Clinical and genetic features of dominant Essential Tremor in Tuscany, Italy: FUS, CAMTA1, ATXN1 and beyond.

OBJECTIVE: Essential Tremor (ET) is one of the most common neurological disorders. In most instances ET is inherited as an autosomal dominant trait with age-related penetrance (virtually complete in advanced age); however, ET genetics remains elusive. The current study aims to identify possibly pathogenic genetic variants in a group of well-characterized ET families. METHODS: 34 individuals from 14 families with dominant ET were clinically evaluated and studied by whole exome sequencing studies (after excluding trinucleotide expansion disorders). RESULTS: Most patients had pure ET. In 4 families, exome studies could identify a genetic variant potentially able to significantly alter the protein structure (CADD >20, REVEL score > 0.25), shared by all the affected individuals (in CAMTA1, FUS, MYH14, SGCE genes). In another family there were two variants in dominant genes (PCDH9 and SQSTM1). Moreover, an interrupted "intermediate" trinucleotide expansion in ATXN1 ("SCA1") was identified in a further family with pure ET. CONCLUSION: Combining our observations together with earlier reports, we can conclude that ET genes confirmed in at least two families to date include CAMTA1 and FUS (reported here), as well as CACNA1G, NOTCH2NLC and TENM4. Most cases of familial ET, inherited with an autosomal dominant inheritance, may result from "mild" variants of many different genes that, when affected by more harmful genetic variants, lead to more severe neurological syndromes (still autosomal dominant). Thus, ET phenotype may be the "mild", incomplete manifestation of many other dominant neurogenetic diseases. These findings further support evidence of genetic heterogeneity for such disease(s). Author's keywords: cerebellar ataxias, movement disorders, neurogenetics, rare neurological disorders, tremor.

CAG repeat mosaicism is gene specific in spinocerebellar ataxias.

Expanded CAG repeats in coding regions of different genes are the most common cause of dominantly inherited spinocerebellar ataxias (SCAs). These repeats are unstable through the germline, and larger repeats lead to earlier onset. We measured somatic expansion in blood samples collected from 30 SCA1, 50 SCA2, 74 SCA3, and 30 SCA7 individuals over a mean interval of 8.5 years, along with postmortem tissues and fetal tissues from SCA1, SCA3, and SCA7 individuals to examine somatic expansion at different stages of life. We showed that somatic mosaicism in the blood increases over time. Expansion levels are significantly different among SCAs and correlate with CAG repeat lengths. The level of expansion is greater in individuals with SCA7 who manifest disease compared to that of those who do not yet display symptoms. Brain tissues from SCA individuals have larger expansions compared to the blood. The cerebellum has the lowest mosaicism among the studied brain regions, along with a high expression of ATXNs and DNA repair genes. This was the opposite in cortices, with the highest mosaicism and lower expression of ATXNs and DNA repair genes. Fetal cortices did not show repeat instability. This study shows that CAG repeats are increasingly unstable during life in the blood and the brain of SCA individuals, with gene- and tissue-specific patterns.

Memantine suppresses the excitotoxicity but fails to rescue the ataxic phenotype in SCA1 model mice.

Spinocerebellar ataxia type 1 (SCA1) is a debilitating neurodegenerative disorder of the cerebellum and brainstem. Memantine has been proposed as a potential treatment for SCA1. It blocks N-methyl-D-aspartate (NMDA) receptors on neurons, reduces excitotoxicity and decreases neurodegeneration in Alzheimer models. However, in cerebellar neurodegenerative diseases, the potential value of memantine is still unclear. We investigated the effects of memantine on motor performance and synaptic transmission in the cerebellum in a mouse model where mutant ataxin 1 is specifically targeted to glia. Lentiviral vectors (LVV) were used to express mutant ataxin 1 selectively in Bergmann glia (BG). In mice transduced with the mutant ataxin 1, chronic treatment with memantine improved motor activity during initial tests, presumably due to preserved BG and Purkinje cell (PC) morphology and numbers. However, mice were unable to improve their rota rod scores during next days of training. Memantine also compromised improvement in the rota rod scores in control mice upon repetitive training. These effects may be due to the effects of memantine on plasticity (LTD suppression) and NMDA receptor modulation. Some effects of chronically administered memantine persisted even after its wash-out from brain slices. Chronic memantine reduced morphological signs of neurodegeneration in the cerebellum of SCA1 model mice. This resulted in an apparent initial reduction of ataxic phenotype, but memantine also affected cerebellar plasticity and ultimately compromised motor learning. We speculate that that clinical application of memantine in SCA1 might be hampered by its ability to suppress NMDA-dependent plasticity in cerebellar cortex.

