G Protein-Coupled Receptor 17 Inhibits Glucagon-like Peptide-1 Secretion via a Gi/o-Dependent Mechanism in Enteroendocrine Cells.

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered.

G protein-coupled receptor 17 inhibits glucagon-like peptide-1 secretion via a Gi/o-dependent mechanism in enteroendocrine cells.

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered.

Dynamic regulation of pancreatic β cell function and gene expression by the SND1 coregulator .

The pancreatic β cell synthesizes, packages, and secretes insulin in response to glucose-stimulation to maintain blood glucose homeostasis. Under diabetic conditions, a subset of β cells fail and lose expression of key transcription factors (TFs) required for insulin secretion. Among these TFs is Pancreatic and duodenal homeobox 1 (PDX1), which recruits a unique subset of transcriptional coregulators to modulate its activity.

Intestinal Gpr17 deficiency improves glucose metabolism by promoting GLP-1 secretion.

G protein-coupled receptors (GPCRs) in intestinal enteroendocrine cells (EECs) respond to nutritional, neural, and microbial cues and modulate the release of gut hormones. Here we show that Gpr17, an orphan GPCR, is co-expressed in glucagon-like peptide-1 (GLP-1)-expressing EECs in human and rodent intestinal epithelium. Acute genetic ablation of Gpr17 in intestinal epithelium improves glucose tolerance and glucose-stimulated insulin secretion (GSIS).

A high-fat diet catalyzes progression to hyperglycemia in mice with selective impairment of insulin action in Glut4-expressing tissues.

Insulin resistance impairs postprandial glucose uptake through glucose transporter type 4 (GLUT4) and is the primary defect preceding type 2 diabetes. We previously generated an insulin-resistant mouse model with human GLUT4 promoter-driven insulin receptor knockout (GIRKO) in the muscle, adipose, and neuronal subpopulations. However, the rate of diabetes in GIRKO mice remained low prior to 6 months of age on normal chow diet (NCD), suggesting that additional factors/mechanisms are responsible for adverse metabolic effects driving the ultimate progression of overt diabetes.

Human GPR17 missense variants identified in metabolic disease patients have distinct downstream signaling profiles.

GPR17 is a G-protein-coupled receptor (GPCR) implicated in the regulation of glucose metabolism and energy homeostasis. Such evidence is primarily drawn from mouse knockout studies and suggests GPR17 as a potential novel therapeutic target for the treatment of metabolic diseases. However, links between human GPR17 genetic variants, downstream cellular signaling, and metabolic diseases have yet to be reported.

Gpr17 deficiency in POMC neurons ameliorates the metabolic derangements caused by long-term high-fat diet feeding.

Background: Proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) control energy homeostasis by sensing hormonal and nutrient cues and activating secondary melanocortin sensing neurons. We identified the expression of a G protein-coupled receptor, Gpr17, in the ARH and hypothesized that it contributes to the regulatory function of POMC neurons on metabolism.

Methods: In order to test this hypothesis, we generated POMC neuron-specific Gpr17 knockout (PGKO) mice and determined their energy and glucose metabolic phenotypes on normal chow diet (NCD) and high-fat diet (HFD).

Detection of Osmotic Shock-Induced Extracellular Nucleotide Release with a Genetically Encoded Fluorescent Sensor of ADP and ATP.

Purinergic signals, such as extracellular adenosine triphosphate (ATP) and adenosine diphosphate (ADP), mediate intercellular communication and stress responses throughout mammalian tissues, but the dynamics of their release and clearance are still not well understood. Although physiochemical methods provide important insight into physiology, genetically encoded optical sensors have proven particularly powerful in the quantification of signaling in live specimens. Indeed, genetically encoded luminescent and fluorescent sensors provide new insights into ATP-mediated purinergic signaling.

Imaging extracellular ATP with a genetically-encoded, ratiometric fluorescent sensor.

Extracellular adenosine triphosphate (ATP) is a key purinergic signal that mediates cell-to-cell communication both within and between organ systems. We address the need for a robust and minimally invasive approach to measuring extracellular ATP by re-engineering the ATeam ATP sensor to be expressed on the cell surface. Using this approach, we image real-time changes in extracellular ATP levels with a sensor that is fully genetically-encoded and does not require an exogenous substrate.

Molecular Modeling Evaluation of the Enantiomers of a Novel Adenylyl Cyclase 2 Inhibitor.

