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ElSheikh A, Driggers CM, Shyng SL. Non-radioactive Rb + Efflux Assay for Screening K ATP Channel Modulators. Methods Mol Biol 2024; 2796:191-210. [PMID: 38856903 DOI: 10.1007/978-1-0716-3818-7_12] [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] [Indexed: 06/11/2024]
Abstract
ATP-sensitive potassium (KATP) channels function as metabolic sensors that link cell membrane excitability to the cellular energy status by controlling potassium ion (K+) flow across the cell membrane according to intracellular ATP and ADP concentrations. As such, KATP channels influence a broad spectrum of physiological processes, including insulin secretion and cardiovascular functions. KATP channels are hetero-octamers, consisting of four inward rectifier potassium channel subunits, Kir6.1 or Kir6.2, and four sulfonylurea receptors (SURs), SUR1, SUR2A, or SUR2B. Different Kir6 and SUR isoforms assemble into KATP channel subtypes with distinct tissue distributions and physiological functions. Mutations in the genes encoding KATP channel subunits underlie various human diseases. Targeted treatment for these diseases requires subtype-specific KATP channel modulators. Rubidium ions (Rb+) also pass through KATP channels, and Rb+ efflux assays can be used to assess KATP channel function and activity. Flame atomic absorption spectroscopy (Flame-AAS) combined with microsampling can measure Rb+ in small volume, which provides an efficient tool to screen for compounds that alter KATP channel activity in Rb+ efflux assays. In this chapter, we describe a detailed protocol for Rb+ efflux assays designed to identify new KATP channel modulators with potential therapeutic utilities.
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Affiliation(s)
- Assmaa ElSheikh
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA.
- Department of Medical Biochemistry, Tanta University, Tanta, Egypt.
| | - Camden M Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
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Gao J, McClenaghan C, Matreyek KA, Grange DK, Nichols CG. Rapid Characterization of the Functional and Pharmacological Consequences of Cantú Syndrome K ATP Channel Mutations in Intact Cells. J Pharmacol Exp Ther 2023; 386:298-309. [PMID: 37527933 PMCID: PMC10449099 DOI: 10.1124/jpet.123.001659] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 05/10/2023] [Accepted: 06/01/2023] [Indexed: 08/03/2023] Open
Abstract
Gain-of-function of KATP channels, resulting from mutations in either KCNJ8 (encoding inward rectifier sub-family 6 [Kir6.1]) or ABCC9 (encoding sulphonylurea receptor [SUR2]), cause Cantú syndrome (CS), a channelopathy characterized by excess hair growth, coarse facial appearance, cardiomegaly, and lymphedema. Here, we established a pipeline for rapid analysis of CS mutation consequences in Landing pad HEK 293 cell lines stably expressing wild type (WT) and mutant human Kir6.1 and SUR2B. Thallium-influx and cell membrane potential, reported by fluorescent Tl-sensitive Fluozin-2 and voltage-sensitive bis-(1,3-dibutylbarbituric acid)trimethine oxonol (DiBAC4(3)) dyes, respectively, were used to assess channel activity. In the Tl-influx assay, CS-associated Kir6.1 mutations increased sensitivity to the ATP-sensitive potassium (KATP) channel activator, pinacidil, but there was strikingly little effect of pinacidil for any SUR2B mutations, reflecting unexpected differences in the molecular mechanisms of Kir6.1 versus SUR2B mutations. Compared with the Tl-influx assay, the DiBAC4(3) assay presents more significant signal changes in response to subtle KATP channel activity changes, and all CS mutants (both Kir6.1 and SUR2B), but not WT channels, caused marked hyperpolarization, demonstrating that all mutants were activated under ambient conditions in intact cells. Most SUR2 CS mutations were markedly inhibited by <100 nM glibenclamide, but sensitivity to inhibition by glibenclamide, repaglinide, and PNU37883A was markedly reduced for Kir6.1 CS mutations. Understanding functional consequences of mutations can help with disease diagnosis and treatment. The analysis pipeline we have developed has the potential to rapidly identify mutational consequences, aiding future CS diagnosis, drug discovery, and individualization of treatment. SIGNIFICANCE STATEMENT: We have developed new fluorescence-based assays of channel activities and drug sensitivities of Cantú syndrome (CS) mutations in human Kir6.1/SUR2B-dependent KATP channels, showing that Kir6.1 mutations increase sensitivity to potassium channel openers, while SUR2B mutations markedly reduce K channel opener (KCO) sensitivity. However, both Kir6.1 and SUR2B CS mutations are both more hyperpolarized than WT cells under basal conditions, confirming pathophysiologically relevant gain-of-function, validating DiBAC4(3) fluorescence to characterize hyperpolarization induced by KATP channel activity under basal, non KCO-activated conditions.
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Affiliation(s)
- Jian Gao
- Department of Cell Biology and Physiology (J.G., C.M.C., C.G.N.), Center for the Investigation of Membrane Excitability Diseases (J.G., C.M.C., D.K.G., C.G.N.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (D.K.G.), Washington University in St. Louis, St. Louis, Missouri; and Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio (K.A.M.)
| | - Conor McClenaghan
- Department of Cell Biology and Physiology (J.G., C.M.C., C.G.N.), Center for the Investigation of Membrane Excitability Diseases (J.G., C.M.C., D.K.G., C.G.N.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (D.K.G.), Washington University in St. Louis, St. Louis, Missouri; and Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio (K.A.M.)
| | - Kenneth A Matreyek
- Department of Cell Biology and Physiology (J.G., C.M.C., C.G.N.), Center for the Investigation of Membrane Excitability Diseases (J.G., C.M.C., D.K.G., C.G.N.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (D.K.G.), Washington University in St. Louis, St. Louis, Missouri; and Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio (K.A.M.)
| | - Dorothy K Grange
- Department of Cell Biology and Physiology (J.G., C.M.C., C.G.N.), Center for the Investigation of Membrane Excitability Diseases (J.G., C.M.C., D.K.G., C.G.N.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (D.K.G.), Washington University in St. Louis, St. Louis, Missouri; and Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio (K.A.M.)
| | - Colin G Nichols
- Department of Cell Biology and Physiology (J.G., C.M.C., C.G.N.), Center for the Investigation of Membrane Excitability Diseases (J.G., C.M.C., D.K.G., C.G.N.), and Division of Genetics and Genomic Medicine, Department of Pediatrics (D.K.G.), Washington University in St. Louis, St. Louis, Missouri; and Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio (K.A.M.)
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ElSheikh A, Shyng SL. K ATP channel mutations in congenital hyperinsulinism: Progress and challenges towards mechanism-based therapies. Front Endocrinol (Lausanne) 2023; 14:1161117. [PMID: 37056678 PMCID: PMC10086357 DOI: 10.3389/fendo.2023.1161117] [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: 02/07/2023] [Accepted: 03/13/2023] [Indexed: 03/30/2023] Open
Abstract
Congenital hyperinsulinism (CHI) is the most common cause of persistent hypoglycemia in infancy/childhood and is a serious condition associated with severe recurrent attacks of hypoglycemia due to dysregulated insulin secretion. Timely diagnosis and effective treatment are crucial to prevent severe hypoglycemia that may lead to life-long neurological complications. In pancreatic β-cells, adenosine triphosphate (ATP)-sensitive K+ (KATP) channels are a central regulator of insulin secretion vital for glucose homeostasis. Genetic defects that lead to loss of expression or function of KATP channels are the most common cause of HI (KATP-HI). Much progress has been made in our understanding of the molecular genetics and pathophysiology of KATP-HI in the past decades; however, treatment remains challenging, in particular for patients with diffuse disease who do not respond to the KATP channel activator diazoxide. In this review, we discuss current approaches and limitations on the diagnosis and treatment of KATP-HI, and offer perspectives on alternative therapeutic strategies.
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Affiliation(s)
- Assmaa ElSheikh
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
- Department of Medical Biochemistry, Tanta University, Tanta, Egypt
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, United States
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Ikle JM, Tryon RC, Singareddy SS, York NW, Remedi MS, Nichols CG. Genome-edited zebrafish model of ABCC8 loss-of-function disease. Islets 2022; 14:200-209. [PMID: 36458573 PMCID: PMC9721409 DOI: 10.1080/19382014.2022.2149206] [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: 04/05/2022] [Revised: 10/25/2022] [Accepted: 11/13/2022] [Indexed: 12/03/2022] Open
Abstract
ATP-sensitive potassium channel (KATP)gain- (GOF) and loss-of-function (LOF) mutations underlie human neonatal diabetes mellitus (NDM) and hyperinsulinism (HI), respectively. While transgenic mice expressing incomplete KATP LOF do reiterate mild hyperinsulinism, KATP knockout animals do not exhibit persistent hyperinsulinism. We have shown that islet excitability and glucose homeostasis are regulated by identical KATP channels in zebrafish. SUR1 truncation mutation (K499X) was introduced into the abcc8 gene to explore the possibility of using zebrafish for modeling human HI. Patch-clamp analysis confirmed the complete absence of channel activity in β-cells from K499X (SUR1-/-) fish. No difference in random blood glucose was detected in heterozygous SUR1+/- fish nor in homozygous SUR1-/- fish, mimicking findings in SUR1 knockout mice. Mutant fish did, however, demonstrate impaired glucose tolerance, similar to partial LOF mouse models. In paralleling features of mammalian diabetes and hyperinsulinism resulting from equivalent LOF mutations, these gene-edited animals provide valid zebrafish models of KATP -dependent pancreatic diseases.
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Affiliation(s)
- Jennifer M. Ikle
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
- Department of Pediatrics, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
| | - Robert C. Tryon
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
| | - Soma S. Singareddy
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
| | - Nathaniel W. York
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
| | - Maria S. Remedi
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
- Department of Medicine, Division of Endocrinology, Metabolism, and Lipid Research, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology, Washington University in St. Louis, St. Louis, Missouri, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University in St. Louis School of Medicine, St. Louis, Missouri, USA
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Mittendorfer B, Patterson BW, Smith GI, Yoshino M, Klein S. Beta-cell function and plasma insulin clearance in people with obesity and different glycemic status. J Clin Invest 2021; 132:154068. [PMID: 34905513 PMCID: PMC8803344 DOI: 10.1172/jci154068] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 12/08/2021] [Indexed: 12/02/2022] Open
Abstract
Background It is unclear how excess adiposity and insulin resistance affect β cell function, insulin secretion, and insulin clearance in people with obesity. Methods We used a hyperinsulinemic-euglycemic clamp procedure and a modified oral glucose tolerance test to evaluate the interrelationships among obesity, insulin sensitivity, insulin kinetics, and glycemic status in 5 groups of individuals: normoglycemic lean and obese individuals with (a) normal fasting glucose and normal glucose tolerance (Ob-NFG-NGT), (b) NFG and impaired glucose tolerance (Ob-NFG-IGT), (c) impaired fasting glucose and IGT (Ob-IFG-IGT), or (d) type 2 diabetes (Ob-T2D). Results Glucose-stimulated insulin secretion (GSIS), an assessment of β cell function, was greater in the Ob-NFG-NGT and Ob-NFG-IGT groups than in the lean group, even when insulin sensitivity was matched in the obese and lean groups. Insulin sensitivity, not GSIS, was decreased in the Ob-NFG-IGT group compared with the Ob-NFG-NGT group, whereas GSIS, not insulin sensitivity, was decreased in the Ob-IFG-IGT and Ob-T2D groups compared with the Ob-NFG-NGT and Ob-NFG-IGT groups. Insulin clearance was directly related to insulin sensitivity and inversely related to the postprandial increase in insulin secretion and plasma insulin concentration. Conclusion Increased adiposity per se, not insulin resistance, enhanced insulin secretion in people with obesity. The obesity-induced increase in insulin secretion, in conjunction with a decrease in insulin clearance, sufficiently raised the plasma insulin concentrations needed to maintain normoglycemia in individuals with moderate, but not severe, insulin resistance. A deterioration in β cell function, not a decrease in insulin sensitivity, was a determinant of IFG and ultimately leads to T2D. CLINICAL TRIALS REGISTRATION ClinicalTrials.gov NCT02706262, NCT04131166, and NCT01977560. FUNDING NIH (P30 DK056341, P30 DK020579, and UL1 TR000448); American Diabetes Association (1-18-ICTS-119); Longer Life Foundation; Pershing Square Foundation; and Washington University-Centene ARCH Personalized Medicine Initiative (P19-00559).
