PKR's protective role in viral myocarditis

Spatiotemporal transcriptomics reveals pathogenesis of viral myocarditis

A significant fraction of sudden death in children and young adults is due to viral myocarditis, an inflammatory disease of the heart. In this study, by using integrated single-cell and spatial transcriptomics, we created a high-resolution, spatially resolved transcriptome map of reovirus-induced myocarditis in neonatal mouse hearts. We assayed hearts collected at three timepoints after infection and studied the temporal, spatial and cellular heterogeneity of host–virus interactions. We further assayed the intestine, the primary site of reovirus infection, to establish a full chronology of molecular events that ultimately lead to myocarditis. We found that inflamed endothelial cells recruit cytotoxic T cells and undergo pyroptosis in the myocarditic tissue. Analyses of spatially restricted gene expression in myocarditic regions and the border zone identified immune-mediated cell-type-specific injury and stress responses. Overall, we observed a complex network of cellular phenotypes and spatially restricted cell–cell interactions associated with reovirus-induced myocarditis in neonatal mice.

The multi-functional reovirus σ3 protein is a virulence factor that suppresses stress granule formation and is associated with myocardial injury

The mammalian orthoreovirus double-stranded (ds) RNA-binding protein σ3 is a multifunctional protein that promotes viral protein synthesis and facilitates viral entry and assembly. The dsRNA-binding capacity of σ3 correlates with its capacity to prevent dsRNA-mediated activation of protein kinase R (PKR). However, the effect of σ3 binding to dsRNA during viral infection is largely unknown. To identify functions of σ3 dsRNA-binding activity during reovirus infection, we engineered a panel of thirteen σ3 mutants and screened them for the capacity to bind dsRNA. Six mutants were defective in dsRNA binding, and mutations in these constructs cluster in a putative dsRNA-binding region on the surface of σ3. Two recombinant viruses expressing these σ3 dsRNA-binding mutants, K287T and R296T, display strikingly different phenotypes. In a cell-type dependent manner, K287T, but not R296T, replicates less efficiently than wild-type (WT) virus. In cells in which K287T virus demonstrates a replication deficit, PKR activation occurs and abundant stress granules (SGs) are formed at late times post-infection. In contrast, the R296T virus retains the capacity to suppress activation of PKR and does not mediate formation of SGs at late times post-infection. These findings indicate that σ3 inhibits PKR independently of its capacity to bind dsRNA. In infected mice, K287T produces lower viral titers in the spleen, liver, lungs, and heart relative to WT or R296T. Moreover, mice inoculated with WT or R296T viruses develop myocarditis, whereas those inoculated with K287T do not. Overall, our results indicate that σ3 functions to suppress PKR activation and subsequent SG formation during viral infection and that these functions correlate with virulence in mice.

The σ3 protein of mammalian orthoreoviruses is a double-stranded RNA binding protein that has classically been thought to function by scavenging dsRNA within infected cells and thus prevents activation of cellular sensors of dsRNA such as the kinase PKR. Here we used mutagenesis to identify the region of σ3 responsible for binding dsRNA. Characterization of mutant viruses expressing σ3 proteins incapable of binding dsRNA show that contrary to expectation, dsRNA binding is not required for σ3-mediated inhibition of PKR. We show that one mutant virus (R296T) despite being deficient in dsRNA-binding can inhibit PKR and replicates similar to WT virus. In contrast, another mutant virus (K287T) that bears a σ3 protein that cannot prevent dsRNA-mediated activation of PKR induces stress granules in infected cells and replicates less efficiently than WT virus. In vivo, the K287T mutant is attenuated in its replication and unlike WT virus and the R296T mutant virus does not cause heart disease (myocarditis).

