Clinical features, neurogenetics and neuropathology of the polyglutamine spinocerebellar ataxias type 1, 2, 3, 6 and 7

SCA2 presenting as a focal dystonia

BACKGROUND

Spinocerebellar ataxia 2 (SCA2) is an autosomal dominant neurodegenerative disorder caused by CAG repeat expansions in ATXN2 on chromosome 12q24. Patients present with adult-onset progressive gait ataxia, slow saccades, nystagmus, dysarthria and peripheral neuropathy. Dystonia is known to occur as SCA2 advances, but is rarely the presenting symptom.

CASE PRESENTATION

A 43-year-old right handed woman presented with focal dystonia of the right hand which started two years earlier with difficulty writing. There were only mild cerebellar signs. Her mother was reported to have a progressive gait disorder and we subsequently learned that she had SCA2. A total of 10 maternal family members were similarly affected. Over the course of 10 years, the patient's cerebellar signs progressed only mildly however the dystonia worsened to the extent of inability to use her right hand. Dystonia did not improve significantly with botulinum toxin, levodopa or trihexyphenidyl, but has shown marked improvement since DBS implantation in the GPi.

CONCLUSIONS

We describe a patient with SCA2 who presented with focal dystonia of the right upper extremity. Subtle cerebellar signs as well as the family history became especially important given the absence of predominant gait ataxia. Our case emphasizes that focal dystonia is not only a feature of SCA2, but can also rarely be the presenting sign as well as the most prominent feature during the disease course.

Astroglia contribute to the pathogenesis of spinocerebellar ataxia Type 1 (SCA1) in a biphasic, stage-of-disease specific manner

Spinocerebellar ataxia type 1 (SCA1) is a fatal, dominantly inherited neurodegenerative disease caused by the expansion of CAG repeats in the Ataxin-1 (ATXN1) gene. SCA1 is characterized by balance and coordination deficits due to the predominant loss of Purkinje neurons in the cerebellum. We previously demonstrated that cerebellar astrogliosis beings during the early stages of SCA1, prior to onset of motor deficits and loss of Purkinje neurons. We communicate here that cerebellar astrogliosis contributes to SCA1 pathogenesis in a biphasic, stage of disease dependent manner. We modulated astrogliosis by selectively reducing pro-inflammatory transcriptional regulator nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling in astroglia via a Cre-lox mouse genetic approach. Our results indicate that inhibition of astroglial NF-κB signaling, prior to motor deficit onset, exacerbates disease severity. This is suggestive of a neuroprotective role mediated by astroglia during early stage SCA1. In contrast, inhibition of astroglial NF-κB signaling during late stage of disease ameliorated motor deficits, indicating a potentially harmful role of astroglia late in SCA1. These results indicate that astrogliosis may have a critical and dual role in disease. If so, our results imply that anti-inflammatory astroglia-based therapeutic approaches may need to consider disease progression to achieve therapeutic efficacy.

Oligonucleotide therapy mitigates disease in spinocerebellar ataxia type 3 mice

OBJECTIVE

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.

METHODS

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 performance.

RESULTS

The ATXN3-targeting ASO achieved sustained reduction of polyglutamine-expanded ATXN3 up to 8 weeks after treatment and prevented oligomeric and nuclear accumulation of ATXN3 up to at least 14 weeks after treatment. Longitudinal ASO therapy rescued motor impairment in SCA3 mice, and this rescue was associated with a recovery of defects in Purkinje neuron firing frequency and afterhyperpolarization.

INTERPRETATION

This preclinical study established efficacy of ATXN3-targeted ASOs as a disease-modifying therapeutic strategy for SCA3. These results support further efforts to develop ASOs for human clinical trials in this polyglutamine disease as well as in other dominantly inherited disorders caused by toxic gain of function. Ann Neurol 2018;83:64-77.

Transcranial magnetic stimulation in hereditary ataxias: Diagnostic utility, pathophysiological insight and treatment

Transcranial magnetic stimulation (TMS) is a valuable technique to assess and modulate human brain function in normal and pathological conditions. This critical review surveys the contributions of TMS to the diagnosis, insight into pathophysiology and treatment of genetically confirmed hereditary ataxias, a heterogeneous group of neurodegenerative disorders that can affect motor cortex and the corticospinal tract. Most studies were conducted on small sample sizes and focused on diagnostic approaches. The available data demonstrate early involvement of the corticospinal tract and motor cortex circuitry, and support the possible efficacy of cerebellar repetitive TMS (rTMS) as therapeutic approach. Further TMS-based studies are warranted, to establish biomarkers for early diagnosis and disease monitoring, explore the involvement of the cerebello-dentato-thalamo-cortical projection, study the effects of rTMS-induced plasticity, and utilize rTMS for treatment.

Autosomal dominant cerebellar ataxias: Imaging biomarkers with high effect sizes

Objective

As gene-based therapies may soon arise for patients with spinocerebellar ataxia (SCA), there is a critical need to identify biomarkers of disease progression with effect sizes greater than clinical scores, enabling trials with smaller sample sizes.

Methods

We enrolled a unique cohort of patients with SCA1 (n = 15), SCA2 (n = 12), SCA3 (n = 20) and SCA7 (n = 10) and 24 healthy controls of similar age, sex and body mass index. We collected longitudinal clinical and imaging data at baseline and follow-up (mean interval of 24 months). We performed both manual and automated volumetric analyses. Diffusion tensor imaging (DTI) and a novel tractography method, called fixel-based analysis (FBA), were assessed at follow-up. Effect sizes were calculated for clinical scores and imaging parameters.

Results

Clinical scores worsened as atrophy increased over time (p < 0.05). However, atrophy of cerebellum and pons showed very large effect sizes (>1.2) compared to clinical scores (<0.8). FBA, applied for the first time to SCA, was sensitive to microstructural cross-sectional differences that were not captured by conventional DTI metrics, especially in the less studied SCA7 group. FBA also showed larger effect sizes than DTI metrics.

Conclusion

This study showed that volumetry outperformed clinical scores to measure disease progression in SCA1, SCA2, SCA3 and SCA7. Therefore, we advocate the use of volumetric biomarkers in therapeutic trials of autosomal dominant ataxias. In addition, FBA showed larger effect size than DTI to detect cross-sectional microstructural alterations in patients relative to controls.

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Biomarkers are needed to test upcoming therapies for spinocerebellar ataxia.

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As spinocerebellar ataxias are rare, biomarkers with high effect sizes are needed.

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We identified imaging biomarkers with higher effect sizes than clinical scores.

Anti-Saccades in Cerebellar Ataxias Reveal a Contribution of the Cerebellum in Executive Functions

OBJECTIVE

Increasing evidence suggests a cerebellar contribution to modulate cognitive aspects of motor behavior and executive functions. Supporting findings come from studies on patients with neurodegenerative diseases, in which however, given the extent of the disease, the specific role of the cerebellum, could not be clearly isolated. Anti-saccades are considered a sensitive tool to test executive functions. The anti-saccade underlying neural network, consisting of different cortical areas and their downstream connections including the lateral cerebellum, has been largely clarified. To separate the role of the cerebellum with respect to other cortical structures in executive control, we compared the anti-saccade performances in two distinct cohorts of patients with cerebellar disorders (with and without cerebral cortical involvement).

METHODS

Eye movements during the execution of anti-saccades were recorded in 12 patients with spinocerebellar ataxia type 2 (a cortical-subcortical neurodegenerative disease), 10 patients with late onset cerebellar ataxia (an isolated cerebellar atrophy), and 34 matched controls.

RESULTS

In the anti-saccade task, besides dynamic changes already demonstrated in the pro-saccades of these patients, we found in both groups of cerebellar patients prolonged latency with larger variability than normal and increased directional error rate. Errors, however, were corrected by cerebellar patients as frequently as normal. No significant differences were found in patients with and without cortical involvement.

CONCLUSION

Our results indicate, in a large cohort of cerebellar patients, that the cerebellum plays a critical role in the regulation of executive motor control not only, as well known, by controlling the end of a movement, but also modulating its initiation and reducing reflexive responses that would perturb voluntary actions.

