Varicella zoster virus-Induced Pain in a Rat Model of Post-Herpetic Neuralgia



 DESCRIPTION (provided by applicant): Post-Herpetic Neuralgia (PHN) is a common, exceedingly painful and debilitating complication of Herpes Zoster that is difficult to treat and i unmet in the need for improved therapies. Zoster and PHN occur when varicella-zoster virus (VZV) reactivates from a latent state that was established in host sensory neurons during chickenpox. Most adults worldwide are at risk for Zoster, PHN and pain, which may be so severe as to profoundly reduce quality of life. Incidence increases with age, and our aging society implies Zoster and PHN may become even more pressing public health concerns. The mechanisms by which VZV causes persistent pain are not understood. This project, directed to FOA PA-13-118, expands a clinically relevant model of PHN in which VZV inoculated into the rat footpad induces prolonged mechanical allodynia and thermal hyperalgesia. Our overlying hypothesis is that this model will provide better comprehension of how VZV interacts with the nervous system to induce pain, and be a platform to test improved approaches for treatment of VZV-induced pain. Aim 1 will define the requirements of VZV expression and replication in the rat to induce pain. We will test the hypothesis that limited VZV expression is sufficient to drive chronic indicators of pain in the absence of productive replication. We will also test the hypothesis that VZV lacking the ORF47 kinase, which does not induce chronic pain, cannot initiate infection of the rat required for pain. Third, we will address the intrinsic properties by which the VZV IE62 transcriptional regulator induces chronic pain behaviors independent of other VZV proteins. These studies will establish the key components of VZV replication and expression in driving the pain state in the model. Aim 2 will focus on the role of infected neurons in contributing to the pain state. We will test the hypothesis that VZV protein expressing neurons directly drive nocifensive behaviors, exploiting an innovative ligand-dependent, neuron- specific pain repression system that involves expression of glycine receptors and activation by ligands. We will also address the neuron subtypes involved in driving a pain state that is induced by specific VZV pain-inducing proteins expressed from neuron-specific promoters in replication defective HSV (rdHSV) vectors. This could also establish a more prolonged model of VZV-induced pain behaviors. Aim 3 will address improved and more specific therapy of VZV-induced pain. We will test rdHSV expressing ligand-dependent glycine receptors for efficacy in blocking VZV induced pain signals in the rat following transcriptionally targeting of specific subpopulations of neurons. This will also reveal those neuron subtypes that transmit the VZV-induced pain signals. Together, these approaches have potential to revolutionize the way we think about how VZV induces pain and how we can more effectively provide relief to those unfortunate human patients suffering from PHN.