Susceptibility of porcine IPI-2I intestinal epithelial cells to infection with swine enteric coronaviruses

Integrin αVβ3 mediates porcine deltacoronavirus infection and inflammatory response through activation of the FAK-PI3K-AKT-nf-κB signalling pathway

Porcine deltacoronavirus (PDCoV) is an emerging porcine enteropathogenic coronavirus that causes acute watery diarrhoea in piglets, resulting in significant economic losses to the global swine industry. However, the underlying mechanism of PDCoV infection is not well defined, which seriously hinders the development of effective drugs and vaccines. Integrins (ITG) are heterodimeric transmembrane glycoproteins that play important roles in the life cycle of many viruses. In the current study, the viral entry pathways of PDCoV were explored and the role of ITGαVβ3 was investigated during PDCoV infection. Our results showed that the lysosomal acidification inhibitor bafilomycin-A1 (Baf-A1) significantly reduced PDCoV infection, while exogenous protease facilitated PDCoV infection and even allowed PDCoV entry to bypass the endosomal pathway, suggesting PDCoV entry into cells via the endocytic pathway and the exogenous protease-mediated pathway simultaneously. Furthermore, ITGαVβ3 was identified to be involved in PDCoV infection, especially during viral entry stages. PDCoV infection triggers the activation of the focal adhesion kinase (FAK)-phosphatidylinositol 3-kinase (PI3K)-serine/threonine-specific protein kinase (AKT) signalling pathway, and this activation is ITGαVβ3-dependent, suggesting that the activation of the FAK-PI3K-AKT signalling pathway during PDCoV infection is mediated by ITGαVβ3. Our results further demonstrated that PDCoV infection induced the expression of inflammatory cytokines, which was mediated by activation of the ITGαVβ3-FAK-PI3K-AKT-nuclear transcription factor-κB (NF-κB) signalling pathway. Overall, the results revealed that ITGαVβ3 is an essential host factor for PDCoV infection and can serve as a supplementary receptor to facilitate PDCoV infection, which can help us to explore the molecular mechanism of PDCoV infection.

Bat Rhinacoviruses Related to Swine Acute Diarrhoea Syndrome Coronavirus Evolve under Strong Host and Geographic Constraints in China and Vietnam

Swine acute diarrhoea syndrome coronavirus (SADS-CoV; Coronaviridae, Rhinacovirus) was detected in 2017 in Guangdong Province (China), where it caused high mortality rates in piglets. According to previous studies, SADS-CoV evolved from horseshoe bat reservoirs. Here, we report the first five Rhinacovirus genomes sequenced in horseshoe bats from Vietnam and their comparisons with data published in China. Our phylogenetic analyses provided evidence for four groups: rhinacoviruses from Rhinolphus pusillus bats, including one from Vietnam; bat rhinacoviruses from Hainan; bat rhinacoviruses from Yunnan showing a divergent synonymous nucleotide composition; and SADS-CoV and related bat viruses, including four rhinacoviruses from Vietnam sampled in Rhinolophus affinis and Rhinolophus thomasi. Our phylogeographic analyses showed that bat rhinacoviruses from Dien Bien (Vietnam) share more affinities with those from Yunnan (China) and that the ancestor of SADS-CoVs arose in Rhinolophus affinis circulating in Guangdong. We detected sequencing errors and artificial chimeric genomes in published data. The two SADS-CoV genomes previously identified as recombinant could also be problematic. The reliable data currently available, therefore, suggests that all SADS-CoV strains originate from a single bat source and that the virus has been spreading in pig farms in several provinces of China for at least seven years since the first outbreak in August 2016.

An inactivated PDCoV vaccine induces robust neutralizing antibodies and immune protection in pigs lasting for three months

Porcine deltacoronavirus (PDCoV), a novel enteropathogenic coronavirus, causes diarrhea mainly in suckling piglets and has the potential to infect humans. Whereas, there is no commercially available vaccine which can effectively prevent this disease. In this study, to ascertain the duration of immune protection of inactivated PDCoV vaccine, suckling piglets were injected subcutaneously with inactivated PDCoV vaccine using a prime/boost strategy at 3 and 17-day-old. Neutralizing antibody assay showed that the level of the inactivated PDCoV group was still ≥1:64 at three months after prime vaccination. The three-month-old pigs were orally challenged with PDCoV strain CZ2020. Two pigs in challenge control group showed mild to severe diarrhea at 10-11 day-post-challenge (DPC), while the inactivated PDCoV group had no diarrhea. High levels of viral shedding, substantial intestinal villus atrophy, and positive straining of viral antigens in ileum were detected in challenge control group, while the pigs in inactivated PDCoV group exhibited significantly reduced viral load, minor intestinal villi damage and negative straining of viral antigens. These results demonstrated that PDCoV was pathogenic against three-month-old pigs and inactivated PDCoV vaccine can provide effective protection in pigs lasting for three months.

