ATXN3: a multifunctional protein involved in the polyglutamine disease spinocerebellar ataxia type 3.

ATXN3 is a ubiquitin hydrolase (or deubiquitinase, DUB), product of the ATXN3 gene, ubiquitously expressed in various cell types including peripheral and neuronal tissues and involved in several cellular pathways. Importantly, the expansion of the CAG trinucleotides within the ATXN3 gene leads to an expanded polyglutamine domain in the encoded protein, which has been associated with the onset of the spinocerebellar ataxia type 3, also known as Machado-Joseph disease, the most common dominantly inherited ataxia worldwide. ATXN3 has therefore been under intensive investigation for decades. In this review, we summarize the main functions of ATXN3 in proteostasis, DNA repair and transcriptional regulation, as well as the emerging role in regulating chromatin structure. The mentioned molecular functions of ATXN3 are also reviewed in the context of the pathological expanded form of ATXN3.

A cost analysis of Machado-Joseph's disease (MJD).

A rare disease is that with a low prevalence in the population. However, it is estimated that there are between 6,000 and 8,000 different types of rare diseases in the world and, generally, they are incurable and deadly. Machado-Joseph's disease (MJD) is one of these cases; of genetic origin, autosomal dominant, with a high chance of transmission between generations and without curative treatment. Given the specificities of MJD and the lack of economic studies associated with it, this article aims to estimate the direct and indirect health-related costs of lost productivity attributable to Machado-Joseph's Disease. The data used were primarily collected at the Hospital de Clínicas de Porto Alegre (HCPA), during the period between October 2019 and March 2020. The bottom-up cost methodology was used, that is to say, to estimate costs across a sample of patients to produce an annual cost per patient. Among the main results, it was found that 90.8% of the sample does not work and of these, 72.73% reported that the reason they had stopped working was due to Machado-Joseph's disease. The average age of men when they stopped working was 39.05 years of age and for women it was 39.64 years of age. In relation to direct non-medical costs, with rehabilitation and transport, it was found that these items affect about 32% of men's income and 36% of women's income, as well as medication and diapers costs affect about 15% of women's income and 14% of the income of men who are no longer able to work. The study also showed that 50% of caregivers, who are generally close relatives of the patient, do not work. Of these, 33.3% reported having left the labor market to provide assistance to the patient, which means that the cost for families is even higher than that estimated for the patient.

Preimplantation Genetic Testing of Spinocerebellar Ataxia Type 3/Machado-Joseph Disease-Robust Tools for Direct and Indirect Detection of the ATXN3 (CAG)n Repeat Expansion.

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a neurodegenerative disorder caused by the ATXN3 CAG repeat expansion. Preimplantation genetic testing for monogenic disorders (PGT-M) of SCA3/MJD should include reliable repeat expansion detection coupled with high-risk allele determination using informative linked markers. One couple underwent SCA3/MJD PGT-M combining ATXN3 (CAG)n triplet-primed PCR (TP-PCR) with customized linkage-based risk allele genotyping on whole-genome-amplified trophectoderm cells. Microsatellites closely linked to ATXN3 were identified and 16 markers were genotyped on 187 anonymous DNAs to verify their polymorphic information content. In the SCA3/MJD PGT-M case, the ATXN3 (CAG)n TP-PCR and linked marker analysis results concurred completely. Among the three unaffected embryos, a single embryo was transferred and successfully resulted in an unaffected live birth. A total of 139 microsatellites within 1 Mb upstream and downstream of the ATXN3 CAG repeat were identified and 8 polymorphic markers from each side were successfully co-amplified in a single-tube reaction. A PGT-M assay involving ATXN3 (CAG)n TP-PCR and linkage-based risk allele identification has been developed for SCA3/MJD. A hexadecaplex panel of highly polymorphic microsatellites tightly linked to ATXN3 has been developed for the rapid identification of informative markers in at-risk couples for use in the PGT-M of SCA3/MJD.

The parkin V380L variant is a genetic modifier of Machado-Joseph disease with impact on mitophagy.

Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative spinocerebellar ataxia caused by a polyglutamine-coding CAG repeat expansion in the ATXN3 gene. While the CAG length correlates negatively with the age at onset, it accounts for approximately 50% of its variability only. Despite larger efforts in identifying contributing genetic factors, candidate genes with a robust and plausible impact on the molecular pathogenesis of MJD are scarce. Therefore, we analysed missense single nucleotide polymorphism variants in the PRKN gene encoding the Parkinson's disease-associated E3 ubiquitin ligase parkin, which is a well-described interaction partner of the MJD protein ataxin-3, a deubiquitinase. By performing a correlation analysis in the to-date largest MJD cohort of more than 900 individuals, we identified the V380L variant as a relevant factor, decreasing the age at onset by 3 years in homozygous carriers. Functional analysis in an MJD cell model demonstrated that parkin V380L did not modulate soluble or aggregate levels of ataxin-3 but reduced the interaction of the two proteins. Moreover, the presence of parkin V380L interfered with the execution of mitophagy-the autophagic removal of surplus or damaged mitochondria-thereby compromising cell viability. In summary, we identified the V380L variant in parkin as a genetic modifier of MJD, with negative repercussions on its molecular pathogenesis and disease age at onset.

Specific Biomarkers in Spinocerebellar Ataxia Type 3: A Systematic Review of Their Potential Uses in Disease Staging and Treatment Assessment.

Spinocerebellar ataxia type 3 (SCA3) is the most common type of disease related to poly-glutamine (polyQ) repeats. Its hallmark pathology is related to the abnormal accumulation of ataxin 3 with a longer polyQ tract (polyQ-ATXN3). However, there are other mechanisms related to SCA3 progression that require identifying trait and state biomarkers for a more accurate diagnosis and prognosis. Moreover, the identification of potential pharmacodynamic targets and assessment of therapeutic efficacy necessitates valid biomarker profiles. The aim of this review was to identify potential trait and state biomarkers and their potential value in clinical trials. Our results show that, in SCA3, there are different fluid biomarkers involved in neurodegeneration, oxidative stress, metabolism, miRNA and novel genes. However, neurofilament light chain NfL and polyQ-ATXN3 stand out as the most prevalent in body fluids and SCA3 stages. A heterogeneity analysis of NfL revealed that it may be a valuable state biomarker, particularly when measured in plasma. Nonetheless, since it could be a more beneficial approach to tracking SCA3 progression and clinical trial efficacy, it is more convenient to perform a biomarker profile evaluation than to rely on only one.

Exploring functional and structural connectivity disruptions in spinocerebellar ataxia type 3: Insights from gradient analysis.

AIMS: Spinocerebellar Ataxia Type 3 (SCA3) is a rare genetic ataxia that impacts the entire brain and is characterized as a neurodegenerative disorder affecting the neural network. This study explores how alterations in the functional hierarchy, connectivity, and structural changes within specific brain regions significantly contribute to the heterogeneity of symptom manifestations in patients with SCA3. METHODS: We prospectively recruited 51 patients with SCA3 and 59 age-and sex-matched healthy controls. All participants underwent comprehensive multimodal neuroimaging and clinical assessments. In SCA3 patients, an innovative approach utilizing gradients in resting-state functional connectivity (FC) was employed to examine atypical patterns of hierarchical processing topology from sensorimotor to supramodal regions in the cerebellum and cerebrum. Coupling analyses of abnormal FC and structural connectivity among regions of interest (ROIs) in the brain were also performed to characterize connectivity alterations. Additionally, relationships between quantitative ROI values and clinical variables were explored. RESULTS: Patients with SCA3 exhibited either compression or expansion within the primary sensorimotor-to-supramodal gradient through four distinct calculation methods, along with disruptions in FC and structural connectivity coupling. A comprehensive correlation was identified between the altered gradients and the clinical manifestations observed in patients. Notably, altered fractional anisotropy values were not significantly correlated with clinical variables. CONCLUSION: Abnormal gradients and connectivity in the cerebellar and cerebral cortices in SCA3 patients may contribute to disrupted motor-to-supramodal functions. Moreover, these findings support the potential utility of FCG analysis as a biomarker for diagnosing SCA3 and assessing treatment efficacy.

Production of Spinocerebellar Ataxia Type 3 Model Mice by Intravenous Injection of AAV-PHP.B Vectors.

