Spaceflight Activates Autophagy Programs and the Proteasome in Mouse Liver

Copper toxicity in the liver of broiler chicken: insights from metabolomics and AMPK-mTOR mediated autophagy perspective

Exposure to copper (Cu) has been associated with metabolic disorders in animals and humans, but the underlying mechanism remains unclear. One-day-old broiler chickens, numbering a total of 192, were nourished with dietary intakes that contained varying concentrations of Cu, specifically 11, 110, 220, and 330 mg/kg of Cu, for a period extending over a duration of 7 wk. As a result of the study, Cu exposure resulted in vacuolization, fragmentation of mitochondria cristae, and the increase of autophagosomes in hepatocytes. Metabolomics analysis illustrated that Cu caused a total of 59 different metabolites in liver, predominantly associated with the glycerophospholipid metabolic pathway, leading to metabolic disruption. Moreover, high-Cu diet markedly reduced the levels of AMPKα1, p-AMPKα1, mTOR, and p-mTOR and enhanced the expression levels of the autophagy-related factors (Atg5, Dynein, Beclin1, and LC3-II). Overall, Cu exposure caused chicken liver injury and resulted in disturbed metabolic processes and mediated autophagy primarily through the AMPK-mTOR axis.

Spaceflight alters host-gut microbiota interactions

The ISS rodent habitat has provided crucial insights into the impact of spaceflight on mammals, inducing symptoms characteristic of liver disease, insulin resistance, osteopenia, and myopathy. Although these physiological responses can involve the microbiome on Earth, host-microbiota interactions during spaceflight are still being elucidated. We explore murine gut microbiota and host gene expression in the colon and liver after 29 and 56 days of spaceflight using multiomics. Metagenomics revealed significant changes in 44 microbiome species, including relative reductions in bile acid and butyrate metabolising bacteria like Extibacter muris and Dysosmobacter welbionis. Functional prediction indicate over-representation of fatty acid and bile acid metabolism, extracellular matrix interactions, and antibiotic resistance genes. Host gene expression described corresponding changes to bile acid and energy metabolism, and immune suppression. These changes imply that interactions at the host-gut microbiome interface contribute to spaceflight pathology and that these interactions might critically influence human health and long-duration spaceflight feasibility.

Space research to explore novel biochemical insights on Earth

Travel to space has overcome unprecedent technological challenges and this has resulted in transfer of these technological results on Earth to better our lives. Health technology, medical devices, and research advancements in human biology are the first beneficiaries of this transfer. The real breakthrough came with the International Space Station, which endorsed multidisciplinary international scientific collaborations and boosted the research on pathophysiological adaptation of astronauts to life on space. These studies evidenced that life in space appeared to have exposed the astronauts to an accelerated aging-related pathophysiological dysregulation across multiple systems. In this review we emphasize the interaction between several biomarkers and their alteration in concentrations/expression/function by space stress factors. These altered interactions, suggest that different biochemical and hormonal factors, and cell signals, contribute to a complex network of pathophysiological mechanisms, orchestrating the homeostatic dysregulation of various organs/metabolic pathways. The main effects of space travel on altering cell organelles biology, ultrastructure, and cross-talk, have been observed in cell aging as well as in the disruption of metabolic pathways, which are also the causal factor of rare inherited metabolic disorders, one of the major pediatric health issue. The pathophysiologic breakthrough from space research could allow the development of precision health both on Earth and Space by promoting the validation of improved biomarker-based risk scores and the exploration of new pathophysiologic hypotheses and therapeutic targets. Nonstandard abbreviations: International Space Station (ISS), Artificial Intelligence (AI), European Space Agency (ESA), National Aeronautics and Space Agency (NASA), Low Earth Orbit (LEO), high sensitive troponin (hs-cTn), high sensitive troponin I (hs-cTn I), high sensitive troponin T, Brain Natriuretic Peptide (BNP), N terminal Brain Natriuretic Peptide (NT-BNP), cardiovascular disease (CVD), parathyroid hormone (PTH), urinary hydroxyproline (uHP), urinary C- and N-terminal telopeptides (uCTX and uNTX), pyridinoline (PYD), deoxypyridinoline (DPD), half-time (HF), serum Bone Alkaline Phosphatase (sBSAP), serum Alkaline Phosphatase (sAP), Carboxy-terminal Propeptide of Type 1 Procollagen (P1CP), serum Osteocalcin (sOC)), advanced glycation end products (AGEs), glycated hemoglobin A1c (HbA1c), Insulin-like growth factor 1 (IGF1), Growth Hormone (GH), amino acid (AA), β-hydroxy-β methyl butyrate (HMB), maple syrup urine disease (MSUD), non-communicable diseases (NCDs).

