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

Porcine deltacoronavirus nonstructural protein 2 inhibits type I and III IFN production by targeting STING for degradation

Porcine deltacoronavirus (PDCoV) is an enteropathogenic coronavirus that has been reported to use various strategies to counter the host antiviral innate immune response. The cGAS-STING signalling pathway plays an important role in antiviral innate immunity. However, it remains unclear whether PDCoV achieves immune evasion by regulating the cGAS-STING pathway. Here, we demonstrated that the nonstructural protein 2 (nsp2) encoded by PDCoV inhibits cGAS-STING-mediated type I and III interferon (IFN) responses via the regulation of porcine STING (pSTING) stability. Mechanistically, ectopically expressed PDCoV nsp2 was found to interact with the N-terminal region of pSTING. Consequently, pSTING was degraded through K48-linked ubiquitination and the proteasomal pathway, leading to the disruption of cGAS-STING signalling. Furthermore, K150 and K236 of pSTING were identified as crucial residues for nsp2-mediated ubiquitination and degradation. In summary, our findings provide a basis for elucidating the immune evasion mechanism of PDCoV and will contribute to the development of targets for anti-coronavirus drugs.

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.

Traditional Chinese medicine Pien-Tze-Huang ameliorates LPS-induced sepsis through bile acid-mediated activation of TGR5-STAT3-A20 signalling

Pien Tze Huang (PZH), a class I nationally protected traditional Chinese medicine (TCM), has been used to treat liver diseases such as hepatitis; however, the effect of PZH on the progression of sepsis is unknown. Here, we reported that PZH attenuated lipopolysaccharide (LPS)-induced sepsis in mice and reduced LPS-induced production of proinflammatory cytokines in macrophages by inhibiting the activation of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signalling. Mechanistically, PZH stimulated signal transducer and activator of transcription 3 (STAT3) phosphorylation to induce the expression of A20, which could inhibit the activation of NF-κB and MAPK signalling. Knockdown of the bile acid (BA) receptor G protein-coupled bile acid receptor 1 (TGR5) in macrophages abolished the effects of PZH on STAT3 phosphorylation and A20 induction, as well as the LPS-induced inflammatory response, suggesting that BAs in PZH may mediate its anti-inflammatory effects by activating TGR5. Consistently, deprivation of BAs in PZH by cholestyramine resin reduced the effects of PZH on the expression of phosphorylated-STAT3 and A20, the activation of NF-κB and MAPK signalling, and the production of proinflammatory cytokines, whereas the addition of BAs to cholestyramine resin-treated PZH partially restored the inhibitory effects on the production of proinflammatory cytokines. Overall, our study identifies BAs as the effective components in PZH that activate TGR5-STAT3-A20 signalling to ameliorate LPS-induced sepsis.

METTL3 enhances E. coli F18 resistance by targeting IKBKG/NF-κB signaling via an m6A-YTHDF1-dependent manner in IPEC-J2 cells

Post-weaning diarrhea caused by enterotoxigenic E. coli F18 introduces enormous losses to the porcine industry. N6-methyladenosine (m6A) is a ubiquitous epitranscriptomic biomarker that modulates host cell resistance to pathogen infection, however, its significance in E. coli F18-treated IPEC-J2 cells remains unexplored. Herein, we revealed that m6A and associated modulators strongly controlled E. coli F18 susceptibility. The data indicated an enhancement of METTL3 contents in E. coli F18-treated IPEC-J2 cells. METTL3 is known to be a major modulator of E. coli F18 adhesion within IPEC-J2 cells. As expected, METTL3 deficiency was observed to reduce m6A content at the IKBKG 5'-UTR, leading to critical suppression of YTHDF1-dependent IKBKG translation. Therefore, the activation of the NF-κB axis was observed, which enhanced IPEC-J2 resistance to E. coli F18 infection. Taken together, these findings uncover a potential mechanism underlying the m6A-mediated control of E. coli F18 susceptibility. This information may contribute to the establishment of new approaches for combating bacteria-induced diarrhea in piglets.

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.