We aimed to produce a mouse model of spinocerebellar ataxia type 3 (SCA3) using the mouse blood-brain barrier (BBB)-penetrating adeno-associated virus (AAV)-PHP.B. Four-to-five-week-old C57BL/6 mice received injections of high-dose (2.0 × 1011 vg/mouse) or low-dose (5.0 × 1010 vg/mouse) AAV-PHP.B encoding a SCA3 causative gene containing abnormally long 89 CAG repeats [ATXN3(Q89)] under the control of the ubiquitous chicken ß-actin hybrid (CBh) promoter. Control mice received high doses of AAV-PHP.B encoding ATXN3 with non-pathogenic 15 CAG repeats [ATXN3(Q15)] or phosphate-buffered saline (PBS) alone. More than half of the mice injected with high doses of AAV-PHP.B encoding ATXN3(Q89) died within 4 weeks after the injection. No mice in other groups died during the 12-week observation period. Mice injected with low doses of AAV-PHP.B encoding ATXN3(Q89) exhibited progressive motor uncoordination starting 4 weeks and a shorter stride in footprint analysis performed at 12 weeks post-AAV injection. Immunohistochemistry showed thinning of the molecular layer and the formation of nuclear inclusions in Purkinje cells from mice injected with low doses of AAV-PHP.B encoding ATXN3(Q89). Moreover, ATXN3(Q89) expression significantly reduced the number of large projection neurons in the cerebellar nuclei to one third of that observed in mice expressing ATXN3(Q15). This AAV-based approach is superior to conventional methods in that the required number of model mice can be created simply by injecting AAV, and the expression levels of the responsible gene can be adjusted by changing the amount of AAV injected. Moreover, this method may be applied to produce SCA3 models in non-human primates.

Trehalose prevents the formation of aggregates of mutant ataxin-3 and reduces soluble ataxin-3 protein levels in an SCA3 cell model.

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder caused by mutant ataxin-3 with an abnormally expanded polyQ tract and is the most common dominantly inherited ataxia worldwide. There are no suitable therapeutic options for this disease. Autophagy, a defense mechanism against the toxic effects of aggregation-prone misfolded proteins, has been shown to have beneficial effects on neurodegenerative diseases. Thus, trehalose, which is an autophagy inducer, may have beneficial effects on SCA3. In the present study, we examined the effects of trehalose on an SCA3 cell model. After trehalose treatment, aggregate formation, soluble ataxin-3 protein levels and cell viability were evaluated in HEK293T cells overexpressing ataxin-3-15Q or ataxin-3-77Q. We also explored the mechanism by which trehalose affects autophagy and stress pathways. A filter trap assay showed that trehalose decreased the number of aggregates formed by mutant ataxin-3 containing an expanded polyQ tract. Western blot and Cell Counting Kit-8 (CCK-8) results demonstrated that trehalose also reduced the ataxin-3 protein levels and was safe for ataxin-3-expressing cells, respectively. Western blot and total antioxidant capacity assays suggested that trehalose had great therapeutic potential for treating SCA3, likely through its antioxidant activity. Our data indicate that trehalose plays a neuroprotective role in SCA3 by inhibiting the aggregation and reducing the protein level of ataxin-3, which is also known to protect against oxidative stress. These findings provide a new insight into the possibility of treating SCA3 with trehalose and highlight the importance of inducing autophagy in SCA3.

Endosome mediated nucleocytoplasmic trafficking and endomembrane allocation is crucial to polyglutamine toxicity.

Aggregation of aberrant proteins is a common pathological hallmark in neurodegeneration such as polyglutamine (polyQ) and other repeat-expansion diseases. Here through overexpression of ataxin3 C-terminal polyQ expansion in Drosophila gut enterocytes, we generated an intestinal obstruction model of spinocerebellar ataxia type3 (SCA3) and reported a new role of nuclear-associated endosomes (NAEs)-the delivery of polyQ to the nucleoplasm. In this model, accompanied by the prominently increased RAB5-positive NAEs are abundant nucleoplasmic reticulum enriched with polyQ, abnormal nuclear envelope invagination, significantly reduced endoplasmic reticulum, indicating dysfunctional nucleocytoplasmic trafficking and impaired endomembrane organization. Consistently, Rab5 but not Rab7 RNAi further decreased polyQ-related NAEs, inhibited endomembrane disorganization, and alleviated disease model. Interestingly, autophagic proteins were enriched in polyQ-related NAEs and played non-canonical autophagic roles as genetic manipulation of autophagic molecules exhibited differential impacts on NAEs and SCA3 toxicity. Namely, the down-regulation of Atg1 or Atg12 mitigated while Atg5 RNAi aggravated the disease phenotypes both in Drosophila intestines and compound eyes. Our findings, therefore, provide new mechanistic insights and underscore the fundamental roles of endosome-centered nucleocytoplasmic trafficking and homeostatic endomembrane allocation in the pathogenesis of polyQ diseases.

