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[beta]-arrestin 1 and 2 (Barr1 and Barr2, respectively) are intracellular signaling molecules that regulate many important metabolic functions. We previously demonstrated that mice lacking Barr2 selectively in pancreatic [beta] cells showed pronounced metabolic impairments. Here we investigated whether Barr1 plays a similar role in regulating [beta] cell function and whole-body glucose homeostasis. Initially, we inactivated the Barrl gene in [beta] cells of adult mice ([beta]-barr1-KO mice). [beta]-barr1-KO mice did not display any obvious phenotypes in a series of in vivo and in vitro metabolic tests. However, glibenclamide and tolbutamide, 2 widely used antidiabetic drugs of the sulfonylurea (SU) family, showed greatly reduced efficacy in stimulating insulin secretion in the KO mice in vivo and in perifused KO islets in vitro. Additional in vivo and in vitro studies demonstrated that Barr1 enhanced SU-stimulated insulin secretion by promoting SU-mediated activation of Epac2. Pull-down and coimmunoprecipitation experiments showed that Barr1 can directly interact with Epac2 and that SUs such as glibenclamide promote Barr1/Epac2 complex formation, triggering enhanced Rap1 signaling and insulin secretion. These findings suggest that strategies aimed at promoting Barr1 signaling in [beta] cells may prove useful for the development of efficacious antidiabetic drugs., Introduction Accumulating evidence suggests that [beta]-arrestins play key roles in regulating many important metabolic functions including [beta] cell activity (1). The 2 [beta]-arrestin isoforms ([beta]-arrestin 1 and 2; referred to [...]

G protein-coupled receptors (GPCRs) regulate virtually all aspects of human physiology and represent an important class of therapeutic drug targets. Many GPCR-targeted drugs resemble endogenous agonists, often resulting in poor selectivity among receptor subtypes and restricted pharmacologic profiles. The muscarinic acetylcholine receptor family exemplifies these problems; thousands of ligands are known, but few are receptor subtype-selective and nearly all are cationic in nature. Using structure-based docking against the M2 and M3 muscarinic receptors, we screened 3.1 million molecules for ligands with new physical properties, chemotypes, and receptor subtype selectivities. Of 19 docking-prioritized molecules tested against the M2 subtype, 11 had substantial activity and 8 represented new chemotypes. Intriguingly, two were uncharged ligands with low micromolar to high nanomolar Ki values, an observation with few precedents among aminergic GPCRs. To exploit a single amino-acid substitution among the binding pockets between the M2 and M3 receptors, we selected molecules predicted by docking to bind to the M3 and but not the M2 receptor. Of 16 molecules tested, 8 bound to the M3 receptor. Whereas selectivity remained modest for most of these, one was a partial agonist at the M3 receptor without measurable M2 agonism. Consistent with this activity, this compound stimulated insulin release from a mouse β-cell line. These results support the ability of structure-based discovery to identify new ligands with unexplored chemotypes and physical properties, leading to new biologic functions, even in an area as heavily explored as muscarinic pharmacology.

An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic [G.sub.s]-linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic [G.sub.i] signaling. Specifically, we used a chemogenetic approach to selectively activate [G.sub.i]-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic [G.sub.i] signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased [G.sub.i] signaling stimulated glucose release in human hepatocytes. A lack of functional [G.sub.i]- type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic [G.sub.i] signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic G-coupled GPCRs may prove beneficial as antidiabetic drugs., Introduction Type 2 diabetes (T2D) has emerged as a major health problem worldwide (1). In addition to other pathophysiological features, T2D is characterized by an increase in hepatic glucose production [...]