Mapping SCA1 regional vulnerabilities reveals neural and skeletal muscle contributions to disease.

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by an expanded polyglutamine tract in the widely expressed ataxin-1 (ATXN1) protein. To elucidate anatomical regions and cell types that underlie mutant ATXN1-induced disease phenotypes, we developed a floxed conditional knockin mouse (f-ATXN1146Q/2Q) with mouse Atxn1 coding exons replaced by human ATXN1 exons encoding 146 glutamines. f-ATXN1146Q/2Q mice manifested SCA1-like phenotypes including motor and cognitive deficits, wasting, and decreased survival. Central nervous system (CNS) contributions to disease were revealed using f-ATXN1146Q/2Q;Nestin-Cre mice, which showed improved rotarod, open field, and Barnes maze performance by 6-12 weeks of age. In contrast, striatal contributions to motor deficits using f-ATXN1146Q/2Q;Rgs9-Cre mice revealed that mice lacking ATXN1146Q/2Q in striatal medium-spiny neurons showed a trending improvement in rotarod performance at 30 weeks of age. Surprisingly, a prominent role for muscle contributions to disease was revealed in f-ATXN1146Q/2Q;ACTA1-Cre mice based on their recovery from kyphosis and absence of muscle pathology. Collectively, data from the targeted conditional deletion of the expanded allele demonstrated CNS and peripheral contributions to disease and highlighted the need to consider muscle in addition to the brain for optimal SCA1 therapeutics.

Diagnostic uplift through the implementation of short tandem repeat analysis using exome sequencing.

To date, approximately 50 short tandem repeat (STR) disorders have been identified; yet, clinical laboratories rarely conduct STR analysis on exomes. To assess its diagnostic value, we analyzed STRs in 6099 exomes from 2510 families with mostly suspected neurogenetic disorders. We employed ExpansionHunter and REViewer to detect pathogenic repeat expansions, confirming them using orthogonal methods. Genotype-phenotype correlations led to the diagnosis of thirteen individuals in seven previously undiagnosed families, identifying three autosomal dominant disorders: dentatorubral-pallidoluysian atrophy (n = 3), spinocerebellar ataxia type 7 (n = 2), and myotonic dystrophy type 1 (n = 2), resulting in a diagnostic gain of 0.28% (7/2510). Additionally, we found expanded ATXN1 alleles (≥39 repeats) with varying patterns of CAT interruptions in twelve individuals, accounting for approximately 0.19% in the Korean population. Our study underscores the importance of integrating STR analysis into exome sequencing pipeline, broadening the application of exome sequencing for STR assessments.

Dysregulation of alternative splicing in spinocerebellar ataxia type 1.

