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Glia Mediates the Neuroprotective Action of Estradiol on ß-Amyloid-Induced Neuronal Death

Departments of Experimental and Clinical Pharmacology (M.A.S., M.Ch., S.M.), Internal Medicine (C.V., M.Ca.), and Pharmaceutical Sciences (A.C.), University of Catania, 95125 Catania, Italy; DISCAFF, University of Piemonte Orientale (P.L.C.), 28100 Novara, Italy; Department of Human Physiology and Pharmacology, University of Rome La Sapienza (F.N.), 00185 Rome, Italy; and INM Neuromed (F.N.), 86077 Pozzilli, Italy

Address all correspondence and requests for reprints to: Dr. M. A. Sortino, Department of Experimental and Clinical Pharmacology, University of Catania, Viale A. Doria 6, 95125 Catania, Italy. E-mail: msortino{at}unict.it.

17ß-Estradiol (17ß-E₂) is known to exert neuroprotective activity against ß-amyloid, but its exact target and mechanism of action in this effect have not been elucidated. The involvement of astroglia in neuroprotection of 17ß-E₂ against the ß-amyloid fragment [ßAP_(25–35)] has been evaluated using an experimental paradigm in which medium conditioned from rat astroglia pretreated with 17ß-E2 was transferred to pure rat cortical neurons challenged with 25 µM ßAP_(25–35) for 24 h. The toxicity of ßAP_(25–35) was assessed by flow cytometry, evaluating the ability of the peptide to induce an aberrant mitotic cell cycle in neurons. The results obtained indicate that conditioned medium from astrocytes preexposed to 17ß-E₂ for 4 h increased the viability of cortical neurons treated with ßAP_(25–35). This effect was not modified by treatment with the estrogen receptor antagonist ICI 182,780, added directly to neurons, nor was it mimicked by direct addition of 17ß-E₂ to neuronal cultures during exposure to ßAP_(25–35). A soluble factor stimulated by 17ß-E₂ seemed to be involved, and accordingly, the intracellular and released levels of TGF-ß1 were increased by 17ß-E₂ treatment, as established by Western blot analysis. In addition, the intracellular content of TGF-ß1 in immunopositive cells, as detected by flow cytometry, was reduced, suggesting that 17ß-E₂ stimulated mainly the release of the cytokine. In support of a role for TGF-ß1 in astrocyte-mediated 17ß-E₂ neuroprotective activity, incubation with a neutralizing anti-TGF-ß1 antibody significantly modified the reduction of neuronal death induced by 17ß-E₂-treated astrocyte-conditioned medium.

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