Neurochemical abnormalities in premanifest and early spinocerebellar ataxias

OBJECTIVE

To investigate whether early neurochemical abnormalities are detectable by high-field magnetic resonance spectroscopy (MRS) in individuals with spinocerebellar ataxias (SCAs) 1, 2, 3, and 6, including patients without manifestation of ataxia.

METHODS

A cohort of 100 subjects (N = 18-21 in each SCA group, including premanifest mutation carriers; mean score on the Scale for the Assessment and Rating of Ataxia [SARA] <10 for all genotypes, and 22 matched controls) was scanned at 7 Tesla to obtain neurochemical profiles of the cerebellum and brainstem. A novel multivariate approach (distance-weighted discrimination) was used to combine regional profiles into an "MRS score."

RESULTS

MRS scores robustly distinguished individuals with SCA from controls, with misclassification rates of 0% (SCA2), 2% (SCA3), 5% (SCA1), and 17% (SCA6). Premanifest mutation carriers with estimated disease onset within 10 years had MRS scores in the range of early-manifest SCA subjects. Levels of neuronal and glial markers significantly correlated with SARA and an Activities of Daily Living score in subjects with SCA. Regional neurochemical alterations were different between SCAs at comparable disease severity, with SCA2 displaying the most extensive neurochemical abnormalities, followed by SCA1, SCA3, and SCA6.

INTERPRETATION

Neurochemical abnormalities are detectable in individuals before manifest disease, which may allow premanifest enrollment in future SCA trials. Correlations with ataxia and quality-of-life scores show that neurochemical levels can serve as clinically meaningful endpoints in trials. Ranking of SCA types by degree of neurochemical abnormalities indicates that the neurochemistry may reflect synaptic function or density. Ann Neurol 2018;83:816-829.

The cerebral metabolic topography of spinocerebellar ataxia type 3

Introduction

We aimed to uncover the pattern of network-level changes in neuronal function in Spinocerebellar ataxia type 3 (SCA3).

Methods

17 genetically-confirmed SCA3 patients and 16 controls underwent structural MRI and static resting-state [¹⁸F]‑Fluoro‑deoxyglucose Positron Emission Tomography (FDG-PET) imaging. A SCA3-related pattern (SCA3-RP) was identified using a multivariate method (scaled subprofile model and principal component analysis (SSM PCA)). Participants were evaluated with the Scale for Assessment and Rating of Ataxia (SARA) and with neuropsychological examination including tests for language, executive dysfunction, memory, and information processing speed. The relationships between SCA3-RP expression and clinical scores were explored. Voxel based morphology (VBM) was applied on MRI-T1 images to assess possible correlations between FDG reduction and grey matter atrophy.

Results

The SCA3-RP disclosed relative hypometabolism of the cerebellum, caudate nucleus and posterior parietal cortex, and relatively increased metabolism in somatosensory areas and the limbic system. This topography, which was not explained by regional atrophy, correlated significantly with ataxia (SARA) scores (ρ = 0.72; P = 0.001). SCA3 patients showed significant deficits in executive function and information processing speed, but only letter fluency correlated with SCA3-RP expression (ρ = 0.51; P = 0.04, uncorrected for multiple comparisons).

Conclusion

The SCA3 metabolic profile reflects network-level alterations which are primarily associated with the motor features of the disease. Striatum decreases additional to cerebellar hypometabolism underscores an intrinsic extrapyramidal involvement in SCA3. Cerebellar-posterior parietal hypometabolism together with anterior parietal (sensory) cortex hypermetabolism may reflect a shift from impaired feedforward to compensatory feedback processing in higher-order motor control. The demonstrated SCA3-RP provides basic insight in cerebral network changes in this disease.

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A metabolic cerebral pattern could be identified in FDG-PET data of SCA3 patients, which was not explained by regional atrophy.

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Striatum decreases in the SCA3-pattern reflect extrapyramidal involvement.

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The SCA3-pattern reflects changes in higher-order motor control.

Autonomic function testing in spinocerebellar ataxia type 2

PURPOSE

To assess whether autonomic failure belongs to the clinical spectrum of spinocerebellar ataxia type 2 (SCA2), an autosomal dominant genetic disorder showing progressive cerebellar and brainstem dysfunction.

METHODS

We evaluated cardiovascular autonomic function in 8 patients with SCA2 and 16 age- and gender-matched healthy controls. Other autonomic domains were examined through standardized questionnaires and by testing the skin sympathetic reflex.

RESULTS

Patients with SCA2 showed normal responses to cardiovascular autonomic function tests, with the exception of lower baroreflex sensitivity upon standing compared to controls. In questionnaires, 7 out of 8 patients reported bladder disturbances, while 3 out of 6 tested patients had no skin sympathetic reflex.

CONCLUSIONS

We did not observe clinically overt cardiovascular autonomic failure in patients with SCA2. Other autonomic domains (i.e., bladder and sudomotor function) may be affected in the disease.

Tandem repeats mediating genetic plasticity in health and disease

Accumulating evidence suggests that many classes of DNA repeats exhibit attributes that distinguish them from other genetic variants, including the fact that they are more liable to mutation; this enables them to mediate genetic plasticity. The expansion of tandem repeats, particularly of short tandem repeats, can cause a range of disorders (including Huntington disease, various ataxias, motor neuron disease, frontotemporal dementia, fragile X syndrome and other neurological disorders), and emerging data suggest that tandem repeat polymorphisms (TRPs) can also regulate gene expression in healthy individuals. TRPs in human genomes may also contribute to the missing heritability of polygenic disorders. A better understanding of tandem repeats and their associated repeatome, as well as their capacity for genetic plasticity via both germline and somatic mutations, is needed to transform our understanding of the role of TRPs in health and disease.

NESSCA Validation and Responsiveness of Several Rating Scales in Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2), caused by a CAG expansion (CAGexp) at ATXN2, has a complex clinical picture. While validated ataxia scales are available, comprehensive instruments to measure all SCA2 neurological manifestations are required. This study aims to validate the Neurological Examination Score for the assessment of Spinocerebellar Ataxias (NESSCA) to be used in SCA2 and to compare its responsiveness to those obtained with other instruments. NESSCA, SARA, SCAFI, and CCFS scales were applied in symptomatic SCA2 patients. Correlations were done with age at onset, disease duration, CAGexp, and between scales. Responsiveness was estimated by comparing deltas of stable to worse patients after 12 months, according to Patient Global Impression of change, and the area under the curve (AUC) of the Receiver Operating Characteristics curve of scores range. Eighty-eight evaluations (49 patients) were obtained. NESSCA had an even distribution and correlated with disease duration (r = 0.55), SARA (r = 0.63), and CAGexp (rho = 0.32): both explained 44% of NESSCA variance. Deltas (95% CI) after 1 year in stable and worse patients were only significantly different for SARA. NESSCA, SARA, SCAFI, and CCFS AUC were 0.63, 0.81, 0.49, and 0.48, respectively. NESSCA is valid to be used in SCA2. However, the only instrument that presented good responsiveness to change in 1 year was SARA. We suggest that NESSCA can be used as a secondary outcome in future trials in SCA2 due to the burden of neurological disabilities related to disease progression.

