Human Molecular Genetics, 2000, Vol. 9, No. 2 275-282
© 2000 Oxford University Press
Clinical, biochemical and molecular genetic correlations in Friedreich’s ataxia
1University Department of Clinical Neurosciences, Royal Free and University College Medical School, London, UK, 2Department of Human Genetics, Imperial College of Medicine at St Mary’s, London, UK and 3Institute of Neurology, University College London, London, UK
Received 17 September 1999; Revised and Accepted 17 November 1999.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
Friedreich’s ataxia (FRDA) is an autosomal recessive disorder with a frequency of 1 in 50 000 live births. In 97% of patients it is caused by the abnormal expansion of a GAA repeat in intron 1 of the FRDA gene on chromosome 9, which encodes a 210 amino acid protein called frataxin. Frataxin is widely expressed and has been localized to mitochondria although its function is unknown. We have investigated mitochondrial function, mitochondrial DNA levels, aconitase activity and iron content in tissues from FRDA patients. There were significant reductions in the activities of complex I, complex II/III and aconitase in FRDA heart. Respiratory chain and aconitase activities were decreased although not significantly in skeletal muscle, but were normal in FRDA cerebellum and dorsal root ganglia, although there was a mild decrease in aconitase activity in the latter. Mitochondrial DNA levels were reduced in FRDA heart and skeletal muscle, although in skeletal muscle this was paralleled by a decline in citrate synthase activity. Increased iron deposition was seen in FRDA heart, liver and spleen in a pattern consistent with a mitochondrial location. The iron accumulation, mitochondrial respiratory chain and aconitase dysfunction and mitochondrial DNA depletion in FRDA heart samples largely paralleled those in the yeast YFH1 knockout model, suggesting that frataxin may be involved in mitochondrial iron regulation or iron sulphur centre synthesis. However, the severe deficiency in aconitase activity also suggests that oxidant stress may induce a self-amplifying cycle of oxidative damage and mitochondrial dysfunction, which may contribute to cellular toxicity.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
FRDA is characterized clinically by onset usually below the age of 20 years of progressive ataxia, tendon areflexia, lower limb weakness and large fibre sensory loss. A significant proportion of patients develop cardiomyopathy (a frequent eventual cause of death), diabetes mellitus and skeletal abnormalities such as kyphoscoliosis. The chromosomal locus for FRDA (9q13) was reported in 1988 (1), and the responsible gene (FRDA) in 1996 (2), which encodes frataxin, a widely expressed protein which has a mitochondrial targeting sequence and has been shown to co-localize to mitochondria (3). In 97% of FRDA patients there is an increase (>200) in the number of GAA repeats in intron 1, over and above those seen in controls (<40). Occasional FRDA patients are compound heterozygotes with a GAA expansion in one allele and a point mutation in the other. The intron 1 mutations in FRDA result in reduced levels of frataxin mRNA and decreased frataxin levels, which correlate with the size of the GAA repeat on the smaller allele (4).
The function of frataxin is unknown but knockout of the yeast homologue YFH1 has provided some clues. YFH1 knockouts exhibit impaired growth on fermentable energy sources, decreased mitochondrial DNA (mtDNA) levels, iron accumulation within mitochondria and an increased susceptibility to reactive oxygen species (5). This combination of factors suggests that frataxin may play a role in regulating mitochondrial iron levels, the synthesis or assembly of iron sulphur (Fe-S) proteins, regulating mitochondrial DNA or the antioxidant defence of mitochondria.
Further clues to the pathogenesis of FRDA come from a recessive neurodegenerative disease caused by mutations in the 
-tocopherol transfer protein associated with vitamin E deficiency (6), which produces a clinical condition similar to FRDA. Vitamin E is an important lipid soluble antioxidant and therefore leads to elevated lipid peroxidation. The clinical similarities between vitamin E deficiency and FRDA suggest that lipid peroxidation may also be involved in FRDA. Lipofuscin accumulation has been observed in FRDA patients, supporting this hypothesis (7).
One study has shown reduced ratios of the activities of complexes I, II and III and aconitase in heart muscle from two patients with FRDA (8). We have undertaken a comprehensive analysis of mitochondrial respiratory chain and aconitase activities and mtDNA in a range of frozen tissues from 10 genetically proven FRDA patients, and iron levels in formalin-fixed tissues from seven patients in order to determine the nature, severity and extent of the mitochondrial dysfunction induced by frataxin deficiency. We provide clear evidence for defects in the mitochondrial respiratory chain and aconitase activity in FRDA tissues in association with iron accumulation and a more moderate decrease in mtDNA levels.
