Identification and characterization of PEDV infection in rat crypt epithelial cells

CRISPR-Mediated Library Screening of Gene-Knockout Cell Lines for Investigating Antiviral Innate Immunity

The application of CRISPR-mediated library screening has fundamentally transformed functional genomics by revealing the complexity of virus-host interactions. This protocol describes the use of CRISPR-mediated library screening to identify key functional genes regulating the innate immune response to PEDV infection. We detail a step-by-step process, starting from the design and construction of a customized CRISPR knockout library targeting genes involved in innate immunity to the effective delivery of these constructs into cells using lentiviral vectors. Subsequently, we outline the process of identifying functional genes postviral attack, including the use of next-generation sequencing (NGS), to analyze and identify knockout cells that exhibit altered responses to infection. This integrated approach provides researchers in immunology and virology with a resource and a robust framework for uncovering the genetic basis of host-pathogen interactions and the arsenal of the innate immune system against viral invasions.

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.

Porcine Epidemic Diarrhea Virus Infection of Porcine Intestinal Epithelial Cells Causes Mitochondrial DNA Release and the Activation of the NLRP3 Inflammasome to Mediate Interleukin-1β Secretion

Porcine epidemic diarrhea virus (PEDV) induces enteritis and diarrhea in piglets. Mitochondrial DNA (mtDNA) contributes to virus-induced inflammatory responses; however, the involvement of inflammasomes in PEDV infection responses remains unclear. We investigated the mechanism underlying inflammasome-mediated interleukin (IL)-1β secretion during the PEDV infection of porcine intestinal epithelial (IPEC-J2) cells. IL-1β production and caspase-1 activity were assessed by quantitative PCR and enzyme-linked immunosorbent assay. NLRP3 inflammasome activation was assessed using immunoprecipitation experiments. Mitochondrial damage was evaluated by analyzing the mitochondrial membrane potential and ATP levels and by the flow cytometry examination of mitochondrial reactive oxygen species (mtROS). Mitochondria and mtDNA localization were observed using immunofluorescence. The inhibition of mtROS and mtDNA production allowed NLRP3 inflammasome and IL-1β expression detection and the evaluation of the pathway underlying NLRP3 inflammasome activation in PEDV-infected IPEC-J2 cells. IPEC-J2 cells upregulated IL-1β upon PEDV infection, where mature IL-1β secretion depended on caspase-1 activity, triggered NLRP3 inflammasome expression and assembly, and caused mitochondrial dysfunction, leading to mtDNA release and NLRP3 inflammasome activation, while mtROS contributed to NF-κB pathway activation, enhancing IL-1β secretion. This is the first demonstration of the mechanism underlying mtDNA release and NLRP3 inflammasome activation facilitating IL-1β secretion from PEDV-infected IPEC-J2 cells. These data enhance our understanding of the inflammatory mechanisms triggered by PEDV.

Advances research in porcine enteric coronavirus therapies and antiviral drugs

The porcine enteric coronaviruses (PECs) currently reported include porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), transmissible gastroenteritis virus (TGEV), and swine acute diarrhea syndrome coronavirus (SADS-CoV). In the absence of effective treatment, they can cause similar clinical characteristics including weight loss, sleepiness, vomiting, anorexia and fatal diarrhea in neonatal piglets, resulting in significant economic losses to the global pig industry. Although many studies on drugs for treating and combating PECs have been issued. There are still no specific drug targeting PECs and used in clinical production. Therefore, it is necessary to sort out and summarize the research on the treatment and anti PECs drugs, and further development of low toxicity and high efficiency drugs is needed. Here, we review the latest progress of anti PECs drugs, focus on the mechanism of anti PECs reaction of drug components, and try to clarify new strategies for effective control and elimination of PECs. These comprehensive and profound insights will help to further investigate, prevent and control the transmission of PECs infection.