Mapping the scientific output of organoids for animal and human modeling infectious diseases: a bibliometric assessment

The escalation of antibiotic resistance, pandemics, and nosocomial infections underscores the importance of research in both animal and human infectious diseases. Recent advancements in three-dimensional tissue cultures, or "organoids", have revolutionized the development of in vitro models for infectious diseases. Our study conducts a bibliometric analysis on the use of organoids in modeling infectious diseases, offering an in-depth overview of this field's current landscape. We examined scientific contributions from 2009 onward that focused on organoids in host‒pathogen interactions using the Web of Science Core Collection and OpenAlex database. Our analysis included temporal trends, reference aging, author, and institutional productivity, collaborative networks, citation metrics, keyword cluster dynamics, and disruptiveness of organoid models. VOSviewer, CiteSpace, and Python facilitated this analytical assessment. The findings reveal significant growth and advancements in organoid-based infectious disease research. Analysis of keywords and impactful publications identified three distinct developmental phases in this area that were significantly influenced by outbreaks of Zika and SARS-CoV-2 viruses. The research also highlights the synergistic efforts between academia and publishers in tackling global pandemic challenges. Through mostly consolidating research efforts, organoids are proving to be a promising tool in infectious disease research for both human and animal infectious disease. Their integration into the field necessitates methodological refinements for better physiological emulation and the establishment of extensive organoid biobanks. These improvements are crucial for fully harnessing the potential of organoids in understanding infectious diseases and advancing the development of targeted treatments and vaccines.

Swine acute diarrhea syndrome coronavirus Nsp1 suppresses IFN-λ1 production by degrading IRF1 via ubiquitin-proteasome pathway

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a novel porcine enteric coronavirus that causes acute watery diarrhea, vomiting, and dehydration in newborn piglets. The type III interferon (IFN-λ) response serves as the primary defense against viruses that replicate in intestinal epithelial cells. However, there is currently no information available on how SADS-CoV modulates the production of IFN-λ. In this study, we utilized IPI-FX cells (a cell line of porcine ileum epithelium) as an in vitro model to investigate the potential immune evasion strategies employed by SADS-CoV against the IFN-λ response. Our results showed that SADS-CoV infection suppressed the production of IFN-λ1 induced by poly(I:C). Through screening SADS-CoV-encoded proteins, nsp1, nsp5, nsp10, nsp12, nsp16, E, S1, and S2 were identified as antagonists of IFN-λ1 production. Specifically, SADS-CoV nsp1 impeded the activation of the IFN-λ1 promoter mediated by MAVS, TBK1, IKKε, and IRF1. Both SADS-CoV and nsp1 obstructed poly(I:C)-induced nuclear translocation of IRF1. Moreover, SADS-CoV nsp1 degraded IRF1 via the ubiquitin-mediated proteasome pathway without interacting with it. Overall, our study provides the first evidence that SADS-CoV inhibits the type III IFN response, shedding light on the molecular mechanisms employed by SADS-CoV to evade the host immune response.

Gut microbiota-derived butyrate promotes coronavirus TGEV infection through impairing RIG-I-triggered local type I interferon responses via class I HDAC inhibition

Gut microbiota-derived metabolites are important for the replication and pathogenesis of many viruses. However, the roles of bacterial metabolites in swine enteric coronavirus (SECoV) infection remain poorly understood. Recent studies show that SECoVs infection in vivo significantly alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota. This prompted us to investigate whether and how SCFAs impact SECoV infection. Employing alphacoronavirus transmissible gastroenteritis virus (TGEV), a major cause of diarrhea in piglets, as a model, we found that SCFAs, particularly butyrate, enhanced TGEV infection both in porcine intestinal epithelial cells and swine testicular (ST) cells at the late stage of viral infection. This effect depended on the inhibited productions of virus-induced type I interferon (IFN) and downstream antiviral IFN-stimulated genes (ISGs) by butyrate. Mechanistically, butyrate suppressed the expression of retinoic acid-inducible gene I (RIG-I), a key viral RNA sensor, and downstream mitochondrial antiviral-signaling (MAVS) aggregation, thereby impairing type I IFN responses and increasing TGEV replication. Using pharmacological and genetic approaches, we showed that butyrate inhibited RIG-I-induced type I IFN signaling by suppressing class I histone deacetylase (HDAC). In summary, we identified a novel mechanism where butyrate enhances TGEV infection by suppressing RIG-I-mediated type I IFN responses. Our findings highlight that gut microbiota-derived metabolites like butyrate can be exploited by SECoV to dampen innate antiviral immunity and establish infection in the intestine.IMPORTANCESwine enteric coronaviruses (SECoVs) infection in vivo alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota, but whether microbiota-derived SCFAs impact coronavirus gastrointestinal infection is largely unknown. Here, we demonstrated that SCFAs, particularly butyrate, substantially increased alphacoronavirus TGEV infection at the late stage of infection, without affecting viral attachment or internalization. Furthermore, enhancement of TGEV by butyrate depended on impeding virus-induced type I interferon (IFN) responses. Mechanistically, butyrate suppressed the cytoplasmic viral RNA sensor RIG-I expression and downstream type I IFN signaling activation by inhibiting class I HDAC, thereby promoting TGEV infection. Our work reveals novel functions of gut microbiota-derived SCFAs in enhancing enteric coronavirus infection by impairing RIG-I-dependent type I IFN responses. This implies that bacterial metabolites could be therapeutic targets against SECoV infection by modulating antiviral immunity in the intestine.

