Affiliations: [a] Research Institute for Medicines and Pharmaceutical Sciences, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal | [b] Department of Medicine, University of Minnesota Medical School, Minneapolis, MN, USA | [c] Department of Genetics, Cell Biology, and Development, University of Minnesota Medical School, Minneapolis, MN, USA | [d] Department of Biochemistry and Human Biology, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal
Correspondence:
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Correspondence to: Cecília M.P. Rodrigues, iMed.UL, Faculty of Pharmacy, University of Lisbon, Lisbon 1649-003, Portugal. Tel.: +351 21 794 6490; Fax: + 351 21 794 6491; E-mail: cmprodrigues@ff.ul.pt.
Abstract: Amyloid-β (Aβ) peptide-induced neurotoxicity is typically associated with cell death through mechanisms not entirely understood. Here, we investigated stress signaling events triggered by soluble Aβ in differentiated rat neuronal-like PC12 cells. Morphologic evaluation of apoptosis confirmed that Aβ induced nuclear fragmentation that was prevented by pre-treatment with the antiapoptotic bile acid tauroursodeoxycholic acid (TUDCA). In addition, Aβ exposure triggered an early signaling response by the endoplasmic reticulum (ER) and caspase-12-mediated apoptosis, which, however, was independent of the ER-stress pathway. Furthermore, ER stress markers, including GRP94, ATF-6α, CHOP, and eIF2α, were strongly downregulated by Aβ, independent of protein degradation, and partially restored by TUDCA. Calpain inhibition prevented caspase-12 activation and reduced levels of ATF-6α. Importantly, Aβ-induced GRP94 downregulation was related to protein secretion and partially rescued through inhibition of the secretory pathway by geldanamycin and brefeldin. In conclusion, we showed that the ER is a proximal stress sensor for soluble Aβ-induced toxicity, resulting in caspase-12 activation and cell death in PC12 neuronal cells. Moreover, ER chaperone GRP94 secretion was associated with Aβ-induced apoptotic signaling. These data provide new information linking apoptotic properties of Aβ peptide to distinct subcellular mechanisms of toxicity. Further characterization of this signaling pathway is likely to provide new perspectives for modulation of amyloid-induced apoptosis.
