Two-Pore-Domain Potassium Channels as Novel Targets for Modulating Islet Hormone Secretion

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Insulin and glucagon secretion are disrupted in patients with type-2 diabetes mellitus (T2DM) and in animal models of the disease, which is due in part to perturbations in islet-cell Ca2+ homeostasis. While two-pore- domain K+ (K2P) channels are key regulators of pancreatic islet-cell Ca2+ handling and hormone secretion, there is a gap in our understanding of how these channels control human islet function and dysfunction under diabetic conditions. The long term goal of this research is to determine the therapeutic potential of targeting K2P channels for treating diabetes and preventing -cell destruction. The overall objective of this project is to elucidate molecular mechanisms regulating secretagogue dependent modulation of islet Ca2+ influx and hor- mone secretion via K2P channels. This project will test the central hypothesis that human islet K2P channels modulate cytoplasmic and endoplasmic reticulum Ca2+ handling, thus, regulating hormone secretion as well as the -cell ER-stress response under diabetic conditions. This project is supported by strong preliminary data that has identified TALK-1 as an important determinant of human and rodent -cell ER Ca2+ handling, mito- chondrial function, and insulin secretion. Further data that has determined that the TALK-1 related channel TALK-2 also controls ER Ca2+ homeostasis and is highly expressed in human islets. Finally, preliminary data finds that the K2P channels, TASK-1 and TALK-2, control -cell ER Ca2+ storage and glucagon secretion. The rationale that underlies the proposed research is that understanding how islet hormone secretion is influenced by K2P channel activity will expose novel therapeutic targets for reducing -cell failure and hyperglycemia dur- ing the pathogenesis of T2DM. This project will be accomplished with the following two specific aims: 1) De- termine how TALK-1 and TALK-2 channels modulate -cell function and dysfunction over time and under stress; and 2) Determine how TASK-1 and TALK-2 channels control of pancreatic -cell glucagon secretion. Under the first aim, the function of human-cell TALK channels will be assessed with a dominant negative (D/N) and ShRNA approach, which have been established as feasible in the applicants’ hands. Moreover, mice with inducible -cell ablation of TALK-1 will be utilized to test the influences of these channels on glucose ho- meostasis. The roles of -cell TALK channels will be assessed under physiological conditions as well as under the stressful conditions associated with diabetes in vivo and/or in vitro. Under the second aim, transgenic mice deficient for TASK-1 as well as a -cell specific D/N and ShRNA approaches will be utilized to assess the roles of TASK-1 during human and mouse -cell Ca2+ handling and glucagon secretion. Finally, TALK-2 channel control of human -cell function will be determined with islet-cell selective D/N and knockdown to monitor their impact on Ca2+ homeostasis and glucagon secretion. This project is significant because it is expected to illumi- nate pharmacological strategies for regulating insulin and glucagon secretion as well as reducing -cell ER- stress; it is essential for uncovering therapies for treating dysglycemia and reducing -cell failure in T2DM.