PROJECT SUMMARY / ABSTRACT Type 2 Diabetes (T2D) is a global health pandemic that results from a combination of defective insulin secretion and impaired insulin action in the peripheral tissues. T2D typically arises in the context of obesity and overnutrition; however, genetic and physiologic data suggest that inadequate insulin secretion from the cell is the chief determinant predicting the development of overt T2D. Recent studies have identified cell dedifferentiation, in which cells downregulate key identity markers, lose insulin secretory function, and differentiate into other endocrine cell types, as one potential mechanism leading to cell failure in T2D; however, the molecular mechanisms leading to cell dedifferentiation in T2D are not well understood. Calcium (Ca2+) plays a vital role in regulating cell health and function. In the cell, the endoplasmic reticulum (ER) serves as the dominant Ca2+ store, and store-operated Ca2+ entry (SOCE) functions to maintain robust ER Ca2+ levels. When ER Ca2+ is depleted, SOCE is activated by stromal interaction molecule 1 (STIM1), which promotes Ca2+ influx from the extracellular space to refill depleted ER Ca2+ stores. Recently our laboratory found that obese female mice with reduced SOCE due to cell-specific genetic deletion of STIM1 had evidence of cell dedifferentiation. Further, islets isolated from these mice had reduced G protein coupled estrogen receptor (GPER) mRNA and protein expression with no change in Estrogen Receptor or expression, suggesting a potential interaction between SOCE, GPER signaling, and cell identity. My preliminary data has extended these observations and linked loss of GPER and loss of estradiol signaling through GPER with loss of cell identity and potential cell dedifferentiation. Against this background, I hypothesize that decreased SOCE leads to reduced GPER signaling and loss of cell identity and function, thereby contributing to the pathophysiology of T2D in females. I will test this hypothesis through two specific aims. In Aim 1, I will define the role of GPER in cell differentiation status. In Aim 2, I will define the relationship between impaired SOCE and GPER function and expression/subcellular localization. Completion of this project has the potential to identify a novel mechanism linking SOCE and GPER signaling to cell failure during T2D. With this F30 Predoctoral Fellowship, I will have the support to complete this research and master the objectives of my training plan: 1) Create a strong foundation of techniques and concepts critical in diabetes research and islet biology, 2) Build strong technical skills in super-resolution nanoscopy, 3) Develop and refine my clinical skills, and 4) Create a strong foundation of written and oral scientific communication. My training will be supported by the experienced faculty provided by the Center for Diabetes and Metabolic Diseases at the Indiana University School of Medicine and the Purdue...