Porcine reproductive and respiratory syndrome virus (PRRSV) induces IL-12p40 production through JNK-AP-1 and NF-κB signaling pathways

Quercetin alleviates inflammation induced by porcine reproductive and respiratory syndrome virus in MARC-145 cells through the regulation of arachidonic acid and glutamine metabolism

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes severe inflammatory response, respiratory disease and sow reproductive failure. Quercetin is among the widely occurring polypheno found abundantly in nature. Quercetin has anti-inflammatory, anti-oxidative and anti-viral properties.

OBJECTIVES

This study aimed to explore the effect and mechanism of quercetin on PRRSV-induced inflammation in MARC-145 cells.

METHODS

Observing the cytopathic effect and measurements of inflammatory markers in MARC-145 cells collectively demonstrate that quercetin elicits a curative effect on PRRSV-induced inflammation. Liquid chromatography-mass spectrometry was further used for a non-targeted metabolic analysis of the role of quercetin in the metabolic regulation of PRRSV inflammation in MARC-145 cells.

RESULTS

It was shown that quercetin attenuated PRRSV-induced cytopathy in MARC-145 cells. Quercetin treatment inhibited PRRSV replication in MARC-145 cells in a dose-dependent manner. We also found that quercetin inhibited PRRSV-induced mRNA expression and secretion levels of tumour necrosis factor-α, interleukin 1β and interleukin 6. Metabolomics analysis revealed that quercetin ameliorated PRRSV-induced inflammation. Pathway analysis results revealed that PRRSV-induced pathways including arachidonic acid metabolism, linoleic acid, glycerophospholipid and alanine, aspartate and glutamate metabolism were suppressed by quercetin. Moreover, we confirmed that quercetin inhibited the activation of NF-κB/p65 pathway, probably by attenuating PLA2, ALOX and COX mRNA expression.

CONCLUSIONS

These results provide a crucial insight into the molecular mechanism of quercetin in alleviating PRRSV-induced inflammation.

Deoxycholic acid inhibits ASFV replication by inhibiting MAPK signaling pathway

African swine fever (ASF) is an acute, febrile, highly contagious infection of pigs caused by the African swine fever virus (ASFV). The purpose of this study is to understand the molecular mechanism of ASFV infection and evaluate the effect of DCA on MAPK pathway, so as to provide scientific basis for the development of new antiviral drugs. The transcriptome analysis found that ASFV infection up-regulated the IL-17 and MAPK signaling pathways to facilitate viral replication. Metabolome analysis showed that DCA levels were up-regulated after ASFV infection, and that exogenous DCA could inhibit activation of the MAPK pathway by ASFV infection and thus inhibit viral replication. Dual-luciferase reporter assays were used to screen the genes of ASFV and revealed that I73R could significantly up-regulate the transcription level of AP-1 transcription factor in the MAPK pathway. Confocal microscopy demonstrated that I73R could promote AP-1 entry into the nucleus, and that DCA could inhibit the I73R-mediated nuclear entry of AP-1, inhibiting MAPK pathway, and I73R interacts with AP-1. These results indicated that DCA can inhibit ASFV-mediated activation of the MAPK pathway, thus inhibiting ASFV replication. This study provides a theoretical basis for research on ASF pathogenesis and for antiviral drug development.

Type I and II interferons, transcription factors and major histocompatibility complexes were enhanced by knocking down the PRRSV-induced transforming growth factor beta in monocytes co-cultured with peripheral blood lymphocytes

The innate and adaptive immune responses elicited by porcine reproductive and respiratory syndrome virus (PRRSV) infection are known to be poor. This study investigates the impact of PRRSV-induced transforming growth factor beta 1 (TGFβ1) on the expressions of type I and II interferons (IFNs), transcription factors, major histocompatibility complexes (MHC), anti-inflammatory and pro-inflammatory cytokines in PRRSV-infected co-cultures of monocytes and peripheral blood lymphocytes (PBL). Phosphorothioate-modified antisense oligodeoxynucleotide (AS ODN) specific to the AUG region of porcine TGFβ1 mRNA was synthesized and successfully knocked down TGFβ1 mRNA expression and protein translation. Monocytes transfected with TGFβAS1 ODN, then simultaneously co-cultured with PBL and inoculated with either classical PRRSV-2 (cPRRSV-2) or highly pathogenic PRRSV-2 (HP-PRRSV-2) showed a significant reduction in TGFβ1 mRNA expression and a significant increase in the mRNA expressions of IFNα, IFNγ, MHC-I, MHC-II, signal transducer and activator of transcription 1 (STAT1), and STAT2. Additionally, transfection of TGFβAS1 ODN in the monocyte and PBL co-culture inoculated with cPRRSV-2 significantly increased the mRNA expression of interleukin-12p40 (IL-12p40). PRRSV-2 RNA copy numbers were significantly reduced in monocytes and PBL co-culture transfected with TGFβAS1 ODN compared to the untransfected control. The yields of PRRSV-2 RNA copy numbers in PRRSV-2-inoculated monocytes and PBL co-culture were sustained and reduced by porcine TGFβ1 (rTGFβ1) and recombinant porcine IFNα (rIFNα), respectively. These findings highlight the strategy employed by PRRSV to suppress the innate immune response through the induction of TGFβ expression. The inclusion of TGFβ as a parameter for future PRRSV vaccine and vaccine adjuvant candidates is recommended.

