Publications by authors named "Frank Reimann"

186 Publications

Glucagon-like peptide-1 (GLP-1) receptor activation dilates cerebral arterioles, increases cerebral blood flow, and mediates remote (pre)conditioning neuroprotection against ischaemic stroke.

Basic Res Cardiol 2021 May 3;116(1):32. Epub 2021 May 3.

Centre for Cardiovascular and Metabolic Neuroscience, Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK.

Stroke remains one of the most common causes of death and disability worldwide. Several preclinical studies demonstrated that the brain can be effectively protected against ischaemic stroke by two seemingly distinct treatments: remote ischaemic conditioning (RIC), involving cycles of ischaemia/reperfusion applied to a peripheral organ or tissue, or by systemic administration of glucagon-like-peptide-1 (GLP-1) receptor (GLP-1R) agonists. The mechanisms underlying RIC- and GLP-1-induced neuroprotection are not completely understood. In this study, we tested the hypothesis that GLP-1 mediates neuroprotection induced by RIC and investigated the effect of GLP-1R activation on cerebral blood vessels, as a potential mechanism of GLP-1-induced protection against ischaemic stroke. A rat model of ischaemic stroke (90 min of middle cerebral artery occlusion followed by 24-h reperfusion) was used. RIC was induced by 4 cycles of 5 min left hind limb ischaemia interleaved with 5-min reperfusion periods. RIC markedly (by ~ 80%) reduced the cerebral infarct size and improved the neurological score. The neuroprotection established by RIC was abolished by systemic blockade of GLP-1R with a specific antagonist Exendin(9-39). In the cerebral cortex of GLP-1R reporter mice, ~ 70% of cortical arterioles displayed GLP-1R expression. In acute brain slices of the rat cerebral cortex, activation of GLP-1R with an agonist Exendin-4 had a strong dilatory effect on cortical arterioles and effectively reversed arteriolar constrictions induced by metabolite lactate or oxygen and glucose deprivation, as an ex vivo model of ischaemic stroke. In anaesthetised rats, Exendin-4 induced lasting increases in brain tissue PO, indicative of increased cerebral blood flow. These results demonstrate that neuroprotection against ischaemic stroke established by remote ischaemic conditioning is mediated by a mechanism involving GLP-1R signalling. Potent dilatory effect of GLP-1R activation on cortical arterioles suggests that the neuroprotection in this model is mediated via modulation of cerebral blood flow and improved brain perfusion.
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http://dx.doi.org/10.1007/s00395-021-00873-9DOI Listing
May 2021

Nutrient-Induced Cellular Mechanisms of Gut Hormone Secretion.

Nutrients 2021 Mar 9;13(3). Epub 2021 Mar 9.

Wellcome Trust-MRC Institute of Metabolic Science Metabolic Research Laboratories, Cambridge University, Addenbrookes Hospital, Cambridge CB2 0QQ, UK.

The gastrointestinal tract can assess the nutrient composition of ingested food. The nutrient-sensing mechanisms in specialised epithelial cells lining the gastrointestinal tract, the enteroendocrine cells, trigger the release of gut hormones that provide important local and central feedback signals to regulate nutrient utilisation and feeding behaviour. The evidence for nutrient-stimulated secretion of two of the most studied gut hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), along with the known cellular mechanisms in enteroendocrine cells recruited by nutrients, will be the focus of this review. The mechanisms involved range from electrogenic transporters, ion channel modulation and nutrient-activated G-protein coupled receptors that converge on the release machinery controlling hormone secretion. Elucidation of these mechanisms will provide much needed insight into postprandial physiology and identify tractable dietary approaches to potentially manage nutrition and satiety by altering the secreted gut hormone profile.
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http://dx.doi.org/10.3390/nu13030883DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8000029PMC
March 2021

Peptidomics of enteroendocrine cells and characterisation of potential effects of a novel preprogastrin derived-peptide on glucose tolerance in lean mice.

Peptides 2021 Mar 17;140:170532. Epub 2021 Mar 17.

University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Hills Road, Cambridge, CB2 0QQ, UK. Electronic address:

Objectives: To analyse the peptidomics of mouse enteroendocrine cells (EECs) and human gastrointestinal (GI) tissue and identify novel gut derived peptides.

Methods: High resolution nano-flow liquid chromatography mass spectrometry (LC-MS/MS) was performed on (i) flow-cytometry purified NeuroD1 positive cells from mouse and homogenised human intestinal biopsies, (ii) supernatants from primary murine intestinal cultures, (iii) intestinal homogenates from mice fed high fat diet. Candidate bioactive peptides were selected on the basis of species conservation, high expression/biosynthesis in EECs and evidence of regulated secretionin vitro. Candidate novel gut-derived peptides were chronically administered to mice to assess effects on food intake and glucose tolerance.

Results: A large number of peptide fragments were identified from human and mouse, including known full-length gut hormones and enzymatic degradation products. EEC-specific peptides were largely from vesicular proteins, particularly prohormones, granins and processing enzymes, of which several exhibited regulated secretion in vitro. No regulated peptides were identified from previously unknown genes. High fat feeding particularly affected the distal colon, resulting in reduced peptide levels from GCG, PYY and INSL5. Of the two candidate novel peptides tested in vivo, a peptide from Chromogranin A (ChgA 435-462a) had no measurable effect, but a progastrin-derived peptide (Gast p59-79), modestly improved glucose tolerance in lean mice.

Conclusion: LC-MS/MS peptidomic analysis of murine EECs and human GI tissue identified the spectrum of peptides produced by EECs, including a potential novel gut hormone, Gast p59-79, with minor effects on glucose tolerance.
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http://dx.doi.org/10.1016/j.peptides.2021.170532DOI Listing
March 2021

Positive Effects of NPY1 Receptor Activation on Islet Structure Are Driven by Pancreatic Alpha- and Beta-Cell Transdifferentiation in Diabetic Mice.

Front Endocrinol (Lausanne) 2021 25;12:633625. Epub 2021 Feb 25.

SAAD Centre for Pharmacy and Diabetes, Ulster University, Coleraine, United Kingdom.

