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

Hair Follicle Damage after 100 mGy Low-Dose Fractionated X-Ray Irradiation and the Protective Effects of TEMPOL, a Stable Nitroxide Radical, against Radiation

The effects of long-term low-dose X-ray irradiation on the outer root sheath (ORS) cells of C3H/He mice were investigated. Mice were irradiated with a regime of 100 mGy/day, 5 days/week, for 12 weeks (Group X) and the results obtained were compared to those in a non-irradiated control (Group C). Potential protection against ORS cells damage induced by this exposure was investigated by adding the stable nitroxide radical 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) at 1 mM to the drinking water of mice (Group X + TEMPOL). The results obtained were compared with Group C and a non-irradiated group treated with TEMPOL (Group C + TEMPOL). After fractionated X-ray irradiation, skin was removed and ORS cells were examined by hematoxylin and eosin staining and electron microscopy for an abnormal nuclear morphology and nuclear condensation changes. Fractionated X-irradiated mice had an increased number of ORS cells with an abnormal nuclear morphology as well as nuclear condensation changes. Sections were also immunohistochemically examined for the presence of TdT-mediated dUTP nick-end labeling (TUNEL), 8-hydroxy-2'-deoxyguanosine (8-OHdG), 4-hydroxynonenal (4-HNE), vascular endothelial growth factor (VEGF), nitrotyrosine, heme oxygenase 1 (HO-1), and protein gene product 9.5 (PGP 9.5). Significant increases were observed in TUNEL, 8-OHdG, and 4-HNE levels in ORS cells from mice in Group X. Electron microscopy also showed irregular shrunken ORS cells in Group X. These changes were prevented by the presence of TEMPOL in the drinking water of the irradiated mice. TEMPOL alone had no significant effects. These results suggest that fractionated doses of radiation induced oxidative damage in ORS cells; however, TEMPOL provided protection against this damage, possibly as a result of the rapid reaction of this nitroxide radical with the reactive oxidants generated by fractionated X-ray irradiation.

Differential Gene Expression in Human Fibroblasts Simultaneously Exposed to Ionizing Radiation and Simulated Microgravity

During future space missions, astronauts will be exposed to cosmic radiation and microgravity (μG), which are known to be health risk factors. To examine the differentially expressed genes (DEG) and their prevalent biological processes and pathways as a response to these two risk factors simultaneously, 1BR-hTERT human fibroblast cells were cultured under 1 gravity (1G) or simulated μG for 48 h in total and collected at 0 (sham irradiated), 3 or 24 h after 1 Gy of X-ray or Carbon-ion (C-ion) irradiation. A three-dimensional clinostat was used for the simulation of μG and the simultaneous radiation exposure of the samples. The RNA-seq method was used to produce lists of differentially expressed genes between different environmental conditions. Over-representation analyses were performed and the enriched biological pathways and targeting transcription factors were identified. Comparing sham-irradiated cells under simulated μG and 1G conditions, terms related to response to oxygen levels and muscle contraction were identified. After irradiation with X-rays or C-ions under 1G, identified DEGs were found to be involved in DNA damage repair, signal transduction by p53 class mediator, cell cycle arrest and apoptosis pathways. The same enriched pathways emerged when cells were irradiated under simulated μG condition. Nevertheless, the combined effect attenuated the transcriptional response to irradiation which may pose a subtle risk in space flights.

Targeting mitochondria as a therapeutic anti-gastric cancer approach

Gastric cancer is regarded as the fifth most common cancer globally but the third most common cancer death. Although systemic chemotherapy is the primary treatment for advanced gastric cancer patients, the outcome of chemotherapy is unsatisfactory. Novel therapeutic strategies and potential alternative treatments are therefore needed to overcome the impact of this disease. At a cellular level, mitochondria play an important role in cell survival and apoptosis. A growing body of studies have shown that mitochondria play a central role in the regulation of cellular function, metabolism, and cell death during carcinogenesis. Interestingly, the impact of mitochondrial dynamics, including fission/fusion and mitophagy, on carcinogenesis and cancer progression has also been reported, suggesting the potential targeting of mitochondrial dynamics for the treatment of cancer. This review not only comprehensively summarizes the homeostasis of gastric cancer cells, but the potential therapeutic interventions for the targeting of mitochondria for gastric cancer therapy are also highlighted and discussed.