Isothermal nucleic acid amplification combined with gold nanoparticles assisted electrochemical impedance for the sensitive and efficient porcine delta coronavirus detection

The emergence of porcine delta coronavirus (PDCoV) has caused huge economic losses in the global pig industry. How to realize the sensitive and efficient detection for it is a difficult problem that need to be resolved. In this work, loop-mediated isothermal amplification (LAMP)-electrochemical impedance spectroscopy (EIS) detection platform for PDCoV based on nucleic acid level was constructed by combining the advantages of efficient amplification for LAMP and sensitive detection for EIS. Referring to a 159 bp fragment of PDCoV N gene (Genbank：KY078891, 641 bp-799 bp), primers (HS-FIP、BIP、F3、B3) were designed to screened and sulfhydryl groups were activated, and then loop-mediated isothermal amplification was carried out. Subsequently, gold nanoparticles were loaded on indium tin oxide glass by electrodeposition technology, and the amplified products were connected to the electrode surface through the formation of Au-S bonds. According to the difference of charge transfer resistance after double-stranded DNA was connected on the electrode surface, the detection platform can achieve valid detection of PDCoV in the concentration range of 102-107 copies/μL, the limit of detection is 28 copies/μL, and can be used for practical analysis of pig small intestine samples.

HSP90AB1 Is a Host Factor Required for Transmissible Gastroenteritis Virus Infection

Transmissible gastroenteritis virus (TGEV) is an important swine enteric coronavirus causing viral diarrhea in pigs of all ages. Currently, the development of antiviral agents targeting host proteins to combat viral infection has received great attention. The heat shock protein 90 (HSP90) is a critical host factor and has important regulatory effects on the infection of various viruses. However, its roles in porcine coronavirus infection remain unclear. In this study, the effect of HSP90 on TGEV infection was evaluated. In addition, the influence of its inhibitor VER-82576 on proinflammatory cytokine (IL-6, IL-12, TNF-α, CXCL10, and CXCL11) production induced by TGEV infection was further analyzed. The results showed that the knockdown of HSP90AB1 and HSP90 inhibitor VER-82576 treatment resulted in a reduction in TGEV M gene mRNA levels, the N protein level, and virus titers in a dose-dependent manner, while the knockdown of HSP90AA1 and KW-2478 treatment had no significant effect on TGEV infection. A time-of-addition assay indicated that the inhibitory effect of VER-82576 on TGEV infection mainly occurred at the early stage of viral replication. Moreover, the TGEV-induced upregulation of proinflammatory cytokine (IL-6, IL-12, TNF-α, CXCL10, and CXCL11) expression was significantly inhibited by VER-82576. In summary, these findings indicated that HSP90AB1 is a host factor enhancing TGEV infection, and the HSP90 inhibitor VER-82576 could reduce TGEV infection and proinflammatory cytokine production, providing a new perspective for TGEV antiviral drug target design.

Porcine Enteric Alphacoronavirus Entry through Multiple Pathways (Caveolae, Clathrin, and Macropinocytosis) Requires Rab GTPases for Endosomal Transport

Porcine enteric alphacoronavirus (PEAV) is a new bat HKU2-like porcine coronavirus, and its endemic outbreak has caused severe economic losses to the pig industry. Its broad cellular tropism suggests a potential risk of cross-species transmission. A limited understanding of PEAV entry mechanisms may hinder a rapid response to potential outbreaks. This study analyzed PEAV entry events using chemical inhibitors, RNA interference, and dominant-negative mutants. PEAV entry into Vero cells depended on three endocytic pathways: caveolae, clathrin, and macropinocytosis. Endocytosis requires dynamin, cholesterol, and a low pH. Rab5, Rab7, and Rab9 GTPases (but not Rab11) regulate PEAV endocytosis. PEAV particles colocalize with EEA1, Rab5, Rab7, Rab9, and Lamp-1, suggesting that PEAV translocates into early endosomes after internalization, and Rab5, Rab7, and Rab9 regulate trafficking to lysosomes before viral genome release. PEAV enters porcine intestinal cells (IPI-2I) through the same endocytic pathway, suggesting that PEAV may enter various cells through multiple endocytic pathways. This study provides new insights into the PEAV life cycle. IMPORTANCE Emerging and reemerging coronaviruses cause severe human and animal epidemics worldwide. PEAV is the first bat-like coronavirus to cause infection in domestic animals. However, the PEAV entry mechanism into host cells remains unknown. This study demonstrates that PEAV enters into Vero or IPI-2I cells through caveola/clathrin-mediated endocytosis and macropinocytosis, which does not require a specific receptor. Subsequently, Rab5, Rab7, and Rab9 regulate PEAV trafficking from early endosomes to lysosomes, which is pH dependent. The results advance our understanding of the disease and help to develop potential new drug targets against PEAV.

Impact of porcine circovirus type 2 on porcine epidemic diarrhea virus replication in the IPI-FX cell line depends on the order of infection

Introduction

A study in 2006 showed that the clinical course of PEDV disease was markedly aggravated by transplacental infection of PCV2. Therefore, we investigated whether the small intestine supports PCV2 replication and the effect of PCV2 infection on PEDV replication in epithelial cells in vitro.

