ADAR1 mutation causes ZBP1-dependent immunopathology

The RNA editing enzyme ADAR1 is essential for suppression of innate immune activation and pathology caused by aberrant recognition of self-RNA, a role it carries out by disrupting the duplex structure of endogenous double-stranded RNA species. A point mutation in the Z-nucleic-acid binding domain (ZBD) of ADAR1 is associated with severe autoinflammatory disease. ZBP1 is the only other ZBD-containing mammalian protein and its activation can trigger both cell death and transcriptional responses via the kinases RIPK1 and RIPK3, and the protease caspase-8. Here, we show that the pathology caused by ADAR1 ZBD mutation is driven by activation of ZBP1. We found that ablation of ZBP1 fully rescued the overt pathology caused by ADAR1 mutation, without reversing the underlying inflammatory program caused by this mutation. While loss of RIPK3 partially phenocopied the protective effects of ZBP1 ablation, combined deletion of caspase-8 and RIPK3, or of caspase-8 and MLKL, unexpectedly exacerbated the pathogenic effects of ADAR1 mutation. These findings indicate that ADAR1 is a negative regulator of sterile ZBP1 activation, and that ZBP1-dependent signaling underlies the autoinflammatory pathology caused by mutation of ADAR1. Comparative gene expression in spleens of 23 day old mice of ADAR P195A/p150- mutants and PKR and ZBP1 knockouts.RNA编辑酶ADAR1对于抑制先天免疫激活及异常识别自身RNA所诱发的病理过程至关重要，其通过破坏内源性双链RNA分子的双链结构来发挥该功能。ADAR1的Z型核酸结合结构域（Z-nucleic-acid binding domain，ZBD）存在点突变，该突变与严重自身炎症性疾病相关。ZBP1是目前已知唯一另一种含ZBD的哺乳动物蛋白，其激活可通过激酶RIPK1、RIPK3及半胱天冬酶-8（caspase-8）同时触发细胞死亡与转录应答。本研究证实，ADAR1 ZBD突变引发的病理过程由ZBP1激活所驱动。我们发现，敲除ZBP1可完全挽救ADAR1突变导致的显性病理表型，却无法逆转该突变所诱发的核心炎症程序。尽管RIPK3缺失可部分重现ZBP1敲除的保护效应，但联合敲除半胱天冬酶-8与RIPK3，或是联合敲除半胱天冬酶-8与MLKL，却意外加剧了ADAR1突变的致病效应。上述研究结果表明，ADAR1是无菌性ZBP1激活的负调控因子，且依赖ZBP1的信号通路是ADAR1突变引发自身炎症性病理的核心机制。本研究对23日龄ADAR1 P195A/p150-突变小鼠、PKR敲除小鼠及ZBP1敲除小鼠的脾脏组织开展了比较基因表达分析。