RIG-1 and MDA-5 signaling pathways contribute to IFN-β production and viral replication in porcine circovirus virus type 2-infected PK-15 cells in vitro

Aminoguanidine alleviates gout in goslings experimentally infected with goose astrovirus-2 by reducing kidney lesions

Goose astrovirus (GAstV)-2, a novel pathogen identified in 2018, mainly causes visceral gout in goslings, leading to approximately 50% mortality. At present, no commercial veterinary products are available to prevent and treat the disease. Our previous studies showed that nitric oxide (NO) and inducible NO synthase (iNOS) were markedly higher in the kidney and spleen of goslings infected with GAstV-2, but their effects during GAstV-2 infection remain unclear. In the present study, goslings were intraperitoneally injected with aminoguanidine (AG)-an iNOS inhibitor-to examine the role of NO during GAstV-2 infection. AG significantly decreased the serum NO concentration and iNOS mRNA expression in the kidney. Moreover, AG reduced the mortality, serum uric acid and creatinine content, and urate deposition in visceral organs and joints. Histopathological analysis demonstrated that AG reduced renal tubular cell necrosis, inflammatory cell infiltration, glycogen deposition in glomerular mesangium, and interstitial fibrosis, suggesting alleviation of kidney lesions. Furthermore, AG decreased the expression of renal injury markers such as KIM-1 and desmin; inflammatory cytokine-related genes such as IL-1β, IL-8, and MMP-9; and autophagy-related genes and proteins such as LC3II, ATG5, and Beclin1. However, quantitative real-time PCR and immunohistochemistry showed that treatment with AG did not affect the kidney and liver viral load. These findings suggest that AG decreases the mortality rate and kidney lesions in goslings infected with GAstV-2 through mechanisms associated with autophagy and inhibition of inflammatory cytokine production in the kidney but not with GAstV-2 replication.

Porcine promyelocytic leukemia protein isoforms suppress Japanese encephalitis virus replication in PK15 cells

BACKGROUND

Promyelocytic leukemia protein (PML) is a primary component of PML nuclear bodies (PML-NBs). PML and PML-NBs play critical roles in processes like the cell cycle, DNA damage repair, apoptosis, and the antiviral immune response. Previously, we identified five porcine PML alternative splicing variants and observed an increase in the expression of these PML isoforms following Japanese encephalitis virus (JEV) infection. In this study, we examined the functional roles of these PML isoforms in JEV infection.

METHODS

PML isoforms were either knocked down or overexpressed in PK15 cells, after which they were infected with JEV. Subsequently, we analyzed the gene expression of PML isoforms, JEV, and the interferon (IFN)-β signaling pathway using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. Viral titers were determined through 50% tissue culture infectious dose (TCID50) assays.

RESULTS

Our results demonstrated that the knockdown of endogenous PML promoted JEV replication, while the overexpression of PML isoforms 1, 3, 4, and 5 (PML1, PML3, PML4, and PML5) inhibited JEV replication. Further investigation revealed that PML1, PML3, PML4, and PML5 negatively regulated the expression of genes involved in the interferon (IFN)-β signaling pathway by inhibiting IFN regulatory factor 3 (IRF3) post-JEV infection.

CONCLUSIONS

These findings demonstrate that porcine PML isoforms PML1, PML3, PML4, and PML5 negatively regulate IFN-β and suppress viral replication during JEV infection. The results of this study provide insight into the functional roles of porcine PML isoforms in JEV infection and the regulation of the innate immune response.

Mitochondrial antiviral signaling protein: a potential therapeutic target in renal disease

Mitochondrial antiviral signaling protein (MAVS) is a key innate immune adaptor on the outer mitochondrial membrane that acts as a switch in the immune signal transduction response to viral infections. Some studies have reported that MAVS mediates NF-κB and type I interferon signaling during viral infection and is also required for optimal NLRP3 inflammasome activity. Recent studies have reported that MAVS is involved in various cancers, systemic lupus erythematosus, kidney diseases, and cardiovascular diseases. Herein, we summarize the structure, activation, pathophysiological roles, and MAVS-based therapies for renal diseases. This review provides novel insights into MAVS's role and therapeutic potential in the pathogenesis of renal diseases.

Replication of Porcine Astrovirus Type 1-Infected PK-15 Cells In Vitro Affected by RIG-I and MDA5 Signaling Pathways

The interferon (IFN) system is an extremely powerful antiviral response in animal cells. The subsequent effects caused by porcine astrovirus type 1 (PAstV1) IFN activation are important for the host's response to viral infections. Here, we show that this virus, which causes mild diarrhea, growth retardation, and damage of the villi of the small intestinal mucosa in piglets, induces an IFN response upon infection of PK-15 cells. Although IFN-β mRNA was detected within infected cells, this response usually occurs during the middle stages of infection, after genome replication has taken place. Treatment of PAstV1-infected cells with the interferon regulatory factor 3 (IRF3) inhibitor BX795 decreased IFN-β expression, whereas the nuclear factor kappa light chain enhancer of activated B cells (NF-κB) inhibitor BAY11-7082 did not. These findings indicate that PAstV induced the production of IFN-β via IRF3-mediated rather than NF-κB-mediated signaling pathways in PK-15 cells. Moreover, PAstV1 increased the protein expression levels of retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated protein 5 (MDA5) in PK-15 cells. The knockdown of RIG-I and MDA5 decreased the expression levels of IFN-β and the viral loads and increased the infectivity of PAstV1. In conclusion, PAstV1 induced the production of IFN-β via the RIG-I and MDA5 signaling pathways, and the IFN-β produced during PAstV1 infection inhibited viral replication. These results will help provide new evidence that PAstV1-induced IFNs may protect against PAstV replication and pathogenesis. IMPORTANCE Astroviruses (AstVs) are widespread and can infect multiple species. Porcine astroviruses produce mainly gastroenteritis and neurological diseases in pigs. However, astrovirus-host interactions are less well studied, particularly with respect to their antagonism of IFN. Here, we report that PAstV1 acts via IRF3 transcription pathway activation of IFN-β. In addition, the knockdown of RIG-I and MDA5 attenuated the production of IFN-β induced by PAstV1 in PK-15 cells and increased efficient viral replication in vitro. We believe that these findings will help us to better understand the mechanism of how AstVs affect the host IFN response.