Spinocerebellar ataxia type 1 is caused by an expansion of the polyglutamine tract in ATAXIN-1. Ataxin-1 is broadly expressed throughout the brain and is involved in regulating gene expression. However, it is not yet known if mutant ataxin-1 can impact the regulation of alternative splicing events. We performed RNA sequencing in mouse models of spinocerebellar ataxia type 1 and identified that mutant ataxin-1 expression abnormally leads to diverse splicing events in the mouse cerebellum of spinocerebellar ataxia type 1. We found that the diverse splicing events occurred in a predominantly cell autonomous manner. A majority of the transcripts with misregulated alternative splicing events were previously unknown, thus allowing us to identify overall new biological pathways that are distinctive to those affected by differential gene expression in spinocerebellar ataxia type 1. We also provide evidence that the splicing factor Rbfox1 mediates the effect of mutant ataxin-1 on misregulated alternative splicing and that genetic manipulation of Rbfox1 expression modifies neurodegenerative phenotypes in a Drosophila model of spinocerebellar ataxia type 1 in vivo. Together, this study provides novel molecular mechanistic insight into the pathogenesis of spinocerebellar ataxia type 1 and identifies potential therapeutic strategies for spinocerebellar ataxia type 1.

Longitudinal single-cell transcriptional dynamics throughout neurodegeneration in SCA1.

Neurodegeneration is a protracted process involving progressive changes in myriad cell types that ultimately results in the death of vulnerable neuronal populations. To dissect how individual cell types within a heterogeneous tissue contribute to the pathogenesis and progression of a neurodegenerative disorder, we performed longitudinal single-nucleus RNA sequencing of mouse and human spinocerebellar ataxia type 1 (SCA1) cerebellar tissue, establishing continuous dynamic trajectories of each cell population. Importantly, we defined the precise transcriptional changes that precede loss of Purkinje cells and, for the first time, identified robust early transcriptional dysregulation in unipolar brush cells and oligodendroglia. Finally, we applied a deep learning method to predict disease state accurately and identified specific features that enable accurate distinction of wild-type and SCA1 cells. Together, this work reveals new roles for diverse cerebellar cell types in SCA1 and provides a generalizable analysis framework for studying neurodegeneration.

Functional implications of paralog genes in polyglutamine spinocerebellar ataxias.

Polyglutamine (polyQ) spinocerebellar ataxias (SCAs) comprise a group of autosomal dominant neurodegenerative disorders caused by (CAG/CAA)n expansions. The elongated stretches of adjacent glutamines alter the conformation of the native proteins inducing neurotoxicity, and subsequent motor and neurological symptoms. Although the etiology and neuropathology of most polyQ SCAs have been extensively studied, only a limited selection of therapies is available. Previous studies on SCA1 demonstrated that ATXN1L, a human duplicated gene of the disease-associated ATXN1, alleviated neuropathology in mice models. Other SCA-associated genes have paralogs (i.e., copies at different chromosomal locations derived from duplication of the parental gene), but their functional relevance and potential role in disease pathogenesis remain unexplored. Here, we review the protein homology, expression pattern, and molecular functions of paralogs in seven polyQ dominant ataxias-SCA1, SCA2, MJD/SCA3, SCA6, SCA7, SCA17, and DRPLA. Besides ATXN1L, we highlight ATXN2L, ATXN3L, CACNA1B, ATXN7L1, ATXN7L2, TBPL2, and RERE as promising functional candidates to play a role in the neuropathology of the respective SCA, along with the parental gene. Although most of these duplicates lack the (CAG/CAA)n region, if functionally redundant, they may compensate for a partial loss-of-function or dysfunction of the wild-type genes in SCAs. We aim to draw attention to the hypothesis that paralogs of disease-associated genes may underlie the complex neuropathology of dominant ataxias and potentiate new therapeutic strategies.

HD and SCA1: Tales from two 30-year journeys since gene discovery.

One of the more transformative findings in human genetics was the discovery that the expansion of unstable nucleotide repeats underlies a group of inherited neurological diseases. A subset of these unstable repeat neurodegenerative diseases is due to the expansion of a CAG trinucleotide repeat encoding a stretch of glutamines, i.e., the polyglutamine (polyQ) repeat neurodegenerative diseases. Among the CAG/polyQ repeat diseases are Huntington's disease (HD) and spinocerebellar ataxia type 1 (SCA1), in which the expansions are within widely expressed proteins. Although both HD and SCA1 are autosomal dominantly inherited, and both typically cause mid- to late-life-onset movement disorders with cognitive decline, they each are characterized by distinct clinical characteristics and predominant sites of neuropathology. Importantly, the respective affected proteins, Huntingtin (HTT, HD) and Ataxin 1 (ATXN1, SCA1), have unique functions and biological properties. Here, we review HD and SCA1 with a focus on how their disease-specific and shared features may provide informative insights.

