Porcine Epidemic Diarrhea Virus and the Host Innate Immune Response

Enteric coronavirus nsp2 is a virulence determinant that recruits NBR1 for autophagic targeting of TBK1 to diminish the innate immune response

Non-structural protein 2 (nsp2) exists in all coronaviruses (CoVs), while its primary function in viral pathogenicity, is largely unclear. One such enteric CoV, porcine epidemic diarrhea virus (PEDV), causes high mortality in neonatal piglets worldwide. To determine the biological role of nsp2, we generated a PEDV mutant containing a complete nsp2 deletion (rPEDV-Δnsp2) from a highly pathogenic strain by reverse genetics, showing that nsp2 was dispensable for PEDV infection, while its deficiency reduced viral replication in vitro. Intriguingly, rPEDV-Δnsp2 was entirely avirulent in vivo, with significantly increased productions of IFNB (interferon beta) and IFN-stimulated genes (ISGs) in various intestinal tissues of challenged newborn piglets. Notably, nsp2 targets and degrades TBK1 (TANK binding kinase 1), the critical kinase in the innate immune response. Mechanistically, nsp2 induced the macroautophagy/autophagy process and recruited a selective autophagic receptor, NBR1 (NBR1 autophagy cargo receptor). NBR1 subsequently facilitated the K48-linked ubiquitination of TBK1 and delivered it for autophagosome-mediated degradation. Accordingly, the replication of rPEDV-Δnsp2 CoV was restrained by reduced autophagy and excess productions of type I IFNs and ISGs. Our data collectively define enteric CoV nsp2 as a novel virulence determinant, propose a crucial role of nsp2 in diminishing innate antiviral immunity by targeting TBK1 for NBR1-mediated selective autophagy, and pave the way to develop a new type of nsp2-based attenuated PEDV vaccine. The study also provides new insights into the prevention and treatment of other pathogenic CoVs.Abbreviations: 3-MA: 3-methyladenine; Baf A1: bafilomycin A1; CoV: coronavirus; CQ: chloroquine; dpi: days post-inoculation; DMVs: double-membrane vesicles; GABARAP: GABA type A receptor-associated protein; GFP: green fluorescent protein; GIGYF2: GRB10 interacting GYF protein 2; hpi: hours post-infection; IFA: immunofluorescence assay; IFIH1: interferon induced with helicase C domain 1; IFIT2: interferon induced protein with tetratricopeptide repeats 2; IFITM1: interferon induced transmembrane protein 1; IFNB: interferon beta; IRF3: interferon regulatory factor 3; ISGs: interferon-stimulated genes; mAb: monoclonal antibody; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; NBR1: NBR1 autophagy cargo receptor; nsp2: non-structural protein 2; OAS1: 2'-5'-oligoadenylate synthetase 1; PEDV: porcine epidemic diarrhea virus; PRRs: pattern recognition receptors; RIGI: RNA sensor RIG-I; RT-qPCR: reverse transcription quantitative polymerase chain reaction; SQSTM1: sequestosome 1; TBK1: TANK binding kinase 1; TCID50: 50% tissue culture infectious doses; VSV: vesicular stomatitis virus.

RBM14 inhibits the replication of porcine epidemic diarrhea virus by recruiting p62 to degrade nucleocapsid protein through the activation of autophagy and interferon pathway

Porcine epidemic diarrhea virus (PEDV) results in PED, which is an infectious intestinal disease with the representative features of diarrhea, vomiting, and dehydration. PEDV infects neonatal piglets, causing high mortality rates. Therefore, elucidating the interaction between the virus and host in preventing and controlling PEDV infection is of immense significance. We found a new antiviral function of the host protein, RNA-binding motif protein 14 (RBM14), which can inhibit PEDV replication via the activation of autophagy and interferon (IFN) signal pathways. We found that RBM14 can recruit cargo receptor p62 to degrade PEDV nucleocapsid (N) protein through the RBM14-p62-autophagosome pathway. Furthermore, RBM14 can also improve the antiviral ability of the hosts through interacting with mitochondrial antiviral signaling protein to induce IFN expression. These results highlight the novel mechanism underlying RBM14-induced viral restriction. This mechanism leads to the degradation of viral N protein via the autophagy pathway and upregulates IFN for inhibiting PEDV replication; thus, offering new ways for preventing and controlling PED.IMPORTANCEPorcine epidemic diarrhea virus (PEDV) is a vital reason for diarrhea in neonatal piglets, which causes high morbidity and mortality rates. There is currently no effective vaccine or drug to treat and prevent infection with the PEDV. During virus infection, the host inhibits virus replication through various antiviral factors, and at the same time, the virus antagonizes the host's antiviral reaction through its own encoded protein, thus completing the process of virus replication. Our study has revealed that the expression of RNA-binding motif protein 14 (RBM14) was downregulated in PEDV infection. We found that RBM14 can recruit cargo receptor p62 to degrade PEDV N protein via the RBM14-p62-autophagosome pathway and interacted with mitochondrial antiviral signaling protein and TRAF3 to activate the interferon signal pathway, resulting in the inhibition of PEDV replication.

PEDV inhibits HNRNPA3 expression by miR-218-5p to enhance cellular lipid accumulation and promote viral replication

Porcine epidemic diarrhea virus (PEDV) requires complete dependence on the metabolic system of the host cell to complete its life cycle. There is a strong link between efficient viral replication and cellular lipid synthesis. However, the mechanism by which PEDV interacts with host cells to hijack cellular lipid metabolism to promote its replication remains unclear. In this study, PEDV infection significantly enhanced the expression of lipid synthesis-related genes and increased cellular lipid accumulation. Furthermore, using liquid chromatography-tandem mass spectrometry, we identified heterogeneous nuclear ribonucleoprotein A3 (HNRNPA3) as the interacting molecule of PEDV NSP9. We demonstrated that the expression of HNRNPA3 was downregulated by PEDV-induced miR-218-5p through targeting its 3' untranslated region. Interestingly, knocking down HNRNPA3 facilitated the PEDV replication by promoting cellular lipid synthesis. We next found that the knockdown of HNRNPA3 potentiated the transcriptional activity of sterol regulatory element-binding transcription factor 1 (SREBF1) through zinc finger protein 135 (ZNF135) as well as PI3K/AKT and JNK signaling pathways. In summary, we propose a model in which PEDV downregulates HNRNPA3 expression to promote the expression and activation of SREBF1 and increase cellular lipid accumulation, providing a novel mechanism by which PEDV interacts with the host to utilize cellular lipid metabolism to promote its replication.IMPORTANCEAs the major components and structural basis of the viral replication complexes of positive-stranded RNA viruses, lipids play an essential role in viral replication. However, how PEDV manipulates host cell lipid metabolism to promote viral replication by interacting with cell proteins remains poorly understood. Here, we found that SREBF1 promotes cellular lipid synthesis, which is essential for PEDV replication. Moreover, HNRNPA3 negatively regulates SREBF1 activation and specifically reduces lipid accumulation, ultimately inhibiting PEDV dsRNA synthesis. Our study provides new insight into the mechanisms by which PEDV hijacks cell lipid metabolism to benefit viral replication, which can offer a potential target for therapeutics against PEDV infection.