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Affiliation(s)
- Bettina Mittendorfer
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, United States of America
| | - Bruce W Patterson
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, United States of America
| | - Gordon I Smith
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, United States of America
| | - Mihoko Yoshino
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, United States of America
| | - Samuel Klein
- Center for Human Nutrition, Washington University School of Medicine, St. Louis, United States of America
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Expression of truncated Kir6.2 promotes insertion of functionally inverted ATP-sensitive K + channels. Sci Rep 2021; 11:21539. [PMID: 34728728 PMCID: PMC8564548 DOI: 10.1038/s41598-021-00988-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 10/06/2021] [Indexed: 11/12/2022] Open
Abstract
ATP-sensitive K+ (KATP) channels couple cellular metabolism to electrical activity in many cell types. Wild-type KATP channels are comprised of four pore forming (Kir6.x) and four regulatory (sulfonylurea receptor, SURx) subunits that each contain RKR endoplasmic reticulum retention sequences that serve to properly translocate the channel to the plasma membrane. Truncated Kir6.x variants lacking RKR sequences facilitate plasma membrane expression of functional Kir6.x in the absence of SURx; however, the effects of channel truncation on plasma membrane orientation have not been explored. To investigate the role of truncation on plasma membrane orientation of ATP sensitive K+ channels, three truncated variants of Kir6.2 were used (Kir6.2ΔC26, 6xHis-Kir6.2ΔC26, and 6xHis-EGFP-Kir6.2ΔC26). Oocyte expression of Kir6.2ΔC26 shows the presence of a population of inverted inserted channels in the plasma membrane, which is not present when co-expressed with SUR1. Immunocytochemical staining of intact and permeabilized HEK293 cells revealed that the N-terminus of 6xHis-Kir6.2ΔC26 was accessible on both sides of the plasma membrane at roughly equivalent ratios, whereas the N-terminus of 6xHis-EGFP-Kir6.2Δ26 was only accessible on the intracellular face. In HEK293 cells, whole-cell electrophysiological recordings showed a ca. 50% reduction in K+ current upon addition of ATP to the extracellular solution for 6xHis-Kir6.2ΔC26, though sensitivity to extracellular ATP was not observed in 6xHis-EGFP-Kir6.2ΔC26. Importantly, the population of channels that is inverted exhibited similar function to properly inserted channels within the plasma membrane. Taken together, these data suggest that in the absence of SURx, inverted channels can be formed from truncated Kir6.x subunits that are functionally active which may provide a new model for testing pharmacological modulators of Kir6.x, but also indicates the need for added caution when using truncated Kir6.2 mutants.
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Sánchez-Alegría K, Bastián-Eugenio CE, Vaca L, Arias C. Palmitic acid induces insulin resistance by a mechanism associated with energy metabolism and calcium entry in neuronal cells. FASEB J 2021; 35:e21712. [PMID: 34110637 DOI: 10.1096/fj.202100243r] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 04/27/2021] [Accepted: 05/17/2021] [Indexed: 01/05/2023]
Abstract
Palmitic acid (PA) is a saturated fatty acid whose high consumption has been largely associated with the development of different metabolic alterations, such as insulin resistance, metabolic syndrome, and type 2 diabetes. Particularly in the brain, insulin signaling disruption has been linked to cognitive decline and is considered a risk factor for Alzheimer's disease. Cumulative evidence has demonstrated the participation of PA in the molecular cascade underlying cellular insulin resistance in peripheral tissues, but its role in the development of neuronal insulin resistance and the mechanisms involved are not fully understood. It has generally been accepted that the brain does not utilize fatty acids as a primary energy source, but recent evidence shows that neurons possess the machinery for fatty acid β-oxidation. However, it is still unclear under what conditions neurons use fatty acids as energy substrates and the implications of their oxidative metabolism in modifying insulin-stimulated effects. In the present work, we have found that neurons differentiated from human neuroblastoma MSN exposed to high but nontoxic concentrations of PA generate ATP through mitochondrial metabolism, which is associated with an increase in the cytosolic Ca2+ and diminished insulin signaling in neurons. These findings reveal a novel mechanism by which saturated fatty acids produce Ca2+ entry and insulin resistance that may play a causal role in increasing neuronal vulnerability associated with metabolic diseases.
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Affiliation(s)
- Karina Sánchez-Alegría
- Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| | - Carlos Ernesto Bastián-Eugenio
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| | - Luis Vaca
- Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
| | - Clorinda Arias
- Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad de México, Mexico
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Characteristics of the New Insulin-Resistant Zebrafish Model. Pharmaceuticals (Basel) 2021; 14:ph14070642. [PMID: 34358068 PMCID: PMC8308799 DOI: 10.3390/ph14070642] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Revised: 06/28/2021] [Accepted: 06/30/2021] [Indexed: 01/09/2023] Open
Abstract
Insulin resistance, which occurs when insulin levels are sufficiently high over a prolonged period, causing the cells to fail to respond normally to the hormone. As a system for insulin resistance and diabetes drug development, insulin-resistant rodent models have been clearly established, but there is a limitation to high-throughput drug screening. Recently, zebrafish have been identified as an excellent system for drug discovery and identification of therapeutic targets, but studies on insulin resistance models have not been extensively performed. Therefore, we aimed to make a rapid insulin-resistant zebrafish model that complements the existing rodent models. To establish this model, zebrafish were treated with 10 μM insulin for 48 h. This model showed characteristics of insulin-resistant disease such as damaged pancreatic islets. Then we confirmed the recovery of the pancreatic islets after pioglitazone treatment. In addition, it was found that insulin-resistant drugs have as significant an effect in zebrafish as in humans, and these results proved the value of the zebrafish insulin resistance model for drug selection. In addition, RNA sequencing was performed to elucidate the mechanism involved. KEGG pathway enrichment analysis of differentially expressed genes showed that insulin resistance altered gene expression due to the MAPK signaling and calcium signaling pathways. This model demonstrates the utility of the zebrafish model for drug testing and drug discovery in insulin resistance and diabetes.
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Nichols CG, York NW, Remedi MS. Preferential Gq signaling in diabetes: an electrical switch in incretin action and in diabetes progression? J Clin Invest 2021; 130:6235-6237. [PMID: 33196460 DOI: 10.1172/jci143199] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Patients with type 2 diabetes (T2D) fail to secrete insulin in response to increased glucose levels that occur with eating. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are two incretins secreted from gastrointestinal cells that amplify insulin secretion when glucose is high. In this issue of the JCI, Oduori et al. explore the role of ATP-sensitive K+ (KATP) channels in maintaining glucose homeostasis. In persistently depolarized β cells from KATP channel knockout (KO) mice, the researchers revealed a shift in G protein signaling from the Gs family to the Gq family. This shift explains why GLP-1, which signals via Gq, but not GIP, which signals preferentially via Gs, can effectively potentiate secretion in islets from the KATP channel-deficient mice and in other models of KATP deficiency, including diabetic KK-Ay mice. Their results provide one explanation for differential insulinotropic potential of incretins in human T2D and point to a potentially unifying model for T2D progression itself.
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Affiliation(s)
- Colin G Nichols
- Center for the Investigation of Membrane Excitability Diseases.,Department of Cell Biology and Physiology
| | - Nathaniel W York
- Center for the Investigation of Membrane Excitability Diseases.,Department of Cell Biology and Physiology
| | - Maria S Remedi
- Center for the Investigation of Membrane Excitability Diseases.,Division of Endocrinology, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA
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Rehman K, Tahir A, Niaz S, Shabbir S, Jabeen K, Faheem A, Akash MSH. Frequency of PPAR-γ, FTO and ABCC8 genetic variation in Pakistani cardiovascular smokers. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2020; 27:42611-42620. [PMID: 32712935 DOI: 10.1007/s11356-020-10226-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 07/20/2020] [Indexed: 06/11/2023]
Abstract
Smoking is considered as one of the major reasons behind genetic variations in cardiometabolic disorders. However, effect of nicotine via smoking on Pakistani population still needs to be elucidated. This study was aimed to investigate genetic variation among PPAR-γ, FTO, and ABCC8 genes in cardiometabolic patients along with their biochemical parameters. A total of 472 CVD patients were enrolled in this study and divided into three groups; n = 144 for PPAR-γ (C/G) variation and n = 164 in each group to investigate FTO (T/A) and ABCC8 (G/T) variation, respectively. Polymorphisms within groups were identified by using Tetra and/or Tri ARM-PCR. This study showed positive association among genetic polymorphisms in PPAR-γ, FTO, and ABCC8 groups with altered metabolic parameters in CVD patients. Findings showed that smoking is major contributory factor for genetic polymorphism that was strongly associated with elevated blood glucose and serum TGs accompanying PPAR-γ, FTO, and ABCC8 genetic polymorphism in 25%, 24%, and 20% in smokers and 11%, 10%, and 5% in non-smoker CVD patients, respectively. However, highest polymorphism occurred in PPAR-γ both in smokers and non-smoker CVD patients that show that smoking-mediated gene polymorphism might be a contributory factor in provoking CVD risk approximately twice in smokers as compared to that in non-smoker CVD patients.
