| Property | Value | [@koob1999] |----------|-------| [@banezcoronel2015] | Protein Name | Ataxin-8 | [@paulson2017] | Aliases | SCA8 polyglutamine protein | [@he2006] | Gene | [ATXN8](/genes/atxn8) | | UniProt ID | [Q156A1](https://www.uniprot.org/uniprot/Q156A1) | | Molecular Weight | Variable (~10-15 kDa, depending on repeat length) | | Protein Family | Polyglutamine disease protein | | Subcellular Localization | Nucleus (intranuclear inclusions) | | Post-translational Modifications | Not well characterized |
</div>
Overview
Ataxin-8 is a protein encoded by the [ATXN8](/genes/atxn8) gene. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Structure
Ataxin-8 is a small protein encoded by the [ATXN8](/genes/atxn8) gene on the sense (CAG) strand of the bidirectionally transcribed SCA8 locus. Unlike most polyglutamine disease proteins (e.g., [Huntingtin](/proteins/huntingtin), [Ataxin-1](/proteins/ataxin-1), [Ataxin-3](/proteins/ataxin-3)), Ataxin-8 lacks well-defined functional domains outside the polyglutamine tract.
| Property | Value | [@koob1999] |----------|-------| [@banezcoronel2015] | Protein Name | Ataxin-8 | [@paulson2017] | Aliases | SCA8 polyglutamine protein | [@he2006] | Gene | [ATXN8](/genes/atxn8) | | UniProt ID | [Q156A1](https://www.uniprot.org/uniprot/Q156A1) | | Molecular Weight | Variable (~10-15 kDa, depending on repeat length) | | Protein Family | Polyglutamine disease protein | | Subcellular Localization | Nucleus (intranuclear inclusions) | | Post-translational Modifications | Not well characterized |
</div>
Overview
Ataxin-8 is a protein encoded by the [ATXN8](/genes/atxn8) gene. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Structure
Ataxin-8 is a small protein encoded by the [ATXN8](/genes/atxn8) gene on the sense (CAG) strand of the bidirectionally transcribed SCA8 locus. Unlike most polyglutamine disease proteins (e.g., [Huntingtin](/proteins/huntingtin), [Ataxin-1](/proteins/ataxin-1), [Ataxin-3](/proteins/ataxin-3)), Ataxin-8 lacks well-defined functional domains outside the polyglutamine tract.
Structural features:
Polyglutamine tract — The central feature of Ataxin-8; normally 15-50 glutamine residues, expanded to 80-250 in [SCA8](/diseases/spinocerebellar-ataxia-type-8)
Flanking sequences — Short N- and C-terminal sequences flanking the polyQ tract; these influence aggregation kinetics and toxicity
No known catalytic domain — Unlike [Ataxin-3](/proteins/ataxin-3) (deubiquitinase) or [Ataxin-1](/proteins/ataxin-1) (AXH domain), Ataxin-8 has no characterized enzymatic activity
Aggregation-prone — The expanded polyQ tract adopts β-sheet-rich amyloid-like conformations that drive protein aggregation
Ataxin-8 contributes to [SCA8](/diseases/spinocerebellar-ataxia-type-8) pathogenesis through multiple mechanisms, forming part of the "triple toxicity" model unique to this disease:
1. Polyglutamine Aggregation
Expanded polyQ Ataxin-8 forms intranuclear inclusions in [Purkinje cells](/cell-types/purkinje-cells) and other cerebellar [neurons](/entities/neurons)
Inclusions are ubiquitin-positive and co-localize with components of the [ubiquitin-proteasome system](/mechanisms/ubiquitin-proteasome-system)
Aggregation follows a nucleation-elongation model: monomeric polyQ undergoes conformational change to β-sheet-rich nuclei, which seed rapid fibril growth
Inclusions sequester transcription factors and proteasomal components, disrupting cellular homeostasis
Disruption of cerebellar gene expression programs critical for Purkinje cell survival
Similar mechanism to [Huntingtin](/proteins/huntingtin)-mediated transcriptional toxicity in [Huntington's disease](/diseases/huntington-disease)
3. RAN Translation Products
In addition to the canonical polyQ Ataxin-8 protein, the expanded CAG/CTG repeat undergoes [repeat-associated non-AUG (RAN) translation](/mechanisms/ran-translation) in all three reading frames:
