Regulation of proinflammatory cytokine expression in primary mouse astrocytes by coronavirus infection

Protective Role of the Toll-Like Receptor 5 Agonist KMRC011 against Murine Colitis Induced by Citrobacter rodentium and Dextran Sulfate Sodium

This study aimed to identify the therapeutic ability of a novel toll-like receptor (TLR) 5 agonist, KMRC011, on ulcerative colitis induced by Citrobacter rodentium and dextran sulfate sodium in a C57BL/6N mouse model. Ulcerative colitis was induced in the mice by the oral administration of 1% dextran sulfate sodium in sterile drinking water for seven days ad libitum, followed by C. rodentium infection on the seventh day by intra-gastric administration (DSS-CT group). KMRC011 was administered intramuscularly at both 24 h and 15 min before (Treatment 1 group), and at both 15 min and 24 h after (Treatment 2 group) the C. rodentium infection. The length of the large intestine and histopathological counts were significantly greater and mucosal thickness was significantly thinner in the Treatment 1 group compared to the DSS-CT and Treatment 2 groups. Il-6 and Il-10 mRNA expression levels were upregulated, while Ifn-γ and Tnf-α mRNA expression levels were significantly downregulated in the Treatment 1 group, compared to the DSS-CT group. NF-κB p65 expression level was elevated due to ulcerative colitis in the DSS-CT group, but was significantly downregulated in the Treatment 1 group. Overall, KMRC011 showed protective effects against murine colitis by inhibiting NF-κB signaling.

Photoprotective effects of Sargassum thunbergii on ultraviolet B-induced mouse L929 fibroblasts and zebrafish

BACKGROUND

Chronic exposure to ultraviolet B (UVB) causes a series of adverse skin reactions, such as erythema, sunburn, photoaging, and cancer, by altering signaling pathways related to inflammation, oxidative stress, and DNA damage. Marine algae have abundant amounts and varieties of bioactive compounds that possess antioxidant and anti-inflammatory properties. Thus, the objective of this study was to investigate the photoprotective effects of an ethanol extract of Sargassum thunbergii.

METHODS

Sargassum thunbergii phenolic-rich extract (STPE) was prepared, and its activity against UVB damage was evaluated using L929 fibroblast cells and zebrafish. STPE was extracted and purified by 40% ethanol and macroporous resin XDA-7. Reactive oxygen species (ROS) and antioxidant markers, such as superoxide dismutase (SOD), catalase (CAT) activities, and malondialdehyde (MDA) content were analyzed. The effect of STPE on UVB-induced inflammation was determined by inflammatory cytokine gene and protein expression. The expression of signaling molecules in the Nuclear Factor KappaB (NF-κB) pathway was determined by western blotting. DNA condensation was analyzed and visualized by Hoechst 33342 staining. In vivo evaluation was performed by tail fin area and ROS measurement using the zebrafish model.

RESULTS

The total polyphenol content of STPE was 72%. STPE reduced ROS content in L929 cells, improved SOD and CAT activities, and significantly reduced MDA content, thereby effectively alleviating UVB radiation-induced oxidative damage. STPE inhibited the mRNA and protein expression of TNF-α, IL-6, and IL-1α. STPE reversed DNA condensation at concentrations of 20 and 40 μg/mL compared with the UVB control. Moreover, STPE inhibited NF-κB signaling pathway activation and alleviated DNA agglutination in L929 cells after UVB irradiation. Additionally, 1.67 μg/mL STPE significantly increased the tail fin area in zebrafish, and 0.8-1.6 μg/mL STPE effectively eliminated excessive ROS after UVB radiation.

CONCLUSIONS

STPE inhibited UVB-induced oxidative stress, inflammatory cytokine expression, and DNA condensation via the downregulation of the NF-κB signaling pathway, suggesting that it prevents UVB-induced photodamage, and has potential for clinical development for skin disease treatment.