Our data suggest that abnormal mitochondrial iron handling, respiratory chain and aconitase dysfunction, and oxidative stress all contribute to the pathogenesis of FRDA.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
Enzyme analysis
Patient data are summarized in Table 1. Mitochondrial respiratory chain activities, expressed as a ratio with citrate synthase (CS) (and calculated on an individual basis), and aconitase activities in control and FRDA heart tissue are shown in Table 2. The activities for the two coronary artery disease samples were very similar to the control samples and were combined for statistical analyses. In the FRDA heart samples there were highly significant decreases in complex I (84% decrease; P = 0.001) and complex II/III (77% decrease; P = 0.001) CS ratios with no overlap in individual data points of the control and FRDA groups (Fig. 1). The complex IV:CS ratio was decreased by 29% but this was not statistically significant.
|
|
|
FRDA skeletal muscle showed a similar pattern of enzyme defect. Mean CS activities and CS ratios for complexes I and II/III were decreased by 46, 40 and 13%, respectively (Fig. 1; Table 2). These changes did not reach statistical significance.
The activities of CS and CS ratios for the respiratory chain enzymes fell within the control ranges for FRDA dorsal root ganglia (DRG) and cerebellum with the exception of the complex I:CS ratio (decreased by 23%) in the cerebellum (Table 2).
Aconitase activities were significantly reduced in FRDA heart (by 86%; P = 0.0025), and in skeletal muscle (by 52%) and DRG (by 41%), but were comparable with control ranges in FRDA cerebellum (Table 2).
Although there was a trend for greater expansion lengths of the smaller FRDA allele to be associated with lower complex I–III and aconitase activities in cardiac tissue, this did not reach statistical significance for the few samples studied (data not shown).
Mitochondrial DNA
Southern blot analysis did not demonstrate any detectable rearrangement (deletions or duplications) in heart, skeletal muscle, cerebellum or DRG samples (Fig. 2). However, when the mtDNA levels were expressed as a ratio with the 18S rDNA there was a decrease in the level of mtDNA in FRDA heart (decreased 33%), skeletal muscle (decreased 60%), cerebellum (decreased 27%) and DRG (decreased 18%). The mtDNA:18S rDNA ratios were similar in the FRDA heart samples and those from the two coronary artery disease patients (Fig. 3). Qualitative analysis of long-range PCR expansion of mtDNA in control and FRDA tissue from heart, skeletal muscle and DRG demonstrated the presence of PCR products <16.5 kb representing deleted molecules, but these were seen in similar amounts in controls and presumably reflect age-accumulated deletions (data not shown).
|
|
Iron staining
Positive iron staining of the hepatocyte cells was observed in the livers of two FRDA patients (P1 and P2), although the extent was noticeably more marked in P1 than P2, whereas iron staining was absent from a third patient (P11). The granular pattern of iron deposition was consistent with mitochondrial localization. In addition, the sinusoidal channels were seen to be bounded by narrow positively stained regions suggesting that iron accumulation occurred within the lining cells of the sinusoids (Fig. 4A). The relevance of this finding with reference to the pathology of the disease is unclear.
|
Positive staining was also found in the spleen of two FRDA patients (P1 and P11) but absent in a third (P2). In P1 it was seen to be largely restricted to the macrophages of the red pulp (Fig. 4B). These cells phagocytically remove particulate material and damaged erythrocytes from the circulation and, as such, the accumulation of iron within their cytoplasm is probably of a secondary nature.
Iron accumulation was seen in the heart tissue from all six FRDA patients studied (Table 1), although the number of affected cells varied considerably between individuals. The pattern of staining, as in the liver, was granular in appearance (Fig. 4C). When viewed under oil immersion at higher magnifications these granules were frequently seen to exist in chains (Fig. 4D), a distribution consistent with mitochondrial iron accumulation.
Cardiomyopathy was a feature of four of the six patients with cardiac iron accumulation. For one patient the information was not available and the patient without cardiomyopathy died relatively young, at 26 years of age.
No evidence of iron accumulation was found in DRG (n = 1), spinal cord (n = 4), skeletal muscle (n = 4), cerebellum (n = 3), peripheral nerve (n = 2) or pancreas (n = 3) from the FRDA patients.
