Friedreich's Ataxia, No Changes in Mitochondrial Labile Iron in Human Lymphoblasts and Fibroblasts

Sturm, Brigitte; Bistrich, Ute; Schranzhofer, Matthias; Sarsero, Joseph P.; Rauen, Ursula; Scheiber-Mojdehkar, Barbara; Groot, Herbert de; Ioannou, Panos; Petrat, Frank

doi:10.1074/jbc.m408717200

Cited by 69 publications

(63 citation statements)

References 59 publications

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“…If endogenous H 2 O 2 is an important factor in pathogenesis arising from DFH deficiency in Drosophila, we would predict that DFH-deficient flies would be hypersensitive to H 2 O 2 exposure. Although susceptibility to H 2 O 2 challenge typifies yeast and cell culture models of frataxin deficiency (3,(27)(28)(29), it has yet do be demonstrated in a whole-animal model of FRDA. Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Elevated ROS production, including generation of the highly reactive hydroxyl radical, by ironcatalyzed Fenton chemistry with endogenous H 2 O 2 as the substrate would be consistent with the susceptibility to H 2 O 2 challenge noted in yeast and cell culture models of frataxin deficiency (3,(27)(28)(29)). Yet no whole-organism animal studies have been presented that investigate the role of H 2 O 2 in mediating frataxin deficiency phenotypes.…”

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confidence: 91%

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Hydrogen peroxide scavenging rescues frataxin deficiency in a Drosophila model of Friedreich's ataxia

Anderson

Kirby

Orr

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 91%

Hydrogen peroxide scavenging rescues frataxin deficiency in a Drosophila model of Friedreich's ataxia

Anderson

Kirby

Orr

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…11 Our results appear to contrast earlier claims that frataxin deficiency results in no detectable iron accumulation in mitochondria, as visualized by electron microscopy, 13 measured spectrophotometrically, 14 and measured by radioactivity using radiolabeled iron loaded into cells 41 and by in situ fluorimetry in cultured lymphoblasts and fibroblasts derived from FRDA patients. 15 We ascribe the discrepant results to 2 factors: (1) phenotypic differences among the experimental cellular systems expressing frataxin deficiency, particularly in light of the inconsistent pattern of phenotypic changes observed in immortalized lines of lymphoblasts and fibroblasts derived from human samples; and (2) methodologic limitations in the quantitative assessment of mitochondrial labile iron with targeted fluorescent phenanthroline probes, which may affect the cell iron distribution. 15 These drawbacks are largely avoided in the present study by using cells with defined patterns of frataxin repression and analytical methods that allow selective detection of redox-active (as opposed to total) iron and minimal interference with intracellular iron distribution.…”

Section: Functional Characterization Of the Frataxin-deficient Phenotypementioning

confidence: 99%

“…11 The contending view, that cardiac iron accumulation is not a causative factor of the disease, but a late event that follows the onset of damage, is based on models of frataxin knockout mouse embryos 12 and conditional cardiac-targeted frataxin knockout mice, 13 as well as frataxin-depleted HeLa cell models 14 and lymphoblastoid cells derived from FRDA patients. 15 Irrespective of the primary or secondary role of iron in the pathology of FRDA, it has been proposed that iron chelation may have potential therapeutic value. 7,16 In contrast to the treatment of systemic iron overload, the presumed association of oxidative damage with regional iron accumulation, observed in FRDA 10 and in a variety of other diseases, calls for the application of a special form of iron chelation.…”

Section: Introductionmentioning

confidence: 99%

“…15 We ascribe the discrepant results to 2 factors: (1) phenotypic differences among the experimental cellular systems expressing frataxin deficiency, particularly in light of the inconsistent pattern of phenotypic changes observed in immortalized lines of lymphoblasts and fibroblasts derived from human samples; and (2) methodologic limitations in the quantitative assessment of mitochondrial labile iron with targeted fluorescent phenanthroline probes, which may affect the cell iron distribution. 15 These drawbacks are largely avoided in the present study by using cells with defined patterns of frataxin repression and analytical methods that allow selective detection of redox-active (as opposed to total) iron and minimal interference with intracellular iron distribution. ) or not with tetracycline for 6 days were treated for 30 hours with 150 M DFO, washed, and recultured for 3 hours in full medium with or without 50 M of the chelators indicated.…”