Role of expression of host cytokines in the pathogenesis of H9N2-PB2 reassortant and non-reassortant H5N1 avian influenza viruses isolated from crows in BALB/c mice

The present experiment was conducted to study the role of cytokine, chemokine and TLRs responses of H9N2-PB2 reassortant H5N1 virus as compared to non-reassortant H5N1 virus isolated from crows in BALB/c mice. Two groups (12 mice each) of 6-8 weeks old BALB/c mice were intranasally inoculated with 10⁶ EID₅₀/ml of viruses A/crow/India/03CA04/2015 (H9N2-PB2 reassortant H5N1) and A/crow/India/02CA01/2012 (non-reassortant H5N1). At each interval, brain, lung and spleen were collected and relative quantification of cytokines, chemokines and TLRs was done by qPCR. The H9N2-PB2 reassortant H5N1 infected mice brain, the transcripts of TLR7 were significantly higher than other cytokines at 3dpi and KC was significantly upregulated at 7dpi. In non-reassortant H5N1 infected mice brain showed, TLR 7 and IFNα upregulation at 3dpi and IFNγ and TLR7 upregulation at 7dpi. The H9N2-PB2 reassortant H5N1 infected mice lung revealed, IL2 and TLR7 significant upregulation at 3dpi and in non-reassortant H5N1 infected mice, IL6 was significantly upregulated. At 7dpi in H9N2-PB2 reassortant H5N1 virus infected group mice, IL1 and TLR 3 were significantly upregulated in lungs and in non-reassortant group mice, IL1 and TLR7 were significantly upregulated. At 3dpi in H9N2-PB2 reassortant H5N1 virus infected mice spleen, IL4, IFNα, IFNβ were significantly downregulated and TLR7 transcript was significantly upregulated. In non-reassortant group mice, IL6, IFNα, IFNβ and TLR 3 were significantly upregulated. At 7dpi in H9N2-PB2 reassortant H5N1 virus infected mice spleen, IFNα, IFNβ and TLR7 were significantly lower than other cytokines and in non-reassortant group mice, IFNα and IFNβ were significantly downregulated. This study concludes that dysregulation of cytokines in lungs and brain might have contributed to the pathogenesis of both the viruses in mice.

Antiviral effects of ergosterol peroxide in a pig model of porcine deltacoronavirus (PDCoV) infection involves modulation of apoptosis and tight junction in the small intestine

Porcine deltacoronavirus (PDCoV) is a newly discovered swine enteropathogenic coronavirus with worldwide distribution. However, efficient strategies to prevent or treat the infection remain elusive. Our in vitro study revealed that ergosterol peroxide (EP) from the mushroom Cryptoporus volvatus has efficient anti-PDCoV properties. The aim of this study is to evaluate the potential of EP as a treatment for PDCoV in vivo and elucidate the possible mechanisms. Seven-day-old piglets were infected with PDCoV by oral administration in the presence or absence of EP. Piglets infected with PDCoV were most affected, whereas administration of EP reduced diarrhea incidence, alleviated intestinal lesion, and decreased viral load in feces and tissues. EP reduced PDCoV-induced apoptosis and enhanced tight junction protein expressions in the small intestine, maintaining the integrity of the intestinal barrier. EP showed immunomodulatory effect by suppressing PDCoV-induced pro-inflammatory cytokines and the activation of IκBα and NF-κB p65, and upregulating IFN-I expression. Knockdown of p38 inhibited PDCoV replication and alleviated PDCoV-induced apoptosis, implying that EP inhibited PDCoV replication and alleviated PDCoV-induced apoptosis via p38/MAPK signaling pathway. Collectively, ergosterol peroxide can protect piglets from PDCoV, revealing the potential of EP for development as a promising strategy for treating and controlling the infection of PDCoV.

Stress-activated protein kinases are involved in the replication of porcine deltacoronavirus

This study was conducted to examine the role of stress-activated protein kinases (SAPKs), including c-Jun NH₂-terminal kinases (JNK1/2) and p38 mitogen-activated protein kinase (MAPK), in porcine deltacoronavirus (PDCoV) infection. Results demonstrated the activation of JNK1/2 and p38 MAPK in PDCoV-infected cells, which occurred concomitant with viral biosynthesis and irrespective of cell type. Pharmacological inhibition or knockdown of either SAPK significantly attenuated PDCoV replication, whereas addition of a signaling activator augmented virus infectivity. Moreover, pharmacological inhibition of JNK1/2 or p38 MAPK activation was innocuous to viral entry but significantly detrimental to post uncoating stages of the replication cycle. Remarkably, cytokine gene expression in PDCoV-infected IPEC-J2 cells was modified by inhibiting the activation of either SAPK. Collectively, these data indicate that JNK1/2 and p38 MAPK signaling pathways contribute to viral biosynthesis and regulate immune responses, thereby favoring the replication of PDCoV.

