Gene expression profiles of normal human fibroblasts after exposure to ionizing radiation: a comparative study of low and high doses

Differential biological effect of low doses of ionizing radiation depending on the radiosensitivity in a cell line model

PURPOSE

Exposure to low doses (LD) of ionizing radiation (IR), such as the ones employed in computed tomography (CT) examination, can be associated with cancer risk. However, cancer development could depend on individual radiosensitivity. In the present study, we evaluated the differences in the response to a CT-scan radiation dose of 20 mGy in two lymphoblastoid cell lines with different radiosensitivity.

MATERIALS AND METHODS

Several parameters were studied: gene expression, DNA damage, and its repair, as well as cell viability, proliferation, and death. Results were compared with those after a medium dose of 500 mGy.

RESULTS

After 20 mGy of IR, the radiosensitive (RS) cell line showed an increase in DNA damage, and higher cell proliferation and apoptosis, whereas the radioresistant (RR) cell line was insensitive to this LD. Interestingly, the RR cell line showed a higher expression of an antioxidant gene, which could be used by the cells as a protective mechanism. After a dose of 500 mGy, both cell lines were affected by IR but with significant differences. The RS cells presented an increase in DNA damage and apoptosis, but a decrease in cell proliferation and cell viability, as well as less antioxidant response.

CONCLUSIONS

A differential biological effect was observed between two cell lines with different radiosensitivity, and these differences are especially interesting after a CT scan dose. If this is confirmed by further studies, one could think that individuals with radiosensitivity-related genetic variants may be more vulnerable to long-term effects of IR, potentially increasing cancer risk after LD exposure.

Radiation Research Society Journal-based Historical Review of the Use of Biomarkers for Radiation Dose and Injury Assessment: Acute Health Effects Predictions

A multiple-parameter based approach using radiation-induced clinical signs and symptoms, hematology changes, cytogenetic chromosomal aberrations, and molecular biomarkers changes after radiation exposure is used for biodosimetry-based dose assessment. In the current article, relevant milestones from Radiation Research are documented that forms the basis of the current consensus approach for diagnostics after radiation exposure. For example, in 1962 the use of cytogenetic chromosomal aberration using the lymphocyte metaphase spread dicentric assay for biodosimetry applications was first published in Radiation Research. This assay is now complimented using other cytogenetic chromosomal aberration assays (i.e., chromosomal translocations, cytokinesis-blocked micronuclei, premature chromosome condensation, γ-H2AX foci, etc.). Changes in blood cell counts represent an early-phase biomarker for radiation exposures. Molecular biomarker changes have evolved to include panels of organ-specific plasma proteomic and blood-based gene expression biomarkers for radiation dose assessment. Maturation of these assays are shown by efforts for automated processing and scoring, development of point-of-care diagnostics devices, service laboratories inter-comparison exercises, and applications for dose and injury assessments in radiation accidents. An alternative and complementary approach has been advocated with the focus to de-emphasize "dose" and instead focus on predicting acute or delayed health effects. The same biomarkers used for dose estimation (e.g., lymphocyte counts) can be used to directly predict the later developing severity degree of acute health effects without performing dose estimation as an additional or intermediate step. This review illustrates contributing steps toward these developments published in Radiation Research.

Short- and long-term effects of radiation exposure at low dose and low dose rate in normal human VH10 fibroblasts

Introduction

Experimental studies complement epidemiological data on the biological effects of low doses and dose rates of ionizing radiation and help in determining the dose and dose rate effectiveness factor.

Methods

Human VH10 skin fibroblasts exposed to 25, 50, and 100 mGy of 137Cs gamma radiation at 1.6, 8, 12 mGy/h, and at a high dose rate of 23.4 Gy/h, were analyzed for radiation-induced short- and long-term effects. Two sample cohorts, i.e., discovery (n = 30) and validation (n = 12), were subjected to RNA sequencing. The pool of the results from those six experiments with shared conditions (1.6 mGy/h; 24 h), together with an earlier time point (0 h), constituted a third cohort (n = 12).

Results

The 100 mGy-exposed cells at all abovementioned dose rates, harvested at 0/24 h and 21 days after exposure, showed no strong gene expression changes. DMXL2, involved in the regulation of the NOTCH signaling pathway, presented a consistent upregulation among both the discovery and validation cohorts, and was validated by qPCR. Gene set enrichment analysis revealed that the NOTCH pathway was upregulated in the pooled cohort (p = 0.76, normalized enrichment score (NES) = 0.86). Apart from upregulated apical junction and downregulated DNA repair, few pathways were consistently changed across exposed cohorts. Concurringly, cell viability assays, performed 1, 3, and 6 days post irradiation, and colony forming assay, seeded just after exposure, did not reveal any statistically significant early effects on cell growth or survival patterns. Tendencies of increased viability (day 6) and reduced colony size (day 21) were observed at 12 mGy/h and 23.4 Gy/min. Furthermore, no long-term changes were observed in cell growth curves generated up to 70 days after exposure.

Discussion

In conclusion, low doses of gamma radiation given at low dose rates had no strong cytotoxic effects on radioresistant VH10 cells.

Evaluation of the relationship between γ-H2AX biomarker levels and dose received after radiation exposure in abdominal-pelvic and chest CT scans

Background

As one of the most informative diagnostic radiation instruments, computed tomography (CT) has seen considerable improvement since its implementation in the 1970s; however, the possibility of low-dose radiation risk after CT procedures is still challenging and little is known about the biological effects of CT exposure on patients. As a result, this research aimed to look at the biological and cytogenetic effects of low-dose abdominal-pelvic and chest CT scans on adults, focusing on the number of γ-H2AX foci formation.

Materials and Methods

Blood tests were taken before and 10 min after CT exams on patients aged 25-55 who were undergoing abdominal-pelvic and chest CT exams with very low-ionizing radiation exposure (TLD doses of 15.67-63.45 mGy). Blood lymphocytes that had been isolated, fixed, and stained were dyed with γ-H2AX antibodies. Finally, the percentage of phosphorylation of histone H2AX as an indicator of double-strand breaks was determined using a cytometry technique.

Results

Our findings showed that after CT examination, the mean value of γ-H2AX foci in patients increased (P < 0.0001). A statistically significant correlation between dose radiation and the number of γ-H2AX foci was also found (P = 0.047, r = 0.4731). The current study also found a pattern of elevated γ-H2AX foci in patients over 40 years of age relative to younger patients.

Conclusion

A Significant activation of γ-H2AX foci was found in lymphocytes of peripheral blood samples of patients after CT compared to before CT scan. This increase in γ-H2AX foci levels in blood cells may be a useful quantitative biomarker of low-level radiation exposure in humans.

Candidate Gene Expression in Regional Population and Its Relevance for Radiation Triage

Quantification of gene expression signatures has been substantiated as a potential and rapid marker for radiation triage and biodosimetry during nuclear emergencies. Similar to the established biodosimetry assays, the gene expression assay has drawbacks such as being highly dynamic and transient, not specific to ionizing radiation, and also influenced by confounding factors such as gender, health status, lifestyle, and inflammation. In view of that, prior knowledge of baseline expression of certain candidate genes in a population could complement the discrimination of the unexposed from the exposed individuals without the need for individual pre-exposure controls. We intended to establish a baseline expression of reported radiation-responsive genes such as CDKN1A, DDB2, FDXR, and PCNA in the blood samples of healthy human participants and then compare it with diabetic/hypertension participants (as a chronic inflammatory condition) drawn from south Indian population. Further, we have examined the appropriateness of the assay for radiation triage-like situations; i.e., the expression profiles of those genes were examined in the participants who underwent X-ray-based medical imaging. Acute inflammation induced by lipopolysaccharide exposure in the blood significantly increased the fold expression of those genes (p < 0.0001) compared to the control. Whereas the basal expression level of those genes among the participants with the inflammatory condition is marginally higher than those observed in the healthy participants; despite the excess, the fold increase in those genes between the groups did not differ significantly. Consistent with the inflammatory participants, the basal expression level of those genes in the blood sample of participants who received X-radiation during neuro-interventional and computed tomography imaging is marginally higher than those observed in the pre-exposure of respective groups. Nevertheless, the fold increase in those genes did not differ significantly as the fold change fell within the two folds. Thus, overall results suggest that the utility of CDKN1A, DDB2, FDXR, and PCNA gene expression for radiation triage specific after very low-dose radiation exposure needs to be interpreted with caution for a much more reliable triage.