The Role of PKR as a Potential Target for Treating Cardiovascular Diseases

Cardiovascular diseases are the leading cause of death globally with limited treatment options. Despite improved pharmacological therapy, scientific understandings on the root mechanisms of cardiovascular diseases are still not fully understood. It is well known that inflammation plays a key role in the pathogenesis of cardiovascular diseases and controlling this inflammatory pathway may inhibit the progression of this chronic disease. Protein Kinase R (PKR), a serine threonine kinase is activated during various pathological conditions. Activation of PKR can induce apoptosis, inflammation and oxidative stress. Since PKR has multidimensional roles, thus PKR is an attractive target for treating cardiovascular and metabolic disorders. The goal of this review is to discuss potential role of PKR in cardiovascular diseases, pathways activated by it and association between pathways activated.

PKR activation enhances replication of classical swine fever virus in PK-15 cells

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CSFV infection triggers PKR and eIF2α protein phosphorylation.

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PKR overexpression stimulates viral replication.

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PKR depletion blocks eIF2α phosphorylation and suppresses viral replication.

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PKR depletion increases IFN-β, and enhances the antiviral effect of IFN.

Classical swine fever (CSF) is a highly contagious swine disease that is responsible for economic losses worldwide. Protein kinase R (PK)R is an important protein in the host viral response; however, the role of PKR in CSFV infection remains unknown. This issue was addressed in the present study using the PK-15 swine kidney cell line. We found that CSFV infection increased the phosphorylation of eukaryotic translation initiation factor (eIF)2α and its kinase PKR. However, the expression of viral proteins continued to increase. Furthermore, PKR overexpression enhanced CSFV replication, while PKR inhibition resulted in reduced CSFV replication and an increase in interferon (IFN) induction. In addition, PKR was responsible for eIF2α phosphorylation in CSFV-infected cells. These results suggest that the activation of PKR during CSFV infection is beneficial to the virus. The virus is able to commandeer the host cell's translation machinery for viral protein synthesis while evading innate immune defenses.

Antiviral innate immunity and stress granule responses

Viral infection triggers the activation of antiviral innate immune responses in mammalian cells. Viral RNA in the cytoplasm activates signaling pathways that result in the production of interferons (IFNs) and IFN-stimulated genes. Some viral infections have been shown to induce cytoplasmic granular aggregates similar to the dynamic ribonucleoprotein aggregates termed stress granules (SGs), suggesting that these viruses may utilize this stress response for their own benefit. By contrast, some viruses actively inhibit SG formation, suggesting an antiviral function for these structures. We review here the relationship between different viral infections and SG formation. We examine the evidence for antiviral functions for SGs and highlight important areas of inquiry towards understanding cellular stress responses to viral infection.

Double-stranded RNA-dependent protein kinase deficiency protects the heart from systolic overload-induced congestive heart failure

BACKGROUND

Double-stranded RNA-dependent protein kinase (PKR) is a eukaryotic initiation factor 2α kinase that inhibits mRNA translation under stress conditions. PKR also mediates inflammatory and apoptotic signaling independently of translational regulation. Congestive heart failure is associated with cardiomyocyte hypertrophy, inflammation, and apoptosis, but the role of PKR in left ventricular hypertrophy and the development of congestive heart failure has not been examined.

METHODS AND RESULTS

We observed increased myocardial PKR expression and translocation of PKR into the nucleus in humans and mice with congestive heart failure. To determine the impact of PKR on the development of congestive heart failure, PKR knockout and wild-type mice were exposed to pressure overload produced by transverse aortic constriction. Although heart size increased similarly in wild-type and PKR knockout mice after transverse aortic constriction, PKR knockout mice exhibited very little pulmonary congestion, well-preserved left ventricular ejection fraction and contractility, and significantly less myocardial fibrosis compared with wild-type mice. Bone marrow-derived cells from wild-type mice did not abolish the cardiac protective effect observed in PKR knockout mice, whereas bone marrow-derived cells from PKR knockout mice had no cardiac protective effect in wild-type mice. Mechanistically, PKR knockout attenuated transverse aortic constriction-induced tumor necrosis factor-α expression and leukocyte infiltration and lowered cardiac expression of proapoptotic factors (Bax and caspase-3), so that PKR knockout hearts were more resistant to transverse aortic constriction-induced cardiomyocyte apoptosis. PKR depletion in isolated cardiomyocytes also conferred protection against tumor necrosis factor-α- or lipopolysaccharide-induced apoptosis.

