly warranted.

Construction and immunogenicity of a trypsin-independent porcine epidemic diarrhea virus variant

Porcine epidemic diarrhea virus (PEDV) is a re-emerging enteropathogenic coronavirus that causes high mortality in neonatal piglets. The addition of trypsin plays a crucial role in the propagation of PEDV, but also increases the complexity of vaccine production and increases its cost. Previous studies have suggested that the S2' site and Y976/977 of the PEDV spike (S) protein might be the determinants of PEDV trypsin independence. In this study, to achieve a recombinant trypsin-independent PEDV strain, we used trypsin-dependent genotype 2 (G2) PEDV variant AJ1102 to generate three recombinant PEDVs with mutations in S (S2' site R894G and/or Y976H). The three recombinant PEDVs were still trypsin dependent, suggesting that the S2' site R894 and Y976 of AJ1102 S are not key sites for PEDV trypsin dependence. Therefore, we used AJ1102 and the classical trypsin-independent genotype 1 (G1) PEDV strain JS2008 to generate a recombinant PEDV carrying a chimeric S protein, and successfully obtained trypsin-independent PEDV strain rAJ1102-S2'_JS2008, in which the S2 (amino acids 894-1386) domain was replaced with the corresponding JS2008 sequence. Importantly, immunization with rAJ1102-S2'_JS2008 induced neutralizing antibodies against both AJ1102 and JS2008. Collectively, these results suggest that rAJ1102-S2'_JS2008 is a novel vaccine candidate with significant advantages, including no trypsin requirement for viral propagation to high titers and the potential provision of protection for pigs against G1 and G2 PEDV infections.

DNAJA3 Interacts with PEDV S1 Protein and Inhibits Virus Replication by Affecting Virus Adsorption to Host Cells

Porcine epidemic diarrhea virus (PEDV) infection causes huge economic losses to the pig industry worldwide. DNAJA3, a member of the Hsp40 family proteins, is known to play an important role in the replication of several viruses. However, it remains unknown if it interacts with PEDV. We found that DNAJA3 interacted with PEDV S1, initially with yeast two-hybrid screening and later with Co-IP, GST pull-down, and confocal imaging. Further experiments showed the functional relationship between DNAJA3 and PEDV in the infected IPEC-J2 cells. DNAJA3 overexpression significantly inhibited PEDV replication while its knockdown had the opposite effect, suggesting that it is a negative regulator of PEDV replication. In addition, DNAJA3 expression could be downregulated by PEDV infection possibly as the viral strategy to evade the suppressive role of DNAJA3. By gene silencing and overexpression, we were able to show that DNAJA3 inhibited PEDV adsorption to IPEC-J2 cells but did not affect virus invasion. In conclusion, our study provides clear evidence that DNAJA3 mediates PEDV adsorption to host cells and plays an antiviral role in IPEC-J2 cells.

PEDV: Insights and Advances into Types, Function, Structure, and Receptor Recognition

Porcine epidemic diarrhea virus (PEDV) has been endemic in most parts of the world since its emergence in the 1970s. It infects the small intestine and intestinal villous cells, spreads rapidly, and causes infectious intestinal disease characterized by vomiting, diarrhea, and dehydration, leading to high mortality in newborn piglets and causing massive economic losses to the pig industry. The entry of PEDV into cells is mediated by the binding of its spike protein (S protein) to a host cell receptor. Here, we review the structure of PEDV, its strains, and the structure and function of the S protein shared by coronaviruses, and summarize the progress of research on possible host cell receptors since the discovery of PEDV.