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
The expanded GAA repeat in intron 1 of the FRDA gene results in a decrease in the level of frataxin. Deficiency of the protein causes FRDA, the multisystemic nature of FRDA reflecting the widespread tissue expression of frataxin. Knockout of the YFH1 yeast homologue of frataxin results in a combination of mitochondrial defects affecting respiratory chain function, iron homeostasis and mtDNA maintenance.
In an attempt to determine whether or not abnormalities in the YFH1 yeast knockout model are paralleled by those in FRDA and also to help elucidate the pathogenetic mechanisms in FRDA, we have analysed mitochondrial respiratory chain activities, mtDNA levels, cellular iron accumulation and aconitase activity in a variety of clinically relevant tissues from FRDA patients. Our results demonstrate striking similarities between FRDA and the yeast model.
Similar to the situation in the YFH1 knockout yeast, we have shown an impaired oxidative phosphorylation system with severe and significant deficiencies of mitochondrial respiratory chain complexes I and II/III and aconitase activities in cardiac muscle from eight patients with FRDA. These results extend and support the provisional report of heart homogenates from two FRDA patients in whom absolute respiratory chain enzyme activities were normal but relative ratios were abnormal and aconitase activity was reduced in both (8). We have also demonstrated decreases in mitochondrial function (in particular complexes II/III) and aconitase activity in FRDA skeletal muscle, and aconitase deficiency in FRDA DRG although these were not statistically significant. The abnormalities in skeletal muscle are supported by our recent finding of a highly significant decrease in the maximum rate of mitochondrial ATP synthesis (Vmax) in vivo in calf muscle from 12 FRDA patients using 31P magnetic resonance spectroscopy (9). There was a strong negative correlation between expansion length and Vmax in these patients. The apparently normal respiratory chain activity in DRG samples is surprising as this tissue is consistently affected in FRDA. However, the disease involves the loss of the larger ganglion cells, which appear to be particularly vulnerable to degeneration, with relative sparing of those of smaller size. By the time of DRG sample collection, the larger ganglion cells had been lost. The smaller ganglion cells may survive by virtue of their normal respiratory chain activity and failure to accumulate iron, and explain the results of our analyses.
The predominant involvement of nervous tissue and muscle in FRDA is reminiscent of mitochondrial encephalomyopathies caused by mtDNA mutations. Indeed the combination of defects in nerve and muscle together with diabetes in FRDA suggests that these are a consequence of deficient respiratory chain function in view of the high dependence of these tissues on oxidative phosphorylation as an energy source. A deficiency of oxidative phosphorylation caused by abnormalities of complexes I–III will be compounded by the defect in aconitase as this is an important component of the Krebs cycle.
Major rearrangements of mtDNA were not observed in any of the FRDA samples analysed; however, decreased levels of mtDNA were apparent in the FRDA cardiac muscle and skeletal muscle although it appeared to be secondary to the loss of mitochondrial mass in the latter. This is in contrast to the YFH1-deleted yeast model where mtDNA was lost (10). It is possible that the loss of mtDNA levels in the yeast cells was secondary to other factors as yeast cells lose mtDNA due to a variety of abnormalities (11). It is possible that similar conditions to those seen in the YFH1 yeast model exist in FRDA, but the loss of mtDNA is less severe because the residual frataxin allows the level of mtDNA to be maintained.
FRDA heart, liver and spleen sections demonstrated a variable but often marked accumulation of iron in selected cells as reported previously (7,12). Although the precise cellular localization of the iron was not identifiable, the punctate cytoplasmic distribution is consistent with a mitochondrial location. This is in agreement with the YFH1 knockout model where iron was shown to accumulate within mitochondria (6). The cause of iron accumulation in FRDA is not known. Frataxin may be involved in regulating iron export from the mitochondrion resulting in iron accumulation when the protein is deficient. However, it is also possible that abnormal intramitochondrial iron handling, possibly affecting its incorporation into Fe-S centres, results in iron accumulation. Accumulations of intramitochondrial iron have been described before in a patient with pure myopathy, a deficiency of complex II/III activity and a defect in the import of the Rieske Fe-S centre of complex III (13), with the iron accumulation presumably secondary to the defective Fe-S formation.
