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Cui D, Feng X, Lei S, Zhang H, Hu W, Yang S, Yu X, Su Z. Pancreatic β-cell failure, clinical implications, and therapeutic strategies in type 2 diabetes. Chin Med J (Engl) 2024; 137:791-805. [PMID: 38479993 PMCID: PMC10997226 DOI: 10.1097/cm9.0000000000003034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Indexed: 04/06/2024] Open
Abstract
ABSTRACT Pancreatic β-cell failure due to a reduction in function and mass has been defined as a primary contributor to the progression of type 2 diabetes (T2D). Reserving insulin-producing β-cells and hence restoring insulin production are gaining attention in translational diabetes research, and β-cell replenishment has been the main focus for diabetes treatment. Significant findings in β-cell proliferation, transdifferentiation, pluripotent stem cell differentiation, and associated small molecules have served as promising strategies to regenerate β-cells. In this review, we summarize current knowledge on the mechanisms implicated in β-cell dynamic processes under physiological and diabetic conditions, in which genetic factors, age-related alterations, metabolic stresses, and compromised identity are critical factors contributing to β-cell failure in T2D. The article also focuses on recent advances in therapeutic strategies for diabetes treatment by promoting β-cell proliferation, inducing non-β-cell transdifferentiation, and reprograming stem cell differentiation. Although a significant challenge remains for each of these strategies, the recognition of the mechanisms responsible for β-cell development and mature endocrine cell plasticity and remarkable advances in the generation of exogenous β-cells from stem cells and single-cell studies pave the way for developing potential approaches to cure diabetes.
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Affiliation(s)
- Daxin Cui
- Molecular Medicine Research Center and Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Xingrong Feng
- State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Siman Lei
- Clinical Translational Innovation Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Hongmei Zhang
- Molecular Medicine Research Center and Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Wanxin Hu
- State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Shanshan Yang
- Molecular Medicine Research Center and Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Xiaoqian Yu
- Molecular Medicine Research Center and Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
| | - Zhiguang Su
- Molecular Medicine Research Center and Department of Endocrinology and Metabolism, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
- State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
- Clinical Translational Innovation Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China
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Ivovic A, Yung JHM, Oprescu AI, Vlavcheski F, Mori Y, Rahman SMN, Ye W, Eversley JA, Wheeler MB, Woo M, Tsiani E, Giacca A. β-Cell Insulin Resistance Plays a Causal Role in Fat-Induced β-Cell Dysfunction In Vitro and In Vivo. Endocrinology 2024; 165:bqae044. [PMID: 38578954 PMCID: PMC11033845 DOI: 10.1210/endocr/bqae044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 03/27/2024] [Accepted: 04/04/2024] [Indexed: 04/07/2024]
Abstract
In the classical insulin target tissues of liver, muscle, and adipose tissue, chronically elevated levels of free fatty acids (FFA) impair insulin signaling. Insulin signaling molecules are also present in β-cells where they play a role in β-cell function. Therefore, inhibition of the insulin/insulin-like growth factor 1 pathway may be involved in fat-induced β-cell dysfunction. To address the role of β-cell insulin resistance in FFA-induced β-cell dysfunction we co-infused bisperoxovanadate (BPV) with oleate or olive oil for 48 hours in rats. BPV, a tyrosine phosphatase inhibitor, acts as an insulin mimetic and is devoid of any antioxidant effect that could prevent β-cell dysfunction, unlike most insulin sensitizers. Following fat infusion, rats either underwent hyperglycemic clamps for assessment of β-cell function in vivo or islets were isolated for ex vivo assessment of glucose-stimulated insulin secretion (GSIS). We also incubated islets with oleate or palmitate and BPV for in vitro assessment of GSIS and Akt (protein kinase B) phosphorylation. Next, mice with β-cell specific deletion of PTEN (phosphatase and tensin homolog; negative regulator of insulin signaling) and littermate controls were infused with oleate for 48 hours, followed by hyperglycemic clamps or ex vivo evaluation of GSIS. In rat experiments, BPV protected against fat-induced impairment of β-cell function in vivo, ex vivo, and in vitro. In mice, β-cell specific deletion of PTEN protected against oleate-induced β-cell dysfunction in vivo and ex vivo. These data support the hypothesis that β-cell insulin resistance plays a causal role in FFA-induced β-cell dysfunction.
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Affiliation(s)
- Aleksandar Ivovic
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Justin Hou Ming Yung
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Andrei I Oprescu
- Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Filip Vlavcheski
- Department of Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada
| | - Yusaku Mori
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Division of Diabetes, Metabolism, and Endocrinology, Anti-Glycation Research Section, Department of Medicine, Showa University School of Medicine, Shinagawa, Tokyo 142-8555, Japan
| | - S M Niazur Rahman
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Wenyue Ye
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Judith A Eversley
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Michael B Wheeler
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Minna Woo
- Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, University of Toronto, Toronto, ON M5G 2C4, Canada
- Division of Endocrinology, Department of Medicine, University Health Network, University of Toronto, Toronto, ON M5G 2C4, Canada
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, ON M5G 2C4, Canada
| | - Evangelia Tsiani
- Department of Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada
| | - Adria Giacca
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, ON M5G 2C4, Canada
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ZnT8 loss-of-function accelerates functional maturation of hESC-derived β cells and resists metabolic stress in diabetes. Nat Commun 2022; 13:4142. [PMID: 35842441 PMCID: PMC9288460 DOI: 10.1038/s41467-022-31829-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 07/04/2022] [Indexed: 12/21/2022] Open
Abstract
Human embryonic stem cell-derived β cells (SC-β cells) hold great promise for treatment of diabetes, yet how to achieve functional maturation and protect them against metabolic stresses such as glucotoxicity and lipotoxicity remains elusive. Our single-cell RNA-seq analysis reveals that ZnT8 loss of function (LOF) accelerates the functional maturation of SC-β cells. As a result, ZnT8 LOF improves glucose-stimulated insulin secretion (GSIS) by releasing the negative feedback of zinc inhibition on insulin secretion. Furthermore, we demonstrate that ZnT8 LOF mutations endow SC-β cells with resistance to lipotoxicity/glucotoxicity-triggered cell death by alleviating endoplasmic reticulum (ER) stress through modulation of zinc levels. Importantly, transplantation of SC-β cells with ZnT8 LOF into mice with preexisting diabetes significantly improves glycemia restoration and glucose tolerance. These findings highlight the beneficial effect of ZnT8 LOF on the functional maturation and survival of SC-β cells that are useful as a potential source for cell replacement therapies. Immature function and fragility hinder application of hESC-derived β cells (SC-β cell) for diabetes cell therapy. Here, the authors identify ZnT8 as a gene editing target to enhance the insulin secretion and cell survival under metabolic stress by abolishing zinc transport in SC-β cells.
