Radiation-induced Bystander Effect in Starfish (Patiria pectinifera) Oocytes

Although multiple studies suggest that ionizing radiation can induce bystander effects (radiation-induced bystander effect, RIBE) in cultured cell lines, it is still unclear whether RIBE is evolutionarily conserved in invertebrates. In this study, we investigated the frequency of cell death of unirradiated starfish (Patiria pectinifera) oocytes co-cultured with oocytes irradiated with X rays (0, 2 and 4 Gy). We observed increased frequencies of cell death determined by morphological abnormality and TUNEL-positive cells in unirradiated oocytes co-cultured with oocytes irradiated with 2 Gy or 4 Gy oocytes. In addition, the seawater cultured with 4 Gy irradiated oocytes induced cell death in unirradiated oocytes, and TUNEL-positive cells were observed. Our results suggest that RIBE is evolutionarily conserved in starfish.

Advances in Targeted Microbeam Irradiation Methods for Live Caenorhabditis elegans

Charged-particle microbeam irradiation devices, which can convert heavy-ion or proton beams into microbeams and irradiate individual animal cells and tissues, have been developed and used for bioirradiation in Japan, the United States, China, and France. Microbeam irradiation technology has been used to analyze the effects of irradiation on mammalian cancer cells, especially bystander effects. In 2006, individual-level microbeam irradiation of the nematode Caenorhabditis elegans was first realized using JAEA-Takasaki's (now QST-TIAQS's) TIARA collimated microbeam irradiation device. As of 2023, microbeam irradiation of C. elegans has been achieved at five sites worldwide (one in Japan, one in the United States, one in China, and two in France). This paper summarizes the global progress in the field of microbeam biology using C. elegans, while focusing on issues unique to microbeam irradiation of live C. elegans, such as the method of immobilizing C. elegans for microbeam experiments.

Proton Microbeam Targeted Irradiation of the Gonad Primordium Region Induces Developmental Alterations Associated with Heat Shock Responses and Cuticle Defense in Caenorhabditis elegans

We describe a methodology to manipulate Caenorhabditis elegans (C. elegans) and irradiate the stem progenitor gonad region using three MeV protons at a specific developmental stage (L1). The consequences of the targeted irradiation were first investigated by considering the organogenesis of the vulva and gonad, two well-defined and characterized developmental systems in C. elegans. In addition, we adapted high-throughput analysis protocols, using cell-sorting assays (COPAS) and whole transcriptome analysis, to the limited number of worms (>300) imposed by the selective irradiation approach. Here, the presented status report validated protocols to (i) deliver a controlled dose in specific regions of the worms; (ii) immobilize synchronized worm populations (>300); (iii) specifically target dedicated cells; (iv) study the radiation-induced developmental alterations and gene induction involved in cellular stress (heat shock protein) and cuticle injury responses that were found.

A Non-Cell-Autonomous Mode of DNA Damage Response in Soma of Caenorhabditis elegans

Life has evolved a mechanism called DNA damage response (DDR) to sense, signal and remove/repair DNA damage, and its deficiency and dysfunction usually lead to genomic instability and development of cancer. The signaling mode of the DDR has been believed to be of cell-autonomy. However, the paradigm is being shifted with in-depth research into model organism Caenorhabditis elegans. Here, we mainly investigate the effect of DDR activation on the radiosensitivity of vulva of C. elegans, and first found that the vulval radiosensitivity is mainly regulated by somatic DDR, rather than the DDR of germline. Subsequently, the worm lines with pharynx-specific rescue of DDR were constructed, and it is shown that the 9-1-1-ATR and MRN-ATM cascades in pharynx restore approximately 90% and 70% of vulval radiosensitivity, respectively, through distantly regulating the NHEJ repair of vulval cells. The results suggest that the signaling cascade of DDR might also operate in a non-cell autonomous mode. To further explore the underlying regulatory mechanisms, the cpr-4 mutated gene is introduced into the DDR-rescued worms, and CPR-4, a cysteine protease cathepsin B, is confirmed to mediate the inter-tissue and inter-individual regulation of DDR as a signaling molecule downstream of 9-1-1-ATR. Our findings throw some light on the regulation of DNA repair in soma of C. elegans, and might also provide new cues for cancer prevention and treatment.

Radiation-Induced Bystander Effect and Cytoplasmic Irradiation Studies with Microbeams

Simple Summary

Microbeams are useful tools in studies on non-target effects, such as the radiation-induced bystander effect, and responses related to cytoplasmic irradiation. A micrometer or even sub-micrometer-level beam size enables the precise delivery of radiation energy to a specific target. Here we summarize the observations of the bystander effect and the cytoplasmic irradiation-related effect using different kinds of microbeam irradiators as well as discuss the cellular and molecular mechanisms that are involved in these responses. Non-target effects may increase the detrimental effect caused by radiation, so a more comprehensive knowledge of the process will enable better evaluation of the damage resulting from irradiation.

Abstract

Although direct damage to nuclear DNA is considered as the major contributing event that leads to radiation-induced effects, accumulating evidence in the past two decades has shown that non-target events, in which cells are not directly irradiated but receive signals from the irradiated cells, or cells irradiated at extranuclear targets, may also contribute to the biological consequences of exposure to ionizing radiation. With a beam diameter at the micrometer or sub-micrometer level, microbeams can precisely deliver radiation, without damaging the surrounding area, or deposit the radiation energy at specific sub-cellular locations within a cell. Such unique features cannot be achieved by other kinds of radiation settings, hence making a microbeam irradiator useful in studies of a radiation-induced bystander effect (RIBE) and cytoplasmic irradiation. Here, studies on RIBE and different responses to cytoplasmic irradiation using microbeams are summarized. Possible mechanisms related to the bystander effect, which include gap-junction intercellular communications and soluble signal molecules as well as factors involved in cytoplasmic irradiation-induced events, are also discussed.