Enzymatically stable and specific neuropeptide Y1 receptor (NPYR1) agonists, such as sea lamprey PYY(1-36) (SL-PYY(1-36)), are believed to improve glucose regulation in diabetes by targeting pancreatic islets. In this study, streptozotocin (STZ) diabetic transgenic ; and ; mouse models have been used to study effects of sustained NPYR1 activation on islet cell composition and alpha- and beta-cell lineage transitioning. STZ induced a particularly severe form of diabetes in ; mice, but twice-daily administration (25 nmol/kg) of SL-PYY(1-36) for 11 days consistently improved metabolic status. Blood glucose was decreased (p < 0.05 - p < 0.001) and both fasted plasma and pancreatic insulin significantly increased by SL-PYY(1-36). In both ; and ; mice, STZ provoked characteristic losses (p < 0.05 - p < 0.001) of islet numbers, beta-cell and pancreatic islet areas together with increases in area and central islet location of alpha-cells. With exception of alpha-cell area, these morphological changes were fully, or partially, returned to non-diabetic control levels by SL-PYY(1-36). Interestingly, STZ apparently triggered decreased (p < 0.001) alpha- to beta-cell transition in ; mice, together with increased loss of beta-cell identity in ; mice, but both effects were significantly (p < 0.001) reversed by SL-PYY(1-36). SL-PYY(1-36) also apparently reduced (p < 0.05) beta- to alpha-cell conversion in ; mice and glucagon expressing alpha-cells in ; mice. These data indicate that islet benefits of prolonged NPY1R activation, and especially restoration of beta-cell mass, are observed irrespective of diabetes status, being linked to cell lineage alterations including transdifferentiation of alpha- to beta-cells.
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http://dx.doi.org/10.3389/fendo.2021.633625DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7949013PMC
February 2021

Central and peripheral GLP-1 systems independently suppress eating.

Nat Metab 2021 02 15;3(2):258-273. Epub 2021 Feb 15.

Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK.

The anorexigenic peptide glucagon-like peptide-1 (GLP-1) is secreted from gut enteroendocrine cells and brain preproglucagon (PPG) neurons, which, respectively, define the peripheral and central GLP-1 systems. PPG neurons in the nucleus tractus solitarii (NTS) are widely assumed to link the peripheral and central GLP-1 systems in a unified gut-brain satiation circuit. However, direct evidence for this hypothesis is lacking, and the necessary circuitry remains to be demonstrated. Here we show that PPG neurons encode satiation in mice, consistent with vagal signalling of gastrointestinal distension. However, PPG neurons predominantly receive vagal input from oxytocin-receptor-expressing vagal neurons, rather than those expressing GLP-1 receptors. PPG neurons are not necessary for eating suppression by GLP-1 receptor agonists, and concurrent PPG neuron activation suppresses eating more potently than semaglutide alone. We conclude that central and peripheral GLP-1 systems suppress eating via independent gut-brain circuits, providing a rationale for pharmacological activation of PPG neurons in combination with GLP-1 receptor agonists as an obesity treatment strategy.
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http://dx.doi.org/10.1038/s42255-021-00344-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116821PMC
February 2021

Inhibition of mitochondrial function by metformin increases glucose uptake, glycolysis and GDF-15 release from intestinal cells.

Sci Rep 2021 Jan 28;11(1):2529. Epub 2021 Jan 28.

MRC Metabolic Diseases Unit, Addenbrooke's Hospital, Wellcome Trust/MRC Institute of Metabolic Science (IMS), University of Cambridge, Hills Road, Cambridge, CB2 0QQ, UK.

Even though metformin is widely used to treat type2 diabetes, reducing glycaemia and body weight, the mechanisms of action are still elusive. Recent studies have identified the gastrointestinal tract as an important site of action. Here we used intestinal organoids to explore the effects of metformin on intestinal cell physiology. Bulk RNA-sequencing analysis identified changes in hexose metabolism pathways, particularly glycolytic genes. Metformin increased expression of Slc2a1 (GLUT1), decreased expression of Slc2a2 (GLUT2) and Slc5a1 (SGLT1) whilst increasing GLUT-dependent glucose uptake and glycolytic rate as observed by live cell imaging of genetically encoded metabolite sensors and measurement of oxygen consumption and extracellular acidification rates. Metformin caused mitochondrial dysfunction and metformin's effects on 2D-cultures were phenocopied by treatment with rotenone and antimycin-A, including upregulation of GDF15 expression, previously linked to metformin dependent weight loss. Gene expression changes elicited by metformin were replicated in 3D apical-out organoids and distal small intestines of metformin treated mice. We conclude that metformin affects glucose uptake, glycolysis and GDF-15 secretion, likely downstream of the observed mitochondrial dysfunction. This may explain the effects of metformin on intestinal glucose utilisation and food balance.
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http://dx.doi.org/10.1038/s41598-021-81349-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7843649PMC
January 2021

Chemosensing in enteroendocrine cells: mechanisms and therapeutic opportunities.

Curr Opin Endocrinol Diabetes Obes 2021 04;28(2):222-231

University of Cambridge, Institute of Metabolic Science and MRC Metabolic Diseases Unit, Addenbrooke's Hospital, Cambridge, UK.

Purpose Of Review: Enteroendocrine cells (EECs) are scattered chemosensory cells in the intestinal epithelium that release hormones with a wide range of actions on intestinal function, food intake and glucose homeostasis. The mechanisms by which gut hormones are secreted postprandially, or altered by antidiabetic agents and surgical interventions are of considerable interest for future therapeutic development.

Recent Findings: EECs are electrically excitable and express a repertoire of G-protein coupled receptors that sense nutrient and nonnutrient stimuli, coupled to intracellular Ca2+ and cyclic adenosine monophosphate. Our knowledge of EEC function, previously developed using mouse models, has recently been extended to human cells. Gut hormone release in humans is enhanced by bariatric surgery, as well as by some antidiabetic agents including sodium-coupled glucose transporter inhibitors and metformin.

Summary: EECs are important potential therapeutic targets. A better understanding of their chemosensory mechanisms will enhance the development of new therapeutic strategies to treat metabolic and gastrointestinal diseases.
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http://dx.doi.org/10.1097/MED.0000000000000614DOI Listing
April 2021

Metabolic Messengers: glucagon-like peptide 1.