Inhibition of anaerobic digestion by various ammonia sources resulted in subtle differences in metabolite dynamics

The impact of ammonia on anaerobic digestion performance and microbial dynamics has been extensively studied, but the concurrent effect of anions brought by ammonium salt should not be neglected. This paper studied this effect using metabolomics and a time-course statistical framework. Metabolomics provides novel perspectives to study microbial processes and facilitates a more profound understanding at the metabolic level. The advanced statistical framework enables deciphering the complexity of large metabolomics data sets. More specifically, a series of lab-scale batch reactors were set up with different ammonia sources added. Samples of nine time points over the degradation were analyzed with liquid chromatography-mass spectrometry. A filtering procedure was applied to select the promising metabolomic peaks from 1262 peaks, followed by modeling their intensities across time. The metabolomic peaks with similar time profiles were clustered, evidencing the correlation of different biological processes. Differential analysis was performed to seek the differences in metabolite dynamics caused by different anions. Finally, tandem mass spectrometry and metabolite annotation provided further information on the molecular structure and possible metabolic pathways. For example, the consumption of 5-aminovaleric acid, a short-chain fatty acid obtained from l-lysine degradation, was slowed down by phosphates. Overall, by investigating the effect of anions on anaerobic digestion, our study demonstrated the effectiveness of metabolomics in providing detailed information in a set of samples from different experimental conditions. With the statistical framework, the approach enables capturing subtle differences in metabolite dynamics between samples while accounting for the differences caused by time variations.

Melatonin ameliorates simulated-microgravity-induced mitochondrial dysfunction and lipid metabolism dysregulation in hepatocytes

The liver is an essential multifunctional organ, which constantly communicates with nearly all tissues. It has raised the concern that microgravity exposure can lead to liver dysfunction and metabolic syndromes. However, molecular mechanisms and intervention measures of the adverse effects of microgravity on hepatocytes are limited. In this study, we utilized the random positioning machine culture system to investigate the adverse effects on hepatocytes under simulated microgravity (SMG). Our results showed that SMG impaired hepatocyte viability, causing cell cycle arrest and apoptosis. Compared to normal gravity, it also triggered lipid accumulation, elevated triglyceride (TG) and ROS levels, and impaired mitochondria function in hepatocytes. Furthermore, RNA sequencing results showed that SMG upregulated genes implicated in lipid metabolisms, including PPARγ, PLIN2, CD36, FABPs, etc. Importantly, all these defects can be suppressed by melatonin, a potent antioxidant secreted by the pineal gland, suggesting its potential use of therapeutic intervention.

Long-term human spaceflight and inflammaging: Does it promote aging?

Spaceflight and its associated stressors, such as microgravity, radiation exposure, confinement, circadian derailment and disruptive workloads represent an unprecedented type of exposome that is entirely novel from an evolutionary stand point. Within this perspective, we aimed to review the effects of prolonged spaceflight on immune-neuroendocrine systems, brain and brain-gut axis, cardiovascular system and musculoskeletal apparatus, highlighting in particular the similarities with an accelerated aging process. In particular, spaceflight-induced muscle atrophy/sarcopenia and bone loss, vascular and metabolic changes, hyper and hypo reaction of innate and adaptive immune system appear to be modifications shared with the aging process. Most of these modifications are mediated by molecular events that include oxidative and mitochondrial stress, autophagy, DNA damage repair and telomere length alteration, among others, which directly or indirectly converge on the activation of an inflammatory response. According to the inflammaging theory of aging, such an inflammatory response could be a driver of an acceleration of the normal, physiological rate of aging and it is likely that all the systemic modifications in turn lead to an increase of inflammaging in a sort of vicious cycle. The most updated countermeasures to fight these modifications will be also discussed in the light of their possible application not only for astronauts' benefit, but also for older adults on the ground.

Addressing Spaceflight Biology through the Lens of a Histologist-Embryologist

Embryogenesis and fetal development are highly delicate and error-prone processes in their core physiology, let alone if stress-associated factors and conditions are involved. Space radiation and altered gravity are factors that could radically affect fertility and pregnancy and compromise a physiological organogenesis. Unfortunately, there is a dearth of information examining the effects of cosmic exposures on reproductive and proliferating outcomes with regard to mammalian embryonic development. However, explicit attention has been given to investigations exploring discrete structures and neural networks such as the vestibular system, an entity that is viewed as the sixth sense and organically controls gravity beginning with the prenatal period. The role of the gut microbiome, a newly acknowledged field of research in the space community, is also being challenged to be added in forthcoming experimental protocols. This review discusses the data that have surfaced from simulations or actual space expeditions and addresses developmental adaptations at the histological level induced by an extraterrestrial milieu.

