β Cell Gαs signaling is critical for physiological and pharmacological enhancement of insulin secretion
Megan E. Capozzi, David Bouslov, Ashot Sargsyan, Michelle Y. Chan, Alex Chen, Sarah M. Gray, Katrina Viloria, Akshay Bareja, Jonathan D. Douros, Sophie L. Lewandowski, Jason C.L. Tong, Annie Hasib, Federica Cuozzo, Elizabeth C. Ross, Matthew W. Foster, Lee S. Weinstein, Mehboob A. Hussain, Matthew J. Merrins, Francis S. Willard, Mark O. Huising, Kyle W. Sloop, David J. Hodson, David A. D’Alessio, Jonathan E. Campbell
Megan E. Capozzi, David Bouslov, Ashot Sargsyan, Michelle Y. Chan, Alex Chen, Sarah M. Gray, Katrina Viloria, Akshay Bareja, Jonathan D. Douros, Sophie L. Lewandowski, Jason C.L. Tong, Annie Hasib, Federica Cuozzo, Elizabeth C. Ross, Matthew W. Foster, Lee S. Weinstein, Mehboob A. Hussain, Matthew J. Merrins, Francis S. Willard, Mark O. Huising, Kyle W. Sloop, David J. Hodson, David A. D’Alessio, Jonathan E. Campbell
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Research Article Endocrinology Metabolism

β Cell Gαs signaling is critical for physiological and pharmacological enhancement of insulin secretion

Abstract

The incretin peptides glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptors coordinate β cell secretion that is proportional to nutrient intake. This effect permits consistent and restricted glucose excursions across a range of carbohydrate intake. The canonical signaling downstream of ligand-activated incretin receptors involves coupling to Gαs protein and generation of intracellular cAMP. However, recent reports have highlighted the importance of additional signaling nodes engaged by incretin receptors, including other G proteins and β-arrestin proteins. Here, the importance of Gαs signaling was tested in mice with conditional, postdevelopmental β cell deletion of Gnas (encoding Gαs) under physiological and pharmacological conditions. Deletion of Gαs/cAMP signaling induced immediate and profound hyperglycemia that responded minimally to incretin receptor agonists, a sulfonylurea, or bethanechol. While islet area and insulin content were not affected in Gnasβcell–/–, perifusion of isolated islets demonstrated impaired responses to glucose, incretins, acetylcholine, and IBMX In the absence of Gαs, incretin-stimulated insulin secretion was impaired but not absent, with some contribution from Gαq signaling. Collectively, these findings validate a central role for cAMP in mediating incretin signaling, but also demonstrate broad impairment of insulin secretion in the absence of Gαs that causes both fasting hyperglycemia and glucose intolerance.

Authors

Megan E. Capozzi, David Bouslov, Ashot Sargsyan, Michelle Y. Chan, Alex Chen, Sarah M. Gray, Katrina Viloria, Akshay Bareja, Jonathan D. Douros, Sophie L. Lewandowski, Jason C.L. Tong, Annie Hasib, Federica Cuozzo, Elizabeth C. Ross, Matthew W. Foster, Lee S. Weinstein, Mehboob A. Hussain, Matthew J. Merrins, Francis S. Willard, Mark O. Huising, Kyle W. Sloop, David J. Hodson, David A. D’Alessio, Jonathan E. Campbell

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Figure 1

Characterization of Gnasβcell–/– mouse islets.

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Characterization of Gnasβcell–/– mouse islets. (A) Gnas and Gnaq express...
(A) Gnas and Gnaq expression in β cell– and α cell–enriched populations (n = 4–5). (B) Ambient fed glycemia over time in 6- to 8-week-old control (n = 29) and Gnasβcell–/– (n = 23) mice at start of tamoxifen delivery (day 0). (C) Body weight of control (n = 24) and Gnasβcell–/– (n = 15) mice and its correlation with fed glycemia. (D) Average islet size and its correlation with blood glucose at the time of sacrifice in control (n = 7) and Gnasβcell–/– (n = 9) mice and its correlation with fed glycemia. (E) Insulin-positive area per total pancreas area in control (n = 7) and Gnasβcell–/– (n = 9) mice. (F) Insulin granule number (localizations/μm2) from control and Gnasβcell–/– mice, with representative images of insulin granules (n = 41 cells from 3 mice per group). Dashed box represents the area selected for zoom, shown in right-hand panel. Scale bars: 18.9 μm (left panels), 1.98 μm (right panels). (G) Proinsulin levels at baseline (t = 0) and 10 minutes after meal challenge with Ensure (t = 10). Data are shown as mean ± SEM, *P < 0.05 as indicated. Data were analyzed by 2-tailed Student’s t test (A and C–G), 2-way ANOVA (B and G), or linear regression (C–E). dSTORM, direct stochastic optical reconstruction microscopy.