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FARA Funded Research

Your generous support has funded all the research listed below.

For more information on FARA-funded research & scientists, please visit FARA Supported Research, Active Clinical Trials and the Featured Scientist.


 

 

Ferroptosis as a novel therapeutic target for Friedreich's ataxia

Friedreich ataxia (FRDA) is a progressive neuro- and cardio-degenerative disorder characterized by ataxia, sensory loss, and hypertrophic cardiomyopathy. In most cases, the disorder is caused by GAA repeat expansions in the first introns of both alleles of the FXN gene, resulting in decreased expression of the encoded protein, frataxin. Frataxin localizes to the mitochondrial matrix and is required for iron-sulfur-cluster biosynthesis. Decreased expression of frataxin is associated with mitochondrial dysfunction, mitochondrial iron accumulation, and increased oxidative stress. Ferropotosis is a recently identified pathway of regulated, iron-dependent cell death, which is biochemically distinct from apoptosis. This group evaluated whether there is evidence for ferroptotic pathway activation in cellular models of FRDA. They found that primary patient-derived fibroblasts, murine fibroblasts with FRDA-associated mutations, and murine fibroblasts in which a repeat expansion had been introduced (KIKO) were more sensitive than normal control cells to erastin, a known ferroptosis inducer. We also found that the ferroptosis inhibitors SRS11-92 and Fer-1, used at 500 nM, were efficacious in protecting human and mouse cellular models of FRDA treated with ferric ammonium citrate (FAC) and an inhibitor of glutathione synthesis (BSO), whereas caspase-3 inhibitors failed to show significant biological activity. Cells treated with FAC and BSO consistently showed decreased glutathione-dependent peroxidase activity and increased lipid peroxidation, both hallmarks of ferroptosis. Finally, the ferroptosis inhibitor SRS11-92 decreased the cell death associated with frataxin knockdown in healthy human fibroblasts. Taken together, these data suggest that ferroptosis inhibitors may have therapeutic potential in FRDA.

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Differences in the determinants of right ventricular and regional left ventricular long-axis dysfunction in Friedreich ataxia

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative condition which also has effects on the heart. In 96% of affected individuals FRDA is due to homozygosity of a GAA repeat expansion in intron 1 of the frataxin (FXN) gene. The number of GAA repeats have been shown to relate to disease severity in FRDA, this thought to be via an inverse relationship of GAA repeat number and cellular frataxin levels. This group investigated the effects of FRDA on regional long axis function of the left and right ventricles, and also the relationship of long axis systolic (s`) and early diastolic (e`) peak velocities with GAA repeat number on the shorter (GAA1) and longer FXN alleles (GAA2). The study group of 78 adult subjects (age 32±9 years) with FRDA and normal left ventricular (LV) ejection fraction were compared to 54 healthy control subjects of similar age, sex and body size. Tissue Doppler imagin g (TDI) signals were recorded at the mitral annulus for measurement of s` and e`of the septal, lateral, anterior and inferior walls and at the tricuspid annulus for measurement of right ventricular (RV) s` and e`. All the regional LV s` and e`, and both RV s` and RV e`, were lower in individuals with FRDA compared to controls (p<0.001 for all). On multivariate analysis, which included LV septal wall thickness (SWT), RV s` and RV e` were both inversely correlated with GAA1 (β = -0.32 & -0.33, respectively, p = 0.01), but not with GAA2, whereas anterior and lateral s` were both inversely correlated with GAA2 (β = -0.25 and β = -0.28, p = 0.02) but not with GAA1. Increasing SWT was the most consistent LV structural correlate of lower s` and e`, whereas age was a consistent inverse correlate of e` but not of s`.There are generalized abnormalities of both LV regional and RV long axis function in FRDA, but there are also regional differences in the association of this dysfunction with the smaller and larger GAA repeats in the FXN gene.