Quantitative proteomics based on TMT revealed the response of PK15 cells infected PEDV wild strain

Porcine epidemic diarrhea (PED), caused by porcine epidemic diarrhea virus (PEDV), is an acute and highly contagious enteric disease with a high mortality rate in suckling piglets. Identification of proteins associated with PEDV infection may provide insights into the pathogenesis of this viral disease. In this study, we employed tandem mass tag (TMT) quantitative protein analysis to investigate proteomic changes in PK15 cells following PEDV infection, and differential protein expression profiles were obtained at 0 h, 24 h, and 48 h post-infection. Overall, a total of 6330 proteins were identified. Applying criteria for fold change >1.5 < 0.67 and p-values <0.05 resulted in the identification of 59 up-regulated proteins and 103 down-regulated proteins that exhibited significant alterations in the H24 group compared to the H0 group. The H48 group demonstrated significant upregulation of 110 proteins and downregulation of 144 proteins compared to the H0 group; additionally, there were also 10 upregulated and 30 downregulated proteins in the H48 group when compared to the H24 group. These differentially expressed proteins (DEPs) were involved in immune response regulation, signal transduction, lipid transport and metabolism processes as well as cell apoptosis pathways. Based on these DEPs, we propose that PEDV may disrupt signal transduction pathways along with lipid transport and metabolism processes leading to maximal viral replication, it may also trigger inflammatory cascades accordingly. These findings could provide valuable information for elucidating specific pathogenesis related to PEDV infection while contributing towards developing new antiviral strategies.

AEN Suppresses the Replication of Porcine Epidemic Diarrhea Virus by Inducing the Expression of Type I IFN and ISGs in MARC-145 Cells

Apoptosis-enhancing nuclease (AEN), which shares close evolutionary relationships with the interferon-stimulated gene 20 protein (ISG20) homologs in humans, is a member of the DEDDh exonuclease family. Numerous studies on various pathogens have identified the essential roles of ISG20 in inhibiting virus replication. However, the fundamental functions of AEN during viral infection remain largely unknown. This study discovered that AEN expression was significantly upregulated in MARC-145 cells infected with Porcine epidemic diarrhea virus (PEDV) strain 85-7. In contrast, the amount of AEN protein decreased as viral replication increased. It was found that PEDV nsp1 and nsp5 mediated the decrease in AEN production, suggesting that an increase in AEN was not conducive to virus replication. By comparing AEN and its exonuclease-inactive mutant AEN-4A, we determined that the antiviral activity of AEN was independent of its exonuclease function. qPCR analyses revealed that AEN and AEN-4A could induce a significant increase in the transcription levels of IFN-α, IFN-β, and ISGs (OASL, IFI44, IFIT2, ISG15, Mx1, Mx2), and that AEN-4A has a higher induction ability. Overexpression of AEN and AEN-4A in MARC-145 cells targeting IFN-β knockdown or IFN-deficient Vero cells showed reduced or a complete loss of antiviral activity of both, suggesting that AEN may activate the type I IFN immune response and promote the expression of ISGs, thereby inhibiting PEDV replication. Taken together, our data prove the novel mechanism of AEN-mediated virus restriction.

Clinical, Pathological and Virological Outcomes of Tissue-Homogenate-Derived and Cell-Adapted Strains of Porcine Epidemic Diarrhea Virus (PEDV) in a Neonatal Pig Model

Porcine epidemic diarrhea virus (PEDV) is characterized by diarrhea, vomiting, dehydration, and high mortality rates in neonatal piglets. Two distinct genogroups, S-INDEL (G1a, G1b) and non-S INDEL (G2a, G2b, and G2c), circulate worldwide and are characterized by varying degrees of virulence. Here, we compared the early pathogenesis of a PEDV S-INDEL strain obtained from intestine homogenate (CALAF-HOMOG) or adapted to cell culture by 22 passages (CALAF-ADAP) and a virulent non-S INDEL strain (PEDV-USA) in newborn piglets. After orogastric inoculation of PEDV strains, body weight, temperature and clinical signs were monitored for 48 hpi. Pathological studies were performed at 48 hpi and RNA extracts from jejunal content (at 48 hpi) and rectal swabs (at 0 and 48 hpi) were tested for the presence of PEDV RNA as well as sequenced and compared to the inoculum. Piglets inoculated with PEDV-USA and CALAF-HOMOG isolates showed more severe weight loss, diarrhea, villi fusion and atrophy compared to CALAF-ADAP inoculated piglets. The viral load of rectal swabs was higher in the PEDV-USA inoculated group, followed by CALAF-HOMOG and CALAF-ADAP isolates. Similarly, viral RNA load in jejunal content was comparable among PEDV-USA and CALAF-HOMOG inoculated piglets and higher than that of CALAF-ADAP ones. The comparison of three full PEDV sequences of the inocula with the corresponding ones of pigs after 48 hpi yielded a nucleotide identity >99.9%. This study highlights variations in virulence among S-INDEL and non-S INDEL strains and between S-INDEL isolates obtained from homogenate and cell culture.

Water Extract of Portulaca Oleracea Inhibits PEDV Infection-Induced Pyrolysis by Caspase-1/GSDMD

Porcine epidemic diarrhea virus (PEDV) belongs to the coronavirus family and the coronavirus genus, causing contact enteric infection in pigs. It is one of the most serious diseases that threatens the pig industry. However, there is currently no specific drug to prevent and treat the disease, indicating that we need to be vigilant about the spread of the disease and the development of anti-PEDV drugs. The dried aerial parts of the plant Portulaca oleracea in the family Portulacaceous, whose decoction can be used to treat acute enteritis, dysentery, diarrhea, and other diseases. This study explored the potential mechanism of water extract of Portulaca oleracea (WEPO) in PEDV-induced pyroptosis in Vero cells. PEDV decreased the viability of Vero cells in a dose- and time-dependent manner, causing cell damage, upregulating the level of intracellular Nlrp3, and inhibiting the level of Gasdermin D (GSDMD) and the activation of Caspase-1. WEPO can inhibit PEDV-induced pyroptosis, reduce the elevation of inflammatory factors caused by infection, and exhibit a dose-dependent effect. Knockdown of Caspase-1 and GSDMD separately can induce the production of the inflammatory factor IL-1β to significantly decrease and increase, respectively. These results suggest that WEPO can inhibit cell pyroptosis caused by PEDV and that the Caspase-1 and GSDMD pathways play an important role in this process.

