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

Patricio Atanes,Guo Cai Huang,Ross Hawkes,Inmaculada Ruz-Maldonado,Israa Mohammed Al-Amily,Min Zhao,Bo Liu,Shanta J Persaud,Albert Salehi,Stefan Amisten

doi:10.1007/s00018-018-2778-z

Patricio Atanes, Guo Cai Huang + Show 8 more

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https://doi.org/10.1007/s00018-018-2778-z

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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.

Highlights

Islets synthesise and secrete numerous peptides, some of which are known to be important regulators of islet function and glucose homeostasis
G protein-coupled receptors (GPCRs) play important roles in regulating secretion of the islet-derived gluco-regulatory hormones insulin, glucagon and somatostatin, and more than one-third of all GPCRs expressed by human islets are activated by ligands that are either proteins or polypeptides [1]
GPCR peptide ligands that are delivered to islets in the circulation include the incretin hormones GLP-1 and GIP, which are secreted by specialised enteroendocrine cells in the gastrointestinal tract [6], and it has recently been reported that the cardiomyocyte-derived atrial natriuretic peptide stimulates insulin secretion via activation of β-cell guanylate cyclase-coupled GC-A receptors [7]

Summary

Introduction

Islets synthesise and secrete numerous peptides, some of which are known to be important regulators of islet function and glucose homeostasis. 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. 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. G protein-coupled receptors (GPCRs) play important roles in regulating secretion of the islet-derived gluco-regulatory hormones insulin, glucagon and somatostatin, and more than one-third of all GPCRs expressed by human islets are activated by ligands that are either proteins or polypeptides [1]. The increased contacts between adjacent endocrine cell populations in human islets suggest that the intra-islet paracrine signalling is likely to be more complicated than in rodent islets, in terms of signalling molecules interacting with their respective receptors and triggering autocrine or paracrine regulatory circuits [15]

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