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GRP75 overexpression rescues frataxin deficiency and mitochondrial phenotypes in Friedreich Ataxia cellular models

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by the deficiency of frataxin, a mitochondrial protein crucial for iron-sulphur cluster biogenesis and ATP production. Currently there is no therapy to slow down the progression of FRDA. Recent evidence indicates that posttranslational regulation of residual frataxin levels can rescue some of the functional deficit of FRDA, raising the possibility of enhancing levels of residual frataxin as a treatment for FRDA. Here, we present evidence that mitochondrial molecular chaperone GRP75, also known as mortalin/mthsp70/PBP74, directly interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Overexpressing GRP75 increases the levels of both wild-type frataxin and clinically relevant missense frataxin variants in HEK293 cells while clinical GRP75 variants such as R126W, A476T and P509S impair the binding of GRP75 with frataxin and the effect of GRP75 on frataxin levels. In addition, GRP75 overexpression rescues frataxin deficiency and abnormal cellular phenotypes such as the abnormal mitochondrial network and decreased ATP levels in FRDA patient-derived cells. The effect of GRP75 on frataxin might be in part mediated by the physical interaction between GRP75 and mitochondrial processing peptidase (MPP), which makes frataxin more accessible to MPP. As GRP75 levels are decreased in multiple cell types of FRDA patients, restoring GRP75 might be effective in treating both typical FRDA patients with two GAA repeat expansions and compound heterozygous patients with point mutations.

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Transcriptional profiling of isogenic Friedreich ataxia neurons and effect of an HDAC inhibitor on disease signatures

Friedreich ataxia (FRDA) is a neurodegenerative disorder caused by transcriptional silencing of the FXN gene, resulting in loss of the essential mitochondrial protein frataxin. Based on the knowledge that a GAA•TTC repeat expansion in the first intron of FXN induces heterochromatin, this group previously showed that 2-aminobenzamide-type histone deacetylase inhibitors (HDACi) increase FXN mRNA levels in induced pluripotent stem cell (iPSC)-derived FRDA neurons and in circulating lymphocytes from patients after HDACi oral administration. How the reduced expression of frataxin leads to neurological and other systemic symptoms in FRDA patients remains unclear. Similar to other triplet-repeat disorders, it is unknown why FRDA affects only specific cell types, primarily the large sensory neurons of the dorsal root ganglia and cardiomyocytes. The combination of iPSC technology and genome-editing techniques offers the unique possibility to address these questions in a relevant cell model of FRDA, obviating confounding effects of variable genetic backgrounds. Here, using "scarless" gene-editing methods, they created isogenic iPSC lines that differ only in the length of the GAA·TTC repeats. To uncover the gene expression signatures due to the GAA·TTC repeat expansion in FRDA neuronal cells and the effect of HDACi on these changes, they performed RNA-seq-based transcriptomic analysis of iPSC-derived central nervous system (CNS) and isogenic sensory neurons. They found that cellular pathways related to neuronal function, regulation of transcription, extracellular matrix organization and apoptosis are affected by frataxin loss in neurons of the CNS and peripheral nervous system and that these changes are partially restored by HDACi treatment.

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Characterization of a new N-terminally acetylated extra-mitochondrial isoform of frataxin in human erythrocytes

Frataxin is a highly conserved protein encoded by the frataxin (FXN) gene. The full-length 210-amino acid form of protein frataxin (1-210; isoform A) expressed in the cytosol of cells rapidly gets moved to the mitochondria, where it is converted to the mature form (81-210). Mature frataxin (81-210) is a critically important protein because it facilitates the assembly of mitochondrial iron-sulfur cluster protein complexes such as aconitase, lipoate synthase, and succinate dehydrogenases. Decreased expression of frataxin protein is responsible for Friedreich's ataxia. The mitochondrial form of frataxin has long been thought to be present in red blood cells even though they lack mitochondria. This paper shows that frataxin in red blood cells is a novel form of frataxin (called isoform E) with 135-amino acids and an N-terminally acetylated methionine residue. There is three times more isoform E in red blood cells from the whole blood of healthy volunteers compared to the mature mitochondrial frataxin present in other blood cells. Isoform E lacks a mitochondrial targeting sequence and so is distributed to both cytosol and the nucleus when expressed in cultured cells. When extra-mitochondrial frataxin isoform E is expressed in HEK 293 cells, it is converted to a shorter isoform identical to the mature frataxin found in mitochondria, which raises the possibility that it is involved in disease etiology. The ability to specifically quantify extra-mitochondrial and mitochondrial isoforms of frataxin in whole blood will make it possible to readily follow the natural history of diseases such as Friedreich's ataxia and monitor the efficacy of therapeutic interventions.

Read the entire article HERE

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