Spike Gene Analysis and Prevalence of Porcine Epidemic Diarrhea Virus from Pigs in South Korea: 2013-2022

From late 2013-2022, 1131 cases of porcine epidemic diarrhea (PED) were reported to the Korean Animal Health Integrated System (KAHIS). There were four major outbreaks from winter to spring (2013-2014, 2017-2018, 2018-2019, and 2021-2022), with the main outbreaks occurring in Chungnam (CN), Jeonbuk (JB), and Jeju (JJ). Analysis of the complete spike (S) gene of 140/1131 KAHIS PEDV cases nationwide confirmed that 139 belonged to the G2b genotype and 1 to the G2a genotype. Among them, two strains (K17GG1 and K17GB3) were similar to an S INDEL isolated in the United States (strain OH851), and 12 strains had deletions (nucleotides (nt) 3-99) or insertions (12 nt) within the S gene. PEDVs in JJ formed a regionally independent cluster. The substitution rates (substitutions/site/year) were as follows: 1.5952 × 10-3 in CN, 1.8065 × 10-3 in JB, and 1.5113 × 10-3 in JJ. A Bayesian skyline plot showed that the effective population size of PEDs in JJ fell from 2013-2022, whereas in CN and JB it was maintained. Genotyping of 340 Korean PEDV strains, including the 140 PEDVs in this study and 200 Korean reference strains from GenBank, revealed that only the highly pathogenic non-INDEL type (G2b) was dominant from 2020 onwards. Therefore, it is predicted that the incidence of PED will be maintained by the G2b (non-INDEL) genotype.

Multiple Porcine Innate Immune Signaling Pathways Are Involved in the Anti-PEDV Response

Porcine epidemic diarrhea virus (PEDV) has caused great damage to the global pig industry. Innate immunity plays a significant role in resisting viral infection; however, the exact role of innate immunity in the anti-PEDV response has not been fully elucidated. In this study, we observed that various porcine innate immune signaling adaptors are involved in anti-PEDV (AJ1102-like strain) activity in transfected Vero cells. Among these, TRIF and MAVS showed the strongest anti-PEDV activity. The endogenous TRIF, MAVS, and STING were selected for further examination of anti-PEDV activity. Agonist stimulation experiments showed that TRIF, MAVS, and STING signaling all have obvious anti-PEDV activity. The siRNA knockdown assay showed that TRIF, MAVS, and STING are also all involved in anti-PEDV response, and their remarkable effects on PEDV replication were confirmed in TRIF-/-, MAVS-/- and STING-/- Vero cells via the CRISPR approach. For further verification, the anti-PEDV activity of TRIF, MAVS, and STING could be reproduced in porcine IPEC-DQ cells treated with siRNAs. In summary, this study reveals that multiple pattern-recognition receptor (PRR) signaling pathways of porcine innate immunity play an important role in the anti-PEDV infection, providing new and useful antiviral knowledge for prevention and control of PEDV spreading.

Transcriptome Profiling of Vero E6 Cells during Original Parental or Cell-Attenuated Porcine Epidemic Diarrhea Virus Infection

Porcine epidemic diarrhea virus (PEDV) has led to significant economic losses in the global porcine industry since the emergence of variant strains in 2010. The high mutability of coronaviruses endows PEDV with the ability to evade the host immune response, which impairs the effectiveness of vaccines. In our previous study, we generated a highly cell-passaged PEDV strain, CT-P120, which showed promise as a live attenuated vaccine candidate by providing satisfactory protection against variant PEDV infection in piglets. However, the mechanism by which the attenuated CT-P120 adapts to cells during passage, resulting in increased replication efficiency, remains unclear. To address this question, we conducted a comparative transcriptomic analysis of Vero E6 cells infected with either the original parental strain (CT-P10) or the cell-attenuated strain (CT-P120) of PEDV at 6, 12, and 24 h post-infection. Compared to CT-P10, CT-P120 infection resulted in a significant decrease in the number of differentially expressed genes (DEGs) at each time point. Functional enrichment analysis of genes revealed the activation of various innate immune-related pathways by CT-P10, notably attenuated during CT-P120 infection. To validate these results, we selected eight genes (TRAF3, IRF3, IFNL1, ISG15, NFKB1, MAP2K3, IL1A, and CCL2) involved in antiviral processes and confirmed their mRNA expression patterns using RT-qPCR, in line with the transcriptomic data. Subsequent protein-level analysis of selected genes via Western blotting and enzyme-linked immunosorbent assay corroborated these results, reinforcing the robustness of our findings. Collectively, our research elucidates the strategies underpinning PEDV attenuation and immune evasion, providing invaluable insights for the development of effective PEDV vaccines.

Coronavirus accessory protein ORF3 biology and its contribution to viral behavior and pathogenesis

Coronavirus porcine epidemic diarrhea virus (PEDV) is classified in the genus Alphacoronavirus, family Coronaviridae that encodes the only accessory protein, ORF3 protein. However, how ORF3 contributes to viral pathogenicity, adaptability, and replication is obscure. In this review, we summarize current knowledge and identify gaps in many aspects of ORF3 protein in PEDV, with emphasis on its unique biological features, including membrane topology, Golgi retention mechanism, potential intrinsic disordered property, functional motifs, protein glycosylation, and codon usage phenotypes related to genetic evolution and gene expression. In addition, we propose intriguing questions related to ORF3 protein that we hope to stimulate further studies and encourage collaboration among virologists worldwide to provide constructive knowledge about the unique characteristics and biological functions of ORF3 protein, by which their potential role in clarifying viral behavior and pathogenesis can be possible.

Porcine Epidemic Diarrhea Virus Antagonizes Host IFN-λ-Mediated Responses by Tilting Transcription Factor STAT1 toward Acetylation over Phosphorylation To Block Its Activation

Porcine epidemic diarrhea virus (PEDV) is the main etiologic agent causing acute swine epidemic diarrhea, leading to severe economic losses to the pig industry. PEDV has evolved to deploy complicated antagonistic strategies to escape from host antiviral innate immunity. Our previous study demonstrated that PEDV downregulates histone deacetylase 1 (HDAC1) expression by binding viral nucleocapsid (N) protein to the transcription factor Sp1, inducing enhanced protein acetylation. We hypothesized that PEDV inhibition of HDAC1 expression would enhance acetylation of the molecules critical in innate immune signaling. Signal transducer and activator of transcription 1 (STAT1) is a crucial transcription factor regulating expression of interferon (IFN)-stimulated genes (ISGs) and anti-PEDV immune responses, as shown by overexpression, chemical inhibition, and gene knockdown in IPEC-J2 cells. We further show that PEDV infection and its N protein overexpression, although they upregulated STAT1 transcription level, could significantly block poly(I·C) and IFN-λ3-induced STAT1 phosphorylation and nuclear localization. Western blotting revealed that PEDV and its N protein promote STAT1 acetylation via downregulation of HDAC1. Enhanced STAT1 acetylation due to HDAC1 inhibition by PEDV or MS-275 (an HDAC1 inhibitor) impaired STAT1 phosphorylation, indicating that STAT1 acetylation negatively regulated its activation. These results, together with our recent report on PEDV N-mediated inhibition of Sp1, clearly indicate that PEDV manipulates the Sp1-HDAC1-STAT1 signaling axis to inhibit transcription of OAS1 and ISG15 in favor of its replication. This novel immune evasion mechanism is realized by suppression of STAT1 activation through preferential modulation of STAT1 acetylation over phosphorylation as a result of HDAC1 expression inhibition. IMPORTANCE PEDV has developed sophisticated evasion mechanisms to escape host IFN signaling via its structural and nonstructural proteins. STAT1 is one of the key transcription factors in regulating expression of ISGs. We found that PEDV and its N protein inhibit STAT1 phosphorylation and nuclear localization via inducing STAT1 acetylation as a result of HDAC1 downregulation, which, in turn, dampens the host IFN signaling activation. Our study demonstrates a novel mechanism that PEDV evades host antiviral innate immunity through manipulating the reciprocal relationship of STAT1 acetylation and phosphorylation. This provides new insights into the pathogenetic mechanisms of PEDV and even other coronaviruses.