A systems biology analysis of reproductive toxicity effects induced by multigenerational exposure to ionizing radiation in C. elegans

Understanding the effects of chronic exposure to pollutants over generations is of primary importance for the protection of humans and the environment; however, to date, knowledge on the molecular mechanisms underlying multigenerational adverse effects is scarce. We employed a systems biology approach to analyze effects of chronic exposure to gamma radiation at molecular, tissue and individual levels in the nematode Caenorhabditis elegans. Our data show a decrease of 23% in the number of offspring on the first generation F0 and more than 40% in subsequent generations F1, F2 and F3. To unveil the impact on the germline, an in-depth analysis of reproductive processes involved in gametes formation was performed for all four generations. We measured a decrease in the number of mitotic germ cells accompanied by increased cell-cycle arrest in the distal part of the gonad. Further impact on the germline was manifested by decreased sperm quantity and quality. In order to obtain insight in the molecular mechanisms leading to decreased fecundity, gene expression was investigated via whole genome RNA sequencing. The transcriptomic analysis revealed modulation of transcription factors, as well as genes involved in stress response, unfolded protein response, lipid metabolism and reproduction. Furthermore, a drastic increase in the number of differentially expressed genes involved in defense response was measured in the last two generations, suggesting a cumulative stress effect of ionizing radiation exposure. Transcription factor binding site enrichment analysis and the use of transgenic strain identified daf-16/FOXO as a master regulator of genes differentially expressed in response to radiation. The presented data provide new knowledge with respect to the molecular mechanisms involved in reproductive toxic effects and accumulated stress resulting from multigenerational exposure to ionizing radiation.

Low dose ionizing radiation and the immune response: what is the role of non-targeted effects?

OBJECTIVES

This review aims to trace the historical narrative surrounding the low dose effects of radiation on the immune system and how our understanding has changed from the beginning of the 20th century to now. The particular focus is on the non-targeted effects (NTEs) of low dose ionizing radiation (LDIR) which are effects that occur when irradiated cells emit signals that cause effects in the nearby or distant non-irradiated cells known as radiation induced bystander effect (RIBE). Moreover, radiation induced genomic instability (RIGI) and abscopal effect (AE) also regarded as NTE. This was prompted by our recent discovery that ultraviolet A (UVA) photons are emitted by the irradiated cells and that these photons can trigger NTE such as the RIBE in unirradiated recipients of these photons. Given the well-known association between UV radiation and the immune response, where these biophotons may pose as bystander signals potentiating processes in deep tissues as a consequence of LDIR, it is timely to review the field with a fresh lens. Various pathways and immune components that contribute to the beneficial and adverse types of modulation induced by LDR will also be revisited.

CONCLUSION

There is limited evidence for LDIR induced immune effects by way of a non-targeted mechanism in biological tissue. The literature examining low to medium dose effects of ionizing radiation on the immune system and its components is complex and controversial. Early work was compromised by lack of good dosimetry while later work mainly looks at the involvement of immune response in radiotherapy. There is a lack of research in the LDIR/NTE field focusing on immune response although bone marrow stem cells and lineages were critical in the identification and characterization of NTE where effects like RIGI and RIBE were heavily researched. This may be in part, a result of the difficulty of isolating NTE in whole organisms which are essential for good immune response studies. Models involving inter organism transmission of NTE are a promising route to overcome these issues.

Review of Biological Effects of Acute and Chronic Radiation Exposure on Caenorhabditis elegans

Knowledge regarding complex radiation responses in biological systems can be enhanced using genetically amenable model organisms. In this manuscript, we reviewed the use of the nematode, Caenorhabditis elegans (C. elegans), as a model organism to investigate radiation’s biological effects. Diverse types of experiments were conducted on C. elegans, using acute and chronic exposure to different ionizing radiation types, and to assess various biological responses. These responses differed based on the type and dose of radiation and the chemical substances in which the worms were grown or maintained. A few studies compared responses to various radiation types and doses as well as other environmental exposures. Therefore, this paper focused on the effect of irradiation on C. elegans, based on the intensity of the radiation dose and the length of exposure and ways to decrease the effects of ionizing radiation. Moreover, we discussed several studies showing that dietary components such as vitamin A, polyunsaturated fatty acids, and polyphenol-rich food source may promote the resistance of C. elegans to ionizing radiation and increase their life span after irradiation.

Study on Caenorhabditis Elegans as a Combined Model of Microdosimetry and Biology

Microdosimetry is a tool for the investigation of microscopic energy deposition of ionizing radiation. This work used Caenorhabditis elegans as a model to estimate the microdosimetric deposition level at the ⁶⁰Co gamma radiation. Monte Carlo software PHITS was employed to establish irradiated nematodes model. The dose deposition of the entire body and gonad irradiated to 100 Gy was calculated. The injury levels of radiation were evaluated by the detection of biological indicators. The result of microdosimetric experiment suggested that the dose of whole body of nematodes was estimated to be 99.9 ± 57.8 Gy, ranging from 19.6 to 332.2 Gy. The dose of gonad was predicted to be 129.4 ± 558.8 Gy (9.5-6597 Gy). The result of biological experiment suggested that there were little changes in the length of nematodes after irradiation. However, times of head thrash per minute and the spawning yield in 3 consecutive days decreased 27.1% and 94.7%, respectively. Nematodes in the irradiated group displayed heterogeneity. Through contour analysis, trends of behavior kinematics and reproductive capacity of irradiated nematodes proved to be consistent with the dose distribution levels estimated by microdosimetric model. Finally, C. elegans presented a suitable combined model of microdosimetry and biology for studying radiation.

