Research PaperBrain inflammation, neurodegeneration and seizure development following picornavirus infection markedly differ among virus and mouse strains and substrains
Introduction
Following viral encephalitis, the risk of seizures, particularly acute symptomatic (“early”) seizures, is increased more than 20% over the risk of seizures in the general population (Getts et al., 2008, Libbey and Fujinami, 2011, Vezzani et al., 2016). In addition, viral encephalitis increases the risk of developing epilepsy with late unprovoked seizures; 4–20% of viral encephalitis survivors go on to develop epilepsy (Getts et al., 2008, Misra et al., 2008). Over 100 different neurotropic viruses cause encephalitis in humans, and of these, several different viruses have been suggested to play a role in the development of seizures and epilepsy (Misra et al., 2008, Singhi, 2011, Vezzani et al., 2016). Viruses from the herpes virus group are prominent among these. In animals, viral encephalitis also leads to seizures; the best known example is canine distemper (Spitzbarth et al., 2012). However, the processes leading from viral encephalitis to early and late seizures are poorly understood. Animal models are useful to study these processes, but most viruses that cause encephalitis in rodents are associated with high mortality, so that the processes leading to epilepsy cannot be investigated (Libbey and Fujinami, 2011).
An exception is Theiler's murine encephalomyelitis virus (TMEV), a non-enveloped, positive-sense, single-stranded RNA virus of the Picornaviridae family and Cardiovirus genus, which is a naturally occurring enteric pathogen of the mouse (Libbey and Fujinami, 2011). Intracerebral infection of SJL/J mice with TMEV results in an acute encephalitis which, due to virus persistence and virus spread, is followed by a chronic inflammatory demyelinating disease predominantly in the spinal cord, so that TMEV-infected SJL/J mice are widely used as an animal model of multiple sclerosis (Drescher and Sosnowska, 2008, Libbey and Fujinami, 2011). In contrast, infection of C57BL/6 (B6) mice with TMEV also causes acute encephalitis but, unlike SJL/J mice, B6 mice can clear the virus during the first weeks following infection, so that this mouse strain is considered resistant to the TMEV-induced demyelinating disease (Libbey and Fujinami, 2011). More recently, the groups of Robert Fujinami and Steve White at the University of Utah have recognized the importance of B6 mice as a model of viral encephalitis-induced early and late seizures. They described that approximately 50–75% of B6 mice (male and female) infected with the Daniel's (DA) strain of TMEV developed acute behavioral (early) seizures (Libbey et al., 2008). Typically, seizures were first observed on day 3 post-infection (pi), the highest seizure activity was on day 6 pi and no seizures were observed after day 10 pi. The development of seizures appeared to be specific for B6 mice as no SJL/J (male and female), FVB/N (male) or BALB/c (male) mice developed seizures after intracerebral infection with the DA strain of TMEV (Libbey et al., 2008). The development of seizures was not specific to the DA strain of TMEV, but other TMEV strains and mutants were also able to induce seizures to various degrees; e.g. 40% of B6 mice exhibited acute seizures after infection with the BeAn 8386 (BeAn) strain (Libbey et al., 2011b).
The relationship between viral infection with acute symptomatic seizures and the subsequent development of epilepsy was examined in this model by studying B6 mice infected with the DA strain of TMEV (Stewart et al., 2010a). Monitoring by using long-term video–EEG at 2, 4 and 7 months pi of the TMEV-infected B6 mice that had experienced acute seizures demonstrated that a significant proportion (65%) of the mice developed spontaneous recurrent epileptic seizures following a latent period in which no behavioral seizures were observed (Stewart et al., 2010a). In addition, those animals with epilepsy had hippocampal damage characterized by neuronal cell loss in the CA1/CA2 pyramidal cell layers and gliosis, reminiscent of hippocampal sclerosis in patients with infection-induced temporal lobe epilepsy (Stewart et al., 2010a). Based on these findings, the TMEV-induced seizure model was proposed to represent the first infection-driven animal model for epilepsy (Libbey and Fujinami, 2011).