Nat Metab 2021 02 11;3(2):142-148. Epub 2021 Jan 11.

Wellcome Trust MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, UK.

Glucagon like peptide-1 (GLP-1), a peptide hormone from the intestinal tract, plays a central role in the coordination of postprandial glucose homeostasis through actions on insulin secretion, food intake and gut motility. GLP-1 forms the basis for a variety of current drugs for the treatment of type 2 diabetes and obesity, as well as new agents currently being developed. Here, we provide a concise overview of the core physiology of GLP-1 secretion and action, and the role of the peptide in human health, disease and therapeutics.
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http://dx.doi.org/10.1038/s42255-020-00327-xDOI Listing
February 2021

A cross-platform approach identifies genetic regulators of human metabolism and health.

Nat Genet 2021 01 7;53(1):54-64. Epub 2021 Jan 7.

Metabolic Research Laboratories, University of Cambridge, Cambridge, UK.

In cross-platform analyses of 174 metabolites, we identify 499 associations (P < 4.9 × 10) characterized by pleiotropy, allelic heterogeneity, large and nonlinear effects and enrichment for nonsynonymous variation. We identify a signal at GLP2R (p.Asp470Asn) shared among higher citrulline levels, body mass index, fasting glucose-dependent insulinotropic peptide and type 2 diabetes, with β-arrestin signaling as the underlying mechanism. Genetically higher serine levels are shown to reduce the likelihood (by 95%) and predict development of macular telangiectasia type 2, a rare degenerative retinal disease. Integration of genomic and small molecule data across platforms enables the discovery of regulators of human metabolism and translation into clinical insights.
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http://dx.doi.org/10.1038/s41588-020-00751-5DOI Listing
January 2021

Organoid Sample Preparation and Extraction for LC-MS Peptidomics.

STAR Protoc 2020 Dec 25;1(3):100164. Epub 2020 Nov 25.

Wellcome Trust - MRC Institute of Metabolic Science Metabolic Research Laboratories, University of Cambridge, Addenbrookes Hospital, Hills Road, Cambridge, UK.

This protocol describes the peptidomic analysis of organoid lysates, FACS-purified cell populations, and 2D culture secretions by liquid chromatography mass spectrometry (LC-MS). Currently, most peptides are quantified by ELISA, limiting the peptides that can be studied. However, an LC-MS-based approach allows more peptides to be monitored. Our group has previously used LC-MS for tissue peptidomics and secretion of enteroendocrine peptides from primary culture. Now, we extend the use to organoid models. For complete details on the use and execution of this protocol, please refer to Goldspink et al. (2020).
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http://dx.doi.org/10.1016/j.xpro.2020.100164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757358PMC
December 2020

Behavioural and neurochemical mechanisms underpinning the feeding-suppressive effect of GLP-1/CCK combinatorial therapy.

Mol Metab 2021 01 19;43:101118. Epub 2020 Nov 19.

MRC Metabolic Diseases Unit, University of Cambridge Metabolic Research Laboratories, WT-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 OQQ, UK. Electronic address:

Objectives: Combinatorial therapies are under intense investigation to develop more efficient anti-obesity drugs; however, little is known about how they act in the brain to produce enhanced anorexia and weight loss. The goal of this study was to identify the brain sites and neuronal populations engaged during the co-administration of GLP-1R and CCK1R agonists, an efficient combination therapy in obese rodents.

Methods: We measured acute and long-term feeding and body weight responses and neuronal activation patterns throughout the neuraxis and in specific neuronal subsets in response to GLP-1R and CCK1R agonists administered alone or in combination in lean and high-fat diet fed mice. We used PhosphoTRAP to obtain unbiased molecular markers for neuronal populations selectively activated by the combination of the two agonists.

Results: The initial anorectic response to GLP-1R and CCK1R co-agonism was mediated by a reduction in meal size, but over a few hours, a reduction in meal number accounted for the sustained feeding suppressive effects. The nucleus of the solitary tract (NTS) is one of the few brain sites where GLP-1R and CCK1R signalling interact to produce enhanced neuronal activation. None of the previously categorised NTS neuronal subpopulations relevant to feeding behaviour were implicated in this increased activation. However, we identified NTS/AP Calcrl neurons as treatment targets.

Conclusions: Collectively, these studies indicated that circuit-level integration of GLP-1R and CCK1R co-agonism in discrete brain nuclei including the NTS produces enhanced rapid and sustained appetite suppression and weight loss.
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http://dx.doi.org/10.1016/j.molmet.2020.101118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7720077PMC
January 2021

Ligand-Specific Factors Influencing GLP-1 Receptor Post-Endocytic Trafficking and Degradation in Pancreatic Beta Cells.

Int J Mol Sci 2020 Nov 9;21(21). Epub 2020 Nov 9.

Section of Endocrinology and Investigative Medicine, Imperial College London, London W12 0NN, UK.

The glucagon-like peptide-1 receptor (GLP-1R) is an important regulator of blood glucose homeostasis. Ligand-specific differences in membrane trafficking of the GLP-1R influence its signalling properties and therapeutic potential in type 2 diabetes. Here, we have evaluated how different factors combine to control the post-endocytic trafficking of GLP-1R to recycling versus degradative pathways. Experiments were performed in primary islet cells, INS-1 832/3 clonal beta cells and HEK293 cells, using biorthogonal labelling of GLP-1R to determine its localisation and degradation after treatment with GLP-1, exendin-4 and several further GLP-1R agonist peptides. We also characterised the effect of a rare GLP1R coding variant, T149M, and the role of endosomal peptidase endothelin-converting enzyme-1 (ECE-1), in GLP1R trafficking. Our data reveal how treatment with GLP-1 versus exendin-4 is associated with preferential GLP-1R targeting towards a recycling pathway. GLP-1, but not exendin-4, is a substrate for ECE-1, and the resultant propensity to intra-endosomal degradation, in conjunction with differences in binding affinity, contributes to alterations in GLP-1R trafficking behaviours and degradation. The T149M GLP-1R variant shows reduced signalling and internalisation responses, which is likely to be due to disruption of the cytoplasmic region that couples to intracellular effectors. These observations provide insights into how ligand- and genotype-specific factors can influence GLP-1R trafficking.
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http://dx.doi.org/10.3390/ijms21218404DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7664906PMC
November 2020

Expected values for gastrointestinal and pancreatic hormone concentrations in healthy volunteers in the fasting and postprandial state.

