Varicella-Zoster Virus ORF63 Inhibits Apoptosis of Primary Human Neurons

Abstract

Virus-encoded modulation of apoptosis may serve as a mechanism to enhance cell survival and virus persistence. The impact of productive varicella-zoster virus (VZV) infection on apoptosis appears to be cell type specific, as infected human sensory neurons are resistant to apoptosis, yet human fibroblasts readily become apoptotic. We sought to identify the viral gene product(s) responsible for this antiapoptotic phenotype in primary human sensory neurons. Treatment with phosphonoacetic acid to inhibit viral DNA replication and late-phase gene expression did not alter the antiapoptotic phenotype, implicating immediate-early (IE) or early genes or a virion component. Compared to the parental VZV strain (rOKA), a recombinant virus unable to express one copy of the diploid IE gene ORF63 (rOka⌬ORF63) demonstrated a significant induction of apoptosis in infected neurons, as determined by three methods: annexin V staining, deoxynucleotidyltransferase-mediated dUTP-biotin nick end label staining, and transmission electron microscopy. Furthermore, neurons transfected with a plasmid expressing ORF63 resisted apoptosis induced by nerve growth factor withdrawal. These results show that ORF63 can suppress apoptosis of neurons and provide the first identification of a VZV gene encoding an antiapoptotic function. As ORF63 is expressed in neurons during both productive and latent infection, it may play a significant role in viral pathogenesis by promoting neuron survival during primary and reactivated infections.Varicella-zoster virus (VZV) is a human alphaherpesvirus that causes varicella (chicken pox) during primary infection and herpes zoster (shingles) following reactivation of latent virus from the dorsal root ganglia (DRG) (16,22). A severe and debilitating complication of herpes zoster is postherpetic neuralgia, which involves chronic pain persisting for months or years following the initial herpes zoster attack (21,14). It has been proposed that the pain associated with herpes zoster and postherpetic neuralgia is due to neural tissue destruction caused by VZV reactivation (35,36). However, we recently reported that VZV-infected neurons, but not VZV-infected human fibroblasts (HF), were resistant to apoptosis (20), suggesting that neuronal destruction in vivo may be a corollary of the host cell immune response. This neuron-specific antiapoptotic function could increase the ability of VZV to efficiently establish latency and allow augmented virion production for axonal transport to the skin and reactivation as zoster lesions.Other alphaherpesviruses, i.e., herpes simplex virus type 1 (HSV-1) and bovine herpesvirus type 1, express latency-associated transcripts and the latency-related gene, respectively, during latent infection of neurons (10,11,13,32,33,34). Both of these have been shown to promote neuronal survival by an antiapoptotic mechanism in the event of induced apoptosis (1,6,16,18,27,31), although VZV does not encode a known homolog of either gene. However, during productive infection HSV-1 expresses a number of o...

Varicella-Zoster Virus (VZV) Infection of Neurons Derived from Human Embryonic Stem Cells: Direct Demonstration of Axonal Infection, Transport of VZV, and Productive Neuronal Infection

“…The only previous report, to our knowledge, using hESC-derived neural cells for study of viral infection was one using hESC-derived oligodendrocyte precursors as a model for studying neural infection by the polyomavirus JC virus (23). In contrast to previous in vitro studies using human fetal ganglia or dissociated neurons (8,9,10), our use of GFP-expressing VZV allowed immediate, live observation of infection of neurons. In preliminary experiments we have also observed infection of these hESC-derived neurons by two additional GFPlabeled herpesviruses, pseudorabies virus (PRV) and HSV-1 (data not shown), suggesting that this model is useful for study of other members of Herpesviridae.…”

“…Two in vitro models are VZV infection of dissociated human neurons and intact human fetal dorsal root ganglia (DRG) (8,9,10). These studies have shed some light on VZV-neuronal interactions, demonstrating, for example, that VZV exerts antiapoptotic activities in neurons in the short term (maximum, 5 days) and that, unlike infected fibroblasts, infectious VZV is released from neurons.…”

Two alphaherpesvirus latency-associated gene products influence calcitonin gene-related peptide levels in rat trigeminal neurons

“…There is evidence from previous studies that LAT promotes neuronal survival in a variety of neuronal cell types (Perng et al, 2000;Thompson and Sawtell, 1997). A recent study has shown that the VZV IE63 protein decreases apoptosis in rat DRG neurons (Hood et al, 2006). Further, recent data from our laboratories indicate that the presence of LAT has effects on axonal regeneration and dendritic growth, whereas VZV IE63 does not (unpublished data).…”

“…Varicella-zoster virus (VZV) is another member of the alphaherpesvirus family that establishes latency in dorsal root ganglia (DRG) and to a lesser extent trigeminal neurons (LaGuardia et al, 1999). There is evidence that the expression of the IE63 protein of VZV also promotes neuronal survival (Hood et al, 2006). However, there is currently no evidence that either LAT or IE63 affect other functional properties of the latently infected neurons.…”

A comparison of herpes simplex virus type 1 and varicella-zoster virus latency and reactivation

“…During productive infection, the highly phosphorylated protein (Mueller et al, 2010) is predominantly located in the nucleus (Mueller et al, 2009). In tissue culture cells, VZV IE63 represses transcription (Di Valentin et al, 2005), most likely through histone modification (Ambagala et al, 2009), as well as reducing translation in response to IFN induction (Ambagala & Cohen, 2007); however, in human ganglia the presence of VZV IE63 is yet to be confirmed, but may function to inhibit VZV-induced apoptosis (Hood et al, 2006;Pugazhenthi et al, 2011).…”