Toward understanding Machado-Joseph 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.

Fructose-2,6-bisphosphate restores DNA repair activity of PNKP and ameliorates neurodegenerative symptoms in Huntington's disease

Huntington's disease (HD) and spinocerebellar ataxia type 3 (SCA3) are the two most prevalent polyglutamine (polyQ) neurodegenerative diseases, caused by CAG (encoding glutamine) repeat expansion in the coding region of the huntingtin (HTT) and ataxin-3 (ATXN3) proteins, respectively. We have earlier reported that the activity, but not the protein level, of an essential DNA repair enzyme, polynucleotide kinase 3'-phosphatase (PNKP), is severely abrogated in both HD and SCA3 resulting in accumulation of double-strand breaks in patients' brain genome. While investigating the mechanistic basis for the loss of PNKP activity and accumulation of DNA double-strand breaks leading to neuronal death, we observed that PNKP interacts with the nuclear isoform of 6-phosphofructo-2-kinase fructose-2,6-bisphosphatase 3 (PFKFB3). Depletion of PFKFB3 markedly abrogates PNKP activity without changing its protein level. Notably, the levels of both PFKFB3 and its product fructose-2,6 bisphosphate (F2,6BP), an allosteric modulator of glycolysis, are significantly lower in the nuclear extracts of post-mortem brain tissues of HD and SCA3 patients. Supplementation of F2,6BP restored PNKP activity in the nuclear extracts of patients' brain. Moreover, intracellular delivery of F2,6BP restored both the activity of PNKP and the integrity of transcribed genome in neuronal cells derived from striatum of HD mouse. Importantly, supplementing F2,6BP rescued the HD phenotype in Drosophila, suggesting F2,6BP to serve in vivo as a cofactor for the proper functionality of PNKP and thereby, of brain health. Our results thus provide a compelling rationale for exploring the therapeutic use of F2,6BP and structurally related compounds for treating polyQ diseases.

Significance

To unravel the biological basis for the loss of PNKP activity in HD and SCA3, the two most prevalent polyglutamine neurodegenerative disorders, we analyzed PNKP interactome and found that the nuclear isoform of a glycolytic enzyme PFKFB3 associated with PNKP and other repair proteins forming a multiprotein complex. Surprisingly, we found that PFKFB3 and its biosynthetic product, F2,6BP are significantly low in the affected region of patients' brain. Exogenous addition of F2,6BP restored PNKP activity in patients' brain nuclear extract. Moreover, supplementing F2,6BP in HD cells and fruit flies restored genome integrity and rescued the disease symptoms. While there is no curative therapy for HD/SCA3, except symptom management, our discovery suggests that F2,6BP supplementation would be a promising therapeutic option.

Progressive degeneration in a new Drosophila model of spinocerebellar ataxia type 7

Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder resulting from abnormal expansion of an uninterrupted polyglutamine (polyQ) repeat in its disease protein, ataxin-7 (ATXN7). ATXN7 is part of Spt-Ada-Gcn5 acetyltransferase (SAGA), an evolutionarily conserved transcriptional coactivation complex with critical roles in chromatin remodeling, cell signaling, neurodifferentiation, mitochondrial health and autophagy. SCA7 is dominantly inherited and characterized by genetic anticipation and high repeat-length instability. Patients with SCA7 experience progressive ataxia, atrophy, spasticity, and blindness. There is currently no cure for SCA7, and therapies are aimed at alleviating symptoms to increase quality of life. Here, we report novel Drosophila lines of SCA7 with polyQ repeats in wild-type and human disease patient range. We find that ATXN7 expression has age- and polyQ repeat length-dependent reduction in fruit fly survival and retinal instability, concomitant with increased ATXN7 protein aggregation. These new lines will provide important insight on disease progression that can be used in the future to identify therapeutic targets for SCA7 patients.

Butyrate as a potential therapeutic agent for neurodegenerative disorders

Maintaining an optimum microbial community within the gastrointestinal tract is intricately linked to human metabolic, immune and brain health. Disturbance to these microbial populations perturbs the production of vital bioactive compounds synthesised by the gut microbiome, such as short-chain fatty acids (SCFAs). Of the SCFAs, butyrate is known to be a major source of energy for colonocytes and has valuable effects on the maintenance of intestinal epithelium and blood brain barrier integrity, gut motility and transit, anti-inflammatory effects, and autophagy induction. Inducing endogenous butyrate production is likely to be beneficial for gut-brain homeostasis and for optimal neuronal function. For these reasons, butyrate has gained interest as a potential therapy for not only metabolic and immunological disorders, but also conditions related to the brain, including neurodegenerative diseases. While direct and indirect sources of butyrate, including prebiotics, probiotics, butyrate pro-drugs and glucosidase inhibitors, offer a promising therapeutic avenue, their efficacy and dosage in neurodegenerative conditions remain largely unknown. Here, we review current literature on effects of butyrate relevant to neuronal function, the impact of butyrate in a range of neurodegenerative diseases and related treatments that may have potential for the treatment of neurodegenerative diseases.

ASOs are an effective treatment for disease-associated oligodendrocyte signatures in premanifest and symptomatic SCA3 mice

Spinocerebellar ataxia type 3 (SCA3) is the most common dominantly inherited ataxia. Currently, no preventive or disease-modifying treatments exist for this progressive neurodegenerative disorder, although efforts using gene silencing approaches are under clinical trial investigation. The disease is caused by a CAG repeat expansion in the mutant gene, ATXN3, producing an enlarged polyglutamine tract in the mutant protein. Similar to other paradigmatic neurodegenerative diseases, studies evaluating the pathogenic mechanism focus primarily on neuronal implications. Consequently, therapeutic interventions often overlook non-neuronal contributions to disease. Our lab recently reported that oligodendrocytes display some of the earliest and most progressive dysfunction in SCA3 mice. Evidence of disease-associated oligodendrocyte signatures has also been reported in other neurodegenerative diseases, including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease. Here, we assess the effects of anti-ATXN3 antisense oligonucleotide (ASO) treatment on oligodendrocyte dysfunction in premanifest and symptomatic SCA3 mice. We report a severe, but modifiable, deficit in oligodendrocyte maturation caused by the toxic gain-of-function of mutant ATXN3 early in SCA3 disease that is transcriptionally, biochemically, and functionally rescued with anti-ATXN3 ASO. Our results highlight the promising use of an ASO therapy across neurodegenerative diseases that requires glial targeting in addition to affected neuronal populations.

Viral-based animal models in polyglutamine disorders

Polyglutamine disorders are a complex group of incurable neurodegenerative disorders caused by an abnormal expansion in the trinucleotide cytosine-adenine-guanine tract of the affected gene. To better understand these disorders, our dependence on animal models persists, primarily relying on transgenic models. In an effort to complement and deepen our knowledge, researchers have also developed animal models of polyglutamine disorders employing viral vectors. Viral vectors have been extensively used to deliver genes to the brain, not only for therapeutic purposes but also for the development of animal models, given their remarkable flexibility. In a time- and cost-effective manner, it is possible to use different transgenes, at varying doses, in diverse targeted tissues, at different ages, and in different species, to recreate polyglutamine pathology. This paper aims to showcase the utility of viral vectors in disease modelling, share essential considerations for developing animal models with viral vectors, and provide a comprehensive review of existing viral-based animal models for polyglutamine disorders.

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.

Blood and cerebellar abundance of ATXN3 splice variants in spinocerebellar ataxia type 3/Machado-Joseph disease

Spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease (MJD) is a heritable proteinopathy disorder, whose causative gene, ATXN3, undergoes alternative splicing. Ataxin-3 protein isoforms differ in their toxicity, suggesting that certain ATXN3 splice variants may be crucial in driving the selective toxicity in SCA3. Using RNA-seq datasets we identified and determined the abundance of annotated ATXN3 transcripts in blood (n = 60) and cerebellum (n = 12) of SCA3 subjects and controls. The reference transcript (ATXN3-251), translating into an ataxin-3 isoform harbouring three ubiquitin-interacting motifs (UIMs), showed the highest abundance in blood, while the most abundant transcript in the cerebellum (ATXN3-208) was of unclear function. Noteworthy, two of the four transcripts that encode full-length ataxin-3 isoforms but differ in the C-terminus were strongly related with tissue expression specificity: ATXN3-251 (3UIM) was expressed in blood 50-fold more than in the cerebellum, whereas ATXN3-214 (2UIM) was expressed in the cerebellum 20-fold more than in the blood. These findings shed light on ATXN3 alternative splicing, aiding in the comprehension of SCA3 pathogenesis and providing guidance in the design of future ATXN3 mRNA-lowering therapies.