Ann Clin Biochem 2021 03 7;58(2):108-116. Epub 2020 Dec 7.

Wellcome Trust-MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Background: Gastrointestinal hormones regulate intestinal transit, control digestion, influence appetite and promote satiety. Altered production or action of gut hormones, including glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and peptide YY (PYY), may contribute to the biological basis of obesity and altered glucose homeostasis. However, challenges in analytical methodology and lack of clarity on expected values for healthy individuals have limited progress in this field. The aim of this study was to describe expected concentrations of gastrointestinal and pancreatic hormones in healthy volunteers following a standardized meal test (SMT) or 75 g oral glucose tolerance test (OGTT).

Methods: A total of 28 healthy volunteers (12 men, 16 women; mean age 31.3 years; mean body mass index 24.9 kg/m) were recruited to attend a hospital clinic on two occasions. Volunteers had blood sampling in the fasting state and were given, in randomized order, an oral glucose tolerance test (OGTT) and standardized mixed liquid meal test with venepuncture at timed intervals for 4 h after ingestion. Analytical methods for gut and pancreatic hormones were assessed and optimized. Concentrations of gut and pancreatic hormones were measured and used to compile ranges of expected values.

Results: Ranges of expected values were created for glucose, insulin, glucagon, GLP-1, GIP, PYY and free fatty acids in response to a standardized mixed liquid meal or OGTT. Intact proinsulin and C-peptide levels were also measured following the OGTT.

Conclusions: These ranges of expected values can now be used to compare gut hormone concentrations between healthy individuals and patient groups.
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http://dx.doi.org/10.1177/0004563220975658DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7961662PMC
March 2021

Antidiabetic drug therapy alleviates type 1 diabetes in mice by promoting pancreatic α-cell transdifferentiation.

Biochem Pharmacol 2020 12 11;182:114216. Epub 2020 Sep 11.

School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine BT52 1SA, UK. Electronic address:

Gut incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP), enhance secretion of insulin in a glucose-dependent manner, predominantly by elevating cytosolic levels of cAMP in pancreatic β-cells. Successful targeting of the incretin pathway by several drugs, however, suggests the antidiabetic mechanism is likely to span beyond the acute effect on hormone secretion and include, for instance, stimulation of β-cell growth and/or proliferation. Likewise, the antidiabetic action of kidney sodium-glucose linked transporter-2 (SGLT-2) inhibitors exceeds simple increase glucose excretion. Potential reasons for these 'added benefits' may lie in the long-term effects of these signals on developmental aspects of pancreatic islet cells. In this work, we explored if the incretin mimetics or SGLT-2 inhibitors can affect the size of the islet α- or β-cell compartments, under the condition of β-cell stress. To that end, we utilised mice expressing YFP specifically in pancreatic α-cells, in which we modelled type 1 diabetes by injecting streptozotocin, followed by a 10-day administration of liraglutide, sitagliptin or dapagliflozin. We observed an onset of diabetic phenotype, which was partially reversed by the administration of the antidiabetic drugs. The mechanism for the reversal included induction of β-cell proliferation, decrease in β-cell apoptosis and, for the incretin mimetics, transdifferentiation of α-cells into β-cells. Our data therefore emphasize the role of chronic incretin signalling in induction of α-/β-cell transdifferentiation. We conclude that incretin peptides may act directly on islet cells, making use of the endogenous local sites of 'ectopic' expression, whereas SGLT-2 inhibitors work via protecting β-cells from chronic hyperglycaemia.
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http://dx.doi.org/10.1016/j.bcp.2020.114216DOI Listing
December 2020

SGLT2 is not expressed in pancreatic α- and β-cells, and its inhibition does not directly affect glucagon and insulin secretion in rodents and humans.

Mol Metab 2020 12 5;42:101071. Epub 2020 Sep 5.

Pole of Endocrinology, Diabetes, and Nutrition (EDIN), Institute of Experimental and Clinical Research (IREC), Université Catholique de Louvain (UCLouvain), 1200, Brussels, Belgium. Electronic address:

Objective: Sodium-glucose cotransporter 2 (SGLT2) inhibitors (SGLT2i), or gliflozins, are anti-diabetic drugs that lower glycemia by promoting glucosuria, but they also stimulate endogenous glucose and ketone body production. The likely causes of these metabolic responses are increased blood glucagon levels, and decreased blood insulin levels, but the mechanisms involved are hotly debated. This study verified whether or not SGLT2i affect glucagon and insulin secretion by a direct action on islet cells in three species, using multiple approaches.

Methods: We tested the in vivo effects of two selective SGLT2i (dapagliflozin, empagliflozin) and a SGLT1/2i (sotagliflozin) on various biological parameters (glucosuria, glycemia, glucagonemia, insulinemia) in mice. mRNA expression of SGLT2 and other glucose transporters was assessed in rat, mouse, and human FACS-purified α- and β-cells, and by analysis of two human islet cell transcriptomic datasets. Immunodetection of SGLT2 in pancreatic tissues was performed with a validated antibody. The effects of dapagliflozin, empagliflozin, and sotagliflozin on glucagon and insulin secretion were assessed using isolated rat, mouse and human islets and the in situ perfused mouse pancreas. Finally, we tested the long-term effect of SGLT2i on glucagon gene expression.

Results: SGLT2 inhibition in mice increased the plasma glucagon/insulin ratio in the fasted state, an effect correlated with a decline in glycemia. Gene expression analyses and immunodetections showed no SGLT2 mRNA or protein expression in rodent and human islet cells, but moderate SGLT1 mRNA expression in human α-cells. However, functional experiments on rat, mouse, and human (29 donors) islets and the in situ perfused mouse pancreas did not identify any direct effect of dapagliflozin, empagliflozin or sotagliflozin on glucagon and insulin secretion. SGLT2i did not affect glucagon gene expression in rat and human islets.

