Pre-Exposure Gene Expression in Baboons with and without Pancytopenia after Radiation Exposure

Abstract

Radiosensitivity differs in humans and likely among primates. The reasons are not well known. We examined pre-exposure gene expression in baboons (n = 17) who developed haematologic acute radiation syndrome (HARS) without pancytopenia or a more aggravated HARS with pancytopenia after irradiation. We evaluated gene expression in a two stage study design where stage I comprised a whole genome screen for messenger RNAs (mRNA) (microarray) and detection of 667 microRNAs (miRNA) (real-time quantitative polymerase chain reaction (qRT-PCR) platform). Twenty candidate mRNAs and nine miRNAs were selected for validation in stage II (qRT-PCR). None of the mRNA species could be confirmed during the validation step, but six of the nine selected candidate miRNA remained significantly different during validation. In particular, miR-425-5p (receiver operating characteristic = 0.98; p = 0.0003) showed nearly complete discrimination between HARS groups with and without pancytopenia. Target gene searches of miR-425-5p identified new potential mRNAs and associated biological processes linked with radiosensitivity. We found that one miRNA species examined in pre-exposure blood samples was associated with HARS characterized by pancytopenia and identified new target mRNAs that might reflect differences in radiosensitivity of irradiated normal tissue.

Keywords: gene expression; haematologic acute radiation syndrome (HARS); miRNA; pancytopenia; radiosensitivity.

Figure 1

The mean change (±standard error of mean (SEM)) of neutrophils (a), platelets (b) and haemoglobin (c) in the blood cell counts of the baboons is displayed over the time, up to 203 days after irradiation. Black circles indicate the mean values for the animals with pancytopenia. White squares indicate the mean values of the animals without pancytopenia. The grey dashed lines show the thresholds for the definition of a pancytopenia (neutrophils 0.5 × 1000/µL; platelets, 10 × 1000/µL; haemoglobin, 8 g/dL). Measurements per time point range from n = 1 to n = 16.

Figure 2

For graphical presentation of validated genes shown in Table 2, we plotted the mean fold change (FC) of miR-425-5p relative to the mean HARS 0 degree values (H0-values) separately for blood samples taken before irradiation in baboons developing HARS either with (squares) or without pancytopenia (circles). Error bars represent the standard error of the mean (SEM) and the numbers of blood samples examined are given in Table 2. Asterisks refer to p-values < 0.005 (*) or < 0.0005 (**). Mean FCs from the screening and the validation stage using ten and all 17 samples together are shown.

Figure 3

Potential target genes of miR-425-5p that were >two-fold up (shadowed) or downregulated between the HARS groups were grouped according to their coding function using their gene ontology data (The National Center for Biotechnology Information (NCBI) data base). Fold changes are given in parentheses.