Advances in the understanding of circRNAs that influence viral replication in host cells

Circular RNAs (circRNAs) are non-coding RNAs discovered in recent years, which are produced by back-splicing involving the 3' and 5' ends of RNA molecules. There is increasing evidence that circRNAs have important roles in cancer, neurological diseases, cardiovascular and cerebrovascular diseases, and other diseases. In addition, host circRNAs and virus-encoded circRNAs participate in the body's immune response, with antiviral roles. This review summarizes the mechanisms by which host and viral circRNAs interact during the host immune response. Comprehensive investigations have revealed that host circRNAs function as miRNA sponges in a particular manner, primarily by inhibiting viral replication. Viral circRNAs have more diverse functions, which generally involve promoting viral replication. In addition, in contrast to circRNAs from RNA viruses, circRNAs from DNA viruses can influence host cell migration, proliferation, and apoptosis, along with their effects on viral replication. In summary, circRNAs have potential as diagnostic and therapeutic targets, offering a foundation for the diagnosis and treatment of viral diseases.

Intragenomic rearrangements involving 5'-untranslated region segments in SARS-CoV-2, other betacoronaviruses, and alphacoronaviruses

BACKGROUND

Variation of the betacoronavirus SARS-CoV-2 has been the bane of COVID-19 control. Documented variation includes point mutations, deletions, insertions, and recombination among closely or distantly related coronaviruses. Here, we describe yet another aspect of genome variation by beta- and alphacoronaviruses that was first documented in an infectious isolate of the betacoronavirus SARS-CoV-2, obtained from 3 patients in Hong Kong that had a 5'-untranslated region segment at the end of the ORF6 gene that in its new location translated into an ORF6 protein with a predicted modified carboxyl terminus. While comparing the amino acid sequences of translated ORF8 genes in the GenBank database, we found a subsegment of the same 5'-UTR-derived amino acid sequence modifying the distal end of ORF8 of an isolate from the United States and decided to carry out a systematic search.

METHODS

Using the nucleotide and in the case of SARS-CoV-2 also the translated amino acid sequence in three reading frames of the genomic termini of coronaviruses as query sequences, we searched for 5'-UTR sequences in regions other than the 5'-UTR in SARS-CoV-2 and reference strains of alpha-, beta-, gamma-, and delta-coronaviruses.

RESULTS

We here report numerous genomic insertions of 5'-untranslated region sequences into coding regions of SARS-CoV-2, other betacoronaviruses, and alphacoronaviruses, but not delta- or gammacoronaviruses. To our knowledge this is the first systematic description of such insertions. In many cases, these insertions would change viral protein sequences and further foster genomic flexibility and viral adaptability through insertion of transcription regulatory sequences in novel positions within the genome. Among human Embecorivus betacoronaviruses, for instance, from 65% to all of the surveyed sequences in publicly available databases contain inserted 5'-UTR sequences.

CONCLUSION

The intragenomic rearrangements involving 5'-untranslated region sequences described here, which in several cases affect highly conserved genes with a low propensity for recombination, may underlie the generation of variants homotypic with those of concern or interest and with potentially differing pathogenic profiles. Intragenomic rearrangements thus add to our appreciation of how variants of SARS-CoV-2 and other beta- and alphacoronaviruses may arise.

Porcine Epidemic Diarrhea Virus nsp13 Protein Downregulates Neonatal Fc Receptor Expression by Causing Promoter Hypermethylation through the NF-κB Signaling Pathway

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic porcine enteric coronavirus that causes severe watery diarrhea and even death in piglets. The neonatal Fc receptor (FcRn) is the only transport receptor for IgG. FcRn expressed by intestinal epithelial cells can transport IgG from breast milk to piglets to provide immune protection. Previous studies have shown that viral infection affects FcRn expression. In this study, we showed for the first time, to our knowledge, that FcRn expression can be influenced by methyltransferases. In addition, we found that PEDV inhibited FcRn protein synthesis in porcine small intestinal epithelial cells postinfection. Then, we found that PEDV interfered with the transcription of genes through aberrant methylation modification of the FcRn promoter. DNA methyltransferase 3b (DNMT3b) has been implicated in this process. Using a series of PEDV structural and nonstructural protein (nsp) expression plasmids, we showed that nsp13 plays an important role in this aberrant methylation modification. PEDV nsp13 can affect the NF-κB canonical pathway and promote DNMT3b protein expression by facilitating p65 protein binding to chromatin. PEDV caused aberrant methylation of the FcRn promoter via DNMT3b. The same phenomenon was found in animal experiments with large white piglets. IgG transcytosis demonstrated that PEDV nsp13 can inhibit bidirectional IgG transport by FcRn. In addition, the core region of nsp13 (230-597 aa) is critical for FcRn inhibition. Taken together, to our knowledge, our findings revealed a novel immune escape mechanism of PEDV and shed new light on the design and development of vaccines and drugs.

