Fatal case of West Nile encephalitis associated with acute anteroseptal ST elevation myocardial infarction (STEMI): a case report.

Cardiac involvement has rarely been reported in West Nile (WNV) infection. We report a fatal case of WNV encephalitis associated with an acute anteroseptal ST elevation myocardial infarction. The patient was hospitalized with a fever, headache, nausea and vomiting. The physical examination revealed positive meningeal signs and an altered level of consciousness. High levels of cardiac enzymes (creatine phosphokinase/MB fraction, lactate dehydrogenase, myoglobin and cardiac troponin I) and ST elevation on electrocardiogram were found. Both CSF and urine samples were positive for WNV RNA. This case highlights the need of awareness of the possibility of a WNV-related myocardial infection, including myocardial infarction.

Targeting host metabolism by inhibition of acetyl-Coenzyme A carboxylase reduces flavivirus infection in mouse models.

Flaviviruses are (re)-emerging RNA viruses strictly dependent on lipid metabolism for infection. In the search for host targeting antivirals, we explored the effect of pharmacological modulation of fatty acid metabolism during flavivirus infection. Considering the central role of acetyl-Coenzyme A carboxylase (ACC) on fatty acid metabolism, we analyzed the effect of three small-molecule ACC inhibitors (PF-05175157, PF-05206574, and PF-06256254) on the infection of medically relevant flaviviruses, namely West Nile virus (WNV), dengue virus, and Zika virus. Treatment with these compounds inhibited the multiplication of the three viruses in cultured cells. PF-05175157 induced a reduction of the viral load in serum and kidney in WNV-infected mice, unveiling its therapeutic potential for the treatment of chronic kidney disease associated with persistent WNV infection. This study constitutes a proof of concept of the reliability of ACC inhibitors to become viable antiviral candidates. These results support the repositioning of metabolic inhibitors as broad-spectrum antivirals.

Phospholipase A2 activity during the replication cycle of the flavivirus West Nile virus.

Positive-sense RNA virus intracellular replication is intimately associated with membrane platforms that are derived from host organelles and comprised of distinct lipid composition. For flaviviruses, such as West Nile virus strain Kunjin virus (WNVKUN) we have observed that these membrane platforms are derived from the endoplasmic reticulum and are rich in (at least) cholesterol. To extend these studies and identify the cellular lipids critical for WNVKUN replication we utilized a whole cell lipidomics approach and revealed an elevation in phospholipase A2 (PLA2) activity to produce lyso-phosphatidylcholine (lyso-PChol). We observed that the PLA2 enzyme family is activated in WNVKUN-infected cells and the generated lyso-PChol lipid moieties are sequestered to the subcellular sites of viral replication. The requirement for lyso-PChol was confirmed using chemical inhibition of PLA2, where WNVKUN replication and production of infectious virus was duly affected in the presence of the inhibitors. Importantly, we could rescue chemical-induced inhibition with the exogenous addition of lyso-PChol species. Additionally, electron microscopy results indicate that lyso-PChol appears to contribute to the formation of the WNVKUN membranous replication complex (RC); particularly affecting the morphology and membrane curvature of vesicles comprising the RC. These results extend our current understanding of how flaviviruses manipulate lipid homeostasis to favour their own intracellular replication.

The nucleolar helicase DDX56 redistributes to West Nile virus assembly sites.

Flaviviruses, including the human pathogen, West Nile virus (WNV), are known to co-opt many host factors for their replication and propagation. To this end, we previously reported that the nucleolar DEAD-box RNA helicase, DDX56, is important for production of infectious WNV virions. In this study, we show that WNV infection results in relocalization of DDX56 from nucleoli to virus assembly sites on the endoplasmic reticululm (ER), an observation that is consistent with a role for DDX56 in WNV virion assembly. Super-resolution microscopy revealed that capsid and DDX56 localized to the same subcompartment of the ER, however, unexpectedly, stable interaction between these two proteins was only detected in the nucleus. Together, these data suggest that DDX56 relocalizes to the site of virus assembly during WNV infection and that its interaction with WNV capsid in the cytoplasm may occur transiently during virion morphogenesis.