Conclusions: The data indicate that the SGLT2i-induced increase of the plasma glucagon/insulin ratio in vivo does not result from a direct action of the gliflozins on islet cells.
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http://dx.doi.org/10.1016/j.molmet.2020.101071DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7554656PMC
December 2020

The cytokine GDF15 signals through a population of brainstem cholecystokinin neurons to mediate anorectic signalling.

Elife 2020 07 29;9. Epub 2020 Jul 29.

Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom.

The cytokine, GDF15, is produced in pathological states which cause cellular stress, including cancer. When over expressed, it causes dramatic weight reduction, suggesting a role in disease-related anorexia. Here, we demonstrate that the GDF15 receptor, GFRAL, is located in a subset of cholecystokinin neurons which span the area postrema and the nucleus of the tractus solitarius of the mouse. GDF15 activates GFRAL neurons and supports conditioned taste and place aversions, while the anorexia it causes can be blocked by a monoclonal antibody directed at GFRAL or by disrupting CCK neuronal signalling. The cancer-therapeutic drug, cisplatin, induces the release of GDF15 and activates GFRAL neurons, as well as causing significant reductions in food intake and body weight in mice. These metabolic effects of cisplatin are abolished by pre-treatment with the GFRAL monoclonal antibody. Our results suggest that GFRAL neutralising antibodies or antagonists may provide a co-treatment opportunity for patients undergoing chemotherapy.
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http://dx.doi.org/10.7554/eLife.55164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7410488PMC
July 2020

Human Labor Pain Is Influenced by the Voltage-Gated Potassium Channel K6.4 Subunit.

Cell Rep 2020 07;32(3):107941

Cambridge Institute for Medical Research, Wellcome Trust MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 0QQ, UK. Electronic address:

By studying healthy women who do not request analgesia during their first delivery, we investigate genetic effects on labor pain. Such women have normal sensory and psychometric test results, except for significantly higher cuff pressure pain. We find an excess of heterozygotes carrying the rare allele of SNP rs140124801 in KCNG4. The rare variant K6.4-Met419 has a dominant-negative effect and cannot modulate the voltage dependence of K2.1 inactivation because it fails to traffic to the plasma membrane. In vivo, Kcng4 (K6.4) expression occurs in 40% of retrograde-labeled mouse uterine sensory neurons, all of which express K2.1, and over 90% express the nociceptor genes Trpv1 and Scn10a. In neurons overexpressing K6.4-Met419, the voltage dependence of inactivation for K2.1 is more depolarized compared with neurons overexpressing K6.4. Finally, K6.4-Met419-overexpressing neurons have a higher action potential threshold. We conclude that K6.4 can influence human labor pain by modulating the excitability of uterine nociceptors.
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http://dx.doi.org/10.1016/j.celrep.2020.107941DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7383234PMC
July 2020

Labeling and Characterization of Human GLP-1-Secreting L-cells in Primary Ileal Organoid Culture.

Cell Rep 2020 06;31(13):107833

Wellcome Trust - MRC Institute of Metabolic Science Metabolic Research Laboratories, Addenbrooke's Hospital, Hills Road, Cambridge CB2 0QQ, UK. Electronic address:

Glucagon-like peptide-1 (GLP-1) from intestinal L-cells stimulates insulin secretion and reduces appetite after food ingestion, and it is the basis for drugs against type-2 diabetes and obesity. Drugs targeting L- and other enteroendocrine cells are under development, with the aim to mimic endocrine effects of gastric bypass surgery, but they are difficult to develop without human L-cell models. Human ileal organoids, engineered by CRISPR-Cas9, express the fluorescent protein Venus in the proglucagon locus, enabling maintenance of live, identifiable human L-cells in culture. Fluorescence-activated cell sorting (FACS)-purified organoid-derived L-cells, analyzed by RNA sequencing (RNA-seq), express hormones, receptors, and ion channels, largely typical of their murine counterparts. L-cells are electrically active and exhibit membrane depolarization and calcium elevations in response to G-protein-coupled receptor ligands. Organoids secrete hormones in response to glucose and other stimuli. The ability to label and maintain human L-cells in organoid culture opens avenues to explore L-cell function and develop drugs targeting the human enteroendocrine system.
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http://dx.doi.org/10.1016/j.celrep.2020.107833DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7342002PMC
June 2020

Mass spectrometric characterisation of the circulating peptidome following oral glucose ingestion in control and gastrectomised patients.

Rapid Commun Mass Spectrom 2020 Sep;34(18):e8849

Wellcome Trust - MRC Institute of Metabolic Science Metabolic Research Laboratories, Cambridge University, Addenbrookes Hospital, Cambridge, CB2 0QQ, UK.

Rationale: Meal ingestion triggers secretion of a variety of gut and endocrine peptides important in diabetes research which are routinely measured by immunoassays. However, similarities between some peptides (glucagon, oxyntomodulin and glicentin) can cause specificity issues with immunoassays. We used a liquid chromatography/tandem mass spectrometry (LC/MS/MS) methodology to unambiguously monitor multiple gut peptides in human plasma.

Methods: A simple acetonitrile-based protein precipitation step, followed by evaporation and solid-phase extraction, removed high-abundance proteins from samples prior to nano-LC/MS/MS analysis on an Orbitrap Q-Exactive Plus mass spectrometer using a data-dependent methodology. Database searching using PEAKS identified multiple gut-derived peptides, including peptides in the mid-pg/mL range. The relative levels of these and previously characterised peptides were assessed in plasma samples from gastrectomised and control subjects during an oral glucose tolerance test.

Results: Analysis of plasma extracts revealed significantly elevated levels of a number of peptides following glucose ingestion in subjects who had undergone gastrectomy compared with controls. These included GLP-1(7-36), GLP-1(9-36), glicentin, oxyntomodulin, GIP(1-42), GIP(3-42), PYY(1-36), PYY(3-36), neurotensin, insulin and C-peptide. Motilin levels decreased following glucose ingestion. Results showed good correlation with immunoassay-derived concentrations of some peptides in the same samples. The gastrectomy group also had higher, but non-glucose-dependent, circulating levels of peptides from PIGR and DMBT1.