The deubiquitinase function of ataxin-3 and its role in the pathogenesis of Machado-Joseph disease and other diseases

Machado-Joseph disease (MJD) is a devastating and incurable neurodegenerative disease characterised by progressive ataxia, difficulty speaking and swallowing. Consequently, affected individuals ultimately become wheelchair dependent, require constant care, and face a shortened life expectancy. The monogenic cause of MJD is expansion of a trinucleotide (CAG) repeat region within the ATXN3 gene, which results in polyglutamine (polyQ) expansion within the resultant ataxin-3 protein. While it is well established that the ataxin-3 protein functions as a deubiquitinating (DUB) enzyme and is therefore critically involved in proteostasis, several unanswered questions remain regarding the impact of polyQ expansion in ataxin-3 on its DUB function. Here we review the current literature surrounding ataxin-3's DUB function, its DUB targets, and what is known regarding the impact of polyQ expansion on ataxin-3's DUB function. We also consider the potential neuroprotective effects of ataxin-3's DUB function, and the intersection of ataxin-3's role as a DUB enzyme and regulator of gene transcription. Ataxin-3 is the principal pathogenic protein in MJD and also appears to be involved in cancer. As aberrant deubiquitination has been linked to both neurodegeneration and cancer, a comprehensive understanding of ataxin-3's DUB function is important for elucidating potential therapeutic targets in these complex conditions. In this review, we aim to consolidate knowledge of ataxin-3 as a DUB and unveil areas for future research to aid therapeutic targeting of ataxin-3's DUB function for the treatment of MJD and other diseases.

Treatment with sodium butyrate induces autophagy resulting in therapeutic benefits for spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3, also known as Machado Joseph disease) is a fatal neurodegenerative disease caused by the expansion of the trinucleotide repeat region within the ATXN3/MJD gene. Mutation of ATXN3 causes formation of ataxin-3 protein aggregates, neurodegeneration, and motor deficits. Here we investigated the therapeutic potential and mechanistic activity of sodium butyrate (SB), the sodium salt of butyric acid, a metabolite naturally produced by gut microbiota, on cultured SH-SY5Y cells and transgenic zebrafish expressing human ataxin-3 containing 84 glutamine (Q) residues to model SCA3. SCA3 SH-SY5Y cells were found to contain high molecular weight ataxin-3 species and detergent-insoluble protein aggregates. Treatment with SB increased the activity of the autophagy protein quality control pathway in the SCA3 cells, decreased the presence of ataxin-3 aggregates and presence of high molecular weight ataxin-3 in an autophagy-dependent manner. Treatment with SB was also beneficial in vivo, improving swimming performance, increasing activity of the autophagy pathway, and decreasing the presence of insoluble ataxin-3 protein species in the transgenic SCA3 zebrafish. Co-treating the SCA3 zebrafish with SB and chloroquine, an autophagy inhibitor, prevented the beneficial effects of SB on zebrafish swimming, indicating that the improved swimming performance was autophagy-dependent. To understand the mechanism by which SB induces autophagy we performed proteomic analysis of protein lysates from the SB-treated and untreated SCA3 SH-SY5Y cells. We found that SB treatment had increased activity of Protein Kinase A and AMPK signaling, with immunoblot analysis confirming that SB treatment had increased levels of AMPK protein and its substrates. Together our findings indicate that treatment with SB can increase activity of the autophagy pathway process and that this has beneficial effects in vitro and in vivo. While our results suggested that this activity may involve activity of a PKA/AMPK-dependent process, this requires further confirmation. We propose that treatment with sodium butyrate warrants further investigation as a potential treatment for neurodegenerative diseases underpinned by mechanisms relating to protein aggregation including SCA3.

IL-4/STAT6 axis observed to reverse proliferative defect in SCA3 patient-derived neural progenitor cells

Spinocerebellar ataxia 3 (SCA3) is an incurable, neurodegenerative genetic disorder that leads to progressive cerebellar ataxia and other parkinsonian-like pathologies because of loss of cerebellar neurons. The role of an expanded polyglutamine aggregate on neural progenitor cells is unknown. Here, we show that SCA3 patient-specific induced neural progenitor cells (iNPCs) exhibit proliferative defects. Moreover, SCA3 iNPCs have reduced autophagic expression compared to control. Furthermore, although SCA3 iNPCs continue to proliferate, they do not survive subsequent passages compared to control iNPCs, indicating the likelihood that SCA3 iNPCs undergo rapid senescence. Exposure to interleukin-4 (IL-4), a type 2 cytokine produced by immune cells, resulted in an observed increase in expression of autophagic programs and a reduction in the proliferation defect observed in SCA3 iNPCs. Our results indicate a previously unobserved role of SCA3 disease ontology on the neural stem cell pool and a potential therapeutic strategy using IL-4 to ameliorate or delay disease pathology in the SCA3 neural progenitor cell population.

Towards Understanding Neurodegenerative Diseases: Insights from Caenorhabditis elegans

The elevated occurrence of debilitating neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD) and Machado-Joseph disease (MJD), demands urgent disease-modifying therapeutics. Owing to the evolutionarily conserved molecular signalling pathways with mammalian species and facile genetic manipulation, the nematode Caenorhabditis elegans (C. elegans) emerges as a powerful and manipulative model system for mechanistic insights into neurodegenerative diseases. Herein, we review several representative C. elegans models established for five common neurodegenerative diseases, which closely simulate disease phenotypes specifically in the gain-of-function aspect. We exemplify applications of high-throughput genetic and drug screenings to illustrate the potential of C. elegans to probe novel therapeutic targets. This review highlights the utility of C. elegans as a comprehensive and versatile platform for the dissection of neurodegenerative diseases at the molecular level.

Progressive degeneration in a new Drosophila model of Spinocerebellar Ataxia type 7

Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder resulting from abnormal expansion of polyglutamine (polyQ) in its disease protein, ataxin-7 (ATXN7). ATXN7 is part of Spt-Ada-Gcn5 acetyltransferase (SAGA), an evolutionarily conserved transcriptional coactivation complex with critical roles in chromatin remodeling, cell signaling, neurodifferentiation, mitochondrial health and autophagy. SCA7 is dominantly inherited and characterized by genetic anticipation and high repeat-length instability. Patients with SCA7 experience progressive ataxia, atrophy, spasticity, and blindness. There is currently no cure for SCA7, and therapies are aimed at alleviating symptoms to increase quality of life. Here, we report novel Drosophila lines of SCA7 with polyQ repeats in wild-type and human disease patient range. We find that ATXN7 expression has age- and polyQ repeat length-dependent reduction in survival and retinal instability, concomitant with increased ATXN7 protein aggregation. These new lines will provide important insight on disease progression that can be used in the future to identify therapeutic targets for SCA7 patients.

Progressive degeneration in a new Drosophila model of Spinocerebellar Ataxia type 7

Spinocerebellar ataxia type 7 (SCA7) is a progressive neurodegenerative disorder resulting from abnormal expansion of polyglutamine (polyQ) in its disease protein, ataxin-7 (ATXN7). ATXN7 is part of Spt-Ada-Gcn5 acetyltransferase (SAGA), an evolutionarily conserved transcriptional coactivation complex with critical roles in chromatin remodeling, cell signaling, neurodifferentiation, mitochondrial health and autophagy. SCA7 is dominantly inherited and characterized by genetic anticipation and high repeat-length instability. Patients with SCA7 experience progressive ataxia, atrophy, spasticity, and blindness. There is currently no cure for SCA7, and therapies are aimed at alleviating symptoms to increase quality of life. Here, we report novel Drosophila lines of SCA7 with polyQ repeats in wild-type and human disease patient range. We find that ATXN7 expression has age- and polyQ repeat length-dependent reduction in survival and retinal instability, concomitant with increased ATXN7 protein aggregation. These new lines will provide important insight on disease progression that can be used in the future to identify therapeutic targets for SCA7 patients.