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Koneshamoorthy A, Seniveratne-Epa D, Calder G, Sawyer M, Kay TWH, Farrell S, Loudovaris T, Mariana L, McCarthy D, Lyu R, Liu X, Thorn P, Tong J, Chin LK, Zacharin M, Trainer A, Taylor S, MacIsaac RJ, Sachithanandan N, Thomas HE, Krishnamurthy B. Case Report: Hypoglycemia Due to a Novel Activating Glucokinase Variant in an Adult - a Molecular Approach. Front Endocrinol (Lausanne) 2022; 13:842937. [PMID: 35370948 PMCID: PMC8969599 DOI: 10.3389/fendo.2022.842937] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 02/17/2022] [Indexed: 11/13/2022] Open
Abstract
We present a case of an obese 22-year-old man with activating GCK variant who had neonatal hypoglycemia, re-emerging with hypoglycemia later in life. We investigated him for asymptomatic hypoglycemia with a family history of hypoglycemia. Genetic testing yielded a novel GCK missense class 3 variant that was subsequently found in his mother, sister and nephew and reclassified as a class 4 likely pathogenic variant. Glucokinase enables phosphorylation of glucose, the rate-limiting step of glycolysis in the liver and pancreatic β cells. It plays a crucial role in the regulation of insulin secretion. Inactivating variants in GCK cause hyperglycemia and activating variants cause hypoglycemia. Spleen-preserving distal pancreatectomy revealed diffuse hyperplastic islets, nuclear pleomorphism and periductular islets. Glucose stimulated insulin secretion revealed increased insulin secretion in response to glucose. Cytoplasmic calcium, which triggers exocytosis of insulin-containing granules, revealed normal basal but increased glucose-stimulated level. Unbiased gene expression analysis using 10X single cell sequencing revealed upregulated INS and CKB genes and downregulated DLK1 and NPY genes in β-cells. Further studies are required to see if alteration in expression of these genes plays a role in the metabolic and histological phenotype associated with glucokinase pathogenic variant. There were more large islets in the patient's pancreas than in control subjects but there was no difference in the proportion of β cells in the islets. His hypoglycemia was persistent after pancreatectomy, was refractory to diazoxide and improved with pasireotide. This case highlights the variable phenotype of GCK mutations. In-depth molecular analyses in the islets have revealed possible mechanisms for hyperplastic islets and insulin hypersecretion.
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Affiliation(s)
- Anojian Koneshamoorthy
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Dilan Seniveratne-Epa
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Genevieve Calder
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Matthew Sawyer
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Thomas W. H. Kay
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
- Department of Medicine, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Stephen Farrell
- Department of Surgery, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Thomas Loudovaris
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - Lina Mariana
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - Davis McCarthy
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
- Melbourne Integrative Genomics, Faculty of Science, University of Melbourne, Melbourne, VIC, Australia
| | - Ruqian Lyu
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
| | - Xin Liu
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
- Melbourne Integrative Genomics, Faculty of Science, University of Melbourne, Melbourne, VIC, Australia
| | - Peter Thorn
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Sydney, NSW, Australia
| | - Jason Tong
- Charles Perkins Centre, School of Medical Sciences, University of Sydney, Sydney, NSW, Australia
| | - Lit Kim Chin
- Department of Diabetes and Endocrinology, Royal Children’s Hospital, Melbourne, VIC, Australia
| | - Margaret Zacharin
- Department of Diabetes and Endocrinology, Royal Children’s Hospital, Melbourne, VIC, Australia
| | - Alison Trainer
- Department of Genomic Medicine, Royal Melbourne Hospital, Melbourne, VIC, Australia
| | - Shelby Taylor
- Department of Genomic Medicine, Royal Melbourne Hospital, Melbourne, VIC, Australia
| | - Richard J. MacIsaac
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
- Department of Medicine, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Nirupa Sachithanandan
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
- Department of Medicine, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Helen E. Thomas
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
- Department of Medicine, St. Vincent’s Hospital, Melbourne, VIC, Australia
| | - Balasubramanian Krishnamurthy
- Department of Endocrinology and Diabetes, St. Vincent’s Hospital, Melbourne, VIC, Australia
- St. Vincent’s Institute of Medical Research, Melbourne, VIC, Australia
- Department of Medicine, St. Vincent’s Hospital, Melbourne, VIC, Australia
- *Correspondence: Balasubramanian Krishnamurthy,
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Rachdaoui N. Insulin: The Friend and the Foe in the Development of Type 2 Diabetes Mellitus. Int J Mol Sci 2020; 21:ijms21051770. [PMID: 32150819 PMCID: PMC7084909 DOI: 10.3390/ijms21051770] [Citation(s) in RCA: 74] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2020] [Revised: 02/29/2020] [Accepted: 03/02/2020] [Indexed: 12/14/2022] Open
Abstract
Insulin, a hormone produced by pancreatic β-cells, has a primary function of maintaining glucose homeostasis. Deficiencies in β-cell insulin secretion result in the development of type 1 and type 2 diabetes, metabolic disorders characterized by high levels of blood glucose. Type 2 diabetes mellitus (T2DM) is characterized by the presence of peripheral insulin resistance in tissues such as skeletal muscle, adipose tissue and liver and develops when β-cells fail to compensate for the peripheral insulin resistance. Insulin resistance triggers a rise in insulin demand and leads to β-cell compensation by increasing both β-cell mass and insulin secretion and leads to the development of hyperinsulinemia. In a vicious cycle, hyperinsulinemia exacerbates the metabolic dysregulations that lead to β-cell failure and the development of T2DM. Insulin and IGF-1 signaling pathways play critical roles in maintaining the differentiated phenotype of β-cells. The autocrine actions of secreted insulin on β-cells is still controversial; work by us and others has shown positive and negative actions by insulin on β-cells. We discuss findings that support the concept of an autocrine action of secreted insulin on β-cells. The hypothesis of whether, during the development of T2DM, secreted insulin initially acts as a friend and contributes to β-cell compensation and then, at a later stage, becomes a foe and contributes to β-cell decompensation will be discussed.
