A microRNA signature and TGF-β1 response were identified as the key master regulators for spaceflight response

Space radiation damage rescued by inhibition of key spaceflight associated miRNAs

Our previous research revealed a key microRNA signature that is associated with spaceflight that can be used as a biomarker and to develop countermeasure treatments to mitigate the damage caused by space radiation. Here, we expand on this work to determine the biological factors rescued by the countermeasure treatment. We performed RNA-sequencing and transcriptomic analysis on 3D microvessel cell cultures exposed to simulated deep space radiation (0.5 Gy of Galactic Cosmic Radiation) with and without the antagonists to three microRNAs: miR-16-5p, miR-125b-5p, and let-7a-5p (i.e., antagomirs). Significant reduction of inflammation and DNA double strand breaks (DSBs) activity and rescue of mitochondria functions are observed after antagomir treatment. Using data from astronaut participants in the NASA Twin Study, Inspiration4, and JAXA missions, we reveal the genes and pathways implicated in the action of these antagomirs are altered in humans. Our findings indicate a countermeasure strategy that can potentially be utilized by astronauts in spaceflight missions to mitigate space radiation damage.

NASA GeneLab derived microarray studies of Mus musculus and Homo sapiens organisms in altered gravitational conditions

One of the greatest challenges of humanity for deep space exploration is to fully understand how altered gravitational conditions affect human physiology. It is evident that the spaceflight environment causes multiple alterations to musculoskeletal, cardiovascular, immune and central nervous systems, to name a few known effects. To better characterize these biological effects, we compare gene expression datasets from microarray studies found in NASA GeneLab, part of the NASA Open Science Data Repository. In this review, we summarize these archived results for various tissues, emphasizing key genes which are highly reproducible in different mice or human experiments. Such exhaustive mining shows the potential of NASA Open Science data to identify and validate mechanisms taking place when mammalian organisms are exposed to microgravity or other spaceflight conditions. Our comparative meta-analysis findings highlight certain degrees of overlap and reproducibility in genes identified as differentially expressed within musculoskeletal tissues in each species across a variety of altered gravity conditions. However, the level of overlap between species was found to be significantly limited, partly attributed to the limited availability of human samples.

Spaceflight causes strain-dependent gene expression changes associated with lipid and extracellular matrix dysregulation in the mouse kidney in vivo

To explore new worlds we must ensure humans can survive and thrive in the space environment. Incidence of kidney stones in astronauts is a major risk factor associated with long term missions, caused by increased blood calcium levels due to bone demineralisation triggered by microgravity and space radiation. Transcriptomic changes have been observed in other tissues during spaceflight, including the kidney. We analysed kidney transcriptome patterns in two different strains of mice flown on the International Space Station, C57BL/6J and BALB/c. Here we show a link between spaceflight and transcriptome patterns associated with dysregulation of lipid and extracellular matrix metabolism and altered transforming growth factor-beta signalling. A stronger response was seen in C57BL/6J mice than BALB/c. Genetic differences in hyaluronan metabolism between strains may confer protection against extracellular matrix remodelling through downregulation of epithelial-mesenchymal transition. We intend for our findings to contribute to development of new countermeasures against kidney disease in astronauts and people here on Earth.

Highlights

Spaceflight has a significant effect on gene expression in the kidney.Responses in the BALB/c indicate milder transcriptomic perturbations than C57BL/6J.Lipid metabolism was altered in both strains of mice.Extracellular matrix metabolism and TGF-β signalling up in BALB/c down in C57BL/6J.Reduced gene expression of hyaluronan synthesis pathway in BALB/c but not in C57BL/6J.