Transmissible Gastroenteritis Virus: An Update Review and Perspective

Transmissible gastroenteritis virus (TGEV) is a member of the alphacoronavirus genus, which has caused huge threats and losses to pig husbandry with a 100% mortality in infected piglets. TGEV is observed to be recombining and evolving unstoppably in recent years, with some of these recombinant strains spreading across species, which makes the detection and prevention of TGEV more complex. This paper reviews and discusses the basic biological properties of TGEV, factors affecting virulence, viral receptors, and the latest research advances in TGEV infection-induced apoptosis and autophagy to improve understanding of the current status of TGEV and related research processes. We also highlight a possible risk of TGEV being zoonotic, which could be evidenced by the detection of CCoV-HuPn-2018 in humans.

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.

Identification of key proteins of cytopathic biotype bovine viral diarrhoea virus involved in activating NF-κB pathway in BVDV-induced inflammatory response

Bovine viral diarrhoea virus (BVDV) is the etiologic agent of bovine viral diarrhea-mucosal disease, one of the most important viral diseases in cattle, with inflammatory diarrhea, enteritis, and mucosa necrosis as the major clinical manifestations. NF-κB is an important transcription complex that regulates the expression of genes involved in inflammation and immune responses. NLRP3 inflammasome plays a key role in the development of inflammatory diseases. However, whether the activation of NF-κB is crucial for BVDV infection-induced inflammatory responses remains unclear. The results of our present study showed that BVDV infection significantly activated the NF-κB pathway and promoted the expression of NLRP3 inflammasome components (NLRP3, ASC, pro-caspase 1) as well inflammatory cytokine pro-IL-1β in BVDV-infected bovine cells, resulting in the cleavage of pro-caspase 1 and pro-IL-1β into active form caspase 1 and IL-1β. However, the levels of the NLRP3 inflammasome components and inflammatory cytokines were obviously inhibited, as well the cleavage of pro-caspase 1 and pro-IL-1β in the pre-treated bovine cells with NF-κB-specific inhibitors after BVDV infection. Further, cytopathic biotype BVDV (cpBVDV) Erns and NS5A proteins with their key functional domains contributed to BVDV-induced inflammatory responses via activating the NF-κB pathway were confirmed experimentally. Especially, the NS5A can promote cholesterol synthesis and accelerate its augmentation, further activating the NF-κB signalling pathway. Conclusively, our data elucidate that the activation of NF-κB signaling pathway plays a crucial role in cpBVDV infection-induced inflammatory responses.

The matrix protein of Newcastle disease virus inhibits inflammatory response through IRAK4/TRAF6/TAK1/NF-κB signaling pathway

The matrix (M) protein of several cytoplasmic RNA viruses has been reported to be an NF-κB pathway antagonist. However, the function and mechanism of NDV M protein antagonizing NF-κB activation remain largely unknown. In this study, we found that the expression levels of IRAK4, TRAF6, TAK1, and RELA/p65 were obviously reduced late in NDV infection. In addition, the cytoplasmic M protein rather than other viral proteins decreased the expression of these proteins in a dose-dependent manner. Further indepth analysis showed that the N-terminal 180 amino acids of M protein were not only responsible for the reduced expression of these proteins, but also responsible for the inhibition of NF-κB activation and nuclear translocation of RELA/p65, as well as the production of inflammatory cytokines. Moreover, small interference RNA-mediated knockdown of IRAK4 or overexpression of IRAK4 markedly enhanced or reduced NDV replication by decreasing or increasing inflammatory cytokines production through the IRAK4/TRAF6/TAK1/NF-κB signaling pathway. Strangely, there were no interactions detected between NDV M protein and IRAK4, TRAF6, TAK1 or RELA/p65. Our findings described here contribute to a better understanding of the innate immune antagonism function of M protein and the molecular mechanism underlying the replication and pathogenesis of NDV.

