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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 Atxn1 175QK772T/2Q mice indicates that transcriptomic aspects of SCA1 pathogenesis differ between the cerebellum, brainstem, cerebral cortex, hippocampus, and striatum. • An SCA1 knockin mouse model with a mutated NLS in ATXN1-polyQ was generated • NLS mutation mitigates ATXN1-polyQ-related lifespan, motor, and cognitive deficits • Gene expression alterations and molecular pathology differ across brain regions • Nuclear localization of ATXN1-polyQ is a critical aspect of SCA1 disease pathology SCA1, a lethal polyglutamine (polyQ) neurodegenerative disease, displays motor and cognitive impairments. Here, CRISPR-Cas9 was used to mutate the nuclear localization sequence of ATXN1-polyQ in a knockin SCA1 mouse model. The results indicate that ATXN1-polyQ nuclear localization contributes to all SCA1-like phenotypes. However, disease-associated changes in gene expression differ between affected brain regions. [ABSTRACT FROM AUTHOR]

Many neurodegenerative disorders, such as Alzheimer's, Parkinson's and polyglutamine diseases, share a common pathogenic mechanism: the abnormal accumulation of disease-causing proteins, due to either the mutant protein's resistance to degradation or overexpression of the wild-type protein. We have developed a strategy to identify therapeutic entry points for such neurodegenerative disorders by screening for genetic networks that influence the levels of disease-driving proteins. We applied this approach, which integrates parallel cell-based and Drosophila genetic screens, to spinocerebellar ataxia type 1 (SCA1), a disease caused by expansion of a polyglutamine tract in ataxin 1 (ATXN1). Our approach revealed that downregulation of several components of the RAS-MAPK-MSK1 pathway decreases ATXN1 levels and suppresses neurodegeneration in Drosophila and mice. Importantly, pharmacological inhibitors of components of this pathway also decrease ATXN1 levels, suggesting that these components represent new therapeutic targets in mitigating SCA1. Collectively, these data reveal new therapeutic entry points for SCA1 and provide a proof-of-principle for tackling other classes of intractable neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Summary: Glutamine tract expansion triggers nine neurodegenerative diseases by conferring toxic properties to the mutant protein. In SCA1, phosphorylation of ATXN1 at Ser776 is thought to be key for pathogenesis. Here, we show that replacing Ser776 with a phosphomimicking Asp converted ATXN1 with a wild-type glutamine tract into a pathogenic protein. ATXN1[30Q]-D776-induced disease in Purkinje cells shared most features with disease caused by ATXN1[82Q] having an expanded polyglutamine tract. However, in contrast to disease induced by ATXN1[82Q] that progresses to cell death, ATXN1[30Q]-D776 failed to induce cell death. These results support a model where pathogenesis involves changes in regions of the protein in addition to the polyglutamine tract. Moreover, disease initiation and progression to neuronal dysfunction are distinct from induction of cell death. Ser776 is critical for the pathway to neuronal dysfunction, while an expanded polyglutamine tract is essential for neuronal death. [ABSTRACT FROM AUTHOR]

Spinocerebellar ataxia type 1 (SCA1) is one of nine inherited neurodegenerative disorders caused by a mutant protein with an expanded polyglutamine tract. Phosphorylation of ataxin-1 (ATXN1) at serine 776 is implicated in SCA1 pathogenesis. Previous studies, utilizing transfected cell lines and a Drosophila photoreceptor model of SCA1, suggest that phosphorylating ATXN1 at S776 renders it less susceptible to degradation. This work also indicated that oncogene from AKR mouse thymoma (Akt) promotes the phosphorylation of ATXN1 at S776 and severity of neurodegeneration. Here, we examined the phosphorylation of ATXN1 at S776 in cerebellar Purkinje cells, a prominent site of pathology in SCA1. We found that while phosphorylation of S776 is associated with a stabilization of ATXN1 in Purkinje cells, inhibition of Akt either in vivo or in a cerebellar extract-based phosphorylation assay did not decrease the phosphorylation of ATXN1-S776. In contrast, immunodepletion and inhibition of cyclic AMP-dependent protein kinase decreased phosphorylation of ATXN1-S776. These results argue against Akt as the in vivo kinase that phosphorylates S776 of ATXN1 and suggest that cyclic AMP-dependent protein kinase is the active ATXN1-S776 kinase in the cerebellum. [ABSTRACT FROM AUTHOR]