Methods

To confirm the intestinal tropism of PCV2, the viral loads in the small-intestinal tissues after PCV2 infection were determined with virus titration, and the viral titers in the infected pig jejunum, ileum, ileocecal valve, and colon were 104.86, 104.09, 102.52, and 102.35 TCID50/g, respectively. We then determined the propagation characteristics of PCV2 in ileal epithelial cells (IPI-FX) and jejunal epithelial cells (IPEC-J2) with an immunoperoxidase monolayer assay, virus titration, and an immunofluorescence assay. Both IPI-FX and IPEC-J2 cells supported the replication of PCV2, with titers of 105.5 and 105.0 TCID50/ml, respectively. We established an infection model of PCV2 and PEDV in IPI-FX cells and found that PEDV and PCV2 infected the cells individually and together. The effects of PCV2 infection on PEDV replication were determined with reverse transcription–quantitative PCR (qPCR), western blotting, and virus titration. When PCV2 infected IPI-FX cells before PEDV, PCV2 significantly inhibited the replication of PEDV in a dose- and time-dependent manner and that the mRNAs of IFN-β, TNF-α, IL1β, and OASL were downregulated (detected with qPCR). Surprisingly, when IPI-FX cells were co-infected with PCV2 and PEDV, PCV2 promoted the replication of PEDV, the expression of the host IFN-β, TNF-α, IL1β, and OASL mRNAs was upregulated.

Discussion

These findings demonstrate that the co-infection of IPI-FX cells with PCV2 and PEDV represents an excellent in vitro model in which to investigate their combined pathogenic mechanisms.

Hypericum japonicum extract inhibited porcine epidemic diarrhea virus in vitro and in vivo

Porcine epidemic diarrhea virus (PEDV) infection causes lethal watery diarrhea and high mortality in neonatal piglets, leading to huge economic losses in the global swine industry. Currently, the existing commercial vaccines cannot fully control PEDV, so it is urgent to develop effective antiviral agents to complement vaccine therapy. In the present study, we investigated the antiviral effect of Hypericum japonicum extract (HJ) against PEDV in vivo and in vitro. In in vitro assays, HJ could directly inactivate PEDV strains; moreover, it inhibited the proliferation of PEDV strains in Vero or IPI-FX cells at its non-cytotoxic concentrations. Time of addition assays revealed that HJ mainly inhibited PEDV at the later stages of the viral life cycle. In in vivo, compared with the model group, HJ could reduce the viral titers in the intestines of infected piglets, and improve their intestinal pathological, indicating that HJ could protect the newborn piglets from highly pathogenic PEDV variant infection. Furthermore, this effect may be related to the fact that HJ can not only directly inhibit viruses, but also regulate the structure of intestinal microbiota. In conclusion, our results indicate that Hypericum japonicum could inhibit PEDV replication in vitro and in vivo and might possess the potential to develop as the anti-PEDV drug.

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.

Metabolomic analysis of porcine intestinal epithelial cells during swine acute diarrhea syndrome coronavirus infection

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an enveloped, positive single-stranded RNA virus belonging to Coronaviridae family, Orthocoronavirinae subfamily, Alphacoronavirus genus. As one of the main causes of swine diarrhea, SADS-CoV has brought huge losses to the pig industry. Although we have a basic understanding of SADS-CoV, the research on the pathogenicity and interactions between host and virus are still limited, especially the metabolic changes induced by SADS-CoV infection. Here, we utilized a combination of untargeted metabolomics and lipomics to analyze the metabolic alteration in SADS-CoV infected cells. Significant changes were observed in 1257 of 2225 metabolites identified in untargeted metabolomics, while the number of lipomics was 435 out of 868. Metabolic pathway enrichment analysis showed that amino acid metabolism, tricarboxylic acid (TCA) cycle and ferroptosis were disrupted during viral infection, suggesting that these metabolic pathways may partake in pathological processes related to SADS-CoV pathogenesis. Collectively, our findings gain insights into the cellular metabolic disorder during SADS-CoV infection, offer a valuable resource for further exploration of the relationship between virus and host metabolic activities, and provide potential targets for the development of antiviral drugs.

Porcine Deltacoronavirus Infection Cleaves HDAC2 to Attenuate Its Antiviral Activity

Protein acetylation plays an important role during virus infection. Thus, it is not surprising that viruses always evolve elaborate mechanisms to regulate the functions of histone deacetylases (HDACs), the essential transcriptional and epigenetic regulators for deacetylation. Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes severe diarrhea in suckling piglets and has the potential to infect humans. In this study, we found that PDCoV infection inhibited cellular HDAC activity. By screening the expressions of different HDAC subfamilies after PDCoV infection, we unexpectedly found that HDAC2 was cleaved. Ectopic expression of HDAC2 significantly inhibited PDCoV replication, while the reverse effects could be observed after treatment with an HDAC2 inhibitor (CAY10683) or the knockdown of HDAC2 expression by specific siRNA. Furthermore, we demonstrated that PDCoV-encoded nonstructural protein 5 (nsp5), a 3C-like protease, was responsible for HDAC2 cleavage through its protease activity. Detailed analyses showed that PDCoV nsp5 cleaved HDAC2 at glutamine 261 (Q261), and the cleaved fragments (amino acids 1 to 261 and 262 to 488) lost the ability to inhibit PDCoV replication. Interestingly, the Q261 cleavage site is highly conserved in HDAC2 homologs from other mammalian species, and the nsp5s encoded by seven tested mammalian coronaviruses also cleaved HDAC2, suggesting that cleaving HDAC2 may be a common strategy used by different mammalian coronaviruses to antagonize the antiviral role of HDAC2. IMPORTANCE As an emerging porcine enteropathogenic coronavirus that possesses the potential to infect humans, porcine deltacoronavirus (PDCoV) is receiving increasing attention. In this work, we found that PDCoV infection downregulated cellular histone deacetylase (HDAC) activity. Of particular interest, the viral 3C-like protease, encoded by the PDCoV nonstructural protein 5 (nsp5), cleaved HDAC2, and this cleavage could be observed in the context of PDCoV infection. Furthermore, the cleavage of HDAC2 appears to be a common strategy among mammalian coronaviruses, including the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), to antagonize the antiviral role of HDAC2. To our knowledge, PDCoV nsp5 is the first identified viral protein that can cleave cellular HDAC2. Results from our study provide new targets to develop drugs combating coronavirus infection.

