Transmissible gastroenteritis virus infection induces NF-κB activation through RLR-mediated signaling

GRP78 recognizes EV-F 3D protein and activates NF-κB to repress virus replication by interacting with CHUK/IKBKB

Enteroviruses are the causative agents associated with several human and animal diseases, posing a significant threat to human and animal health. As one of the host immune defense strategies, innate immunity plays a crucial role in defending against invading pathogens, where the host utilizes a variety of mechanisms to inhibit or eliminate the pathogen. Here, we report a new strategy for the host to repress enterovirus replication by the 78 kDa glucose-regulated protein (GRP78), also known as heat shock protein family A member 5 (HSPA5). The GRP78 recognizes the EV-encoded RNA-dependent RNA polymerases (RdRPs) 3D protein and interacts with the nuclear factor kappa B kinase complex (CHUK) and subunit beta gene (IKBKB) to facilitate the phosphorylation and nuclear translocation of NF-κB, which induces the production of inflammatory factors and leads to a broad inhibition of enterovirus replication. These findings demonstrate a new role of GRP78 in regulating host innate immunity in response to viral infection and provide new insights into the mechanism underlying enterovirus replication and NF-κB activation.IMPORTANCEGRP78 is known as a molecular chaperone for protein folding and plays a critical role in maintaining protein folding and participating in cell proliferation, cell survival, apoptosis, and metabolism. However, the functions of GRP78 to participate in enterovirus genome replication and innate immune responses are rarely documented. In this study, we explored the functions of the EV-3D-interacting protein GRP78 and found that GRP78 inhibits enterovirus replication by activating NF-κB through binding to EV-F 3D and interacting with the NF-κB signaling molecules CHUK/IKBKB. This is the first report that GRP78 interacts with CHUK/IKBKB to activate the NF-κB signaling pathway, which leads to the expression of the proinflammatory cytokines and inhibition of enterovirus replication. These results demonstrate a unique mechanism of virus replication regulation by GRP78 and provide insights into the prevention and treatment of viral infections.

Transmissible gastroenteritis virus induces inflammatory responses via RIG-I/NF-κB/HIF-1α/glycolysis axis in intestinal organoids and in vivo

Transmissible gastroenteritis virus (TGEV)-induced enteritis is characterized by watery diarrhea, vomiting, and dehydration, and has high mortality in newborn piglets, resulting in significant economic losses in the pig industry worldwide. Conventional cell lines have been used for many years to investigate inflammation induced by TGEV, but these cell lines may not mimic the actual intestinal environment, making it difficult to obtain accurate results. In this study, apical-out porcine intestinal organoids were employed to study TEGV-induced inflammation. We found that apical-out organoids were susceptible to TGEV infection, and the expression of representative inflammatory cytokines was significantly upregulated upon TGEV infection. In addition, retinoic acid-inducible gene I (RIG-I) and the nuclear factor-kappa B (NF-κB) pathway were responsible for the expression of inflammatory cytokines induced by TGEV infection. We also discovered that the transcription factor hypoxia-inducible factor-1α (HIF-1α) positively regulated TGEV-induced inflammation by activating glycolysis in apical-out organoids, and pig experiments identified the same molecular mechanism as the ex vivo results. Collectively, we unveiled that the inflammatory responses induced by TGEV were modulated via the RIG-I/NF-κB/HIF-1α/glycolysis axis ex vivo and in vivo. This study provides novel insights into TGEV-induced enteritis and verifies intestinal organoids as a reliable model for investigating virus-induced inflammation.

IMPORTANCE

Intestinal organoids are a newly developed culture system for investigating immune responses to virus infection. This culture model better represents the physiological environment compared with well-established cell lines. In this study, we discovered that inflammatory responses induced by TGEV infection were regulated by the RIG-I/NF-κB/HIF-1α/glycolysis axis in apical-out porcine organoids and in pigs. Our findings contribute to understanding the mechanism of intestinal inflammation upon viral infection and highlight apical-out organoids as a physiological model to mimic virus-induced inflammation.

Development of a multiplex reverse transcription-quantitative PCR (qPCR) method for detecting common causative agents of swine viral diarrhea in China

BACKGROUND

Diarrheal diseases caused by viral agents have led to a great morbidity, mortality, and economic loss in global pig industry. Porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine deltacoronavirus (PDCoV), and group A porcine rotavirus (RVA) are main causative agents of swine viral diarrhea with similar clinical signs on Chinese farms and their co-infection is also common. However, it is still lack of a convenient method to detect these four agents.

METHODS

A TaqMan multiplex qPCR method was developed to detect PEDV, TGEV, PDCoV, and RVA, simultaneously. This method was then applied to investigate 7,342 swine fecal samples or rectal swabs, as well as 1,246 swine intestinal samples collected from 2075 farms in China in 2022.

RESULTS

Minimum detection limits of this method were 3 copies/µL for PEDV, 4 copies/µL for TGEV, 8 copies/µL for RVA, and 8 copies/µL for PDCoV, suggesting a good sensitivity. No signals were observed by using this method detecting other viral agents commonly prevalent in pigs, which is suggestive of a good specificity. Application of this method on investigating clinical samples demonstrated a relatively high positive rate for PEDV (22.21%, 1907/8588) and RVA (44.00%, 3779/8588). In addition, co-infection between PEDV and RVA was observed on 360 investigated farms, accounting for 17.35% (360/2075) of the farms where co-infection events were screened.

CONCLUSIONS

A TaqMan multiplex qPCR method targeting PEDV, TGEV, PDCoV, and RVA was developed in this study. This method demonstrated a good specificity and sensitivity on investigating these four common viruses responsible for viral diarrhea on Chinese pig farms, which represents a convenient method for the monitoring and differential diagnosis of swine viral diarrhea.

A study on the association between gut microbiota, inflammation, and type 2 diabetes

Type 2 diabetes mellitus (T2DM) was reported to be associated with impaired immune response and alterations in microbial composition and function. However, the underlying mechanism remains elusive. To investigate the association among retinoic acid-inducible gene-I-like receptors (RLRs) signaling pathway, intestinal bacterial microbiome, microbial tryptophan metabolites, inflammation, and a longer course of T2DM, 14 patients with T2DM and 7 healthy controls were enrolled. 16S rRNA amplicon sequencing and untargeted metabolomics were utilized to analyze the stool samples. RNA sequencing (RNA-seq) was carried out on the peripheral blood samples. Additionally, C57BL/6J specific pathogen-free (SPF) mice were used. It was found that the longer course of T2DM could lead to a decrease in the abundance of probiotics in the intestinal microbiome. In addition, the production of microbial tryptophan derivative skatole declined as a consequence of the reduced abundance of related intestinal microbes. Furthermore, low abundances of probiotics, such as Bacteroides and Faecalibacterium, could trigger the inflammatory response by activating the RLRs signaling pathway. The increased level of the member of TNF receptor-associated factors (TRAF) family, nuclear factor kappa-B (NF-κB) activator (TANK), in the animal colon activated nuclear factor kappa B subunit 2 (NFκB2), resulting in inflammatory damage. In summary, it was revealed that the low abundances of probiotics could activate the RLR signaling pathway, which could in turn activate its downstream signaling pathway, NF-κB, highlighting a relationship among gut microbes, inflammation, and a longer course of T2DM. KEY POINTS: Hyperglycemia may suppress tryptophanase activity. The low abundance of Bacteroides combined with the decrease of Dopa decarboxylase (DDC) activity may lead to the decrease of the production of tryptophan microbial derivative skatole, and the low abundance of Bacteroides or reduced skatole may further lead to the increase of blood glucose by downregulating the expression of glucagon-like peptide-1 (GLP1). A low abundance of anti-inflammatory bacteria may induce an inflammatory response by triggering the RLR signaling pathway and then activating its downstream NF-κB signaling pathway in prolonged T2DM.

All-trans retinoic acid alleviates transmissible gastroenteritis virus-induced intestinal inflammation and barrier dysfunction in weaned piglets

BACKGROUND

Transmissible gastroenteritis virus (TGEV) is one of the main pathogens causing severe diarrhea of piglets. The pathogenesis of TGEV is closely related to intestinal inflammation. All-trans retinoic acid (ATRA) is the main active metabolite of vitamin A, which has immunomodulatory and anti-inflammatory properties. However, it is unclear whether ATRA can alleviate TGEV-induced intestinal inflammation and barrier dysfunction in piglets. This study aimed to investigate the effects of ATRA on growth performance, diarrhea, intestinal inflammation and intestinal barrier integrity of TGEV-challenged piglets.

METHODS

In a 19-d study, 32 weaned piglets were randomly divided into 4 treatments: Control group (basal diet), TGEV group (basal diet + TGEV challenge), TGEV + ATRA5 group (basal diet + 5 mg/d ATRA + TGEV challenge) and TGEV + ATRA15 group (basal diet + 15 mg/d ATRA + TGEV challenge). On d 14, piglets were orally administered TGEV or the sterile medium.

