Antiviral Effects of a Transgenic RNA-Dependent RNA Polymerase▿

Transgenic expression of the RNA-dependent RNA polymerase 3Dpol inhibited infection of Theiler's murine encephalitis virus (TMEV), a picornavirus from which it was derived. Here, we infected 3Dpol transgenic mice with another picornavirus, as well as an alphaherpesvirus and a rhabdovirus. 3Dpol transgenic FVB mice had significantly lower viral loads and survived longer after infection with all three types of viruses than nontransgenic FVB mice. Viral inhibition among three different types of virus by transgenic 3Dpol suggests that the mechanism of action is not the direct interference with picornaviral 3Dpol but instead may be the changing of host cells to an antiviral state before or after viral infection occurs, as basal interferon levels were higher in 3Dpol transgenic mice before infection. Further study of this mechanism may open new possibilities for future antiviral therapy

Gamma Interferon Is Critical for Neuronal Viral Clearance and Protection in a Susceptible Mouse Strain following Early Intracranial Theiler's Murine Encephalomyelitis Virus Infection

We evaluated the role of gamma interferon (IFN-γ) in protecting neurons from virus-induced injury following central nervous system infection. IFN-γ(−/−) and IFN-γ(+/+) mice of the resistant major histocompatibility complex (MHC) H-2(b) haplotype and intracerebrally infected with Theiler's murine encephalomyelitis virus (TMEV) cleared virus infection from anterior horn cell neurons. IFN-γ(+/+) H-2(b) mice also cleared virus from the spinal cord white matter, whereas IFN-γ(−/−) H-2(b) mice developed viral persistence in glial cells of the white matter and exhibited associated spinal cord demyelination. In contrast, infection of IFN-γ(−/−) mice of the susceptible H-2(q) haplotype resulted in frequent deaths and severe neurologic deficits within 16 days of infection compared to the results obtained for controls. Morphologic analysis demonstrated severe injury to spinal cord neurons in IFN-γ(−/−) H-2(q) mice during early infection. More virus RNA was detected in the brain and spinal cord of IFN-γ(−/−) H-2(q) mice than in those of control mice at 14 and 21 days after TMEV infection. Virus antigen was localized predominantly to anterior horn cells in infected IFN-γ(−/−) H-2(q) mice. IFN-γ deletion did not affect the humoral response directed against the virus. However, the level of expression of CD4, CD8, class I MHC, or class II MHC in the central nervous system of IFN-γ(−/−) H-2(q) mice was lower than those in IFN-γ(+/+) H-2(q) mice. Finally, in vitro analysis of virus-induced death in NSC34 cells and spinal motor neurons showed that IFN-γ exerted a neuroprotective effect in the absence of other aspects of the immune response. These data support the hypothesis that IFN-γ plays a critical role in protecting spinal cord neurons from persistent infection and death

A 40-cM Region on Chromosome 14 Plays a Critical Role in the Development of Virus Persistence, Demyelination, Brain Pathology and Neurologic Deficits in a Murine Viral Model of Multiple Sclerosis

International audienceTheiler's virus persists and induces immunemediated demyelination in susceptible mice and serves as a model of multiple sclerosis. Previously, we identified 4 markers-D14Mit54, D14Mit60, D14Mit61, and D14Mit90-in a 40-cM region of chromosome 14 that are associated with demyelination in a cross between susceptible DBA/2 and resistant B10.D2 mice. We generated congenic-inbred mice to examine the contribution of this 40-cM region to disease. DBA Chr.14 B10 mice, containing the chromosomal segment marked by the microsatellite polymorphisms, developed less spinal cord demyelination than did DBA/2 mice. More demyelination was found in the reciprocal congenic mouse B10.D2 Chr.14 D2 than in the B10.D2 strain. Introduction of the DBA/2 chromosomal region onto the B10.D2 genetic background resulted in more severe disease in the striatum and cortex relative to B10.D2 mice. The importance of the marked region of chromosome 14 is indicated by the decrease in neurological performance using the Rotarod test during chronic disease in B10.D2 Chr.14 D2 mice in comparison to B10.D2 mice. Viral replication was increased in B10.D2 Chr.14 D2 mice as determined by quantitative real-time RT-PCR. These results indicate that the 40-cM region on chromosome 14 of DBA/2 mice contributes to viral persistence, subsequent demyelination, and loss of neurological function

