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Human Molecular Genetics Advance Access published online on November 27, 2007
Human Molecular Genetics, doi:10.1093/hmg/ddm346
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© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

The Friedreich ataxia GAA repeat expansion mutation induces comparable epigenetic changes in human and transgenic mouse brain and heart tissues

Sahar Al-Mahdawi, Ricardo Mouro Pinto, Ozama Ismail, Dhaval Varshney, Stefania Lymperi, Chiranjeevi Sandi, Daniah Trabzuni and Mark Pook*

Hereditary Ataxia Group, Centre for Cell & Chromosome Biology and Brunel Institute of Cancer Genetics & Pharmacogenomics, Division of Biosciences, School of Health Sciences & Social Care, Brunel University, Uxbridge UB8 3PH UK

* To whom correspondence should be addressed Tel: 44 1895 267243; Fax: 44 1895 274348; E-mail: Mark.Pook{at}brunel.ac.uk

Received September 20, 2007; Revised November 25, 2007; Accepted November 25, 2007

Friedreich ataxia (FRDA) is caused by a homozygous GAA repeat expansion mutation within intron 1 of the FXN gene, leading to reduced expression of frataxin protein. Evidence suggests that the mutation may induce epigenetic changes and heterochromatin formation, thereby impeding gene transcription. In particular, studies using FRDA patient blood and lymphoblastoid cell lines have detected increased DNA methylation of specific CpG sites upstream of the GAA repeat and histone modifications in regions flanking the GAA repeat. In this report we show that such epigenetic changes are also present in FRDA patient brain, cerebellum and heart tissues, the primary affected systems of the disorder. Bisulfite sequence analysis of the FXN flanking GAA regions reveals a shift in the FRDA DNA methylation profile, with upstream CpG sites becoming consistently hypermethylated and downstream CpG sites becoming consistently hypomethylated. We also identify differential DNA methylation at three specific CpG sites within the FXN promoter and one CpG site within exon 1. Furthermore, we show by chromatin immunoprecipitation (ChIP) analysis that there is overall decreased histone H3K9 acetylation together with increased H3K9 methylation of FRDA brain tissue. Further studies of brain, cerebellum and heart tissues from our GAA repeat expansion-containing FRDA YAC transgenic mice reveal comparable epigenetic changes to those detected in FRDA patient tissue. We have thus developed a mouse model that will be a valuable resource for future therapeutic studies targeting epigenetic modifications of the FXN gene to increase frataxin expression.


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