RESULTS

Feeding piglets with 5 and 15 mg/d ATRA alleviated the growth inhibition and diarrhea induced by TGEV (P < 0.05). Feeding piglets with 5 and 15 mg/d ATRA also inhibited the increase of serum diamine oxidase (DAO) activity and the decrease of occludin and claudin-1 protein levels in jejunal mucosa induced by TGEV, and maintained intestinal barrier integrity (P < 0.05). Meanwhile, 5 mg/d ATRA feeding increased the sucrase activity and the expressions of nutrient transporter related genes (GLUT2 and SLC7A1) in jejunal mucosa of TGEV-challenged piglets (P < 0.05). Furthermore, 5 mg/d ATRA feeding attenuated TGEV-induced intestinal inflammatory response by inhibiting the release of interleukin (IL)-1β, IL-8 and tumor necrosis factor-α (TNF-α), and promoting the secretion of IL-10 and secretory immunoglobulin A (sIgA) (P < 0.05). Feeding 5 mg/d ATRA also down-regulated the expressions of Toll-like receptors and RIG-I like receptors signaling pathway related genes (TLR3, TLR4, RIG-I, MyD88, TRIF and MAVS) and the phosphorylation level of nuclear factor-κB-p65 (NF-κB p65), and up-regulated the inhibitor kappa B alpha (IκBα) protein level in jejunal mucosa of TGEV-challenged piglets (P < 0.05).

CONCLUSIONS

ATRA alleviated TGEV-induced intestinal barrier damage by inhibiting inflammatory response, thus improving the growth performance and inhibiting diarrhea of piglets. The mechanism was associated with the inhibition of NF-κB signaling pathway mediated by TLR3, TLR4 and RIG-I.

Deciphering the role of fucoidan from brown macroalgae in inhibiting SARS-CoV-2 by targeting its main protease and receptor binding domain: Invitro and insilico approach

The current study investigated the role of fucoidan from Padina tetrastromatica and Turbinaria conoides against 3-chymotrypsin like protease (3CLpro) and receptor binding domain (RBD) spike protein of SARS-CoV-2 using an invitro and computational approach. The 3CLpro and RBD genes were successfully cloned in pET28a vector, expressed in BL-21DE3 E. coli rosetta cells and purified by ion exchange affinity and size exclusion chromatography. Fucoidan extracted from both biomass using green approach, subcritical water, was found to inhibit 3CLpro of SARS-CoV-2 with an IC50 value of up to 0.35 mg mL-1. However, fucoidan was found to be inactive against the RBD protein. Molecular docking studies demonstrated that fucoidan binds to the active sites of 3CLpro with an affinity of -5.0 kcal mol-1. In addition, molecular dynamic simulations recorded stabilized interactions of protein-ligand complexes in terms of root mean square deviation, root mean square fluctuation, the radius of gyration, solvent accessible surface area and hydrogen bond interaction. The binding energy of fucoidan with 3CLpro was determined to be -101.821 ± 12.966 kJ mol-1 using Molecular Mechanic/Poisson-Bolt-Boltzmann Surface Area analysis. Fucoidan satisfies the Absorption, Distribution, Metabolism, and Excretion (ADME) properties, including Lipinski's rule of five, which play an essential role in drug design. According to the toxicity parameters, fucoidan does not exhibit skin sensitivity, hepatotoxicity, or AMES toxicity. Therefore, this work reveals that fucoidan from brown macroalgae could act as possible inhibitors in regulating the function of the 3CLpro protein, hence inhibiting viral replication and being effective against COVID-19.

Activation of the NLRP1 Inflammasome and Its Role in Transmissible Gastroenteritis Coronavirus Infection

The inflammasome pathway is a critical early response mechanism of the host that detects pathogens, initiates the production of inflammatory cytokines, and recruits effector cells to the infection site. Nonetheless, the mechanism of inflammasome activation in coronavirus infection and its biological functions in host defense remain unclear. Transmissible gastroenteritis virus (TGEV), a member of the genus Alphacoronavirus, is a significant pathogen that mainly infects piglets and causes intestinal inflammation and inflammatory cell infiltration. Here, we investigated the mechanism of inflammasome activation in intestinal epithelial cells (IECs) infected with TGEV. We observed a substantial increase in interleukin 1β (IL-1β) and IL-18 levels in both IECs and TGEV-infected porcine intestinal tissues. Furthermore, TGEV infection resulted in increased activation of caspase-1 and the NLRP1 (NOD-like receptor [NLR]-containing pyrin domain [PYD]) inflammasome. Our findings revealed that TGEV infection impeded the interaction between porcine NLRP1 (pNLRP1) and porcine dipeptidyl peptidases 9 (pDPP9), yet it did not reduce the expression of pDPP9. Importantly, the ZU5 domain, not the function-to-find domain (FIIND) reported in human NLRP1, was identified as the minimal domain of pNLRP1 for pDPP9 binding. In addition, the robust type I IFN expression induced by TGEV infection also upregulated pNLRP1 expression and pNLRP1 itself acts as an interferon-stimulated gene to counteract TGEV infection. Our data demonstrate that pNLRP1 has antiviral capabilities against coronavirus infection, which highlights its potential as a novel therapeutic target for coronavirus antiviral therapy. IMPORTANCE Coronavirus primarily targets the epithelial cells of the respiratory and gastrointestinal tracts, leading to damage in both humans and animals. NLRP1 is a direct sensor for RNA virus infection which is highly expressed in epithelial barrier tissues. However, until recently, the precise molecular mechanisms underlying its activation in coronavirus infection and subsequent downstream events remained unclear. In this study, we demonstrate that the alphacoronavirus TGEV induces the production of IL-1β and IL-18 and upregulates the expression of pNLRP1. Furthermore, we found that pNLRP1 can serve as an interferon-stimulated gene (ISG) to inhibit the infection of enterovirus TGEV. Our research highlights the crucial role of NLRP1 as a regulator of innate immunity in TGEV infection and shows that it may serve as a potential therapeutic target for the treatment of coronavirus infection.

Different Mechanisms Are Utilized by Coronavirus Transmissible Gastroenteritis Virus To Regulate Interferon Lambda 1 and Interferon Lambda 3 Production

Type III interferons (IFN-λ) are shown to be preferentially produced by epithelial cells, which provide front-line protection at barrier surfaces. Transmissible gastroenteritis virus (TGEV), belonging to the genus Alphacoronavirus of the family Coronaviridae, can cause severe intestinal injuries in porcine, resulting in enormous economic losses for the swine industry, worldwide. Here, we demonstrated that although IFN-λ1 had a higher basal expression, TGEV infection induced more intense IFN-λ3 production in vitro and in vivo than did IFN-λ1. We explored the underlying mechanism of IFN-λ induction by TGEV and found a distinct regulation mechanism of IFN-λ1 and IFN-λ3. The classical RIG-I-like receptor (RLR) pathway is involved in IFN-λ3 but not IFN-λ1 production. Except for the signaling pathways mediated by RIG-I and MDA5, TGEV nsp1 induces IFN-λ1 and IFN-λ3 by activating NF-κB via the unfolded protein responses (UPR) PERK-eIF2α pathway. Furthermore, functional domain analysis indicated that the induction of IFN-λ by the TGEV nsp1 protein was located at amino acids 85 to 102 and was dependent on the phosphorylation of eIF2α and the nuclear translocation of NF-κB. Moreover, the recombinant TGEV with the altered amino acid motif of nsp1 85-102 was constructed, and the nsp1 (85-102sg) mutant virus significantly reduced the production of IFN-λ, compared with the wild strain. Compared to the antiviral activities of IFN-λ1, the administration of IFN-λ3 showed greater antiviral activity against TGEV infections in IPEC-J2 cells. In summary, our data point to the significant role of IFN-λ in the host innate antiviral responses to coronavirus infections within mucosal organs and in the distinct mechanisms of IFN-λ1 and IFN-λ3 regulation. IMPORTANCE Coronaviruses cause infectious diseases in various mammals and birds and exhibit an epithelial cell tropism in enteric and respiratory tracts. It is critical to explore how coronavirus infections modulate IFN-λ, a key innate cytokine against mucosal viral infection. Our results uncovered the different processes of IFN-λ1 and IFN-λ3 production that are involved in the classical RLR pathway and determined that TGEV nsp1 induces IFN-λ1 and IFN-λ3 production by activating NF-κB via the PERK-eIF2α pathway in UPR. These studies highlight the unique regulation of antiviral defense in the intestine during TGEV infection. We also demonstrated that IFN-λ3 induced greater antiviral activity against TGEV replication than did IFN-λ1 in IPEC-J2 cells, which is helpful in finding a novel strategy for the treatment of coronavirus infections.

