An AGS-associated mutation in ADAR1 catalytic domain causes early-onset and MDA5- dependent encephalopathy with IFN pathway activation in the brain

Abstract Background:Aicardi-Goutières syndrome (AGS) is a severe autoimmune disease characterized by inflammatory encephalopathy with an elevated Type 1 interferon-stimulated gene (ISG) expression signature in the brain. It is featured by early-onset encephalopathy and progressive loss of intellectual abilities and motor control. Gene mutations in 7 protein-coding genes were found to be associated with AGS. However, the causative role of these mutations in the early-onset neuropathogenesis has not been demonstrated in animal models, and the mechanism of neurodegeneration of AGS remains ambiguous.Methods:Via CRISPR/Cas-9 technology, we established a mutant mouse model in which a genetic mutation found in AGS patients at the ADAR1 coding gene loci was introduced into mouse genome. A mouse model carrying double gene mutations encoding ADAR1 and MDA-5 was prepared through breeding strategy. Phenotype, gene expression, RNA sequencing, innate immune pathway activation, and pathologic studies including RNA in situ hybridization (ISH) and immunohistochemistry (IHC) were used for characterization of the mouse models to determine the disease mechanisms.Results:We established a mouse model bearing a mutation in the catalytic domain of ADAR1, the D1113H mutation found in AGS patients. With this mouse model, we demonstrated a causative role of this mutation for the early-onset brain injuries in AGS and determined the signaling pathway underlying the neuropathogenesis. First, this mutation altered RNA editing profile in neural transcripts and led to robust IFN stimulated gene (ISG) expression in the brain. By in situ hybridization, the brain of mutant mice showed an unusual multifocal increased expression of ISGs that was cell-type dependent. An early onset astrocytosis and microgliosis, and later stage calcification in the deep white matter areas were observed in the mutant mice. Brain ISG activation and neuroglial reaction were completely prevented in the D1113H ADAR1 mutant mice by blocking RNA-sensing through deletion of the cytosolic RNA receptor MDA-5.Conclusions:The D1113H ADAR1 mutation causes RNA editing alteration in the brain, activating MDA5-dependent RNA sensing pathway activation and ISG expression, leading to the early-onset brain pathogenesis of AGS.