Induction of gene expression as a monitor of exposure to ionizing radiation.

The complex molecular responses to genotoxic stress are mediated by a variety of regulatory pathways. The transcription factor TP53 plays a central role in the cellular response to DNA-damaging agents such as ionizing radiation, but other pathways also play important roles. In addition, differences in radiation quality, such as the exposure to high-LET radiation that occurs during space travel, may influence the pattern of responses. The premise is developed that stress gene responses can be employed as molecular markers for radiation exposure using a combination of informatics and functional genomics approaches. Published studies from our laboratory have already demonstrated such transcriptional responses with doses of gamma rays as low as 2 cGy, and in peripheral blood lymphocytes (PBLs) irradiated ex vivo with doses as low as 20 cGy. We have also found several genes elevated in vivo 24 h after whole-body irradiation of mice with 20 cGy. Such studies should provide insight into the molecular responses to physiologically relevant doses, which cannot necessarily be extrapolated from high-dose studies. In addition, ongoing experiments are identifying large numbers of potential biomarkers using microarray hybridization and various irradiation protocols including expression at different times after exposure to low- and high-LET radiation. Computation-intensive informatics analysis methods are also being developed for management of the complex gene expression profiles resulting from these experiments. With further development of these approaches, it may be feasible to monitor changes in gene expression after low-dose radiation exposure and other physiological stresses that may be encountered during manned space flight, such as the planned mission to Mars.