Roles of RNA Sensors in Host Innate Response to Influenza Virus and Coronavirus Infections

Influenza virus and coronavirus are two important respiratory viruses, which often cause serious respiratory diseases in humans and animals after infection. In recent years, highly pathogenic avian influenza virus (HPAIV) and SARS-CoV-2 have become major pathogens causing respiratory diseases in humans. Thus, an in-depth understanding of the relationship between viral infection and host innate immunity is particularly important to the stipulation of effective control strategies. As the first line of defense against pathogens infection, innate immunity not only acts as a natural physiological barrier, but also eliminates pathogens through the production of interferon (IFN), the formation of inflammasomes, and the production of pro-inflammatory cytokines. In this process, the recognition of viral pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) is the initiation and the most important part of the innate immune response. In this review, we summarize the roles of RNA sensors in the host innate immune response to influenza virus and coronavirus infections in different species, with a particular focus on innate immune recognition of viral nucleic acids in host cells, which will help to develop an effective strategy for the control of respiratory infectious diseases.

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.

Chemical Nature of Metals and Metal-Based Materials in Inactivation of Viruses

In response to the enormous threat to human survival and development caused by the large number of viruses, it is necessary to strengthen the defense against and elimination of viruses. Metallic materials have been used against viruses for thousands of years due to their broad-spectrum antiviral properties, wide sources and excellent physicochemical properties; in particular, metal nanoparticles have advanced biomedical research. However, researchers in different fields hold dissimilar views on the antiviral mechanisms, which has slowed down the antiviral application of metal nanoparticles. As such, this review begins with an exhaustive compilation of previously published work on the antiviral capacity of metal nanoparticles and other materials. Afterwards, the discussion is centered on the antiviral mechanisms of metal nanoparticles at the biological and physicochemical levels. Emphasis is placed on the fact that the strong reducibility of metal nanoparticles may be the main reason for their efficient inactivation of viruses. We hope that this review will benefit the promotion of metal nanoparticles in the antiviral field and expedite the construction of a barrier between humans and viruses.

A first glimpse into the transcriptomic changes induced by the PaV1 infection in the gut of Caribbean spiny lobsters, Panulirus argus (Latreille, 1804) (Decapoda: Achelata: Palinuridae)

The Caribbean spiny lobster, Panulirus argus (Latreille, 1804) supports important fisheries in the Caribbean region. This species is affected by a deadly virus, Panulirus argus Virus 1 (PaV1), the only known pathogenic virus for this species. As infection progresses, the effects of PaV1 on its host become systemic, with far reaching impacts on the host's physiology, including structural injuries to its gastrointestinal organs, such as the hepatopancreas and the gut. This last one becomes highly compromised in the last stages of infection. Since the gut is a key organ for the physiological stability of lobsters, we compared the transcriptomic changes in the gut of juvenile individuals of Panulirus argus naturally infected with PaV1. In the RNA-Seq analysis, we obtained a total of 485 × 10⁶ raw reads. After cleaning, reads were de novo assembled into 68,842 transcripts and 50,257 unigenes. The length of unigenes ranged from 201 bp to 28,717 bp, with a N50 length of 2079, and a GC content of 40.61%. In the differential gene expression analysis, we identified a total of 3,405 non redundant differential transcripts, of which 1,920 were up-regulated and 1,485 were down-regulated. We found alterations in transcripts encoding for proteins involved in transcriptional regulation, splicing, postraductional regulation, protein signaling, transmembrane transport, cytoskeletal regulation, and proteolysis, among others. This is the first insight into the transcriptomic regulation of PaV1-P. argus interaction. The information generated can help to unravel the molecular mechanisms that may intervene in the gut during PaV1 infection.

All-Trans Retinoic Acid Attenuates Transmissible Gastroenteritis Virus-Induced Inflammation in IPEC-J2 Cells via Suppressing the RLRs/NF-κB Signaling Pathway

Transmissible gastroenteritis virus (TGEV) infection can cause transmissible gastroenteritis (TGE), especially in suckling piglets, resulting in a significant economic loss for the global pig industry. The pathogenesis of TGEV infection is closely related to intestinal inflammation. All-trans retinoic acid (ATRA) has anti-inflammatory activity and immunomodulatory properties, but it is unclear whether ATRA can attenuate the inflammatory response induced by TGEV. This study aimed to investigate the protective effect of ATRA on TGEV-induced inflammatory injury in intestinal porcine epithelial cells (IPEC-J2) and to explore the underlying molecular mechanism. The results showed that TGEV infection triggered inflammatory response and damaged epithelial barrier integrity in IPEC-J2 cells. However, ATRA attenuated TGEV-induced inflammatory response by inhibiting the release of pro-inflammatory cytokines, including IL-1β, IL-6, IL-8 and TNF-α. ATRA also significantly reversed the reduction of ZO-1 and Occludin protein levels induced by TGEV infection and maintained epithelial barrier integrity. Moreover, ATRA treatment significantly prevented the upregulation of IкBα and NF-κB p65 phosphorylation levels and the nuclear translocation of NF-кB p65 induced by TGEV. On the other hand, treatment of TGEV-infected IPEC-J2 cells with the NF-κB inhibitors (BAY11-7082) significantly decreased the levels of inflammatory cytokines. Furthermore, ATRA treatment significantly downregulated the mRNA abundance and protein levels of TLR3, TLR7, RIG-I and MDA5, and downregulated their downstream signaling molecules TRIF, TRAF6 and MAVS mRNA expressions in TGEV-infected IPEC-J2 cells. However, the knockdown of RIG-I and MDA5 but not TLR3 and TLR7 significantly reduced the NF-κB p65 phosphorylation level and inflammatory cytokines levels in TGEV-infected IPEC-J2 cells. Our results indicated that ATRA attenuated TGEV-induced IPEC-J2 cells damage via suppressing inflammatory response, the mechanism of which is associated with the inhibition of TGEV-mediated activation of the RLRs/NF-κB signaling pathway.

The Role of Unfolded Protein Response in Coronavirus Infection and Its Implications for Drug Design

Coronavirus is an important pathogen with a wide spectrum of infection and potential threats to humans and animals. Its replication occurs in the cytoplasm and is closely related to the endoplasmic reticulum (ER). Studies reported that coronavirus infection causes ER stress, and cells simultaneously initiate unfolded protein response (UPR) to alleviate the disturbance of ER homeostasis. Activation of the three branches of UPR (PERK, IRE1, and ATF6) modulates various signaling pathways, such as innate immune response, microRNA, autophagy, and apoptosis. Therefore, a comprehensive understanding of the relationship between coronavirus and ER stress is helpful to understand the replication and pathogenesis of coronavirus. This paper summarizes the current knowledge of the complex interplay between coronavirus and UPR branches, focuses on the effect of ER stress on coronavirus replication and coronavirus resistance to host innate immunity, and summarizes possible drug targets to regulate the impact of coronavirus infection.

Role of intestinal extracellular matrix-related signaling in porcine epidemic diarrhea virus infection

Porcine epidemic diarrhea virus (PEDV) is emerging as a major threat to the global swine industry. Clinical PEDV infection is associated with severe intestinal lesions, resulting in absorptive dysfunction and high mortality rates in suckling piglets. The extracellular matrix (ECM) is an important component of intestinal tissue, providing a structural framework and conveying tissue-specific signals to nearby enterocytes. In this study, we investigated the extensive ECM remodeling observed in intestinal epithelial cells infected with PEDV and elucidated the associated activated ECM receptor-related pathways. Protein-protein interaction network analysis revealed two significantly differentially expressed genes (cluster of differentiation 44 [CD44] and serpin family E member 1 [SERPINE1]) associated with the ECM. At the transcriptional level, both genes exhibited significant positive correlation with the extent of PEDV replication. Similarly, the expression of CD44 and PAI-1 (encoded by SERPINE1) was also increased in the intestines of piglets during viral infection. Furthermore, CD44 exhibited antiviral activity by enhancing the expression of antiviral cytokines (e.g., interleukin [IL]-6, IL-18, IL-11, and antimicrobial peptide beta-defensin 1) by activating nuclear factor-κB signaling. Conversely, PAI-1 was found to promote the release of progeny virions during PEDV infection, despite a decreased intracellular viral load. Nevertheless, the underlying mechanisms are still unclear. Taken together, our results highlighted the biological roles of specific ECM-regulated genes, i.e., CD44 and SERPINE1 in suppressing and promoting PEDV infection, thereby providing a theoretical foundation for the role of the ECM in intestinal infections and identifying potential therapeutic targets for PEDV.

Functions of Coronavirus Accessory Proteins: Overview of the State of the Art

Coronavirus accessory proteins are a unique set of proteins whose genes are interspersed among or within the genes encoding structural proteins. Different coronavirus genera, or even different species within the same coronavirus genus, encode varying amounts of accessory proteins, leading to genus- or species-specificity. Though accessory proteins are dispensable for the replication of coronavirus in vitro, they play important roles in regulating innate immunity, viral proliferation, and pathogenicity. The function of accessory proteins on virus infection and pathogenesis is an area of particular interest. In this review, we summarize the current knowledge on accessory proteins of several representative coronaviruses that infect humans or animals, including the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with an emphasis on their roles in interaction between virus and host, mainly involving stress response, innate immunity, autophagy, and apoptosis. The cross-talking among these pathways is also discussed.

