Altered Gene Expression and DNA Damage in Peripheral Blood Cells from Friedreich's Ataxia Patients: Cellular Model of Pathology

Abstract

The neurodegenerative disease Friedreich's ataxia (FRDA) is the most common autosomal-recessively inherited ataxia and is caused by a GAA triplet repeat expansion in the first intron of the frataxin gene. In this disease, transcription of frataxin, a mitochondrial protein involved in iron homeostasis, is impaired, resulting in a significant reduction in mRNA and protein levels. Global gene expression analysis was performed in peripheral blood samples from FRDA patients as compared to controls, which suggested altered expression patterns pertaining to genotoxic stress. We then confirmed the presence of genotoxic DNA damage by using a gene-specific quantitative PCR assay and discovered an increase in both mitochondrial and nuclear DNA damage in the blood of these patients (p<0.0001, respectively). Additionally, frataxin mRNA levels correlated with age of onset of disease and displayed unique sets of gene alterations involved in immune response, oxidative phosphorylation, and protein synthesis. Many of the key pathways observed by transcription profiling were downregulated, and we believe these data suggest that patients with prolonged frataxin deficiency undergo a systemic survival response to chronic genotoxic stress and consequent DNA damage detectable in blood. In conclusion, our results yield insight into the nature and progression of FRDA, as well as possible therapeutic approaches. Furthermore, the identification of potential biomarkers, including the DNA damage found in peripheral blood, may have predictive value in future clinical trials.

Identification of a de novo thymidylate biosynthesis pathway in mammalian mitochondria

“…Other studies support a role for de novo thymidylate biosynthesis in maintaining DNA integrity. Patients with the mitochondrial disorder, Friedrich's ataxia, which leads to large increases in mtDNA damage, exhibited elevated DHFRL1 mRNA (26). Elevated DHFRL1 expression may help limit some deleterious changes in mtDNA.…”

Mitoferrin modulates iron toxicity in a Drosophila model of Friedreich׳s ataxia

“…The Drosophila model of FRDA generated by our group and collaborators ( [36], fhRNAi-2) displays a systemic and moderate reduction of frataxin expression of approximately 70%; a reduction akin to that observed in patients [44,45]. The remaining 30% frataxin is sufficient to bypass any developmental lethality, to facilitate normal aconitase or complex II activities, to induce a strong sensitivity against oxidative insult and to increase the production of lipid peroxides [36,38].…”

Quantitative PCR-Based Measurement of Nuclear and Mitochondrial DNA Damage and Repair in Mammalian Cells

“…These include the utilization of the QPCR method to determine the ability of modulating experimental conditions to influence DNA damage levels or repair in mtDNA or nDNA, such as a 2009 study by Jung et [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. QPCR has also been employed to directly compare mtDNA and nDNA damage in aged tissues [42,43] as well as determine the effects of disease conditions [37,[44][45][46] and conditions such as oxidative stress [31,40] on repair in mtDNA and nDNA. The assay has also been used to show that repair of UV photoproducts is reduced by approx 50 % in aging nematodes [47].…”