Identification of Cell Types and Transcriptome Landscapes of Porcine Epidemic Diarrhea Virus-Infected Porcine Small Intestine Using Single-Cell RNA Sequencing

Swine coronavirus-porcine epidemic diarrhea virus (PEDV) with specific susceptibility to pigs has existed for decades, and recurrent epidemics caused by mutant strains have swept the world again since 2010. In this study, single-cell RNA sequencing was used to perform for the first time, to our knowledge, a systematic analysis of pig jejunum infected with PEDV. Pig intestinal cell types were identified by representative markers and identified a new tuft cell marker, DNAH11. Excepting enterocyte cells, the goblet and tuft cells confirmed susceptibility to PEDV. Enrichment analyses showed that PEDV infection resulted in upregulation of cell apoptosis, junctions, and the MAPK signaling pathway and downregulation of oxidative phosphorylation in intestinal epithelial cell types. The T cell differentiation and IgA production were decreased in T and B cells, respectively. Cytokine gene analyses revealed that PEDV infection downregulated CXCL8, CXCL16, and IL34 in tuft cells and upregulated IL22 in Th17 cells. Further studies found that infection of goblet cells with PEDV decreased the expression of MUC2, as well as other mucin components. Moreover, the antimicrobial peptide REG3G was obviously upregulated through the IL33-STAT3 signaling pathway in enterocyte cells in the PEDV-infected group, and REG3G inhibited the PEDV replication. Finally, enterocyte cells expressed almost all coronavirus entry factors, and PEDV infection caused significant upregulation of the coronavirus receptor ACE2 in enterocyte cells. In summary, this study systematically investigated the responses of different cell types in the jejunum of piglets after PEDV infection, which deepened the understanding of viral pathogenesis.

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.

Multifaceted Effects and Mechanisms of N-Acetylcysteine on Intestinal Injury in a Porcine Epidemic Diarrhea Virus-Infected Porcine Model

SCOPE

This study investigates the potential effects of N-acetylcysteine (NAC) on intestinal injury in a porcine epidemic diarrhea virus (PEDV)-infected porcine model.

METHODS AND RESULTS

Thirty-two piglets are randomly assigned to one of four groups: the control, PEDV, NAC, and NAC+PEDV. Piglets in the NAC+PEDV group are orally administrated with NAC (100 mg (kg·BW)^-1  day^-1 ) for 4 consecutive days after 2 days of PEDV infection. The results show that NAC administration decreases the diarrhea rate and improves intestinal morphology. The concentration of diamine oxidase and intestinal fatty-acid binding protein, as well as IL-1β, IL-8, and TNF-α in the plasma, is decreased by NAC. Intriguingly, NAC administration significantly increases the viral load in the jejunum and ileum and down-regulates the expression of interferon-related genes. Microarray and proteomic analyses show that the differentially expressed genes/proteins between NAC+PEDV and PEDV groups are highly enriched in substance transport. Furthermore, aquaporin 8/10 expression is significantly increased by NAC upon PEDV infection.

CONCLUSION

NAC administration alleviates PEDV-induced intestinal injury by inhibiting inflammatory responses and improving substance transport, but promotes viral replication by inhibiting interferon signaling. These results suggest NAC exhibits multifaceted effects upon PEDV infection, and thus caution is required when using NAC as a dietary supplement to prevent viral infection.

Nonstructural Protein 1 of Variant PEDV Plays a Key Role in Escaping Replication Restriction by Complement C3

Zoonotic coronaviruses represent an ongoing threat to public health. The classical porcine epidemic diarrhea virus (PEDV) first appeared in the early 1970s. Since 2010, outbreaks of highly virulent PEDV variants have caused great economic losses to the swine industry worldwide. However, the strategies by which PEDV variants escape host immune responses are not fully understood. Complement component 3 (C3) is considered a central component of the three complement activation pathways and plays a crucial role in preventing viral infection. In this study, we found that C3 significantly inhibited PEDV replication in vitro, and both variant and classical PEDV strains induced high levels of interleukin-1β (IL-1β) in Huh7 cells. However, the PEDV variant strain reduces C3 transcript and protein levels induced by IL-1β compared with the PEDV classical strain. Examination of key molecules of the C3 transcriptional signaling pathway revealed that variant PEDV reduced C3 by inhibiting CCAAT/enhancer-binding protein β (C/EBP-β) phosphorylation. Mechanistically, PEDV nonstructural protein 1 (NSP1) inhibited C/EBP-β phosphorylation via amino acid residue 50. Finally, we constructed recombinant PEDVs to verify the critical role of amino acid 50 of NSP1 in the regulation of C3 expression. In summary, we identified a novel antiviral role of C3 in inhibiting PEDV replication and the viral immune evasion strategies of PEDV variants. Our study reveals new information on PEDV-host interactions and furthers our understanding of the pathogenic mechanism of this virus. IMPORTANCE The complement system acts as a vital link between the innate and the adaptive immunity and has the ability to recognize and neutralize various pathogens. Activation of the complement system acts as a double-edged sword, as appropriate levels of activation protect against pathogenic infections, but excessive responses can provoke a dramatic inflammatory response and cause tissue damage, leading to pathological processes, which often appear in COVID-19 patients. However, how PEDV, as the most severe coronavirus causing diarrhea in piglets, regulates the complement system has not been previously reported. In this study, for the first time, we identified a novel mechanism of a PEDV variant in the suppression of C3 expression, showing that different coronaviruses and even different subtype strains differ in regulation of C3 expression. In addition, this study provides a deeper understanding of the mechanism of the PEDV variant in immune escape and enhanced virulence.

Differential expression analysis of mRNAs, lncRNAs, and miRNAs expression profiles and construction of ceRNA networks in PEDV infection

BACKGROUND

Porcine Epidemic Diarrhea Virus (PEDV) is a coronavirus that seriously affects the swine industry. MicroRNAs and long noncoding RNAs are two relevant non-coding RNAs (ncRNAs) class and play crucial roles in a variety of physiological processes. Increased evidence indicates a complex interaction between mRNA and ncRNA. However, our understanding of the function of ncRNA involved in host-PEDV interaction is limited.

