Differentiation of Human Induced Pluripotent or Embryonic Stem Cells Decreases the DNA Damage Repair by Homologous Recombination

Abstract

SummaryThe nitric oxide (NO)-cyclic GMP pathway contributes to human stem cell differentiation, but NO free radical production can also damage DNA, necessitating a robust DNA damage response (DDR) to ensure cell survival. How the DDR is affected by differentiation is unclear. Differentiation of stem cells, either inducible pluripotent or embryonic derived, increased residual DNA damage as determined by γ-H2AX and 53BP1 foci, with increased S-phase-specific chromosomal aberration after exposure to DNA-damaging agents, suggesting reduced homologous recombination (HR) repair as supported by the observation of decreased HR-related repair factor foci formation (RAD51 and BRCA1). Differentiated cells also had relatively increased fork stalling and R-loop formation after DNA replication stress. Treatment with NO donor (NOC-18), which causes stem cell differentiation has no effect on double-strand break (DSB) repair by non-homologous end-joining but reduced DSB repair by HR. Present studies suggest that DNA repair by HR is impaired in differentiated cells.

Chromosomal aberration arises during somatic reprogramming to pluripotent stem cells

“…When DSBs are introduced, embryonic stem cells (ESCs) predominantly adopt high delity HRR to repair the lesions rather than NHEJ [24][25][26][27][28].However, when ES cells differentiate into somatic cells, the expression of HRR-related enzymes is down-regulated, whereas the expression of NHEJ-related enzymes, such as DNA Ligase IV, is up-regulated. As a result, DSB repair pathway shifts from HRR to NHEJ [26,29]. Consistently, the expression level of DNA Ligase IV during reprogramming displayed a signi cant downregulation after KMOS mRNAs transfection (Fig.…”

“…6e, f). In contrast, the expression levels of the HRR pathway-related proteins Rad51 and Rad52 increased gradually [29], reaching a peak on day 7 ( Fig. 6g-j).…”

Chondrocytes differentiated from human induced pluripotent stem cells: Response to ionizing radiation

“…Some studies have also shown that, compared with neural SCs, terminally differentiated descendant astrocytes lack functional DDR signaling. Mature astrocytes and dopaminergic neurons exhibit significantly higher residual damage, in comparison with their undifferentiated and neuronal progenitor cells, as demonstrated by the delayed disappearance of γ-H2AX foci 8–12 hr post irradiation [ 28 ].…”

Dimethyl Sulfoxide Prevents Radiation-Induced Oral Mucositis Through Facilitating DNA Double-Strand Break Repair in Epithelial Stem Cells

“…This phenomenon was not observed in DNA repairedeficient xrs5 cells (Ku80-deficient), which indicated that DMSO at a lower concentration facilitated DNA DSB repair rather than suppressing the indirect action of irradiation (26). Recently, several studies reported that adult stem cells, such as cycling crypt base columnar cells, are relatively radioresistant, repairing DNA by homologous recombination significantly more efficiently than transitamplifying progenitors, and DNA damage repair by homologous recombination decreases along with the differentiation of human-induced pluripotent or embryonic stem cells (27)(28)(29). By analyzing phosphorylated H2AX (another marker of DNA DSBs), we found that DMSO treatment on local irradiated mice significantly decreased the average levels of g-H2AX foci in p63-positive lingual epithelial stem cells at 6 hours but not at 2 hours after irradiation.…”