Radiation-response in primary fibroblasts of long-term survivors of childhood cancer with and without second primary neoplasms: the KiKme study

Background

The etiology and most risk factors for a sporadic first primary neoplasm in childhood or subsequent second primary neoplasms are still unknown. One established causal factor for therapy-associated second primary neoplasms is the exposure to ionizing radiation during radiation therapy as a mainstay of cancer treatment. Second primary neoplasms occur in 8% of all cancer survivors within 30 years after the first diagnosis in Germany, but the underlying factors for intrinsic susceptibilities have not yet been clarified. Thus, the purpose of this nested case–control study was the investigation and comparison of gene expression and affected pathways in primary fibroblasts of childhood cancer survivors with a first primary neoplasm only or with at least one subsequent second primary neoplasm, and controls without neoplasms after exposure to a low and a high dose of ionizing radiation.

Methods

Primary fibroblasts were obtained from skin biopsies from 52 adult donors with a first primary neoplasm in childhood (N1), 52 with at least one additional primary neoplasm (N2+), as well as 52 without cancer (N0) from the KiKme study. Cultured fibroblasts were exposed to a high [2 Gray (Gy)] and a low dose (0.05 Gy) of X-rays. Messenger ribonucleic acid was extracted 4 h after exposure and Illumina-sequenced. Differentially expressed genes (DEGs) were computed using limma for R, selected at a false discovery rate level of 0.05, and further analyzed for pathway enrichment (right-tailed Fisher’s Exact Test) and (in-) activation (z ≥|2|) using Ingenuity Pathway Analysis.

Results

After 0.05 Gy, least DEGs were found in N0 (n = 236), compared to N1 (n = 653) and N2+ (n = 694). The top DEGs with regard to the adjusted p-value were upregulated in fibroblasts across all donor groups (SESN1, MDM2, CDKN1A, TIGAR, BTG2, BLOC1S2, PPM1D, PHLDB3, FBXO22, AEN, TRIAP1, and POLH). Here, we observed activation of p53 Signaling in N0 and to a lesser extent in N1, but not in N2+. Only in N0, DNA (excision-) repair (involved genes: CDKN1A, PPM1D, and DDB2) was predicted to be a downstream function, while molecular networks in N2+ were associated with cancer, as well as injury and abnormalities (among others, downregulation of MSH6, CCNE2, and CHUK). After 2 Gy, the number of DEGs was similar in fibroblasts of all donor groups and genes with the highest absolute log₂ fold-change were upregulated throughout (CDKN1A, TIGAR, HSPA4L, MDM2, BLOC1SD2, PPM1D, SESN1, BTG2, FBXO22, PCNA, and TRIAP1). Here, the p53 Signaling-Pathway was activated in fibroblasts of all donor groups. The Mitotic Roles of Polo Like Kinase-Pathway was inactivated in N1 and N2+. Molecular Mechanisms of Cancer were affected in fibroblasts of all donor groups. P53 was predicted to be an upstream regulator in fibroblasts of all donor groups and E2F1 in N1 and N2+. Results of the downstream analysis were senescence in N0 and N2+, transformation of cells in N0, and no significant effects in N1. Seven genes were differentially expressed in reaction to 2 Gy dependent on the donor group (LINC00601, COBLL1, SESN2, BIN3, TNFRSF10A, EEF1AKNMT, and BTG2).

Conclusion

Our results show dose-dependent differences in the radiation response between N1/N2+ and N0. While mechanisms against genotoxic stress were activated to the same extent after a high dose in all groups, the radiation response was impaired after a low dose in N1/N2+, suggesting an increased risk for adverse effects including carcinogenesis, particularly in N2+.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00520-6.

The radiation adaptive response and priming dose influence: the quantification of the Raper-Yonezawa effect and its three-parameter model for postradiation DNA lesions and mutations

The priming dose effect, called also the Raper-Yonezawa effect or simply the Yonezawa effect, is a special case of the radiation adaptive response phenomenon (radioadaptation), which refers to: (a) faster repair of direct DNA lesions (damage), and (b) DNA mutation frequency reduction after irradiation, by applying a small priming (conditioning) dose prior to the high detrimental (challenging) one. This effect is observed in many (but not all) radiobiological experiments which present the reduction of lesion, mutation or even mortality frequency of the irradiated cells or species. Additionally, the multi-parameter model created by Dr. Yonezawa and collaborators tried to explain it theoretically based on experimental data on the mortality of mice with chronic internal irradiation. The presented paper proposes a new theoretical approach to understanding and explaining the priming dose effect: it starts from the radiation adaptive response theory and moves to the three-parameter model, separately for two previously mentioned situations: creation of fast (lesions) and delayed damage (mutations). The proposed biophysical model was applied to experimental data-lesions in human lymphocytes and chromosomal inversions in mice-and was shown to be able to predict the Yonezawa effect for future investigations. It was also found that the strongest radioadaptation is correlated with the weakest cellular radiosensitivity. Additional discussions were focussed on more general situations where many small priming doses are used.

Radiation-induced DNA damage and altered expression of p21, cyclin D1 and Mre11 genes in human fibroblast cell lines with different radiosensitivity

PURPOSE

Radiotherapy plays a pivotal role in the treatment of cancer. One of the main challenges in this treatment modality is radiation-induced complications in some patients affected by high radiosensitivity (RS). The differences in RS are determined mainly by genetic factors. Therefore, identifying the genes and mechanisms that affect RS in different cells is essential for evaluating radiotherapy outcomes. In the present study, the ability to repair DNA double-stranded breaks (DSB) is evaluated, followed by examining the expression levels of CDKN1A (p21), cyclinD1, and Mre11 genes in human fibroblasts with different RSs.

MATERIALS & METHODS

Cellular RS was measured by survival fraction at 2 Gy (SF2). The γ-H2AX assay was used for assessing DNA repair capacity. Eventually, gene expression levels from each cell line 4 and 24 h after irradiation (at 2, 4, and 8 Gy) were measured by real-time PCR.

RESULTS

The SF2 values for the cell lines ranged from 0.286 to 0.641, and RS differences of fibroblast cells were identified. Among the studied genes, the expression of Mre11 was the most important. Analysis of the real-time PCR data showed that changes in Mre11 gene expression (4 h after 8 Gy irradiation) were directly correlated with the RS (R² = 0.905). The difference in the expression of the p21 gene (4 h after 4 Gy irradiation) was also promising. Finally, the flow cytometry analysis showed that the radioresistant cell lines quickly repaired DBS damages. However, the repair process was slow in the radiosensitive cell line, and the residual damage is significantly higher than other cell lines (P < 0.01).

CONCLUSIONS

This study indicates that changes in the expression of p21 and Mre11 genes play an important role in cell response to radiation and thus these genes can be introduced as biomarkers to predict RS in normal cell lines.

Single nucleotide polymorphism and expression of genes for immune competent cell proliferation and differentiation in radiation-exposed individuals

It is known that ionizing radiation influences the expression of the genes that play a key role in the mechanisms of maintaining the stability of cellular homeostasis. As a rule, changes in the transcriptome of an exposed cell occur within the first 24 hours following radiation exposure. And it predetermines early response in the case of genome damage. Later on modulations in gene transcription activity are also possible and could result in a carcinogenic effect. However, in order to find the role of exogenous factors (ionizing radiation), it is also necessary to take into account the contribution of endogenous factors that are able to modify gene transcription activity. This is especially important for long after the onset of radiation exposure. Single nucleotide polymorphisms located in regulatory regions of the genes may belong to this group of factors. The objective of the current study was to analyze the influence of ionizing radiation on the transcription activity of the STAT3, GATA3, NFkB1, PADI4 genes, which regulate proliferation and differentiation of immune competent human cells; and to assess the potential influence of single nucleotide polymorphisms located in regulatory regions of the genes on the amount of mRNA. The study involved people who had been chronically exposed due to releases of radioactive waste into the Techa River. It was observed that 60 years after the onset of radiation exposure changes in the transcription activity of the NFkB1 and PADI4 genes were registered in people with cumulative doses to RBM within the range 78–3510 mGy. In people who had been chronically exposed, the effect of allelic variations in rs1053023, rs4143094, rs28362491, rs874881 on the level of mRNAs of the STAT3, GATA3, PADI4, NFkB1 genes has not been established.

Gene Expression Profiles Reveal Extracellular Matrix and Inflammatory Signaling in Radiation-Induced Premature Differentiation of Human Fibroblast in vitro

Purpose

Fibroblasts are considered to play a major role in the development of fibrotic reaction after radiotherapy and premature radiation-induced differentiation has been proposed as a cellular basis. The purpose was to relate gene expression profiles to radiation-induced phenotypic changes of human skin fibroblasts relevant for radiogenic fibrosis.

