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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.

Frataxin deficiency lowers lean mass and triggers the integrated stress response in skeletal muscle

Neurological and cardiac comorbidities are prominent in FRDA and have been a major focus of study. Skeletal muscle has received less attention despite indications that FXN loss affects it. Here, the authors show that lean mass is lower, whereas body mass index is unaltered, in separate cohorts of adults and children with FRDA. In adults, lower lean mass correlated with disease severity. To further investigate FXN loss in skeletal muscle, a transgenic mouse model of whole-body inducible and progressive FXN depletion was used. There was little impact of FXN loss when FXN was approximately 20% of control levels. When residual FXN was approximately 5% of control levels, muscle mass was lower along with absolute grip strength. When we examined mechanisms that can affect muscle mass, only global protein translation was lower, accompanied by integrated stress response (ISR) activation. Also in mice, aerobic exercise training, initiated prior to the muscle mass difference, improved running capacity, yet, muscle mass and the ISR remained as in untrained mice. Thus, FXN loss can lead to lower lean mass, with ISR activation, both of which are insensitive to exercise training.

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Posttranslational Regulation of Mitochondrial Frataxin and Identification of Compounds that Increase Frataxin Levels in Friedreich's Ataxia

This study shows that conditions that result in increased mitochondrial reactive oxygen species (ROS) in yeast or mammalian cell culture give rise to increased turnover of frataxin, but not of other iron-sulfur cluster (ISC) synthesis proteins. The authors demonstrate that the mitochondrial Lon protease is involved in frataxin degradation and that iron export through the mitochondrial metal transporter Mmt1 protects yeast frataxin from degradation. When FRDA fibroblasts were grown in media containing elevated iron, mitochondrial ROS increased and frataxin decreased compared to WT fibroblasts. Furthermore, a library of FDA-approved compounds was screened and 38 compounds that increased yeast frataxin levels identified, including the azole Bifonazole, antiparasitic Fipronil, anti-tumor compound Dibenzoylmethane (DBM), antihypertensive 4-hydroxychalcone (4'-OHC), and a non-specific anion channel inhibitor 4,4-diisothiocyanostilbene-2,2-sulfonic acid (DIDS). The authors show that top hits 4'-OHC and DBM increased mRNA levels of transcription factor Nrf2 in FRDA patient-derived fibroblasts, as well as downstream antioxidant targets thioredoxin (TXN), glutathione reductase (GSR), and superoxide dismutase 2 (SOD2). Taken together, these findings reveal that FRDA progression may be in part due to oxidant-mediated decreases in frataxin, and that some approved compounds may be effective in increasing mitochondrial frataxin in FRDA, delaying disease progression.

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Bone Mineral Density and Current Bone Health Screening Practices in Friedreich's Ataxia

Impaired bone health is a complication of disorders affecting mobility, but there is little information regarding bone health in FRDA. Dual energy X-ray absorptiometry (DXA) scan-based assessments of areal bone mineral density (aBMD) in individuals with FRDA were abstracted from four studies at the Children's Hospital of Philadelphia (CHOP). Disease outcomes, including the modified FRDA Rating Scale (mFARS), were abstracted from the FRDA Clinical Outcomes Measures Study (FACOMS), a longitudinal natural history study. A survey regarding bone health and fractures was sent to individuals in FACOMS-CHOP. Adults with FRDA (n = 24) have lower mean whole body (WB) (-0.45 vs. 0.33, p = 0.008) and femoral neck (FN) (-0.71 vs. 0.004, p = 0.02) aBMD Z-scores than healthy controls (n = 24). Children with FRDA (n = 10) have a lower WB-less-head (-2.2 vs. 0.19, p < 0.0001) and FN (-1.1 vs. 0.04, p = 0.01) aBMD than a reference population (n = 30). In adults, lower FN aBMD correlated with functional disease severity, as reflected by mFARS (R = -0.56, p = 0.04). Of 137 survey respondents (median age 27 y, 50% female), 70 (51%) reported using wheelchairs as their primary ambulatory device: of these, 20 (29%) reported a history of potentially pathologic fracture and 11 (16%) had undergone DXA scans. Low aBMD is prevalent in FRDA, but few of even the highest risk individuals are undergoing screening. These findings highlight potential missed opportunities for the screening and treatment of low aBMD in FRDA.

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DNA methylation in Friedreich ataxia silences expression of frataxin isoform E

Epigenetic silencing in Friedreich ataxia (FRDA), induced by an expanded GAA triplet-repeat in intron 1 of the FXN gene, results in deficiency of the mitochondrial protein, frataxin. A lesser known extramitochondrial isoform of frataxin detected in erythrocytes, frataxin-E, is encoded via an alternate transcript (FXN-E) originating in intron 1 that lacks a mitochondrial targeting sequence. The authors show that FXN-E is deficient in FRDA, including in patient-derived cell lines, iPS-derived proprioceptive neurons, and tissues from a humanized mouse model. In a series of FRDA patients, deficiency of frataxin-E protein correlated with the length of the expanded GAA triplet-repeat, and with repeat-induced DNA hypermethylation that occurs in close proximity to the intronic origin of FXN-E. CRISPR-induced epimodification to mimic DNA hypermethylation seen in FRDA reproduced FXN-E transcriptional deficiency. Deficiency of frataxin E is a consequence of FRDA-specific epigenetic silencing, and therapeutic strategies may need to address this deficiency.


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Recent Advances in the Elucidation of Frataxin Biochemical Function Open Novel Perspectives for the Treatment of Friedreich's Ataxia

Frataxin (FXN) is a mitochondrial protein involved in iron metabolism but its exact function has remained elusive and highly debated since its discovery. At the cellular level, Friedreich's ataxia (FRDA) is characterized by a general deficit in the biosynthesis of iron-sulfur (Fe-S) clusters and heme, iron accumulation and deposition in mitochondria, and sensitivity to oxidative stress. Based on these phenotypes and the proposed ability of FXN to bind iron, a role as an iron storage protein providing iron for Fe-S cluster and heme biosynthesis was initially proposed. However, this model was challenged by several other studies and it is now widely accepted that FXN functions primarily in Fe-S cluster biosynthesis, with iron accumulation, heme deficiency and oxidative stress sensitivity appearing later on as secondary defects. Nonetheless, the biochemical function of FXN in Fe-S cluster biosynthesis is still debated. Several roles have been proposed for FXN: iron chaperone, gate-keeper of detrimental Fe-S cluster biosynthesis, sulfide production stimulator and sulfur transfer accelerator. A picture is now emerging which points toward a unique function of FXN as an accelerator of a key step of sulfur transfer between two components of the Fe-S cluster biosynthetic complex. These findings should foster the development of new strategies for the treatment of FRDA. The authors review here the latest discoveries on the biochemical function of frataxin and the implication for a potential therapeutic treatment of FRDA.


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