Transgenic Expression of the 3D Polymerase Inhibits Theiler's Virus Infection and Demyelination▿ †

The RNA-dependent RNA polymerase 3Dpol is required for the elongation of positive- and negative-stranded picornavirus RNA. During the course of investigating the effect of the transgenic expression of viral genes on the host immune response, we evaluated the viral load present in the host after infection. To our surprise, we found that 3D transgenic expression in genetically susceptible FVB mice led to substantially lower viral loads after infection with Theiler's murine encephalomyelitis virus (TMEV). As a result, spinal cord damage caused by chronic viral infection in the central nervous system was reduced in FVB mice that expressed 3D. This led to the preservation of large-diameter axons and motor function in these mice. The 3D transgene also lowered early viral loads when expressed in FVB-Db mice resistant to persistent TMEV infection. The protective effect of 3D transgenic expression was not altered in FVB-Rag−/−.3D mice that are deficient in T and B cells, thus ruling out a mechanism by which the overexpression of 3D enhanced the adaptive immune clearance of the virus. Understanding how endogenously overexpressed 3D polymerase inhibits viral replication may lead to new strategies for targeting therapies to all picornaviruses

Human HLA-DR Transgenes Protect Mice from Fatal Virus-Induced Encephalomyelitis and Chronic Demyelination▿

We evaluated the participatory role of human HLA-DR molecules in control of virus from the central nervous system and in the development of subsequent spinal cord demyelination. The experiments utilized intracranial infection with Theiler's murine encephalomyelitis virus (TMEV), a picornavirus that, in some strains of mice, results in primary demyelination. We studied DR2 and DR3 transgenic mice that were bred onto a combined class I-deficient mouse (beta-2 microglobulin deficient; β2m0) and class II-deficient mouse (Aβ0) of the H-2b background. Aβ0.β2m0 mice infected with TMEV died within 18 days of infection. These mice showed severe encephalomyelitis due to rapid replication of virus genome. In contrast, transgenic mice with insertion of a single human class II major histocompatibility complex (MHC) gene (DR2 or DR3) survived the acute infection. DR2 and DR3 mice controlled virus infection by 45 days and did not develop spinal cord demyelination. Levels of virus RNA were reduced in HLA-DR transgenic mice compared to Aβ0.β2m0 mice. Virus-neutralizing antibody responses did not explain why DR mice survived the infection and controlled virus replication. However, DR mice showed an increase in gamma interferon and interleukin-2 transcripts in the brain, which were associated with protection. The findings support the hypothesis that the expression of a single human class II MHC molecule can, by itself, influence the control of an intracerebral pathogen in a host without a competent class I MHC immune response. The mechanism of protection appears to be the result of cytokines released by CD4+ T cells

Additional file 1: Figure S1. of Human class I major histocompatibility complex alleles determine central nervous system injury versus repair

Spinal cord lesions in mice infected for 45 days with DA strain of TMEV. The class I antigen expression was up-regulated in areas of injury. Panel A. Immunoperoxidase A11 staining in Aβ0.β2m0.Hβ2m+.A11+ mice. Panel B. B27 staining in Aβ0.β2m0.Hβ2m+.A11+ mice. Panel C. B27 staining in Aβ0.β2m0.Hβ2m+.B27+ mice. Panel D. A11 staining in Aβ0.β2m0.Hβ2m+.B27+ mice. Images were collected at ×60. The weak staining is either the result of the quality of antibodies that do not work well with immunocytochemistry or the fact that the CNS normally has low level expression of MHC. Scale bar = 20 μm. (TIF 1561 kb

A natural human IgM that binds to gangliosides is therapeutic in murine models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, fatal neurological disease that primarily affects spinal cord anterior horn cells and their axons for which there is no treatment. Here we report the use of a recombinant natural human IgM that binds to the surface of neurons and supports neurite extension, rHIgM12, as a therapeutic strategy in murine models of human ALS. A single 200 µg intraperitoneal dose of rHIgM12 increases survival in two independent genetic-based mutant SOD1 mouse strains (SOD1G86R and SOD1G93A) by 8 and 10 days, delays the onset of neurological deficits by 16 days, delays the onset of weight loss by 5 days, and preserves spinal cord axons and anterior horn neurons. Immuno-overlay of thin layer chromatography and surface plasmon resonance show that rHIgM12 binds with high affinity to the complex gangliosides GD1a and GT1b. Addition of rHIgM12 to neurons in culture increases α-tubulin tyrosination levels, suggesting an alteration of microtubule dynamics. We previously reported that a single peripheral dose of rHIgM12 preserved neurological function in a murine model of demyelination with axon loss. Because rHIgM12 improves three different models of neurological disease, we propose that the IgM might act late in the cascade of neuronal stress and/or death by a broad mechanism

