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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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Grenko CM, Bonnycastle LL, Taylor HJ, Yan T, Swift AJ, Robertson CC, Narisu N, Erdos MR, Collins FS, Taylor DL. Single-cell transcriptomic profiling of human pancreatic islets reveals genes responsive to glucose exposure over 24 hours. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.06.543931. [PMID: 37333221 PMCID: PMC10274787 DOI: 10.1101/2023.06.06.543931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Disruption of pancreatic islet function and glucose homeostasis can lead to the development of sustained hyperglycemia, beta cell glucotoxicity, and ultimately type 2 diabetes (T2D). In this study, we sought to explore the effects of hyperglycemia on human pancreatic islet (HPI) gene expression by exposing HPIs from two donors to low (2.8mM) and high (15.0mM) glucose concentrations over 24 hours, assaying the transcriptome at seven time points using single-cell RNA sequencing (scRNA-seq). We modeled time as both a discrete and continuous variable to determine momentary and longitudinal changes in transcription associated with islet time in culture or glucose exposure. Across all cell types, we identified 1,528 genes associated with time, 1,185 genes associated with glucose exposure, and 845 genes associated with interaction effects between time and glucose. We clustered differentially expressed genes across cell types and found 347 modules of genes with similar expression patterns across time and glucose conditions, including two beta cell modules enriched in genes associated with T2D. Finally, by integrating genomic features from this study and genetic summary statistics for T2D and related traits, we nominate 363 candidate effector genes that may underlie genetic associations for T2D and related traits.
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Affiliation(s)
- Caleb M. Grenko
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Lori L. Bonnycastle
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Henry J. Taylor
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
- British Heart Foundation Cardiovascular Epidemiology Unit, Department of Public Health and Primary Care, University of Cambridge, Cambridge CB1 8RN, UK
| | - Tingfen Yan
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Amy J. Swift
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Catherine C. Robertson
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Narisu Narisu
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Michael R. Erdos
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Francis S. Collins
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - D. Leland Taylor
- Center for Precision Health Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
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Udhaya Kumar S, Kamaraj B, Varghese RP, Preethi VA, Bithia R, George Priya Doss C. Mutations in G6PC2 gene with increased risk for development of type 2 diabetes: Understanding via computational approach. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2022; 130:351-373. [PMID: 35534112 DOI: 10.1016/bs.apcsb.2022.02.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
An increase in the fast blood glucose (FBG) levels has been linked to an increased risk of developing a chronic condition, type 2 diabetes (T2D). The mutation in the G6PC2 gene was identified to have a lead role in the modulation of FBG levels. The abnormal regulation of this enzyme influences glucose-stimulated insulin secretion (GSIS), which controls the insulin levels corresponding to the system's glucose level. This study focuses on the mutations at the G6PC2 gene, which cause the variation from normal expression levels and increase the risk of T2D. We examined the non-synonymous single nucleotide polymorphisms (nsSNPs) present in the G6PC2 and subjected them to pathogenicity, stability, residue conservation, and membrane simulation. The individual representation of surrounding amino acids in the mutant (I63T) model showed the loss of hydrophobic interactions compared to the native G6PC2. In addition, the trajectory results from the membrane simulation exhibited reduced stability, and the least compactness was identified for the I63T mutant model. Our study shed light on the structural and conformational changes at the transmembrane region due to the I63T mutation in G6PC2. Additionally, the Gibbs free energy landscape analysis against the two principal components showed structural differences and decreased the conformational stability of the I63T mutant model compared to the native. Like those presented in this study, dynamical simulations may indeed be crucial to comprehending the structural insights of G6PC2 mutations in cardiovascular-associated mortality and T2D.
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Affiliation(s)
- S Udhaya Kumar
- Laboratory of Integrative Genomics, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India
| | - Balu Kamaraj
- Department of Neuroscience Technology, College of Applied Medical Sciences, Imam Abdulrahman Bin Faisal University, Jubail, Saudi Arabia
| | - Rinku Polachirakkal Varghese
- Laboratory of Integrative Genomics, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India
| | - V Anu Preethi
- School of Computer Science and Engineering, Vellore Institute of Technology, Vellore, Tamil Nadu, India
| | - R Bithia
- Laboratory of Integrative Genomics, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India
| | - C George Priya Doss
- Laboratory of Integrative Genomics, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, Tamil Nadu, India.
