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Cha J, Tong X, Walker EM, Dahan T, Cochrane VA, Ashe S, Russell R, Osipovich AB, Mawla AM, Guo M, Liu JH, Loyd ZA, Huising MO, Magnuson MA, Hebrok M, Dor Y, Stein R. Species-specific roles for the MAFA and MAFB transcription factors in regulating islet β cell identity. JCI Insight 2023; 8:e166386. [PMID: 37606041 PMCID: PMC10543725 DOI: 10.1172/jci.insight.166386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 07/06/2023] [Indexed: 08/23/2023] Open
Abstract
Type 2 diabetes (T2D) is associated with compromised identity of insulin-producing pancreatic islet β cells, characterized by inappropriate production of other islet cell-enriched hormones. Here, we examined how hormone misexpression was influenced by the MAFA and MAFB transcription factors, closely related proteins that maintain islet cell function. Mice specifically lacking MafA in β cells demonstrated broad, population-wide changes in hormone gene expression with an overall gene signature closely resembling islet gastrin+ (Gast+) cells generated under conditions of chronic hyperglycemia and obesity. A human β cell line deficient in MAFB, but not one lacking MAFA, also produced a GAST+ gene expression pattern. In addition, GAST was detected in human T2D β cells with low levels of MAFB. Moreover, evidence is provided that human MAFB can directly repress GAST gene transcription. These results support a potentially novel, species-specific role for MafA and MAFB in maintaining adult mouse and human β cell identity, respectively. Here, we discuss the possibility that induction of Gast/GAST and other non-β cell hormones, by reduction in the levels of these transcription factors, represents a dysfunctional β cell signature.
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Affiliation(s)
- Jeeyeon Cha
- Division of Diabetes, Endocrinology, and Metabolism, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Xin Tong
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Emily M. Walker
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Tehila Dahan
- Department of Developmental Biology and Cancer Research, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Veronica A. Cochrane
- Diabetes Center, Department of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Sudipta Ashe
- Diabetes Center, Department of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Ronan Russell
- Diabetes Center, Department of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Anna B. Osipovich
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Alex M. Mawla
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California, Davis, Davis, California, USA
| | - Min Guo
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Jin-hua Liu
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Zachary A. Loyd
- Division of Diabetes, Endocrinology, and Metabolism, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Mark O. Huising
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California, Davis, Davis, California, USA
| | - Mark A. Magnuson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Matthias Hebrok
- Diabetes Center, Department of Medicine, University of California, San Francisco, San Francisco, California, USA
| | - Yuval Dor
- Department of Developmental Biology and Cancer Research, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Roland Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
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Rawlinson S, Reichenbach A, Clarke RE, Nuñez-Iglesias J, Dempsey H, Lockie SH, Andrews ZB. In Vivo Photometry Reveals Insulin and 2-Deoxyglucose Maintain Prolonged Inhibition of VMH Vglut2 Neurons in Male Mice. Endocrinology 2022; 163:6631280. [PMID: 35788848 DOI: 10.1210/endocr/bqac095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Indexed: 11/19/2022]
Abstract
The ventromedial hypothalamic (VMH) nucleus is a well-established hub for energy and glucose homeostasis. In particular, VMH neurons are thought to be important for initiating the counterregulatory response to hypoglycemia, and ex vivo electrophysiology and immunohistochemistry data indicate a clear role for VMH neurons in sensing glucose concentration. However, the temporal response of VMH neurons to physiologically relevant changes in glucose availability in vivo has been hampered by a lack of available tools for measuring neuronal activity over time. Since the majority of neurons within the VMH are glutamatergic and can be targeted using the vesicular glutamate transporter Vglut2, we expressed cre-dependent GCaMP7s in Vglut2 cre mice and examined the response profile of VMH to intraperitoneal injections of glucose, insulin, and 2-deoxyglucose (2DG). We show that reduced available glucose via insulin-induced hypoglycemia and 2DG-induced glucoprivation, but not hyperglycemia induced by glucose injection, inhibits VMH Vglut2 neuronal population activity in vivo. Surprisingly, this inhibition was maintained for at least 45 minutes despite prolonged hypoglycemia and initiation of a counterregulatory response. Thus, although VMH stimulation, via pharmacological, electrical, or optogenetic approaches, is sufficient to drive a counterregulatory response, our data suggest VMH Vglut2 neurons are not the main drivers required to do so, since VMH Vglut2 neuronal population activity remains suppressed during hypoglycemia and glucoprivation.
