title: Ribosomal RNA in Alzheimer disease is oxidized by bound redox-active iron.
abstract: Oxidative modification of cytoplasmic RNA in vulnerable neurons is an important, well documented feature of the pathophysiology of Alzheimer disease. Here we report that RNA-bound iron plays a pivotal role for RNA oxidation in vulnerable neurons in Alzheimer disease brain. The cytoplasm of hippocampal neurons showed significantly higher redox activity and iron(II) staining than age-matched controls. Notably, both were susceptible to RNase, suggesting a physical association of iron(II) with RNA. Ultrastructural analysis further suggested an endoplasmic reticulum association. Both rRNA and mRNA showed twice the iron binding as tRNA. rRNA, extremely abundant in neurons, was considered to provide the greatest number of iron binding sites among cytoplasmic RNA species. Interestingly, the difference of iron binding capacity disappeared after denaturation of RNA, suggesting that the higher order structure may contribute to the greater iron binding of rRNA. Reflecting the difference of iron binding capacity, oxidation of rRNA by the Fenton reaction formed 13 times more 8-hydroxyguanosine than tRNA. Consistent with in situ findings, ribosomes purified from Alzheimer hippocampus contained significantly higher levels of RNase-sensitive iron(II) and redox activity than control. Furthermore, only Alzheimer rRNA contains 8-hydroxyguanosine in reverse transcriptase-PCR. Addressing the biological significance of ribosome oxidation by redox-active iron, in vitro translation with oxidized ribosomes from rabbit reticulocyte showed a significant reduction of protein synthesis. In conclusion these results suggest that rRNA provides a binding site for redox-active iron and serves as a redox center within the cytoplasm of vulnerable neurons in Alzheimer disease in advance of the appearance of morphological change indicating neurodegeneration.
authors.affiliation: Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Honda
authors.forename: Mark A
authors.initials: MA
authors.lastname: Smith
authors.forename: Xiongwei
authors.initials: X
authors.lastname: Zhu
authors.forename: Diane
authors.initials: D
authors.lastname: Baus
authors.forename: William C
authors.initials: WC
authors.lastname: Merrick
authors.forename: Alan M
authors.initials: AM
authors.lastname: Tartakoff
authors.forename: Thomas
authors.initials: T
authors.lastname: Hattier
authors.forename: Peggy L
authors.initials: PL
authors.lastname: Harris
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Siedlak
authors.forename: Hisashi
authors.initials: H
authors.lastname: Fujioka
authors.forename: Quan
authors.initials: Q
authors.lastname: Liu
authors.forename: Paula I
authors.initials: PI
authors.lastname: Moreira
authors.forename: Frank P
authors.initials: FP
authors.lastname: Miller
authors.forename: Akihiko
authors.initials: A
authors.lastname: Nunomura
authors.forename: Shun
authors.initials: S
authors.lastname: Shimohama
authors.forename: George
authors.initials: G
authors.lastname: Perry
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D001921:Brain / Q000378:metabolism; D002417:Cattle; D003593:Cytoplasm / Q000378:metabolism; D006151:Guanosine / Q000031:analogs & derivatives* / Q000737:chemistry; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007091:Image Processing, Computer-Assisted; D047468:Immunoprecipitation; D007501:Iron / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D008854:Microscopy, Electron; D009474:Neurons / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D014176:Protein Biosynthesis; D012313:RNA / Q000737:chemistry; D012335:RNA, Ribosomal / Q000737:chemistry*; D012343:RNA, Transfer / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012260:Ribonucleases / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism
chemical_list: C045076:Fenton's reagent; D012335:RNA, Ribosomal; D006151:Guanosine; C046215:8-hydroxyguanosine; D012313:RNA; D012343:RNA, Transfer; D006861:Hydrogen Peroxide; D007501:Iron; D012260:Ribonucleases; D010100:Oxygen