The present study had various aims. First, because all previous experiments on the novel TMEV model of infection-induced epilepsy have been performed by the same group of researchers, we wanted to replicate their findings. This was initiated by the fact that we had used the BeAn strain of TMEV in thousands of SJL/J and B6 mice over the last ~ 10 years in studies on mechanisms involved in virus-induced demyelination but never observed any seizures in B6 mice (Ulrich et al., 2006, Ulrich et al., 2008, Jafari et al., 2012, Prajeeth et al., 2014). Thus, we hypothesized that either the substrain of B6 mice or the BeAn substrain used in our experiments may have been responsible for the lack of seizures. This hypothesis was addressed by comparing two B6 and two BeAn substrains, including the mouse and virus substrains used in the original studies of Fujinami and White. In addition, we compared the potency of the BeAn and DA TMEV strains to induce seizures and epilepsy in mice. In all experiments, the severity of inflammation and hippocampal damage was examined and correlated with the development of seizures. Finally, because interleukin (IL)-6 and interferon (IFN)-β production of macrophages is thought to play a crucial role in the development of seizures following TMEV infection (Cusick et al., 2013, Moore et al., 2013), the expression of IFN-inducible antiviral effectors was examined in the hippocampus.
Section snippets
Animals
Overall, 198 mice were used in this study. Three-week-old female SJL/J and B6 mice were purchased from Harlan Laboratories (Eystrup, Germany) and from Charles River (Sulzfeld, Germany) and kept in groups of five to eight animals in isolated ventilated cages (Tecniplast, Hohenpeißenberg, Germany) under controlled environmental conditions (22–24 °C; 50–60% humidity; 12/12 h light/dark cycle) with free access to standard rodent diet (R/M-H; Ssniff Spezialdiäten GmbH, Soest, Germany) and tap water.
We
BeAn-1 TMEV
In all BeAn-1-infected mice, a transient mild increase of the TCS was observed on the first day after surgery in infected compared to mock-infected animals (Fig. 2A, B & C; P < 0.05). In accordance with previous studies (Ulrich et al., 2006, Ulrich et al., 2010), clinical signs related to the chronic phase started to occur in TMEV-infected SJL/J mice at day 42 pi. Clinical signs in affected animals mainly consisted of gait abnormalities and comprised ataxia, reduction of righting reflex, and
Discussion
The present study is the first to confirm and significantly extend the data of Robert Fujinami's and Steve White's groups (cf., Libbey and Fujinami, 2011, Vezzani et al., 2016), substantiating that TMEV infection in B6 mice provides an animal model of infection-induced acute and late seizures with a variety of interesting features. While most experiments of Fujinami, White and colleagues used intracerebral infection of B6J mice with the DA strain of TMEV, we used three (sub)strains of virus and
Acknowledgments
We thank Robert S. Fujinami for providing the BeAn-2 and DA strains of TMEV and helpful discussion and advice during preparation of this study. We also thank H. Steve White and Karen S. Wilcox for discussion on the TMEV model. We thank D. Waschke, B. Buck, K. Schöne, P. Grünig, C. Schütz, G. Bougamra, B. Tegtmeyer, N. Weegh, I. Waltl, C. Brandt, K. Töllner, and P. Hampel for skillful technical assistance. The authors declare no competing financial interests. The study was supported by the
References (70)
- et al.
Generation and characterization of pilocarpine-sensitive C57BL/6 mice as a model of temporal lobe epilepsy
Behav. Brain Res.
(2012) - et al.
Neuronal and glial pathological changes during epileptogenesis in the mouse pilocarpine model
Exp. Neurol.
(2003) - et al.
Interferon and the central nervous system
Eur. J. Pharmacol.
(2005) - et al.
Theiler's murine encephalomyelitis virus (TMEV)-induced demyelination: a model for human multiple sclerosis
Methods
(1996) - et al.
