Herpes simplex virus (HSV) persists for the lifetime of the host in the form of a latent infection of neurons. Importantly, periodic reactivation of the vius results in significant morbidity and mortality, particularly in the immunocompromised host. However, the unique characteristics of neurons and molecular events that allow viral persistence and its reactivation are not understood. So far, obstacles to understanding the interaction of the virus with neurons have been i) the limited use of an in vitro model of latency and ii) challenges in gene manipulation techniques in primary neurons. Infection of sympathetic neurons has been found to recapitulate HSV latency in vivo. Therefore, in this project I will use sympathetic neurons and state-of-art techniques to examine viral gene function, and the mechanism of viral reactivation at the molecular and cellular level in neurons. The latency-associated transcript (LAT) encodes a family of non-coding RNAs and is the only viral gene product expressed to high levels during latency.
In Aim 1, I will test the hypothesis that LAT expression inhibits apoptosis and promotes survival of infected neurons, thus allowing for long-term viral persistence and enhanced reactivation. LAT expressing plasmids will be introduced into neurons by microinjection. The ability of the LAT to protect neurons against different triggers of apoptosis and the mechanism by which the LAT exerts protection will also be determined.
In Aim 2, I will focus on examining the signaling events within neurons that trigger HSV reactivation. Viral reactivation is triggered when sympathetic neurons are deprived of nerve growth factor (NGF). Since NGF deprivation activates apoptosis in neurons, I will identify the key event in the apoptotic pathway after NGF deprivation that activates the expression of HSV lytic genes to allow viral reactivation. An understanding of how HSV latency is maintained at the cellular level and knowledge of key events within neurons that trigger its reactivation are critica to identify potential targets for novel therapeutics that prevent HSV reactivation from neurons.
Herpes Simplex Virus is able to hide for the lifetime of an individual in the form of a latent infection of neurons. The experiments proposed in this project will help uncover how the virus is able to persist and what triggers the virus to reactivate from neurons and cause disease. The long-term goals are to identify new targets for drugs that would prevent the reactivation of Herpes Simplex Virus.