Nucleosides Rescue Replication-Mediated Genome Instability of Human Pluripotent Stem Cells

Human pluripotent stem cells (PSCs) are subject to the appearance of recurrent genetic variants on prolonged culture. We have now found that, compared with isogenic differentiated cells, PSCs exhibit evidence of considerably more DNA damage during the S phase of the cell cycle, apparently as a consequence of DNA replication stress marked by slower progression of DNA replication, activation of latent origins of replication, and collapse of replication forks. As in many cancers, which, like PSCs, exhibit a shortened G1 phase and DNA replication stress, the resulting DNA damage may underlie the higher incidence of abnormal and abortive mitoses in PSCs, resulting in chromosomal non-dysjunction or cell death. However, we have found that the extent of DNA replication stress, DNA damage, and consequent aberrant mitoses can be substantially reduced by culturing PSCs in the presence of exogenous nucleosides, resulting in improved survival, clonogenicity, and population growth. •Human pluripotent stem cells are susceptible to replication stress•Nucleosides modulate replication stress and DNA damage in human PSCs•Nucleosides alleviate mitotic errors and improve the growth kinetics of human PSCs•These findings provide a means to reduce the incidence of recurrent genetic change Halliwell et al. document the susceptibility of human PSCs to replication stress, which may lead to genetic instability. The results presented show that this phenotype can be moderated by culture in the presence of exogenous nucleosides. The findings provide an approach to reducing the incidence of recurrent genetic changes that may compromise the use of human PSCs in regenerative medicine.