ABSTRACT: Rapid and reliable methods for conducting biological dosimetry are a necessity in the event of a large-scale nuclear event. Timely and accurate methods are thus critical in order to correctly evaluate and identify radiation dose exposure and triage appropriately. Alterations in microRNAs (miRNAs), small non-coding RNAs of 19-22 nucleotides, have been reported in cells/tumors subjected to radiation exposure, implying that miRNAs play an important role in cellular stress response to radiation. To examine the possibility of using microRNA as stable blood based biomarkers for radiation response, we have used microRNA microarray analysis. Differential microRNA expression pattern was evaluated (>1.5 fold and p value <0.05) at 6, 24, 48 h and 7day time points in whole blood from mice exposed to 2, 4, 8, 12 and 15Gy irradiation. More differentially expressed microRNAs (up and down) were seen after higher dose of radiation and later time points. Among the significantly upregulated microRNAs, miR-193b-3p and mir-92a-3p were consistently upregulated for all doses at earlier time points. We observed significant downregulation of several members of the miR-17 family (miR-17-5p, miR-20a-5p, miR-93-5p and miR-106b-5p) in response to radiation from 2 Gy onwards at 24 h, 48 h and at higher doses for the 7 d time-point. Whereas miR-34a, which regulates G1/S cell cycle checkpoint activation in response to radiation induced DNA damage, showed consistent upregulation for both low and high doses at later time points up to one week after exposure. Significant down regulation of miR-150-5p, miR-101, miR-140, miR-29b, miR-193b and miR-30 family of microRNAs were seen for low and high doses of radiation for all time points up to 7day. Low dose radiation (2Gy) exposure also resulted in down regulation of a group of microRNAs after one week; whereas these microRNAs showed upregulation after high dose exposure (8, 12 and 15Gy) up to one week. This dose and time dependent differential microRNA expression pattern might be useful in evaluating radiation response during and after therapeutic radiation treatment in patients. Ultimately, a combined approach of identifying biomarkers by assessing functional miRNA, target mRNAs and the resulting proteins to assess radiation exposure after mass-casualty incidents could provide a valuable tool in developing and implementing effective and timely medical countermeasures.