The TAM receptor Mertk protects against neuroinvasive viral infection by maintaining blood-brain barrier integrity.

The TAM receptors Tyro3, Axl and Mertk are receptor tyrosine kinases that dampen host innate immune responses following engagement with their ligands Gas6 and Protein S, which recognize phosphatidylserine on apoptotic cells. In a form of apoptotic mimicry, many enveloped viruses display phosphatidylserine on the outer leaflet of their membranes, enabling TAM receptor activation and downregulation of antiviral responses. Accordingly, we hypothesized that a deficiency of TAM receptors would enhance antiviral responses and protect against viral infection. Unexpectedly, mice lacking Mertk and/or Axl, but not Tyro3, exhibited greater vulnerability to infection with neuroinvasive West Nile and La Crosse encephalitis viruses. This phenotype was associated with increased blood-brain barrier permeability, which enhanced virus entry into and infection of the brain. Activation of Mertk synergized with interferon-ß to tighten cell junctions and prevent virus transit across brain microvascular endothelial cells. Because TAM receptors restrict pathogenesis of neuroinvasive viruses, these findings have implications for TAM antagonists that are currently in clinical development.

Death receptor-mediated apoptotic signaling is activated in the brain following infection with West Nile virus in the absence of a peripheral immune response.

Apoptosis is an important mechanism of West Nile virus (WNV) pathogenesis within the central nervous system (CNS). The signaling pathways that result in WNV-induced apoptotic neuronal death within the CNS have not been established. In this study, we identified death receptor (DR)-induced apoptosis as a pathway that may be important in WNV pathogenesis, based on the pattern of differential gene expression in WNV-infected, compared to uninfected, brains. Reverse transcription-PCR (RT-PCR) and Western blotting confirmed that genes involved in DR-induced apoptotic signaling are upregulated in the brain following WNV infection. Activity of the DR-associated initiator caspase, caspase 8, was also increased in the brains of WNV-infected mice and occurred in association with cleavage of Bid and activation of caspase 9. These results demonstrate that DR-induced apoptotic signaling is activated in the brain following WNV infection and suggest that the caspase 8-dependent cleavage of Bid promotes intrinsic apoptotic signaling within the brains of infected animals. Utilization of a novel ex vivo brain slice culture (BSC) model of WNV encephalitis revealed that inhibition of caspase 8 decreases virus-induced activation of caspase 3 and tissue injury. The BSC model allows us to examine WNV-induced pathogenesis in the absence of a peripheral immune response. Thus, our results indicate that WNV-induced neuronal injury in the brain is mediated by DR-induced apoptosis signaling and can occur in the absence of infiltrating immune cells. However, astrocytes and microglia were activated in WNV-infected BSC, suggesting that local immune responses influence WNV pathogenesis.

West Nile virus-induced disruption of the blood-brain barrier in mice is characterized by the degradation of the junctional complex proteins and increase in multiple matrix metalloproteinases.

West Nile virus (WNV) encephalitis is characterized by neuroinflammation, neuronal loss and blood-brain barrier (BBB) disruption. However, the mechanisms associated with the BBB disruption are unclear. Complex interactions between the tight junction proteins (TJP) and the adherens junction proteins (AJP) of the brain microvascular endothelial cells are responsible for maintaining the BBB integrity. Herein, we characterized the relationship between the BBB disruption and expression kinetics of key TJP, AJP and matrix metalloproteinases (MMPs) in the mice brain. A dramatic increase in the BBB permeability and extravasation of IgG was observed at later time points of the central nervous system (CNS) infection and did not precede virus-CNS entry. WNV-infected mice exhibited significant reduction in the protein levels of the TJP ZO-1, claudin-1, occludin and JAM-A, and AJP ß-catenin and vascular endothelial cadherin, which correlated with increased levels of MMP-1, -3 and -9 and infiltrated leukocytes in the brain. Further, intracranial inoculation of WNV also demonstrated increased extravasation of IgG in the brain, suggesting the role of virus replication in the CNS in BBB disruption. These data suggest that altered expression of junction proteins is a pathological event associated with WNV infection and may explain the molecular basis of BBB disruption. We propose that WNV initially enters CNS without altering the BBB integrity and later virus replication in the brain initiates BBB disruption, allowing enhanced infiltration of immune cells and contribute to virus neuroinvasion via the 'Trojan-horse' route. These data further implicate roles of multiple MMPs in the BBB disruption and strategies to interrupt this process may influence the WNV disease outcome.

