Abstract
Varicella Zoster Virus (VZV), the alphaherpesvirus that causes varicella upon primary infection and Herpes zoster (shingles) following reactivation in latently infected neurons, is known to be fusogenic. It forms polynuclear syncytia in culture, in varicella skin lesions and in infected fetal human ganglia xenografted to mice. After axonal infection using VZV expressing green fluorescent protein (GFP) in compartmentalized microfluidic cultures there is diffuse filling of axons with GFP as well as punctate fluorescence corresponding to capsids. Use of viruses with fluorescent fusions to VZV proteins reveals that both proteins encoded by VZV genes and those of the infecting cell are transferred in bulk from infecting non-neuronal cells to axons. Similar transfer of protein to axons was observed following cell associated HSV1 infection. Fluorescence recovery after photobleaching (FRAP) experiments provide evidence that this transfer is by diffusion of proteins from the infecting cells into axons. Time-lapse movies and immunocytochemical experiments in co-cultures demonstrate that non-neuronal cells fuse with neuronal somata and proteins from both cell types are present in the syncytia formed. The fusogenic nature of VZV therefore may enable not only conventional entry of virions and capsids into axonal endings in the skin by classical entry mechanisms, but also by cytoplasmic fusion that permits viral protein transfer to neurons in bulk.
Highlights
Varicella Zoster Virus (VZV) is a ubiquitous pathogenic alphaherpesvirus, causing varicella upon primary infection and Herpes zoster following reactivation from a latent state that was established in sensory and autonomic neurons upon primary infection
We have previously shown that human embryonic stem cells-derived neurons can be infected with VZV and support in vitro productive replication [9]
In order to first confirm the rapid appearance of green fluorescent protein (GFP) in axons after contact with VZV-infected non neuronal cells with a different recombinant virus, we seeded MeWo cells infected with VZV-GFP, a recombinant virus that expresses GFP driven by an independent SV40 promoter [13], into the axonal compartment of microfluidic chambers (Fig 1A) and monitored the cultures for GFP fluorescence (Fig 1B)
Summary
Varicella Zoster Virus (VZV) is a ubiquitous pathogenic alphaherpesvirus, causing varicella upon primary infection and Herpes zoster (shingles) following reactivation from a latent state that was established in sensory and autonomic neurons upon primary infection. VZV is a highly fusogenic virus, and productively infected cells frequently form multinucleate syncytia. Direct Protein Transfer from VZV-Infected Cells to Axons vision research, https://www.nei.nih.gov/funding/p30, EY08098, PRK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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