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Tan LS, Lau HH, Abdelalim EM, Khoo CM, O'Brien RM, Tai ES, Teo AKK. The role of glucose-6-phosphatase activity in glucose homeostasis and its potential for diabetes therapy. Trends Mol Med 2024:S1471-4914(24)00244-2. [PMID: 39426930 DOI: 10.1016/j.molmed.2024.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2024] [Revised: 09/13/2024] [Accepted: 09/20/2024] [Indexed: 10/21/2024]
Abstract
Glucose-6-phosphatase catalytic subunit (G6PC)1 and G6PC2 are crucial for glucose metabolism, regulating processes like glycolysis, gluconeogenesis, and glycogenolysis. Despite their structural and functional similarities, G6PC1 and G6PC2 exhibit distinct tissue-specific expression patterns, G6P hydrolysis kinetics, and physiological functions. This review provides a comprehensive overview of their enzymology and distinct roles in glucose homeostasis. We examine how inactivating mutations in G6PC1 lead to glycogen storage disease, and how elevated G6PC1 and G6PC2 expression can affect the incidence of diabetic complications, risk for type 2 diabetes mellitus (T2DM) and various cancers. We also discuss the potential of inhibiting G6PC1 and G6PC2 to protect against complications from elevated blood glucose levels, and highlight drug development efforts targeting G6PC1 and G6PC2, and the therapeutic potential of inhibitors for disease prevention.
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Affiliation(s)
- Lay Shuen Tan
- Stem Cells and Diabetes Laboratory, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore; Dean's Office, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Hwee Hui Lau
- Stem Cells and Diabetes Laboratory, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore
| | - Essam M Abdelalim
- Laboratory of Pluripotent Stem Cell Disease Modeling, Translational Medicine Department, Research Branch, Sidra Medicine, P.O. Box 26999, Doha, Qatar; College of Health and Life Sciences, Hamad Bin Khalifa University (HBKU), Qatar Foundation, Education City, Doha, Qatar
| | - Chin Meng Khoo
- Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Precision Medicine Translational Research Program (TRP), Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - E Shyong Tai
- Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Precision Medicine Translational Research Program (TRP), Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Adrian Kee Keong Teo
- Stem Cells and Diabetes Laboratory, Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore; Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Precision Medicine Translational Research Program (TRP), Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
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Hawes EM, Rahim M, Haratipour Z, Orun AR, O'Rourke ML, Oeser JK, Kim K, Claxton DP, Blind RD, Young JD, O'Brien RM. Biochemical and metabolic characterization of a G6PC2 inhibitor. Biochimie 2024; 222:109-122. [PMID: 38431189 DOI: 10.1016/j.biochi.2024.02.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 02/28/2024] [Accepted: 02/29/2024] [Indexed: 03/05/2024]
Abstract
Three glucose-6-phosphatase catalytic subunits, that hydrolyze glucose-6-phosphate (G6P) to glucose and inorganic phosphate, have been identified, designated G6PC1-3, but only G6PC1 and G6PC2 have been implicated in the regulation of fasting blood glucose (FBG). Elevated FBG has been associated with multiple adverse clinical outcomes, including increased risk for type 2 diabetes and various cancers. Therefore, G6PC1 and G6PC2 inhibitors that lower FBG may be of prophylactic value for the prevention of multiple conditions. The studies described here characterize a G6PC2 inhibitor, designated VU0945627, previously identified as Compound 3. We show that VU0945627 preferentially inhibits human G6PC2 versus human G6PC1 but activates human G6PC3. VU0945627 is a mixed G6PC2 inhibitor, increasing the Km but reducing the Vmax for G6P hydrolysis. PyRx virtual docking to an AlphaFold2-derived G6PC2 structural model suggests VU0945627 binds two sites in human G6PC2. Mutation of residues in these sites reduces the inhibitory effect of VU0945627. VU0945627 does not inhibit mouse G6PC2 despite its 84% sequence identity with human G6PC2. Mutagenesis studies suggest this lack of inhibition of mouse G6PC2 is due, in part, to a change in residue 318 from histidine in human G6PC2 to proline in mouse G6PC2. Surprisingly, VU0945627 still inhibited glucose cycling in the mouse islet-derived βTC-3 cell line. Studies using intact mouse liver microsomes and PyRx docking suggest that this observation can be explained by an ability of VU0945627 to also inhibit the G6P transporter SLC37A4. These data will inform future computational modeling studies designed to identify G6PC isoform-specific inhibitors.
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Affiliation(s)
- Emily M Hawes
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Mohsin Rahim
- Department of Chemical and Biomolecular Engineering, Vanderbilt School of Engineering, Nashville, TN, 37232, USA
| | - Zeinab Haratipour
- Austin Peay State University, 601 College St, Clarksville, TN 37044, USA; Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Abigail R Orun
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Margaret L O'Rourke
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - James K Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Kwangho Kim
- Department of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Ray D Blind
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Jamey D Young
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA; Department of Chemical and Biomolecular Engineering, Vanderbilt School of Engineering, Nashville, TN, 37232, USA
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA.
