RAN translation of the expanded CAG repeats in the SCA3 disease context

ABSTRACTSpinocerebellar ataxia type 3 (SCA3) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the ATXN3 gene encoding the ataxin-3 protein. Despite extensive research the exact pathogenic mechanisms of SCA3 are still not understood in depth. In the present study, to gain insight into the toxicity induced by the expanded CAG repeats in SCA3, we comprehensively investigated repeat-associated non-ATG (RAN) translation in various cellular models expressing translated or non-canonically translated ATXN3 sequences with an increasing number of CAG repeats. We demonstrate that two SCA3 RAN proteins, polyglutamine (polyQ) and polyalanine (polyA), are found only in the case of CAG repeats of pathogenic length. Despite having distinct cellular localization, RAN polyQ and RAN polyA proteins are very often coexpressed in the same cell, impairing nuclear integrity and inducing apoptosis. We provide for the first time mechanistic insights into SCA3 RAN translation indicating that ATXN3 sequences surrounding the repeat region have an impact on SCA3 RAN translation initiation and efficiency. We revealed that RAN translation of polyQ proteins starts at non-cognate codons upstream of the CAG repeats, whereas RAN polyA proteins are likely translated within repeats. Furthermore, integrated stress response activation enhances SCA3 RAN translation. We suggest that RAN translation in SCA3 is a common event substantially contributing to SCA3 pathogenesis and that the ATXN3 sequence context plays an important role in triggering this unconventional translation.

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Homozygous spinocerebellar ataxia type 3 in China: a case report

Journal of International Medical Research ◽

10.1177/03000605211021370 ◽

2021 ◽

Vol 49 (6) ◽

pp. 030006052110213

Author(s):

Yuchao Chen ◽

Dan Li ◽

Minger Wei ◽

Menglu Zhou ◽

Linan Zhang ◽

...

Keyword(s):

Spinocerebellar Ataxia ◽

Clinical Phenotype ◽

Gene Dosage ◽

Cag Repeat ◽

Cag Repeats ◽

Spinocerebellar Ataxia Type ◽

Contraction Pattern ◽

Spinocerebellar Ataxia Type 3 ◽

Type 3 ◽

Stable Transmission

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by a heterozygous CAG repeat expansion in the ataxin 3 gene ( ATXN3). However, patients with homozygous SCA3 carrying expanded CAG repeats in both alleles of ATXN3 are extremely rare. Herein, we present a case of a 50-year-old female who had homozygous SCA3 with expansion of 62/62 repeats. Segregation analysis of the patient’s family showed both a contraction pattern of CAG repeat length and stable transmission. The present case demonstrated an earlier onset and more severe clinical phenotype than that seen in heterozygous individuals, suggesting that the gene dosage enhances disease severity.

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Silencing of genes responsible for polyQ diseases using chemically modified single-stranded siRNAs

Acta Biochimica Polonica ◽

10.18388/abp.2016_1336 ◽

2017 ◽

Vol 63 (4) ◽

Cited By ~ 4

Author(s):

Agnieszka Fiszer ◽

Marianna E Ellison-Klimontowicz ◽

Wlodzimierz J Krzyzosiak

Keyword(s):

Genetic Disorders ◽

Mutant Gene ◽

Cag Repeat ◽

Spinocerebellar Ataxia Type ◽

Spinocerebellar Ataxia Type 3 ◽

Mutation Site ◽

Protein Levels ◽

Cellular Models ◽

Polyq Diseases ◽

Type 3

Polyglutamine (polyQ) diseases comprise a group of nine genetic disorders that are caused by the expansion of the CAG triplet repeat, which encodes glutamine, in unrelated single genes. The pathogenesis is caused by the disruption of cellular pathways by the expression products of the mutant gene, i.e., proteins containing polyQ tracts and mutant transcripts. In considering oligonucleotide (ON)-based therapeutic approaches for polyQ diseases, the very attractive CAG repeat-targeting strategy offers selective silencing of the mutant allele by directly targeting the mutation site. CAG repeat-targeting miRNA-like siRNAs have been shown to specifically inhibit mutant gene expression, and their characteristic feature is the formation of mismatches in their interactions with the target site. Here, we designed novel single-stranded siRNAs that contain base substitutions and chemical modifications and tested these oligonucleotides in cellular models of Huntington’s disease (HD), spinocerebellar ataxia type 3 (SCA3) and dentatorubral-pallidoluysian atrophy (DRPLA), including HD mouse striatal cells. Selected siRNAs caused the efficient and selective downregulation of the mutant protein levels.

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Dystonia in Patients with Spinocerebellar Ataxia 3 - Machado-Joseph disease: An Underestimated Diagnosis?

