Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts

Despite years of research, understanding of the space radiation environment and the risk it poses to long-duration astronauts remains limited. There is a disparity between research results and observed empirical effects seen in human astronaut crews, likely due to the numerous factors that limit terrestrial simulation of the complex space environment and extrapolation of human clinical consequences from varied animal models. Given the intended future of human spaceflight, with efforts now to rapidly expand capabilities for human missions to the moon and Mars, there is a pressing need to improve upon the understanding of the space radiation risk, predict likely clinical outcomes of interplanetary radiation exposure, and develop appropriate and effective mitigation strategies for future missions. To achieve this goal, the space radiation and aerospace community must recognize the historical limitations of radiation research and how such limitations could be addressed in future research endeavors. We have sought to highlight the numerous factors that limit understanding of the risk of space radiation for human crews and to identify ways in which these limitations could be addressed for improved understanding and appropriate risk posture regarding future human spaceflight.Comment: Accepted for publication by Nature Microgravity (2018

H2AX phosphorylation at the sites of DNA double-strand breaks in cultivated mammalian cells and tissues

A sequence variant of histone H2A called H2AX is one of the key components of chromatin involved in DNA damage response induced by different genotoxic stresses. Phosphorylated H2AX (γH2AX) is rapidly concentrated in chromatin domains around DNA double-strand breaks (DSBs) after the action of ionizing radiation or chemical agents and at stalled replication forks during replication stress. γH2AX foci could be easily detected in cell nuclei using immunofluorescence microscopy that allows to use γH2AX as a quantitative marker of DSBs in various applications. H2AX is phosphorylated in situ by ATM, ATR, and DNA-PK kinases that have distinct roles in different pathways of DSB repair. The γH2AX serves as a docking site for the accumulation of DNA repair proteins, and after rejoining of DSBs, it is released from chromatin. The molecular mechanism of γH2AX dephosphorylation is not clear. It is complicated and requires the activity of different proteins including phosphatases and chromatin-remodeling complexes. In this review, we summarize recently published data concerning the mechanisms and kinetics of γH2AX loss in normal cells and tissues as well as in those deficient in ATM, DNA-PK, and DSB repair proteins activity. The results of the latest scientific research of the low-dose irradiation phenomenon are presented including the bystander effect and the adaptive response estimated by γH2AX detection in cells and tissues

Transcriptional modulations induced by proton irradiation in mice skin in function of adsorbed dose and distance

Hadron therapy by proton beams represents an advanced anti-cancer strategy due to its highly localized dose deposition allowing a greater sparing of normal tissue and/or organs at risk compared to photon/electron radiotherapy. However, it is not clear to what extent non-targeted effects such as transcriptional modulations produced along the beamline may diffuse and impact the surrounding tissue. In this work, we analyze the transcriptome of proton-irradiated mouse skin and choose two biomarker genes to trace their modulation at different distances from the beam's target and at different doses and times from irradiation to understand to what extent and how far it may propagate, using RNA-Seq and quantitative RT-PCR. In parallel, assessment of lipids alteration is performed by FTIR spectroscopy as a measure of tissue damage. Despite the observed high individual variability of expression, we can show evidence of transcriptional modulation of two biomarker genes at considerable distance from the beam's target where a simulation system predicts a significantly lower adsorbed dose. The results are compatible with a model involving diffusion of transcripts or regulatory molecules from high dose irradiated cells to distant tissue's portions adsorbing a much lower fraction of radiation

A systems genetics approach to the characterization of differential low dose radiation responses in BXD recombinant inbred mice

High doses of radiation (HDR) are clearly detrimental to human health, but relatively little is known about the health consequences following exposure to low doses of radiation (LDR, \u3c10cGy). Understanding the risks associated with LDR is of great importance to the general public due to the recent dramatic increase in diagnostic radiological imaging. While HDR clearly suppress immune function, there is evidence that LDR can be immunostimulatory. Within the organism, defining the consequences of LDR is further complicated by the impact of genetic background, particularly in systems such as the immune system for which both radiosensitivity and genetic effects are profound. We addressed the issue of genetic susceptibility to LDR using the immune system as a target system and treated the LDR response as a complex trait analyzed using a systems genetics framework. Using the BXD recombinant inbred strain mouse panel as a genetic reference population allowed us to address the radiation response within the context of natural genetic variation. Our overarching hypothesis is that, within a population, the immunological effects of LDR exposure depend in part on the individual’s baseline immunoprofile and gene expression which are ultimately dependent upon genetic background. We began by establishing the immunophenotypic variation (i.e., T:B cell ratio, CD4:CD8 ratio) within the BXD panel and used baseline spleen transcriptome profiling to identify putative candidate genes controlling these traits, specifically Acp1 and Ptprk for CD4:CD8 ratio. The same set of BXD strains was exposed to LDR (10cGy gamma radiation) to determine effects on immune function and oxidative stress. LDR significantly enhanced neutrophil phagocytosis in a manner that was independent of genetic background. In contrast, genetic background significantly impacted LDR-induced changes in spleen superoxide dismutase activity. By integrating these results with our previous analyses of BXD RI strains, we have demonstrated that baseline expression of Sod2 correlates with LDR-induced SOD activity, and baseline CD4:CD8 ratio is inversely correlated with LDR-induced neutrophil phagocytosis. In addition, spleen transcriptomic data from the BXD parental strains further highlighted the impact of genetic background on LDR responses. These data provide the groundwork for predicting LDR responses using baseline expression, immunophenotypes, and/or genotype