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Affiliation(s)
- Sasha Rawlinson
- Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Alex Reichenbach
- Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Rachel E Clarke
- Department of Neurosciences, Medical University of South Carolina, Charleston, South Carolina 29425, USA
| | - Juan Nuñez-Iglesias
- Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, 3800, Australia
| | - Harry Dempsey
- Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Sarah H Lockie
- Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Zane B Andrews
- Monash Biomedicine Discovery Institute and Department of Physiology, Monash University, Clayton, Victoria, 3800, Australia
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3
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Khan D, Moffett RC, Flatt PR, Tarasov AI. Classical and non-classical islet peptides in the control of β-cell function. Peptides 2022; 150:170715. [PMID: 34958851 DOI: 10.1016/j.peptides.2021.170715] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 11/25/2021] [Accepted: 12/17/2021] [Indexed: 12/25/2022]
Abstract
The dual role of the pancreas as both an endocrine and exocrine gland is vital for food digestion and control of nutrient metabolism. The exocrine pancreas secretes enzymes into the small intestine aiding digestion of sugars and fats, whereas the endocrine pancreas secretes a cocktail of hormones into the blood, which is responsible for blood glucose control and regulation of carbohydrate, protein and fat metabolism. Classical islet hormones, insulin, glucagon, pancreatic polypeptide and somatostatin, interact in an autocrine and paracrine manner, to fine-tube the islet function and insulin secretion to the needs of the body. Recently pancreatic islets have been reported to express a number of non-classical peptide hormones involved in metabolic signalling, whose major production site was believed to reside outside pancreas, e.g. in the small intestine. We highlight the key non-classical islet peptides, and consider their involvement, together with established islet hormones, in regulation of stimulus-secretion coupling as well as proliferation, survival and transdifferentiation of β-cells. We furthermore focus on the paracrine interaction between classical and non-classical islet hormones in the maintenance of β-cell function. Understanding the functional relationships between these islet peptides might help to develop novel, more efficient treatments for diabetes and related metabolic disorders.
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Affiliation(s)
- Dawood Khan
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK.
| | - R Charlotte Moffett
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK
| | - Peter R Flatt
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK
| | - Andrei I Tarasov
- Biomedical Sciences Research Institute, School of Biomedical Sciences, Ulster University, Coleraine, Northern Ireland, UK
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English A, Irwin N. Nonclassical Islet Peptides: Pancreatic and Extrapancreatic Actions. CLINICAL MEDICINE INSIGHTS-ENDOCRINOLOGY AND DIABETES 2019; 12:1179551419888871. [PMID: 32425629 PMCID: PMC7216561 DOI: 10.1177/1179551419888871] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 10/21/2019] [Indexed: 02/06/2023]
Abstract
The pancreas has physiologically important endocrine and exocrine functions; secreting enzymes into the small intestine to aid digestion and releasing multiple peptide hormones via the islets of Langerhans to regulate glucose metabolism, respectively. Insulin and glucagon, in combination with ghrelin, pancreatic polypeptide and somatostatin, are the main classical islet peptides critical for the maintenance of blood glucose. However, pancreatic islets also synthesis numerous ‘nonclassical’ peptides that have recently been demonstrated to exert fundamental effects on overall islet function and metabolism. As such, insights into the physiological relevance of these nonclassical peptides have shown impact on glucose metabolism, insulin action, cell survival, weight loss, and energy expenditure. This review will focus on the role of individual nonclassical islet peptides to stimulate pancreatic islet secretions as well as regulate metabolism. In addition, the more recognised actions of these peptides on satiety and energy regulation will also be considered. Furthermore, recent advances in the field of peptide therapeutics and obesity-diabetes have focused on the benefits of simultaneously targeting several hormone receptor signalling cascades. The potential for nonclassical islet hormones within such combinational approaches will also be discussed.
