Induced pluripotent stem cells carrying novel APTX mutations presented defective neural differentiation with the accumulation of DNA single-strand breaks

Ataxia with oculomotor apraxia type 1 (AOA1) is a rare, autosomal recessive, early-onset, progressive cerebellar ataxia caused by mutations in the APTX gene, which encodes aprataxin, a DNA-adenylate hydrolase involved in DNA damage repair. The pathogenesis of AOA1 remains unclear. The purpose of this study was to investigate the pathogenesis of a novel mutation, p.H201P/H201R, carried by our AOA1 patient and the mechanism of AOA1 in an induced pluripotent stem cells (iPSCs) model. We edited iPSCs derived from a healthy individual to carry the APTX homozygous mutation p.H201P (H201P-iPSCs) or p.H201R (H201R-iPSCs) via CRISPR/Cas9. We found that aprataxin expression was absent in both H201P- and H201R-iPSCs. The capacity of these APTX-mutant iPSCs to differentiate into neural progenitor cells (NPCs) and mature neurons was diminished. We observed an increase in DNA single-strand breaks (SSB) via a comet assay and poly(ADP-ribose) staining, and an increase in the ratio of cleaved PARP-1/total PARP-1 in APTX-mutant NPCs and early immature neurons (EiNs), in addition of a heightened sensitivity to tert-butyl hydroperoxide in APTX-mutant EiNs. Moreover, a decrease of APE1 expression was observed in APTX-mutant NPCs and H201R-EiNs during neural differentiation. Our study established a practical iPSCs model to investigate AOA1 disease. We found that mutant aprataxin leads to defective neural differentiation, accompanied by the accumulation of DNA SSBs with increased cleaved PARP-1 and reduced APE1 expression of the base excision repair pathway.