Antiviral activity of flavonol against porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) remains one of the major causative microorganisms of viral diarrhea in piglets worldwide, with no approved drugs for treatment. We identified a natural molecule, flavonol, which is widely found in tea, vegetables and herbs. Subsequently, the antiviral activity of compound flavonol was evaluated in Vero cells and IPEC-J2 cells, and its anti-PEDV mechanism was analyzed by molecular docking and molecular dynamics. The results showed that flavonol could effectively inhibit viral progeny production, RNA synthesis and protein expression of PEDV strains in a dose-dependent manner. When flavonol was added simultaneously with viral infection in Vero cells, it demonstrated potent anti-PEDV activity by affecting the viral attachment and internalization phases. Similarly, in IPEC-J2 cells, flavonol effectively inhibited PEDV infection at different stages of infection, except for the release phase. Moreover, flavonol mainly interacts with PEDV Mpro through hydrogen bonds and hydrophobic forces, and the complex formed by it has high stability. Importantly, flavonol also showed broad-spectrum activity against other porcine enteric coronaviruses such as TGEV and PDCoV in vitro. These findings suggest that flavonol may exert antiviral effects by interacting with viral Mpro, thereby affecting viral replication. This means that flavonol is expected to become a potential drug to prevent or treat porcine enteric coronavirus.

AhR ligands from LGG metabolites promote piglet intestinal ILC3 activation and IL-22 secretion to inhibit PEDV infection

In maintaining organismal homeostasis, gut immunity plays a crucial role. The coordination between the microbiota and the immune system through bidirectional interactions regulates the impact of microorganisms on the host. Our research focused on understanding the relationships between substantial changes in jejunal intestinal flora and metabolites and intestinal immunity during porcine epidemic diarrhea virus (PEDV) infection in piglets. We discovered that Lactobacillus rhamnosus GG (LGG) could effectively prevent PEDV infection in piglets. Further investigation revealed that LGG metabolites interact with type 3 innate lymphoid cells (ILC3s) in the jejunum of piglets through the aryl hydrocarbon receptor (AhR). This interaction promotes the activation of ILC3s and the production of interleukin-22 (IL-22). Subsequently, IL-22 facilitates the proliferation of IPEC-J2 cells and activates the STAT3 signaling pathway, thereby preventing PEDV infection. Moreover, the AhR receptor influences various cell types within organoids, including intestinal stem cells (ISCs), Paneth cells, and enterocytes, to promote their growth and development, suggesting that AhR has a broad impact on intestinal health. In conclusion, our study demonstrated the ability of LGG to modulate intestinal immunity and effectively prevent PEDV infection in piglets. These findings highlight the potential application of LGG as a preventive measure against viral infections in livestock.IMPORTANCEWe observed high expression of the AhR receptor on pig and human ILC3s, although its expression was negligible in mouse ILC3s. ILC3s are closely related to the gut microbiota, particularly the secretion of IL-22 stimulated by microbial signals, which plays a crucial regulatory role in intestinal immunity. In our study, we found that metabolites produced by beneficial gut bacteria interact with ILC3s through AhR, thereby maintaining intestinal immune homeostasis in pigs. Moreover, LGG feeding can enhance the activation of ILC3s and promote IL-22 secretion in the intestines of piglets, ultimately preventing PEDV infection.

Assessing immunogenicity of CRISPR-NCas9 engineered strain against porcine epidemic diarrhea virus

Porcine epidemic diarrhea (PED) caused by porcine epidemic diarrhea virus (PEDV), is an acute and highly infectious disease, resulting in substantial economic losses in the pig industry. Given that PEDV primarily infects the mucosal surfaces of the intestinal tract, it is crucial to improve the mucosal immunity to prevent viral invasion. Lactic acid bacteria (LAB) oral vaccines offer unique advantages and potential applications in combatting mucosal infectious diseases, making them an ideal approach for controlling PED outbreaks. However, traditional LAB oral vaccines use plasmids for exogenous protein expression and antibiotic genes as selection markers. Antibiotic genes can be diffused through transposition, transfer, or homologous recombination, resulting in the generation of drug-resistant strains. To overcome these issues, genome-editing technology has been developed to achieve gene expression in LAB genomes. In this study, we used the CRISPR-NCas9 system to integrate the PEDV S1 gene into the genome of alanine racemase-deficient Lactobacillus paracasei △Alr HLJ-27 (L. paracasei △Alr HLJ-27) at the thymidylate synthase (thyA) site, generating a strain, S1/△Alr HLJ-27. We conducted immunization assays in mice and piglets to evaluate the level of immune response and evaluated its protective effect against PEDV through challenge tests in piglets. Oral administration of the strain S1/△Alr HLJ-27 in mice and piglets elicited mucosal, humoral, and cellular immune responses. The strain also exhibited a certain level of resistance against PEDV infection in piglets. These results demonstrate the potential of S1/△Alr HLJ-27 as an oral vaccine candidate for PEDV control. KEY POINTS: • A strain S1/△Alr HLJ-27 was constructed as the candidate for an oral vaccine. • Immunogenicity response and challenge test was carried out to analyze the ability of the strain. • The strain S1/△Alr HLJ-27 could provide protection for piglets to a certain extent.