Materials and Methods

Exponentially growing or confluent human skin fibroblast strains were irradiated in vitro with 1–3 fractions of 4 Gy X-rays. The differentiated phenotype was detected by cytomorphological scoring and immunofluorescence microscopy. Microarray analysis was performed on Human Genome U133 plus2.0 microarrays (Affymetrix) with JMP Genomics software, and pathway analysis with Reactome R-package. The expression levels and kinetics of selected genes were validated with quantitative real-time PCR (qPCR) and Western blotting.

Results

Irradiation of exponentially growing fibroblast with 1 × 4 Gy resulted in phenotypic differentiation over a 5-day period. This was accompanied by downregulation of cell cycle-related genes and upregulation of collagen and other extracellular matrix (ECM)-related genes. Pathway analysis confirmed inactivation of proliferation and upregulation of ECM- and glycosaminoglycan (GAG)-related pathways. Furthermore, pathways related to inflammatory reactions were upregulated, and potential induction and signaling mechanisms were identified. Fractionated irradiation (3 × 4 Gy) of confluent cultures according to a previously published protocol for predicting the risk of fibrosis after radiotherapy showed similar downregulation but differences in upregulated genes and pathways.

Conclusion

Gene expression profiles after irradiation of exponentially growing cells were related to radiation-induced differentiation and inflammatory reactions, and potential signaling mechanisms. Upregulated pathways by different irradiation protocols may reflect different aspects of the fibrogenic process thus providing a model system for further hypothesis-based studies of radiation-induced fibrogenesis.

Gene Activation as a Cell Protection Mechanism Against Gamma-Ray radiation

Introduction: Gamma radiation is accompanied by prominent biological effects and damages. Cell proliferation and tumorigenesis are highlighted as the main resulted effects of gamma radiation on cultured cells. This study aims to assess the dysregulated mode of gene function after gamma radiation in human Jurkat cells. Methods: Six gene expression profiles from Gene Expression Omnibus (GEO) were analyzed by GEO2R to find the significant differentially expressed genes (DEGs) via gamma radiation. Action map analysis was applied to screen the query DEGs. Results: Among 108 study genes, 20 critical DEGs including AURKA, AURKB, BORA, CCNB1, CCNB2, CCNF, CDC20, CDCA8, CENPA, CENPE, CENPF, KIF18A, KIF20A, KIF23, BUB1, DLGAP5, ECT2, PLK1, SGO2, and TPX2 were introduced as down-regulated genes by the gamma ray. Conclusion: Activators of the introduced critical genes may be the cell protector against gamma radiation.

The Response of Living Organisms to Low Radiation Environment and Its Implications in Radiation Protection

Life has evolved on Earth for about 4 billion years in the presence of the natural background of ionizing radiation. It is extremely likely that it contributed, and still contributes, to shaping present form of life. Today the natural background radiation is extremely small (few mSv/y), however it may be significant enough for living organisms to respond to it, perhaps keeping memory of this exposure. A better understanding of this response is relevant not only for improving our knowledge on life evolution, but also for assessing the robustness of the present radiation protection system at low doses, such as those typically encountered in everyday life. Given the large uncertainties in epidemiological data below 100 mSv, quantitative evaluation of these health risk is currently obtained with the aid of radiobiological models. These predict a health detriment, caused by radiation-induced genetic mutations, linearly related to the dose. However a number of studies challenged this paradigm by demonstrating the occurrence of non-linear responses at low doses, and of radioinduced epigenetic effects, i.e., heritable changes in genes expression not related to changes in DNA sequence. This review is focused on the role that epigenetic mechanisms, besides the genetic ones, can have in the responses to low dose and protracted exposures, particularly to natural background radiation. Many lines of evidence show that epigenetic modifications are involved in non-linear responses relevant to low doses, such as non-targeted effects and adaptive response, and that genetic and epigenetic effects share, in part, a common origin: the reactive oxygen species generated by ionizing radiation. Cell response to low doses of ionizing radiation appears more complex than that assumed for radiation protection purposes and that it is not always detrimental. Experiments conducted in underground laboratories with very low background radiation have even suggested positive effects of this background. Studying the changes occurring in various living organisms at reduced radiation background, besides giving information on the life evolution, have opened a new avenue to answer whether low doses are detrimental or beneficial, and to understand the relevance of radiobiological results to radiation protection.

Organ-Specific Effects of Low Dose Radiation Exposure: A Comprehensive Review

Ionizing radiation (IR) is a high-energy radiation whose biological effects depend on the irradiation doses. Low-dose radiation (LDR) is delivered during medical diagnoses or by an exposure to radioactive elements and has been linked to the occurrence of chronic diseases, such as leukemia and cardiovascular diseases. Though epidemiological research is indispensable for predicting and dealing with LDR-induced abnormalities in individuals exposed to LDR, little is known about epidemiological markers of LDR exposure. Moreover, difference in the LDR-induced molecular events in each organ has been an obstacle to a thorough investigation of the LDR effects and a validation of the experimental results in in vivo models. In this review, we summarized the recent reports on LDR-induced risk of organ-specifically arranged the alterations for a comprehensive understanding of the biological effects of LDR. We suggested that LDR basically caused the accumulation of DNA damages, controlled systemic immune systems, induced oxidative damages on peripheral organs, and even benefited the viability in some organs. Furthermore, we concluded that understanding of organ-specific responses and the biological markers involved in the responses is needed to investigate the precise biological effects of LDR.

Comparison of time and dose dependent gene expression and affected pathways in primary human fibroblasts after exposure to ionizing radiation

Background

Exposure to ionizing radiation induces complex stress responses in cells, which can lead to adverse health effects such as cancer. Although a variety of studies investigated gene expression and affected pathways in human fibroblasts after exposure to ionizing radiation, the understanding of underlying mechanisms and biological effects is still incomplete due to different experimental settings and small sample sizes. Therefore, this study aims to identify the time point with the highest number of differentially expressed genes and corresponding pathways in primary human fibroblasts after irradiation at two preselected time points.

Methods

Fibroblasts from skin biopsies of 15 cell donors were exposed to a high (2Gy) and a low (0.05Gy) dose of X-rays. RNA was extracted and sequenced 2 h and 4 h after exposure. Differentially expressed genes with an adjusted p-value < 0.05 were flagged and used for pathway analyses including prediction of upstream and downstream effects. Principal component analyses were used to examine the effect of two different sequencing runs on quality metrics and variation in expression and alignment and for explorative analysis of the radiation dose and time point of analysis.

Results

More genes were differentially expressed 4 h after exposure to low and high doses of radiation than after 2 h. In experiments with high dose irradiation and RNA sequencing after 4 h, inactivation of the FAT10 cancer signaling pathway and activation of gluconeogenesis I, glycolysis I, and prostanoid biosynthesis was observed taking p-value (< 0.05) and (in) activating z-score (≥2.00 or ≤ − 2.00) into account. Two hours after high dose irradiation, inactivation of small cell lung cancer signaling was observed. For low dose irradiation experiments, we did not detect any significant (p < 0.05 and z-score ≥ 2.00 or ≤ − 2.00) activated or inactivated pathways for both time points.

Conclusions

Compared to 2 h after irradiation, a higher number of differentially expressed genes were found 4 h after exposure to low and high dose ionizing radiation. Differences in gene expression were related to signal transduction pathways of the DNA damage response after 2 h and to metabolic pathways, that might implicate cellular senescence, after 4 h. The time point 4 h will be used to conduct further irradiation experiments in a larger sample.

Microarray data analysis reveals gene expression changes in response to ionizing radiation in MCF7 human breast cancer cells

Background

The aim of this study was to identify potential therapeutic target genes for breast cancer (BC) by the investigation of gene expression changes after ionizing radiation (IR) in BC cells. Gene expression profile GSE21748, including BC cell line MCF-7 samples at different time points after IR treatment, were downloaded from Gene Expression Omnibus. Differentially expressed genes (DEGs) were identified in different time points following IR compared with cell samples before IR, respectively. Gene ontology functions and The Kyoto Encyclopedia of Genes and Genomes pathways of the overlapping DEGs were enriched using DAVID. Transcription factor (TFs)-encoding genes were identified from the overlapping DEGs, followed by construction of transcriptional regulatory network and co-expression network.

