Synergistic decrease of DNA single-strand break repair rates in mouse neural cells lacking both Tdp1 and aprataxin

Area of Science:

• Molecular Biology
• Neuroscience
• Genetics

Background:

• Ataxia oculomotor apraxia-1 (AOA1) is a neurodegenerative disease caused by mutations in aprataxin (APTX).
• APTX's role in DNA repair, particularly removing 5'-AMP from DNA strand breaks, is unclear in cellular contexts.
• Previous studies yielded conflicting results regarding DNA repair defects in APTX-deficient cells.

Purpose of the Study:

• To investigate the necessity of aprataxin (APTX) in chromosomal single- and double-strand break repair.
• To elucidate APTX's function by creating a cellular environment with increased dependency on its activity.
• To clarify the cellular role of APTX in DNA repair pathways, especially in conjunction with TDP1.

Main Methods:

• Generated a double knockout mouse model lacking both aprataxin (APTX) and tyrosyl DNA phosphodiesterase (TDP1).
• Assessed the repair rates of oxidative and alkylation-induced single-strand breaks (SSBs) in quiescent mouse astrocytes.
• Examined the accumulation of camptothecin-induced Top1-SSBs and evaluated double-strand break repair efficiency.

Main Results:

• The repair rate of oxidative and alkylation-induced SSBs was significantly slower in Tdp1(-/-)/Aptx(-/-) double knockout astrocytes compared to single knockouts.
• Camptothecin-induced Top1-SSBs accumulated similarly in Tdp1(-/-) and Tdp1(-/-)/Aptx(-/-) astrocytes, indicating no additional defect.
• No measurable defect in double-strand break repair was observed in any of the knockout astrocyte lines.

Conclusions:

• Aprataxin (APTX) is essential for efficient chromosomal single-strand break repair in primary neural cells lacking TDP1.
• The study provides direct evidence for APTX's requirement in SSB repair under specific cellular conditions.
• These findings contribute to understanding the molecular mechanisms underlying AOA1 and DNA repair pathways.