Comparison of spinocerebellar ataxia type 3 mouse models identifies early gain-of-function, cell-autonomous transcriptional changes in oligodendrocytes

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder caused by a polyglutamine-encoding CAG repeat expansion in the ATXN3 gene. This expansion leads to misfolding and aggregation of mutant ataxin-3 (ATXN3) and degeneration of select brain regions. A key unanswered question in SCA3 and other polyglutamine diseases is the extent to which neurodegeneration is mediated through gain-of-function versus loss-of-function. To address this question in SCA3, we performed transcriptional profiling on the brainstem, a highly vulnerable brain region in SCA3, in a series of mouse models with varying degrees of ATXN3 expression and aggregation. We include two SCA3 knock-in mouse models: our previously published model that erroneously harbors a tandem duplicate of the CAG repeat-containing exon, and a corrected model, introduced here. Both models exhibit dose-dependent neuronal accumulation and aggregation of mutant ATXN3, but do not exhibit a behavioral phenotype. We identified a molecular signature that correlates with ATXN3 neuronal aggregation yet is primarily linked to oligodendrocytes, highlighting early white matter dysfunction in SCA3. Two robustly elevated oligodendrocyte transcripts, Acy3 and Tnfrsf13c, were confirmed as elevated at the protein level in SCA3 human disease brainstem. To determine if mutant ATXN3 acts on oligodendrocytes cell-autonomously, we manipulated the repeat expansion in the variant SCA3 knock-in mouse by cell-type specific Cre/LoxP recombination. Changes in oligodendrocyte transcripts are driven cell-autonomously and occur independent of neuronal ATXN3 aggregation. Our findings support a primary toxic gain of function mechanism and highlight a previously unrecognized role for oligodendrocyte dysfunction in SCA3 disease pathogenesis.

An miRNA-mediated therapy for SCA6 blocks IRES-driven translation of the CACNA1A second cistron

Spinocerebellar ataxia type 6 (SCA6) is a dominantly inherited neurodegenerative disease characterized by slowly progressive ataxia and Purkinje cell degeneration. SCA6 is caused by a polyglutamine repeat expansion within a second CACNA1A gene product, α1ACT. α1ACT expression is under the control of an internal ribosomal entry site (IRES) present within the CACNA1A coding region. Whereas SCA6 allele knock-in mice show indistinguishable phenotypes from wild-type littermates, expression of SCA6-associated α1ACT (α1ACTSCA6) driven by a Purkinje cell-specific promoter in mice produces slowly progressive ataxia and cerebellar atrophy. We developed an early-onset SCA6 mouse model using an adeno-associated virus (AAV)-based gene delivery system to ectopically express CACNA1A IRES-driven α1ACTSCA6 to test the potential of CACNA1A IRES-targeting therapies. Mice expressing AAV9-mediated CACNA1A IRES-driven α1ACTSCA6 exhibited early-onset ataxia, motor deficits, and Purkinje cell degeneration. We identified miR-3191-5p as a microRNA (miRNA) that targeted CACNA1A IRES and preferentially inhibited the CACNA1A IRES-driven translation of α1ACT in an Argonaute 4 (Ago4)-dependent manner. We found that eukaryotic initiation factors (eIFs), eIF4AII and eIF4GII, interacted with the CACNA1A IRES to enhance α1ACT translation. Ago4-bound miR-3191-5p blocked the interaction of eIF4AII and eIF4GII with the CACNA1A IRES, attenuating IRES-driven α1ACT translation. Furthermore, AAV9-mediated delivery of miR-3191-5p protected mice from the ataxia, motor deficits, and Purkinje cell degeneration caused by CACNA1A IRES-driven α1ACTSCA6 We have established proof of principle that viral delivery of an miRNA can rescue a disease phenotype through modulation of cellular IRES activity in a mouse model.

Vulnerability of Purkinje Cells Generated from Spinocerebellar Ataxia Type 6 Patient-Derived iPSCs

Spinocerebellar ataxia type 6 (SCA6) is a dominantly inherited neurodegenerative disease characterized by loss of Purkinje cells in the cerebellum. SCA6 is caused by CAG trinucleotide repeat expansion in CACNA1A, which encodes Cav2.1, α1A subunit of P/Q-type calcium channel. However, the pathogenic mechanism and effective therapeutic treatments are still unknown. Here, we have succeeded in generating differentiated Purkinje cells that carry patient genes by combining disease-specific iPSCs and self-organizing culture technologies. Patient-derived Purkinje cells exhibit increased levels of full-length Cav2.1 protein but decreased levels of its C-terminal fragment and downregulation of the transcriptional targets TAF1 and BTG1. We further demonstrate that SCA6 Purkinje cells exhibit thyroid hormone depletion-dependent degeneration, which can be suppressed by two compounds, thyroid releasing hormone and Riluzole. Thus, we have constructed an in vitro disease model recapitulating both ontogenesis and pathogenesis. This model may be useful for pathogenic investigation and drug screening.

Bicistronic CACNA1A Gene Expression in Neurons Derived from Spinocerebellar Ataxia Type 6 Patient-Induced Pluripotent Stem Cells

Spinocerebellar ataxia type 6 (SCA6) is an autosomal-dominant neurodegenerative disorder that is caused by a CAG trinucleotide repeat expansion in the CACNA1A gene. As one of the few bicistronic genes discovered in the human genome, CACNA1A encodes not only the α1A subunit of the P/Q type voltage-gated Ca²⁺ channel Ca_V2.1 but also the α1ACT protein, a 75 kDa transcription factor sharing the sequence of the cytoplasmic C-terminal tail of the α1A subunit. Isoforms of both proteins contain the polyglutamine (polyQ) domain that is expanded in SCA6 patients. Although certain SCA6 phenotypes appear to be specific for Purkinje neurons, other pathogenic effects of the SCA6 polyQ mutation can affect a broad spectrum of central nervous system (CNS) neuronal subtypes. We investigated the expression and function of CACNA1A gene products in human neurons derived from induced pluripotent stem cells from two SCA6 patients. Expression levels of CACNA1A encoding α1A subunit were similar between SCA6 and control neurons, and no differences were found in the subcellular distribution of Ca_V2.1 channel protein. The α1ACT immunoreactivity was detected in the majority of cell nuclei of SCA6 and control neurons. Although no SCA6 genotype-dependent differences in Ca_V2.1 channel function were observed, they were found in the expression levels of the α1ACT target gene Granulin (GRN) and in glutamate-induced cell vulnerability.

Dystonia and ataxia progression in spinocerebellar ataxias

BACKGROUND

Dystonia is a common feature in spinocerebellar ataxias (SCAs). Whether the presence of dystonia is associated with different rate of ataxia progression is not known.

OBJECTIVES

To study clinical characteristics and ataxia progression in SCAs with and without dystonia.

METHODS

We studied 334 participants with SCA 1, 2, 3 and 6 from the Clinical Research Consortium for Spinocerebellar Ataxias (CRC-SCA) and compared the clinical characteristics of SCAs with and without dystonia. We repeatedly measured ataxia progression by the Scale for Assessment and Rating of Ataxia every 6 months for 2 years. Regression models were employed to study the association between dystonia and ataxia progression after adjusting for age, sex and pathological CAG repeats. We used logistic regression to analyze the impact of different repeat expansion genes on dystonia in SCAs.

RESULTS

Dystonia was most commonly observed in SCA3, followed by SCA2, SCA1, and SCA6. Dystonia was associated with longer CAG repeats in SCA3. The CAG repeat number in TBP normal alleles appeared to modify the presence of dystonia in SCA1. The presence of dystonia was associated with higher SARA scores in SCA1, 2, and 3. Although relatively rare in SCA6, the presence of dystonia was associated with slower progression of ataxia.

CONCLUSIONS

The presence of dystonia is associated with greater severity of ataxia in SCA1, 2, and 3, but predictive of a slower progression in SCA6. Complex genetic interactions among repeat expansion genes can lead to diverse clinical symptoms and progression in SCAs.

Early corticospinal tract damage in prodromal SCA2 revealed by EEG-EMG and EMG-EMG coherence

OBJECTIVE

Clinical data suggest early involvement of the corticospinal tract (CST) in spinocerebellar ataxia type 2 (SCA2). Here we tested if early CST degeneration can be detected in prodromal SCA2 mutation carriers by electrophysiological markers of CST integrity.

METHODS

CST integrity was tested in 15 prodromal SCA2 mutation carriers, 19 SCA2 patients and 25 age-matched healthy controls, using corticomuscular (EEG-EMG) and intermuscular (EMG-EMG) coherence measures in upper and lower limb muscles.

RESULTS

Significant reductions of EEG-EMG and EMG-EMG coherences were observed in the SCA2 patients, and to a similar extent in the prodromal SCA2 mutation carriers. In prodromal SCA2, EEG-EMG and EMG-EMG coherences correlated with the predicted time to ataxia onset.