The Open Neurology Journal ◽

10.2174/1874205x01812010041 ◽

2018 ◽

Vol 12 (1) ◽

pp. 41-49 ◽

Cited By ~ 2

Author(s):

Ligia Maria Perrucci Catai ◽

Carlos Henrique Ferreira Camargo ◽

Adriana Moro ◽

Gustavo Ribas ◽

Salmo Raskin ◽

...

Keyword(s):

Spinocerebellar Ataxia ◽

Movement Disorders ◽

Disease Onset ◽

Cag Repeat ◽

Spinocerebellar Ataxia Type ◽

Spinocerebellar Ataxia Type 3 ◽

Generalized Dystonia ◽

Machado Joseph Disease ◽

Sca3 Patient ◽

Type 3

Background:Spinocerebellar Ataxia type 3 (SCA3) or Machado-Joseph Disease (MJD) is characterized by cerebellar, central and peripheral symptoms, including movement disorders. Dystonia can be classified as hereditary and neurodegenerative when present in SCA3.Objective:The objective of this study was to evaluate the dystonia characteristics in patients with MJD.Method:We identified all SCA3 patients with dystonia from the SCA3 HC-UFPR database, between December 2015 and December 2016.Their medical records were reviewed to verify the diagnosis of dystonia and obtain demographic and clinical data. Standardized evaluation was carried out through the classification of Movement Disorders Society of 2013 and Burke Fahn-Marsden scale (BFM).Results:Amongst the presenting some common characteristics, 381 patients with SCA3, 14 (3.7%) subjects presented dystonia: 5 blepharospasm, 1 cervical dystonia, 3 oromandibular, 3 multifocal and 2 generalized dystonia. Regarding dystonia's subtypes, 71.4% had SCA3 subtype I and 28.6% SCA3 subtype II. The average age of the disease onset was 40±10.7 years; the SCA3 disease duration was 11.86± 6.13 years; the CAG repeat lengths ranged from 75 to 78, and the BFM scores ranged from 1.0 to 40. There was no correlation between the dystonia severity and CAG repeat lengths or the SCA3 clinical evolution.Conclusion:Dystonia in SCA3 is frequent and displays highly variable clinical profiles and severity grades. Dystonia is therefore a present symptom in SCA3, which may precede the SCA3 classic symptoms. Dystonia diagnosis is yet to be properly recognized within SCA3 patient.

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A Novel SCA3 Knock-in Mouse Model Mimics the Human SCA3 Disease Phenotype Including Neuropathological, Behavioral, and Transcriptional Abnormalities Especially in Oligodendrocytes

Molecular Neurobiology ◽

10.1007/s12035-021-02610-8 ◽

2021 ◽

Author(s):

Eva Haas ◽

Rana D. Incebacak ◽

Thomas Hentrich ◽

Chrisovalantou Huridou ◽

Thorsten Schmidt ◽

...

Keyword(s):

Mouse Model ◽

Brain Regions ◽

Cag Repeat ◽

Spinocerebellar Ataxia Type ◽

The Novel ◽

Spinocerebellar Ataxia Type 3 ◽

Transcriptional Changes ◽

Cerebellar Tissue ◽

Type 3 ◽

Polyq Expansion

AbstractSpinocerebellar ataxia type 3 is the most common autosomal dominant inherited ataxia worldwide, caused by a CAG repeat expansion in the Ataxin-3 gene resulting in a polyglutamine (polyQ)-expansion in the corresponding protein. The disease is characterized by neuropathological, phenotypical, and specific transcriptional changes in affected brain regions. So far, there is no mouse model available representing all the different aspects of the disease, yet highly needed for a better understanding of the disease pathomechanisms. Here, we characterized a novel Ataxin-3 knock-in mouse model, expressing a heterozygous or homozygous expansion of 304 CAACAGs in the murine Ataxin-3 locus using biochemical, behavioral, and transcriptomic approaches. We compared neuropathological, and behavioral features of the new knock-in model with the in SCA3 research mostly used YAC84Q mouse model. Further, we compared transcriptional changes found in cerebellar samples of the SCA3 knock-in mice and post-mortem human SCA3 patients. The novel knock-in mouse is characterized by the expression of a polyQ-expansion in the murine Ataxin-3 protein, leading to aggregate formation, especially in brain regions known to be vulnerable in SCA3 patients, and impairment of Purkinje cells. Along these neuropathological changes, the mice showed a reduction in body weight accompanied by gait and balance instability. Transcriptomic analysis of cerebellar tissue revealed age-dependent differential expression, enriched for genes attributed to myelinating oligodendrocytes. Comparing these changes with those found in cerebellar tissue of SCA3 patients, we discovered an overlap of differentially expressed genes pointing towards similar gene expression perturbances in several genes linked to myelin sheaths and myelinating oligodendrocytes.