Upregulation of DUSP6 impairs infectious bronchitis virus replication by negatively regulating ERK pathway and promoting apoptosis

Elucidating virus-cell interactions is fundamental to understanding viral replication and identifying targets for therapeutic control of viral infection. The extracellular signal-regulated kinase (ERK) pathway has been shown to regulate pathogenesis during many viral infections, but its role during coronavirus infection is undetermined. Infectious bronchitis virus is the representative strain of Gammacoronavirus, which causes acute and highly contagious diseases in the poultry farm. In this study, we investigated the role of ERK1/2 signaling pathway in IBV infection. We found that IBV infection activated ERK1/2 signaling and the up-regulation of phosphatase DUSP6 formed a negative regulation loop. Pharmacological inhibition of MEK1/2-ERK1/2 signaling suppressed the expression of DUSP6, promoted cell death, and restricted virus replication. In contrast, suppression of DUSP6 by chemical inhibitor or siRNA increased the phosphorylation of ERK1/2, protected cells from apoptosis, and facilitated IBV replication. Overexpression of DUSP6 decreased the level of phospho-ERK1/2, promoted apoptosis, while dominant negative mutant DUSP6-DN lost the regulation function on ERK1/2 signaling and apoptosis. In conclusion, these data suggest that MEK-ERK1/2 signaling pathway facilitates IBV infection, probably by promoting cell survival; meanwhile, induction of DUSP6 forms a negative regulation loop to restrict ERK1/2 signaling, correlated with increased apoptosis and reduced viral load. Consequently, components of the ERK pathway, such as MEK1/2 and DUSP6, represent excellent targets for the development of antiviral drugs.

Lung pathology due to hRSV infection impairs blood-brain barrier permeability enabling astrocyte infection and a long-lasting inflammation in the CNS

The human respiratory syncytial virus (hRSV) is the most common infectious agent that affects children before two years of age. hRSV outbreaks cause a significant increase in hospitalizations during the winter season associated with bronchiolitis and pneumonia. Recently, neurologic alterations have been associated with hRSV infection in children, which include seizures, central apnea, and encephalopathy. Also, hRSV RNA has been detected in cerebrospinal fluids (CSF) from patients with neurological symptoms after hRSV infection. Additionally, previous studies have shown that hRSV can be detected in the lungs and brains of mice exposed to the virus, yet the potential effects of hRSV infection within the central nervous system (CNS) remain unknown. Here, using a murine model for hRSV infection, we show a significant behavior alteration in these animals, up to two months after the virus exposure, as shown in marble-burying tests. hRSV infection also produced the expression of cytokines within the brain, such as IL-4, IL-10, and CCL2. We found that hRSV infection alters the permeability of the blood-brain barrier (BBB) in mice, allowing the trespassing of macromolecules and leading to increased infiltration of immune cells into the CNS together with an increased expression of pro-inflammatory cytokines in the brain. Finally, we show that hRSV infects murine astrocytes both, in vitro and in vivo. We identified the presence of hRSV in the brain cortex where it colocalizes with vWF, MAP-2, Iba-1, and GFAP, which are considered markers for endothelial cells, neurons, microglia, and astrocyte, respectively. hRSV-infected murine astrocytes displayed increased production of nitric oxide (NO) and TNF-α. Our results suggest that hRSV infection alters the BBB permeability to macromolecules and immune cells and induces CNS inflammation, which can contribute to the behavioral alterations shown by infected mice. A better understanding of the neuropathy caused by hRSV could help to reduce the potential detrimental effects on the CNS in hRSV-infected patients.

