PROJECT SUMMARY/ABSTRACT Type 1 diabetes (T1D) results from autoimmune-mediated destruction of pancreatic β-cells. Despite its autoimmune etiology, emerging data suggest that intrinsic β-cell stress and defective adaptive stress responses can play an important role in the loss of functional β-cell mass in T1D. However, the molecular mechanisms by which the stress responses regulate β-cell death/survival in T1D have remained elusive, due primarily to a lack of in vivo preclinical genetic models, hindering the development of novel, effective, and alternative therapeutic strategies against T1D. Endoplasmic reticulum (ER) stress is caused by protein misfolding, chronic inflammation, and environmental factors. Upon ER stress, the unfolded protein response (UPR), a signaling cascade mediated by ER membrane-localized sensors ATF6, IRE1α and PERK, is triggered to re-establish cellular homeostasis. While these proteins induce adaptive responses under acute stress, under prolonged stress the UPR initiates apoptosis. The decision mechanisms for switching between adaptive and maladaptive responses, and the specific adaptive or maladaptive functions of each UPR sensors in distinct cell types and disease contexts, are yet to be uncovered. To this end, we have recently deleted Atf6 in β-cells (Atf6β-/-) of a well-established preclinical T1D model, non-obese diabetes (NOD) mice, before the initiation of islet inflammation. Remarkably, Atf6β-/- mice exhibited significantly reduced diabetes incidence . Transcriptome analysis of sorted β-cells of NOD Atf6β-/- mice revealed p53/p21 signaling pathway as the top enriched pathway and uncovered a previously not recognized pro-survival adaptative program in β-cells during T1D progression, which ultimately confers protection from T1D. Atf6β-/- mice also showed reduced insulitis and increased expression of immune inhibitory markers in β- cells, suggesting a non-cell autonomous effect of loss of function of Atf6 on the immune system. Therefore, in light of these data we hypothesize that upon loss of Atf6 in β-cells, a novel adaptive program governed by p21 signaling prevails, which in a non-cell autonomous manner alters β-cells-immune cell communication. Moreover, we hypothesize that under acute versus mild and prolonged stress conditions ATF6 triggers distinct transcriptional programs to regulate cellular homeostasis in human β-cells. Here, by utilizing a mouse model and human islets combined with a comprehensive toolbox of techniques and novel reagents we propose to (i) identify the mechanisms, by which loss of Atf6 in b-cells impact, b-cell-immune cell crosstalk (ii) define the mechanisms of p21 upregulation and reduced pathology in Atf6β-/- mice, and (iii) determine the ATF6-mediated stress adaptation mechanisms in human islets exposed to acute and prolonged ER stress. The successful completion of these studies will fill an existing gap in our knowledge base regarding the function of Atf6 in β-cells, identify a novel mechanism for β-cell-immune cell crosstalk, and significantly improve our understanding of mechanisms of β- cell failure in T1D. It will also provide mechanistic insight for future studies and support alternative translational strategies for T1D that target the b-cell UPR.

PROJECT NARRATIVE We have made the striking discovery that deletion of a key stress response gene, Atf6, in β-cells of a type 1 diabetes (T1D) preclinical model confers protection against T1D by inducing a previously not recognized multi- pronged pro-survival adaptative mechanism. We will investigate the regulation of β-cell-immune cell dialogue as well as the molecular mechanisms of diabetes protection in β-cell-specific Atf6-deficient mice and test the translatability of our work in stressed human islets. Our work will provide valuable insight on the molecular mechanisms of adaptive and maladaptive stress responses in β-cells during T1D progression and thus holds the potential to reveal new therapeutic strategies or targets for T1D.