Adenylyl cyclase 2 (AC2) is one of nine membrane-bound isoforms of adenylyl cyclase that converts ATP into cyclic AMP (cAMP), an important second messenger molecule. Upregulation of AC2 is linked to cancers like pancreatic and small intestinal neuroendocrine tumors (NETs). The structures of the various isoforms of adenylyl cyclases are highly homologous, posing a significant challenge to drug discovery efforts for an effective, isoform-selective modulator of AC2.

Imaging Adenosine Triphosphate (ATP).

Adenosine triphosphate (ATP) is a universal mediator of metabolism and signaling across unicellular and multicellular species. There is a fundamental interdependence between the dynamics of ATP and the physiology that occurs inside and outside the cell. Characterizing and understanding ATP dynamics provide valuable mechanistic insight into processes that range from neurotransmission to the chemotaxis of immune cells.

Gα(i/o)-coupled receptor-mediated sensitization of adenylyl cyclase: 40 years later.

Heterologous sensitization of adenylyl cyclase (also referred to as superactivation, sensitization, or supersensitization of adenylyl cyclase) is a cellular adaptive response first described 40 years ago in the laboratory of Dr. Marshall Nirenberg. This apparently paradoxical cellular response occurs following persistent activation of Gαi/o-coupled receptors and causes marked enhancement in the activity of adenylyl cyclases, thereby increasing cAMP production.

Drug-induced sensitization of adenylyl cyclase: assay streamlining and miniaturization for small molecule and siRNA screening applications.

Sensitization of adenylyl cyclase (AC) signaling has been implicated in a variety of neuropsychiatric and neurologic disorders including substance abuse and Parkinson's disease. Acute activation of Gαi/o-linked receptors inhibits AC activity, whereas persistent activation of these receptors results in heterologous sensitization of AC and increased levels of intracellular cAMP. Previous studies have demonstrated that this enhancement of AC responsiveness is observed both in vitro and in vivo following the chronic activation of several types of Gαi/o-linked receptors including D2 dopamine and μ opioid receptors.

Development of a high-throughput screening paradigm for the discovery of small-molecule modulators of adenylyl cyclase: identification of an adenylyl cyclase 2 inhibitor.

Adenylyl cyclase (AC) isoforms are implicated in several physiologic processes and disease states, but advancements in the therapeutic targeting of AC isoforms have been limited by the lack of potent and isoform-selective small-molecule modulators. The discovery of AC isoform-selective small molecules is expected to facilitate the validation of AC isoforms as therapeutic targets and augment the study of AC isoform function in vivo. Identification of chemical probes for AC2 is particularly important because there are no published genetic deletion studies and few small-molecule modulators.

Differential effects of AGS3 expression on D(2L) dopamine receptor-mediated adenylyl cyclase signaling.

Activator of G protein signaling 3 (AGS3) binds Gα(i) subunits in the GDP-bound state, implicating AGS3 as an important regulator of Gα(i)-linked receptor (e.g., D2 dopamine and μ-opioid) signaling.

Bimolecular fluorescence complementation analysis of G protein-coupled receptor dimerization in living cells.

Emerging evidence indicates that G protein-coupled receptor (GPCR) signaling is mediated by receptor-receptor interactions at multiple levels. Thus, understanding the biochemistry and pharmacology of those receptor complexes is an important part of delineating the fundamental processes associated with GPCR-mediated signaling in human disease. A variety of experimental approaches have been used to explore these complexes, including bimolecular fluorescence complementation (BiFC) and multicolor BiFC (mBiFC).

Identification of a 2-phenyl-substituted octahydrobenzo[f]quinoline as a dopamine D₃ receptor-selective full agonist ligand.

This work describes the identification of a novel class of octahydrobenzo[f]quinolines as dopamine D(3)-selective full agonists. We developed a facile method that utilizes Suzuki coupling for easy incorporations of various substituted pendant rings into the scaffold. A small focused library of octahydrobenzo[f]quinolines 5 was synthesized, and these compounds demonstrated at least 14-fold D(2)-like selectivity over D(1) in native porcine striatal tissue.

A point mutation to Galphai selectively blocks GoLoco motif binding: direct evidence for Galpha.GoLoco complexes in mitotic spindle dynamics.

Heterotrimeric G-protein Galpha subunits and GoLoco motif proteins are key members of a conserved set of regulatory proteins that influence invertebrate asymmetric cell division and vertebrate neuroepithelium and epithelial progenitor differentiation. GoLoco motif proteins bind selectively to the inhibitory subclass (Galphai) of Galpha subunits, and thus it is assumed that a Galphai.GoLoco motif protein complex plays a direct functional role in microtubule dynamics underlying spindle orientation and metaphase chromosomal segregation during cell division.