Improvement of TaC9‐ABE mediated correction of human SMN2 gene

Abstract

Spinal muscular atrophy (SMA) is a devastating neuromuscular disease caused by mutations in the survival motor neuron 1 (SMN1) gene. Gene editing technology repairs the conversion of the 6th base T to C in exon 7 of the paralogous SMN2 gene, compensating for the SMN protein expression and promoting the survival and function of motor neurons. However, low editing efficiency and unintended off‐target effects limit the application of this technology. Here, we optimized a TaC9‐adenine base editor (ABE) system by combining Cas9 nickase with the transcription activator‐like effector (TALE)‐adenosine deaminase fusion protein to effectively and precisely edit SMN2 without detectable Cas9 dependent off‐target effects in human cell lines. We also generated human SMA‐induced pluripotent stem cells (SMA‐iPSCs) through the mutation of the splice acceptor or deletion of the exon 7 of SMN1. TaC9‐R10 induced 45% SMN2 T6 > C conversion in the SMA‐iPSCs. The SMN2 T6 > C splice‐corrected SMA‐iPSCs were directionally differentiated into motor neurons, exhibiting SMN protein recovery and antiapoptosis ability. Therefore, the TaC9‐ABE system with dual guides from the combination of Cas9 with TALE could be a potential therapeutic strategy for SMA with high efficacy and safety.