Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, C43
Insulin stabilizes microvascular endothelial barrier function via PI3K/Akt-mediated Rac1 activation
M. Aslam1, J. Thom2, H. Piper1, T. Noll1, D. Gündüz2
1. Institute of Physiology, Justus Liebig University, Giessen, Germany. 2. Zentrum f?r Innere Medizin, Abteilung f?r Kardiologie/Angiologie, Universit?tsklinikum Giessen und Marburg GmbH, Giessen, Germany.
Insulin is a key regulator of metabolism, but besides this it also confers protective effects on the cardiovascular system. Here the mechanism is analyzed by which insulin stabilizes endothelial barrier function. Insulin reduced basal and antagonized TNFα-induced macromolecule permeability of rat coronary microvascular endothelial monolayers. It also abolished reperfusion-induced vascular leakage in isolated-perfused rat hearts. Insulin induced dephosphorylation of the regulatory myosin light chains as well as translocation of actin and VE-cadherin to cell borders, indicating a reduction in contractile activation and stabilization of cell adhesion structures. These protective effects were blocked by genistein or HNMP(AM)3, a pan-tyrosine-kinase or specific insulin-receptor-kinase inhibitor, respectively. Insulin stimulated PI3K/Akt pathway, NO production and activated Rac1. Inhibition of PI3K/Akt abrogated, while inhibition of the eNOS/guanylyl cyclase pathway partially inhibited Rac1 activation and insulin-induced barrier protection. Inhibition of Rac1 abrogated the assembly of actin at cell borders. Accordingly, it abolished the protective effect of insulin on barrier function of cultured endothelial monolayer as well as the intact coronary system of ischemic-reperfused hearts. Insulin stabilizes endothelial barrier via inactivation of the endothelial contractile machinery and enhancing cell-cell adhesions. These effects are mediated via PI3K/Akt- and NO/cGMP-induced Rac1 activation.
Where applicable, experiments conform with Society ethical requirements