Genetic background influences pig responses to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly infectious and economically significant virus that causes respiratory and reproductive diseases in pigs. It results in reduced productivity and increased mortality in pigs, causing substantial economic losses in the industry. Understanding the factors affecting pig responses to PRRSV is crucial to develop effective control strategies. Genetic background has emerged as a significant determinant of susceptibility and resistance to PRRSV in pigs. This review provides an overview of the basic infection process of PRRSV in pigs, associated symptoms, underlying immune mechanisms, and roles of noncoding RNA and alternative splicing in PRRSV infection. Moreover, it emphasized breed-specific variations in these aspects that may have implications for individual treatment options.

Therapeutic efficacy of tylvalosin combined with Poria cocos polysaccharides against porcine reproductive and respiratory syndrome

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important infectious diseases of pigs worldwide. Vaccination and various management measures have been implemented to control PRRS. However, due to high genetic diversity and insufficient understanding of the pathogenesis and immunological mechanisms, PRRS is still a challenge to the pig industry. Therefore, it is important to develop novel strategies to combat PRRS virus (PRRSV) infection. In this study, our data show that tylvalosin, a third-generation animal-specific macrolide, could inhibit PRRSV replication in MARC-145 cells, and suppress the PRRSV-induced NF-κB activation and cytokines expression. The pig infection experiment further demonstrated that tylvalosin could significantly reduce the virus loads in serum and tissues, and alleviate lung lesions of pigs infected with highly pathogenic PRRSV strains. The fever and loss of daily gain (LoDG) of the pigs were decreased as well. Considering the feature of immune suppression of PRRSV, a combination of tylvalosin with the immunopotentiator Poria cocos polysaccharides (PCP) was developed. Pig experiment showed this combination had a better therapeutic efficacy against PRRSV infection than tylvalosin and PCP alone in attenuating lung lesions, alleviating fever, and suppressing cytokines production. This study suggests that tylvalosin has significant antiviral and anti-inflammatory effects against PRRSV infection, and the combination of tylvalosin and PCP provides a promising strategy for PRRS treatment.

Andrographolide and Its Derivative Potassium Dehydrographolide Succinate Suppress PRRSV Replication in Primary and Established Cells via Differential Mechanisms of Action

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause significant economic loss worldwide and remains a serious threat to the pork industry. Currently, vaccination strategies provide limited protection against PRRSV infection, and consequently, new antiviral strategies are urgently required. Andrographolide (Andro) and its derivative potassium dehydrographolide succinate (PDS) have been used clinically in China and other Asian countries as therapies for inflammation-related diseases, including bacterial and viral infections, for decades. Here, we demonstrate that Andro and PDS exhibit robust activity against PRRSV replication in Marc-145 cells and primary porcine alveolar macrophages (PAMs). The two compounds exhibited broad-spectrum inhibitory activities in vitro against clinically circulating type 2 PRRSV GD-HD, XH-GD, and NADC30-like HNhx strains in China. The EC₅₀ values of Andro against three tested PRRSV strain infections in Marc-145 cells ranged from 11.7 to 15.3 μmol/L, with selectivity indexes ranging from 8.3 to 10.8, while the EC₅₀ values of PDS ranged from 57.1 to 85.4 μmol/L, with selectivity indexes ranging from 344 to 515. Mechanistically, the anti-PRRSV activity of the two compounds is closely associated with their potent suppression on NF-κB activation and enhanced oxidative stress induced by PRRSV infection. Further mechanistic investigations revealed that PDS, but not Andro, is able to directly interact with PRRSV particles. Taken together, our findings suggest that Andro and PDS are promising PRRSV inhibitors in vitro and deserves further in vivo studies in swine.

Molecular and Cellular Mechanisms for PRRSV Pathogenesis and Host Response to Infection

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PRRSV has evolved to arm with various strategies to modify host antiviral response.