CONCLUSION

PKR is a maladaptive factor upregulated in hemodynamic overload that contributes to myocardial inflammation, cardiomyocyte apoptosis, and the development of congestive heart failure.

Interferon-inducible transmembrane protein 3 (IFITM3) restricts reovirus cell entry

Reoviruses are double-stranded RNA viruses that infect the mammalian respiratory and gastrointestinal tract. Reovirus infection elicits production of type I interferons (IFNs), which trigger antiviral pathways through the induction of interferon-stimulated genes (ISGs). Although hundreds of ISGs have been identified, the functions of many of these genes are unknown. The interferon-inducible transmembrane (IFITM) proteins are one class of ISGs that restrict the cell entry of some enveloped viruses, including influenza A virus. One family member, IFITM3, localizes to late endosomes, where reoviruses undergo proteolytic disassembly; therefore, we sought to determine whether IFITM3 also restricts reovirus entry. IFITM3-expressing cell lines were less susceptible to infection by reovirus, as they exhibited significantly lower percentages of infected cells in comparison to control cells. Reovirus replication was also significantly reduced in IFITM3-expressing cells. Additionally, cells expressing an shRNA targeting IFITM3 exhibited a smaller decrease in infection after IFN treatment than the control cells, indicating that endogenous IFITM3 restricts reovirus infection. However, IFITM3 did not restrict entry of reovirus infectious subvirion particles (ISVPs), which do not require endosomal proteolysis, indicating that restriction occurs in the endocytic pathway. Proteolysis of outer capsid protein μ1 was delayed in IFITM3-expressing cells in comparison to control cells, suggesting that IFITM3 modulates the function of late endosomal compartments either by reducing the activity of endosomal proteases or delaying the proteolytic processing of virions. These data provide the first evidence that IFITM3 restricts infection by a nonenveloped virus and suggest that IFITM3 targets an increasing number of viruses through a shared requirement for endosomes during cell entry.

Reovirus receptors, cell entry, and proapoptotic signaling

Mammalian orthoreoviruses (reoviruses) are members of the Reoviridae. Reoviruses contain 10 double-stranded (ds) RNA gene segments enclosed in two concentric protein shells, called outer capsid and core. These viruses serve as a versatile experimental system for studies of viral replication events at the virus-cell interface, including engagement of cell-surface receptors, internalization and disassembly, and activation of the innate immune response, including NF-κB-dependent cellular signaling pathways. Reoviruses also provide a model system for studies of virus-induced apoptosis and organ-specific disease in vivo.Reoviruses attach to host cells via the filamentous attachment protein, σ1. The σ1 protein of all reovirus serotypes engages junctional adhesion molecule-A (JAM-A), an integral component of intercellular tight junctions. The σ1 protein also binds to cell-surface carbohydrate, with the type of carbohydrate bound varying by serotype. Following attachment to JAM-A and carbohydrate, reovirus internalization is mediated by β1 integrins, most likely via clathrin-dependent endocytosis. In the endocytic compartment, reovirus outer-capsid protein σ3 is removed by acid-dependent cysteine proteases in most cell types. Removal of σ3 results in the exposure of a hydrophobic conformer of the viral membrane-penetration protein, μ1, which pierces the endosomal membrane and delivers transcriptionally active reovirus core particles into the cytoplasm.Reoviruses induce apoptosis in both cultured cells and infected mice. Perturbation of reovirus disassembly using inhibitors of endosomal acidification or protease activity abrogates apoptosis. The μ1-encoding M2 gene is genetically linked to strain-specific differences in apoptosis-inducing capacity, suggesting a function for μ1 in induction of death signaling. Reovirus disassembly leads to activation of transcription factor NF-κB, which modulates apoptotic signaling in numerous types of cells. Inhibition of NF-κB nuclear translocation using either pharmacologic agents or expression of transdominant forms of IκB blocks reovirus-induced apoptosis, suggesting an essential role for NF-κB activation in the death response. Multiple effector pathway s downstream of NF-κB-directed gene expression execute reovirus-induced cell death. This chapter will focus on the mechanisms by which reovirus attachment and disassembly activate NF-κB and stimulate the cellular proapoptotic machinery.

