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 membrane potential (??p) and Ca2+ entry. While ion channels that regulate excitability are key regulators of Ca2+ influx, there is a gap in our understanding of the background potassium currents that stabilize the ??p from where action potentials fire during glucose stimulation. Existence of this gap represents an important problem because, until it is filled, our understanding of glucagon and insulin secretion is incomplete, which limits the therapeutic targets that can be utilized for treating dysglycemia. The long term goal of this research is to understand physiological and pathophysiological islet hormone secretion in the context of leak two-pore-domain (K2P) potassium channel activity. The overall objective of this proposal, which is the next step toward attainment of the long term goal, is to elucidate molecular mechanisms regulating secretagogue dependent modulation of islet Ca2+ influx and hormone secretion via K2P channels. This project will test the central hypothesis that K2P channels modulate the islet-cell membrane potential (??p), thus, regulating Ca2+ influx and hormone secretion. This hypothesis has been formulated from preliminary data that finds that the K2P channels TASK-1 and TASK-3 regulate glucose stimulated ?-cell ??p, Ca2+ influx, and insulin secretion. Further data find that the K2P channel TREK-2 is expressed in islet ?-cells where it modulates electrical activity and glucagon secretion. The rationale that underlies the proposed research is that understanding how blood glucose is influenced by islet-cell K2P channel activity will expose new therapeutic targets for treating diabetes. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Determine the influence of K2P channels on islet ?-cell insulin secretion; and 2) Determine the role that K2P channels play in limiting islet ?-cell excitability and glucagon secretion. Under the first aim, mie with inducible ?-cell ablation of TASK-1 andTASK-3, which are already on hand, will be utilized to test the influences of these channels on mouse glucose homeostasis. The function of human ?-cell TASK channels will also be assessed with specific and potent pharmacology and a dominant negative (D/N) approach, which have been established as feasible in the applicants' hands. Finally, the influence of TASK channels on ?-cell function under stress will be assessed in animals treated with a high fat diet. Under the second aim, transgenic mice with fluorescent protein expressing ?-cells that are deficient for TREK- 2, which are on hand, will be utilized to assess the roles of these channels during ?-cell glucagon secretion. An ?-cell specific D/N approach, which has been validated, will also be utilized to assess the function of human ?- cell TREK-2 channels. The proposed research is significant because it is the first step in a continuum of research that is expected to lead to pharmacological strategies for regulating insulin and glucagon secretion; it is essential for uncovering therapies for treating dysglycemia in diseases such as T2DM and hyperinsulinemia.
The proposed research is relevant to public health because the discovery of the function of islet K2P channels is ultimately expected to increase understanding of hormone secretion and how it becomes perturbed during the pathogenesis T2DM. Results from this project are expected to provide significant insights into the potential of utilizing K2P channels as therapeutic targets for treating T2DM and hyperinsulinemia. Thus, the proposed research is relevant to the part of the NIH's mission that pertains to developing fundamental knowledge that will help reduce the burdens of human illness.
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