title: Reduced C9orf72 gene expression in c9FTD/ALS is caused by histone trimethylation, an epigenetic event detectable in blood.
abstract: Individuals carrying (GGGGCC) expanded repeats in the C9orf72 gene represent a significant portion of patients suffering from amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Elucidating how these expanded repeats cause "c9FTD/ALS" has since become an important goal of the field. Toward this end, we sought to investigate whether epigenetic changes are responsible for the decrease in C9orf72 expression levels observed in c9FTD/ALS patients. We obtained brain tissue from ten c9FTD/ALS individuals, nine FTD/ALS cases without a C9orf72 repeat expansion, and nine disease control participants, and generated fibroblastoid cell lines from seven C9orf72 expanded repeat carriers and seven participants carrying normal alleles. Chromatin immunoprecipitation using antibodies for histone H3 and H4 trimethylated at lysines 9 (H3K9), 27 (H3K27), 79 (H3K79), and 20 (H4K20) revealed that these trimethylated residues bind strongly to C9orf72 expanded repeats in brain tissue, but not to non-pathogenic repeats. Our finding that C9orf72 mRNA levels are reduced in the frontal cortices and cerebella of c9FTD/ALS patients is consistent with trimethylation of these histone residues, an event known to repress gene expression. Moreover, treating repeat carrier-derived fibroblasts with 5-aza-2-deoxycytidine, a DNA and histone demethylating agent, not only decreased C9orf72 binding to trimethylated histone residues, but also increased C9orf72 mRNA expression. Our results provide compelling evidence that trimethylation of lysine residues within histones H3 and H4 is a novel mechanism involved in reducing C9orf72 mRNA expression in expanded repeat carriers. Of importance, we show that mutant C9orf72 binding to trimethylated H3K9 and H3K27 is detectable in blood of c9FTD/ALS patients. Confirming these exciting results using blood from a larger cohort of patients may establish this novel epigenetic event as a biomarker for c9FTD/ALS.
authors.affiliation: Department of Research, Neuroscience, Mayo Clinic College of Medicine, 4500 San Pablo Road, Jacksonville, FL, 32224, USA.
authors.forename: Veronique V
authors.initials: VV
authors.lastname: Belzil
authors.forename: Peter O
authors.initials: PO
authors.lastname: Bauer
authors.forename: Mercedes
authors.initials: M
authors.lastname: Prudencio
authors.forename: Tania F
authors.initials: TF
authors.lastname: Gendron
authors.forename: Caroline T
authors.initials: CT
authors.lastname: Stetler
authors.forename: Irene K
authors.initials: IK
authors.lastname: Yan
authors.forename: Luc
authors.initials: L
authors.lastname: Pregent
authors.forename: Lillian
authors.initials: L
authors.lastname: Daughrity
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Baker
authors.forename: Rosa
authors.initials: R
authors.lastname: Rademakers
authors.forename: Kevin
authors.initials: K
authors.lastname: Boylan
authors.forename: Tushar C
authors.initials: TC
authors.lastname: Patel
authors.forename: Dennis W
authors.initials: DW
authors.lastname: Dickson
authors.forename: Leonard
authors.initials: L
authors.lastname: Petrucelli
mesh_terms: D000328:Adult; D000483:Alleles; D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000378:metabolism; D000073885:C9orf72 Protein; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D006657:Histones; D011506:Proteins