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Lubkemann A, Carpenter H, O'Brien R, Baldwin S, Lister R. Cardiac Morphology and Collagen Deposition in A Glucose-6-Phosphatase Catalytic Subunit 3 (G6PC3) Knockout Mouse model. ACTA ACUST UNITED AC 2021. [PMID: 34263175 DOI: 10.33425/2639-944x.1188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Background Glucose-6-phosphatase-- β (3), one of multiple isoforms of glucose-6-phosphatase, catalyzes the final step in gluconeogenesis. It is known that mutated G6P3 is associated with severe neutropenia in addition to congenital heart defects, but little is known about the histological changes in cardiac tissue as a result of mutated or deleted G6PC34. Objectives We sought to further characterize the histological alterations caused by deleted G6PC3 and determine the role of collagen deposition, myocyte proliferation and apoptosis in these changes. Methods Cardiac tissue from G6PC3 knockout mice and WT mice were harvested, imbedded and stained for markers of collagen (Trichrome), proliferation (KI-67), apoptosis (caspase 3) and hematopoietic stem cells (CD34). Slides were digitally uploaded, and Leica stain quantification was calculated. Results We demonstrated that in G6PC3 knock out adult mice have significant differences in heart morphology including decreased left ventricular collagen, decreased cellular proliferation and increased apoptosis histologically. Conclusions As compared to wild type, the hearts of G6PC3 knockout mice demonstrated significantly decreased collagen globally, a crucial component for adequate strength and contractility of myocardial tissue. More investigation should be done to further explore the functional effects of such alterations via echocardiograms.
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Affiliation(s)
- Austin Lubkemann
- Vanderbilt University Medical Center, Nashville, Tennessee.,UNC Chapel Hill, North Carolina
| | - Heidi Carpenter
- Vanderbilt University Medical Center, Nashville, Tennessee.,UNC Chapel Hill, North Carolina
| | | | - Scott Baldwin
- Vanderbilt University Medical Center, Nashville, Tennessee
| | - Rolanda Lister
- Vanderbilt University Medical Center, Nashville, Tennessee
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Dienel GA. Hypothesis: A Novel Neuroprotective Role for Glucose-6-phosphatase (G6PC3) in Brain-To Maintain Energy-Dependent Functions Including Cognitive Processes. Neurochem Res 2020; 45:2529-2552. [PMID: 32815045 DOI: 10.1007/s11064-020-03113-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 08/10/2020] [Accepted: 08/13/2020] [Indexed: 12/11/2022]
Abstract
The isoform of glucose-6-phosphatase in liver, G6PC1, has a major role in whole-body glucose homeostasis, whereas G6PC3 is widely distributed among organs but has poorly-understood functions. A recent, elegant analysis of neutrophil dysfunction in G6PC3-deficient patients revealed G6PC3 is a neutrophil metabolite repair enzyme that hydrolyzes 1,5-anhydroglucitol-6-phosphate, a toxic metabolite derived from a glucose analog present in food. These patients exhibit a spectrum of phenotypic characteristics and some have learning disabilities, revealing a potential linkage between cognitive processes and G6PC3 activity. Previously-debated and discounted functions for brain G6PC3 include causing an ATP-consuming futile cycle that interferes with metabolic brain imaging assays and a nutritional role involving astrocyte-neuron glucose-lactate trafficking. Detailed analysis of the anhydroglucitol literature reveals that it competes with glucose for transport into brain, is present in human cerebrospinal fluid, and is phosphorylated by hexokinase. Anhydroglucitol-6-phosphate is present in rodent brain and other organs where its accumulation can inhibit hexokinase by competition with ATP. Calculated hexokinase inhibition indicates that energetics of brain and erythrocytes would be more adversely affected by anhydroglucitol-6-phosphate accumulation than heart. These findings strongly support the paradigm-shifting hypothesis that brain G6PC3 removes a toxic metabolite, thereby maintaining brain glucose metabolism- and ATP-dependent functions, including cognitive processes.
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Affiliation(s)
- Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, 4301 W. Markham St., Mail Slot 500, Little Rock, AR, 72205, USA.
- Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM, 87131, USA.
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Syring KE, Bosma KJ, Goleva SB, Singh K, Oeser JK, Lopez CA, Skaar EP, McGuinness OP, Davis LK, Powell DR, O’Brien RM. Potential positive and negative consequences of ZnT8 inhibition. J Endocrinol 2020; 246:189-205. [PMID: 32485672 PMCID: PMC7351606 DOI: 10.1530/joe-20-0138] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 06/02/2020] [Indexed: 12/31/2022]
Abstract
SLC30A8 encodes the zinc transporter ZnT8. SLC30A8 haploinsufficiency protects against type 2 diabetes (T2D), suggesting that ZnT8 inhibitors may prevent T2D. We show here that, while adult chow fed Slc30a8 haploinsufficient and knockout (KO) mice have normal glucose tolerance, they are protected against diet-induced obesity (DIO), resulting in improved glucose tolerance. We hypothesize that this protection against DIO may represent one mechanism whereby SLC30A8 haploinsufficiency protects against T2D in humans and that, while SLC30A8 is predominantly expressed in pancreatic islet beta cells, this may involve a role for ZnT8 in extra-pancreatic tissues. Consistent with this latter concept we show in humans, using electronic health record-derived phenotype analyses, that the 'C' allele of the non-synonymous rs13266634 SNP, which confers a gain of ZnT8 function, is associated not only with increased T2D risk and blood glucose, but also with increased risk for hemolytic anemia and decreased mean corpuscular hemoglobin (MCH). In Slc30a8 KO mice, MCH was unchanged but reticulocytes, platelets and lymphocytes were elevated. Both young and adult Slc30a8 KO mice exhibit a delayed rise in insulin after glucose injection, but only the former exhibit increased basal insulin clearance and impaired glucose tolerance. Young Slc30a8 KO mice also exhibit elevated pancreatic G6pc2 gene expression, potentially mediated by decreased islet zinc levels. These data indicate that the absence of ZnT8 results in a transient impairment in some aspects of metabolism during development. These observations in humans and mice suggest the potential for negative effects associated with T2D prevention using ZnT8 inhibitors.