Activation of the JNK/MAPK Signaling Pathway by TGF-β1 Enhances Neonatal Fc Receptor Expression and IgG Transcytosis

The neonatal Fc receptor (FcRn) transports maternal immunoglobulin G (IgG) to the foetus or newborn and protects the IgG from degradation. FcRn is expressed in several porcine tissues and cell types and its expression levels are regulated by immune and inflammatory events. IPEC-J2 cells are porcine intestinal columnar epithelial cells that were isolated from neonatal piglet mid-jejunum. We hypothesized that transforming growth factor β1 (TGF-β1) upregulated pFcRn expression in IPEC-J2 cells. To test this hypothesis, we treated IPEC-J2 cells with TGF-β1 and demonstrated that porcine FcRn (pFcRn) expression was significantly increased. SP600125, a specific mitogen-activated protein kinase (MAPK) inhibitor, reduced TGF-β1-induced pFcRn expression in IPEC-J2 cells. We performed luciferase reporter assays and showed that the c-JUN sensitive region of the pFcRn promoter gene was located between positions -1215 and -140. The c-JUN sequence, in combination with the pFcRn promoter, regulated luciferase reporter activity in response to TGF-β1 stimulation. Chromatin immunoprecipitation confirmed that there were three c-JUN binding sites in the pFcRn promoter. Furthermore, in addition to increased pFcRn expression, TGF-β1 also enhanced IgG transcytosis in IPEC-J2 cells. In summary, our data showed that the modulation of JNK/MAPK signaling by TGF-β1 was sufficient to upregulate pFcRn expression.

Porcine enteric coronaviruses: an updated overview of the pathogenesis, prevalence, and diagnosis

The recent prevalence of coronavirus (CoV) poses a serious threat to animal and human health. Currently, porcine enteric coronaviruses (PECs), including the transmissible gastroenteritis virus (TGEV), the novel emerging swine acute diarrhoea syndrome coronavirus (SADS-CoV), porcine delta coronavirus (PDCoV), and re-emerging porcine epidemic diarrhoea virus (PEDV), which infect pigs of different ages, have caused more frequent occurrences of diarrhoea, vomiting, and dehydration with high morbidity and mortality in piglets. PECs have the potential for cross-species transmission and are causing huge economic losses in the pig industry in China and the world, which therefore needs to be urgently addressed. Accordingly, this article summarises the pathogenicity, prevalence, and diagnostic methods of PECs and provides an important reference for their improved diagnosis, prevention, and control.

Antiviral effects of Bovine antimicrobial peptide against TGEV in vivo and in vitro

Background

In suckling piglets, transmissible gastroenteritis virus (TGEV) causes lethal diarrhea accompanied by high infection and mortality rates, leading to considerable economic losses. This study explored methods of preventing or inhibiting their production. Bovine antimicrobial peptide-13 (APB-13) has antibacterial, antiviral, and immune functions.

Objectives

This study analyzed the efficacy of APB-13 against TGEV through in vivo and in vitro experiments.

Methods

The effects of APB-13 toxicity and virus inhibition rate on swine testicular (ST) cells were detected using 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT). The impact of APB-13 on virus replication was examined through the 50% tissue culture infective dose (TCID₅₀). The mRNA and protein levels were investigated by real-time quantitative polymerase chain reaction and western blot (WB). Tissue sections were used to detect intestinal morphological development.

Results

The safe and effective concentration range of APB-13 on ST cells ranged from 0 to 62.5 µg/mL, and the highest viral inhibitory rate of APB-13 was 74.1%. The log₁₀TCID₅₀ of 62.5 µg/mL APB-13 was 3.63 lower than that of the virus control. The mRNA and protein expression at 62.5 µg/mL APB-13 was significantly lower than that of the virus control at 24 hpi. Piglets in the APB-13 group showed significantly lower viral shedding than that in the virus control group, and the pathological tissue sections of the jejunum morphology revealed significant differences between the groups.

Conclusions

APB-13 exhibited good antiviral effects on TGEV in vivo and in vitro.

Porcine deltacoronavirus nucleocapsid protein species-specifically suppressed IRF7-induced type I interferon production via ubiquitin-proteasomal degradation pathway

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The emerging PDCoV broadly infects porcine, human and chicken cells in vitro.

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PDCoV N protein interacts with the IRF7 in a species-specific manner.

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PDCoV N protein induces the porcine IRF7 degradation via ubiquitin-proteasomal pathway.

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The mechanism of PDCoV N protein suppressing the porcine type I IFN is different from those by other CoVs, such as SARS-CoV, MERS-CoV and PEDV.

Coronaviruses (CoVs) is showing obvious interspecies transmission, such as the SARS-CoV, MERS-CoV and SARS-CoV-2. Here, the emerging porcine deltacoronavirus (PDCoV) strain, isolated from Shanghai, China, broadly infects porcine, human and chicken cells in vitro. Previously studies by our group and others have confirmed that PDCoV nucleocapsid (N) protein performs an important role in antagonizing retinoic acid-induced gene I-like receptor (RLR) activation. However, the mechanism of PDCoV N protein suppressing porcine type I IFN production remains unclear, especially the downstream of porcine RLR signaling pathway. In the present study, porcine IRF7 (poIRF7) was identified as the interaction protein of PDCoV N protein through LC-MS/MS. The poIRF7 (268-487aa) was the key region of binding PDCoV N protein. Although IRF7 is a conserved functional protein in species, the PDCoV N protein has been confirmed to interact with only poIRF7 and significantly decrease poIRF7-induced type I IFN production, but not human or chicken IRF7. Furthermore, PDCoV N protein can promote poIRF7 degradation via the ubiquitin-proteasome pathway, which directly increased the K6, K11, and K29-linked polyubiquitination of poIRF7. Lysine 359 of poIRF7 was a key site in PDCoV N protein inducing poIRF7 degradation. Taken together, our results reveal a novel mechanism that PDCoV N protein could species-specifically interact with poIRF7 and then promote its degradation to suppress porcine type I IFN production. The novel findings provide a new insight into PDCoV and other zoonotic coronavirus evading the innate immune response of different species.

A synthetic stigmastane displays antiadenoviral activity and reduces the inflammatory response to viral infection

Although human adenovirus (ADV) infections are mild and self-limited in immunocompetent individuals, they can be severe and life-threatening in immunocompromised patients. Despite their significant clinical impact, there are not currently approved antiviral therapies for ADV infections. On the other hand, in some cases, the immune response induced by ADV infection can cause tissue damage. Even more, in the case of adenovirus vectors used in gene therapy, host immunity generally antagonize viral efficacy. Therefore, the need for searching an effective and safe therapy is increasing. In this work, we describe the antiadenoviral activity of the synthetic stigmastane (22S, 23S)-22,23-dihydroxystigmast-4-en-3-one (Compound 1) with already reported antiviral and antiinflammatory activities against other viruses of clinical importance. Compound 1 displayed no virucidal activity and did not affect ADV entry to the cells. The compound inhibited viral replication and it also reduced cytokine secretion in epithelial and inflammatory infected cells. Thus, Compound 1 would be a promissory drug potentially useful against adenoviral infections as well as an adjuvant of adenoviral vectors in gene therapy.

Transcriptome analysis provides insights into the antiviral response in the spleen of gibel carp (Carassius auratus gibelio) after poly I: C treatment

Gibel carp (Carassius auratus gibelio) is an important commercial fish that has become one of the most cultured fishes in the region of Yangtze River in China. However, the fish faces increasing hazard due to cyprinid herpesvirus 2 (CyHV-2) infection, which has caused great economic losses. In this study, healthy gibel carp were intraperitoneally injected with different doses of poly I:C at 24 h before CyHV-2 challenge. Results showed that the mortality decreased and peak death time appeared later in the fish injected with poly I:C at a dose of 10 μg/g body weight. To explore what gene plays an important role after poly I:C treatment, the transcriptome analysis of the gibel carp spleen was further performed. Compared with the PBS group, 1286 differentially expressed genes (DEGs) were obtained in the poly I:C-treated fish, including 1006 up-regulated and 280 down-regulated DEGs. GO analysis revealed that the most enriched DEGs responded to "biological regulation", "regulation of cellular process" and "regulation of biological process". Meanwhile, KEGG enrichment analysis showed that the DEGs were mainly mapped on the immune pathways like "TNF signal pathway", "p53 signal pathway" and "JAK-STAT signal pathway", suggesting that these signal pathways may be responsible for the delayed peak of CyHV-2 infection in gibel carp after poly I:C treatment. Taken together, this study provides insights into the immune protection effect of poly I:C against CyHV-2 infection, as well as providing useful information for antiviral defense in gibel carp.