DNA repair, recombination, and damage signaling

DNA must be accurately copied and propagated from one cell division to the next, and from one generation to the next. To ensure the faithful transmission of the genome, a plethora of distinct as well as overlapping DNA repair and recombination pathways have evolved. These pathways repair a large variety of lesions, including alterations to single nucleotides and DNA single and double-strand breaks, that are generated as a consequence of normal cellular function or by external DNA damaging agents. In addition to the proteins that mediate DNA repair, checkpoint pathways have also evolved to monitor the genome and coordinate the action of various repair pathways. Checkpoints facilitate repair by mediating a transient cell cycle arrest, or through initiation of cell suicide if DNA damage has overwhelmed repair capacity. In this chapter, we describe the attributes of Caenorhabditis elegans that facilitate analyses of DNA repair, recombination, and checkpoint signaling in the context of a whole animal. We review the current knowledge of C. elegans DNA repair, recombination, and DNA damage response pathways, and their role during development, growth, and in the germ line. We also discuss how the analysis of mutational signatures in C. elegans is helping to inform cancer mutational signatures in humans.

In vivo assessment of reactive oxygen species production and oxidative stress effects induced by chronic exposure to gamma radiation in Caenorhabditis elegans

In the current study, effects of chronic exposure to ionizing gamma radiation were assessed in the radioresistant nematode Caenorhabditis elegans in order to understand whether antioxidant defences (AODs) could ameliorate radical formation, or if increased ROS levels would cause oxidative damage. This analysis was accompanied by phenotypical as well as molecular investigations, via assessment of reproductive capacity, somatic growth and RNA-seq analysis. The use of a fluorescent reporter strain (sod1::gfp) and two ratiometric biosensors (HyPer and Grx1-roGFP2) demonstrated increased ROS production (H₂O₂) and activation of AODs (SOD1 and Grx) in vivo. The data showed that at dose-rates ≤10 mGy h^-1 defence mechanisms were able to prevent the manifestation of oxidative stress. In contrast, at dose-rates ≥40 mGy h^-1 the continuous formation of radicals caused a redox shift, which lead to oxidative stress transcriptomic responses, including changes in mitochondrial functions, protein degradation, lipid metabolism and collagen synthesis. Moreover, genotoxic effects were among the most over-represented functions affected by chronic gamma irradiation, as indicated by differential regulation of genes involved in DNA damage, DNA repair, cell-cycle checkpoints, chromosome segregation and chromatin remodelling. Ultimately, the exposure to gamma radiation caused reprotoxic effects, with >20% reduction in the number of offspring per adult hermaphrodite at dose-rates ≥40 mGy h^-1, accompanied by the down-regulation of more than 300 genes related to reproductive system, apoptosis, meiotic functions and gamete development and fertilization.

Gamma radiation induces life stage-dependent reprotoxicity in Caenorhabditis elegans via impairment of spermatogenesis

The current study investigated life stage, tissue and cell dependent sensitivity to ionizing radiation of the nematode Caenorhabditis elegans. Results showed that irradiation of post mitotic L4 stage larvae induced no significant effects with respect to mortality, morbidity or reproduction at either acute dose ≤6 Gy (1500 mGy·h^-1) or chronic exposure ≤15 Gy (≤100 mGy·h^-1). In contrast, chronic exposure from the embryo to the L4-young adult stage caused a dose and dose-rate dependent reprotoxicity with 43% reduction in total brood size at 6.7 Gy (108 mGy·h^-1). Systematic irradiation of the different developmental stages showed that the most sensitive life stage was L1 to young L4. Exposure during these stages was associated with dose-rate dependent genotoxic effects, resulting in a 1.8 to 2 fold increase in germ cell apoptosis in larvae subjected to 40 or 100 mGy·h^-1, respectively. This was accompanied by a dose-rate dependent reduction in the number of spermatids, which was positively correlated to the reprotoxic effect (0.99, PCC). RNAseq analysis of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of differentially expressed genes related to both male and hermaphrodite reproductive processes. Gene network analysis revealed effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. Furthermore, the expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatid production was correlated (R² 0.80) to the reduction in reproduction and the number of spermatids. Collectively these observations corroborate the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes maintained much of their reproductive capacity in spite of the reduced growth.

