title: Deep sequencing of mitochondrial genomes reveals increased mutation load in Friedreich's ataxia.
abstract: Friedreich's ataxia (FRDA) is an autosomal recessive trinucleotide repeat expansion disorder caused by epigenetic silencing of the frataxin gene (FXN). Current research suggests that damage and variation of mitochondrial DNA (mtDNA) contribute to the molecular pathogenesis of FRDA. We sought to establish the extent of the mutation burden across the mitochondrial genome in FRDA cells and investigate the molecular mechanisms connecting FXN downregulation and the acquisition of mtDNA damage.
  
  
  
  Damage and mutation load in mtDNA of a panel of FRDA and control fibroblasts were determined using qPCR and next-generation MiSeq sequencing, respectively. The capacity of FRDA and control cells to repair oxidative lesions in their mtDNA was measured using a quantitative DNA damage assay. Comprehensive RNA sequencing gene expression analyses were conducted to assess the status of DNA repair and metabolism genes in FRDA cells.
  
  
  
  Acute or prolonged downregulation of FXN expression resulted in a significant increase in mtDNA damage that translated to a significant elevation of mutation load in mtDNA. The predominant mutations identified throughout the mtDNA were C>T, G>A transitions (P = 0.007). Low FXN expression reduced capacity to repair oxidative damage in mtDNA. Downregulation of FXN expression strongly correlated (r = 0.73) with decreased levels of base excision repair (BER) DNA glycosylase NTHL1.
  
  
  
  Downregulation of FXN expression in FRDA cells elevates mtDNA damage, increases mutation load of the mitochondrial genome, and diminishes DNA repair capacity. Progressive accumulation of mtDNA mutations in vulnerable FRDA patient cells reduces mitochondrial fitness ultimately leading to cell death.
authors.affiliation: Department of Biochemistry and Molecular Genetics University of Alabama at Birmingham UAB Stem Cell Institute 1825 University Blvd. Birmingham Alabama 35294.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Bhalla
authors.affiliation: Department of Biochemistry and Molecular Genetics University of Alabama at Birmingham UAB Stem Cell Institute 1825 University Blvd. Birmingham Alabama 35294.
authors.forename: Alireza
authors.initials: A
authors.lastname: Khodadadi-Jamayran
authors.affiliation: Department of Biochemistry and Molecular Genetics University of Alabama at Birmingham UAB Stem Cell Institute 1825 University Blvd. Birmingham Alabama 35294.
authors.forename: Yanjie
authors.initials: Y
authors.lastname: Li
authors.affiliation: Division of Neurology and Pediatrics Children's Hospital of Philadelphia Abramson Research Center Room 502 Philadelphia Pennsylvania 19104.
authors.forename: David R
authors.initials: DR
authors.lastname: Lynch
authors.affiliation: Department of Biochemistry and Molecular Genetics University of Alabama at Birmingham UAB Stem Cell Institute 1825 University Blvd. Birmingham Alabama 35294; Department of Molecular Biomedicine Institute of Bioorganic Chemistry Polish Academy of Sciences Poznan 61-704 Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Napierala