RESULTS

A total of 1,197 mRNA transcripts, 539 lncRNA transcripts, and 208 miRNA transcripts were differentially regulated at 24 h and 48 h post-infection. Gene ontology (GO) and KEGG pathway enrichment analysis showed that DE mRNAs and DE lncRNAs were mainly involved in biosynthesis, innate immunity, and lipid metabolism. Moreover, we constructed a miRNA-mRNA-pathway network using bioinformatics, including 12 DE mRNAs, 120 DE miRNAs, and 11 pathways. Finally, the target genes of DE miRNAs were screened by bioinformatics, and we constructed immune-related lncRNA-miRNA-mRNA ceRNA networks. Then, the selected DE genes were validated by qRT-PCR, which were consistent with the results from RNA-Seq data.

CONCLUSIONS

This study provides the comprehensive analysis of the expression profiles of mRNAs, lncRNAs, and miRNAs during PEDV infection. We characterize the ceRNA networks which can provide new insights into the pathogenesis of PEDV.

Porcine epidemic diarrhea virus strain FJzz1 infection induces type I/III IFNs production through RLRs and TLRs-mediated signaling

Interferons (IFNs) including type I/III IFNs are the major components of the host innate immune response against porcine epidemic diarrhea virus (PEDV) infection, and several viral proteins have been identified to antagonize type I/III IFNs productions through diverse strategies. However, the modulation of PEDV infection upon the activation of the host’s innate immune response has not been fully characterized. In this study, we observed that various IFN-stimulated genes (ISGs) were upregulated significantly in a time- and dose-dependent manner in LLC-PK1 cells infected with the PEDV G2 strain FJzz1. The transcriptions of IRF9 and STAT1 were increased markedly in the late stage of FJzz1 infection and the promotion of the phosphorylation and nuclear translocation of STAT1, implicating the activation of the JAK-STAT signaling pathway during FJzz1 infection. In addition, abundant type I/III IFNs were produced after FJzz1 infection. However, type I/III IFNs and ISGs decreased greatly in FJzz1-infected LLC-PK1 cells following the silencing of the RIG-I-like receptors (RLRs), including RIG-I and MDA5, and the Toll-like receptors (TLRs) adaptors, MyD88 and TRIF. Altogether, FJzz1 infection induces the production of type-I/III IFNs in LLC-PK1 cells, in which RLRs and TLRs signaling pathways are involved, followed by the activation of the JAK-STAT signaling cascade, triggering the production of numerous ISGs to exert antiviral effects of innate immunity.

Mechanisms of host type I interferon response modulation by the nucleocapsid proteins of alpha- and betacoronaviruses

Coronaviruses can have a devastating impact on the health of humans and animals. Porcine epidemic diarrhea virus (PEDV) causes extremely high fatality rates in neonatal piglets, whereas severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the current COVID-19 pandemic in humans. As a critical component of the host antiviral innate immune response, type I interferon production and signaling play a very important role, especially in the initial phase of the antiviral responses. Coronaviruses have evolved multiple ways to counteract type I interferon responses. Although the primary functions of the nucleocapsid protein are to facilitate viral RNA replication and package viral genomic RNA into virions, recent studies have shown that the nucleocapsid protein is also involved in virus-host interactions. The aim of this review is to summarize our current understanding of how the nucleocapsid proteins of PEDV and SARS-CoV-2 modulate type I interferon responses. This knowledge will be useful for developing strategies to combat coronavirus infections.

FUBP3 Degrades the Porcine Epidemic Diarrhea Virus Nucleocapsid Protein and Induces the Production of Type I Interferon

Porcine epidemic diarrhea virus (PEDV) is the globally distributed alphacoronavirus that can cause lethal watery diarrhea in piglets, causing substantial economic damage. However, the current commercial vaccines cannot effectively the existing diseases. Thus, it is of great necessity to identify the host antiviral factors and the mechanism by which the host immune system responds against PEDV infection required to be explored. The current work demonstrated that the host protein, the far upstream element-binding protein 3 (FUBP3), could be controlled by the transcription factor TCFL5, which could suppress PEDV replication through targeting and degrading the nucleocapsid (N) protein of the virus based on selective autophagy. For the ubiquitination of the N protein, FUBP3 was found to recruit the E3 ubiquitin ligase MARCH8/MARCHF8, which was then identified, transported to, and degraded in autolysosomes via NDP52/CALCOCO2 (cargo receptors), resulting in impaired viral proliferation. Additionally, FUBP3 was found to positively regulate type-I interferon (IFN-I) signaling and activate the IFN-I signaling pathway by interacting and increasing the expression of tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3). Collectively, this study showed a novel mechanism of FUBP3-mediated virus restriction, where FUBP3 was found to degrade the viral N protein and induce IFN-I production, aiming to hinder the replication of PEDV.

IMPORTANCE PEDV refers to the alphacoronavirus that is found globally and has re-emerged recently, causing severe financial losses. In PEDV infection, the host activates various host restriction factors to maintain innate antiviral responses to suppress virus replication. Here, FUBP3 was detected as a new host restriction factor. FUBP3 was found to suppress PEDV replication via the degradation of the PEDV-encoded nucleocapsid (N) protein via E3 ubiquitin ligase MARCH8 as well as the cargo receptor NDP52/CALCOCO2. Additionally, FUBP3 upregulated the IFN-I signaling pathway by interacting with and increasing tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3) expression. This study further demonstrated that another layer of complexity could be added to the selective autophagy and innate immune response against PEDV infection are complicated.

Study of the effect of intestinal immunity in neonatal piglets coinfected with porcine deltacoronavirus and porcine epidemic diarrhea virus

Porcine deltacoronavirus (PDCoV) and porcine epidemic diarrhea virus (PEDV) have often been detected simultaneously in piglets with coronavirus diarrhea. However, the intestinal immune response to the interaction between circulating PDCoV and PEDV is unknown. Therefore, this study was conducted to investigate the intestinal immunity of neonatal piglets that were exposed first to PDCoV and then to PEDV. The amounts and distribution of CD3⁺ T lymphocytes, B lymphocytes, and goblet cells (GCs) in the small intestine were analyzed by immunohistochemistry and periodic acid–Schiff staining, respectively. The expression levels of pattern recognition receptors and downstream mediator cytokines were analyzed by qPCR and ELISA. The results showed that the numbers of GCs, CD3⁺ T lymphocytes, and B lymphocytes in the duodenum and jejunum of the PDCoV + PEDV coinoculated piglets were increased compared with those of piglets inoculated with PEDV alone. The piglets in the PDCoV + PEDV group had significantly upregulated IFN-α and IFN-λ₁ compared with the PEDV single-inoculated piglets. These results suggest that PDCoV + PEDV-coinfected piglets can activate intestinal antiviral immunity more strongly than piglets infected with PEDV alone, which provides new insight into the pathogenesis mechanism of swine enteric coronavirus coinfection that may be used for vaccination in the future.