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Affiliation(s)
- Kristen E. Syring
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
| | - Karin J. Bosma
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
| | - Slavina B. Goleva
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Kritika Singh
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - James K. Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
| | - Christopher A. Lopez
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Eric P. Skaar
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - Owen P. McGuinness
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
| | - Lea K. Davis
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232
| | - David R. Powell
- Lexicon Pharmaceuticals Incorporated, 8800 Technology Forest Place, The Woodlands, Texas 77381
| | - Richard M. O’Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine
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Bosma KJ, Rahim M, Oeser JK, McGuinness OP, Young JD, O'Brien RM. G6PC2 confers protection against hypoglycemia upon ketogenic diet feeding and prolonged fasting. Mol Metab 2020; 41:101043. [PMID: 32569842 PMCID: PMC7369601 DOI: 10.1016/j.molmet.2020.101043] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 05/26/2020] [Accepted: 06/16/2020] [Indexed: 12/14/2022] Open
Abstract
Objective G6PC2 is predominantly expressed in pancreatic islet beta cells. G6PC2 hydrolyzes glucose-6-phosphate to glucose and inorganic phosphate, thereby creating a futile substrate cycle that opposes the action of glucokinase. This substrate cycle determines the sensitivity of glucose-stimulated insulin secretion to glucose and hence regulates fasting blood glucose (FBG) but not fasting plasma insulin (FPI) levels. Our objective was to explore the physiological benefit this cycle confers. Methods We investigated the response of wild type (WT) and G6pc2 knockout (KO) mice to changes in nutrition. Results Pancreatic G6pc2 expression was little changed by ketogenic diet feeding but was inhibited by 24 hr fasting and strongly induced by high fat feeding. When challenged with either a ketogenic diet or 24 hr fasting, blood glucose fell to 70 mg/dl or less in G6pc2 KO but not WT mice, suggesting that G6PC2 may have evolved, in part, to prevent hypoglycemia. Prolonged ketogenic diet feeding reduced the effect of G6pc2 deletion on FBG. The hyperglycemia associated with high fat feeding was partially blunted in G6pc2 KO mice, suggesting that under these conditions the presence of G6PC2 is detrimental. As expected, FPI changed but did not differ between WT and KO mice in response to fasting, ketogenic and high fat feeding. Conclusions Since elevated FBG levels are associated with increased risk for cardiovascular-associated mortality (CAM), these studies suggest that, while G6PC2 inhibitors would be useful for lowering FBG and the risk of CAM, partial inhibition will be important to avoid the risk of hypoglycemia. G6pc2 deletion lowers fasting blood glucose (FBG) in chow and high fat fed mice. Elevated FBG increases the risk of cardiovascular-associated mortality (CAM). G6pc2 deletion results in hypoglycemia in mice on a ketogenic diet. G6pc2 deletion results in hypoglycemia in mice following prolonged fasting. G6PC2 inhibitors may prevent CAM but increase risk of hypoglycemia.
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Affiliation(s)
- Karin J Bosma
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Mohsin Rahim
- Department of Chemical and Biomolecular Engineering, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - James K Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Owen P McGuinness
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Jamey D Young
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA; Department of Chemical and Biomolecular Engineering, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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Miyamoto T, Amrein H. Neuronal Gluconeogenesis Regulates Systemic Glucose Homeostasis in Drosophila melanogaster. Curr Biol 2019; 29:1263-1272.e5. [DOI: 10.1016/j.cub.2019.02.053] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 01/21/2019] [Accepted: 02/25/2019] [Indexed: 11/25/2022]
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Syring KE, Boortz KA, Oeser JK, Ustione A, Platt KA, Shadoan MK, McGuinness OP, Piston DW, Powell DR, O'Brien RM. Combined Deletion of Slc30a7 and Slc30a8 Unmasks a Critical Role for ZnT8 in Glucose-Stimulated Insulin Secretion. Endocrinology 2016; 157:4534-4541. [PMID: 27754787 PMCID: PMC5133349 DOI: 10.1210/en.2016-1573] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Polymorphisms in the SLC30A8 gene, which encodes the ZnT8 zinc transporter, are associated with altered susceptibility to type 2 diabetes (T2D), and SLC30A8 haploinsufficiency is protective against the development of T2D in obese humans. SLC30A8 is predominantly expressed in pancreatic islet β-cells, but surprisingly, multiple knockout mouse studies have shown little effect of Slc30a8 deletion on glucose tolerance or glucose-stimulated insulin secretion (GSIS). Multiple other Slc30a isoforms are expressed at low levels in pancreatic islets. We hypothesized that functional compensation by the Slc30a7 isoform, which encodes ZnT7, limits the impact of Slc30a8 deletion on islet function. We therefore analyzed the effect of Slc30a7 deletion alone or in combination with Slc30a8 on in vivo glucose metabolism and GSIS in isolated islets. Deletion of Slc30a7 alone had complex effects in vivo, impairing glucose tolerance and reducing the glucose-stimulated increase in plasma insulin levels, hepatic glycogen levels, and pancreatic insulin content. Slc30a7 deletion also affected islet morphology and increased the ratio of islet α- to β-cells. However, deletion of Slc30a7 alone had no effect on GSIS in isolated islets, whereas combined deletion of Slc30a7 and Slc30a8 abolished GSIS. These data demonstrate that the function of ZnT8 in islets can be unmasked by removal of ZnT7 and imply that ZnT8 may affect T2D susceptibility through actions in other tissues where it is expressed at low levels rather than through effects on pancreatic islet function.