Enhancement of DNA damage repair potential in germ cells of Caenorhabditis elegans by a volatile signal from their irradiated partners

Radiation-induced bystander effects have been demonstrated within organisms. Recently, it is found that the organisms can also signal irradiation cues to their co-cultured partners in a waterborne manner. In contrast, there is a limited understanding of radiation-induced airborne signaling between individuals, especially on the aspect of DNA damage responses (DDR). Here, we establish a co-culture experimental system using Caenorhabdis elegans in a top-bottom layout, where communication between "top" and "bottom" worms is airborne. The radiation response of top worms is evaluated using radio-adaptive response (RAR) of embryonic lethality (F1), which reflects an enhancement in repair potential of germ cells to subsequent DNA damage. It is shown that gamma-irradiation of bottom worms alleviates the embryonic lethality of top worms caused by 25 Gy of subsequent gamma-irradiation, i.e. RAR, indicating that a volatile signal might play an essential role in radiation-induced inter-worm communication. The RAR is absent in the top worms impaired in DNA damage checkpoint, nucleotide excision repair, and olfactory sensory neurons, respectively. The induction of RAR is restricted to the mitotic zone of the female germline of hermaphrodites. These results indicate that the top worms sense the volatile signal through cephalic sensory neurons, and the neural stimulation distantly modulates the DDR in germ mitotic cells, leading to the enhancement of DNA damage repair potential. The volatile signal is produced specifically by the L3-stage bottom worms and functionally distinct from the known sex pheromone. Its production and/or release are regulated by water-soluble ascaroside pheromones in a population-dependent manner.

Current status of space radiobiological studies in China

After successfully launching two space laboratories, namely, Tiangong-1 and Tiangong-2, China has announced her next plan of constructing the Chinese Space Station (CSS) in 2022. The CSS will provide not only platforms for Chinese scientists to carry out experimental studies in outer space but also opportunities for open international cooperation. In this article, we review the development of China's manned space exploration missions and the preliminary plan for CSS. Additionally, China has initiated space radiation research decades ago with both ground-based simulation research platform and space vehicles and has made noticeable progresses in several aspects. These include studies on human health risk assessment using mammalian cell cultures and animals as models. Furthermore, there have been numerous studies on assessing the space environment in plant breeding.

Monte-Carlo dosimetry and real-time imaging of targeted irradiation consequences in 2-cell stage Caenorhabditis elegans embryo

Charged-particle microbeams (CPMs) provide a unique opportunity to investigate the effects of ionizing radiation on living biological specimens with a precise control of the delivered dose, i.e. the number of particles per cell. We describe a methodology to manipulate and micro-irradiate early stage C. elegans embryos at a specific phase of the cell division and with a controlled dose using a CPM. To validate this approach, we observe the radiation-induced damage, such as reduced cell mobility, incomplete cell division and the appearance of chromatin bridges during embryo development, in different strains expressing GFP-tagged proteins in situ after irradiation. In addition, as the dosimetry of such experiments cannot be extrapolated from random irradiations of cell populations, realistic three-dimensional models of 2 cell-stage embryo were imported into the Geant4 Monte-Carlo simulation toolkit. Using this method, we investigate the energy deposit in various chromatin condensation states during the cell division phases. The experimental approach coupled to Monte-Carlo simulations provides a way to selectively irradiate a single cell in a rapidly dividing multicellular model with a reproducible dose. This method opens the way to dose-effect investigations following targeted irradiation.

Enhancing low-dose risk assessment using mechanistic mathematical models of radiation effects

Mechanistic mathematical modeling of ionizing radiation (IR) effects has a long history spanning several decades. Models that mathematically represent current knowledge and hypotheses about how radiation damages cells and organs, leading to deleterious outcomes such as carcinogenesis, are particularly useful for estimating radiation risks at doses that are relevant for radiation protection, but are too low to provide a strong 'signal-to-noise ratio' in epidemiological or experimental studies with realistic sample sizes. Here, I discuss examples of models in several relevant areas, including radionuclide biokinetics, non-targeted IR effects, DNA double-strand break (DSB) rejoining and radiation carcinogenesis. I do not provide a detailed review of the vast modeling literature in these fields, but focus on concepts that we have implemented, such as using continuous probability distributions of exponential rates to model radionuclide biokinetics and DSB rejoining, and combining short and long time scales in carcinogenesis models. Improvements in models, including the ability to generate new hypotheses based on model predictions, may come from the introduction of additional novel concepts and from integrating multiple data types.

Review of microbial resistance to chronic ionizing radiation exposure under environmental conditions

Ionizing radiation (IR) produces multiple types of damage to nucleic acids, proteins and other crucial cellular components. Nevertheless, various microorganisms from phylogenetically distant taxa (bacteria, archaea, fungi) can resist IR levels many orders of magnitude above natural background. This intriguing phenomenon of radioresistance probably arose independently many times throughout evolution as a byproduct of selective pressures from other stresses (e.g. desiccation, UV radiation, chemical oxidants). Most of the literature on microbial radioresistance is based on acute γ-irradiation experiments performed in the laboratory, typically involving pure cultures grown under near-optimal conditions. There is much less information about the upper limits of radioresistance in the field, such as in radioactively-contaminated areas, where several radiation types (e.g. α and β, as well as γ) and other stressors (e.g. non-optimal temperature and nutrient levels, toxic chemicals, interspecific competition) act over multiple generations. Here we discuss several examples of radioresistant microbes isolated from extremely radioactive locations (e.g. Chernobyl and Mayak nuclear plant sites) and estimate the radiation dose rates they were able to tolerate. Some of these organisms (e.g. the fungus Cladosporium cladosporioides, the cyanobacterium Geitlerinema amphibium) are widely-distributed and colonize a variety of habitats. These examples suggest that resistance to chronic IR and chemical contamination is not limited to rare specialized strains from extreme environments, but can occur among common microbial taxa, perhaps due to overlap between mechanisms of resistance to IR and other stressors.

