Varicella-zoster virus (VZV), a human alphaherpesvirus (?HV), establishes lifelong latent infection in ganglionic neurons of >90% humans worldwide. It reactivates to cause herpes zoster (HZ), which is often followed by debilitating pain and life changing complications. How VZV maintains latency remains unclear. Despite the availability of two FDA-approved HZ vaccines, HZ will remain a common and clinically important disease for many years. The VZV latent state cannot yet be targeted and the triggers of reactivation are not clear. There is no animal model to study human VZV latency/reactivation. We argue that better knowledge of VZV latency and reactivation will establish a firm basis for new anti-VZV strategies to reduce the HZ burden. Our groups pioneered the study of VZV latency by analyzing naturally VZV-infected human trigeminal ganglia (TG) and human stem cell-derived cultured (hESC) neuron models. We have now identified novel spliced VZV RNAs in human TG termed the VZV latency-associated transcripts (VLT). Remarkably, these are positionally conserved to latent RNAs made by other neurotropic ?HVs, and are antisense to the VZV transactivator, open reading frame 61 (ORF61, ortholog of HSV ICP0). However, VZV VLTs are different in that they can encode proteins of unknown function that also link to ORF63, an immediate-early protein that regulates VZV gene expression. Our overlying hypothesis is that VLT is important for the establishment and/or maintenance of VZV latency, while VLT-ORF63 is important for reactivation from latency. Our three specific aims are designed to address the VZV VLT and ORF63 loci in depth, using both cadaveric human TG and cultured neuron models of VZV latency and reactivation.
In Aim 1, we will perform in-depth in situ analyses of latently VZV-infected human TG and VZV-infected cultured hESC neurons to determine the specific human neuron subtypes that host VZV latency and support reactivation. This will establish a basis for neuron specific targeting of the latent state.
Aim 2 will genetically dissect components of VLT and its proteins with defined recombinant viruses to determine how each contributes to lytic, latent and reactivated VZV infections.
Aim 3 will determine the changes in molecular chromatin occurring at the VLT and ORF63 loci as VZV transitions from latency to reactivation, focusing on CTCF binding, histone modifications and resultant transcription on VZV genomes. This application represents the combination of unique expertise from three VZV labs that will share complementary materials, tool and techniques to resolve how the RNAs, proteins and chromatin changes of the VLT locus contribute to virus growth, latency and reactivation. Successful completion of our proposal will provide insight into molecular mechanisms that regulate VZV latency and reactivation. This will provide leads towards the development of novel intervention strategies that effectively target latent VZV and consequently the burden of HZ disease.
Varicella-zoster virus (VZV), a human alphaherpesvirus, establishes lifelong latent neuronal infection in the ganglia of the majority of humans worldwide, reactivating in one-third to cause shingles, debilitating pain and stroke. Recently, we discovered that latent VZV gene expression is restricted to two newly identified transcripts in human ganglia: VZV Latency-associated Transcript (VLT) and a read-through transcript that combines VLT with VZV gene 63. Our application will determine the role of both viral genes in latency establishment/maintenance/reactivation in human neurons ex vivo, in situ and in vitro.