Alpha/Beta Interferon (IFN-α/β) Signaling in Astrocytes Mediates Protection against Viral Encephalomyelitis and Regulates IFN-γ-Dependent Responses

The contribution of distinct central nervous system (CNS) resident cells to protective alpha/beta interferon (IFN-α/β) function following viral infections is poorly understood. Based on numerous immune regulatory functions of astrocytes, we evaluated the contribution of astrocyte IFN-α/β signaling toward protection against the nonlethal glia- and neuronotropic mouse hepatitis virus (MHV) strain A59. Analysis of gene expression associated with IFN-α/β function, e.g., pattern recognition receptors (PRRs) and interferon-stimulated genes (ISGs), revealed lower basal mRNA levels in brain-derived astrocytes than in microglia. Although astrocytes poorly induced Ifnβ mRNA following infection, they upregulated various mRNAs in the IFN-α/β pathway to a higher extent than microglia, supporting effective IFN-α/β responsiveness. Ablation of the IFN-α/β receptor (IFNAR) in astrocytes using mGFAPcre IFNAR^fl/fl mice resulted in severe encephalomyelitis and mortality, coincident with uncontrolled virus replication. Further, virus spread was not restricted to astrocytes but also affected microglia and neurons, despite increased and sustained Ifnα/β and ISG mRNA levels within the CNS. IFN-γ, a crucial mediator for MHV control, was not impaired in infected mGFAPcre IFNAR^fl/fl mice despite reduced T cell CNS infiltration. Unexpectedly however, poor induction of IFN-γ-dependent major histocompatibility complex (MHC) class II expression on microglia supported that defective IFN-γ signaling contributes to uncontrolled virus replication. A link between sustained elevated IFN-α/β and impaired responsiveness to IFN-γ supports the novel concept that temporally limited early IFN-α/β responses are critical for effective antiviral IFN-γ function. Overall, our results imply that IFN-α/β signaling in astrocytes is not only critical in limiting early CNS viral spread but also promotes protective antiviral IFN-γ function.IMPORTANCE An antiviral state established by IFN-α/β contains initial viral spread as adaptive immunity develops. While it is apparent that the CNS lacks professional IFN-α/β producers and that resident cells have distinct abilities to elicit innate IFN-α/β responses, protective interactions between inducer and responder cells require further investigation. Infection with a glia- and neuronotropic coronavirus demonstrates that astrocytes mount a delayed but more robust response to infection than microglia, despite their lower basal mRNA levels of IFN-α/β-inducing components. Lethal, uncontrolled viral dissemination following ablation of astrocyte IFN-α/β signaling revealed the importance of IFN-α/β responses in a single cell type for protection. Sustained global IFN-α/β expression associated with uncontrolled virus did not suffice to protect neurons and further impaired responsiveness to protective IFN-γ. The results support astrocytes as critical contributors to innate immunity and the concept that limited IFN-α/β responses are critical for effective subsequent antiviral IFN-γ function.

A murine colitis model developed using a combination of dextran sulfate sodium and Citrobacter rodentium

Adult mice were treated with dextran sulfate sodium (DSS) and infected with Citrobacter rodentium for developing a novel murine colitis model. C57BL/6N mice (7-week-old) were divided into four groups. Each group composed of control, dextran sodium sulfate-treated (DSS), C. rodentium-infected (CT), and DSS-treated and C. rodentium-infected (DSS-CT) mice. The DSS group was administered 1% DSS in drinking water for 7 days. The CT group was supplied with normal drinking water for 7 days and subsequently infected with C. rodentium via oral gavage. The DSS-CT group was supplied with 1% DSS in drinking water for 7 days and subsequently infected with C. rodentium via oral gavage. The mice were sacrificed 10 days after the induction of C. rodentium infection. The DSS-CT group displayed significantly shorter colon length, higher spleen to body weight ratio, and higher histopathological score compared to the other three groups. The mRNA expression levels of tumor necrosis factor (TNF)-α and interferon (INF)-γ were significantly upregulated; however, those of interleukin (IL)-6 and IL-10 were significantly downregulated in the DSS-CT group than in the control group. These results demonstrated that a combination of low DSS concentration (1%) and C. rodentium infection could effectively induce inflammatory bowel disease (IBD) in mice. This may potentially be used as a novel IBD model, in which colitis is induced in mice by the combination of a chemical and a pathogen.

