Glycogen Synthase Kinase-3 and Mammalian Target of Rapamycin Pathways Contribute to DNA Synthesis, Cell Cycle Progression, and Proliferation in Human Islets

  1. Hui Liu1,
  2. Maria S. Remedi2,
  3. Kirk L. Pappan1,
  4. Guim Kwon3,
  5. Nidhi Rohatgi1,
  6. Connie A. Marshall1 and
  7. Michael L. McDaniel1
  1. 1Department of Pathology and Immunology, Washington University, St. Louis, Missouri
  2. 2Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri
  3. 3Department of Pharmaceutical Sciences, School of Pharmacy, Southern Illinois University, Edwardsville, Illinois
  1. Corresponding author: Michael L. McDaniel, mmcdaniel{at}wustl.edu

Abstract

OBJECTIVE—Our previous studies demonstrated that nutrient regulation of mammalian target of rapamycin (mTOR) signaling promotes regenerative processes in rodent islets but rarely in human islets. Our objective was to extend these findings by using therapeutic agents to determine whether the regulation of glycogen synthase kinase-3 (GSK-3)/β-catenin and mTOR signaling represent key components necessary for effecting a positive impact on human β-cell mass relevant to type 1 and 2 diabetes.

RESEARCH DESIGN AND METHODS—Primary adult human and rat islets were treated with the GSK-3 inhibitors, LiCl and the highly potent 1-azakenpaullone (1-Akp), and with nutrients. DNA synthesis, cell cycle progression, and proliferation of β-cells were assessed. Measurement of insulin secretion and content and Western blot analysis of GSK-3 and mTOR signaling components were performed.

RESULTS—Human islets treated for 4 days with LiCl or 1-Akp exhibited significant increases in DNA synthesis, cell cycle progression, and proliferation of β-cells that displayed varying degrees of sensitivity to rapamycin. Intermediate glucose (8 mmol/l) produced a striking degree of synergism in combination with GSK-3 inhibition to enhance bromodeoxyuridine (BrdU) incorporation and Ki-67 expression in human β-cells. Nuclear translocation of β-catenin responsible for cell proliferation was found to be particularly sensitive to rapamycin.

CONCLUSIONS—A combination of GSK-3 inhibition and nutrient activation of mTOR contributes to enhanced DNA synthesis, cell cycle progression, and proliferation of human β-cells. Identification of therapeutic agents that appropriately regulate GSK-3 and mTOR signaling may provide a feasible and available approach to enhance human islet growth and proliferation.

Footnotes

  • Published ahead of print at http://diabetes.diabetesjournals.org on 10 December 2008.

    H.L., M.S.R., and K.L.P. contributed equally to this work.

    The contents of this work are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health (NIH) or American Diabetes Association (ADA).

    Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.

    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.

    • Accepted November 30, 2008.
    • Received August 27, 2007.
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  1. Diabetes vol. 58 no. 3 663-672
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