Region-specific irradiation system with heavy-ion microbeam for active individuals of Caenorhabditis elegans

Radiation may affect essential functions and behaviors such as locomotion, feeding, learning and memory. Although whole-body irradiation has been shown to reduce motility in the nematode Caenorhabditis elegans, the detailed mechanism responsible for this effect remains unknown. Targeted irradiation of the nerve ring responsible for sensory integration and information processing would allow us to determine whether the reduction of motility following whole-body irradiation reflects effects on the central nervous system or on the muscle cells themselves. We therefore addressed this issue using a collimating microbeam system. However, radiation targeting requires the animal to be immobilized, and previous studies have anesthetized animals to prevent their movement, thus making it impossible to assess their locomotion immediately after irradiation. We developed a method in which the animal was enclosed in a straight, microfluidic channel in a polydimethylsiloxane chip to inhibit free motion during irradiation, thus allowing locomotion to be observed immediately after irradiation. The head region (including the central nervous system), mid region around the intestine and uterus, and tail region were targeted independently. Each region was irradiated with 12 000 carbon ions (12C; 18.3 MeV/u; linear energy transfer = 106.4 keV/μm), corresponding to 500 Gy at a φ20 μm region. Motility was significantly decreased by whole-body irradiation, but not by irradiation of any of the individual regions, including the central nervous system. This suggests that radiation inhibits locomotion by a whole-body mechanism, potentially involving motoneurons and/or body-wall muscle cells, rather than affecting motor control via the central nervous system and the stimulation response.

A dynamic energy-based model to analyze sublethal effects of chronic gamma irradiation in the nematode Caenorhabditis elegans

Understanding how toxic contaminants affect wildlife species at various levels of biological organization (subcellular, histological, physiological, organism, and population levels) is a major research goal in both ecotoxicology and radioecology. A mechanistic understanding of the links between different observed perturbations is necessary to predict the consequences for survival, growth, and reproduction, which are critical for population dynamics. In this context, experimental and modeling studies were conducted using the nematode Caenorhabditis elegans. A chronic exposure to external gamma radiation was conducted under controlled conditions. Results showed that somatic growth and reproduction were reduced with increasing dose rate. Modeling was used to investigate whether radiation effects might be assessed using a mechanistic model based upon the dynamic energy budget (DEB) theory. A DEB theory in toxicology (DEB-tox), specially adapted to the case of gamma radiation, was developed. Modelling results demonstrated the suitability of DEB-tox for the analysis of radiotoxicity and suggested that external gamma radiation predominantly induced a direct reduction in reproductive capacity in C. elegans and produced an increase in costs for growth and maturation, resulting in a delay in growth and spawning observed at the highest tested dose rate.

Bystander signaling via oxidative metabolism

The radiation-induced bystander effect (RIBE) is the initiation of biological end points in cells (bystander cells) that are not directly traversed by an incident-radiation track, but are in close proximity to cells that are receiving the radiation. RIBE has been indicted of causing DNA damage via oxidative stress, besides causing direct damage, inducing tumorigenesis, producing micronuclei, and causing apoptosis. RIBE is regulated by signaling proteins that are either endogenous or secreted by cells as a means of communication between cells, and can activate intracellular or intercellular oxidative metabolism that can further trigger signaling pathways of inflammation. Bystander signals can pass through gap junctions in attached cell lines, while the suspended cell lines transmit these signals via hormones and soluble proteins. This review provides the background information on how reactive oxygen species (ROS) act as bystander signals. Although ROS have a very short half-life and have a nanometer-scale sphere of influence, the wide variety of ROS produced via various sources can exert a cumulative effect, not only in forming DNA adducts but also setting up signaling pathways of inflammation, apoptosis, cell-cycle arrest, aging, and even tumorigenesis. This review outlines the sources of the bystander effect linked to ROS in a cell, and provides methods of investigation for researchers who would like to pursue this field of science.

Characterizing responses to gamma radiation by a highly clonogenic fish brain endothelial cell line

PURPOSE

The clonogenic property and radiobiological responses of a fish brain endothelial cell line, eelB, derived from the American eel were studied.

METHODS

Clonogenic assays were performed to determine the plating efficiency of the eelB cells and to evaluate the clonogenic survival fractions after direct irradiation to low-dose low-LET gamma radiation or receiving irradiated cell conditioned medium in the bystander effect experiments.

RESULT

eelB had the second highest plating efficiency ever reported to date for fish cell lines. Large eelB macroscopic colonies could be formed in a short period of time and were easy to identify and count. Unlike with other fish clonogenic cell lines, which had a relatively slow proliferation profile, clonogenic assays with the eelB cells could be completed as early as 12 days in culture. After direct irradiation with gamma rays at low doses ranging from 0.1Gy to 5Gy, the dose-clonogenic survival curve of the eelB cell line showed a linear trend and did not develop a shoulder region. A classical radio-adaptive response was not induced with the clonogenic survival endpoint when the priming dose (0.1 or 0.5Gy) was delivered 6h before the challenge dose (3 or 5Gy). However, a radio-adaptive response was observed in progeny cells that survived 5Gy and developed lethal mutations. eelB appeared to lack the ability to produce damaging radiation-induced bystander signals on both eelB and HaCaT recipient cells.

CONCLUSION

eelB cell line could be a very useful cell model in the study of radiation impacts on the aquatic health.

