Functional characterization of frataxin isoforms and mechanisms of regulation of frataxin expression

• Autores: Mauro Agrò
• Directores de la Tesis: Javier Díaz Nido (dir. tes.), Alfredo Giménez-Cassina Sendón (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2019
• Idioma: español
• Programa de doctorado: Programa de Doctorado en Biociencias Moleculares por la Universidad Autónoma de Madrid
• Materias:
  • Ciencias de la vida
    • Biología molecular
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Friedreich’s Ataxia (FRDA) is a mainly neurodegenerative recessive disease caused by the deficiency of frataxin protein. This deficiency is mostly due to the expansion of the GAA triplet located in the first intron of frataxin gene. This mutation leads to the reduction in the levels of the protein, which fall around 20-30% of normal levels. Frataxin, in its canonical mature form, is a protein localized to the mitochondria, where it exerts its roles, mostly involved in iron storage, in the formation and regulation of Iron-Sulfur clusters and in maintaining mitochondrial homeostasis.

    Recently the existence of different isoforms of frataxin with an extra-mitochondrial localization has been indicated. We found that the overexpression of both mitochondrial isoform I and cytosolic isoform II is able to improve mitochondrial respiration in FRDA patient cells, increasing basal respiration rates and oxygen consumption rates and incrementing the levels of mitochondrial biomarkers like VDAC and Aconitase. Besides, the overexpression of canonical Isoform I is directly affecting the development of mitochondrial network, exerting a positive effect on both the number of isolated mitochondria as well as the number of mitochondria structured in networks. Finally, both isoforms seem to interact with Fe-S cluster containing proteins, like cytosolic and mitochondrial Aconitase, being also able to protect the enzymes in an oxidative-stressing environment.

    The regulation of frataxin gene expression is another issue of major interest for its possible therapeutic relevance. Several factors including Erythropoietin and some Epo-mimetic molecules have been reported to increase frataxin levels. There are some drawbacks, since canonical Epo can cause hematocrit problems, while some of the derivative peptides described are known to be highly unstable, with a very low half-life in the organism. For this reason, we decided to focus on a retro-enantiomeric version of a HBSP-based peptide, called EPO2. We described in this work the positive regulatory effects on frataxin of this synthetic epomimetic peptide, both in vitro in several cell models and in vivo in the cerebellum of wild type mice.

    Finally, we reported the effects of spontaneous physical activity in wild type mouse cerebellum on frataxin expression. Frataxin levels appeared positively modulated after exercise, suggesting a post-transcriptional regulation mechanism. We investigated for possible mediators of this beneficial effect by qPCRs and through a cytokine array which highlighted the upregulation of several factors, including the neurotrophin NT-3, SHH protein, MIP-1α and IFN-γ, pointing the way to a multi-layered regulatory complex behind frataxin modulation set up by physical exercise.

    Together, these results give more insight on part of the mechanisms underlying frataxin regulation, which could prove useful in the development of potential new strategies in the treatment of FRDA.