Blood transcriptome sequencing identifies biomarkers able to track disease stages in spinocerebellar ataxia type 3

Transcriptional dysregulation has been described in spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD), an autosomal dominant ataxia caused by a polyglutamine expansion in the ataxin-3 protein. As ataxin-3 is ubiquitously expressed, transcriptional alterations in blood may reflect early changes that start before clinical onset and might serve as peripheral biomarkers in clinical and research settings. Our goal was to describe enriched pathways and report dysregulated genes, which can track disease onset, severity or progression in carriers of the ATXN3 mutation (pre-ataxic subjects and patients). Global dysregulation patterns were identified by RNA sequencing of blood samples from 40 carriers of ATXN3 mutation and 20 controls and further compared with transcriptomic data from post-mortem cerebellum samples of MJD patients and controls. Ten genes-ABCA1, CEP72, PTGDS, SAFB2, SFSWAP, CCDC88C, SH2B1, LTBP4, MEG3 and TSPOAP1-whose expression in blood was altered in the pre-ataxic stage and simultaneously, correlated with ataxia severity in the overt disease stage, were analysed by quantitative real-time PCR in blood samples from an independent set of 170 SCA3/MJD subjects and 57 controls. Pathway enrichment analysis indicated the Gαi signalling and the oestrogen receptor signalling to be similarly affected in blood and cerebellum. SAFB2, SFSWAP and LTBP4 were consistently dysregulated in pre-ataxic subjects compared to controls, displaying a combined discriminatory ability of 79%. In patients, ataxia severity was associated with higher levels of MEG3 and TSPOAP1. We propose expression levels of SAFB2, SFSWAP and LTBP4 as well as MEG3 and TSPOAP1 as stratification markers of SCA3/MJD progression, deserving further validation in longitudinal studies and in independent cohorts.

High throughput compound screening in neuronal cells identifies statins as activators of ataxin 3 expression

The spinocerebellar ataxias (SCA) comprise a group of inherited neurodegenerative diseases. SCA3 is the most common form, caused by the expansion of CAG repeats within the ataxin 3 (ATXN3) gene. The mutation results in the expression of an abnormal protein, containing long polyglutamine (polyQ) stretches. The polyQ stretch confers a toxic gain of function and leads to misfolding and aggregation of ATXN3 in neurons. Thus, modulators of ATXN3 expression could potentially ameliorate the pathology in SCA3 patients. Therefore, we generated a CRISPR/Cas9 modified ATXN3-Exon4-Luciferase (ATXN3-LUC) genomic fusion- and control cell lines to perform a reporter cell line-based high-throughput screen comprising 2640 bioactive compounds, including the FDA approved drugs. We found no unequivocal inhibitors of, but identified statins as activators of the LUC signal in the ATXN3-LUC screening cell line. We further confirmed that Simvastatin treatment of wild type SK-N-SH cells increases ATXN3 mRNA and protein levels which likely results from direct binding of the activated sterol regulatory element binding protein 1 (SREBP1) to the ATXN3 promotor. Finally, we observed an increase of normal and expanded ATXN3 protein levels in a patient-derived cell line upon Simvastatin treatment, underscoring the potential medical relevance of our findings.

ATXN3 controls DNA replication and transcription by regulating chromatin structure

The deubiquitinating enzyme Ataxin-3 (ATXN3) contains a polyglutamine (PolyQ) region, the expansion of which causes spinocerebellar ataxia type-3 (SCA3). ATXN3 has multiple functions, such as regulating transcription or controlling genomic stability after DNA damage. Here we report the role of ATXN3 in chromatin organization during unperturbed conditions, in a catalytic-independent manner. The lack of ATXN3 leads to abnormalities in nuclear and nucleolar morphology, alters DNA replication timing and increases transcription. Additionally, indicators of more open chromatin, such as increased mobility of histone H1, changes in epigenetic marks and higher sensitivity to micrococcal nuclease digestion were detected in the absence of ATXN3. Interestingly, the effects observed in cells lacking ATXN3 are epistatic to the inhibition or lack of the histone deacetylase 3 (HDAC3), an interaction partner of ATXN3. The absence of ATXN3 decreases the recruitment of endogenous HDAC3 to the chromatin, as well as the HDAC3 nuclear/cytoplasm ratio after HDAC3 overexpression, suggesting that ATXN3 controls the subcellular localization of HDAC3. Importantly, the overexpression of a PolyQ-expanded version of ATXN3 behaves as a null mutant, altering DNA replication parameters, epigenetic marks and the subcellular distribution of HDAC3, giving new insights into the molecular basis of the disease.

Tissue-Specific Vulnerability to Apoptosis in Machado-Joseph Disease

Machado-Joseph disease (MJD) is a dominant neurodegenerative disease caused by an expanded CAG repeat in the ATXN3 gene encoding the ataxin-3 protein. Several cellular processes, including transcription and apoptosis, are disrupted in MJD. To gain further insights into the extent of dysregulation of mitochondrial apoptosis in MJD and to evaluate if expression alterations of specific apoptosis genes/proteins can be used as transcriptional biomarkers of disease, the expression levels of BCL2, BAX and TP53 and the BCL2/BAX ratio (an indicator of susceptibility to apoptosis) were assessed in blood and post-mortem brain samples from MJD subjects and MJD transgenic mice and controls. While patients show reduced levels of blood BCL2 transcripts, this measurement displays low accuracy to discriminate patients from matched controls. However, increased levels of blood BAX transcripts and decreased BCL2/BAX ratio are associated with earlier onset of disease, indicating a possible association with MJD pathogenesis. Post-mortem MJD brains show increased BCL2/BAX transcript ratio in the dentate cerebellar nucleus (DCN) and increased BCL2/BAX insoluble protein ratio in the DCN and pons, suggesting that in these regions, severely affected by degeneration in MJD, cells show signs of apoptosis resistance. Interestingly, a follow-up study of 18 patients further shows that blood BCL2 and TP53 transcript levels increase over time in MJD patients. Furthermore, while the similar levels of blood BCL2, BAX, and TP53 transcripts observed in preclinical subjects and controls is mimicked by pre-symptomatic MJD mice, the expression profile of these genes in patient brains is partially replicated by symptomatic MJD mice. Globally, our findings indicate that there is tissue-specific vulnerability to apoptosis in MJD subjects and that this tissue-dependent behavior is partially replicated in a MJD mouse model.

Machado Joseph disease severity is linked with gut microbiota alterations in transgenic mice

Emerging evidence suggests the presence of bidirectional interactions between the central nervous system and gut microbiota that may contribute to the pathogenesis of neurodegenerative diseases. However, the potential role of gut microbes in forms of spinocerebellar ataxia, such as the fatal neurodegenerative disease Machado Joseph disease (MJD), remains unexplored. Here, we examined whether gut microbiota alterations may be an early disease phenotype of MJD. We profiled the gut microbiota of male and female transgenic MJD mice (CMVMJD135) expressing human ATXN3 with expanded CAG repeats (133-143 CAG) at pre-symptomatic, symptomatic and well-established stages of the disease (7, 11 and 15 weeks of age, respectively). We compared these profiles with the gut microbiota of male and female wild-type (WT) littermate control mice at same ages. Correlation network analyses were employed to explore the relevance of microbiota changes to disease progression. The results demontrated distinct sex-dependent effects in disease development whereby male MJD mice displayed earlier motor impairments than female MJD mice. The gut microbiota community structure and composition also demonstrated sex-specific differences between MJD and WT mice. In both male and female MJD mice, the shifts in the microbiota were present by 7 weeks, before the onset of any symptoms. These pre-symptomatic microbial changes correlated with the severity of neurological impairments present at later stages of the disease. Previous efforts towards developing treatments for MJD have failed to yield meaningful outcomes. Our study reports a novel relationship between the gut microbiota and MJD development and severity. Elucidating how gut microbes are involved in MJD pathogenesis may offer new and efficacious treatment strategies for this currently untreatable disease.

A standardised protocol for blood and cerebrospinal fluid collection and processing for biomarker research in ataxia

The European Spinocerebellar Ataxia Type 3/Machado-Joseph Disease Initiative (ESMI) is a consortium established with the ambition to set up the largest European longitudinal trial-ready cohort of Spinocerebellar Ataxia Type 3/Machado-Joseph Disease (SCA3/MJD), the most common autosomal dominantly inherited ataxia worldwide. A major focus of ESMI has been the identification of SCA3/MJD biomarkers to enable future interventional studies. As biosample collection and processing variables significantly impact the outcomes of biomarkers studies, biosampling procedures standardisation was done previously to study visit initiation. Here, we describe the ESMI consensus biosampling protocol, developed within the scope of ESMI, that ultimately might be translated to other neurodegenerative disorders, particularly ataxias, being the first step to protocol harmonisation in the field.

