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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: 8] [Impact Index Per Article: 4.0] [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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Bosma KJ, Rahim M, Singh K, Goleva SB, Wall ML, Xia J, Syring KE, Oeser JK, Poffenberger G, McGuinness OP, Means AL, Powers AC, Li WH, Davis LK, Young JD, O’Brien RM. Pancreatic islet beta cell-specific deletion of G6pc2 reduces fasting blood glucose. J Mol Endocrinol 2020; 64:235-248. [PMID: 32213654 PMCID: PMC7331801 DOI: 10.1530/jme-20-0031] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 03/13/2020] [Indexed: 12/25/2022]
Abstract
The G6PC1, G6PC2 and G6PC3 genes encode distinct glucose-6-phosphatase catalytic subunit (G6PC) isoforms. In mice, germline deletion of G6pc2 lowers fasting blood glucose (FBG) without affecting fasting plasma insulin (FPI) while, in isolated islets, glucose-6-phosphatase activity and glucose cycling are abolished and glucose-stimulated insulin secretion (GSIS) is enhanced at submaximal but not high glucose. These observations are all consistent with a model in which G6PC2 regulates the sensitivity of GSIS to glucose by opposing the action of glucokinase. G6PC2 is highly expressed in human and mouse islet beta cells however, various studies have shown trace G6PC2 expression in multiple tissues raising the possibility that G6PC2 also affects FBG through non-islet cell actions. Using real-time PCR we show here that expression of G6pc1 and/or G6pc3 are much greater than G6pc2 in peripheral tissues, whereas G6pc2 expression is much higher than G6pc3 in both pancreas and islets with G6pc1 expression not detected. In adult mice, beta cell-specific deletion of G6pc2 was sufficient to reduce FBG without changing FPI. In addition, electronic health record-derived phenotype analyses showed no association between G6PC2 expression and phenotypes clearly unrelated to islet function in humans. Finally, we show that germline G6pc2 deletion enhances glycolysis in mouse islets and that glucose cycling can also be detected in human islets. These observations are all consistent with a mechanism by which G6PC2 action in islets is sufficient to regulate the sensitivity of GSIS to glucose and hence influence FBG without affecting FPI.
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Affiliation(s)
- Karin J. Bosma
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Mohsin Rahim
- Department of Chemical and Biomolecular Engineering, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Kritika Singh
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Slavina B. Goleva
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Martha L. Wall
- Department of Chemical and Biomolecular Engineering, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Jing Xia
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039
| | - Kristen E. Syring
- Department of Molecular Physiology and Biophysics, 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
| | - Greg Poffenberger
- Department of Medicine, 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
| | - Anna L. Means
- Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Alvin C. Powers
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
- VA Tennessee Valley Healthcare System, Nashville, TN 37232
| | - Wen-hong Li
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039
| | - Lea K. Davis
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Jamey D. Young
- Department of Chemical and Biomolecular Engineering, 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
- 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,
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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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Corbin LJ, Richmond RC, Wade KH, Burgess S, Bowden J, Smith GD, Timpson NJ. BMI as a Modifiable Risk Factor for Type 2 Diabetes: Refining and Understanding Causal Estimates Using Mendelian Randomization. Diabetes 2016; 65:3002-7. [PMID: 27402723 PMCID: PMC5279886 DOI: 10.2337/db16-0418] [Citation(s) in RCA: 114] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 07/05/2016] [Indexed: 12/20/2022]
Abstract
This study focused on resolving the relationship between BMI and type 2 diabetes. The availability of multiple variants associated with BMI offers a new chance to resolve the true causal effect of BMI on type 2 diabetes; however, the properties of these associations and their validity as genetic instruments need to be considered alongside established and new methods for undertaking Mendelian randomization (MR). We explore the potential for pleiotropic genetic variants to generate bias, revise existing estimates, and illustrate value in new analysis methods. A two-sample MR approach with 96 genetic variants was used with three different analysis methods, two of which (MR-Egger and the weighted median) have been developed specifically to address problems of invalid instrumental variables. We estimate an odds ratio for type 2 diabetes per unit increase in BMI (kg/m(2)) of between 1.19 and 1.38, with the most stable estimate using all instruments and a weighted median approach (1.26 [95% CI 1.17, 1.34]). TCF7L2(rs7903146) was identified as a complex effect or pleiotropic instrument, and removal of this variant resulted in convergence of causal effect estimates from different causal analysis methods. This indicated the potential for pleiotropy to affect estimates and differences in performance of alternative analytical methods. In a real type 2 diabetes-focused example, this study demonstrates the potential impact of invalid instruments on causal effect estimates and the potential for new approaches to mitigate the bias caused.
