Total Body Irradiation Causes Residual Bone Marrow Injury by Induction of Persistent Oxidative Stress in Murine Hematopoietic Stem Cells.

Abstract 3209

Poster Board III-146

Ionizing radiation (IR) and/or chemotherapy cause not only acute tissue injury but also have late effects including long-term bone marrow (BM) suppression. The induction of residual BM injury is primarily attributable to induction of hematopoietic stem cell (HSC) senescence. However, neither the molecular mechanisms by which IR and/or chemotherapy induce HSC senescence have been clearly defined, nor has an effective treatment been developed to ameliorate the injury, which were investigated in the present study using a total body irradiation (TBI) mouse model. The results showed that exposure of mice to 6.5 Gy TBI induced a persistent increase in reactive oxygen species (ROS) production in HSCs only for up to 8 weeks, primarily via up-regulation of NADPH oxidase 4 (NOX4). This finding provides the foremost direct evidence demonstrating that in vivo exposure to IR causes persistent oxidative stress selectively in a specific population of BM hematopoietic cells (HSCs). The induction of chronic oxidative stress in HSCs was associated with sustained increases in oxidative DNA damage, DNA double strand breaks, inhibition of HSC clonogenic function, and induction of HSC senescence but not apoptosis. Treatment of the irradiated mice with N-acetyl-cysteine (NAC) after TBI significantly attenuated IR-induced inhibition of HSC clonogenic function and reduction of HSC long-term engraftment after transplantation. These findings suggest that selective induction of chronic oxidative stress in HSCs by TBI leads to induction of HSC senescence and residual BM injury and that antioxidant therapy may be used as an effective strategy to mitigate IR- and chemotherapy-induced residual BM injury.