title: Aggregation-prone c9FTD/ALS poly(GA) RAN-translated proteins cause neurotoxicity by inducing ER stress.
abstract: The occurrence of repeat-associated non-ATG (RAN) translation, an atypical form of translation of expanded repeats that results in the synthesis of homopolymeric expansion proteins, is becoming more widely appreciated among microsatellite expansion disorders. Such disorders include amyotrophic lateral sclerosis and frontotemporal dementia caused by a hexanucleotide repeat expansion in the C9ORF72 gene (c9FTD/ALS). We and others have recently shown that this bidirectionally transcribed repeat is RAN translated, and the "c9RAN proteins" thusly produced form neuronal inclusions throughout the central nervous system of c9FTD/ALS patients. Nonetheless, the potential contribution of c9RAN proteins to disease pathogenesis remains poorly understood. In the present study, we demonstrate that poly(GA) c9RAN proteins are neurotoxic and may be implicated in the neurodegenerative processes of c9FTD/ALS. Specifically, we show that expression of poly(GA) proteins in cultured cells and primary neurons leads to the formation of soluble and insoluble high molecular weight species, as well as inclusions composed of filaments similar to those observed in c9FTD/ALS brain tissues. The expression of poly(GA) proteins is accompanied by caspase-3 activation, impaired neurite outgrowth, inhibition of proteasome activity, and evidence of endoplasmic reticulum (ER) stress. Of importance, ER stress inhibitors, salubrinal and TUDCA, provide protection against poly(GA)-induced toxicity. Taken together, our data provide compelling evidence towards establishing RAN translation as a pathogenic mechanism of c9FTD/ALS, and suggest that targeting the ER using small molecules may be a promising therapeutic approach for these devastating diseases.
authors.affiliation: Department of Neuroscience, Mayo Clinic Florida, Jacksonville, FL, 32224, USA.
authors.forename: Yong-Jie
authors.initials: YJ
authors.lastname: Zhang
authors.forename: Karen
authors.initials: K
authors.lastname: Jansen-West
authors.forename: Ya-Fei
authors.initials: YF
authors.lastname: Xu
authors.forename: Tania F
authors.initials: TF
authors.lastname: Gendron
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Bieniek
authors.forename: Wen-Lang
authors.initials: WL
authors.lastname: Lin
authors.forename: Hiroki
authors.initials: H
authors.lastname: Sasaguri
authors.forename: Thomas
authors.initials: T
authors.lastname: Caulfield
authors.forename: Jaime
authors.initials: J
authors.lastname: Hubbard
authors.forename: Lillian
authors.initials: L
authors.lastname: Daughrity
authors.forename: Jeannie
authors.initials: J
authors.lastname: Chew
authors.forename: Veronique V
authors.initials: VV
authors.lastname: Belzil
authors.forename: Mercedes
authors.initials: M
authors.lastname: Prudencio
authors.forename: Jeannette N
authors.initials: JN
authors.lastname: Stankowski
authors.forename: Monica
authors.initials: M
authors.lastname: Castanedes-Casey
authors.forename: Ena
authors.initials: E
authors.lastname: Whitelaw
authors.forename: Peter E A
authors.initials: PE
authors.lastname: Ash
authors.forename: Michael
authors.initials: M
authors.lastname: DeTure
authors.forename: Rosa
authors.initials: R
authors.lastname: Rademakers
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Boylan
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Dickson
authors.forename: Leonard
authors.initials: L
authors.lastname: Petrucelli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001921:Brain / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D000073885:C9orf72 Protein; D002466:Cell Nucleolus / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D002756:Cholagogues and Choleretics / Q000494:pharmacology; D042622:DNA Repeat Expansion / Q000235:genetics* / Q000276:immunology; D004622:Embryo, Mammalian; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005260:Female; D057180:Frontotemporal Dementia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000528:radiation effects; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000378:metabolism; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000906:Antibodies; D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D002756:Cholagogues and Choleretics; D009419:Nerve Tissue Proteins; D011506:Proteins