Somatic instability of the expanded GAA repeats in Friedreich’s ataxia

Ashlee Long, Jill S. Napierala, Urszula Polak, Lauren Hauser, Arnulf H. Koeppen, David R. Lynch, Marek Napierala; PLoS ONE 12(12): e0189990. Doi:10.1371/journal.pone.0189990

Friedreich’s ataxia (FRDA) is a genetic neurodegenerative disorder caused by transcriptional silencing of the frataxin gene (FXN) due to expansions of GAA repeats in intron 1. FRDA manifests with multiple symptoms, which may include ataxia, cardiomyopathy and diabetes mellitus. Expanded GAA tracts are genetically unstable, exhibiting both expansions and contractions. GAA length correlates with severity of FRDA symptoms and inversely with age of onset. Thus, tissue-specific somatic instability of long GAA repeats may be implicated in the development of symptoms and disease progression. Herein, we determined the extent of somatic instability of the GAA repeats in heart, cerebral cortex, spinal cord, cerebellar cortex, and pancreatic tissues from 15 FRDA patients. Results demonstrate differences in the lengths of the expanded GAAs among different tissues, with significantly longer GAA tracts detected in heart and pancreas than in other tissues. The expansion bias detected in heart and pancreas may contribute to disease onset and progression, making the mechanism of somatic instability an important target for therapy. Additionally, we detected significant differences in GAA tract lengths between lymphocytes and fibroblast pairs derived from 16 FRDA patients, with longer GAA tracts present in the lymphocytes. This result urges caution in direct comparisons of data obtained in these frequently used FRDA models. Furthermore, we conducted a longitudinal analysis of the GAA repeat length in lymphocytes collected over a span of 7–9 years and demonstrated progressive expansions of the GAAs with maximum gain of approximately 9 repeats per year. Continuous GAA expansions throughout the patient’s lifespan, as observed in FRDA lymphocytes, should be considered in clinical trial designs and data interpretation.

Fisiopatología de la ataxia de Friedreich: Transporte y degeneración axonal

Muñoz Lasso, DC. (2017). Fisiopatología de la ataxia de Friedreich: Transporte y degeneración axonal [Tesis doctoral no publicada]. Universitat Politècnica de València. doi:10.4995/Thesis/10251/92842

Friedreich ataxia (FRDA) is a recessive human disease of central and peripheral nervous system that affects children and young adults. FRDA is a peripheral neuropathy characterized by a initial degeneration of the large neurons of the dorsal root ganglia (DRG) or proprioceptive neurons. Most of the patients with FRDA have a homozygous guanine-adenine-adenine (GAA) expansion within the first intron of the gen that codifies for a small mitochondrial protein, frataxin (FXN). This mutation leads to a reduction of frataxin expression in all human cells, which produces changes in both the cell and mitochondrial physiology, resulting in a dysfunction of the mitochondrial energetic metabolism linked to the increase of oxidative stress and calcium dyshomeostasis. These cellular proceses are tightly related with the regulation of the actin and microtubule cytoskeletons and with vesicle trafficking. Here, we show how the absence of frataxin in the mouse models YG8R and YG8sR affects the axonal cytoskeleton of adult sensory neurons. Changes of actin and microtubule cytoskeletons and the failure of Ca 2+ signaling induce alterations of dynamics growth cones of sensory neurons, which in turn produce a reduction of their capacity to grow and regenerate their axons. This study shows how these events can lead to the neurodegeneration in Friedreich's ataxia.

Development of an iron-selective antioxidant probe with protective effects on neuronal function

