Polyglutamine expanded Ataxin-7 induces DNA damage and alters FUS localization and function

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Polyglutamine (polyQ) diseases, including Spinocerebellar ataxia type 7 (SCA7), are linked to expanded polyQ repeats in proteins.
• Protein aggregation and sequestration of essential cellular components are proposed mechanisms in polyQ disorders.
• The RNA-binding protein FUS is found in polyQ aggregates, but its specific role in SCA7 pathogenesis is not well understood.

Purpose of the Study:

• To investigate the localization and function of the FUS protein in a cellular model of Spinocerebellar ataxia type 7 (SCA7).
• To determine if FUS sequestration affects its RNA regulatory functions and contributes to neuronal dysfunction in SCA7.
• To assess the extent of DNA damage in SCA7 models and patient cells.

Main Methods:

• Utilized a stable inducible PC12 cell model expressing the SCA7 polyQ protein ATXN7.
• Analyzed FUS localization and expression of FUS-regulated mRNAs.
• Assessed the formation of DNA damage foci (γH2AX) and DNA strand breaks using comet assays.
• Examined DNA damage in SCA7 patient-derived fibroblasts.

Main Results:

• Significant sequestration of FUS protein was observed, correlating with increased cytoplasmic localization.
• Reduced expression of FUS-regulated messenger RNAs (mRNAs) was detected in mutant ATXN7 cells.
• While FUS's role in γH2AX foci formation remained unchanged, mutant ATXN7 cells showed a statistical increase in γH2AX foci and DNA strand breaks.
• SCA7 patient fibroblasts exhibited a trend towards increased DNA damage.

Conclusions:

• FUS sequestration and subsequent disruption of its RNA regulatory functions may contribute to SCA7 pathology.
• Increased DNA damage, evidenced by γH2AX foci and strand breaks, is a significant feature in SCA7 models and patients.
• Combined alterations in FUS function and DNA damage pathways likely play a role in the neurodegenerative mechanisms of SCA7.