Mitochondrial involvement in the radiation response of human hematopoietic stem cells

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  • ヒト造血幹細胞の放射線応答におけるミトコンドリアの関与

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Abstract

[Introduction] Hematopoietic stem cells (HSCs) have high radiation sensitivity because of their high proliferative potential. In addition, stem cells have relatively lower intracellular mitochondrial content, which is the source of reactive oxygen species (ROS) and plays a crucial role in cell death through apoptosis, than mature cells. However, the relationship between radiosensitivity of HSCs and mitochondrial function has not been reported. We evaluated the ROS production and mitochondrial function after exposing CD34 positive cells derived from human placental/umbilical cord blood to radiation. <BR>[Materials and Methods] The CD34 positive cells were purified using a magnetic cell sorting kit and frozen at -150°C until the experiment. The thawed cells suspended in serum-free medium were exposed to X-irradiation. These cells were incubated at 37°C under 5% CO2 for 0-7 days with or without cytokines (G-CSF, GM-CSF, IL-3, SCF, and EPO). Harvested cells were assayed for the progenitors by using methylcellulose culture stimulated with the same cytokines. Intercellular ROS, mitochondrial superoxide, and mitochondrial contents were analyzed using CM-H2DCFDA, MitoSOX Red, and MitoTracker, respectively, by flow cytometry.<BR>[Results and Discussion] There was an approximately 20% reduction in the number of generated living cells and progenitors in the culture of 4-Gy X-irradiated cells for 3 and 7 days with cytokine as compared to non-irradiated cells. However, irradiated cells showed a similar increase in mitochondrial level as non-irradiated cells. There was a 4-fold increase in the intracellular ROS production peak on day 3, but no significant difference in mitochondrial superoxide level was observed. Our findings suggest that radiation-induced intercellular ROS causes serious damage to HSCs; however, mitochondrial involvement may be low.

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