Conclusions: Overall, the approach showed that a fast, generic and reproducible LC/MS/MS methodology requiring only a small volume of plasma was capable of the multiplexed detection of a variety of diabetes-related peptides.
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http://dx.doi.org/10.1002/rcm.8849DOI Listing
September 2020

PPG neurons in the nucleus of the solitary tract modulate heart rate but do not mediate GLP-1 receptor agonist-induced tachycardia in mice.

Mol Metab 2020 09 21;39:101024. Epub 2020 May 21.

Centre for Cardiovascular and Metabolic Neuroscience, Department of Neuroscience, Physiology & Pharmacology, UCL, London, UK. Electronic address:

Objective: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used as anti-diabetic drugs and are approved for obesity treatment. However, GLP-1RAs also affect heart rate (HR) and arterial blood pressure (ABP) in rodents and humans. Although the activation of GLP-1 receptors (GLP-1R) is known to increase HR, the circuits recruited are unclear, and in particular, it is unknown whether GLP-1RAs activate preproglucagon (PPG) neurons, the brain source of GLP-1, to elicit these effects.

Methods: We investigated the effect of GLP-1RAs on heart rate in anaesthetized adult mice. In a separate study, we manipulated the activity of nucleus tractus solitarius (NTS) PPG neurons (PPG) in awake, freely behaving transgenic Glu-Cre mice implanted with biotelemetry probes and injected with AAV-DIO-hM3Dq:mCherry or AAV-mCherry-FLEX-DTA.

Results: Systemic administration of the GLP-1RA Ex-4 increased resting HR in anaesthetized or conscious mice, but had no effect on ABP in conscious mice. This effect was abolished by β-adrenoceptor blockade with atenolol, but unaffected by the muscarinic antagonist atropine. Furthermore, Ex-4-induced tachycardia persisted when PPG neurons were ablated, and Ex-4 did not induce expression of the neuronal activity marker cFos in PPG neurons. PPG ablation or acute chemogenetic inhibition of these neurons via hM4Di receptors had no effect on resting HR. In contrast, chemogenetic activation of PPG neurons increased resting HR. Furthermore, the application of GLP-1 within the subarachnoid space of the middle thoracic spinal cord, a major projection target of PPG neurons, increased HR.

Conclusions: These results demonstrate that both systemic application of Ex-4 or GLP-1 and chemogenetic activation of PPG neurons increases HR. Ex-4 increases the activity of cardiac sympathetic preganglionic neurons of the spinal cord without recruitment of PPG neurons, and thus likely recapitulates the physiological effects of PPG neuron activation. These neurons therefore do not play a significant role in controlling resting HR and ABP but are capable of inducing tachycardia and so are likely involved in cardiovascular responses to acute stress.
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http://dx.doi.org/10.1016/j.molmet.2020.101024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7317700PMC
September 2020

Ileo-colonic delivery of conjugated bile acids improves glucose homeostasis via colonic GLP-1-producing enteroendocrine cells in human obesity and diabetes.

EBioMedicine 2020 May 25;55:102759. Epub 2020 Apr 25.

Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Division of Gastroenterology and Hepatology, Mayo Clinic, Charlton 8-142, 200 First St. S.W., Rochester, MN 55905, United States. Electronic address:

Background: The bile acid (BA) pathway plays a role in regulation of food intake and glucose metabolism, based mainly on findings in animal models. Our aim was to determine whether the BA pathway is altered and correctable in human obesity and diabetes.

Methods: We conducted 3 investigations: 1) BA receptor pathways were studied in NCI-H716 enteroendocrine cell (EEC) line, whole human colonic mucosal tissue and in human colonic EEC isolated by Fluorescence-activated Cell Sorting (ex vivo) from endoscopically-obtained biopsies colon mucosa; 2) We characterized the BA pathway in 307 participants by measuring during fasting and postprandial levels of FGF19, 7αC4 and serum BA; 3) In a placebo-controlled, double-blind, randomised, 28-day trial, we studied the effect of ileo-colonic delivery of conjugated BAs (IC-CBAS) on glucose metabolism, incretins, and lipids, in participants with obesity and diabetes.

Findings: Human colonic GLP-1-producing EECs express TGR5, and upon treatment with bile acids in vitro, human EEC differentially expressed GLP-1 at the protein and mRNA level. In Ussing Chamber, GLP-1 release was stimulated by Taurocholic acid in either the apical or basolateral compartment. FGF19 was decreased in obesity and diabetes compared to controls. When compared to placebo, IC-CBAS significantly decreased postprandial glucose, fructosamine, fasting insulin, fasting LDL, and postprandial FGF19 and increased postprandial GLP-1 and C-peptide. Increase in faecal BA was associated with weight loss and with decreased fructosamine.

Interpretations: In humans, BA signalling machinery is expressed in colonic EECs, deficient in obesity and diabetes, and when stimulated with IC-CBAS, improved glucose homeostasis. ClinicalTrials.gov number, NCT02871882, NCT02033876.

Funding: Research support and drug was provided by Satiogen Pharmaceuticals (San Diego, CA). AA, MC, and NFL report grants (AA- C-Sig P30DK84567, K23 DK114460; MC- NIH R01 DK67071; NFL- R01 DK057993) from the NIH. JR was supported by an Early Career Grant from Society for Endocrinology.
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http://dx.doi.org/10.1016/j.ebiom.2020.102759DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7186521PMC
May 2020

Selective stimulation of colonic L cells improves metabolic outcomes in mice.

Diabetologia 2020 07 27;63(7):1396-1407. Epub 2020 Apr 27.

Wellcome Trust-MRC Institute of Metabolic Science-Metabolic Research Laboratories, University of Cambridge, Cambridge, CB2 OQQ, UK.

Aims/hypothesis: Insulin-like peptide-5 (INSL5) is found only in distal colonic L cells, which co-express glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). GLP-1 is a well-known insulin secretagogue, and GLP-1 and PYY are anorexigenic, whereas INSL5 is considered orexigenic. We aimed to clarify the metabolic impact of selective stimulation of distal colonic L cells in mice.