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Affiliation(s)
- Kristen E Syring
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Kayla A Boortz
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - James K Oeser
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Alessandro Ustione
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Kenneth A Platt
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Melanie K Shadoan
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Owen P McGuinness
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - David W Piston
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - David R Powell
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics (K.E.S., K.A.B., J.K.O., O.P.M., R.M.O.), Vanderbilt University Medical School, Nashville, Tennessee 37232; Department of Cell Biology and Physiology (A.U., D.W.P.), Washington University School of Medicine, St. Louis, Missouri 63110; and Lexicon Pharmaceuticals Incorporated (K.A.P., M.K.S., D.R.P.), The Woodlands, Texas 77381
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Banka S, Newman WG. A clinical and molecular review of ubiquitous glucose-6-phosphatase deficiency caused by G6PC3 mutations. Orphanet J Rare Dis 2013; 8:84. [PMID: 23758768 PMCID: PMC3718741 DOI: 10.1186/1750-1172-8-84] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Accepted: 05/22/2013] [Indexed: 12/14/2022] Open
Abstract
The G6PC3 gene encodes the ubiquitously expressed glucose-6-phosphatase enzyme (G-6-Pase β or G-6-Pase 3 or G6PC3). Bi-allelic G6PC3 mutations cause a multi-system autosomal recessive disorder of G6PC3 deficiency (also called severe congenital neutropenia type 4, MIM 612541). To date, at least 57 patients with G6PC3 deficiency have been described in the literature. G6PC3 deficiency is characterized by severe congenital neutropenia, recurrent bacterial infections, intermittent thrombocytopenia in many patients, a prominent superficial venous pattern and a high incidence of congenital cardiac defects and uro-genital anomalies. The phenotypic spectrum of the condition is wide and includes rare manifestations such as maturation arrest of the myeloid lineage, a normocellular bone marrow, myelokathexis, lymphopaenia, thymic hypoplasia, inflammatory bowel disease, primary pulmonary hypertension, endocrine abnormalities, growth retardation, minor facial dysmorphism, skeletal and integument anomalies amongst others. Dursun syndrome is part of this extended spectrum. G6PC3 deficiency can also result in isolated non-syndromic severe neutropenia. G6PC3 mutations in result in reduced enzyme activity, endoplasmic reticulum stress response, increased rates of apoptosis of affected cells and dysfunction of neutrophil activity. In this review we demonstrate that loss of function in missense G6PC3 mutations likely results from decreased enzyme stability. The condition can be diagnosed by sequencing the G6PC3 gene. A number of G6PC3 founder mutations are known in various populations and a possible genotype-phenotype relationship also exists. G6PC3 deficiency should be considered as part of the differential diagnoses in any patient with unexplained congenital neutropenia. Treatment with G-CSF leads to improvement in neutrophil numbers, prevents infections and improves quality of life. Mildly affected patients can be managed with prophylactic antibiotics. Untreated G6PC3 deficiency can be fatal. Echocardiogram, renal and pelvic ultrasound scans should be performed in all cases of suspected or confirmed G6PC3 deficiency. Routine assessment should include biochemical profile, growth profile and monitoring for development of varicose veins or venous ulcers.
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Affiliation(s)
- Siddharth Banka
- Manchester Centre for Genomic Medicine, Institute of Human Development, University of Manchester, Manchester, UK.
