ATF4-mediated transcriptional regulation protects against -cell loss during endoplasmic reticulum stress in a mouse model

Objective: Activating transcription factor 4 (ATF4) is a transcriptional regulator of the unfolded protein response and integrated stress response (ISR) that promote the restoration of normal endoplasmic reticulum (ER) function. Previous reports demonstrated that dysregulation of the ISR led to development of severe diabetes. However, the contribution of ATF4 to pancreatic 13-cells remains poorly understood. In this study, we aimed to analyze the effect of ISR enhancer Sephin1 and ATF4-deficient 13-cells to clarify the role of ATF4 in 13-cells under ER stress conditions. Methods: To examine the role of ATF4 in vivo, ISR enhancer Sephin1 (5 mg/kg body weight, p.o.) was administered daily for 21 days to Akita mice. We also established 13-cell-specific Atf4 knockout (13Atf4-KO) mice that were further crossed with Akita mice. These mice were analyzed for characteristics of diabetes, 13-cell function, and morphology of the islets. To identify the downstream factors of ATF4 in 13-cells, the islets of 13Atf4-KO mice were subjected to cDNA microarray analyses. To examine the transcriptional regulation by ATF4, we also performed in situ PCR analysis of pancreatic sections from mice and ChIP-qPCR analysis of CT215 13-cells. Results: Administration of the ISR enhancer Sephin1 improved glucose metabolism in Akita mice. Sephin1 also increased the insulinimmunopositive area and ATF4 expression in the pancreatic islets. Akita/13Atf4-KO mice exhibited dramatically exacerbated diabetes, shown by hyperglycemia at an early age, as well as a remarkably short lifespan owing to diabetic ketoacidosis. Moreover, the islets of Akita/13Atf4-KO mice presented increased numbers of cells stained for glucagon, somatostatin, and pancreatic polypeptide and increased expression of aldehyde dehydrogenase 1 family member 3, a marker of dedifferentiation. Using microarray analysis, we identified atonal BHLH transcription factor 8 (ATOH8) as a downstream factor of ATF4. Deletion of ATF4 in 13-cells showed reduced Atoh8 expression and increased expression of undifferentiated markers, Nanog and Pou5f1. Atoh8 expression was also abolished in the islets of Akita/13Atf4-KO mice. Conclusions: We conclude that transcriptional regulation by ATF4 maintains 13-cell identity via ISR modulation. This mechanism provides a promising target for the treatment of diabetes. (c) 2021 The Author(s). Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Transcriptional regulation by ATF4 maintains β-cell identity via ISR modulation, providing a promising target for the treatment of diabetes.