CONCLUSIONS

Findings indicate early CST neurodegeneration in SCA2. EEG-EMG and EMG-EMG coherence may serve as biomarkers of early CST neurodegeneration in prodromal SCA2 mutation carriers.

SIGNIFICANCE

Findings are important for developing preclinical disease markers in the context of currently emerging disease-modifying therapies of neurodegenerative disorders.

The polyglutamine protein ataxin-3 enables normal growth under heat shock conditions in the methylotrophic yeast Pichia pastoris

The protein ataxin-3 carries a polyglutamine stretch close to the C-terminus that triggers a neurodegenerative disease in humans when its length exceeds a critical threshold. A role as a transcriptional regulator but also as a ubiquitin hydrolase has been proposed for this protein. Here, we report that, when expressed in the yeast Pichia pastoris, full-length ataxin-3 enabled almost normal growth at 37 °C, well above the physiological optimum of 30 °C. The N-terminal Josephin domain (JD) was also effective but significantly less, whereas catalytically inactive JD was completely ineffective. Based on MudPIT proteomic analysis, we observed that the strain expressing full-length, functional ataxin-3 displayed persistent upregulation of enzymes involved in mitochondrial energy metabolism during growth at 37 °C compared with the strain transformed with the empty vector. Concurrently, in the transformed strain intracellular ATP levels at 37 °C were even higher than normal ones at 30 °C. Elevated ATP was also paralleled by upregulation of enzymes involved in both protein biosynthesis and biosynthetic pathways, as well as of several stress-induced proteins. A similar pattern was observed when comparing a strain expressing JD with another expressing its catalytically inactive counterpart. We suggest that such effects mostly result from mechanisms of transcriptional regulation.

Peripheral neuropathy in complex inherited diseases: an approach to diagnosis

Peripheral neuropathy is a common finding in patients with complex inherited neurological diseases and may be subclinical or a major component of the phenotype. This review aims to provide a clinical approach to the diagnosis of this complex group of patients by addressing key questions including the predominant neurological syndrome associated with the neuropathy, for example, spasticity, the type of neuropathy and the other neurological and non-neurological features of the syndrome. Priority is given to the diagnosis of treatable conditions. Using this approach, we associated neuropathy with one of three major syndromic categories: (1) ataxia, (2) spasticity and (3) global neurodevelopmental impairment. Syndromes that do not fall easily into one of these three categories can be grouped according to the predominant system involved in addition to the neuropathy, for example, cardiomyopathy and neuropathy. We also include a separate category of complex inherited relapsing neuropathy syndromes, some of which may mimic Guillain-Barré syndrome, as many will have a metabolic aetiology and be potentially treatable.

Polyglutamine spinocerebellar ataxias - from genes to potential treatments

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.

Arginine vasopressin relates with spatial learning and memory in a mouse model of spinocerebellar ataxia type 3

Spinocerebellar ataxia is an inherited neurodegenerative disorder that the most prevalent type is type 3 (SCA3). Arginine vasopressin (AVP) is released within the lateral septum for controlling the learning and memory. This communication studied the effect of AVP on the spatial learning and memory of SCA3 mice. The spatial learning and memory were analyzed by Morris water maze test (MWM), and AVP concentration was measured by radioimmunoassay. The results showed that (Alves et al., 2010) the swimming velocity, distance traveled and latency to the platform of MWM in SCA3 mice were reduced slower than those in WT mice over 4 training days (p<0.05, 0.01 or 0.001); (Antunes and Zimmerman, 1978) SCA3 mice showed a lower performance of spatial learning and memory of MWM during the fifth day (test day) compared to WT mice; (Bao et al., 2014) SCA3 mice had a decrease of AVP concentration in cerebral cortex (6.3±0.6pg/mg vs. 11.4±1.0pg/mg, p<0.01), hypothalamus (6.1±1.3ng/mg vs. 10.3±2.1ng/mg, p<0.05), hippocampus (3.2±0.5pg/mg vs. 5.2±1.0pg/mg, p<0.01) and cerebellum (4.7±0.9pg/mg vs. 8.3±1.1pg/mg, p<0.01), not in spinal cord, pituitary and serum; and (Barberies and Tribollet, 1996) intraventricular AVP could significantly quicken swimming velocity, cut down distance traveled and reduce latency to the platform of MWM in a dose-dependent manner, but intraventricular AVP receptor antagonist weakened the spatial learning and memory of MWM in SCA3 mice during the fifth day. The data suggested that AVP in the brain, not spinal cord and peripheral system of SCA3 mice related with the change of the spatial learning and memory of MWM.

Atxn2 Knockout and CAG42-Knock-in Cerebellum Shows Similarly Dysregulated Expression in Calcium Homeostasis Pathway

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited neurodegenerative disorder with preferential affection of Purkinje neurons, which are known as integrators of calcium currents. The expansion of a polyglutamine (polyQ) domain in the RNA-binding protein ataxin-2 (ATXN2) is responsible for this disease, but the causal roles of deficient ATXN2 functions versus aggregation toxicity are still under debate. Here, we studied mouse mutants with Atxn2 knockout (KO) regarding their cerebellar global transcriptome by microarray and RT-qPCR, in comparison with data from Atxn2-CAG42-knock-in (KIN) mouse cerebellum. Global expression downregulations involved lipid and growth signaling pathways in good agreement with previous data. As a novel effect, downregulations of key factors in calcium homeostasis pathways (the transcription factor Rora, transporters Itpr1 and Atp2a2, as well as regulator Inpp5a) were observed in the KO cerebellum, and some of them also occurred subtly early in KIN cerebellum. The ITPR1 protein levels were depleted from soluble fractions of cerebellum in both mutants, but accumulated in its membrane-associated form only in the SCA2 model. Coimmunoprecipitation demonstrated no association of ITPR1 with Q42-expanded or with wild-type ATXN2. These findings provide evidence that the physiological functions and protein interactions of ATXN2 are relevant for calcium-mediated excitation of Purkinje cells as well as for ATXN2-triggered neurotoxicity. These insights may help to understand pathogenesis and tissue specificity in SCA2 and other polyQ ataxias like SCA1, where inositol regulation of calcium flux and RORalpha play a role.

Parkinson's disease associated with pure ATXN10 repeat expansion

Large, non-coding pentanucleotide repeat expansions of ATTCT in intron 9 of the ATXN10 gene typically cause progressive spinocerebellar ataxia with or without seizures and present neuropathologically with Purkinje cell loss resulting in symmetrical cerebellar atrophy. These ATXN10 repeat expansions can be interrupted by sequence motifs which have been attributed to seizures and are likely to act as genetic modifiers. We identified a Mexican kindred with multiple affected family members with ATXN10 expansions. Four affected family members showed clinical features of spinocerebellar ataxia type 10 (SCA10). However, one affected individual presented with early-onset levodopa-responsive parkinsonism, and one family member carried a large repeat ATXN10 expansion, but was clinically unaffected. To characterize the ATXN10 repeat, we used a novel technology of single-molecule real-time (SMRT) sequencing and CRISPR/Cas9-based capture. We sequenced the entire span of ~5.3-7.0 kb repeat expansions. The Parkinson's patient carried an ATXN10 expansion with no repeat interruption motifs as well as an unaffected sister. In the siblings with typical SCA10, we found a repeat pattern of ATTCC repeat motifs that have not been associated with seizures previously. Our data suggest that the absence of repeat interruptions is likely a genetic modifier for the clinical presentation of l-Dopa responsive parkinsonism, whereas repeat interruption motifs contribute clinically to epilepsy. Repeat interruptions are important genetic modifiers of the clinical phenotype in SCA10. Advanced sequencing techniques now allow to better characterize the underlying genetic architecture for determining accurate phenotype-genotype correlations.

