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Functional Modulation of Nuclear Steroid Receptors by Tauroursodeoxycholic Acid Reduces Amyloid ß-Peptide-Induced Apoptosis

Centro de Patogénese Molecular (S.S., J.D.A., P.M.B., R.M.R., R.E.C., M.M.A., C.M.P.R.), Faculty of Pharmacy, University of Lisbon, Lisbon 1600-083, Portugal; and Departments of Medicine (C.J.S.), and Genetics, Cell Biology, and Development (C.J.S.), University of Minnesota Medical School, Minneapolis, Minnesota 55455

Address all correspondence and requests for reprints to: Dr. Cecília M. P. Rodrigues, Avenida das Forças Armadas, 1600–083 Lisbon, Portugal. E-mail: cmprodrigues{at}ff.ul.pt.

Tauroursodeoxycholic acid (TUDCA) prevents amyloid ß-peptide (Aß)-induced neuronal apoptosis, by modulating both classical mitochondrial pathways and specific upstream targets. In addition, activation of nuclear steroid receptors (NSRs), such as the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) differentially regulates apoptosis in the brain. In this study we investigated whether TUDCA, a cholesterol-derived endogenous molecule, requires NSRs for inhibiting Aß-induced apoptosis in primary neurons. Our results confirmed that TUDCA significantly reduced Aß-induced apoptosis; in addition, the fluorescently labeled bile acid molecule was detected diffusely in both cytoplasm and nucleus of rat cortical neurons. Interestingly, experiments using small interfering RNAs (siRNAs) revealed that, in contrast to GR siRNA, MR siRNA abolished the antiapoptotic effect of TUDCA. Aß incubation reduced MR nuclear translocation while increasing nuclear GR levels. Notably, pretreatment with TUDCA markedly altered Aß-induced changes in NSRs, including MR dissociation from its cytosolic chaperone, heat shock protein 90, and subsequent translocation to the nucleus. Furthermore, when a carboxy terminus-deleted form of MR was used, nuclear trafficking of both MR and the bile acid was abrogated, suggesting that they translocate to the nucleus as a steroid-receptor complex. Transfection experiments with wild-type or mutant MR confirmed that this interaction was required for TUDCA protection against Aß-induced apoptosis. Finally, in cotransfection experiments with NSR response element reporter and overexpression constructs, pretreatment with TUDCA significantly modulated Aß-induced changes in MR and GR transactivation. In conclusion, these results provide novel insights into the specific cellular mechanism of TUDCA antiapoptotic function against Aß-induced apoptosis and suggest targets for potential therapeutic intervention.

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Nuclear Receptors:   GR  |  MR