EUROPEAN RADIATION RESEARCH 2012

In vitro and in vivo gene expression studies highlight differential expression profiles of low doses of ionizing radiation when compared to high doses

17 Oct 2012, 16:14

1m

Poster Hall (Vietri sul Mare)

poster preferred Non-Targeted Effects of Radiation Poster Session 2

Speaker

Mr Houssein El Saghire (Faculty of Life Sciences and Medicine, Ghent University AND Radiobiology Unit, Belgian Nuclear Research Centre, Belgium)

Description

DNA microarrays are widely utilized to study cellular responses of complex nature, and when studying ionizing radiation, especially when the interest is low doses, we are faced with the dilemma of technique sensitivity, except for γ-H2AX foci. Previous studies have shown that microarrays are effective in the determination of pathways and genes that can be induced by ionizing radiation. In our study, we examined the global gene expression profiles of whole blood samples before and after exposure to a typically low and high X-irradiation dose (0.05, and 1 Gy), at a rate of 30 mGy/min (250kV, 1.6 mA, 1 mmCu).We investigated the gene expression profiles after 8 hours. Gene Set Enrichment Analysis (GSEA) revealed two distant dose-dependent profiles. In contrast to high doses, we found that a low dose of 0.05 Gy showed higher statistical ranking of immune-related pathways that are mainly involved in response and/or secretion of growth factors, chemokines and cytokines. This response is typically related to bystander effects and tissue response. On the other hand, a domination of classical radiation response was ranked higher at 1 Gy; these include tumor suppressor protein 53, apoptosis, DNA damage and repair. In order to validate our in vitro conclusions we moved to an in vivo study. Blood samples were collected from prostate cancer patients undergoing arc therapy before and 24 hours after the first fraction of radiotherapy. Dosimetric calculations showed that the circulating blood of these patients received a dose in the range 0.03-0.1 Gy. RNA was isolated and DNA microarrays were performed on a total of 7 patients. We found 890 genes that were significantly modulated between controls and irradiated samples (FDR <5%). Pathway enrichment analysis showed the involvement of the significant genes in immune modulation, cytokine secretion, DNA damage, and cell cycle. Some of these genes (XRRC4, BMX, and TNFAIP6) were confirmed using qRT-PCR. GSEA analysis revealed similar pathways as observed in the individual gene list analysis, with more emphasis on the involvement of certain immune related pathways such as toll-like receptors and and MAPK. Both in vitro and in vivo results show that low doses of ionizing radiation can elicit an immune response involving intercellular communication and probably increased radiation-induced damage. This work is supported by the Federal Agency of Nuclear Control (FANC-AFCN, Belgium) and by the Euratom FP7 EPI-CT project.