West nile virus infections suppress early viral RNA synthesis and avoid inducing the cell stress granule response.

West Nile virus (WNV) recently became endemic in the United States and is a significant cause of human morbidity and mortality. Natural WNV strain infections do not induce stress granules (SGs), while W956IC (a lineage 2/1 chimeric WNV infectious clone) virus infections produce high levels of early viral RNA and efficiently induce SGs through protein kinase R (PKR) activation. Additional WNV chimeric viruses made by replacing one or more W956IC genes with the lineage 1 Eg101 equivalent in the W956IC backbone were analyzed. The Eg-NS4b+5, Eg-NS1+3+4a, and Eg-NS1+4b+5 chimeras produced low levels of viral RNA at early times of infection and inefficiently induced SGs, suggesting the possibility that interactions between viral nonstructural proteins and/or between viral nonstructural proteins and cell proteins are involved in suppressing early viral RNA synthesis and membrane remodeling during natural WNV strain infections. Detection of exposed viral double-stranded RNA (dsRNA) in W956IC-infected cells suggested that the enhanced early viral RNA synthesis surpassed the available virus-induced membrane protection and allowed viral dsRNA to activate PKR.

Inhibition of Dengue virus and West Nile virus proteases by click chemistry-derived benz[d]isothiazol-3(2H)-one derivatives.

Two click chemistry-derived focused libraries based on the benz[d]isothiazol-3(2H)-one scaffold were synthesized and screened against Dengue virus and West Nile virus NS2B-NS3 proteases. Several compounds (4l, 7j-n) displayed noteworthy inhibitory activity toward Dengue virus NS2B-NS3 protease in the absence and presence of added detergent. These compounds could potentially serve as a launching pad for a hit-to-lead optimization campaign.

West Nile virus infection does not induce PKR activation in rodent cells.

dsRNA-activated protein kinase (PKR) is activated by viral dsRNAs and phosphorylates eIF2a reducing translation of host and viral mRNA. Although infection with a chimeric West Nile virus (WNV) efficiently induced PKR and eIF2a phosphorylation, infections with natural lineage 1 or 2 strains did not. Investigation of the mechanism of suppression showed that among the cellular PKR inhibitor proteins tested, only Nck, known to interact with inactive PKR, colocalized and co-immunoprecipitated with PKR in WNV-infected cells and PKR phosphorylation did not increase in infected Nck1,2-/- cells. Several WNV stem-loop RNAs efficiently activated PKR in vitro but not in infected cells. WNV infection did not interfere with intracellular PKR activation by poly(I:C) and similar virus yields were produced by control and PKR-/- cells. The results indicate that PKR phosphorylation is not actively suppressed in WNV-infected cells but that PKR is not activated by the viral dsRNA in infected cells.

Virus-induced Ca2+ influx extends survival of west nile virus-infected cells.