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Friis G, Atwell JW, Fudickar AM, Greives TJ, Yeh PJ, Price TD, Ketterson ED, Milá B. Rapid evolutionary divergence of a songbird population following recent colonization of an urban area. Mol Ecol 2022; 31:2625-2643. [DOI: 10.1111/mec.16422] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 01/14/2022] [Accepted: 03/01/2022] [Indexed: 11/27/2022]
Affiliation(s)
- Guillermo Friis
- National Museum of Natural Sciences Department of Biodiversity and Evolutionary Biology Spanish National Research Council (CSIC) Madrid 28006 Spain
| | | | - Adam M. Fudickar
- Department of Biology Indiana University Bloomington IN 47405 USA
| | - Timothy J. Greives
- Department of Biological Sciences North Dakota State University Fargo ND 58105 USA
| | - Pamela J. Yeh
- Department of Ecology and Evolutionary Biology University of California Los Angeles Los Angeles CA 90095 USA
| | - Trevor D. Price
- Department of Ecology and Evolution University of Chicago Chicago IL 60637 USA
| | | | - Borja Milá
- National Museum of Natural Sciences Department of Biodiversity and Evolutionary Biology Spanish National Research Council (CSIC) Madrid 28006 Spain
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Overway EM, Bosma KJ, Claxton DP, Oeser JK, Singh K, Breidenbach LB, Mchaourab HS, Davis LK, O'Brien RM. Nonsynonymous single-nucleotide polymorphisms in the G6PC2 gene affect protein expression, enzyme activity, and fasting blood glucose. J Biol Chem 2022; 298:101534. [PMID: 34954144 PMCID: PMC8800118 DOI: 10.1016/j.jbc.2021.101534] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/16/2021] [Accepted: 12/17/2021] [Indexed: 12/30/2022] Open
Abstract
G6PC2 encodes a glucose-6-phosphatase (G6Pase) catalytic subunit that modulates the sensitivity of insulin secretion to glucose and thereby regulates fasting blood glucose (FBG). A common single-nucleotide polymorphism (SNP) in G6PC2, rs560887 is an important determinant of human FBG variability. This SNP has a subtle effect on G6PC2 RNA splicing, which raises the question as to whether nonsynonymous SNPs with a major impact on G6PC2 stability or enzyme activity might have a broader disease/metabolic impact. Previous attempts to characterize such SNPs were limited by the very low inherent G6Pase activity and expression of G6PC2 protein in islet-derived cell lines. In this study, we describe the use of a plasmid vector that confers high G6PC2 protein expression in islet cells, allowing for a functional analysis of 22 nonsynonymous G6PC2 SNPs, 19 of which alter amino acids that are conserved in mouse G6PC2 and the human and mouse variants of the related G6PC1 isoform. We show that 16 of these SNPs markedly impair G6PC2 protein expression (>50% decrease). These SNPs have variable effects on the stability of human and mouse G6PC1, despite the high sequence homology between these isoforms. Four of the remaining six SNPs impaired G6PC2 enzyme activity. Electronic health record-derived phenotype analyses showed an association between high-impact SNPs and FBG, but not other diseases/metabolites. While homozygous G6pc2 deletion in mice increases the risk of hypoglycemia, these human data reveal no evidence that the beneficial use of partial G6PC2 inhibitors to lower FBG would be associated with unintended negative consequences.
