title: Neurotoxic mechanisms by which the USP14 inhibitor IU1 depletes ubiquitinated proteins and Tau in rat cerebral cortical neurons: Relevance to Alzheimer's disease.
abstract: In Alzheimer's disease proteasome activity is reportedly downregulated, thus increasing it could be therapeutically beneficial. The proteasome-associated deubiquitinase USP14 disassembles polyubiquitin-chains, potentially delaying proteasome-dependent protein degradation. We assessed the protective efficacy of inhibiting or downregulating USP14 in rat and mouse (Usp14axJ) neuronal cultures treated with prostaglandin J2 (PGJ2). IU1 concentrations (HIU1>25μM) reported by others to inhibit USP14 and be protective in non-neuronal cells, reduced PGJ2-induced Ub-protein accumulation in neurons. However,HIU1 alone or with PGJ2 is neurotoxic, induces calpain-dependent Tau cleavage, and decreases E1~Ub thioester levels and 26S proteasome assembly, which are energy-dependent processes. We attribute the two latterHIU1 effects to ATP-deficits and mitochondrial Complex I inhibition, as shown herein. TheseHIU1 effects mimic those of mitochondrial inhibitors in general, thus supporting that ATP-depletion is a major mediator ofHIU1-actions. In contrast, low IU1 concentrations (LIU1≤25μM) or USP14 knockdown by siRNA in rat cortical cultures or loss of USP14 in cortical cultures from ataxia (Usp14axJ) mice, failed to prevent PGJ2-induced Ub-protein accumulation. PGJ2 alone induces Ub-protein accumulation and decreases E1~Ub thioester levels. This seemingly paradoxical result may be attributed to PGJ2 inhibiting some deubiquitinases (such as UCH-L1 but not USP14), thus triggering Ub-protein stabilization. Overall, IU1-concentrations that reduce PGJ2-induced accumulation of Ub-proteins are neurotoxic, trigger calpain-mediated Tau cleavage, lower ATP, E1~Ub thioester and E1 protein levels, and reduce proteasome activity. In conclusion, pharmacologically inhibiting (with low or high IU1 concentrations) or genetically down-regulating USP14 fail to enhance proteasomal degradation of Ub-proteins or Tau in neurons.
authors.affiliation: Department of Biological Sciences, Hunter College, Biology and Biochemistry Programs, Graduate Center, The City University of New York, New York, NY 10065, USA.
authors.forename: Magdalena J
authors.initials: MJ
authors.lastname: Kiprowska
authors.affiliation: School of Biological Sciences, Queen's University Belfast, Belfast BT9 7BL, United Kingdom; N.K. Koltzov Institute of Developmental Biology, Russian Academy of Sciences, Moscow 119334, Russia.
authors.forename: Anna
authors.initials: A
authors.lastname: Stepanova
authors.affiliation: Department of Biochemistry and Molecular Biology, LSU Health Sciences Center, New Orleans, LA 70112, USA.
authors.forename: Dustin R
authors.initials: DR
authors.lastname: Todaro
authors.affiliation: School of Biological Sciences, Queen's University Belfast, Belfast BT9 7BL, United Kingdom; Feil Family Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY 10065, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Galkin
authors.affiliation: Department of Biochemistry and Molecular Biology, LSU Health Sciences Center, New Orleans, LA 70112, USA.
authors.forename: Arthur
authors.initials: A
authors.lastname: Haas
authors.affiliation: Department of Neurobiology, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Wilson
authors.affiliation: Department of Biological Sciences, Hunter College, Biology and Biochemistry Programs, Graduate Center, The City University of New York, New York, NY 10065, USA. Electronic address: pereira@genectr.hunter.cuny.edu.
authors.forename: Maria E
authors.initials: ME
authors.lastname: Figueiredo-Pereira
mesh_terms: D000544:Alzheimer Disease / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism* / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D042967:Electron Transport Complex I / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D020258:Neurotoxicity Syndromes / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011758:Pyrroles / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043222:Ubiquitin Thiolesterase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects*; D016875:tau Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C000594744:1-(1-(4-fluorophenyl)-2,5-dimethylpyrrol-3-yl)-2-pyrrolidin-1-ylethanone; C558298:Mapt protein, mouse; C489131:Mapt protein, rat; D011758:Pyrroles; D011759:Pyrrolidines; C000609601:USP14 protein, rat; C469268:Usp14 protein, mouse; D016875:tau Proteins; D043222:Ubiquitin Thiolesterase; D042967:Electron Transport Complex I
keywords: Alzheimer's; Calpain; Deubiquitinase; Mitochondria; Tau; USP14; Ubiquitin-activating enzyme