One of the earliest and most important pathophysiological signs of type 2 diabetes (T2D) is impaired insulin release. A number of therapies used in the clinic, such as GLP1- agonists and DPP-4 inhibitors, act to sensitize the release machinery and enhance insulin release from the beta cell. Gi/o-coupled G-protein coupled receptors (GPCRs) inhibit insulin release through liberating G protein ?? subunits, which can inhibit calcium entry through voltage-gated calcium channels. We have demonstrated that G?? can also directly inhibit exocytosis at a point distal to Ca2+ entry by binding to the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. Beta cell ?2A adrenergic receptors (2AAR) profoundly inhibit insulin release by this mechanism. This proposal aims to investigate the role of the ?2AAR in the inhibition of insulin release in animal models of T2D. We hypothesize that overactive inhibition of insulin secretion by Gi/o- coupled GPCRs is a part of the impaired insulin secretion in the pathogenesis of T2D. No studies have previously investigated whether blocking this inhibitory mechanism is an alternative approach for enhancing insulin secretion in an animal model of T2D, the diet-induced obese (DIO) aged mouse.
In Aim 1, we will test whether 2AAR-mediated inhibition is enhanced in islets isolated from DIO mice.
In Aim 2, we will determine whether negating the impact of G?? on the exocytotic fusion machinery can improve GSIS in DIO mice. We have both small molecule inhibitors of the G??-SNARE interaction, as well as a mutant mouse that is resistant to G??'s inhibitory effect. The truncated SNAP25 mutant mouse (SNAP253) has an impaired ability to interact with G while exocytosis itself remains intact. We will assess GSIS in isolated islets in vitro as well as in vivo using hyperglycemic clamps from both lean and DIO WT and SNAP253 mice.
In Aim 3, we will determine whether dual addition of low levels of secretogogues and G??-SNARE inhibitors synergize with each other, potentially providing us with a therapeutic window of selectivity for enhanced insulin secretion over secretion events in other cell types. Regulation of the exocytotic fusion machinery by G?? is a new mechanism that targets the very final step of insulin secretion. Importantly, our studies have the potential to open up a new therapeutic approach to impaired insulin release. Reversing the inhibitory signals at the exocytotic machinery could amplify insulin release while still maintaining the critical physiological control f insulin release by glucose and other modulators.

Public Health Relevance

Regulation of insulin secretion by Gi/o-coupled receptors is important for normal pancreatic function and may be a part of the pathological inhibition of insulin secretion in T2D. Inhibition of insulin secretion by ?2A receptors works via G-SNARE interaction. Our proposal is to determine if reversing G??-SNARE interaction can enhance glucose-stimulated insulin secretion in normal mice and in animal models of T2D.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Molecular and Integrative Signal Transduction Study Section (MIST)
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Sato, Sheryl M
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Vanderbilt University Medical Center
Schools of Medicine
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Zurawski, Zack; Page, Brian; Chicka, Michael C et al. (2017) G?? directly modulates vesicle fusion by competing with synaptotagmin for binding to neuronal SNARE proteins embedded in membranes. J Biol Chem 292:12165-12177
Van Hook, Matthew J; Babai, Norbert; Zurawski, Zack et al. (2017) A Presynaptic Group III mGluR Recruits G??/SNARE Interactions to Inhibit Synaptic Transmission by Cone Photoreceptors in the Vertebrate Retina. J Neurosci 37:4618-4634
Yim, Yun Young; McDonald, W Hayes; Hyde, Karren et al. (2017) Quantitative Multiple-Reaction Monitoring Proteomic Analysis of G? and G? Subunits in C57Bl6/J Brain Synaptosomes. Biochemistry 56:5405-5416
Zurawski, Zack; Rodriguez, Shelagh; Hyde, Karren et al. (2016) G?? Binds to the Extreme C Terminus of SNAP25 to Mediate the Action of Gi/o-Coupled G Protein-Coupled Receptors. Mol Pharmacol 89:75-83