Transcriptome profiling highlights regulated biological processes and type III interferon antiviral responses upon Crimean-Congo hemorrhagic fever virus infection

Crimean-Congo hemorrhagic fever virus (CCHFV) is a biosafety level-4 (BSL-4) pathogen that causes Crimean-Congo hemorrhagic fever (CCHF) characterized by hemorrhagic manifestation, multiple organ failure and high mortality rate, posing great threat to public health. Despite the recently increasing research efforts on CCHFV, host cell responses associated with CCHFV infection remain to be further characterized. Here, to better understand the cellular response to CCHFV infection, we performed a transcriptomic analysis in human kidney HEK293 ​cells by high-throughput RNA sequencing (RNA-seq) technology. In total, 496 differentially expressed genes (DEGs), including 361 up-regulated and 135 down-regulated genes, were identified in CCHFV-infected cells. These regulated genes were mainly involved in host processes including defense response to virus, response to stress, regulation of viral process, immune response, metabolism, stimulus, apoptosis and protein catabolic process. Therein, a significant up-regulation of type III interferon (IFN) signaling pathway as well as endoplasmic reticulum (ER) stress response was especially remarkable. Subsequently, representative DEGs from these processes were well validated by RT-qPCR, confirming the RNA-seq results and the typical regulation of IFN responses and ER stress by CCHFV. Furthermore, we demonstrate that not only type I but also type III IFNs (even at low dosages) have substantial anti-CCHFV activities. Collectively, the data may provide new and comprehensive insights into the virus-host interactions and particularly highlights the potential role of type III IFNs in restricting CCHFV, which may help inform further mechanistic delineation of the viral infection and development of anti-CCHFV strategies.

New Insights into the Crosstalk among the Interferon and Inflammatory Signaling Pathways in Response to Viral Infections: Defense or Homeostasis

Innate immunity plays critical roles in eliminating viral infections, healing an injury, and restoring tissue homeostasis. The signaling pathways of innate immunity, including interferons (IFNs), nuclear factor kappa B (NF-κB), and inflammasome responses, are activated upon viral infections. Crosstalk and interplay among signaling pathways are involved in the complex regulation of antiviral activity and homeostasis. To date, accumulating evidence has demonstrated that NF-κB or inflammasome signaling exhibits regulatory effects on IFN signaling. In addition, several adaptors participate in the crosstalk between IFNs and the inflammatory response. Furthermore, the key adaptors in innate immune signaling pathways or the downstream cytokines can modulate the activation of other signaling pathways, leading to excessive inflammatory responses or insufficient antiviral effects, which further results in tissue injury. This review focuses on the crosstalk between IFN and inflammatory signaling to regulate defense and homeostasis. A deeper understanding of the functional aspects of the crosstalk of innate immunity facilitates the development of targeted treatments for imbalanced homeostasis.

Hepatitis B virus X gene impacts on the innate immunity and immune-tolerant phase in chronic hepatitis B virus infection

BACKGROUND AND AIMS

The immunologic features involved in the immune-tolerant phase of chronic hepatitis B (CHB) virus (HBV) infection are unclear. The hepatitis B virus X (HBx) protein disrupts IFN-β induction by downregulating MAVS and may destroy subsequent HBV-specific adaptive immunity. We aimed to analyse the impacts of genetic variability of HBx in CHB patients on the immune-tolerant phase during long-term follow-up.

METHODS

Children with CHB in the immune-tolerant phase were recruited and followed longitudinally. HBx gene sequencing of infecting HBV strains was performed, and the effects of HBx mutations on the immune-tolerant phase were assessed. Restoration of the host immune response to end the immune-tolerant phase was investigated by immunoblotting, immunostaining, ELISA and reporter assays of MAVS/IFN-β signalling in liver cell lines, patient liver tissues and the HBV plasmid replication system.

RESULTS

A total of 173 children (median age, 6.92 years) were recruited. Patients carrying HBx R87G, I127V and R87G + I127V double mutations exhibited higher cumulative incidences of immune-tolerant phase breakthrough (p = .011, p = .006 and p = .017 respectively). Cells transfected with HBx R87G and I127V mutants and pHBV1.3-B6.3 replicons containing the HBx R87G and I127V mutations exhibited statistically increased levels of IFN-β, especially under poly(I:C) stimulation or Flag-MAVS cotransfection. HA-HBx wild-type interacted with Flag-MAVS and enhanced its ubiquitination, but this ability was diminished in the R87G and I127V mutants.

