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Transcriptomic Profiling of Pancreatic Alpha, Beta and Delta Cell Populations Identifies Delta Cells As a Principal Target for Ghrelin in Mouse Islets

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Transcriptomic Profiling of Pancreatic Alpha, Beta and Delta Cell Populations Identifies Delta Cells As a Principal Target for Ghrelin in Mouse Islets Transcriptomic profiling of pancreatic alpha, beta and delta cell populations identifies delta cells as a principal target for ghrelin in mouse islets Adriaenssens, Alice E; Svendsen, Berit; Lam, Brian Y H; Yeo, Giles S H; Holst, Jens J; Reimann, Frank; Gribble, Fiona M Published in: Diabetologia DOI: 10.1007/s00125-016-4033-1 Publication date: 2016 Document version Publisher's PDF, also known as Version of record Document license: CC BY Citation for published version (APA): Adriaenssens, A. E., Svendsen, B., Lam, B. Y. H., Yeo, G. S. H., Holst, J. J., Reimann, F., & Gribble, F. M. (2016). Transcriptomic profiling of pancreatic alpha, beta and delta cell populations identifies delta cells as a principal target for ghrelin in mouse islets. Diabetologia, 59(10), 2156-2165. https://doi.org/10.1007/s00125-016- 4033-1 Download date: 23. Sep. 2021 Diabetologia (2016) 59:2156–2165 DOI 10.1007/s00125-016-4033-1 ARTICLE Transcriptomic profiling of pancreatic alpha, beta and delta cell populations identifies delta cells as a principal target for ghrelin in mouse islets Alice E. Adriaenssens1 & Berit Svendsen2,3 & Brian Y. H. Lam1 & Giles S. H. Yeo1 & Jens J. Holst2,3 & Frank Reimann1 & Fiona M. Gribble 1 Received: 15 March 2016 /Accepted: 1 June 2016 /Published online: 7 July 2016 # The Author(s) 2016. This article is published with open access at Springerlink.com Abstract using islets with delta cell restricted expression of the calcium Aims/hypothesis Intra-islet and gut–islet crosstalk are critical reporter GCaMP3, and in perfused mouse pancreases. in orchestrating basal and postprandial metabolism. The aim Results A database was constructed of all genes expressed in of this study was to identify regulatory proteins and receptors alpha, beta and delta cells. The gene encoding the ghrelin underlying somatostatin secretion though the use of receptor, Ghsr, was highlighted as being highly expressed transcriptomic comparison of purified murine alpha, beta and enriched in delta cells. Activation of the ghrelin receptor and delta cells. raised cytosolic calcium levels in primary pancreatic delta Methods Sst-Cre mice crossed with fluorescent reporters were cells and enhanced somatostatin secretion in perfused used to identify delta cells, while Glu-Venus (with Venus re- pancreases, correlating with a decrease in insulin and gluca- ported under the control of the Glu [also known as Gcg]pro- gon release. The inhibition of insulin secretion by ghrelin was moter) mice were used to identify alpha and beta cells. Alpha, prevented by somatostatin receptor antagonism. beta and delta cells were purified using flow cytometry and Conclusions/interpretation Our transcriptomic database of analysed by RNA sequencing. The role of the ghrelin receptor genes expressed in the principal islet cell populations will facil- was validated by imaging delta cell calcium concentrations itate rational drug design to target specific islet cell types. The present study indicates that ghrelin acts specifically on delta cells within pancreatic islets to elicit somatostatin secretion, which in turn inhibits insulin and glucagon release. This highlights a Alice E. Adriaenssens, Berit Svendsen and Brian Y. H. Lam are co-first potential role for ghrelin in the control of glucose metabolism. authors. Frank Reimann and Fiona M. Gribble are joint senior authors. Electronic supplementary material The online version of this article Keywords Alpha cells . Beta cells . Delta cells . Ghrelin . (doi:10.1007/s00125-016-4033-1) contains peer-reviewed but unedited Glucagon . Insulin . RNA sequencing . Somatostatin supplementary material, which is available to authorised users. * Frank Reimann [email protected] Abbreviations * Fiona M. Gribble EYFP Enhanced yellow fluorescent protein [email protected] FPKM Fragments per kilobase of transcript per million mapped reads 1 Metabolic Research Laboratories, Wellcome Trust–MRC Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge CB2 0QQ, GHSR Growth hormone secretagogue receptor UK GPCR G-protein coupled receptor 2 Novo Nordisk Foundation Center for Basic Metabolic Research, qPCR Quantitative PCR University of Copenhagen, Copenhagen, Denmark Sst/SST Somatostatin 3 Department of Biomedical Sciences, Faculty of Health and Medical SSTR Somatostatin receptor Sciences, University of Copenhagen, Copenhagen, Denmark tdRFP Tandem red fluorescent protein Diabetologia (2016) 59:2156–2165 2157 Introduction insulin release are purportedly through direct receptor- mediated modulation of beta cell activity [23, 24]. However, The pancreatic islets provide a centre