Porcine Epidemic Diarrhea Virus nsp7 Inhibits Interferon-Induced JAK-STAT Signaling through Sequestering the Interaction between KPNA1 and STAT1

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus that causes high mortality in piglets. Interferon (IFN) responses are the primary defense mechanism against viral infection; however, viruses always evolve elaborate strategies to antagonize the antiviral action of IFN. Previous study showed that PEDV nonstructural protein 7 (nsp7), a component of the viral replicase polyprotein, can antagonize ploy(I:C)-induced type I IFN production. Here, we found that PEDV nsp7 also antagonized IFN-α-induced JAK-STAT signaling and the production of IFN-stimulated genes. PEDV nsp7 did not affect the protein and phosphorylation levels of JAK1, Tyk2, STAT1, and STAT2 or the formation of the interferon-stimulated gene factor 3 (ISGF3) complex. However, PEDV nsp7 prevented the nuclear translocation of STAT1 and STAT2. Mechanistically, PEDV nsp7 interacted with the DNA binding domain of STAT1/STAT2, which sequestered the interaction between karyopherin α1 (KPNA1) and STAT1, thereby blocking the nuclear transport of ISGF3. Collectively, these data reveal a new mechanism developed by PEDV to inhibit type I IFN signaling pathway. IMPORTANCE In recent years, an emerging porcine epidemic diarrhea virus (PEDV) variant has gained attention because of serious outbreaks of piglet diarrhea in China and the United States. Coronavirus nonstructural protein 7 (nsp7) has been proposed to act with nsp8 as part of an RNA primase to generate RNA primers for viral RNA synthesis. However, accumulating evidence indicates that coronavirus nsp7 can also antagonize type I IFN production. Our present study extends previous findings and demonstrates that PEDV nsp7 also antagonizes IFN-α-induced IFN signaling by competing with KPNA1 for binding to STAT1, thereby enriching the immune regulation function of coronavirus nsp7.

Long-Term Expansion of Porcine Intestinal Organoids Serves as an in vitro Model for Swine Enteric Coronavirus Infection

A reliable and reproducible model in vitro for swine enteric coronaviruses infection would be intestinal models that support virus replication and can be long-term cultured and manipulated experimentally. Here, we designed a robust long-term culture system for porcine intestinal organoids from the intestinal crypt or single LGR5⁺ stem cell by combining previously defined insights into the growth requirements of the intestinal epithelium of humans. We showed that long-term cultured swine intestinal organoids were expanded in vitro for more than 6 months and maintained the potential to differentiate into different types of cells. These organoids were successfully infected with porcine enteric coronavirus, including porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV), and were capable of supporting virus replication and progeny release. RNA-seq analysis showed robust induction of transcripts associated with antiviral signaling in response to enteric coronavirus infection, including hundreds of interferon-stimulated genes and cytokines. Moreover, gene set enrichment analysis indicated that PEDV infection could suppress the immune response in organoids. This 3D intestinal organoid model offers a long-term, renewable resource for investigating porcine intestinal infections with various pathogens.

The Interplay Between Coronavirus and Type I IFN Response

In the past few decades, newly evolved coronaviruses have posed a global threat to public health and animal breeding. To control and prevent the coronavirus-related diseases, understanding the interaction of the coronavirus and the host immune system is the top priority. Coronaviruses have evolved multiple mechanisms to evade or antagonize the host immune response to ensure their replication. As the first line and main component of innate immune response, type I IFN response is able to restrict virus in the initial infection stage; it is thus not surprising that the primary aim of the virus is to evade or antagonize the IFN response. Gaining a profound understanding of the interaction between coronaviruses and type I IFN response will shed light on vaccine development and therapeutics. In this review, we provide an update on the current knowledge on strategies employed by coronaviruses to evade type I IFN response.

Predicted 3D model of the M protein of Porcine Epidemic Diarrhea Virus and analysis of its immunogenic potential

The membrane protein M of the Porcine Epidemic Diarrhea Virus (PEDV) is the most abundant component of the viral envelope. The M protein plays a central role in the morphogenesis and assembly of the virus through protein interactions of the M-M, M-Spike (S) and M-nucleocapsid (N) type. The M protein is known to induce protective antibodies in pigs and to participate in the antagonistic response of the cellular antiviral system coordinated by the type I and type III interferon pathways. The 3D structure of the PEDV M protein is still unknown. The present work exposes a predicted 3D model of the M protein generated using the Robetta protocol. The M protein model is organized into a transmembrane and a globular region. The obtained 3D model of the PEDV M protein was compared with 3D models of the SARS-CoV-2 M protein created using neural networks and with initial machine learning-based models created using trRosetta. The 3D model of the present study predicted four linear B-cell epitopes (RSVNASSGTG and KHGDYSAVSNPSALT peptides are noteworthy), six discontinuous B-cell epitopes, forty weak binding and fourteen strong binding T-cell epitopes in the CV777 M protein. A high degree of conservation of the epitopes predicted in the PEDV M protein was observed among different PEDV strains isolated in different countries. The data suggest that the M protein could be a potential candidate for the development of new treatments or strategies that activate protective cellular mechanisms against viral diseases.

Genome-wide transcriptome analysis of porcine epidemic diarrhea virus virulent or avirulent strain-infected porcine small intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) is the main cause of diarrhea, vomiting, and mortality in pigs, which results in devastating economic loss to the pig industry around the globe. In recent years, the advent of RNA-sequencing technologies has led to delineate host responses at late stages of PEDV infection; however, the comparative analysis of host responses to early-stage infection of virulent and avirulent PEDV strains is currently unknown. Here, using the BGI DNBSEQ RNA-sequencing, we performed global gene expression profiles of pig intestinal epithelial cells infected with virulent (GDS01) or avirulent (HX) PEDV strains for 3, 6, and 12 ​h. It was observed that over half of all significantly dysregulated genes in both infection groups exhibited a down-regulated expression pattern. Functional enrichment analyses indicated that the differentially expressed genes (DEGs) in the GDS01 group were predominantly related to autophagy and apoptosis, whereas the genes showing the differential expression in the HX group were strongly enriched in immune responses/inflammation. Among the DEGs, the functional association of TLR3 and IFIT2 genes with the HX and GDS01 strains replication was experimentally validated by TLR3 inhibition and IFIT2 overexpression systems in cultured cells. TLR3 expression was found to inhibit HX strain, but not GDS01 strain, replication by enhancing the IFIT2 expression in infected cells. In conclusion, our study highlights similarities and differences in gene expression patterns and cellular processes/pathways altered at the early-stage infection of PEDV virulent and avirulent strains. These findings may provide a foundation for establishing novel therapies to control PEDV infection.

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Differentially expressed genes (DEGs) in the GDS01 group were predominantly related to autophagy and apoptosis.

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DEGs in the HX group were strongly enriched in immune responses/inflammation.

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TLR3 inhibits HX strain replication, but not GDS01 strain, by enhancing the IFIT2 expression.

