Role of redox signaling in the autonomous proliferative response of endothelial cells to hypoxia

Endothelial cells exhibit an autonomous proliferative response to hypoxia, independent of paracrine effectors. In cultured endothelial cells of porcine aorta, we analyzed the signaling of this response, with a focus on the roles of redox signaling and the MEK/ERK pathway. Transient hypoxia (1 hour) stimulated proliferation by 61+/-4% (n=16; P<0.05 versus control), quantified after 24 hours normoxic postincubation. Hypoxia induced an activation of ERK2 and of NAD(P)H oxidase and a burst of reactive oxygen species (ROS), determined by DCF fluorescence. To inhibit the MEK/ERK pathway, we used PD 98059 (PD, 20 μmol/L); to downregulate NAD(P)H oxidase, we applied p22(phox) antisense oligonucleotides; and to inhibit mitochondrial ROS generation, we used the ubiquinone derivate mitoQ (MQ, 10 μmol/L). All three inhibitions suppressed the proliferative response: PD inhibited NAD(P)H oxidase activation; p22(phox) antisense transfection did not inhibit ERK2 activation, but suppressed ROS production; and MQ inhibited ERK2 activation and ROS production. The autonomous proliferative response depends on the MEK/ERK pathway and redox signaling steps upstream and downstream of ERK. Located upstream is ROS generation by mitochondria, downstream is NAD(P)H oxidase.