Mitochondria-Derived Reactive Oxygen Species Mediate Heme Oxygenase-1 Expression in Sheared Endothelial Cells

Bovine aortic endothelial cells (ECs) respond to nitric oxide (NO) donors by activating the redox-sensitive NF-E2-related factor 2/antioxidant response element pathway and up-regulating heme oxygenase (HO)-1 expression. EC exposure to steady laminar shear stress causes a sustained increase in NO, a transient increase in reactive oxygen species (ROS), and activation of the HO-1 gene. Because steady laminar flow increases the mitochondrial superoxide (O-(2)over dot(-).) production, we hypothesized that mitochondria-derived ROS play a role in shear-induced HO-1 expression. Flow (10 dynes/cm(2), 6 h)induced expression of HO-1 protein was abolished when BAECs were preincubated and sheared in the presence of either N-G-nitro-L-arginine methyl ester or N-acetyl-L-cysteine, suggesting that either NO or ROS up-regulates HO-1. Ebselen and diphenylene iodonium blocked HO-1 expression, and uric acid had no effect. The mitochondrial electron transport chain inhibitors, myxothiazol, rotenone, or antimycin A, and the mitochondria-targeted antioxidant peptide, Szeto-Schiller (SS)31, which scavenges O-(2) over dot(-), hydrogen peroxide (H2O2), peroxynitrite, and hydroxyl radicals, markedly inhibited the increase in HO-1 expression. These data collectively suggest that mitochondrial H2O2 mediates the HO-1 induction. MitoSOX and 2', 7'-dichlorofluorescin (DCF) fluorescence showed that mitochondrial O-(2) over dot(-). levels and intracellular peroxides, respectively, are higher in sheared ECs compared with static controls and, in part, dependent on NO. SS-31 significantly inhibited both the shear-induced MitoSOX and DCF fluorescence signals. Either phosphatidylinositol 3-kinase or mitogen-activated protein kinase cascade inhibitors blocked the HO-1 induction. In conclusion, under shear, EC mitochondria-derived H2O2 diffuses to the cytosol, where it initiates oxidative signaling leading to HO-1 up-regulation and maintenance of the atheroprotective EC status.