Simulated microgravity altered the proliferation, apoptosis, and extracellular matrix formation of L929 fibroblasts and the transforming growth factor-β1/Smad3 signaling pathway

Exposure to microgravity can adversely affect the fitness of astronauts. The integrity of the skin plays a crucial role in protecting against mechanical forces and infections, fluid imbalance, and thermal dysregulation. In brief, the skin wound may cause unknown challenges to the implementation of space missions. Wound healing is a physiological process that relies on the synergistic action of inflammatory cells, extracellular matrix (ECM), and various growth factors to maintain the integrity of skin after trauma. Fibroblasts are present almost throughout the entire process of wound repair, especially in the scar formation at the endpoint of wound healing. However, there is limited knowledge about the extent to which fibroblasts are affected by the lack of gravity during wound healing. In this study, we utilized the rotary cell culture system, a ground-based facility that mimics the weightless condition, to study the alterations of L929 fibroblast cells under simulated microgravity (SMG). Our results demonstrated that the SM condition exerted negative influences on the proliferation and ECM formation of the L929 fibroblast. Whereas, the apoptosis of fibroblast was significantly upregulated upon exposure to SMG conditions. Moreover, the transforming growth factor-β1/Smad3 (TGF-β1/smad3) signaling pathway of L929 fibroblast related to wound repair was also altered significantly under a weightless environment. Overall, our study provided evidence that fibroblasts are strongly sensitive to SMG and elucidated the potential value of the TGF-β1/Smad3 signaling pathway modulating wound healing in the future practice of space medicine.

Heavy-ion radiation-induced colitis and colorectal carcinogenesis in Il10-/- mice display co-activation of β-catenin and NF-κB signaling

Space radiation-induced gastrointestinal (GI) cancer risk models for future interplanetary astronauts are being developed that primarily rely on quantitative animal model studies to assess radiation-quality effects of heavy-ion space radiation exposure in relation to γ-rays. While current GI-cancer risk estimation efforts are focused on sporadic GI-cancer mouse models, emerging in-vivo data on heavy-ion radiation-induced long-term GI-inflammation are indicative of a higher but undetermined risk of GI-inflammation associated cancers, such as colitis-associated cancer (CAC). Therefore, we aimed to assess radiation quality effects on colonic inflammation, colon cancer incidence, and associated signaling events using an in-vivo CAC model i.e., Il10-/- mice. Male Il10-/- mice (8-10 weeks, n = 12/group) were irradiated with either sham, γ-rays or heavy-ions (28Si or 56Fe), and histopathological assessments for colitis and CAC were conducted at 2.5 months post-exposure. qPCR analysis for inflammation associated gene transcripts (Ptges and Tgfb1), and in-situ staining for markers of cell-proliferation (phospho-histone H3), oncogenesis (active-β-catenin, and cyclin D1), and inflammation (phospho-p65NF-κB, iNOS, and COX2) were performed. Significantly higher colitis and CAC frequency were noted after heavy-ion exposure, relative to γ and control mice. Higher CAC incidence after heavy-ion exposure was associated with greater activation of β-catenin and NF-κB signaling marked by induced expression of common downstream inflammatory (iNOS and COX2) and pro-proliferative (Cyclin D1) targets. In summary, IR-induced colitis and CAC incidence in Il10-/- mice depends on radiation quality and display co-activation of β-catenin and NF-κB signaling.

High throughput screen of small molecules as potential countermeasures to galactic cosmic radiation induced cellular dysfunction

Space travel increases galactic cosmic ray exposure to flight crews and this is significantly elevated once travel moves beyond low Earth orbit. This includes combinations of high energy protons and heavy ions such as ⁵⁶Fe or ¹⁶O. There are distinct differences in the biological response to low-energy transfer (x-rays) or high-energy transfer (High-LET). However, given the relatively low fluence rate of exposure during flight operations, it might be possible to manage these deleterious effects using small molecules currently available. Virtually all reports to date examining small molecule management of radiation exposure are based on low-LET challenges. To that end an FDA approved drug library (725 drugs) was used to perform a high throughput screen of cultured cells following exposure to galactic cosmic radiation. The H9c2 myoblasts, ES-D3 pluripotent cells, and Hy926 endothelial cell lines were exposed to a single exposure (75 cGy) using the 5-ion GCRsim protocol developed at the NASA Space Radiation Laboratory (NSRL). Following GCR exposure cells were maintained for up to two weeks. For each drug (@10µM), a hierarchical cumulative score was developed incorporating measures of mitochondrial and cellular function, oxidant stress and cell senescence. The top 160 scores were retested following a similar protocol using 1µM of each drug. Within the 160 drugs, 33 are considered to have an anti-inflammatory capacity, while others also indirectly suppressed pro-inflammatory pathways or had noted antioxidant capacity. Lead candidates came from different drug classes that included angiotensin converting enzyme inhibitors or AT1 antagonists, COX2 inhibitors, as well as drugs mediated by histamine receptors. Surprisingly, different classes of anti-diabetic medications were observed to be useful including sulfonylureas and metformin. Using a hierarchical decision structure, we have identified several lead candidates. That no one drug or even drug class was completely successful across all parameters tested suggests the complexity of managing the consequences of galactic cosmic radiation exposure.

