Investigating IRG1-driven regulation of flavivirus-induced neuroinflammation

Project Summary/ Abstract The goal of this proposal is to investigate the anti-viral and anti-inflammatory roles of the metabolite, itaconate, in the central nervous system (CNS), during Zika virus (ZIKV)-encephalitis. ZIKV is an emerging mosquito-borne flavivirus of global concern. In the recent epidemic, ZIKV infection in adults was associated with a range of neurological disorders such as Guillain-Barré syndrome, encephalitis, and Myasthenia Gravis. These pathologies are largely thought to be a consequence of ZIKV tropism for neurons and neural progenitor cells. As such, there has been an intense effort to study ZIKV-immunity in the CNS. Recently our lab discovered a neuron intrinsic anti-viral defense mechanism against ZIKV infection, whereby infected neurons induce the expression of the mitochondrial enzyme IRG1. Here, IRG1 and its metabolic product itaconate, remodel neuronal metabolism to inhibit viral replication. Our study also found that Irg1-/- mice are highly susceptible to infection, but whether this phenotype is strictly due to the role of neuronal-itaconate or concurrent involvement of glia- derived itaconate remains unknown. Itaconate has garnered significant attention as an immunomodulatory metabolite in myeloid cells. Specifically, itaconate has been shown to be an indispensable immunoregulatory metabolite necessary to limit inflammation in bacterial models of infection. Moreover, published work has shown itaconate to be secreted by macrophages, implying the potential for itaconate to act in a non-cell-autonomous manner. Preliminary data generated in our lab using a model of ZIKV-encephalitis revealed that mice lacking Irg1 have significant leukocyte infiltration in the brain compared to WT mice, data supporting the anti-inflammatory role of itaconate. However, this effect was not a result of increased inflammatory gene transcription in ZIKV-infected neurons, implying a neuron-extrinsic source of itaconate necessary to regulate neuroinflammation. Notably, resting microglia, the resident macrophages of the CNS, express high levels of Irg1, suggesting to us that this cell type might also be a key source of itaconate during ZIKV-infection. Therefore, based on preliminary data, we hypothesize that microglia-derived itaconate acts as an antiviral and anti-inflammatory mediator during ZIKV- encephalitis. Specifically, we hypothesize that microglia-derived itaconate signals to neurons in trans to limit both viral replication and neuroinflammation in a non-cell-autonomous manner.