Abbreviated Exposure to Hypoxia Is Sufficient to Induce CNS Dysmyelination, Modulate Spinal Motor Neuron Composition, and Impair Motor Development in Neonatal Mice

<div><p>Neonatal white matter injury (nWMI) is an increasingly common cause of cerebral palsy that results predominantly from hypoxic injury to progenitor cells including those of the oligodendrocyte lineage. Existing mouse models of nWMI utilize prolonged periods of hypoxia during the neonatal period, require complex cross-fostering and exhibit poor growth and high mortality rates. Abnormal CNS myelin composition serves as the major explanation for persistent neuro-motor deficits. Here we developed a simplified model of nWMI with low mortality rates and improved growth without cross-fostering. Neonatal mice are exposed to low oxygen from postnatal day (P) 3 to P7, which roughly corresponds to the period of human brain development between gestational weeks 32 and 36. CNS hypomyelination is detectable for 2–3 weeks post injury and strongly correlates with levels of body and brain weight loss. Immediately following hypoxia treatment, cell death was evident in multiple brain regions, most notably in superficial and deep cortical layers as well as the subventricular zone progenitor compartment. PDGFαR, Nkx2.2, and Olig2 positive oligodendrocyte progenitor cell were significantly reduced until postnatal day 27. In addition to CNS dysmyelination we identified a novel pathological marker for adult hypoxic animals that strongly correlates with life-long neuro-motor deficits. Mice reared under hypoxia reveal an abnormal spinal neuron composition with increased small and medium diameter axons and decreased large diameter axons in thoracic lateral and anterior funiculi. Differences were particularly pronounced in white matter motor tracts left and right of the anterior median fissure. Our findings suggest that 4 days of exposure to hypoxia are sufficient to induce experimental nWMI in CD1 mice, thus providing a model to test new therapeutics. Pathological hallmarks of this model include early cell death, decreased OPCs and hypomyelination in early postnatal life, followed by dysmyelination, abnormal spinal neuron composition, and neuro-motor deficits in adulthood.</p></div

Antiviral Protection via RdRP-Mediated Stable Activation of Innate Immunity

<div><p>For many emerging and re-emerging infectious diseases, definitive solutions via sterilizing adaptive immunity may require years or decades to develop, if they are even possible. The innate immune system offers alternative mechanisms that do not require antigen-specific recognition or <i>a priori</i> knowledge of the causative agent. However, it is unclear whether effective stable innate immune system activation can be achieved without triggering harmful autoimmunity or other chronic inflammatory sequelae. Here, we show that transgenic expression of a picornavirus RNA-dependent RNA polymerase (RdRP), in the absence of other viral proteins, can profoundly reconfigure mammalian innate antiviral immunity by exposing the normally membrane-sequestered RdRP activity to sustained innate immune detection. RdRP-transgenic mice have life-long, quantitatively dramatic upregulation of 80 interferon-stimulated genes (ISGs) and show profound resistance to normally lethal viral challenge. Multiple crosses with defined knockout mice (<i>Rag1</i>, <i>Mda5</i>, <i>Mavs</i>, <i>Ifnar1</i>, <i>Ifngr1</i>, and <i>Tlr3)</i> established that the mechanism operates via MDA5 and MAVS and is fully independent of the adaptive immune system. Human cell models recapitulated the key features with striking fidelity, with the RdRP inducing an analogous ISG network and a strict block to HIV-1 infection. This RdRP-mediated antiviral mechanism does not depend on secondary structure within the RdRP mRNA but operates at the protein level and requires RdRP catalysis. Importantly, despite lifelong massive ISG elevations, RdRP mice are entirely healthy, with normal longevity. Our data reveal that a powerfully augmented MDA5-mediated activation state can be a well-tolerated mammalian innate immune system configuration. These results provide a foundation for augmenting innate immunity to achieve broad-spectrum antiviral protection.</p></div