CONCLUSIONS

HBx suppresses IFN-β induction. R87G and I127V mutation restored IFN-β production by preventing MAVS degradation, contributing to curtailing the HBV immune-tolerant phase in CHB patients.

Advances in Crosstalk between Porcine Circoviruses and Host

Porcine circoviruses (PCVs), including PCV1 to PCV4, are non-enveloped DNA viruses with a diameter of about 20 nm, belonging to the genus Circovirus in the family Circoviridae. PCV2 is an important causative agent of porcine circovirus disease or porcine circovirus-associated disease (PCVD/PCVAD), which is highly prevalent in pigs and seriously affects the swine industry globally. Furthermore, PCV2 mainly causes subclinical symptoms and immunosuppression, and PCV3 and PCV4 were detected in healthy pigs, sick pigs, and other animals. Although the pathogenicity of PCV3 and PCV4 in the field is still controversial, the infection rates of PCV3 and PCV4 in pigs are increasing. Moreover, PCV3 and PCV4 rescued from infected clones were pathogenic in vivo. It is worth noting that the interaction between virus and host is crucial to the infection and pathogenicity of the virus. This review discusses the latest research progress on the molecular mechanism of PCVs–host interaction, which may provide a scientific basis for disease prevention and control.

A Review of the Potential Effects of Melatonin in Compromised Mitochondrial Redox Activities in Elderly Patients With COVID-19

Melatonin, an endogenous indoleamine, is an antioxidant and anti-inflammatory molecule widely distributed in the body. It efficiently regulates pro-inflammatory and anti-inflammatory cytokines under various pathophysiological conditions. The melatonin rhythm, which is strongly associated with oxidative lesions and mitochondrial dysfunction, is also observed during the biological process of aging. Melatonin levels decline considerably with age and are related to numerous age-related illnesses. The signs of aging, including immune aging, increased basal inflammation, mitochondrial dysfunction, significant telomeric abrasion, and disrupted autophagy, contribute to the increased severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. These characteristics can worsen the pathophysiological response of the elderly to SARS-CoV-2 and pose an additional risk of accelerating biological aging even after recovery. This review explains that the death rate of coronavirus disease (COVID-19) increases with chronic diseases and age, and the decline in melatonin levels, which is closely related to the mitochondrial dysfunction in the patient, affects the virus-related death rate. Further, melatonin can enhance mitochondrial function and limit virus-related diseases. Hence, melatonin supplementation in older people may be beneficial for the treatment of COVID-19.

Tumor-associated fibroblasts derived exosomes induce the proliferation and cisplatin resistance in esophageal squamous cell carcinoma cells through RIG-I/IFN-β signaling

Esophageal squamous cell carcinoma (ESCC) is a common type of malignant cancer. There is growing evidence suggesting that exosomes may participate in the cellular communication of tumor-associated fibroblasts (TAFs). However, the cisplatin resistance of TAF-derived exosomes to ESCC cells remains to be further studied. Exosomes were isolated from TAFs and characterized with Western blot and TEM assays. ESCC cell lines (TE-1 and KYSE-150) were incubated with TAFs-derived exosomes. To explore the biological function of TAF-derived exosomes in ESCC cell proliferation, apoptosis, and chemosensitivity, we conducted MTT assays and Flow Cytometry. The effects in vivo were also verified via Xenograft mice models. We found that TAFs-derived exosomes led to enhanced cell proliferation and reduced apoptosis of cells, accompanied by increased expression of RIG-I/IFN-β, and TAFs derived exosomes may affect the chemosensitivity to cisplatin via RIG-I/IFN-β signaling in ESCC. Taken together, ESCC cells could communicate with TAFs cells via TAFs-derived exosomes. Our findings might represent a novel mechanism involved in ESCC and may provide a potential biomarker for ESCC.

Regulatory effect of Panax notoginseng saponins on the oxidative stress and histone acetylation induced by porcine circovirus type 2

Porcine circovirus type 2 (PCV2) exists widely in swine populations worldwide, and healthy PCV2 virus carriers have enhanced the severity of the infection, which is becoming more difficult to control. This study investigated the regulatory effect of Panax notoginseng saponins (PNS) on the oxidative stress and histone acetylation modification induced by PCV2 in vitro and in mice. In vitro, PNS significantly increased the scavenging capacities of superoxide anion radicals (O2•-) and hydroxyl radicals (•OH) and reduced the content of hydrogen peroxide (H2O2) induced by PCV2 in porcine alveolar macrophages (3D4/2). In addition, PNS decreased the protein expression level of histone H4 acetylation (Ac-H4) by increasing the activity of histone deacetylase (HDAC) in PCV2-infected 3D4/2 cells. In vivo, PNS enhanced the scavenging capacities of •OH and O2•- and reduced the content of H2O2 in the spleens of PCV2-infected mice. PNS also reduced the protein expression level of histone H3 acetylation (Ac-H3) by reducing the activity of histone acetylase (HAT) and increasing the activity of HDAC in the spleens of PCV2-infected mice. PCV2 infection activated oxidative stress and histone acetylation in vitro and in mice, but PNS ameliorated this oxidative stress. The research can provide experimental basis for exploring the antioxidant effect and the regulation of histone acetylation of PNS on PCV2-infected 3D4/2 cells and mice in vitro and in vivo, and provide new ideas for the treatment of PCV2 infection.