Emodin from Aloe inhibits Swine acute diarrhea syndrome coronavirus in cell culture

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an emerging swine enteropathogenic coronavirus that causes severe diarrhea in neonatal piglets, leading to serious economic losses to the pig industries. At present, there are no effective control measures for SADS, making an urgent need to exploit effective antiviral therapies. Here, we confirmed that Aloe extract (Ae) can strongly inhibit SADS-CoV in Vero and IPI-FX cells in vitro. Furthermore, we detected that Emodin from Ae had anti-SADS-CoV activity in cells but did not impair SADS-CoV infectivity directly. The time-of-addition assay showed that Emodin inhibits SADS-CoV infection at the whole stages of the viral replication cycle. Notably, we found that Emodin can significantly reduce virus particles attaching to the cell surface and induce TLR3 (p < 0.001), IFN-λ3 (p < 0.01), and ISG15 (p < 0.01) expressions in IPI-FX cells, indicating that the anti-SADS-CoV activity of Emodin might be due to blocking viral attachment and the activation of TLR3-IFN-λ3-ISG15 signaling axis. These results suggest that Emodin has the potential value for the development of anti-SADS-CoV drugs.

Porcine Intestinal Organoids: Overview of the State of the Art

The intestinal tract is a crucial part of the body for growth and development, and its dysregulation can cause several diseases. The lack of appropriate in vitro models hampers the development of effective preventions and treatments against these intestinal tract diseases. Intestinal organoids are three-dimensional (3D) polarized structures composed of different types of cells capable of self-organization and self-renewal, resembling their organ of origin in architecture and function. Porcine intestinal organoids (PIOs) have been cultured and are used widely in agricultural, veterinary, and biomedical research. Based on the similarity of the genomic sequence, anatomic morphology, and drug metabolism with humans and the difficulty in obtaining healthy human tissue, PIOs are also considered ideal models relative to rodents. In this review, we summarize the current knowledge on PIOs, emphasizing their culturing, establishment and development, and applications in the study of host-microbe interactions, nutritional development, drug discovery, and gene editing potential.

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.

Porcine Deltacoronavirus (PDCoV) Entry into PK-15 Cells by Caveolae-Mediated Endocytosis

(1) Background: Porcine deltacoronavirus (PDCoV) is a newly emerged enteric virus affecting pig breeding industries worldwide, and its pathogenic mechanism remains unclear. (2) Methods: In this study, we preliminarily identified the endocytic pathway of PDCoV in PK-15 cells, using six chemical inhibitors (targeting clathrin-mediated endocytosis, caveolae-mediated endocytosis, macropinocytosis pathway and endosomal acidification), overexpression of dominant-negative (DN) mutants to treat PK-15 cells and proteins knockdown. (3) Results: The results revealed that PDCoV entry was not affected after treatment with chlorpromazine (CPZ), 5-(N-ethyl-N-isopropyl) amiloride (EIPA)or ammonium chloride (NH4Cl), indicating that the entry of PDCoV into PK-15 cells were clathrin-, micropinocytosis-, PH-independent endocytosis. Conversely, PDCoV infection was sensitive to nystatin, dynasore and methyl-β-cyclodextrin (MβCD) with reduced PDCoV internalization, indicating that entry of PDCoV into PK-15 cells was caveolae-mediated endocytosis that required dynamin and cholesterol; indirect immunofluorescence and shRNA interference further validated these results. (4) Conclusions: In conclusion, PDCoV entry into PK-15 cells depends on caveolae-mediated endocytosis, which requires cholesterol and dynamin. Our finding is the first initial identification of the endocytic pathway of PDCoV in PK-15 cells, providing a theoretical basis for an in-depth understanding of the pathogenic mechanism of PDCoV and the design of new antiviral targets.

Photoactive "Bionic Virus" Robustly Elicits the Synergy Anticancer Activity of Immunophotodynamic Therapy

Coronavirus represents an inspiring model for designing drug delivery systems due to its unique infection machinery mechanism. Herein, we have developed a biomimetic viruslike nanocomplex, termed SDN, for improving cancer theranostics. SDN has a unique core-shell structure consisting of photosensitizer chlorin e6 (Ce6)-loaded nanostructured lipid carrier (CeNLC) (virus core)@poly(allylamine hydrochloride)-functionalized MnO₂ nanoparticles (virus spike), generating a virus-mimicking nanocomplex. SDN not only prompted cellular uptake through rough-surface-mediated endocytosis but also achieved mitochondrial accumulation by the interaction of cationic spikes and the anionic mitochondrial surface, leading to mitochondria-specific photodynamic therapy. Meanwhile, SDN could even mediate oxygen generation to relieve tumor hypoxia and, consequently, improve macrophage-associated anticancer immune response. Importantly, SDN served as a robust magnetic resonance imaging (MRI) contrast agent due to the fast release of Mn²⁺ in the presence of intracellular redox components. We identified that SDN selectively accumulated in tumors and released Mn²⁺ to generate a 5.71-fold higher T₁-MRI signal, allowing for effectively detecting suspected tumors. Particularly, SDN induced synergistic immunophotodynamic effects to eliminate malignant tumors with minimal adverse effects. Therefore, we present a novel biomimetic strategy for improving targeted theranostics, which has a wide range of potential biomedical applications.