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Affiliation(s)
- Nadia Rachdaoui
- Department of Animal Sciences, Room 108, Foran Hall, Rutgers, the State University of New Jersey, 59 Dudley Rd, New Brunswick, NJ 08901, USA
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Chan CB, Ahuja P, Ye K. Developing Insulin and BDNF Mimetics for Diabetes Therapy. Curr Top Med Chem 2019; 19:2188-2204. [PMID: 31660832 DOI: 10.2174/1568026619666191010160643] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Revised: 08/29/2019] [Accepted: 09/05/2019] [Indexed: 01/06/2023]
Abstract
Diabetes is a global public health concern nowadays. The majority of diabetes mellitus (DM) patients belong to type 2 diabetes mellitus (T2DM), which is highly associated with obesity. The general principle of current therapeutic strategies for patients with T2DM mainly focuses on restoring cellular insulin response by potentiating the insulin-induced signaling pathway. In late-stage T2DM, impaired insulin production requires the patients to receive insulin replacement therapy for maintaining their glucose homeostasis. T2DM patients also demonstrate a drop of brain-derived neurotrophic factor (BDNF) in their circulation, which suggests that replenishing BDNF or enhancing its downstream signaling pathway may be beneficial. Because of their protein nature, recombinant insulin or BDNF possess several limitations that hinder their clinical application in T2DM treatment. Thus, developing orally active "insulin pill" or "BDNF pill" is essential to provide a more convenient and effective therapy. This article reviews the current development of non-peptidyl chemicals that mimic insulin or BDNF and their potential as anti-diabetic agents.
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Affiliation(s)
- Chi Bun Chan
- School of Biological Sciences, The University of Hong Kong, Hong Kong
| | - Palak Ahuja
- School of Biological Sciences, The University of Hong Kong, Hong Kong
| | - Keqiang Ye
- Department of Pathology and Laboratory Medicine, Emory University of School of Medicine, Atlanta, GA, United States
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Rachdaoui N, Polo-Parada L, Ismail-Beigi F. Prolonged Exposure to Insulin Inactivates Akt and Erk 1/2 and Increases Pancreatic Islet and INS1E β-Cell Apoptosis. J Endocr Soc 2018; 3:69-90. [PMID: 30697602 PMCID: PMC6344346 DOI: 10.1210/js.2018-00140] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Accepted: 10/29/2018] [Indexed: 12/18/2022] Open
Abstract
Chronic hyperinsulinemia, in vivo, increases the resistance of peripheral tissues to insulin by desensitizing insulin signaling. Insulin, in a heterologous manner, can also cause IGF-1 resistance. The aim of the current study was to investigate whether insulin-mediated insulin and IGF-1 resistance develops in pancreatic β-cells and whether this resistance results in β-cell decompensation. Chronic exposure of rat islets or INS1E β-cells to increasing concentrations of insulin decreased AktS473 phosphorylation in response to subsequent acute stimulation with 10 nM insulin or IGF-1. Prolonged exposure to high insulin levels not only inhibited AktS473 phosphorylation, but it also resulted in a significant inhibition of the phosphorylation of P70S6 kinase and Erk1/2 phosphorylation in response to the acute stimulation by glucose, insulin, or IGF-1. Decreased activation of Akt, P70S6K, and Erk1/2 was associated with decreased insulin receptor substrate 2 tyrosine phosphorylation and insulin receptor β-subunit abundance; neither IGF receptor β-subunit content nor its phosphorylation were affected. These signaling impairments were associated with decreased SERCA2 expression, perturbed plasma membrane calcium current and intracellular calcium handling, increased endoplasmic reticulum stress markers such as eIF2αS51 phosphorylation and Bip (GRP78) expression, and increased islet and β-cell apoptosis. We demonstrate that prolonged exposure to high insulin levels induces not only insulin resistance, but in a heterologous manner causes resistance to IGF-1 in rat islets and insulinoma cells resulting in decreased cell survival. These findings suggest the possibility that chronic exposure to hyperinsulinemia may negatively affect β-cell mass by increasing β-cell apoptosis.
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Affiliation(s)
- Nadia Rachdaoui
- Division of Clinical and Molecular Endocrinology, Department of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Luis Polo-Parada
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri
| | - Faramarz Ismail-Beigi
- Division of Clinical and Molecular Endocrinology, Department of Medicine, Case Western Reserve University, Cleveland, Ohio
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Jiang WJ, Peng YC, Yang KM. Cellular signaling pathways regulating β-cell proliferation as a promising therapeutic target in the treatment of diabetes. Exp Ther Med 2018; 16:3275-3285. [PMID: 30233674 PMCID: PMC6143874 DOI: 10.3892/etm.2018.6603] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 07/27/2018] [Indexed: 12/30/2022] Open
Abstract
It is established that a decrease in β-cell number and deficiency in the function of existing β-cells contribute to type 1 and type 2 diabetes mellitus. Therefore, a major focus of current research is to identify novel methods of improving the number and function of β-cells, so as to prevent and/or postpone the development of diabetes mellitus and potentially reverse diabetes mellitus. Based on prior knowledge of the above-mentioned causes, promising therapeutic approaches may include direct transplantation of islets, implantation and subsequent induced differentiation of progenitors/stem cells to β-cells, replication of pre-existing β-cells, or activation of endogenous β-cell progenitors. More recently, with regards to cell replacement and regenerative treatment for diabetes patients, the identification of cellular signaling pathways with related genes or corresponding proteins involved in diabetes has become a topic of interest. However, the majority of pathways and molecules associated with β-cells remain unresolved, and the specialized functions of known pathways remain unclear, particularly in humans. The current article has evaluated the progress of research on pivotal cellular signaling pathways involved with β-cell proliferation and survival, and their validity for therapeutic adult β-cell regeneration in diabetes. More efforts are required to elucidate the cellular events involved in human β-cell proliferation in terms of the underlying mechanisms and functions.
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Affiliation(s)
- Wen-Juan Jiang
- Institute of Anatomy, Basic Medical College of Dali University, Dali, Yunnan 671000, P.R. China
| | - Yun-Chuan Peng
- Institute of Anatomy, Basic Medical College of Dali University, Dali, Yunnan 671000, P.R. China
| | - Kai-Ming Yang
- Institute of Anatomy, Basic Medical College of Dali University, Dali, Yunnan 671000, P.R. China
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Josephy-Hernandez S, Jmaeff S, Pirvulescu I, Aboulkassim T, Saragovi HU. Neurotrophin receptor agonists and antagonists as therapeutic agents: An evolving paradigm. Neurobiol Dis 2016; 97:139-155. [PMID: 27546056 DOI: 10.1016/j.nbd.2016.08.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Revised: 08/10/2016] [Accepted: 08/16/2016] [Indexed: 12/12/2022] Open
Abstract
Neurodegenerative disorders are prevalent, complex and devastating conditions, with very limited treatment options currently available. While they manifest in many forms, there are commonalities that link them together. In this review, we will focus on neurotrophins - a family of related factors involved in neuronal development and maintenance. Neurodegenerative diseases often present with a neurotrophin imbalance, in which there may be decreases in trophic signaling through Trk receptors for example, and/or increases in pro-apoptotic activity through p75. Clinical trials with neurotrophins have continuously failed due to their poor pharmacological properties as well as the unavoidable activation of p75. Thus, there is a need for drugs without such setbacks. Small molecule neurotrophin mimetics are favorable options since they can selectively activate Trks or inactivate p75. In this review, we will initially present a brief outline of how these molecules are synthesized and their mechanisms of action; followed by an update in the current state of neurotrophins and small molecules in major neurodegenerative diseases. Although there has been significant progress in the development of potential therapeutics, more studies are needed to establish clear mechanisms of action and target specificity in order to transition from animal models to the assessment of safety and use in humans.
