title: Downregulation of AβPP enhances both calcium content of endoplasmic reticulum and acidic stores and the dynamics of store operated calcium channel activity.
abstract: The amyloid-β protein precursor (AβPP) is a type-1 transmembrane protein involved in Alzheimer's disease (AD). It has become increasingly evident that AβPP, its protein-protein interactions, and its proteolytical fragments may affect calcium homeostasis and vice versa. In addition, there is evidence that calcium dysregulation contributes to AD. To study the role of AβPP in calcium homeostasis, we downregulated its expression in SH-SY5Y cells using shRNA (SH-SY5Y/AβPP-) or increased expression of AβPP695 by transfection (SH-SY5Y/AβPP+). The levels of cytosolic Ca2+ after treatment with thapsigargin, monensin, activation of capacitative calcium entry (CCE), and treatment with SKF, a store operated channel (SOCs) inhibitor, were measured by fura-2AM fluorimetry. SH-SY5Y/AβPP+ cells show reduced response to thapsigargin and reduced CCE, although this reduction is not statistically significant. On the other hand, we found that, relative to SH-SY5Y, SH-SY5Y/AβPP- cells show a significant increase in the response to thapsigargin but not in CCE and their SOCs were more susceptible to SKF inhibition. Additionally, downregulation of AβPP resulted in increased response to monensin that induces calcium release from acidic stores. The increase of calcium release from the endoplasmic reticulum and the acidic stores, when AβPP is downregulated, could be attributed to elevated Ca2+ content or to a dysregulation of Ca2+ transfer through their membranes. These data, along with already existing evidence regarding the role of AβPP in calcium homeostasis and the early occurring structural and functional abnormalities of endosomes, further substantiate the role of AβPP in calcium homeostasis and in AD.
authors.affiliation: Division of Human and Animal Physiology, Department of Biology, National and Kapodistrian University of Athens, Ilisia, Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Chatzistavraki
authors.forename: Elli
authors.initials: E
authors.lastname: Kyratzi
authors.forename: Angeliki
authors.initials: A
authors.lastname: Fotinopoulou
authors.forename: Panagiota
authors.initials: P
authors.lastname: Papazafiri
authors.forename: Spiros
authors.initials: S
authors.lastname: Efthimiopoulos
mesh_terms: D016564:Amyloid beta-Protein Precursor / Q000037:antagonists & inhibitors* / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D056004:Molecular Dynamics Simulation
chemical_list: D016564:Amyloid beta-Protein Precursor; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002118:Calcium