Rapid and efficient detection methods of pathogenic swine enteric coronaviruses

Abstract

Porcine enteric coronaviruses (CoVs) cause highly contagious enteric diarrhea in suckling piglets. These COV infections are characterized by clinical signs of vomiting, watery diarrhea, dehydration, and high morbidity and mortality, resulting in significant economic losses and tremendous threats to the pig farming industry worldwide. Because the clinical manifestations of pigs infected by different CoVs are similar, it is difficult to differentiate between the specific pathogens. Effective high-throughput detection methods are powerful tools used in the prevention and control of diseases. The immune system of piglets is not well developed, so serological methods to detect antibodies against these viruses are not suitable for rapid and early detection. This paper reviews various PCR-based methods used for the rapid and efficient detection of these pathogenic CoVs in swine intestines.

Key points

Swine enteric coronaviruses (CoVs) emerged and reemerged in past years.

Enteric CoVs infect pigs at all ages with high mortality rate in suckling pigs.

Rapid and efficient detection methods are needed and critical for diagnosis.

Activation of C-Type Lectin Receptor and (RIG)-I-Like Receptors Contributes to Proinflammatory Response in Middle East Respiratory Syndrome Coronavirus-Infected Macrophages

BACKGROUND

Human infection with Middle East respiratory syndrome coronavirus (MERS-CoV) poses an ongoing threat to public health worldwide. The studies of MERS patients with severe disease and experimentally infected animals showed that robust viral replication and intensive proinflammatory response in lung tissues contribute to high pathogenicity of MERS-CoV. We sought to identify pattern recognition receptor (PRR) signaling pathway(s) that mediates the inflammatory cascade in human macrophages upon MERS-CoV infection.

METHODS

The potential signaling pathways were manipulated individually by pharmacological inhibition, small interfering ribonucleic acid (siRNA) depletion, and antibody blocking. The MERS-CoV-induced proinflammatory response was evaluated by measuring the expression levels of key cytokines and/or chemokines. Reverse transcription-quantitative polymerase chain reaction assay, flow cytometry analysis, and Western blotting were applied to evaluate the activation of related PRRs and engagement of adaptors.

RESULTS

MERS-CoV replication significantly upregulated C-type lectin receptor (CLR) macrophage-inducible Ca2+-dependent lectin receptor (Mincle). The role of Mincle for MERS-CoV-triggered cytokine/chemokine induction was established based on the results of antibody blockage, siRNA depletion of Mincle and its adaptor spleen tyrosine kinase (Syk), and Syk pharmacological inhibition. The cytokine and/or chemokine induction was significantly attenuated by siRNA depletion of retinoic acid-inducible-I-like receptors (RLR) or adaptor, indicating that RLR signaling also contributed to MERS-CoV-induced proinflammatory response.

CONCLUSIONS

The CLR and RLR pathways are activated and contribute to the proinflammatory response in MERS-CoV-infected macrophages.

Prevalence and phylogenetic analysis of porcine diarrhea associated viruses in southern China from 2012 to 2018

Background

In China, large-scale outbreaks of severe diarrhea caused by viruses have occurred in pigs since late 2010. To investigate the prevalence and genetic evolution of diarrhea-associated viruses responsible for the outbreaks, a total of 2987 field diarrheal samples collected from 168 pig farms in five provinces in Southern China during 2012–2018 were tested.

Results

Porcine epidemic diarrhea virus (PEDV) was most frequently detected virus with prevalence rates between 50.21 and 62.10% in samples, and 96.43% (162/168) in premises, respectively. Porcine deltacoronavirus (PDCoV) was the second prevalent virus with prevalence rates ranging from 19.62 to 29.19% in samples, and 70.24% (118/168) in premises, respectively. Both transmissible gastroenteritis virus (TGEV) and porcine rotavirus (PoRV) were detected at low prevalence rates of < 3% in samples and 10.12% in premises. In this study, we identified a newly emerged swine acute diarrhea syndrome coronavirus (SADS-CoV) in diarrheal samples of piglets from Fujian province in Southern China, and the prevalence rate of SADS-CoV was 10.29% (7/68). Co-infections of these diarrhea-associated viruses were common. The most frequent co-infection was PEDV with PDCoV, with an average detection rate of 12.72% (380/2987, ranging from 8.26–17.33%). Phylogenetic analysis revealed that PEDVs circulating in Southern China during the last 7 years were clustered with the variant strains of PEDV in genotype IIa. The most frequent mutations were present in the collagenase equivalent (COE) and epitope regions of the spike gene of the PEDVs currently circulating in the field. Genetic relationships of PDCoVs were closely related with Chinese strains, other than those present in the USA, South Korea, Thailand and Lao’s public.

Conclusions

The findings of this study indicated that variant PEDV, PDCoV, and SADS-CoV were leading etiologic agents of porcine diarrhea, and either mono-infections or co-infections of pathogenic enteric CoVs were common in pigs in Southern China during 2012–2018. Thus, significant attention should be paid in order to effectively prevent and control porcine viral diarrhea.

Identification and analysis of long non-coding RNAs that are involved in inflammatory process in response to transmissible gastroenteritis virus infection

Background

Transmissible gastroenteritis virus (TGEV) infection can cause acute inflammation. Long noncoding RNAs (lncRNAs) play important roles in a number of biological process including inflammation response. However, whether lncRNAs participate in TGEV-induced inflammation in porcine intestinal epithelial cells (IPECs) is largely unknown.

Results

In this study, the next-generation sequencing (NGS) technology was used to analyze the profiles of lncRNAs in Mock and TGEV-infected porcine intestinal epithelial cell-jejunum 2 (IPEC-J2) cell line. A total of 106 lncRNAs were differentially expressed. Many differentially expressed lncRNAs act as elements to competitively attach microRNAs (miRNAs) which target to messenger RNA (mRNAs) to mediate expression of genes that related to toll-like receptors (TLRs), NOD-like receptors (NLRs), tumor necrosis factor (TNF), and RIG-I-like receptors (RLRs) pathways. Functional analysis of the binding proteins and the up/down-stream genes of the differentially expressed lncRNAs revealed that lncRNAs were principally related to inflammatory response. Meanwhile, we found that the differentially expressed lncRNA TCONS_00058367 might lead to a reduction of phosphorylation of transcription factor p65 (p-p65) in TGEV-infected IPEC-J2 cells by negatively regulating its antisense gene promyelocytic leukemia (PML).

Conclusions

The data showed that differentially expressed lncRNAs might be involved in inflammatory response induced by TGEV through acting as miRNA sponges, regulating their up/down-stream genes, or directly binding proteins.

Manipulation of Intestinal Antiviral Innate Immunity and Immune Evasion Strategies of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) infection causes watery diarrhea, dehydration, and high mortality in neonatal pigs, due to its clinical pathogenesis of the intestinal mucosal barrier dysfunction. The host's innate immune system is the first line of defence upon virus invasion of the small intestinal epithelial cells. In turn, the virus has evolved to modulate the host's innate immunity during infection, resulting in pathogen virulence, survival, and the establishment of successful infection. In this review, we gather current knowledge concerning the interplay between PEDV and components of host innate immunity, focusing on the role of cytokines and interferons in intestinal antiviral innate immunity, and the mechanisms underlying the immune evasion strategies of PEDV invasion. Finally, we provide some perspectives on the potential prevention and treatment for PEDV infection.

Porcine transmissible gastroenteritis virus inhibits NF-κB activity via nonstructural protein 3 to evade host immune system

Background

Transmissible gastroenteritis virus (TGEV), a member of the family Coronaviridae, causes lethal watery diarrhea in piglets. Previous studies have revealed that the coronaviruses develop various strategies to evade the host innate immunity through the inhibition of nuclear factor kappa B (NF-κB) signaling pathway. However, the ability of TGEV to inhibit the host innate immune response by modulating the NF-κB signaling pathway is not clear.

Methods

In this study, a dual luciferase reporter assay was used to confirm the inhibition of NF-κB by TGEV infection and to identify the major viral proteins involved in the inhibition of NF-κB signaling. Real-time quantitative PCR was used to quantify the mRNA expression of inflammatory factors. The deubiquitination of Nsp3 domains and its effect on IκBα and p65 were analyzed by western blotting. The ubiquitination level of IκBα was analyzed by immunoprecipitation.

Results

In ST and IPEC-J2 cells, TGEV exhibited a dose-dependent inhibition of NF-κB activity. Individual TGEV protein screening revealed the high potential of non-structural protein 3 (Nsp3) to inhibit NF-κB signaling, and leading to the downregulation of the NF-κB-induced cytokine production. We demonstrated that the inhibitory effect of Nsp3 was mainly mediated through the suppression of IκBα degradation as well as the inhibition of p65 phosphorylation and nuclear translocation. Furthermore, the amino acid residues at positions 590–1,215 in Nsp3 were demonstrated to inhibit the degradation of IκBα by inhibiting the IκBα ubiquitination.

Conclusion

TGEV infection can inhibit the activation of the NF-κB signaling pathway, which is mainly mediated by Nsp3 through the canonical pathway. The amino acid residues at positions 590–1,215 in Nsp3 compose the critical domain that mediates NF-κB inhibition. We speculate that this inhibitory effect is likely to be related to the structure of PLP2 with deubiquitinating enzyme activity of the amino acid residues at positions 590–1,215 in Nsp3. Our study provides a better understanding of the TGEV-mediated innate immune modulation and lays the basis for studies on the pathogenesis of coronavirus.