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Survival and differentiation defects contribute to neutropenia in glucose-6-phosphatase-β (G6PC3) deficiency in a model of mouse neutrophil granulocyte differentiation. Cell Death Differ 2013; 20:1068-79. [PMID: 23686134 DOI: 10.1038/cdd.2013.39] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Revised: 04/03/2013] [Accepted: 04/05/2013] [Indexed: 01/15/2023] Open
Abstract
Differentiation of neutrophil granulocytes (neutrophils) occurs through several steps in the bone marrow and requires a coordinate regulation of factors determining survival and lineage-specific development. A number of genes are known whose deficiency disrupts neutrophil generation in humans and in mice. One of the proteins encoded by these genes, glucose-6-phosphatase-β (G6PC3), is involved in glucose metabolism. G6PC3 deficiency causes neutropenia in humans and in mice, linked to enhanced apoptosis and ER stress. We used a model of conditional Hoxb8 expression to test molecular and functional differentiation as well as survival defects in neutrophils from G6PC3(-/-) mice. Progenitor lines were established and differentiated into neutrophils when Hoxb8 was turned off. G6PC3(-/-) progenitor cells underwent substantial apoptosis when differentiation was started. Transgenic expression of Bcl-XL rescued survival; however, Bcl-XL-protected differentiated cells showed reduced proliferation, immaturity and functional deficiency such as altered MAP kinase signaling and reduced cytokine secretion. Impaired glucose utilization was found and was associated with ER stress and apoptosis, associated with the upregulation of Bim and Bax; downregulation of Bim protected against apoptosis during differentiation. ER-stress further caused a profound loss of expression and secretion of the main neutrophil product neutrophil elastase during differentiation. Transplantation of wild-type Hoxb8-progenitor cells into irradiated mice allowed differentiation into neutrophils in the bone marrow in vivo. Transplantation of G6PC3(-/-) cells yielded few mature neutrophils in bone marrow and peripheral blood. Transgenic Bcl-XL permitted differentiation of G6PC3(-/-) cells in vivo. However, functional deficiencies and differentiation abnormalities remained. Differentiation of macrophages from Hoxb8-dependent progenitors was only slightly disturbed. A combination of defects in differentiation and survival thus underlies neutropenia in G6PC3(-/-) deficiency, both originating from a reduced ability to utilize glucose. Hoxb8-dependent cells are a model to study differentiation and survival of the neutrophil lineage.
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Multiple roles of glucose-6-phosphatases in pathophysiology. Biochim Biophys Acta Gen Subj 2013; 1830:2608-18. [DOI: 10.1016/j.bbagen.2012.12.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 12/11/2012] [Accepted: 12/13/2012] [Indexed: 12/28/2022]
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Froissart R, Piraud M, Boudjemline AM, Vianey-Saban C, Petit F, Hubert-Buron A, Eberschweiler PT, Gajdos V, Labrune P. Glucose-6-phosphatase deficiency. Orphanet J Rare Dis 2011; 6:27. [PMID: 21599942 PMCID: PMC3118311 DOI: 10.1186/1750-1172-6-27] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 05/20/2011] [Indexed: 01/01/2023] Open
Abstract
Glucose-6-phosphatase deficiency (G6P deficiency), or glycogen storage disease type I (GSDI), is a group of inherited metabolic diseases, including types Ia and Ib, characterized by poor tolerance to fasting, growth retardation and hepatomegaly resulting from accumulation of glycogen and fat in the liver. Prevalence is unknown and annual incidence is around 1/100,000 births. GSDIa is the more frequent type, representing about 80% of GSDI patients. The disease commonly manifests, between the ages of 3 to 4 months by symptoms of hypoglycemia (tremors, seizures, cyanosis, apnea). Patients have poor tolerance to fasting, marked hepatomegaly, growth retardation (small stature and delayed puberty), generally improved by an appropriate diet, osteopenia and sometimes osteoporosis, full-cheeked round face, enlarged kydneys and platelet dysfunctions leading to frequent epistaxis. In addition, in GSDIb, neutropenia and neutrophil dysfunction are responsible for tendency towards infections, relapsing aphtous gingivostomatitis, and inflammatory bowel disease. Late complications are hepatic (adenomas with rare but possible transformation into hepatocarcinoma) and renal (glomerular hyperfiltration leading to proteinuria and sometimes to renal insufficiency). GSDI is caused by a dysfunction in the G6P system, a key step in the regulation of glycemia. The deficit concerns the catalytic subunit G6P-alpha (type Ia) which is restricted to expression in the liver, kidney and intestine, or the ubiquitously expressed G6P transporter (type Ib). Mutations in the genes G6PC (17q21) and SLC37A4 (11q23) respectively cause GSDIa and Ib. Many mutations have been identified in both genes,. Transmission is autosomal recessive. Diagnosis is based on clinical presentation, on abnormal basal values and absence of hyperglycemic response to glucagon. It can be confirmed by demonstrating a deficient activity of a G6P system component in a liver biopsy. To date, the diagnosis is most commonly confirmed by G6PC (GSDIa) or SLC37A4 (GSDIb) gene analysis, and the indications of liver biopsy to measure G6P activity are getting rarer and rarer. Differential diagnoses include the other GSDs, in particular type III (see this term). However, in GSDIII, glycemia and lactacidemia are high after a meal and low after a fast period (often with a later occurrence than that of type I). Primary liver tumors and Pepper syndrome (hepatic metastases of neuroblastoma) may be evoked but are easily ruled out through clinical and ultrasound data. Antenatal diagnosis is possible through molecular analysis of amniocytes or chorionic villous cells. Pre-implantatory genetic diagnosis may also be discussed. Genetic counseling should be offered to patients and their families. The dietary treatment aims at avoiding hypoglycemia (frequent meals, nocturnal enteral feeding through a nasogastric tube, and later oral addition of uncooked starch) and acidosis (restricted fructose and galactose intake). Liver transplantation, performed on the basis of poor metabolic control and/or hepatocarcinoma, corrects hypoglycemia, but renal involvement may continue to progress and neutropenia is not always corrected in type Ib. Kidney transplantation can be performed in case of severe renal insufficiency. Combined liver-kidney grafts have been performed in a few cases. Prognosis is usually good: late hepatic and renal complications may occur, however, with adapted management, patients have almost normal life span. DISEASE NAME AND SYNONYMS: Glucose-6-phosphatase deficiency or G6P deficiency or glycogen storage disease type I or GSDI or type I glycogenosis or Von Gierke disease or Hepatorenal glycogenosis.