Altered calcium signaling in Bergmann glia contributes to spinocerebellar ataxia type-1 in a mouse model of SCA1.

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disease caused by an abnormal expansion of glutamine (Q) encoding CAG repeats in the ATAXIN1 (ATXN1) gene and characterized by progressive cerebellar ataxia, dysarthria, and eventual deterioration of bulbar functions. SCA1 shows severe degeneration of cerebellar Purkinje cells (PCs) and activation of Bergmann glia (BG), a type of cerebellar astroglia closely associated with PCs. Combining electrophysiological recordings, calcium imaging techniques, and chemogenetic approaches, we have investigated the electrical intrinsic and synaptic properties of PCs and the physiological properties of BG in SCA1 mouse model expressing mutant ATXN1 only in PCs. PCs of SCA1 mice displayed lower spontaneous firing rate and larger slow afterhyperpolarization currents (sIAHP) than wildtype mice, whereas the properties of the synaptic inputs were unaffected. BG of SCA1 mice showed higher calcium hyperactivity and gliotransmission, manifested by higher frequency of NMDAR-mediated slow inward currents (SICs) in PC. Preventing the BG calcium hyperexcitability of SCA1 mice by loading BG with the calcium chelator BAPTA restored sIAHP and spontaneous firing rate of PCs to similar levels of wildtype mice. Moreover, mimicking the BG hyperactivity by activating BG expressing Gq-DREADDs in wildtype mice reproduced the SCA1 pathological phenotype of PCs, i.e., enhancement of sIAHP and decrease of spontaneous firing rate. These results indicate that the intrinsic electrical properties of PCs, but not their synaptic properties, were altered in SCA1 mice and that these alterations were associated with the hyperexcitability of BG. Moreover, preventing BG hyperexcitability in SCA1 mice and promoting BG hyperexcitability in wildtype mice prevented and mimicked, respectively, the pathological electrophysiological phenotype of PCs. Therefore, BG plays a relevant role in the dysfunction of the electrical intrinsic properties of PCs in SCA1 mice, suggesting that they may serve as potential targets for therapeutic approaches to treat the spinocerebellar ataxia type 1.

Early molecular layer interneuron hyperactivity triggers Purkinje neuron degeneration in SCA1.

Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in behaving spinocerebellar ataxia type 1 (Sca1) mice, wherein Purkinje neurons (PNs) degenerate, we identify an inhibitory circuit element (molecular layer interneurons [MLINs]) that becomes prematurely hyperexcitable, compromising sensorimotor signals in the cerebellum at early stages. Mutant MLINs express abnormally elevated parvalbumin, harbor high excitatory-to-inhibitory synaptic density, and display more numerous synaptic connections on PNs, indicating an excitation/inhibition imbalance. Chemogenetic inhibition of hyperexcitable MLINs normalizes parvalbumin expression and restores calcium signaling in Sca1 PNs. Chronic inhibition of mutant MLINs delayed PN degeneration, reduced pathology, and ameliorated motor deficits in Sca1 mice. Conserved proteomic signature of Sca1 MLINs, shared with human SCA1 interneurons, involved the higher expression of FRRS1L, implicated in AMPA receptor trafficking. We thus propose that circuit-level deficits upstream of PNs are one of the main disease triggers in SCA1.

Stressing the role of a short linear motif in ataxin-2 condensation.

Ataxin-2, an RNA-binding protein that is conserved across eukaryotes, is involved in stress granule assembly and age-associated neurodegenerative diseases. In this issue of Molecular Cell, Boeynaems et al.1 identify a short linear motif in ataxin-2 as a condensation switch, providing molecular insights into its essential role in cellular stress response.