Loss-of-Function Variants in DRD1 in Infantile Parkinsonism-Dystonia

The human dopaminergic system is vital for a broad range of neurological processes, including the control of voluntary movement. Here we report a proband presenting with clinical features of dopamine deficiency: severe infantile parkinsonism-dystonia, characterised by frequent oculogyric crises, dysautonomia and global neurodevelopmental impairment. CSF neurotransmitter analysis was unexpectedly normal. Triome whole-genome sequencing revealed a homozygous variant (c.110C>A, (p.T37K)) in DRD1, encoding the most abundant dopamine receptor (D1) in the central nervous system, most highly expressed in the striatum. This variant was absent from gnomAD, with a CADD score of 27.5. Using an in vitro heterologous expression system, we determined that DRD1-T37K results in loss of protein function. Structure-function modelling studies predicted reduced substrate binding, which was confirmed in vitro. Exposure of mutant protein to the selective D1 agonist Chloro APB resulted in significantly reduced cyclic AMP levels. Numerous D1 agonists failed to rescue the cellular defect, reflected clinically in the patient, who had no benefit from dopaminergic therapy. Our study identifies DRD1 as a new disease-associated gene, suggesting a crucial role for the D1 receptor in motor control.

The Josephin domain (JD) containing proteins are predicted to bind to the same interactors: Implications for spinocerebellar ataxia type 3 (SCA3) studies using Drosophila melanogaster mutants

Spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/ MJD), is the most frequent polyglutamine (polyQ) neurodegenerative disorder. It is caused by a pathogenic expansion of the polyQ tract, located at the C-terminal region of the protein encoded by the ATXN3 gene. This gene codes for a deubiquitinating enzyme (DUB) that belongs to a gene family, that in humans is composed by three more genes (ATXN3L, JOSD1, and JOSD2), that define two gene lineages (the ATXN3 and the Josephins). These proteins have in common the N-terminal catalytic domain (Josephin domain, JD), that in Josephins is the only domain present. In ATXN3 knock-out mouse and nematode models, the SCA3 neurodegeneration phenotype is not, however, reproduced, suggesting that in the genome of these species there are other genes that are able to compensate for the lack of ATXN3. Moreover, in mutant Drosophila melanogaster, where the only JD protein is coded by a Josephin-like gene, expression of the expanded human ATXN3 gene reproduces multiple aspects of the SCA3 phenotype, in contrast with the results of the expression of the wild type human form. In order to explain these findings, phylogenetic, as well as, protein–protein docking inferences are here performed. Here we show multiple losses of JD containing genes across the animal kingdom, suggesting partial functional redundancy of these genes. Accordingly, we predict that the JD is essential for binding with ataxin-3 and proteins of the Josephin lineages, and that D. melanogaster mutants are a good model of SCA3 despite the absence of a gene from the ATXN3 lineage. The molecular recognition regions of the ataxin-3 binding and those predicted for the Josephins are, however, different. We also report different binding regions between the two ataxin-3 forms (wild-type (wt) and expanded (exp)). The interactors that show an increase in the interaction strength with exp ataxin-3, are enriched in extrinsic components of mitochondrial outer membrane and endoplasmatic reticulum membrane. On the other hand, the group of interactors that show a decrease in the interaction strength with exp ataxin-3 is significantly enriched in extrinsic component of cytoplasm.

Regional and age-dependent changes in ubiquitination in cellular and mouse models of Spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3), also known as Machadoâ€"Joseph disease, is the most common dominantly inherited ataxia. SCA3 is caused by a CAG repeat expansion in the ATXN3 gene that encodes an expanded tract of polyglutamine (polyQ) in the disease protein ataxin-3 (ATXN3). As a deubiquitinating enzyme, ATXN3 regulates numerous cellular processes including proteasome- and autophagy-mediated protein degradation. In SCA3 disease brain, polyQ-expanded ATXN3 accumulates with other cellular constituents, including ubiquitin (Ub)-modified proteins, in select areas like the cerebellum and the brainstem, but whether pathogenic ATXN3 affects the abundance of ubiquitinated species is unknown. Here, in mouse and cellular models of SCA3, we investigated whether elimination of murine Atxn3 or expression of wild-type or polyQ-expanded human ATXN3 alters soluble levels of overall ubiquitination, as well as K48-linked (K48-Ub) and K63-linked (K63-Ub) chains. Levels of ubiquitination were assessed in the cerebellum and brainstem of 7- and 47-week-old Atxn3 knockout and SCA3 transgenic mice, and also in relevant mouse and human cell lines. In older mice, we observed that wild-type ATXN3 impacts the cerebellar levels of K48-Ub proteins. In contrast, pathogenic ATXN3 leads to decreased brainstem abundance of K48-Ub species in younger mice and changes in both cerebellar and brainstem K63-Ub levels in an age-dependent manner: younger SCA3 mice have higher levels of K63-Ub while older mice have lower levels of K63-Ub compared to controls. Human SCA3 neuronal progenitor cells also show a relative increase in K63-Ub proteins upon autophagy inhibition. We conclude that wild-type and mutant ATXN3 differentially impact K48-Ub- and K63-Ub-modified proteins in the brain in a region- and age-dependent manner.

The Homogeneous Azorean Machado-Joseph Disease Cohort: Characterization and Contributions to Advances in Research

Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3) is the most common autosomal dominant ataxia worldwide. MJD is characterized by late-onset progressive cerebellar ataxia associated with variable clinical findings, including pyramidal signs and a dystonic-rigid extrapyramidal syndrome. In the Portuguese archipelago of the Azores, the worldwide population cluster for this disorder (prevalence of 39 in 100,000 inhabitants), a cohort of MJD mutation carriers belonging to extensively studied pedigrees has been followed since the late 1990s. Studies of the homogeneous Azorean MJD cohort have been contributing crucial information to the natural history of this disease as well as allowing the identification of novel molecular biomarkers. Moreover, as interventional studies for this globally rare and yet untreatable disease are emerging, this cohort should be even more important for the recruitment of trial participants. In this paper, we profile the Azorean cohort of MJD carriers, constituted at baseline by 20 pre-ataxic carriers and 52 patients, which currently integrates the European spinocerebellar ataxia type 3/Machado-Joseph disease Initiative (ESMI), a large European longitudinal MJD cohort. Moreover, we summarize the main studies based on this cohort and highlight the contributions made to advances in MJD research. Knowledge of the profile of the Azorean MJD cohort is not only important in the context of emergent interventional trials but is also pertinent for the implementation of adequate interventional measures, constituting relevant information for Lay Associations and providing data to guide healthcare decision makers.

Ubiquitin-binding site 1 of pathogenic ataxin-3 regulates its toxicity in Drosophila models of Spinocerebellar Ataxia Type 3

Spinocerebellar Ataxia Type 3 (SCA3) is a member of the family of polyglutamine (polyQ) diseases that are caused by anomalous CAG triplet repeat expansions in several genes. SCA3 results from abnormal polyQ expansion in the deubiquitinase (DUB), ataxin-3 (Atxn3). To understand the role of the different domains of mutant Atxn3 on its pathogenicity, with the hope that they can be explored for therapeutic interventions, we have systematically studied their individual and collective effects on its toxicity. One such domain is ubiquitin-binding site 1 (UbS1) on the catalytic domain of Atxn3; UbS1 is necessary for the enzymatic activity of Atxn3. Here, we investigated the importance of UbS1 on the toxicity of pathogenic Atxn3. We generated transgenic Drosophila melanogaster lines that express polyQ-expanded Atxn3 with and without a functional UbS1. We found that mutating UbS1 markedly exacerbates the toxicity of pathogenic Atxn3. Additional studies indicated that UbS1 regulates the toxicity of Atxn3 not by affecting its aggregation or sub-cellular localization, but by impacting its role in ubiquitin processing. Our findings provide additional insights into the role of Atxn3's domains in the pathogenicity of SCA3.

