TERF1 and TERF2 downregulate telomere length in cognitive deficit at the late period after low-dose exposure. / Negatyvna reguljacija dovzhyny telomer genamy TERF1 ta TERF2 pry kognityvnomu deficyti u viddalenomu periodi pislja oprominennja u malyh dozah.

Purpose - to explore the role of radiation dose on gene regulation of telomere length and its influence on the patho-genesis of cerebrovascular neurocognitive deficit at the remote period of low-dose irradiation as a result of the Chornobyl accident. Materials and methods. We performed a study of TERF1, TERF2 and TERT genes expression (GE) by RT-PCR, and relative telomere length (RTL) by flow-FISH in 258 clean-up workers of Chornobyl accident divided by radiation dose groups (range 22-2800 mSv) and 78 controls with vascular cognitive deficit. Detailed psychometric interviews were performed to obtain quantitative data on the stage of cognitive deficit. Results. Statistically significant telomere shortening was demonstrated in groups of clean-up workers with radiation doses in 100-250 mSv and 250-500 mSv range (subsequently M ± SD: 15.85 ± 0.27; p< 0.02; 15.89 ± 0,33; p< 0.02; control: 17.21 ± 0,23). A decrease in RTL was in parallel to radiation dose increase and overexpression of negative telomere length regulators: TERF2 genes and, to a lesser extent TERF1; the opposite tendency was demonstrated for TERT GE. In exposed over 500 mSv a significant TERT overexpression was combined with decreased TERF1 and TERF2 GE, and absence of significant RTL changes in comparison with clean-up workers exposed to lower doses indicating a certain independency between gene expression and telomere length changes and possible threshold effects at this dose range. Analysis of the group of exposed in comparison with non-exposed demonstrated a significant decrease (p = 0.03) both of the mean MMSE and RTL parameters suggesting influence of previous exposure. Conclusion. This study shows parallel changes in decline of cognitive function and telomere length and differences in TERF2, TERT and TERF1 gene regulation at the late period after low dose and over 500 mSv exposure.

Joint research towards a better radiation protection-highlights of the Fifth MELODI Workshop.

MELODI is the European platform dedicated to low-dose radiation risk research. From 7 October through 10 October 2013 the Fifth MELODI Workshop took place in Brussels, Belgium. The workshop offered the opportunity to 221 unique participants originating from 22 countries worldwide to update their knowledge and discuss radiation research issues through 118 oral and 44 poster presentations. In addition, the MELODI 2013 workshop was reaching out to the broader radiation protection community, rather than only the low-dose community, with contributions from the fields of radioecology, emergency and recovery preparedness, and dosimetry. In this review, we summarise the major scientific conclusions of the workshop, which are important to keep the MELODI strategic research agenda up-to-date and which will serve to establish a joint radiation protection research roadmap for the future.

Transgenerational developmental effects and genomic instability after X-irradiation of preimplantation embryos: studies on two mouse strains.

Recent results have shown that irradiation of a single cell, the zygote or 1-cell embryo of various mouse strains, could lead to congenital anomalies in the fetuses. In the Heiligenberger strain, a link between the radiation-induced congenital anomalies and the development of a genomic instability was also suggested. Moreover, further studies showed that in that strain, both congenital anomalies and genomic instability could be transmitted to the next generation. The aim of the experiments described in this paper was to investigate whether such non-targeted transgenerational effects could also be observed in two other radiosensitive mouse strains (CF1 and ICR), using lower radiation doses. Irradiation of the CF1 and ICR female zygotes with 0.2 or 0.4Gy did not result in a decrease of their fertility after birth, when they had reached sexual maturity. Moreover, females of both strains that had been X-irradiated with 0.2Gy exhibited higher rates of pregnancy, less resorptions and more living fetuses. Additionally, the mean weight of living fetuses in these groups had significantly increased. Exencephaly and dwarfism were observed in CF1 fetuses issued from control and X-irradiated females. In the control group of that strain, polydactyly and limb deformity were also found. The yields of abnormal fetuses did not differ significantly between the control and X-irradiated groups. Polydactyly, exencephaly and dwarfism were observed in fetuses issued from ICR control females. In addition to these anomalies, gastroschisis, curly tail and open eye were observed at low frequencies in ICR fetuses issued from X-irradiated females. Again, the frequencies of abnormal fetuses found in the different groups did not differ significantly. In both CF1 and ICR mouse strains, irradiation of female zygotes did not result in the development of a genomic instability in the next generation embryos. Overall, our results suggest that, at the moderate doses used, developmental defects observed after X-irradiation of female zygotes of these two sensitive mouse strains should not be transmitted to the next generation. Paradoxically, other studies would be needed to address the question of a potential increase of fertility after doses lower than 0.2Gy in both strains.