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Altered retinal structure and function in Spinocerebellar ataxia type 3

10.1101/2022.01.10.475670 ◽

2022 ◽

Author(s):

Vasileios Toulis ◽

Ricardo Casaroli-Marano ◽

Anna Camos-Carreras ◽

Marc Figueras-Roca ◽

Bernardo Sanchez-Dalmau ◽

...

Keyword(s):

Transgenic Mice ◽

Spinocerebellar Ataxia ◽

Neurodegenerative Disorder ◽

Retinal Pigment ◽

Structure And Function ◽

Spinocerebellar Ataxia Type ◽

Spinocerebellar Ataxia Type 3 ◽

Retinal Structure ◽

And Function ◽

Type 3

Spinocerebellar ataxia type 3 is an autosomal dominant neurodegenerative disorder caused by expansion of a polyglutamine (polyQ)-encoding CAG repeat in the ATXN3 gene. Because the ATXN3 protein regulates photoreceptor ciliogenesis and phagocytosis, we aimed to explore whether expanded polyQ ATXN3 impacts retinal function and integrity in SCA3 patients and transgenic mice. We evaluated the retinal structure and function in five patients with Spinocerebellar ataxia type 3 and in a transgenic mouse model of this disease (YACMJD84.2, Q84) using, respectively, optical coherence tomography (OCT) and electroretinogram (ERG). We further determined in the transgenic mice: a) the retinal expression pattern of ATXN3 and assessed the distribution of cones and rods by immunofluorescence (IF); and b) the retinal ultrastructure by transmission electron microscopy (TEM). Some patients with Spinocerebellar ataxia type 3 in our cohort revealed: i) reduced central macular thickness indirectly correlated with disease duration; ii) decreased thickness of the macula and the ganglion cell layer, and reduced macula volume inversely correlated with disease severity (SARA score); and iii) electrophysiological dysfunction of cones, rods, and inner retinal cells. Transgenic mice replicated the human OCT and ERG findings with aged homozygous Q84/Q84 mice showing a stronger phenotype accompanied by further thinning of the outer nuclear layer and photoreceptor layer and highly reduced cone and rod activities, thus supporting severe retinal dysfunction in these mice. In addition, Q84 mice showed progressive accumulation of ATXN3-positive aggregates throughout several retinal layers and depletion of cones alongside the disease course. TEM analysis of aged Q84/Q84 mouse retinas supported the IF ATXN3 aggregation findings by revealing the presence of high number of negative electron dense puncta in ganglion cells, inner plexiform and inner nuclear layers, and further showed thinning of the outer plexiform layer, thickening of the retinal pigment epithelium and elongation of apical microvilli. Our results indicate that retinal alterations detected by non-invasive eye examination using OCT and ERG could represent a biological marker of disease progression and severity in patients with Spinocerebellar ataxia type 3.

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Polyglutamine-expanded ataxin-3: a target engagement marker for Spinocerebellar ataxia type 3 in peripheral blood

10.21203/rs.3.rs-384325/v1 ◽

2021 ◽

Author(s):

Jeannette Huebener-Schmid ◽

Kirsten Kuhlbrodt ◽

Julien Peladan ◽

Jennifer Faber ◽

Magda M Santana ◽

...

Keyword(s):

Spinocerebellar Ataxia ◽

Repeat Expansion ◽

Cag Repeat ◽

Spinocerebellar Ataxia Type ◽

Clinical Parameters ◽

Target Engagement ◽

Spinocerebellar Ataxia Type 3 ◽

Curative Therapy ◽

Cag Repeat Expansion ◽

Type 3

Abstract Spinocerebellar ataxia type 3 is a rare neurodegenerative disease, caused by a CAG repeat expansion leading to polyglutamine elongation in the ataxin-3 protein. While no curative therapy is yet available, preclinical gene silencing approaches to reduce polyglutamine-toxicity demonstrate promising results. In view of upcoming clinical trials, quantitative and easily accessible molecular markers are of critical importance as pharmacodynamic and particularly as target engagement markers. We developed a novel ultrasensitive immunoassay to measure specifically polyQ-expanded ataxin-3 in plasma and cerebrospinal fluid. Statistical analyses revealed a correlation with clinical parameters and a stability of polyglutamine-expanded ataxin-3 during conversion from the pre-ataxic to the ataxic phase.

