Clinical epidemiology has indicated that the endothelial injury is a potential contributor to the pathogenesis of ischemic neurovascular damage. In this report, we assessed S-nitrosylation and nitration of Keap1 to identify downstream
nitric oxide redox signaling targets into endothelial cells during
ischemia. Here,
oxygen-
glucose deprivation (OGD) exposure initiates the nuclear import of Keap1 in endothelial cells, which interacted with nuclear-localized Nrf2, as demonstrated through co-immunoprecipitation and immunocytochemical assay. Paralleling the
ischemia-induced nuclear import of Keap1, increased
nitrotyrosine immunoreactivity in endothelial cells was also observed. Consistently, the addition of
peroxynitrite provoked nuclear import of Keap1 and a concomitant Nrf2 nuclear import in the endothelial cells. Importantly, pharmacological inhibition of nitrosative stress by
melatonin partially inhibited the OGD-induced constitutive nuclear import of Keap1 and subsequently disturbance of Nrf2/Keap1 signaling. Moreover, the effect of
melatonin on nitration and S-nitrosylation of keap1 was examined in endothelial cells with 6 hr OGD exposure. Here, we demonstrated that OGD induced
tyrosine nitration of Keap1, which was blocked by
melatonin treatment, while there were no significant changes in S-nitrosylation of Keap1. The specific
amino acid residues of Keap1 involved in
tyrosine nitration were identified as Y473 by mass spectrometry. Moreover, the protective role of
melatonin against damage to endothelial tight junction integrity was addressed by ZO-1 expression, paralleled with the restored
heme oxygenase-1 levels during OGD. Together, our results emphasize that upon nitrosative stress, the protective effect of
melatonin on endothelial cells is likely mediated at least in part by inhibition of
ischemia-evoked
protein nitration of Keap1, hence contributing to relieve the disturbance of Nrf2/Keap1 antioxidative signaling.