Results

A total of 864 overlapping DEGs were identified, which were significantly enriched in regulation of cell proliferation and apoptosis, and cell cycle process. We found that FOXD1, STAT6, XBP1, STAT2, LMO2, TFAP4, STAT3, STAT1 were hub nodes in the transcriptional regulatory network of the overlapping DEGs. The co-expression network of target genes regulated by STAT3, STAT1, STAT6 and STAT2 included some key genes such as BCL2L1.

Conclusion

STAT1, STAT2, STAT3, STAT6, XBP1, BCL2L1, CYB5D2, ESCO2, and PARP2 were significantly affected by IR and they may be used as therapeutic gene targets in the treatment of BC.

Ionizing Radiation-Induced Epigenetic Modifications and Their Relevance to Radiation Protection

The present system of radiation protection assumes that exposure at low doses and/or low dose-rates leads to health risks linearly related to the dose. They are evaluated by a combination of epidemiological data and radiobiological models. The latter imply that radiation induces deleterious effects via genetic mutation caused by DNA damage with a linear dose-dependence. This picture is challenged by the observation of radiation-induced epigenetic effects (changes in gene expression without altering the DNA sequence) and of non-linear responses, such as non-targeted and adaptive responses, that in turn can be controlled by gene expression networks. Here, we review important aspects of the biological response to ionizing radiation in which epigenetic mechanisms are, or could be, involved, focusing on the possible implications to the low dose issue in radiation protection. We examine in particular radiation-induced cancer, non-cancer diseases and transgenerational (hereditary) effects. We conclude that more realistic models of radiation-induced cancer should include epigenetic contribution, particularly in the initiation and progression phases, while the impact on hereditary risk evaluation is expected to be low. Epigenetic effects are also relevant in the dispute about possible "beneficial" effects at low dose and/or low dose-rate exposures, including those given by the natural background radiation.

Chronic low dose irradiation alters hepatic transcriptional profiles, but not global DNA methylation in medaka (Oryzias latipes)

Ionizing radiation (IR) resulting from both natural and anthropogenic sources is ubiquitous throughout the environment. Historically, studies on the biological impacts of radiation primarily focused on responses to acute doses of radiation, with little advancement in our understanding of environmentally relevant exposures. Epigenetic mechanisms are capable of mediating organismal responses to environmental stressors and DNA methylation plays important roles in gene regulation and promoting chromosomal stability. Here, we assess broad-scale transcriptional and epigenetic variation resulting from chronic exposure to low doses of ionizing radiation (LDIR; 5.78, 53.76, or 520.23 mGy/day) using Japanese medaka fish (Oryzias latipes) in a replicated mesocosm design. We observed significant changes to the hepatic transcriptome induced by a 3-month chronic exposure to IR, whereas global DNA methylation appeared largely unaffected. Our findings reveal a set of genes, including those involved in immune function, responding to environmentally relevant IR exposures, which do not appear to be mediated by a systemic global shift in DNA methylation.

Molecular karyotyping and gene expression analysis in childhood cancer patients

Abstract

The genetic etiology of sporadic childhood cancer cases remains unclear. We recruited a cohort of 20 patients who survived a childhood malignancy and then developed a second primary cancer (2N), and 20 carefully matched patients who survived a childhood cancer without developing a second malignancy (1N). Twenty matched cancer-free (0N) and additional 1000 (0N) GHS participants served as controls. Aiming to identify new candidate loci for cancer predisposition, we compared the genome-wide DNA copy number variations (CNV) with the RNA-expression data obtained after in vitro irradiation of primary fibroblasts. In 2N patients, we detected a total of 142 genes affected by CNV. A total of 53 genes of these were not altered in controls. Six genes (POLR3F, SEC23B, ZNF133, C16orf45, RRN3, and NTAN1) that we found to be overexpressed after irradiation were also duplicated in the genome of the 2N patients. For the 1N collective, 185 genes were affected by CNV and 38 of these genes were not altered in controls. Five genes (ZCWPW2, SYNCRIP, DHX30, DHRS4L2, and THSD1) were located in duplicated genomic regions and exhibited altered RNA expression after irradiation. One gene (ABCC6) was partially duplicated in one 1N and one 2N patient. Analysis of methylation levels of THSD1 and GSTT2 genes which were detected in duplicated regions and are frequently aberrantly methylated in cancer showed no changes in patient’s fibroblasts. In summary, we describe rare and radiation-sensitive genes affected by CNV in childhood sporadic cancer cases, which may have an impact on cancer development.

Key messages

• Rare CNV’s may have an impact on cancer development in sporadic, non-familial, non-syndromic childhood cancer cases.

• In our cohort, each patient displayed a unique pattern of cancer-related gene CNVs, and only few cases shared similar CNV.

• Genes that are transcriptionally regulated after radiation can be located in CNVs in cancer patients and controls.

• THSD1 and GSTT2 methylation is not altered by CNV.

Electronic supplementary material

The online version of this article (10.1007/s00109-020-01937-4) contains supplementary material, which is available to authorized users.

Replicative and radiation-induced aging: a comparison of gene expression profiles

All living organisms are subject to the aging process and experience the effect of ionizing radiation throughout their life. There have been a number of studies that linked ionizing radiation process to accelerated aging, but comprehensive signalome analysis of both processes was rarely conducted. Here we present a comparative signaling pathway based analysis of the transcriptomes of fibroblasts irradiated with different doses of ionizing radiation, replicatively aged fibroblasts and fibroblasts collected from young, middle age and old patients. We demonstrate a significant concordance between irradiation-induced and replicative senescence signalome signatures of fibroblasts. Additionally, significant differences in transcriptional response were also observed between fibroblasts irradiated with high and low dose. Our data shows that the transcriptome of replicatively aged fibroblasts is more similar to the transcriptome of the cells irradiated with 2 Gy, than with 5 сGy.This work revealed a number of signaling pathways that are shared between senescence and irradiation processes and can potentially be targeted by the new generation of gero- and radioprotectors.

Integrative Analysis for the Roles of lncRNAs in the Immune Responses of Mouse PBMC Exposed to Low-Dose Ionizing Radiation

It is well accepted that low-dose ionizing radiation (LDIR) modulates a variety of immune responses that have exhibited the properties of immune hormesis. Alterations in messenger RNA (mRNA) and long noncoding RNA (lncRNA) expression were to crucially underlie these LDIR responses. However, lncRNAs in LDIR-induced immune responses have been rarely reported, and its functions and molecular mechanisms have not yet been characterized. Here, we used microarray profiling to determine lncRNA in BALB/c mice exposed to single (0.5 Gy×1) and chronic (0.05 Gy×10) low-dose γ-rays radiation (Co⁶⁰). We observed that a total of 8274 lncRNAs and 7240 mRNAs were altered in single LDIR, while 2077 lncRNAs and 796 mRNAs in chronic LDIR. The biological functions of these upregulated mRNAs in both 2 groups using Gene Ontology functional and pathway enrichment analysis were significantly enriched in immune processes and immune signaling pathways. Subsequently, we screened out the lncRNAs involved in regulating these immune signaling pathways and examined their potential functions by lncRNAs-mRNAs coexpression networks. This is the first study to comprehensively identify lncRNAs in single and chronic LDIR responses and to demonstrate the involvement of different lncRNA expression patterns in LDIR-induced immune signaling pathways. Further systematic research on these lncRNAs will provide new insights into our understanding of LDIR-modulated immune hormesis responses.

An Integrated Preprocessing Approach for Exploring Single-Cell Gene Expression in Rare Cells

Exploring the variability in gene expressions of rare cells at the single-cell level is critical for understanding mechanisms of differentiation in tissue function and development as well as for disease diagnostics and cancer treatment. Such studies, however, have been hindered by major difficulties in tracking the identity of individual cells. We present an approach that combines single-cell picking, lysing, reverse transcription and digital polymerase chain reaction to enable the isolation, tracking and gene expression analysis of rare cells. The approach utilizes a photocleavage bead-based microfluidic device to synthesize and deliver stable cDNA for downstream gene expression analysis, thereby allowing chip-based integration of multiple reactions and facilitating the minimization of sample loss or contamination. The utility of the approach was demonstrated with QuantStudio digital PCR by analyzing the radiation and bystander effect on individual IMR90 human lung fibroblasts. Expression levels of the Cyclin-dependent kinase inhibitor 1a (CDKN1A), Growth/differentiation factor 15 (GDF15), and Prostaglandin-endoperoxide synthase 2 (PTGS2) genes, previously shown to have different responses to direct and bystander irradiation, were measured across individual control, microbeam-irradiated or bystander IMR90 cells. In addition to the confirmation of accurate tracking of cell treatments through the system and efficient analysis of single-cell responses, the results enable comparison of activation levels of different genes and provide insight into signaling pathways within individual cells.

