Abstract
Glioblastoma is one of most lethal human tumors because of radioresistance. Recent reports suggested that the reason for the radioresistance of glioblastoma was due to the existence of cancer stem cells that had high ability of DNA repair and DNA damage response. Although neural stem cells and brain cancer stem cells share common features including some stem cell markers, radiation-induced DNA damage response has not been examined in neural stem cells. In the present study, we investigated the repair kinetics of radiation-induced DNA double strand breaks (DSBs) by scoring phosphorylated histone H2AX (ganmma-H2AX) in mouse neural stem cell enriched (CD133 positive) neurosphere cells and the remaining (CD133 negative) neurosphere cells. To enrich neural stem cells, neurosphere cells were stained with phycoerthrin (PE) conjugated anti-CD133 antibodies, and mixed with anti-PE antibodies that were crosslinked to magnetic nanoparticles. Then, CD133 positive cells were enriched by using a magnetic column. The repair kinetics study indicated that the number of gamma-H2AX immediately after 1 Gy of X-irradiation was 31 per cell in mouse embryo fibroblast (MEF) cells whereas 23 per cell in mouse neurosphere cells, showing the significant difference between them. However, the significant difference was not evident between CD133 positive and negative cells. The significantly less focus number per cell was observed in neurosphere cells than in MEF cells until 1 hr after X-irradiation. The difference became small at 3 h and disappeared at 12 h. The present result suggests that the repair ability of DSBs in neurosphere cells is higher than that in MEF cells, implying that the high repair ability in cancer stem cells might be originated from stem cells.
