ADAR1 interaction with Z-RNA promotes editing of endogenous double-stranded RNA and prevents MDA5-dependent immune activation.

Loss-of-function of ADAR1 causes the severe autoinflammatory disease Aicardi-Goutieres Syndrome (AGS). ADAR1 converts adenosines into inosines within double-stranded (ds) RNA. This process called A-to-I editing masks self-dsRNA from detection by the antiviral dsRNA sensor MDA5. ADAR1 binds to dsRNA in both the canonical A-form and in the poorly defined Z-conformation (Z-RNA). Mutations in the Z-RNA binding Z-domain of ADAR1 are common in AGS patients. How loss of ADAR1/Z-RNA interaction contributes to disease development is unknown. Using ADAR1 Z-domain mutant human cells and knock-in mice, we demonstrate that abrogated binding of ADAR1 to Z-RNA leads to reduced A-to-I editing of dsRNA structures formed by pairing of inversely oriented SINEs. As a result, ADAR1 Z-domain mutant human cells and transgenic mice develop a spontaneous MDA5-dependent immune response. This shows that the interaction between ADAR1 and Z-RNA restricts sensing of self-dsRNA and prevents AGS development.