Análisis genético y funcional de la frataxina y otras proteínas mitocrondriales relacionadas con ataxias cerebelosas.

Resumo

Frataxin deficiency causes Friedreich ataxia, a neurodegenerative genetic disorder affecting sensory neurons of dorsal root ganglia and spinocerebellar tracts. Physiological function of frataxin in mitochondria has not been established yet, although several hypotheses have been postulated including mitochondrial iron homeostasis, iron storing, response to oxidative stress, iron-sulphur cluster biogenesis, modulation of mitochondrial aconitase activity and a role in oxidative phosphorylation. We showed that frataxin and its orthologue Saccharomyces cerevisiae, Yfh1p, interacts physically with proteins from the mitochondrial electron transfer chain. We demonstrated that Yfh1p co-immunoprecipitates with yeast succinate dehydrogenase complex subunits Sdh1p and Sdh2p, and with yeast orthologues of the electron transfer flavoprotein complex subunits ETFa and ETF¿Â. Genetic synthetic interaction experiments confirmed a functional relationship between YFH1 and succinate dehydrogenase genes SDH1 and SDH2. We postulate that Yfh1p might regulate the delivery of electrons via complex II and ETF systems towards ubiquinone in yeast. We also demonstrate a physical interaction between human frataxin and human succinate dehydrogenase complex subunits, suggesting also a key role of frataxin in the mitochondrial electron transport chain in humans. Consequently, we postulate a direct participation of the respiratory chain in the pathogenesis of the Friedreich ataxia, which we propose to be considered as an OXPHOS disease. Since the discovery of frataxin and its location within the mitocondrial matrix, Friedreich ataxia has become the prototype of mitocondrial disease caused by a nuclear gene. However, it is not the unique Mendelian ataxia that can be considered mitocondrial. Another example is the X-linked sideroblastic anemia with ataxia (XLSA/A), due to mutations in the gene encoding the mitocondrial transporter ABC7. This disease is directly related to the iron homeostasis, as Friedreich ataxia. We have characterized the genomic structure of Y74C10AM.1, the Caenorhabditis elegans ABC7 gene, and we have developed a transient knock-down model of C. elegans ABC7 deficiency by RNA interference. Y74C10AM.1(RNAi) worms show a phenotype that includes embryonic lethality (Emb), slow growth (Gro), egg laying defects (Egl), altered defecation and lifespan increase. This phenotype is similar to other phenotypes associated to transient knock-down models in C. elegans of genes related to the iron-sulphur cluster biogenesis in yeast.