Gene expression analysis of circulating hematopoietic progenitor cells from irradiated mice and humans provides a molecular profile of radiation injury

Abstract

The risk for terrorist-mediated nuclear or radiological attack has been identified as a major threat to the United States in the coming decade. Radiation exposure can cause a spectrum of hematological toxicities, from mild immunosuppression to myeloablation with concordant life threatening complications. Accurate biological dosimetry will be critical, therefore, for caregivers to triage individuals to the appropriate medical management. Currently, biodosimetric tools include lymphocyte depletion kinetic and cytogenetic analysis, both of which require several days for results to be obtained. We propose that high throughput genomic analysis of peripheral blood mononuclear cells (PB MNCs) can sensitively identify patterns of molecular changes which occur following different levels of radiation exposure. In this study, we collected primary PB MNCs from 10 week old C57Bl6 mice at 6 hours following 4 different levels of radiation exposure: normal (non-irradiated), 50 cGy (trivial exposure), 200 cGy (myelosuppressive) and 1000 cGy (lethal). RNA was extracted and used for synthesis of probes for hybridization to spotted arrays. We performed a binary regression analysis to elucidate patterns of gene expression to distinguish between a normal animal and one that had been exposed to various levels of radiation. Distinct gene expression patterns were evident within PB MNCs at each of the 4 exposure levels, demonstrating the feasibility of this approach. We found that the selected metagene pattern for “normal” was able to distinguish normal from 50 cGy, 200 cGy and 1000 cGy exposure with 100% predictive capacity. The predictors selected for 50 cGy, 200 cGy and 1000 cGy were equally powerful at distinguishing these levels of exposure from all others. These data demonstrate the power of this approach to correctly distinguish clinically relevant levels of radiation exposure. In order to validate these molecular predictors generated in mice as profiles of human radiation response, we are currently testing, in a blinded manner, whether these predictors can distinguish different levels of radiation exposure in human PB samples collected from patients who have undergone 200 cGy or 1000 cGy total body irradiation. These validated biomarkers of radiation response can serve as templates for rapid screening tests for radiation exposure and, more broadly, are potential targets for therapeutic intervention.