García-Beltrán O, Mena NP, Aguirre P, Barriga-González G, Galdámez A, Nagles E, et al. (2017). PLoS ONE 12(12): e0189043. doi:10.1371/journal.pone.0189043

ron accumulation, oxidative stress and calcium signaling dysregulation are common pathognomonic signs of several neurodegenerative diseases, including Parkinson´s and Alzheimer’s diseases, Friedreich ataxia and Huntington’s disease. Given their therapeutic potential, the identification of multifunctional compounds that suppress these damaging features is highly desirable. Here, we report the synthesis and characterization of N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetamide, named CT51, which exhibited potent free radical neutralizing activity both in vitro and in cells. CT51 bound Fe2+ with high selectivity and Fe3+ with somewhat lower affinity. Cyclic voltammetric analysis revealed irreversible binding of Fe3+ to CT51, an important finding since stopping Fe2+/Fe3+ cycling in cells should prevent hydroxyl radical production resulting from the Fenton-Haber-Weiss cycle. When added to human neuroblastoma cells, CT51 freely permeated the cell membrane and distributed to both mitochondria and cytoplasm. Intracellularly, CT51 bound iron reversibly and protected against lipid peroxidation. Treatment of primary hippocampal neurons with CT51 reduced the sustained calcium release induced by an agonist of ryanodine receptor-calcium channels. These protective properties of CT51 on cellular function highlight its possible therapeutic use in diseases with significant oxidative, iron and calcium dysregulation.

Health-related quality of life among adults with diverse rare disorders

Kathleen R. Bogart and Veronica L. Irvin; Orphanet Journal of Rare Diseases 201712:177 doi:10.1186/s13023-017-0730-1

Twenty-five to 30 million Americans live with a rare disease (RD) and share challenges unique to RD. The majority of research on RDs has focused on etiology, treatment and care, while the limited health-related quality of life (HRQL) research has been restricted to single RDs, small samples, or non-validated measures. This study reports HRQL among adults with diverse RDs, and compares their scores to those of the U.S. population and people with common chronic health conditions.

Biochemical Analyses of Human Iron–Sulfur Protein Biogenesis and of Related Diseases

Oliver Stehling, Viktoria D. Paul, Janina Bergmann, Somsuvro Basu, Roland Lill, Methods in Enzymology, Academic Press, ISSN 0076-6879, doi:10.1016/bs.mie.2017.11.004.

Maturation of Fe/S proteins in mammals is an intricate process mediated by two assembly systems located in the mitochondrial and cytosolic–nuclear compartments. Malfunction particularly of the mitochondrial system gives rise to severe neurological, metabolic, or hematological disorders, often with fatal outcome. In this chapter, we describe approaches for the differential biochemical investigation of cellular Fe/S protein maturation in mitochondria, cytosol, and nucleus. The analyses may also facilitate the identification of the affected Fe/S protein assembly step in diseased state. As Fe/S cluster insertion into target apoproteins is a frequent determinant of protein stability, examination of protein steady-state levels in biological samples frequently permits reliable first clues about the maturation process. In some specific cases, this approach allows the assessment of enzymatic or regulatory functions of Fe/S proteins, including the formation of lipoate cofactor by mitochondrial lipoic acid synthase or the posttranscriptional regulation of transferrin receptor and ferritin expression by the cytosolic iron regulatory proteins. More direct Fe/S protein maturation assays like enzymatic analyses may further validate the observed maturation defects. Here, we present a simple protocol for the determination of dihydropyrimidine dehydrogenase enzyme activity by thin-layer chromatography. In order to directly monitor Fe/S cluster insertion into target apoproteins, we have developed a 55Fe radiolabeling technique tracing the in vivo Fe/S cofactor formation in mammalian tissue culture. The combination of the presented techniques represents a comprehensive strategy to assess the multiple facets of Fe/S protein assembly for both mechanistic analyses and for the elucidation of specific defects in Fe/S diseases.

Computational drug repositioning for rare diseases in the era of precision medicine

Brian Delavan, Ruth Roberts, Ruili Huang, Wenjun Bao, Weida Tong, Zhichao Liu, Drug Discovery Today, 2017, , ISSN 1359-6446, doi:10.1016/j.drudis.2017.10.009.

There are tremendous unmet needs in drug development for rare diseases. Computational drug repositioning is a promising approach and has been successfully applied to the development of treatments for diseases. However, how to utilize this knowledge and effectively conduct and implement computational drug repositioning approaches for rare disease therapies is still an open issue. Here, we focus on the means of utilizing accumulated genomic data for accelerating and facilitating drug repositioning for rare diseases. First, we summarize the current genome landscape of rare diseases. Second, we propose several promising bioinformatics approaches and pipelines for computational drug repositioning for rare diseases. Finally, we discuss recent regulatory incentives and other enablers in rare disease drug development and outline the remaining challenges.