Activation of the c-Jun NH2-terminal kinase pathway by coronavirus infectious bronchitis virus promotes apoptosis independently of c-Jun

Mitogen-activated protein kinases (MAPKs) are conserved protein kinases that regulate a variety of important cellular signaling pathways. Among them, c-Jun N-terminal kinases (JNK) are known to be activated by various environmental stresses including virus infections. Previously, activation of the JNK pathway has been detected in cells infected with several coronaviruses. However, detailed characterization of the pathway as well as its implication in host-virus interactions has not been fully investigated. Here we report that the JNK pathway was activated in cells infected with the avian coronavirus infectious bronchitis virus (IBV). Of the two known upstream MAPK kinases (MKK), MKK7, but not MKK4, was shown to be responsible for IBV-induced JNK activation. Moreover, knockdown and overexpression experiments demonstrated that JNK served as a pro-apoptotic protein during IBV infection. Interestingly, pro-apoptotic activity of JNK was not mediated via c-Jun, but involved modulation of the anti-apoptotic protein B-cell lymphoma 2 (Bcl2). Taken together, JNK constitutes an important aspect of coronavirus-host interaction, along with other MAPKs.

Coronavirus Infections in the Central Nervous System and Respiratory Tract Show Distinct Features in Hospitalized Children

Background/Aims

Coronavirus (CoV) infections induce respiratory tract illnesses and central nervous system (CNS) diseases. We aimed to explore the cytokine expression profiles in hospitalized children with CoV-CNS and CoV-respiratory tract infections.

Methods

A total of 183 and 236 hospitalized children with acute encephalitis-like syndrome and respiratory tract infection, respectively, were screened for anti-CoV IgM antibodies. The expression profiles of multiple cytokines were determined in CoV-positive patients.

Results

Anti-CoV IgM antibodies were detected in 22/183 (12.02%) and 26/236 (11.02%) patients with acute encephalitis-like syndrome and respiratory tract infection, respectively. Cytokine analysis revealed that the level of serum granulocyte colony-stimulating factor (G-CSF) was significantly higher in both CoV-CNS and CoV-respiratory tract infection compared with healthy controls. Additionally, the serum level of granulocyte macrophage colony-stimulating factor (GM-CSF) was significantly higher in CoV-CNS infection than in CoV-respiratory tract infection. In patients with CoV-CNS infection, the levels of IL-6, IL-8, MCP-1, and GM-CSF were significantly higher in their cerebrospinal fluid samples than in matched serum samples.

Conclusion

To the best of our knowledge, this is the first report showing a high incidence of CoV infection in hospitalized children, especially with CNS illness. The characteristic cytokine expression profiles in CoV infection indicate the importance of host immune response in disease progression.

Regulation of Stress Responses and Translational Control by Coronavirus

Similar to other viruses, coronavirus infection triggers cellular stress responses in infected host cells. The close association of coronavirus replication with the endoplasmic reticulum (ER) results in the ER stress responses, which impose a challenge to the viruses. Viruses, in turn, have come up with various mechanisms to block or subvert these responses. One of the ER stress responses is inhibition of the global protein synthesis to reduce the amount of unfolded proteins inside the ER lumen. Viruses have evolved the capacity to overcome the protein translation shutoff to ensure viral protein production. Here, we review the strategies exploited by coronavirus to modulate cellular stress response pathways. The involvement of coronavirus-induced stress responses and translational control in viral pathogenesis will also be briefly discussed.

JNK and p38 mitogen-activated protein kinase pathways contribute to porcine epidemic diarrhea virus infection

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PEDV infection activated p38 MAPK and JNK1/2 in vitro.

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UV-inactivated virus failed to induce p38 MAPK and JNK1/2 activation.

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Pharmacological inhibition of p38 MAPK or JNK activation impaired PEDV replication.

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SAPK cascades do not affect the apoptosis pathway during PEDV infection.

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PEDV exploits the p38 MAPK and JNK signaling pathways for optimal replication.