Porcine Deltacoronaviruses: Origin, Evolution, Cross-Species Transmission and Zoonotic Potential

Porcine deltacoronavirus (PDCoV) is an emerging enteropathogenic coronavirus of swine that causes acute diarrhoea, vomiting, dehydration and mortality in seronegative neonatal piglets. PDCoV was first reported in Hong Kong in 2012 and its etiological features were first characterized in the United States in 2014. Currently, PDCoV is a concern due to its broad host range, including humans. Chickens, turkey poults, and gnotobiotic calves can be experimentally infected by PDCoV. Therefore, as discussed in this review, a comprehensive understanding of the origin, evolution, cross-species transmission and zoonotic potential of epidemic PDCoV strains is urgently needed.

HSP90 inhibitors 17-AAG and VER-82576 inhibit porcine deltacoronavirus replication in vitro

Porcine deltacoronavirus (PDCoV) is highly pathogenic to piglets, and no specific drugs or vaccines are available for the prevention and treatment of PDCoV infection, the need for antiviral therapies is pressing. HSP90 inhibitors have potent inhibitory effects against the replication of numerous viruses, hence we evaluated three HSP90 inhibitors, 17-AAG, VER-82576, and KW-2478, for their effects on PDCoV infection in vitro. We evaluated their effectivenesses at suppressing PDCoV by qRT-PCR, western blot, and TCID₅₀ assay, and found that 17-AAG and VER-82576 inhibited PDCoV at the early stage of replication, while KW-2478 showed no significant antiviral activity at any stage of infection. These results indicated that the PDCoV-inhibitory effects of 17-AAG and VER-82576 might be exerted by targeting host cell factor HSP90AB1 but not HSP90AA1. Further study showed that HSP90AB1 mRNA and protein levels were not significantly different in 17-AAG and VER-82576-treated cells versus control cells. 17-AAG and VER-82576 were also evaluated for their effects on the expressions of TNF-α, IL-6, and IL-12, which are PDCoV-induced proinflammatory cytokines. We found that both 17-AAG and VER-82576 inhibited the expressions of TNF-α, IL-6, and IL-12 to varying degrees, but in a dose dependent manner. From our data we can conclude that the HSP90 inhibitors 17-AAG and VER-82576 are promising candidates for the treatment of PDCoV infection.

Construction, Characterization and Application of Recombinant Porcine Deltacoronavirus Expressing Nanoluciferase

Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes diarrhoea in suckling piglets and has the potential for cross-species transmission. No effective PDCoV vaccines or antiviral drugs are currently available. Here, we successfully generated an infectious clone of PDCoV strain CHN-HN-2014 using a combination of bacterial artificial chromosome (BAC)-based reverse genetics system with a one-step homologous recombination. The recued virus (rCHN-HN-2014) possesses similar growth characteristics to the parental virus in vitro. Based on the established infectious clone and CRISPR/Cas9 technology, a PDCoV reporter virus expressing nanoluciferase (Nluc) was constructed by replacing the NS6 gene. Using two drugs, lycorine and resveratrol, we found that the Nluc reporter virus exhibited high sensibility and easy quantification to rapid antiviral screening. We further used the Nluc reporter virus to test the susceptibility of different cell lines to PDCoV and found that cell lines derived from various host species, including human, swine, cattle and monkey enables PDCoV replication, broadening our understanding of the PDCoV cell tropism range. Taken together, our reporter viruses are available to high throughput screening for antiviral drugs and uncover the infectivity of PDCoV in various cells, which will accelerate our understanding of PDCoV.

Development of an indirect ELISA for detecting swine acute diarrhoea syndrome coronavirus IgG antibodies based on a recombinant spike protein

Swine acute diarrhoea syndrome coronavirus (SADS-CoV) is a newly identified swine enteropathogenic coronavirus that causes watery diarrhoea in neonatal piglets, leading to significant economic losses to the swine industry. Currently, there are no suitable serological methods to assess the infection of SADS-CoV and effectiveness of vaccines, making an urgent need to exploit effective enzyme-linked immunosorbent assay (ELISA) to compensate for this deficiency. Here, a recombinant plasmid that expresses the spike (S) protein of SADS-CoV fused to the Fc domain of human IgG was constructed to generate recombinant baculovirus and expressed in HEK 293F cells. The S-Fc protein was purified with protein G Resin, which retained reactivity with anti-human Fc and anti-SADS-CoV antibodies. The S-Fc protein was then used to develop an indirect ELISA (S-iELISA) and the reaction conditions of S-iELISA were optimized. As a result, the cut-off value was determined as 0.3711 by analyzing OD_450nm values of 40 SADS-CoV-negative sera confirmed by immunofluorescence assay (IFA) and western blot. The coefficient of variation (CV) of 6 SADS-CoV-positive sera within and between runs of S-iELISA were both less than 10%. The cross-reactivity assays demonstrated that S-iELISA was non-cross-reactive with other swine viruses' sera. Furthermore, the overall coincidence rate between IFA and S-iELISA was 97.3% based on testing 111 clinical serum samples. Virus neutralization test with seven different OD_450nm values of the sera showed that the OD_450nm values tested by S-iELISA are positively correlated with the virus neutralization assay. Finally, a total of 300 pig field serum samples were tested by S-iELISA and commercial kits of other swine enteroviruses showed that the IgG-positive for SADS-CoV, TGEV, PDCoV and PEDV was 81.7, 54, 65.3 and 6%, respectively. The results suggest that this S-iELISA is specific, sensitive, repeatable and can be applied for the detection of the SADS-CoV infection in the swine industry.

