Defining G protein-coupled receptor peptide ligand expressomes and signalomes in human and mouse islets

Abstract

IntroductionIslets synthesise and secrete numerous peptides, some of which are known to be important regulators of islet function and glucose homeostasis. In this study, we quantified mRNAs encoding all peptide ligands of islet G protein-coupled receptors (GPCRs) in isolated human and mouse islets and carried out in vitro islet hormone secretion studies to provide functional confirmation for the species-specific role of peptide YY (PYY) in mouse islets.Materials and methodsGPCR peptide ligand mRNAs in human and mouse islets were quantified by quantitative real-time PCR relative to the reference genes ACTB, GAPDH, PPIA, TBP and TFRC. The pathways connecting GPCR peptide ligands with their receptors were identified by manual searches in the PubMed, IUPHAR and Ingenuity databases. Distribution of PYY protein in mouse and human islets was determined by immunohistochemistry. Insulin, glucagon and somatostatin secretion from islets was measured by radioimmunoassay.ResultsWe have quantified GPCR peptide ligand mRNA expression in human and mouse islets and created specific signalomes mapping the pathways by which islet peptide ligands regulate human and mouse GPCR signalling. We also identified species-specific islet expression of several GPCR ligands. In particular, PYY mRNA levels were ~ 40,000-fold higher in mouse than human islets, suggesting a more important role of locally secreted Pyy in mouse islets. This was confirmed by IHC and functional experiments measuring insulin, glucagon and somatostatin secretion.DiscussionThe detailed human and mouse islet GPCR peptide ligand atlases will allow accurate translation of mouse islet functional studies for the identification of GPCR/peptide signalling pathways relevant for human physiology, which may lead to novel treatment modalities of diabetes and metabolic disease.Electronic supplementary materialThe online version of this article (10.1007/s00018-018-2778-z) contains supplementary material, which is available to authorized users.

Inhibitory effect of UDP-glucose on cAMP generation and insulin secretion

“…Our results are thus in good agreement with recent report showing that P2Y14 receptors signals through a Gi-coupled protein, thereby inhibiting adenylate cyclase activity resulting in a reduced cAMP generation (17) which is an important signaling molecule for GSIS (18,19). Concerning pancreatic β-cells, it is well known that activation of GPCRs that signal through Gi proteins is associated with a reduced insulin secretory capacity (8,(20)(21)(22). In the current study, we show that activation of P2Y14 receptor by the specific agonist UDP-G is associated with a reduced β-cell functionality through the involvement of a PTX sensitive Gi protein.…”

RORB and RORC associate with human islet dysfunction and inhibit insulin secretion in INS-1 cells

“…44 Lastly, it is worth noting that pancreatic islets express a wide range of receptors, many of which are still designated as orphan receptors. 45,46 Consistent with previous reports, data presented here further implicates Retinoic acid in the induction of a wide range of receptors in pancreatic β cells with the action site distal to RORB and RORC. 26,47 A possible limitation of our study relates to the utility of correlating ROR gene expression with insulin secretion or HbA 1c levels in diabetic donors who are on DM medications that could normalize fasting blood glucose and glucose tolerance.…”

GPCRomics: An Approach to Discover GPCR Drug Targets

“…However, numerous questions exist in the field (see Outstanding Questions) and will likely be addressed in future studies. A focus will be on assessing GPCR expression in single cells, which, as noted above, may identify sub-populations of cell types with distinct GPCR profiles, perhaps cell-and disease-specific functional splice variants and interactions of GPCRs with G proteins and other partners [45,[76][77][78][79][80]. Studies are also needed to identify the mechanisms that mediate changes in GPCR mRNA expression in physiological and disease settings.…”