Disrupted cerebellar structural connectome in spinocerebellar ataxia type 3 and its association with transcriptional profiles.

Spinocerebellar ataxia type 3 (SCA3) is primarily characterized by progressive cerebellar degeneration, including gray matter atrophy and disrupted anatomical and functional connectivity. The alterations of cerebellar white matter structural network in SCA3 and the underlying neurobiological mechanism remain unknown. Using a cohort of 20 patients with SCA3 and 20 healthy controls, we constructed cerebellar structural networks from diffusion MRI and investigated alterations of topological organization. Then, we mapped the alterations with transcriptome data from the Allen Human Brain Atlas to identify possible biological mechanisms for regional selective vulnerability to white matter damage. Compared with healthy controls, SCA3 patients exhibited reduced global and nodal efficiency, along with a widespread decrease in edge strength, particularly affecting edges connected to hub regions. The strength of inter-module connections was lower in SCA3 group and negatively correlated with the Scale for the Assessment and Rating of Ataxia score, International Cooperative Ataxia Rating Scale score, and cytosine-adenine-guanine repeat number. Moreover, the transcriptome-connectome association study identified the expression of genes involved in synapse-related and metabolic biological processes. These findings suggest a mechanism of white matter vulnerability and a potential image biomarker for the disease severity, providing insights into neurodegeneration and pathogenesis in this disease.

Global DNA methylation is not elevated in blood samples from Machado-Joseph disease mutation carriers.

Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar ataxia (SCA) caused by a polyglutamine expansion in the ataxin-3 protein, which initiates a cascade of pathogenic events, including transcriptional dysregulation. Genotype-phenotype correlations in MJD are incomplete, suggesting an influence of additional factors, such as epigenetic modifications, underlying the MJD pathogenesis. DNA methylation is known to impact the pathophysiology of neurodegenerative disorders through gene expression regulation and increased methylation has been reported for other SCAs. In this work we aimed to analyse global methylation in MJD carriers. Global 5-mC levels were quantified in blood samples of 33 MJD mutation carriers (patients and preclinical subjects) and 33 healthy controls, matched by age, sex, and smoking status. For a subset of 16 MJD subjects, a pilot follow-up analysis with two time points was also conducted. No differences were found in median global 5-mC levels between MJD mutation carriers and controls and no correlations between methylation levels and clinical or genetic variables were detected. Also, no alterations in global 5-mC levels were observed over time. Our findings do not support an increase in global blood methylation levels associated with MJD.

Randomized double-blind placebo-controlled trial of the effects of oral trehalose in spinocerebellar ataxia type 3: An interim analysis.

INTRODUCTION: Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease characterized by increasingly worsening ataxia and non-ataxia features, negatively impacting patients' quality of life. This study was designed to test formally evaluate whether oral trehalose was effective in SCA3 patients. METHODS: In this double-blind, randomized controlled trial, SCA3 patients received either 100 g oral trehalose or 30 g maltose to improve ataxia severity over six months. We also measured other clinical (non-ataxia), patient-reported (quality of life, motivations), and safety endpoints. An unscheduled interim analysis was conducted using two-way ANOVAs to analyze the interaction between time (baseline, 3-months, 6-months) and intervention (Trehalose vs. Placebo). RESULTS: Fifteen participants (Trehalose = 7 vs. Placebo = 8) completed the study at the time of interim analysis. There was no interaction effect on the ataxia severity, and available data suggested an estimated sample size of 132 (66 per arm) SCA3 patients required to demonstrate changes in a 6-month trial. There were significant interaction effects for executive function (ƞ2 = 0.28-0.43). Safety data indicated that 100 g oral trehalose was well-tolerated. CONCLUSION: We performed an unplanned interim analysis due to a slow recruitment rate. The new estimated sample size was deemed unfeasible, leading to premature termination of the clinical trial. In this small, current sample of SCA3 patients, 100 g oral trehalose did not differentially impact on ataxia severity compared to placebo. Interestingly, our findings may suggest an improvement in executive function. Future efforts will require a large multi-country, multi-center study to investigate the potential effect of trehalose.

Feasibility and impact of a physical activity and lifestyle program for Aboriginal families with Machado-Joseph disease in the Top End of Australia.