Regional and age-dependent changes in ubiquitination in cellular and mouse models of spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is the most common dominantly inherited ataxia. SCA3 is caused by a CAG repeat expansion in the ATXN3 gene that encodes an expanded tract of polyglutamine in the disease protein ataxin-3 (ATXN3). As a deubiquitinating enzyme, ATXN3 regulates numerous cellular processes including proteasome- and autophagy-mediated protein degradation. In SCA3 disease brain, polyQ-expanded ATXN3 accumulates with other cellular constituents, including ubiquitin (Ub)-modified proteins, in select areas like the cerebellum and the brainstem, but whether pathogenic ATXN3 affects the abundance of ubiquitinated species is unknown. Here, in mouse and cellular models of SCA3, we investigated whether elimination of murine Atxn3 or expression of wild-type or polyQ-expanded human ATXN3 alters soluble levels of overall ubiquitination, as well as K48-linked (K48-Ub) and K63-linked (K63-Ub) chains. Levels of ubiquitination were assessed in the cerebellum and brainstem of 7- and 47-week-old Atxn3 knockout and SCA3 transgenic mice, and also in relevant mouse and human cell lines. In older mice, we observed that wild-type ATXN3 impacts the cerebellar levels of K48-Ub proteins. In contrast, pathogenic ATXN3 leads to decreased brainstem abundance of K48-Ub species in younger mice and changes in both cerebellar and brainstem K63-Ub levels in an age-dependent manner: younger SCA3 mice have higher levels of K63-Ub while older mice have lower levels of K63-Ub compared to controls. Human SCA3 neuronal progenitor cells also show a relative increase in K63-Ub proteins upon autophagy inhibition. We conclude that wild-type and mutant ATXN3 differentially impact K48-Ub- and K63-Ub-modified proteins in the brain in a region- and age-dependent manner.

Disease-associated oligodendrocyte signatures are spatiotemporally dysregulated in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by a CAG repeat expansion in the ATXN3 gene. Though the ATXN3 protein is expressed ubiquitously throughout the CNS, regional pathology in SCA3 patients is observed within select neuronal populations and more recently within oligodendrocyte-rich white matter tracts. We have previously recapitulated these white matter abnormalities in an overexpression mouse model of SCA3 and demonstrated that oligodendrocyte maturation impairments are one of the earliest and most progressive changes in SCA3 pathogenesis. Disease-associated oligodendrocyte signatures have recently emerged as significant contributors to several other neurodegenerative diseases, including Alzheimer's disease, Huntington's disease, and Parkinson's disease, but their role in regional vulnerability and disease progression remains unexplored. Here, we are the first to comparatively assess myelination in human tissue in a region-dependent manner. Translating these findings to SCA3 mouse models of disease, we confirmed endogenous expression of mutant Atxn3 leads to regional transcriptional dysregulation of oligodendrocyte maturation markers in Knock-In models of SCA3. We then investigated the spatiotemporal progression of mature oligodendrocyte transcriptional dysregulation in an overexpression SCA3 mouse model and how it relates to the onset of motor impairment. We further determined that regional reduction in mature oligodendrocyte cell counts in SCA3 mice over time parallels the onset and progression of brain atrophy in SCA3 patients. This work emphasizes the prospective contributions of disease-associated oligodendrocyte signatures to regional vulnerability and could inform timepoints and target regions imperative for biomarker assessment and therapeutic intervention in several neurodegenerative diseases.

Multi-Faceted Roles of DNAJB Protein in Cancer Metastasis and Clinical Implications

Heat shock proteins (HSPs) are highly conserved molecular chaperones with diverse cellular activities, including protein folding, assembly or disassembly of protein complexes, and maturation process under diverse stress conditions. HSPs also play essential roles in tumorigenesis, metastasis, and therapeutic resistance across cancers. Among them, HSP40s are widely accepted as regulators of HSP70/HSP90 chaperones and an accumulating number of biological functions as molecular chaperones dependent or independent of either of these chaperones. Despite large numbers of HSP40s, little is known about their physiologic roles, specifically in cancer progression. This article summarizes the multi-faceted role of DNAJB proteins as one subclass of the HSP40 family in cancer development and metastasis. Regulation and deregulation of DNAJB proteins at transcriptional, post-transcriptional, and post-translational levels contribute to tumor progression, particularly cancer metastasis. Furthermore, understanding differences in function and regulating mechanism between DNAJB proteins offers a new perspective on tumorigenesis and metastasis to improve therapeutic opportunities for malignant diseases.

Natural Products Targeting Hsp90 for a Concurrent Strategy in Glioblastoma and Neurodegeneration

Glioblastoma multiforme (GBM) is one of the most common aggressive, resistant, and invasive primary brain tumors that share neurodegenerative actions, resembling many neurodegenerative diseases. Although multiple conventional approaches, including chemoradiation, are more frequent in GBM therapy, these approaches are ineffective in extending the mean survival rate and are associated with various side effects, including neurodegeneration. This review proposes an alternative strategy for managing GBM and neurodegeneration by targeting heat shock protein 90 (Hsp90). Hsp90 is a well-known molecular chaperone that plays essential roles in maintaining and stabilizing protein folding to degradation in protein homeostasis and modulates signaling in cancer and neurodegeneration by regulating many client protein substrates. The therapeutic benefits of Hsp90 inhibition are well-known for several malignancies, and recent evidence highlights that Hsp90 inhibitors potentially inhibit the aggressiveness of GBM, increasing the sensitivity of conventional treatment and providing neuroprotection in various neurodegenerative diseases. Herein, the overview of Hsp90 modulation in GBM and neurodegeneration progress has been discussed with a summary of recent outcomes on Hsp90 inhibition in various GBM models and neurodegeneration. Particular emphasis is also given to natural Hsp90 inhibitors that have been evidenced to show dual protection in both GBM and neurodegeneration.

The equilibrium of tumor suppression: DUBs as active regulators of PTEN

PTEN is among the most commonly lost or mutated tumor suppressor genes in human cancer. PTEN, a bona fide lipid phosphatase that antagonizes the highly oncogenic PI3K-AKT-mTOR pathway, is considered a major dose-dependent tumor suppressor. Although PTEN function can be compromised by genetic mutations in inherited syndromes and cancers, posttranslational modifications of PTEN may also play key roles in the dynamic regulation of its function. Notably, deregulated ubiquitination and deubiquitination lead to detrimental impacts on PTEN levels and subcellular partitioning, promoting tumorigenesis. While PTEN can be targeted by HECT-type E3 ubiquitin ligases for nuclear import and proteasomal degradation, studies have shown that several deubiquitinating enzymes, including HAUSP/USP7, USP10, USP11, USP13, OTUD3 and Ataxin-3, can remove ubiquitin from ubiquitinated PTEN in cancer-specific contexts and thus reverse ubiquitination-mediated PTEN regulation. Researchers continue to reveal the precise molecular mechanisms by which cancer-specific deubiquitinases of PTEN regulate its roles in the pathobiology of cancer, and new methods of pharmacologically for modulating PTEN deubiquitinases are critical areas of investigation for cancer treatment and prevention. Here, we assess the mechanisms and functions of deubiquitination as a recently appreciated mode of PTEN regulation and review the link between deubiquitinases and PTEN reactivation and its implications for therapeutic strategies.

Sleep Alterations in a Mouse Model of Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder showing progressive neuronal loss in several brain areas and a broad spectrum of motor and non-motor symptoms, including ataxia and altered sleep. While sleep disturbances are known to play pathophysiologic roles in other neurodegenerative disorders, their impact on SCA3 is unknown. Using spectrographic measurements, we sought to quantitatively characterize sleep electroencephalography (EEG) in SCA3 transgenic mice with confirmed disease phenotype. We first measured motor phenotypes in 18-31-week-old homozygous SCA3 YACMJD84.2 mice and non-transgenic wild-type littermate mice during lights-on and lights-off periods. We next implanted electrodes to obtain 12-h (zeitgeber time 0-12) EEG recordings for three consecutive days when the mice were 26-36 weeks old. EEG-based spectroscopy showed that compared to wild-type littermates, SCA3 homozygous mice display: (i) increased duration of rapid-eye movement sleep (REM) and fragmentation in all sleep and wake states; (ii) higher beta power oscillations during REM and non-REM (NREM); and (iii) additional spectral power band alterations during REM and wake. Our data show that sleep architecture and EEG spectral power are dysregulated in homozygous SCA3 mice, indicating that common sleep-related etiologic factors may underlie mouse and human SCA3 phenotypes.

