Space radiation research "Rad Gene" at Kibo-report 2: Exposure to space radiations with low dose; γH2AX positive foci as a track and radio-adaptive response

Abstract

A physiological dosimetry for space radiations was performed with Bio Passive dosimeter for life science experiment in space (PADLES) in ISS for 133 days. For biological dosimetry, we applied two human cultured lymphoblastoid cell lines bearing wild-type p53 gene (wtp53) and mutated p53 gene (mp53) at frozen state. We detected DNA damage induced by space radiations including the high linear energy transfer (LET) particles as a track of γH2AX positive foci in the nuclei. From the frequency of the track of γH2AX, we speculated that total dose equivalent of high LET radiations was calculated to be about 0.7 mSv per day as 200 keV/μm Fe-ions of a relatively high energy component among space radiation species. We also estimated radio-adaptive response in space-flown samples by analysis of cell death, apoptosis, chromosomal aberrations and mutations. We irradiated with X-rays at high doses to space and the ground control samples. We found all of the radio-adaptive responses investigated here only in space-flown wtp53 cells, but not mp53 cells and the ground control cells with wtp53 and mp53 genes. These results suggested that the space-flown cells were exposed to space radiations with the range of 20-100 mSv as a "window" for radio-adaptive response.