Cholesterol 25-hydroxylase suppresses porcine deltacoronavirus infection by inhibiting viral entry

Cholesterol 25-hydroxylase (CH25 H) is a key enzyme regulating cholesterol metabolism and also acts as a broad antiviral host restriction factor. Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that can cause vomiting, diarrhea, dehydration and even death in newborn piglets. In this study, we found that PDCoV infection significantly upregulated the expression of CH25H in IPI-FX cells, a cell line of porcine ileum epithelium. Overexpression of CH25H inhibited PDCoV replication, whereas CH25H silencing using RNA interference promoted PDCoV infection. Treatment with 25-hydroxycholesterol (25HC), the catalysate of cholesterol via CH25H, inhibited PDCoV proliferation by impairing viral invasion of IPI-FX cells. Furthermore, a mutant CH25H (CH25H-M) lacking hydroxylase activity also inhibited PDCoV infection to a lesser extent. Taken together, our data suggest that CH25H acts as a host restriction factor to inhibit the proliferation of PDCoV but this inhibitory effect is not completely dependent on its enzymatic activity.

Replicative capacity of four porcine enteric coronaviruses in LLC-PK1 cells

Enteric coronaviruses (CoVs) are major pathogens that cause diarrhea in piglets. To date, four porcine enteric CoVs have been identified: transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), and HKU2-like porcine enteric alphacoronavirus (PEAV). In this study, we investigated the replicative capacity of these four enteric CoVs in LLC-PK1 cells, a porcine kidney cell line. The results showed that LLC-PK1 cells are susceptible to all four enteric CoVs, particularly to TGEV and PDCoV infections, indicating that LLC-PK1 cells can be applied to porcine enteric CoV research in vitro, particularly for coinfection studies.

Next-Generation Porcine Intestinal Organoids: an Apical-Out Organoid Model for Swine Enteric Virus Infection and Immune Response Investigations

The intestinal organoid culture system is a pathbreaking working model for investigating pathogen-host interactions in the intestines. However, due to the limitations of the first generation of intestinal organoids, basal-out structure and growth in Matrigel, most pathogens can rarely attach to the apical membrane directly and hardly initiate infection. In this study, we first developed a next-generation porcine intestinal organoid culture system, characterized by an apical membrane on the surface, called apical-out. To investigate the infectivity and antiviral immune responses of this apical-out porcine intestinal organoid, a swine enteric virus, transmissible gastroenteritis virus (TGEV), was employed to inoculate the culture system. Both reverse transcription-quantitative PCR (RT-qPCR) and immunofluorescence assay (IFA) analysis demonstrated that TGEV replicated in the apical-out porcine intestinal organoid culture system. Additionally, our results illustrated that TGEV infection significantly upregulated the expression levels of alpha interferon (IFN-α), IFN-λ1, interferon-stimulated gene 15 (ISG15), ISG58, tumor necrosis factor alpha (TNF-α), and interleukin 6 (IL-6) in this culture system. Hence, we successfully developed a porcine intestinal apical-out organoid culture system, which will facilitate the investigation of pathogen-host interactions in pig intestines.IMPORTANCE Intestinal organoids are a newly developed culture system for investigating pathogen-host interactions. Intestinal organoid models have been widely used since their development, because the results obtained from this type of culture model better represent physiological conditions than those from well-established cell lines. The three-dimensional (3D) porcine intestinal organoid model was reported in 2018 and 2019 for the investigation of intestinal pathogens. However, those organoid culture models were basal-out intestinal organoids, which are not suitable for porcine enteric virus research because they invade the intestines via the apical side of epithelial cells on villi. In this study, we developed a porcine apical-out intestinal organoid culture system and verified its infectivity, type I and type III interferon (IFN) antiviral responses, and inflammatory responses following infection by a swine enteric virus. Our results imply that this apical-out porcine intestinal organoid culture system is an ideal model for the investigation of interactions between swine enteric viruses and the intestines.