Implications of Altered Endosome and Lysosome Biology in Space Environments

Space exploration poses multiple challenges for mankind, not only on a technical level but also to the entire physiology of the space traveller. The human system must adapt to several environmental stressors, microgravity being one of them. Lysosomes are ubiquitous to every cell and essential for their homeostasis, playing significant roles in the regulation of autophagy, immunity, and adaptation of the organism to changes in their environment, to name a few. Dysfunction of the lysosomal system leads to age-related diseases, for example bone loss, reduced immune response or cancer. As these conditions have been shown to be accelerated following exposure to microgravity, this review elucidates the lysosomal response to real and simulated microgravity. Microgravity activates the endo-lysosomal system, with resulting impacts on bone loss, muscle atrophy and stem cell differentiation. The investigation of lysosomal adaptation to microgravity can be beneficial in the search for new biomarkers or therapeutic approaches to several disease pathologies on earth as well as the potential to mitigate pathophysiology during spaceflight.

Expression Profile of Cell Cycle-Related Genes in Human Fibroblasts Exposed Simultaneously to Radiation and Simulated Microgravity

Multiple unique environmental factors such as space radiation and microgravity (μG) pose a serious threat to human gene stability during space travel. Recently, we reported that simultaneous exposure of human fibroblasts to simulated μG and radiation results in more chromosomal aberrations than in cells exposed to radiation alone. However, the mechanisms behind this remain unknown. The purpose of this study was thus to obtain comprehensive data on gene expression using a three-dimensional clinostat synchronized to a carbon (C)-ion or X-ray irradiation system. Human fibroblasts (1BR-hTERT) were maintained under standing or rotating conditions for 3 or 24 h after synchronized C-ion or X-ray irradiation at 1 Gy as part of a total culture time of 2 days. Among 57,773 genes analyzed with RNA sequencing, we focused particularly on the expression of 82 cell cycle-related genes after exposure to the radiation and simulated μG. The expression of cell cycle-suppressing genes (ABL1 and CDKN1A) decreased and that of cell cycle-promoting genes (CCNB1, CCND1, KPNA2, MCM4, MKI67, and STMN1) increased after C-ion irradiation under μG. The cell may pass through the G₁/S and G₂ checkpoints with DNA damage due to the combined effects of C-ions and μG, suggesting that increased genomic instability might occur in space.

Increased Chromosome Aberrations in Cells Exposed Simultaneously to Simulated Microgravity and Radiation

Space radiation and microgravity (μG) are two major environmental stressors for humans in space travel. One of the fundamental questions in space biology research is whether the combined effects of μG and exposure to cosmic radiation are interactive. While studies addressing this question have been carried out for half a century in space or using simulated μG on the ground, the reported results are ambiguous. For the assessment and management of human health risks in future Moon and Mars missions, it is necessary to obtain more basic data on the molecular and cellular responses to the combined effects of radiation and µG. Recently we incorporated a μG⁻irradiation system consisting of a 3D clinostat synchronized to a carbon-ion or X-ray irradiation system. Our new experimental setup allows us to avoid stopping clinostat rotation during irradiation, which was required in all other previous experiments. Using this system, human fibroblasts were exposed to X-rays or carbon ions under the simulated μG condition, and chromosomes were collected with the premature chromosome condensation method in the first mitosis. Chromosome aberrations (CA) were quantified by the 3-color fluorescent in situ hybridization (FISH) method. Cells exposed to irradiation under the simulated μG condition showed a higher frequency of both simple and complex types of CA compared to cells irradiated under the static condition by either X-rays or carbon ions.

