Improving the Efficiency of CRISPR/Cas9-Mediated Non-Homologous End Joining Gene Knockout Using Small Molecules in Porcine Cells

The CRISPR/Cas9 genome editing system has emerged as an effective platform to generate loss-of-function gene edits through non-homologous end joining (NHEJ) without a repair template. To verify whether small molecules can enhance the efficiency of CRISPR/ Cas9-mediated NHEJ gene editing in porcine cells, this experiment investigated the effects of six small-molecule compounds, namely Repsox, Zidovudine, IOX1, GSK-J4, YU238259, and GW843682X, on the efficiency of CRISPR/Cas9-mediated NHEJ gene editing. The results showed the optimal concentrations of the small molecules, including Repsox, Zidovudine, IOX1, GSK-J4, YU238259, and GW843682X, for in vitro-cultured PK15 viability. Compared with the control group, the single small molecules Repsox, Zidovudine, GSK-J4, and IOX1 increased the efficiency of NHEJ-mediated gene editing 3.16-fold, 1.17-fold, 1.16-fold, and 1.120-fold, respectively, in the Cas9-sgRNA RNP delivery system. There were no benefits when using YU238259 and GW843682X compared with the control group. In the CRISPR/Cas9 plasmid delivery system, the Repsox, Zidovudine, IOX1, and GSK-J4 treatments increased the efficiency of NHEJ-mediated gene editing 1.47-fold, 1.15-fold, 1.21-fold, and 1.23-fold, respectively, compared with the control group. Repsox can also improve the efficiency of NHEJ-mediated multi-gene editing based on a CRISPR sgRNA-tRNA array. We also explored the mechanism of Repsox's effect on the efficiency of NHEJ-mediated gene editing. The results showed that Repsox reduces the expression levels of SMAD2, SMAD3, and SMAD4 in the TGF-β pathway, indicating that Repsox can increase the efficiency of CRISPR NHEJ-mediated gene editing in porcine cells through the TGF-β pathway.