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Affiliation(s)
- Kanwal Rehman
- Department of Pharmacy, University of Agriculture, Faisalabad, Pakistan
- Institute of Physiology and Pharmacology, University of Agriculture, Faisalabad, Pakistan
| | - Ayesha Tahir
- Institute of Physiology and Pharmacology, University of Agriculture, Faisalabad, Pakistan
| | - Sania Niaz
- Institute of Physiology and Pharmacology, University of Agriculture, Faisalabad, Pakistan
| | - Sara Shabbir
- Department of Pharmacy, University of Agriculture, Faisalabad, Pakistan
| | - Komal Jabeen
- Department of Pharmacy, University of Agriculture, Faisalabad, Pakistan
- Institute of Physiology and Pharmacology, University of Agriculture, Faisalabad, Pakistan
| | - Amna Faheem
- Institute of Physiology and Pharmacology, University of Agriculture, Faisalabad, Pakistan
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Gϋemes M, Rahman SA, Kapoor RR, Flanagan S, Houghton JAL, Misra S, Oliver N, Dattani MT, Shah P. Hyperinsulinemic hypoglycemia in children and adolescents: Recent advances in understanding of pathophysiology and management. Rev Endocr Metab Disord 2020; 21:577-597. [PMID: 32185602 PMCID: PMC7560934 DOI: 10.1007/s11154-020-09548-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Hyperinsulinemic hypoglycemia (HH) is characterized by unregulated insulin release, leading to persistently low blood glucose concentrations with lack of alternative fuels, which increases the risk of neurological damage in these patients. It is the most common cause of persistent and recurrent hypoglycemia in the neonatal period. HH may be primary, Congenital HH (CHH), when it is associated with variants in a number of genes implicated in pancreatic development and function. Alterations in fifteen genes have been recognized to date, being some of the most recently identified mutations in genes HK1, PGM1, PMM2, CACNA1D, FOXA2 and EIF2S3. Alternatively, HH can be secondary when associated with syndromes, intra-uterine growth restriction, maternal diabetes, birth asphyxia, following gastrointestinal surgery, amongst other causes. CHH can be histologically characterized into three groups: diffuse, focal or atypical. Diffuse and focal forms can be determined by scanning using fluorine-18 dihydroxyphenylalanine-positron emission tomography. Newer and improved isotopes are currently in development to provide increased diagnostic accuracy in identifying lesions and performing successful surgical resection with the ultimate aim of curing the condition. Rapid diagnostics and innovative methods of management, including a wider range of treatment options, have resulted in a reduction in co-morbidities associated with HH with improved quality of life and long-term outcomes. Potential future developments in the management of this condition as well as pathways to transition of the care of these highly vulnerable children into adulthood will also be discussed.
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Affiliation(s)
- Maria Gϋemes
- Genetics and Genomic Medicine Programme, UCL Great Ormond Street Institute of Child Health, Great Ormond Street, London, WC1N 3JH, UK
- Department of Pediatric Endocrinology, Great Ormond Street Hospital for Children, London, UK
- Endocrinology Service, Hospital Infantil Universitario Niño Jesús, Madrid, Spain
| | - Sofia Asim Rahman
- Genetics and Genomic Medicine Programme, UCL Great Ormond Street Institute of Child Health, Great Ormond Street, London, WC1N 3JH, UK
| | - Ritika R Kapoor
- Pediatric Diabetes and Endocrinology, King's College Hospital NHS Trust, Denmark Hill, London, UK
| | - Sarah Flanagan
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK
| | - Jayne A L Houghton
- Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK
- Royal Devon and Exeter Foundation Trust, Exeter, UK
| | - Shivani Misra
- Department of Diabetes, Endocrinology and Metabolic Medicine, Faculty of Medicine, Imperial College Healthcare NHS Trust, London, UK
| | - Nick Oliver
- Department of Diabetes, Endocrinology and Metabolic Medicine, Faculty of Medicine, Imperial College Healthcare NHS Trust, London, UK
| | - Mehul Tulsidas Dattani
- Genetics and Genomic Medicine Programme, UCL Great Ormond Street Institute of Child Health, Great Ormond Street, London, WC1N 3JH, UK
- Department of Pediatric Endocrinology, Great Ormond Street Hospital for Children, London, UK
| | - Pratik Shah
- Genetics and Genomic Medicine Programme, UCL Great Ormond Street Institute of Child Health, Great Ormond Street, London, WC1N 3JH, UK.
- Department of Pediatric Endocrinology, Great Ormond Street Hospital for Children, London, UK.
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12
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Law NC, Marinelli I, Bertram R, Corbin KL, Schildmeyer C, Nunemaker CS. Chronic stimulation induces adaptive potassium channel activity that restores calcium oscillations in pancreatic islets in vitro. Am J Physiol Endocrinol Metab 2020; 318:E554-E563. [PMID: 32069073 PMCID: PMC7191410 DOI: 10.1152/ajpendo.00482.2019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin pulsatility is important to hepatic response in regulating blood glucose. Growing evidence suggests that insulin-secreting pancreatic β-cells can adapt to chronic disruptions of pulsatility to rescue this physiologically important behavior. We determined the time scale for adaptation and examined potential ion channels underlying it. We induced the adaptation both by chronic application of the ATP-sensitive K+ [K(ATP)] channel blocker tolbutamide and by application of the depolarizing agent potassium chloride (KCl). Acute application of tolbutamide without pretreatment results in elevated Ca2+ as measured by fura-2AM and the loss of endogenous pulsatility. We show that after chronic exposure to tolbutamide (12-24 h), Ca2+ oscillations occur with subsequent acute tolbutamide application. The same experiment was conducted with potassium chloride (KCl) to directly depolarize the β-cells. Once again, following chronic exposure to the cell stimulator, the islets produced Ca2+ oscillations when subsequently exposed to tolbutamide. These experiments suggest that it is the chronic stimulation, and not tolbutamide desensitization, that is responsible for the adaptation that rescues oscillatory β-cell activity. This compensatory response also causes islet glucose sensitivity to shift rightward following chronic tolbutamide treatment. Mathematical modeling shows that a small increase in the number of K(ATP) channels in the membrane is one adaptation mechanism that is compatible with the data. To examine other compensatory mechanisms, pharmacological studies provide support that Kir2.1 and TEA-sensitive channels play some role. Overall, this investigation demonstrates β-cell adaptability to overstimulation, which is likely an important mechanism for maintaining glucose homeostasis in the face of chronic stimulation.
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Affiliation(s)
- Nathan C Law
- Department of Biomedical Sciences Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | | | - Richard Bertram
- Department of Mathematics and Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, Florida
| | - Kathryn L Corbin
- Department of Biomedical Sciences Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | - Cara Schildmeyer
- Department of Biomedical Sciences Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
| | - Craig S Nunemaker
- Department of Biomedical Sciences Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
- Diabetes Institute, Heritage College of Osteopathic Medicine, Ohio University, Athens, Ohio
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13
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Martin GM, Sung MW, Yang Z, Innes LM, Kandasamy B, David LL, Yoshioka C, Shyng SL. Mechanism of pharmacochaperoning in a mammalian K ATP channel revealed by cryo-EM. eLife 2019; 8:46417. [PMID: 31343405 PMCID: PMC6699824 DOI: 10.7554/elife.46417] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 07/22/2019] [Indexed: 01/03/2023] Open
Abstract
ATP-sensitive potassium (KATP) channels composed of a pore-forming Kir6.2 potassium channel and a regulatory ABC transporter sulfonylurea receptor 1 (SUR1) regulate insulin secretion in pancreatic β-cells to maintain glucose homeostasis. Mutations that impair channel folding or assembly prevent cell surface expression and cause congenital hyperinsulinism. Structurally diverse KATP inhibitors are known to act as pharmacochaperones to correct mutant channel expression, but the mechanism is unknown. Here, we compare cryoEM structures of a mammalian KATP channel bound to pharmacochaperones glibenclamide, repaglinide, and carbamazepine. We found all three drugs bind within a common pocket in SUR1. Further, we found the N-terminus of Kir6.2 inserted within the central cavity of the SUR1 ABC core, adjacent the drug binding pocket. The findings reveal a common mechanism by which diverse compounds stabilize the Kir6.2 N-terminus within SUR1’s ABC core, allowing it to act as a firm ‘handle’ for the assembly of metastable mutant SUR1-Kir6.2 complexes.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Min Woo Sung
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Zhongying Yang
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Laura M Innes
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Balamurugan Kandasamy
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Larry L David
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
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14
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Toro-Huamanchumo CJ, Urrunaga-Pastor D, Guarnizo-Poma M, Lazaro-Alcantara H, Paico-Palacios S, Pantoja-Torres B, Ranilla-Seguin VDC, Benites-Zapata VA. Triglycerides and glucose index as an insulin resistance marker in a sample of healthy adults. Diabetes Metab Syndr 2019; 13:272-277. [PMID: 30641711 DOI: 10.1016/j.dsx.2018.09.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Accepted: 09/11/2018] [Indexed: 12/12/2022]
Abstract
AIM To assess the association between elevated triglycerides/glucose index (TGI) and insulin resistance (IR) or hyperinsulinemia after oral glucose tolerance test (OGTT) in a sample of healthy adults. METHODS We conducted an analytical cross-sectional study in euthyroid non-diabetic adults, who attended the outpatient service of a private clinic in Lima-Peru during the 2012-2016 period. Participants were categorized in two groups according to the presence or absence of elevated TGI, IR or hyperinsulinemia after OGTT. A TGI value ≥ 8.65 was considered as elevated. We defined IR as a Homeostasis Model Assessment (HOMA-IR) value ≥ 2.28 and hyperinsulinemia after OGTT as a serum insulin value ≥ 80μU/mL after 120 min of 75-g glucose intake. We elaborated crude and adjusted Poisson regression models to assess the association between elevated TGI and IR or hyperinsulinemia after OGTT. The reported association measure was the prevalence ratio (PR) with their respective 95% confidence intervals (95%CI). RESULTS We analyzed 118 individuals, the average age was 37.5 ± 11.3 years, 21 (17.8%) were males and the median BMI was 22.7 ± 1.6 kg/m2. The prevalence of elevated TGI was 25.4% (n=30) while the prevalence of IR and hyperinsulinemia after OGTT was 24.6% (n=29) and 17.0% (n=20) respectively. In the adjusted model, elevated TGI was associated with both IR (aPR=6.36; 95%CI: 3.41-11.86) and hyperinsulinemia after OGTT (aPR=4.19; 95%CI: 1.81-9.70). CONCLUSIONS We found that elevated TGI was associated with both IR markers in a sample of euthyroid adults without T2DM and with a normal BMI. The simplicity of the TGI calculation makes it the first-choice alternative when the hyperinsulinemic-euglycemic clamp or HOMA-IR are not available.
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Affiliation(s)
- Carlos J Toro-Huamanchumo
- Unidad de Investigación para la Generación y Síntesis de Evidencias en Salud, Universidad San Ignacio de Loyola, Lima, Peru.
| | - Diego Urrunaga-Pastor
- Unidad de Investigación para la Generación y Síntesis de Evidencias en Salud, Universidad San Ignacio de Loyola, Lima, Peru.
| | | | | | | | | | | | - Vicente A Benites-Zapata
- Unidad de Investigación para la Generación y Síntesis de Evidencias en Salud, Universidad San Ignacio de Loyola, Lima, Peru.
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15
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Tao YX, Conn PM. Pharmacoperones as Novel Therapeutics for Diverse Protein Conformational Diseases. Physiol Rev 2018; 98:697-725. [PMID: 29442594 DOI: 10.1152/physrev.00029.2016] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
After synthesis, proteins are folded into their native conformations aided by molecular chaperones. Dysfunction in folding caused by genetic mutations in numerous genes causes protein conformational diseases. Membrane proteins are more prone to misfolding due to their more intricate folding than soluble proteins. Misfolded proteins are detected by the cellular quality control systems, especially in the endoplasmic reticulum, and proteins may be retained there for eventual degradation by the ubiquitin-proteasome system or through autophagy. Some misfolded proteins aggregate, leading to pathologies in numerous neurological diseases. In vitro, modulating mutant protein folding by altering molecular chaperone expression can ameliorate some misfolding. Some small molecules known as chemical chaperones also correct mutant protein misfolding in vitro and in vivo. However, due to their lack of specificity, their potential as therapeutics is limited. Another class of compounds, known as pharmacological chaperones (pharmacoperones), binds with high specificity to misfolded proteins, either as enzyme substrates or receptor ligands, leading to decreased folding energy barriers and correction of the misfolding. Because many of the misfolded proteins are misrouted but do not have defects in function per se, pharmacoperones have promising potential in advancing to the clinic as therapeutics, since correcting routing may ameliorate the underlying mechanism of disease. This review will comprehensively summarize this exciting area of research, surveying the literature from in vitro studies in cell lines to transgenic animal models and clinical trials in several protein misfolding diseases.
