Activation of Interferon-Stimulated Genes following Varicella-Zoster Virus Infection in a Human iPSC-Derived Neuronal In Vitro Model Depends on Exogenous Interferon-α

Abstract

Varicella-zoster virus (VZV) infection of neuronal cells and the activation of cell-intrinsic antiviral responses upon infection are still poorly understood mainly due to the scarcity of suitable human in vitro models that are available to study VZV. We developed a compartmentalized human-induced pluripotent stem cell (hiPSC)-derived neuronal culture model that allows axonal VZV infection of the neurons, thereby mimicking the natural route of infection. Using this model, we showed that hiPSC-neurons do not mount an effective interferon-mediated antiviral response following VZV infection. Indeed, in contrast to infection with Sendai virus, VZV infection of the hiPSC-neurons does not result in the upregulation of interferon-stimulated genes (ISGs) that have direct antiviral functions. Furthermore, the hiPSC-neurons do not produce interferon-α (IFNα), a major cytokine that is involved in the innate antiviral response, even upon its stimulation with strong synthetic inducers. In contrast, we showed that exogenous IFNα effectively limits VZV spread in the neuronal cell body compartment and demonstrated that ISGs are efficiently upregulated in these VZV-infected neuronal cultures that are treated with IFNα. Thus, whereas the cultured hiPSC neurons seem to be poor IFNα producers, they are good IFNα responders. This could suggest an important role for other cells such as satellite glial cells or macrophages to produce IFNα for VZV infection control.

Lack of strong innate immune reactivity renders macrophages alone unable to control productive Varicella-Zoster Virus infection in an isogenic human iPSC-derived neuronal co-culture model

“…A previously established hiPSC-derived neural stem cell line (hiPSC-NSC) ( 25 ) was differentiated to obtain Tuj1 + NeuN + peripherin + neurons, according to the protocol described in our earlier work ( 9 ). In brief, expanded hiPSC-NSC were grown onto poly-L-ornithine (20 µg/ml, Sigma) and laminin (10 µg/ml, Sigma)-coated well plates in neuronal differentiation medium (Neurobasal Plus medium (Gibco), 1 × B27 plus supplement (Gibco), 2 mM L-glutamine (Gibco), 1 × CultureOne supplement (Gibco), 200 µM ascorbic acid (Sigma), 1% PS (Gibco), 10 ng/ml recombinant human brain-derived neurotrophic factor (rhBDNF) and recombinant human glial cell line-derived neurotrophic factor (rhGDNF) (Immunotools)) for a minimum of 21 days.…”

“…Nevertheless, many key aspects of the VZV-neural cell interaction remain incompletely understood. Unfortunately, the human-tropic nature of VZV and the lack of small animal models able to evoke a response to VZV that is fully equivalent to that in humans complicate our understanding of its neurobiology ( 5 , 9 ). In vitro , the scarce availability and inherent variability of primary human neural tissue have been hampering progress in VZV research.…”

“…In a previous study by our group, a compartmentalized hiPSC-derived neuronal model of VZV infection was developed to evaluate neuronal type-I IFN response following VZV infection ( 9 ). Although Sen and colleagues point to the superior potency of the type-II IFN response (IFN-γ) in the control of VZV infection ( 15 ), both experimental and clinical observations also illustrate the importance of the type-I IFN response (IFN-α/β) during the early infection stages ( 6 , 16 ).…”

“…In fact, many immunodeficiencies associated with severe VZV infections affect type-I IFN signaling pathways ( 16 , 17 ). We showed that while hiPSC-neurons adequately respond to exogenous IFN-α treatment by the production of interferon stimulated genes (ISGs) and the reduction of VZV replication and spread, they do not produce detectable levels of IFN-α2 or upregulate ISGs by themselves upon infection with VZV ( 9 ). We therefore hypothesized the potential role of circulating innate immune cells in the production of type-I IFNs that could limit neuronal VZV infection.…”

Unraveling the immune signature of herpes zoster: Insights into pathophysiology and the HLA risk profile

“…Following VZV infection, VZV is immediately sensed by the innate immune system via pattern-recognition receptors (PRRs) like RNA Polymerase III [15][16][17][18][19]. Subsequent activation of downstream pathways leads to the production of type I IFNs and proinflammatory cytokines that inhibit viral replication and recruit inflammatory cells to the site of infection [16,20]. Binding of these type I IFNs to their receptor ultimately leads to the induction of a large range of interferon-stimulated genes (ISGs) with direct antiviral effector functions [21].…”