Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0016719 (Friedreich's ataxia)
 2,098 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Friedreich ataxia (FA) is caused by decreased frataxin expression that results in mitochondrial iron (Fe) overload. However, the role of frataxin in mammalian Fe metabolism remains unclear. In this investigation we examined the function of frataxin in Fe metabolism by implementing a well-characterized model of erythroid differentiation, namely, Friend cells induced using dimethyl sulfoxide (DMSO). We have characterized the changes in frataxin expression compared to molecules that play key roles in Fe metabolism (the transferrin receptor [TfR] and the Fe transporter Nramp2) and hemoglobinization (beta-globin). DMSO induction of hemoglobinization results in a marked decrease in frataxin gene (Frda) expression and protein levels. To a lesser extent, Nramp2 messenger RNA (mRNA) levels were also decreased on erythroid differentiation, whereas TfR and beta-globin mRNA levels increased. Intracellular Fe depletion using desferrioxamine or pyridoxal isonicotinoyl hydrazone, which chelate cytoplasmic or cytoplasmic and mitochondrial Fe pools, respectively, have no effect on frataxin expression. Furthermore, cytoplasmic or mitochondrial Fe loading of induced Friend cells with ferric ammonium citrate, or the heme synthesis inhibitor, succinylacetone, respectively, also had no effect on frataxin expression. Although frataxin has been suggested by others to be a mitochondrial ferritin, the lack of effect of intracellular Fe levels on frataxin expression is not consistent with an Fe storage role. Significantly, protoporphyrin IX down-regulates frataxin protein levels, suggesting a regulatory role of frataxin in Fe or heme metabolism. Because decreased frataxin expression leads to mitochondrial Fe loading in FA, our data suggest that reduced frataxin expression during erythroid differentiation results in mitochondrial Fe sequestration for heme biosynthesis.
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PMID: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. 1198 41

The mitochondrial protein frataxin helps maintain appropriate iron levels in the mitochondria of yeast and humans. A deficiency of this protein in humans causes Friedreich's ataxia, while its complete absence in yeast (Delta yfh1 mutant) results in loss of mitochondrial DNA, apparently due to radicals generated by excess iron. We found that the absence of frataxin in yeast also leads to nuclear damage, as evidenced by inducibility of a nuclear DNA damage reporter, increased chromosomal instability including recombination and mutation, and greater sensitivity to DNA-damaging agents, as well as slow growth. Addition of a human frataxin mutant did not prevent nuclear damage, although it partially complemented the Delta yfh1 mutant in preventing mitochondrial DNA loss. The effects in Delta yfh1 mutants result from reactive oxygen species (ROS), since (i) Delta yfh1 cells produce more hydrogen peroxide, (ii) the effects are alleviated by a radical scavenger and (iii) the glutathione peroxidase gene prevents an increase in mutation rates. Thus, the frataxin protein is concluded to have a protective role for the nucleus as well as the mitochondria.
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PMID:The mitochondrial protein frataxin prevents nuclear damage. 1201 17

The discovery of the genetic cause of Friedreich ataxia has significantly affected our understanding of the disorder at both the clinical and basic science levels. Friedreich ataxia results from a deficiency of functional frataxin, a protein that appears to be involved in mitochondrial iron homeostasis. This leads to iron accumulation and mitochondrial abnormalities with consequent oxidant damage. The clinical spectrum of Friedreich ataxia has also expanded with the recognition of broader phenotypic features, including the absence of classical Friedreich ataxia features, later age at onset, and spasticity instead of ataxia. Although no proven therapy is yet available, antioxidants are a potential method for therapeutic intervention.
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PMID:Friedreich ataxia: effects of genetic understanding on clinical evaluation and therapy. 1243 76

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease causing limb and gait ataxia and cardiomyopathy. The disease gene encodes a mitochondrial protein of unknown function, frataxin. The loss of functional frataxin is caused by a large GAA trinucleotide expansion in the first intron of the gene, thus impairing gene transcription. The lack of frataxin appears to result primarily in disabled recruitment of early antioxidant defenses, resulting in oxidative insult to the highly sensitive iron-sulfur proteins aconitase and three mitochondrial respiratory chain complexes (I-III). Accordingly, antioxidant-based therapy appears promising in counteracting the course of the disease.
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PMID:Molecular insights into Friedreich's ataxia and antioxidant-based therapies. 1206 31