where signals indicating the predominant Gαq coupling of GHSR [25]andthe the nutritional status of the body, including factors such as insulinostatic effects of ghrelin, if indeed mediated directly enteroendocrine hormones, nutrients, metabolites and neuronal via beta cells, are paradoxical. Because of the therapeutic po- signals, can converge and initiate changes in pancreatic hormone tential of manipulating the ghrelin axis in individuals with secretion to regulate blood glucose levels. Insulin (released from obesity and diabetes [26], the mechanism by which ghrelin beta cells) and glucagon (released from alpha cells) exert oppo- inhibits insulin release warrants further exploration. site effects on glycaemia, with insulin promoting glucose uptake The aims of this study were to build a transcriptomic profile in conditions of high glucose and glucagon initiating hepatic of pancreatic delta cells, in comparison with alpha and beta cells, glucose production in periods of decreasing glucose levels [1]. and to identify specific delta cell markers and regulators. Having Nuanced interactions and crosstalk between islet cell types are demonstrated Ghsr expression to be highly enriched in delta critical in maintaining tight control over blood glucose equilibri- cells, we further aimed to characterise the effects of ghrelin on um, and elucidating the ways in which enteric signals and islet delta cell signalling pathways and islet cell secretory profiles. cells interact to influence circulating glucose levels could provide insights into the mechanisms underlying altered glycaemic con- trol and diabetes [2, 3]. Methods A key paracrine mediator within islet cells is somatostatin (SST), which is produced by pancreatic delta cells. SSTappears Solutions Unless otherwise stated, all chemicals were ob- to exert tonic suppression of insulin and glucagon release with- tained from Sigma-Aldrich (Poole, UK). The standard bath in islets [4]. The importance of this potent paracrine mechanism solution contained 138 mmol/l NaCl, 4.5 mmol/l KCl, is illustrated by experiments showing that whole-animal genet- 4.2 mmol/l NaHCO3, 1.2 mmol/l NaH2PO4, 2.6 mmol/l ic ablation of Sst results in aberrant secretion of both insulin and CaCl2,1.2mmol/lMgCl2 and 10 mmol/l HEPES glucagon from isolated islets in response to glucose [5]. Indeed, (pH 7.4, NaOH). Mouse ghrelin and SST receptor the dysregulation of SST-mediated negative-feedback loops (SSTR) antagonists (H-5884 + H-6056) were obtained from has been implicated in the development of type 2 diabetes Bachem (Bubendorf, Switzerland). [6]. Compared with our knowledge of insulin and glucagon release, there is still much to learn about the regulatory path- Animals All animal procedures were approved by the local ways and cellular machinery underlying SST secretion. ethics committee and conformed to UK Home Office regula- Identifying how delta cells differ from their neighbouring alpha tions or those of the Animal Experiments Inspectorate, and beta cells is crucial for interpreting transcriptomic and func- Ministry of Justice, Denmark, and the eighth edition of the tional data obtained from whole islets [7]. Guide for the Care and Use of Laboratory Animals (2011) Ghrelin is a peptide hormone that has been identified as a (http://grants.nih.gov/grants/olaw/guide-for-the-care-and-use- key component of the gut–brain axis [8]. It is synthesised of-laboratory-animals.pdf). For the isolation of purified predominantly in the stomach [9, 10] and gastrointestinal tract populations of alpha and beta cells, transgenic mice [11], although there have been reports of ghrelin-producing expressing the Venus fluorophore under the control of the epsilon cells in adult islets [12, 13]. Ghrelin levels in plasma proglucagon promoter, Glu (also known as Gcg), (Glu-Venus) are influenced by nutritional status and may influence growth [27] were used. For the introduction of delta cell specific hormone secretion, appetite and fat deposition [14]. transgenes for FACS-mediated purification or the introduction Importantly, there are indications that ghrelin plays a role in of the genetically encoded calcium sensor GCaMP3 [28], trans- the regulation of the pancreas in response to changes in glu- genic mice expressing Cre under the control of the Sst promoter cose levels [15]. A large number of reports have examined the [29, 30] were used. These mice were crossed with reporter effects of the active acylated form of ghrelin on glucose- strains containing genes encoding tandem red fluorescent pro- stimulated insulin secretion. The consensus of these studies tein (tdRFP) (a gift from H. J. Fehling, University Clinic Ulm, is that ghrelin exerts acute inhibition of insulin release Ulm, Germany), GCaMP3 (Charles River, Margate, UK) or [16–19], and that ghrelin infusions lead to impaired glucose enhanced yellow fluorescent protein (EYFP) (Charles River) tolerance [20, 21]. In addition, pharmacological
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