Potential Roles of YAP/TAZ Mechanotransduction in Spaceflight-Induced Liver Dysfunction

Microgravity exposure during spaceflight causes the disordered regulation of liver function, presenting a specialized mechano-biological coupling process. While YAP/TAZ serves as a typical mechanosensitive pathway involved in hepatocyte metabolism, it remains unclear whether and how it is correlated with microgravity-induced liver dysfunction. Here, we discussed liver function alterations induced by spaceflight or simulated effects of microgravity on Earth. The roles of YAP/TAZ serving as a potential bridge in connecting liver metabolism with microgravity were specifically summarized. Existing evidence indicated that YAP/TAZ target gene expressions were affected by mechanotransductive pathways and phase separation, reasonably speculating that microgravity might regulate YAP/TAZ activation by disrupting these pathways via cytoskeletal remodeling or nuclear deformation, or disturbing condensates formation via diffusion limit, and then breaking liver homeostasis.

Hepatology in space: Effects of spaceflight and simulated microgravity on the liver

Microgravity as experienced during spaceflight affects a number of physiological processes in various organs. However, effects on the liver have yet been poorly documented. Nevertheless, the liver is a metabolically highly active organ involved in carbohydrate metabolism, lipid metabolism and xenobiotic biotransformation. The present paper provides an overview of the effects of microgravity on the liver observed in experimental animals during actual spaceflight and upon simulation of microgravity on Earth. These include (i) induction of liver injury and inflammation associated with apoptosis and oxidative stress, (ii) changes in liver carbohydrate metabolism resulting in the onset of a diabetogenic phenotype, (iii) modifications in hepatic lipid metabolism leading to early non-alcoholic fatty liver disease and (iv) alterations of the hepatic xenobiotic biotransformation machinery. Although most of these observations remain to be fully validated in humans, appropriate measures to counteract liver pathogenesis should be considered, especially in view of long-term space missions.

Effects of long-term simulated microgravity on liver metabolism in rhesus macaques

The liver is an essential multifunctional organ and constantly communicates with nearly all the tissues in the body. Spaceflight or simulated microgravity has a significant impact on the livers of rodent models, including lipid accumulation and inflammatory cell infiltration. Whether similar liver lipotoxicity could occur in humans is not known, even though altered circulating cholesterol profile has been reported in astronauts. Using a 42-day head-down bed rest (HDBR) model in rhesus macaques, the present study investigated whether simulated microgravity alters the liver of non-human primates at the transcriptome and metabolome levels. Its association with stress and intestinal changes was also explored. Compared to the controls, the HDBR monkeys showed mild liver injury, elevated ANGPTL3 level in the plasma, and accumulation of fat vacuoles and inflammatory cells in the liver. Altered transcriptome signatures with up-regulation of genes in lipid metabolisms and down-regulation of genes in innate immune defense were also found in HDBR group-derived liver samples. The metabolic profiling of the liver revealed mildly disturbed fatty acid metabolism in the liver of HDBR monkeys. The intestinal dysbiosis, its associated endotoxemia and changes in the composition of bile acids, and elevated stress hormone in HDBR monkeys may contribute to the altered lipid metabolisms in the liver. These data indicate that liver metabolic functions and gut-liver axis should be closely monitored in prolonged spaceflight to facilitate strategy design to improve and maintain metabolic homeostasis.

Leveraging Spaceflight to Advance Cardiovascular Research on Earth

The direct (eg, radiation, microgravity) and indirect (eg, lifestyle perturbations) effects of spaceflight extend across multiple systems resulting in whole-organism cardiovascular deconditioning. For over 50 years, National Aeronautics and Space Administration has continually enhanced a countermeasures program designed to characterize and offset the adverse cardiovascular consequences of spaceflight. In this review, we provide a historical overview of research evaluating the effects of spaceflight on cardiovascular health in astronauts and outline mechanisms underpinning spaceflight-related cardiovascular alterations. We also discuss how spaceflight could be leveraged for aging, industry, and model systems such as human induced pluripotent stem cell-derived cardiomyocytes, organoid, and organ-on-a-chip technologies. Finally, we outline the increasing opportunities for scientists and clinicians to engage in cardiovascular research in space and on Earth.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.

Impact of spaceflight and artificial gravity on sulfur metabolism in mouse liver: sulfur metabolomic and transcriptomic analysis

Spaceflight induces hepatic damage, partially owing to oxidative stress caused by the space environment such as microgravity and space radiation. We examined the roles of anti-oxidative sulfur-containing compounds on hepatic damage after spaceflight. We analyzed the livers of mice on board the International Space Station for 30 days. During spaceflight, half of the mice were exposed to artificial earth gravity (1 g) using centrifugation cages. Sulfur-metabolomics of the livers of mice after spaceflight revealed a decrease in sulfur antioxidants (ergothioneine, glutathione, cysteine, taurine, thiamine, etc.) and their intermediates (cysteine sulfonic acid, hercynine, N-acethylserine, serine, etc.) compared to the controls on the ground. Furthermore, RNA-sequencing showed upregulation of gene sets related to oxidative stress and sulfur metabolism, and downregulation of gene sets related to glutathione reducibility in the livers of mice after spaceflight, compared to controls on the ground. These changes were partially mitigated by exposure to 1 g centrifugation. For the first time, we observed a decrease in sulfur antioxidants based on a comprehensive analysis of the livers of mice after spaceflight. Our data suggest that a decrease in sulfur-containing compounds owing to both microgravity and other spaceflight environments (radiation and stressors) contributes to liver damage after spaceflight.