Effects of low-dose irradiation on human osteoblasts and periodontal ligament cells

OBJECTIVE

To investigate the effects of dental x-ray on proliferation and mineralization in human primary osteoblasts as well as on proliferation and apoptotic potential in human periodontal ligament (PDL) cells.

DESIGN

Primary osteoblasts and PDL cells were irradiated with various doses of periapical radiography by repeated exposures and further incubated for 1, 3 or 7 days. Cell proliferation was assayed by BrdU incorporation. The effect of dental x-ray on mineralization in osteoblasts either before or after x-ray exposures was determined by Alizarin red staining. Both mRNA and protein expressions of BCL-2, an anti-apoptotic gene, and BAX, a pro-apoptotic gene, in PDL cells were analyzed by RT-qPCR and immunoblotting analysis, respectively.

RESULTS

Neither the proliferative nor the mineralization ability of irradiated osteoblasts was different from that of non-irradiated osteoblasts at any doses or time points. By contrast, there was a significant decrease in the proliferation of PDL cells on day 3 after repeated exposures to dental x-ray for 20 times (P < 0.05), whereas the ratio of BCL-2 to BAX mRNA and protein expressions in these irradiated PDL cells was significantly increased (P < 0.05).

CONCLUSIONS

Upon multiple exposures to dental x-ray used in intraoral radiography up to 20 times, there is no effect on the proliferation or the mineralization of osteoblasts, whereas the proliferative and apoptotic potentials of PDL cells are transiently decreased.

Low Doses of Ionizing Radiation Enhance the Angiogenic Potential of Adipocyte Conditioned Medium

At low doses, ionizing radiation activates endothelial cells and promotes angiogenesis. However, it is still unknown if other cells may contribute to this process. In this study, the effect of low-dose ionizing radiation (LDIR) in modulating the pro-angiogenic potential of adipocytes was investigated. Adipocytes are known to secrete multiple angiogenic factors and adipokines that induce angiogenesis. In this work, a confluent monolayer of 3T3-L1 pre-adipocytes was exposed to low doses (0.1 and 0.3 Gy) and to higher doses (0.5, 0.8 and 1.0 Gy), as control. Our data show that the adipocyte-conditioned media (A-CM) from mature adipocytes differentiated from low-dose irradiated pre-adipocytes presented a higher angiogenic potential, compared to mature adipocytes differentiated from sham-irradiated control preadipocytes. The vascular endothelial growth factor (VEGF)-A levels were significantly increased in A-CM from the 0.1 Gy (P < 0.05) and 0.3 Gy (P < 0.01) experimental conditions and a significant increase was found in response to 0.3 Gy dose of radiation for VEGF-C, angiopoietin-2 (ANG-2) and hepatocyte growth factor (HGF). Moreover, 0.3 Gy dose of radiation significantly increased the expression of matrix metalloproteinase (MMP)-2 active forms. In vitro, the A-CM from the 0.1 and 0.3 Gy doses experimental conditions significantly accelerated endothelial cell migration after an in vitro wound healing assay. Importantly, in vivo, the A-CM corresponding to the 0.3 Gy experimental condition significantly induced the growth of more blood vessels towards the inoculation area in the chick embryo chorioallantoic membrane (CAM). In conclusion, this work reveals a new mechanism by which low-dose radiation might promote angiogenesis, enhancing the angiogenic potential of A-CM.

Response of the freshwater mussel, Dreissena polymorpha to sub-lethal concentrations of samarium and yttrium after chronic exposure

Samarium (Sm) and yttrium (Y) are commonly used rare earth elements (REEs) but there is a scarcity of information concerning their biological effects in non-target aquatic organisms. The purpose of this study was to determine the bioavailability of those REEs and their toxicity on Dreissena polymorpha after exposure to increasing concentration of Sm and Y for 28 days at 15 °C. At the end of the exposure period, the gene expression of superoxide dismutase (SOD), catalase (CAT), metallothionein (MT), glutathione-S-transferase (GST), cytochrome c oxidase 1 (CO1) and cyclin D (Cyc D) were analysed. In addition, we examined lipid peroxidation (LPO), DNA strand breaks (DSB), GST and prostaglandin cyclooxygenase (COX) activities. Results showed a concentration dependent increase in the level of the REEs accumulated in the soft tissue of mussels. Both REEs decreased CAT but did not significantly modulated SOD and MT expressions. Furthermore, Sm³⁺ up-regulated GST, CO1 and Cyc D, while Y³⁺ increased and decreased GST and CO1 transcripts levels, respectively. Biomarker activities showed no oxidative damage as evidenced by LPO, while COX activity was decreased and DNA strand breaks levels were changed suggesting that Sm and Y exhibit anti-inflammatory and genotoxic effects. Factorial analysis revealed that the major impacted biomarkers by Sm were LPO, CAT, CO1 and COX, while GST gene expression, COX, Cyc D and CAT as the major biomarkers affected by Y. We conclude that these REEs display different mode of action but further investigations are required in order to define the exact mechanism involved in their toxicity.

BIOLOGICAL MARKERS OF EXTERNAL AND INTERNAL EXPOSURE IN SHELTER CONSTRUCTION WORKERS: A 13-YEAR EXPERIENCE

OBJECTIVE

The aim of this study is to investigate the cellular, molecular, genetic and non-invasive functional biomarkers of occupational irradiation in workers exposed to a combination of external gamma-radiation and incorporation of transuranium elements.

RESULTS

A study was performed in 688 radiation workers of Shelter object conversion into a safe system with mean shift dose of external exposure of 26.06 mSv (range: 0.1-113.35) and risk of internal exposure with transuranium elements. Several biological parameters could serve as biomarkers of exposure at radiation doses below 100 mSv and even in 20-50 mSv interval. The parallel changes were shown in decline of brain electric activity, telomere length, differences in CCND1, CDKN1A, CDKN2A, VEGFA, TP53, DDB2 genes expression. An increase in counts of dicentrics, pair fragments and TCR-variant lymphocytes at doses over professional limits shows the need of biological dosimetry. The most sensitive markers include TCR-CD4+, γ-H2AX+ and CyclinD1+ cell counts. Implementation of flow cytometry approach for these markers enables quick obtaining of quantitative data. Confounding factors included respiratory function and smoking. The study of the radiation workers with the history of chronic exposure in radiation area during 3-5 years demonstrates changes of compensatory origin, i.e. absence of telomere shortening, increased number of NK-cells in combination with lower expression of intracellular γ-H2AX.

CONCLUSION

This study confirms the presence of radiation-induced changes in gene regulation of cell proliferation, telomere function and apoptosis in radiation workers exposed to external and internal exposure at doses above professional limits and increase of compensatory changes.

Low dose ionizing irradiation suppresses cellular senescence in normal human fibroblasts

PURPOSE

Exposure to high dose ionizing radiation leads to premature cell senescence and suppression of cell proliferation. In contrast, low dose and low dose-rate gamma-irradiation can lead to stimulation of cell proliferation. We aimed to examine whether the low dose radiation-induced proliferation of normal human fibroblasts can lead to a progressive depletion of proliferation potential and to an early onset of senescence.

MATERIALS AND METHODS

Normal human embryonic lung fibroblasts (HELF-104) at passage 22-24 were gamma-irradiated with doses of 0 (sham-irradiation), 10, 30, 50, 90, 120, 150, 200, and 500 mGy as well as 1 and 2 Gy. After irradiation, the fraction of cells positively stained for senescence-associated β-galactosidase activity was measured weekly until the cell culture completely ceased to proliferate.

RESULTS

We show that single irradiation of HELF-104 cells with 30 and 50 mGy resulted in deceleration of senescence. The suppression of senescence was observed during almost the entire length of the study up to a complete arrest of cell growth.

CONCLUSIONS

Our data, together with the previously published observation of delayed stimulation of proliferation in HELF-104 cells exposed to 30 mGy, suggest that low dose gamma-irradiation can increase the overall proliferative potential of normal human fibroblasts.