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Affiliation(s)
- Emily M Overway
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Karin J Bosma
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Derek P Claxton
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - James K Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Kritika Singh
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Lindsay B Breidenbach
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Lea K Davis
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA; Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Richard M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
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Cao M, Bu C, Zhang J, Ren Y, Zhou G, Chen C, Han G, Jiang SW, Wen J. Exosomal Circular RNA hsa_circ_0046060 of Umbilical Cord Mesenchymal Stromal Cell Ameliorates Glucose Metabolism and Insulin Resistance in Gestational Diabetes Mellitus via the miR-338-3p/G6PC2 Axis. Int J Endocrinol 2022; 2022:9218113. [PMID: 35726320 PMCID: PMC9206588 DOI: 10.1155/2022/9218113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 05/13/2022] [Accepted: 05/20/2022] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Impaired glucose metabolism and insulin sensitivity have been linked to the pathogenesis of gestational diabetes mellitus (GDM). Exosomes secreted by the umbilical cord mesenchymal stromal cells (UMSCs) and circular RNAs (circRNAs) derived from exosomes have been shown to be associated with the progression of GDM-related complications. METHODS UMSCs were isolated from umbilical cords and identified through flow cytometry. Exosomes were isolated from UMSCs and were then characterized. The expression levels of RNA of hsa_circ_0046060, mmu_circ_0002819, and miR-338-3p were determined by quantitative real-time polymerase chain reaction (RT-qPCR). The intracellular glucose intake and glycogen content were measured using a High Sensitivity Glucose Assay Kit and Glycogen Assay Kit, respectively. Bioinformatics analysis and luciferase reporter assay were used to validate interactions among hsa_circ_0046060, miR-338-3p, and G6PC2. The expression of insulin receptor substrate-1 (IRS-1) and its phosphorylated form, (p-IRS-1), as well as G6PC2, was determined through western blotting. RESULTS UMSCs and exosomes were successfully isolated and identified. The upregulation of hsa_circ_0046060 decreased the intracellular glucose content in L-02 cells (43.45 vs. 16.87 pM/mg, P=0.0002), whereas shRNA-mediated downregulation reversed this effect (16.87 vs. 33.16 pM/mg, P=0.0011). Mmu_circ_0002819 in mice aggravated dysregulated glucose metabolism (49.88 vs. 21.69 pM/mg, P=0.0031) and insulin sensitivity (0.20 vs. 0.11 mg/mL, P=0.03) in GDM mice, which was abrogated by the knockdown of mmu_circ_0002819. The results of luciferase reporter assay revealed that miR-338-3p and G6PC2 were the potential targets of has_circ_0046060. Western blotting results showed that the reduced activation of IRS-1 induced by GDM (1.25 vs. 0.54, P=0.0001) could be rescued by the administration of si-circ-G-UMSC-EXOs (0.54 vs. 1.17, P=0.0001). CONCLUSION Taken together, the inhibition of hsa_circ_0046060 expression in exosomes from GDM-derived UMSCs can alleviate GDM by reversing abnormal glucose metabolism and insulin resistance in vivo and in vitro.
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Affiliation(s)
- Minkai Cao
- Department of Gynecology and Obstetrics, The Second Hospital of Nanjing, Nanjing University of Chinese Medicine, Nanjing 210003, China
- Department of Obstetrics and Gynecology, The Affiliated Wuxi Matemity and Child Health Care Hospital of Nanjing Medical University, Wuxi 214002, Jiangsu, China
| | - Chaozhi Bu
- Center of Reproductive Medicine, State Key Laboratory of Reproductive Medicine, Research Institute for Reproductive Health and Genetic Diseases, The Affiliated Wuxi Matemity and Child Health Care Hospital of Nanjing Medical University, Wuxi 214002, Jiangsu, China
| | - Jingjing Zhang
- Department of Obstetrics and Gynecology, Qilu Hospital of Shandong University, Jinan 250012, Shandong, China
| | - Yongwei Ren
- Center of Reproductive Medicine, State Key Laboratory of Reproductive Medicine, Research Institute for Reproductive Health and Genetic Diseases, The Affiliated Wuxi Matemity and Child Health Care Hospital of Nanjing Medical University, Wuxi 214002, Jiangsu, China
| | - Guanlun Zhou
- Department of Gynecology and Obstetrics, The Second Hospital of Nanjing, Nanjing University of Chinese Medicine, Nanjing 210003, China
| | - Chao Chen
- Department of Gynecology and Obstetrics, The Second Hospital of Nanjing, Nanjing University of Chinese Medicine, Nanjing 210003, China
| | - Guorong Han
- Department of Gynecology and Obstetrics, The Second Hospital of Nanjing, Nanjing University of Chinese Medicine, Nanjing 210003, China
| | - Shi-Wen Jiang
- Center of Reproductive Medicine, State Key Laboratory of Reproductive Medicine, Research Institute for Reproductive Health and Genetic Diseases, The Affiliated Wuxi Matemity and Child Health Care Hospital of Nanjing Medical University, Wuxi 214002, Jiangsu, China
| | - Juan Wen
- Nanjing Maternity and Child Health Care Institute, Women's Hospital of Nanjing Medical University, Nanjing Maternity and Child Health Care Hospital, Nanjing 210004, China
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Li C, Yang Y, Liu X, Li Z, Liu H, Tan Q. Glucose metabolism-related gene polymorphisms as the risk predictors of type 2 diabetes. Diabetol Metab Syndr 2020; 12:97. [PMID: 33292424 PMCID: PMC7643457 DOI: 10.1186/s13098-020-00604-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 10/22/2020] [Accepted: 10/26/2020] [Indexed: 02/07/2023] Open
Abstract
Type 2 diabetes mellitus (T2DM) is a complex polygenic metabolic disease characterized by elevated blood glucose. Multiple environmental and genetic factors can increase the risk of T2DM and its complications, and genetic polymorphisms are no exception. This review is mainly focused on the related genes involved in glucose metabolic, including G6PC2, GCK, GCKR and OCT3. In this review, we have summarized the results reported globally and found that the genetic variants of GCK and OCT3 genes is a risk factor for T2DM while G6PC2 and GCKR genes are controversial in different ethnic groups. Hopefully, this summary could possibly help researchers and physicians understand the mechanism of T2DM so as to diagnose and even prevent T2DM at early time.