Spatial function of the oxidative DNA damage response in radiation induced bystander effects in intra- and inter-system of Caenorhabditis elegans

Though the signaling events involved in radiation induced bystander effects (RIBE) have been investigated both in vitro and in vivo, the spatial function of these communications, especially the related signaling pathways, is not fully elucidated. In the current study, significant increases of DNA damage were clearly observed in C. elegans germline upon irradiation to both intra-system of posterior pharynx and inter-system of vulva, in which more severe damage, even to F1 generation worms, was shown for vulva irradiation. Spatial function assay indicated the DDR key components of mrt-2/hus-1/cep-1/ced-4 were indispensable in germ cells for both sites irradiation, while those components in somatic cells were either not (cep-1/ced-4) or partially (mrt-2/hus-1) required to promote apoptosis. Moreover, production of reactive oxygen species (ROS) indicated by the superoxide dismutase expression and the unfolded protein response of the mitochondria was found systemically involved in the initiation of these processes for both two site irradiation. These results will give a better understanding of the RIBE mechanisms in vivo, and invaluable to assess the clinical relevance to radiotherapy.

Interaction between Radioadaptive Response and Radiation-Induced Bystander Effect in Caenorhabditis elegans : A Unique Role of the DNA Damage Checkpoint

Although radioadaptive responses (RAR) and radiation-induced bystander effects (RIBE) are two important biological effects of low-dose radiation, there are currently only limited data that directly address their interaction, particularly in the context of whole organisms. In previous studies, we separately demonstrated RAR and RIBE using an in vivo system of C. elegans . In the current study, we further investigated their interaction in C. elegans , with the ratio of protruding vulva as the biological end point for RAR. Fourteen-hour-old worms were first locally targeted with a proton microbeam, and were then challenged with a high dose of whole-body gamma radiation. Microbeam irradiation of the posterior pharynx bulbs and rectal valves of C. elegans could significantly suppress the induction of protruding vulva by subsequent gamma irradiation, suggesting a contribution of RIBE to RAR in the context of the whole organism. Moreover, C. elegans has a unique DNA damage response in which the upstream DNA damage checkpoint is not active in most of somatic cells, including vulval cells. However, its impairment in atm-1 and hus-1 mutants blocked the RIBE-initiated RAR of vulva. Similarly, mutations in the atm-1 and hus-1 genes inhibited the RAR of vulva initiated by microbeam irradiation of the vulva itself. These results further confirm that the DNA damage checkpoint participates in the induction of RAR of vulva in C. elegans in a cell nonautonomous manner.

A pivotal role of the jasmonic acid signal pathway in mediating radiation-induced bystander effects in Arabidopsis thaliana

Although radiation-induced bystander effects (RIBE) in Arabidopsis thaliana have been well demonstrated in vivo, little is known about their underlying mechanisms, particularly with regard to the participating signaling molecules and signaling pathways. In higher plants, jasmonic acid (JA) and its bioactive derivatives are well accepted as systemic signal transducers that are produced in response to various environmental stresses. It is therefore speculated that the JA signal pathway might play a potential role in mediating radiation-induced bystander signaling of root-to-shoot. In the present study, pretreatment of seedlings with Salicylhydroxamic acid, an inhibitor of lipoxigenase (LOX) in JA biosynthesis, significantly suppressed RIBE-mediated expression of the AtRAD54 gene. After root irradiation, the aerial parts of A. thaliana mutants deficient in JA biosynthesis (aos) and signaling cascades (jar1-1) showed suppressed induction of the AtRAD54 and AtRAD51 genes and TSI and 180-bp repeats, which have been extensively used as endpoints of bystander genetic and epigenetic effects in plants. These results suggest an involvement of the JA signal pathway in the RIBE of plants. Using the root micro-grafting technique, the JA signal pathway was shown to participate in both the generation of bystander signals in irradiated root cells and radiation responses in the bystander aerial parts of plants. The over-accumulation of endogenous JA in mutant fatty acid oxygenation up-regulated 2 (fou2), in which mutation of the Two Pore Channel 1 (TPC1) gene up-regulates expression of the LOX and allene oxide synthase (AOS) genes, inhibited RIBE-mediated expression of the AtRAD54 gene, but up-regulated expression of the AtKU70 and AtLIG4 genes in the non-homologous end joining (NHEJ) pathway. Considering that NHEJ is employed by plants with increased DNA damage, the switch from HR to NHEJ suggests that over-accumulation of endogenous JA might enhance the radiosensitivity of plants in terms of RIBE.

Radioadaptive Response for Reproductive Cell Death Demonstrated in In Vivo Tissue Model of Caenorhabditis elegans

Reproductive cell death (RCD) occurs after one or more cell divisions resulting from an insult such as radiation exposure or other treatments with carcinogens or mutagens. The radioadaptive response for RCD is usually investigated by in vitro or in vivo clonogenic assay. To date, this has not been demonstrated in the vulval tissue in Caenorhabditis elegans ( C. elegans ), which is a well established in vivo model for radiation-induced RCD. In this study to determine whether radioadaptive response occurs in the vulval tissue model of C. elegans , early larval worms were gamma irradiated with lower adaptive doses, followed by higher challenge doses. The ratio of protruding vulva was used to assess the RCD of vulval cells. The results of this study showed that the radioadaptive response for RCD in this vulval tissue model could be well induced by dose combinations of 5 + 75 Gy and 5 + 100 Gy at the time point of 14-16 h in worm development. In addition, the time course analysis indicated that radioresistance in vulval cells developed within 1.75 h after an adaptive dose and persisted for only a short period of time (2-4 h). DNA damage checkpoint and non-homologous end joining were involved in the radioadaptive response, exhibiting induction of protruding vulva in worms deficient in these two pathways similar to their controls. Interestingly, the DNA damage checkpoint was not active in the somatic vulval cells, and it was therefore suggested that the DNA damage checkpoint might mediate the radioadaptive response in a cell nonautonomous manner. Here, we show evidence of the occurrence of a radioadaptive response for RCD in the vulval tissue model of C. elegans . This finding provides a potential opportunity to gain further insight into the underlying mechanisms of the radioadaptive response for RCD, in view of the abundant genetic resources of C. elegans .