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Affiliation(s)
- Andrew English
- School of Pharmacy and Pharmaceutical Sciences, Ulster University, Coleraine, Northern Ireland, UK
| | - Nigel Irwin
- School of Pharmacy and Pharmaceutical Sciences, Ulster University, Coleraine, Northern Ireland, UK
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Abstract
Type 1 diabetes is a disease characterized by the destruction of insulin-secreting β-cells in the pancreas. Individuals are treated for this disease with lifelong insulin replacement. However, one attractive treatment possibility is to reprogram an individual’s endogenous cells to acquire the ability to secrete insulin, essentially replacing destroyed β-cells. Herein, we review the literature on the topic of reprogramming endodermal cells to produce insulin.
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Affiliation(s)
- Wendy M McKimpson
- Department of Medicine (Endocrinology), Columbia University, New York, New York
| | - Domenico Accili
- Department of Medicine (Endocrinology), Columbia University, New York, New York
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Dahan T, Ziv O, Horwitz E, Zemmour H, Lavi J, Swisa A, Leibowitz G, Ashcroft FM, In't Veld P, Glaser B, Dor Y. Pancreatic β-Cells Express the Fetal Islet Hormone Gastrin in Rodent and Human Diabetes. Diabetes 2017; 66:426-436. [PMID: 27864307 PMCID: PMC5248995 DOI: 10.2337/db16-0641] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 11/11/2016] [Indexed: 12/20/2022]
Abstract
β-Cell failure in type 2 diabetes (T2D) was recently proposed to involve dedifferentiation of β-cells and ectopic expression of other islet hormones, including somatostatin and glucagon. Here we show that gastrin, a stomach hormone typically expressed in the pancreas only during embryogenesis, is expressed in islets of diabetic rodents and humans with T2D. Although gastrin in mice is expressed in insulin+ cells, gastrin expression in humans with T2D occurs in both insulin+ and somatostatin+ cells. Genetic lineage tracing in mice indicates that gastrin expression is turned on in a subset of differentiated β-cells after exposure to severe hyperglycemia. Gastrin expression in adult β-cells does not involve the endocrine progenitor cell regulator neurogenin3 but requires membrane depolarization, calcium influx, and calcineurin signaling. In vivo and in vitro experiments show that gastrin expression is rapidly eliminated upon exposure of β-cells to normal glucose levels. These results reveal the fetal hormone gastrin as a novel marker for reversible human β-cell reprogramming in diabetes.