The Swine IFN System in Viral Infections: Major Advances and Translational Prospects

Interferons (IFNs) are a family of cytokines that play a pivotal role in orchestrating the innate immune response during viral infections, thus representing the first line of defense in the host. After binding to their respective receptors, they are able to elicit a plethora of biological activities, by initiating signaling cascades which lead to the transcription of genes involved in antiviral, anti-inflammatory, immunomodulatory and antitumoral effector mechanisms. In hindsight, it is not surprising that viruses have evolved multiple IFN escape strategies toward efficient replication in the host. Hence, in order to achieve insight into preventive and treatment strategies, it is essential to explore the mechanisms underlying the IFN response to viral infections and the constraints thereof. Accordingly, this review is focused on three RNA and three DNA viruses of major importance in the swine farming sector, aiming to provide essential data as to how the IFN system modulates the antiviral immune response, and is affected by diverse, virus-driven, immune escape mechanisms.

Porcine TRIM21 Enhances Porcine Circovirus 2 Infection and Host Immune Responses, But Inhibits Apoptosis of PCV2-Infected Cells

Tripartite motif protein 21 (TRIM21) is an interferon-inducible E3 ligase, containing one RING finger domain, one B-box motif, one coiled-coil domain at the N-terminal, as well as one PRY domain and one SPRY domain at the C-terminal. TRIM21 is expressed in many tissues and plays an important role in systemic autoimmunity. However, TRIM21 plays different roles in different virus infections. In this study, we evaluate the relationship between porcine TRIM21 and PCV2 infection as well as host immune responses. We found that PCV2 infection modulated the expression of porcine TRIM21. TRIM21 can enhance interferons and proinflammatory factors and decrease cellular apoptosis in PCV2-infected cells. These results indicate that porcine TRIM21 plays a critical role in enhancing PCV2 infection, which is a promising target for controlling and developing the treatment of PCV2 infection.

Goose nephritic astrovirus infection increases autophagy, destroys intercellular junctions in renal tubular epithelial cells, and damages podocytes in the kidneys of infected goslings

Goose nephritic astrovirus (GNAstV) has recently been identified, which causes kidney swelling and visceral gout in goslings. However, the pathological changes in kidney tissue due to GNAstV infection have not yet been described. In the study, fifty goslings were orally infected with GNAstV, and fifty goslings received PBS as a control. Kidney tissue was collected at different days following infection (dpi) to assess the injury. GNAstV infection reduced body weight, increased the relative weight of the kidney, and increased serum uric acid and creatinine levels. GNAstV was found within renal epithelial cells, and the viral load in the kidney peaked at 7 dpi. Pale and swollen kidney tissue was observed in infected goslings, especially at 5 and 7 dpi. GNAstV infection caused degeneration and necrosis of renal epithelial cells, structural destruction of the brush border, glycogen deposition in the glomerular mesangium, increased fibrosis, and infiltration of inflammatory cells into the renal interstitium. Moreover, swollen mitochondria, broken mitochondrial ridges, autophagosomes, and autophagolysosomes were observed under ultrahistopathological examination. GNAstV infection increased levels of LC3B, ATG5, and Beclin 1, and decreased p62, and downregulated WT1 mRNA and upregulated desmin mRNA. At early stages, GNAstV infection decreased expression of intercellular junction-related genes, including ZO-1, occludin, claudin-10, and catenin-α2. In conclusion, GNAstV infection causes renal epithelial cell autophagy, destruction of brush border and intercellular junctions, podocyte damage, and increased fibrosis, ultimately resulting in damage to the kidney.

NLRX1 can counteract innate immune response induced by an external stimulus favoring HBV infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells

INTRODUCTION

This study is aimed at the determination of the effect of the immune-regulatory factor NLRX1 on the antiviral activity of hepatocytes against an external stimuli favoring hepatitis B virus infection, and to explore its mechanism of action.

METHODS

A HepG2-NTCP model was established using the LV003 lentivirus. Cells were transfected using an overexpression vector and NLRX1 siRNA to achieve overexpression and interference of NLRX1 expression (OV-NLRX1, si-NLRX1). Levels of HBsAg and HBcAg were determined using Western blotting analysis and immunohistochemical analysis. The levels of hepatitis B virus DNA and hepatitis B virus cccDNA were determined by real-time quantitative polymerase chain reaction. The expression and transcriptional activity of IFN-α, IFN-β, and IL-6 were measured using real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and promoter-luciferase reporter plasmids. Co-immunoprecipitation was used to determine the effect of NLRX1 on the interaction between MAVS and RIG-1. Western blotting was used to obtain the phosphorylation of essential proteins in the MAVS-RLRs signaling pathways.

RESULTS

NLRX1 promoted HepG2-NTCP cell hepatitis B virus infection. Compared to the control group, the levels of HBsAg, HBcAg, hepatitis B virus cccDNA, and hepatitis B virus DNA increased in the OV-NLRX1 group and decreased in the si-NLRX1. Co-immunoprecipitation results showed that NLRX1 competitively inhibited the interaction between MAVS and RIG-1, and inhibited the phosphorylation of p65, IRF3, and IRF7. Additionally, NLRX1 reduced the transcription activity and expression levels of the final products: IFN-α, IFN-β, and IL-6.

