An oestrogen membrane receptor participates in estradiol actions for the prevention of amyloid-β peptide1-40-induced toxicity in septal-derived cholinergic SN56 cells

Although oestrogen [17beta-estradiol (E2)]-related neuroprotection has been demonstrated in different models, the involvement of non-classical oestrogen receptors (ERs) remains unexplored. Using the SN56 cholinergic cell line, we present evidence indicating that an ER associated with the plasma membrane participates in oestrogen-dependent inhibition of cell death induced by amyloid-beta peptide (Abeta) toxicity. Similarly to E2 alone, a 15-min exposure to estradiol-horseradish peroxidase (E-HRP) significantly reduced Abeta-induced cell death. This effect was decreased by the ER antagonist ICI 182,780 as well as by MC-20 antibody directed to a region neighbouring the ligand-binding domain of ERalpha. Using confocal microscopy on unpermeabilized SN56 cells exposed to MC-20 antibody, we identified a protein at the plasma membrane level. Western blot analysis of purified SN56 cell membrane fractions using MC-20 antibody revealed the presence of one band with the same electrophoretic mobility as intracellular ERalpha. Using conjugated forms of the steroid, E-HRP and E2 conjugated to bovine serum albumin-FITC, we demonstrated by confocal microscopy that SN56 cells contain surface binding sites for E2. Binding of both conjugates was blocked by pre-incubation with E2 and decreased by either ICI 182,780 or MC-20 antibody in a concentration-dependent manner. Thus, a membrane-related ER that shares some structural homologies with ERalpha may participate in oestrogen-mediated neuroprotection.