The mitogen-activated protein kinase (MAPK) pathways, which are central building blocks in the intracellular signaling network, are often manipulated by viruses of diverse families to favor their replication. Among the MAPK family, the extracellular signal-regulated kinase (ERK) pathway is known to be modulated during the infection with porcine epidemic diarrhea virus (PEDV); however, involvement of stress-activated protein kinases (SAPKs) comprising p38 MAPK and c-Jun NH₂-terminal kinase (JNK) remains to be determined. Therefore, in the present study, we investigated whether activation of p38 MAPK and JNK cascades is required for PEDV replication. Our results showed that PEDV activates p38 MAPK and JNK1/2 up to 24 h post-infection, whereas, thereafter their phosphorylation levels recede to baseline levels or even fall below them. Notably, UV-irradiated inactivated PEDV, which can enter cells but cannot replicate inside them, failed to induce phosphorylation of p38 MAPK and JNK1/2 suggesting that viral biosynthesis is essential for activation of these kinases. Treatment of cells with selective p38 or JNK inhibitors markedly impaired PEDV replication in a dose-dependent manner and these antiviral effects were found to be maximal during the early times of the infection. Furthermore, direct pharmacological inhibition of p38 MAPK or JNK1/2 activation resulted in a significant reduction of viral RNA synthesis, viral protein expression, and progeny release. However, independent treatments with either SAPK inhibitor did not inhibit PEDV-induced apoptotic cell death mediated by activation of mitochondrial apoptosis-inducing factor (AIF) suggesting that SAPKs are irrelevant to the apoptosis pathway during PEDV infection. In summary, our data demonstrated critical roles of the p38 and JNK1/2 signaling pathways in facilitating successful viral infection during the post-entry steps of the PEDV life cycle.

Coronavirus-induced ER stress response and its involvement in regulation of coronavirus-host interactions

Coronavirus replication is structurally and functionally associated with the endoplasmic reticulum (ER), a major site of protein synthesis, folding, modification and sorting in the eukaryotic cells. Disturbance of ER homeostasis may occur under various physiological or pathological conditions. In response to the ER stress, signaling pathways of the unfolded protein response (UPR) are activated. UPR is mediated by three ER transmembrane sensors, namely the PKR-like ER protein kinase (PERK), the inositol-requiring protein 1 (IRE1) and the activating transcriptional factor 6 (ATF6). UPR facilitates adaptation to ER stress by reversible translation attenuation, enhancement of ER protein folding capacity and activation of ER-associated degradation (ERAD). In cells under prolonged and irremediable ER stress, UPR can also trigger apoptotic cell death. Accumulating evidence has shown that coronavirus infection causes ER stress and induces UPR in the infected cells. UPR is closely associated with a number of major signaling pathways, including autophagy, apoptosis, the mitogen-activated protein (MAP) kinase pathways, innate immunity and pro-inflammatory response. Therefore, studies on the UPR are pivotal in elucidating the complicated issue of coronavirus-host interaction. In this paper, we present the up-to-date knowledge on coronavirus-induced UPR and discuss its potential involvement in regulation of innate immunity and apoptosis.

The endoplasmic reticulum stress sensor IRE1α protects cells from apoptosis induced by the coronavirus infectious bronchitis virus

The unfolded-protein response (UPR) is a signal transduction cascade triggered by perturbation of the homeostasis of the endoplasmic reticulum (ER). UPR resolves ER stress by activating a cascade of cellular responses, including the induction of molecular chaperones, translational attenuation, ER-associated degradation, and other mechanisms. Under prolonged and irremediable ER stress, however, the UPR can also trigger apoptosis. Here, we report that in cells infected with the avian coronavirus infectious bronchitis virus (IBV), ER stress was induced and the IRE1α-XBP1 pathway of UPR was activated. Knockdown and overexpression experiments demonstrated that IRE1α protects infected cells from IBV-induced apoptosis, which required both its kinase and RNase activities. Our data also suggest that splicing of XBP1 mRNA by IRE1α appears to convert XBP1 from a proapoptotic XBP1u protein to a prosurvival XBP1s protein. Moreover, IRE1α antagonized IBV-induced apoptosis by modulating the phosphorylation status of the proapoptotic c-Jun N-terminal kinase (JNK) and the prosurvival RAC-alpha serine/threonine-protein kinase (Akt). Taken together, the data indicate that the ER stress sensor IRE1α is activated in IBV-infected cells and serves as a survival factor during coronavirus infection.