Therapeutic Strategies for Spinocerebellar Ataxia Type 1.

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder that affects one or two individuals per 100,000. The disease is caused by an extended CAG repeat in exon 8 of the ATXN1 gene and is characterized mostly by a profound loss of cerebellar Purkinje cells, leading to disturbances in coordination, balance, and gait. At present, no curative treatment is available for SCA1. However, increasing knowledge on the cellular and molecular mechanisms of SCA1 has led the way towards several therapeutic strategies that can potentially slow disease progression. SCA1 therapeutics can be classified as genetic, pharmacological, and cell replacement therapies. These different therapeutic strategies target either the (mutant) ATXN1 RNA or the ataxin-1 protein, pathways that play an important role in downstream SCA1 disease mechanisms or which help restore cells that are lost due to SCA1 pathology. In this review, we will provide a summary of the different therapeutic strategies that are currently being investigated for SCA1.

TR-FRET-Based Immunoassay to Measure Ataxin-2 as a Target Engagement Marker in Spinocerebellar Ataxia Type 2.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited neurodegenerative disease, which belongs to the trinucleotide repeat disease group with a CAG repeat expansion in exon 1 of the ATXN2 gene resulting in an ataxin-2 protein with an expanded polyglutamine (polyQ)-stretch. The disease is late manifesting leading to early death. Today, therapeutic interventions to cure the disease or even to decelerate disease progression are not available yet. Furthermore, primary readout parameter for disease progression and therapeutic intervention studies are limited. Thus, there is an urgent need for quantifiable molecular biomarkers such as ataxin-2 becoming even more important due to numerous potential protein-lowering therapeutic intervention strategies. The aim of this study was to establish a sensitive technique to measure the amount of soluble polyQ-expanded ataxin-2 in human biofluids to evaluate ataxin-2 protein levels as prognostic and/or therapeutic biomarker in SCA2. Time-resolved fluorescence energy transfer (TR-FRET) was used to establish a polyQ-expanded ataxin-2-specific immunoassay. Two different ataxin-2 antibodies and two different polyQ-binding antibodies were validated in three different concentrations and tested in cellular and animal tissue as well as in human cell lines, comparing different buffer conditions to evaluate the best assay conditions. We established a TR-FRET-based immunoassay for soluble polyQ-expanded ataxin-2 and validated measurements in human cell lines including iPSC-derived cortical neurons. Additionally, our immunoassay was sensitive enough to monitor small ataxin-2 expression changes by siRNA or starvation treatment. We successfully established the first sensitive ataxin-2 immunoassay to measure specifically soluble polyQ-expanded ataxin-2 in human biomaterials.

BDNF is altered in a brain-region specific manner and rescues deficits in Spinocerebellar Ataxia Type 1.

Spinocerebellar ataxia type 1 (SCA1) is an adult-onset, dominantly inherited neurodegenerative disease caused by the expanded polyQ tract in the protein ATAXIN1 (ATXN1) and characterized by progressive motor and cognitive impairments. There are no disease-modifying treatments or cures for SCA1. Brain-derived neurotrophic factor (BDNF) plays important role in cerebellar physiology and has shown therapeutic potential for cerebellar pathology in the transgenic mouse model of SCA1, ATXN1[82Q] line that overexpress mutant ATXN1 under a cerebellar Purkinje-cell-specific promoter. Here we demonstrate decreased expression of brain derived neurotrophic factor (BDNF) in the cerebellum and medulla of patients with SCA1. Early stages of disease seem most amenable to therapy. Thus, we next quantified Bdnf expression in Atxn1154Q/2Q mice, a knock-in mouse model of SCA1, during the early symptomatic disease stage in four clinically relevant brain regions: cerebellum, medulla, hippocampus and motor cortex. We found that during the early stages of disease, Bdnf mRNA expression is reduced in the hippocampus and cerebellum, while it is increased in the cortex and brainstem. Importantly, we observed that pharmacological delivery of recombinant BDNF improved motor and cognitive performance, and mitigated pathology in the cerebellum and hippocampus of Atxn1154Q/2Q mice. Our findings demonstrate brain-region specific deficiency of BDNF in SCA1 and show that reversal of low BDNF levels offers the potential for meaningful treatment of motor and cognitive deficits in SCA1.

