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Nephrin Is Expressed on the Surface of Insulin Vesicles and Facilitates Glucose-Stimulated Insulin Release

  1. Alessia Fornoni1,2,
  2. Jongmin Jeon1,
  3. Javier Varona Santos1,
  4. Lorenzo Cobianchi1,3,
  5. Alexandra Jauregui1,2,
  6. Luca Inverardi1,
  7. Slavena A. Mandic4,
  8. Christina Bark4,
  9. Kevin Johnson1,
  10. George McNamara1,
  11. Antonello Pileggi1,
  12. R. Damaris Molano1,
  13. Jochen Reiser2,
  14. Karl Tryggvason5,
  15. Dontscho Kerjaschki6,
  16. Per-Olof Berggren1,4,
  17. Peter Mundel2,7 and
  18. Camillo Ricordi1
  1. 1Diabetes Research Institute, University of Miami L. Miller School of Medicine, Miami, Florida;
  2. 2Division of Nephrology and Hypertension–Miami Institute of Renal Medicine, University of Miami L. Miller School of Medicine, Miami, Florida;
  3. 3Istituto di Ricovero e Cura a Carattere Scientifico Fondazione Policlinico San Matteo, Università degli Studi di Pavia, Pavia, Italy;
  4. 4The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden;
  5. 5Cell Matrix Biology, Karolinska Institutet, Stockholm, Sweden;
  6. 6Clinical Institute of Pathology, Medical University, Vienna, Austria;
  7. 7Division of Molecular Medicine, University of Miami L. Miller School of Medicine, Miami, Florida.
  1. Corresponding author: Alessia Fornoni, afornoni{at}med.miami.edu.

Abstract

OBJECTIVE Nephrin, an immunoglobulin-like protein essential for the function of the glomerular podocyte and regulated in diabetic nephropathy, is also expressed in pancreatic β-cells, where its function remains unknown. The aim of this study was to investigate whether diabetes modulates nephrin expression in human pancreatic islets and to explore the role of nephrin in β-cell function.

RESEARCH DESIGN AND METHODS Nephrin expression in human pancreas and in MIN6 insulinoma cells was studied by Western blot, PCR, confocal microscopy, subcellular fractionation, and immunogold labeling. Islets from diabetic (n = 5) and nondiabetic (n = 7) patients were compared. Stable transfection and siRNA knockdown in MIN-6 cells/human islets were used to study nephrin function in vitro and in vivo after transplantation in diabetic immunodeficient mice. Live imaging of green fluorescent protein (GFP)-nephrin–transfected cells was used to study nephrin endocytosis.

RESULTS Nephrin was found at the plasma membrane and on insulin vesicles. Nephrin expression was decreased in islets from diabetic patients when compared with nondiabetic control subjects. Nephrin transfection in MIN-6 cells/pseudoislets resulted in higher glucose-stimulated insulin release in vitro and in vivo after transplantation into immunodeficient diabetic mice. Nephrin gene silencing abolished stimulated insulin release. Confocal imaging of GFP-nephrin–transfected cells revealed nephrin endocytosis upon glucose stimulation. Actin stabilization prevented nephrin trafficking as well as nephrin-positive effect on insulin release.

CONCLUSIONS Our data suggest that nephrin is an active component of insulin vesicle machinery that may affect vesicle-actin interaction and mobilization to the plasma membrane. Development of drugs targeting nephrin may represent a novel approach to treat diabetes.

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 May 1, 2009.
    • Accepted October 1, 2009.
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This Article

  1. Published online before print October 15, 2009, doi: 10.2337/db09-0655 Diabetes January 2010 vol. 59 no. 1 190-199
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