.The islet of Langerhans is a multi-cellular micro-organ located in the pancreas. It is central to maintainingblood glucose homeostasis through secretion of hormones such as insulin and glucagon. Interactions betweencells in the islet are crucial to the regulation of glucose stimulated insulin secretion (GSIS). Beta cells withinthe islet secrete insulin with a many-fold increase in GSIS response compared to isolated beta cells.Furthermore beta cells in the islet exhibit synchronized oscillations which lead to pulsatile insulin from thewhole pancreas. These coordinated insulin pulses are thought to be more effective in lowering blood glucoseand maintaining insulin sensitivity. The importance of the structure and signaling within the islet is highlightedby the fact that type 1 diabetes can be effectively reversed by the transplantation of intact islets (but not byisolated beta cells). Previous research and preliminary data shows that gap junction coupling has aphysiological role in islet function. However other research has also shown possible roles for paracrine andjuxtacrine mechanisms in cell-cell communication. We hypothesize that it is primarily gap junction coupling ofelectrical activity which serves to coordinate and enhance GSIS, but coupling of cAMP mediated signalingbetween alpha and beta cells within the islet can further modulate GSIS. To test this hypothesis it will benecessary to introduce precise experimental perturbations, and use quantitative techniques to monitor theresulting impact on signaling pathways underlying GSIS. During the mentored phase of this proposal we willestablish the necessary physiological and biochemical assays, as well as to refine the quantitativemathematical models currently in use.
Two specific aims are then proposed for the independent researchphase: 1) quantify the relative role of gap junction coupling and KATP channel regulated membrane polarizationin regulating GSIS, 2) determine the mechanism and role for coupling of cAMP signaling between beta cellsand alpha cells within the islet. These two aims can proceed independently, although the results from eachaim will be complimentary to testing the overall hypothesis. Experiments will be performed on a number of gapjunction knockout and KATP channel transgenic mouse models as well as human islets, and will utilize state-of-the art quantitative imaging approaches, fluorescent protein biosensors and mathematical models along withmore established biochemical and physiological assays. These experiments will yield a more completeunderstanding of signaling mechanisms within the islet which will be important for the development oftransplantation and stem cell therapies for type1 diabetes as well as identifying novel therapeutic drug targetsfor type2 diabetes.
. The pancreatic islet plays a central role in glucose homeostasis and the failure of the islet leads to the development of diabetes. Communication between cells is crucial to the function of the islet, but knowledge of the mechanisms involved is unclear. A precise understanding of the signaling between different cells within the islet will improve the development of transplantation and stem cell therapies and identify drug targets to effectively treat individuals with diabetes.
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