Probing cell type–specific functions of Gi in vivo identifies GPCR regulators of insulin secretion
Jean B. Regard, … , Matthias Hebrok, Shaun R. Coughlin
Jean B. Regard, … , Matthias Hebrok, Shaun R. Coughlin
Published November 8, 2007
Citation Information: J Clin Invest. 2007;117(12):4034-4043. https://doi.org/10.1172/JCI32994.
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Research Article Technical Advance Cardiology

Probing cell type–specific functions of Gi in vivo identifies GPCR regulators of insulin secretion

Abstract

The in vivo roles of the hundreds of mammalian G protein–coupled receptors (GPCRs) are incompletely understood. To explore these roles, we generated mice expressing the S1 subunit of pertussis toxin, a known inhibitor of Gi/o signaling, under the control of the ROSA26 locus in a Cre recombinase–dependent manner (ROSA26PTX). Crossing ROSA26PTX mice to mice expressing Cre in pancreatic β cells produced offspring with constitutive hyperinsulinemia, increased insulin secretion in response to glucose, and resistance to diet-induced hyperglycemia. This phenotype underscored the known importance of Gi/o and hence of GPCRs for regulating insulin secretion. Accordingly, we quantified mRNA for each of the approximately 373 nonodorant GPCRs in mouse to identify receptors highly expressed in islets and examined the role of several. We report that 3-iodothyronamine, a thyroid hormone metabolite, could negatively and positively regulate insulin secretion via the Gi-coupled α2A-adrenergic receptor and the Gs-coupled receptor Taar1, respectively, and protease-activated receptor–2 could negatively regulate insulin secretion and may contribute to physiological regulation of glucose metabolism. The ROSA26PTX system used in this study represents a new genetic tool to achieve tissue-specific signaling pathway modulation in vivo that can be applied to investigate the role of Gi/o-coupled GPCRs in multiple cell types and processes.

Authors

Jean B. Regard, Hiroshi Kataoka, David A. Cano, Eric Camerer, Liya Yin, Yao-Wu Zheng, Thomas S. Scanlan, Matthias Hebrok, Shaun R. Coughlin

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Figure 5

Administration of T1AM causes Adra2a- and Gi-dependent hyperglycemia and hypoinsulinemia.

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Administration of T1AM causes Adra2a- and Gi-dependent hyperglycemia and...
(A) Blood glucose levels following administration of T1AM (50 mg/kg, i.p.) or vehicle. T1AM induced hyperglycemia in wild-type (n = 6–7; *P < 0.01, **P < 0.001) but not in RIP-PTX mice. (B) Blood insulin levels 2 hours following vehicle or T1AM injection as in A relative to preinjection levels. Note the 60% decrease in insulin levels after T1AM in wild-type (n = 6; #P < 0.005) but not RIP-PTX mice. (C and D) The effects of T1AM on GSIS in isolated islets from mice (C) and humans (D). T1AM (10 μM) was capable of inhibiting GSIS in a PTX-sensitive manner in both species (PTX pretreatment 50 ng/ml for 16 hours). Data are presented as relative insulin secreted/total insulin (mean ± SEM; n = 3–4; ##P < 0.05). (E) Chemical similarity of T1AM and catecholamines. (F) Competition of T1AM and epinephrine for [3H]RX821002 binding to membranes from Cos cells transfected with an expression vector for human or mouse Adra2a. Binding of [3H]RX821002 was Adra2a transfection dependent. (G) Blood glucose levels 1 hour following T1AM administration to control mice and Adra2a-null mice. Note that control mice became hyperglycemic following T1AM administration (n = 9; ΧP = 0.001), but Adra2a-null mice became hypoglycemic (n = 11–12; ΧΧP = 0.003).