The Lowest Radiation Dose Having Molecular Changes in the Living Body

We herein attempted to identify the lowest radiation dose causing molecular changes in the living body. We investigated the effects of radiation in human cells, animals, and humans. DNA double-strand breaks (DSBs) formed in cells at γ- or X-ray irradiation doses between 1 mGy and 0.5 Gy; however, the extent of DSB formation differed depending on the cell species. The formation of micronuclei (MNs) and nucleoplasmic bridges (NPBs) was noted at radiation doses between 0.1 and 0.2 Gy. Stress-responsive genes were upregulated by lower radiation doses than those that induced DNA DSBs or MN and NPBs. These γ- or X-ray radiation doses ranged between approximately 10 and 50 mGy. In animals, chromosomal aberrations were detected between 50 mGy and 0.1 Gy of low linear energy transfer radiation, 0.1 Gy of metal ion beams, and 9 mGy of fast neutrons. In humans, DNA damage has been observed in children who underwent computed tomography scans with an estimated blood radiation dose as low as 0.15 mGy shortly after examination. The frequencies of chromosomal translocations were lower in residents of high background areas than in those of control areas. In humans, systemic adaptive responses may have been prominently expressed at these radiation doses.

Differential miRNA expression profiling reveals miR-205-3p to be a potential radiosensitizer for low- dose ionizing radiation in DLD-1 cells

Enhanced radiosensitivity at low doses of ionizing radiation (IR) (0.2 to 0.6 Gy) has been reported in several cell lines. This phenomenon, known as low doses hyper-radiosensitivity (LDHRS), appears as an opportunity to decrease toxicity of radiotherapy and to enhance the effects of chemotherapy. However, the effect of low single doses IR on cell death is subtle and the mechanism underlying LDHRS has not been clearly explained, limiting the utility of LDHRS for clinical applications. To understand the mechanisms responsible for cell death induced by low-dose IR, LDHRS was evaluated in DLD-1 human colorectal cancer cells and the expression of 80 microRNAs (miRNAs) was assessed by qPCR array. Our results show that DLD-1 cells display an early DNA damage response and apoptotic cell death when exposed to 0.6 Gy. miRNA expression profiling identified 3 over-expressed (miR-205-3p, miR-1 and miR-133b) and 2 down-regulated miRNAs (miR-122-5p, and miR-134-5p) upon exposure to 0.6 Gy. This miRNA profile differed from the one in cells exposed to high-dose IR (12 Gy), supporting a distinct low-dose radiation-induced cell death mechanism. Expression of a mimetic miR-205-3p, the most overexpressed miRNA in cells exposed to 0.6 Gy, induced apoptotic cell death and, more importantly, increased LDHRS in DLD-1 cells. Thus, we propose miR-205-3p as a potential radiosensitizer to low-dose IR.

Global transcriptome profile reveals abundance of DNA damage response and repair genes in individuals from high level natural radiation areas of Kerala coast

The high level natural radiation areas (HLNRA) of Kerala coast in south west India is unique for its wide variation in the background radiation dose (<1.0mGy to 45mGy/year) and vast population size. Several biological studies conducted in this area did not reveal any adverse effects of chronic low dose and low dose rate radiation on human population. In the present study, global transcriptome analysis was carried out in peripheral blood mono-nuclear cells of 36 individuals belonging to different background dose groups [NLNRA, (Group I, ≤1.50 mGy/year) and three groups of HLNRA; Group II, 1.51–5.0 mGy/year), Group III, 5.01-15mGy/year and Group IV, >15.0 mGy/year] to find out differentially expressed genes and their biological significance in response to chronic low dose radiation exposure. Our results revealed a dose dependent increase in the number of differentially expressed genes with respect to different background dose levels. Gene ontology analysis revealed majority of these differentially expressed genes are involved in DNA damage response (DDR) signaling, DNA repair, cell cycle arrest, apoptosis, histone/chromatin modification and immune response. In the present study, 64 background dose responsive genes have been identified as possible chronic low dose radiation signatures. Validation of 30 differentially expressed genes was carried out using fluorescent based universal probe library. Abundance of DDR and DNA repair genes along with pathways such as MAPK, p53 and JNK in higher background dose groups (> 5.0mGy/year) indicated a possible threshold dose for DDR signaling and are plausible reason of observing in vivo radio-adaptive response and non-carcinogenesis in HLNRA population. To our knowledge, this is the first study on molecular effect of chronic low dose radiation exposure on human population from high background radiation areas at transcriptome level using high throughput approach. These findings have tremendous implications in understanding low dose radiation biology especially, the effect of low dose radiation exposure in humans.

Radiation-induced alternative transcripts as detected in total and polysome-bound mRNA

Alternative splicing is a critical event in the posttranscriptional regulation of gene expression. To investigate whether this process influences radiation-induced gene expression we defined the effects of ionizing radiation on the generation of alternative transcripts in total cellular mRNA (the transcriptome) and polysome-bound mRNA (the translatome) of the human glioblastoma stem-like cell line NSC11. For these studies, RNA-Seq profiles from control and irradiated cells were compared using the program SpliceSeq to identify transcripts and splice variations induced by radiation. As compared to the transcriptome (total RNA) of untreated cells, the radiation-induced transcriptome contained 92 splice events suggesting that radiation induced alternative splicing. As compared to the translatome (polysome-bound RNA) of untreated cells, the radiation-induced translatome contained 280 splice events of which only 24 were overlapping with the radiation-induced transcriptome. These results suggest that radiation not only modifies alternative splicing of precursor mRNA, but also results in the selective association of existing mRNA isoforms with polysomes. Comparison of radiation-induced alternative transcripts to radiation-induced gene expression in total RNA revealed little overlap (about 3%). In contrast, in the radiation-induced translatome, about 38% of the induced alternative transcripts corresponded to genes whose expression level was affected in the translatome. This study suggests that whereas radiation induces alternate splicing, the alternative transcripts present at the time of irradiation may play a role in the radiation-induced translational control of gene expression and thus cellular radioresponse.

Radiation-induced translational control of gene expression

Radiation-induced gene expression has long been hypothesized to protect against cell death. Defining this process would provide not only insight into the mechanisms mediating cell survival after radiation exposure, but also a novel source of targets for radiosensitization. However, whereas the radiation-induced gene expression profiles using total cellular mRNA have been generated for cell lines as well as normal tissues, with few exception, the changes in mRNA do not correlate with changes in the corresponding protein. The traditional approach to profiling gene expression, i.e., using total cellular RNA, does not take into account posttranscriptional regulation. In this review, we describe the use of gene expression profiling of polysome-bound RNA to establish that radiation modifies gene expression via translational control. Because changes in polysome-bound mRNA correlate with changes in protein, analysis of the translational profiles provides a unique data set for investigating the mechanisms mediating cellular radioresponse.

Distinct Sets of lncRNAs are Differentially Modulated after Exposure to High and Low Doses of X Rays

High- and low-dose X rays are used in medicine as therapeutic and diagnostic tools, respectively. While the cellular response to high-dose radiation is well known, studies on the effects of low-dose radiation and its ability to trigger a proper DNA damage response have had contradictory results. The functions of many signaling and effector proteins of the DNA damage response (DDR) have been described, and are attributed to well-known DDR pathways. However, there has been little known about the contribution of long noncoding RNAs (lncRNAs) to DDR, although there is recent evidence that lncRNAs may be associated with almost all biological functions, including DDR. In this work, we investigated the participation of lncRNAs in the response to different X-ray doses. By microarray analysis, we observed that in human breast epithelial cells, distinct sets of coding and noncoding transcripts are differentially regulated after moderate- and high-dose irradiation compared to those regulated after low-dose irradiation. While the modulated coding and noncoding genes at low doses relate to cell signaling pathways, those affected by moderate and high doses are mostly enriched for cell cycle regulation and apoptotic pathways. Quantification using qPCR of the lncRNAs identified by microarrays allowed the validation of 75% of those regulated at the higher doses. These results indicate that lncRNA expression is regulated by ionizing radiation and that this expression is dose dependent.

Radioresistance of GGG sequences to prompt strand break formation from direct-type radiation damage

As humans, we are constantly exposed to ionizing radiation from natural, man-made and cosmic sources which can damage DNA, leading to deleterious effects including cancer incidence. In this work, we introduce a method to monitor strand breaks resulting from damage due to the direct effect of ionizing radiation and provide evidence for sequence-dependent effects leading to strand breaks. To analyze only DNA strand breaks caused by radiation damage due to the direct effect of ionizing radiation, we combined an established technique to generate dehydrated DNA samples with a technique to analyze single-strand breaks on short oligonucleotide sequences via denaturing gel electrophoresis. We find that direct damage primarily results in a reduced number of strand breaks in guanine triplet regions (GGG) when compared to isolated guanine (G) bases with identical flanking base context. In addition, we observe strand break behavior possibly indicative of protection of guanine bases when flanked by pyrimidines and sensitization of guanine to strand break when flanked by adenine (A) bases in both isolated G and GGG cases. These observations provide insight into the strand break behavior in GGG regions damaged via the direct effect of ionizing radiation. In addition, this could be indicative of DNA sequences that are naturally more susceptible to strand break due to the direct effect of ionizing radiation.

