PROJECT SUMMARY/ABSTRACT Type 1 diabetes (T1D) results from an autoimmune-mediated destruction of pancreatic β-cells and affects approximately 3 million people in the United States and 10–20 million worldwide. The rapidly increasing incidence of T1D, as much as 3-5% per year, is of great concern. Although autoimmune-mediated β-cell destruction is the major cause of T1D, emerging data suggest that intrinsic β-cell stress, defective adaptive stress responses, and β-cell dedifferentiation can contribute to the loss of functional β-cell mass not only in T2D, but also in T1D. Despite these intriguing findings, mechanisms by which β-cells recover from stress and restore their function and identity remain largely unknown, and there is an urgent need to address this critical gap in knowledge to improve the therapeutic options of patients with diabetes. We recently reported that deletion of the key stress response sensor, IRE1α, in β-cells of non-obese diabetes (NOD) mice (IRE1αβ-/-), leads to transient β-cell dedifferentiation. Interestingly, these mice recover from stress and are protected from T1D. IRE1αβ-/- mice serve as an excellent model to study how β-cells adapt to stress and restore their identity and function under stress conditions. Ample data show that cellular stress triggers numerous adaptive responses, including metabolic rewiring. Consistent with this observation, our preliminary data obtained from this model showed significant alterations in metabolism and mitochondrial morphology. Based on our preliminary data, we hypothesize that stress adaptation in β-cells is governed by metabolic reprogramming and mitochondrial remodeling. To test this hypothesis, we propose the following specific aims: Aim 1: Identify the temporal dynamics and regulation of mitochondrial processes and bioenergetics in β-cells of IRE1αβ-/- mice: (1) Through imaging, and metabolic flux analyses at different states of differentiation, we will examine mitochondrial respiration and fusion, and (2) unravel the regulation of key fusion genes and the activity of the master regulator of respiration in β-cells of IRE1αβ-/-. Aim 2: Determine the role of metabolic reprogramming and mitochondrial remodeling in identity, function, and stress recovery of β-cells of IRE1αβ-/- mice. We will genetically and pharmacologically (1) alter the metabolic state in stressed islets from T1D animal models, (2) modulate the mitochondrial dynamics in stressed β-cells of IRE1αβ-/- mice ex vivo, and then examine β-cell function, identity, and survival in these systems. Aim 3: Elucidate the effects of metabolic alterations on β- cell redifferentiation and function in a mouse model of T2D and human islets. To complement our studies with the NOD model, we will perform the experiments from Aim 2, in β-cells of leptin-deficient obese ob/ob mice (a model of T2D), and in islets from T2D donors. This work will define the role of oxidative metabolism and mitochondrial dynamics in stress adaptation, mainten...