As subunits of complexes I, II and III, in addition to aconitase, contain Fe-S centres, it is possible that the defects in the activities of these enzymes in FRDA reflect the inability of the mitochondria to incorporate iron into the Fe-S centre. The site of iron incorporation into the respiratory chain subunits is not known but may follow import of the protein into the mitochondrial matrix and this could involve frataxin. In contrast, however, aconitase exists as both a mitochondrial and a cytosolic enzyme. Although the Fe-S centre may be incorporated into the mitochondrial enzyme within the mitochondria, presumably it is incorporated into the cytosolic enzyme in the cytoplasm. The severe deficiency of aconitase in FRDA heart and skeletal muscle suggests that the enzyme activities in both compartments are affected. Whereas a direct mitochondrial effect on Fe-S centres due to frataxin deficiency might explain the defect in complexes I–III, it would not explain all the aconitase deficiency. Aconitase is, however, extremely sensitive to inhibition by superoxide and peroxynitrite (14) and so may signify an alternate and additional mechanism of pathogenesis in FRDA involving oxidative stress. Therefore, we suggest that the decline in the activity of aconitase is at least partly a result of superoxide ion generation, which itself will be promoted by the presence of both increased iron and a complex I–III defect (15). The involvement of free radicals in FRDA is further supported by the pattern of enzyme defect and its tissue distribution. Another model of mitochondrial free radical damage is the manganese superoxide dismutase knockout mouse. This mouse has a reduced defence against free radicals generated by the mitochondrion and similarly to FRDA develops a cardiomyopathy and severe deficiencies of complexes II/III and aconitase in cardiac muscle but with a less severe defect in complexes II/III in skeletal muscle (16).
The precise sequence of events in FRDA pathogenesis is uncertain. We suggest that impaired intramitochondrial iron metabolism results in defective Fe-S formation resulting in decreased complex I–III and mitochondrial aconitase activities and iron overload. Increased free iron levels and a defective mitochondrial respiratory chain will result in increased free radical generation, which will cause oxidative damage including further inhibition of aconitase activity. Impaired respiratory chain activity and decreased aconitase activity will impair ATP synthesis, which, together with oxidative damage to cellular components, will compromise cell viability (Fig. 5).
|
Our results predict that FRDA tissues will suffer oxidative stress and damage. This may include oxidation of protein, DNA and lipid and presumably compensatory responses (i.e. increased superoxide dismutase). Furthermore, antioxidant therapy may help to reduce tissue damage and retard disease progression. Evidence of oxidative stress and damage has been identified in other neurodegenerative disorders, including Alzheimer’s disease, Parkinson’s disease (PD) and motor neuron disease (amyotrophic lateral sclerosis) (for a review see ref. 17). FRDA offers a unique opportunity to intervene with ‘neuroprotective’ therapy before the disease becomes established. In contrast to PD, where patients have lost >50% of nigral dopaminergic neurons at presentation, and any attempt at neuroprotection must be in the presence of advanced disease and established pathogenetic mechanisms, FRDA patients can be diagnosed by genetic analysis either presymptomatically or early in the course of their disease when they may present before, for instance, cardiomyopathy becomes established. Inevitably, such a trial of antioxidants in FRDA would be over several years but could serve as a paradigm for antioxidant therapy in other neurodegenerative diseases.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
Tissue samples for enzyme and mitochondrial DNA analysis
Frozen samples of heart (n = 9), skeletal muscle (n = 5), DRG (n = 2) and cerebellar tissues (n = 2) were obtained at autopsy or biopsy from a total of 10 patients (P1–2 and 5–12) with FRDA. The diagnosis of FRDA was initially based on clinical presentation but confirmed by the presence of a GAA repeat expansion in the FRDA gene (2). Formalin-fixed tissues were available from four of these patients, and from a further two patients (P3 and P4) where genetic analysis was not available. Frozen tissue samples were obtained from 16 controls with no evidence of neurological or mitochondrial disease. The age of the FRDA patients (38.6 ± 10.4 years; n = 12) was not significantly different from the controls (53.3 ± 21.5 years; n = 19). The time from either biopsy or post-mortem to freezing the sample was matched for the samples (FRDA, 8.7 ± 4.6 h; control, 12.0 ± 15.3 h). Nine patients had evidence of cardiomyopathy and four patients were known to have non-insulin-dependent diabetes (Table 1). Disease control heart samples were also obtained from two patients with coronary artery disease.