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Viral modulation of homeostatic cellular processes provides favorable conditions for PRRSV survival during infection.

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PRRSV modulation of cellular processes includes pathways for interferons, apoptosis, microRNAs, cytokines, autophagy, and viral genome recombination.

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused tremendous amounts of economic losses to the swine industry for more than three decades, but its control is still unsatisfactory. A significant amount of information is available for host cell-virus interactions during infection, and it is evident that PRRSV has evolved to equip various strategies to disrupt the host antiviral system and provide favorable conditions for survival. The current study reviews viral strategies for modulations of cellular processes including innate immunity, apoptosis, microRNAs, inflammatory cytokines, and other cellular pathways.

Analysis of Swine Conventional Dendritic Cells, DEC205+CD172a+/-CADM1+, from Blood and Spleen in Response to PRRSV and PEDV

Conventional dendritic cells (cDCs) cannot be infected by porcine reproductive and respiratory syndrome virus (PRRSV) but respond to infection via cytokine production, indicating a possible role in initiation/regulation of the immune response against PRRSV. In this work, we evaluated the responses of splenic and blood cDCs, with DEC205⁺CADM1⁺CD172a^+/− phenotype, as well as those of CD163⁺ cells against PRRSV and porcine epidemic diarrhea virus (PEDV). Both populations were incubated in the presence of PRRSV or PEDV with and without naïve CD3⁺ T cells, and cytokine responses were evaluated by qPCR and ELISA. Our results showed that cDCs, but not CD163⁺ cells, produced IL-12 in response to PRRSV. PEDV did not induce IL-12 production. Cocultures of cDCs and autologous naïve CD3⁺ cells resulted in decreased IL-12 production and low expression of IFN-γ transcripts in response to PRRSV. Interestingly, cDCs increased the proliferation of naïve T cells in the presence of PRRSV compared with that achieved with monocytes and peripheral blood mononuclear cells (PBMCs). Cocultures of CD163⁺ cells induced IL-10 and IL-4 expression in the presence of PRRSV and PEDV, respectively. In conclusion, cDCs can selectively produce IL-12 in response to PRRSV but poorly participate in the activation of naïve T cells.

An Escherichia coli-Expressed Porcine Reproductive and Respiratory Syndrome Virus Chimeric Protein Induces a Specific Immunoglobulin G Response in Immunized Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) still poses a threat to the swine industry worldwide. Currently, commercial vaccines against PRRSV, which consist of modified live or inactivated virus, reduce symptoms and viremia in immunized pigs, but efficacy against heterologous strains is variable. This has led to the development of subunit vaccines that contain viral antigens that show the highest variability. In this work, a chimeric protein comprising short amino acid sequences from glycoprotein 3 (GP3), glycoprotein 4 (GP4), glycoprotein 5 (GP5), and M (matrix protein) proteins of PRRSV was designed and expressed in Escherichia coli. This protein, designated as PRRSVchim, was purified by immobilized metal affinity chromatography and evaluated. PRRSVchim was identified by immunoglobulin G (IgG) presence in serum samples from PRRSV-positive pigs. Also, the protein probed to be antigenic in immunized mice and piglets and provided some degree of protection against challenge with a PRRSV field isolate. These results show the potential of PRRSVchim protein for both PRRSV diagnostic and immunoprophylaxis.

Interaction of PIAS1 with PRRS virus nucleocapsid protein mediates NF-κB activation and triggers proinflammatory mediators during viral infection

Porcine reproductive and respiratory syndrome virus (PRRSV) activates NF-κB during infection. We examined the ability of all 22 PRRSV genes for NF-κB regulation and determined the nucleocapsid (N) protein as the NF-κB activator. Protein inhibitor of activated STAT1 (signal transducer and activator of transcription 1) (PIAS1) was identified as a cellular protein binding to N. PIAS1 is known to bind to p65 (RelA) in the nucleus and blocks its DNA binding, thus functions as a repressor of NF-κB. Binding of N to PIAS1 released p65 for NF-κB activation. The N-terminal half of PIAS1 was mapped as the N-binding domain, and this region overlapped its p65-binding domain. For N, the region between 37 and 72 aa was identified as the binding domain to PIAS1, and this domain alone was able to activate NF-κB. A nuclear localization signal (NLS) knock-out mutant N did not activate NF-κB, and this is mostly likely due to the lack of its interaction with PIAS1 in the nucleus, demonstrating the positive correlation between the binding of N to PIAS1 and the NF-κB activation. Our study reveals a role of N in the nucleus for NF-κB activation and proinflammatory cytokine production during infection.