An exploratory review of Potential Adjunct Therapies for the Treatment of Coronavirus Infections

Objective

The purpose of this exploratory review c, including vitamin D, zinc, vitamin A, elderberry (S nigra), garlic (A sativum), licorice (G glabra), stinging nettle (U dioica), N-acetylcysteine, quercetin and selenium as potential adjunct therapies for the treatment of coronavirus infections.

Methods

A search of PubMed was performed for articles published from 2005 to 2021. Key words searched were zinc, vitamin A, vitamin D, Sambucus nigra, Allium sativum, Glycyrrhiza glabra, Urtica dioica, N-Acetylcysteine, quercetin, selenium and coronavirus.

Results

There were 47 articles selected for this review. Findings included that vitamin D, zinc, vitamin A, S nigra, A sativum, G glabra, U dioica, N-acetylcysteine, quercetin and selenium have been shown to produce anti-inflammatory, immunostimulatory or antiviral effects that may enhance the actions of standard therapeutics for the treatment of CoV infections. We found only research articles related to the effects of vitamin D, zinc, G glabra, quercetin and selenium against COVID-19.

Conclusion

We identified non-pharmaceutical supplements (Vitamin D, zinc, vitamin A, S nigra, A sativum, G glabra and U dioica) which may have potential to provide support for those with coronavirus infections. However, rigorous clinical studies need to be performed before any clinical recommendations can be made at this time.

Porcine Epidemic Diarrhea Virus Envelope Protein Blocks SLA-DR Expression in Barrow-Derived Dendritic Cells by Inhibiting Promoters Activation

Porcine epidemic diarrhea (PED) is an acute, highly contagious intestinal swine disease caused by porcine epidemic diarrhea virus (PEDV). In addition to known PEDV infection targets (villous small intestinal epithelial cells), recent reports suggest that dendritic cells (DCs) may also be targeted by PEDV in vivo. Thus, in this study we used bone marrow-derived dendritic cells (BM-DCs) as an in vitro model of antigen-presenting cells (APCs). Our results revealed that PEDV replicated in BM-DCs and that PEDV infection of cells inhibited expression of swine leukocyte antigen II DR (SLA-DR), a key MHC-II molecule involved in antigen presentation and initiation of CD4⁺ T cell activation. Notably, SLA-DR inhibition in BM-DCs did not require PEDV replication, suggesting that PEDV structural proteins participated in SLA-DR transcriptional inhibition. Moreover, reporter assay-based screening indicated that PEDV envelope protein blocked activation of SLA-DRα and β promoters, as did PEDV-ORF3 protein when present during PEDV replication. Meanwhile, treatment of PEDV-infected BM-DCs with MG132, a ubiquitin-proteasome degradation pathway inhibitor, did not restore SLA-DR protein levels. Additionally, PEDV infection of BM-DCs did not alter SLA-DR ubiquitination status, suggesting that PEDV infection did not affect SLA-DR degradation. Furthermore, additions of PEDV structural proteins to HEK-293T-SLA-DR stably transfected cells had no effect on SLA-DR protein levels, indicating that PEDV-mediated inhibition of SLA-DR expression acted mainly at the transcriptional level, not at the protein level. These results provide novel insights into PEDV pathogenic mechanisms and viral-host interactions.

Changes in the spike and nucleocapsid protein of porcine epidemic diarrhea virus strain in Vietnam-a molecular potential for the vaccine development?

Background

Porcine epidemic diarrhea virus (PEDV) is a dangerous virus causing large piglet losses. PEDV spread rapidly between pig farms and caused the death of up to 90% of infected piglets. Current vaccines are only partially effective in providing immunity to suckling due to the rapid dissemination and ongoing evolution of PEDV.

Methods

In this study, the complete genome of a PEDV strain in Vietnam 2018 (IBT/VN/2018 strain) has been sequenced. The nucleotide sequence of each fragment was assembled to build a continuous complete sequence using the DNASTAR program. The complete nucleotide sequences and amino acid sequences of S, N, and ORF3 genes were aligned and analyzed to detect the mutations.

Results

The full-length genome was determined with 28,031 nucleotides in length which consisted of the 5'UTR, ORF1ab, S protein, ORF3, E protein, M protein, N protein, and 3'UTR region. The phylogenetic analysis showed that the IBT/VN/2018 strain was highly virulent belonged to the G2b subgroup along with the Northern American and Asian S-INDEL strains. Multiple sequence alignment of deduced amino acids revealed numerous mutations in the S, N, and ORF3 regions including one substitution ⁷⁶⁶P > L⁷⁶⁶ in the epitope SS6; two in the S⁰subdomain (¹³⁵DN¹³⁶ > ¹³⁵SI¹³⁶ and N¹⁴⁴> D¹⁴⁴); two in subdomain S^HR1 at aa ¹⁰⁰⁹L > M¹⁰⁰⁹ and ¹⁰⁸⁹S > L¹⁰⁸⁹; one at aa ¹²⁷⁹P > S¹²⁷⁹ in subdomain S^HR2 of the S protein; two at aa ³⁶⁴N > I³⁶⁴ and ³⁷⁸N > S³⁷⁸ in the N protein; four at aa ²⁵L > S²⁵, ⁷⁰I > V⁷⁰, ¹⁰⁷C > F¹⁰⁷, and ¹⁶⁸D > N¹⁶⁸ in the ORF3 protein. We identified two insertions (at aa ⁵⁹NQGV⁶² and aa ¹⁴⁵N) and one deletion (at aa ¹⁶⁸DI¹⁶⁹) in S protein. Remarkable, eight amino acid substitutions (²⁹⁴I > M²⁹⁴, ³¹⁸A > S³¹⁸, ³³⁵V > I³³⁵, ³⁶¹A > T³⁶¹, ⁴⁹⁷R > T⁴⁹⁷, ⁵⁰¹SH⁵⁰² > ⁵⁰¹IY⁵⁰², ⁵⁰⁶I > T⁵⁰⁶, ⁶⁸²V > I⁶⁸², and ⁷⁷⁷P > L⁷⁷⁷) were found in S^A subdomain. Besides, N- and O-glycosylation analysis of S, N, and ORF3 protein reveals three known sites (25^G+, 123^N+, and 62^V+) and three novel sites (144^D+, 1009^M+, and 1279^L+) in the IBT/VN/2018 strain compared with the vaccine strains. Taken together, the results showed that mutations in the S, N, and ORF3 genes can affect receptor specificity, viral pathogenicity, and the ability to evade the host immune system of the IBT/VN/2018 strain. Our results highlight the importance of molecular characterization of field strains of PEDV for the development of an effective vaccine to control PEDV infections in Vietnam.