Ophthalmic features of spinocerebellar ataxia type 7

PurposeTo analyze the relation between ophthalmologic and motor changes in spinocerebellar ataxia type 7 (SCA7).Patients and methodsThis was a case series study. Sixteen SCA7 patients underwent a comprehensive ophthalmic examination, including ocular extrinsic motility testing, color vision test, and optical coherence tomography of the optic nerve and macula. Changes in the corneal endothelium, electroretinographic patterns, and a complete neurologic evaluation using the Scale for the Assessment and Rating of Ataxia (SARA) were evaluated. Correlations of endothelial cell density (ECD) with number of CAG repetitions and the SARA scores were estimated.ResultsAll patients showed various degrees of visual impairment mainly due to macular deterioration. Notably, they also presented decreased ECD. Pairwise correlations of ECD with number of CAG repeats and severity of motor symptoms quantified with the SARA scores were inverse (r=-0.46, P=0.083 and r=-0.64, P=0.009, respectively). Further analyses indicated an average ECD decrease of 48 cells/mm² (P=0.006) per unit of change on the number of CAG repeats, and of 75 cells/mm² (P=0.001) per unit of change on the SARA scores.ConclusionsThe results agree with previous ophthalmological findings regarding the widespread effect of SCA7 mutation on the patient's visual system. However, the results also show a significant negative correlation of decreased ECD with both CAG repetitions and SARA scores. This suggests that motor systems could degenerate in parallel with visual systems, although more research is needed to determine whether the degeneration is caused by the same mechanisms.

The Multiple Faces of Spinocerebellar Ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is among the most common forms of autosomal dominant ataxias, accounting for 15% of the total families. Occurrence is higher in specific populations such as the Cuban and Southern Italian. The disease is caused by a CAG expansion in ATXN2 gene, leading to abnormal accumulation of the mutant protein, ataxin‐2, in intracellular inclusions. The clinical picture is mainly dominated by cerebellar ataxia, although a number of other neurological signs have been described, ranging from parkinsonism to motor neuron involvement, making the diagnosis frequently challenging for neurologists, particularly when information about the family history is not available. Although the functions of ataxin‐2 have not been completely elucidated, the protein is involved in mRNA processing and control of translation. Recently, it has also been shown that the size of the CAG repeat in normal alleles represents a risk factor for ALS, suggesting that ataxin‐2 plays a fundamental role in maintenance of neuronal homeostasis.

Cognitive Changes in the Spinocerebellar Ataxias Due to Expanded Polyglutamine Tracts: A Survey of the Literature

The dominantly-inherited ataxias characterised by expanded polyglutamine tracts—spinocere bellar ataxias (SCAs) 1, 2, 3, 6, 7, 17, dentatorubral pallidoluysian atrophy (DRPLA) and, in part, SCA 8—have all been shown to result in various degrees of cognitive impairment. We survey the literature on the cognitive consequences of each disorder, attempting correlation with their published neuropathological, magnetic resonance imaging (MRI) and clinical features. We suggest several psychometric instruments for assessment of executive function, whose results are unlikely to be confounded by visual, articulatory or upper limb motor difficulties. Finally, and with acknowledgement of the inadequacies of the literature to date, we advance a tentative classification of these disorders into three groups, based on the reported severity of their cognitive impairments, and correlated with their neuropathological topography and MRI findings: group 1—SCAs 6 and 8—mild dysexecutive syndrome based on disruption of cerebello-cortical circuitry; group 2—SCAs 1, 2, 3, and 7—more extensive deficits based largely on disruption of striatocortical in addition to cerebello-cerebral circuitry; and group 3—SCA 17 and DRPLA—in which cognitive impairment severe enough to cause a dementia syndrome is a frequent feature.

Calpain Inhibition Is Protective in Machado-Joseph Disease Zebrafish Due to Induction of Autophagy

The neurodegenerative disease Machado-Joseph disease (MJD), also known as spinocerebellar ataxin-3, affects neurons of the brain and spinal cord, disrupting control of the movement of muscles. We have successfully established the first transgenic zebrafish (Danio rerio) model of MJD by expressing human ataxin-3 protein containing either 23 glutamines (23Q, wild-type) or 84Q (MJD-causing) within neurons. Phenotypic characterization of the zebrafish (male and female) revealed that the ataxin-3-84Q zebrafish have decreased survival compared with ataxin-3-23Q and develop ataxin-3 neuropathology, ataxin-3 cleavage fragments and motor impairment. Ataxin-3-84Q zebrafish swim shorter distances than ataxin-3-23Q zebrafish as early as 6 days old, even if expression of the human ataxin-3 protein is limited to motor neurons. This swimming phenotype provides a valuable readout for drug treatment studies. Treating the EGFP-ataxin-3-84Q zebrafish with the calpain inhibitor compound calpeptin decreased levels of ataxin-3 cleavage fragments, but also removed all human ataxin-3 protein (confirmed by ELISA) and prevented the early MJD zebrafish motor phenotype. We identified that this clearance of ataxin-3 protein by calpeptin treatment resulted from an increase in autophagic flux (indicated by decreased p62 levels and increased LC3II). Cotreatment with the autophagy inhibitor chloroquine blocked the decrease in human ataxin-3 levels and the improved movement produced by calpeptin treatment. This study demonstrates that this first transgenic zebrafish model of MJD is a valuable tool for testing potential treatments for MJD. Calpeptin treatment is protective in this model of MJD and removal of human ataxin-3 through macro-autophagy plays an important role in this beneficial effect.SIGNIFICANCE STATEMENT We have established the first transgenic zebrafish model of the neurodegenerative disease MJD, and identified relevant disease phenotypes, including impaired movement from an early age, which can be used in rapid drug testing studies. We have found that treating the MJD zebrafish with the calpain inhibitor compound calpeptin produces complete removal of human ataxin-3 protein, due to induction of the autophagy quality control pathway. This improves the movement of the MJD zebrafish. Artificially blocking the autophagy pathway prevents the removal of human ataxin-3 and improved movement produced by calpeptin treatment. These findings indicate that induction of autophagy, and removal of ataxin-3 protein, plays an important role in the protective effects of calpain inhibition for the treatment of MJD.

Antisense Oligonucleotide-Mediated Removal of the Polyglutamine Repeat in Spinocerebellar Ataxia Type 3 Mice

Spinocerebellar ataxia type 3 (SCA3) is a currently incurable neurodegenerative disorder caused by a CAG triplet expansion in exon 10 of the ATXN3 gene. The resultant expanded polyglutamine stretch in the mutant ataxin-3 protein causes a gain of toxic function, which eventually leads to neurodegeneration. One important function of ataxin-3 is its involvement in the proteasomal protein degradation pathway, and long-term downregulation of the protein may therefore not be desirable. In the current study, we made use of antisense oligonucleotides to mask predicted exonic splicing signals, resulting in exon 10 skipping from ATXN3 pre-mRNA. This led to formation of a truncated ataxin-3 protein lacking the toxic polyglutamine expansion, but retaining its ubiquitin binding and cleavage function. Repeated intracerebroventricular injections of the antisense oligonucleotides in a SCA3 mouse model led to exon skipping and formation of the modified ataxin-3 protein throughout the mouse brain. Exon skipping was long lasting, with the modified protein being detectable for at least 2.5 months after antisense oligonucleotide injection. A reduction in insoluble ataxin-3 and nuclear accumulation was observed following antisense oligonucleotide treatment, indicating a beneficial effect on pathogenicity. Together, these data suggest that exon 10 skipping is a promising therapeutic approach for SCA3.

