Mitochondrial ROS-PKCε signaling axis is uniquely involved in hypoxic increase in [Ca2+]i in pulmonary artery smooth muscle cells

The molecular mechanisms underlying hypoxic responses in pulmonary and systemic arteries remain obscure. Here we for the first time report that acute hypoxia significantly increased total PKC and PKCε activity in pulmonary, but not mesenteric arteries, while these two tissues showed comparable PKCε protein expression and activation by the PKC activator phorbol 12-myristate 13-acetate. Hypoxia induced an increase in intracellular reactive oxygen species (ROS) generation in isolated pulmonary artery smooth muscle cells (PASMCs), but not in mesenteric artery SMCs. Inhibition of mitochondrial ROS generation with rotenone, myxothiazol, or glutathione peroxidase-1 overexpression prevented hypoxia-induced increases in total PKC and PKCε activity in pulmonary arteries. The inhibitory effects of rotenone were reversed by exogenous hydrogen peroxide. A PKCε translocation peptide inhibitor or PKCε gene deletion decreased hypoxic increase in [Ca2+]i in PASMCs, whereas the conventional PKC inhibitor GÖ6976 had no effect. These data suggest that acute hypoxia may specifically increase mitochondrial ROS generation, which subsequently activates PKC, particularly PKCε, contributing to hypoxia-induced increase in [Ca2+]i and contraction in PASMCs.