The early interferon response to rotavirus is regulated by PKR and depends on MAVS/IPS-1, RIG-I, MDA-5, and IRF3

In mouse embryonic fibroblasts (MEFs), the bovine rotavirus (UK strain) but not the simian rhesus rotavirus (RRV) robustly triggers beta interferon (IFN-β) secretion, resulting in an IFN-dependent restriction of replication. We now find that both rotavirus strains trigger antiviral transcriptional responses early during infection and that both transcriptional responses and IFN-β secretion are completely abrogated in MAVS/IPS-1(-/-) MEFs. Replication of UK virus could be rescued in MAVS/IPS-1(-/-) MEFs, and synthesis of viral RNA significantly increased early during virus infection. UK virus induced IFN-β secretion and transcription of IFN-stimulated genes (ISGs) in both RIG-I(-/-) and MDA-5(-/-) MEFs, and neither receptor was essential by itself for the antiviral response to UK rotavirus. However, when receptors RIG-I and MDA-5 were depleted using RNA interference, we found that both contribute to the magnitude of the IFN response. IRF3 was found to be essential for MAVS/IPS-1-directed ISG transcription and IFN-β secretion during rotavirus infection. Interestingly, absence of the double-stranded RNA-dependent protein kinase PKR led to a profound defect in the capacity of host cells to secrete IFN-β in response to virus. Both PKR and IRF3 restricted the early replication of UK as indicated by significant increases in viral RNA in fibroblasts lacking either gene. Despite the loss in IFN-β secretion in PKR(-/-) MEFs, we did not observe decreased IRF3- or NF-κB-dependent early ISG transcription in these cells. Levels of transcripts encoding IFN-α4, IFN-α5, and IFN-β were high in infected PKR(-/-) MEFs, indicating that during rotavirus infection, PKR functions at a stage between IFN gene transcription and subsequent IFN-β secretion. These findings reveal that activation of the antiviral response by rotavirus is dependent on MAVS/IPS-1 and IRF3 and involves both RIG-I and MDA-5 and that IFN-β secretion during rotavirus infection is regulated by PKR.

CUG2, a novel oncogene confers reoviral replication through Ras and p38 signaling pathway

As we have recently found a novel oncogene, the cancer-upregulated gene 2 (CUG2), which was elevated in a variety of tumor tissues such as the ovary, liver, lung and pancreas, we examined whether reovirus could efficiently induce cytolysis in cancer cells expressing CUG2 and thus be used as a potential cancer therapeutic agent. In this study, we describe experiments in which we use reovirus to treat NIH3T3 cells stably expressing either CUG2 (NIH-CUG2) or vector only (NIH-Vec). NIH-CUG2 cells readily support reoviral proliferation and undergo apoptosis, whereas NIH-Vec cells are highly resistant to reoviral infection and virus-induced apoptosis. This notable result may be explained by the observation that CUG2 expression inhibits PKR activation, leading to reoviral proliferation in nonpermissive NIH3T3 cells. Furthermore, reovirus infection results in almost complete regression of tumorgenic NIH-CUG2 cells in transplanted nude mice. As we found that CUG2 enhances activation of MAPK (ERK, JNK and p38), Src kinase and Ras, we examined whether CUG2 confers reoviral replication independent of the Ras or p38 MAPK signaling pathway. From these experiments we found that either inhibition of p38 MAPK or Ras blocks reoviral proliferation even in the presence of CUG2 but inhibition of ERK, JNK and Src kinase does not, indicating that activation of p38 MAPK and Ras has critical roles in reoviral replication in CUG2-expressing tumor cells. Accordingly, we propose that reovirus can be useful in the treatment of transformed cells expressing CUG2, which is commonly detected in various tumor tissues.

Cardiac cell-specific apoptotic and cytokine responses to reovirus infection: determinants of myocarditic phenotype

BACKGROUND

The pathophysiologic mechanisms underlying viral myocarditis are not well defined. As a result, effective treatments do not exist and viral myocarditis remains a potentially lethal infection of the heart.