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Affiliation(s)
- Sylvia Josephy-Hernandez
- Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Quebec, Canada; Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada
| | - Sean Jmaeff
- Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Quebec, Canada; Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
| | - Iulia Pirvulescu
- Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Quebec, Canada; Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
| | - Tahar Aboulkassim
- Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Quebec, Canada
| | - H Uri Saragovi
- Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Quebec, Canada; Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada; Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada.
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10
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Velasco M, Díaz-García CM, Larqué C, Hiriart M. Modulation of Ionic Channels and Insulin Secretion by Drugs and Hormones in Pancreatic Beta Cells. Mol Pharmacol 2016; 90:341-57. [PMID: 27436126 DOI: 10.1124/mol.116.103861] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 07/18/2016] [Indexed: 12/11/2022] Open
Abstract
Pancreatic beta cells, unique cells that secrete insulin in response to an increase in glucose levels, play a significant role in glucose homeostasis. Glucose-stimulated insulin secretion (GSIS) in pancreatic beta cells has been extensively explored. In this mechanism, glucose enters the cells and subsequently the metabolic cycle. During this process, the ATP/ADP ratio increases, leading to ATP-sensitive potassium (KATP) channel closure, which initiates depolarization that is also dependent on the activity of TRP nonselective ion channels. Depolarization leads to the opening of voltage-gated Na(+) channels (Nav) and subsequently voltage-dependent Ca(2+) channels (Cav). The increase in intracellular Ca(2+) triggers the exocytosis of insulin-containing vesicles. Thus, electrical activity of pancreatic beta cells plays a central role in GSIS. Moreover, many growth factors, incretins, neurotransmitters, and hormones can modulate GSIS, and the channels that participate in GSIS are highly regulated. In this review, we focus on the principal ionic channels (KATP, Nav, and Cav channels) involved in GSIS and how classic and new proteins, hormones, and drugs regulate it. Moreover, we also discuss advances on how metabolic disorders such as metabolic syndrome and diabetes mellitus change channel activity leading to changes in insulin secretion.
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Affiliation(s)
- Myrian Velasco
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Carlos Manlio Díaz-García
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Carlos Larqué
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
| | - Marcia Hiriart
- Department of Neurodevelopment and Physiology, Neuroscience Division, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Markwardt ML, Seckinger KM, Rizzo MA. Regulation of Glucokinase by Intracellular Calcium Levels in Pancreatic β Cells. J Biol Chem 2015; 291:3000-9. [PMID: 26698632 DOI: 10.1074/jbc.m115.692160] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Indexed: 01/01/2023] Open
Abstract
Glucokinase (GCK) controls the rate of glucose metabolism in pancreatic β cells, and its activity is rate-limiting for insulin secretion. Posttranslational GCK activation can be stimulated through either G protein-coupled receptors or receptor tyrosine kinase signaling pathways, suggesting a common mechanism. Here we show that inhibiting Ca(2+) release from the endoplasmic reticulum (ER) decouples GCK activation from receptor stimulation. Furthermore, pharmacological release of ER Ca(2+) stimulates activation of a GCK optical biosensor and potentiates glucose metabolism, implicating rises in cytoplasmic Ca(2+) as a critical regulatory mechanism. To explore the potential for glucose-stimulated GCK activation, the GCK biosensor was optimized using circularly permuted mCerulean3 proteins. This new sensor sensitively reports activation in response to insulin, glucagon-like peptide 1, and agents that raise cAMP levels. Transient, glucose-stimulated GCK activation was observed in βTC3 and MIN6 cells. An ER-localized channelrhodopsin was used to manipulate the cytoplasmic Ca(2+) concentration in cells expressing the optimized FRET-GCK sensor. This permitted quantification of the relationship between cytoplasmic Ca(2+) concentrations and GCK activation. Half-maximal activation of the FRET-GCK sensor was estimated to occur at ∼400 nm Ca(2+). When expressed in islets, fluctuations in GCK activation were observed in response to glucose, and we estimated that posttranslational activation of GCK enhances glucose metabolism by ∼35%. These results suggest a mechanism for integrative control over GCK activation and, therefore, glucose metabolism and insulin secretion through regulation of cytoplasmic Ca(2+) levels.
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Affiliation(s)
- Michele L Markwardt
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Kendra M Seckinger
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Mark A Rizzo
- From the University of Maryland School of Medicine, Baltimore, Maryland 21201
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Yang SN, Shi Y, Yang G, Li Y, Yu J, Berggren PO. Ionic mechanisms in pancreatic β cell signaling. Cell Mol Life Sci 2014; 71:4149-77. [PMID: 25052376 PMCID: PMC11113777 DOI: 10.1007/s00018-014-1680-6] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2014] [Revised: 07/03/2014] [Accepted: 07/10/2014] [Indexed: 01/07/2023]
Abstract
The function and survival of pancreatic β cells critically rely on complex electrical signaling systems composed of a series of ionic events, namely fluxes of K(+), Na(+), Ca(2+) and Cl(-) across the β cell membranes. These electrical signaling systems not only sense events occurring in the extracellular space and intracellular milieu of pancreatic islet cells, but also control different β cell activities, most notably glucose-stimulated insulin secretion. Three major ion fluxes including K(+) efflux through ATP-sensitive K(+) (KATP) channels, the voltage-gated Ca(2+) (CaV) channel-mediated Ca(2+) influx and K(+) efflux through voltage-gated K(+) (KV) channels operate in the β cell. These ion fluxes set the resting membrane potential and the shape, rate and pattern of firing of action potentials under different metabolic conditions. The KATP channel-mediated K(+) efflux determines the resting membrane potential and keeps the excitability of the β cell at low levels. Ca(2+) influx through CaV1 channels, a major type of β cell CaV channels, causes the upstroke or depolarization phase of the action potential and regulates a wide range of β cell functions including the most elementary β cell function, insulin secretion. K(+) efflux mediated by KV2.1 delayed rectifier K(+) channels, a predominant form of β cell KV channels, brings about the downstroke or repolarization phase of the action potential, which acts as a brake for insulin secretion owing to shutting down the CaV channel-mediated Ca(2+) entry. These three ion channel-mediated ion fluxes are the most important ionic events in β cell signaling. This review concisely discusses various ionic mechanisms in β cell signaling and highlights KATP channel-, CaV1 channel- and KV2.1 channel-mediated ion fluxes.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, SE-171 76, Stockholm, Sweden,
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13