Mitochondrial Effects in the Liver of C57BL/6 Mice by Low Dose, High Energy, High Charge Irradiation

Galactic cosmic rays are primarily composed of protons (85%), helium (14%), and high charge/high energy ions (HZEs) such as ⁵⁶Fe, ²⁸Si, and ¹⁶O. HZE exposure is a major risk factor for astronauts during deep-space travel due to the possibility of HZE-induced cancer. A systems biology integrated omics approach encompassing transcriptomics, proteomics, lipidomics, and functional biochemical assays was used to identify microenvironmental changes induced by HZE exposure. C57BL/6 mice were placed into six treatment groups and received the following irradiation treatments: 600 MeV/n ⁵⁶Fe (0.2 Gy), 1 GeV/n ¹⁶O (0.2 Gy), 350 MeV/n ²⁸Si (0.2 Gy), ¹³⁷Cs (1.0 Gy) gamma rays, ¹³⁷Cs (3.0 Gy) gamma rays, and sham irradiation. Left liver lobes were collected at 30, 60, 120, 270, and 360 days post-irradiation. Analysis of transcriptomic and proteomic data utilizing ingenuity pathway analysis identified multiple pathways involved in mitochondrial function that were altered after HZE irradiation. Lipids also exhibited changes that were linked to mitochondrial function. Molecular assays for mitochondrial Complex I activity showed significant decreases in activity after HZE exposure. HZE-induced mitochondrial dysfunction suggests an increased risk for deep space travel. Microenvironmental and pathway analysis as performed in this research identified possible targets for countermeasures to mitigate risk.

Key points for the development of antioxidant cocktails to prevent cellular stress and damage caused by reactive oxygen species (ROS) during manned space missions

Exposure to microgravity and ionizing radiation during spaceflight missions causes excessive reactive oxygen species (ROS) production that contributes to cellular stress and damage in astronauts. Average spaceflight mission time is expected to lengthen as humanity aims to visit other planets. However, longer missions or spaceflights will undoubtedly lead to an increment in microgravity, ionizing radiation and ROS production. Strategies to minimize ROS damage are necessary to maintain the health of astronauts, future space colonists, and tourists during and after spaceflight missions. An antioxidant cocktail formulated to prevent or mitigate ROS damage during space exploration could help maintain the health of space explorers. We propose key points to consider when developing an antioxidant cocktail. We discuss how ROS damages our body and organs, the genetic predisposition of astronauts to its damage, characteristics and evidence of the effectiveness of antioxidants to combat excess ROS, differences in drug metabolism when on Earth and in space that could modify antioxidant effects, and the characteristics and efficacy of common antioxidants. Based on this information we propose a workflow for assessing astronaut resistance to ROS damage, infight monitoring of ROS production, and an antioxidant cocktail. Developing an antioxidant cocktail represents a big challenge to translate current medical practices from an Earth setting to space. The key points presented in this review could promote the development of different antioxidant formulations to maintain space explorers' health in the future.

Cdkn1a deletion or suppression by cyclic stretch enhance the osteogenic potential of bone marrow mesenchymal stem cell-derived cultures

CDKN1A/P21 is a potent inhibitor of cell cycle progression and its overexpression is thought to be associated with inhibition of normal bone regenerative osteogenesis during spaceflight. To test whether CDKN1A/P21 regulates osteogenesis in response to mechanical loading we studied cyclic stretch versus static culture of Cdkn1a^-/- (null) or wildtype primary mouse bone marrow osteoprogenitors during 21-day ex-vivo mineralization assays. Cyclically stretched Cdkn1a^-/- cells are 3.95-fold more proliferative than wildtype, while static Cdkn1a^-/- cells show a 2.50-fold increase. Furthermore, stage-specific single cell RNAseq analyses show expression of Cdkn1a is strongly suppressed by cyclic stretch in early and late osteoblasts, and minimally in the progenitor population. Lastly, both stretch and/or Cdkn1a deletion cause population shift from osteoprogenitors to osteoblasts, also indicating increased differentiation. Collectively, our results support the hypothesis that Cdkn1a constitutively plays a mechano-reversible anti-proliferative role during osteogenesis and suggests a new molecular target to counter regenerative deficits caused by disuse.