Modulation of Innate Antiviral Immune Response by Porcine Enteric Coronavirus

Host’s innate immunity is the front-line defense against viral infections, but some viruses have evolved multiple strategies for evasion of antiviral innate immunity. The porcine enteric coronaviruses (PECs) consist of porcine epidemic diarrhea virus (PEDV), porcine deltacoronavirus (PDCoV), transmissible gastroenteritis coronavirus (TGEV), and swine acute diarrhea syndrome-coronavirus (SADS-CoV), which cause lethal diarrhea in neonatal pigs and threaten the swine industry worldwide. PECs interact with host cells to inhibit and evade innate antiviral immune responses like other coronaviruses. Moreover, the immune escape of porcine enteric coronaviruses is the key pathogenic mechanism causing infection. Here, we review the most recent advances in the interactions between viral and host’s factors, focusing on the mechanisms by which viral components antagonize interferon (IFN)-mediated innate antiviral immune responses, trying to shed light on new targets and strategies effective for controlling and eliminating porcine enteric coronaviruses.

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.

Paeonol Ameliorates Abdominal Aortic Aneurysm Progression by the NF-κB Pathway

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by localized progressive dilatation. Currently, paeonol has been shown to possess anti-inflammatory and protective cardiovascular properties. Our study aimed to investigate the potential influences of paeonol on AAA progression.

METHODS

Experimental AAAs were created in C57BL/6J mice by intra-aortic infusion of porcine pancreatic elastase, and then intragastrically administered paeonol (20 mg/kg/day) for 14 days. The effects of paeonol on experimental AAA were measured by ultrasound imaging, histopathology, and western blot analyses.

RESULTS

Paeonol treatment limited the enlargement of the aneurysmal diameter and alleviated the depletion of elastic fibers and vascular smooth muscle cells (VSMCs). Furthermore, the infiltration of CD68+ macrophages and CD8+ lymphocytes was obviously attenuated after paeonol administration, along with mural neoangiogenesis. Western blot results showed that paeonol inhibited the expression of matrix metalloproteinase (MMP) and the NF-κB pathway activation.

CONCLUSIONS

Paeonol might prevent experimental AAA progression by inhibiting the NF-κB pathway, which suggests that it is a potential drug for AAA.

Transcriptomics Analysis Reveals the Immune Response Mechanism of Rabbits with Diarrhea Fed an Antibiotic-Free Diet

Simple Summary

Feeding an antibiotic-free diet is an inevitable trend in animal husbandry in China. In this study, high-throughput sequencing was used to analyze the gene expression differences in various intestinal segments of rabbits. Our analysis identified 168, 593, 2069, 334, 321, and 1423 DEGs in the comparison groups S_Z (the duodenum of healthy rabbits) vs. S_B (diarrhea in the duodenum of rabbits), K_Z (healthy rabbit jejunum) vs. K_B (rabbits with diarrhea in the jejunum), H_Z (healthy rabbit ileum) vs. H_B (rabbits with diarrhea in the ileum), M_Z (healthy cecum of rabbits) vs. M_B (rabbit with diarrhea in the cecum), J_Z (healthy rabbit colon) vs. J_B (colon of rabbits with diarrhea), and Z_Z (healthy rabbit rectum) vs. Z_B (rectum of rabbits with diarrhea), respectively. The reproducibility and repeatability of the results were validated by RT-qPCR. Enrichment analyses of GO annotations and KEGG pathways revealed the host DEGs that are potentially related to acute inflammation, stress response, tissue dehydration, adaptive immune response, protein binding, activation of related enzymes, migration of immune cells, and so on. In this descriptive study, our findings revealed the changes in the host transcriptome expression profile while feeding an antibiotic-free diet and suggested that feeding an antibiotic-free diet alters the host’s metabolic network and the expression of antiviral proteins.