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Non-peptidyl insulin mimetics as a potential antidiabetic agent. Drug Discov Today 2013; 18:748-55. [DOI: 10.1016/j.drudis.2013.04.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Revised: 03/21/2013] [Accepted: 04/11/2013] [Indexed: 12/29/2022]
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14
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Lai MC, Lo YS, Yang C. The effect of demethylasterriquinone B-1 on insulin secretion in rat pancreas. ACTA ACUST UNITED AC 2013. [DOI: 10.4236/jdm.2013.33017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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Meng R, Götz C, Montenarh M. The role of protein kinase CK2 in the regulation of the insulin production of pancreatic islets. Biochem Biophys Res Commun 2010; 401:203-6. [DOI: 10.1016/j.bbrc.2010.09.028] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Accepted: 09/05/2010] [Indexed: 10/19/2022]
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16
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Zhang Y, Xie Z, Zhou G, Zhang H, Lu J, Zhang WJ. Fructose-1,6-bisphosphatase regulates glucose-stimulated insulin secretion of mouse pancreatic beta-cells. Endocrinology 2010; 151:4688-95. [PMID: 20719858 DOI: 10.1210/en.2009-1185] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Pancreatic β-cells can precisely sense glucose stimulation and accordingly adjust their insulin secretion. Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme, but its physiological significance in β-cells is not established. Here we determined its physiological role in regulating glucose sensing and insulin secretion of β-cells. Considerable FBPase mRNA was detected in normal mouse islets and β-cell lines, although their protein levels appeared to be quite low. Down-regulation of FBP1 in MIN6 cells by small interfering RNA could enhance the glucose-stimulated insulin secretion (GSIS), whereas FBP1-overexpressing MIN6 cells exhibited decreased GSIS. Inhibition of FBPase activity in islet β-cells by its specific inhibitor MB05032 led to significant increase of their glucose utilization and cellular ATP to ADP ratios and consequently enhanced GSIS in vitro. Pretreatment of mice with the MB05032 prodrug MB06322 could potentiate GSIS in vivo and improve their glucose tolerance. Therefore, FBPase plays an important role in regulating glucose sensing and insulin secretion of β-cells and serves a promising target for diabetes treatment.
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Affiliation(s)
- Ye Zhang
- Center for Obesity & Diabetes Research and Innovation, Department of Pathophysiology, Second Military Medical University, 800 Xiangyin Road, Shanghai 200433, China
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17
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Regulation of glucose-dependent insulin secretion by insulin: Possible role of AMP-activated protein kinase. Life Sci 2009; 85:178-83. [DOI: 10.1016/j.lfs.2009.05.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 05/07/2009] [Accepted: 05/16/2009] [Indexed: 11/18/2022]
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Abstract
The appropriate function of insulin-producing pancreatic beta-cells is crucial for the regulation of glucose homeostasis, and its impairment leads to diabetes mellitus, the most common metabolic disorder in man. In addition to glucose, the major nutrient factor, inputs from the nervous system, humoral components, and cell-cell communication within the islet of Langerhans act together to guarantee the release of appropriate amounts of insulin in response to changes in blood glucose levels. Data obtained within the past decade in several laboratories have revitalized controversy over the autocrine feedback action of secreted insulin on beta-cell function. Although insulin historically has been suggested to exert a negative effect on beta-cells, recent data provide evidence for a positive role of insulin in transcription, translation, ion flux, insulin secretion, proliferation, and beta-cell survival. Current insights on the role of insulin on pancreatic beta-cell function are discussed.
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Affiliation(s)
- Ingo B Leibiger
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden.
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Involvement of phosphatidylinositol-3 kinase/AKT/PKCzeta/lambda pathway in the effect of palmitate on glucose-induced insulin secretion. Pancreas 2008; 37:309-15. [PMID: 18815554 DOI: 10.1097/mpa.0b013e318168dac3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
OBJECTIVES In the present study, a novel pathway by which palmitate potentiates glucose-induced insulin secretion by pancreatic beta cells was investigated. METHODS Groups of freshly isolated islets were incubated in 10 mM glucose with palmitate, LY294002, wortmannin, and fumonisin B1 for measurement of insulin secretion by radioimmunoassay (RIA). Also, phosphorylation and content of AKT and PKC proteins were evaluated by immunoblotting. RESULTS Glucose plus palmitate and glucose plus LY294002 or wortmannin (PI3K inhibitors) increased glucose-induced insulin secretion by isolated pancreatic islets. Glucose at 10 mM induced AKT and PKCzeta/lambda phosphorylation. Palmitate (0.1 mM) abolished glucose stimulation of AKT and PKCzeta/lambda phosphorylation possibly through PI3K inhibition because both LY294002 (50 microM) and wortmannin (100 nM) caused the same effect. The inhibitory effect of palmitate on glucose-induced AKT and PKCzeta/lambda phosphorylation and the stimulatory effect of palmitate on glucose-induced insulin secretion were not observed in the presence of fumonisin B1, an inhibitor of ceramide synthesis. CONCLUSIONS These findings support the proposition that palmitate increases insulin release in the presence of 10 mM glucose by inhibiting PI3K activity through a mechanism that involves ceramide synthesis.
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Hee-Park S, Lim B, Baek WK, Bae JH, Song DK. Negative and positive feedback regulation of insulin in glucose-stimulated Ca2+ response in pancreatic beta cells. Diabetes Res Clin Pract 2007; 77 Suppl 1:S143-9. [PMID: 17467844 DOI: 10.1016/j.diabres.2007.02.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/02/2007] [Indexed: 10/23/2022]
Abstract
Secreted insulin from pancreatic beta cells exerts autocrine and paracrine effects within the islets. The present study has evaluated how exogenous insulin participates in cytosolic Ca(2+) response to high glucose, according to glucose concentration at which insulin is applied. When 100 nM insulin was pretreated to the bath solution containing islet cells in the presence of basal level of glucose, the elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) by subsequently applied 10mM glucose was remarkably attenuated. In contrast, the glucose-stimulated [Ca(2+)](c) elevation was more potentiated when insulin was superimposed on the high glucose stimulation. These insulin actions were modestly inhibited by the application of LY294002, the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, but not completely, suggesting that another mechanism is also involved. By 100 nM insulin, phosphorylated form of AMP-activated protein kinases (p-AMPK) was dramatically decreased in basal glucose but increased in high glucose, when compared with their reciprocal controls. These results may suggest that the extent of AMPK activation may be a tool for insulin receptors to monitor blood glucose level, with which insulin-induced insulin receptor activation determines the way to go negatively or positively toward [Ca(2+)](c).