Enzyme analysis
Tissue homogenates (10%) were prepared in homogenization medium (320 mM sucrose, 1 mM EDTA, 10 mM Tris–HCl pH 7.4) using a glass/teflon homogenizer. Following three freeze–thaw cycles, mitochondrial complex I (rotenone-sensitive NADH CoQ1 reductase), complex II/III (succinate cytochrome c reductase), complex IV (cytochrome oxidase) and citrate synthase activities were analysed at 30°C as described previously (18). Aconitase activity was analysed by the method described by Gardner et al. (19).
Mitochondrial DNA analysis
Total DNA was isolated from tissue samples using a standard phenol–chloroform extraction method (20) following overnight digestion with proteinase K. DNA (3 µg) from each sample was digested with PvuII and separated on a 0.8% agarose gel followed by blotting onto Hybond N membrane (Amersham, Little Chalfont, UK). The blot was prehybridized with heat-denatured sonicated salmon sperm DNA in 5x Denhart’s solution for 2 h followed by hybridization with whole mtDNA and an 18S rDNA probe, as a measure of total DNA loaded, labelled with [32P]dCTP (Redi Prime random prime labelling kit; Amersham) (20). The blot was visualized by 3 h exposure to autoradiographic film and subsequently to the phosphorimager plate. The radioactive signals from each mtDNA and 18S ribosomal band were quantified on a phosphorimager using ImageQuant software (Molecular Dynamics, Sunnyvale, CA).
Long PCR was performed with 1 µg of total tissue DNA using the forward (TTT CAT CAT GCG GAG ATG TTG GAT GG) and reverse (TGA GGC CAA ATA TCA TTC TGA GGG GU) primers with the GeneAmp XL PCR kit (Perkin Elmer, Langen, Germany). The ethidium-bromide-stained PCR products were visualized under UV light.
Histochemical analysis
Formalin-fixed paraffin-embedded tissue sections (4 µm) of heart, cerebellum, DRG, liver, pancreas, spinal cord, peripheral nerve, skeletal muscle and spleen were examined for iron content using Perl’s stain, and counter-stained with neutral red.
|
ACKNOWLEDGEMENT |
|---|
This research was supported by the Friedreich’s Ataxia Group.
|
FOOTNOTES |
|---|
+ To whom correspondence should be addressed at: University Department of Clinical Neurosciences, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK. Tel: +44 171 830 2012; Fax: +44 171 431 1577; Email: schapira@fhsm.ac.uk
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONRESULTSDISCUSSIONMATERIALS AND METHODSREFERENCES |
|---|
1 Chamberlain, S., Shaw, J., Rowland, A., Wallis, J., South, S., Nakamura, Y., Von Gabain, A., Farrall, M. and Williamson, R. (1988) Mapping of mutation causing Friedreich’s ataxia to human chromosome 9. Nature, 334, 248–250.[Medline]
2 Campuzano, V., Montermini, L., Molto, M.D., Pianese, L., Cossee, M., Cavalcanti, F., Monros, E., Rodius, F., Duclos, F., Monticella, A. et al. (1996) Friedreich’s ataxia: autosomal recessive disease caused by an intronic GAA triplet repeat expansion. Science, 217, 1423–1427.
3 Priller, J., Scherzer, C.R., Faber, P.W., MacDonald, M.E. and Young, A.B. (1997) Frataxin gene of Friedreich’s ataxia is targeted to mitochondria. Ann. Neurol., 42, 265–269.[Web of Science][Medline]
4 Campuzano, V., Montermini, L., Lutz, Y., Cova, L., Hindelang, C., Jiralerspong, S., Trottier, Y., Kish, S.J., Faucheux, B., Trouillas, P. et al. (1997) Frataxin is reduced in Friedreich ataxia patients and is associated with mitochondrial membranes. Hum. Mol. Genet., 6, 1771–1780.
5 Babcock, M., DeSilva, D., Oaks, R., Davis-Kaplan, S., Jiralerspong, S., Montermini, L., Pandolfo, M. and Kaplan, J. (1997) Regulation of mitochondrial iron accumulation by Yfh1p, a putative homolog of frataxin. Science, 276, 1709–1712.
6 Ouahchi, K., Arita, M., Kayden, H., Hentati, F., Ben Hamida, M., Sokol, R., Aria, H., Inoue, K., Mandel, J.L. and Koenig, M. (1995) Ataxia with isolated vitamin E deficiency is caused by mutations in the alpha-tocopherol transfer protein. Nature Genet., 9, 141–145.[Web of Science][Medline]
7 La Marche, J.B., Cote, M. and Lemieux, B. (1980) The cardiomyopathy of Friedreich’s ataxia. Can. J. Neurosci., 7, 389–396.
