Impaired functioning of pancreatic ␤ cells is a key hallmark of type 2 diabetes. ␤ cell function is modulated by the actions of different classes of heterotrimeric G proteins. The functional consequences of activating specific ␤ cell G protein signaling pathways in vivo are not well understood at present, primarily due to the fact that ␤ cell G protein-coupled receptors (GPCRs) are also expressed by many other tissues. To circumvent these difficulties, we developed a chemicalgenetic approach that allows for the conditional and selective activation of specific ␤ cell G proteins in intact animals. Specifically, we created two lines of transgenic mice each of which expressed a specific designer GPCR in ␤ cells only. Importantly, the two designer receptors differed in their G protein-coupling properties (Gq/11 versus Gs). They were unable to bind endogenous ligand(s), but could be efficiently activated by an otherwise pharmacologically inert compound (clozapine-N-oxide), leading to the conditional activation of either ␤ cell Gq/11 or Gs G proteins. Here we report the findings that conditional and selective activation of ␤ cell Gq/11 signaling in vivo leads to striking increases in both first-and second-phase insulin release, greatly improved glucose tolerance in obese, insulin-resistant mice, and elevated ␤ cell mass, associated with pathway-specific alterations in islet gene expression levels. Selective stimulation of ␤ cell Gs triggered qualitatively similar in vivo metabolic effects. Thus, this developed chemical-genetic strategy represents a powerful approach to study G protein regulation of ␤ cell function in vivo.beta cells ͉ G protein-coupled receptors ͉ transgenic mice ͉ type 2 diabetes T ype 2 diabetes has emerged as one of the major threats to human health in the 21st century (1). Impaired function of pancreatic ␤ cells is one of the key hallmarks of type 2 diabetes, and therapies targeted at improving ␤ cell function are predicted to offer considerable therapeutic benefit (2).␤ Cell function is modulated by the actions of different classes of heterotrimeric G proteins which are the immediate downstream targets of a multitude of G protein-coupled receptors (GPCRs). Like most other cell types, pancreatic ␤ cells are predicted to express many different GPCRs (3-5). Several lines of evidence suggest that activation of G s -coupled receptors expressed by pancreatic ␤ cells, including the glucagon-like peptide (GLP-1) receptor, improves ␤ cell function and can increase in ␤ cell mass via cAMP-dependent mechanisms (5-7). Pancreatic ␤ cells also express several G q/11 -coupled receptors, including the M 3 muscarinic acetylcholine (ACh) receptor (M3R) and GPR40, which can promote insulin release in an agonist-dependent fashion [for recent reviews, see (5,8)].Studies with GLP-1 receptor agonists have yielded detailed information about the beneficial effects of G s signaling on ␤ cell function and whole body glucose homeostasis (note that the GLP-1 receptor is enriched in pancreatic ␤ cells) (5-7). In contrast, much...

Type 2 diabetes (T2D) has emerged as a major threat to human health in most parts of the world. Therapeutic strategies aimed at improving pancreatic β cell function are predicted to prove beneficial for the treatment of T2D. In the present study, we demonstrate that drug-mediated, chronic, and selective activation of β cell G q signaling greatly improve β cell function and glucose homeostasis in mice. These beneficial metabolic effects were accompanied by the enhanced expression of many genes critical for β cell function, maintenance, and differentiation. By employing a combination of in vivo and in vitro approaches, we identified a novel β cell pathway through which receptor-activated G q leads to the sequential activation of ERK1/2 and IRS2 signaling, thus triggering a series of events that greatly improve β cell function. Importantly, we found that chronic stimulation of a designer G q -coupled receptor selectively expressed in β cells prevented both streptozotocin-induced diabetes and the metabolic deficits associated with the consumption of a high-fat diet in mice. Since β cells are endowed with numerous receptors that mediate their cellular effects via activation of G q -type G proteins, our findings provide a rational basis for the development of novel antidiabetic drugs targeting this class of receptors.

Therapeutic strategies that augment insulin release from pancreatic β-cells are considered beneficial in the treatment of type 2 diabetes. We previously demonstrated that activation of β-cell M 3 muscarinic receptors (M3Rs) greatly promotes glucose-stimulated insulin secretion (GSIS), suggesting that strategies aimed at enhancing signaling through β-cell M3Rs may become therapeutically useful. M3R activation leads to the stimulation of G proteins of the G q family, which are under the inhibitory control of proteins known as regulators of G protein signaling (RGS proteins). At present, it remains unknown whether RGS proteins play a role in regulating insulin release. To address this issue, we initially demonstrated that MIN6 insulinoma cells express functional M3Rs and that RGS4 was by far the most abundant RGS protein expressed by these cells. Strikingly, siRNA-mediated knockdown of RGS4 expression in MIN6 cells greatly enhanced M3R-mediated augmentation of GSIS and calcium release. We obtained similar findings using pancreatic islets prepared from RGS4-deficient mice. Interestingly, RGS4 deficiency had little effect on insulin release caused by activation of other β-cell GPCRs. Finally, treatment of mutant mice selectively lacking RGS4 in pancreatic β-cells with a muscarinic agonist (bethanechol) led to significantly increased plasma insulin and reduced blood glucose levels, as compared to control littermates. Studies with β-cell-specific M3R knockout mice showed that these responses were mediated by β-cell M3Rs. These findings indicate that RGS4 is a potent negative regulator of M3R function in pancreatic β-cells, suggesting that RGS4 may represent a potential target to promote insulin release for therapeutic purposes. knockout mice | muscarinic receptor | RGS proteins | G protein-coupled receptor T ype 2 diabetes (T2D) has emerged as a major threat to human health worldwide. Besides peripheral insulin resistance, T2D is usually associated with β-cell dysfunction (1). Thus, the development of new drugs aimed at improving β-cell function, including stimulation of insulin release, is the focus of many laboratories (2).β-cell function is regulated by many hormones and neurotransmitters most of which act on specific G protein-coupled receptors (GPCRs) that are expressed on the surface of pancreatic β-cells (3, 4). Following ligand-induced activation, a specific GPCR interacts with and activates one or more classes of heterotrimeric G proteins (consisting of α, β, and γ subunits), which in turn modulate various intracellular signal transduction pathways (5).Stimulation of the muscarinic cholinergic (parasympathetic) nerves innervating the endocrine pancreas leads to a pronounced increase in glucose-stimulated insulin secretion (GSIS) (4, 6). Studies with pancreatic islets prepared from M 3 muscarinic acetylcholine receptor (M3R) KO mice demonstrated that muscarinic enhancement of GSIS is mediated by the M3R subtype (7,8). The M3R is a member of the muscarinic receptor family (M 1 -M 5 ) that is selectively coupled ...

Food addiction is linked to obesity and eating disorders and is characterized by a loss of behavioral control and compulsive food intake. Here, using a food addiction mouse model, we report that the lack of cannabinoid type-1 receptor in dorsal telencephalic glutamatergic neurons prevents the development of food addiction-like behavior, which is associated with enhanced synaptic excitatory transmission in the medial prefrontal cortex (mPFC) and in the nucleus accumbens (NAc). In contrast, chemogenetic inhibition of neuronal activity in the mPFC-NAc pathway induces compulsive food seeking. Transcriptomic analysis and genetic manipulation identified that increased dopamine D2 receptor expression in the mPFC-NAc pathway promotes the addiction-like phenotype. Our study unravels a new neurobiological mechanism underlying resilience and vulnerability to the development of food addiction, which could pave the way towards novel and efficient interventions for this disorder.