Comprehensive analysis of time- and dose-dependent patterns of gene expression in a human mesenchymal stem cell line exposed to low-dose ionizing radiation

Abstract

Abstract.We focused on the transcriptional responses induced by low and very low doses of ionizing radiation with time effect. Regardless of their importance only a few limited studies have been done. Here we applied a large-scale gene transcript profile to elucidate the genes and biological pathways. Immortalized human mesenchymal stem cells were irradiated with 0.01, 0.05, 0.2 and 1 Gy of gamma radiation and total RNA was extracted from each cell line at 1, 4, 12 and 48 h after exposure. The essential transcriptional responses were identified according to dose and time. A total of 6,016 genes showed altered expression patterns at more than one time point or dose level among the investigated 10,800 genes. Genes that showed dose-dependent expression responses were involved in signal transduction, regulation of transcription, proteolysis, peptidolysis and metabolism. Those that showed time-dependent responses were divided into two distinct groups: the up-and-down group was associated with 'cellular defense mechanisms' such as apoptosis, cell adhesion, stress response and immune response and the down-and-up group with 'fundamental cellular processes' such as DNA replication, mitosis, RNA splicing, DNA repair and translation initiation. Genes showing both dose-and time-dependent responses exhibited a mixture of both features. A highly non-linear relationship between the IR dose and the transcriptional relative response was obtained from the dose-dependent group. The timedependent group also exhibited a non-linear relationship as the complex effect group did. Some of the early-reactive-phase (1-4 h) genes showed a differential expression response to 0.01, 0.05 and 0.2 Gy but were unresponsive to 1 Gy. Some of the late-recovery-phase (12-48 h) genes showed a differential expression to 1 Gy but were relatively unresponsive to other doses. We further characterized the gene expression patterns that could be implicated in the molecular mechanism of the cellular responses to low and very low-dose irradiation.

Low dose radiation response curves, networks and pathways in human lymphoblastoid cells exposed from 1 to 10cGy of acute gamma radiation

“…Our finding of significant transcript modulation changes induced by 10 cGy is consistent with prior findings [14,[33][34][35][36][37]53]. Also consistent with our findings, Jin and colleagues [38] reported non-linear transcription responses after low dose exposures. Non-linear dose-response relationships have previously been reported at higher doses for non-genomic endpoints, such as chromosome aberrations [57] and cell killing [58] after exposures to low-LET radiation, and more recently in a more limited study of low dose effects on transcript levels [35,37].…”

“…We compared our radiation-responsive genes (Table1 and Table S1) with findings of other low-dose transcript studies [13,15,[33][34][35][36][37][38][39]41]. Using our 81-gene set, elevated GGH transcript was in common with the mouse brain findings [19], TNFRSF6 with ML-1 cells [13], SCAMP1 with keratinocytes [34] and RPL5 with HUVE cells [36].…”

“…Long et al [37] examined the early X-ray radiation response of human lymphoblastoid AHH-1 cells and reported the induction of genes associated with signal transduction pathways at 4 hours after 5 cGy exposures. Jin et al [38] did a more extensive study in B10 stem cells where they reported distinct clusters in the early response category (1-4 hr) that exhibited dose-, time-, and dose-time dependent responses after 10-50 cGy of gamma radiation. Our lymphoblastoid cell study supports their conclusions that the global transcription response to low doses of gamma radiation appears to follow a nonlinear threshold response that involves multiple genes.…”

“…Transcriptional profiling is a sensitive biomarker of radiation exposure and has been used to gain insight into the molecular mechanisms induced by low dose exposures in a variety of cell types: cell cultures of human myeloid cells [14,33], keratinocytes [34], lymphocytes [35], umbilical vein endothelial cells [36], lymphoblastoid cells [37], and mesenchymal stem cells [38]. Only a few studies investigated transcript profiles after in vivo low-dose exposures.…”

Response to low-dose X-irradiation is p53-dependent in a papillary thyroid carcinoma model system

“…However, they did show that the detection of γ-H2AX foci is possible even at such low doses, thus making it a suitable method for the study of the biological effects of low doses of radiation. Furthermore, another study on the effects of low and very low doses of radiation on a human mesenchymal cell line at different time-points supports a non-linear model at low doses (5). Currently, low doses of radiation are commonly defined as anything between background radiation [~0.01 millisievert (mSv)/day] and high doses of radiation (≥150 mSv/day) (6).…”