Induction of varicella zoster virus DNA replication in dissociated human trigeminal ganglia

Abstract

Varicella zoster virus (VZV), a human neurotropic alphaherpesvirus, becomes latent after primary infection and reactivates to produce zoster. To study VZV latency and reactivation, human trigeminal ganglia removed within 24 h after death were mechanically dissociated, randomly distributed into six-well tissue culture plates and incubated with reagents to inactivate nerve growth factor (NGF) or phosphoinositide 3-kinase (PI3-kinase) pathways. At 5 days, VZV DNA increased in control and PI3-kinase inhibitor-treated cultures to the same extent, but was significantly more abundant in anti-NGF-treated cultures (p = 0.001). Overall, VZV DNA replication is regulated in part by an NGF pathway that is PI3-kinase-independent.

Herpesviral Latency—Common Themes

“…Thus, withdrawal of NGF from latently infected cultures leads to reactivation of the lytic cycle [252,253]. Inhibition of NGF signaling also induces VZV DNA production in axotomized cadaver ganglia [254]. Recently, it was shown, that NaBu, is able to reactivate alphaherpesviruses in cell culture [255,256].…”

Molecular Aspects of Varicella-Zoster Virus Latency

“…The nerve growth factor (NGF) receptor, TrkA, is expressed by a subpopulation of sensory neurons and signals via the PI3K-Akt and MAPK pathways [ 135 ], and depletion of NGF from VZV-latently infected neurons can lead to the reactivation of VZV in some in vitro latency systems [ 56 , 97 ]. The role of NGF signalling in contributing to the maintenance of VZV latency has been confirmed in VZV-latently infected human TG removed within 24 h after death [ 136 ]. Intriguingly, the effect of chemical PI3K blockade on VZV reactivation depends on the experimental conditions, as PI3K inhibition did not reactivate VZV in ex vivo cultures of naturally infected human TG neurons [ 136 ] and variable effects have been obtained in hESC-derived neurons [ 56 , 97 ].…”

“…The role of NGF signalling in contributing to the maintenance of VZV latency has been confirmed in VZV-latently infected human TG removed within 24 h after death [ 136 ]. Intriguingly, the effect of chemical PI3K blockade on VZV reactivation depends on the experimental conditions, as PI3K inhibition did not reactivate VZV in ex vivo cultures of naturally infected human TG neurons [ 136 ] and variable effects have been obtained in hESC-derived neurons [ 56 , 97 ]. NGF depletion results in the phosphorylation and activation of the MAPK family member, c-Jun N-terminal kinase (JNK) and is critical for efficient VZV replication in hESC neurons.…”

“…It is now critical to determine the roles of (and potential interplay between) VLT and ORF63 RNA in latently infected short-PMI human TG [ 106 ] and to analyse their functions in the establishment of quiescence in human pluripotent stem cell (hPSC; hESC/hiPSC)-derived neuronal models [ 56 , 97 , 160 , 161 ] or in the reactivation from latency using these same models and/or ex vivo cultures of dissociated naturally VZV-infected human ganglia [ 136 ]. Human TG are composed of diverse subtypes of neurons [ 162 ], and not all neuronal subpopulations may be equally susceptible to VZV infection [ 140 ], as has been shown for HSV-1 [ 163 , 164 ].…”

“…Local immune responses mediated by VZV-specific T RM in skin [ 156 , 166 ] or ganglion, or neuron-interacting SGC [ 143 , 144 ] are likely to be pivotal factors controlling VZV reactivation, e.g., by secreting IFNs to block early reactivation attempts [ 167 ]. The recently developed in vitro and ex vivo models to study VZV reactivation [ 56 , 97 , 136 , 160 , 161 ] facilitate systematic analysis of the signalling pathways modulating viral latency, and could be used to investigate the roles of non-neuronal cells and their secreted antiviral factors in this process.…”