Effect of space flight on the behavior of human retinal pigment epithelial ARPE-19 cells and evaluation of coenzyme Q10 treatment

Astronauts on board the International Space Station (ISS) are exposed to the damaging effects of microgravity and cosmic radiation. One of the most critical and sensitive districts of an organism is the eye, particularly the retina, and > 50% of astronauts develop a complex of alterations designated as spaceflight-associated neuro-ocular syndrome. However, the pathogenesis of this condition is not clearly understood. In the current study, we aimed to explore the cellular and molecular effects induced in the human retinal pigment ARPE-19 cell line by their transfer to and 3-day stay on board the ISS in the context of an experiment funded by the Agenzia Spaziale Italiana. Treatment of cells on board the ISS with the well-known bioenergetic, antioxidant, and antiapoptotic coenzyme Q10 was also evaluated. In the ground control experiment, the cells were exposed to the same conditions as on the ISS, with the exception of microgravity and radiation. The transfer of ARPE-19 retinal cells to the ISS and their living on board for 3 days did not affect cell viability or apoptosis but induced cytoskeleton remodeling consisting of vimentin redistribution from the cellular boundaries to the perinuclear area, underlining the collapse of the network of intermediate vimentin filaments under unloading conditions. The morphological changes endured by ARPE-19 cells grown on board the ISS were associated with changes in the transcriptomic profile related to the cellular response to the space environment and were consistent with cell dysfunction adaptations. In addition, the results obtained from ARPE-19 cells treated with coenzyme Q10 indicated its potential to increase cell resistance to damage.

Gene expression changes related to bone mineralization, blood pressure and lipid metabolism in mouse kidneys after space travel

Space travel burdens health by imposing considerable environmental stress associated with radioactivity and microgravity. In particular, gravity change predominantly impacts blood pressure and bone homeostasis, both of which are controlled mainly by the kidneys. Nuclear factor erythroid-2-related transcription factor 2 (Nrf2) plays essential roles in protecting the kidneys from various environmental stresses and injuries. To elucidate the effects of space travel on mammals in preparation for the upcoming space era, our study investigated the contribution of Nrf2 to kidney function in mice two days after their return from a 31-day stay in the International Space Station using Nrf2 knockout mice. Meaningfully, expression levels of genes regulating bone mineralization, blood pressure and lipid metabolism were found to be significantly altered in the kidneys after space travel in an Nrf2-independent manner. In particular, uridine diphosphate-glucuronosyltransferase 1A (Ugt1a) isoform genes were found to be expressed in an Nrf2-dependent manner and induced exclusively in the kidneys after return to Earth. Since spaceflight elevated the concentrations of fatty acids in the mouse plasma, we suggest that Ugt1a isoform expression in the kidneys was induced to promote glucuronidation of excessively accumulated lipids and excrete them into urine after the return from space. Thus, the kidneys were proven to play central roles in adaptation to gravity changes caused by going to and returning from space by controlling blood pressure and bone mineralization. Additionally, kidney Ugt1a isoform induction after space travel implies a significant role of the kidneys for space travelers in the excretion of excessive lipids.

