β-Estradiol Protects Against Acidosis-Mediated and Ischemic Neuronal Injury by Promoting ASIC1a (Acid-Sensing Ion Channel 1a) Protein Degradation

Background and Purpose-Sex differences in the incidence and outcome of stroke have been well documented. The severity of stroke in women is, in general, significantly lower than that in men, which is mediated, at least in part, by the protective effects of beta-estradiol. However, the detailed mechanisms underlying the neuroprotection by beta-estradiol are still elusive. Recent studies have demonstrated that activation of ASIC1a (acid-sensing ion channel 1a) by tissue acidosis, a common feature of brain ischemia, plays an important role in ischemic brain injury. In the present study, we assessed the effects of beta-estradiol on acidosis-mediated and ischemic neuronal injury both in vitro and in vivo and explored the involvement of ASIC1a and underlying mechanism. Methods-Cultured neurons and NS20Y cells were subjected to acidosis-mediated injury in vitro. Cell viability and cytotoxicity were measured by methylthiazolyldiphenyl-tetrazolium bromide and lactate dehydrogenase assays, respectively. Transient (60 minutes) focal ischemia in mice was induced by suture occlusion of the middle cerebral artery in vivo. ASIC currents were recorded using whole-cell patch-clamp technique while intracellular Ca2+ concentration was measured with fluorescence imaging using Fura-2. ASIC1a expression was detected by Western blotting and quantitative real-time polymerase chain reaction. Results-Treatment of neuronal cells with beta-estradiol decreased acidosis-induced cytotoxicity. ASIC currents and acid-induced elevation of intracellular Ca2+ were all attenuated by beta-estradiol treatment. In addition, we showed that beta-estradiol treatment reduced ASIC1a protein expression, which was mediated by increased protein degradation, and that estrogen receptor alpha was involved. Finally, we showed that the level of ASIC1a protein expression in brain tissues and the degree of neuroprotection by ASIC1a blockade were lower in female mice, which could be attenuated by ovariectomy. Conclusions-beta-estradiol can protect neurons against acidosis-mediated neurotoxicity and ischemic brain injury by suppressing ASIC1a protein expression and channel function.