METHODS AND RESULTS

We used cultured rat cardiac myocytes and fibroblasts to investigate apoptosis and cytokine production in response to infection by myocarditic vs. non-myocarditic strains of reovirus. Myocarditic reovirus strain 8B and non-myocarditic strain DB188 replicate comparably in each cardiac cell type. However, strain 8B and related myocarditic reoviruses preferentially increase apoptosis of myocytes relative to fibroblasts, whereas DB188 and nonmyocarditic strains preferentially increase fibroblast apoptosis. Infection of cardiac fibroblasts with the nonmyocarditic strain DB188 elicits substantial increases in a panel of cytokines compared to fibroblasts infected with strain 8B or mock-infected controls. Analysis of culture supernatants using cytometric bead arrays revealed that DB188 enhanced release of interleukin (IL)-1beta, IL-4, IL-6, IL-10, IL-12(p70), GRO-KC, tumor necrosis factor-alpha, and MCP-1 relative to 8B or mock-infected controls (all P < .05).

CONCLUSION

We hypothesize that differential cytokine production and cell-specific apoptosis are important determinants of myocarditic potential of reoviral strains. Therapies that target the beneficial effects of cytokines in limiting cytopathic damage may offer an effective and novel treatment approach to viral myocarditis.

Expression of HBX, an oncoprotein of hepatitis B virus, blocks reoviral oncolysis of hepatocellular carcinoma cells

Although reovirus has been used in tests as a potential cancer therapeutic agent against a variety of cancer cells, its application to hepatocellular carcinoma cells, in which the hepatitis B virus (HBV) X (HBX) protein of HBV plays a primary role, has not yet been explored. Here, we describe experiments in which we use reovirus to treat Chang liver carcinoma cells expressing either a vector only (Chang-vec) or a vector encoding HBX protein (Chang-HBX). Although Chang-vec cells readily support reoviral proliferation and undergo apoptosis, Chang-HBX cells are highly resistant to reoviral infection and virus-induced apoptosis, even though HBX protein induces activation of Ras and inactivation of PKR, which are normally thought to enhance reoviral oncolysis. The resistance of Chang-HBX cells to reovirus may instead be explained by HBX-induced downregulation of death receptor 5 and activation of Stat1. Phosphorylated Stat1 activates interferon (IFN)-stimulated regulatory element (ISRE)- and IFN-gamma-activated sequence (GAS)-mediated transcription, leading to the production of IFN-beta, whereas the reduced expression of Stat1 with its siRNA results in a decrease in IFN-beta production, by which Chang-HBX cells eventually succumb to reovirus infection. This result further indicates that HBX induces the establishment of an antiviral state through Stat1 activation. Thus, it appears that active Ras does not override the antiviral effect mediated by the activation of Stat1. Accordingly, we report that HBX, an oncoprotein of HBV, can prevent reoviral oncolysis of hepatocellular carcinoma. This suggests there may be limits to the practical application of reovirus in the treatment of human cancers already expressing other oncoviral proteins.

Contribution of MX dynamin, oligoadenylate synthetase, and protein kinase R to anti-paramyxovirus activity of type 1 interferons in vitro

OBJECTIVE

To determine the contribution of MX dynamin, oligoadenylate synthetase (OAS), and double-stranded RNA-dependent protein kinase R (PKR) to the antiviral effects of type 1 interferons (IFNs) against bovine parainfluenza-3 virus (PI-3V) infection of Vero cells.

SAMPLE POPULATION

Vero cell cultures.

PROCEDURES

PI-3V yield was first compared between control and transfected type 1 IFNs-incompetent Vero cells expressing recombinant OAS or MX proteins. Afterwards, phosphorylation of eukaryotic initiation factor 2 alpha (eIF2alpha) was used to scale the degree of PKR activation upon infection of Vero cells by PI-3V.

RESULTS

Overexpression of OAS did not result in significantly decreased viral replication. Phosphorylated eIF2alpha forms, the hallmark of PKR activation, were not increased in IFNalpha-primed infected Vero cells. Although human MXA contributed to partial blockade of replication of bovine PI-3V, the antiviral effect was not as strong as that of IFNalpha.