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Affiliation(s)
- Roseline Froissart
- Centre de Référence Maladies Héréditaires du Métabolisme Hépatique, Service de Pédiatrie, APHP, Clamart cedex, France
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13
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Further delineation of the phenotype of severe congenital neutropenia type 4 due to mutations in G6PC3. Eur J Hum Genet 2010; 19:18-22. [PMID: 20717171 DOI: 10.1038/ejhg.2010.136] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Severe congenital neutropenia type 4 (SCN4) is an autosomal recessive condition, which was defined recently with identification of the causative mutations in G6PC3. To date there are only three reports in the literature describing patients with SCN4 with mutations in the G6PC3 gene. We report four individuals with SCN4 who belong to a single large consanguineous kindred. We provide an overview of the non-haematological features of the condition with a focus on the adult phenotype, which has not been previously described in detail. We show that the superficial venous changes seen in SCN4 patients can develop into varicose veins and venous ulcers in adulthood. We review the range of congenital anomalies associated with SCN4. We demonstrate that secundum atrial septal defect, patent ductus arteriosus and valvular defects are the most frequent cardiac anomalies in SCN4. Drawing parallels with type 1 glycogen storage disease, we propose that poor growth of prenatal onset, mild-to-moderate learning disability, primary pulmonary hypertension, delayed or incomplete puberty, hypothyroidism and dysmorphism likely represent features of this syndrome. We also suggest monitoring for lipid anomalies, and kidney and liver function in affected patients. Delineation of the SCN4 phenotype may help in appropriate treatment and management and provide further insights into the pathogenesis of this multisystem disease.
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Abstract
Glucose-6-phosphatase catalyzes the hydrolysis of glucose 6-phosphate (G6P) to glucose and inorganic phosphate. It is a multicomponent system located in the endoplasmic reticulum that comprises several integral membrane proteins, namely a catalytic subunit (G6PC) and transporters for G6P, inorganic phosphate, and glucose. The G6PC gene family contains three members, designated G6PC, G6PC2, and G6PC3. The tissue-specific expression patterns of these genes differ, and mutations in all three genes have been linked to distinct diseases in humans. This minireview discusses the disease association and transcriptional regulation of the G6PC genes as well as the biological functions of the encoded proteins.
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Affiliation(s)
- John C Hutton
- Barbara Davis Center for Childhood Diabetes, University of Colorado at Denver, Aurora, Colorado 80045, USA
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Koeberl DD, Kishnani PS, Bali D, Chen YT. Emerging therapies for glycogen storage disease type I. Trends Endocrinol Metab 2009; 20:252-8. [PMID: 19541498 DOI: 10.1016/j.tem.2009.02.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Revised: 02/10/2009] [Accepted: 02/11/2009] [Indexed: 10/20/2022]
Abstract
Glycogen storage disease type I (GSD I) is caused by deficiency of the glucose-6-phosphatase catalytic subunit in type Ia or of glucose-6-phosphate transporter in type Ib. The cellular bases for disruptions of homeostasis have been increasingly understood in GSD I, including those for anemia, renal failure and neutropenia. Advances in the understanding of cellular abnormalities in GSD I have provided rationales for new therapy, and recent developments in gene therapy have led to potential curative treatments for GSD I. These advances will benefit patients with GSD I in the future, improving both quality of life and survival, as well as illuminating the molecular effects of altered metabolism upon multiple organ systems.
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Affiliation(s)
- D D Koeberl
- Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, Durham, NC 27710, USA.
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Pillot B, Soty M, Gautier-Stein A, Zitoun C, Mithieux G. Protein feeding promotes redistribution of endogenous glucose production to the kidney and potentiates its suppression by insulin. Endocrinology 2009; 150:616-24. [PMID: 18845639 DOI: 10.1210/en.2008-0601] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The aim of this study was to assess in rats the effect of protein feeding on the: 1) distribution of endogenous glucose production (EGP) among gluconeogenic organs, and 2) repercussion on the insulin sensitivity of glucose metabolism. We used gene expression analyses, a combination of glucose tracer dilution and arteriovenous balance to quantify specific organ release, and hyperinsulinemic euglycemic clamps to assess EGP and glucose uptake. Protein feeding promoted a dramatic induction of the main regulatory gluconeogenic genes (glucose-6 phosphatase and phosphoenolpyruvate carboxykinase) in the kidney, but not in the liver. As a consequence, the kidney glucose release was markedly increased, compared with rats fed a normal starch diet. Protein feeding ameliorated the suppression of EGP by insulin and the sparing of glycogen storage in the liver but had no effect on glucose uptake. Combined with the previously reported induction of gluconeogenesis in the small intestine, the present work strongly suggests that a redistribution of glucose production among gluconeogenic organs might occur upon protein feeding. This phenomenon is in keeping with the improvement of insulin sensitivity of EGP, most likely involving the hepatic site. These data shed a new light on the improvement of glucose tolerance, previously observed upon increasing the amount of protein in the diet, in type 2 diabetic patients.