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Affiliation(s)
- Sung Hee-Park
- Department of Physiology, Keimyung University School of Medicine and Chronic Disease Research Center, 194, Dongsan-Dong, Jung-Gu, Daegu 700-712, Korea
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Hu Z, Dun X, Zhang M, Zhu H, Xie L, Wu Z, Chen Z, Xu T. PA1b, a plant peptide, induces intracellular [Ca2+] increase via Ca2+ influx through the L-type Ca2+ channel and triggers secretion in pancreatic beta cells. SCIENCE IN CHINA. SERIES C, LIFE SCIENCES 2007; 50:285-91. [PMID: 17609883 DOI: 10.1007/s11427-007-0052-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2006] [Accepted: 01/16/2007] [Indexed: 12/19/2022]
Abstract
Using alginic acid to adsorb polypeptides at pH 2.7, we isolated a peptide pea albumin 1b (PA1b) from pea seeds. The PA1b is a single chain peptide consisting of 37 amino acid residues with 6 cysteines which constitutes the cystine-knot structure. Using microfluorometry and patch clamp techniques, we found that PA1b significantly elevated the intracellular calcium level ([Ca2+]i) and elicited membrane capacitance increase in the primary rat pancreatic beta cells. The PA1b effect on [Ca2+]i elevation was abolished in the absence of extracellular Ca2+ or in the presence of L-type Ca2+ channel blocker, nimodipine. Interestingly, we found that PA1b significantly depolarized membrane potential, which could lead to the opening of voltage-dependent L-type Ca2+ channels and influx of extracellular Ca2+, and then evoke robust secretion. In this study we identified the plant peptide PA1b which is capable of affecting the excitability and function of mammalian pancreatic beta cell.
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Affiliation(s)
- ZhiTao Hu
- Joint Laboratory of Institute of Biophysics and Huazhong University of Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China
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Yang SN, Berggren PO. The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology. Endocr Rev 2006; 27:621-76. [PMID: 16868246 DOI: 10.1210/er.2005-0888] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology L1:03, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
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23
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Velliquette RA, Friedman JE, Shao J, Zhang BB, Ernsberger P. Therapeutic Actions of an Insulin Receptor Activator and a Novel Peroxisome Proliferator-Activated Receptor γ Agonist in the Spontaneously Hypertensive Obese Rat Model of Metabolic Syndrome X. J Pharmacol Exp Ther 2005; 314:422-30. [PMID: 15833894 DOI: 10.1124/jpet.104.080606] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Insulin resistance clusters with hyperlipidemia, impaired glucose tolerance, and hypertension as metabolic syndrome X. We tested a low molecular weight insulin receptor activator, demethylasterriquinone B-1 (DMAQ-B1), and a novel indole peroxisome proliferator-activated receptor gamma agonist, 2-(2-(4-phenoxy-2-propylphenoxy)ethyl)indole-5-acetic acid (PPEIA), in spontaneously hypertensive obese rats (SHROB), a genetic model of syndrome X. Agents were given orally for 19 days. SHROB showed fasting normoglycemia but impaired glucose tolerance after an oral load, as shown by increased glucose area under the curve (AUC) [20,700 mg x min/ml versus 8100 in lean spontaneously hypertensive rats (SHR)]. Insulin resistance was indicated by 20-fold excess fasting insulin and increased insulin AUC (6300 ng x min/ml versus 990 in SHR). DMAQ-B1 did not affect glucose tolerance (glucose AUC = 21,300) but reduced fasting insulin 2-fold and insulin AUC (insulin AUC = 4300). PPEIA normalized glucose tolerance (glucose AUC = 9100) and reduced insulin AUC (to 3180) without affecting fasting insulin. PPEIA also increased food intake, fat mass, and body weight gain (81 +/- 12 versus 45 +/- 8 g in untreated controls), whereas DMAQ-B1 had no effect on body weight but reduced subscapular fat mass. PPEIA but not DMAQ-B1 reduced blood pressure. In skeletal muscle, insulin-stimulated phosphorylation of the insulin receptor and insulin receptor substrate protein 1-associated phosphatidylinositol 3-kinase activity were decreased by 40 to 55% in SHROB relative to lean SHR. PPEIA, but not DMAQ-B1, enhanced both insulin actions. SHROB also showed severe hypertriglyceridemia (355 +/- 42 mg/dl versus 65 +/- 3 in SHR) attenuated by both agents (DMAQ-B1, 228 +/- 18; PPEIA, 79 +/- 3). Both these novel antidiabetic agents attenuate insulin resistance and hypertriglyceridemia associated with metabolic syndrome but via distinct mechanisms.
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Affiliation(s)
- Rodney A Velliquette
- Department of Nutrition, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4906, USA
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24
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Abstract
The beta-cell is equipped with at least six voltage-gated Ca2+ (CaV) channel alpha1-subunits designated CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1. These principal subunits, together with certain auxiliary subunits, assemble into different types of CaV channels conducting L-, P/Q-, N-, R-, and T-type Ca2+ currents, respectively. The beta-cell shares customary mechanisms of CaV channel regulation with other excitable cells, such as protein phosphorylation, Ca2+-dependent inactivation, and G protein modulation. However, the beta-cell displays some characteristic features to bring these mechanisms into play. In islet beta-cells, CaV channels can be highly phosphorylated under basal conditions and thus marginally respond to further phosphorylation. In beta-cell lines, CaV channels can be surrounded by tonically activated protein phosphatases dominating over protein kinases; thus their activity is dramatically enhanced by inhibition of protein phosphatases. During the last 10 years, we have revealed some novel mechanisms of beta-cell CaV channel regulation under physiological and pathophysiological conditions, including the involvement of exocytotic proteins, inositol hexakisphosphate, and type 1 diabetic serum. This minireview highlights characteristic features of customary mechanisms of CaV channel regulation in beta-cells and also reviews our studies on newly identified mechanisms of beta-cell CaV channel regulation.
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Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Center for Diabetes Research, Karolinska Diabetes Center, Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
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25
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Hinnuliquinone, a C2-symmetric dimeric non-peptide fungal metabolite inhibitor of HIV-1 protease. Biochem Biophys Res Commun 2004; 324:108-13. [PMID: 15464989 DOI: 10.1016/j.bbrc.2004.08.234] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Indexed: 11/21/2022]
Abstract
HIV-1 protease is one of several key enzymes required for the replication and maturation of HIV-1 virus. An almost two-decade research effort by academic and pharmaceutical institutions resulted in the successful commercialization of seven drugs that are potent inhibitors of HIV-1 protease activity and which, if used correctly, are highly effective in managing viral load. However, identification of clinical viral isolates that are resistant to these drugs indicates that this is a significant problem and that new classes of inhibitors are continually needed. Screening of microbial extracts followed by bioassay-guided isolation led to the discovery of a natural hinnuliquinone, a C(2)-symmetric bis-indolyl quinone natural product that inhibited the wild-type and a clinically resistant (A44) strain of HIV-1 protease with K(i) values of 0.97 and 1.25microM, respectively. Crystallographic analysis of the inhibitor-bound HIV-1 protease helped explain the importance of the C(2)-symmetry of hinnuliquinone for activity. Details of the isolation, biological activity, and crystallographic analysis of the inhibitor-bound protease are herein described.