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Affiliation(s)
- Cuilin Li
- Department of Pharmacy, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, Hunan, China.
| | - Yuping Yang
- Department of Pharmacy, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, Hunan, China
| | - Xin Liu
- Department of Pharmacy, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, Hunan, China
| | - Zhongyu Li
- Laboratory Medical Center, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, China
| | - Hong Liu
- Department of Metabolism and Endocrinology, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, China
| | - Qiuhong Tan
- Department of Pharmacy, The Affiliated Zhuzhou Hospital Xiangya Medical College CSU, Zhuzhou, 412007, Hunan, China
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8
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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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9
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Affiliation(s)
- Raúl Aguilar-Roblero
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Coyoacán, Mexico
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Boortz KA, Syring KE, Pound LD, Mo H, Bastarache L, Oeser JK, McGuinness OP, Denny JC, O’Brien RM. Effects of G6pc2 deletion on body weight and cholesterol in mice. J Mol Endocrinol 2017; 58:127-139. [PMID: 28122818 PMCID: PMC5380368 DOI: 10.1530/jme-16-0202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 01/24/2017] [Indexed: 11/08/2022]
Abstract
Genome-wide association study (GWAS) data have linked the G6PC2 gene to variations in fasting blood glucose (FBG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit that forms a substrate cycle with the beta cell glucose sensor glucokinase. This cycle modulates the glucose sensitivity of insulin secretion and hence FBG. GWAS data have not linked G6PC2 to variations in body weight but we previously reported that female C57BL/6J G6pc2-knockout (KO) mice were lighter than wild-type littermates on both a chow and high-fat diet. The purpose of this study was to compare the effects of G6pc2 deletion on FBG and body weight in both chow-fed and high-fat-fed mice on two other genetic backgrounds. FBG was reduced in G6pc2 KO mice largely independent of gender, genetic background or diet. In contrast, the effect of G6pc2 deletion on body weight was markedly influenced by these variables. Deletion of G6pc2 conferred a marked protection against diet-induced obesity in male mixed genetic background mice, whereas in 129SvEv mice deletion of G6pc2 had no effect on body weight. G6pc2 deletion also reduced plasma cholesterol levels in a manner dependent on gender, genetic background and diet. An association between G6PC2 and plasma cholesterol was also observed in humans through electronic health record-derived phenotype analyses. These observations suggest that the action of G6PC2 on FBG is largely independent of the influences of environment, modifier genes or epigenetic events, whereas the action of G6PC2 on body weight and cholesterol are influenced by unknown variables.