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Factors Associated with Intergenerational Instability of ATXN3 CAG Repeat and Genetic Anticipation in Chinese Patients with Spinocerebellar Ataxia Type 3

The Cerebellum ◽

10.1007/s12311-020-01167-x ◽

2020 ◽

Vol 19 (6) ◽

pp. 902-906

Author(s):

Yi-Chu Du ◽

Yin Ma ◽

Ya-Ru Shao ◽

Shi-Rui Gan ◽

Yi Dong ◽

...

Keyword(s):

Spinocerebellar Ataxia ◽

Cag Repeat ◽

Chinese Patients ◽

Spinocerebellar Ataxia Type ◽

Spinocerebellar Ataxia Type 3 ◽

Genetic Anticipation ◽

Factors Associated ◽

Type 3

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A genetic model for human polyglutamine-repeat disease in Drosophila melanogaster

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1999.0458 ◽

1999 ◽

Vol 354 (1386) ◽

pp. 1057-1060 ◽

Cited By ~ 15

Author(s):

Nancy M. Bonini

Keyword(s):

Drosophila Melanogaster ◽

Genetic Model ◽

Late Onset ◽

Spinocerebellar Ataxia Type ◽

Gene Encoding ◽

Spinocerebellar Ataxia Type 3 ◽

Neural Degeneration ◽

Polyglutamine Repeat ◽

Disease Protein ◽

Type 3

To apply genetics to the problem of human polyglutamine–repeat disease, we recreated polyglutamine–repeat disease in Drosophila melanogaster . To do this, we expressed forms of the human gene encoding spinocerebellar ataxia type 3, also called Machado–Joseph disease (SCA–3/MJD). This gene is responsible for the most common form of human ataxia worldwide. Expression of a normal form of the MJD protein with 27 polyglutamines (MJDtr–Q27) had no phenotype. However, expression of a form of the protein with an expanded run of 78 glutamines (MJDtr–Q78) caused late onset progressive degeneration. In addition, the MJDtr–Q78 formed abnormal protein aggregates, or nuclear inclusions (NIs), whereas the control protein was cytoplasmic. These data indicate that the mechanisms of human polyglutamine–repeat disease are conserved to Drosophila . We are currently using this model to address potential mechanisms by which the mutant disease protein causes neural degeneration, as well as to define genes that can prevent polyglutamine–induced degeneration. By applying the power of Drosophila genetics to the problem of human polyglutamine–induced neural degeneration, we hope to identify ways to prevent and treat these diseases in humans.

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Karyopherin α-3 is a key protein in the pathogenesis of spinocerebellar ataxia type 3 controlling the nuclear localization of ataxin-3

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1716071115 ◽

2018 ◽

Vol 115 (11) ◽

pp. E2624-E2633 ◽

Cited By ~ 19

Author(s):

Anna Sergeevna Sowa ◽

Elodie Martin ◽

Inês Morgado Martins ◽

Jana Schmidt ◽

Reinhard Depping ◽

...

Keyword(s):

Spinocerebellar Ataxia ◽

Nuclear Localization ◽

Neurodegenerative Disorder ◽

Nucleocytoplasmic Transport ◽

Spinocerebellar Ataxia Type ◽

Nuclear Pore ◽

Spinocerebellar Ataxia Type 3 ◽

Nuclear Localization Signals ◽

Positive Effects ◽

Type 3

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder caused by a CAG expansion in the ATXN3 gene leading to a polyglutamine expansion in the ataxin-3 protein. The nuclear presence and aggregation of expanded ataxin-3 are critical steps in disease pathogenesis. To identify novel therapeutic targets, we investigated the nucleocytoplasmic transport system by screening a collection of importins and exportins that potentially modulate this nuclear localization. Using cell, Drosophila, and mouse models, we focused on three transport proteins, namely, CRM1, IPO13, KPNA3, and their respective Drosophila orthologs Emb, Cdm, and Kap-α3. While overexpression of CRM1/Emb demonstrated positive effects in Drosophila, KPNA3/Kap-α3 emerged as the most promising target, as knockdown via multiple RNAi lines demonstrated its ability to shuttle both truncated and full-length expanded ataxin-3, rescue neurodegeneration, restore photoreceptor formation, and reduce aggregation. Furthermore, KPNA3 knockout in SCA3 mice resulted in an amelioration of molecular and behavioral disturbances such as total activity, anxiety, and gait. Since KPNA3 is known to function as an import protein and recognize nuclear localization signals (NLSs), this work unites ataxin-3 structure to the nuclear pore machinery and provides a link between karyopherins, NLS signals, and polyglutamine disease, as well as demonstrates that KPNA3 is a key player in the pathogenesis of SCA3.

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