The ADAR G1007R mutation in Aicardi-Goutières Syndrome causes neuroinflammation through RNA sensing signaling pathways in mice
The ADARG1007R mutation is one of the most frequent mutations found in type six Aicardi-Goutières Syndrome (AGS), a progressive inflammatory encephalopathy in pediatric patients, typically begins to manifest  in newborns or infants. Due to the rarity of this disease and the limited accessibility of the human brain tissues, the pathologic features and the underlying mechanism of this mutation has not been well understood.  In this study, we generated a genetic mutant mouse model which successfully recapitulated the genetic and pathologic features of human ADARG1007R AGS, including the early-onset brain inflammatory reaction in heterozygous mutant mice and the deep gray matter area ISG expression. Through analysis of the homozygous ADARG1007R/G1007 mice, we found that the G1007R mutation interrupts the RNA splicing donor site in the RNA transcripts that alters ADAR1 RNA splicing, leading to depletion of ADAR1 protein and embryonic death. Furthermore, we demonstrated that the brain inflammation could be reversed by deletion of the cellular RNA receptor MDA5 which blocks the cellular RNA sensing signaling pathway. Collectively, this study generated a clinically relevant AGS animal model, revealed the molecular mechanism of the ADARG1007R mutation in AGS, and demonstrated that the MDA5-dependent RNA sensing signaling pathway plays a critical role in neuroinflammation. Overall design: All mice used in this study were kept in a specific pathogen-free animal facility and all studies were carried out following protocols approved by our Institutional Animal Care and Use Committee. The G1007R mutation was introduced into the mouse genome using our CRISPR/Cas9 protocol as described previously. Considering the genetic diversity of human diseases of ADAR1 mutations, mice used in this study, including AdarG1007R/G1007R and AdarG1007R/G1007R; Ifih1-/- mice, were purposely maintained in C57/BL6J and DBA2 mixed background. Three repeats for wild-type (WT), three repeats for G1007R mutant, and three repeats for G1007R mutatant + MDA5 retreat