IMPORTANCE

Animal coronaviruses are important veterinary viruses, which could cross the species barrier, becoming severe human pathogens. Molecular characterization of the interactions between coronaviruses and host cells is pivotal to understanding the pathogenicity and species specificity of coronavirus infection. It has been well established that the endoplasmic reticulum (ER) is closely associated with coronavirus replication. Here, we report that inositol-requiring protein 1 alpha (IRE1α), a key sensor of ER stress, is activated in cells infected with the avian coronavirus infectious bronchitis virus (IBV). Moreover, IRE1α is shown to protect the infected cells from apoptosis by modulating the unfolded-protein response (UPR) and two kinases related to cell survival. This study demonstrates that UPR activation constitutes a major aspect of coronavirus-host interactions. Manipulations of the coronavirus-induced UPR may provide novel therapeutic targets for the control of coronavirus infection and pathogenesis.

Inhibition of glycogen synthase kinase-3β by lithium chloride suppresses 6-hydroxydopamine-induced inflammatory response in primary cultured astrocytes

An increasing amount of evidence has emerged to suggest that neuroinflammatory process is involved in the pathogenesis of Parkinson's disease (PD). Activated microglia and astrocytes are found in the substantia nigra (SN) of Parkinson's disease brains as well as in animal models of Parkinson's disease. Although reactive astrocytes are involved in the progression of PD, the role of reactive astrocytes in neuroinflammation of PD has received limited attention to date. Recently, Glycogen synthase kinase-3β (GSK-3β) was identified as a crucial regulator of the inflammatory response. The purpose of this study was to explore the mechanism by which 6-hydroxydopamine (6-OHDA) induces inflammatory response in astrocytes and observe the anti-inflammatory effect of lithium chloride (LiCl) on 6-OHDA-treated astrocytes. In the present study, we found that glial fibrillary acidic protein (GFAP) was markedly upregulated in the presence of 6-OHDA. Moreover, our results revealed that proinflammatory molecules including inducible nitric oxide synthase (iNOS), nitric oxide (NO), cyclooxygenase-2(COX-2), prostaglandins E2 (PGE2), and tumor necrosis factor-α (TNF-α) were obviously increased in astrocytes exposed to 6-OHDA. Western blot analysis revealed that 6-OHDA significantly increased dephosphorylation/activation of GSK-3β as well as the nuclear translocation of nuclear factor-κB (NF-κB) p65. Besides, GSK-3β inhibitor LiCl and SB415286 inhibited the GSK-3β/NF-κB signaling pathway, leading to the reduction of proinflammatory molecules in 6-OHDA-activated astrocytes. These results confirmed that GSK-3β inhibitor LiCl and SB415286 provide protection against neuroinflammation in 6-OHDA-treated astrocytes. Therefore, GSK-3β may be a potential therapeutic target for the treatment of PD.

Stress-activated protein kinases are involved in porcine reproductive and respiratory syndrome virus infection and modulate virus-induced cytokine production

The present study examined the role of the p38 MAPK and JNK pathways during PRRSV infection in immortalized porcine alveolar macrophage (PAM) cells. Infection with PRRSV was found to progressively activate p38 and JNK1/2 up to 36 h postinfection and then their phosphorylation levels dramatically decreased to baseline at 48 h postinfection. In contrast, UV-inactivated PRRSV failed to trigger phosphorylation of these SAPKs, indicating that the post-entry process is responsible for their activation. Independent treatment of cells with a selective p38 or JNK inhibitor markedly impaired PRRSV infection, resulting in significant reduction in synthesis of viral genomic and subgenomic RNAs, viral protein expression, and progeny virus production. Notably, cytokine production in PAM cells infected with PRRSV was shown to be altered by inhibiting these SAPKs. Altogether, our data suggest that the p38 and JNK signaling pathways play pivotal roles in PRRSV replication and may regulate immune responses during virus infection.

Roles of stress-activated protein kinases in the replication of Singapore grouper iridovirus and regulation of the inflammatory responses in grouper cells

Stress-activated protein kinases (SAPKs), including p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK), are usually activated in response to different environmental stimuli, including virus infection. In the present study, the roles of SAPKs during Singapore grouper iridovirus (SGIV) infection were investigated in fish cells. The results showed that increased phosphorylation of JNK1/2 and p38 MAPK occurred during active replication of SGIV in grouper cell cultures. Moreover, downstream effectors (c-Jun, MAPK-activated protein kinase 2, p53, activator protein 1, Myc and nuclear factor of activated T cells) were activated after SGIV infection, suggesting that SGIV replication activated the JNK and p38 MAPK signalling pathways. Notably, using specific inhibitors, it was found that viral gene transcripts, protein expression and viral titres were not affected by inhibition of p38 MAPK but were suppressed significantly by inhibiting JNK1/2 activation. In addition, transcription of grouper immune genes including interferon regulatory factor 1, interleukin-8 and tumour necrosis factor alpha (TNF-α) were regulated by JNK, whilst only TNF-α was regulated by p38 MAPK. It is proposed that the JNK pathway is important for SGIV replication and modulates the inflammatory responses during virus infection.