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Affiliation(s)
- Bruno Pillot
- Institut National de la Santé et de la Recherche Médicale, Unité 855 and Université de Lyon, Lyon, France
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Onuma H, Oeser JK, Nelson BA, Wang Y, Flemming BP, Scheving LA, Russell WE, O'Brien RM. Insulin and epidermal growth factor suppress basal glucose-6-phosphatase catalytic subunit gene transcription through overlapping but distinct mechanisms. Biochem J 2009; 417:611-20. [PMID: 18847435 PMCID: PMC2929524 DOI: 10.1042/bj20080999] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The G6Pase (glucose-6-phosphatase catalytic subunit) catalyses the final step in the gluconeogenic and glycogenolytic pathways, the hydrolysis of glucose-6-phosphate to glucose. We show here that, in HepG2 hepatoma cells, EGF (epidermal growth factor) inhibits basal mouse G6Pase fusion gene transcription. Several studies have shown that insulin represses basal mouse G6Pase fusion gene transcription through FOXO1 (forkhead box O1), but Stoffel and colleagues have recently suggested that insulin can also regulate gene transcription through FOXA2 (forkhead box A2) [Wolfrum, Asilmaz, Luca, Friedman and Stoffel (2003) Proc. Natl. Acad. Sci. 100, 11624-11629]. A combined GR (glucocorticoid receptor)-FOXA2 binding site is located between -185 and -174 in the mouse G6Pase promoter overlapping two FOXO1 binding sites located between (-188 and -182) and (-174 and -168). Selective mutation of the FOXO1 binding sites reduced the effect of insulin, whereas mutation of the GR/FOXA2 binding site had no effect on the insulin response. In contrast, selective mutation of the FOXO1 and GR/FOXA2 binding sites both reduced the effect of EGF. The effect of these mutations was additive, since the combined mutation of both FOXO1 and GR/FOXA2 binding sites reduced the effect of EGF to a greater extent than the individual mutations. These results suggest that, in HepG2 cells, GR and/or FOXA2 are required for the inhibition of basal G6Pase gene transcription by EGF but not insulin. EGF also inhibits hepatic G6Pase gene expression in vivo, but in cultured hepatocytes EGF has the opposite effect of stimulating expression, an observation that may be explained by a switch in ErbB receptor sub-type expression following hepatocyte isolation.
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Affiliation(s)
- Hiroshi Onuma
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical School, Nashville, TN 37232, U.S.A
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Boztug K, Appaswamy G, Ashikov A, Schäffer AA, Salzer U, Diestelhorst J, Germeshausen M, Brandes G, Lee-Gossler J, Noyan F, Gatzke AK, Minkov M, Greil J, Kratz C, Petropoulou T, Pellier I, Bellanné-Chantelot C, Rezaei N, Mönkemöller K, Irani-Hakimeh N, Bakker H, Gerardy-Schahn R, Zeidler C, Grimbacher B, Welte K, Klein C. A syndrome with congenital neutropenia and mutations in G6PC3. N Engl J Med 2009; 360:32-43. [PMID: 19118303 PMCID: PMC2778311 DOI: 10.1056/nejmoa0805051] [Citation(s) in RCA: 250] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
BACKGROUND The main features of severe congenital neutropenia are the onset of severe bacterial infections early in life, a paucity of mature neutrophils, and an increased risk of leukemia. In many patients, the genetic causes of severe congenital neutropenia are unknown. METHODS We performed genomewide genotyping and linkage analysis on two consanguineous pedigrees with a total of five children affected with severe congenital neutropenia. Candidate genes from the linkage interval were sequenced. Functional assays and reconstitution experiments were carried out. RESULTS All index patients were susceptible to bacterial infections and had very few mature neutrophils in the bone marrow; structural heart defects, urogenital abnormalities, and venous angiectasia on the trunk and extremities were additional features. Linkage analysis of the two index families yielded a combined multipoint lod score of 5.74 on a linkage interval on chromosome 17q21. Sequencing of G6PC3, the candidate gene encoding glucose-6-phosphatase, catalytic subunit 3, revealed a homozygous missense mutation in exon 6 that abolished the enzymatic activity of glucose-6-phosphatase in all affected children in the two families. The patients' neutrophils and fibroblasts had increased susceptibility to apoptosis. The myeloid cells showed evidence of increased endoplasmic reticulum stress and increased activity of glycogen synthase kinase 3beta (GSK-3beta). We identified seven additional, unrelated patients who had severe congenital neutropenia with syndromic features and distinct biallelic mutations in G6PC3. CONCLUSIONS Defective function of glucose-6-phosphatase, catalytic subunit 3, underlies a severe congenital neutropenia syndrome associated with cardiac and urogenital malformations.
