CARD9 Deficiency Increases Hippocampal Injury Following Acute Neurotropic Picornavirus Infection but Does Not Affect Pathogen Elimination

Suvarin Pavasutthipaisit,Andreas Beineke,Theresa Störk,Melanie Stoff,Malgorzata Ciurkiewicz,Kevin D Pavelko,Tim Ebbecke,Bernd Lepenies,Sabine Mayer-Lambertz

doi:10.3390/ijms22136982

Abstract

Neurotropic viruses target the brain and contribute to neurologic diseases. Caspase recruitment domain containing family member 9 (CARD9) controls protective immunity in a variety of infectious disorders. To investigate the effect of CARD9 in neurotropic virus infection, CARD9−/− and corresponding C57BL/6 wild-type control mice were infected with Theiler’s murine encephalomyelitis virus (TMEV). Brain tissue was analyzed by histology, immunohistochemistry and molecular analyses, and spleens by flow cytometry. To determine the impact of CARD9 deficiency on T cell responses in vitro, antigen presentation assays were utilized. Genetic ablation of CARD9 enhanced early pro-inflammatory cytokine responses and accelerated infiltration of T and B cells in the brain, together with a transient increase in TMEV-infected cells in the hippocampus. CARD9−/− mice showed an increased loss of neuronal nuclear protein+ mature neurons and doublecortin+ neuronal precursor cells and an increase in β-amyloid precursor protein+ damaged axons in the hippocampus. No effect of CARD9 deficiency was found on the initiation of CD8+ T cell responses by flow cytometry and co-culture experiments using virus-exposed dendritic cells or microglia-enriched glial cell mixtures, respectively. The present study indicates that CARD9 is dispensable for the initiation of early antiviral responses and TMEV elimination but may contribute to the modulation of neuroinflammation, thereby reducing hippocampal injury following neurotropic virus infection.

Highlights

Neurotropic viruses cause infections of the central nervous system (CNS) in humans and animals worldwide that can either be asymptomatic and self-limiting or fulminant and fatal [1,2]
Histology of infected mice revealed the presence of inflammatory responses within the hippocampus characterized by mononuclear infiltrates and gliosis associated with neuronal loss of the stratum pyramidale
A significantly increased severity of hippocampal damage, as determined by semiquantitative scoring, was found in CARD9−/− mice compared to wild-type control mice (WT) mice at 7 dpi (p = 0.03; Figure 1A–C)

Summary

Introduction

Neurotropic viruses cause infections of the central nervous system (CNS) in humans and animals worldwide that can either be asymptomatic and self-limiting or fulminant and fatal [1,2]. Theiler’s murine encephalomyelitis virus (TMEV) is a neurotropic picornavirus that transiently infects the hippocampus, causing neuronal damage in C57BL/6 mice [9,10,11], making TMEV infection a valuable model to study virus-induced neurologic disorders [2,10,11,12,13,14,15]. Early innate responses are a “double-edged sword” and need to be tightly controlled during the course of TMEV infection [13,19,20,21,22,23]

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