An Integrative Network Science and Artificial Intelligence Drug Repurposing Approach for Muscle Atrophy in Spaceflight Microgravity

Muscle atrophy is a side effect of several terrestrial diseases which also affects astronauts severely in space missions due to the reduced gravity in spaceflight. An integrative graph-theoretic network-based drug repurposing methodology quantifying the interplay of key gene regulations and protein-protein interactions in muscle atrophy conditions is presented. Transcriptomic datasets from mice in spaceflight from GeneLab have been extensively mined to extract the key genes that cause muscle atrophy in organ muscle tissues such as the thymus, liver, and spleen. Top muscle atrophy gene regulators are selected by Bayesian Markov blanket method and gene-disease knowledge graph is constructed using the scalable precision medicine knowledge engine. A deep graph neural network is trained for predicting links in the network. The top ranked diseases are identified and drugs are selected for repurposing using drug bank resource. A disease drug knowledge graph is constructed and the graph neural network is trained for predicting new drugs. The results are compared with machine learning methods such as random forest, and gradient boosting classifiers. Network measure based methods shows that preferential attachment has good performance for link prediction in both the gene-disease and disease-drug graphs. The receiver operating characteristic curves, and prediction accuracies for each method show that the random walk similarity measure and deep graph neural network outperforms the other methods. Several key target genes identified by the graph neural network are associated with diseases such as cancer, diabetes, and neural disorders. The novel link prediction approach applied to the disease drug knowledge graph identifies the Monoclonal Antibodies drug therapy as suitable candidate for drug repurposing for spaceflight induced microgravity. There are a total of 21 drugs identified as possible candidates for treating muscle atrophy. Graph neural network is a promising deep learning architecture for link prediction from gene-disease, and disease-drug networks.

Alterations in Saliva and Plasma Cytokine Concentrations During Long-Duration Spaceflight

Long-duration spaceflight is known to cause immune dysregulation in astronauts. Biomarkers of immune system function are needed to determine both the need for and effectiveness of potential immune countermeasures for astronauts. Whereas plasma cytokine concentrations are a well-established biomarker of immune status, salivary cytokine concentrations are emerging as a sensitive indicator of stress and inflammation. For this study, to aid in characterizing immune dysregulation during spaceflight, plasma and saliva cytokines were monitored in astronauts before, during and after long-duration spaceflight onboard the International Space Station. Blood was collected from 13 astronauts at 3 timepoints before, 5 timepoints during and 3 timepoints after spaceflight. Saliva was collected from 6 astronauts at 2 timepoints before spaceflight, 2 timepoints during and 3 timepoints following spaceflight. Samples were analyzed using multiplex array technology. Significant increases in the plasma concentration of IL-3, IL-15, IL-12p40, IFN-α2, and IL-7 were observed during spaceflight compared to before flight baseline. Significant decreases in saliva GM-CSF, IL-12p70, IL-10 and IL-13 were also observed during spaceflight as compared to compared to before flight baseline concentrations. Additionally, plasma TGFβ1 and TGFβ2 concentrations tended to be consistently higher during spaceflight, although these did not reach statistical significance. Overall, the findings confirm an in-vivo hormonal dysregulation of immunity, appearing pro-inflammatory and Th1 in nature, persists during long-duration orbital spaceflight. These biomarkers may therefore have utility for monitoring the effectiveness of biomedical countermeasures for astronauts, with potential application in terrestrial research and medicine.

Mammalian and Invertebrate Models as Complementary Tools for Gaining Mechanistic Insight on Muscle Responses to Spaceflight

Bioinformatics approaches have proven useful in understanding biological responses to spaceflight. Spaceflight experiments remain resource intensive and rare. One outstanding issue is how to maximize scientific output from a limited number of omics datasets from traditional animal models including nematodes, fruitfly, and rodents. The utility of omics data from invertebrate models in anticipating mammalian responses to spaceflight has not been fully explored. Hence, we performed comparative analyses of transcriptomes of soleus and extensor digitorum longus (EDL) in mice that underwent 37 days of spaceflight. Results indicate shared stress responses and altered circadian rhythm. EDL showed more robust growth signals and Pde2a downregulation, possibly underlying its resistance to atrophy versus soleus. Spaceflight and hindlimb unloading mice shared differential regulation of proliferation, circadian, and neuronal signaling. Shared gene regulation in muscles of humans on bedrest and space flown rodents suggest targets for mitigating muscle atrophy in space and on Earth. Spaceflight responses of C. elegans were more similar to EDL. Discrete life stages of D. melanogaster have distinct utility in anticipating EDL and soleus responses. In summary, spaceflight leads to shared and discrete molecular responses between muscle types and invertebrate models may augment mechanistic knowledge gained from rodent spaceflight and ground-based studies.