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Affiliation(s)
- Ya-Xiong Tao
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University , Auburn, Alabama ; and Departments of Internal Medicine and Cell Biology, Texas Tech University Health Science Center , Lubbock, Texas
| | - P Michael Conn
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University , Auburn, Alabama ; and Departments of Internal Medicine and Cell Biology, Texas Tech University Health Science Center , Lubbock, Texas
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16
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Wrutniak-Cabello C, Casas F, Cabello G. Mitochondrial T3 receptor and targets. Mol Cell Endocrinol 2017; 458:112-120. [PMID: 28167126 DOI: 10.1016/j.mce.2017.01.054] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 01/28/2017] [Accepted: 01/31/2017] [Indexed: 12/25/2022]
Abstract
The demonstration that TRα1 mRNA encodes a nuclear thyroid hormone receptor and two proteins imported into mitochondria with molecular masses of 43 and 28 kDa has brought new clues to better understand the pleiotropic influence of iodinated hormones. If p28 activity remains unknown, p43 binds to T3 responsive elements occurring in the organelle genome, and, in the T3 presence, stimulates mitochondrial transcription and the subsequent synthesis of mitochondrial encoded proteins. This influence increases mitochondrial activity and through changes in the mitochondrial/nuclear cross talk affects important nuclear target genes regulating cell proliferation and differentiation, oncogenesis, or apoptosis. In addition, this pathway influences muscle metabolic and contractile phenotype, as well as glycaemia regulation. Interestingly, according to the process considered, p43 exerts opposite or cooperative effects with the well-known T3 pathway, thus allowing a fine tuning of the physiological influence of this hormone.
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Affiliation(s)
- Chantal Wrutniak-Cabello
- INRA, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France; Université de Montpellier, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France.
| | - François Casas
- INRA, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France; Université de Montpellier, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France
| | - Gérard Cabello
- INRA, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France; Université de Montpellier, UMR 866 Dynamique Musculaire et Métabolisme, 34060 Montpellier, France
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17
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Ng CM, Tang F, Seeholzer SH, Zou Y, De León DD. Population pharmacokinetics of exendin-(9-39) and clinical dose selection in patients with congenital hyperinsulinism. Br J Clin Pharmacol 2017; 84:520-532. [PMID: 29077992 DOI: 10.1111/bcp.13463] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Revised: 09/06/2017] [Accepted: 10/23/2017] [Indexed: 12/01/2022] Open
Abstract
AIMS Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycaemia in infants and children. Exendin-(9-39), an inverse glucagon-like peptide 1 (GLP-1) agonist, is a novel therapeutic agent for HI that has demonstrated glucose-raising effect. We report the first population pharmacokinetic (PopPK) model of the exendin-(9-39) in patients with HI and propose the optimal dosing regimen for future clinical trials in neonates with HI. METHODS A total of 182 pharmacokinetic (PK) observations from 26 subjects in three clinical studies were included for constructing the PopPK model using first order conditional estimation (FOCE) with interaction method in nonlinear mixed-effects modelling (NONMEM). Exposure metrics (area under the curve [AUC] and maximum plasma concentration [Cmax ]) at no observed adverse effect levels (NOAELs) in rats and dogs were determined in toxicology studies. RESULTS Observed concentration-time profiles of exendin-(9-39) were described by a linear two-compartmental PK model. Following allometric scaling of PK parameters, age and creatinine clearance did not significantly affect clearance. The calculated clearance and elimination half-life for adult subjects with median weight of 69 kg were 11.8 l h-1 and 1.81 h, respectively. The maximum recommended starting dose determined from modelling and simulation based on the AUC0-last at the NOAEL and predicted AUC0-inf using the PopPK model was 27 mg kg-1 day-1 intravenously. CONCLUSIONS This is the first study to investigate the PopPK of exendin-(9-39) in humans. The final PopPK model was successfully used with preclinical toxicology findings to propose the optimal dosing regimen of exendin-(9-39) for clinical studies in neonates with HI, allowing for a more targeted dosing approach to achieve desired glycaemic response.
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Affiliation(s)
- Chee M Ng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY, USA
| | - Fei Tang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY, USA
| | | | - Yixuan Zou
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY, USA
| | - Diva D De León
- The Children's Hospital of Philadelphia, Philadelphia, PA, USA
- Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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18
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Flanagan SE, Dũng VC, Houghton JAL, De Franco E, Ngoc CTB, Damhuis A, Ashcroft FM, Harries LW, Ellard S. An ABCC8 Nonsense Mutation Causing Neonatal Diabetes Through Altered Transcript Expression. J Clin Res Pediatr Endocrinol 2017; 9:260-264. [PMID: 28663158 PMCID: PMC5596808 DOI: 10.4274/jcrpe.4624] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The pancreatic ATP-sensitive K+ (K-ATP) channel is a key regulator of insulin secretion. Gain-of-function mutations in the genes encoding the Kir6.2 (KCNJ11) and SUR1 (ABCC8) subunits of the channel cause neonatal diabetes, whilst loss-of-function mutations in these genes result in congenital hyperinsulinism. We report two patients with neonatal diabetes in whom we unexpectedly identified recessively inherited loss-of-function mutations. The aim of this study was to investigate how a homozygous nonsense mutation in ABCC8 could result in neonatal diabetes. The ABCC8 p.Glu747* was identified in two unrelated Vietnamese patients. This mutation is located within the in-frame exon 17 and RNA studies confirmed (a) the absence of full length SUR1 mRNA and (b) the presence of the alternatively spliced transcript lacking exon 17. Successful transfer of both patients to sulphonylurea treatment suggests that the altered transcript expression enhances the sensitivity of the K-ATP channel to Mg-ADP/ATP. This is the first report of an ABCC8 nonsense mutation causing a gain-of-channel function and these findings extend the spectrum of K-ATP channel mutations observed in patients with neonatal diabetes.
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Affiliation(s)
- Sarah E. Flanagan
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
,* Address for Correspondence: University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom E-mail:
| | - Vũ Chí Dũng
- National Children’s Hospital, Department of Endocrinology, Metabolism and Genetics, Hanoi, Vietnam
| | - Jayne A. L. Houghton
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Elisa De Franco
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Can Thi Bich Ngoc
- National Children’s Hospital, Department of Endocrinology, Metabolism and Genetics, Hanoi, Vietnam
| | - Annet Damhuis
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Frances M. Ashcroft
- University of Oxford, Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Oxford, United Kingdom
| | - Lorna W. Harries
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Sian Ellard
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
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19
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Demirbilek H, Rahman SA, Buyukyilmaz GG, Hussain K. Diagnosis and treatment of hyperinsulinaemic hypoglycaemia and its implications for paediatric endocrinology. INTERNATIONAL JOURNAL OF PEDIATRIC ENDOCRINOLOGY 2017; 2017:9. [PMID: 28855921 PMCID: PMC5575922 DOI: 10.1186/s13633-017-0048-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 08/15/2017] [Indexed: 12/14/2022]
Abstract
Glucose homeostasis requires appropriate and synchronous coordination of metabolic events and hormonal activities to keep plasma glucose concentrations in a narrow range of 3.5–5.5 mmol/L. Insulin, the only glucose lowering hormone secreted from pancreatic β-cells, plays the key role in glucose homeostasis. Insulin release from pancreatic β-cells is mainly regulated by intracellular ATP-generating metabolic pathways. Hyperinsulinaemic hypoglycaemia (HH), the most common cause of severe and persistent hypoglycaemia in neonates and children, is the inappropriate secretion of insulin which occurs despite low plasma glucose levels leading to severe and persistent hypoketotic hypoglycaemia. Mutations in 12 different key genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, UCP2, HNF4A, HNF1A, HK1, PGM1 and PMM2) constitute the underlying molecular mechanisms of congenital HH. Since insulin supressess ketogenesis, the alternative energy source to the brain, a prompt diagnosis and immediate management of HH is essential to avoid irreversible hypoglycaemic brain damage in children. Advances in molecular genetics, imaging methods (18F–DOPA PET-CT), medical therapy and surgical approach (laparoscopic and open pancreatectomy) have changed the management and improved the outcome of patients with HH. This up to date review article provides a background to the diagnosis, molecular genetics, recent advances and therapeutic options in the field of HH in children.
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Affiliation(s)
- Huseyin Demirbilek
- Department of Paediatric Endocrinology, Hacettepe University, Faculty of Medicine, Ankara, Turkey
| | - Sofia A Rahman
- Great Ormond Street Institute of Child Health, Genetics and Genomic Medicine, University College London, 30 Guilford Street, London, WC1N 1EH UK
| | - Gonul Gulal Buyukyilmaz
- Department of Paediatric Endocrinology, Hacettepe University, Faculty of Medicine, Ankara, Turkey
| | - Khalid Hussain
- Department of Paediatric Medicine Sidra Medical & Research Center, OPC, C6-337, PO Box 26999, Doha, Qatar
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20
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Alvarez CP, Stagljar M, Muhandiram DR, Kanelis V. Hyperinsulinism-Causing Mutations Cause Multiple Molecular Defects in SUR1 NBD1. Biochemistry 2017; 56:2400-2416. [PMID: 28346775 DOI: 10.1021/acs.biochem.6b00681] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The sulfonylurea receptor 1 (SUR1) protein forms the regulatory subunit in ATP sensitive K+ (KATP) channels in the pancreas. SUR proteins are members of the ATP binding cassette (ABC) superfamily of proteins. Binding and hydrolysis of MgATP at the SUR nucleotide binding domains (NBDs) lead to channel opening. Pancreatic KATP channels play an important role in insulin secretion. SUR1 mutations that result in increased levels of channel opening ultimately inhibit insulin secretion and lead to neonatal diabetes. In contrast, SUR1 mutations that disrupt trafficking and/or decrease gating of KATP channels cause congenital hyperinsulinism, where oversecretion of insulin occurs even in the presence of low glucose levels. Here, we present data on the effects of specific congenital hyperinsulinism-causing mutations (G716V, R842G, and K890T) located in different regions of the first nucleotide binding domain (NBD1). Nuclear magnetic resonance (NMR) and fluorescence data indicate that the K890T mutation affects residues throughout NBD1, including residues that bind MgATP, NBD2, and coupling helices. The mutations also decrease the MgATP binding affinity of NBD1. Size exclusion and NMR data indicate that the G716V and R842G mutations cause aggregation of NBD1 in vitro, possibly because of destabilization of the domain. These data describe structural characterization of SUR1 NBD1 and shed light on the underlying molecular basis of mutations that cause congenital hyperinsulinism.