Porcine deltacoronavirus nucleocapsid protein antagonizes IFN-β production by impairing dsRNA and PACT binding to RIG-I

Porcine deltacoronavirus (PDCoV) is an emerging swine enteropathogenic coronavirus that causes watery diarrhea, vomiting and mortality in newborn piglets. Previous studies have suggested that PDCoV infection antagonizes RIG-I-like receptor (RLR)-mediated IFN-β production to evade host innate immune defense, and PDCoV-encoded nonstructural protein nsp5 and accessory protein NS6 are associated with this process. However, whether the structural protein(s) of PDCoV also antagonize IFN-β production remains unclear. In this study, we found that PDCoV nucleocapsid (N) protein, the most abundant viral structural protein, suppressed Sendai virus (SEV)-induced IFN-β production and transcription factor IRF3 activation, but did not block IFN-β production induced by overexpressing RIG-I/MDA5. Furthermore, study revealed that PDCoV N protein interacted with RIG-I and MDA5 in an in vitro overexpression system and evident interactions between N protein and RIG-I could be detected in the context of PDCoV infection, which interfered with the binding of dsRNA and protein activator of protein kinase R (PACT) to RIG-I. Together, our results demonstrate that PDCoV N protein is an IFN antagonist and utilizes diverse strategies to attenuate RIG-I recognition and activation.

Arterivirus nsp4 Antagonizes Interferon Beta Production by Proteolytically Cleaving NEMO at Multiple Sites

Equine arteritis virus (EAV) and porcine reproductive and respiratory syndrome virus (PRRSV) represent two members of the family Arteriviridae and pose major threats for the horse- and swine-breeding industries worldwide. A previous study suggested that PRRSV nsp4, a 3C-like protease, antagonizes interferon beta (IFN-β) production by cleaving the NF-κB essential modulator (NEMO) at a single site, glutamate 349 (E349). Here, we demonstrated that EAV nsp4 also inhibited virus-induced IFN-β production by targeting NEMO for proteolytic cleavage and that the scission occurred at four sites: E166, E171, glutamine 205 (Q205), and E349. Additionally, we found that, besides the previously reported cleavage site E349 in NEMO, scission by PRRSV nsp4 took place at two additional sites, E166 and E171. These results imply that while cleaving NEMO is a common strategy utilized by EAV and PRRSV nsp4 to antagonize IFN induction, EAV nsp4 adopts a more complex substrate recognition mechanism to target NEMO. By analyzing the abilities of the eight different NEMO fragments resulting from EAV or PRRSV nsp4 scission to induce IFN-β production, we serendipitously found that a NEMO fragment (residues 1 to 349) could activate IFN-β transcription more robustly than full-length NEMO, whereas all other NEMO cleavage products were abrogated for the IFN-β-inducing capacity. Thus, NEMO cleavage at E349 alone may not be sufficient to completely inactivate the IFN response via this signaling adaptor. Altogether, our findings suggest that EAV and PRRSV nsp4 cleave NEMO at multiple sites and that this strategy is critical for disarming the innate immune response for viral survival.IMPORTANCE The arterivirus nsp4-encoded 3C-like protease (3CLpro) plays an important role in virus replication and immune evasion, making it an attractive target for antiviral therapeutics. Previous work suggested that PRRSV nsp4 suppresses type I IFN production by cleaving NEMO at a single site. In contrast, the present study demonstrates that both EAV and PRRSV nsp4 cleave NEMO at multiple sites and that this strategy is essential for disruption of type I IFN production. Moreover, we reveal that EAV nsp4 also cleaves NEMO at glutamine 205 (Q205), which is not targeted by PRRSV nsp4. Notably, targeting a glutamine in NEMO for cleavage has been observed only with picornavirus 3C proteases (3Cpro) and coronavirus 3CLpro In aggregate, our work expands knowledge of the innate immune evasion mechanisms associated with NEMO cleavage by arterivirus nsp4 and describes a novel substrate recognition characteristic of EAV nsp4.

Porcine Deltacoronavirus Nucleocapsid Protein Suppressed IFN-β Production by Interfering Porcine RIG-I dsRNA-Binding and K63-Linked Polyubiquitination

Porcine deltacoronavirus (PDCoV) is a newly detected porcine coronavirus causing serious vomiting and diarrhea in piglets, especially newborn piglets. There has been an outbreak of PDCoV in worldwide since 2014, causing significant economic losses in the pig industry. The interferon (IFN)-mediated antiviral response is an important component of virus-host interactions and plays an essential role in inhibiting virus infection. However, the mechanism of PDCoV escaping the porcine immune surveillance is unclear. In the present study, we demonstrated that the PDCoV nucleocapsid (N) protein antagonizes porcine IFN-β production after vesicular stomatitis virus (VSV) infection or poly(I:C) stimulation. PDCoV N protein also suppressed the activation of porcine IFN-β promoter when it was stimulated by porcine RLR signaling molecules. PDCoV N protein targeted porcine retinoic acid-inducible gene I (pRIG-I) and porcine TNF receptor associated factor 3 (pTRAF3) by directly interacting with them. The N-terminal region (1–246 aa) of PDCoV N protein was important for interacting with pRIG-I and interfere its function. We confirmed that PDCoV N antagonizes IFN-β production by associating with pRIG-I to impede it from binding double-stranded RNA. Furthermore, porcine Riplet (pRiplet) was an important activator for pRIG-I by mediating the K63-linked polyubiquitination. However, PDCoV N protein restrained the pRiplet binding pRIG-I to inhibit pRIG-I K63-linked polyubiquitination. Taken together, our results revealed a novel mechanism by which PDCoV N protein interferes with the early activation of pRIG-I in the host antiviral response. The novel findings provide a new insight into PDCoV on evading the host innate immune response and may provide new therapeutic targets and more efficacious vaccines strategies for PDCoV infections.

Porcine transmissible gastroenteritis virus nonstructural protein 2 contributes to inflammation via NF-κB activation

Transmissible gastroenteritis virus (TGEV) infection causes acute enteritis in swine of all ages, and especially in suckling piglets. Small intestinal inflammation is considered a central event in the pathogenesis of TGEV infections, and nuclear factor-kappa B (NF-κB) is a key transcription factor in the inflammatory response. However, it is unclear whether NF-κB is crucial for inducing inflammation during a TGEV infection. Our results show that NF-κB was activated in swine testicular (ST) cells and intestinal epithelial cell lines J2 (IPEC-J2) cells infected with TGEV, which is consistent with the up-regulation of pro-inflammatory cytokines. Treatment of TGEV-infected ST cells and IPEC-J2 cells with the NF-κB-specific inhibitor caused the down-regulation of pro-inflammatory cytokine expression, but did not significantly affect TGEV replication. Individual TGEV protein screening results demonstrated that Nsp2 exhibited a high potential for activating NF-κB and enhancing the expression of pro-inflammatory cytokines. Functional domain analyzes indicated that the first 120 amino acid residues of Nsp2 were essential for NF-κB activation. Taken together, these data suggested that NF-κB activation was a major contributor to TGEV infection-induced inflammation, and that Nsp2 was the key viral protein involved in the regulation of inflammation, with amino acids 1–120 playing a critical role in activating NF-κB.

Abbreviations: TCID50: 50% tissue culture infectious dose; DMEM: Dulbecco’s Modified Eagle Medium; eNOS: Endothelial nitric oxide synthase; FBS: fetal bovine serum; IFA: Indirect immunofluorescence; IκB: inhibitor of nuclear factor kappa-B; IL: interleukin; IPEC-J2: intestinal epithelial cell lines J2; IKK: IκB kinase; Luc: luciferase reporter gene; mAbs: monoclonal antibodies; MOI: multiple of infection; Nsp: nonstructural protein; NF-κB: nuclear factor-kappa ; ORFs: open reading frames; PBS: phosphate-buffered saline; p65 p-p65: phosphorylated; RT-PCR: reverse transcription PC; SeV: Sendai virus; ST: swine testicular; TGEV: Transmissible gastroenteritis virus; TNF-α: tumor necrosis factor α; UV-TGEV: Ultraviolet light-inactivated TGEV; ZnF: zinc finger

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

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IPI-2I cells are susceptible to TGEV, PDCoV, and PEAV.

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IPI-2I cells can be infected with PEDV, but with low efficiency.

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A homogeneous cell line IPI-FX is obtained from IPI-2I cells by sub-cloning.

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IPI-FX cells are highly susceptible to PEDV, TGEV, PDCoV, and PEAV.

