Astrocyte-like cells as a main target for estrogen action during neuronal differentiation

Neurospheres from the subventricular zone of adult mice were used as an experimental model to analyse the early differential effects of 17β-estradiol (17β-E2). Both floating and differentiating neurospheres expressed estrogen receptors (ERs) α and β. The initial phases of differentiation coincided with a peak of ERα expression as by Western blot analysis. Treatment with 10 nM 17β-E2 induced a significant increase in the glial fibrillary acidic protein (GFAP)-positive population and a greater expression of GFAP, an effect sensitive to the estrogen receptor antagonist ICI 182,780. The GFAP-positive cell population induced by 17β-E2 was characterized by a highly differentiated phenotype and intense immunostaining as by immunocytochemistry and flow cytometry. These cells co-expressed ERα and were positive to BrdU. 17β-E2 also affected neuronal differentiation by rapidly and transiently increasing the percentage of polysialylated–neural cell adhesion molecule (PSA–NCAM)-positive progenitors, and by accelerating the appearance of a mature neuronal phenotype, as evaluated by microtubule-associated protein 2 (MAP2) staining. Our results point to a key role for ERα during initial phases of differentiation of brain cells and to an effect of 17β-E2 that sequentially involves both glia and neurons.