Spaceflight Modulates the Expression of Key Oxidative Stress and Cell Cycle Related Genes in Heart

Spaceflight causes cardiovascular changes due to microgravity-induced redistribution of body fluids and musculoskeletal unloading. Cardiac deconditioning and atrophy on Earth are associated with altered Trp53 and oxidative stress-related pathways, but the effects of spaceflight on cardiac changes at the molecular level are less understood. We tested the hypothesis that spaceflight alters the expression of key genes related to stress response pathways, which may contribute to cardiovascular deconditioning during extended spaceflight. Mice were exposed to spaceflight for 15 days or maintained on Earth (ground control). Ventricle tissue was harvested starting ~3 h post-landing. We measured expression of select genes implicated in oxidative stress pathways and Trp53 signaling by quantitative PCR. Cardiac expression levels of 37 of 168 genes tested were altered after spaceflight. Spaceflight downregulated transcription factor, Nfe2l2 (Nrf2), upregulated Nox1 and downregulated Ptgs2, suggesting a persistent increase in oxidative stress-related target genes. Spaceflight also substantially upregulated Cdkn1a (p21) and cell cycle/apoptosis-related gene Myc, and downregulated the inflammatory response gene Tnf. There were no changes in apoptosis-related genes such as Trp53. Spaceflight altered the expression of genes regulating redox balance, cell cycle and senescence in cardiac tissue of mice. Thus, spaceflight may contribute to cardiac dysfunction due to oxidative stress.

The biological effects of radiation-induced liver damage and its natural protective medicine

The biological damage caused by the environmental factors such as radiation and its control methods are one of the frontiers of life science research that has received widespread attention. Ionizing radiation can directly interact with target molecules (such as DNA, proteins and lipids) or decomposed by radiation from water, leading to changes in oxidative events and biological activities in cells. Liver is a radiation-sensitive organ, and its radiosensitivity is second only to bone marrow, lymph, gastrointestinal tissue, gonads, embryos and kidneys. In addition, as a key organ of mammals, liver performs a series of functions, including the production of bile, the metabolism of nutrients, the elimination of waste, the storage of glycogen, and the synthesis of proteins. Therefore, liver is prone to various pathophysiological changes. In this review, the effects of radiation on liver injury, its pathogenesis, bystander effect and the natural traditional Chinese medicine to protect the radiation induced liver damage are discussed.

Spaceflight affects neuronal morphology and alters transcellular degradation of neuronal debris in adult Caenorhabditis elegans

Extended space travel is a goal of government space agencies and private companies. However, spaceflight poses risks to human health, and the effects on the nervous system have to be better characterized. Here, we exploited the unique experimental advantages of the nematode Caenorhabditis elegans to explore how spaceflight affects adult neurons in vivo. We found that animals that lived 5 days of adulthood on the International Space Station exhibited hyperbranching in PVD and touch receptor neurons. We also found that, in the presence of a neuronal proteotoxic stress, spaceflight promotes a remarkable accumulation of neuronal-derived waste in the surrounding tissues, suggesting an impaired transcellular degradation of debris released from neurons. Our data reveal that spaceflight can significantly affect adult neuronal morphology and clearance of neuronal trash, highlighting the need to carefully assess the risks of long-duration spaceflight on the nervous system and to develop adequate countermeasures for safe space exploration.

Comparative Transcriptomics Identifies Neuronal and Metabolic Adaptations to Hypergravity and Microgravity in Caenorhabditis elegans

Deep space exploration is firmly within reach, but health decline during extended spaceflight remains a key challenge. In this study, we performed comparative transcriptomic analysis of Caenorhabditis elegans responses to varying degrees of hypergravity and to two spaceflight experiments (ICE-FIRST and CERISE). We found that progressive hypergravitational load concomitantly increases the extent of differential gene regulation and that subtle changes in ∼1,000 genes are reproducibly observed during spaceflight-induced microgravity. Consequently, we deduce those genes that are concordantly regulated by altered gravity per se or that display inverted expression profiles during hypergravity versus microgravity. Through doing so, we identify several candidate targets with terrestrial roles in neuronal function and/or cellular metabolism, which are linked to regulation by daf-16/FOXO signaling. These data offer a strong foundation from which to expedite mechanistic understanding of spaceflight-induced maladaptation in higher organisms and, ultimately, promote future targeted therapeutic development.

•

Comparative transcriptomics in C. elegans exposed to hypergravity and spaceflight

•

Bioinformatics identifies novel putative regulators of altered gravitational load

•

Candidate molecules infer a close gravity > daf-16/FOXO > neuronal link

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

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.