Depressive symptoms in Friedreich ataxia

Antonieta Nieto, Atteneri Hernández-Torres, Javier Pérez-Flores, Fernando Montón, International Journal of Clinical and Health Psychology, Available online 8 December 2017, ISSN 1697-2600, doi:10.1016/j.ijchp.2017.11.004.

Almost no attention has been paid to depression in Friedreich ataxia (FRDA), a highly disabling cerebellar degenerative disease. Our aim was to study the presence and the profile of depressive symptoms in FRDA and their relationship with demographic-disease variables and cognitive processing speed. Method: The study groups consisted of 57 patients with a diagnosis of FRDA. The Beck Depression Inventory-II was used to assess symptoms of depression. Speed of information processing was measured with a Choice Reaction time task. The mean BDI score for patients was significantly higher than the mean score in the general population. Twenty one percent of participants scored in the moderate/severe range. A Cognitive-Affective score and a Somatic-Motivational score was calculated for each patient. Patients’ scores in both dimensions were significantly higher than the scores in the general population. Demographic and disease variables were not related with symptoms of depression, except for severity of ataxia. Depressive symptoms predict cognitive reaction times. The greater proportion of variance was explained by the Cognitive-Affective dimension. Our data show that both somatic-motivational and cognitive affective symptoms of depression are frequent in individuals with FRDA. In addition, depressive symptoms may influence cognition, especially, the cognitive and affective symptoms.

Mitochondrial pore opening and loss of Ca2 + exchanger NCLX levels occur after frataxin depletion

R. Purroy, E. Britti, F. Delaspre, J. Tamarit, J. Ros, Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, Available online 6 December 2017, ISSN 0925-4439, doi:10.1016/j.bbadis.2017.12.005.

Frataxin-deficient neonatal rat cardiomyocytes and dorsal root ganglia neurons have been used as cell models of Friedreich ataxia. In previous work we show that frataxin depletion resulted in mitochondrial swelling and lipid droplet accumulation in cardiomyocytes, and compromised DRG neurons survival. Now, we show that these cells display reduced levels of the mitochondrial calcium transporter NCLX that can be restored by calcium-chelating agents and by external addition of frataxin fused to TAT peptide. Also, the transcription factor NFAT3, involved in cardiac hypertrophy and apoptosis, becomes activated by dephosphorylation in both cardiomyocytes and DRG neurons. In cardiomyocytes, frataxin depletion also results in mitochondrial permeability transition pore opening. Since the pore opening can be inhibited by cyclosporin A, we show that this treatment reduces lipid droplets and mitochondrial swelling in cardiomyocytes, restores DRG neuron survival and inhibits NFAT dephosphorylation. These results highlight the importance of calcium homeostasis and that targeting mitochondrial pore by repurposing cyclosporin A, could be envisaged as a new strategy to treat the disease.

Friedreich ataxia: Clinical feature and electrophysiological symptoms

Oguri M. ; J Neurosci Rural Pract [serial online] 2017 [cited 2017 Dec 6];8:691-2. DOI: 10.4103/jnrp.jnrp_248_17

The ataxia is slowly progressive and involves the lower extremities to a greater degree than the upper extremities. In general, results of electrophysiologic studies including visual, auditory brainstem, and somatosensory-evoked potentials are often abnormal.

Iron-induced oligomerization of human FXN 81-210 and bacterial CyaY frataxin and the effect of iron chelators

Eva-Christina Ahlgren, Mostafa Fekry, Mathias Wiemann, Christopher A. Söderberg, Katja Bernfur, Olex Gakh, Morten Rasmussen, Peter Højrup, Cecilia Emanuelsson, Grazia Isaya, Salam Al-Karadaghi. PLoS ONE 12(12): e0188937. doi:10.1371/journal.pone.0188937

Patients suffering from the progressive neurodegenerative disease Friedreich’s ataxia have reduced expression levels of the protein frataxin. Three major isoforms of human frataxin have been identified, FXN42-210, FXN56-210 and FXN81-210, of which FXN81-210 is considered to be the mature form.