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Collier JJ, White SM, Dick GM, Scott DK. Phosphatidylinositol 3-kinase inhibitors reveal a unique mechanism of enhancing insulin secretion in 832/13 rat insulinoma cells. Biochem Biophys Res Commun 2004; 324:1018-23. [PMID: 15485656 DOI: 10.1016/j.bbrc.2004.09.149] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Indexed: 11/22/2022]
Abstract
Hyperinsulinemia exists before the onset of overt type 2 diabetes mellitus. This response is at least partly due to enhanced insulin release from pancreatic beta-cells. Increased insulin secretion can be mimicked in vitro by acute culture of 832/13 rat insulinoma cells with phosphatidylinositol 3-kinase (PI-3K) inhibitors, a treatment that would theoretically simulate insulin resistance. We demonstrate in this study that while the PI-3K inhibitors Wortmannin and LY294002 both block Akt phosphorylation, only LY29002 significantly augments insulin secretion. LY294002 treatment potentiates insulin secretion over both basal and stimulatory glucose concentrations. This effect correlates with a significant increase in action potential duration. There was no change in resting or peak membrane potential under any of the treatment conditions, demonstrating that the cells remain healthy under the acute treatments used in this study. By contrast, Wortmannin has no effect on action potential duration. A partial explanation for these findings is that LY294002 potently inhibits voltage-dependent potassium channels, but does not affect voltage-gated calcium currents. We conclude that while PI-3K may play a role in regulating insulin secretion, there are diverse effects of the established inhibitors of this enzyme on beta-cell insulin secretory responses.
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Affiliation(s)
- J Jason Collier
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA
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27
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Strowski MZ, Li Z, Szalkowski D, Shen X, Guan XM, Jüttner S, Moller DE, Zhang BB. Small-molecule insulin mimetic reduces hyperglycemia and obesity in a nongenetic mouse model of type 2 diabetes. Endocrinology 2004; 145:5259-68. [PMID: 15297448 DOI: 10.1210/en.2004-0610] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Adiposity positively correlates with insulin resistance and is a major risk factor of type 2 diabetes. Administration of exogenous insulin, which acts as an anabolic factor, facilitates adipogenesis. Recently nonpeptidal insulin receptor (IR) activators have been discovered. Here we evaluate the effects of the orally bioavailable small-molecule IR activator (Compound-2) on metabolic abnormalities associated with type 2 diabetes using a nongenetic mouse model in comparison with the effects of a novel non-thiazolidinedione (nTZD) peroxisome proliferator-activated receptor-gamma agonist. Both Compound-2 and nTZD alleviated fasting and postprandial hyperglycemia; accelerated glucose clearance rate; and normalized plasma levels of nonesterified fatty acids, triglycerides, and leptin. Unlike nTZD, which increased body weight gain, and total fat mass, which is a common feature for PPARgamma agonists, Compound-2 prevented body weight gain and hypertrophy of brown, and white adipose tissue depots and the development of hepatic steatosis in the mouse model of type 2 diabetes. The effect of the two compounds on proximal steps in insulin signal transduction pathway was analyzed in tissues. Compound-2 enhanced insulin-stimulated phosphorylation of IR tyrosine and/or Akt in the liver, skeletal muscle, and white adipose tissue, whereas nTZD potentiated the phosphorylation of IR and Akt in the adipose tissue only. In conclusion, small-molecule IR activators have unique features as insulin sensitizers and hold potential utility in the treatment of type 2 diabetes and obesity.
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Affiliation(s)
- Mathias Z Strowski
- Medizinische Klinik mit Schwerpunkt Hepatologie, Gastroenterologie, Endokrinologie, und Stoffwechsel Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany.
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Nunemaker CS, Zhang M, Satin LS. Insulin feedback alters mitochondrial activity through an ATP-sensitive K+ channel-dependent pathway in mouse islets and beta-cells. Diabetes 2004; 53:1765-72. [PMID: 15220200 DOI: 10.2337/diabetes.53.7.1765] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Recent work suggests that insulin may exert both positive and negative feedback directly on pancreatic beta-cells. To investigate the hypothesis that insulin modulates beta-cell metabolism, mouse islets and beta-cell clusters were loaded with rhodamine 123 to dynamically monitor mitochondrial membrane potential (DeltaPsi(m)). Spontaneous oscillations in DeltaPsi(m) (period: 218 +/- 26 s) were observed in 17 of 30 islets exposed to 11.1 mmol/l glucose. Acute insulin application (100 nmol/l) hyperpolarized DeltaPsi(m), indicating a change in mitochondrial activity. The ATP-sensitive K(+) (K(ATP)) channel opener diazoxide or the l-type calcium channel blocker nifedipine mimicked the effect of insulin, suggesting that insulin activates K(ATP) channels to hyperpolarize DeltaPsi(m) by inhibiting calcium influx. Treatment with forskolin, which increases endogenous insulin secretion, also mimicked the effect of exogenous insulin, suggesting physiological feedback. Pretreatment with nifedipine or the K(ATP) inhibitor glyburide prevented insulin action, further implicating a K(ATP) channel pathway. Together, these data suggest a feedback mechanism whereby insulin receptor activation opens K(ATP) channels to inhibit further secretion. The resulting reduction in beta-cell calcium increases the energy stored in the mitochondrial gradient that drives ATP production. Insulin feedback onto mitochondria may thus help to calibrate the energy needs of the beta-cell on a minute-to-minute basis.
