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 G i/o signaling, under the control of the ROSA26 locus in a Cre recombinase-dependent manner (ROSA26 PTX ). Crossing ROSA26 PTX mice to mice expressing Cre in pancreatic β cells produced offspring with constitutive hyperinsulinemia, increased insulin secretion in response to glucose, and resistance to dietinduced hyperglycemia. This phenotype underscored the known importance of G i/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 G i -coupled α 2A -adrenergic receptor and the G s -coupled receptor Taar1, respectively, and proteaseactivated receptor-2 could negatively regulate insulin secretion and may contribute to physiological regulation of glucose metabolism. The ROSA26 PTX 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 G i/o -coupled GPCRs in multiple cell types and processes.

The selective antagonist EPPTB reveals TAAR1-mediated regulatory mechanisms in dopaminergic neurons of the mesolimbic system

“…Instead, we found that in Xenopus oocytes TAAR1 directly activates Kir3 channels via PTX-insensitive G-proteins, most likely G s proteins. This challenges an earlier report failing to demonstrate TAAR1 coupling to Kir3 channels (24). Our data reinforce that GPCRs coupled to G proteins other than G i/o can gate Kir3 channels (25)(26)(27)(28)(29).…”

Gα i/o -coupled receptor signaling restricts pancreatic β-cell expansion

“…To answer this question, we expressed the Gα i/o signaling inhibitor pertussis toxin (PTX) in β cells by crossing ROSA-PTX knockin mice to ePet1-cre transgenic mice (islet-PTX mice) (18,24). These animals responded to a glucosetolerance test with lower blood glucose elevations and markedly increased glucose-stimulated insulin secretion ( Fig.…”

The impact of scopolamine pretreatment on 3-iodothyronamine (T1AM) effects on memory and pain in mice

“…However, also T1AM has a complex pharmacodynamic profile, being considered a multi-target molecule since amine interaction at several Gprotein-coupled receptors including trace amine-associated receptors (TAAR1 and 8; Scanlan et al, 2004;Mühlhaus et al, 2014), α2 (Regard et al, 2007;Dinter et al 2015a), β2 adrenoreceptors (Dinter et al, 2015b) and ion channels (Lucius et al, 2015) have been reported. Until now, none of these targets has been recognized to be involved in the behavioral effects of low T1AM doses, including memory stimulation and hyperalgesia.…”