Friedreich's ataxia (FRDA), the most common inherited ataxia, is an autosomal recessive degenerative disorder caused by a GAA triplet expansion or point mutations in the FRDA gene on chromosome 9q13. The FRDA gene product, frataxin, is a widely expressed mitochondrial protein, which is severely reduced in FRDA patients. The demonstration that deficit of frataxin in FRDA is associated with mitochondrial iron accumulation, increased sensitivity to oxidative stress, deficit of respiratory chain complex activities and in vivo impairment of cardiac and skeletal muscle tissue energy metabolism, has established FRDA as a "new" nuclear encoded mitochondrial disease. Pilot studies have shown the potential effect of antioxidant therapy based on idebenone or coenzyme Q10 plus Vitamin E administration in this condition and provide a strong rationale for designing larger randomized clinical trials.
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PMID:Mitochondrial dysfunction in Friedreich's ataxia: from pathogenesis to treatment perspectives. 1206 11

Friedreich's ataxia (FRDA) is a neuro-degenerative disease causing limb and gait ataxia and hypertrophic cardiomyopathy. It results from a triplet expansion in the first intron of the frataxin gene encoding a mitochondrial protein of yet unknown function. Cells with low frataxin content display generalized deficiency of mitochondrial iron-sulfur cluster-containing proteins, which presumably denotes overproduction of superoxide radicals in these organelles. Idebenone, a short-chain quinone, may act as a potent free radical scavenger protecting mitochondria against oxidative stress. We therefore carried out an open trial of idebenone (oral supplementation; 5mg/kg/day) in a large series of FRDA patients and followed their left ventricular mass and function. Consistent and definitive worsening being observed in the natural course of the disease and cardiac hypertrophy having no chance of spontaneous reversal and to be subject to a placebo effect, the patient's heart status before and after the treatment was used to unambiguously establish the effect of the drug. After six months, heart ultrasound revealed more than 20% reduction of left ventricular mass in about half of the patients (p < 0.001) and no significant change in the other half. Since any measurable reversion of this pathogenic trait is highly significant, this demonstrates the efficiency of idebenone in controlling heart hypertrophy in FRDA. Owing to the absence of side effects of the drug, idebenone (up to 15mg/kg/day) should be prescribed for FRDA patients continuously as early as possible.
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PMID:Heart hypertrophy and function are improved by idebenone in Friedreich's ataxia. 1206 12

Friedreich ataxia (FRDA), a progressive neurodegenerative disease, is due to the partial loss of function of frataxin, a mitochondrial protein of unknown function. Loss of frataxin causes mitochondrial iron accumulation, deficiency in the activities of iron-sulfur (Fe-S) proteins, and increased oxidative stress. Mouse models for FRDA demonstrate that the Fe-S deficit precedes iron accumulation, suggesting that iron accumulation is a secondary event. Furthermore, increased oxidative stress in FRDA patients has been demonstrated, and in vitro experiments imply that the frataxin defect impairs early antioxidant defenses. These results taken together suggest that frataxin may function either in mitochondrial iron homeostasis, in Fe-S cluster biogenesis, or directly in the response to oxidative stress. It is clear, however, that the pathogenic mechanism in FRDA involves free-radical production and oxidative stress, a process that appears to be sensitive to antioxidant therapies.
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PMID:Friedreich ataxia: a paradigm for mitochondrial diseases. 1207 69