On the identification of potential novel therapeutic targets for spinocerebellar ataxia type 1 (SCA1) neurodegenerative disease using EvoPPI3.

EvoPPI (http://evoppi.i3s.up.pt), a meta-database for protein-protein interactions (PPI), has been upgraded (EvoPPI3) to accept new types of data, namely, PPI from patients, cell lines, and animal models, as well as data from gene modifier experiments, for nine neurodegenerative polyglutamine (polyQ) diseases caused by an abnormal expansion of the polyQ tract. The integration of the different types of data allows users to easily compare them, as here shown for Ataxin-1, the polyQ protein involved in spinocerebellar ataxia type 1 (SCA1) disease. Using all available datasets and the data here obtained for Drosophila melanogaster wt and exp Ataxin-1 mutants (also available at EvoPPI3), we show that, in humans, the Ataxin-1 network is much larger than previously thought (380 interactors), with at least 909 interactors. The functional profiling of the newly identified interactors is similar to the ones already reported in the main PPI databases. 16 out of 909 interactors are putative novel SCA1 therapeutic targets, and all but one are already being studied in the context of this disease. The 16 proteins are mainly involved in binding and catalytic activity (mainly kinase activity), functional features already thought to be important in the SCA1 disease.

Ataxin-1 controls the expression of specific noncoding RNAs in B cells upon autoimmune demyelination.

B cells play a key mechanistic role in the pathogenesis of multiple sclerosis (MS), a chronic neurological disease of the central nervous system with an autoimmune etiology. B cells contribute to disease initiation and progression by acting as professional antigen-presenting cells as well as via secreting autoantibodies and proinflammatory cytokines. We have recently shown that the polyglutamine protein ataxin-1, which was first linked to the movement disorder spinocerebellar ataxia type 1, also acts as a master regulator of B-cell functions in the context of central nervous system autoimmunity. In fact, ataxin-1-deficient mice display an aggravated manifestation of the MS disease model experimental autoimmune encephalomyelitis along with aberrant B-cell functions. Consistent with this scenario, transcriptomic analysis of Atxn1-null B cells highlighted distinct genetic signatures involved in cell activation, proliferation and antigen presentation. To further characterize the role of ataxin-1, we profiled the noncoding transcriptome controlled by ataxin-1 in the B-cell compartment upon an encephalitogenic challenge. We show that two specific classes of noncoding RNAs, namely, processed pseudogenes and intergenic long noncoding RNAs, are differentially regulated along disease. Furthermore, pathway and protein network analyses on their putative protein-coding gene targets found a significant enrichment in ontologies related to cell mitosis, together with molecular processes relevant to MS such as chitin metabolism. Altogether, these findings shed light on the possible contribution of noncoding RNAs to B-cell biology and MS pathogenesis, and further establish the immunomodulatory role of ataxin-1 in autoimmune demyelination.

Elevation of hsa-miR-7-5p level mediated by CtBP1-p300-AP1 complex targets ATXN1 to trigger NF-κB-dependent inflammation response.

