With few exceptions, viral infections of the central nervous system (CNS) begin in peripheral tissues and then reach the CNS either by hematogenous routes or transport in nerves. This proposal focuses on the first step in the nerve route pathway ? invasion of the peripheral nervous system (PNS). The primary emphasis is on alpha herpesviruses that have evolved to enter the PNS efficiently. The overarching questions are why PNS invasion by alpha herpesviruses is so efficient and how do peripheral axons defend themselves against viral invaders. Our recent studies revealed that axonal entry by alpha herpesvirus particles rapidly stimulated new, local protein synthesis to increase efficiency of virus particle retrograde transport to cell bodies. We suggested that axonal infection induces an immediate damage response that increases efficiency of axonal transport. Axons also sense both type I and II interferons (IFN) produced in infected peripheral tissues, resulting in a novel antiviral response (local axonal production of phosphorylated STAT1 after IFN exposure resulting in reduction of virus particle transport toward the cell bodies). A hallmark of the axonal response to viral infection and IFN exposure is rapid translation of new axonal proteins from repressed axonal mRNAs. Remarkably, infection by herpesviruses, as well as IFN exposure rapidly changes the total axonal proteome and does so before new viral proteins are produced. Our data suggests that the PNS axons not only sense peripheral virus infection. We are interested in the mechanisms of these axonal responses and their virus specificity. We will explore the interplay and specificity between axonal detection and local defensive action. The unique focus of this proposal is on axon biology immediately after virion entry and subsequent transport of distinctive viral/cellular cargos in PNS axons with or without cytokine exposure before viral gene products are made. Our hypotheses are (1) that axons are front-line sensors and responders to diverse viral PNS invasion; (2) they locally sense and respond to entry of different virus particles; and (3) they respond to IFN produced by infected non-neuronal tissues and mount distinct, local antiviral responses. We have developed three technologies to explore these ideas: tri-compartment Campenot chambers to physically isolate axons from their cell bodies; optical imaging technology to follow entry events and subsequent axonal transport of individual virus particles in the presence or absence of IFN; and bioorthogonal noncanonical amino acid tagging (BONCAT) or Click chemistry and SILAC mass spectrometry approaches to label and quantitate new proteins synthesized immediately in axons after infection or IFN treatment. Understanding the fundamentals of the immediate and local response of PNS axons to incoming virus particles and inflammatory cytokines before any new viral gene products are expressed will lead to a deeper understanding of how the PNS and ultimately the CNS, is protected from infection.
Herpes simplex encephalitis and rabies in humans are global problems leading to significant morbidity and mortality without treatment. Understanding the fundamentals of the rapid and local response of PNS axons (not cell bodies or dendrites) to virus particles and to inflammatory cytokines produced by infected peripheral tissues before any new viral gene products are expressed, will lead to a deeper understanding of how the PNS and ultimately the central nervous system are protected from peripheral infection. I seek to understand how successful neuroinvasive viruses have evolved to bypass these defenses.
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