title: C9orf72 hypermethylation protects against repeat expansion-associated pathology in ALS/FTD.
abstract: Hexanucleotide repeat expansions of C9orf72 are the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal degeneration. The mutation is associated with reduced C9orf72 expression and the accumulation of potentially toxic RNA and protein aggregates. CpG methylation is known to protect the genome against unstable DNA elements and to stably silence inappropriate gene expression. Using bisulfite cloning and restriction enzyme-based methylation assays on DNA from human brain and peripheral blood, we observed CpG hypermethylation involving the C9orf72 promoter in cis to the repeat expansion mutation in approximately one-third of C9orf72 repeat expansion mutation carriers. Promoter hypermethylation of mutant C9orf72 was associated with transcriptional silencing of C9orf72 in patient-derived lymphoblast cell lines, resulting in reduced accumulation of intronic C9orf72 RNA and reduced numbers of RNA foci. Furthermore, demethylation of mutant C9orf72 with 5-aza-deoxycytidine resulted in increased vulnerability of mutant cells to oxidative and autophagic stress. Promoter hypermethylation of repeat expansion carriers was also associated with reduced accumulation of RNA foci and dipeptide repeat protein aggregates in human brains. These results indicate that C9orf72 promoter hypermethylation prevents downstream molecular aberrations associated with the hexanucleotide repeat expansion, suggesting that epigenetic silencing of the mutant C9orf72 allele may represent a protective counter-regulatory response to hexanucleotide repeat expansion.
authors.affiliation: Translational Neuropathology Research Laboratory, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA, 19104, USA.
authors.forename: Elaine Y
authors.initials: EY
authors.lastname: Liu
authors.forename: Jenny
authors.initials: J
authors.lastname: Russ
authors.forename: Kathryn
authors.initials: K
authors.lastname: Wu
authors.forename: Donald
authors.initials: D
authors.lastname: Neal
authors.forename: Eunran
authors.initials: E
authors.lastname: Suh
authors.forename: Anna G
authors.initials: AG
authors.lastname: McNally
authors.forename: David J
authors.initials: DJ
authors.lastname: Irwin
authors.forename: Vivianna M
authors.initials: VM
authors.lastname: Van Deerlin
authors.forename: Edward B
authors.initials: EB
authors.lastname: Lee
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000473:pathology*; D000704:Analysis of Variance; D000073885:C9orf72 Protein; D002461:Cell Line, Transformed; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics*; D004252:DNA Mutational Analysis; D042622:DNA Repeat Expansion / Q000235:genetics*; D005260:Female; D057180:Frontotemporal Dementia / Q000235:genetics* / Q000473:pathology*; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins; D012333:RNA, Messenger