The emerging role of Deubiquitinases (DUBs) in parasites: A foresight review

Before the discovery of the proteasome complex, the lysosomes with acidic proteases and caspases in apoptotic pathways were thought to be the only pathways for the degradation of damaged, unfolded, and aged proteins. However, the discovery of 26S and 20S proteasome complexes in eukaryotes and microbes, respectively, established that the degradation of most proteins is a highly regulated ATP-dependent pathway that is significantly conserved across each domain of life. The proteasome is part of the ubiquitin-proteasome system (UPS), where the covalent tagging of a small molecule called ubiquitin (Ub) on the proteins marks its proteasomal degradation. The type and chain length of ubiquitination further determine whether a protein is designated for further roles in multi-cellular processes like DNA repair, trafficking, signal transduction, etc., or whether it will be degraded by the proteasome to recycle the peptides and amino acids. Deubiquitination, on the contrary, is the removal of ubiquitin from its substrate molecule or the conversion of polyubiquitin chains into monoubiquitin as a precursor to ubiquitin. Therefore, deubiquitylating enzymes (DUBs) can maintain the dynamic state of cellular ubiquitination by releasing conjugated ubiquitin from proteins and controlling many cellular pathways that are essential for their survival. Many DUBs are well characterized in the human system with potential drug targets in different cancers. Although, proteasome complex and UPS of parasites, like plasmodium and leishmania, were recently coined as multi-stage drug targets the role of DUBs is completely unexplored even though structural domains and functions of many of these parasite DUBs are conserved having high similarity even with its eukaryotic counterpart. This review summarizes the identification & characterization of different parasite DUBs based on in silico and a few functional studies among different phylogenetic classes of parasites including Metazoan (Schistosoma, Trichinella), Apicomplexan protozoans (Plasmodium, Toxoplasma, Eimeria, Cryptosporidium), Kinetoplastidie (Leishmania, Trypanosoma) and Microsporidia (Nosema). The identification of different homologs of parasite DUBs with structurally similar domains with eukaryotes, and the role of these DUBs alone or in combination with the 20S proteosome complex in regulating the parasite survival/death is further elaborated. We propose that small molecules/inhibitors of human DUBs can be potential antiparasitic agents due to their significant structural conservation.

A survey of protein interactions and posttranslational modifications that influence the polyglutamine diseases

The presence and aggregation of misfolded proteins has deleterious effects in the nervous system. Among the various diseases caused by misfolded proteins is the family of the polyglutamine (polyQ) disorders. This family comprises nine members, all stemming from the same mutation—the abnormal elongation of a polyQ repeat in nine different proteins—which causes protein misfolding and aggregation, cellular dysfunction and disease. While it is the same type of mutation that causes them, each disease is distinct: it is influenced by regions and domains that surround the polyQ repeat; by proteins with which they interact; and by posttranslational modifications they receive. Here, we overview the role of non-polyQ regions that control the pathogenicity of the expanded polyQ repeat. We begin by introducing each polyQ disease, the genes affected, and the symptoms experienced by patients. Subsequently, we provide a survey of protein-protein interactions and posttranslational modifications that regulate polyQ toxicity. We conclude by discussing shared processes and pathways that bring some of the polyQ diseases together and may serve as common therapeutic entry points for this family of incurable disorders.

Pathogenetic Mechanisms Underlying Spinocerebellar Ataxia Type 3 Are Altered in Primary Oligodendrocyte Culture

Emerging evidence has implicated non-neuronal cells, particularly oligodendrocytes, in the pathophysiology of many neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, Huntington’s disease and Spinocerebellar ataxia type 3 (SCA3). We recently demonstrated that cell-autonomous dysfunction of oligodendrocyte maturation is one of the of the earliest and most robust changes in vulnerable regions of the SCA3 mouse brain. However, the cell- and disease-specific mechanisms that underlie oligodendrocyte dysfunction remain poorly understood and are difficult to isolate in vivo. In this study, we used primary oligodendrocyte cultures to determine how known pathogenic SCA3 mechanisms affect this cell type. We isolated oligodendrocyte progenitor cells from 5- to 7-day-old mice that overexpress human mutant ATXN3 or lack mouse ATXN3 and differentiated them for up to 5 days in vitro. Utilizing immunocytochemistry, we characterized the contributions of ATXN3 toxic gain-of-function and loss-of-function in oligodendrocyte maturation, protein quality pathways, DNA damage signaling, and methylation status. We illustrate the utility of primary oligodendrocyte culture for elucidating cell-specific pathway dysregulation relevant to SCA3. Given recent work demonstrating disease-associated oligodendrocyte signatures in other neurodegenerative diseases, this novel model has broad applicability in revealing mechanistic insights of oligodendrocyte contribution to pathogenesis.

Autophagic vacuolar myopathy involving the phenotype of spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is a form of autosomal dominant cerebellar ataxia with a wide range of clinical manifestations, including ataxia and pyramidal and extrapyramidal signs. A few SCA3 patients have been noticed to be predisposed to the development of inclusion body myositis. It is still unknown whether muscle can be primarily involved in the pathogenesis of SCA3. This study reported an SCA3 family in which the index patient initially presented with parkinsonism, sensory ataxia, and distal myopathy but the absence of cerebellar and pyramidal symptoms. The clinical and electrophysiological studies implied a possible combination of distal myopathy and sensory-motor neuropathy or neuronopathy. MRI muscle showed selective fat infiltration and absence of denervated edema-like changes, indicating the distal muscle weakness had a myopathic origin. Muscle pathology showed the myopathic involvement, besides neurogenic involvement, characterized by chronic myopathic changes with multiple autophagic vacuoles. Genetic screening revealed expanded CAG of 61 repeats in the ATXN3 gene, which showed co-segregation in the family. Besides the neurogenic origin, the myopathic origin may be partly attributed to the limb weakness of SCA3 patients, which expands the spectrum of the clinical manifestation of SCA3.

Transcription factor EB-mediated mesenchymal stem cell therapy induces autophagy and alleviates spinocerebellar ataxia type 3 defects in neuronal cells model

Defects in ataxin-3 proteins and CAG repeat expansions in its coding gene ATXN3 cause Spinocerebellar Ataxia Type 3 (SCA3) or Machado-Joseph disease (MJD) polyglutamine neurodegenerative disease. The mutant proteins aggregate as inclusion bodies in cells and compete with wild-type ataxin-3, which leads to neuronal dysfunction or death and impairs Beclin1-mediated autophagy. It has been reported that Mesenchymal stem cells (MSCs) can reliably treat several neurodegenerative diseases. Herein, we used a Transcription Factor EB (TFEB) nuclear translocation-mediated MSCs co-culture approach to reconstitute autophagy and lysosomal biogenesis, and reduce SCA3-like behaviors in induced pluripotent stem cells (iPSCs)-derived neuron cells models. Our iPSCs model showed enhanced expression of autophagy proteins, attenuated the expression and toxic effects of mutant ataxin-3 on neurons, and alleviated the effects of ataxin-3 on autophagy. Therefore, MSCs are associated with autophagy-inducing therapy and compared to animal models, our MSCs co-culture could be used as a novel and potential therapeutic approach to study SCA3 disease and other neurodegenerative diseases.

KPNB1 modulates the Machado-Joseph disease protein ataxin-3 through activation of the mitochondrial protease CLPP

Machado–Joseph disease (MJD) is characterized by a pathological expansion of the polyglutamine (polyQ) tract within the ataxin-3 protein. Despite its primarily cytoplasmic localization, polyQ-expanded ataxin-3 accumulates in the nucleus and forms intranuclear aggregates in the affected neurons. Due to these histopathological hallmarks, the nucleocytoplasmic transport machinery has garnered attention as an important disease relevant mechanism. Here, we report on MJD cell model-based analysis of the nuclear transport receptor karyopherin subunit beta-1 (KPNB1) and its implications in the molecular pathogenesis of MJD. Although directly interacting with both wild-type and polyQ-expanded ataxin-3, modulating KPNB1 did not alter the intracellular localization of ataxin-3. Instead, overexpression of KPNB1 reduced ataxin-3 protein levels and the aggregate load, thereby improving cell viability. On the other hand, its knockdown and inhibition resulted in the accumulation of soluble and insoluble ataxin-3. Interestingly, the reduction of ataxin-3 was apparently based on protein fragmentation independent of the classical MJD-associated proteolytic pathways. Label-free quantitative proteomics and knockdown experiments identified mitochondrial protease CLPP as a potential mediator of the ataxin-3-degrading effect induced by KPNB1. We confirmed reduction of KPNB1 protein levels in MJD by analyzing two MJD transgenic mouse models and induced pluripotent stem cells (iPSCs) derived from MJD patients. Our results reveal a yet undescribed regulatory function of KPNB1 in controlling the turnover of ataxin-3, thereby highlighting a new potential target of therapeutic value for MJD.