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Affiliation(s)
- Claudia P Alvarez
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
| | - Marijana Stagljar
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.,Department of Cell and Systems Biology, University of Toronto , 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
| | - D Ranjith Muhandiram
- Department of Molecular Genetics, University of Toronto , 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
| | - Voula Kanelis
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.,Department of Cell and Systems Biology, University of Toronto , 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
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21
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Mitochondrial pyruvate transport: a historical perspective and future research directions. Biochem J 2015; 466:443-54. [PMID: 25748677 DOI: 10.1042/bj20141171] [Citation(s) in RCA: 157] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Pyruvate is the end-product of glycolysis, a major substrate for oxidative metabolism, and a branching point for glucose, lactate, fatty acid and amino acid synthesis. The mitochondrial enzymes that metabolize pyruvate are physically separated from cytosolic pyruvate pools and rely on a membrane transport system to shuttle pyruvate across the impermeable inner mitochondrial membrane (IMM). Despite long-standing acceptance that transport of pyruvate into the mitochondrial matrix by a carrier-mediated process is required for the bulk of its metabolism, it has taken almost 40 years to determine the molecular identity of an IMM pyruvate carrier. Our current understanding is that two proteins, mitochondrial pyruvate carriers MPC1 and MPC2, form a hetero-oligomeric complex in the IMM to facilitate pyruvate transport. This step is required for mitochondrial pyruvate oxidation and carboxylation-critical reactions in intermediary metabolism that are dysregulated in several common diseases. The identification of these transporter constituents opens the door to the identification of novel compounds that modulate MPC activity, with potential utility for treating diabetes, cardiovascular disease, cancer, neurodegenerative diseases, and other common causes of morbidity and mortality. The purpose of the present review is to detail the historical, current and future research investigations concerning mitochondrial pyruvate transport, and discuss the possible consequences of altered pyruvate transport in various metabolic tissues.
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22
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Jahnavi S, Poovazhagi V, Kanthimathi S, Balamurugan K, Bodhini D, Yadav J, Jain V, Khadgawat R, Sikdar M, Bhavatharini A, Das AK, Kaur T, Mohan V, Radha V. Novel ABCC8 (SUR1) gene mutations in Asian Indian children with congenital hyperinsulinemic hypoglycemia. Ann Hum Genet 2015; 78:311-9. [PMID: 25117148 DOI: 10.1111/ahg.12070] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 04/20/2014] [Indexed: 11/30/2022]
Abstract
Congenital hyperinsulinemic hypoglycemia (HI) is a heterogeneous genetic disorder of insulin secretion characterized by persistent hypoglycemia, most commonly associated with inactivating mutations of the β-cell ATP-sensitive K(+) channel (K(ATP) channel) genes ABCC8 (encoding SUR1) and KCNJ11(encoding Kir6.2). This study aimed to screen the mutations in the genes associated with congenital HI in Asian Indian children. Recessive mutations of these genes cause hyperinsulinism that is unresponsive to treatment with channel agonists like diazoxide. Dominant K(ATP) mutations have been associated with diazoxide-responsive disease. The KCNJ11, ABCC8, GCK, HNF4A, and GLUD1 genes were analyzed by sequence analysis in 22 children with congenital HI. We found 10 novel mutations (c.1delA, c.61delG, c.267delT, c.619-629delCCCGAGGACCT, Gln444*, Leu724Pro, Ala847Thr, Trp898*, IVS30-2A>C, and Leu1454Arg) and two known mutations (Gly111Arg and Arg598*) in the ABCC8 gene. This study describes novel and known ABCC8 gene mutations in children with congenital HI. This is the first large genetic screening study on HI in India and our results will help clinicians in providing optimal treatment for patients with hyperinsulinemia and in assisting affected families with genetic counseling.
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Affiliation(s)
- Suresh Jahnavi
- Madras Diabetes Research Foundation, ICMR Advanced Centre for Genomics of Type 2 Diabetes and Dr. Mohan's Diabetes Specialities Centre, WHO Collaborating Centre for Non-Communicable Diseases Prevention & Control, IDF Centre of Education, Gopalapuram, Chennai, India
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Nunemaker CS, Satin LS. Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 2014; 47:49-63. [PMID: 24610206 PMCID: PMC4382805 DOI: 10.1007/s12020-014-0212-3] [Citation(s) in RCA: 26] [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] [Received: 01/04/2014] [Accepted: 02/13/2014] [Indexed: 01/01/2023]
Abstract
Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.
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Affiliation(s)
- Craig S. Nunemaker
- Division of Endocrinology and Metabolism, Department of, Medicine, University of Virginia, P.O. Box 801413, Charlottesville, VA 22901, USA,
| | - Leslie S. Satin
- Pharmacology Department, University of Michigan Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
- Brehm Diabetes Research Center, University of Michigan, Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
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24
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Mitochondrial pyruvate carrier 2 hypomorphism in mice leads to defects in glucose-stimulated insulin secretion. Cell Rep 2014; 7:2042-2053. [PMID: 24910426 DOI: 10.1016/j.celrep.2014.05.017] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 04/15/2014] [Accepted: 05/08/2014] [Indexed: 01/04/2023] Open
Abstract
Carrier-facilitated pyruvate transport across the inner mitochondrial membrane plays an essential role in anabolic and catabolic intermediary metabolism. Mitochondrial pyruvate carrier 2 (Mpc2) is believed to be a component of the complex that facilitates mitochondrial pyruvate import. Complete MPC2 deficiency resulted in embryonic lethality in mice. However, a second mouse line expressing an N-terminal truncated MPC2 protein (Mpc2(Δ16)) was viable but exhibited a reduced capacity for mitochondrial pyruvate oxidation. Metabolic studies demonstrated exaggerated blood lactate concentrations after pyruvate, glucose, or insulin challenge in Mpc2(Δ16) mice. Additionally, compared with wild-type controls, Mpc2(Δ16) mice exhibited normal insulin sensitivity but elevated blood glucose after bolus pyruvate or glucose injection. This was attributable to reduced glucose-stimulated insulin secretion and was corrected by sulfonylurea KATP channel inhibitor administration. Collectively, these data are consistent with a role for MPC2 in mitochondrial pyruvate import and suggest that Mpc2 deficiency results in defective pancreatic β cell glucose sensing.
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25
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Chen PC, Olson EM, Zhou Q, Kryukova Y, Sampson HM, Thomas DY, Shyng SL. Carbamazepine as a novel small molecule corrector of trafficking-impaired ATP-sensitive potassium channels identified in congenital hyperinsulinism. J Biol Chem 2013; 288:20942-20954. [PMID: 23744072 DOI: 10.1074/jbc.m113.470948] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels consisting of sulfonylurea receptor 1 (SUR1) and the potassium channel Kir6.2 play a key role in insulin secretion by coupling metabolic signals to β-cell membrane potential. Mutations in SUR1 and Kir6.2 that impair channel trafficking to the cell surface lead to loss of channel function and congenital hyperinsulinism. We report that carbamazepine, an anticonvulsant, corrects the trafficking defects of mutant KATP channels previously identified in congenital hyperinsulinism. Strikingly, of the 19 SUR1 mutations examined, only those located in the first transmembrane domain of SUR1 responded to the drug. We show that unlike that reported for several other protein misfolding diseases, carbamazepine did not correct KATP channel trafficking defects by activating autophagy; rather, it directly improved the biogenesis efficiency of mutant channels along the secretory pathway. In addition to its effect on channel trafficking, carbamazepine also inhibited KATP channel activity. Upon subsequent removal of carbamazepine, however, the function of rescued channels was recovered. Importantly, combination of the KATP channel opener diazoxide and carbamazepine led to enhanced mutant channel function without carbamazepine washout. The corrector effect of carbamazepine on mutant KATP channels was also demonstrated in rat and human β-cells with an accompanying increase in channel activity. Our findings identify carbamazepine as a novel small molecule corrector that may be used to restore KATP channel expression and function in a subset of congenital hyperinsulinism patients.
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Affiliation(s)
- Pei-Chun Chen
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Erik M Olson
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Qing Zhou
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Yelena Kryukova
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and
| | - Heidi M Sampson
- Department of Biochemistry, McGill University, Montréal, Québec H3G 1Y6, Canada
| | - David Y Thomas
- Department of Biochemistry, McGill University, Montréal, Québec H3G 1Y6, Canada
| | - Show-Ling Shyng
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239 and.
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26
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Steneberg P, Bernardo L, Edfalk S, Lundberg L, Backlund F, Östenson CG, Edlund H. The type 2 diabetes-associated gene ide is required for insulin secretion and suppression of α-synuclein levels in β-cells. Diabetes 2013; 62:2004-14. [PMID: 23349488 PMCID: PMC3661649 DOI: 10.2337/db12-1045] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Genome-wide association studies have identified several type 2 diabetes (T2D) risk loci linked to impaired β-cell function. The identity and function of the causal genes in these susceptibility loci remain, however, elusive. The HHEX/IDE T2D locus is associated with decreased insulin secretion in response to oral glucose stimulation in humans. Here we have assessed β-cell function in Ide knockout (KO) mice. We find that glucose-stimulated insulin secretion (GSIS) is decreased in Ide KO mice due to impaired replenishment of the releasable pool of granules and that the Ide gene is haploinsufficient. We also show that autophagic flux and microtubule content are reduced in β-cells of Ide KO mice. One important cellular role for IDE involves the neutralization of amyloidogenic proteins, and we find that α-synuclein and IDE levels are inversely correlated in β-cells of Ide KO mice and T2D patients. Moreover, we provide evidence that both gain and loss of function of α-synuclein in β-cells in vivo impair not only GSIS but also autophagy. Together, these data identify the Ide gene as a regulator of GSIS, suggest a molecular mechanism for β-cell degeneration as a consequence of Ide deficiency, and corroborate and extend a previously established important role for α-synuclein in β-cell function.
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Affiliation(s)
- Pär Steneberg
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
| | - Lisandro Bernardo
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
| | - Sara Edfalk
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
| | - Lisa Lundberg
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
| | - Fredrik Backlund
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
| | - Claes-Göran Östenson
- Department of Molecular Medicine and Surgery, Endocrinology and Diabetology Unit, Karolinska Institutet, Karolinska University Hospital-Solna, Stockholm, Sweden
| | - Helena Edlund
- Umeå Center for Molecular Medicine, University of Umeå, Umeå, Sweden
- Corresponding author: Helena Edlund,
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27
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Abstract
CME EDUCATIONAL OBJECTIVES: 1.Review common endocrine conditions that often present in the newborn and perinatal period.2.Determine the enzymes involved in steroidogenesis.3.Discuss the diagnostic evaluation of hypoglycemia. Many endocrine conditions are unique to the perinatal period. In this article, we review many such conditions, including disorders of the pituitary gland, disorders of sexual differentiation, disorders of glucose homeostasis, disorders of the thyroid gland, and disorders of calcium homeostasis. Rather than serving as a comprehensive resource, the article is meant to serve as a guide for general pediatricians and neonatologists caring for infants with endocrine disorders. Moreover, because the field of pediatric endocrinology continues to evolve, consultation with a pediatric endocrinologist for any child with an endocrinopathy is recommended.
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28
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Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia. Acta Pharmacol Sin 2013; 34:24-32. [PMID: 23123646 DOI: 10.1038/aps.2012.138] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are weak, inward rectifiers that couple metabolic status to cell membrane electrical activity, thus modulating many cellular functions. An increase in the ADP/ATP ratio opens K(ATP) channels, leading to membrane hyperpolarization. K(ATP) channels are ubiquitously expressed in neurons located in different regions of the brain, including the hippocampus and cortex. Brief hypoxia triggers membrane hyperpolarization in these central neurons. In vivo animal studies confirmed that knocking out the Kir6.2 subunit of the K(ATP) channels increases ischemic infarction, and overexpression of the Kir6.2 subunit reduces neuronal injury from ischemic insults. These findings provide the basis for a practical strategy whereby activation of endogenous K(ATP) channels reduces cellular damage resulting from cerebral ischemic stroke. K(ATP) channel modulators may prove to be clinically useful as part of a combination therapy for stroke management in the future.