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Affiliation(s)
- Tehila Dahan
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Oren Ziv
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Elad Horwitz
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Hai Zemmour
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Judith Lavi
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Avital Swisa
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
| | - Gil Leibowitz
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Frances M Ashcroft
- Department of Physiology, Anatomy & Genetics, Oxford University, Oxford, U.K
| | - Peter In't Veld
- Diabetes Research Center, Brussels Free University, Brussels, Belgium
| | - Benjamin Glaser
- Endocrinology and Metabolism Service, Department of Internal Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Yuval Dor
- Department of Developmental Biology and Cancer Research, The Institute for Medical Research Israel-Canada, The Hebrew University Hadassah Medical School, Jerusalem, Israel
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Malmgren S, Ahrén B. Deciphering the Hypoglycemic Glucagon Response: Development of a Graded Hyperinsulinemic Hypoglycemic Clamp Technique in Female Mice. Endocrinology 2015; 156:3866-71. [PMID: 26132921 DOI: 10.1210/en.2015-1314] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Glucose lowering therapy in type 1 and type 2 diabetes is often associated with hypoglycemic events. To avoid this, glucose lowering therapies need to be developed that support the hypoglycemic defense mechanisms. Such development needs a tool for evaluating counterregulatory mechanisms in vivo. A sustained glucagon release during hypoglycemia is of most importance to hypoglycemic defense mechanisms. We have therefore developed a graded hyperinsulinemic hypoglycemic clamp in mice and used it to evaluate counterregulatory glucagon dynamics. Glucose was clamped at narrow intervals aiming at 2.5, 3.5, 4.5, and 6.0 mmol/L. Glucagon levels were increased during hypoglycemia in a glucose-dependent way with a glucagon counterregulatory threshold between 3.5 and 4.0 mmol/L. Modelling the glucose-glucagon relationship using a hyperbolic curve with the equation: plasma glucagon = -4.20 + 90.79/blood glucose showed high correlation. When comparing this method to the insulin tolerance test as an approach to study glucagon dynamics in vivo, we found that the graded clamp more efficiently evoked a robust, predictable, glucagon response with considerably less variation in blood glucose. In conclusion, we have developed a tool for the study of in vivo glucagon dynamics during hypoglycemia in mice and demonstrated a hyperbolic glucose-counterregulatory glucagon relationship.
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Affiliation(s)
- Siri Malmgren
- Department of Clinical Sciences, Lund, Medicine, Lund University, SE-221 84 Lund, Sweden
| | - Bo Ahrén
- Department of Clinical Sciences, Lund, Medicine, Lund University, SE-221 84 Lund, Sweden
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Saqui-Salces M, Dowdle WE, Reiter JF, Merchant JL. A high-fat diet regulates gastrin and acid secretion through primary cilia. FASEB J 2012; 26:3127-39. [PMID: 22516298 DOI: 10.1096/fj.11-197426] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The role of primary cilia in the gastrointestinal tract has not been examined. Here we report the presence of primary cilia on gastric endocrine cells producing gastrin, ghrelin, and somatostatin (Sst), hormones regulated by food intake. During eating, cilia in the gastric antrum decreased, whereas gastric acid and circulating gastrin increased. Mice fed high-fat chow showed a delayed decrease in antral cilia, increased plasma gastrin, and gastric acidity. Mice fed high-fat chow for 3 wk showed lower cilia numbers and acid but higher gastrin levels than mice fed a standard diet, suggesting that fat affects gastric physiology. Ex vivo experiments showed that cilia in the corpus responded to acid and distension, whereas cilia in the antrum responded to food. To analyze the role of gastric cilia, we conditionally deleted the intraflagellar transport protein Ift88 (Ift88(-/fl)). In fed Ift88(-/fl) mice, gastrin levels were higher, and gastric acidity was lower. Moreover, gastrin and Sst gene expression did not change in response to food as in controls. At 8 mo, Ift88(-/fl) mice developed foveolar hyperplasia, hypergastrinemia, and hypochlorhydria associated with endocrine dysfunction. Our results show that components of food (fat) are sensed by antral cilia on endocrine cells, which modulates gastrin secretion and gastric acidity.
