Friedreich ataxia (FA) is a neurodegenerative disease caused by the deficiency of frataxin, a mitochondrial protein. In primary cultures of dorsal root ganglia neurons, we showed that frataxin depletion resulted in decreased levels of the mitochondrial calcium exchanger NCLX, neurite degeneration and apoptotic cell death. Here, we describe that frataxin-deficient dorsal root ganglia neurons display low levels of ferredoxin 1 (FDX1), a mitochondrial Fe/S cluster-containing protein that interacts with frataxin and, interestingly, is essential for the synthesis of calcitriol, the active form of vitamin D. We provide data that calcitriol supplementation, used at nanomolar concentrations, is able to reverse the molecular and cellular markers altered in DRG neurons. Calcitriol is able to recover both FDX1 and NCLX levels and restores mitochondrial membrane potential indicating an overall mitochondrial function improvement. Accordingly, reduction in apoptotic markers and neurite degeneration was observed and, as a result, cell survival was also recovered. All these beneficial effects would be explained by the finding that calcitriol is able to increase the mature frataxin levels in both, frataxin-deficient DRG neurons and cardiomyocytes; remarkably, this increase also occurs in lymphoblastoid cell lines derived from FA patients. In conclusion, these results provide molecular bases to consider calcitriol for an easy and affordable therapeutic approach for FA patients.
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Tumor organoids are a relevant, 3-dimensional, culture method which allows long-term growth preserving the stem cell identity and reconstituting to some extent the morphological and phenotypic heterogeneity of the original tumor. Representative fluorescence image of a tumour organoid derived from patient derived GSCs after 23 days of culture, stained for anti-αTubulin (microtubules, white) and Phalloidin (actin red). In this issue Pinto and colleagues (pp. 21–39) observed that different types of cell protrusions (TMs and TNTs) connecting cells were present and coexist inside the organoid. The image was captured by Inés Saenz-de-Santa-Maria with an inverted confocal microscope LSM700, Pln-Apo 10X/0.45 objective.
Calcitriol increases frataxin levels and restores mitochondrial function in cell models of Friedreich Ataxia
Elena Britti, Fabien Delaspre, A. Sanz-Alcázar, Marta Medina-Carbonero, Marta Llovera, Rosa Purroy, Stefka Mincheva-Tasheva, Jordi Tamarit, Joaquim Ros; Calcitriol increases frataxin levels and restores mitochondrial function in cell models of Friedreich Ataxia. Biochem J 15 January 2021; 478 (1): 1–20. doi: https://doi.org/10.1042/BCJ20200331
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