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29
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Faletra F, Snider K, Shyng SL, Bruno I, Athanasakis E, Gasparini P, Dionisi-Vici C, Ventura A, Zhou Q, Stanley CA, Burlina A. Co-inheritance of two ABCC8 mutations causing an unresponsive congenital hyperinsulinism: clinical and functional characterization of two novel ABCC8 mutations. Gene 2012; 516:122-5. [PMID: 23266803 DOI: 10.1016/j.gene.2012.12.055] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Accepted: 12/03/2012] [Indexed: 11/19/2022]
Abstract
Congenital hyperinsulinism (CHI) occurs as a consequence of unregulated insulin secretion from the pancreatic beta-cells. Severe recessive mutations and milder dominant mutations have been described in the ABCC8 and KCNJ11 genes encoding SUR1 and Kir6.2 subunits of the beta-cell ATP-sensitive K(+) channel. Here we report two patients with CHI unresponsive to medical therapy with diazoxide. Sequencing analysis identified a compound heterozygous mutation in ABCC8 in both patients. The first one is a carrier for the known mild dominant mutation p.Glu1506Lys jointly with the novel mutation p.Glu1323Lys. The second carries the p.Glu1323Lys mutation and a second novel mutation, p.Met1394Arg. Functional studies of both novel alleles showed reduced or null cell surface expression, typical of recessive mutations. Compound heterozygous mutations in congenital hyperinsulinism result in complex interactions. Studying these mechanisms can improve the knowledge of this disease and modify its therapy.
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Affiliation(s)
- Flavio Faletra
- Medical Genetics, Institute for Maternal and Child Health - IRCCS "Burlo Garofolo", Trieste, Italy.
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30
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Zaydman MA, Silva JR, Cui J. Ion channel associated diseases: overview of molecular mechanisms. Chem Rev 2012; 112:6319-33. [PMID: 23151230 DOI: 10.1021/cr300360k] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Mark A Zaydman
- Department of Biomedical Engineering, Washington University, Saint Louis, Missouri 63130, United States
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31
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Abstract
Hyperglycaemia has multiple effects on β-cells, some clearly prosecretory, including hyperplasia and elevated insulin content, but eventually, a 'glucotoxic' effect which leads to pancreatic β-cell dysfunction, reduced β-cell mass and insulin deficiency, is an important part of diabetes pathophysiology. Myriad underlying cellular and molecular processes could lead to such dysfunction. High glucose will stimulate glycolysis and oxidative phosphorylation, which will in turn increase β-cell membrane excitability through K(ATP) channel closure. Chronic hyperexcitability will then lead to persistently elevated [Ca(2+)](i), a key trigger to insulin secretion. Thus, at least a part of the consequence of 'hyperstimulation' by glucose has been suggested to be a result of 'hyperexcitability' and chronically elevated [Ca(2+)](i). This link is lost when the [glucose], K(ATP) -channel activity link is broken, either pharmacologically or genetically. In isolated islets, such studies reveal that hyperexcitability causes a largely reversible chronic loss of insulin content, but in vivo chronic hyperexcitability per se does not lead to β-cell death or loss of insulin content. On the other hand, chronic inexcitability in vivo leads to systemic diabetes and consequential β-cell death, even while [Ca(2+)](i) remains low.
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Affiliation(s)
- C G Nichols
- Department of Cell Biology and Physiology and Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA.
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32
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Wang F, Olson EM, Shyng SL. Role of Derlin-1 protein in proteostasis regulation of ATP-sensitive potassium channels. J Biol Chem 2012; 287:10482-10493. [PMID: 22311976 DOI: 10.1074/jbc.m111.312223] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels composed of sulfonylurea receptor 1 (SUR1) and Kir6.2 regulate insulin secretion by linking glucose metabolism with membrane potential. The number of K(ATP) channels in the plasma membrane affects the sensitivity of β-cells to glucose. Aberrant surface channel expression leads to insulin secretion disease. Previously, we have shown that K(ATP) channel proteins undergo endoplasmic reticulum (ER)-associated degradation (ERAD) via the ubiquitin-proteasome pathway, and inhibition of proteasome function results in an increase in channel surface expression. Here, we investigated whether Derlin-1, a protein involved in retrotranslocation of misfolded or misassembled proteins across the ER membrane for degradation by cytosolic proteasomes, plays a role in ERAD and, in turn, biogenesis efficiency of K(ATP) channels. We show that both SUR1 and Kir6.2 form a complex with Derlin-1 and an associated AAA-ATPase, p97. Overexpression of Derlin-1 led to a decrease in the biogenesis efficiency and surface expression of K(ATP) channels. Conversely, knockdown of Derlin-1 by RNA interference resulted in increased processing of SUR1 and a corresponding increase in surface expression of K(ATP) channels. Importantly, knockdown of Derlin-1 increased the abundance of disease-causing misfolded SUR1 or Kir6.2 proteins and even partially rescued surface expression in a mutant channel. We conclude that Derlin-1, by being involved in ERAD of SUR1 and Kir6.2, has a role in modulating the biogenesis efficiency and surface expression of K(ATP) channels. The results suggest that physiological or pathological changes in Derlin-1 expression levels may affect glucose-stimulated insulin secretion by altering surface expression of K(ATP) channels.
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Affiliation(s)
- Fang Wang
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Erik M Olson
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239.
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33
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Pattnaik BR, Asuma MP, Spott R, Pillers DAM. Genetic defects in the hotspot of inwardly rectifying K(+) (Kir) channels and their metabolic consequences: a review. Mol Genet Metab 2012; 105:64-72. [PMID: 22079268 PMCID: PMC3253982 DOI: 10.1016/j.ymgme.2011.10.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 10/11/2011] [Accepted: 10/12/2011] [Indexed: 02/07/2023]
Abstract
Inwardly rectifying potassium (Kir) channels are essential for maintaining normal potassium homeostasis and the resting membrane potential. As a consequence, mutations in Kir channels cause debilitating diseases ranging from cardiac failure to renal, ocular, pancreatic, and neurological abnormalities. Structurally, Kir channels consist of two trans-membrane domains, a pore-forming loop that contains the selectivity filter and two cytoplasmic polar tails. Within the cytoplasmic structure, clusters of amino acid sequences form regulatory domains that interact with cellular metabolites to control the opening and closing of the channel. In this review, we present an overview of Kir channel function and recent progress in the characterization of selected Kir channel mutations that lie in and near a C-terminal cytoplasmic 'hotspot' domain. The resultant molecular mechanisms by which the loss or gain of channel function leads to organ failure provide potential opportunities for targeted therapeutic interventions for this important group of channelopathies.
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Affiliation(s)
- Bikash R. Pattnaik
- Department of Pediatrics, University of Wisconsin, Madison
- Department of Ophthalmology & Visual Sciences, University of Wisconsin, Madison
- Department of Eye Research Institute, University of Wisconsin, Madison
| | - Matti P. Asuma
- Department of Pediatrics, University of Wisconsin, Madison
| | - Ryan Spott
- Department of Pediatrics, University of Wisconsin, Madison
| | - De-Ann M. Pillers
- Department of Pediatrics, University of Wisconsin, Madison
- Department of Eye Research Institute, University of Wisconsin, Madison
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34
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Quan Y, Barszczyk A, Feng ZP, Sun HS. Current understanding of K ATP channels in neonatal diseases: focus on insulin secretion disorders. Acta Pharmacol Sin 2011; 32:765-80. [PMID: 21602835 PMCID: PMC4009965 DOI: 10.1038/aps.2011.57] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Accepted: 04/13/2011] [Indexed: 12/25/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are cell metabolic sensors that couple cell metabolic status to electric activity, thus regulating many cellular functions. In pancreatic beta cells, K(ATP) channels modulate insulin secretion in response to fluctuations in plasma glucose level, and play an important role in glucose homeostasis. Recent studies show that gain-of-function and loss-of-function mutations in K(ATP) channel subunits cause neonatal diabetes mellitus and congenital hyperinsulinism respectively. These findings lead to significant changes in the diagnosis and treatment for neonatal insulin secretion disorders. This review describes the physiological and pathophysiological functions of K(ATP) channels in glucose homeostasis, their specific roles in neonatal diabetes mellitus and congenital hyperinsulinism, as well as future perspectives of K(ATP) channels in neonatal diseases.
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Affiliation(s)
- Yi Quan
- Departments of Physiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - Andrew Barszczyk
- Departments of Physiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - Zhong-ping Feng
- Departments of Physiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
| | - Hong-shuo Sun
- Departments of Physiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
- Departments of Surgery, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
- Departments of Pharmacology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
- Institute of Medical Science, Faculty of Medicine, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8
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35
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Abstract
The use of mouse models in medical research has greatly contributed to our understanding of the development of type 2 diabetes mellitus and the mechanisms of disease progression in the context of insulin resistance and β-cell dysfunction. Maintenance of glucose homeostasis involves a complex interplay of many genes and their actions in response to exogenous stimuli. In recent years, the availability of large population-based cohorts and the capacity to genotype enormous numbers of common genetic variants have driven various large-scale genome-wide association studies, which has greatly accelerated the identification of novel genes likely to be involved in the development of type 2 diabetes. The increasing demand for verifying novel genes is met by the timely development of new mouse resources established as various collaborative projects involving major transgenic and phenotyping centres and laboratories worldwide. The surge of new data will ultimately enable translational research into potential improvement and refinement of current type 2 diabetes therapy options, and hopefully restore quality of life for patients.
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36
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Chen PC, Bruederle CE, Gaisano HY, Shyng SL. Syntaxin 1A regulates surface expression of beta-cell ATP-sensitive potassium channels. Am J Physiol Cell Physiol 2011; 300:C506-16. [PMID: 21209369 DOI: 10.1152/ajpcell.00429.2010] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pancreatic ATP-sensitive potassium (K(ATP)) channel consisting of four inwardly rectifying potassium channel 6.2 (Kir6.2) and four sulfonylurea receptor SUR1 subunits plays a key role in insulin secretion by linking glucose metabolism to membrane excitability. Syntaxin 1A (Syn-1A) is a plasma membrane protein important for membrane fusion during exocytosis of insulin granules. Here, we show that Syn-1A and K(ATP) channels endogenously expressed in the insulin-secreting cell INS-1 interact. Upregulation of Syn-1A by overexpression in INS-1 leads to a decrease, whereas downregulation of Syn-1A by small interfering RNA (siRNA) leads to an increase, in surface expression of K(ATP) channels. Using COSm6 cells as a heterologous expression system for mechanistic investigation, we found that Syn-1A interacts with SUR1 but not Kir6.2. Furthermore, Syn-1A decreases surface expression of K(ATP) channels via two mechanisms. One mechanism involves accelerated endocytosis of surface channels. The other involves decreased biogenesis and processing of channels in the early secretory pathway. This regulation is K(ATP) channel specific as Syn-1A has no effect on another inward rectifier potassium channel Kir3.1/3.4. Our results demonstrate that in addition to a previously documented role in modulating K(ATP) channel gating, Syn-1A also regulates K(ATP) channel expression in β-cells. We propose that physiological or pathological changes in Syn-1A expression may modulate insulin secretion by altering glucose-secretion coupling via changes in K(ATP) channel expression.