Synergistic Effects of Weightlessness, Isoproterenol, and Radiation on DNA Damage Response and Cytokine Production in Immune Cells

The implementation of rotating-wall vessels (RWVs) for studying the effect of lack of gravity has attracted attention, especially in the fields of stem cells, tissue regeneration, and cancer research. Immune cells incubated in RWVs exhibit several features of immunosuppression including impaired leukocyte proliferation, cytokine responses, and antibody production. Interestingly, stress hormones influence cellular immune pathways affected by microgravity, such as cell proliferation, apoptosis, DNA repair, and T cell activation. These pathways are crucial defense mechanisms that protect the cell from toxins, pathogens, and radiation. Despite the importance of the adrenergic receptor in regulating the immune system, the effect of microgravity on the adrenergic system has been poorly studied. Thus, we elected to investigate the synergistic effects of isoproterenol (a sympathomimetic drug), radiation, and microgravity in nonstimulated immune cells. Peripheral blood mononuclear cells were treated with the sympathomimetic drug isoproterenol, exposed to 0.8 or 2 Gy γ-radiation, and incubated in RWVs. Mixed model regression analyses showed significant synergistic effects on the expression of the β2-adrenergic receptor gene (ADRB2). Radiation alone increased ADRB2 expression, and cells incubated in microgravity had more DNA strand breaks than cells incubated in normal gravity. We observed radiation-induced cytokine production only in microgravity. Prior treatment with isoproterenol clearly prevents most of the microgravity-mediated effects. RWVs may be a useful tool to provide insight into novel regulatory pathways, providing benefit not only to astronauts but also to patients suffering from immune disorders or undergoing radiotherapy.

Effects of Iron Overload and Oxidative Damage on the Musculoskeletal System in the Space Environment: Data from Spaceflights and Ground-Based Simulation Models

The space environment chiefly includes microgravity and radiation, which seriously threatens the health of astronauts. Bone loss and muscle atrophy are the two most significant changes in mammals after long-term residency in space. In this review, we summarized current understanding of the effects of microgravity and radiation on the musculoskeletal system and discussed the corresponding mechanisms that are related to iron overload and oxidative damage. Furthermore, we enumerated some countermeasures that have a therapeutic potential for bone loss and muscle atrophy through using iron chelators and antioxidants. Future studies for better understanding the mechanism of iron and redox homeostasis imbalance induced by the space environment and developing the countermeasures against iron overload and oxidative damage consequently may facilitate human to travel more safely in space.

Development and performance evaluation of a three-dimensional clinostat synchronized heavy-ion irradiation system

Outer space is an environment characterized by microgravity and space radiation, including high-energy charged particles. Astronauts are constantly exposed to both microgravity and radiation during long-term stays in space. However, many aspects of the biological effects of combined microgravity and space radiation remain unclear. We developed a new three-dimensional (3D) clinostat synchronized heavy-ion irradiation system for use in ground-based studies of the combined exposures. Our new system uses a particle accelerator and a respiratory gating system from heavy-ion radiotherapy to irradiate samples being rotated in the 3D clinostat with carbon-ion beams only when the samples are in the horizontal position. A Peltier module and special sample holder were loaded on a static stage (standing condition) and the 3D clinostat (rotation condition) to maintain a suitable temperature under atmospheric conditions. The performance of the new device was investigated with normal human fibroblasts 1BR-hTERT in a disposable closed cell culture chamber. Live imaging revealed that cellular adhesion and growth were almost the same for the standing control sample and rotation sample over 48h. Dose flatness and symmetry were judged according to the relative density of Gafchromic films along the X-axis and Y-axis of the positions of the irradiated sample to confirm irradiation accuracy. Doses calculated using the carbon-ion calibration curve were almost the same for standing and rotation conditions, with the difference being less than 5% at 1Gy carbon-ion irradiation. Our new device can accurately synchronize carbon-ion irradiation and simulated microgravity while maintaining the temperature under atmospheric conditions at ground level.

Changes in mitochondrial homeostasis and redox status in astronauts following long stays in space

The effects of long-term exposure to extreme space conditions on astronauts were investigated by analyzing hair samples from ten astronauts who had spent six months on the International Space Station (ISS). Two samples were collected before, during and after their stays in the ISS; hereafter, referred to as Preflight, Inflight and Postflight, respectively. The ratios of mitochondrial (mt) to nuclear (n) DNA and mtRNA to nRNA were analyzed via quantitative PCR. The combined data of Preflight, Inflight and Postflight show a significant reduction in the mtDNA/nDNA in Inflight, and significant reductions in the mtRNA/nRNA ratios in both the Inflight and Postflight samples. The mtRNA/mtDNA ratios were relatively constant, except in the Postflight samples. Using the same samples, the expression of redox and signal transduction related genes, MnSOD, CuZnSOD, Nrf2, Keap1, GPx4 and Catalase was also examined. The results of the combined data from Preflight, Inflight and Postflight show a significant decrease in the expression of all of the redox-related genes in the samples collected Postflight, with the exception of Catalase, which show no change. This decreased expression may contribute to increased oxidative stress Inflight resulting in the mitochondrial damage that is apparent Postflight.