CONCLUSIONS AND CLINICAL RELEVANCE

The powerful anti-Paramyxovirus activity of type 1 IFNs is mediated by noncanonic pathways.

Induction of antiviral genes, Mx and vig-1, by dsRNA and Chum salmon reovirus in rainbow trout monocyte/macrophage and fibroblast cell lines

The expression of potential antiviral genes, Mx1, Mx2, Mx3 and vig-1, was studied in two rainbow trout cell lines: monocyte/macrophage RTS11 and fibroblast-like RTG-2. Transcripts were monitored by RT-PCR; Mx protein by Western blotting. In unstimulated cultures Mx1 and vig-1 transcripts were seen occasionally in RTS11 but rarely in RTG-2. A low level of Mx protein was seen in unstimulated RTS11 but not in RTG-2. In both cell lines, Mx and vig-1 transcripts were induced by a dsRNA, poly inosinic: poly cytidylic acid (poly IC), and by Chum salmon reovirus (CSV). Medium conditioned by cells previously exposed to poly IC or CSV and assumed to contain interferon (IFN) induced the antiviral genes in RTS11. However, RTG-2 responded only to medium conditioned by RTG-2 exposed previously to CSV. In both cell lines, poly IC and CSV induced Mx transcripts in the presence of cycloheximide, suggesting a direct induction mechanism, independent of IFN, was also possible. For CSV, ribavirin blocked induction in RTS11 but not in RTG-2, suggesting viral RNA synthesis was required for induction only in RTS11. In both RTS11 and RTG-2 cultures, Mx protein showed enhanced accumulation by 24h after exposure to poly IC and CSV, but subsequently Mx protein levels declined back to control levels in RTS11 but not in RTG-2. These results suggest that Mx can be regulated differently in macrophages and fibroblasts.

Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.

Astragaloside IV exerts antiviral effects against coxsackievirus B3 by upregulating interferon-gamma

Coxsackievirus B3 (CVB3) is a major pathogen for viral myocarditis and dilated cardiomyopathy in children and young adults. The aim of this study was to determine the antiviral effects of astragaloside IV against CVB3, and the underlying mechanism. First, we evaluated antiviral effects of astragaloside IV in vitro by measuring the virus titers of CVB3 in primarily cultured myocardial cells infected with CVB3, and in vivo by assessing the morbidity, mortality, heart-to-body weight ratio (HW/BW), and virus titers in BALB/c mice infected with CVB3. Then, we performed serum pharmacological experiments by testing the effect of sera from SD rats treated with astragaloside IV on proliferation of CVB3 in primarily cultured myocardial cells. Finally, we determined the effect of astragaloside IV on IFN-gamma mRNA expression in the hearts of infected BALB/c mice. We observed that astragaloside IV decreased virus titers of CVB3 in primarily cultured myocardial cells. Morbidity, mortality, HW/BW, and virus titers all decreased, and necrosis and mononuclear cell infiltration were alleviated in CVB3-infected mice treated with astragaloside IV, compared with those infected mice without the treatment. In addition, proliferation of CVB3 was inhibited by the sera of rats treated with astragaloside IV. Moreover, we observed that IFN-gamma mRNA expression was increased in mice treated with astragaloside IV. Therefore, we conclude that astragaloside IV exerts antiviral effects against CVB3 by upregulating expression of IFN-gamma mRNA.

Antiviral effects of sophoridine against coxsackievirus B3 and its pharmacokinetics in rats

