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

Pathological expansions of GAA repeats in the first intron of the frataxin gene cause most cases of Friedreich ataxia, a progressively debilitating neurodegenerative disease. The disease is inherited in an autosomal recessive manner and the GAA repeats are suspected to form unusual non B-DNA conformations that decrease transcription and subsequently reduce levels of the encoded protein, frataxin. Recent work has shown that GAA repeats induce heterochromatin formation and silencing of the frataxin gene locus. Frataxin plays a crucial role in iron metabolism and detoxification and interacts with electron transport chain proteins. Clinical trials are currently underway to examine the efficacy of antioxidants in the treatment of Friedreich ataxia, but therapeutics designed to increase frataxin message levels are still in the developmental stages. This review will focus on the progress of potential treatment strategies for Friedreich ataxia that target the GAA expanded gene and seek to increase the level of frataxin message and protein.
 ...
PMID:Targeting the gene in Friedreich ataxia. 1820 56

Friedreich ataxia is caused by reduced activity of frataxin, a conserved iron-binding protein of the mitochondrial matrix, thought to supply iron for formation of Fe-S clusters on the scaffold protein Isu. Frataxin binds Isu in an iron-dependent manner in vitro. However, the biological relevance of this interaction and whether in vivo the interaction between frataxin and Isu is mediated by adaptor proteins is a matter of debate. Here, we report that alterations of conserved, surface-exposed residues of yeast frataxin, which have deleterious effects on cell growth, impair Fe-S cluster biogenesis and interaction with Isu while altering neither iron binding nor oligomerization. Our results support the idea that the surface of the beta-sheet, adjacent to the acidic, iron binding ridge, is important for interaction of Yfh1 with the Fe-S cluster scaffold and point to a critical role for frataxin in Fe-S cluster biogenesis.
 ...
PMID:Binding of yeast frataxin to the scaffold for Fe-S cluster biogenesis, Isu. 1831 50

Frataxin is a small conserved mitochondrial protein; in humans, mutations affecting frataxin expression or function result in Friedreich's ataxia. Much of the current understanding of frataxin function comes from informative studies with yeast models, but considerable debates remain with regard to the primary functions of this ubiquitous protein. We exploit the tractable reverse genetics of Trypanosoma brucei in order to specifically consider the importance of frataxin in an early branching lineage. Using inducible RNAi, we show that frataxin is essential in T. brucei and that its loss results in reduced activity of the marker Fe-S cluster-containing enzyme aconitase in both the mitochondrion and cytosol. Activities of mitochondrial succinate dehydrogenase and fumarase also decreased, but the concentration of reactive oxygen species increased. Trypanosomes lacking frataxin also exhibited a low mitochondrial membrane potential and reduced oxygen consumption. Crucially, however, iron did not accumulate in frataxin-depleted mitochondria, and as T. brucei frataxin does not form large complexes, it suggests that it plays no role in iron storage. Interestingly, RNAi phenotypes were ameliorated by expression of frataxin homologues from hydrogenosomes of another divergent protist Trichomonas vaginalis. Collectively, the data suggest trypanosome frataxin functions primarily only in Fe-S cluster biogenesis and protection from reactive oxygen species.
 ...
PMID:Ancestral roles of eukaryotic frataxin: mitochondrial frataxin function and heterologous expression of hydrogenosomal Trichomonas homologues in trypanosomes. 1843 47

Frataxin, a mitochondrial protein that is directly involved in regulating cellular iron homeostasis, has been suggested to serve as an iron chaperone during cellular Fe-S cluster biosynthesis. In humans, decreased amounts or impaired function of frataxin causes the autosomal recessive neurodegenerative disorder Friedreich's ataxia. Cellular production of Fe-S clusters is accomplished by the Fe cofactor assembly platform enzymes Isu (eukaryotes) and IscU (prokaryotes). In this report, we have characterized the overall stability and iron binding properties of the Drosophila frataxin homologue (Dfh). Dfh is highly folded with secondary structural elements consistent with the structurally characterized frataxin orthologs. While the melting temperature ( T M approximately 59 degrees C) and chemical stability ([urea] 50% approximately 2.4 M) of Drosophila frataxin, measured using circular dichroism (CD) and fluorescence spectroscopy, closely match values determined for the human ortholog, pure Dfh is more stable against autodegradation than both the human and yeast proteins. The ferrous iron binding affinity ( K d approximately 6.0 microM) and optimal metal to protein stoichiometry (1:1) for Dfh have been measured using isothermal titration calorimetry (ITC). Under anaerobic conditions with salt present, holo-Dfh is a stable iron-loaded protein monomer. Frataxin prevents reactive oxygen species-induced oxidative damage to DNA when presented with both Fe(II) and H 2O 2. Ferrous iron bound to Dfh is high-spin and held in a partially symmetric Fe-(O/N) 6 coordination environment, as determined by X-ray absorption spectroscopy (XAS). Extended X-ray absorption fine structure (EXAFS) simulations indicate the average Fe-O/N bond length in Dfh is 2.13 A, consistent with a ligand geometry constructed by water and carboxylate oxygens most likely supplied in part by surface-exposed conserved acidic residues located on helix 1 and strand 1 in the structurally characterized frataxin orthologs. The iron-dependent binding affinity ( K d approximately 0.21 microM) and optimal holo-Dfh to Isu monomer stoichiometry (1:1) have also been determined using ITC. Finally, frataxin mediates the delivery of Fe(II) to Isu, promoting Fe-S cluster assembly in vitro. The Dfh-assisted assembly of Fe-S clusters occurs with an observed kinetic rate constant ( k obs) of 0.096 min (-1).
 ...
PMID:Drosophila frataxin: an iron chaperone during cellular Fe-S cluster bioassembly. 1854 Jun 37

