17β-Estradiol increases expression of the oxidative stress response and DNA repair protein apurinic endonuclease (Ape1) in the cerebral cortex of female mice following hypoxia

While it is well established that 17β-estradiol (E₂) protects the rodent brain from ischemia-induced damage, it has been unclear how this neuroprotective effect is mediated. Interestingly, convincing evidence has also demonstrated that maintaining or increasing the expression of the oxidative stress response and DNA repair protein apurinic endonuclease 1 (Ape1) is instrumental in reducing ischemia-induced damage in the brain. Since E ₂ increases expression of the oxidative stress response proteins Cu/Zn superoxide dismutase and thioredoxin in the brain, we hypothesized that E₂ may also increase Ape1 expression and that this E ₂-induced expression of Ape1 may help to mediate the neuroprotective effects of E₂ in the brain. To test this hypothesis, we utilized three model systems including primary cortical neurons, brain slice cultures, and whole animals. Although estrogen receptor α and Ape1 were expressed in primary cortical neurons, E₂ did not alter Ape1 expression in these cells. However, immunofluorescent staining and quantitative Western blot analysis demonstrated that estrogen receptor α and Ape1 were expressed in the nuclei of cortical neurons in brain slice cultures and that E₂ increased Ape1 expression in the cerebral cortex of these cultures. Furthermore, Ape1 expression was increased and oxidative DNA damage was decreased in the cerebral cortices of ovariectomized female C57Bl/6J mice that had been treated with E₂ and exposed to hypoxia. Taken together, our studies demonstrate that the neuronal microenvironment may be required for increased Ape1 expression and that E₂ enhances expression of Ape1 and reduces oxidative DNA damage, which may in turn help to reduce ischemia-induced damage in the cerebral cortex and mediate the neuroprotective effects of E₂.