Hydrogen peroxide induces S1P1 receptors and sensitizes vascular endothelial cells to sphingosine 1-phosphate, a platelet-derived lipid mediator

Sphingosine 1-phosphate (S1P) is a platelet-derived angiogenic lipid growth factor, modulating G-protein-coupled S1P1 receptors (S1P1-R) to activate endothelial nitric oxide synthase (eNOS), as well as MAPK pathways in endothelial cells. We explored whether and how hydrogen peroxide (H2O2), a representative reactive oxygen species, alters S1P1-R expression and influences S1P signaling in cultured bovine aortic endothelial cells (BAECs). When BAECs are treated with pathophysiologically relevant concentrations of H2O2 (150 μM for 30 min), S1P1-R protein expression levels are acutely augmented by ∼30-fold in a dose-dependent fashion. When BAECs have been pretreated with H2O2, subsequent S1P stimulation (100 nM) leads to a higher degree of eNOS enzyme activation (assessed as intracellular cGMP content, 1.7 ± 0.2-fold vs. no H2O2 pretreatment groups, P < 0.05), associated with a higher magnitude of phosphorylation responses of eNOS and MAPK ERK1/2. PP2, an inhibitor of Src-family tyrosine kinase, abolished the effects of H2O2 on both S1P1-R protein upregulation and enhanced BAEC responses to S1P. H2O2 does not augment S1P1 mRNA expression, whereas VEGF under identical cultures leads to increases in S1P1 mRNA signals. Whereas H2O2 attenuates proliferation of BAECs, addition of S1P restores growth responses of these cells. These results demonstrate that extracellularly administered H2O2 increases S1P1-R expression and promotes endothelial responses for subsequent S1P treatment. These results may identify potentially important points of cross-talk between reactive oxygen species and sphingolipid pathways in vascular responses.