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Insulin attenuates vascular smooth muscle calcification but increases vascular smooth muscle cell phosphate transport

  • Author Footnotes
    1 These authors contributed equally to this manuscript.
    Cecilia C. Low Wang
    Correspondence
    Corresponding author at: Denver VA Medical Center, Research Section/Endocrine Service, 1055 Clermont Street (111H), Denver, CO 80220, United States. Tel.: +1 303 399 8020x2691; fax: +1 303 393 5271.
    Footnotes
    1 These authors contributed equally to this manuscript.
    Affiliations
    Research Service, Denver Veterans Affairs Medical Center, Denver, CO 80220, United States

    Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80045, United States
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  • Author Footnotes
    1 These authors contributed equally to this manuscript.
    Victor Sorribas
    Footnotes
    1 These authors contributed equally to this manuscript.
    Affiliations
    Laboratory of Molecular Toxicology, University of Zaragoza, Spain
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  • Girish Sharma
    Affiliations
    Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80045, United States
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  • Moshe Levi
    Affiliations
    Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, United States
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  • Boris Draznin
    Affiliations
    Research Service, Denver Veterans Affairs Medical Center, Denver, CO 80220, United States

    Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Health Sciences Center, Denver, CO 80045, United States
    Search for articles by this author
  • Author Footnotes
    1 These authors contributed equally to this manuscript.

      Abstract

      Medial artery vascular smooth muscle cell (VSMC) calcification increases the risk of cardiovascular mortality in type 2 diabetes. However, the influence of insulin on VSMC calcification is unclear. We explored the effects of insulin on rat VSMC calcification in vitro and found that in a dose-dependent fashion, insulin attenuates VSMC calcification induced by high phosphate conditions as quantified by the o-cresolphthalein calcium (OCPC) method. In an in vitro model of insulin resistance in which cells are exposed to elevated insulin concentrations and the PI 3-kinase pathway is selectively inhibited, increased VSMC calcification was observed, suggesting that the PI 3-kinase pathway is involved in this attenuating effect of insulin. We postulated that insulin may also have an effect on phosphate or calcium transport in VSMC. We found that insulin increases phosphate transport at 3 and 24 h. This effect was mediated by increased Vmax for phosphate transport but not Km. Because type III sodium-phosphate co-transporters Pit-1 and Pit-2 are found in VSMC, we examined their expression by Western blot and real-time RT-PCR. Insulin stimulates Pit-1 mRNA modestly (*p < 0.01 versus control), an effect inhibited by PD98059 but not by wortmannin. Pit-1 protein expression is induced by insulin, an effect also inhibited by PD98059 (*p < 0.001 versus insulin alone). Our results suggest a role for insulin in attenuating VSMC calcification which may be disrupted in selective insulin signaling impairment seen in insulin resistance. This effect of insulin contrasts with its effect to induce phosphate transport in VSMC.

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