title: Phosphatase 2A Inhibition Affects Endoplasmic Reticulum and Mitochondria Homeostasis Via Cytoskeletal Alterations in Brain Endothelial Cells.
abstract: The loss of endothelial cells (ECs) homeostasis is a trigger for cerebrovascular dysfunction that is a common event in several neurodegenerative disorders such as Alzheimer's disease (AD). The present work addressed the role of phosphatase 2A (PP2A) in cytoskeleton rearrangement, endoplasmic reticulum (ER) homeostasis, ER-mitochondria communication and mitochondrial dynamics in brain ECs. For this purpose, rat brain endothelial (RBE4) cells were exposed to okadaic acid, a well-known inhibitor of PP2A activity. An increase in the levels of tau phosphorylated on Ser396 and Thr181 residues was observed upon PP2A inhibition, concomitantly with the rearrangement of microtubules and actin cytoskeleton. Under these conditions, an increase in the levels of ER stress markers, namely GRP78, XBP1, p-eIF2αSer51, and ERO1α, was observed. Moreover, PP2A inhibition upregulated the Sigma-1 receptor, an ER chaperone located at the ER-mitochondria interface, and enhanced inter-organelle Ca2+transfer, culminating in mitochondrial Ca2+overload and activation of mitochondria-dependent apoptosis. The inhibition of PP2A activity also promoted an alteration of the structural and spatial mitochondria network due to upregulation of mitochondrial fission (Drp1 and Fis1) and fusion (Mfn1, Mfn2 and OPA1) proteins, suggesting detrimental changes in mitochondrial dynamics. In accordance with our in vitro observations, brain vessels from 3xTg-AD mice showed a significant decrease in PP2A protein levels accompanied by an increase in tau phosphorylated on Ser396 and GRP78 protein levels. Collectively, these results suggest that the loss of cerebrovascular homeostasis that occurs in AD might be a downstream event of the compromised activity and/or expression of PP2A, which is observed in the brain of individuals affected with this devastating neurodegenerative disorder.
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal.|Faculty of Medicine, University of Coimbra, Coimbra, 3000-548, Portugal.
authors.forename: Ana I
authors.initials: AI
authors.lastname: Plácido
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal. cpereira@cnc.cj.uc.pt.|Faculty of Medicine, University of Coimbra, Coimbra, 3000-548, Portugal. cpereira@cnc.cj.uc.pt.
authors.forename: Cláudia M F
authors.initials: CMF
authors.lastname: Pereira
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal.|Institute for Interdisciplinary Research, University of Coimbra, Coimbra, Portugal.
authors.forename: Sónia C
authors.initials: SC
authors.lastname: Correira
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal.|Institute for Interdisciplinary Research, University of Coimbra, Coimbra, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Carvalho
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal.|Faculty of Medicine, University of Coimbra, Coimbra, 3000-548, Portugal.
authors.forename: Catarina R
authors.initials: CR
authors.lastname: Oliveira
authors.affiliation: CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, 3004-504, Portugal. venta@ci.uc.pt.|Faculty of Medicine, University of Coimbra, Coimbra, 3000-548, Portugal. venta@ci.uc.pt.
authors.forename: Paula I
authors.identifier: http://orcid.org/0000-0001-5177-6747
authors.initials: PI
authors.lastname: Moreira
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D002460:Cell Line; D003599:Cytoskeleton / Q000187:drug effects / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D042783:Endothelial Cells / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D051381:Rats
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; C000717248:Hspa5 protein, mouse; D019319:Okadaic Acid; D043263:Myosin-Light-Chain Phosphatase
keywords: Cytoskeleton; Endoplasmic reticulum stress; Mitochondria dynamics; Protein phosphatases 2A