Role of G protein-coupled receptors in regulating glucose and energy homeostasis

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Use of designer GPCRs to study GPCR regulation of key metabolic pathways Armbruster et al. (PNAS 104, 5163-8, 2007) first described a set of muscarinic receptor-based designer GPCRs which are now generally referred to as DREADDs ('designer receptors exclusively activated by designer drugs'). These designer receptors are unable to bind the endogenous muscarinic receptor agonist, acetylcholine, due to two single point mutations introduced into the transmembrane receptor core. Importantly, DREADDs can be efficiently activated by a compound called clozapine-N-oxide (CNO), an agent that is otherwise pharmacologically inert. The first DREADDs that were developed represent GPCRs that selectively activate G proteins of the Gq or Gi family, respectively. We subsequently generated additional DREADDs endowed with different coupling properties, including a Gs DREADD and a functionally promiscuous DREADD (Guettier et al., PNAS 106, 19197-202, 2009). More recently, we generated an M3R-based DREADD that is uncoupled from G proteins but retains arrestin-dependent signaling (Nakajima and Wess, Mol Pharmacol 82, 575-82, 2012). Analogously, we recently designed an M3R-based DREADD that shows the opposite coupling profile: lack of arrestin recruitment but efficient coupling to Gq-type G proteins (Hu et al., J Biol Chem 291, 7809-20, 2016) (for a recent review see: Wess J. Use of Designer G protein-coupled receptors to dissect metabolic pathways. Trends Endocrinol Metab. 2016 Sep;27(9):600-3). We are currently in the process of expressing DREADDs with different coupling properties in various metabolically relevant cell types. These cell types include adipocytes, pancreatic beta-cells, skeletal muscle cells, hepatocytes, and certain neuronal subpopulations of the hypothalamus. Preliminary results indicate that CNO treatment of some of these mutant mouse strains has pronounced effect on glucose and energy homeostasis (unpublished results). The data summarized below were obtained in a collaborative study. A mouse model in which Gs DREADD expression can be induced in a cell type-specific, temporally controlled fashion Activation of many G protein-coupled receptors (GPCRs) leads to the stimulation of Gs, a heterotrimeric protein that promotes the formation of cAMP. To facilitate studies of cAMP signaling in specific cell populations in vivo, we used DREADD technology to create ROSA26-based knock-in mice for the conditional expression of a Gs DREADD. After expression of Cre recombinase, this DREADD can be activated by the administration CNO, a selective DREADD agonist. After viral delivery of Cre recombinase to mouse hepatocytes in vivo, the Gs DREADD is selectively expressed in hepatocytes. In these animals, long-term DREADD activity leads to enhanced cAMP signaling and glycogen breakdown, accompanied by hyperglycemia. Thus, these new mutant mice represent an excellent tool to study the physiological effects of Gs signaling, acutely or chronically, in any tissue or cell type for which transgenic or viral Cre drivers are available. (Akhmedov D, Mendoza-Rodriguez MG, Rajendran K, Rossi M, Wess J, Berdeaux R. Gs-DREADD knock-in mice for tissue-specific, temporal stimulation of cyclic AMP signaling. Mol Cell Biol. 2017 Apr 14;37(9). pii: e00584-16) Beta-Arrestin-2 is essential for the proper function of pancreatic beta-cells We recently found that mice selectively lacking beta-arrestin-2 (barr2) in pancreatic beta-cells (beta-barr2-KO mice) showed several striking metabolic deficits, including greatly impaired glucose-stimulated insulin secretion and Ca2+ entry into beta-cells, and a pronounced reduction of glucose tolerance when -barr2-KO mice were maintained on a high-fat diet. We demonstrated that barr2 is required for the proper activation of CAMKII and that disruption of this pathway can fully account for the metabolic deficits observed with the beta-barr2-KO mice. Moreover, knockdown of barr2 expression virtually abolished glucose-induced insulin release in human beta-cells. These results may lead to the development of novel drugs aimed at modulating barr2 function in beta-cells for therapeutic purposes. (Zhu L, Almaa J, Dadi PK, Hong H, Sakamoto W, Rossi M, Lee RJ, Vierra NC, Lu H, Cui Y, McMillin SM, Perry NA, Gurevich VV, Lee A, Kuo B, Leapman RD, Matschinsky FM, Doliba NM, Urs NM, Caron MG, Jacobson DA, Caicedo A, Wess J. Beta-arrestin-2 is an essential regulator of pancreatic beta-cell function under physiological and pathophysiological conditions. Nat Commun. 2017 Feb 1;8:14295.) Hepatic beta-arrestin-2 by is required for maintaining normal blood glucose levels A key feature of type 2 diabetes is an increase in hepatic glucose production (HGP). This metabolic deficit critically depends on enhanced signaling through hepatic glucagon receptors (GCGRs). The regulation of GCGR activity in vivo remains largely unexplored. We showed that selective inactivation of beta-arrestin-2 (barr2) in hepatocytes of adult mice leads to greatly increased hepatic GCGR signaling, leading to striking deficits in glucose homeostasis. Interestingly, mice selectively lacking beta-arrestin-1 in hepatocytes do not show any changes in glucose homeostasis. Importantly, mice that over-express barr2 in hepatocytes display greatly reduced hepatic GCGR signaling and are protected against the metabolic deficits caused by the consumption of a high-fat diet. These findings support the novel concept that strategies aimed at enhancing hepatic barr2 activity could prove useful to suppress HGP for the treatment of type 2 diabetes. (Zhu L, Rossi M, Cui Y, Lee RJ, Sakamoto W, Perry NA, Urs NM, Caron MG, Gurevich VV, Godlewski G, Kunos G, Chen M, Chen W, Wess J. Hepatic beta-arrestin 2 is essential for maintaining euglycemia. J Clin Invest. 2017 Jun 26. pii: 92913. doi: 10.1172/JCI92913. Epub ahead of print)