Friedreich's Ataxia (FRDA) is a neurodegenerative disease caused by decreased expression of a mitochondrial protein, frataxin, leading to increased mitochondrial iron, oxidative stress, and loss of iron sulfur cluster synthesis. The YFH1 gene is the Saccharomyces cerevisiae homologue of the human frataxin gene. In collaboration with Dr. Copeland and Dr. Resnicks laboratories, we have found cells lacking YFH1 exhibit 1) accumulation of iron, which cannot be exported from the mitochondria; 2) oxidation of proteins; 3) oxidative DNA damage, which leads to petite colony formation with defects or loss of mitochondrial DNA and 4) nuclear chromosomal damage. The cellular impact of mitochondrial iron overload in yeast is being determined by global gene expression profiling (in collaboration with the NIEHS Microarray Center) in an yfh1 deletion mutant with defective mitochondrial function and no mitochondrial DNA (i.e., rho0). In order to better replicate the human disease process , we in collaboration with Dr. Mike Resnick also conducted transcription profiling on a yeast strain with a rheostatable system that can lead to a lowering of the expressing of the YFH1 gene. We examined the gene profiles in yeast in which frataxin was reduced twofold to sevenfold in generations 3 through 24, resulted in nearly identical events as those occurring in the knockout experiment. These transpired even with the initial reduction of frataxin at generation 3. Overall, we found the mostly downregulated cytochrome, heme, and iron/sulfur cluster assembly pathways, to indicate that frataxin has a role in iron transport, iron/sulfur cluster biosynthesis, oxidative phosphorylation, and as an antioxidant. Furthermore, we find these data correlate very well with a recently published iron deficiency profile. ? ? This inter-institute collaborative project between a clinical laboratory (Drs. Nicholas DiProspero and Kennetth Fischbeck) at NINDS and the Van Houten laboratory at NIEHS seeks to test the hypothesis that FRDA patients will: 1) accumulate mitochondrial DNA damage in peripheral lymphocytes; 2) share common gene expression patterns unique to the pathogenesis of the disease; and 3) show diminution of both of these effects by idebenone treatment. This collaborative project represents new research and would not be possible without a direct collaboration between these two laboratories and is supported by a grant from the Office of Rare Diseases. Frataxin, a conserved mitochondrial protein involved in iron homeostasis, is reduced in patients with Friedreichs ataxia (FRDA). Transcription profiling and DNA damage assays were performed on blood cells from 48 FRDA children. Microarrays for the analysis of gene expression were completed on a 22,000 gene Agilent array using a universal RNA standard design. These children were compared to a group of normal young adults. Significance Analysis of Microarray (SAM) revealed 1,500 differentially expressed genes at a false discovery rate of 1%. Expression patterns identified altered immune response, signaling pathways, transcription, apoptosis, and genotoxic stress pathways. In support of this last finding, compared to a control group of young adults, FRDA patients had significantly more mitochondrial and nuclear DNA damage as measured by a gene-specific quantitative PCR assay. DNA lesions, multiplied by the years of disease duration, were highly correlated with ICAR scores. Frataxin mRNA levels correlated with age of onset, and those patients with the lowest levels of frataxin displayed a unique set of gene alterations involved in reduced protein synthesis and reduced oxidative phosphorylation. Validation of gene expression changes was performed by analysis of 14 adult French FRDA patients and analysis of 10 FRDA lymphoblastoid cell lines. This study demonstrates how analysis of blood in FRDA patients yields molecular insight into the nature and progression of the disease.
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