Cyclical mechanical stretch enhances angiopoietin-2 and Tie2 receptor expression in cultured human umbilical vein endothelial cells

Endothelial cells are essential for neovascularization. Angiopoietins and Tie receptors are required for a normal vasculature. How cyclical mechanical stretch affects the expression of components of the angiopoietin system is not known. In this study, we investigated the regulation of angiopoietins and Tie receptors by cyclical mechanical stretch in cultured human umbilical vein endothelial cells (HUVECs). HUVECs grown on a flexible membrane base were stretched by vacuum to 20% elongation, at 60 cycles/min. The levels of angiopoietin-2 protein began to increase as early as 2 h after stretch was initially applied, reached a maximum of 2.7-fold over the control value by 6 h. The Tie2 receptor protein showed the same pattern as Ang-2. These increases in angiopoietin-2 and Tie2 receptor proteins at 6 h were blocked by the addition (30 min before stretch) of the protein kinase C inhibitor G66976 (16 nM) or the tyrosine kinase inhibitor herbimycin A (24 muM). Similar to protein expression, the levels of angiopoietin-2 and Tie2 receptor mRNAs in HUVECs increased 3.1-fold and 2.5-fold respectively after stretch for 6 h. These increases were also blocked by G66976 or herbimycin A. Cyclical mechanical stretch increased (and G66976 or herbimycin A abrogated these increases) the immunohistochemical labelling of angiopoietin-2 and Tie2 receptor after a 6 h stretch. The levels of angiopoietin-1 and Tiel receptor proteins, mRNAs and immunohistochemical staining were unaffected by cyclical mechanical stretch. Thus cyclical mechanical stretch activates the expression of angiopoietin-2 and the Tie2 receptor, but not angiopoietin-1 or the Tie1 receptor, in cultured HUVECs. This mechanical effect is probably mediated by the tyrosine kinase and protein kinase C pathways.