RNA editing in islet function and inflammation

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RNA editing, a fundamental cellular process, involves the deamination of some adenosines in RNA to inosines, by the adenosine deaminases Adar1 (ADAR) and Adar2 (ADARB1). Recent studies have shown that a critical role of RNA editing is to disrupt double-stranded RNA (dsRNA) structures that are generated by retroelements inserted in the genome in an inverted orientation within expressed genes. The dsRNA formed by such sequence configurations is a powerful and dangerous activator of the ancient antiviral interferon response, which may lead to pathogenic inflammation. While RNA editing has been studied in the context of some organs and in cancer, very little is known about the role of ADAR enzymes in islet cell function and health. Our goal is to elucidate the role of RNA editing in islets, and particularly in alpha and beta cells. Strikingly, GWAS studies of type 1 diabetes (T1D) have revealed protective variants of IFIH1/MDA5, a cytosolic receptor that recognizes double-stranded RNA (dsRNA) from either viral or endogenous origins, and elicits an inflammatory response. Thus, defective RNA editing can in principle contribute to the islet anti-viral response which precedes autoimmunity. We hypothesize that impaired RNA editing and accumulation of endogenous dsRNA in beta cells trigger an IFIH1-dependent interferon response causing islet inflammation, which leads to beta cell dysfunction and potentially to autoimmunity. In our preliminary findings, we found that disruption of A-to-I RNA editing in adult mouse beta-cells in vivo or in human islets triggers an interferon response. In mice with Adar1-deficient beta cells, this leads to massive immune response localized to islets, including both innate immune cells and T cells. Alpha cells appear to resist Adar1 disruption or islet inflammation brought about by Adar1 deficiency in beta cells. We propose to 1) characterize mouse and human islet cells following genetic disruption of RNA editing, via knockout or knockdown of the key RNA editing enzyme Adar1; 2) examine the effects of Adar1 deficiency on beta and alpha cell function and viability, as well as islet inflammation and autoimmunity; and 3) investigate the molecular basis for the differential dependence of alpha and other islet cell types on Adart1. The proposed research is a close collaboration between 3 teams with complementary expertise: Al Powers (human islet biology and function), Yuval Dor (mouse models, molecular biology) and Erez Levanon (computational analysis of RNA editing). This work will shed light on the role of RNA editing, a key epitranscriptomic modification, in islet cells. It will also refute or provide pre-clinical support for the provocative hypothesis that defective RNA editing may contribute to aspects of T1D pathogenesis, particularly the early, anti-viral inflammatory response. 1