137Cs γ Ray and 28Si Irradiation Induced Murine Hepatocellular Carcinoma Lipid Changes in Liver Assessed by MALDI-MSI Combined with Spatial Shrunken Centroid Clustering Algorithm: A Pilot Study

Characterization of lipids by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is of great interest because not only are lipids important structural molecules in both the cell and internal organelle membranes, but they are also important signaling molecules. MALDI-MSI combined with spatial image segmentation has been previously used to identify tumor heterogeneities within tissues with distinct anatomical regions such as the brain. However, there has been no systematic study utilizing MALDI-MSI combined with spatial image segmentation to assess the tumor microenvironment in the liver. Here, we present that image segmentation can be used to evaluate the tumor microenvironment in the liver. In particular, to better understand the molecular mechanisms of irradiation-induced hepatic carcinogenesis, we used MALDI-MSI in the negative ion mode to identify lipid changes 12 months post exposure to low dose ²⁸Si and ¹³⁷Cs γ ray irradiation. We report here the changes in the lipid profiles of male C3H/HeNCrl mice liver tissues after exposure to irradiation and analyzed using the spatial shrunken centroid clustering algorithm. These findings provide valuable information as astronauts will be exposed to high-charge high-energy (HZE) particles and low-energy γ-ray irradiation during deep space travel. Even at low doses, exposure to these irradiations can lead to cancer. Previous studies infer that irradiation of mice with low-dose HZE particles induces oxidative damage and microenvironmental changes that are thought to play roles in the pathophysiology of hepatocellular carcinoma.

Validation of a New Rodent Experimental System to Investigate Consequences of Long Duration Space Habitation

Animal models are useful for exploring the health consequences of prolonged spaceflight. Capabilities were developed to perform experiments in low earth orbit with on-board sample recovery, thereby avoiding complications caused by return to Earth. For NASA’s Rodent Research-1 mission, female mice (ten 32 wk C57BL/6NTac; ten 16 wk C57BL/6J) were launched on an unmanned vehicle, then resided on the International Space Station for 21/22d or 37d in microgravity. Mice were euthanized on-orbit, livers and spleens dissected, and remaining tissues frozen in situ for later analyses. Mice appeared healthy by daily video health checks and body, adrenal, and spleen weights of 37d-flight (FLT) mice did not differ from ground controls housed in flight hardware (GC), while thymus weights were 35% greater in FLT than GC. Mice exposed to 37d of spaceflight displayed elevated liver mass (33%) and select enzyme activities compared to GC, whereas 21/22d-FLT mice did not. FLT mice appeared more physically active than respective GC while soleus muscle showed expected atrophy. RNA and enzyme activity levels in tissues recovered on-orbit were of acceptable quality. Thus, this system establishes a new capability for conducting long-duration experiments in space, enables sample recovery on-orbit, and avoids triggering standard indices of chronic stress.

NASA GeneLab Platform Utilized for Biological Response to Space Radiation in Animal Models

Background: Ionizing radiation from galactic cosmic rays (GCR) is one of the major risk factors that will impact the health of astronauts on extended missions outside the protective effects of the Earth's magnetic field. The NASA GeneLab project has detailed information on radiation exposure using animal models with curated dosimetry information for spaceflight experiments. Methods: We analyzed multiple GeneLab omics datasets associated with both ground-based and spaceflight radiation studies that included in vivo and in vitro approaches. A range of ions from protons to iron particles with doses from 0.1 to 1.0 Gy for ground studies, as well as samples flown in low Earth orbit (LEO) with total doses of 1.0 mGy to 30 mGy, were utilized. Results: From this analysis, we were able to identify distinct biological signatures associating specific ions with specific biological responses due to radiation exposure in space. For example, we discovered changes in mitochondrial function, ribosomal assembly, and immune pathways as a function of dose. Conclusions: We provided a summary of how the GeneLab's rich database of omics experiments with animal models can be used to generate novel hypotheses to better understand human health risks from GCR exposures.

Multi-omics analysis of multiple missions to space reveal a theme of lipid dysregulation in mouse liver

Spaceflight has several detrimental effects on the physiology of astronauts, many of which are recapitulated in rodent models. Mouse studies performed on the Space Shuttle showed disruption of lipid metabolism in liver. However, given that these animals were not sacrificed on-orbit and instead returned live to earth, it is unclear if these disruptions were solely induced by space stressors (e.g. microgravity, space radiation) or in part explained by the stress of return to Earth. In this work we analyzed three liver datasets from two different strains of mice (C57BL/6 (Jackson) & BALB/c (Taconic)) flown aboard the International Space Station (ISS). Notably, these animals were sacrificed on-orbit and exposed to varying spaceflight durations (i.e. 21, 37, and 42 days vs 13 days for the Shuttle mice). Oil Red O (ORO) staining showed abnormal lipid accumulation in all space-flown mice compared to ground controls regardless of strain or exposure duration. Similarly, transcriptomic analysis by RNA-sequencing revealed several pathways that were affected in both strains related to increased lipid metabolism, fatty acid metabolism, lipid and fatty acid processing, lipid catabolic processing, and lipid localization. In addition, key upstream regulators were predicted to be commonly regulated across all conditions including Glucagon (GCG) and Insulin (INS). Moreover, quantitative proteomic analysis showed that a number of lipid related proteins were changed in the livers during spaceflight. Taken together, these data indicate that activation of lipotoxic pathways are the result of space stressors alone and this activation occurs in various genetic backgrounds during spaceflight exposures of weeks to months. If similar responses occur in humans, a prolonged change of these pathways may result in the development of liver disease and should be investigated further.