Systemic mechanisms and effects of ionizing radiation: A new 'old' paradigm of how the bystanders and distant can become the players

Exposure of cells to any form of ionizing radiation (IR) is expected to induce a variety of DNA lesions, including double strand breaks (DSBs), single strand breaks (SSBs) and oxidized bases, as well as loss of bases, i.e., abasic sites. The damaging potential of IR is primarily related to the generation of electrons, which through their interaction with water produce free radicals. In their turn, free radicals attack DNA, proteins and lipids. Damage is induced also through direct deposition of energy. These types of IR interactions with biological materials are collectively called 'targeted effects', since they refer only to the irradiated cells. Earlier and sometimes 'anecdotal' findings were pointing to the possibility of IR actions unrelated to the irradiated cells or area, i.e., a type of systemic response with unknown mechanistic basis. Over the last years, significant experimental evidence has accumulated, showing a variety of radiation effects for 'out-of-field' areas (non-targeted effects-NTE). The NTE involve the release of chemical and biological mediators from the 'in-field' area and thus the communication of the radiation insult via the so called 'danger' signals. The NTE can be separated in two major groups: bystander and distant (systemic). In this review, we have collected a detailed list of proteins implicated in either bystander or systemic effects, including the clinically relevant abscopal phenomenon, using improved text-mining and bioinformatics tools from the literature. We have identified which of these genes belong to the DNA damage response and repair pathway (DDR/R) and made protein-protein interaction (PPi) networks. Our analysis supports that the apoptosis, TLR-like and NOD-like receptor signaling pathways are the main pathways participating in NTE. Based on this analysis, we formulate a biophysical hypothesis for the regulation of NTE, based on DNA damage and apoptosis gradients between the irradiation point and various distances corresponding to bystander (5mm) or distant effects (5cm). Last but not least, in order to provide a more realistic support for our model, we calculate the expected DSB and non-DSB clusters along the central axis of a representative 200.6MeV pencil beam calculated using Monte Carlo DNA damage simulation software (MCDS) based on the actual beam energy-to-depth curves used in therapy.

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.

Microfluidics as a new tool in radiation biology

Ionizing radiations interact with molecules at the cellular and molecular levels leading to several biochemical modifications that may be responsible for biological effects on tissue or whole organisms. The study of these changes is difficult because of the complexity of the biological response(s) to radiations and the lack of reliable models able to mimic the whole molecular phenomenon and different communications between the various cell networks, from the cell activation to the macroscopic effect at the tissue or organismal level. Microfluidics, the science and technology of systems that can handle small amounts of fluids in confined and controlled environment, has been an emerging field for several years. Some microfluidic devices, even at early stages of development, may already help radiobiological research by proposing new approaches to study cellular, tissue and total-body behavior upon irradiation. These devices may also be used in clinical biodosimetry since microfluidic technology is frequently developed for integrating complex bioassay chemistries into automated user-friendly, reproducible and sensitive analyses. In this review, we discuss the use, numerous advantages, and possible future of microfluidic technology in the field of radiobiology. We will also examine the disadvantages and required improvements for microfluidics to be fully practical in radiation research and to become an enabling tool for radiobiologists and radiation oncologists.

The crosstalk between α-irradiated Beas-2B cells and its bystander U937 cells through MAPK and NF-κB signaling pathways

Although accumulated evidence suggests that α-particle irradiation induced bystander effect may relevant to lung injury and cancer risk assessment, the exact mechanisms are not yet elucidated. In the present study, a cell co-culture system was used to investigate the interaction between α-particle irradiated human bronchial epithelial cells (Beas-2B) and its bystander macrophage U937 cells. It was found that the cell co-culture amplified the detrimental effects of α-irradiation including cell viability decrease and apoptosis promotion on both irradiated cells and bystander cells in a feedback loop which was closely relevant to the activation of MAPK and NF-κB pathways in the bystander U937 cells. When these two pathways in U937 cells were disturbed by special pharmacological inhibitors before cell co-culture, it was found that a NF-κB inhibitor of BAY 11-7082 further enhanced the proliferation inhibition and apoptosis induction in bystander U937 cells, but MAPK inhibitors of SP600125 and SB203580 protected cells from viability loss and apoptosis and U0126 presented more beneficial effect on cell protection. For α-irradiated epithelial cells, the activation of NF-κB and MAPK pathways in U937 cells participated in detrimental cellular responses since the above inhibitors could largely attenuate cell viability loss and apoptosis of irradiated cells. Our results demonstrated that there are bilateral bystander responses between irradiated lung epithelial cells and macrophages through MAPK and NF-κB signaling pathways, which accounts for the enhancement of α-irradiation induced damage.