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Affiliation(s)
- Laura J Corbin
- MRC Integrative Epidemiology Unit, University of Bristol, Bristol, U.K
| | | | - Kaitlin H Wade
- MRC Integrative Epidemiology Unit, University of Bristol, Bristol, U.K
| | - Stephen Burgess
- MRC Integrative Epidemiology Unit, University of Bristol, Bristol, U.K. Department of Public Health and Primary Care, University of Cambridge, Cambridge, U.K
| | - Jack Bowden
- MRC Integrative Epidemiology Unit, University of Bristol, Bristol, U.K. MRC Biostatistics Unit, Cambridge Institute of Public Health, Cambridge, U.K
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Transcription Factor 7-Like 2 (TCF7L2) rs7903146 Polymorphism as a Risk Factor for Gestational Diabetes Mellitus: A Meta-Analysis. PLoS One 2016; 11:e0153044. [PMID: 27058589 PMCID: PMC4825985 DOI: 10.1371/journal.pone.0153044] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 03/22/2016] [Indexed: 12/13/2022] Open
Abstract
Background There are racial and ethnic differences in the prevalence of gestational diabetes mellitus (GDM). Prior meta-analyses included small samples and very limited non-Caucasian populations. Studies to determine the relationship between transcription factor 7 like-2 (TCF7L2) rs7903146 polymorphism and risk of GDM in Hispanics/Latinos are recently available. The present meta-analysis was to estimate the impact of allele variants of TCF7L2 rs7903146 polymorphism on GDM susceptibility in overall population and racial/ethnic subgroups. Methods Literature was searched in multiple databases including PubMed, Web of Science, EMBASE (Ovid SP), Airiti Library, Medline Complete, and ProQuest up to July 2015. Allelic frequency for TCF7L2 rs7903146 polymorphism in GDM and control subjects was extracted and statistical analysis was performed using Comprehensive Meta-Analysis (CMA) 2.0 statistical software. The association between TCF7L2 rs7903146 polymorphism and GDM risk was assessed by pooled odd ratios (ORs) using five gene models (dominant, recessive, homozygote, heterozygote, and allele). Stratified analysis based on race/ethnicity was also conducted. The between-study heterogeneity and contribution of each single study to the final result was tested by Cochran Q test and sensitivity analyses, respectively. Publication bias was evaluated using Egger’s linear regression test. Results A total of 16 studies involving 4,853 cases and 10,631 controls were included in this meta-analysis. Significant association between the T-allele of rs7903146 and GDM risk was observed under all genetic models, dominant model (OR = 1.44, 95% CI = 1.19–1.74), recessive model (OR = 1.35, 95% CI = 1.08–1.70), heterozygous model (OR = 1.31, 95% CI = 1.12–1.53), homozygous model (OR = 1.67, 95% CI = 1.31–2.12), and allele model (OR = 1.31, 95% CI = 1.12–1.53). Stratified analysis by race/ethnicity showed a statistically significant association between rs7903146 polymorphism and susceptibility to GDM under homozygous genetic model (TT versus CC) among whites, Hispanics/Latinos and Asians. Sensitivity analysis showed that the overall findings were robust to potentially influential decisions of the 16 studies included. No significant evidence for publication bias was observed in this meta-analysis for overall studies and subgroup studies. Conclusions This meta-analysis showed that the T allele of TCF7L2 rs7903146 polymorphism was associated with susceptibility of GDM in overall population in white, Hispanic/Latino and Asian sub-groups. Asians with homozygous TT allele of rs7903146 polymorphism have highest risk of GDM (OR = 2.08) followed by Hispanics/Latinos (OR = 1.80) and whites (OR = 1.51). The highest and lowest frequency of T allele of rs7903146 was found in Malaysia and South Korea, respectively. Future studies are needed to profile genetic risk for GDM among high risk Asian and Pacific Islander subgroups.
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