A Novel lncRNA Regulates the Toll-Like Receptor Signaling Pathway and Related Immune Function by Stabilizing FOS mRNA as a Competitive Endogenous RNA

Long non-coding RNAs (lncRNAs) have recently emerged as new regulatory molecules with diverse functions in regulating gene expression and significant roles in the immune response. However, the function of many unknown lncRNAs is still unclear. By studying the regulatory effect of daidzein (DA) on immunity, we identified a novel lncRNA with an immune regulatory function: lncRNA- XLOC_098131. In vivo, DA treatment upregulated the expression of lncRNA- XLOC_098131, FOS, and JUN in chickens and affected the expression of activator protein 1 (AP-1) to regulate MAPK signaling, Toll-like receptor signaling, and related mRNA expression. It also enhanced macrophage activity and increased the numbers of blood neutrophils and mononuclear cells, which can improve the body's ability to respond to stress and bacterial and viral infections. Furthermore, DA treatment also reduced B lymphocyte apoptosis and promoted the differentiation of B lymphocytes into plasma cells, which in turn resulted in the production of more immunoglobulins and the promotion of antigen presentation. In vitro, using HEK293FT cells, we demonstrated that mir-548s could bind to and decrease the expression of both FOS and lncRNA- XLOC_098131. LncRNA- XLOC_098131 served as a competitive endogenous RNA to stabilize FOS by competitively binding to miR-548s and thereby reducing its inhibitory effect of FOS expression. Therefore, we concluded that the novel lncRNA XLOC_098131 acts as a key regulatory molecule that can regulate the Toll-like receptor signaling pathway and related immune function by serving as a competitive endogenous RNA to stabilize FOS mRNA expression.

Tonsil conventional dendritic cells are not infected by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) infects monocyte-derived DCs, and previous reports have shown that PRRSV does not infect conventional DCs (cDCs) in vitro, but the effects on cDCs from lymphoid tissues are unknown. This study analyzed the response and susceptibility of tonsil DEC205⁺cDCs from infected pigs. We confirmed the phenotype and lineage of bona fide tonsil cDCs with the mRNA expression of FLT3⁺ and the phenotype MHCII⁺CADM1^highDEC205⁺ (DEC205⁺cDCs). These cells were not infected by PRRSV, whereas CD163⁺ tonsil cells were infected. The numbers of tonsil cDCs and CD163⁺ cells were not affected by PRRSV, in contrast to the reduction in alveolar macrophage numbers. DEC205⁺cDCs exhibited an increase in the expression of IL-12 at 5 days postinfection, suggesting a proinflammatory response by these cells to the virus. In summary, this study confirms that, in vitro and in vivo, cDCs are not susceptible to PRRSV but can respond against it.

Porcine Circovirus Type 2 Suppresses IL-12p40 Induction via Capsid/gC1qR-Mediated MicroRNAs and Signalings

Porcine circovirus (PCV) type 2 (PCV2), an immunosuppression pathogen, is often found to increase the risk of other pathogenic infections. Yet the relative immune mechanisms determining the susceptibility of PCV2-infected animals remain unclear. In this study, we confirmed that PCV2 infection suppressed IL-12p40 expression and host Th1 immune response, leading to a weakened pathogenic clearance upon porcine reproductive respiratory syndrome virus (PRRSV) or Haemophilus parasuis infection. PCV2 infection suppressed pathogens, LPS/IFN-γ, or LPS/R848-induced IL-12p40 expression in porcine alveolar macrophages. PCV2 capsid (Cap) was the major component to suppress IL-12p40 induction by LPS/IFN-γ, LPS/R848, PRRSV, or H. parasuis Either wild-type PCV2 or mutants PCV2-replicase 1 and PCV type 1-Cap2, which contained PCV2 Cap, significantly decreased IL-12p40 levels and increased the replication of PRRSV and H. parasuis in the lung tissues relative to mock or PCV type 1 infection. gC1qR, a Cap binding protein, was not involved in IL-12p40 induction but mediated the inhibitory effect of PCV2 Cap on IL-12p40 induction. PCV2 also activated PI3K/Akt1 and p38 MAPK signalings to inhibit IL-12p40 expression via inhibition of NF-κB p65 binding to il12B promoter and upregulation of miR-23a and miR-29b. Knockdown of Akt1 and p38 MAPK downregulated miR-23a and miR-29b and increased IL-12p40 expression. Inhibition of miR-23a and miR-29b attenuated the inhibitory effect of PCV2 on IL-12p40 induction, resulting in an increased IL-12p40 expression and Th1 cell population and reduced susceptibility to PRRSV or H. parasuis Taken together, these results demonstrate that PCV2 infection suppresses IL-12p40 expression to lower host Th1 immunity to increase the risk of other pathogenic infection via gC1qR-mediated PI3K/Akt1 and p38 MAPK signaling activation.

