Genetically engineered mouse models of the trinucleotide-repeat spinocerebellar ataxias (original) (raw)
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Polyglutamine spinocerebellar ataxias — from genes to potential treatments
Nature Reviews Neuroscience, 2017
The dominantly inherited spinocerebellar ataxias (SCAs) are a large and diverse group of neurodegenerative diseases. The most prevalent SCAs (SCA1, SCA2, SCA3, SCA6 and SCA7) are caused by expansion of a glutamine-encoding CAG repeat in the affected gene. These SCAs represent a substantial portion of the polyglutamine neurodegenerative disorders and provide insight into this class of diseases as a whole. Recent years have seen considerable progress in deciphering the clinical, pathological, physiological and molecular aspects of the polyglutamine SCAs, with these advances establishing a solid base from which to pursue potential therapeutic approaches. The spinocerebellar ataxias (SCAs) are a large and diverse group of autosomal-dominant, progressive neurodegenerative diseases. They share the clinical feature of progressive ataxia, reflecting degeneration of the cerebellum and, often, other connected regions of the nervous system. The prevalence of the SCAs varies markedly depending on geography and ethnicity but is estimated to be 1-3 per 100,000 among Europeans 1. Although many of the SCAs result from point mutations, DNA rearrangements (SCA15, SCA16 and SCA20) or expansions of non-coding repeats (SCA8, SCA10, SCA31 and SCA36) (BOXES 1,2), the most common SCAs are caused by expansion of a CAG nucleotide repeat that encodes polyglutamine (polyQ) in the relevant disease proteins. These polyQ SCAs include SCA1-SCA3, SCA6, SCA7 and SCA17, which are caused by expanded polyQ sequences in ataxin 1 (ATXN1), ATXN2, ATXN3, subunit-α of the Cav2.1 voltage-gated calcium channel (CACNA1A), ATXN7 and TATA-box-binding protein (TBP), respectively. Disease severity
Towards A Therapeutic Intervention in Polyglutamine Ataxias: From Models to Clinical Trials
The autosomal dominant (AD) forms of hereditary ataxias compose a heterogeneous group of diseases, in which cerebellar degeneration and dysfunction is consistently present. Polyglutamine (polyQ) ataxias are a subset of AD ataxias, comprising spinocerebellar ataxias (SCAs) 1, 2, 3, 6, 7 and 17, as well as dentatorubral-pallydoluysian atrophy (DRPLA), all caused by a CAG expansion in the coding region of the corresponding gene, leading to the formation of a pathological polyglutamine stretch. The pathogenic process underlying these disorders has been extensively investigated, but it remains incompletely understood; as a consequence, therapeutic targets have been difficult to identify. Models of polyQ SCAs have proven to be of great utility for the understanding of the underlying pathogenic processes; in particular, animal models mimicking the evolution of these diseases are considered to be of great utility in the evaluation of the efficacy of disease-modifying compounds, before they can be translated into patient trials. In this chapter, we review the common mechanisms in polyQ ataxias pathogenesis and summarize the evidence provided by cell and animal models of SCAs concerning the potential benefits of several compounds which have been studied in a preclinical setup. A collection of the published data on clinical trials conducted so far in polyQ SCAs is presented and the main limitations currently imposed to trials in this group of disorders are discussed.
Neurobiology of Disease, 2010
Keywords: Spinocerebellar ataxia type 3 Machado-Joseph disease SCA3 MJD Polyglutamine Intranuclear inclusion bodies Transgenic mouse model CAG repeat instability Late onset Spinocerebellar ataxia type 3 (SCA3), or Machado-Joseph disease (MJD), is caused by the expansion of a polyglutamine repeat in the ataxin-3 protein. We generated a mouse model of SCA3 expressing ataxin-3 with 148 CAG repeats under the control of the huntingtin promoter, resulting in ubiquitous expression throughout the whole brain. The model resembles many features of the disease in humans, including a late onset of symptoms and CAG repeat instability in transmission to offspring. We observed a biphasic progression of the disease, with hyperactivity during the first months and decline of motor coordination after about 1 year of age; however, intranuclear aggregates were not visible at this age. Few and small intranuclear aggregates appeared first at the age of 18 months, further supporting the claim that neuronal dysfunction precedes the formation of intranuclear aggregates.
Oligonucleotide therapy mitigates disease in Spinocerebellar Ataxia Type 3 mice
Annals of neurology, 2018
Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is the most common dominantly inherited ataxia. Despite advances in understanding this CAG repeat/polyglutamine expansion disease, there are still no therapies to alter its progressive fatal course. Here we investigate whether an antisense oligonucleotide (ASO) targeting the SCA3 disease gene, ATXN3, can prevent molecular, neuropathological, electrophysiological and behavioral features of the disease in a mouse model of SCA3. The top ATXN3-targeting ASO from an in vivo screen was injected intracerebroventricularly into early symptomatic transgenic SCA3 mice that express the full human disease gene and recapitulate key disease features. Following a single ASO treatment at 8 weeks of age, mice were evaluated longitudinally for ATXN3 suppression and rescue of disease-associated pathological changes. Mice receiving an additional repeat injection at 21 weeks were evaluated longitudinally up to 29 weeks for motor ...