CONCLUSIONS

NLRX1 can counteract innate immune response induced by an external stimuli favoring hepatitis B virus infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells. Inhibition of the MAVS-RLR-mediated signaling pathways leads to a decline in the expression levels of I-IFN and IL-6.

Resveratrol as an Adjunctive Therapy for Excessive Oxidative Stress in Aging COVID-19 Patients

The coronavirus disease 2019 (COVID-19) pandemic continues to burden healthcare systems worldwide. COVID-19 symptoms are highly heterogeneous, and the patient may be asymptomatic or may present with mild to severe or fatal symptoms. Factors, such as age, sex, and comorbidities, are key determinants of illness severity and progression. Aging is accompanied by multiple deficiencies in interferon production by dendritic cells or macrophages in response to viral infections, resulting in dysregulation of inflammatory immune responses and excess oxidative stress. Age-related dysregulation of immune function may cause a more obvious pathophysiological response to SARS-CoV-2 infection in elderly patients and may accelerate the risk of biological aging, even after recovery. For more favorable treatment outcomes, inhibiting viral replication and dampening inflammatory and oxidative responses before induction of an overt cytokine storm is crucial. Resveratrol is a potent antioxidant with antiviral activity. Herein, we describe the reasons for impaired interferon production, owing to aging, and the impact of aging on innate and adaptive immune responses to infection, which leads to inflammation distress and immunosuppression, thereby causing fulminant disease. Additionally, the molecular mechanism by which resveratrol could reverse a state of excessive basal inflammatory and oxidative stress and low antiviral immunity is discussed.

Open reading frame 5 protein of porcine circovirus type 2 induces RNF128 (GRAIL) which inhibits mRNA transcription of interferon-β in porcine epithelial cells

A previous study has indicated that mRNA transcript of Rnf128 (Grail) is significantly increased in porcine epithelial cells expressing porcine circovirus type 2 (PCV2) open reading frame 5 (ORF5). RNF128 is an E3 ubiquitin ligase that can modulate the activity of target protein via ubiquitination of specific lysine residues. However, the function of RNF128 in PCV2-infected epithelial cells has not been well studied yet. Thus, the objective of the present study was to examine the functional role of RNF128 in porcine epithelial cells (PK15 cells) after PCV2 infection. Results clearly indicated that PCV2 ORF5 increased the expression of RNF128 which inhibited type I IFN production and enhanced viral replication of PCV2 in PK15 cells. Therefore, up-regulating RNF128 by PCV2 ORF5 can help PCV2 circumvent initial immune surveillance of porcine epithelial cells.

Goose Nephritic Astrovirus Infection of Goslings Induces Lymphocyte Apoptosis, Reticular Fiber Destruction, and CD8 T-Cell Depletion in Spleen Tissue

The emergence of a novel goose nephritic astrovirus (GNAstV) has caused economic losses to the Chinese goose industry. High viral load is found in the spleen of goslings infected with GNAstV, but pathological injuries to the spleen due to GNAstV are largely unknown. In this study, 50 two-day-old goslings were infected orally with GNAstV, and 50 goslings were treated with PBS as control. Spleens were collected at different times following infection to assess damage. GNAstV infection caused visceral gout and urate deposition in joints, and resulted in 16% mortality. GNAstV was found in the lymphocytes and macrophages within the spleen. Lymphocyte loss, especially around the white pulp, and destruction and decline in the number of reticular fibers was observed in GNAstV-infected goslings. Moreover, in GNAstV-infected goslings, ultrahistopathological examination found that splenic lymphocytes exhibited condensed chromatin and apoptotic bodies, and reticular cells displayed damage to plasma membrane integrity and swollen mitochondria. Furthermore, TUNEL staining confirmed apoptosis of lymphocytes, and the mRNA levels of Fas and FasL were significantly increased in the GNAstV-infected goslings. In addition, GNAstV infection reduced the number and protein expression of CD8. In conclusion, GNAstV infection causes lymphocyte depletion, reticular cell necrosis, reticular fiber destruction, lymphocyte apoptosis, and reduction in CD8 levels, which contribute to spleen injury.

Porcine circovirus type 3 capsid protein induces NF-κB activation and upregulates pro-inflammatory cytokine expression in HEK-293T cells

Porcine circovirus type 3 (PCV3) has been widely detected throughout the world since it was first discovered on pig farms in 2015. PCV3 is closely associated with cardiac and multisystem inflammation, respiratory disease, congenital tremors, myocarditis, diarrhea, encephalitis and neurologic disease, and periarteritis. However, there have been few reports on the relationship between PCV3 and inflammatory pathways. The NF-κB signaling pathway plays an important role in the defense against viral infection. Here, we demonstrate that the capsid protein (Cap) of PCV3 plays a key role in the activation of NF-κB signaling in HEK-293T cells. Furthermore, PCV3 Cap promotes the mRNA expression of the pro-inflammatory cytokines IL6 and TNFα. In addition, PCV3 Cap promotes RIG-I and MDA5 mRNA expression in RIG-like receptor (RLR) signaling and MyD88 mRNA expression in Toll-like receptor (TLR) signaling but does not influence TRIF mRNA expression in TLR signaling. These results show that PCV3 Cap activates NF-κB signaling, possibly through the RLR and the TLR signaling pathways. This work illustrates that PCV3 Cap activates NF-κB signaling and thus may provide a basis for the pathogenesis of PCV3 and the innate immunity of the host.