Methods: Insl5 promoter-driven expression of Gq-coupled Designer Receptor Exclusively Activated by Designer Drugs (DREADD) was employed to activate distal colonic L cells (L). IPGTT and food intake were assessed with and without DREADD activation.

Results: L cell stimulation with clozapine N-oxide (CNO; 0.3 mg/kg i.p.) increased plasma GLP-1 and PYY (2.67- and 3.31-fold, respectively); INSL5 was not measurable in plasma but was co-secreted with GLP-1 and PYY in vitro. IPGTT (2 g/kg body weight) revealed significantly improved glucose tolerance following CNO injection. CNO-treated mice also exhibited reduced food intake and body weight after 24 h, and increased defecation, the latter being sensitive to 5-hydroxytryptamine (5-HT) receptor 3 inhibition. Pre-treatment with a GLP1 receptor-blocking antibody neutralised the CNO-dependent improvement in glucose tolerance but did not affect the reduction in food intake, and an independent group of animals pair-fed to the CNO-treatment group demonstrated attenuated weight loss. Pre-treatment with JNJ-31020028, a neuropeptide Y receptor type 2 antagonist, abolished the CNO-dependent effect on food intake. Assessment of whole body physiology in metabolic cages revealed L cell stimulation increased energy expenditure and increased activity. Acute CNO-induced food intake and glucose homeostasis outcomes were maintained after 2 weeks on a high-fat diet.

Conclusions/interpretation: This proof-of-concept study demonstrates that selective distal colonic L cell stimulation has beneficial metabolic outcomes. Graphical abstract.
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http://dx.doi.org/10.1007/s00125-020-05149-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286941PMC
July 2020

Impact of global PTP1B deficiency on the gut barrier permeability during NASH in mice.

Mol Metab 2020 05 6;35:100954. Epub 2020 Feb 6.

Instituto de Investigaciones Biomédicas Alberto Sols (CSIC-UAM), Madrid, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, Madrid, Spain. Electronic address:

Objective: Non-alcoholic steatohepatitis (NASH) is characterized by a robust pro-inflammatory component at both hepatic and systemic levels together with a disease-specific gut microbiome signature. Protein tyrosine phosphatase 1 B (PTP1B) plays distinct roles in non-immune and immune cells, in the latter inhibiting pro-inflammatory signaling cascades. In this study, we have explored the role of PTP1B in the composition of gut microbiota and gut barrier dynamics in methionine and choline-deficient (MCD) diet-induced NASH in mice.

Methods: Gut features and barrier permeability were characterized in wild-type (PTP1B WT) and PTP1B-deficient knockout (PTP1B KO) mice fed a chow or methionine/choline-deficient (MCD) diet for 4 weeks. The impact of inflammation was studied in intestinal epithelial and enteroendocrine cells. The secretion of GLP-1 was evaluated in primary colonic cultures and plasma of mice.

Results: We found that a shift in the gut microbiota shape, disruption of gut barrier function, higher levels of serum bile acids, and decreased circulating glucagon-like peptide (GLP)-1 are features during NASH. Surprisingly, despite the pro-inflammatory phenotype of global PTP1B-deficient mice, they were partly protected against the alterations in gut microbiota composition during NASH and presented better gut barrier integrity and less permeability under this pathological condition. These effects concurred with higher colonic mucosal inflammation, decreased serum bile acids, and protection against the decrease in circulating GLP-1 levels during NASH compared with their WT counterparts together with increased expression of GLP-2-sensitive genes in the gut. At the molecular level, stimulation of enteroendocrine STC-1 cells with a pro-inflammatory conditioned medium (CM) from lipopolysaccharide (LPS)-stimulated macrophages triggered pro-inflammatory signaling cascades that were further exacerbated by a PTP1B inhibitor. Likewise, the pro-inflammatory CM induced GLP-1 secretion in primary colonic cultures, an effect augmented by PTP1B inhibition.

Conclusion: Altogether our results have unraveled a potential role of PTP1B in the gut-liver axis during NASH, likely mediated by increased sensitivity to GLPs, with potential therapeutic value.
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http://dx.doi.org/10.1016/j.molmet.2020.01.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7082558PMC
May 2020

Essential Role of Syntaxin-Binding Protein-1 in the Regulation of Glucagon-Like Peptide-1 Secretion.

Endocrinology 2020 05;161(5)

Departments of Physiology, University of Toronto, Toronto, ON, Canada.

Circadian secretion of the incretin, glucagon-like peptide-1 (GLP-1), correlates with expression of the core clock gene, Bmal1, in the intestinal L-cell. Several SNARE proteins known to be circadian in pancreatic α- and β-cells are also necessary for GLP-1 secretion. However, the role of the accessory SNARE, Syntaxin binding protein-1 (Stxbp1; also known as Munc18-1) in the L-cell is unknown. The aim of this study was to determine whether Stxbp1 is under circadian regulation in the L-cell and its role in the control of GLP-1 secretion. Stxbp1 was highly-enriched in L-cells, and STXBP1 was expressed in a subpopulation of L-cells in mouse and human intestinal sections. Stxbp1 transcripts and protein displayed circadian patterns in mGLUTag L-cells line, while chromatin-immunoprecipitation revealed increased interaction between BMAL1 and Stxbp1 at the peak time-point of the circadian pattern. STXBP1 recruitment to the cytosol and plasma membrane within 30 minutes of L-cell stimulation was also observed at this time-point. Loss of Stxbp1 in vitro and in vivo led to reduced stimulated GLP-1 secretion at the peak time-point of circadian release, and impaired GLP-1 secretion ex vivo. In conclusion, Stxbp1 is a circadian regulated exocytotic protein in the intestinal L-cell that is an essential regulatory component of GLP-1 secretion.
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http://dx.doi.org/10.1210/endocr/bqaa039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7124137PMC
May 2020

L-Cell Differentiation Is Induced by Bile Acids Through GPBAR1 and Paracrine GLP-1 and Serotonin Signaling.

Diabetes 2020 04 10;69(4):614-623. Epub 2020 Feb 10.