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Affiliation(s)
- Milena Saqui-Salces
- Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan, USA
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Vuguin PM, Charron MJ. Novel insight into glucagon receptor action: lessons from knockout and transgenic mouse models. Diabetes Obes Metab 2011; 13 Suppl 1:144-50. [PMID: 21824268 PMCID: PMC4287250 DOI: 10.1111/j.1463-1326.2011.01447.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Using knockout and transgenic technology, genetically modified animal models allowed us to understand the role of glucagon signalling in metabolism. Mice with a global deletion of the glucagon receptor gene (Gcgr) were designed using gene targeting. The phenotype of Gcgr(-/-) mouse provided important clues about the role of Gcgr in foetal growth, pancreatic development and glucose and lipid homeostasis. The lack of Gcgr activation was associated with: (i) hypoglycaemic pregnancies, poor foetal growth and increased foetal-neonatal demise; (ii) altered cytoarchitecture of pancreatic islets; (iii) altered glucose, lipid and hormonal milieu; (iv) reduced gastric emptying; (v) altered body composition and protection from diet-induced obesity; (vi) altered energy state; (vii) impaired hepatocyte survival; (viii) altered metabolic response to prolonged fasting and exercise and (ix) prevented development of diabetes in insulin-deficient mice. In contrast, mice overexpressing the Gcgr on pancreatic β-cells displayed an increase insulin secretion, pancreatic insulin content and β-cell mass, and partially protected against hyperglycaemia and impaired glucose tolerance when fed a high-fat diet. These findings suggest that glucagon signalling plays a significant role in the regulation of glucose and lipid homeostasis. Treatment options designed to block Gcgr activation may have negative implications in the treatment of diabetes.
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Affiliation(s)
- P M Vuguin
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10467, USA.
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10
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11
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Lavine JA, Raess PW, Stapleton DS, Rabaglia ME, Suhonen JI, Schueler KL, Koltes JE, Dawson JA, Yandell BS, Samuelson LC, Beinfeld MC, Davis DB, Hellerstein MK, Keller MP, Attie AD. Cholecystokinin is up-regulated in obese mouse islets and expands beta-cell mass by increasing beta-cell survival. Endocrinology 2010; 151:3577-88. [PMID: 20534724 PMCID: PMC2940525 DOI: 10.1210/en.2010-0233] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
An absolute or functional deficit in beta-cell mass is a key factor in the pathogenesis of diabetes. We model obesity-driven beta-cell mass expansion by studying the diabetes-resistant C57BL/6-Leptin(ob/ob) mouse. We previously reported that cholecystokinin (Cck) was the most up-regulated gene in obese pancreatic islets. We now show that islet cholecystokinin (CCK) is up-regulated 500-fold by obesity and expressed in both alpha- and beta-cells. We bred a null Cck allele into the C57BL/6-Leptin(ob/ob) background and investigated beta-cell mass and metabolic parameters of Cck-deficient obese mice. Loss of CCK resulted in decreased islet size and reduced beta-cell mass through increased beta-cell death. CCK deficiency and decreased beta-cell mass exacerbated fasting hyperglycemia and reduced hyperinsulinemia. We further investigated whether CCK can directly affect beta-cell death in cell culture and isolated islets. CCK was able to directly reduce cytokine- and endoplasmic reticulum stress-induced cell death. In summary, CCK is up-regulated by islet cells during obesity and functions as a paracrine or autocrine factor to increase beta-cell survival and expand beta-cell mass to compensate for obesity-induced insulin resistance.
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Affiliation(s)
- Jeremy A Lavine
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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12
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Sachdeva MM, Stoffers DA. Minireview: Meeting the demand for insulin: molecular mechanisms of adaptive postnatal beta-cell mass expansion. Mol Endocrinol 2009; 23:747-58. [PMID: 19196831 DOI: 10.1210/me.2008-0400] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Type 2 diabetes results from pancreatic ss-cell failure in the setting of insulin resistance. This model of disease progression has received recent support from the results of genome-wide association studies that identify genes potentially regulating ss-cell growth and function as type 2 diabetes susceptibility loci. Normal ss-cell compensation for an increased insulin demand includes both enhanced insulin-secretory capacity and an expansion of morphological ss-cell mass, due largely to changes in the balance between ss-cell proliferation and apoptosis. Recent years have brought significant progress in the understanding of both extrinsic signals stimulating ss-cell growth as well as mediators intrinsic to the ss-cell that regulate the compensatory response. Here, we review the current knowledge of mechanisms underlying adaptive expansion of ss-cell mass, focusing on lessons learned from experimental models of physiologically occurring insulin-resistant states including diet-induced obesity and pregnancy, and highlighting the potential importance of interorgan cross talk. The identification of critical mediators of islet compensation may direct the development of future therapeutic strategies to enhance the response of ss-cells to insulin resistance.