Coxsackievirus B3 (CVB3) is a major pathogen for acute and chronic viral myocarditis. The aim of this study was to investigate the antiviral effects of sophoridine, an alkaloid extracted from Chinese medicinal herb, Sophora flavescens, against CVB3, and the underlying pharmacokinetics. First, we determined the antiviral effects of sophoridine against CVB3 in in vitro (primarily cultured myocardial cells), in vivo (BALB/c mice) and serum pharmacological experiments. Then, we determined the pharmacokinetic behavior in serum samples of SD rats after oral administration by HPLC. Finally, we determined the effects of sophoridine on the production of cytokines in a murine viral myocarditis model by measuring mRNA expression of some important cytokines in hearts of infected BALB/c mice by RT-PCR. We found that sophoridine exhibited obvious antiviral effects both in vitro and in vivo, and serum samples obtained from rats with oral administration of sophoridine reduced the virus titers in infected myocardial cells. The serum concentration profile correlated closely with antiviral activity profile. Moreover, sophoridine significantly enhanced mRNA expression of IL-10 and IFN-gamma, but decreased TNF-alpha mRNA expression. In conclusion, sophoridine possesses antiviral activities against CVB3, by regulating cytokine expression, and it is likely that sophoridine itself, not its metabolites, is mainly responsible for the antiviral activities. Therefore, sophoridine may represent a potential therapeutic agent for viral myocarditis.

Mechanisms of reovirus-induced cell death and tissue injury: role of apoptosis and virus-induced perturbation of host-cell signaling and transcription factor activation

Reoviruses have provided insight into the roles played by specific viral genes and the proteins they encode in virus-induced cell death and tissue injury. Apoptosis is a major mechanism of cell death induced by reoviruses. Reovirus-induced apoptosis involves both death-receptor and mitochondrial cell death pathways. Reovirus infection is associated with selective activation of mitogen activated protein kinase (MAPK) cascades including JNK/SAPK. Infection also perturbs transcription factor signaling resulting in the activation of c-Jun and initial activation followed by strain-specific inhibition of NF-kappaB. Infection results in changes in the expression of genes encoding proteins involved in cell cycle regulation, apoptosis, and DNA damage and repair processes. Apoptosis is a major mechanism of reovirus-induced injury to key target organs including the CNS and heart. Inhibition of apoptosis through the use of caspase or calpain inhibitors, minocycline, or in caspase 3(-/-) mice all reduce virus-associated tissue injury and enhance survival of infected animals. Reoviruses induce apoptotic cell death (oncolysis) in a wide variety of cancer cells and tumors. The capacity of reoviruses to grow efficiently in transformed cells is enhanced by the presence of an activated Ras signaling pathway likely through mechanisms involving inhibition of antiviral PKR signaling and activation of Ras/RalGEF/p38 pathways. The potential of reovirus-induced oncolysis in therapy of human cancers is currently being investigated in phase I/II clinical trials.

Inhibition of NF-kappa B activity and cFLIP expression contribute to viral-induced apoptosis

Virus-induced activation of nuclear factor-kappa B (NF-kappaB) is required for Type 3 (T3) reovirus-induced apoptosis. We now show that NF-kappaB is also activated by the prototypic Type 1 reovirus strain Lang (T1L), which induces significantly less apoptosis than T3 viruses, indicating that NF-kappaB activation alone is not sufficient for apoptosis in reovirus-infected cells. A second phase of virus-induced NF-kappaB regulation, where NF-kappaB activation is inhibited at later times following infection with T3 Abney (T3A), is absent in T1L-infected cells. This suggests that inhibition of NF-kappaB activation at later times post infection also contributes to reovirus-induced apoptosis. Reovirus-induced inhibition of stimulus-induced activation of NF-kappaB is significantly associated with apoptosis following infection of HEK293 cells with reassortant reoviruses and is determined by the T3 S1 gene segment, which is also the primary determinant of reovirus-induced apoptosis. Inhibition of stimulus-induced activation of NF-kappaB also occurs following infection of primary cardiac myocytes with apoptotic (8B) but not non-apoptotic (T1L) reoviruses. Expression levels of the NF-kappaB-regulated cellular FLICE inhibitory protein (cFLIP) reflect NF-kappaB activation in reovirus-infected cells. Further, inhibition of NF-kappaB activity and cFLIP expression promote T1L-induced apoptosis. These results demonstrate that inhibition of stimulus-induced activation of NF-kappaB and the resulting decrease in cFLIP expression promote reovirus-induced apoptosis.