The role of dose rate in radiation cancer risk: evaluating the effect of dose rate at the molecular, cellular and tissue levels using key events in critical pathways following exposure to low LET radiation

PURPOSE

This review evaluates the role of dose rate on cell and molecular responses. It focuses on the influence of dose rate on key events in critical pathways in the development of cancer. This approach is similar to that used by the U.S. EPA and others to evaluate risk from chemicals. It provides a mechanistic method to account for the influence of the dose rate from low-LET radiation, especially in the low-dose region on cancer risk assessment. Molecular, cellular, and tissues changes are observed in many key events and change as a function of dose rate. The magnitude and direction of change can be used to help establish an appropriate dose rate effectiveness factor (DREF).

CONCLUSIONS

Extensive data on key events suggest that exposure to low dose-rates are less effective in producing changes than high dose rates. Most of these data at the molecular and cellular level support a large (2-30) DREF. In addition, some evidence suggests that doses delivered at a low dose rate decrease damage to levels below that observed in the controls. However, there are some data human and mechanistic data that support a dose-rate effectiveness factor of 1. In summary, a review of the available molecular, cellular and tissue data indicates that not only is dose rate an important variable in understanding radiation risk but it also supports the selection of a DREF greater than one as currently recommended by ICRP ( 2007 ) and BEIR VII (NRC/NAS 2006 ).

Lack of increased DNA double-strand breaks in peripheral blood mononuclear cells of individuals from high level natural radiation areas of Kerala coast in India

The high level natural radiation area (HLNRA) of Kerala is a 55km long and 0.5km wide strip in south west coast of India. The level of background radiation in this area varies from <1.0mGy/year to 45.0mGy/year. It offers unique opportunity to study the effect of chronic low dose/low dose-rate radiation directly on human population. Spontaneous level of DNA double strand breaks (DSBs) was quantified in peripheral blood mononuclear cells of 91 random individuals from HLNRA (N=61, mean age: 36.1±7.43years) and normal level natural radiation area (NLNRA) (N=30, mean age: 35.5±6.35years) using gamma-H2AX as a marker. The mean annual dose received by NLNRA and HLNRA individuals was 1.28±0.086mGy/year and 8.28±4.96mGy/year, respectively. The spontaneous frequency of DSBs in terms of gamma-H2AX foci among NLNRA and HLNRA individuals were 0.095±0.009 and 0.084±0.004 per cell (P=0.22). The individuals from HLNRA were further classified as low dose group (LDG, 1.51-5.0mGy/year, mean dose: 2.63±0.76mGy/year) and high dose group (HDG, >5.0mGy/year, mean dose: 11.04±3.57mGy/year). The spontaneous frequency of gamma-H2AX foci per cell in NLNRA, LDG and HDG was observed to be 0.095±0.009, 0.096±0.008 and 0.078±0.004 respectively. Individuals belonging to HDG of HLNRA showed marginally lower frequency of DSBs as compared to NLNRA and LDG of HLNRA. This could be suggestive of either lower induction or better repair of DSBs in individuals from HDG of HLNRA. The present study indicated that 5.0mGy/year could be a possible threshold dose for DSB induction at chronic low-dose radiation exposure in vivo. However, further studies on DNA damage induction and repair kinetics are required to draw firm conclusions.

Temporal Responses to X-Radiation Exposure in Spleen in the pKZ1 Mouse Recombination Assay

The in vivo mouse transgenic pKZ1 chromosomal inversion assay is a sensitive assay that responds to very low doses of DNA-damaging agents. pKZ1 inversions are measured as the frequency of cells expressing E. coli β-galactosidase protein, which can only be produced from an inverted pKZ1 transgene. In previous studies we reported that a single whole-body low dose of 0.01 mGy X rays alone caused an increase in pKZ1 chromosomal inversions in spleen when analyzed 3 days postirradiation, and yet this same dose could protect from high-dose-induced inversions when delivered as a conditioning dose 4 h before or after a 1 Gy challenge dose. In an attempt to explain these results, we performed temporal studies over a wide radiation dose range to determine if the inversion response was temporally different at different doses. pKZ1 mice were irradiated with a single whole-body X-ray dose of 0.01 mGy, 1 mGy or 1 Gy, and spleen sections were then analyzed for pKZ1 inversions at 7 h, 1 day or 7 days after exposure. No change in inversion frequency was observed at the 7 h time point at any dose. At day 1, an increase in inversions was observed in response to the 0.01 mGy dose, whereas a decrease in inversions below sham-treated frequency was observed for the 1 mGy dose. Inversion frequency for both doses returned to sham-treated inversion frequency by day 7. To our knowledge, this is the first reported study to examine the temporal nature of a radiation response spanning a wide dose range, including doses relevant to occupational exposure, and the results are dynamic and dose specific. The results suggest that inversions induced after low-dose irradiation are removed by homeostatic mechanisms within a short time frame, and underscore the importance of studying responses over a period of time when interpreting radiation effects.

X-ray radiation effect of C-arm on adipose tissue-mesenchymal stem cell viability and population doubling time

Background: Adipose tissue derived mesenchymal stem cells (AT-MSCs) are relatively easy in isolation procedure compared to bone marrow-derived. Minimally invasive MSC injections need C-arm as guidance that potentially influence the cell viability and doubling time. This study aimsed to determine the effect of C-arm X-ray exposure on AT-MSC viability and population doubling time (PDT).Methods: This experimental study used cryopreserved adipose tissue derived MSCs stored in Stem Cell Medical Technology Integrated Service Unit Cipto Mangunkusumo Hospital. Cells were thawed, propagated, and exposed to varying doses of C-arm X-ray radiation. Stem cell viability was measured, and then the cells were cultured to assess their PDT. Generalized linear models test was used to compare cell viability between post-thaw, post-propagation, post-radiation, post-culture post-radiation, and control and between radiation dose groups. Kruskal-Wallis test assessed PDT between various radiation doses in post-radiation groups. Wilcoxon test was used to assess PDT between pre-radiation and post-radiation groups.Results: Mean confluence period of adipose MSCs post- irradiation was 4.33 days. There was no statistically significant difference in MSC viability after X-ray exposure between pre- and post-irradiation groups (p=0.831). There was no correlation between post-irradiation viability and radiation dose (p=0.138, r=0.503). There were no significant differences in PDT between pre- and post-culture post-irradiation groups and between various radiation doses in post-irradiation groups (p=0.792).  Conclusion: MSC viability and PDT were not influenced by radiation exposure up to 32.34 mgray.

Differential Response and Priming Dose Effect on the Proteome of Human Fibroblast and Stem Cells Induced by Exposure to Low Doses of Ionizing Radiation

It has been suggested that a mechanistic understanding of the cellular responses to low dose and dose rate may be valuable in reducing some of the uncertainties involved in current risk estimates for cancer- and non-cancer-related radiation effects that are inherited in the linear no-threshold hypothesis. In this study, the effects of low-dose radiation on the proteome in both human fibroblasts and stem cells were investigated. Particular emphasis was placed on examining: 1. the dose-response relationships for the differential expression of proteins in the low-dose range (40-140 mGy) of low-linear energy transfer (LET) radiation; and 2. the effect on differential expression of proteins of a priming dose given prior to a challenge dose (adaptive response effects). These studies were performed on cultured human fibroblasts (VH10) and human adipose-derived stem cells (ADSC). The results from the VH10 cell experiments demonstrated that low-doses of low-LET radiation induced unique patterns of differentially expressed proteins for each dose investigated. In addition, a low priming radiation dose significantly changed the protein expression induced by the subsequent challenge exposure. In the ADSC the number of differentially expressed proteins was markedly less compared to VH10 cells, indicating that ADSC differ in their intrinsic response to low doses of radiation. The proteomic results are further discussed in terms of possible pathways influenced by low-dose irradiation.