Genomic analysis and functional characterization of immune genes from the RIG-I- and MAVS-mediated antiviral signaling pathway in lamprey

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are well-known viral RNA sensors in the cytoplasm. RIG-I-mediated antiviral signals are activated by interacting with the adapter protein mitochondrial antiviral signaling (MAVS), which triggers interferon (IFN) responses via a signaling cascade. Although the complete RIG-I receptor signaling pathway has been traced back to teleosts, definitive evidence of its presence in lampreys is lacking. Here, we identified 13 pivotal molecules in the RIG-I signaling pathway in lamprey, and demonstrated that the original RIG-I/MAVS signaling pathway was activated and mediated the expression of unique immunity factors such as RRP4, to inhibit viral proliferation after viral infection in vivo and in vitro. This study confirmed the conservation of the RIG-I pathway, and the uniqueness of the RRP4 effector molecule in lamprey, and further clarified the evolutionary process of the RIG-I antiviral signaling pathway, providing evidence on the origins of innate antiviral immunity in vertebrates.

Melatonin may decrease risk for and aid treatment of COVID-19 and other RNA viral infections

A recent retrospective study has provided evidence that COVID-19 infection may be notably less common in those using supplemental melatonin. It is suggested that this phenomenon may reflect the fact that, via induction of silent information regulator 1 (Sirt1), melatonin can upregulate K63 polyubiquitination of the mitochondrial antiviral-signalling protein, thereby boosting virally mediated induction of type 1 interferons. Moreover, Sirt1 may enhance the antiviral efficacy of type 1 interferons by preventing hyperacetylation of high mobility group box 1 (HMGB1), enabling its retention in the nucleus, where it promotes transcription of interferon-inducible genes. This nuclear retention of HMGB1 may also be a mediator of the anti-inflammatory effect of melatonin therapy in COVID-19-complementing melatonin's suppression of nuclear factor kappa B activity and upregulation of nuclear factor erythroid 2-related factor 2. If these speculations are correct, a nutraceutical regimen including vitamin D, zinc and melatonin supplementation may have general utility for the prevention and treatment of RNA virus infections, such as COVID-19 and influenza.

Azithromycin and glucosamine may amplify the type 1 interferon response to RNA viruses in a complementary fashion

Previous research demonstrates that, in clinically relevant concentrations, azithromycin can boost the ability of RNA viruses to induce type 1 interferon by amplifying the expression and virally-mediated activation of MDA5. O-GlcNAcylation of MAVS, a down-stream target of MDA5, renders it more effective for type 1 interferon induction. High-dose glucosamine administration up-regulates O-GlcNAcylation by increasing the cellular pool of UDP-N-acetylglucosamine. Hence, it is proposed that joint administration of azithromycin and high-dose glucosamine, early in the course of RNA virus infections, may interact in a complementary fashion to aid their control by enhancing type 1 interferon induction.

Porcine circovirus type 2 upregulates endothelial-derived IL-8 production in porcine iliac artery endothelial cells via the RIG-I/MDA-5/MAVS/JNK signaling pathway

Background

Dysfunction of endothelial cells and vascular system is one of the most important pathological changes of porcine circovirus disease (PCVD) caused by porcine circovirus type 2 (PCV2). PCV2-infected endothelial cells can upregulate the production of endothelial-derived IL-8, which can inhibit the maturation of dendritic cells. Endothelial-derived IL-8 has different structural and biological characteristics compared with monocyte-derived IL-8. However, the mechanism of endothelial-derived IL-8 production is still unclear.

Results

Key molecules of RIG-I-like signaling pathway RIG-I, MDA-5, MAVS and a key molecule of JNK signaling pathway c-Jun in PCV2-infected porcine iliac artery endothelial cells (PIECs) were upregulated significantly detected with quantitative PCR, Western blot and fluorescence confocal microscopy, while no significant changes were found in NF-κB signaling pathway. Meanwhile, the expression of endothelial-derived IL-8 was downregulated after RIG-I, MDA-5, or MAVS genes in PIECs were knocked down and PIECs were treated by JNK inhibitor.

Conclusions

PCV2 can activate RIG-I/MDA-5/MAVS/JNK signaling pathway to induce the production of endothelial-derived IL-8 in PIECs, which provides an insight into the further study of endothelial dysfunction and vascular system disorder caused by PCV2.

Micronutrients as immunomodulatory tools for COVID-19 management

COVID-19 rapidly turned to a global pandemic posing lethal threats to overwhelming health care capabilities, despite its relatively low mortality rate. The clinical respiratory symptoms include dry cough, fever, anosmia, breathing difficulties, and subsequent respiratory failure. No known cure is available for COVID-19. Apart from the anti-viral strategy, the supports of immune effectors and modulation of immunosuppressive mechanisms is the rationale immunomodulation approach in COVID-19 management. Diet and nutrition are essential for healthy immunity. However, a group of micronutrients plays a dominant role in immunomodulation. The deficiency of most nutrients increases the individual susceptibility to virus infection with a tendency for severe clinical presentation. Despite a shred of evidence, the supplementation of a single nutrient is not promising in the general population. Individuals at high-risk for specific nutrient deficiencies likely benefit from supplementation. The individual dietary and nutritional status assessments are critical for determining the comprehensive actions in COVID-19.