The role of Trp53 in the transcriptional response to ionizing radiation in the developing brain.

Brain formation results from a series of well-timed consecutive waves of cellular proliferation, migration and differentiation. Acute irradiation during pregnancy selectively interferes with these events to result in malformations such as microcephaly, reduced cortical thickness and mental retardation. In the present study we performed a straight-through cDNA-microarray analysis of the developing mouse brain at embryonic day E13, 3 h after in utero exposure to 50 cGy X-radiation. This dataset was used as an indication of genes involved in different pathways that are activated upon early radiation exposure, and for further evaluation using quantitative PCR (qPCR). Microarray and qPCR data revealed that the main activated pathways in irradiated wild-type embryos are involved in the regulation of a p53-mediated pathway that may lead to cell cycle delay/arrest and increased levels of apoptosis. To define whether the transcriptional radiation response was solely p53 mediated, we analysed the expression of cell cycle regulating genes in a Trp53 null mutant. The modulated expression of cell cycle regulating genes such as cyclins and Cdk genes indicated the induction of a cell cycle arrest, without evidence for the onset of apoptosis. Additional gene-expression studies have shown that various E2F transcription factors may be involved in this event. Together, these results provide a detailed view of the different p53-related mechanisms that are triggered in response to ionizing radiation in the developing brain.

Transcriptional response to ionizing radiation in lymphocyte subsets.

Human lymphocyte subpopulations differ in their cellular responses to ionizing radiation. To shed light on the molecular basis of this effect, we characterized the transcriptional response to 1 Gy X-rays of CD4+ T lymphocytes. Of 18,433 genes tested, 102 were modulated more than 1.5-fold. The majority of the strongly activated genes were p53 targets involved in DNA repair and apoptosis. The expression of three of these genes was further tested by quantitative RT-PCR in lymphocyte subpopulations [CD4+ and CD8+ T, CD19+ B, CD56+ natural killer cells and peripheral blood lymphocytes (PBLs)] from ten adult donors. In contrast to DDB2, TNFRSF10B and BAX were differentially modulated among the subpopulations and the PBLs, being more activated in irradiated CD19+ B and CD8+ T lymphocytes. The level of BAX activation in the various subpopulations correlated with the sensitivity of the cells to radiation, suggesting its possible role in the differential radiosensitivity of hematopoietic cell subsets.

Effect of ionizing radiation on gene expression in CD4+ T lymphocytes and in Jurkat cells: unraveling novel pathways in radiation response.

To better understand at the molecular level the effect of ionizing radiation in leukocytes, the global transcriptional response to X-ray irradiation was studied in human CD4+ T lymphocytes and in Jurkat cells. Microarray analysis performed on freshly isolated human CD4+ lymphocytes 8 h after an LD50 irradiation dose of 1 Gy revealed that out of 13,825 genes, 1084 were modulated more than 1.5-fold. The most strongly up-regulated genes were predominantly p53 targets. In contrast, exposure of the CD4+ T lymphocyte-derived Jurkat leukemic cell line (with no functional p53 gene) to an equivalent LD50 dose (0.5 Gy) induced a partly different and more limited set of genes. Interestingly, this set of genes belonged to the Rho and cytokine signaling pathways regulated by low-dose ionizing radiation.

Molecular aspects of individual radiosensitivity.

Radiation therapy is a clinical treatment modality where ionizing radiation is used to treat patients with malignant neoplasms. The goal is to deliver a measured dose of radiation to a defined volume with minimal damage to surrounding normal tissue, resulting in eradication of the tumor. Radiotherapy is generally given in divided doses or fractionated. Molecular biology methods have enhanced our ability to investigate the response of cells to ionizing radiation. These methods can be applied to tissue-culture systems or to biopsies from patients both to develop a quick and easy way to predict the radiosensitivity of a patient and to understand how cells respond to stress produced by ionizing radiation. In this review we will mainly explain two major mechanisms involved in human individual radiosensitivity: the DNA-damage repair defect mechanism and the DNA-repair signaling via cell cycle checkpoint defect.

Gene expression induced by X-ray irradiation in human blood cell lines.

The response to X-ray irradiation of three different human hematopoietic cell lines originating from T (Jurkat), B (Raji), and promyelocytic (HL60) leukemia was analyzed. The survival after irradiation differed among the three cell lines, with Jurkat cells being the most vulnerable and HL60 being the least sensitive. The profile of gene expression was studied with the microarray technique in both Jurkat and HL60 cell lines. Out of the 13,800 different genes spotted on microarrays, very few genes (<0.5%) appeared to be induced more than 2-fold or repressed more than 2.5-fold in both cell lines.