Estrogen receptor subtypes alpha and beta contribute to neuroprotection and increased Bcl-2 expression in primary hippocampal neurons

Estrogen receptor (ER) mediated neuroprotection has been demonstrated in both in vitro and in vivo model systems. However, the relative contribution by either ER subtype, ERα or ERβ, to estrogen-induced neuroprotection remains unresolved. To address this question, we investigated the impact of selective ER agonists for either ERα, PPT, or ERβ, DPN, to prevent neurodegeneration in cultured hippocampal neurons exposed to excitotoxic glutamate. Using three indicators of neuronal viability and survival, we demonstrated that both the ERα selective agonist PPT and the ERβ selective agonist DPN protected hippocampal neurons against glutamate-induced cell death in a dose-dependent manner, with the maximal response occurring at 100 pM. Further analyses showed that both PPT and DPN enhanced Bcl-2 expression in hippocampal neurons, with an efficacy comparable to their neuroprotective capacity. Collectively, the present data indicate that activation of either ERα or ERβ can promote neuroprotection in hippocampal neurons, suggesting that both receptor subtypes could be involved in estrogen neuroprotection. As ERβ is highly expressed in the brain and has little or no expression in the breast or uterus, discovery and design of ERβ selective molecules could provide a strategy for activating the beneficial effects of estrogen in the brain without activating untoward effects of estrogen in reproductive organs.