West Nile virus (WNV) infection leads to rapid and sustained Ca(2+) influx. This influx was observed with different strains of WNV and in different types of cells. Entry during virion endocytosis as well as through calcium channels contributed to the Ca(2+) influx observed in WNV-infected cells. Ca(2+) influx was not detected after infection with vesicular stomatitis virus (VSV) and occurred only through endocytosis in Sindbis virus-infected cells. Caspase 3 cleavage and activation of several kinases, including focal adhesion kinase (FAK), mitogen-activated extracellular signal-regulated protein kinase (ERK1/2), and protein-serine kinase B alpha (Akt), at early times after WNV infection were shown to be dependent on Ca(2+) influx. Although the activation of these kinases was sustained in virus-infected cells throughout infection, UV-inactivated WNV induced only a transient activation of FAK and ERK1/2 at early times after infection. The Ca(2+)-dependent FAK activation observed in WNV-infected cells was not mediated by alphavbeta3 integrins. Reduction of Ca(2+) influx at early times of infection by various treatments decreased the viral yield and delayed both the early transient caspase 3 cleavage and the activation of FAK, Akt, and ERK signaling. The results indicate that Ca(2+) influx is required for early infection events needed for efficient viral replication, possibly for virus-induced rearrangement of the endoplasmic reticulum (ER) membrane. Increased caspase 3 cleavage at both early (transient) and late times of infection correlated with decreased activation of the FAK and ERK1/2 pathways, indicating a role for these kinases in extending the survival of flavivirus-infected cells.

OAS1 polymorphisms are associated with susceptibility to West Nile encephalitis in horses.

West Nile virus, first identified within the United States in 1999, has since spread across the continental states and infected birds, humans and domestic animals, resulting in numerous deaths. Previous studies in mice identified the Oas1b gene, a member of the OAS/RNASEL innate immune system, as a determining factor for resistance to West Nile virus (WNV) infection. A recent case-control association study described mutations of human OAS1 associated with clinical susceptibility to WNV infection. Similar studies in horses, a particularly susceptible species, have been lacking, in part, because of the difficulty in collecting populations sufficiently homogenous in their infection and disease states. The equine OAS gene cluster most closely resembles the human cluster, with single copies of OAS1, OAS3 and OAS2 in the same orientation. With naturally occurring susceptible and resistant sub-populations to lethal West Nile encephalitis, we undertook a case-control association study to investigate whether, similar to humans (OAS1) and mice (Oas1b), equine OAS1 plays a role in resistance to severe WNV infection. We identified naturally occurring single nucleotide mutations in equine (Equus caballus) OAS1 and RNASEL genes and, using Fisher's Exact test, we provide evidence that mutations in equine OAS1 contribute to host susceptibility. Virtually all of the associated OAS1 polymorphisms were located within the interferon-inducible promoter, suggesting that differences in OAS1 gene expression may determine the host's ability to resist clinical manifestations associated with WNV infection.

Crystal structure of the RNA polymerase domain of the West Nile virus non-structural protein 5.

Viruses of the family Flaviviridae are important human and animal pathogens. Among them, the Flaviviruses dengue (DENV) and West Nile (WNV) cause regular outbreaks with fatal outcomes. The RNA-dependent RNA polymerase (RdRp) activity of the non-structural protein 5 (NS5) is a key activity for viral RNA replication. In this study, crystal structures of enzymatically active and inactive WNV RdRp domains were determined at 3.0- and 2.35-A resolution, respectively. The determined structures were shown to be mostly similar to the RdRps of the Flaviviridae members hepatitis C and bovine viral diarrhea virus, although with unique elements characteristic for the WNV RdRp. Using a reverse genetic system, residues involved in putative interactions between the RNA-cap methyltransferase (MTase) and the RdRp domain of Flavivirus NS5 were identified. This allowed us to propose a model for the structure of the full-length WNV NS5 by in silico docking of the WNV MTase domain (modeled from our previously determined structure of the DENV MTase domain) onto the RdRp domain. The Flavivirus RdRp domain structure determined here should facilitate both the design of anti-Flavivirus drugs and structure-function studies of the Flavivirus replication complex in which the multifunctional NS5 protein plays a central role.

PKR and RNase L contribute to protection against lethal West Nile Virus infection by controlling early viral spread in the periphery and replication in neurons.