Swine enteric coronavirus (CoV) is an important group of pathogens causing diarrhea in piglets. At least four kinds of swine enteric CoVs have been identified, including transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), and the emerging HKU2-like porcine enteric alphacoronavirus (PEAV). The small intestines, particularly the jejunum and ileum, are the most common targets of these four CoVs in vivo, and co-infections by these CoVs are frequently observed in clinically infected pigs. This study was conducted to investigate the susceptibility of the porcine ileum epithelial cell line, IPI-2I, to different swine enteric CoVs. We found that IPI-2I cells are highly susceptible to TGEV, PDCoV, and PEAV, as demonstrated by cytopathic effect and virus multiplication. However, only a small number of cells could be infected by PEDV, possibly due to the heterogeneity of IPI-2I cells. A homogeneous cell line, designated IPI-FX, obtained from IPI-2I cells by sub-cloning with limited serial dilutions, was found to be highly susceptible to PEDV. Furthermore, IPI-FX cells were also highly susceptible to TGEV, PDCoV, as well as PEAV. Thus, this sub-cloned IPI-FX cell line is an ideal cell model to study the mechanisms of infection, particularly co-infections of swine enteric CoVs.

Icariin Attenuates High Glucose-Induced Apoptosis, Oxidative Stress, and Inflammation in Human Umbilical Venous Endothelial Cells

Endothelial dysfunction is closely associated with diabetic complications. Icariin, a flavonoid glycoside isolated from the Epimedium plant species, exhibits antidiabetic properties. However, its impact on endothelial function remains poorly understood, particularly under hyperglycemia. In this study, we investigated the potential protective effect of icariin on high glucose-induced detrimental effects on vascular endothelial cells. Human umbilical venous endothelial cells were incubated in media containing 5.5 mM glucose (normal glucose) or 25 mM glucose (high glucose) in the presence or absence of 50 µM icariin for 72 h. We found that high glucose markedly induced cell apoptosis, enhanced reactive oxygen species generation, and elevated expression levels of inflammatory factors and cell adhesion molecules, which were greatly subdued by icariin supplementation. In conclusion, icariin exerted a beneficial effect on high glucose-induced endothelial dysfunction. This new finding provides a promising strategy for future treatment of diabetic vascular complications.

microRNA-222 Attenuates Mitochondrial Dysfunction During Transmissible Gastroenteritis Virus Infection

Transmissible gastroenteritis virus (TGEV) is a member of Coronaviridae family. Our previous research showed that TGEV infection could induce mitochondrial dysfunction and upregulate miR-222 level. Therefore, we presumed that miR-222 might be implicated in regulating mitochondrial dysfunction induced by TGEV infection. To verify the hypothesis, the effect of miR-222 on mitochondrial dysfunction was tested and we showed that miR-222 attenuated TGEV-induced mitochondrial dysfunction. To investigate the underlying molecular mechanism of miR-222 in TGEV-induced mitochondrial dysfunction, a quantitative proteomic analysis of PK-15 cells that were transfected with miR-222 mimics and infected with TGEV was performed. In total, 4151 proteins were quantified and 100 differentially expressed proteins were obtained (57 upregulated, 43 downregulated), among which thrombospondin-1 (THBS1) and cluster of differentiation 47 (CD47) were downregulated. THBS1 was identified as the target of miR-222. Knockdown of THBS1 and CD47 decreased mitochondrial Ca2+ level and increased mitochondrial membrane potential (MMP) level. Reversely, overexpression of THBS1 and CD47 elevated mitochondrial Ca2+ level and reduced mitochondrial membrane potential (MMP) level. Together, our data establish a significant role of miR-222 in regulating mitochondrial dysfunction in response to TGEV infection.

Differentially expressed non-coding RNAs induced by transmissible gastroenteritis virus potentially regulate inflammation and NF-κB pathway in porcine intestinal epithelial cell line

Background

Transmissible gastroenteritis virus (TGEV) infection can activate NF-κB pathway in porcine intestinal epithelial cells and result in severe inflammation. Non-coding RNAs (ncRNAs) are not translated into proteins and play an important role in many biological and pathological processes such as inflammation, viral infection, and mitochondrial damage. However, whether ncRNAs participate in TGEV-induced inflammation in porcine intestinal epithelial cells is largely unknown.

Results

In this study, the next-generation sequencing (NGS) technology was used to analyze the profiles of mRNAs, miRNAs, and circRNAs in Mock- and TGEV-infected intestinal porcine epithelial cell-jejunum 2 (IPEC-J2) cell line. A total of 523 mRNAs, 65 microRNAs (miRNAs), and 123 circular RNAs (circRNAs) were differentially expressed. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed differentially expressed mRNAs were linked to inflammation-related pathways, including NF-κB, Toll-like receptor, NOD-like receptor, Jak-STAT, TNF, and RIG-I-like receptor pathways. The interactions among mRNA, miRNA, and circRNA were analyzed. The data showed that ssc_circ_009380 and miR-22 might have interaction relationship. Dual-luciferase reporter assay confirmed that miR-22 directly bound to ssc_circ_009380. We also observed that overexpression of miR-22 led to a reduction of p-IκB-α and accumulation of p65 in nucleus in TGEV-infected IPEC-J2 cells. In contrast, inhibition of miR-22 had the opposite effects. Moreover, silencing of ssc_circ_009380 inhibited accumulation of p65 in nucleus and phosphorylation of IκB-α.

Conclusions

The data revealed that differentially expressed mRNAs and ncRNAs were primarily enriched in inflammation-related pathways and ssc_circ_009380 promoted activation of NF-κB pathway by binding miR-22 during TGEV-induced inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5128-5) contains supplementary material, which is available to authorized users.

[Retinal transcriptome profile in mice following dexamethasone treatment for endotoxin-induced uveitis]

OBJECTIVE

To investigate the changes in retinal transcriptome profile of mice with endotoxin-induced uveitis (EIU)following dexamethasone (DEX) treatment and explore the mechanisms underlying the therapeutic effect of DEX.

METHODS

EIU was induced in BALB/c mice by intravitreal injection of 125 ng lipopolysaccharide (LPS), followed by topical applicationof DEX (0.1%) eye drops every 4 h for 24 h. The anterior chamber inflammation was examined with a slit lamp and the clinicalscores were assessed. The morphological changes in the eyes were assessed at 24 h after LPS injection. The retinas wereharvested for analysis of transcriptome profile using the next-generation sequencing (NGS)-based RNA sequencing (RNA-seq), and the expressions of the inflammatory cytokines and the differentially expressed genes (DEGs) were verified using real-timePCR.

RESULTS

DEX alleviated the inflammatory response and reduced the mRNA expressions of IL-6, TNF- a, MCP-1 andICAM-1 at 24 h after LPS injection. A total of 52 DEGs were identified by RNA-seq. Within these DEGs, 37 genes were upregulated and 15 genes were down-regulated in LPS group as compared with DEX+LPS group. No significantly enriched GeneOntology (GO) terms was noted. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed 6up-regulated and 2 down-regulated KEGG pathways. RIG-I-like receptor signaling pathway and several immune- andinflammation-related genes including Ifit1, H2-T24, Mx2 and Eif2ak2 were significantly down regulated by DEX. Verificationwith RT-PCR yielded results consistent with these findings.

CONCLUSIONS

DEX alleviates LPS-induced inflammatory response inthe retina of mice, and such protective effect is probably mediated by RIG-I like receptor signal pathway and the immune-andinflammation-related genes.

The PERK Arm of the Unfolded Protein Response Negatively Regulates Transmissible Gastroenteritis Virus Replication by Suppressing Protein Translation and Promoting Type I Interferon Production

Coronavirus replication is closely associated with the endoplasmic reticulum (ER), the primary cellular organelle for protein synthesis, folding, and modification. ER stress is a common consequence in coronavirus-infected cells. However, how the virus-induced ER stress influences coronavirus replication and pathogenesis remains controversial. Here, we demonstrated that infection with the alphacoronavirus transmissible gastroenteritis virus (TGEV) induced ER stress and triggered the unfolded protein response (UPR) in vitro and in vivo, and ER stress negatively regulated TGEV replication in vitro Although TGEV infection activated all three UPR pathways (activating transcription factor 6 [ATF6], inositol-requiring enzyme 1 [IRE1], and protein kinase R-like ER kinase [PERK]), the virus-triggered UPR suppressed TGEV replication in both swine testicular (ST) and IPEC-J2 cells primarily through activation of the PERK-eukaryotic initiation factor 2α (eIF2α) axis, as shown by functional studies with overexpression, small interfering RNA (siRNA), or specific chemical inhibitors. Moreover, we demonstrated that PERK-eIF2α axis-mediated inhibition of TGEV replication occurs through phosphorylated eIF2α-induced overall attenuation of protein translation. In addition to direct inhibition of viral production, the PERK-eIF2α pathway activated NF-κB and then facilitated type I IFN production, resulting in TGEV suppression. Taken together, our results suggest that the TGEV-triggered PERK-eIF2α pathway negatively regulates TGEV replication and represents a vital aspect of host innate responses to invading pathogens.IMPORTANCE The induction of ER stress is a common outcome in cells infected with coronaviruses. The UPR initiated by ER stress is actively involved in viral replication and modulates the host innate responses to the invading viruses, but these underlying mechanisms remain incompletely understood. We show here that infection with the alphacoronavirus TGEV elicited ER stress in vitro and in vivo, and the UPR PERK-eIF2α branch was predominantly responsible for the suppression of TGEV replication by ER stress. Furthermore, the PERK-eIF2α axis inhibited TGEV replication through direct inhibition of viral proteins due to global translation inhibition and type I IFN induction. These findings highlight a critical role of the UPR PERK-eIF2α pathway in modulating host innate immunity and coronavirus replication.