Polyglutamine (polyQ) — from the CAG reading frame (canonical Ataxin-8)
Polyalanine (polyA) — from the GCA reading frame; forms cytoplasmic aggregates
Polyserine (polyS) — from the AGC reading frame; accumulates preferentially in cerebellar white matter and is particularly toxic
These RAN translation products:
Accumulate without requiring an AUG start codon
Form distinct aggregates in different subcellular compartments
Are regulated by [eIF3F](/proteins/eif3f-protein) and other translation factors
Contribute to cerebellar degeneration independently of the canonical polyQ protein
Cellular Effects
Purkinje Cell Vulnerability
[Purkinje cells](/cell-types/purkinje-cells) are preferentially affected in SCA8 due to:
High expression of both ATXN8 (sense) and ATXN8OS (antisense) transcripts in the cerebellum
Purkinje cells' large size and high metabolic demands make them susceptible to proteostatic stress
GABAergic signaling disruption through [MBNL1](/genes/mbnl1)-mediated missplicing of GABA-A receptor subunits (from the antisense RNA toxicity mechanism)
Glutamate transporter ([EAAT1/GLAST](/proteins/slc1a3-protein)) missplicing leads to excitotoxic vulnerability
Proteostasis Disruption
PolyQ Ataxin-8 aggregates impair [proteasome](/mechanisms/ubiquitin-proteasome-system) function
[Autophagy](/mechanisms/autophagy) is activated as a compensatory clearance mechanism
[Chaperone](/mechanisms/protein-folding) systems ([Hsp70](/genes/hsp70), [Hsp40](/proteins/dnajb1-protein)) attempt to refold or sequester misfolded polyQ protein
Chronic proteostatic stress leads to ER stress and [unfolded protein response](/mechanisms/er-stress-unfolded-protein-response) activation
Filter trap assay — Detects SDS-insoluble aggregates in brain tissue
No established fluid biomarkers — Unlike [neurofilament light (NfL)](/proteins/neurofilament-light) for general neurodegeneration, no Ataxin-8-specific blood or CSF biomarker exists
Imaging biomarkers — Cerebellar atrophy on MRI correlates with disease progression
Therapeutic Targeting
| Strategy | Target | Rationale | Status | |----------|--------|-----------|--------| | Antisense oligonucleotides | ATXN8 mRNA | Reduce toxic polyQ protein production | Preclinical | | PolyQ aggregation inhibitors | Ataxin-8 protein | Prevent inclusion formation | Early research | | [Autophagy](/entities/autophagy) enhancers | Aggregated Ataxin-8 | Promote clearance of polyQ aggregates | Preclinical | | RAN translation blockers | Repeat RNA | Prevent toxic polyS/polyA production | Early research | | CRISPR repeat contraction | ATXN8 gene | Shorten the pathogenic repeat | Proof-of-concept |
[Moseley et al., Bidirectional expression of CUG and CAG expansion transcripts and intranuclear polyglutamine inclusions in spinocerebellar ataxia type 8 (2006) (2006)](https://doi.org/10.1038/ng1827)
[Zu et al., Non-ATG-initiated translation directed by microsatellite expansions (2011) (2011)](https://doi.org/10.1073/pnas.1013343108)
[Ayhan et al., SCA8 RAN polySer protein preferentially accumulates in white matter regions and is regulated by eIF3F (2018) (2018)](https://doi.org/10.1038/s41418-018-0132-7)
[Daughters et al., RNA gain-of-function in spinocerebellar ataxia type 8 (2009) (2009)](https://doi.org/10.1371/journal.pgen.1000600)
[Koob et al., An untranslated CTG expansion causes a novel form of spinocerebellar ataxia (SCA8) (1999) (1999)](https://doi.org/10.1038/8307)
[Banez-Coronel et al., RAN translation in Huntington disease (2015) (2015)](https://doi.org/10.1016/j.neuron.2015.10.038)
[Paulson et al., Polyglutamine spinocerebellar ataxias — from genes to potential treatments (2017) (2017)](https://doi.org/10.1038/nrn.2017.92)
[He et al., Targeted deletion of a single Sca8 ataxia locus allele in mice causes abnormal gait, progressive loss of motor coordination, and Purkinje cell dendritic deficits (2006) (2006)](https://doi.org/10.1523/JNEUROSCI.2595-06.2006)