Basal and reovirus-induced beta interferon (IFN-beta) and IFN-beta-stimulated gene expression are cell type specific in the cardiac protective response

Viral myocarditis is an important human disease, with a wide variety of viruses implicated. Cardiac myocytes are not replenished yet are critical for host survival and thus may have a unique response to infection. Previously, we determined that the extent of reovirus induction of beta interferon (IFN-beta) and IFN-beta-mediated protection in primary cardiac myocyte cultures was inversely correlated with the extent of reovirus-induced cardiac damage in a mouse model. Surprisingly, and in contrast, the IFN-beta response did not determine reovirus replication in skeletal muscle cells. Here we compared the IFN-beta response in cardiac myocytes to that in primary cardiac fibroblast cultures, a readily replenished cardiac cell type. We compared basal and reovirus-induced expression of IFN-beta, IRF-7 (an interferon-stimulated gene [ISG] that further induces IFN-beta), and another ISG (561) in the two cell types by using real-time reverse transcription-PCR. Basal IFN-beta, IRF-7, and 561 expression was higher in cardiac myocytes than in cardiac fibroblasts. Reovirus T3D induced greater expression of IFN-beta in cardiac myocytes than in cardiac fibroblasts but equivalent expression of IRF-7 and 561 in the two cell types (though fold induction for IRF-7 and 561 was higher in fibroblasts than in myocytes because of the differences in basal expression). Interestingly, while reovirus replicated to equivalent titers in cardiac myocytes and cardiac fibroblasts, removal of IFN-beta resulted in 10-fold-greater reovirus replication in the fibroblasts than in the myocytes. Together the data suggest that the IFN-beta response controls reovirus replication equivalently in the two cell types. In the absence of reovirus-induced IFN-beta, however, reovirus replicates to higher titers in cardiac fibroblasts than in cardiac myocytes, suggesting that the higher basal IFN-beta and ISG expression in myocytes may play an important protective role.

Reading the viral signature by Toll-like receptors and other pattern recognition receptors

Successful host defense against viral infections relies on early production of type I interferon (IFN) and subsequent activation of a cellular cytotoxic response. The acute IFN and inflammatory response against virus infections is mediated by cellular pattern-recognition receptors (PRRs) that recognize specific molecular structures on viral particles or products of viral replication. Toll-like receptors (TLRs) constitute a class of membrane-bound PRRs capable of detecting microbial infections. While TLR2 and TLR4, which were first identified to recognize Gram-positive and Gram-negative bacteria, respectively, sense specific viral proteins on the cell surface, TLRs 3, 7, 8, and 9 serve as receptors for viral nucleic acids in endosomic compartments. In addition to TLRs, cells express cytoplasmic PRRs such as the RNA helicase retinoic acid inducible gene I and the kinase double-stranded RNA-activated protein kinase R, both of which sense dsRNA, a characteristic signature of viral replication, and initiate a protective cellular response. Here we review the recent progress in our understanding of PRRs and viral infections and discuss the molecular and cellular responses evoked by virus-activated PRRs. Finally, we look into what is currently known about the role of PRRs in viral infections in vivo.

Protective Role for Interferon-β in Coxsackievirus B3 Infection

Background— Coxsackievirus-induced myocarditis can be a serious cause of heart failure. In the absence of a specific antiviral therapy, modulating the host immune response may be protective. Interferons (IFNs)-α and -β perform a fundamental role in innate and adaptive antiviral responses, thereby presenting as candidate therapeutics for coxsackievirus infections.

Methods and Results— To examine the contribution of IFN-β in protection from coxsackievirus B3 (CVB3) infection, mice lacking the IFN-β gene were infected with 10 3 plaque-forming units of CVB3. In contrast to wild-type mice that exhibit an intact IFN-β response, we observed increased susceptibility to infection (70% mortality), a downregulation of IFN-stimulated gene targets (2′-5′ oligoadenylate synthetase, serine/threonine protein kinase, the GTPase Mx), and cardiomyocyte breakdown and disruption in the IFN-β −/− mice.

Conclusions— Viewed together, these results clearly demonstrate that IFN-β is important in mediating protection against CVB3-induced myocarditis.