Activin Receptor-Like Kinase 5 Inhibition Reverses Impairment of Endothelial Cell Viability by Endogenous Islet Mesenchymal Stromal Cells

Authors

  • Claire E. Clarkin,

    Corresponding author
    1. Diabetes Research Group, Division of Diabetes and Nutritional Sciences, School of Medicine, Kings College London, London, United Kingdom
    • Centre for Biological Sciences, University of Southampton, Southampton General Hospital, Tremona Road, Southampton S016 6YD. United Kingdom
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    • Telephone: +44 (0)2380795725; Fax: +44 (0)2380796085

  • Aileen J. King,

    1. Diabetes Research Group, Division of Diabetes and Nutritional Sciences, School of Medicine, Kings College London, London, United Kingdom
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  • Paramjeet Dhadda,

    1. Diabetes Research Group, Division of Diabetes and Nutritional Sciences, School of Medicine, Kings College London, London, United Kingdom
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  • Pedro Chagastelles,

    1. Department of Genetics, Universidade Federal do Rio Grande do Sul, Brazil
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  • Nance Nardi,

    1. Laboratory of Stem Cells and Tissue Engineering, Universidade Luterana do Brasil, Brazil
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  • Caroline P. Wheeler-Jones,

    1. Comparative Biomedical Sciences, The Royal Veterinary College, London, United Kingdom
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  • Peter M. Jones

    1. Diabetes Research Group, Division of Diabetes and Nutritional Sciences, School of Medicine, Kings College London, London, United Kingdom
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  • Author contributions: C.C.: conception and design, collection of data, data analysis and interpretation, and manuscript writing; A.J.K. and P.C.: provision of study material and final approval of manuscript; P.D.: collection of data; N.N.: provision of study material and final approval of manuscript; C.P.W.-J. and P.J.: conception and design, data interpretation, and manuscript writing. C.P.W.J. and P.M.J. contributed equally to this article.

  • Disclosure of potential conflicts of interest is found at the end of this article.

  • First published online in STEM CELLSEXPRESS December 19, 2012.

Abstract

Following islet transplantation, islet graft revascularization is compromised due to loss of endothelial cells (ECs) during islet culture. TGF-β signaling pathways are essential for vascular homeostasis but their importance for islet EC function is unclear. We have identified a population of multipotent mesenchymal stromal cells (MSCs) within islets and investigated how modulation of TGF-β signaling by these cells influences islet EC viability. Cultured islets exhibited reduced expression of EC markers (VEGFR2, VE-cadherin and CD31), which was associated with diminished but sustained expression of endoglin a marker of both ECs and MSCs. Double fluorescent labeling of islets in situ with the EC marker CD31 disclosed a population of CD31-negative cells which were positive for endoglin. In vitro coculture of microvascular ECs with endoglin-positive, CD31-negative islet MSCs reduced VEGFR2 protein expression, disrupted EC angiogenic behavior, and increased EC detachment. Medium conditioned by islet MSCs significantly decreased EC viability and increased EC caspase 3/7 activity. EC:MSC cocultures showed enhanced Smad2 phosphorylation consistent with altered ALK5 signaling. Pharmacological inhibition of ALK5 activity with SB431542 (SB) improved EC survival upon contact with MSCs, and SB-treated cultured islets retained EC marker expression and sensitivity to exogenous VEGF164. Thus, endoglin-expressing islet MSCs influence EC ALK5 signaling in vitro, which decreases EC viability, and changes in ALK5 activity in whole cultured islets contribute to islet EC loss. Modifying TGF-β signaling may enable maintenance of islet ECs during islet isolation and thus improve islet graft revascularization post-transplantation. STEM CELLS2013;31:547–559

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