Low-intensity pulsed ultrasound promotes apoptosis and inhibits angiogenesis via p38 signaling-mediated endoplasmic reticulum stress in human endothelial cells

Aberrant increase in angiogenesis contributes to the progression of malignant solid tumors. An alternative anti-angiogenesis therapy is critical for cancer, since the current anti-angiogenesis drugs lack specificity for tumor cells. In the present study, the effects and mechanisms of low-intensity pulsed ultrasound (LIPUS) on human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells (HMECs) were investigated, and the therapeutic potential of this technology was assessed. HUVECs and HMECs were treated with LIPUS (0.5 MHz; 210 mW/cm(2)) for 1 min and cultured for 24 h. Flow cytometry and Cell Counting Kit-8 assays demonstrated that LIPUS treatment at a dose of 210 mW/cm(2) promoted apoptosis and decreased the viability in HUVECs and HMECs. Real-time cell analysis also revealed that LIPUS did not affect the proliferation or migration of HUVECs. An endothelial cell tube formation assay indicated that LIPUS treatment inhibited the angiogenic ability of HUVECs and HMECs. Furthermore, LIPUS increased the protein levels of the apoptosis-associated cleaved Caspase-3 and decreased the B-cell lymphoma-2 levels. LIPUS increased the phosphorylation of p38 mitogen-activated protein kinase (MAPK), and the levels of endoplasmic reticulum (ER) stress-associated markers, including activating transcription factor-4 (ATF-4) and phosphorylated eukaryotic initiation factor 2α (eIF2α). The p38 inhibitor SB203580 reversed the pro-apoptotic and anti-angiogenic effects of LIPUS in cells. Finally, inhibition of p38 decreased the LIPUS-induced elevation of p-eIF2α and ATF-4 levels. Taken together, these results suggested that LIPUS promoted apoptosis and inhibited angiogenesis in human endothelial cells via the activation of p38 MAPK-mediated ER stress signaling.