The plasma membrane electron transport system (PMET) is an important extra-mitochondrial pathway that participates in the regulation of beta cell redox status and metabolism via NAD (P) H-dependent quinone oxidoreductase, NQO1. The PMET/NQO1 pathway functions to reoxidize glycolytically-derived NADH and to export protons and electrons from the cell, generating the second messenger hydrogen peroxide. Furthermore, NQO1 participates in the glucose-dependent process of quinone redox cycling, which also plays an important role in glucose-stimulated insulin secretion (GSIS) from beta cells. NAD kinase, a novel NADPH- regulating enzyme, is responsible for the de novo production of NADPH and participates in the protection of beta cells from oxidative stress. These extra-mitochondrial pathways of redox control are critical for normal cell function, and have not been characterized in islets. Our Preliminary Data demonstrate the critical role of these pathways for beta cell function, survival, and GSIS. We will employ over-expression or knockdown using shRNA and adenoviral vectors strategies as well as NQO1 knockout pancreatic islets to analyze the role of these components in beta cell intermediary metabolism and insulin secretion. We will analyze the role of NQO1 and NAD kinase in the response of islets to glucose or other stimulatory agents using a custom- made integrated electrochemical-confocal imaging platform to simultaneously study islet metabolism, respiration, and signaling. These studies will provide greater insight into the mechanism of redox signaling in regulating insulin secretion and identify novel targets for the development of therapeutics for type 2 diabetes.
This application investigates how redox systems in pancreatic beta cells regulate insulin secretion. Our preliminary and published studies have identified a novel cytosolic redox circuit, which involves Plasma Membrane Electron Transport system (PMET), NAD (P) H-dependent Quinone Oxidoreductase 1 (NQO1), and the NAD kinase, responsible for regulation of beta cell redox status, survival and insulin secretion. These studies will not only lead to a better understanding of glucose stimulated insulin secretion, but will also enable the design of new therapeutic strategies to enhance beta cell secretory response in the treatment of type 2 diabetes.
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