Abstract

China officially promulgated the announcement of banning the use of antibiotics in the animal industry in 2020. However, the prohibition of antibiotics in the animal industry would reduce the feed conversion rate and increase the mortality of animals. In order to obtain information about the pathogenesis and host immune response of rabbits with diarrhea after being fed an antibiotic-free diet, we first analyzed the intestinal tissue sections of rabbits. Secondly, the gene expression differences of rabbit intestinal segments were analyzed by high-throughput sequencing. Our analysis identified 168, 593, 2069, 334, 321, and 1423 DEGs in the comparison groups S_Z (the duodenum of healthy rabbits) vs. S_B (diarrhea in the duodenum of rabbits), K_Z (healthy rabbit jejunum) vs. K_B (rabbits with diarrhea in the jejunum), H_Z (healthy rabbit ileum) vs. H_B (rabbits with diarrhea in the ileum), M_Z (healthy cecum of rabbits) vs. M_B (rabbits with diarrhea in the cecum), J_Z (healthy rabbit colon) vs. J_B (colon of rabbits with diarrhea), and Z_Z (healthy rabbit rectum) vs. Z_B (rectum of rabbits with diarrhea), respectively. The reproducibility and repeatability of the results were validated by RT-qPCR. Enrichment analyses of GO annotations and KEGG pathways revealed the host DEGs that are potentially related to acute inflammation, stress response, tissue dehydration, adaptive immune response, protein binding, activation of related enzymes, migration of immune cells, and so on. In this descriptive study, our findings revealed the changes in the host transcriptome expression profile after feeding an antibiotic-free diet and suggested that feeding an antibiotic-free diet alters the host’s metabolic network and the expression of antiviral proteins, which provides a theoretical basis for further study on the immune response of animals fed an antibiotic-free diet.

Transmissible gastroenteritis virus ORF3b up-regulates miR-885-3p to counteract TNF-α production via inhibiting NF-κB pathway

Transmissible gastroenteritis (TGE) is an acute viral disease and characterized as severe acute inflammation response that leads to diarrhea, vomiting, and high lethality of piglets. Transmissible gastroenteritis virus (TGEV), a member of coronavirus, is the pathogen of TGE. We previously found NF-κB pathway was activated and 65 miRNAs were changed in response to inflammation caused by TGEV in cell line porcine intestinal epithelial cells-jejunum 2 (IPEC-J2). Bioinformatics results showed that these altered miRNAs were relevant to inflammation. In this study, the candidate targets of differentially expressed (DE) miRNAs were predicted and analyzed using Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Based on the results of KEGG analysis, miR-885-3p might participate in regulating activation of NF-κB pathway and TNF pathway. To study the function of miR-885-3p, miR-885-3p mimics and inhibitors were artificially synthesized and respectively used for overexpression and silence of miR-885-3p in cells. Our results showed that miR-885-3p inhibited NF-κB signaling pathway and tumor necrosis factor-α (TNF-α) production. B-cell CLL/lymphoma 10 (Bcl-10) was identified as the target of miR-885-3p, and promoted NF-κB pathway activation and TNF-α production. It was found that TGEV open reading frame 3b (TGEV-ORF3b) suppressed Bcl-10 expression, activation of NF-κB pathway, and TNF-α production by uniquely up-regulated miR-885-3p expression. Overall, the results indicated that TGEV-ORF3b counteracted NF-κB pathway and TNF-α via regulating miR-885-3p and Bcl-10.

Chlamydia suis is associated with intestinal NF-κB activation in experimentally infected gnotobiotic piglets