8 Rötig, A., De Lonlay, P., Chretien, D., Foury, F., Koenig, M., Sidi, D., Munnich, A. and Rustin, P. (1997) Aconitase and mitochondrial iron-sulphur protein deficiency in Friedreich ataxia. Nature Genet., 17, 215–217.[Web of Science][Medline]
9 Lodi, R., Cooper, J.M., Bradley, J.L., Manners, M., Styles, P., Taylor, D.J. and Schapira, A.H.V. (1999) Deficit of in vivo mitochondrial ATP production in patients with Friedreich ataxia. Proc. Natl Acad. Sci. USA, 96, 11492–11495.
10 Wilson, R.B. and Roof, D.M. (1997) Respiratory deficiency due to loss of mitochondrial DNA in yeast lacking the frataxin homologue. Nature Genet., 16, 352–357.[Web of Science][Medline]
11 Sanyal, A., Harington, A., Herbert, C.J., Groudinsky, O., Slonimski, P.P., Tung, B. and Getz, G.S. (1995) Heat shock protein HSP60 can alleviate the phenotype of mitochondrial RNA-deficient temperature-sensitive mna2 pet mutants. Mol. Gen. Genet., 246, 56–64.[Web of Science][Medline]
12 Sanchez-Casis, G., Cote, M. and Barbeau, A. (1976) Pathology of the heart in Friedreich’s ataxia. Can. J. Neurosci., 3, 349–354.
13 Schapira, A.H.V., Cooper, J.M., Morgan-Hughes, J.A., Landon, D.N. and Clark, J.B. (1990) Mitochondrial myopathy with a defect of mitochondrial protein transport. N. Engl. J. Med., 323, 37–42.[Web of Science][Medline]
14 Hausladen, A. and Fridovich, I. (1994) Superoxide and peroxynitrite inactivates aconitases, but nitric oxide does not. J. Biol. Chem., 269, 29405–29408.
15 Turrens, J.F. and Boveris, A. (1980) Generation of superoxide anion by the NADH dehydrogenase of bovine heart mitochondria. Biochem. J., 191, 421–427.[Web of Science][Medline]
16 Melov, S., Coskun, P., Patel, M., Tuinstra, R., Cottrell, B., Jun, A.S., Zastawny, T.H., Dizdaroglu, M., Goodman, S.I., Huang, T.T. et al. (1999) Mitochondrial disease in superoxide dismutase 2 mutant mice. Proc. Natl Acad. Sci. USA, 96, 846–851.
17 Schapira, A.H.V. (1996) Oxidative stress and mitochondrial dysfunction in neurodegeneration. Curr. Opin. Neurol., 9, 260–264.[Web of Science][Medline]
18 Schapira, A.H.V., Mann, V.M., Cooper, J.M., Dexter, D., Daniel, S.E., Jenner, P., Clark, J.B. and Marsden, C.D. (1990) Anatomic and disease specificity of NADH CoQ1 reductase (complex I) deficiency in Parkinson’s disease. J. Neurochem., 55, 2142–2145.[Web of Science][Medline]
19 Gardner, P.R., Nguyen, D.D.H. and White, C.W. (1994) Aconitase is a sensitive and critical target of oxygen poisoning in cultured mammalian cells and rat lungs. Proc. Natl Acad. Sci. USA, 91, 12248–12252.