Large normal-range TBP and ATXN7 CAG repeat lengths are associated with increased lifetime risk of depression

Depression is one of the most prevalent and debilitating psychiatric disorders worldwide. Recently, we showed that both relatively short and relatively long cytosine-adenine-guanine (CAG) repeats in the huntingtin gene (HTT) are associated with an increased risk of lifetime depression. However, to what extent the variations in CAG repeat length in the other eight polyglutamine disease-associated genes (PDAGs) are associated with depression is still unknown. We determined the CAG repeat sizes of ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, TBP, ATN1 and AR in two well-characterized Dutch cohorts-the Netherlands Study of Depression and Anxiety and the Netherlands Study of Depression in Older Persons-including 2165 depressed and 1058 non-depressed individuals-aged 18-93 years. The association between PDAG CAG repeat size and the risk for depression was assessed via binary logistic regression. We found that the odds ratio (OR) for lifetime depression was significantly higher for individuals with >10, compared with subjects with ≤10, CAG repeats in both ATXN7 alleles (OR=1.90, confidence interval (CI) 1.26-2.85). For TBP we found a similar association: A CAG repeat length exceeding the median in both alleles was associated with an increased risk for lifetime depression (OR=1.33, CI 1.00-1.76). In conclusion, we observed that carriers of either ATXN7 or TBP alleles with relatively large CAG repeat sizes in both alleles had a substantially increased risk of lifetime depression. Our findings provide critical evidence for the notion that repeat polymorphisms can act as complex genetic modifiers of depression.

Molecular dynamics analysis of the aggregation propensity of polyglutamine segments

Protein misfolding and aggregation is a pathogenic feature shared among at least ten polyglutamine (polyQ) neurodegenerative diseases. While solvent-solution interaction is a key factor driving protein folding and aggregation, the solvation properties of expanded polyQ tracts are not well understood. By using GPU-enabled all-atom molecular dynamics simulations of polyQ monomers in an explicit solvent environment, this study shows that solvent-polyQ interaction propensity decreases as the lengths of polyQ tract increases. This study finds a predominance in long-distance interactions between residues far apart in polyQ sequences with longer polyQ segments, that leads to significant conformational differences. This study also indicates that large loops, comprised of parallel β-structures, appear in long polyQ tracts and present new aggregation building blocks with aggregation driven by long-distance intra-polyQ interactions. Finally, consistent with previous observations using coarse-grain simulations, this study demonstrates that there is a gain in the aggregation propensity with increased polyQ length, and that this gain is correlated with decreasing ability of solvent-polyQ interaction. These results suggest the modulation of solvent-polyQ interactions as a possible therapeutic strategy for treating polyQ diseases.

Altered striatal endocannabinoid signaling in a transgenic mouse model of spinocerebellar ataxia type-3

Spinocerebellar ataxia type-3 (SCA-3) is the most prevalent autosomal dominant inherited ataxia. We recently found that the endocannabinoid system is altered in the post-mortem cerebellum of SCA-3 patients, and similar results were also found in the cerebellar and brainstem nuclei of a SCA-3 transgenic mouse model. Given that the neuropathology of SCA-3 is not restricted to these two brain regions but rather, it is also evident in other structures (e.g., the basal ganglia), we studied the possible changes to endocannabinoid signaling in the striatum of these transgenic mice. SCA-3 mutant mice suffer defects in motor coordination, balance and they have an abnormal gait, reflecting a cerebellar/brainstem neuropathology. However, they also show dystonia-like behavior (limb clasping) that may be related to the malfunction/deterioration of specific neurons in the striatum. Indeed, we found a loss of striatal projecting neurons in SCA-3 mutant mice, accompanied by a reduction in glial glutamate transporters that could potentially aggravate excitotoxic damage. In terms of endocannabinoid signaling, no changes in CB2 receptors were evident, yet an important reduction in CB1 receptors was detected by qPCR and immunostaining. The reduction in CB1 receptors was presumed to occur in striatal afferent and efferent neurons, also potentially aggravating excitotoxicity. We also measured the endocannabinoid lipids in the striatum and despite a marked increase in the FAAH enzyme in this area, no overall changes in these lipids were found. Collectively, these studies confirm that the striatal endocannabinoid system is altered in SCA-3 mutant mice, adding to the equivalent changes found in other strongly affected CNS structures in this type of ataxia (i.e.: the cerebellum and brainstem). These data open the way to search for drugs that might correct these changes.

Early strong intrathecal inflammation in cerebellar type multiple system atrophy by cerebrospinal fluid cytokine/chemokine profiles: a case control study

BACKGROUND

The pathology of multiple system atrophy cerebellar-type (MSA-C) includes glial inflammation; however, cerebrospinal fluid (CSF) inflammatory cytokine profiles have not been investigated. In this study, we determined CSF cytokine/chemokine/growth factor profiles in MSA-C and compared them with those in hereditary spinocerebellar ataxia (SCA).

METHODS

We collected clinical data and CSF from 20 MSA-C patients, 12 hereditary SCA patients, and 15 patients with other non-inflammatory neurological diseases (OND), and measured 27 cytokines/chemokines/growth factors using a multiplexed fluorescent bead-based immunoassay. The size of each part of the hindbrain and hot cross bun sign (HCBS) in the pons was studied by magnetic resonance imaging.

RESULTS

Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-6, IL-7, IL-12, and IL-13 levels were significantly higher in MSA-C and SCA compared with OND. In MSA-C, IL-5, IL-6, IL-9, IL-12, IL-13, platelet-derived growth factor-bb, macrophage inflammatory protein (MIP)-1α, and GM-CSF levels positively correlated with anteroposterior diameters of the pontine base, vermis, or medulla oblongata. By contrast, in SCA patients, IL-12 and MIP-1α showed significant negative correlations with anteroposterior diameters of the pontine base, and unlike MSA-C, there was no cytokine with a positive correlation in SCA. IL-6 was significantly higher in MSA-C patients with the lowest grade of HCBS compared with those with the highest grade. Macrophage chemoattractant protein-1 (MCP-1) had a significant negative correlation with disease duration only in MSA-C patients. Tumor necrosis factor-alpha, IL-2, IL-15, IL-4, IL-5, IL-10, and IL-8 were all significantly lower in MSA-C and SCA compared with OND, while IL-1ra, an anti-inflammatory cytokine, was elevated only in MSA-C. IL-1β and IL-8 had positive correlations with Unified Multiple System Atrophy Rating Scale part 1 and 2, respectively, in MSA-C.

CONCLUSIONS

Although CSF cytokine/chemokine/growth factor profiles were similar between MSA-C and SCA, pro-inflammatory cytokines, such as IL-6, GM-CSF, and MCP-1, correlated with the disease stage in a way higher at the beginning only in MSA-C, reflecting early stronger intrathecal inflammation.

Evaluation of Antisense Oligonucleotides Targeting ATXN3 in SCA3 Mouse Models

The most common dominantly inherited ataxia, spinocerebellar ataxia type 3 (SCA3), is an incurable neurodegenerative disorder caused by a CAG repeat expansion in the ATXN3 gene that encodes an abnormally long polyglutamine tract in the disease protein, ATXN3. Mice lacking ATXN3 are phenotypically normal; hence, disease gene suppression offers a compelling approach to slow the neurodegenerative cascade in SCA3. Here we tested antisense oligonucleotides (ASOs) that target human ATXN3 in two complementary mouse models of SCA3: yeast artificial chromosome (YAC) MJD-Q84.2 (Q84) mice expressing the full-length human ATXN3 gene and cytomegalovirus (CMV) MJD-Q135 (Q135) mice expressing a human ATXN3 cDNA. Intracerebroventricular injection of ASOs resulted in widespread delivery to the most vulnerable brain regions in SCA3. In treated Q84 mice, three of five tested ASOs reduced disease protein levels by >50% in the diencephalon, cerebellum, and cervical spinal cord. Two ASOs also significantly reduced mutant ATXN3 in the mouse forebrain and resulted in no signs of astrogliosis or microgliosis. In Q135 mice expressing a single ATXN3 isoform via a cDNA transgene, ASOs did not result in similar robust ATXN3 silencing. Our results indicate that ASOs targeting full-length human ATXN3 would likely be well tolerated and could lead to a preventative therapy for SCA3.