Over 100 mutations of mitochondrial DNA (mtDNA) have been associated with human disease. The phenotypic manifestation of mtDNA mutations is extremely broad, from oligosymptomatic patients with isolated deafness, diabetes, ophthalmoplegia, etc., to complex encephalomyopathic disorders that may include dementia, seizures, ataxia, stroke-like episodes, etc. The genotype variants are also wide, with rearrangements (deletions, duplications) and point mutations affecting protein coding genes, tRNAs and rRNAs. There are some broad genotype/phenotype correlations but also substantial overlap. The pathogenetic mechanisms involved in the expression of mtDNA mutations are still not yet fully understood. More recently, mutations of nuclear genes encoding subunits of the respiratory chain, particularly those of complex I, have been identified. These predominantly, but not exclusively, involve infant onset disease with early death. Recently it has become clear that the function of the respiratory chain may be impaired by mutations affecting other mitochondrial proteins or as a secondary phenomenon to other intracellular biochemical derangements. Examples include Friedreich ataxia where a mutation of a nuclear encoded protein (frataxin), probably involved in iron homeostasis in mitochondria, results in severe deficiency of the respiratory chain in a pattern indicative of free radical mediated damage. Mutations of nuclear encoded proteins involved in cytochrome oxidase assembly and maintenance have been characterised and, as predicted, are associated with severe deficiency of cytochrome oxidase and, most frequently, Leigh syndrome. Defects of intracellular metabolism, with particularly excess-free radical generation including nitric oxide or peroxynitrite, may cause secondary damage to the respiratory chain. This is probably of relevance in Huntington disease, motor neuron disease (amyotrophic lateral sclerosis) and Wilson disease. These disorders seem to have defective oxidative phosphorylation as a common pathway in their pathogenesis and it may be that treatments designed to improve respiratory chain function may ameliorate the progression of these disorders.
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PMID:Primary and secondary defects of the mitochondrial respiratory chain. 1213 29

Friedreich's ataxia (FRDA), an autosomal recessive cardio- and neurodegenerative disease, is caused by low expression of frataxin, a small mitochondrial protein, encoded in the nucleus. At the biochemical level, the lack of frataxin leads to dysregulation of mitochondrial iron homeostasis and oxidative damage, which eventually causes neuronal death. It is, however, still unclear whether frataxin is directly involved in iron binding, since the yeast orthologue, but not the human protein, has been shown to form large aggregates in the presence of large iron excess. We have compared the properties of three proteins from the frataxin family--the bacterial CyaY from Escherichia coli, the yeast Yfh1 and human frataxin--as representative of organisms of increasing complexity. We show that the three proteins have the same fold but different thermal stabilities and iron-binding properties. While human frataxin has no tendency to bind iron, CyaY forms iron-promoted aggregates with a behaviour similar to that of yeast frataxin. However, aggregation can be competed by chelator agents or by ionic strength. At physiological salt conditions, almost no aggregation is observed. The design of mutants produced to identify the protein surface involved in iron-promoted aggregation allows us to demonstrate that the process is mediated by a negatively charged surface ridge. Mutation of three of these residues is sufficient to convert CyaY in a protein with properties similar to those of human frataxin. On the other hand, mutation of the exposed surface of the beta sheet, which contains most of the conserved residues, does not affect aggregation, suggesting that iron binding is a non-conserved part of a more complex cellular function of frataxins.
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PMID:A structural approach to understanding the iron-binding properties of phylogenetically different frataxins. 1214 Jan 89

The mitochondrial matrix protein frataxin is depleted in patients with Friedreich's ataxia, the most common autosomal recessive ataxia. While frataxin is important for intracellular iron homeostasis, its exact cellular role is unknown. Deletion of the yeast frataxin homolog YFH1 yields mutants ((Delta)yfh1) that, depending on the genetic background, display various degrees of phenotypic defects. This renders it difficult to distinguish primary (early) from secondary (late) consequences of Yfh1p deficiency. We have constructed a yeast strain (Gal-YFH1) that carries the YFH1 gene under the control of a galactose-regulated promoter. Yfh1p-deficient Gal-YFH1 cells are far less sensitive to oxidative stress than (Delta)yfh1 mutants, maintain mitochondrial DNA, and synthesize heme at wild-type rates. Yfh1p depletion causes a strong reduction in the assembly of mitochondrial Fe/S proteins both in vivo and in detergent extracts of mitochondria. Impaired Fe/S protein biogenesis explains the respiratory deficiency of Gal-YFH1 cells. Furthermore, Yfh1p-depleted Gal-YFH1 cells show decreased maturation of cytosolic Fe/S proteins and accumulation of mitochondrial iron. This latter phenotype is common for defects in cytosolic Fe/S protein assembly. Together, our data demonstrate a specific role of frataxin in the biosynthesis of cellular Fe/S proteins and exclude most of the previously suggested functions. Friedreich's ataxia may therefore represent a disorder caused by defects in Fe/S protein maturation.
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PMID:The yeast frataxin homolog Yfh1p plays a specific role in the maturation of cellular Fe/S proteins. 1216 64


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