Deficiency in the nuclear-encoded mitochondrial protein frataxin causes Friedreich ataxia (FRDA), a progressive neurodegenerative disorder associating spinocerebellar ataxia and cardiomyopathy. Although the exact function of frataxin is still a matter of debate, it is widely accepted that frataxin is a mitochondrial iron chaperone involved in iron-sulfur cluster and heme biosynthesis. Frataxin is synthesized as a precursor polypeptide, directed to the mitochondrial matrix where it is proteolytically cleaved by the mitochondrial processing peptidase to the mature form via a processing intermediate. The mature form was initially reported to be encoded by amino acids 56-210 (m(56)-FXN). However, two independent reports have challenged these studies describing two different forms encoded by amino acids 78-210 (m(78)-FXN) and 81-210 (m(81)-FXN). Here, we provide evidence that mature human frataxin corresponds to m(81)-FXN, and can rescue the lethal phenotype of fibroblasts completely deleted for frataxin. Furthermore, our data demonstrate that the migration profile of frataxin depends on the experimental conditions, a behavior which most likely contributed to the confusion concerning the endogenous mature frataxin. Interestingly, we show that m(56)-FXN and m(78)-FXN can be generated when the normal maturation process of frataxin is impaired, although the physiological relevance is not clear. Furthermore, we determine that the d-FXN form, previously reported to be a degradation product, corresponds to m(78)-FXN. Finally, we demonstrate that all frataxin isoforms are generated and localized within the mitochondria. The clear identification of the N-terminus of mature FXN is an important step for designing therapeutic approaches for FRDA based on frataxin replacement.
 ...
PMID:The in vivo mitochondrial two-step maturation of human frataxin. 1872 97

In a "proof-of-concept" study, we demonstrated that recombinant human erythropoietin (rhuEPO) increases frataxin levels in Friedreich's ataxia (FRDA) patients. We now report a 6-month open-label clinical pilot study of safety and efficacy of rhuEPO treatment in FRDA. Eight adult FRDA patients received 2.000 IU rhuEPO thrice a week subcutaneously. Clinical outcome measures included Ataxia Rating Scales. Frataxin levels and indicators for oxidative stress were assessed. Hematological parameters were monitored biweekly. Scores in Ataxia Rating Scales such as FARS (P = 0.0063) and SARA (P = 0.0045) improved significantly. Frataxin levels increased (P = 0.017) while indicators of oxidative stress such as urine 8-OHdG (P = 0.012) and peroxide levels decreased (P = 0.028). Increases in hematocrit requiring phlebotomies occurred in 4 of 8 patients. In this explorative open-label clinical pilot study, we found an evidence for clinical improvement together with a persistent increase of frataxin levels and a reduction of oxidative stress parameters in patients with FRDA receiving chronic treatment with rhuEPO. Safety monitoring with regular blood cell counts and parameters of iron metabolism is a potential limitation of this approach.
 ...
PMID:Neurological effects of recombinant human erythropoietin in Friedreich's ataxia: a clinical pilot trial. 1875 45

Trypanosoma brucei, the agent of human sleeping sickness and ruminant nagana, is the most genetically tractable representative of the domain Excavata. It is evolutionarily very distant from humans, with a last common ancestor over 1 billion years ago. Frataxin, a highly conserved small protein involved in iron-sulfur cluster synthesis, is present in both organisms, and its deficiency is responsible for Friedreich's ataxia in humans. We have found that T. brucei growth-inhibition phenotype caused by down-regulated frataxin is rescued by means of human frataxin. The rescue is fully dependent on the human frataxin being imported into the trypanosome mitochondrion. Processing of the imported protein by mitochondrial processing peptidase can be blocked by mutations in the signal peptide, as in human cells. Although in human cells frataxin must be processed to execute its function, the same protein in the T. brucei mitochondrion is functional even in the absence of processing. Our results illuminate remarkable conservation of the mechanisms of mitochondrial protein import and processing.
 ...
PMID:Mitochondrial localization of human frataxin is necessary but processing is not for rescuing frataxin deficiency in Trypanosoma brucei. 1876 99