Drosophila melanogaster As a Model Organism to Study RNA Toxicity of Repeat Expansion-Associated Neurodegenerative and Neuromuscular Diseases

For nearly a century, the fruit fly, Drosophila melanogaster, has proven to be a valuable tool in our understanding of fundamental biological processes, and has empowered our discoveries, particularly in the field of neuroscience. In recent years, Drosophila has emerged as a model organism for human neurodegenerative and neuromuscular disorders. In this review, we highlight a number of recent studies that utilized the Drosophila model to study repeat-expansion associated diseases (READs), such as polyglutamine diseases, fragile X-associated tremor/ataxia syndrome (FXTAS), myotonic dystrophy type 1 (DM1) and type 2 (DM2), and C9ORF72-associated amyotrophic lateral sclerosis/frontotemporal dementia (C9-ALS/FTD). Discoveries regarding the possible mechanisms of RNA toxicity will be focused here. These studies demonstrate Drosophila as an excellent in vivo model system that can reveal novel mechanistic insights into human disorders, providing the foundation for translational research and therapeutic development.

Cytokines in Machado Joseph Disease/Spinocerebellar Ataxia 3

The aim of the present study is to describe the serum concentrations of a broad spectrum of cytokines in symptomatic and asymptomatic carriers of Machado Joseph disease (SCA3/MJD) CAG expansions. Molecularly confirmed carriers and controls were studied. Age at onset, disease duration, and clinical scales Scale for the Assessment and Rating of Ataxia (SARA), Neurological Examination Score for Spinocerebellar Ataxias (NESSCA), SCA Functional Index (SCAFI), and Composite Cerebellar Functional Score (CCFS) were obtained from the symptomatic carriers. Serum was obtained from all individuals and a cytokine panel "consisted of" eotaxin, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-α, IFN-γ, interleukin (IL)-1β, IL-1RA, IL-2, IL-2R, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-15, IL-17, interferon gamma-induced protein (IP)-10, monocyte chemoattractant protein (MCP)-1, monokine induced by gamma interferon (MIG), macrophage inflammatory protein (MIP)-a, MIP-b, regulated on activation, normal T cell expressed and secreted (RANTES) and tumor necrosis factor (TNF)-α was analyzed. In a subgroup of symptomatic carriers, the cytokine panel was repeated after 360 days. Cytokine distribution among groups was studied by discriminant analysis; changes in serum levels after 360 days were studied by generalized estimation equation. Sixty-six symptomatic carriers, 13 asymptomatic carriers, and 43 controls were studied. No differences in cytokine patterns were found between controls and carriers of the CAG expansions or between controls and symptomatic carriers only. In contrast, eotaxin concentrations were significantly higher in asymptomatic than in symptomatic carriers or in controls (p = 0.001, ANCOVA). Eotaxin did not correlate with age, disease duration, CAG expansion, NESSCA score, and SARA score. Among symptomatic carriers, eotaxin dropped after 360 days (p = 0.039, GEE). SCA3/MJD patients presented a benign pattern of serum cytokines. In contrast, levels of eotaxin, a peptide secreted by astrocytes, were elevated in the asymptomatic carriers, suggesting that a specific response of these cells can be related to symptom progression, in SCA3/MJD.

Identification of early neurodegenerative change in presymptomatic spinocerebellar ataxia type 1: A diffusion tensor imaging study

We report a 41-year-old man of presymptomatic spinocerebellar ataxia type 1. Diffusion tensor imaging (DTI) verified decreased fractional anisotropy of cerebellar afferent and efferent pathways compared to 5 age-matched healthy controls while conventional MRI revealed normal brain. DTI was valuable in detection of early microstructural damage of cerebellar pathways.

Gene dosage effect in spinocerebellar ataxia type 6 homozygotes: A clinical and neuropathological study

Spinocerebellar ataxia type 6 (SCA6) is an autosomal dominant neurodegenerative disorder. However, it remains unclear whether SCA6 shows a gene dosage effect, defined by earlier age-of-onset in homozygotes than heterozygotes. Herein, we retrospectively analyzed four homozygous SCA6 subjects from our single institution cohort of 120 SCA6 subjects. We also performed a neuropathological investigation into an SCA6 individual with compound heterozygous expansions. In the 116 heterozygotes, there was an inverse correlation of age-of-onset with the number of CAG repeats in the expanded allele, and with the total number of CAG repeats, in both normal and expanded alleles. The age-of-onset in the four homozygotes was within the 95% confidence interval of the age-of-onset versus the repeat-lengths correlations determined in the 116 heterozygotes. Nevertheless, all homozygotes had earlier onset than their parents, and showed rapid disease progression. Neuropathology revealed neuronal loss, as well as α1A-calcium channel protein aggregates in Purkinje cells, a few α1A-calcium channel protein aggregates in the neocortex and basal ganglia, and neuronal loss in Clarke's column and the globus pallidus not seen in heterozygotes. These data suggest a mild clinical and neuropathological gene dosage effect in SCA6 subjects.

Mutant CAG Repeats Effectively Targeted by RNA Interference in SCA7 Cells

Spinocerebellar ataxia type 7 (SCA7) is a human neurodegenerative polyglutamine (polyQ) disease caused by a CAG repeat expansion in the open reading frame of the ATXN7 gene. The allele-selective silencing of mutant transcripts using a repeat-targeting strategy has previously been used for several polyQ diseases. Herein, we demonstrate that the selective targeting of a repeat tract in a mutant ATXN7 transcript by RNA interference is a feasible approach and results in an efficient decrease of mutant ataxin-7 protein in patient-derived cells. Oligonucleotides (ONs) containing specific base substitutions cause the downregulation of the ATXN7 mutant allele together with the upregulation of its normal allele. The A2 ON shows high allele selectivity at a broad range of concentrations and also restores UCHL1 expression, which is downregulated in SCA7.

Motor Dysfunctions and Neuropathology in Mouse Models of Spinocerebellar Ataxia Type 2: A Comprehensive Review

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant ataxia caused by an expansion of CAG repeats in the exon 1 of the gene ATXN2, conferring a gain of toxic function that triggers the appearance of the disease phenotype. SCA2 is characterized by several symptoms including progressive gait ataxia and dysarthria, slow saccadic eye movements, sleep disturbances, cognitive impairments, and psychological dysfunctions such as insomnia and depression, among others. The available treatments rely on palliative care, which mitigate some of the major symptoms but ultimately fail to block the disease progression. This persistent lack of effective therapies led to the development of several models in yeast, C. elegans, D. melanogaster, and mice to serve as platforms for testing new therapeutic strategies and to accelerate the research on the complex disease mechanisms. In this work, we review 4 transgenic and 1 knock-in mouse that exhibit a SCA2-related phenotype and discuss their usefulness in addressing different scientific problems. The knock-in mice are extremely faithful to the human disease, with late onset of symptoms and physiological levels of mutant ataxin-2, while the other transgenic possess robust and well-characterized motor impairments and neuropathological features. Furthermore, a new BAC model of SCA2 shows promise to study the recently explored role of non-coding RNAs as a major pathogenic mechanism in this devastating disorder. Focusing on specific aspects of the behavior and neuropathology, as well as technical aspects, we provide a highly practical description and comparison of all the models with the purpose of creating a useful resource for SCA2 researchers worldwide.

Association of glutathione S-transferase omega polymorphism and spinocerebellar ataxia type 2

BACKGROUND

Spinocerebellar ataxia type 2 is a neurodegenerative disorder caused by a CAG repeat expansion in ATXN2 gene. There is high clinical variability among affected patients suggesting the occurring of modifier genes influencing the clinical phenotype.

OBJECTIVE

The objective is to assess the association of GSTO1 rs4925 and GSTO2 rs2297235 SNPs on the clinical phenotype in SCA2 patients.

METHODS

A case-control study was performed in a sample of 120 SCA2 Cuban patients and 100 healthy subjects. Age at onset, 60° Maximal Saccade Velocity and SARA score were used as clinical markers. GSTO1 rs4925 and GSTO2 rs2297235 SNPs were determined by PCR/RFLP.

RESULTS

Distribution of the GSTO1 alleles and genotypes was nearly equal between the control group and SCA2 patients. GSTO1 genotypes were not associated to clinical markers in SCA2 patients. Distribution of the GSTO2 "G" allele and "AG" genotype differed significantly between SCA2 patients and controls. Symptomatic SCA2 individuals had a 2.29-fold higher chance of carrying at least one "G" allele at GSTO2 rs2297235 than controls (OR=2.29, 95% CI: 1.29-4.04). GSTO2 genotypes were significantly associated to age at onset (p=0.037) but not to 60° Maximal Saccade Velocity or SARA score in SCA2 patients.