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Affiliation(s)
- Kayla A. Boortz
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Kristen E. Syring
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Lynley D. Pound
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Huan Mo
- Department of Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Lisa Bastarache
- Department of Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - James K. Oeser
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Owen P. McGuinness
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Joshua C. Denny
- Department of Biomedical Informatics, Vanderbilt University School of Medicine, Nashville, TN 37232
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Richard M. O’Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
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11
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Boortz KA, Syring KE, Lee RA, Dai C, Oeser JK, McGuinness OP, Wang JC, O'Brien RM. G6PC2 Modulates the Effects of Dexamethasone on Fasting Blood Glucose and Glucose Tolerance. Endocrinology 2016; 157:4133-4145. [PMID: 27653037 PMCID: PMC5086534 DOI: 10.1210/en.2016-1678] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The glucose-6-phosphatase catalytic subunit 2 (G6PC2) gene encodes an islet-specific glucose-6-phosphatase catalytic subunit. G6PC2 forms a substrate cycle with glucokinase that determines the glucose sensitivity of insulin secretion. Consequently, deletion of G6pc2 lowers fasting blood glucose (FBG) without affecting fasting plasma insulin. Although chronic elevation of FBG is detrimental to health, glucocorticoids induce G6PC2 expression, suggesting that G6PC2 evolved to transiently modulate FBG under conditions of glucocorticoid-related stress. We show, using competition and mutagenesis experiments, that the synthetic glucocorticoid dexamethasone (Dex) induces G6PC2 promoter activity through a mechanism involving displacement of the islet-enriched transcription factor MafA by the glucocorticoid receptor. The induction of G6PC2 promoter activity by Dex is modulated by a single nucleotide polymorphism, previously linked to altered FBG in humans, that affects FOXA2 binding. A 5-day repeated injection paradigm was used to examine the chronic effect of Dex on FBG and glucose tolerance in wild-type (WT) and G6pc2 knockout mice. Acute Dex treatment only induces G6pc2 expression in 129SvEv but not C57BL/6J mice, but this chronic treatment induced G6pc2 expression in both. In 6-hour fasted C57BL/6J WT mice, Dex treatment lowered FBG and improved glucose tolerance, with G6pc2 deletion exacerbating the decrease in FBG and enhancing the improvement in glucose tolerance. In contrast, in 24-hour fasted C57BL/6J WT mice, Dex treatment raised FBG but still improved glucose tolerance, with G6pc2 deletion limiting the increase in FBG and enhancing the improvement in glucose tolerance. These observations demonstrate that G6pc2 modulates the complex effects of Dex on both FBG and glucose tolerance.
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Affiliation(s)
- Kayla A Boortz
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Kristen E Syring
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Rebecca A Lee
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Chunhua Dai
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - James K Oeser
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Owen P McGuinness
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Jen-Chywan Wang
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
| | - Richard M O'Brien
- Departments of Molecular Physiology and Biophysics (K.A.B., K.E.S., J.K.O., O.P.M., R.M.O.) and Medicine (C.D.), Vanderbilt University School of Medicine, Nashville, Tennessee 37232; and Department of Nutritional Sciences and Toxicology (R.A.L., J.-C.W.), University of California at Berkeley, Berkeley, California 94720
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Functional Analysis of Mouse G6pc1 Mutations Using a Novel In Situ Assay for Glucose-6-Phosphatase Activity and the Effect of Mutations in Conserved Human G6PC1/G6PC2 Amino Acids on G6PC2 Protein Expression. PLoS One 2016; 11:e0162439. [PMID: 27611587 PMCID: PMC5017610 DOI: 10.1371/journal.pone.0162439] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Accepted: 08/23/2016] [Indexed: 11/19/2022] Open
Abstract
Elevated fasting blood glucose (FBG) has been associated with increased risk for development of type 2 diabetes. Single nucleotide polymorphisms (SNPs) in G6PC2 are the most important common determinants of variations in FBG in humans. Studies using G6pc2 knockout mice suggest that G6pc2 regulates the glucose sensitivity of insulin secretion. G6PC2 and the related G6PC1 and G6PC3 genes encode glucose-6-phosphatase catalytic subunits. This study describes a functional analysis of 22 non-synonymous G6PC2 SNPs, that alter amino acids that are conserved in human G6PC1, mouse G6pc1 and mouse G6pc2, with the goal of identifying variants that potentially affect G6PC2 activity/expression. Published data suggest strong conservation of catalytically important amino acids between all four proteins and the related G6PC3 isoform. Because human G6PC2 has very low glucose-6-phosphatase activity we used an indirect approach, examining the effect of these SNPs on mouse G6pc1 activity. Using a novel in situ functional assay for glucose-6-phosphatase activity we demonstrate that the amino acid changes associated with the human G6PC2 rs144254880 (Arg79Gln), rs149663725 (Gly114Arg) and rs2232326 (Ser324Pro) SNPs reduce mouse G6pc1 enzyme activity without affecting protein expression. The Arg79Gln variant alters an amino acid mutation of which, in G6PC1, has previously been shown to cause glycogen storage disease type 1a. We also demonstrate that the rs368382511 (Gly8Glu), rs138726309 (His177Tyr), rs2232323 (Tyr207Ser) rs374055555 (Arg293Trp), rs2232326 (Ser324Pro), rs137857125 (Pro313Leu) and rs2232327 (Pro340Leu) SNPs confer decreased G6PC2 protein expression. In summary, these studies identify multiple G6PC2 variants that have the potential to be associated with altered FBG in humans.
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