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confidence: 99%

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Cell functions impaired by frataxin deficiency are restored by drug-mediated iron relocation

Kakhlon

Manning

Breuer

et al. 2008

Blood

114

100

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Various human disorders are associated with misdistribution of iron within or across cells. Friedreich ataxia (FRDA), a deficiency in the mitochondrial ironchaperone frataxin, results in defective use of iron and its misdistribution between mitochondria and cytosol. We assessed the possibility of functionally correcting the cellular properties affected by frataxin deficiency with a siderophore capable of relocating iron and facilitating its metabolic use. Adding the chelator deferiprone at clinical concentrations to inducibly frataxin-deficient HEK-293 cells resulted in chelation of mitochondrial labile iron involved in oxidative stress and in reactivation of iron-depleted aconitase. These led to (1) restoration of impaired mitochondrial membrane and redox potentials, (2) increased adenosine triphosphate production and oxygen consumption, and (3) attenuation of mitochondrial DNA damage and reversal of hypersensitivity to staurosporine-induced apoptosis. Permeant chelators of higher affinity than deferiprone were not as efficient in restoring affected functions. Thus, although iron chelation might protect cells from iron toxicity, rendering the chelated iron bioavailable might underlie the capacity of deferiprone to restore cell functions affected by frataxin deficiency, as also observed in FRDA patients. The siderophore-like properties of deferiprone provide a rational basis for treating diseases of iron misdistribution, such as FRDA, anemia of chronic disease, and X-linked sideroblastic anemia with ataxia. IntroductionHumoral factors or mutations of genes that affect iron metabolism often result in pathologic changes linked to systemic or cellular misdistribution of iron. In anemia of chronic disease (ACD), 1 plasma iron deficiency results from retention of iron in the reticuloendothelial system because of hepcidin-mediated inhibition of iron export into plasma. 2 Defective delivery and distribution of iron resulting from deficiency in the iron-chaperone protein frataxin are also considered to be key causative factors in Friedreich ataxia (FRDA). 3,4 The disease is expressed in individuals carrying a GAA repeat expansion in the first intron of frataxin that reduces frataxin levels, leading to reduced iron-sulfur cluster (ISC)-protein (ISP) synthesis and a combined deficiency in aconitase and respiratory chain (complex I-III) activity. This leads to a concomitant deficiency in cell respiratory functions 5 that is further exacerbated by mitochondrial iron accumulation and ensuing oxidative damage. 6,7 FRDA is a neurodegenerative disorder that is often accompanied by hypertrophic cardiomyopathy and increased predisposition for diabetes mellitus. 8 The precise role of iron in FRDA pathophysiology has hitherto remained controversial. 9 Support for its direct involvement in the disease is based on histopathologic examination of human specimens and magnetic resonance imaging of patients. 10 Similar conclusions were drawn from biochemical studies with frataxin-deficient yeast and animal cell models. 11 The contending ...

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Deep sequencing of mitochondrial genomes reveals increased mutation load in Friedreich's ataxia

Bhalla

Khodadadi‐Jamayran

et al. 2016

Ann Clin Transl Neurol

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ObjectiveFriedreich'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.MethodsDamage 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.ResultsAcute 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.InterpretationDownregulation 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.

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Friedreich's Ataxia, No Changes in Mitochondrial Labile Iron in Human Lymphoblasts and Fibroblasts

Cited by 69 publications

References 59 publications

Hydrogen peroxide scavenging rescues frataxin deficiency in a Drosophila model of Friedreich's ataxia

Hydrogen peroxide scavenging rescues frataxin deficiency in a Drosophila model of Friedreich's ataxia

Cell functions impaired by frataxin deficiency are restored by drug-mediated iron relocation

Deep sequencing of mitochondrial genomes reveals increased mutation load in Friedreich's ataxia

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