PEDV promotes the differentiation of CD4+T cells towards Th1, Tfh, and Treg cells via CD103+DCs

Porcine epidemic diarrhea virus (PEDV) can infect all ages of pigs, particularly newborn piglets with a mortality almost reaching to 80-100%, causing significant economic losses to the global pig industry. The mucosal immune response is crucial for PEDV prevention, in which specific dendritic cells (DCs) and differentiated T cells play vital roles. In this study, CD103+DCs were differentiated successfully with retinoic acid (RA) treatment in vitro. PEDV could not replicate efficiently in differentiated CD103+DCs but could promote maturation of CD103+DCs by up-regulating the expression of SLA-DR, CD1a, CD86, and cytokines of IL-1β and IL-10. In addition, PEDV-infected CD103+DCs and CD4+T cells were co-cultured, and the results showed that the differentiation of CD4+T cells toward Th1, Tfh, and Treg, but not Th2. These results demonstrate that PEDV-infected CD103+DCs could promote the differentiation of CD4+T cells, which provided the basis for further study of mucosal response induced by PEDV via CD103+DCs.

Establishment of Replication Deficient Vesicular Stomatitis Virus for Studies of PEDV Spike-Mediated Cell Entry and Its Inhibition

The porcine epidemic diarrhea virus (PEDV) is a highly contagious and virulent enteric coronavirus that causes severe enteric disease in pigs worldwide. PEDV infection causes profound diarrhea, vomiting, and dehydration in pigs of all ages, resulting in high mortality rates, particularly among neonatal piglets. The spike glycoprotein (S) of PEDV plays a crucial role in binding to the host cell receptor and facilitating fusion between the viral and host membranes. Pseudotyped viral particles featuring the PEDV S protein are valuable tools for investigating virus entry, identifying neutralizing antibodies, and developing small molecules to impede virus replication. In this study, we used a codon-optimized PEDV S protein to generate recombinant pseudotyped vesicular stomatitis virus (VSV) particles (rVSV-ΔG-EGFP-S). The full-length S protein was efficiently incorporated into VSV particles. The S protein pseudotyped VSV exhibited infectivity towards permissive cell lines of PEDV. Moreover, we identified a new permissive cell line, JHH7, which showed robust support for PEDV replication. In contrast to the SARS-CoV-2 spike protein, the removal of amino acids from the cytoplasmic tail resulted in reduced efficiency of viral pseudotyping. Furthermore, we demonstrated that 25-hydroxycholesterol inhibited rVSV-ΔG-EGFP-S entry, while human APN facilitated rVSV-ΔG-EGFP-S entry through the use of ANPEP knockout Huh7 cells. Finally, by transducing swine intestinal organoids with the rVSV-ΔG-EGFP-S virus, we observed efficient infection of the swine intestinal organoids by the PEDV spike-pseudotyped VSV. Our work offers valuable tools for studying the cellular entry of PEDV and developing interventions to curb its transmission.

Linoleic acid stimulation results in TGF-β1 production and inhibition of PEDV infection in vitro

Linoleic acid (LA) is recommended to improve pork quality. However, whether it affects the intestinal immune response in pigs is still unclear. Our ex vivo experiments demonstrated that LA stimulation resulted in increased frequencies of Tregs in PBMCs but not in Peyer's Patches (PPs). The results of RT-qPCR, flow cytometry, and ELISA indicated that LA increased the TGF-β1 expression level in DCs isolated from PEDV infected pigs. Furthermore, RT-qPCR and flow cytometry results demonstrated that TGF-β1 was associated with higher frequencies of Tregs both in PBMCs and PPs. Additional investigations showed that TGF-β1 inhibited PEDV infection in vitro. Besides, knocking-out TGF-β1 in IPEC-J2 cells resulted in higher viral load. Taken together, our results demonstrated that LA stimulation resulted in enhanced production of TGF-β1 by DC, which resulted in higher frequencies of Tregs production and inhibition of PEDV infection.