Interleukin-10 expression during the acute phase is a putative prerequisite for delayed viral elimination in a murine model for multiple sclerosis
J. Neuroimmunol.
(2012) - et al.
Generation and characterization of a polyclonal antibody for the detection of Theiler's murine encephalomyelitis virus by light and electron microscopy
J. Virol. Methods
(2009) - et al.
Chronic neurologic disease in Theiler's virus infection of SJL/J mice
J. Neurol. Sci.
(1976) - et al.
IRF3 helps control acute TMEV infection through IL-6 expression but contributes to acute hippocampus damage following TMEV infection
Virus Res.
(2013) - et al.
The antiviral activities of ISG15
J. Mol. Biol.
(2013) - et al.
Revised guides for organ sampling and trimming in rats and mice—part 3. A joint publication of the RITA and NACAD groups
Exp. Toxicol. Pathol.
(2004)
Molecular and cellular basis of epileptogenesis in symptomatic epilepsy
Epilepsy Behav.
Modification of seizure activity by electrical stimulation: II. Motor seizure
Electroencephalogr. Clin. Neurophysiol.
Analysis of genetic variation in Theiler's virus during persistent infection in the mouse central nervous system
Virology
Distinct kinetics of viral replication, T cell infiltration, and fibrosis in three phases of myocarditis following Theiler's virus infection
Cell. Immunol.
The role of pro- and anti-inflammatory cytokines in the pathogenesis of spontaneous canine CNS diseases
Vet. Immunol. Immunopathol.
Impaired cognitive ability and anxiety-like behavior following acute seizures in the Theiler's virus model of temporal lobe epilepsy
Neurobiol. Dis.
C57BLack/BOX? The importance of exact mouse strain nomenclature
Trends Genet.
Evaluating an etiologically relevant platform for therapy development for temporal lobe epilepsy: effects of carbamazepine and valproic acid on acute seizures and chronic behavioral comorbidities in the Theiler's murine encephalomyelitis virus mouse model
J. Pharmacol. Exp. Ther.
CCR2 regulates development of Theiler's murine encephalomyelitis virus-induced demyelinating disease
Viral Immunol.
Analysis of surrogate gene expression markers in peripheral blood of melanoma patients to predict treatment outcome of adjuvant pegylated interferon alpha 2b (EORTC 18991 side study)
Cancer Immunol. Immunother.
Demyelinating lesions due to Theiler's virus are associated with ongoing central nervous system infection
J. Virol.
Infiltrating macrophages are key to the development of seizures following virus infection
J. Virol.
Observations on encephalomyelitis of mice (DA strain)
J. Exp. Med
Being a mouse in a man's world: what TMEV has taught us about human disease
Front. Biosci.
Identification of interferon-inducible genes as diagnostic biomarker for systemic lupus erythematosus
Clin. Rheumatol.
Origins and Characteristics of Inbred Strains of Mice
The Mouse Brain in Stereotaxic Coordinates
Induction of activator protein-1 and nuclear factor-kappaB as a prerequisite for disease development in susceptible SJL/J mice after theiler murine encephalomyelitis
J. Neuropathol. Exp. Neurol.
Viruses and the immune system: their roles in seizure cascade development
J. Neurochem.
Fine-tuning of type I IFN-signaling in microglia — implications for homeostasis, CNS autoimmunity and interferonopathies
Curr. Opin. Neurobiol.
Analysis of biomarker data: logs, odds ratios, and receiver operating characteristic curves
Curr. Opin. HIV AIDS
Central nervous system chemokine expression during Theiler's virus-induced demyelinating disease
J. Neurovirol.
Hippocampal protection in mice with an attenuated inflammatory monocyte response to acute CNS picornavirus infection
Sci. Rep.
Impact of Theiler's virus infection on hippocampal neuronal progenitor cells: differential effects in two mouse strains
Neuropathol. Appl. Neurobiol.
Segregation of seizure traits in C57 black mouse substrains using the repeated-flurothyl model
PloS One
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Present address: Boehringer Ingelheim Veterinary Research Center, Hannover, Germany.