HYPOXIA-INDUCED CELL DEATH IS PREVENTED BY 17-Â ESTRADIOL VIA ESTROGEN RECEPTORS IN DEVELOPING BRAIN

S.FISZER DE PLAZAS; V.M.POZO DEVOTO; S.GIUSTI

San Diego, California

Congreso; Society for Neuroscience 2007, 37th Annual Meeting; 2007

Neuroprotective activities of estrogens have been demonstrated against a variety of insults including excitotoxicity, oxidative stress and  cerebral ischemia under certain conditions. However, the molecular mechanisms of estrogen neuroprotection are still unclear. We aimed to determine if 17-b estradiol (E2) administration 30 min post-hypoxia was neuroprotective and if this actions were mediated through estrogen receptors (ER). For this purpose, 12-embryonic-day old chicken embryos were subjected to acute hypoxia (8%[O2], 60 min), followed by different reoxygenation periods: 2,4,6 and 9h. To test the neuroprotective role of E2 and its mechanism, embryos were injected 30 min after the end of hypoxia with E2 alone or with ICI 182,780, a competitive antagonist of ER. Cytochrome c (cyt c) release, an indicator of mitochondria-mediated apoptosis, was measured by western blot in cytosolic extracts from optic lobes and DNA fragmentation, a cell-death marker, was detected by TUNEL fluorescence on optic lobe sections.  We found a maximal increase of cyt c release at 4h ( 285.3±49.6% from control values, P< 0.01) followed by an increase of TUNEL+ cells two hours later ( 181±13% form control values, P<0.01). Administration of E2 (0.5 mg/egg) 30 min post-hypoxia prevented cyt c release and DNA fragmentation when compared to vehicle-treated animals. In the E2-ICI 182,780 treated embryos cyt c release at 4 h p-hx was similar to the hypoxic embryos, thus suggesting the requirement of E2-ER interaction for E2 neuroprotective effects. In conclusion, E2  prevents hypoxia induced cyt c release and posterior cell death and this effect is mediated by estrogen receptors.