An AGS associated mutation causes cellular RNA editing deficiency in mouse brain which lead to IFN pathway activation, mimicking the interferonopathy of patient brains

Abstract

Abstract Objective: To determine whether and how a gene mutation found in Aicardi-Goutières syndrome (AGS), a severe autoimmune encephalopathy, is sufficient to activate the interferon signaling pathway in the brain. Background: Genetic mutations in six coding genes were found associated with AGS patients, however, none of them was demonstrated able to cause IFN pathway activation in the brain tissue, the most critical pathogenetic change of AGS. How an AGS-associated mutation activates the IFN pathway in the brain that leads to brain injury remains to be revealed. Methods: A knock-In mouse model was established through CRISPR/Cas9 gene editing approach, in which a single G>T nucleotide replacement was introduced into mouse genome, that encodes the change for p.K948N in mouse ADAR1 at its catalytic domain, equivalent to the p.K999N mutation found in AGS patients. We analyzed the enzyme activity of ADAR1 on the neuron specific mRNA substrates in the KI mice through RNA sequencing, the activities of IFN signaling pathway by measuring expressions of IFN stimulated inflammatory cytokines. Brain injury was observed by pathology studies. Results: The genetic mutation was confirmed. RNA transcription and protein translation were tested not affected by the mutation. The cellular RNA process in neurons was altered due to decreased enzyme activity of mutant ADAR1 on certain mRNA substrates. ISG expression were significantly increased at RNA and protein levels. Cell death in the brain was observed in the KI mice. Conclusion: A mouse model was successfully established recapitulating the genetic and innate immunologic features of AGS. An ADAR1 gene mutation is sufficient to cause IFN pathway activation in the brain through altering cellular RNA process.