Effects of spaceflight on the mouse submandibular gland

OBJECTIVE

This study was conducted to determine if the morphology and biochemistry of the mouse submandibular gland is affected by microgravity and the spaceflight environment.

DESIGN

Tissues from female mice flown on the US space shuttle missions Space Transportation System (STS)-131 and STS-135 for 15 and 13 d, respectively, and from male mice flown on the 30 d Russian Bion-M1 biosatellite, were examined using transmission electron microscopy and light and electron microscopic immunohistochemistry.

RESULTS

In contrast to the parotid gland, morphologic changes were not apparent in the submandibular gland. No significant changes in protein expression, as assessed by quantitative immunogold labeling, occurred in female mice flown for 13-15 d. In male mice, however, increased labeling for salivary androgen binding protein alpha (in acinar cell secretory granules), and epidermal growth factor and nerve growth factor (in granular convoluted duct cell granules) was seen after 30 d in space.

CONCLUSION

These results indicate that spaceflight alters secretory protein expression in the submandibular gland and suggest that the sex of the animals and the length of the flight may affect the response. These findings also show that individual salivary glands respond differently to spaceflight. Saliva contains proteins secreted from salivary glands and is easily collected, therefore is a useful biofluid for general medical analyses and in particular for monitoring the physiology and health of astronauts.

The Trends in Global Gene Expression in Mouse Embryonic Stem Cells During Spaceflight

The environment in space differs greatly from the environment on the ground. Spaceflight causes a number of physiological changes in astronauts, such as bone loss and immune system dysregulation. These effects threaten astronauts’ space missions, and understanding the underlying cellular and molecular mechanisms is important to manage the risks of space missions. The biological effects of spaceflight on mammalian cells, especially with regards to DNA damage, have attracted much attention. Rad9^−/− mouse embryonic stem cells (mESCs) are known to be extremely sensitive to DNA damage agents. In this study, a project of the SJ-10 satellite programme, we investigated the gene expression profiles of both Rad9^−/− mESCs and Rad9^+/+ (wild-type) mESCs in space with a focus on genes critical for inducing, preventing, or repairing genomic DNA lesions. We found that spaceflight downregulated more genes than it upregulated in both wild-type and Rad9^−/− mESCs, indicating a suppressive effect of spaceflight on global gene expression. In contrast, Rad9 deletion upregulated more genes than it downregulated. Of note, spaceflight mainly affected organ development and influenced a wide range of cellular functions in mESCs, while Rad9 deletion mainly affected the development and function of the hematological system, especially the development, differentiation and function of immune cells. The patterns of gene expression in mouse embryonic stem cells in space is distinct from those in other types of cells. In addition, both spaceflight and Rad9 deletion downregulated DNA repair genes, suggesting a possibility that spaceflight has negative effects on genome for embryonic stem cells and the effects are likely worsen when the genome maintenance mechanism is defective.

Reptiles in Space Missions: Results and Perspectives

Reptiles are a rare model object for space research. However, some reptile species demonstrate effective adaptation to spaceflight conditions. The main scope of this review is a comparative analysis of reptile experimental exposure in weightlessness, demonstrating the advantages and shortcomings of this model. The description of the known reptile experiments using turtles and geckos in the space and parabolic flight experiments is provided. Behavior, skeletal bones (morphology, histology, and X-ray microtomography), internal organs, and the nervous system (morphology, histology, and immunohistochemistry) are studied in the spaceflight experiments to date, while molecular and physiological results are restricted. Therefore, the results are discussed in the scope of molecular data collected from mammalian (mainly rodents) specimens and cell cultures in the parabolic and orbital flights and simulated microgravity. The published data are compared with the results of the gecko model studies after the 12–44.5-day spaceflights with special reference to the unique peculiarities of the gecko model for the orbital experiments. The complex study of thick-toed geckos after three spaceflights, in which all geckos survived and demonstrated effective adaptation to spaceflight conditions, was performed. However, future investigations are needed to study molecular mechanisms of gecko adaptation in space.

Supplying a pharmacy for NASA exploration spaceflight: challenges and current understanding

In order to maintain crew health and performance during long-duration spaceflight outside of low-Earth orbit, NASA and its international partners must be capable of providing a safe and effective pharmacy. Given few directed studies of pharmaceuticals in the space environment, it is difficult to characterize pharmaceutical effectiveness or stability during spaceflight; this in turn makes it challenging to select an appropriate formulary for exploration. Here, we present the current state of literature regarding pharmaceutical stability, metabolism, and effectiveness during spaceflight. In particular, we have attempted to highlight the gaps in current knowledge and the difficulties in translating terrestrial-based drug studies to a meaningful interpretation of drug stability, safety, and effectiveness in space. We hope to identify high-yield opportunities for future research that might better define and mitigate pharmaceutical risk for exploration missions.