Nuclear transporter karyopherin subunit alpha 3 levels modulate Porcine circovirus type 2 replication in PK-15 cells

Entering the nucleus is important for Porcine circovirus type 2 (PCV2) replication. Karyopherins (KPNs) mediate the nuclear import of many cytoplasmic proteins. Our previous study showed that KPNA3 is involved in interferon production during PCV2 infection induced by Poly I:C and ISD (Interferon stimulatory DNA). However, it remains unclear whether PCV2 replication is associated with KPNA3. In the present study, knockdown of KPNA3 promoted the replication of PCV2, whereas overexpression of KPNA3 inhibited PCV2 replication in PK-15 cells. Furthermore, KPNA3 knockdown inhibited IRF3 and reduced the expression of antiviral genes including IFN-β, ISG54, Mx1 and ISG56, while the opposite results were obtained after KPNA3 overexpression. KPNA3 knockdown also promoted p65 nuclear translocation and increased the mRNA expression of IL-10 and IL-1β. These results suggested that KPNA3 facilitates IRF3 entry into the nucleus and the production of an antiviral response, resulting in PCV2 replication inhibition and blockage of NF-κB signal activation.

Structural Insights into Escherichia coli Shiga Toxin (Stx) Glycosphingolipid Receptors of Porcine Renal Epithelial Cells and Inhibition of Stx-Mediated Cellular Injury Using Neoglycolipid-Spiked Glycovesicles

Shiga toxin (Stx) producing Escherichia coli (STEC) cause the edema disease in pigs by releasing the swine-pathogenic Stx2e subtype as the key virulence factor. Stx2e targets endothelial cells of animal organs including the kidney harboring the Stx receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα1-4Galβ1-4Glcβ1-1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ1-3Galα1-4Galβ1-4Glcβ1-1Cer). Since the involvement of renal epithelial cells in the edema disease is unknown, in this study, we analyzed the porcine kidney epithelial cell lines, LLC-PK1 and PK-15, regarding the presence of Stx-binding GSLs, their sensitivity towards Stx2e, and the inhibitory potential of Gb3- and Gb4-neoglycolipids, carrying phosphatidylethanolamine (PE) as the lipid anchor, towards Stx2e. Immunochemical and mass spectrometric analysis revealed various Gb3Cer and Gb4Cer lipoforms as the dominant Stx-binding GSLs in both LLC-PK1 and PK-15 cells. A dihexosylceramide with proposed Galα1-4Gal-sequence (Gal₂Cer) was detected in PK-15 cells, whereas LLC-PK1 cells lacked this compound. Both cell lines were susceptible towards Stx2e with LLC-PK1 representing an extremely Stx2e-sensitive cell line. Gb3-PE and Gb4-PE applied as glycovesicles significantly reduced the cytotoxic activity of Stx2e towards LLC-PK1 cells, whereas only Gb4-PE exhibited some protection against Stx2e for PK-15 cells. This is the first report identifying Stx2e receptors of porcine kidney epithelial cells and providing first data on their Stx2e-mediated damage suggesting possible involvement in the edema disease.

Toll-like receptor 3 agonist poly I:C reinforces the potency of cytotoxic chemotherapy via the TLR3-UNC93B1-IFN-β signaling axis in paclitaxel-resistant colon cancer

Type I interferon (IFN) signaling in neoplastic cells has a chemo-sensitizing effect in cancer therapy. Toll-like receptor 3 (TLR3) activation promotes IFN-β production, which induces apoptosis and impairs proliferation in some cancer cells. Herein, we tested whether the TLR3 agonist polyinosinic: polycytidylic acid (poly I:C) can improve chemotherapeutic efficacy in paclitaxel (PTX) resistant cell lines. Human colon cancer cell lines HCT116, SW620, HCT-8 (sensitive to PTX), and HCT-8/PTX (resistant to PTX) were treated with poly I:C and the cell viability was measured. Results showed that poly I:C specifically impaired the cell viability of HCT-8/PTX by simultaneously promoting cell apoptosis and inhibiting cell proliferation. In addition, when TLR3 was overexpressed in HCT-8/PTX cells, we found that TLR3 contributed to the production of IFN-β that reduced cell viability, and poly I:C preferentially activated the TLR3-UNC93B1 signaling pathway to mediate this effect. Moreover, cotreatment of poly I:C and PTX acted synergistically to induce cell apoptosis of HCT-8/PTX via upregulating the expression of TLR3 and its molecular chaperone UNC93B1, assisting in the secretion of IFN-β. Notably, a combination of poly I:C and PTX synergistically inhibited the PTX-resistant tumor growth in vivo without side effects. In conclusion, our studies demonstrate that poly I:C reinforces the potency of cytotoxic chemotherapeutics in PTX-resistant cell line through the TLR3-UNC93B1-IFN-β signaling pathway, which supplies a novel mechanism of poly I:C for the chemotherapy sensitizing effect in a PTX-resistant tumor.

