Insulin Storage and Glucose Homeostasis in Mice Null for the Granule Zinc Transporter ZnT8 and Studies of the Type 2 Diabetes–Associated Variants

  1. Tamara J. Nicolson1,
  2. Elisa A. Bellomo1,
  3. Nadeeja Wijesekara2,
  4. Merewyn K. Loder1,
  5. Jocelyn M. Baldwin3,
  6. Armen V. Gyulkhandanyan2,
  7. Vasilij Koshkin2,
  8. Andrei I. Tarasov1,
  9. Raffaella Carzaniga4,
  10. Katrin Kronenberger4,
  11. Tarvinder K. Taneja1,
  12. Gabriela da Silva Xavier1,
  13. Sarah Libert5,
  14. Philippe Froguel6,7,
  15. Raphael Scharfmann8,
  16. Volodymir Stetsyuk8,
  17. Philippe Ravassard9,
  18. Helen Parker10,
  19. Fiona M. Gribble10,
  20. Frank Reimann10,
  21. Robert Sladek11,
  22. Stephen J. Hughes12,
  23. Paul R.V. Johnson12,
  24. Myriam Masseboeuf13,
  25. Remy Burcelin13,
  26. Stephen A. Baldwin3,
  27. Ming Liu14,
  28. Roberto Lara-Lemus14,
  29. Peter Arvan14,
  30. Frans C. Schuit15,
  31. Michael B. Wheeler3,
  32. Fabrice Chimienti6 and
  33. Guy A. Rutter1
  1. 1Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K.;
  2. 2Department of Physiology, University of Toronto, Toronto, Canada;
  3. 3Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K.;
  4. 4Electron Microscopy Centre, Imperial College London, London, U.K.;
  5. 5Mellitech, Grenoble, France;
  6. 6Section of Genomic Medicine, Division of Medicine, Imperial College London, London, U.K.;
  7. 7Centre National de la Recherche Scientifique Unite Mixte de Recherche 8090, Institute of Biology, Lille, France;
  8. 8INSERM U845, University Paris Descartes, Paris, France;
  9. 9Centre National de la Recherche Scientifique and Université Pierre et Marie Curie, Paris, France;
  10. 10Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K.;
  11. 11Department of Human Genetics, McGill University, Montreal, Canada;
  12. 12Nuffield Department of Surgery, University of Oxford, Oxfordshire, U.K.;
  13. 13Institut de Medecine Moleculaire de Rangueil, INSERM U858, IFR31, Toulouse III University, CHU Rangueil, Toulouse Cedex, Toulouse, France;
  14. 14Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan;
  15. 15Gene Expression Unit, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium.
  1. Corresponding author: Guy A. Rutter, g.rutter{at}imperial.ac.uk.
  1. T.J.N., E.A.B., N.W., M.K.L., and J.M.B. contributed equally to this study.

Abstract

OBJECTIVE Zinc ions are essential for the formation of hexameric insulin and hormone crystallization. A nonsynonymous single nucleotide polymorphism rs13266634 in the SLC30A8 gene, encoding the secretory granule zinc transporter ZnT8, is associated with type 2 diabetes. We describe the effects of deleting the ZnT8 gene in mice and explore the action of the at-risk allele.

RESEARCH DESIGN AND METHODS Slc30a8 null mice were generated and backcrossed at least twice onto a C57BL/6J background. Glucose and insulin tolerance were measured by intraperitoneal injection or euglycemic clamp, respectively. Insulin secretion, electrophysiology, imaging, and the generation of adenoviruses encoding the low- (W325) or elevated- (R325) risk ZnT8 alleles were undertaken using standard protocols.

RESULTS ZnT8−/− mice displayed age-, sex-, and diet-dependent abnormalities in glucose tolerance, insulin secretion, and body weight. Islets isolated from null mice had reduced granule zinc content and showed age-dependent changes in granule morphology, with markedly fewer dense cores but more rod-like crystals. Glucose-stimulated insulin secretion, granule fusion, and insulin crystal dissolution, assessed by total internal reflection fluorescence microscopy, were unchanged or enhanced in ZnT8−/− islets. Insulin processing was normal. Molecular modeling revealed that residue-325 was located at the interface between ZnT8 monomers. Correspondingly, the R325 variant displayed lower apparent Zn2+ transport activity than W325 ZnT8 by fluorescence-based assay.

CONCLUSIONS ZnT8 is required for normal insulin crystallization and insulin release in vivo but not, remarkably, in vitro. Defects in the former processes in carriers of the R allele may increase type 2 diabetes risks.

Footnotes

  • The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Received April 15, 2009.
    • Accepted June 2, 2009.
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  1. Diabetes vol. 58 no. 9 2070-2083
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