The Natural History of Spinocerebellar Ataxia Type 3 in Mainland China: A 2-Year Cohort Study

Objective

The natural history of spinocerebellar ataxia type 3 (SCA3) has been reported in several populations and shows heterogeneity in progression rate and affecting factors. However, it remains unexplored in the population of Mainland China. This study aimed to identify the disease progression rate and its potential affecting factors in patients with SCA3 in Mainland China.

Participants and Methods

We enrolled patients with genetically confirmed SCA3 in Mainland China. Patients were seen at three visits, i.e., baseline, 1 year, and 2 years. The primary outcome was the Scale for the Assessment and Rating of Ataxia (SARA), and the secondary outcomes were the Inventory of Non-Ataxia Signs (INAS) as well as the SCA Functional Index (SCAFI).

Results

Between 1 October 2015, and 30 September 2016, we enrolled 263 patients with SCA3. We analyzed 247 patients with at least one follow-up visit. The annual progression rate of SARA was 1.49 points per year (SE 0.08, 95% confidence interval [CI] 1.33–1.65, p < 0.0001). The annual progression rates of INAS and SCAFI were 0.56 points per year (SE 0.05, 95% CI 0.47–0.66, p < 0.001) and −0.30 points per year (SE 0.01, 95% CI −0.33∼-0.28, p < 0.001), respectively. Faster progression in SARA was associated with longer length of the expanded allele of ATXN3 (p < 0.0001); faster progression in INAS was associated with lower INAS at baseline (p < 0.0001); faster decline in SCAFI was associated with shorter length of the normal allele of ATXN3 (p = 0.036) and higher SCAFI at baseline (p < 0.0001).

Conclusion

Our results provide quantitative data on the disease progression of patients with SCA3 in Mainland China and its corresponding affecting factors, which could facilitate the sample size calculation and patient stratification in future clinical trials.

Trial Registration

This study was registered with Chictr.org on 15 September 2015, number ChiCTR-OOC-15007124.

Drosophila as a Model of Unconventional Translation in Spinocerebellar Ataxia Type 3

RNA toxicity contributes to diseases caused by anomalous nucleotide repeat expansions. Recent work demonstrated RNA-based toxicity from repeat-associated, non-AUG-initiated translation (RAN translation). RAN translation occurs around long nucleotide repeats that form hairpin loops, allowing for translation initiation in the absence of a start codon that results in potentially toxic, poly-amino acid repeat-containing proteins. Discovered in Spinocerebellar Ataxia Type (SCA) 8, RAN translation has been documented in several repeat-expansion diseases, including in the CAG repeat-dependent polyglutamine (polyQ) disorders. The ATXN3 gene, which causes SCA3, also known as Machado–Joseph Disease (MJD), contains a CAG repeat that is expanded in disease. ATXN3 mRNA possesses features linked to RAN translation. In this paper, we examined the potential contribution of RAN translation to SCA3/MJD in Drosophila by using isogenic lines that contain homomeric or interrupted CAG repeats. We did not observe unconventional translation in fly neurons or glia. However, our investigations indicate differential toxicity from ATXN3 protein-encoding mRNA that contains pure versus interrupted CAG repeats. Additional work suggests that this difference may be due in part to toxicity from homomeric CAG mRNA. We conclude that Drosophila is not suitable to model RAN translation for SCA3/MJD, but offers clues into the potential pathogenesis stemming from CAG repeat-containing mRNA in this disorder.

Deubiquitinating enzymes (DUBs): decipher underlying basis of neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by the aggregation of neurotoxic proteins in the central nervous system. Aberrant protein accumulation in NDs is largely caused by the dysfunction of the two principal protein catabolism pathways, the ubiquitin-proteasome system (UPS), and the autophagy-lysosomal pathway (ALP). The two protein quality control pathways are bridged by ubiquitination, a post-translational modification that can induce protein degradation via both the UPS and the ALP. Perturbed ubiquitination leads to the formation of toxic aggregates and inclusion bodies that are deleterious to neurons. Ubiquitination is promoted by a cascade of ubiquitinating enzymes and counter-regulated by deubiquitinating enzymes (DUBs). As fine-tuning regulators of ubiquitination and protein degradation, DUBs modulate the stability of ND-associated pathogenic proteins including amyloid β protein, Tau, and α-synuclein. Besides, DUBs also influence ND-associated mitophagy, protein secretion, and neuroinflammation. Given the various and critical functions of DUBs in NDs, DUBs may become potential therapeutic targets for NDs.

Novel Machado-Joseph disease-modifying genes and pathways identified by whole-exome sequencing

Machado-Joseph disease (MJD/SCA3) is a neurodegenerative polyglutamine disorder exhibiting a wide spectrum of phenotypes. The abnormal size of the (CAG)n at ATXN3 explains ~55% of the age at onset variance, suggesting the involvement of other factors, namely genetic modifiers, whose identification remains limited. Our aim was to find novel genetic modifiers, analyse their epistatic effects and identify disease-modifying pathways contributing to MJD variable expressivity. We performed whole-exome sequencing in a discovery sample of four age at onset concordant and four discordant first-degree relative pairs of Azorean patients, to identify candidate variants which genotypes differed for each discordant pair but were shared in each concordant pair. Variants identified by this approach were then tested in an independent multi-origin cohort of 282 MJD patients. Whole-exome sequencing identified 233 candidate variants, from which 82 variants in 53 genes were prioritized for downstream analysis. Eighteen disease-modifying pathways were identified; two of the most enriched pathways were relevant for the nervous system, namely the neuregulin signaling and the agrin interactions at neuromuscular junction. Variants at PARD3, NFKB1, CHD5, ACTG1, CFAP57, DLGAP2, ITGB1, DIDO1 and CERS4 modulate age at onset in MJD, with those identified in CFAP57, ACTG1 and DIDO1 showing consistent effects across cohorts of different geographical origins. Network analyses of the nine novel MJD modifiers highlighted several important molecular interactions, including genes/proteins previously related with MJD pathogenesis, namely between ACTG1/APOE and VCP/ITGB1. We describe novel pathways, modifiers, and their interaction partners, providing a broad molecular portrait of age at onset modulation to be further exploited as new disease-modifying targets for MJD and related diseases.

Brain structural abnormalities in the preclinical stage of Machado-Joseph disease/spinocerebellar ataxia type 3 (MJD/SCA3): evaluation by MRI morphometry, diffusion tensor imaging and neurite orientation dispersion and density imaging

OBJECTIVE

To investigate whether neurite orientation dispersion and density imaging (NODDI) could provide the added value for detecting brain microstructural alterations in the preclinical stage of Machado-Joseph disease/spinocerebellar ataxia type 3 (MJD/SCA3) compared with MRI morphometry and diffusion tensor imaging (DTI).

METHODS

Twenty preclinical MJD/SCA3 patients and 21 healthy controls were enrolled. Three b values DWI and 3D T1-weighted images were acquired at 3.0 T. Tract-based spatial statistics (TBSS) approach was used to investigate the white matter (WM) alterations in the DTI metrics and NODDI metrics. Gray matter-based spatial statistics (GBSS) approach was used to investigate the grey matter (GM) alterations in the NODDI metrics. Voxel-based morphometry (VBM) approach was performed on the 3D T1-weighted images. The relationship between the cytosine-adenine-guanine (CAG) repeat length and brain microstructural alterations of preclinical MJD/SCA3 was identified.

RESULTS

Compared with healthy controls, the preclinical MJD/SCA3 patients showed decreased FA and NDI as well as increased MD, AD, and RD in the WM of cerebellum and brainstem (corrected P < 0.05), and decreased NDI in the GM of cerebellar vermis (corrected P < 0.05). The CAG repeat length in preclinical MJD/SCA3 patients was negatively correlated with the reduced FA and NDI of the infratentorial WM and the reduced NDI of the cerebellum, and positively with the increased MD and RD of the infratentorial WM.