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Affiliation(s)
- Pei-Chun Chen
- Dept. of Biochemistry and Molecular Biology, School of Medicine, Oregon Health & Science Univ., 3181 S. W. Sam Jackson Park Rd., Portland, OR 97239, USA
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37
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Loechner KJ, Akrouh A, Kurata HT, Dionisi-Vici C, Maiorana A, Pizzoferro M, Rufini V, de Ville de Goyet J, Colombo C, Barbetti F, Koster JC, Nichols CG. Congenital hyperinsulinism and glucose hypersensitivity in homozygous and heterozygous carriers of Kir6.2 (KCNJ11) mutation V290M mutation: K(ATP) channel inactivation mechanism and clinical management. Diabetes 2011; 60:209-17. [PMID: 20980454 PMCID: PMC3012173 DOI: 10.2337/db10-0731] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE The ATP-sensitive K(+) channel (K(ATP)) controls insulin secretion from the islet. Gain- or loss-of-function mutations in channel subunits underlie human neonatal diabetes and congenital hyperinsulinism (HI), respectively. In this study, we sought to identify the mechanistic basis of K(ATP)-induced HI in two probands and to characterize the clinical course. RESEARCH DESIGN AND METHODS We analyzed HI in two probands and characterized the course of clinical treatment in each, as well as properties of mutant K(ATP) channels expressed in COSm6 cells using Rb efflux and patch-clamp methods. RESULTS We identified mutation V290M in the pore-forming Kir6.2 subunit in each proband. In vitro expression in COSm6 cells supports the mutation resulting in an inactivating phenotype, which leads to significantly reduced activity in intact cells when expressed homomerically, and to a lesser extent when expressed heteromerically with wild-type subunits. In one heterozygous proband, a fluoro-DOPA scan revealed a causal focal lesion, indicating uniparental disomy with loss of heterozygosity. In a second family, the proband, homozygous for the mutation, was diagnosed with severe diazoxide-unresponsive hypersinsulinism at 2 weeks of age. The patient continues to be treated successfully with octreotide and amlodipine. The parents and a male sibling are heterozygous carriers without overt clinical HI. Interestingly, both the mother and the sibling exhibit evidence of abnormally enhanced glucose tolerance. CONCLUSIONS V290M results in inactivating K(ATP) channels that underlie HI. Homozygous individuals may be managed medically, without pancreatectomy. Heterozygous carriers also show evidence of enhanced glucose sensitivity, consistent with incomplete loss of K(ATP) channel activity.
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Affiliation(s)
- Karen J. Loechner
- Department of Pediatrics, University of North Carolina School of Medicine, Chapel Hill, North Carolina
| | - Alejandro Akrouh
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Harley T. Kurata
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Carlo Dionisi-Vici
- Unit of Metabolic Diseases, Department of Pediatrics, Bambino Gesù Children's Hospital, Rome, Italy
| | - Arianna Maiorana
- Unit of Metabolic Diseases, Department of Pediatrics, Bambino Gesù Children's Hospital, Rome, Italy
| | - Milena Pizzoferro
- Unit of Nuclear Medicine, Department of Radiology, Bambino Gesù Children's Hospital, Rome, Italy
| | - Vittoria Rufini
- Department of Nuclear Medicine, Catholic University of the Sacred Heart, Rome, Italy
| | | | - Carlo Colombo
- Laboratory of Monogenic Diabetes, Bambino Gesù Children's Hospital Istituto Di Ricovero e Cura a Carattere Scientifico, Rome, Italy
| | - Fabrizio Barbetti
- Laboratory of Monogenic Diabetes, Bambino Gesù Children's Hospital Istituto Di Ricovero e Cura a Carattere Scientifico, Rome, Italy
- Department of Internal Medicine, University of Tor Vergata, and Laboratory of Monogenic Diabetes, Bambino Gesù Children's Hospital Istituto Di Ricovero e Cura a Carattere Scientifico, Rome, Italy
- Corresponding authors: Colin G. Nichols, , and Fabrizio Barbetti,
| | - Joseph C. Koster
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Colin G. Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
- Corresponding authors: Colin G. Nichols, , and Fabrizio Barbetti,
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38
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Aw S, Koster J, Pearson W, Nichols C, Shi NQ, Carneiro K, Levin M. The ATP-sensitive K(+)-channel (K(ATP)) controls early left-right patterning in Xenopus and chick embryos. Dev Biol 2010; 346:39-53. [PMID: 20643119 PMCID: PMC2937067 DOI: 10.1016/j.ydbio.2010.07.011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2010] [Revised: 06/21/2010] [Accepted: 07/08/2010] [Indexed: 11/17/2022]
Abstract
Consistent left-right asymmetry requires specific ion currents. We characterize a novel laterality determinant in Xenopus laevis: the ATP-sensitive K(+)-channel (K(ATP)). Expression of specific dominant-negative mutants of the Xenopus Kir6.1 pore subunit of the K(ATP) channel induced randomization of asymmetric organ positioning. Spatio-temporally controlled loss-of-function experiments revealed that the K(ATP) channel functions asymmetrically in LR patterning during very early cleavage stages, and also symmetrically during the early blastula stages, a period when heretofore largely unknown events transmit LR patterning cues. Blocking K(ATP) channel activity randomizes the expression of the left-sided transcription of Nodal. Immunofluorescence analysis revealed that XKir6.1 is localized to basal membranes on the blastocoel roof and cell-cell junctions. A tight junction integrity assay showed that K(ATP) channels are required for proper tight junction function in early Xenopus embryos. We also present evidence that this function may be conserved to the chick, as inhibition of K(ATP) in the primitive streak of chick embryos randomizes the expression of the left-sided gene Sonic hedgehog. We propose a model by which K(ATP) channels control LR patterning via regulation of tight junctions.
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Affiliation(s)
- Sherry Aw
- Center for Regenerative and Developmental Biology, and Biology Department, Tufts University, Medford, MA 02155, USA
- Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Joseph Koster
- Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Wade Pearson
- Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Colin Nichols
- Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Nian-Qing Shi
- Department of Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Katia Carneiro
- Center for Regenerative and Developmental Biology, and Biology Department, Tufts University, Medford, MA 02155, USA
| | - Michael Levin
- Center for Regenerative and Developmental Biology, and Biology Department, Tufts University, Medford, MA 02155, USA
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Abstract
The pancreatic β-cell ATP-sensitive K(+) channel (K(ATP) channel) plays a critical role in glucose homeostasis by linking glucose metabolism to electrical excitability and insulin secretion. Changes in the intracellular ratio of ATP/ADP mediate the metabolic regulation of channel activity. The β-cell K(ATP) channel is a hetero-octameric complex composed of two types of subunits: four inward-rectifying potassium channel pore-forming (Kir6.2) subunits and four high-affinity sulfonylurea receptor 1 (SUR1) subunits. Kir6.2 and SUR1 are encoded by the genes KCNJ11 and ABCC8, respectively. Mutations in these genes can result in congenital hyperinsulinism and permanent neonatal diabetes. This review highlights the important role of the β-cell K(ATP) channel in glucose physiology and provides an introduction to some of the other review articles in this special edition of the Reviews in Endocrine and Metabolic Disorders.
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Affiliation(s)
- Kate Bennett
- Developmental Endocrinology Research Group, Clinical and Molecular Genetics Unit, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK
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40
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Bushman JD, Gay JW, Tewson P, Stanley CA, Shyng SL. Characterization and functional restoration of a potassium channel Kir6.2 pore mutation identified in congenital hyperinsulinism. J Biol Chem 2009; 285:6012-23. [PMID: 20032456 DOI: 10.1074/jbc.m109.085860] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inwardly rectifying potassium channel Kir6.2 assembles with sulfonylurea receptor 1 to form the ATP-sensitive potassium (K(ATP)) channels that regulate insulin secretion in pancreatic beta-cells. Mutations in K(ATP) channels underlie insulin secretion disease. Here, we report the characterization of a heterozygous missense Kir6.2 mutation, G156R, identified in congenital hyperinsulinism. Homomeric mutant channels reconstituted in COS cells show similar surface expression as wild-type channels but fail to conduct potassium currents. The mutated glycine is in the pore-lining transmembrane helix of Kir6.2; an equivalent glycine in other potassium channels has been proposed to serve as a hinge to allow helix bending during gating. We found that mutation of an adjacent asparagine, Asn-160, to aspartate, which converts the channel from a weak to a strong inward rectifier, on the G156R background restored ion conduction in the mutant channel. Unlike N160D channels, however, G156R/N160D channels are not blocked by intracellular polyamines at positive membrane potential and exhibit wild-type-like nucleotide sensitivities, suggesting the aspartate introduced at position 160 interacts with arginine at 156 to restore ion conduction and gating. Using tandem Kir6.2 tetramers containing G156R and/or N160D in designated positions, we show that one mutant subunit in the tetramer is insufficient to abolish conductance and that G156R and N160D can interact in the same or adjacent subunits to restore conduction. We conclude that the glycine at 156 is not essential for K(ATP) channel gating and that the Kir6.2 gating defect caused by the G156R mutation could be rescued by manipulating chemical interactions between pore residues.
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Affiliation(s)
- Jeremy D Bushman
- Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, Portland, Oregon 97239, USA
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41
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Akrouh A, Halcomb SE, Nichols CG, Sala-Rabanal M. Molecular biology of K(ATP) channels and implications for health and disease. IUBMB Life 2009; 61:971-8. [PMID: 19787700 DOI: 10.1002/iub.246] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The ATP-sensitive potassium (K(ATP)) channel is expressed in most excitable tissues and plays a critical role in numerous physiological processes by coupling intracellular energetics to electrical activity. The channel is comprised of four Kir6.x subunits associated with four regulatory sulfonylurea receptors (SUR). Intracellular ATP acts on Kir6.x to inhibit channel activity, while MgADP stimulates channel activity through SUR. Changes in the cytosolic [ATP] to [ADP] ratio thus determine channel activity. Multiple mutations in Kir6.x and SUR genes have implicated K(ATP) channels in various diseases ranging from diabetes and hyperinsulinism to cardiac arrhythmias and cardiovascular disease. Continuing studies of channel physiology and pathology will bring new insights to the molecular basis of K(ATP) channel function, leading to a better understanding of the role that K(ATP) channels play in both health and disease.
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Affiliation(s)
- Alejandro Akrouh
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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42
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Hyperinsulinism and diabetes: genetic dissection of beta cell metabolism-excitation coupling in mice. Cell Metab 2009; 10:442-53. [PMID: 19945402 PMCID: PMC3245718 DOI: 10.1016/j.cmet.2009.10.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Revised: 10/13/2009] [Accepted: 10/27/2009] [Indexed: 12/24/2022]
Abstract
The role of metabolism-excitation coupling in insulin secretion has long been apparent, but in recent years, in parallel with studies of human hyperinsulinism and diabetes, genetic manipulation of proteins involved in glucose transport, metabolism, and excitability in mice has brought the central importance of this pathway into sharp relief. We focus on these animal studies and how they provide important insights into not only metabolic and electrical regulation of insulin secretion, but also downstream consequences of alterations in this pathway and the etiology and treatment of insulin-secretion diseases in humans.