From Target Identification to Drug Development in Space: Using the Microgravity Assist

The unique nature of microgravity encountered in space provides an opportunity for drug discovery and development that cannot be replicated on Earth. From the production of superior protein crystals to the identification and validation of new drug targets to microarray analyses of transcripts attenuated by microgravity, there are numerous examples which demonstrate the benefit of exploiting the space environment. Moreover, studies conducted on Space Shuttle missions, the International Space Station and other craft have had a direct benefit for drug development programmes such as those directed against reducing bone and muscle loss or increasing bone formation. This review will highlight advances made in both drug discovery and development and offer some future insight into how drug discovery and associated technologies may be further advanced using the microgravity assist.

Transcriptome analysis of gravitational effects on mouse skeletal muscles under microgravity and artificial 1 g onboard environment

Spaceflight causes a decrease in skeletal muscle mass and strength. We set two murine experimental groups in orbit for 35 days aboard the International Space Station, under artificial earth-gravity (artificial 1 g; AG) and microgravity (μg; MG), to investigate whether artificial 1 g exposure prevents muscle atrophy at the molecular level. Our main findings indicated that AG onboard environment prevented changes under microgravity in soleus muscle not only in muscle mass and fiber type composition but also in the alteration of gene expression profiles. In particular, transcriptome analysis suggested that AG condition could prevent the alterations of some atrophy-related genes. We further screened novel candidate genes to reveal the muscle atrophy mechanism from these gene expression profiles. We suggest the potential role of Cacng1 in the atrophy of myotubes using in vitro and in vivo gene transductions. This critical project may accelerate the elucidation of muscle atrophy mechanisms.

Characterization of exosome release and extracellular vesicle-associated miRNAs for human bronchial epithelial cells irradiated with high charge and energy ions

Exosomes are extracellular vesicles that mediate transport of nucleic acids, proteins, and other molecules. Prior work has implicated exosomes in the transmission of radiation nontargeted effects. Here we investigate the ability of energetic heavy ions, representative of species found in galactic cosmic rays, to stimulate exosome release from human bronchial epithelial cells in vitro. Immortalized human bronchial epithelial cells (HBEC3-KT F25F) were irradiated with 1.0 Gy of high linear energy transfer (LET) ⁴⁸Ti, ²⁸Si, or ¹⁶O ions, or with 10 Gy of low-LET reference γ-rays, and extracellular vesicles were collected from conditioned media. Preparations were characterized by single particle tracking analysis, transmission electron microscopy, and immunoblotting for the exosomal marker, TSG101. Based on TSG101 levels, irradiation with high-LET ions, but not γ-rays, stimulated exosome release by about 4-fold, relative to mock-irradiated controls. The exosome-enriched vesicle preparations contained pro-inflammatory damage-associated molecular patterns, including HSP70 and calreticulin. Additionally, miRNA profiling was performed for vesicular RNAs using NanoString technology. The miRNA profile was skewed toward a small number of species that have previously been shown to be involved in cancer initiation and progression, including miR-1246, miR-1290, miR-23a, and miR-205. Additionally, a set of 24 miRNAs was defined as modestly over-represented in preparations from HZE ion-irradiated versus other cells. Gene set enrichment analysis based on the over-represented miRNAs showed highly significant association with nonsmall cell lung and other cancers.