p53 mediated IFN-β signaling to affect viral replication upon TGEV infection

TGEV can induce IFN-β production, which in turn plays a vital role in host antiviral immune responses. Our previous studies showed that TGEV infection activated p53 signaling to induce host cell apoptosis, which might influence virus replication. However, whether there be an interaction between p53 and IFN-β signaling in the process of TGEV infection is unknown. In the present study, we used low dose of TGEV to infect p53 wild-type PK-15 cells (WT PK-15 cells) and p53 deficient cells (p53-/- PK-15 cells), to investigate the modulation of IFN signaling and virus replication by p53. The results showed that the IFN-β expression and production were notably inhibited in p53-/- PK-15 cells compared with that in WT PK-15 cells at early stage of TGEV infection. In addition, TGEV-induced the changes in mRNA levels of TRIF, TRAM, MDA5, RIG-I, IPS-1, IRF9, IRF3, ISG15 and ISG20 were notably hindered in p53-/- PK-15 cells before 36 h post infection (p.i.). Moreover, TGEV genomic RNA and sub genomic mRNA (N gene and ORF7) levels showed significant increase in p53-/- PK-15 cells compared with WT PK-15 cells after TGEV infection. And viral titers were observably enhanced in p53-/- PK-15 cells. Furthermore, exogenous IFN-β and polyinosinic-polycytidylic acid (poly (I:C)) treatment markedly inhibited the mRNA levels of TGEV gRNA, N and ORF7 in WT PK-15 cells and p53-/- PK-15 cells compared to control. Taken together, these results demonstrated that p53 may mediate IFN-β signaling to inhibit viral replication early after TGEV infection.

PCV2 infection activates the cGAS/STING signaling pathway to promote IFN-β production and viral replication in PK-15 cells

PCV2 is a single-stranded DNA virus that we previously found to induce IFN-β production via RIG-I and MDA-5. cGAS is known to be the most important DNA sensor for the recognition of cytosolic DNA; however, it remains unclear whether the interferon production induced by PCV2 is associated with cGAS. In the present study, PCV2 infection was found to increase the level of cGAS and STING expression, promote the release of cyclic dinucleotide cGAMP, and induce STING dimerization and translocation into the nucleus of PK-15 cells. These findings indicate that PCV2 infection activates both cGAS and STING. Furthermore, the knockdown of cGAS and STING decreased both the mRNA expression and promoter activity of IFN-β, demonstrating that the cGAS/STING signaling pathway contributes to the production of IFN-β. In addition, a knockdown of cGAS and STING also decreased the PCV2 viral load and infectivity. Therefore, PCV2 infection activates the cGAS/STING signaling pathway to induce IFN-β production and the knockdown of cGAS and STING decreases viral replication in PK-15 cells. These results provide further insight into the relationship between PCV2 and host innate immunity.

The ORF5 protein of porcine circovirus type 2 enhances viral replication by dampening type I interferon expression in porcine epithelial cells

Identifying the functional role of each porcine circovirus type 2 (PCV2) ORF associated with host cell modulation might provide better knowledge about the pathogenesis of postweaning multisystemic wasting syndrome (PMWS). PCV2 ORF5 was recently identified and the functional role of ORF5 during pathogenesis after PCV2 infection is largely unknown. In this study, we used RNA-seq to investigate the functional role of PCV2 ORF5 in PCV2-infected porcine epithelial cells. Our data demonstrates that PCV2 ORF5 could inhibit type I interferon (IFN) expression via transcriptional repression of genes involved in type I IFN production, thus enhancing replication of PCV2 in porcine epithelial cells. Therefore, PCV2 ORF5 might have an inhibitory role against host immune surveillance.

Establishment and characterization of a telomerase-immortalized porcine bronchial epithelial cell line

Primary porcine bronchial epithelial cells (PBECs) are an ideal model to study the molecular and pathogenic mechanisms of various porcine respiratory pathogens. However, the short lifespan of primary PBECs greatly limit their application. Here, we isolated and cultured primary PBECs and established immortalized PBECs by transfecting primary PBECs with the pEGFP-hTERT recombinant plasmid containing human telomerase reverse transcriptase (hTERT). Immortalized PBECs (hTERT-PBECs) retained the morphological and functional features of primary PBECs as indicated by cytokeratin 18 expression, telomerase activity assay, proliferation assays, karyotype analysis, and quantitative reverse-transcriptase polymerase chain reaction. Compared to primary PBECs, hTERT-PBECs had higher telomerase activity, extended replicative lifespan, and displayed enhanced proliferative activity. Moreover, this cell line is not transformed in vitro and does not exhibit a malignant phenotype in vivo, suggesting that it can be safely used in further studies. Besides, hTERT-PBECs were susceptible to swine influenza virus of H3N2 subtype and porcine circovirus type 2. In conclusion, the immortalized hTERT-PBECs represent a valuable in vitro model, which can be widely used in the study of porcine respiratory pathogenic infections.

Porcine circovirus type 2 inhibits inter-β expression by targeting Karyopherin alpha-3 in PK-15 cells

Interferon (IFN)-mediated antiviral response is an important part of host defense. Previous studies reported that porcine circovirus type 2 (PCV2) inhibits interferon production, but the mechanism is still poorly understood. In this study, PCV2 suppresses IFN-β and IRF3 promoters and mRNA level of IFN-β induced by ISD or Poly(I:C), but has no effect on the activation of AP-1 and NF-κB. Furthermore, PCV2 decreases the mRNA level of IFN-β and IFN-β promoter activity driven by STING, TBK1, IRF3, and IRF3/5D, and causes a reduction in the protein level of nuclear p-IRF3. In addition, PCV2 interrupts the interaction of KPNA3, rather than KPNA4, with p-IRF3. Overexpression of KPNA3 restores IFN-β promoter activity. These results indicate that PCV2 disrupts the interaction of KPNA3 with p-IRF3 and blocks p-IRF3 translocation to the nucleus, thereby inhibiting IFN-β induction in PK-15 cells.