INTRODUCTION: Physical activity and lifestyle programs are scarce for people with hereditary ataxias and neurodegenerative diseases. Aboriginal families in the Top End of Australia who have lived with Machado-Joseph disease (MJD) for generations co-designed a physical activity and lifestyle program called the Staying Strong Toolbox. The aim of the present study was to explore feasibility and impact of the program on walking and moving around. METHODS: A mixed-methods, multiple case study design was used to pilot the Staying Strong Toolbox. Eight individuals with MJD participated in the program for 4 weeks. Participants tailored their own program using the Toolbox workbook. Families, support workers and researchers facilitated each individual's program. Feasibility was determined through program participation, adherence, coinciding or serious adverse events, participant acceptability and cost. Impact was determined through measures of mobility, ataxia, steps, quality of life, wellbeing and goal attainment, assessed before and after the program. RESULTS: All participants completed the program, averaging five activity sessions per week, 66 minutes per session, of walking (63.5%), strengthening/balance-based activities (16%), cycling (11.4%) and activities of daily living, cultural and lifestyle activities (10.5%). Seven participants were assessed on all measures on three occasions (baseline, pre-program and post-program), while one participant could not complete post-program measures due to ceremonial responsibilities. All had significant improvements in mobility, steps taken and ataxia severity (p<0.05) after the program. Quality of life and wellbeing were maintained. CONCLUSION: The program helped participants remain 'strong on the inside and outside'. Participants recommended implementation in 4-week blocks and for the program to be shared internationally. The Staying Strong Toolbox program was feasible for families with MJD. The program had a positive impact on walking and moving around, with participants feeling stronger on the outside (physically) and inside (emotionally, spiritually, psychosocially). The program could be adapted for use by other families with MJD.

Imbalanced optimal feedback motor control system in spinocerebellar ataxia type 3.

BACKGROUND AND PURPOSE: Human motor planning and control depend highly on optimal feedback control systems, such as the neocortex-cerebellum circuit. Here, diffusion tensor imaging was used to verify the disruption of the neocortex-cerebellum circuit in spinocerebellar ataxia type 3 (SCA3), and the circuit's disruption correlation with SCA3 motor dysfunction was investigated. METHODS: This study included 45 patients with familial SCA3, aged 17-67 years, and 49 age- and sex-matched healthy controls, aged 21-64 years. Tract-based spatial statistics and probabilistic tractography was conducted using magnetic resonance images of the patients and controls. The correlation between the local probability of probabilistic tractography traced from the cerebellum and clinical symptoms measured using specified symptom scales was also calculated. RESULTS: The cerebellum-originated probabilistic tractography analysis showed that structural connectivity, mainly in the subcortical cerebellar-thalamo-cortical tract, was significantly reduced and the cortico-ponto-cerebellar tract was significantly stronger in the SCA3 group than in the control group. The enhanced tract was extended to the right lateral parietal region and the right primary motor cortex. The enhanced neocortex-cerebellum connections were highly associated with disease progression, including duration and symptomatic deterioration. Tractography probabilities from the cerebellar to parietal and sensorimotor areas were significantly negatively correlated with motor abilities in patients with SCA3. CONCLUSION: To our knowledge, this study is the first to reveal that disrupting the neocortex-cerebellum loop can cause SCA3-induced motor dysfunctions. The specific interaction between the cerebellar-thalamo-cortical and cortico-ponto-cerebellar pathways in patients with SCA3 and its relationship with ataxia symptoms provides a new direction for future research.

A combination of chlorzoxazone and folic acid improves recognition memory, anxiety and depression in SCA3-84Q mice.

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is reported to be the most common type of autosomal dominant cerebellar ataxia (ADCA). SCA3 patients suffer from a progressive decline in motor coordination and other disease-associated symptoms. Moreover, recent studies have reported that SCA3 patients also exhibit symptoms of cerebellar cognitive affective syndrome (CCAS). We previously observed signs of CCAS in mouse model of SCA3. Particularly, SCA3-84Q mice suffer from anxiety, recognition memory decline, and also exhibit signs of low mood and aversion to activity. Here we studied the effect of long-term injections of SK channels activator chlorzoxazone (CHZ) together and separately with the folic acid (FA) on the cerebellar Purkinje cell (PC) firing and histology, and also on the motor and cognitive functions as well as mood alterations in SCA3-84Q hemizygous transgenic mice. We realized that both CHZ and CHZ-FA combination had similar positive effect on pure cerebellum impairments including PC firing precision, PC histology, and motor performance in SCA3-84Q mice. However, only the CHZ-FA combination, but not CHZ, had significantly ameliorated the signs of anxiety and depression, and also noticeably improved recognition memory in SCA3-84Q mice. Our results suggest that the combination therapy for both ataxia and non-motor symptoms is required for the complex treatment of ADCA.