Novo Nordisk Foundation Center for Basic Metabolic Research Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

Glucagon-like peptide 1 (GLP-1) mimetics are effective drugs for treatment of type 2 diabetes, and there is consequently extensive interest in increasing endogenous GLP-1 secretion and L-cell abundance. Here we identify G-protein-coupled bile acid receptor 1 (GPBAR1) as a selective regulator of intestinal L-cell differentiation. Lithocholic acid and the synthetic GPBAR1 agonist, L3740, selectively increased L-cell density in mouse and human intestinal organoids and elevated GLP-1 secretory capacity. L3740 induced expression of and transcription factors and L3740 also increased the L-cell number and GLP-1 levels and improved glucose tolerance in vivo. Further mechanistic examination revealed that the effect of L3740 on L cells required intact GLP-1 receptor and serotonin 5-hydroxytryptamine receptor 4 (5-HT4) signaling. Importantly, serotonin signaling through 5-HT4 mimicked the effects of L3740, acting downstream of GLP-1. Thus, GPBAR1 agonists and other powerful GLP-1 secretagogues facilitate L-cell differentiation through a paracrine GLP-1-dependent and serotonin-mediated mechanism.
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http://dx.doi.org/10.2337/db19-0764DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224989PMC
April 2020

Secretin release after Roux-en-Y gastric bypass reveals a population of glucose-sensitive S cells in distal small intestine.

Int J Obes (Lond) 2020 09 3;44(9):1859-1871. Epub 2020 Feb 3.

Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.

Objectives: Gastrointestinal hormones contribute to the beneficial effects of Roux-en-Y gastric bypass surgery (RYGB) on glycemic control. Secretin is secreted from duodenal S cells in response to low luminal pH, but it is unknown whether its secretion is altered after RYGB and if secretin contributes to the postoperative improvement in glycemic control. We hypothesized that secretin secretion increases after RYGB as a result of the diversion of nutrients to more distal parts of the small intestine, and thereby affects islet hormone release.

Methods: A specific secretin radioimmunoassay was developed, evaluated biochemically, and used to quantify plasma concentrations of secretin in 13 obese individuals before, 1 week after, and 3 months after RYGB. Distribution of secretin and its receptor was assessed by RNA sequencing, mass-spectrometry and in situ hybridization in human and rat tissues. Isolated, perfused rat intestine and pancreas were used to explore the molecular mechanism underlying glucose-induced secretin secretion and to study direct effects of secretin on glucagon, insulin, and somatostatin secretion. Secretin was administered alone or in combination with GLP-1 to non-sedated rats to evaluate effects on glucose regulation.

Results: Plasma postprandial secretin was more than doubled in humans after RYGB (P < 0.001). The distal small intestine harbored secretin expressing cells in both rats and humans. Glucose increased the secretion of secretin in a sodium-glucose cotransporter dependent manner when administered to the distal part but not into the proximal part of the rat small intestine. Secretin stimulated somatostatin secretion (fold change: 1.59, P < 0.05) from the perfused rat pancreas but affected neither insulin (P = 0.2) nor glucagon (P = 0.97) secretion. When administered to rats in vivo, insulin secretion was attenuated and glucagon secretion increased (P = 0.04), while blood glucose peak time was delayed (from 15 to 45 min) and gastric emptying time prolonged (P = 0.004).

Conclusions: Glucose-sensing secretin cells located in the distal part of the small intestine may contribute to increased plasma concentrations observed after RYGB. The metabolic role of the distal S cells warrants further studies.
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http://dx.doi.org/10.1038/s41366-020-0541-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7445113PMC
September 2020

Somatostatin secretion by Na-dependent Ca-induced Ca release in pancreatic delta-cells.

Nat Metab 2020 01 20;2(1):32-40. Epub 2020 Jan 20.

Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, Churchill Hospital, Oxford, UK.

Pancreatic islets are complex micro-organs consisting of at least three different cell types: glucagon-secreting α-, insulin-producing β- and somatostatin-releasing δ-cells. Somatostatin is a powerful paracrine inhibitor of insulin and glucagon secretion. In diabetes, increased somatostatinergic signalling leads to defective counter-regulatory glucagon secretion. This increases the risk of severe hypoglycaemia, a dangerous complication of insulin therapy. The regulation of somatostatin secretion involves both intrinsic and paracrine mechanisms but their relative contributions and whether they interact remains unclear. Here we show that dapagliflozin-sensitive glucose- and insulin-dependent sodium uptake stimulates somatostatin secretion by elevating the cytoplasmic Na concentration ([Na]) and promoting intracellular Ca-induced Ca release (CICR). This mechanism also becomes activated when [Na] is elevated following the inhibition of the plasmalemmal Na-K pump by reductions of the extracellular K concentration emulating those produced by exogenous insulin . Islets from some donors with type-2 diabetes hypersecrete somatostatin, leading to suppression of glucagon secretion that can be alleviated by a somatostatin receptor antagonist. Our data highlight the role of Na as an intracellular second messenger, illustrate the significance of the intraislet paracrine network and provide a mechanistic framework for pharmacological correction of the hormone secretion defects associated with diabetes that selectively target the δ-cells.
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http://dx.doi.org/10.1038/s42255-019-0158-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6986923PMC
January 2020

Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics.

Nat Commun 2020 01 24;11(1):467. Epub 2020 Jan 24.

Institute of Metabolism and Systems Research (IMSR), and Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.

The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in metabolism. Presently, its visualization is limited to genetic manipulation, antibody detection or the use of probes that stimulate receptor activation. Herein, we present LUXendin645, a far-red fluorescent GLP1R antagonistic peptide label. LUXendin645 produces intense and specific membrane labeling throughout live and fixed tissue. GLP1R signaling can additionally be evoked when the receptor is allosterically modulated in the presence of LUXendin645. Using LUXendin645 and LUXendin651, we describe islet, brain and hESC-derived β-like cell GLP1R expression patterns, reveal higher-order GLP1R organization including membrane nanodomains, and track single receptor subpopulations. We furthermore show that the LUXendin backbone can be optimized for intravital two-photon imaging by installing a red fluorophore. Thus, our super-resolution compatible labeling probes allow visualization of endogenous GLP1R, and provide insight into class B GPCR distribution and dynamics both in vitro and in vivo.
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http://dx.doi.org/10.1038/s41467-020-14309-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6981144PMC
January 2020