on February 9, 2006
Published online before print February 9, 2006, doi: 10.1161/01.ATV.0000209500.15801.4e
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Submitted on December 14, 2005
Accepted on January 20, 2006
Regulation of Vascular Endothelial Growth Factor Expression and Vascularization in the Myocardium by Insulin Receptor and PI3K/Akt Pathways in Insulin Resistance and Ischemia
Zhiheng He ;
From the Research Division (Z.H., D.M.O., K.J.W., K.U., R.N.K., R.K., G.L.K.), Joslin Diabetes Center, Harvard Medical School, the Cardiovascular Division (P.M.K., S.I.), Beth Israel Deaconess Medical Center, Harvard Medical School, and theWhitaker Cardiovascular Institute (B.W., R.L.), Boston University Medical School, Boston, Mass. Current affiliation for B.W. and R.L.: Cardiovascular Division, Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass.
* To whom correspondence should be addressed. E-mail: george.king{at}joslin.harvard.edu.
Objective--This study characterized the role of insulin receptors and resistance on vascular endothelial growth factor (VEGF) expression and myocardial vascularization in physiological conditions and after ischemia.
Methods and Results--Cardiac microvascular density was reduced by 30% in insulin-resistant Zucker fatty rats versus lean controls. This was associated with a parallel 40% inhibition of insulin-stimulated activation of both Akt and VEGF expression in the myocardium and cardiomyocytes. In contrast, the activation of Erk1/2 by insulin remained unchanged. In cultured cardiomyocytes, insulin or insulin-like growth factor (IGF)-1 increased VEGF mRNA and protein expression by 2-fold. Inhibition of PI3K/Akt, especially Akt2-mediated cascades but not the Ras/MEK/Erk pathway, using chemical inhibitors, dominant negative adenoviral constructs, or siRNA approaches suppressed VEGF mRNA expression by insulin. Ventricular tissues from muscle insulin receptor knockout (MIRKO) mice, which lack insulin receptors in the myocardium, have significant reductions in insulin but not IGF-1 signaling, VEGF expression, and vascular density before and after ischemia versus controls.
Conclusions--Insulin regulates VEGF gene expression and vascularization in the myocardium specifically via insulin receptors and the activation of PI3K/Akt pathway. Selective inhibition of this pathway may lead to the decreases in VEGF expression and capillary density in the myocardium of patients with insulin resistance.
Key words: cardiomyocyte • collateral circulation • diabetes • insulin resistance • vascularization • VEGF
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