Modeling cell response to low doses of photon irradiation: Part 2--application to radiation-induced chromosomal aberrations in human carcinoma cells

The biological phenomena observed at low doses of ionizing radiation (adaptive response, bystander effects, genomic instability, etc.) are still not well understood. While at high irradiation doses, cellular death may be directly linked to DNA damage, at low doses, other cellular structures may be involved in what are known as non-(DNA)-targeted effects. Mitochondria, in particular, may play a crucial role through their participation in a signaling network involving oxygen/nitrogen radical species. According to the size of the implicated organelles, the fluctuations in the energy deposited into these target structures may impact considerably the response of cells to low doses of ionizing irradiation. Based on a recent simulation of these fluctuations, a theoretical framework was established to have further insight into cell responses to low doses of photon irradiation, namely the triggering of radioresistance mechanisms by energy deposition into specific targets. Three versions of a model are considered depending on the target size and on the number of targets that need to be activated by energy deposition to trigger radioresistance mechanisms. These model versions are applied to the fraction of radiation-induced chromosomal aberrations measured at low doses in human carcinoma cells (CAL51). For this cell line, it was found in the present study that the mechanisms of radioresistance could not be triggered by the activation of a single small target (nanometric size, 100 nm), but could instead be triggered by the activation of a large target (micrometric, 10 μm) or by the activation of a great number of small targets. The mitochondria network, viewed either as a large target or as a set of small units, might be concerned by these low-dose effects.

Non-targeted effects and radiation-induced carcinogenesis: a review

Exposure to ionising radiation is clearly associated with an increased risk of developing some types of cancer. However, the contribution of non-targeted effects to cancer development after exposure to ionising radiation is far less clear. The currently used cancer risk model by the international radiation protection community states that any increase in radiation exposure proportionately increases the risk of developing cancer. However, this stochastic cancer risk model does not take into account any contribution from non-targeted effects. Nor does it consider the possibility of a bystander mechanism in the induction of genomic instability. This paper reviews the available evidence to date for a possible role for non-targeted effects to contribute to cancer development after exposure to ionising radiation. An evolution in the understanding of the mechanisms driving non-targeted effects after exposure to ionising radiation is critical to determine the true contribution of non-targeted effects on the risk of developing cancer. Such an evolution will likely only be achievable through coordinated multidisciplinary teams combining several fields of study including: genomics, proteomics, cell biology, molecular epidemiology, and traditional epidemiology.

Effect of combined radiation injury on cell death and inflammation in skin

In the event of a nuclear disaster, the individuals proximal to the source of radiation will be exposed to combined radiation injury. As irradiation delays cutaneous repair, the purpose of this study was to elucidate the effect of combined radiation and burn injury (CRBI) on apoptosis and inflammation at the site of skin injury. Male C57Bl/6 mice were exposed to no injury, thermal injury only, radiation only (1 and 6 Gy) and CRBI (1 and 6 Gy) and euthanized at various times after for skin collection. TUNEL staining revealed that the CRBI 6 Gy group had a delayed and increased apoptotic response. This correlated with decreased recovery of live cells as compared to the other injuries. Similar response was observed when cleaved-caspase-3 immunohistochemical staining was compared between CRBI 6 Gy and thermal injury. TNFR1, caspase 8, Bax and IL-6 mRNA expression revealed that the higher CRBI group had delayed increase in mRNA expression as compared to thermal injury alone. RIPK1 mRNA expression and necrotic cell counts were delayed in the CRBI 6 Gy group to day 5. TNF-α and NFκB expression peaked in the CRBI 6 Gy group at day 1 and was much higher than the other injuries. Also, inflammatory cell counts in the CRBI 6 Gy group were lower at early time points as compared to thermal injury by itself. These data suggest that CRBI delays and exacerbates apoptosis and inflammation in skin as well as increases necrosis thus resulting in delayed wound healing.

Key mechanisms involved in ionizing radiation-induced systemic effects. A current review

Organisms respond to physical, chemical and biological threats by a potent inflammatory response, aimed at preserving tissue integrity and restoring tissue homeostasis and function. Systemic effects in an organism refer to an effect or phenomenon which originates at a specific point and can spread throughout the body affecting a group of organs or tissues. Ionizing radiation (IR)-induced systemic effects arise usually from a local exposure of an organ or part of the body. This stress induces a variety of responses in the irradiated cells/tissues, initiated by the DNA damage response and DNA repair (DDR/R), apoptosis or immune response, including inflammation. Activation of this IR-response (IRR) system, especially at the organism level, consists of several subsystems and exerts a variety of targeted and non-targeted effects. Based on the above, we believe that in order to understand this complex response system better one should follow a 'holistic' approach including all possible mechanisms and at all organization levels. In this review, we describe the current status of knowledge on the topic, as well as the key molecules and main mechanisms involved in the 'spreading' of the message throughout the body or cells. Last but not least, we discuss the danger-signal mediated systemic immune effects of radiotherapy for the clinical setup.

Global Gene Expression Alterations as a Crucial Constituent of Human Cell Response to Low Doses of Ionizing Radiation Exposure

Exposure to ionizing radiation (IR) is inevitable to humans in real-life scenarios; the hazards of IR primarily stem from its mutagenic, carcinogenic, and cell killing ability. For many decades, extensive research has been conducted on the human cell responses to IR delivered at a low dose/low dose (LD) rate. These studies have shown that the molecular-, cellular-, and tissue-level responses are different after low doses of IR (LDIR) compared to those observed after a short-term high-dose IR exposure (HDIR). With the advent of high-throughput technologies in the late 1990s, such as DNA microarrays, changes in gene expression have also been found to be ubiquitous after LDIR. Very limited subset of genes has been shown to be consistently up-regulated by LDIR, including CDKN1A. Further research on the biological effects and mechanisms induced by IR in human cells demonstrated that the molecular and cellular processes, including transcriptional alterations, activated by LDIR are often related to protective responses and, sometimes, hormesis. Following LDIR, some distinct responses were observed, these included bystander effects, and adaptive responses. Changes in gene expression, not only at the level of mRNA, but also miRNA, have been found to crucially underlie these effects having implications for radiation protection purposes.

Early Cellular Response to Radiation in Human Vocal Fold Fibroblasts

OBJECTIVES

Radiation therapy is a common treatment strategy for laryngeal carcinoma. However, radiation is not without adverse side effects, especially toward healthy vocal fold tissue, which can lead to long-term impairments in vocal function. The objective of this preliminary study was to investigate early responses of healthy human vocal fold fibroblasts (VFF) to radiation.

METHODS

VFF were exposed to a single or fractionated dose radiation scheme. Nonradiated VFF served as controls. Morphology of radiated and control VFF was subjectively examined. Quantitative polymerase chain reaction was used to evaluate the effect of radiation on extracellular matrix and inflammatory-related genes. VFF viability was investigated using a LIVE/DEAD and clonogenic assay.

RESULTS

Single or fractioned dose radiated VFF were morphologically indistinguishable from control VFF. No significant differences in gene expression were observed following either radiation scheme and as compared to controls. Clonogenic assay revealed reduced VFF viability following the fractionated but not single dose scheme. No changes in viability were detected using the LIVE/DEAD assay.

CONCLUSIONS

We present one of the first investigations to evaluate early responses of healthy VFF to radiation. Findings will contribute to a growing body of literature seeking to elucidate the biological mechanisms underlying voice changes following radiation therapy for laryngeal carcinoma.

MnSOD downregulation induced by extremely low 0.1 mGy single and fractionated X-rays and microgravity treatment in human neuroblastoma cell line, NB-1

A human neuroblastoma cell line, NB-1, was treated with 24 h of microgravity simulation by clinostat, or irradiated with extremely small X-ray doses of 0.1 or 1.0 mGy using single and 10 times fractionation regimes with 1 and 2 h time-intervals. A quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) examination was performed for apoptosis related factors (BAX, CYTC, APAF1, VDAC1–3, CASP3, CASP8, CASP9 P53, AIF, ANT1 and 2, BCL2, MnSOD, autophagy related BECN and necrosis related CYP-40. The qRT-PCR results revealed that microgravity did not result in significant changes except for a upregulation of proapoptotic VDAC2, and downregulations of proapoptotic CASP9 and antiapoptotic MnSOD. After 0.1 mGy fractionation irradiation, there was increased expression of proapoptotic APAF1 and downregulation of proapoptotic CYTC, VDAC2, VDAC3, CASP8, AIF, ANT1, and ANT2, as well as an increase in expression of antiapoptotic BCL2. There was also a decrease in MnSOD expression with 0.1 mGy fractionation irradiation. These results suggest that microgravity and low-dose radiation may decrease apoptosis but may potentially increase oxidative stress.