Radiation-induced micro-RNA expression changes in peripheral blood cells of radiotherapy patients

Abstract

Purpose: MicroRNAs (miRNAs), a class of noncoding small RNAs that regulate gene expression, are involved in numerous physiologic processes in normal and malignant cells. Our in vivo study measured miRNA and gene expression changes in human blood cells in response to ionizing radiation, to develop miRNA signatures that can be used as biomarkers for radiation exposure.

Methods and materials: Blood from 8 radiotherapy patients in complete remission 1 or 2 was collected immediately before and 4 hours after total body irradiation with 1.25 Gy x-rays. Both miRNA and gene expression changes were measured by means of quantitative polymerase chain reaction and microarray hybridization, respectively. Hierarchic clustering, multidimensional scaling, class prediction, and gene ontology analysis were performed to investigate the potential of miRNAs to serve as radiation biomarkers and to elucidate their likely physiologic roles in the radiation response.

Results: The expression levels of 45 miRNAs were statistically significantly upregulated 4 hours after irradiation with 1.25 Gy x-rays, 27 of them in every patient. Nonirradiated and irradiated samples form separate clusters in hierarchic clustering and multidimensional scaling. Out of 223 differentially expressed genes, 37 were both downregulated and predicted targets of the upregulated miRNAs. Paired and unpaired miRNA-based classifiers that we developed can predict the class membership of a sample with unknown irradiation status, with accuracies of 100% when all 45 upregulated miRNAs are included. Both miRNA control of and gene involvement in biologic processes such as hemopoiesis and the immune response are increased after irradiation, whereas metabolic processes are underrepresented among all differentially expressed genes and the genes controlled by miRNAs.

Conclusions: Exposure to ionizing radiation leads to the upregulation of the expression of a considerable proportion of the human miRNAome of peripheral blood cells. These miRNA expression signatures can be used as biomarkers of radiation exposure.

Conflict of interest statement

Conflict of interest: none.

Copyright © 2011 Elsevier Inc. All rights reserved.

Figures

Fig. 1

Significant changes in miRNA signatures after irradiation. (A) Hierarchic clustering. A heat map shows miRNA expression levels for all samples (columns) and miRNAs (rows). All patient control samples (labels starting with C) form a separate cluster from the samples obtained after radiation therapy (labels starting with R). (B) Multidimensional scaling. Control samples (shown in green) and samples that were collected after total body irradiation (displayed in red) form two separate clusters.

Fig. 2

Regulation of several biologic processes by miRNAs after total body irradiation. Gene ontology analysis of the predicted miRNA target genes revealed the biologic processes in which the predicted target genes significantly responding to radiation are overrepresented (red columns) or underrepresented (blue columns). Processes above the horizontal dashed line show statistically significant over- or underrepresentation at a p value of <0.05.