title: Continued 26S proteasome dysfunction in mouse brain cortical neurons impairs autophagy and the Keap1-Nrf2 oxidative defence pathway.
abstract: The ubiquitin-proteasome system (UPS) and macroautophagy (autophagy) are central to normal proteostasis and interdependent in that autophagy is known to compensate for the UPS to alleviate ensuing proteotoxic stress that impairs cell function. UPS and autophagy dysfunctions are believed to have a major role in the pathomechanisms of neurodegenerative disease. Here we show that continued 26S proteasome dysfunction in mouse brain cortical neurons causes paranuclear accumulation of fragmented dysfunctional mitochondria, associated with earlier recruitment of Parkin and lysine 48-linked ubiquitination of mitochondrial outer membrane (MOM) proteins, including Mitofusin-2. Early events also include phosphorylation of p62/SQSTM1 (p62) and increased optineurin, as well as autophagosomal LC3B and removal of some mitochondria, supporting the induction of selective autophagy. Inhibition of the degradation of ubiquitinated MOM proteins with continued 26S proteasome dysfunction at later stages may impede efficient mitophagy. However, continued 26S proteasome dysfunction also decreases the levels of essential autophagy proteins ATG9 and LC3B, which is characterised by decreases in their gene expression, ultimately leading to impaired autophagy. Intriguingly, serine 351 phosphorylation of p62 did not enhance its binding to Keap1 or stabilise the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor in this neuronal context. Nrf2 protein levels were markedly decreased despite transcriptional activation of the Nrf2 gene. Our study reveals novel insights into the interplay between the UPS and autophagy in neurons and is imperative to understanding neurodegenerative disease where long-term proteasome inhibition has been implicated.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Nottingham, UK.
authors.forename: Aslihan
authors.initials: A
authors.lastname: Ugun-Klusek
authors.affiliation: Centre for Gene Regulation and Expression, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee, UK.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Tatham
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Tripoli, Tripoli, Libya.
authors.forename: Jamal
authors.initials: J
authors.lastname: Elkharaz
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, UK.
authors.forename: Dumitru
authors.initials: D
authors.lastname: Constantin-Teodosiu
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, UK.
authors.forename: Karen
authors.initials: K
authors.lastname: Lawler
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, UK.
authors.forename: Hala
authors.initials: H
authors.lastname: Mohamed
authors.affiliation: Nottingham University Hospitals NHS Trust, Queen's Medical Centre, Nottingham, UK.
authors.forename: Simon M L
authors.initials: SM
authors.lastname: Paine
authors.affiliation: Department of Histopathology, Great Ormond Street Hospital for Children NHS Trust, London, UK.
authors.forename: Glen
authors.initials: G
authors.lastname: Anderson
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, UK.
authors.forename: R
authors.initials: R
authors.lastname: John Mayer
authors.affiliation: School of Medicine, University of Nottingham, Nottingham, UK.
authors.forename: James
authors.initials: J
authors.lastname: Lowe
authors.affiliation: School of Science and Technology, Nottingham Trent University, Nottingham, UK.
authors.forename: E
authors.initials: E
authors.lastname: Ellen Billett
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, UK.
authors.forename: Lynn
authors.initials: L
authors.lastname: Bedford
mesh_terms: D000818:Animals; D001343:Autophagy / Q000235:genetics*; D018797:Cell Cycle Proteins; D005136:Eye Proteins / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D000072019:Kelch-Like ECH-Associated Protein 1 / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D063306:Mitophagy / Q000235:genetics*; D051267:NF-E2-Related Factor 2 / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics; D000071456:Sequestosome-1 Protein / Q000235:genetics* / Q000378:metabolism; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D005136:Eye Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D026901:Membrane Transport Proteins; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; C501288:Optn protein, mouse; D000071456:Sequestosome-1 Protein; C101343:Sqstm1 protein, mouse; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D020558:GTP Phosphohydrolases; C488751:Mfn2 protein, mouse