In Vitro Enabling Technologies for use in the Aquatic Environment

O’Dowd, C., Mothersill, C.E., Cairns, M.T., Austin, B., Lyng, F.M., McClean, B. and Murphy, J.E.J. Assessing the mitochondrion as a biomarker of fish tissue damage using g radiation as a stress model in vitro. There is an ever-increasing need for biomarkers to identify toxic stress in the aquatic environment. Such techniques need to be accurate, expeditious, ethical and economical. Typically, in vitro based platforms fit these criteria however many of these systems often undergo ‘assay drift’ and consequently do not fully represent the real-life situation. In recent years, there has been growing interest in the mitochondrion and its (dys)function or altered function and dynamics as a marker of toxic assault. The mitochondrion is an essential organelle in the cell and is associated with energy production and metabolism in the organism as it is the site of oxidative phosphorylation (OXPHOS). It has its own genetic material which is more susceptible to damage than nuclear DNA (nDNA) due to its proximity to the site of OXPHOS, the absence of introns, the lack of a protective histone coat and effective repair mechanisms which are present in nDNA. Stress responses including increases in mitochondrial mass and alteration in the activity of proteins associated with OXPHOS have been reported and offer potential as putative biomarkers of toxicity. In this study, we used real-time PCR to identify alterations in mitochondrial genome copy number in cultured fish tissues exposed to g radiation. These values were compared to the activity of the citrate synthase enzyme, an established marker of mitochondrial mass in cells. Results show that while this approach is appropriate and the technique is robust, expeditious and straightforward, further development is required to yield greater enhancement and sensitivity

Low-Dose Radiation Effects on Animals and Ecosystems

This open access book summarizes the latest scientific findings regarding the biological effects of the Fukushima Daiichi Nuclear Power Plant (FNPP) accident in 2011. Various cases of changes in animals and organisms have been reported since the FNPP accident. However, it is often unknown whether they are actually due to radiation, since the dose or dose-rate are not necessarily associated with the changes observed. This book brings together the works of radiation biologists and ecologists to provide reliable radioecology data and gives insight into future radioprotection. The book examines the environmental pollution and radiation exposure, and contains valuable data from abandoned livestock in the ex-evacuation zone and from wild animals including invertebrates and vertebrates, aqueous and terrestrial animals, and plants that are subjected to long-term exposure in the area still affected by radiation. It also analyzes dose evaluation, and offers new perspectives gained from the accident, as well as an overview for future studies to promote radioprotection of humans and the ecosystem. Since the biological impact of radiation is influenced by various factors, it is difficult to scientifically define the effects of low-dose/low-dose-rate radiation. However, the detailed research data presented can be combined with the latest scientific and technological advances, such as artificial intelligence, to provide new insights in the future. This book is a unique and valuable resource for researchers, professionals and anyone interested in the impact of exposure to radiation or contamination with radioactive materials

Correlation of DNA double strand break repair efficiency and susceptibility to lung tumor development

2015 Spring.Includes bibliographical references.In this dissertation we describe the use of many CcS/Dem recombinant congenic strains (RCS) of mice to determine if there is any correlation between the DNA double strand break (DSB) repair efficiency and susceptibility to lung tumor development. A previous study involving 20 different CcS/Dem RCS of mice all derived from cross of BALB/c x STS progenitors (BALB/c is the recipient strain that is susceptible to tumor development and STS the donor is resistant) showed wide inter-strain variations in susceptibility to radiation-induced lung tumor development. As formalin fixation was used to obtain paraffin embedded tissue sections for immunofluorescence, we first evaluated different methods of euthanasia, perfusion techniques, autofluorescence reduction and antigen retrieval methods to optimize the procedures used so as to obtain reproducible results. The formation of phosphorylated histone H2AX (γ-H2AX) into discrete foci was used as the marker for DSB repair and its co-localization with 53BP1, another component of repair foci, was examined during the optimization. From the optimization phase, CO₂ asphyxiation, right ventricular perfusion, use of sodium borohydride for quenching autofluorescence and the use of sodium citrate for heat-induced epitope retrieval (antigen retrieval) gave very good quality images and were adopted for use in all subsequent experiments. To explore a possible link between heritable differences in DNA DSB repair efficiency and susceptibility to RI lung cancer in a mouse model, we quantified residual γH2AX foci in lungs of 16 different CcS/Dem RCS mice together with their founders after irradiation from a ¹³⁷Cs source of γ-rays at a low-dose rate of 10 cGy/hr for 24 h. We also explored residual γH2AX foci in the peripheral blood leukocytes to compare it with foci in the lungs with the intention of using PBLs as a surrogate to assess DNA repair efficiency in the lungs for possible use in clinical applications to pre-screening patients and assess their suitability as candidates for radiotherapy, especially in fairly young. In the lungs, the results showed a high correlation between mean residual γH2AX foci number per nucleus and radiation-induced lung tumor observed in the previous study (R=0.968, p t transition resulting in amino acid substitution that abolishes a BsmBI restriction site. The outcome of these restriction patterns suggests no direct correlation between DNA-PK and DSB repair efficiency and that another gene (or other genes) polymorphic between BALB/c and STS/A may determine the strain differences in DSB repair efficiencies

Loss of ATM/Chk2/p53 Pathway Components Accelerates Tumor Development and Contributes to Radiation Resistance in Gliomas

SummaryMaintenance of genomic integrity is essential for adult tissue homeostasis and defects in the DNA-damage response (DDR) machinery are linked to numerous pathologies including cancer. Here, we present evidence that the DDR exerts tumor suppressor activity in gliomas. We show that genes encoding components of the DDR pathway are frequently altered in human gliomas and that loss of elements of the ATM/Chk2/p53 cascade accelerates tumor formation in a glioma mouse model. We demonstrate that Chk2 is required for glioma response to ionizing radiation in vivo and is necessary for DNA-damage checkpoints in the neuronal stem cell compartment. Finally, we observed that the DDR is constitutively activated in a subset of human GBMs, and such activation correlates with regions of hypoxia