Porcine Epidemic Diarrhea Virus Inhibits HDAC1 Expression To Facilitate Its Replication via Binding of Its Nucleocapsid Protein to Host Transcription Factor Sp1

Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus causing acute intestinal infection in pigs, with high mortality often seen in neonatal pigs. The newborns rely on innate immune responses against invading pathogens because of lacking adaptive immunity. However, how PEDV disables the innate immunity of newborns toward severe infection remains unknown. We found that PEDV infection led to reduced expression of histone deacetylases (HDACs), especially HDAC1, in porcine IPEC-J2 cells. HDACs are considered important regulators of innate immunity. We hypothesized that PEDV interacts with certain host factors to regulate HDAC1 expression in favor of its replication. We show that HDAC1 acted as a negative regulator of PEDV replication in IPEC-J2 cells, as shown by chemical inhibition, gene knockout, and overexpression. A GC-box (GCCCCACCCCC) within the HDAC1 promoter region was identified for Sp1 binding in IPEC-J2 cells. Treatment of the cells with Sp1 inhibitor mithramycin A inhibited HDAC1 expression, indicating direct regulation of HDAC1 expression by Sp1. Of the viral proteins that were overexpressed in IPEC-J2 cells, the N protein was found to be present in the nuclei and more inhibitory to HDAC1 transcription. The putative nuclear localization sequence ²⁶¹PKKNKSR²⁶⁷ contributed to its nuclear localization. The N protein interacted with Sp1 and interfered with its binding to the promoter region, thereby inhibiting its transcriptional activity for HDAC1 expression. Our findings reveal a novel mechanism of PEDV evasion of the host responses, offering implications for studying the infection processes of other coronaviruses. IMPORTANCE The enteric coronavirus porcine epidemic diarrhea virus (PEDV) causes fatal acute intestinal infection in neonatal pigs that rely on innate immune responses. Histone deacetylases (HDACs) play important roles in innate immune regulation. Our study found PEDV suppresses HDAC1 expression via the interaction of its N protein and porcine Sp1, which identified a novel mechanism of PEDV evasion of the host responses to benefit its replication. This study suggests that other coronaviruses, including SARS-CoV and SARS-CoV-2, also make use of their N proteins to intercept the host immune responses in favor of their infection.

Novel Vaccine Technologies in Veterinary Medicine: A Herald to Human Medicine Vaccines

The success of inactivated and live-attenuated vaccines has enhanced livestock productivity, promoted food security, and attenuated the morbidity and mortality of several human, animal, and zoonotic diseases. However, these traditional vaccine technologies are not without fault. The efficacy of inactivated vaccines can be suboptimal with particular pathogens and safety concerns arise with live-attenuated vaccines. Additionally, the rate of emerging infectious diseases continues to increase and with that the need to quickly deploy new vaccines. Unfortunately, first generation vaccines are not conducive to such urgencies. Within the last three decades, veterinary medicine has spearheaded the advancement in novel vaccine development to circumvent several of the flaws associated with classical vaccines. These third generation vaccines, including DNA, RNA and recombinant viral-vector vaccines, induce both humoral and cellular immune response, are economically manufactured, safe to use, and can be utilized to differentiate infected from vaccinated animals. The present article offers a review of commercially available novel vaccine technologies currently utilized in companion animal, food animal, and wildlife disease control.

Dynamic Dissection of the Endocytosis of Porcine Epidemic Diarrhea Coronavirus Cooperatively Mediated by Clathrin and Caveolae as Visualized by Single-Virus Tracking

Coronaviruses (CoVs) have caused severe diseases in humans and animals. Endocytic pathways, such as clathrin-mediated endocytosis (CME) and caveolae-mediated endocytosis (CavME), play an important role for CoVs to penetrate the cell membrane barrier. In this study, a novel CoV entry manner is unraveled in which clathrin and caveolae can cooperatively mediate endocytosis of porcine epidemic diarrhea coronavirus (PEDV). Using multicolor live-cell imaging, the dynamics of the fluorescently labeled clathrin structures, caveolae structures, and PEDV were dissected. During CavME of PEDV, we found that clathrin structures can fuse with caveolae near the cell plasma membrane, and the average time of PEDV penetrating the cell membrane was within ∼3 min, exhibiting a rapid course of PEDV entry. Moreover, based on the dynamic recruitment of clathrin and caveolae structures and viral motility, the direct evidence also shows that about 20% of PEDVs can undergo an abortive entry via CME and CavME. Additionally, the dynamic trafficking of PEDV from clathrin and caveolae structures to early endosomes, and from early endosomes to late endosomes, and viral fusion were directly dissected, and PEDV fusion mainly occurred in late endosomes within ∼6.8 min after the transport of PEDV to late endosomes. Collectively, this work systematically unravels the early steps of PEDV infection, which expands our understanding of the mechanism of CoV infection.IMPORTANCE Emerging and re-emerging coronaviruses cause serious human and animal epidemics worldwide. For many enveloped viruses, including coronavirus, it is evident that breaking the plasma membrane barrier is a pivotal and complex process, which contains multiple dynamic steps. Although great efforts have been made to understand the mechanisms of coronavirus endocytic pathways, the direct real-time imaging of individual porcine epidemic diarrhea coronavirus (PEDV) internalization has not been achieved yet. In this study, we not only dissected the kinetics of PEDV entry via clathrin-mediated endocytosis and caveolae-mediated endocytosis and the kinetics of endosome trafficking and viral fusion but also found a novel productive coronavirus entry manner in which clathrin and caveolae can cooperatively mediate endocytosis of PEDV. Moreover, we uncovered the existence of PEDV abortive endocytosis. In summary, the productive PEDV entry via the cooperation between clathrin and caveolae structures and the abortive endocytosis of PEDV provide new insights into coronavirus penetrating the plasma membrane barrier.

Bacillus Amyloliquefaciens-9 as an Alternative Approach to Cure Diarrhea in Saanen Kids

Bacillus amyloliquefaciens-9 (GBacillus-9), derived from the intestinal tract of the white-spotted bamboo shark, secretes a variety of antimicrobial compounds that inhibit the growth of pathogenic bacteria. In this study, the role of GBacillus-9 in the prevention and treatment of Saanen kids with diarrhea was assessed. Six healthy kids (HL) and six kids with diarrhea (DL) were selected. All kids were fed with 0.3% (w/v) GBacillus-9 (spray power) in raw milk for two weeks. The proportion of kids with diarrhea decreased gradually as the trial progressed, and 100% DL kids were cured at day 15. GBacillus-9 increased the serum immunoglobulin (Ig) G, interleukin (IL)-4, and IL-6 concentration (p < 0.05). The amplicon sequencing analysis of the fecal bacterial community revealed that the fecal microbiota was remarkably different between the HL and the DL groups at day 0. After two weeks of feeding with GBacillus-9, no significant difference in fecal microbiota was observed between HL and DL groups at the phylum level. GBacillus-9 restored the intestinal microbial disorder associated with serum immunoglobulin and interleukin concentration. Correlation analysis showed that GBacillus-9 altered globulin and interleukin concentration and that immunoglobulin was associated with Firmicutes. Collectively, our results revealed that GBacillus-9 improved the gut health of kids by improving microbial homeostasis.

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.