Simulated Ischemia in Flow-Adapted Endothelial Cells Leads to Generation of Reactive Oxygen Species and Cell Signaling

Abstract

Abstract —We have previously shown that increased reactive oxygen species (ROS) generation occurs with ischemia in the oxygenated lung and have hypothesized that mechanotransduction is the initiating event. In the present study, we developed an in vitro model of oxygenated ischemia by interrupting medium flow to flow-adapted bovine pulmonary artery endothelial cells in an artificial capillary system. Cellular oxygenation during the “ischemic” period was maintained by perfusing medium over the abluminal surface of porous capillaries. Cells were assessed for ROS generation, nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) binding activities, and DNA synthesis using dichlorofluorescein fluorescence by flow cytometry and spectrofluorometry, electrophoretic mobility shift assay of nuclear extracts with NF-κB–specific or AP-1–specific 32 P-labeled oligonucleotides, and 3 H-thymidine incorporation into DNA. Cells that were flow adapted for 2 to 7 days with 1 to 2 dyne/cm 2 shear stress exhibited a 1.6- to 1.9-fold increase in ROS generation during 1 hour of simulated ischemia compared with continuously perfused cells. This effect was abolished by diphenyleneiodonium chloride (DPI), indicating a role for a flavoprotein such as NADPH oxidase. The increase in ROS generation with ischemia was similar for cells from low and high passages. With ischemia, flow-adapted cells exhibited increases of 1.7-fold in nuclear NF-κB and 1.5-fold in nuclear AP-1; these changes were abolished by pretreatment with N -acetylcysteine or DPI. Ischemia for 24 hours resulted in a 1.8-fold increase of 3 H-thymidine incorporation into DNA and a significant increase of cells entering the cell cycle, as indicated by flow cytometry with propidium iodide. We conclude that flow-adapted endothelial cells generate ROS with ischemia that results in activation of NF-κB and AP-1 and an increase of DNA synthesis. This effect is not mediated by hypoxia, implicating a role for mechanotransduction in ischemia-mediated cell signaling.