OLIGONUCLEOTIDE MICROARRAY ANALYSIS OF LOW-DOSE IONIZING RADIATION EXPOSURE

The manipulation of nuclear resources for medical purposes has a considerable concern in occupational exposure but the health risk due to low-dose ionizing radiation is still debated. Functional genomics approaches provide an opportunity to explore further complex biological processes and may lead to an increased understanding of the pathways that are induced by ionizing irradiation (IR). We used Agilent’s Oligo 60-mer technology to identify genes that are transcriptionally regulated by low-dose IR in occupationally exposed workers. To this purpose, 28 exposed professional were compared with a reference sample of non-exposed people, working at the same place at a large health care facility. The expression profile of their peripheral blood lymphocytes (PBMC) was investigated according to a balanced block design, consisting in the equal distribution of cyanine 5 and cyanine 3 labels within the two classes of exposed and control samples. The raw intensity data derived from Feature Extraction software 7.5 were analysed by MAANOVA (MicroArray ANalysis Of VAriance) data analysis package of R programming environments and we carried out hypothesis testing using F statistics computed on the James-Stein shrinkage estimates of the error variance. By this approach, we identified 270 genes which were correlated to occupational low-dose IR exposure, including chromatin assembly genes as well as genes involved in apoptosis, DNA repair and response to stress. Since exposed individuals were recruited from two distinct departments and showed different ranges of accumulated doses, we furthermore performed a MAANOVA analysis to determine the differentially expressed genes discriminating between these two divisions. In this case, a list of 284 genes was obtained and the use of agglomerative hierarchical clustering with Ward’s linkage partly confirmed the homogeneity of the two sets of exposed individuals. Some of the genes, that were found to be differentially expressed between the workers of the two departments, were under the direct control of p53, such as p21-Waf1, ATF3 or TNFRSF10B. Moreover, beside chromatin assembly,which was strongly affected, many regulated genes were specifically involved in mRNA processing and protein biosynthesis, as well. In conclusion, we assessed the expression profile of peripheral blood lymphocytes from radio-exposed workers and identified a 270-gene set, referred to the whole sample of 28 exposed individuals, and an additional list of 284 genes that potentially serve as a signature for workers showing different cumulative doses. We aimed at providing further insight into the transcriptional fingerprint of low-dose IR in humans in order to improve the classical methods to estimate IR exposure and add information to the current models of the risk assessment for chronic low-dose exposure.