Low-level contamination of deoxynivalenol: A threat from environmental toxins to porcine epidemic diarrhea virus infection

Mycotoxins are toxic metabolites produced by fungal species that commonly present in the global environment, especially in cereals and animal forages. The changing global environment may further increase the exposure to these toxins, posing a serious threat to humans and animals. Recently, coronavirus has become one of the most important pathogens threatening human and animal health. It is not clear whether environmental toxins, such as mycotoxins, will affect coronavirus infection. Given that pigs are among the animals most affected by coronavirus and highly homologous to humans, weaned piglets and IPEC-J2 cells were respectively chosen as in vivo and in vitro model to explore the impacts of deoxynivalenol (DON), the most abundant trichothecene mycotoxin in feed, on porcine epidemic diarrhea virus (PEDV) infection and the mechanisms involved. In vivo, twenty-seven piglets infected naturally with PEDV were randomly divided into three groups, receiving the basal diet containing 0, 750 and 1500 μg/kg DON, respectively. Significant increases in the diarrhea rates, gut barrier injury and PEDV proliferation of piglets' small intestine were observed in experimental groups compared with the control. Additionally, the autophagosome-like vesicles and the autophagy-related proteins expression were also increased in experimental groups. In vitro, we observed that 0.1, 0.5 and 1.0 μM DON significantly promoted the entry and replication of PEDV in IPEC-J2 cells, along with the induction of a complete autophagy. CRISPR-Cas9-mediated knockout of LC3B indicated a vital role of autophagy in the promotion. Pretreatment with p38 signaling inhibitor could significantly block the induction of autophagy, indicating that DON could promote the PEDV infection by triggering p38-mediated autophagy. Our findings suggest that mycotoxin could influence the prevalence of coronavirus and provide new ideas for the prevention and control of coronavirus.

Identification and characterization of PEDV infection in rat crypt epithelial cells

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The rat crypt epithelial cells (IEC-6) were highly susceptible to different subtypes of PEDV.

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The PEDV replication capacity in IEC-6 cells was similar to Vero cells and superior to that in IPEC-J2 cells.

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PEDV infection activated a robust immune response in IEC-6 cells.

Porcine epidemic diarrhea (PED) is a devastating enteric disease to the world's swine production. Porcine epidemic diarrhea virus (PEDV), as the PED causative agent, has been commonly propagated and investigated in Vero cells, as well as in IPEC-J2, a porcine epithelial cell-jejunum 2. However, Vero cells, which are defective in interferon production, cannot represent the host response in enteric cells while PEDV replicates poorly in IPEC-J2 cells. In this study, we observed that rat crypt epithelial cells (IEC-6) were highly susceptible to different subtypes of PEDV. The replication kinetics of PEDV in IEC-6 cells is similar to that in Vero cells, but it is much higher than in IPEC-J2 cells. Besides that, PEDV infection in IEC-6 cells can induce the production of inflammatory cytokines and interferon, especially the type III IFNs. Collectively, our findings suggest that IEC-6 is an ideal cell line for PEDV replication and immune response studies.

Identification of a Novel Linear B-Cell Epitope on the Nucleocapsid Protein of Porcine Deltacoronavirus

Porcine deltacoronavirus (PDCoV), first identified in 2012, is a swine enteropathogen now found in many countries. The nucleocapsid (N) protein, a core component of PDCoV, is essential for virus replication and is a significant candidate in the development of diagnostics for PDCoV. In this study, monoclonal antibodies (mAbs) were generated and tested for reactivity with three truncations of the full protein (N1, N2, N3) that contained partial overlaps; of the five monoclonals chosen tested, each reacted with only the N3 truncation. The antibody designated 4E88 had highest binding affinity with the N protein and was chosen for in-depth examination. The 4E88 epitope was located to amino acids 308-AKPKQQKKPKK-318 by testing the 4E88 monoclonal for reactivity with a series of N3 truncations, then the minimal epitope, 309-KPKQQKKPK-317 (designated EP-4E88), was pinpointed by testing the 4E88 monoclonal for reactivity with a series of synthetic peptides of this region. Homology analysis showed that the EP-4E88 sequence is highly conserved among PDCoV strains, and also shares high similarity with sparrow coronavirus (HKU17), Asian leopard cat coronavirus (ALCCoV), quail coronavirus (UAE-HKU30), and sparrow deltacoronavirus (SpDCoV). Of note, the PDCoV EP-4E88 sequence shared very low similarity (<22.2%) with other porcine coronaviruses (PEDV, TGEV, PRCV, SADS-CoV, PHEV), demonstrating that it is an epitope that can be used for distinguishing PDCoV and other porcine coronavirus. 3D structural analysis revealed that amino acids of EP-4E88 were in close proximity and may be exposed on the surface of the N protein.

Porcine deltacoronavirus (PDCoV) modulates calcium influx to favor viral replication

Ionic calcium (Ca²⁺) is a versatile intracellular second messenger that plays important roles in cellular physiological and pathological processes. Porcine deltacoronavirus (PDCoV) is an emerging enteropathogenic coronavirus that causes serious vomiting and diarrhea in suckling piglets. In this study, the role of Ca²⁺ to PDCoV infection was investigated. PDCoV infection was found to upregulate intracellular Ca²⁺ concentrations of IPI-2I cells. Chelating extracellular Ca²⁺ by EGTA inhibited PDCoV replication, and this inhibitory effect was overcome by replenishment with CaCl₂. Treatment with Ca²⁺ channel blockers, particularly the L-type Ca²⁺ channel blocker diltiazem hydrochloride, inhibited PDCoV infection significantly. Mechanistically, diltiazem hydrochloride reduces PDCoV infection by inhibiting the replication step of the viral replication cycle. Additionally, knockdown of CACNA1S, the L-type Ca²⁺ voltage-gated channel subunit, inhibited PDCoV replication. The combined results demonstrate that PDCoV modulates calcium influx to favor its replication.