The Immunological Regulation Roles of Porcine β-1, 4 Galactosyltransferase V (B4GALT5) in PRRSV Infection

B4GALT5, also known as β-1, 4 galactosyltransferase V, is one of the members of β-1, 4 galactosyltransferase gene (B4GALT) family, which was concerned with embryonic development, tumor generation, other malignant diseases. In this study, we firstly cloned porcine B4GALT (pB4GALT5) from porcine alveolar macrophages, and predicted the structural domain and function of seven porcine β-1, 4 galactosyltransferase (I–VII) based on transcriptome analysis of PRRSV infected cells. Additionally, the upregulated porcine B4GALT5 expression was detected from PRRSV infected porcine alveolar macrophage (PAM) cells. The PRRSV proliferation were slightly inhibited in overexpression of pB4GALT5 transfected cells, the interaction of B4GALT5 and GP5 of PRRSV was firstly be detected by Co-IP, and the co-location between B4GALT5 and GP5 were also observed in golgi membranes by confocal microscopy. A significant increasing mRNA transcription, including inflammatory cytokines (IFN-α, IL-6, IL-18, IL-1β, TNF-α) and some cell surface glycosylated protein involved in antigen present (MHC-I/II), cell adhesion and migration (chemokine MCP-1 and receptor CCR2; LFA-1, ICAM-1) were upregulated in B4GALT5 overexpressed PRRSV infected cells. Our results demonstrated that the regulation of pB4GALT5 plays an important roles in PRRSV proliferation and modification function in viral infection cells. And these results will make achievements by supporting the research of latent mechanisms of β-1, 4 galactosyltransferase V in antiviral immunity.

The Nucleocapsid Protein and Nonstructural Protein 10 of Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus Enhance CD83 Production via NF-κB and Sp1 Signaling Pathways

Porcine reproductive and respiratory syndrome, caused by porcine reproductive and respiratory syndrome virus (PRRSV), is a panzootic disease that is one of the most economically costly diseases to the swine industry. A key aspect of PRRSV virulence is that the virus suppresses the innate immune response and induces persistent infection, although the underlying mechanisms are not well understood. The dendritic cell (DC) marker CD83 belongs to the immunoglobulin superfamily and is associated with DC activation and immunosuppression of T cell proliferation when expressed as soluble CD83 (sCD83). In this study, we show that PRRSV infection strongly stimulates CD83 expression in porcine monocyte-derived DCs (MoDCs) and that the nucleocapsid (N) protein and nonstructural protein 10 (nsp10) of PRRSV enhance CD83 promoter activity via the NF-κB and Sp1 signaling pathways. R43A and K44A amino acid substitution mutants of the N protein suppress the N protein-mediated increase of CD83 promoter activity. Similarly, P192-5A and G214-3A mutants of nsp10 (with 5 and 3 alanine substitutions beginning at residues P192 and G214, respectively) abolish the nsp10-mediated induction of the CD83 promoter. Using reverse genetics, four mutant viruses (rR43A, rK44A, rP192-5A, and rG214-3A) and four revertants [rR43A(R), rK44A(R), rP192-5A(R), and rG214-3A(R)] were generated. Decreased induction of CD83 in MoDCs was observed after infection by mutants rR43A, rK44A, rP192-5A, and rG214-3A, in contrast to the results obtained using rR43A(R), rK44A(R), rP192-5A(R), and rG214-3A(R). These findings suggest that PRRSV N and nsp10 play important roles in modulating CD83 signaling and shed light on the mechanism by which PRRSV modulates host immunity.IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically costly pathogens affecting the swine industry. It is unclear how PRRSV inhibits the host's immune response and induces persistent infection. The dendritic cell (DC) marker CD83 belongs to the immunoglobulin superfamily and has previously been associated with DC activation and immunosuppression of T cell proliferation and differentiation when expressed as soluble CD83 (sCD83). In this study, we found that PRRSV infection induces sCD83 expression in porcine MoDCs via the NF-κB and Sp1 signaling pathways. The viral nucleocapsid protein, nonstructural protein 1 (nsp1), and nsp10 were shown to enhance CD83 promoter activity. Amino acids R43 and K44 of the N protein, as well as residues 192 to 196 (P192-5) and 214 to 216 (G214-3) of nsp10, play important roles in CD83 promoter activation. These findings provide new insights into the molecular mechanism of immune suppression by PRRSV.