ELECTRICAL CONTROL OF INSULIN SECRETION

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DESCRIPTION (provided by applicant): Animals with reduced KATP channel activity (KATP loss-of-function, LOF) are hyperexcitable and initially hypersecrete insulin, but secondarily progress, either spontaneously or in response to dietary stress, to undersecretion and glucose- intolerance. In contrast, animals with overactive KATP channels (KATP gain-of-function, GOF) are underexcitable and initially undersecrete insulin, and then secondarily progress to profound loss of pancreatic insulin content, resulting in diabetes that can be severe enough to cause neonatal lethality. Based on our initial studies we predicted that KATP GOF mutations could underlie human neonatal diabetes (NDM) and this has been dramatically confirmed over the last five years: not only have KATP GOF mutations been shown to be the major cause of human NDM, but many patients have since successfully switched from injected insulin treatments to oral sulfonylureas, which act to block the KATP channel, thereby treating the molecular defect directly. Our second generation KATP GOF transgenic mice provide temporal and tissue-specific control of transgene expression and thereby provide a tractable experimental model of NDM (xNDM). In explaining and informing the response to ¿-cell underexcitability, our preliminary findings with these mice have potentially broad implications for fundamental mechanisms in both human NDM and type 2 diabetes. To pursue the implications, we will utilise our inducible transgenic KATP GOF animals to determine the response to ¿-cell underexcitability at the cellular and islet level using a combination of imaging and electrophysiological techniques. We will determine the treatability of experimental NDM at different stages, informing otherwise unaddressable issues in human NDM. We will determine the potential involvement of environmental and genetic modulators in the ¿-cell response to inexcitability at the whole animal level, and the role of electrical activity in modulating islet sensitivity to glucotoxicity in isolated islets from hyperexcitable (Kir6.2-/-, SUR1-/-) and underexcitable (tamoxifen-induced Pdx-DTG) animals. The proposed experiments will test mechanistic hypotheses of the role of electrical excitability in stimulus-secretion coupling in ¿-cells and in the etiology of different forms of diabetes and will provide mechanistic information that will impact treatment approaches to both neonatal and type 2 diabetes. PUBLIC HEALTH RELEVANCE: Diabetes is a major world health problem, characterized by a hyperglycemic state caused by depressed secretion of insulin, unresponsivity to circulating insulin, or a combination of both. We have generated unique mouse models of diabetes due to depressed secretion and the analysis of these animals led us to correctly predict that this is a major cause of neonatal diabetes in humans, as well as a risk factor for type 2 diabetes. The project makes use of these animals to understand the disease process in a way that is impossible in humans, and thereby helps us to develop appropriate therapies to treat the disease.