Summary: Spinocerebellar ataxia type 1 (SCA1) is one of nine inherited, typically adult onset, polyglutamine neurodegenerative diseases. To examine whether development impacts SCA1, we used a conditional transgenic mouse model of SCA1 to delay the postnatal expression of mutant ATXN1 until after completion of cerebellar development. Delayed postnatal expression of mutant ATXN1 led to a substantial reduction in severity of disease in adults in comparison with early postnatal gene expression. This was linked to a destabilization of RORα, a transcription factor critical for cerebellar development. In SCA1 mice, there was a depletion of RORα and a reduction in expression of genes controlled by RORα. Partial loss of RORα enhanced mutant ATXN1 pathogenicity. Additionally, evidence points to the existence of a complex containing ATXN1, RORα, and the RORα coactivator Tip60. These studies indicate RORα and Tip60 have a role in SCA1 and suggest a mechanism by which compromising cerebellar development contributes to severity of neurodegeneration in an adult. [Copyright &y& Elsevier]

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant, polyglutamine-induced neurodegenerative disorder that results in loss of motor coordination caused primarily by a disruption of cerebellar Purkinje cell function. In this study, we developed a conditional SCA1 mouse model to examine whether stopping expression of mutant ataxin-1 alters the disease phenotype. After cessation of SCA1[82Q] transgene expression, mutant ataxin-1, including that in nuclear inclusions, was cleared rapidly from Purkinje cells. At an early stage of disease, Purkinje cell pathology and motor dysfunction were completely reversible. After halting SCA1 expression at later stages of disease, only a partial recovery was seen. Interestingly, restoration of the ability to perform a complex motor task, the accelerating Rotarod, correlated with localization of mGluR1α to the Purkinje cell-parallel fiber synapse. These results show that the progression of SCA1 pathogenesis is dependent on the continuous expression of mutant ataxin-1. Of note, even at a late stage of disease, Purkinje cells retain at least some ability to repair the damage caused by mutant ataxin-1. [ABSTRACT FROM AUTHOR]

Summary SCA1, a fatal neurodegenerative disorder, is caused by a CAG expansion encoding a polyglutamine stretch in the protein ATXN1. We used RNA sequencing to profile cerebellar gene expression in Pcp2-ATXN1[82Q] mice with ataxia and progressive pathology and Pcp2-ATXN1[30Q]D776 animals having ataxia in absence of Purkinje cell progressive pathology. Weighted Gene Coexpression Network Analysis of the cerebellar expression data revealed two gene networks that significantly correlated with disease and have an expression profile correlating with disease progression in ATXN1[82Q] Purkinje cells. The Magenta Module provides a signature of suppressed transcriptional programs reflecting disease progression in Purkinje cells, while the Lt Yellow Module reflects transcriptional programs activated in response to disease in Purkinje cells as well as other cerebellar cell types. Furthermore, we found that upregulation of cholecystokinin ( Cck ) and subsequent interaction with the Cck1 receptor likely underlies the lack of progressive Purkinje cell pathology in Pcp2-ATXN1[30Q]D776 mice. [ABSTRACT FROM AUTHOR]

Spinocerebellar ataxia type 1 (SCA1) is a polyglutamine (polyQ) repeat neurodegenerative disease in which a primary site of pathogenesis are cerebellar Purkinje cells. In addition to polyQ expansion of ataxin-1 protein (ATXN1), phosphorylation of ATXN1 at the serine 776 residue (ATXN1-pS776) plays a significant role in protein toxicity. Utilizing a biochemical approach, pharmacological agents and cell-based assays, including SCA1 patient iPSC-derived neurons, we examine the role of Protein Kinase A (PKA) as an effector of ATXN1-S776 phosphorylation. We further examine the implications of PKA-mediated phosphorylation at ATXN1-S776 on SCA1 through genetic manipulation of the PKA catalytic subunit Cα in Pcp2 - ATXN1 [ 82Q ] mice. Here we show that pharmacologic inhibition of S776 phosphorylation in transfected cells and SCA1 patient iPSC-derived neuronal cells lead to a decrease in ATXN1. In vivo , reduction of PKA-mediated ATXN1-pS776 results in enhanced degradation of ATXN1 and improved cerebellar-dependent motor performance. These results provide evidence that PKA is a biologically important kinase for ATXN1-pS776 in cerebellar Purkinje cells. [ABSTRACT FROM AUTHOR]

Summary Polyglutamine (polyQ) diseases are caused by expansion of translated CAG repeats in distinct genes leading to altered protein function. In spinocerebellar ataxia type 1 (SCA1), a gain of function of polyQ-expanded ataxin-1 (ATXN1) contributes to cerebellar pathology. The extent to which cerebellar toxicity depends on its cognate partner capicua (CIC), versus other interactors, remains unclear. It is also not established whether loss of the ATXN1-CIC complex in the cerebellum contributes to disease pathogenesis. In this study, we exclusively disrupt the ATXN1-CIC interaction in vivo and show that it is at the crux of cerebellar toxicity in SCA1. Importantly, loss of CIC in the cerebellum does not cause ataxia or Purkinje cell degeneration. Expression profiling of these gain- and loss-of-function models, coupled with data from iPSC-derived neurons from SCA1 patients, supports a mechanism in which gain of function of the ATXN1-CIC complex is the major driver of toxicity. [ABSTRACT FROM AUTHOR]