Chlamydia suis intestinal infection of single-animal experimental groups of gnotobiotic newborn piglets was previously reported to cause severe, temporary small intestinal epithelium damage. We investigated archived intestinal samples for pro-inflammatory nuclear factor kappa B (NF-κB) activation, Interleukin (IL)-6 and IL-8 production and immune cell influx. Samples were collected 2, 4 and 7 days post-inoculation with C. suis strain S45/6 or mock inoculum (control). Increased nuclear localization of epithelial NF-κB, representative of activation, in the jejunum and ileum of C. suis-infected animals, compared to uninfected controls, began by 2 days post-infection (dpi) and persisted through 7 dpi. Infected animals showed increased production of IL-8, peaking at 2 dpi, compared to controls. Infection-mediated CD45-positive immune cell influx into the jejunal lamina propria peaked at 7 dpi, when epithelial damage was largely resolved. Activation of NF-κB appears to be a key early event in the innate response of the unprimed porcine immune system challenged with C. suis. This results in an acute phase, coinciding with the most severe clinical symptoms, diarrhea and weight loss. Immune cells recruited shortly after infection remain present in the lamina propria during the recovery phase, which is characterized by reduced chlamydial shedding and restored intestinal epithelium integrity.

Amachawadi R, Dash AP, Yadav MP, Prasad KS, P S, Jain AS, Shivamallu C. COVID-19 PANDEMIC: A SYSTEMATIC REVIEW ON THE CORONAVIRUSES OF ANIMALS AND SARS-CoV-2

Coronaviruses (CoVs), classified into four genera, viz., alpha-, beta-, gamma-, and Delta- CoV, represent an important group of diverse transboundary pathogens that can infect a variety of mammalian and avian species including humans, animals, poultry, and non-poultry birds. CoVs primarily infect lung and gut epithelial cells, besides monocytes and macrophages. CoVs have high mutation rates causing changes in host specificity, tissue tropism, and mode of virus excretion and transmissions. The recent CoV zoonoses are SARS, MERS, and COVID-19 that are caused by the transmission of beta-CoVs of bats to humans. Recently, reverse zoonoses of the COVID-19 virus have been detected in dogs, tigers, and minks. Beta-CoV strains also infect bovine (BCoV) and canine species (CRCoV); both these beta-CoVs might have originated from a common ancestor. Despite the high genetic similarity between BCoV, CRCoV, and HCoV-OC43, these differ in species specificity. Alpha-CoV strains infect canine (CCoV), feline (FIPV), swine (TGEV and PEDV), and humans (HCoV229E and NL63). Six coronavirus species are known to infect and cause disease in pigs, seven in human beings, and two in dogs. The high mutation rate in CoVs is attributed to error-prone 3′-5′ exoribonuclease (NSP 14), and genetic recombination to template shift by the polymerase. The present compilation describes the important features of the CoVs and diseases caused in humans, animals, and birds that are essential in surveillance of diverse pool of CoVs circulating in nature, and monitoring interspecies transmission, zoonoses, and reverse zoonoses.

Bio-Inorganic Hybrid Nongenetically Modified Viruses as an Immune Agonist for Systemic Elimination of Cancer Cells

Microbial-based cancer therapy is nowadays considered as an interesting approach, especially with viruses which are attracting more attention owing to their simple structure and nanoscale. However, because of the need for cumbersome genetic modification and poor biosafety, its application is seriously limited. Here, nonpathogenic natural Sendai viruses (SEVs) are used as an alternative immune agonist after being mineralized by calcium ions. Both in vitro and in vivo studies indicated that virus-inorganic hybrids can effectively excite antigen-presenting cells (APCs). Then, the tumor antigens were released in large amounts by photothermal damage. Meanwhile, these released antigens were presented to lymph nodes to mature antitumor T lymphocytes via the peritumoral APCs previously recruited by the SEV. Our results demonstrated that even after administration at one point, the nanohybrids could still effectively stimulate systemic antitumor immune response to suppress the potential cancer metastatic spread. The bio-inorganic hybrid nongenetically modified virus-inorganic nanocomposites might serve as an alternative strategy for synergistic immune therapy.