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Affiliation(s)
- Mira M Sachdeva
- Department of Medicine, Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, 19104, USA
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Dunning BE, Gerich JE. The role of alpha-cell dysregulation in fasting and postprandial hyperglycemia in type 2 diabetes and therapeutic implications. Endocr Rev 2007; 28:253-83. [PMID: 17409288 DOI: 10.1210/er.2006-0026] [Citation(s) in RCA: 275] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The hyperglycemic activity of pancreatic extracts was encountered some 80 yr ago during efforts to optimize methods for the purification of insulin. The hyperglycemic substance was named "glucagon," and it was subsequently determined that glucagon is a 29-amino acid peptide synthesized and released from pancreatic alpha-cells. This article begins with a brief overview of the discovery of glucagon and the contributions that somatostatin and a sensitive and selective assay for pancreatic (vs. gut) glucagon made to understanding the physiological and pathophysiological roles of glucagon. Studies utilizing these tools to establish the function of glucagon in normal nutrient homeostasis and to document a relative glucagon excess in type 2 diabetes mellitus (T2DM) and precursors thereof are then discussed. The evidence that glucagon excess contributes to the development and maintenance of fasting hyperglycemia and that failure to suppress glucagon secretion contributes to postprandial hyperglycemia is then reviewed. Although key human studies are emphasized, salient animal studies highlighting the importance of glucagon in normal and defective glucoregulation are also described. The past eight decades of research in this area have led to development of new therapeutic approaches to treating T2DM that have been shown to, or are expected to, improve glycemic control in patients with T2DM in part by improving alpha-cell function or by blocking glucagon action. Accordingly, this review ends with a discussion of the status and therapeutic potential of glucagon receptor antagonists, alpha-cell selective somatostatin agonists, glucagon-like peptide-1 agonists, and dipeptidyl peptidase-IV inhibitors. Our overall conclusions are that there is considerable evidence that relative hyperglucagonemia contributes to fasting and postprandial hyperglycemia in patients with T2DM, and there are several new and emerging pharmacotherapies that may improve glycemic control in part by ameliorating the hyperglycemic effects of this relative glucagon excess.
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Abstract
The gastrointestinal tract has a crucial role in the control of energy homeostasis through its role in the digestion, absorption, and assimilation of ingested nutrients. Furthermore, signals from the gastrointestinal tract are important regulators of gut motility and satiety, both of which have implications for the long-term control of body weight. Among the specialized cell types in the gastrointestinal mucosa, enteroendocrine cells have important roles in regulating energy intake and glucose homeostasis through their actions on peripheral target organs, including the endocrine pancreas. This article reviews the biological actions of gut hormones regulating glucose homeostasis, with an emphasis on mechanisms of action and the emerging therapeutic roles of gut hormones for the treatment of type 2 diabetes mellitus.
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Affiliation(s)
- Daniel J Drucker
- Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada.
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15
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Friis-Hansen L. Lessons from the gastrin knockout mice. ACTA ACUST UNITED AC 2007; 139:5-22. [DOI: 10.1016/j.regpep.2006.12.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 11/30/2006] [Accepted: 12/01/2006] [Indexed: 12/22/2022]
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Abstract
Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.