Modulation of polymorphonuclear neutrophil functions by astrocytes

Background

Neuroinflammation is a complex process involving cells from the immune system and the central nerve system (CNS). Polymorphonuclear neutrophils (PMN) are the most abundant class of white blood cells, and typically the first type of leukocyte recruited to sites of inflammation. In the CNS, astrocytes are the most abundant glial cell population and participate in the local innate immune response triggered by a variety of insults. In the present study, we investigated the impacts of astrocytes on PMN function.

Methods

Primary astrocyte cultures were derived from postnatal C57BL/6 mice and primary neutrophils were isolated from 8 to 12 weeks old C57BL/6 mice. PMNs respiratory burst was analyzed by H2DCFDA assay. For phagocytosis assay, neutrophils were incubated with FITC-labeled E. coli and the phagocytosis of E coli was determined by flow cytometer. PMNs degranulation was determined by myeloperoxidase assay. Cytokine expression was determined by real-time PCR. To determine the involvement of different signaling pathway, protein lysates were prepared and western blots were conducted to assess the activation of Akt, Erk1/2, and p38.

Results

Using ex vivo neutrophils and primary astrocyte cultures, our study demonstrated that astrocytes differentially regulate neutrophil functions, depending upon whether the interactions between the two cell types are direct or indirect. Upon direct cell-cell contact, astrocytes attenuate neutrophil apoptosis, respiratory bust, and degranulation, while enhancing neutrophil phagocytic capability and pro-inflammatory cytokine expression. Through indirect interaction with neutrophils, astrocytes attenuate apoptosis and enhance necrosis in neutrophils, augment neutrophil phagocytosis and respiratory burst, and inhibit neutrophil degranulation. In addition, astrocytes could augment Akt, Erk1/2, and p38 activation in neutrophils.

Conclusions

Astrocytes differentially regulate neutrophil functions through direct or indirect interactions between the two cell types. The diversified actions of astrocytes on neutrophils might provide protection against potential microbial infections given compromised blood-brain barrier integrity under certain neuropathological conditions. The complex actions of astrocytes on neutrophils could provide further insight to harness the inflammatory response to promote CNS repair.

Murine coronavirus induces type I interferon in oligodendrocytes through recognition by RIG-I and MDA5

The murine coronavirus mouse hepatitis virus (MHV) induced the expression of type I interferon (alpha/beta interferon [IFN-alpha/beta]) in mouse oligodendrocytic N20.1 cells. This induction is completely dependent on virus replication, since infection with UV light-inactivated virus could no longer induce IFN-alpha/beta. We show that MHV infection activated both transcription factors, the IFN regulatory factor 3 (IRF-3) and nuclear factor kappaB (NF-kappaB), as evidenced by phosphorylation and nuclear translocation of IRF-3 and an increased promoter binding activity for IRF-3 and NF-kappaB. Furthermore, the cytoplasmic pattern recognition receptor retinoic acid-inducible gene I (RIG-I) was induced by MHV infection. Knockdown of RIG-I by small interfering RNAs blocked the activation of IRF-3 and subsequent IFN-alpha/beta production induced by MHV infection. Knockdown of another cytoplasmic receptor, the melanoma-differentiation-associated gene 5 (MDA5), by small interfering RNAs also blocked IFN-beta induction. These results demonstrate that MHV is recognized by both RIG-I and MDA5 and induces IFN-alpha/beta through the activation of the IRF-3 signaling pathway. However, knockdown of RIG-I only partially blocked NF-kappaB activity induced by MHV infection and inhibition of NF-kappaB activity by a decoy peptide inhibitor had little effect on IFN-alpha/beta production. These data suggest that activation of the NF-kappaB pathway might not play a critical role in IFN-alpha/beta induction by MHV infection in oligodendrocytes.