West Nile virus (WNV) is a neurotropic, mosquito-borne flavivirus that can cause lethal meningoencephalitis. Type I interferon (IFN) plays a critical role in controlling WNV replication, spread, and tropism. In this study, we begin to examine the effector mechanisms by which type I IFN inhibits WNV infection. Mice lacking both the interferon-induced, double-stranded-RNA-activated protein kinase (PKR) and the endoribonuclease of the 2',5'-oligoadenylate synthetase-RNase L system (PKR(-/-) x RL(-/-)) were highly susceptible to subcutaneous WNV infection, with a 90% mortality rate compared to the 30% mortality rate observed in congenic wild-type mice. PKR(-/-) x RL(-/-) mice had increased viral loads in their draining lymph nodes, sera, and spleens, which led to early viral entry into the central nervous system (CNS) and higher viral burden in neuronal tissues. Although mice lacking RNase L showed a higher CNS viral burden and an increased mortality, they were less susceptible than the PKR(-/-) x RL(-/-) mice; thus, we also infer an antiviral role for PKR in the control of WNV infection. Notably, a deficiency in both PKR and RNase L resulted in a decreased ability of type I IFN to inhibit WNV in primary macrophages and cortical neurons. In contrast, the peripheral neurons of the superior cervical ganglia of PKR(-/-) x RL(-/-) mice showed no deficiency in the IFN-mediated inhibition of WNV. Our data suggest that PKR and RNase L contribute to IFN-mediated protection in a cell-restricted manner and control WNV infection in peripheral tissues and some neuronal subtypes.

Rhabdomyolysis in patients with west nile encephalitis and meningitis.

Since 1999, more than 6,500 cases of West Nile virus neuroinvasive disease (WNND) have been reported in the United States. Patients with WNND can present with muscle weakness that is often assumed to be of neurological origin. During 2002, nearly 3,000 persons with WNV meningitis or encephalitis (or both) were reported in the United States; in suburban Cook County, Illinois, with 244 persons were hospitalized for WNV illnesses. The objective of this investigation was to describe the clinical and epidemiological features of identified cases of WNV neuroinvasive disease and rhabdomyolysis. Public health officials investigated patients hospitalized in Cook County, and identified a subset of WNV neuroinvasive disease patients with elevated creatine kinase levels. Cases were defined as hospitalized persons with a WNV infection, encephalitis or meningitis, and rhabdomyolysis. Retrospective medical record reviews were conducted and data was abstracted with a standardized data collection instrument. Eight patients with West Nile encephalitis and one with West Nile meningitis were identified with rhabdomyolysis. Median age of the nine patients was 70 years (range, 45-85 years), and eight were men. For all nine patients, the peak CK level was documented a median of 2 days after hospitalization (range, 1-24 days). Median CK level during hospitalization for all case-patients was 3,037 IU (range, 1,153-42,113 IU). Six patients had history of recent falls prior to admission. Although the temporal relationship of rhabdomyolysis and neurological WNV illness suggested a common etiology, these patients presented with complex clinical conditions which may have led to development of rhabdomyolysis from other causes. The spectrum of WNV disease requires further investigation to describe this and other clinical conditions associated with WNV infection.

Plasma lactic dehydrogenase in mice infected with Japanese encephalitis & West Nile viruses.

A study of the total and isoenzymes fractions of lactic dehydrogenase (LDH) enzyme was carried out in the plasma of mice infected with Japanese encephalitis (JE) and West Nile (WN) viruses. Only 2 isoenzymes (LDH 4 and LDH 5) were present in control mice. There was a rapid increase of total LDH in the animals infected with the wild strain of viruses. Mice infected with wild strains of JE showed all 5 isoenzymes. LDH 1 disappeared after 12 days of infection but LDH 2 and LDH 3 persisted for 3 wk. The attenuated strain of JE did not produce any change either of the total content of the enzyme or of the isoenzyme pattern. In the plasma of mice infected with wild strains of WN viruses only 4 isoenzyme bands (LDH 2, 3, 4, 5) were detected. The LDH 3 persisted longer than LDH 2. With one strain of WN virus an extra band near LDH 4 was seen.