349-OR: Reduction of RNA-Editing Enzyme ADAR1 in Human Islets Triggers an Interferon Response and Impairs Beta-Cell Function

Introduction & Objective: It is thought that viral infection triggers islet inflammation, an interferon signature, and autoimmunity resulting in type 1 diabetes. Despite extensive research, an inciting virus has not been identified. We hypothesized that impaired RNA editing and accumulation of double-stranded RNA in beta cells triggers an interferon response, causing islet inflammation, autoimmunity, and beta cell destruction. While RNA editing regulated by adenosine deaminases acting on RNA (ADAR) has been studied in some organs and in cancer, little is known about the role of ADAR in human islets.

Method: To elucidate the role of ADAR1 in human islets, we first studied ADAR expression and distribution in human pancreas across postnatal developmental timeline (1 day, 4 months, 2, 6, 10, 35 years). Then we transduced human pseudoislets with a shRNA for ADAR and examined their function and gene expression. The transduced pseudoislets were also transplanted into NSG mice. Insulin secretion was measured and grafts were studied.

Results: We found that ADAR1 expression at all ages was greater in endocrine cells than acinar cells. Using the shRNA approach, ADAR mRNA levels were reduced by 70% (n=11 donors). After 7-day culture, expression of dsRNA sensors, IFNB1, IRF7, IRF9, and interferon-stimulated genes was increased while INS and MAFA expression was reduced in ADAR knockdown islets without changes in insulin secretion. However, 3 weeks post transplantation, glucose/arginine-stimulated human insulin secretion was significantly decreased in mice with the ADAR shRNA graft compared with scrambled shRNA control graft (0.117 vs 0.300 ng/mL, p=0.0001, n=3 donors). Analysis of pseudoislet grafts 4 weeks after transplantation showed marked accumulation of mouse CD45⁺ cells around ADAR-knockdown islet grafts.

Conclusion: Interruption of RNA editing in human islets activates the interferon signaling pathway leading to islet inflammation and beta cell dysfunction.