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Affiliation(s)
- Kaan Boztug
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
| | | | - Angel Ashikov
- Departments of Cellular Chemistry, Hannover Medical School, Germany
| | | | - Ulrich Salzer
- Department of Rheumatology and Clinical Immunology, University Medical Center Freiburg, Freiburg, Germany
| | - Jana Diestelhorst
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
| | | | - Gudrun Brandes
- Departments of Cell Biology, Hannover Medical School, Germany
| | | | - Fatih Noyan
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
| | | | | | - Johann Greil
- Department of Pediatric Oncology, Hematology and Immunology, Children’s Hospital, University of Heidelberg, Germany
| | - Christian Kratz
- Division of, Pediatric Hematology/Oncology, Department of Pediatrics and Adolescent Medicine, University of Freiburg, Germany
| | - Theoni Petropoulou
- 1Department of Pediatrics, Aghia Sophia Children’s Hospital, University of Athens, Greece
| | - Isabelle Pellier
- Department of Pediatric Hematology, Immunology and Oncology, CHU Angers, France
| | | | - Nima Rezaei
- Immunology, Asthma and, Allergy Research Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Kirsten Mönkemöller
- Department of, General Pediatrics, Children’s Hospital Amsterdamer Straße, Cologne, Germany
| | - Noha Irani-Hakimeh
- Department of, Laboratory Medicine, Saint Georges University Hospital, Beirut, Lebanon
| | - Hans Bakker
- Departments of Cellular Chemistry, Hannover Medical School, Germany
| | | | - Cornelia Zeidler
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
| | - Bodo Grimbacher
- Department of, Immunology, Royal Free Hospital and University College London, London, UK
| | - Karl Welte
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
| | - Christoph Klein
- Departments of Pediatric Hematology/Oncology, Hannover Medical School, Germany
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Martin CC, Flemming BP, Wang Y, Oeser JK, O’Brien RM. Foxa2 and MafA regulate islet-specific glucose-6-phosphatase catalytic subunit-related protein gene expression. J Mol Endocrinol 2008; 41:315-28. [PMID: 18753309 PMCID: PMC2614309 DOI: 10.1677/jme-08-0062] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP/G6PC2) is a major autoantigen in both mouse and human type 1 diabetes. IGRP is selectively expressed in islet beta cells and polymorphisms in the IGRP gene have recently been associated with variations in fasting blood glucose levels and cardiovascular-associated mortality in humans. Chromatin immunoprecipitation (ChIP) assays have shown that the IGRP promoter binds the islet-enriched transcription factors Pax-6 and BETA2. We show here, again using ChIP assays, that the IGRP promoter also binds the islet-enriched transcription factors MafA and Foxa2. Single binding sites for these factors were identified in the proximal IGRP promoter, mutation of which resulted in decreased IGRP fusion gene expression in betaTC-3, Hamster insulinoma tumor (HIT), and Min6 cells. ChiP assays have shown that the islet-enriched transcription factor Pdx-1 also binds the IGRP promoter, but mutational analysis of four Pdx-1 binding sites in the proximal IGRP promoter revealed surprisingly little effect of Pdx-1 binding on IGRP fusion gene expression in betaTC-3 cells. In contrast, in both HIT and Min6 cells mutation of these four Pdx-1 binding sites resulted in a approximately 50% reduction in fusion gene expression. These data suggest that the same group of islet-enriched transcription factors, namely Pdx-1, Pax-6, MafA, BETA2, and Foxa2, directly or indirectly regulate expression of the two major autoantigens in type 1 diabetes.
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Affiliation(s)
| | | | | | | | - Richard M. O’Brien
- To whom correspondence should be addressed: Department of Molecular Physiology and Biophysics, 8415 MRB IV, 2213 Garland Ave, Vanderbilt University Medical School, Nashville, TN 37232-0615, Telephone (615) 936-1503; Facsimile (615) 322-7236, E-mail:
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Wang Y, Flemming BP, Martin CC, Allen SR, Walters J, Oeser JK, Hutton JC, O'Brien RM. Long-range enhancers are required to maintain expression of the autoantigen islet-specific glucose-6-phosphatase catalytic subunit-related protein in adult mouse islets in vivo. Diabetes 2008; 57:133-41. [PMID: 17942825 DOI: 10.2337/db07-0092] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is selectively expressed in islet beta-cells and is a major autoantigen in both mouse and human type 1 diabetes. This study describes the use of a combination of transgenic and transfection approaches to characterize the gene regions that confer the islet-specific expression of IGRP. RESEARCH DESIGN AND METHODS Transgenic mice were generated containing the IGRP promoter sequence from -306, -911, or -3911 to +3 ligated to a LacZ reporter gene. Transgene expression was monitored by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining of pancreatic tissue. RESULTS In all the transgenic mice, robust LacZ expression was detected in newborn mouse islets, but expression became mosaic as animals aged, suggesting that additional elements are required for the maintenance of IGRP gene expression. VISTA analyses identified two conserved regions in the distal IGRP promoter and one in the third intron. Transfection experiments demonstrated that all three regions confer enhanced luciferase reporter gene expression in beta TC-3 cells when ligated to a minimal IGRP promoter. A transgene containing all three conserved regions was generated by using a bacterial recombination strategy to insert a LacZ cassette into exon 5 of the IGRP gene. Transgenic mice containing a 15-kbp fragment of the IGRP gene were then generated. This transgene conferred LacZ expression in newborn mouse islets; however, expression was still suppressed as animals aged. CONCLUSIONS The data suggest that long-range enhancers 5' or 3' of the IGRP gene are required for the maintenance of IGRP gene expression in adult mice.
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Affiliation(s)
- Yingda Wang
- Department of Molecular Physiology and Biophysics, 761 PRB, Vanderbilt University Medical School, Nashville, TN 37232-0615, USA
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