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Affiliation(s)
- Craig S Nunemaker
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University Medical Center, Richmond, USA
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Srivastava S, Goren HJ. Insulin constitutively secreted by beta-cells is necessary for glucose-stimulated insulin secretion. Diabetes 2003; 52:2049-56. [PMID: 12882922 DOI: 10.2337/diabetes.52.8.2049] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Four hypotheses have been posited on the role of insulin in glucose-stimulated insulin secretion; available evidence has supported insulin as being 1) essential, 2) a positive modulator, 3) a negative modulator, or 4) not necessary. Because circulating insulin levels in mice, before or after intraperitoneal glucose injection, are sufficient to elicit insulin responses in insulin-sensitive tissues, it is likely that beta-cell insulin receptors are continuously exposed to stimulating concentrations of insulin. To determine whether constitutively secreted insulin is necessary for glucose-stimulated insulin secretion, CD1 male mouse islets were incubated for 30 min at 4 degrees C in the absence (control) or presence of anti-insulin (1 micro g/ml) or anti-IgG (1 micro g/ml). Then islets were exposed to 3, 11, or 25 mmol/l glucose or to 20 mmol/l arginine. Nontreated islets exhibited first- and second-phase glucose-stimulated insulin secretion. Control and anti-IgG-treated islets, after a 5-min lag phase, increased their insulin secretion in 25 mmol/l glucose. Anti-insulin-treated islets secreted insulin at a basal rate in 3 or 25 mmol/l glucose buffers. Insulin secretion stimulated by 20 mmol/l arginine was the same in islets pretreated with either antibody and showed no lag phase. Taken together, these data suggest that constitutively secreted insulin is required and sufficient for beta-cells to maintain sensitivity to glucose.
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Affiliation(s)
- Siddhartha Srivastava
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
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El-Kholy W, Macdonald PE, Lin JH, Wang J, Fox JM, Light PE, Wang Q, Tsushima RG, Wheeler MB. The phosphatidylinositol 3-kinase inhibitor LY294002 potently blocks K(V) currents via a direct mechanism. FASEB J 2003; 17:720-2. [PMID: 12586735 DOI: 10.1096/fj.02-0802fje] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Voltage-dependent K+ (Kv) channels negatively regulate Ca2+ entry into pancreatic beta-cells by repolarizing glucose-stimulated action potentials. A role for phosphatidylinositol 3-kinase (PI3K) modulation of Kv channel function was investigated using the PI3K inhibitors wortmannin and LY294002, and LY303511, a negative control compound with respect to PI3K activity. In MIN6 insulinoma cells, wortmannin (100 nM) had no effect on whole-cell outward K+ currents, but LY294002 and LY303511 reversibly blocked currents in a dose-dependent manner (IC50=9.0+/-0.7 microM and 64.6+/-9.1 microM, respectively). Western blotting confirmed the specific inhibitory effects of LY294002 and wortmannin on insulin-stimulated PI3K activity. Kv currents in rat beta-cells at near physiological temperatures were inhibited 92% by 25 microM LY294002. Kv2.1 and Kv1.4 are highly expressed in beta-cells, and in Kv2.1-transfected tsA201 cells, 50 microM LY294002 and 100 microM LY303511 reversibly inhibited currents by 99% and 41%, respectively. In Kv1.4-transfected tsA201 cells, 50 microM LY294002 reduced the inactivation time constant from 73 to 18 ms. The insulinotropic properties of LY294002 and its effects in other excitable cells may be caused by inhibition of Kv currents rather than PI3K antagonism. Furthermore, LY294002 may represent a novel structure from which future Kv channel blockers may be developed.
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Affiliation(s)
- Wasim El-Kholy
- Department of Medicine, University of Toronto, Ontario, Canada
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Abstract
Pancreatic beta-cell function is essential for the regulation of glucose homeostasis and its impairment leads to diabetes mellitus. Besides glucose, the major nutrient factor, inputs from neural and humoral components and intraislet cell-cell communication act together to guarantee an appropriate pancreatic beta-cell function. Data obtained over the last 5 years in several laboratories have revitalized a controversial concept, namely the autocrine feedback action of secreted insulin on beta-cell function. While, historically, insulin was suggested to exert a negative effect on beta-cells, recent data provide evidence for a positive role of insulin in transcription, translation, ion flux, insulin secretion and beta-cell survival.
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Affiliation(s)
- Ingo B Leibiger
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Hospital L3, Karolinska Institutet, S-171 76 Stockholm, Sweden.
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Borge PD, Moibi J, Greene SR, Trucco M, Young RA, Gao Z, Wolf BA. Insulin receptor signaling and sarco/endoplasmic reticulum calcium ATPase in beta-cells. Diabetes 2002; 51 Suppl 3:S427-33. [PMID: 12475786 DOI: 10.2337/diabetes.51.2007.s427] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucose is the main physiological secretagogue for insulin secretion by pancreatic beta-cells, and the major biochemical mechanisms involved have been elucidated. In particular, an increase in intracellular calcium is important for insulin exocytosis. More recently, it has become apparent that the beta-cell also has many of the elements of the insulin receptor signal transduction pathway, including the insulin receptor and insulin receptor substrate (IRS) proteins 1 and 2. Studies with transgenic models have shown that the beta-cell-selective insulin receptor knockout and the IRS-1 knockout lead to reduced glucose-induced insulin secretion. Overexpression of the insulin receptor and IRS-1 in beta-cells results in increased insulin secretion and increased cytosolic Ca(2+). We have thus postulated the existence of a novel autocrine-positive feedback loop of insulin on its own secretion involving interaction with the insulin receptor signal transduction pathway and regulation of intracellular calcium homeostasis. Our current working hypothesis is that this glucose-dependent interaction occurs at the level of IRS-1 and the sarco(endo)plasmic reticulum calcium ATPase, the calcium pump of the endoplasmic reticulum.
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Affiliation(s)
- Prabakhar D Borge
- Department of Pathology and Laboratory Medicine, the Children's Hospital of Philadelphia and the University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4399, USA
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Araujo EP, Amaral MEC, Souza CT, Bordin S, Ferreira F, Saad MJA, Boschero AC, Magalhães EC, Velloso LA. Blockade of IRS1 in isolated rat pancreatic islets improves glucose-induced insulin secretion. FEBS Lett 2002; 531:437-42. [PMID: 12435589 DOI: 10.1016/s0014-5793(02)03580-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Several neural, hormonal and biochemical inputs actively participate in the balance of insulin secretion induced by blood glucose fluctuations. The exact role of insulin as an autocrine and paracrine participant in the control of its own secretion remains to be determined, mostly due to insufficient knowledge about the molecular phenomena that govern insulin signaling in pancreatic islets. In the present experiments we demonstrate that higher insulin receptor and insulin receptor substrates-1 and -2 (IRS1 and IRS2) concentrations are predominantly encountered in cells of the periphery of rat pancreatic islets, as compared to centrally located cells, and that partial blockade of IRS1 protein expression by antisense oligonucleotide treatment leads to improved insulin secretion induced by glucose overload, which is accompanied by lower steady-state glucagon secretion and blunted glucose-induced glucagon fall. These data reinforce the inhibitory role of insulin upon its own secretion in isolated, undisrupted pancreatic islets.
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Affiliation(s)
- Eliana P Araujo
- Department of Physiology and Biophysics, University of Campinas, Campinas, Brazil
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