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Affiliation(s)
- Marlène Dufresne
- Institut National de la Santé et de la Recherche Médicale U. 531, Institut Louis Bugnard, Centre Hospitalier Universitaire Rangueil, France
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Volinic JL, Lee JH, Eto K, Kaur V, Thomas MK. Overexpression of the Coactivator Bridge-1 Results in Insulin Deficiency and Diabetes. Mol Endocrinol 2006; 20:167-82. [PMID: 16099819 DOI: 10.1210/me.2005-0127] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
AbstractMultiple forms of heritable diabetes are associated with mutations in transcription factors that regulate insulin gene transcription and the development and maintenance of pancreatic β-cell mass. The coactivator Bridge-1 (PSMD9) regulates the transcriptional activation of glucose-responsive enhancers in the insulin gene in a dose-dependent manner via PDZ domain-mediated interactions with E2A transcription factors. Here we report that the pancreatic overexpression of Bridge-1 in transgenic mice reduces insulin gene expression and results in insulin deficiency and severe diabetes. Dysregulation of Bridge-1 signaling increases pancreatic apoptosis with a reduction in the number of insulin-expressing pancreatic β-cells and an expansion of the complement of glucagon-expressing pancreatic α-cells in pancreatic islets. Increased expression of Bridge-1 alters pancreatic islet, acinar, and ductal architecture and disrupts the boundaries between endocrine and exocrine cellular compartments in young adult but not neonatal mice, suggesting that signals transduced through this coactivator may influence postnatal pancreatic islet morphogenesis. Signals mediated through the coactivator Bridge-1 may regulate both glucose homeostasis and pancreatic β-cell survival. We propose that coactivator dysfunction in pancreatic β-cells can limit insulin production and contribute to the pathogenesis of diabetes.
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Affiliation(s)
- Jamie L Volinic
- Laboratory of Molecular Endocrinology and Diabetes Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Raju B, Cryer PE. Maintenance of the postabsorptive plasma glucose concentration: insulin or insulin plus glucagon? Am J Physiol Endocrinol Metab 2005; 289:E181-6. [PMID: 16014355 DOI: 10.1152/ajpendo.00460.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The prevalent view is that the postabsorptive plasma glucose concentration is maintained within the physiological range by the interplay of the glucose-lowering action of insulin and the glucose-raising action of glucagon. It is supported by a body of evidence derived from studies of suppression of glucagon (and insulin, among other effects) with somatostatin in animals and humans, immunoneutralization of glucagon, defective glucagon synthesis, diverse mutations, and absent or reduced glucagon receptors in animals and glucagon antagonists in cells, animals, and humans. Many of these studies are open to alternative interpretations, and some lead to seemingly contradictory conclusions. For example, immunoneutralization of glucagon lowered plasma glucose concentrations in rabbits, but administration of a glucagon antagonist did not lower plasma glucose concentrations in healthy humans. Evidence that the glycemic threshold for glucagon secretion, unlike that for insulin secretion, lies below the physiological range, and the finding that selective suppression of insulin secretion without stimulation of glucagon secretion raises fasting plasma glucose concentrations in humans underscore the primacy of insulin in the regulation of the postabsorptive plasma glucose concentration and challenge the prevalent view. The alternative view is that the postabsorptive plasma glucose concentration is maintained within the physiological range by insulin alone, specifically regulated increments and decrements in insulin, and the resulting decrements and increments in endogenous glucose production, respectively, and glucagon becomes relevant only when glucose levels drift below the physiological range. Although the balance of evidence suggests that glucagon is involved in the maintenance of euglycemia, more definitive evidence is needed, particularly in humans.
