Depolarization is the trigger for PI3K/Akt activation and leads to ROS production in a model of pulmonary ischemia

Abstract

We reported that ischemia or loss of shear in the lung endothelium causes endothelial plasma membrane depolarization (via KATP channel closure) that leads to NADPH oxidase activation and reactive oxygen species (ROS) production. Both high K+ induced depolarization and ischemia resulted in activation of PI3K; its inhibitor (wortmanin) prevented NADPH oxidase assembly and ROS production with ischemia. We used pulmonary microvascular endothelial cells, either wild type (WT), KATP−/−, gp91phox−/− or WT infected with dominant negative (DN) PI3K, and isolated Akt‐1 null lungs to study signal transduction with ischemia. Cells with DN PI3K and lungs with Akt1−/−, both showed the depolarization response but failed to show NADPH oxidase assembly and ROS generation. In WT cells, Akt activation (as monitored by the expression of p‐Akt) that was observed with ischemia was abolished in KATP−/− but not in gp91phox−/− cells. Blocking the ischemic depolarization by addition of cromakalim (KATP channel agonist) to gp91phox−/− cells prevented Akt phosphorylation. These results indicate that KATP induced depolarization leads to NADPH oxidase assembly and ROS generation and precedes PI3K/Akt activation. Thus, ROS which has hitherto been shown to activate PI3K/Akt in other systems lies downstream of PI3K/Akt in our model of pulmonary ischemia.