Characteristics of human CD34+ cells exposed to ionizing radiation under cytokine-free conditions

To clarify the mechanisms underlying radiation-induced hematopoietic stem cell death,we investigated the effects of excessive ionizing radiation on the clonogenic potential of cd34+ cells obtained from human umbilical cord blood under cytokine-free conditions. the cd34+ cells were x-ray-irradiated (up to 2 gy) and were cultured for 0-48 h under cytokine-free conditions. at various time-points,the cd34+ cells were investigated for survival,clonogenic potential and the generation of mitochondrial superoxide. at 12 h after x-ray irradiation,the number of viable cells had decreased to ∼70-80% compared with the 0-h non-irradiated control,whereas the clonogenic potential in the x-ray-irradiated cells had decreased to ∼50%-60% compared with the 0-h non-irradiated control. furthermore,significant generation of mitochondrial superoxide was observed at 6 h,and reached a maximum value between 12 and 24 h after x-ray irradiation. however,no significant differences were observed between nonirradiated and x-ray-irradiated cells in terms of the generation of reactive oxygen species or in the intracellular mitochondrial contents. in addition,a cdna microarray analysis showed that the majority of the altered genes in the cd34+ cells at 6 h after x-ray irradiation were apoptosis-related genes. these results suggest the possibility that the elimination of the clonogenic potentials of cd34+ cells involves the generation of mitochondrial superoxide induced by ionizing radiation. © the author 2015.