Mitochondria-targeted antioxidant mitotempo protects mitochondrial function against amyloid beta toxicity in primary cultured mouse neurons

Mitochondrial defects including excess reactive oxygen species (ROS) production and compromised ATP generation are featured pathology in Alzheimer's disease (AD). Amyloid beta (Aβ)-mediated mitochondrial ROS overproduction disrupts intra-neuronal Redox balance, in turn exacerbating mitochondrial dysfunction leading to neuronal injury. Previous studies have found the beneficial effects of mitochondria-targeted antioxidants in preventing mitochondrial dysfunction and neuronal injury in AD animal and cell models, suggesting that mitochondrial ROS scavengers hold promise for the treatment of this neurological disorder. In this study, we have determined that mitotempo, a novel mitochondria-targeted antioxidant protects mitochondrial function from the toxicity of Aβ in primary cultured neurons. Our results showed that Aβ-promoted mitochondrial superoxide production and neuronal lipid oxidation were significantly suppressed by the application of mitotempo. Moreover, mitotempo also demonstrated protective effects on mitochondrial bioenergetics evidenced by preserved mitochondrial membrane potential, cytochrome c oxidase activity as well as ATP production. In addition, the Aβ-induced mitochondrial DNA (mtDNA) depletion and decreased expression levels of mtDNA replication-related DNA polymerase gamma (DNA pol γ) and Twinkle were substantially mitigated by mitotempo. Therefore, our study suggests that elimination of excess mitochondrial ROS rescues mitochondrial function in Aβ-insulted neruons; and mitotempo has the potential to be a promising therapeutic agent to protect mitochondrial and neuronal function in AD.

Simulated Microgravity Disrupts Cytoskeleton Organization and Increases Apoptosis of Rat Neural Crest Stem Cells Via Upregulating CXCR4 Expression and RhoA-ROCK1-p38 MAPK-p53 Signaling

Neural crest stem cells (NCSCs) are a population of multipotent stem cells that are distributed broadly in many tissues and organs and are capable of differentiating into a variety of cell types that are dispersed throughout three germ layers. We are interested in studying the effects of simulated microgravity on the survival and self-renewal of NCSCs. NCSCs extracted from the hair follicle bulge region of the rat whisker pad were cultured in vitro, respectively, in a 2D adherent environment and a 3D suspension environment using the rotatory cell culture system (RCCS) to simulate microgravity. We found that rat NCSCs (rNCSCs) cultured in the RCCS for 24 h showed disrupted organization of filamentous actin, increased globular actin level, formation of plasma membrane blebbing and neurite-like artifact, as well as decreased levels of cortactin and vimentin. Interestingly, ∼70% of RCCS-cultured rNCSCs co-expressed cleaved (active) caspase-3 and neuronal markers microtubule-associated protein 2 (MAP2) and Tuj1 instead of NCSC markers, suggesting stress-induced formation of neurite-like artifact in rNCSCs. In addition, rNCSCs showed increased C-X-C chemokine receptor 4 (CXCR4) expression, RhoA GTPase activation, Rho-associated kinase 1 (ROCK1) and p38 mitogen-activated protein kinase (MAPK) phosphorylation, and p53 expression in the nucleus. Incubation of rNCSCs with the Gα protein inhibitor pertussis toxin or CXCR4 siRNA during RCCS-culturing prevented cytoskeleton disorganization and plasma membrane blebbing, and it suppressed apoptosis of rNCSCs. Taken together, we demonstrate for the first time that simulated microgravity disrupts cytoskeleton organization and increases apoptosis of rNCSCs via upregulating CXCR4 expression and the RhoA-ROCK1-p38 MAPK-p53 signaling pathway.