Oral administration of Lactic acid bacteria inhibits PEDV infection in young piglets

Since the emergence of the highly pathogenic porcine epidemic diarrhea virus (PEDV) strain in 2010, the prevention of porcine epidemic diarrhea (PED) in pig farms remains problematic. To find the reasons behind the high mortality in young piglets, the relative mRNA expression of inflammation-related factors in infected pigs of different ages as well as uninfected pigs were detected by RT-qPCR. The results showed that the mRNA expression of these factors including IL-6 and TNF-α was more increased in infected younger piglets than infected older pigs. To clarify the relationship between these inflammation related factors, the pairwise linear correlation between the relative expression of these factors were analyzed and showed as network mapping with different correlation coefficients. A strong positive correlation was observed between the expression of various factors in 1-week-old piglets. Combined with the difference in mortality of PEDV infection in pigs of different ages, we hypothesized that lactic acid bacteria (LAB) could inhibit PEDV infection in newborn piglets, and an in vivo experiment was carried out. The results of survival rate and wet/dry ratio showed that LAB alleviated PEDV indued mortality and diarrhea. The detection of viral copies and tissue section staining showed less observed viruses in LAB treated pig. RT-qPCR results of gene expression in intestines showed that LAB modulated the gene expression of various host barrier genes, indicating that LAB is potential to inhibit PEDV infection by regulating the host intestinal barrier. However, to use LAB as therapy, how to improve the efficiency on inhibiting PEDV infection needs further studies.

Identification and Characterization of Cell Lines HepG2, Hep3B217 and SNU387 as Models for Porcine Epidemic Diarrhea Coronavirus Infection

Porcine epidemic diarrhea virus (PEDV), a member of the genera alphacoronavirus, causes acute watery diarrhea and dehydration in suckling piglets and results in enormous economic losses in the swine industry worldwide. Identification and characterization of different cell lines are not only invaluable for PEDV entry and replication studies but also important for the development of various types of biological pharmaceuticals against PEDV. In this study, we present an approach to identify suitable permissive cell lines for PEDV research. Human cell lines were screened for a high correlation coefficient with the established PEDV infection model Huh7 based on RNA-seq data from the Cancer Cell Line Encyclopedia (CCLE). Experimentally testing permissiveness towards PEDV infection, three highly permissive human cell lines, HepG2, Hep3B217, and SNU387 were identified. The replication kinetics of PEDV in HepG2, Hep3B217, and SNU387 cells were similar to that in Vero and Huh7 cells. Additionally, the transcriptomes analysis showed robust induction of transcripts associated with the innate immune in response to PEDV infection in all three cell lines, including hundreds of inflammatory cytokine and interferon genes. Moreover, the expression of inflammatory cytokines and interferons were confirmed by qPCR assay. Our findings indicate that HepG2, Hep3B217, and SNU387 are suitable cell lines for PEDV replication and innate immune response studies.

Differences in cytokines expression between Vero cells and IPEC-J2 cells infected with porcine epidemic diarrhea virus

Porcine epidemic diarrhea virus (PEDV) primarily infects suckling piglets and causes severe economic losses to the swine industry. Cytokines, as part of the innate immune response, are important in PEDV infection. The cytokines secreted by cell infection models in vitro might reflect true response to viral infection of target cells in vivo. Vero cells and IPEC-J2 are commonly used as an in vitro model to investigate PEDV infection. However, it is not clear which type of cells is more beneficial to the study of PEDV. In our study, firstly, Vero cells and IPEC-J2 were successfully infected with PEDV virulent strains (HBQY2016) and attenuated vaccine strains (CV777) and were capable of supporting virus replication and progeny release. Moreover, cytokine differences expression by Vero cells and IPEC-J2 cells infected with two PEDV strains were analyzed. Compared with IPEC-J2 cells, only the mRNA levels of TGF-β, MIP-1β and MCP-1 were detected in Vero cells. ELISA assay indicated that compared to the control group, the PEDV-infected group had significantly induced expression levels of IL-1β, MIP-1β, MCP-1, IL-8, and CXCL10 in IPEC-J2 cells, while only secretion level of IL-1β, MIP-1β and IL-8 in Vero cells were higher in PEDV infected group. Finally, cytokines change of piglets infected PEDV-HBQY2016 strains were detected by cDNA microarray, and similar to those of IPEC-J2 cells infected PEDV. Collectively, these data determined that the IPEC-J2 could be more suitable used as a cell model for studying PEDV infection in vitro compared with Vero cells, based on the close approximation of cytokine expression profile to in vivo target cells.