Polyglutamine ataxias: From Clinical and Molecular Features to Current Therapeutic Strategies
Journal of Genetic Syndromes & Gene Therapy, 2017
Spinocerebellar ataxias are a large group of heterogeneous diseases that all involve selective neuronal degeneration and accompanied cerebellar ataxia. These diseases can be further broken down into discrete groups according to their underlying molecular genetic cause. The most common are the polyglutamine ataxias, of which there are six; Spinocerebellar ataxia type 1, 2, 3, 6, 7 and 17. These diseases are characterised by a pathological expanded cytosine-adenine-guanine (CAG) repeat sequence, in the protein coding region of a given gene. Common clinical features include lack of coordination and gait ataxia, speech and swallowing difficulties, as well as impaired hand and motor functions. The polyglutamine spinocerebellar ataxias are typically late onset diseases that are progressive in nature and often lead to premature death, for which there is currently no known cure or effective treatment strategy. Although caused by the same molecular mechanism, the causative gene and associated protein differ for each disease. The exact mechanism by which disease pathogenesis is caused remains elusive. However, the variable (CAG) n repeats are codons that may be translated to an expanded glutamine tract, leading to conformational changes in the protein, giving it a toxic gain of function. Several pathogenic pathways have been implicated in polyglutamine spinocerebellar ataxia diseases, such as the hallmark feature of neuronal nuclear inclusions, protein misfolding and aggregation, as well as transcriptional dysregulation. These pathways are attractive avenues for potential therapeutic interventions, as the potential to treat more than one disease exists. Research is ongoing, and several promising therapies are currently underway in an attempt to provide relief for this devastating class of diseases..
Protein engineering, 2003
In recent years, nine neurodegenerative diseases have been found to be caused by the expansion of a CAG-triplet repeat in the coding region of the respective genes, resulting in lengthening of an otherwise harmless polyglutamine tract in the gene products. To facilitate structural studies of these disease mechanisms, a general protocol is described that allows site-specific mutations to be introduced into the polyglutamine tract. Based on 'cassette mutagenesis', this protocol involves engineering unique restriction sites into the flanking regions of the CAG repeat and subsequently replacing the wild-type CAG repeat with a double-stranded synthetic DNA fragment containing the desired mutations. This method was applied to the spinocerebellar ataxin-3 protein, such that the wild-type amino acid sequence -Q 3 KQ 22 -was replaced by a -Q 9 CQ 9 -sequence. In this case, the incorporated cysteine residue can be exploited for various chemical modifications, lending the host glutamine repeat to many structural and biophysical techniques for the resolution of a specific residue. The method reported here bypasses many problems that can arise from PCRbased mutagenesis methods.
Spinocerebellar ataxias: an update
Current Opinion in Neurology, 2007
Purpose of review Here we discuss recent advances regarding the molecular genetic basis of dominantly inherited ataxias. Recent findings Important recent observations include insights into the mechanisms by which expanded polyglutamine causes cerebellar degeneration; new findings regarding how noncoding expansions may cause disease; the discovery that conventional (i.e. nonrepeat) mutations underlie recently identified ataxias; and growing recognition that multiple biological pathways, when perturbed, can cause cerebellar degeneration. Summary The dominant ataxias, also known as spinocerebellar ataxias, continue to grow in number. Here we review the major categories of spinocerebellar ataxias: expanded polyglutamine ataxias; noncoding repeat ataxias; and ataxias caused by conventional mutations. After discussing features shared by these disorders, we present recent evidence supporting a toxic protein mechanism for the polyglutamine spinocerebellar ataxias and the recognition that both protein misfolding and perturbations in nuclear events represent key events in pathogenesis. Less is known about pathogenic mechanisms in spinocerebellar ataxias due to noncoding repeats, though a toxic RNA effect remains possible. Newly discovered, conventional mutations in spinocerebellar ataxias suggest a wide range of biological pathways can be disrupted to cause progressive ataxia. Finally, we discuss how new mechanistic insights can drive the push toward preventive treatment.
Characterization of a new transgenic mouse model of the Spinocerebellar Ataxia type 2 disease
The objective of this work was the generation of an animal model of the SCA2 disease for future studies on the benefits of therapeutic molecules and the underlying neuropathological mechanisms in this human disorder. The transgenic fragment was microinjected into pronuclei of B6D2F1 X OF1 mouse hybrid strain. For Northern blots, RNAs were hybridized with a human cDNA fragment from the SCA2 gene and a mouse b-actin cDNA fragment. Monoclonal antibodies directed at the N-terminal of the ataxin 2 protein with 22Q were used for Western blot analysis. A rotating rod apparatus was utilized to measure motor coordination of mice. Immunohistochemical detection of Purkinje neurons was performed with anti-calbindin 28K as the primary antibody. An ubiquitous expression of the SCA2 transgene with 75 CAG repeats regulated by the SCA2 self promoter was obtained after the generation of our transgenic mice. The analysis of transgenic mice revealed significant differences of motor coordination compared with the wild type littermates. A specific degeneration of Purkinje neurons and transgene over-expression in the brain, liver and skeletal muscle, rather than in lungs and kidneys was also observed, resembling the expression pattern of the ataxin 2 in humans.
Nature Genetics, 2006
We previously reported that a (CTG) n expansion causes spinocerebellar ataxia type 8 (SCA8), a slowly progressive ataxia with reduced penetrance. We now report a transgenic mouse model in which the full-length human SCA8 mutation is transcribed using its endogenous promoter. (CTG) 116 expansion, but not (CTG) 11 control lines, develop a progressive neurological phenotype with in vivo imaging showing reduced cerebellar-cortical inhibition. 1C2-positive intranuclear inclusions in cerebellar Purkinje and brainstem neurons in SCA8 expansion mice and human SCA8 autopsy tissue result from translation of a polyglutamine protein, encoded on a previously unidentified antiparallel transcript (ataxin 8, ATXN8) spanning the repeat in the CAG direction. The neurological phenotype in SCA8 BAC expansion but not BAC control lines demonstrates the pathogenicity of the (CTG-CAG) n expansion. Moreover, the expression of noncoding (CUG) n expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and the discovery of intranuclear polyglutamine inclusions suggests SCA8 pathogenesis involves toxic gain-of-function mechanisms at both the protein and RNA levels.