Biological effects of space environmental factors: A possible interaction between space radiation and microgravity

In the mid-1980s, space experiments began to examine if microgravity could alter the biological effects of space radiation. In the late 1990s, repair of DNA strand breaks was reported to not be influenced by microgravity using the pre-irradiated cells, because the exposure doses of space radiation were few due to the short spaceflight. There were, however, conflicting reports depending on the biological endpoints used in various systems. While almost no attempts were made to assess the possibility that the microgravity effects could be altered by space radiation. This was probably due to the general understanding that microgravity plays a major role in space and works independently from space radiation. Recent ground-based simulation studies focusing on DNA oxidative damage and signal transduction suggested that combined effects of microgravity and space radiation might exist. These studies also implicated the importance of research focusing not only on chromosomal DNA but also on cytoplasm, especially mitochondria. Therefore, we propose a new model which accounts for the combined-effects through the window of cellular responses. In this model, the interactions between microgravity and space radiation might occur during the following cellular-responses; (A) damaging and signaling by ROS, (B) damage responses on DNA (repair, replication, transcription, etc.), and (C) expression of gene and protein (regulation by chromatin, epigenetic control, etc.).

Proteomic Analysis of Mouse Brain Subjected to Spaceflight

There is evidence that spaceflight poses acute and late risks to the central nervous system. To explore possible mechanisms, the proteomic changes following spaceflight in mouse brain were characterized. Space Shuttle Atlantis (STS-135) was launched from the Kennedy Space Center (KSC) on a 13-day mission. Within 3–5 h after landing, brain tissue was collected to evaluate protein expression profiles using quantitative proteomic analysis. Our results showed that there were 26 proteins that were significantly altered after spaceflight in the gray and/or white matter. While there was no overlap between the white and gray matter in terms of individual proteins, there was overlap in terms of function, synaptic plasticity, vesical activity, protein/organelle transport, and metabolism. Our data demonstrate that exposure to the spaceflight environment induces significant changes in protein expression related to neuronal structure and metabolic function. This might lead to a significant impact on brain structural and functional integrity that could affect the outcome of space missions.

Effects of Space Flight on Mouse Liver versus Kidney: Gene Pathway Analyses

Understanding genome wide, tissue-specific, and spaceflight-induced changes in gene expression is critical to develop effective countermeasures. Transcriptome analysis has been performed on diverse tissues harvested from animals flown in space, but not the kidney. We determined the genome wide gene expression using a gene array analysis of kidney and liver tissue from mice flown in space for 12 days versus ground based control animals. By comparing the transcriptome of liver and kidney from animals flown in space versus ground control animals, we tested a unique hypothesis: Are there common gene expression pathways activated in multiple tissue types in response to spaceflight stimuli? Although there were tissue-specific changes, both liver and kidney overexpressed genes in the same four areas: (a) cellular responses to peptides, hormones, and nitrogen/organonitrogen compounds; (b) apoptosis and cell death; (c) fat cell differentiation and (d) negative regulation of protein kinase.

Oxidative Stress as Cause, Consequence, or Biomarker of Altered Female Reproduction and Development in the Space Environment

Oxidative stress has been implicated in the pathophysiology of numerous terrestrial disease processes and associated with morbidity following spaceflight. Furthermore, oxidative stress has long been considered a causative agent in adverse reproductive outcomes. The purpose of this review is to summarize the pathogenesis of oxidative stress caused by cosmic radiation and microgravity, review the relationship between oxidative stress and reproductive outcomes in females, and explore what role spaceflight-induced oxidative damage may have on female reproductive and developmental outcomes.

Transcriptional Homeostasis of Oxidative Stress-Related Pathways in Altered Gravity

Whereby several types of cultured cells are sensitive to gravity, the immune system belongs to the most affected systems during spaceflight. Since reactive oxygen species/reactive nitrogen species (ROS/RNS) are serving as signals of cellular homeostasis, particularly in the cells of the immune system, we investigated the immediate effect of altered gravity on the transcription of 86 genes involved in reactive oxygen species metabolism, antioxidative systems, and cellular response to oxidative stress, using parabolic flight and suborbital ballistic rocket experiments and microarray analysis. In human myelomonocytic U937 cells, we detected a rapid response of 19.8% of all of the investigated oxidative stress-related transcripts to 1.8 g of hypergravity and 1.1% to microgravity as early as after 20 s. Nearly all (97.2%) of the initially altered transcripts adapted after 75 s of hypergravity (max. 13.5 g), and 100% adapted after 5 min of microgravity. After the almost complete adaptation of initially altered transcripts, a significant second pool of differentially expressed transcripts appeared. In contrast, we detected nearly no response of oxidative stress-related transcripts in human Jurkat T cells to altered gravity. In conclusion, we assume a very well-regulated homeostasis and transcriptional stability of oxidative stress-related pathways in altered gravity in cells of the human immune system.

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.