Nuclear factor-κB (NF-κB)-mediated inflammation is a major cause of acute respiratory distress syndrome (ARDS). However, the regulatory mechanisms by which NF-κB transactivates proinflammatory cytokines remain unclear in the pathogenesis of ARDS. Herein, we report that the activating protein 1 (AP1) transcription factor recruits a histone acetyltransferase p300 and a transcriptional regulator C-terminal binding protein 1 (CtBP1) to assemble the CtBP1-p300-AP1 complex, which transactivates the expression of hsa-miR-7-5p in ARDS biopsies. Overexpressed hsa-miR-7-5p binds to the three prime untranslated regions (3'-UTRs) of ataxin 1 (ATXN1), suppressing its expression. Decreased ATXN1 expression relieves its repression of NF-κB, causing the induction of proinflammatory cytokine genes and triggering an inflammatory response. Depletion of CtBP1 or treatments with two CtBP1 inhibitors (NSC95397 and 4-methylthio-2-oxobutanoate (MTOB)) in human macrophages impairs the assembly of the CtBP2-p300-AP1 complex, resulting in decreased hsa-miR-7-5p levels, upregulation of ATXN1, and attenuation of proinflammatory cytokines. A similar regulatory mechanism was observed in lipopolysaccharide-treated mice. Our results reveal that increased hsa-miR-7-5p level mediated by the CtBP1-p300-AP1 complex targets ATXN1 to trigger an NF-κB-dependent inflammatory response. Interfering with this signaling pathway to block the inflammatory response may be a strategy for treating ARDS. KEY MESSAGES : The transcription factor AP1 recruits p300 and CtBP1 to form a transcriptional complex, which transactivates the expression of hsa-miR-7-5p in ARDS biopsies. Overexpressed hsa-miR-7-5p binds to the 3'-UTR of ATXN1, suppressing its expression. The decreased ATXN1 impaired its suppression of NF-κB, causing the induction of proinflammatory cytokine genes and triggering inflammation response. Disruption of the assembly of CtBP2-p300-AP1 complex upregulates ATXN1 and attenuates inflammation.

Disruption of the ATXN1-CIC complex reveals the role of additional nuclear ATXN1 interactors in spinocerebellar ataxia type 1.

Spinocerebellar ataxia type 1 (SCA1) is a paradigmatic neurodegenerative disease in that it is caused by a mutation in a broadly expressed protein, ATXN1; however, only select populations of cells degenerate. The interaction of polyglutamine-expanded ATXN1 with the transcriptional repressor CIC drives cerebellar Purkinje cell pathogenesis; however, the importance of this interaction in other vulnerable cells remains unknown. Here, we mutated the 154Q knockin allele of Atxn1154Q/2Q mice to prevent the ATXN1-CIC interaction globally. This normalized genome-wide CIC binding; however, it only partially corrected transcriptional and behavioral phenotypes, suggesting the involvement of additional factors in disease pathogenesis. Using unbiased proteomics, we identified three ATXN1-interacting transcription factors: RFX1, ZBTB5, and ZKSCAN1. We observed altered expression of RFX1 and ZKSCAN1 target genes in SCA1 mice and patient-derived iNeurons, highlighting their potential contributions to disease. Together, these data underscore the complexity of mechanisms driving cellular vulnerability in SCA1.

Decreasing mutant ATXN1 nuclear localization improves a spectrum of SCA1-like phenotypes and brain region transcriptomic profiles.

Spinocerebellar ataxia type 1 (SCA1) is a dominant trinucleotide repeat neurodegenerative disease characterized by motor dysfunction, cognitive impairment, and premature death. Degeneration of cerebellar Purkinje cells is a frequent and prominent pathological feature of SCA1. We previously showed that transport of ATXN1 to Purkinje cell nuclei is required for pathology, where mutant ATXN1 alters transcription. To examine the role of ATXN1 nuclear localization broadly in SCA1-like disease pathogenesis, CRISPR-Cas9 was used to develop a mouse with an amino acid alteration (K772T) in the nuclear localization sequence of the expanded ATXN1 protein. Characterization of these mice indicates that proper nuclear localization of mutant ATXN1 contributes to many disease-like phenotypes including motor dysfunction, cognitive deficits, and premature lethality. RNA sequencing analysis of genes with expression corrected to WT levels in Atxn1175QK772T/2Q mice indicates that transcriptomic aspects of SCA1 pathogenesis differ between the cerebellum, brainstem, cerebral cortex, hippocampus, and striatum.