Estradiol prevents amyloid-beta peptide-induced cell death in a cholinergic cell line via modulation of a classical estrogen receptor.

The pathology of Alzheimer's disease includes amyloid-beta peptide aggregation that contributes to degeneration of cholinergic neurons. Even though the underlying molecular mechanisms remain unclear, recent in vitro evidence supports a protective role for estrogens against several neurotoxic agents. Here we report that, in a murine cholinergic cell line (SN56), the massive cell death induced by 1-40 fragment of amyloid-beta peptide was prevented by 17beta-estradiol through a mechanism that may involve estrogen receptor activation. The protective effect of estradiol was observed in a dose-dependent manner, and was completely blocked by the pure antiestrogen ICI 182,780. In contrast, the inactive isomer 17alpha-estradiol consistently showed weaker neuroprotection than the native hormone that was unaffected by ICI 182,780 treatment. In addition, equivalent concentrations of 17beta-estradiol enhanced luciferase activity in cells transfected with a luciferase reporter gene driven by tandem estrogen response elements. Estrogen-induced luciferase activity was blocked by ICI 182,780, indicating estrogen receptor-dependent transcriptional activity. We also observed by reverse transcription-polymerase chain reaction, Western blot and immunocytochemistry that increasing concentrations of 17beta-estradiol enhanced the expression of estrogen receptor alpha mRNA and protein during amyloid-beta-induced toxicity. Under these conditions, it was found by confocal microscopy that the localization of estrogen receptor alpha in the absence of hormone was mainly extranuclear. However, the receptor was consistently observed also at the nuclear region after estrogen exposure. Overall, these data suggest that estrogen may exert neuroprotective effects against amyloid-beta-induced toxicity by activation of estrogen receptor-mediated pathways. In addition, intracellular estrogen receptors are up-regulated by their cognate hormone even during exposure to neurotoxic agents.