Author ORCID Identifier

0000-0003-1647-7113

Date of Award

12-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Mukesh Kumar

Second Advisor

Richard Dix

Third Advisor

Sang-moo Kang

Abstract

Powassan virus (POWV) is a newly emerging tick-borne neurotropic flavivirus. POWV entry into the central nervous system (CNS) is a critical event determining clinical outcome. Upon successful neuroinvasion POWV causes a range of neurological complications. POWV causes fatal encephalitis in approximately 10-30% of neurological cases, and long-lasting neurological sequelae in approximately 50% of survivors. However, the mechanisms of POWV neuroinvasion and neuropathogenesis are still not well understood. In this study we comprehensively characterized POWV infection in the C57BL/6J mice following a subcutaneous footpad inoculation. POWV caused robust viral replication in serum of mice early after infection which quickly became undetectable as the virus was able to penetrate the CNS. Viral replication in the brain coincided with decreased tight junction protein expression and extravasation of Evan’s blue dye into the brain parenchyma indicating that POWV can disrupt the blood brain barrier (BBB).

To further understand the host-pathogen response, brains underwent whole genome sequencing to reveal key genes altered in response to POWV infection. Differential gene expression in POWV infected brains were concentrated on cytokine signaling, neuroinflammatory pathways, IFN signaling, and upregulation of proinflammatory cell death pathways. We further investigated the role of cell death pathway genes in POWV-infected brains. In addition, we further investigated the role of type-I interferon (IFN) response in mice. We used an IFN alpha receptor (IFNAR) knock-out mouse model. Our data demonstrate that IFN signaling is a critical component of anti-viral immune response following POWV infection. IFNAR1-/- mice died rapidly and displayed enhanced pro-inflammatory immune response and well as increased viral burden in multiple organs. IFNAR1-/- mice presented with a stunted innate immune response with a significant reduction in activated macrophages in the spleen. They exhibited signs of early neuroinflammation and astrocyte activation when compared to WT controls. Overall, this study provides a comprehensive characterization of POWV infection in C57BL/6J mice and demonstrates that POWV can disrupt the BBB. Furthermore, we show that type-I IFN is critical to protect mice against early POWV infection.

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