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Affiliation(s)
- Bharathi Raju
- Division of Endocrinology, Metabolism and Lipid Research, Washington Univ. School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110, USA
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Cowey SL, Quast M, Belalcazar LM, Wei J, Deng X, Given R, Singh P. Abdominal obesity, insulin resistance, and colon carcinogenesis are increased in mutant mice lacking gastrin gene expression. Cancer 2005; 103:2643-53. [PMID: 15864814 DOI: 10.1002/cncr.21094] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
BACKGROUND The authors recently reported that gastrin gene knockout (GAS-KO) mice had an increased risk for colon carcinogenesis in response to azoxymethane (AOM) compared with their wild type (WT) littermates. In the current report, the authors discuss the predisposition of GAS-KO mice to develop obesity and metabolic hormonal changes that may contribute to their increased risk of colon carcinogenesis. METHODS The weight and deposition of fat was monitored in the mice over a 14 month period, using magnetic resonance imaging and nuclear magnetic resonance techniques. Changes in plasma concentrations of ghrelin, leptin, insulin, and glucose were assessed using radioimmunoassay analysis and enzyme-linked immunosorbent assays. Preneoplastic markers of colon carcinogenesis (aberrant crypt foci [ACFs]), in response to AOM, were measured in a subset of obese versus lean GAS-KO mice and were compared with the markers in WT mice. RESULTS Increases in visceral adiposity were evident by age 2 months in GAS-KO mice, resulting in macroscopic obesity by age 7 months. Hyperinsulinemia and insulin:glucose ratios were increased significantly in GAS-KO mice as young as 1 month and preceded alterations in nonfasting leptin and ghrelin levels. The number of ACFs per mouse colon were increased significantly in the following order: obese GAS-KO mice > lean GAS-KO mice > WT mice. Fasting plasma insulin levels were 0.88 +/- 0.1 ng/mL, 1.45 +/- 0.3, and 2.76 +/- 0.9 ng/mL in the WT, GAS-KO lean, and GAS-KO obese mice, respectively. CONCLUSIONS The current results suggest the novel possibility that loss of amidated gastrins may increase adipogenesis, hyperinsulinemia, and colon carcinogenesis in GAS-KO mice. The increase in colon carcinogenesis may be due in part to hyperinsulinemia, increased obesity, and other associated hormone changes that were measured in GAS-KO mice.
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Affiliation(s)
- Stephanie L Cowey
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555-1043, USA
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Leung-Theung-Long S, Roulet E, Clerc P, Escrieut C, Marchal-Victorion S, Ritz-Laser B, Philippe J, Pradayrol L, Seva C, Fourmy D, Dufresne M. Essential interaction of Egr-1 at an islet-specific response element for basal and gastrin-dependent glucagon gene transactivation in pancreatic alpha-cells. J Biol Chem 2004; 280:7976-84. [PMID: 15611055 DOI: 10.1074/jbc.m407485200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The peptide hormone gastrin is secreted from G cells of the gastric antrum and is the main inducer of gastric acid secretion via activation of its receptor the cholecystokinin 2 (CCK2) receptor. Both gastrin and CCK2 receptors are also transiently detected in the fetal pancreas and believed to exert growth/differentiation effects during endocrine pancreatic development. We demonstrated previously that whereas gastrin expression is extinguished in adult pancreas, CCK2 receptors are present in human glucagon-producing cells where their activation stimulates glucagon secretion. Based on these findings, we investigate in the present study whether gastrin regulates glucagon gene expression. To this aim, the CCK2 receptor was stably expressed into a glucagon-producing pancreatic islet cell line, and a glucagon-reporter fusion gene was transiently transfected in this new cellular model. We report that gastrin stimulates glucagon gene expression in glucagon-producing pancreatic cells. By using progressively 5'-increased sequences of the glucagon gene, gastrin responsiveness was located within the minimal promoter. Moreover, we clearly identified early growth response protein 1 (Egr-1) as an essential transcription factor interacting with the islet cell-specific G4 element. Egr-1 was shown to be essential for basal and gastrin-dependent glucagon gene transactivation. Furthermore, our results demonstrate that the MEK1/ERK1/2 pathway couples the CCK2 receptor to nuclearization and DNA binding of Egr-1. In conclusion, our data provide new information concerning the transcriptional regulation of the glucagon gene. Moreover they open new working hypothesis with reference to a potential role of gastrin in glucagon-producing pancreatic cells.
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