Agaricus blazei Murill Polysaccharides Protect Against Cadmium-Induced Oxidative Stress and Inflammatory Damage in Chicken Spleens

Agaricus blazei Murill polysaccharide (ABP) has exhibited antioxidant and immunoregulatory activity. The aim of this study was to investigate the effect of ABP on cadmium (Cd)-induced antioxidant functions and inflammatory damage in chicken spleens. In this study, groups of 7-day-old chickens were fed with normal saline (0.2 mL single/day), CdCl₂ (140 mg/kg/day), ABP (30 mg/mL, 0.2 mL single/day), and Cd + ABP (140 mg/kg/day + 0.2 mL ABP). Spleens were separated on the 20th, 40th, and 60th day for each group. The Cd contents, expression of melanoma-associated differentiation gene 5 (MDA5) and its downstream signaling molecules (interferon promoter-stimulating factor 1 (IPS-1), transcription factors interferon regulatory factor 3 (IRF3), and nuclear factor kappa-light chain-enhancer of activated B cells (NF-κB)), the content of cytokines (interleukin 1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α) and beta interferon (IFN-β)), protein levels of heat shock proteins (HSPs), levels of malondialdehyde (MDA), activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and histopathological changes of spleens were detected on the 20th, 40th, and 60th day. The results showed that ABP significantly reduced the accumulation of Cd in the chicken spleens and reduced the expression of MDA5, IPS-1, IRF-3, and NF-κB; their downstream inflammatory cytokines, IL-1β, IL-6, TNF-α, and IFN-β; and the protein levels of HSPs (HSP60, HSP70, and HSP90) in spleens. The activities of antioxidant enzymes (SOD and GSH-Px) significantly increased, and the level of MDA decreased in the ABP + Cd group. The results indicate that ABP has a protective effect on Cd-induced damage in chicken spleens.

The mechanisms of Ag85A DNA vaccine activates RNA sensors through new signal transduction

Low immunogenicity is one of the major problems limiting the clinical use for DNA vaccines, which makes it impossible to obtain a strong protective immune response after vaccination. In order to explore whether Ag85A DNA vaccine could mount more efficiently protective immune response through new RNA sensor and its signal transduction pathway of antigen presentation we designed and synthesized Ag85A gene fragment containing multiple points mutations and transfected the gene fragment into the dendritic cell line (DC2.4) by CRISPR/Cas9. Subsequently, we focused on the changes of RNA sensors RIG-I, Mda-5, and the downstream adaptors MAVS, IRF3, IRF7 and IFN-β. The results indicated the significant increases in the mRNA and protein expression of RNA sensors RIG-I, Mda-5 and related adaptors MAVS, IRF3, IRF7, and IFN-β in the mutant DC 2.4 cells. The flow cytometry results demonstrated that the expression of MHC II on the surface of DC 2.4 significantly increased when compared with that in control. Therefore, it is suggested that Ag85A mutant DNA could release immunogenic message through RNA sensors and related adaptors via non protein pathway. There is at least one RNA signal transduction pathway of Ag85A DNA in DC2.4 cell. The work provides a new mode of action for nucleic acid vaccine to improve immunogenicity and meaningful data for the better understanding of the mechanisms of DNA vaccine.

microRNA-4331 Promotes Transmissible Gastroenteritis Virus (TGEV)-induced Mitochondrial Damage Via Targeting RB1, Upregulating Interleukin-1 Receptor Accessory Protein (IL1RAP), and Activating p38 MAPK Pathway In Vitro

Transmissible gastroenteritis virus (TGEV), a member of the coronaviridae family, could cause fatal diarrhea of piglets and result in numerous economic losses. Previous studies demonstrated that TGEV infection could lead to mitochondrial damage and upregulate miR-4331 level. So miR-4331 may play an important regulatory role in the control of mitochondrial function. To explore the potential role of miR-4331 in mitochondrial damage, we adopted a strategy consisting of quantitative proteomic analysis of porcine kidney (PK-15) cells in response to miR-4331 and TGEV infection. Eventually, 69 differentially expressed proteins were gained. The target of miR-4331 was identified. The effects of miR-4331 and its target RB1 on mitochondrial Ca²⁺ level, mitochondrial membrane potential (MMP), interleukin-1 receptor accessory protein (IL1RAP), p38 MAPK signaling pathway were investigated. The results showed that miR-4331 elevated mitochondrial Ca²⁺ level, reduced MMP, targets Retinoblastoma 1 (RB1), upregulated IL1RAP, and induced activation of p38 MAPK pathway during TGEV infection. RB1 was identified as the direct targets of miR-4331 and downregulated IL1RAP, suppressed the activation of p38 MPAK, and attenuated TGEV-induced mitochondrial damage. In addition, IL1RAP played a positive role in activating p38 MAPK signaling and negative role in TGEV-induced mitochondrial damage. The data indicate that miR-4331 aggravates TGEV-induced mitochondrial damage by repressing expression of RB1, promoting IL1RAP, and activating p38 MAPK pathway.

Transmissible Gastroenteritis Virus Papain-Like Protease 1 Antagonizes Production of Interferon-β through Its Deubiquitinase Activity

Coronaviruses (CoVs), such as human coronavirus NL63 (HCoV-NL63), severe acute respiratory syndrome CoV (SARS-CoV), murine hepatitis virus (MHV), porcine epidemic diarrhea virus (PEDV), and Middle East Respiratory Syndrome Coronavirus (MERS-CoV), encode papain-like (PL) proteases that inhibit Sendai virus- (SeV-) induced interferon (IFN-β) production. Recently, the crystal structure of transmissible gastroenteritis virus (TGEV) PL1 has been solved, which was similar to that of SARS-CoV PL2pro, which may antagonize host innate immunity. However, very little is known about whether TGEV PL1 can antagonize host innate immune response. Here, we presented evidence that TGEV PL1 encoded by the replicase gene could suppress the IFN-β expression and inhibit the nuclear translocation of interferon regulatory factor 3 (IRF3). The ability to antagonize IFN-β production was dependent on the intact catalytic activity of PL1. Furthermore, TGEV PL1 exerted deubiquitinase (DUB) activity which strongly inhibited the retinoic acid-induced gene I- (RIG-1-) and stimulator of interferon gene- (STING-) dependent IFN expression. Our data collectively suggest that TGEV PL1 can inhibit the IFN-β expression and interfere with RIG-1- and STING-mediated signaling through a viral DUB activity. Our study has yielded strong evidence for the TGEV PL1 mechanisms that counteract the host innate immunity.

Astragalus Polysaccharide Protect against Cadmium-Induced Cytotoxicity through the MDA5/NF-κB Pathway in Chicken Peripheral Blood Lymphocytes

Cadmium (Cd) is a known environmental pollutant that is associated with inflammation, oxidative stress, and cell apoptosis. Astragalus polysaccharide (APS) is a major component of Astragalus membranaceus, a vital qi-reinforcing herb medicine with favorable immuneregulation properties. To study the effect of APS on the inhibition of the cadmium-induced injury of peripheral blood lymphocytes (PBLs) in chickens through the MDA5/NF-κB signaling pathway, PLBs acquired from 15-day-old chickens were divided into control group, Cd group, APS + Cd group, anti-MDA5 mAb + Cd group, BAY 11-7082 (a nuclear factor kappa-light chain-enhancer of activated B cells [NF-κB] inhibitor) +Cd group, APS group, anti-MDA5 mAb group, and BAY 11-7082 group. The transcription levels of melanoma differentiation-associated gene 5 (MDA5), interferon promoter-stimulating factor 1 (IPS-1), NF-κB, and inflammatory factors tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured by quantitative real-time PCR. MDA5 protein expression was measured by western blotting. Levels of malondialdehyde (MDA), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) were measured by corresponding antioxidant kit. The morphological change of PBLs was measured by transmission electron microscopy. The results showed that Cd significantly increased the expression of MDA5, IPS-1, NF-κB, and their downstream cytokines, IL-1β and TNF-α, IL-6 in PLBs. In addition, a high level of MDA was observed in the Cd treatment group; the activities of GSH-Px and SOD were significantly lower in the Cd treatment group than those in controls (p < 0.05). Ultrastructural changes of PBLs showed that Cd promoted autophagy, apoptosis, and necrosis in PBLs. However, APS can efficiently improve Cd-induced cell damage by decreasing the activation of the MDA5 signaling pathway. The effect is consistent with that of anti-MDA5 mAb or/and BAY. The results indicated that APS inhibited Cd-induced cytotoxicity through the regulation of MDA5/NF-κB signaling.