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43
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The nucleosome binding protein HMGN3 modulates the transcription profile of pancreatic beta cells and affects insulin secretion. Mol Cell Biol 2009; 29:5264-76. [PMID: 19651901 DOI: 10.1128/mcb.00526-09] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Improper glucose-stimulated insulin secretion from pancreatic beta cells is a major factor in the onset of type 2 diabetes. We now report that HMGN3, a nuclear protein that binds to nucleosomes and affects chromatin function, is highly expressed in beta cells and that in mice, loss of HMGN3 impairs glucose-stimulated insulin secretion and leads to a diabetic phenotype. In pancreatic beta cells, loss of HMGN3 affects the transcription of several genes involved in glucose-stimulated insulin secretion, including that of the Glut2 glucose transporter. Chromatin immunoprecipitation reveals that HMGN3 and the transcription factor PDX1 mutually reinforce their specific binding to the chromatin in the promoter of the Glut2 gene, thereby regulating GLUT2 protein levels in pancreatic islets and in beta cells. Our results identify a new regulator of glucose homeostasis and demonstrate a link between the activity of a nucleosome binding structural protein and the regulation of insulin secretion.
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Flanagan SE, Clauin S, Bellanné-Chantelot C, de Lonlay P, Harries LW, Gloyn AL, Ellard S. Update of mutations in the genes encoding the pancreatic beta-cell K(ATP) channel subunits Kir6.2 (KCNJ11) and sulfonylurea receptor 1 (ABCC8) in diabetes mellitus and hyperinsulinism. Hum Mutat 2009; 30:170-80. [PMID: 18767144 DOI: 10.1002/humu.20838] [Citation(s) in RCA: 191] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The beta-cell ATP-sensitive potassium (K(ATP)) channel is a key component of stimulus-secretion coupling in the pancreatic beta-cell. The channel couples metabolism to membrane electrical events bringing about insulin secretion. Given the critical role of this channel in glucose homeostasis it is therefore not surprising that mutations in the genes encoding for the two essential subunits of the channel can result in both hypo- and hyperglycemia. The channel consists of four subunits of the inwardly rectifying potassium channel Kir6.2 and four subunits of the sulfonylurea receptor 1 (SUR1). It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinism of infancy, while activating mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes. This review focuses on reported mutations in both genes, the spectrum of phenotypes, and the implications for treatment on diagnosing patients with mutations in these genes.
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Affiliation(s)
- Sarah E Flanagan
- Institute of Biomedical and Clinical Science, Peninsula Medical School, Exeter, United Kingdom
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45
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Aittoniemi J, Fotinou C, Craig TJ, de Wet H, Proks P, Ashcroft FM. Review. SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator. Philos Trans R Soc Lond B Biol Sci 2009; 364:257-67. [PMID: 18990670 DOI: 10.1098/rstb.2008.0142] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
SUR1 is an ATP-binding cassette (ABC) transporter with a novel function. In contrast to other ABC proteins, it serves as the regulatory subunit of an ion channel. The ATP-sensitive (KATP) channel is an octameric complex of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits, and it links cell metabolism to electrical activity in many cell types. ATPase activity at the nucleotide-binding domains of SUR results in an increase in KATP channel open probability. Conversely, ATP binding to Kir6.2 closes the channel. Metabolic regulation is achieved by the balance between these two opposing effects. Precisely how SUR1 talks to Kir6.2 remains unclear, but recent studies have identified some residues and domains that are involved in both physical and functional interactions between the two proteins. The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes. This paper reviews recent data on the regulation of Kir6.2 by SUR1 and considers the molecular mechanisms by which SUR1 mutations produce disease.
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Affiliation(s)
- Jussi Aittoniemi
- Department of Physiology, Henry Wellcome Centre for Gene Function, University of Oxford, Parks Road, Oxford, UK
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46
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Remedi MS, Nichols CG. Chronic antidiabetic sulfonylureas in vivo: reversible effects on mouse pancreatic beta-cells. PLoS Med 2008; 5:e206. [PMID: 18959471 PMCID: PMC2573909 DOI: 10.1371/journal.pmed.0050206] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 09/09/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Pancreatic beta-cell ATP-sensitive potassium (K ATP) channels are critical links between nutrient metabolism and insulin secretion. In humans, reduced or absent beta-cell K ATP channel activity resulting from loss-of-function K ATP mutations induces insulin hypersecretion. Mice with reduced K ATP channel activity also demonstrate hyperinsulinism, but mice with complete loss of K ATP channels (K ATP knockout mice) show an unexpected insulin undersecretory phenotype. Therefore we have proposed an "inverse U" hypothesis to explain the response to enhanced excitability, in which excessive hyperexcitability drives beta-cells to insulin secretory failure without cell death. Many patients with type 2 diabetes treated with antidiabetic sulfonylureas (which inhibit K ATP activity and thereby enhance insulin secretion) show long-term insulin secretory failure, which we further suggest might reflect a similar progression. METHODS AND FINDINGS To test the above hypotheses, and to mechanistically investigate the consequences of prolonged hyperexcitability in vivo, we used a novel approach of implanting mice with slow-release sulfonylurea (glibenclamide) pellets, to chronically inhibit beta-cell K ATP channels. Glibenclamide-implanted wild-type mice became progressively and consistently diabetic, with significantly (p < 0.05) reduced insulin secretion in response to glucose. After 1 wk of treatment, these mice were as glucose intolerant as adult K ATP knockout mice, and reduction of secretory capacity in freshly isolated islets from implanted animals was as significant (p < 0.05) as those from K ATP knockout animals. However, secretory capacity was fully restored in islets from sulfonylurea-treated mice within hours of drug washout and in vivo within 1 mo after glibenclamide treatment was terminated. Pancreatic immunostaining showed normal islet size and alpha-/beta-cell distribution within the islet, and TUNEL staining showed no evidence of apoptosis. CONCLUSIONS These results demonstrate that chronic glibenclamide treatment in vivo causes loss of insulin secretory capacity due to beta-cell hyperexcitability, but also reveal rapid reversibility of this secretory failure, arguing against beta-cell apoptosis or other cell death induced by sulfonylureas. These in vivo studies may help to explain why patients with type 2 diabetes can show long-term secondary failure to secrete insulin in response to sulfonylureas, but experience restoration of insulin secretion after a drug resting period, without permanent damage to beta-cells. This finding suggests that novel treatment regimens may succeed in prolonging pharmacological therapies in susceptible individuals.
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47
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Abstract
K(ATP) channels (ATP-sensitive potassium channels), comprising four subunits each of Kir6.2 (inwardly rectifying potassium channel 6.2) and the SUR1 (sulfonylurea receptor 1), play a central role in glucose-stimulated insulin secretion by the pancreatic beta-cell. Changes in the number of channels at the cell surface are associated with genetic diseases of aberrant insulin secretion, including CHI (congenital hyperinsulinism) and NDM (neonatal diabetes mellitus). The present review summarizes advances in our understanding of the vesicular trafficking of normal K(ATP) channels and how genetic mutations in Kir6.2 interfere with such trafficking. A mutation, E282K, causing CHI, was found to disrupt a DXE [di-acidic ER (endoplasmic reticulum)-exit signal], thereby preventing its assembly into COPII (coatamer protein II)-coated vesicles and subsequent ER exit. The resultant decrease in the cell-surface density of the channel could explain the disease phenotype. Two mutations, Y330C and F333I, reported in patients with NDM, disrupted an endocytic traffic signal, thereby impairing CCV (clathrin-coated vesicle) formation and endocytosis. The consequent increase in the density of K(ATP) channels, together with an attenuated sensitivity to ATP reported previously, may account for the severe form of NDM.
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48
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Lin YW, Bushman JD, Yan FF, Haidar S, MacMullen C, Ganguly A, Stanley CA, Shyng SL. Destabilization of ATP-sensitive potassium channel activity by novel KCNJ11 mutations identified in congenital hyperinsulinism. J Biol Chem 2008; 283:9146-56. [PMID: 18250167 DOI: 10.1074/jbc.m708798200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inwardly rectifying potassium channel Kir6.2 is the pore-forming subunit of the ATP-sensitive potassium (K(ATP)) channel, which controls insulin secretion by coupling glucose metabolism to membrane potential in beta-cells. Loss of channel function because of mutations in Kir6.2 or its associated regulatory subunit, sulfonylurea receptor 1, causes congenital hyperinsulinism (CHI), a neonatal disease characterized by persistent insulin secretion despite severe hypoglycemia. Here, we report a novel K(ATP) channel gating defect caused by CHI-associated Kir6.2 mutations at arginine 301 (to cysteine, glycine, histidine, or proline). These mutations in addition to reducing channel expression at the cell surface also cause rapid, spontaneous current decay, a gating defect we refer to as inactivation. Based on the crystal structures of Kir3.1 and KirBac1.1, Arg-301 interacts with several residues in the neighboring Kir6.2 subunit. Mutation of a subset of these residues also induces channel inactivation, suggesting that the disease mutations may cause inactivation by disrupting subunit-subunit interactions. To evaluate the effect of channel inactivation on beta-cell function, we expressed an alternative inactivation mutant R301A, which has equivalent surface expression efficiency as wild type channels, in the insulin-secreting cell line INS-1. Mutant expression resulted in more depolarized membrane potential and elevated insulin secretion at basal glucose concentration (3 mm) compared with cells expressing wild type channels, demonstrating that the inactivation gating defect itself is sufficient to cause loss of channel function and hyperinsulinism. Our studies suggest the importance of Kir6.2 subunit-subunit interactions in K(ATP) channel gating and function and reveal a novel gating defect underlying CHI.
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Affiliation(s)
- Yu-Wen Lin
- Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA
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49
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Abstract
Nutrient oxidation in beta cells generates a rise in [ATP]:[ADP] ratio. This reduces K(ATP) channel activity, leading to depolarization, activation of voltage-dependent Ca(2+) channels, Ca(2+) entry and insulin secretion. Consistent with this paradigm, loss-of-function mutations in the genes (KCNJ11 and ABCC8) that encode the two subunits (Kir6.2 and SUR1, respectively) of the ATP-sensitive K(+) (K(ATP)) channel underlie hyperinsulinism in humans, a genetic disorder characterized by dysregulated insulin secretion. In mice with genetic suppression of K(ATP) channel subunit expression, partial loss of K(ATP) channel conductance also causes hypersecretion, but unexpectedly, complete loss results in an undersecreting, mildly glucose-intolerant phenotype. When challenged by a high-fat diet, normal mice and mice with reduced K(ATP) channel density respond with hypersecretion, but mice with more significant or complete loss of K(ATP) channels cross over, or progress further, to an undersecreting, diabetic phenotype. It is our contention that in mice, and perhaps in humans, there is an inverse U-shaped response to hyperexcitabilty, leading first to hypersecretion but with further exacerbation to undersecretion and diabetes. The causes of the overcompensation and diabetic susceptibility are poorly understood but may have broader implications for the progression of hyperinsulinism and type 2 diabetes in humans.
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Affiliation(s)
- C G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
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50
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Nichols CG. Alchemy in the soup: transforming metabolic signals to excitability. ACTA ACUST UNITED AC 2007; 2007:pe59. [PMID: 17971567 DOI: 10.1126/stke.4102007pe59] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The intersection of cell metabolism with electrical signaling links the environment and cell function over time scales ranging from milliseconds to lifetimes. In responding to cellular metabolites, adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels are an important component of this intersection. Recent studies have begun to delineate the roles of K(ATP) channels in multiple tissues and the far-reaching consequences of aberrant K(ATP) channel activity and disturbed sensing of cell metabolism.
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Affiliation(s)
- Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
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