20 Sambrook, J., Fritsch, E.F. and Maniatis, T. (1989) Molecular Cloning: A Laboratory Manual. 2nd edn. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, NY, pp. 3–4.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  S. Leidgens, S. De Smet, and F. Foury Frataxin interacts with Isu1 through a conserved tryptophan in its {beta}-sheet Hum. Mol. Genet., November 11, 2009; (2009) ddp495v2. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I Castaldo, M Pinelli, A Monticelli, F Acquaviva, M Giacchetti, A Filla, S Sacchetti, S Keller, V E Avvedimento, L Chiariotti, et al. DNA methylation in intron 1 of the frataxin gene is related to GAA repeat length and age of onset in Friedreich ataxia patients J. Med. Genet., December 1, 2008; 45(12): 808 - 812. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F M Skidmore, V Drago, P Foster, I M Schmalfuss, K M Heilman, and R R Streiff Aceruloplasminaemia with progressive atrophy without brain iron overload: treatment with oral chelation J. Neurol. Neurosurg. Psychiatry, April 1, 2008; 79(4): 467 - 470. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Condo, N. Ventura, F. Malisan, A. Rufini, B. Tomassini, and R. Testi In vivo maturation of human frataxin Hum. Mol. Genet., July 1, 2007; 16(13): 1534 - 1540. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Ribai, F. Pousset, M.-L. Tanguy, S. Rivaud-Pechoux, I. Le Ber, F. Gasparini, P. Charles, A.-S. Beraud, M. Schmitt, M. Koenig, et al. Neurological, Cardiological, and Oculomotor Progression in 104 Patients With Friedreich Ataxia During Long-term Follow-up Arch Neurol, April 1, 2007; 64(4): 558 - 564. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. V. Llorens, J. A. Navarro, M. J. Martinez-Sebastian, M. K. Baylies, S. Schneuwly, J. A. Botella, and M. D. Molto Causative role of oxidative stress in a Drosophila model of Friedreich ataxia FASEB J, February 1, 2007; 21(2): 333 - 344. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Nikali, A. Suomalainen, J. Saharinen, M. Kuokkanen, J. N. Spelbrink, T. Lonnqvist, and L. Peltonen Infantile onset spinocerebellar ataxia is caused by recessive mutations in mitochondrial proteins Twinkle and Twinky Hum. Mol. Genet., October 15, 2005; 14(20): 2981 - 2990. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Sturm, U. Bistrich, M. Schranzhofer, J. P. Sarsero, U. Rauen, B. Scheiber-Mojdehkar, H. de Groot, P. Ioannou, and F. Petrat Friedreich's Ataxia, No Changes in Mitochondrial Labile Iron in Human Lymphoblasts and Fibroblasts: A DECREASE IN ANTIOXIDATIVE CAPACITY? J. Biol. Chem., February 25, 2005; 280(8): 6701 - 6708. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 X. J. Chen, X. Wang, B. A. Kaufman, and R. A. Butow Aconitase Couples Metabolic Regulation to Mitochondrial DNA Maintenance Science, February 4, 2005; 307(5710): 714 - 717. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Lange, U. Muhlenhoff, M. Denzel, G. Kispal, and R. Lill The Heme Synthesis Defect of Mutants Impaired in Mitochondrial Iron-Sulfur Protein Biogenesis Is Caused by Reversible Inhibition of Ferrochelatase J. Biol. Chem., July 9, 2004; 279(28): 29101 - 29108. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. A. Wilkinson, A. H. Crosby, C. Turner, L. J. Bradley, L. Ginsberg, N. W. Wood, A. H. Schapira, and T. T. Warner A clinical, genetic and biochemical study of SPG7 mutations in hereditary spastic paraplegia Brain, May 1, 2004; 127(5): 973 - 980. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Simon, H. Seznec, A. Gansmuller, N. Carelle, P. Weber, D. Metzger, P. Rustin, M. Koenig, and H. Puccio Friedreich Ataxia Mouse Models with Progressive Cerebellar and Sensory Ataxia Reveal Autophagic Neurodegeneration in Dorsal Root Ganglia J. Neurosci., February 25, 2004; 24(8): 1987 - 1995. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Karthikeyan, J. H. Santos, M. A. Graziewicz, W. C. Copeland, G. Isaya, B. V. Houten, and M. A. Resnick Reduction in frataxin causes progressive accumulation of mitochondrial damage Hum. Mol. Genet., December 15, 2003; 12(24): 3331 - 3342. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Crisp, A. Pollington, C. Galea, S. Jaron, Y. Yamaguchi-Iwai, and J. Kaplan Inhibition of Heme Biosynthesis Prevents Transcription of Iron Uptake Genes in Yeast J. Biol. Chem., November 14, 2003; 278(46): 45499 - 45506. