Mitochondrial DNA deletion and aging induced by low dose rate of radiation in mice

Mitochondrial DNA (mtDNA) is a closed circular DNA molecule and more than 100 copies are present in a cell. Deletion mutation of mtDNA accumulates with aging and can be a suitable marker for estimating biological effects on radiation-induced mutation in mice. The mice life span study in the Institute for Environmental Sciences suggests that low dose rate of radiation might accelerate aging in mice prolongly irradiated by 137Cs γ-rays (20 mGy/day for 400 days). To know the relationships between low dose rate irradiation, aging and mutation, we observed deletion mutations of mtDNA from mice irradiated by 137Cs γ-rays (20 mGy/day) for different dates. The real-time fluorescence PCR method was sensitive enough to determine the relative amount of deletion in several tissues. Age-dependent accumulations of deletion mutations were observed in aged mice (250-700 days). However, a significant increase of deletion mutation related to accumulated dose was not detected in 137Cs γ-ray irradiated mice for 4-12 Gy. These data suggest that the effect of the low dose rate irradiation on mtDNA is within a background level. (author)