Evolution of Transmissible Gastroenteritis Virus (TGEV): A Codon Usage Perspective

Transmissible gastroenteritis virus (TGEV) is a coronavirus associated with diarrhea and high mortality in piglets. To gain insight into the evolution and adaptation of TGEV, a comprehensive analysis of phylogeny and codon usage bias was performed. The phylogenetic analyses of maximum likelihood and Bayesian inference displayed two distinct genotypes: genotypes I and II, and genotype I was classified into subtypes Ia and Ib. The compositional properties revealed that the coding sequence contained a higher number of A/U nucleotides than G/C nucleotides, and that the synonymous codon third position was A/U-enriched. The principal component analysis based on the values of relative synonymous codon usage (RSCU) showed the genotype-specific codon usage patterns. The effective number of codons (ENC) indicated moderate codon usage bias in the TGEV genome. Dinucleotide analysis showed that CpA and UpG were over-represented and CpG was under-represented in the coding sequence of the TGEV genome. The analyses of Parity Rule 2 plot, ENC-plot, and neutrality plot displayed that natural selection was the dominant evolutionary driving force in shaping codon usage preference in genotypes Ia and II. In addition, natural selection played a major role, while mutation pressure had a minor role in driving the codon usage bias in genotype Ib. The codon adaptation index (CAI), relative codon deoptimization index (RCDI), and similarity index (SiD) analyses suggested that genotype I might be more adaptive to pigs than genotype II. Current findings contribute to understanding the evolution and adaptation of TGEV.

Molecular Targets in the Chemotherapy of Coronavirus Infection

In the pathogenesis of the infectious process in the respiratory tract by SARS, MERS, and COVID-19 coronaviruses, two stages can be distinguished: early (etiotropic) and late (pathogenetic) ones. In the first stage, when the virus multiplication and accumulation are prevalent under insufficient host immune response, the use of chemotherapeutic agents blocking the reproduction of the virus is reasonable to suppress the development of the disease. This article considers six major chemotherapeutic classes aimed at certain viral targets: inhibitors of viral RNA polymerase, inhibitors of viral protease Mpro, inhibitors of proteolytic activation of viral protein S allowing virus entry into the target cell, inhibitors of virus uncoating in cellular endosomes, compounds of exogenous interferons, and compounds of natural and recombinant virus-neutralizing antibodies. In the second stage, when the multiplication of the virus decreases and threatening pathological processes of excessive inflammation, acute respiratory distress syndrome, pulmonary edema, hypoxia, and secondary bacterial pneumonia and sepsis events develop, a pathogenetic therapeutic approach including extracorporeal blood oxygenation, detoxification, and anti-inflammatory and anti-bacterial therapy seems to be the most effective way for the patient’s recovery.

Reverse genetic systems: Rational design of coronavirus live attenuated vaccines with immune sequelae

Since the end of 2019, the global COVID-19 outbreak has once again made coronaviruses a hot topic. Vaccines are hoped to be an effective way to stop the spread of the virus. However, there are no clinically approved vaccines available for coronavirus infections. Reverse genetics technology can realize the operation of RNA virus genomes at the DNA level and provide new ideas and strategies for the development of new vaccines. In this review, we systematically describe the role of reverse genetics technology in studying the effects of coronavirus proteins on viral virulence and innate immunity, cell and tissue tropism and antiviral drug screening. An efficient reverse genetics platform is useful for obtaining the ideal attenuated strain to prepare an attenuated live vaccine.

Nonstructural protein 6 of porcine epidemic diarrhea virus induces autophagy to promote viral replication via the PI3K/Akt/mTOR axis

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Autophagy is beneficial to PEDV replication.

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PEDV nonstructural protein 6 (nsp6) is a key protein involved in PEDV-induced autophagy.

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Nsp6 of PEDV induced autophagy via the PI3K/Akt/mTOR signaling pathway.