CONCLUSION

The GSTO1 rs4925 polymorphism is not associated to SCA2. Meanwhile, the GSTO2 rs2297235 "AG" genotype is associated to SCA2 but failed to show any association with clinical markers, with the exception of a potential association with the age at disease onset.

Huntington's disease (HD): the neuropathology of a multisystem neurodegenerative disorder of the human brain

Huntington's disease (HD) is an autosomal dominantly inherited, and currently untreatable, neuropsychiatric disorder. This progressive and ultimately fatal disease is named after the American physician George Huntington and according to the underlying molecular biological mechanisms is assigned to the human polyglutamine or CAG-repeat diseases. In the present article we give an overview of the currently known neurodegenerative hallmarks of the brains of HD patients. Subsequent to recent pathoanatomical studies the prevailing reductionistic concept of HD as a human neurodegenerative disease, which is primarily and more or less exclusively confined to the striatum (ie, caudate nucleus and putamen) has been abandoned. Many recent studies have improved our neuropathological knowledge of HD; many of the early groundbreaking findings of neuropathological HD research have been rediscovered and confirmed. The results of this investigation have led to the stepwise revision of the simplified pathoanatomical and pathophysiological HD concept and culminated in the implementation of the current concept of HD as a multisystem degenerative disease of the human brain. The multisystem character of the neuropathology of HD is emphasized by a brain distribution pattern of neurodegeneration (i) which apart from the striatum includes the cerebral neo-and allocortex, thalamus, pallidum, brainstem and cerebellum, and which (ii) therefore, shares more similarities with polyglutamine spinocerebellar ataxias than previously thought.

Impact of Ataxin-2 knock out on circadian locomotor behavior and PER immunoreaction in the SCN of mice

In Drosophila melanogaster, Ataxin-2 is a crucial activator of Period and is involved in the control of circadian rhythms. However, in mammals the function of Ataxin-2 is unknown despite its involvement in the inherited neurogenerative disease Spinocerebellar Ataxia type 2 in humans. Therefore, we analyzed locomotor behavior of Atxn2-deficient mice and their WT littermates under entrained- and free-running conditions as well as after experimental jet lag. Furthermore, we compared the PER1 and PER2 immunoreaction (IR) in the SCN. Atxn2^-/- mice showed an unstable rhythmicity of locomotor activity, but the level of PER1 and PER2 IR in the SCN did not differ between genotypes.

Episodic ataxia and SCA6 within the same family due to the D302N CACNA1A gene mutation

Several dominant mutations of CACNA1A gene were associated with at least three different allelic disorders: spino-cerebellar ataxia type 6 (SCA6), episodic ataxia type 2 (EA2), and familial hemiplegic migraine-1 (FHM1). It is generally thought that loss-of-function mutations are associated with EA2, gain-of-function missense mutations with FHM1, and abnormal CAG expansions with SCA6. But, overlapping features, atypical symptoms and co-occurrence of distinct phenotypes within the same family were reported. We describe a four generation family showing different phenotypes ranging from EA2 to SCA6 and carrying the p.D302N CACNA1A gene mutation. In our family the phenotypes maintained separate and gender differences corresponding to different phenotypes were observed.

Dysregulation of the endocannabinoid signaling system in the cerebellum and brainstem in a transgenic mouse model of spinocerebellar ataxia type-3

Spinocerebellar ataxia type-3 (SCA-3) is a rare disease but it is the most frequent type within the autosomal dominant inherited ataxias. The disease lacks an effective treatment to alleviate major symptoms and to modify disease progression. Our recent findings that endocannabinoid receptors and enzymes are significantly altered in the post-mortem cerebellum of patients affected by autosomal-dominant hereditary ataxias suggest that targeting the endocannabinoid signaling system may be a promising therapeutic option. Our goal was to investigate the status of the endocannabinoid signaling system in a transgenic mouse model of SCA-3, in the two CNS structures most affected in this disease - cerebellum and brainstem. These animals exhibited progressive motor incoordination, imbalance, abnormal gait, muscle weakness, and dystonia, in parallel to reduced in vivo brain glucose metabolism, deterioration of specific neuron subsets located in the dentate nucleus and pontine nuclei, small changes in microglial morphology, and reduction in glial glutamate transporters. Concerning the endocannabinoid signaling, our data indicated no changes in CB₂ receptors. By contrast, CB₁ receptors increased in the Purkinje cell layer, in particular in terminals of basket cells, but they were reduced in the dentate nucleus. We also measured the levels of endocannabinoid lipids and found reductions in anandamide and oleoylethanolamide in the brainstem. These changes correlated with an increase in the FAAH enzyme in the brainstem, which also occurred in some cerebellar areas, whereas other endocannabinoid-related enzymes were not altered. Collectively, our results in SCA-3 mutant mice confirm a possible dysregulation in the endocannabinoid system in the most important brain structures affected in this type of ataxia, suggesting that a pharmacological manipulation addressed to correct these changes could be a promising option in SCA-3.

Search for SCA2 blood RNA biomarkers highlights Ataxin-2 as strong modifier of the mitochondrial factor PINK1 levels

Ataxin-2 (ATXN2) polyglutamine domain expansions of large size result in an autosomal dominantly inherited multi-system-atrophy of the nervous system named spinocerebellar ataxia type 2 (SCA2), while expansions of intermediate size act as polygenic risk factors for motor neuron disease (ALS and FTLD) and perhaps also for Levodopa-responsive Parkinson's disease (PD). In view of the established role of ATXN2 for RNA processing in periods of cell stress and the expression of ATXN2 in blood cells such as platelets, we investigated whether global deep RNA sequencing of whole blood from SCA2 patients identifies a molecular profile which might serve as diagnostic biomarker. The bioinformatic analysis of SCA2 blood global transcriptomics revealed various significant effects on RNA processing pathways, as well as the pathways of Huntington's disease and PD where mitochondrial dysfunction is crucial. Notably, an induction of PINK1 and PARK7 expression was observed. Conversely, expression of Pink1 was severely decreased upon global transcriptome profiling of Atxn2-knockout mouse cerebellum and liver, in parallel to strong effects on Opa1 and Ghitm, which encode known mitochondrial dynamics regulators. These results were validated by quantitative PCR and immunoblots. Starvation stress of human SH-SY5Y neuroblastoma cells led to a transcriptional phasic induction of ATXN2 in parallel to PINK1, and the knockdown of one enhanced the expression of the other during stress response. These findings suggest that ATXN2 may modify the known PINK1 roles for mitochondrial quality control and autophagy during cell stress. Given that PINK1 is responsible for autosomal recessive juvenile PD, this genetic interaction provides a concept how the degeneration of nigrostriatal dopaminergic neurons and the Parkinson phenotype may be triggered by ATXN2 mutations.

Mammalian ataxin-2 modulates translation control at the pre-initiation complex via PI3K/mTOR and is induced by starvation

Ataxin-2 is a cytoplasmic protein, product of the ATXN2 gene, whose deficiency leads to obesity, while its gain-of-function leads to neural atrophy. Ataxin-2 affects RNA homeostasis, but its effects are unclear. Here, immunofluorescence analysis suggested that ataxin-2 associates with 48S pre-initiation components at stress granules in neurons and mouse embryonic fibroblasts, but is not essential for stress granule formation. Coimmunoprecipitation analysis showed associations of ataxin-2 with initiation factors, which were concentrated at monosome fractions of polysome gradients like ataxin-2, unlike its known interactor PABP. Mouse embryonic fibroblasts lacking ataxin-2 showed increased phosphorylation of translation modulators 4E-BP1 and ribosomal protein S6 through the PI3K-mTOR pathways. Indeed, human neuroblastoma cells after trophic deprivation showed a strong induction of ATXN2 transcript via mTOR inhibition. Our results support the notion that ataxin-2 is a nutritional stress-inducible modulator of mRNA translation at the pre-initiation complex.