Varicella zoster virus (VZV) causes varicella (chickenpox) in billions of children worldwide annually, after which virus becomes latent in ganglionic neurons along the entire neuraxis. Decades later, VZV-specific cell-mediated immunity declines and virus reactivates, resulting in zoster (shingles), characterized by pain and rash restricted to 1-3 dermatomes. Zoster affects ~1 million Americans yearly and is often complicated by chronic radicular pain (postherpetic neuralgia, PHN) and other serious neurological (cerebellitis, myelitis and vasculopathy) and ocular disorders that collectively cause paralysis, blindness and death. By 2030, 22% of Americans (65 million people) will be >age 65, and the >85 population will triple to >8 million. The incidence and severity of zoster range from a natural decline in VZV-specific immunity with advancing age to more serious host immune deficits seen in organ transplant recipients and in patients with cancer and AIDS. Zoster vaccine reduces the incidence of zoster by 50% for up to 3 years, yet even immunization of everyone >age 60 still predicts 500,000 cases of zoster and 200,000 cases of PHN annually. Thus, as the elderly population increases, so does the incidence of zoster and its attendant neurological and ocular complications. After first proving in 1983 that VZV is latent in human ganglia, our subsequent analyses of >7,000 human ganglia from >900 randomly autopsied subjects revealed the presence of the entire virus genome in neurons, most likely maintained as a histone-coated episome with variable VZV DNA abundance, VZV transcription restricted to ORF63, and epigenetic regulation of VZV gene expression. To more precisely define the extent of viral gene expression and epigenetic markers on the latent VZV genome, we examined VZV-infected differentiated neurons, which remained viable in culture up to 3 weeks without a cytopathic effect; treatment of these neurons with interferon- significantly reduced viral gene expression. Thus, we hypothesize that neurons treated to limit VZV gene expression will yield a model system that recapitulates VZV transcription in latently infected human ganglionic neurons. To test our hypothesis, we will: treat VZV non-lytically infected neurons in vitro with antiviral agents and molecules produced by cells of the innate and adaptive immune systems and examine VZV gene expression by RT-PCR (Aim 1); determine the physical state of VZV DNA, VZV gene expression and epigenetic markers present on VZV genomes within non-lytically infected neurons after treatment with acyclovir and multiple cytokines (Aim 2). Developing a model of VZV latency in vitro will allow studies that would normally require acquisition of thousands of human ganglia. An in-depth understanding of how VZV resides long-term in latently infected human nerve cells is prerequisite to developing strategies that prevent the cascade of events leading to virus reactivation, a cause of serious neurologic disease and blindness, particularly in the rapidly increasing elderly and immunocompromised populations.
Varicella zoster virus (VZV) reactivation from neurons in latently infected ganglia causes zoster (shingles) and other serious neurological and ocular disease. We will develop a model of VZV latency in neurons in tissue culture to allow studies that would normally require acquisition of thousands of human ganglia. An in-depth understanding of how VZV resides long-term in latently infected human nerve cells is prerequisite to developing strategies to prevent the cascade of events leading to virus reactivation, a cause of serious chronic pain, stroke paralysis and blindness, particularly in the rapidly increasing elderly and immunocompromised populations.
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