Porcine epidemic diarrhea virus (PEDV) has caused, and continues to cause, severe economic losses to the swine industry worldwide. The pathogenic mechanism and immune regulatory interactions between PEDV and the host remain largely unknown. In this study, the interaction between autophagy and PEDV replication in intestinal porcine epithelial (IPEC-J2) cells was investigated. The effects of the structural and nonstructural proteins of PEDV on the autophagy process and the autophagy-related signaling pathways were also examined. The results shown that PEDV replication increased the autophagy flux in IPEC-J2 cells, and that autophagy was beneficial to PEDV replication, which may be one of the reasons for the rapid damage to intestinal epithelial cells and the enhanced virulence of PEDV in both newborn piglets and finishing pigs. When autophagy was pharmacologically induced by rapamycin, PEDV replication increased from 8.5 × 10⁵ TCID₅₀/mL to 8.8 × 10⁶ TCID₅₀/mL in IPEC-J2 cells. When autophagy was pharmacologically suppressed by hydroxychloroquine, PEDV replication decreased from 8.5 × 10⁵ TCID₅₀/mL to 7.9 × 10⁴ TCID₅₀/mL. To identify which PEDV proteins were the key inducers of autophagy, all 4 structural proteins and 17 nonstructural proteins of PEDV were eukaryotic expressed. It was found that the nonstructural protein 6 (nsp6) and ORF3 of PEDV were able to induce significant autophagy in IPEC-J2 cells, but the other proteins were unable to induce autophagy. It was indicated that nsp6-induced autophagy mainly occurred via the PI3K/Akt/mTOR signaling pathway. The results accelerate the understanding of the biology and pathogenesis of PEDV infection and provide new insights into the development of effective therapeutic strategies.

Transmissible Gastroenteritis Virus Infection Up-Regulates FcRn Expression via Nucleocapsid Protein and Secretion of TGF-β in Porcine Intestinal Epithelial Cells

Transmissible gastroenteritis virus (TGEV) is a porcine intestinal coronavirus that causes fatal severe watery diarrhea in piglets. The neonatal Fc receptor (FcRn) is the only IgG transport receptor, its expression on mucosal surfaces is triggered upon viral stimulation, which significantly enhances mucosal immunity. We utilized TGEV as a model pathogen to explore the role of FcRn in resisting viral invasion in overall intestinal mucosal immunity. TGEV induced FcRn expression by activating NF-κB signaling in porcine small intestinal epithelial (IPEC-J2) cells, however, the underlying mechanisms are unclear. First, using small interfering RNAs, we found that TGEV up-regulated FcRn expression via TLR3, TLR9 and RIG-I. Moreover, TGEV induced IL-1β, IL-6, IL-8, TGF-β, and TNF-α production. TGF-β-stimulated IPEC-J2 cells highly up-regulated FcRn expression, while treatment with a JNK-specific inhibitor down-regulated the expression. TGEV nucleocapsid (N) protein also enhanced FcRn promoter activity via the NF-κB signaling pathway and its central region (aa 128–252) was essential for FcRn activation. Additionally, N protein-mediated FcRn up-regulation promotes IgG transcytosis. Thus, TGEV N protein and TGF-β up-regulated FcRn expression, further clarifying the molecular mechanism of up-regulation of FcRn expression by TGEV.

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.

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.

Circular RNA CircEZH2 Suppresses Transmissible Gastroenteritis Coronavirus-induced Opening of Mitochondrial Permeability Transition Pore via Targeting MiR-22 in IPEC-J2

Transmissible gastroenteritis (TGE) is a contagious and infectious disease that is characterized by severe vomiting and diarrhea of swine , especially piglet, and caused by transmissible gastroenteritis coronavirus (TGEV) . TGEV infection provokes mitochondrial damage of porcine intestinal epthelial cell (IPEC), which is responsible for inflammation and cell death. In our previous study, we have demonstrated that circular RNA circEZH2 was down-regulated during TGEV infection and promoted the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) via targeting miR-22 in porcine intestinal epithelial cell line (IPEC-J2). Activation of NF-κB is an important factor for mitochondrial damage. Mitochondrial permeability transition pore (mPTP) opening is a key reason for mitochondrial damage. So, we speculate that circEZH2 may regulate TGEV-induced mPTP opening via NF-kB pathway. In the present study, we found that mPTP opening of IPEC-J2 was occured during TGEV infection and suppressed by circEZH2 via attaching miR-22. Hexokinase 2 (HK2) and interleukin 6 (IL-6) were identified as the targets of miR-22. Silencing HK2 enhanced TGEV-induced mPTP opening, while no effect on NF-κB pathway. Silencing IL-6 promoted TGEV-induced mPTP opening and inhibited NF-κB pathway. Inhibitor of NF-κB increased TGEV-induced mPTP opening. The data revealed that TGEV-induced mPTP opening was regulated via two pathways: circEZH2/miR-22/HK2 axis and circEZH2/miR-22/IL-6/NF-κB axis.