A Mouse Ear Model for Bystander Studies Induced by Microbeam Irradiation

Radiation-induced bystander effects have been observed in vitro and in cell and tissue culture models, however, there are few reported studies showing these effects in vivo. To our knowledge, this is the first reported study on bystander effects induced by microbeam irradiation in an intact living mammal. The mouse ear was used to investigate radiation-induced bystander effects in keratinocytes, utilizing a 3 MeV proton microbeam (LET 13.1 keV/μm) with a range in skin of about 135 μm. Using a custom-designed holder, the ear of an anesthetized C57BL/6J mouse was flattened by gentle suction and placed over the microbeam port to irradiate cells along a 35 μm wide, 6 mm long path. Immunohistochemical analysis of γ-H2AX foci formation in tissue sections revealed, compared to control tissue, proton-induced γ-H2AX foci formation in one of the two epidermal layers of the mouse ear. Strikingly, a higher number of cells than expected showed foci from direct irradiation effects. Although the proton-irradiated line was ~35 μm wide, the average width spanned by γ-H2AX-positive cells exceeded 150 μm. Cells adjacent to or in the epidermal layer opposite the γ-H2AX-positive region did not exhibit foci. These findings validate this mammalian model as a viable system for investigating radiation-induced bystander effects in an intact living organism.

Effects of chronic gamma irradiation: a multigenerational study using Caenorhabditis elegans

The effects of chronic exposure to (137)Cs gamma radiation (dose rate ranging from 6.6 to 42.7 mGy h(-1)) on growth and reproductive ability were carried out over three generations of Caenorhabditis elegans (F0, F1, and F2). Exposure began at the egg stage for the first generation and was stopped at the end of laying of third-generation eggs (F2). At the same time, the two subsequent generations from parental exposure were returned to the control conditions (F1' and F2'). There was no radiation-induced significant effect on growth, hatchability, and cumulative number of larvae within generations. Moreover, no significant differences were found in growth parameters (hatching length, maximal length, and a constant related to growth rate) among the generations. However, a decrease in the cumulative number of larvae across exposed generations was observed between F0 and F2 at the highest dose rate (238.8 ± 15.4 and 171.2 ± 13.1 number of larvae per individual, respectively). Besides, the F1' generation was found to lay significantly fewer eggs than the F1 generation for tested dose rates 6.6, 8.1, 19.4, and 28.1 mGy h(-1). Our results confirmed that reproduction (here, cumulative number of larvae) is the most sensitive endpoint affected by chronic exposure to ionizing radiation. The results obtained revealed transgenerational effects from parental exposure in the second generation, and the second non-exposed generation was indeed more affected than the second exposed generation.

Connexins and cyclooxygenase-2 crosstalk in the expression of radiation-induced bystander effects

Background:

Signalling events mediated by connexins and cyclooxygenase-2 (COX-2) have important roles in bystander effects induced by ionising radiation. However, whether these proteins mediate bystander effects independently or cooperatively has not been investigated.

Methods:

Bystander normal human fibroblasts were cocultured with irradiated adenocarcinoma HeLa cells in which specific connexins (Cx) are expressed in the absence of endogenous Cx, before and after COX-2 knockdown, to investigate DNA damage in bystander cells and their progeny.

Results:

Inducible expression of gap junctions composed of connexin26 (Cx26) in irradiated HeLa cells enhanced the induction of micronuclei in bystander cells (P<0.01) and reduced the coculture time necessary for manifestation of the effect. In contrast, expression of connexin32 (Cx32) conferred protective effects. COX-2 knockdown in irradiated HeLa Cx26 cells attenuated the bystander response due to connexin expression. However, COX-2 knockdown resulted in enhanced micronucleus formation in the progeny of the bystander cells (P<0.001). COX-2 knockdown delayed junctional communication in HeLa Cx26 cells, and reduced, in the plasma membrane, the physical interaction of Cx26 with MAPKKK, a controller of the MAPK pathway that regulates COX-2 and connexin.

Conclusions:

Junctional communication and COX-2 cooperatively mediate the propagation of radiation-induced non-targeted effects. Characterising the mediating events affected by both mechanisms may lead to new approaches that mitigate secondary debilitating effects of cancer radiotherapy.

Bystander effects as manifestation of intercellular communication of DNA damage and of the cellular oxidative status

It is becoming increasingly clear that cells exposed to ionizing radiation (IR) and other genotoxic agents (targeted cells) can communicate their DNA damage response (DDR) status to cells that have not been directly irradiated (bystander cells). The term radiation-induced bystander effects (RIBE) describes facets of this phenomenon, but its molecular underpinnings are incompletely characterized. Consequences of DDR in bystander cells have been extensively studied and include transformation and mutation induction; micronuclei, chromosome aberration and sister chromatid exchange formation; as well as modulations in gene expression, proliferation and differentiation patterns. A fundamental question arising from such observations is why targeted cells induce DNA damage in non-targeted, bystander cells threatening thus their genomic stability and risking the induction of cancer. Here, we review and synthesize available literature to gather support for a model according to which targeted cells modulate as part of DDR their redox status and use it as a source to generate signals for neighboring cells. Such signals can be either small molecules transported to adjacent non-targeted cells via gap-junction intercellular communication (GJIC), or secreted factors that can reach remote, non-targeted cells by diffusion or through the circulation. We review evidence that such signals can induce in the recipient cell modulations of redox status similar to those seen in the originating targeted cell - occasionally though self-amplifying feedback loops. The resulting increase of oxidative stress in bystander cells induces, often in conjunction with DNA replication, the observed DDR-like responses that are at times strong enough to cause apoptosis. We reason that RIBE reflect the function of intercellular communication mechanisms designed to spread within tissues, or the entire organism, information about DNA damage inflicted to individual, constituent cells. Such responses are thought to protect the organism by enhancing repair in a community of cells and by eliminating severely damaged cells.