Defects in frataxin result in Friedreich ataxia, a genetic disease characterized by early onset of neurodegeneration, cardiomyopathy, and diabetes. Frataxin is a conserved mitochondrial protein that controls iron needed for iron-sulfur cluster assembly and heme synthesis and also detoxifies excess iron. Studies in vitro have shown that either monomeric or oligomeric frataxin delivers iron to other proteins, whereas ferritin-like frataxin particles convert redox-active iron to an inert mineral. We have investigated how these different forms of frataxin are regulated in vivo. In Saccharomyces cerevisiae, only monomeric yeast frataxin (Yfh1) was detected in unstressed cells when mitochondrial iron uptake was maintained at a steady, low nanomolar level. Increments in mitochondrial iron uptake induced stepwise assembly of Yfh1 species ranging from trimer to > or = 24-mer, independent of interactions between Yfh1 and its major iron-binding partners, Isu1/Nfs1 or aconitase. The rate-limiting step in Yfh1 assembly was a structural transition that preceded conversion of monomer to trimer. This step was induced, independently or synergistically, by mitochondrial iron increments, overexpression of wild type Yfh1 monomer, mutations that stabilize Yfh1 trimer, or heat stress. Faster assembly kinetics correlated with reduced oxidative damage and higher levels of aconitase activity, respiratory capacity, and cell survival. However, deregulation of Yfh1 assembly resulted in Yfh1 aggregation, aconitase sequestration, and mitochondrial DNA depletion. The data suggest that Yfh1 assembly responds to dynamic changes in mitochondrial iron uptake or stress exposure in a highly controlled fashion and that this may enable frataxin to simultaneously promote respiratory function and stress tolerance.
 ...
PMID:Assembly of the iron-binding protein frataxin in Saccharomyces cerevisiae responds to dynamic changes in mitochondrial iron influx and stress level. 1878 75

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by decreased expression of the protein Frataxin. Frataxin deficiency leads to excessive free radical production and dysfunction of chain complexes. Mitochondrial DNA (mtDNA) could be considered a candidate modifier factor for FRDA disease, since mitochondrial oxidative stress is thought to be involved in the pathogenesis of this disease. It prompted us to focus on the mtDNA and monitor the nucleotide changes of genome which are probably the cause of respiratory chain defects and reduced ATP generation. We searched about 46% of the entire mitochondrial genome by temporal temperature gradient gel electrophoresis (TTGE) and DNA fragments showing abnormal banding patterns were sequenced for the identification of exact mutations. In 18 patients, for the first time, we detected 26 mtDNA mutations; of which 5 (19.2%) was novel and 21 (80.8%) have been reported in other diseases. Heteroplasmic C13806A polymorphisms were associated with Iranian FRDA patients (55.5%). Our results showed that NADH dehydrogenase (ND) genes mutations in FRDA samples were higher than normal controls (P < 0.001) and we found statistically significant inverse correlation (r = -0.8) between number of mutation in ND genes and age of onset in FRDA patients. It is possible that mutations in ND genes could constitute a predisposing factor which in combination with environmental risk factors affects age of onset and disease progression.
 ...
PMID:A novel mitochondrial heteroplasmic C13806A point mutation associated with Iranian Friedreich's ataxia. 1880 69

Friedreich's ataxia (FA) is the most frequent autosomal recessive ataxia and essentially considered a disease of the dorsal root ganglia and spinal cord. It is caused by homozygous GAA expansions in the Frataxin gene in most cases. Although only a few studies have addressed cerebral involvement in FA, cognitive symptoms have lately been emphasized. To evaluate brain damage in vivo, we employed whole-brain VBM and analysis of pre-defined regions of interest (ROIs) over the cerebellum to compare 24 patients with 24 age-and-sex-matched normal controls. (1)H-MRS of deep cerebral white matter (WM) was subsequently performed. Mean age of patients was 28 years (range 14-45), mean duration of disease was 14 years (range 5-28) and 11 were men. Mean length of shorter (GAA1) and longer (GAA2) alleles were 735 and 863, respectively. VBM analysis identified WM atrophy in the posterior cyngulate gyrus, paracentral lobule and middle frontal gyrus. ROIs over the infero-medial cerebellar hemispheres and dorsal brainstem presented gray matter atrophy, which correlated with duration of disease (r = -0.4). NAA/Cr ratios were smaller among patients (P = 0.006), but not Cho/Cr (P = 0.08). Our results provide evidence of axonal damage in the cerebellum, brainstem and subcortical WM in FA. This suggests that neuronal dysfunction is more widespread than previously thought in FA.
 ...
PMID:A combined voxel-based morphometry and 1H-MRS study in patients with Friedreich's ataxia. 1928 Jan 6


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>