Insight into the early pathogenesis and therapeutic strategies of spinocerebellar ataxia type 3/machado-joseph disease from mouse models.

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is the most common subtype of hereditary ataxia (HA), which is characterized by motor deficits and a lack of effective treatments, and imposes a huge physical, mental, and financial burden on patients and their families. Therefore, it is important to study the early pathogenesis of spinal cerebellar ataxia type 3 based on a mouse model for subsequent preventive treatment and seeking new therapeutic targets.

Gene editing as a therapeutic strategy for spinocerebellar ataxia type-3.

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is a neurodegenerative disease caused by expanded polyglutamine repeats in exon 10 of the ataxin-3 gene, ATXN3. The accumulation of mutant ATXN3 protein leads to severe clinical manifestations and premature death. Clinically, SCA3 pathology is characterized by progressive ataxia leading to motor incoordination that may affect balance, gait and speech, and neuropathologically by a progressive degeneration of the spinal cord and cerebellum, as well as the cerebral cortex and basal ganglia. Although SCA3 is a rare disease, it is the most common autosomal dominant spinocerebellar ataxia worldwide. Its geographical distribution varies worldwide, with peak prevalence in certain regions of Brazil, Portugal and China. In 1994, the identification of the polyglutamine expansion in the ATXN3 gene made it possible not only to diagnose this pathology but also to dissect the mechanisms leading to cellular degeneration. As a monogenic disease for which only symptomatic treatment is available, the ATXN3 gene represents an attractive therapeutic target for gene editing strategies.

Molecular Imaging in CANVAS: A Contribution for Differential Diagnosis?

BACKGROUND: Phenotypes of CANVAS are increasingly diversified, including bradykinesia and dysautonomia, so that its primary differential diagnoses are multiple system atrophy-cerebellar type (MSA-c), and spinocerebellar ataxia type 3 (SCA3). This case series aims to highlight key molecular imaging findings in CANVAS. CASES: We report a case series of six patients with CANVAS who underwent nuclear medicine examinations in our center and 13 patients from the literature. These include 18F-FDG brain positron emission tomography (PET), single photon emission computed tomography (SPECT) of dopamine transporter (DaT) activity, and 123I-MIBG cardiac scintigraphy of noradrenergic transmission. CONCLUSIONS: In CANVAS, 18F-FDG brain PET mainly shows cerebellar hypometabolism, with preserved brainstem and striatum metabolism, contrasting with SCA3 and MSA-c. Dopaminergic denervation on scintigraphy seems to be associated with clinical parkinsonism, ranging from normal to severely impaired DaT SPECT. Additionally, 123I-MIBG cardiac scintigraphy might show denervation in CANVAS, similar to SCA3, but not in most MSA-c patients.

Spinocerebellar Ataxia Type 3 Pathophysiology-Implications for Translational Research and Clinical Studies.

The spinocerebellar ataxias (SCA) comprise a group of inherited neurodegenerative diseases. Machado-Joseph Disease (MJD) or spinocerebellar ataxia 3 (SCA3) is the most common autosomal dominant form, caused by the expansion of CAG repeats within the ataxin-3 (ATXN3) gene. This mutation results in the expression of an abnormal protein containing long polyglutamine (polyQ) stretches that confers a toxic gain of function and leads to misfolding and aggregation of ATXN3 in neurons. As a result of the neurodegenerative process, SCA3 patients are severely disabled and die prematurely. Several screening approaches, e.g., druggable genome-wide and drug library screenings have been performed, focussing on the reduction in stably overexpressed ATXN3(polyQ) protein and improvement in the resultant toxicity. Transgenic overexpression models of toxic ATXN3, however, missed potential modulators of endogenous ATXN3 regulation. In another approach to identify modifiers of endogenous ATXN3 expression using a CRISPR/Cas9-modified SK-N-SH wild-type cell line with a GFP-T2A-luciferase (LUC) cassette under the control of the endogenous ATXN3 promotor, four statins were identified as potential activators of expression. We here provide an overview of the high throughput screening approaches yet performed to find compounds or genomic modifiers of ATXN3(polyQ) toxicity in different SCA3 model organisms and cell lines to ameliorate and halt SCA3 progression in patients. Furthermore, the putative role of cholesterol in neurodegenerative diseases (NDDs) in general and SCA3 in particular is discussed.