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Pastore, G. Tozzi, L. M. Gaeta, E. Bertini, V. Serafini, S. D. Cesare, V. Bonetto, F. Casoni, R. Carrozzo, G. Federici, et al. Actin Glutathionylation Increases in Fibroblasts of Patients with Friedreich's Ataxia: A POTENTIAL ROLE IN THE PATHOGENESIS OF THE DISEASE J. Biol. Chem., October 24, 2003; 278(43): 42588 - 42595. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Tan, E. Napoli, F. Taroni, and G. Cortopassi Decreased expression of genes involved in sulfur amino acid metabolism in frataxin-deficient cells Hum. Mol. Genet., July 15, 2003; 12(14): 1699 - 1711. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Lesuisse, R. Santos, B. F. Matzanke, S. A. B. Knight, J.-M. Camadro, and A. Dancis Iron use for haeme synthesis is under control of the yeast frataxin homologue (Yfh1) Hum. Mol. Genet., April 15, 2003; 12(8): 879 - 889. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Adinolfi, M. Trifuoggi, A. S. Politou, S. Martin, and A. Pastore A structural approach to understanding the iron-binding properties of phylogenetically different frataxins Hum. Mol. Genet., August 1, 2002; 11(16): 1865 - 1877. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Karthikeyan, L. K. Lewis, and M. A. Resnick The mitochondrial protein frataxin prevents nuclear damage Hum. Mol. Genet., May 16, 2002; 11(11): 1351 - 1362. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. M. Becker, J. M. Greer, P. Ponka, and D. R. Richardson Erythroid differentiation and protoporphyrin IX down-regulate frataxin expression in Friend cells: characterization of frataxin expression compared to molecules involved in iron metabolism and hemoglobinization Blood, May 15, 2002; 99(10): 3813 - 3822. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G Tozzi, M Nuccetelli, M Lo Bello, S Bernardini, L Bellincampi, S Ballerini, L M Gaeta, C Casali, A Pastore, G Federici, et al. Antioxidant enzymes in blood of patients with Friedreich's ataxia Arch. Dis. Child., May 1, 2002; 86(5): 376 - 379. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Cavadini, H. A. O'Neill, O. Benada, and G. Isaya Assembly and iron-binding properties of human frataxin, the protein deficient in Friedreich ataxia Hum. Mol. Genet., February 1, 2002; 11(3): 217 - 227. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Melov, S. R. Doctrow, J. A. Schneider, J. Haberson, M. Patel, P. E. Coskun, K. Huffman, D. C. Wallace, and B. Malfroy Lifespan Extension and Rescue of Spongiform Encephalopathy in Superoxide Dismutase 2 Nullizygous Mice Treated with Superoxide Dismutase-Catalase Mimetics J. Neurosci., November 1, 2001; 21(21): 8348 - 8353. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. N. Roy and N. C. Andrews Recent advances in disorders of iron metabolism: mutations, mechanisms and modifiers Hum. Mol. Genet., October 1, 2001; 10(20): 2181 - 2186. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Lodi, B. Rajagopalan, A. M Blamire, J.M. Cooper, C. H Davies, J. L Bradley, P. Styles, and A. H.V Schapira Cardiac energetics are abnormal in Friedreich ataxia patients in the absence of cardiac dysfunction and hypertrophy: An in vivo 31P magnetic resonance spectroscopy study Cardiovasc Res, October 1, 2001; 52(1): 111 - 119. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Tan, L.-S. Chen, B. Lonnerdal, C. Gellera, F. A. Taroni, and G. A. Cortopassi Frataxin expression rescues mitochondrial dysfunctions in FRDA cells Hum. Mol. Genet., September 1, 2001; 10(19): 2099 - 2107. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C.W. Shults and A.H.V. Schapira A cue to queue for CoQ? Neurology, August 14, 2001; 57(3): 375 - 376. [Full Text] [PDF]
|
|
|
|
|
|
P. Cavadini, C. Gellera, P. I. Patel, and G. Isaya Human frataxin maintains mitochondrial iron homeostasis in Saccharomyces cerevisiae Hum. Mol. Genet., October 1, 2000; 9(17): 2523 - 2530. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Puccio Recent advances in the molecular pathogenesis of Friedreich ataxia Hum. Mol. Genet., April 1, 2000; 9(6): 887 - 892. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Dhe-Paganon, R. Shigeta, Y.-I. Chi, M. Ristow, and S. E. Shoelson Crystal Structure of Human Frataxin J. Biol. Chem., September 29, 2000; 275(40): 30753 - 30756. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Cavadini, J. Adamec, F. Taroni, O. Gakh, and G. Isaya Two-step Processing of Human Frataxin by Mitochondrial Processing Peptidase. PRECURSOR AND INTERMEDIATE FORMS ARE CLEAVED AT DIFFERENT RATES J. Biol. Chem., December 22, 2000; 275(52): 41469 - 41475. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||