The stimulative effects and the associated mechanism of low-intensity ultrasound on endothelial cells were investigated in this study. Human umbilical cord endothelial cells (HUVECs) were exposed to 1 MHz pulsed ultrasound at 34 mW/cm2 for 10 min daily. The cell proliferation, nitric oxide release, intracellular calcium concentration, and endothelial nitric oxide synthase (eNOS) gene and protein expressions after ultrasound exposure were analyzed. It was found that ultrasound exposure did not change the cell proliferation, but it enhanced the release of nitric oxide and Ca2+ ions, and increased the eNOS activity. The induced phosphorylation of eNOS (Ser1177) by the ultrasound exposure was inhibited by the addition of N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinoline sulfonamide (H89, a protein kinase A inhibitor), but not 2-(4-morpholino)-8-phenyl-4H-1-benzopyran-4-one hydrochloride (LY294002, a phosphoatidylinositol 3-kinase inhibitor). The induced phosphorylation of Akt (protein kinase B, Ser473) by the ultrasound exposure was inhibited by the addition of LY294002, but not by the presence of H89. The results also applied to bovine carotid artery endothelial cells (BAECs) exposed to ultrasound at a larger intensity (68 mW/cm2). The above experiments suggested that low-intensity ultrasound may promote eNOS activity of endothelial cells via the phosphatidylinositol 3-kinase/Akt/protein kinase A signaling pathway. This may have implications on the therapeutic effect of ultrasound in tissue repair.
Shear stress stimulates phosphorylation of protein kinase A substrate proteins including endothelial nitric oxide synthase in endothelial cells