CONCLUSIONS

NOODI can provide novel quantitative microstructural changes in MJD/SCA3 carriers, expanding our understanding of the gray and white matter (axons and dendrites) degeneration in this frequent ataxia syndrome.

Flow cytometry allows rapid detection of protein aggregates in cellular and zebrafish models of spinocerebellar ataxia 3

Spinocerebellar ataxia 3 (SCA3, also known as Machado-Joseph disease) is a neurodegenerative disease caused by inheritance of a CAG repeat expansion within the ATXN3 gene, resulting in polyglutamine (polyQ) repeat expansion within the ataxin-3 protein. In this study, we have identified protein aggregates in both neuronal-like (SHSY5Y) cells and transgenic zebrafish expressing human ataxin-3 with expanded polyQ. We have adapted a previously reported flow cytometry methodology named flow cytometric analysis of inclusions and trafficking, allowing rapid quantification of detergent insoluble forms of ataxin-3 fused to a GFP in SHSY5Y cells and cells dissociated from the zebrafish larvae. Flow cytometric analysis revealed an increased number of detergent-insoluble ataxin-3 particles per nuclei in cells and in zebrafish expressing polyQ-expanded ataxin-3 compared to those expressing wild-type human ataxin-3. Treatment with compounds known to modulate autophagic activity altered the number of detergent-insoluble ataxin-3 particles in cells and zebrafish expressing mutant human ataxin-3. We conclude that flow cytometry can be harnessed to rapidly count ataxin-3 aggregates, both in vitro and in vivo, and can be used to compare potential therapies targeting protein aggregates. This article has an associated First Person interview with the first author of the paper.

A Novel Calpain Inhibitor Compound Has Protective Effects on a Zebrafish Model of Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3) is a hereditary ataxia caused by inheritance of a mutated form of the human ATXN3 gene containing an expanded CAG repeat region, encoding a human ataxin-3 protein with a long polyglutamine (polyQ) repeat region. Previous studies have demonstrated that ataxin-3 containing a long polyQ length is highly aggregation prone. Cleavage of the ataxin-3 protein by calpain proteases has been demonstrated to be enhanced in SCA3 models, leading to an increase in the aggregation propensity of the protein. Here, we tested the therapeutic potential of a novel calpain inhibitor BLD-2736 for the treatment of SCA3 by testing its efficacy on a transgenic zebrafish model of SCA3. We found that treatment with BLD-2736 from 1 to 6 days post-fertilisation (dpf) improves the swimming of SCA3 zebrafish larvae and decreases the presence of insoluble protein aggregates. Furthermore, delaying the commencement of treatment with BLD-2736, until a timepoint when protein aggregates were already known to be present in the zebrafish larvae, was still successful at removing enhanced green fluorescent protein (EGFP) fused-ataxin-3 aggregates and improving the zebrafish swimming. Finally, we demonstrate that treatment with BLD-2736 increased the synthesis of LC3II, increasing the activity of the autophagy protein quality control pathway. Together, these findings suggest that BLD-2736 warrants further investigation as a treatment for SCA3 and related neurodegenerative diseases.

Targeting the VCP-binding motif of ataxin-3 improves phenotypes in Drosophila models of Spinocerebellar Ataxia Type 3

Of the family of polyglutamine (polyQ) neurodegenerative diseases, Spinocerebellar Ataxia Type 3 (SCA3) is the most common. Like other polyQ diseases, SCA3 stems from abnormal expansions in the CAG triplet repeat of its disease gene resulting in elongated polyQ repeats within its protein, ataxin-3. Various ataxin-3 protein domains contribute to its toxicity, including the valosin-containing protein (VCP)-binding motif (VBM). We previously reported that VCP, a homo-hexameric protein, enhances pathogenic ataxin-3 aggregation and exacerbates its toxicity. These findings led us to explore the impact of targeting the SCA3 protein by utilizing a decoy protein comprising the N-terminus of VCP (N-VCP) that binds ataxin-3's VBM. The notion was that N-VCP would reduce binding of ataxin-3 to VCP, decreasing its aggregation and toxicity. We found that expression of N-VCP in Drosophila melanogaster models of SCA3 ameliorated various phenotypes, coincident with reduced ataxin-3 aggregation. This protective effect was specific to pathogenic ataxin-3 and depended on its VBM. Increasing the amount of N-VCP resulted in further phenotype improvement. Our work highlights the protective potential of targeting the VCP-ataxin-3 interaction in SCA3, a key finding in the search for therapeutic opportunities for this incurable disorder.

CRISPR/Cas9 mediated gene correction ameliorates abnormal phenotypes in spinocerebellar ataxia type 3 patient-derived induced pluripotent stem cells

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a progressive autosomal dominant neurodegenerative disease caused by abnormal CAG repeats in the exon 10 of ATXN3. The accumulation of the mutant ataxin-3 proteins carrying expanded polyglutamine (polyQ) leads to selective degeneration of neurons. Since the pathogenesis of SCA3 has not been fully elucidated, and no effective therapies have been identified, it is crucial to investigate the pathogenesis and seek new therapeutic strategies of SCA3. Induced pluripotent stem cells (iPSCs) can be used as the ideal cell model for the molecular pathogenesis of polyQ diseases. Abnormal CAG expansions mediated by CRISPR/Cas9 genome engineering technologies have shown promising potential for the treatment of polyQ diseases, including SCA3. In this study, SCA3-iPSCs can be corrected by the replacement of the abnormal CAG expansions (74 CAG) with normal repeats (17 CAG) using CRISPR/Cas9-mediated homologous recombination (HR) strategy. Besides, corrected SCA3-iPSCs retained pluripotent and normal karyotype, which can be differentiated into a neural stem cell (NSCs) and neuronal cells, and maintained electrophysiological characteristics. The expression of differentiation markers and electrophysiological characteristics were similar among the neuronal differentiation from normal control iPSCs (Ctrl-iPSCs), SCA3-iPSCs, and isogenic control SCA3-iPSCs. Furthermore, this study proved that the phenotypic abnormalities in SCA3 neurons, including aggregated IC2-polyQ protein, decreased mitochondrial membrane potential (MMP) and glutathione expressions, increased reactive oxygen species (ROS), intracellular Ca²⁺ concentrations, and lipid peroxidase malondialdehyde (MDA) levels, all were rescued in the corrected SCA3-NCs. For the first time, this study demonstrated the feasibility of CRISPR/Cas9-mediated HR strategy to precisely repair SCA3-iPSCs, and reverse the corresponding abnormal disease phenotypes. In addition, the importance of genetic control using CRISPR/Cas9-mediated iPSCs for disease modeling. Our work may contribute to providing a potential ideal model for molecular mechanism research and autologous stem cell therapy of SCA3 or other polyQ diseases, and offer a good gene therapy strategy for future treatment.

Sodium valproate increases activity of the sirtuin pathway resulting in beneficial effects for spinocerebellar ataxia-3 in vivo

Machado-Joseph disease (MJD, also known as spinocerebellar ataxia type 3) is a fatal neurodegenerative disease that impairs control and coordination of movement. Here we tested whether treatment with the histone deacetylase inhibitor sodium valproate (valproate) prevented a movement phenotype that develops in larvae of a transgenic zebrafish model of the disease. We found that treatment with valproate improved the swimming of the MJD zebrafish, affected levels of acetylated histones 3 and 4, but also increased expression of polyglutamine expanded human ataxin-3. Proteomic analysis of protein lysates generated from the treated and untreated MJD zebrafish also predicted that valproate treatment had activated the sirtuin longevity signaling pathway and this was confirmed by findings of increased SIRT1 protein levels and sirtuin activity in valproate treated MJD zebrafish and HEK293 cells expressing ataxin-3 84Q, respectively. Treatment with resveratrol (another compound known to activate the sirtuin pathway), also improved swimming in the MJD zebrafish. Co-treatment with valproate alongside EX527, a SIRT1 activity inhibitor, prevented induction of autophagy by valproate and the beneficial effects of valproate on the movement in the MJD zebrafish, supporting that they were both dependent on sirtuin activity. These findings provide the first evidence of sodium valproate inducing activation of the sirtuin pathway. Further, they indicate that drugs that target the sirtuin pathway, including sodium valproate and resveratrol, warrant further investigation for the treatment of MJD and related neurodegenerative diseases.