PROJECT SUMMARY Diabetes affects over 400 million people worldwide and there is still no cure. Islets of Langerhans in the pancreas contain the insulin producing β-cell which helps maintain blood glucose homeostasis. β-cells are excitable cells that respond to high glucose by releasing insulin. These cells coordinate their behavior through electrical activity. Cell-cell communication occurs through gap junctions between β-cells that allow a wave of depolarization to propagate across the islet. Despite this coordinated response to glucose, β-cells show significant functional variability. Various subpopulations have been identified that show distinct functional characteristics and are altered in type 2 diabetes (T2D). It is unknown how these subpopulations interact and affect multicellular islet dynamics. My overall goal is to understand the physiological importance of β-cell heterogeneity and whether disruptions to this heterogeneity contribute to islet decline. To accomplish this goal, I will use live cell fluorescence microscopy of primary human islets and computational models. Computational models can overcome limitations associated with cell lines, murine models, and human tissue. These experimental systems are used extensively to study islet function, but there are limitations to the extent of perturbation that can be introduced to these systems. The electrophysiology of the islet follows well-defined physical principles that lends itself to modeling. Using well-defined mathematical principles to explain experimental data, we can make predictions that guide future research. In this project, I will test the overall hypothesis that a large proportion of electrically-coupled, metabolically functional β-cells are required for proper calcium dynamics of the intact human islet. My first aim will use primary human islets, photopharmacology, and image analysis to characterize human β-cell subpopulation activity and metabolism in intact islets from healthy and T2D individuals. My second aim will use a computational model of human islet electrophysiology to investigate how β-cell subpopulations contribute to islet function. The outcomes of this project will lead to a better understanding of how each subpopulation contributes to the function of the islet and which β-cells are required for islet function. This will be valuable for developing more targeted therapies for diabetes that help preserve specific populations of β-cells in order to maintain islet dynamics under disease conditions. This will also help guide stem cell differentiation protocols to create higher functioning β-cell clusters. These novel treatments will help to slow the progression of diabetes and improve the quality of life for those living with this disease.