Interferon (IFN) induction and signaling is an early antiviral response that can be triggered by viral double- stranded (ds)RNA. While critical to limiting viral replication and spread, overexpression of the IFN response can be detrimental to human health. For example, Aicardi-Goutires syndrome (AGS) is a severe autoimmune, neurodevelopmental and inflammatory disease, caused by mutation of any of several genes involved in IFN production and signaling, characterized by excessive IFN (primarily IFN-?) production and signaling in the absence of virus infection. Mutation of the ADAR1 (adenosine deaminase acting on RNA) gene is one cause of AGS. ADAR1 destabilizes dsRNA, and mutations in the ADAR1 gene lead to accumulation of endogenous self-dsRNA and as a consequence chronic induction of IFN and other cytokines, leading to cell death and damage primarily to the central nervous system (CNS) and the skin. Studies in mouse models have shown that Adar1 knockout (KO) is embryonic lethal and can be rescued by KO of genes encoding proteins involved in IFN production (MDA5 or MAVS). However the downstream activities mediating lethality have not been identified nor have the pathological effects of Adar1 KO in the CNS been addressed in these mouse model systems. Thus, there is a gap in our understanding of where the IFN is generated, in the periphery and/or the CNS and in which cell types and how IFN signaling promotes CNS pathology. We recently found that the potent antiviral oligoadenylate synthetase (OAS)-ribonuclease (RNase) L pathway is induced by self-dsRNA in the absence of ADAR1 in uninfected human lung epithelial derived A549 cells and importantly that activation of RNase L is a dominant pathway leading to cell death. Moreover, we found that ADAR1 KO is also lethal in A549 cells and that lethality can be rescued by KO of RNase L or by MAVS. These data suggest that RNase L activity may play a role in promoting cell death and CNS damage in AGS patients and/or in mouse models. We will utilize our expertise in IFN response during neurotropic coronavirus infection in a mouse model and our recent findings on endogenous dsRNA induction of RNase L in human A549 cells to test the following hypothesis : In the absence of Adar1 gene expression, endogenous dsRNA induces IFN in the periphery and/or in the CNS, leading to an IFN signaling response and activation of RNase L resulting in cell death and CNS pathology. We will use a novel approach centered on tamoxifen inducible Adar1 KO in Adar1fl/flERT2Cre mice and cell type specific Adar1 KO mice to ablate Adar1 expression in vitro in primary CNS cell cultures and in vivo in mice. We will 1) compare cytokine production, RNase L activation and cell death in primary murine CNS cells as well as myeloid cells following Adar1 ablation in vitro and 2) investigate the role of the blood brain barrier and the cell type specific role of ADAR1 in controlling CNS pathogenesis in vivo. These findings will contribute toward understanding the impact of endogenous dsRNA in promoting CNS pathology and in the long term will aid in identifying targets for therapy of AGS.
While critical to limiting viral replication and spread, overexpression of interferon (IFN) and its downstream signaling response can be damaging to the central nervous system (CNS). These studies will identify the cellular source(s) of IFN induced by endogenous self double-stranded RNA in the absence of ADAR1 RNA editing and indicate the extent to which RNase L activation contributes to CNS damage. The data obtained may contribute to identifying therapeutic strategies for interferonopathies, including Aicardi-Goutires syndrome .