LET-Dependent Low Dose and Synergistic Inhibition of Human Angiogenesis by Charged Particles: Validation of miRNAs that Drive Inhibition

Space radiation inhibits angiogenesis by two mechanisms depending on the linear energy transfer (LET). Using human 3D micro-vessel models, blockage of the early motile stage of angiogenesis was determined to occur after exposure to low LET ions (<3 KeV/AMU), whereas inhibition of the later stages occurs after exposure to high LET ions (>8 KeV/AMU). Strikingly, the combined effect is synergistic, detectible as low as 0.06 Gy making mixed ion space radiation more potent. Candidates for bystander transmission are microRNAs (miRNAs), and analysis on miRNA-seq data from irradiated mice shows that angiogenesis would in theory be downregulated. Further analysis of three previously identified miRNAs showed downregulation of their targets associated with angiogenesis and confirmed their involvement in angiogenesis pathways and increased health risks associated with cardiovascular disease. Finally, synthetic molecules (antagomirs) designed to inhibit the predicted miRNAs were successfully used to reverse the inhibition of angiogenesis.

Beyond Low-Earth Orbit: Characterizing Immune and microRNA Differentials following Simulated Deep Spaceflight Conditions in Mice

Spaceflight missions can cause immune system dysfunction in astronauts with little understanding of immune outcomes in deep space. This study assessed immune responses in mice following ground-based, simulated deep spaceflight conditions, compared with data from astronauts on International Space Station missions. For ground studies, we simulated microgravity using the hindlimb unloaded mouse model alone or in combination with acute simulated galactic cosmic rays or solar particle events irradiation. Immune profiling results revealed unique immune diversity following each experimental condition, suggesting each stressor results in distinct circulating immune responses, with clear consequences for deep spaceflight. Circulating plasma microRNA sequence analysis revealed involvement in immune system dysregulation. Furthermore, a large astronaut cohort showed elevated inflammation during low-Earth orbit missions, thereby supporting our simulated ground experiments in mice. Herein, circulating immune biomarkers are defined by distinct deep space irradiation types coupled to simulated microgravity and could be targets for future space health initiatives.

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.

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Comparative transcriptomics in C. elegans exposed to hypergravity and spaceflight

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Bioinformatics identifies novel putative regulators of altered gravitational load

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

Circulating miRNA Spaceflight Signature Reveals Targets for Countermeasure Development

We have identified and validated a spaceflight-associated microRNA (miRNA) signature that is shared by rodents and humans in response to simulated, short-duration and long-duration spaceflight. Previous studies have identified miRNAs that regulate rodent responses to spaceflight in low-Earth orbit, and we have confirmed the expression of these proposed spaceflight-associated miRNAs in rodents reacting to simulated spaceflight conditions. Moreover, astronaut samples from the NASA Twins Study confirmed these expression signatures in miRNA sequencing, single-cell RNA sequencing (scRNA-seq), and single-cell assay for transposase accessible chromatin (scATAC-seq) data. Additionally, a subset of these miRNAs (miR-125, miR-16, and let-7a) was found to regulate vascular damage caused by simulated deep space radiation. To demonstrate the physiological relevance of key spaceflight-associated miRNAs, we utilized antagomirs to inhibit their expression and successfully rescue simulated deep-space-radiation-mediated damage in human 3D vascular constructs.

Next-generation sequencing analysis of circulating micro-RNA expression in response to parabolic flight as a spaceflight analogue

Understanding physiologic reactions to weightlessness is an indispensable requirement for safe human space missions. This study aims to analyse changes in the expression of circulating miRNAs following exposure to gravitational changes. Eight healthy volunteers (age: 24.5 years, male: 4, female: 4) were included. Each subject underwent 31 short-term phases of weightlessness and hypergravity induced by parabolic flight as a spaceflight analogue. At baseline, 1 and 24 h after parabolic flight, venous blood was withdrawn. Analysis of circulating miRNAs in serum was conducted by means of next generation sequencing. In total, 213 miRNAs were robustly detected (TPM > 5) by small RNA sequencing in all 24 samples. Four miRNAs evidenced a significant change in expression after adjusting for multiple testing. Only miR-223-3p showed a consistent significant decrease 24 h after parabolic flight compared to baseline values and values at 1 h after parabolic flight. miR-941 and miR-24-3p showed a significant decrease 24 h after parabolic flight compared to 1 h after parabolic flight but not to baseline values. miR-486-5p showed a significant increase 24 h after parabolic flight compared to 1 h after parabolic flight but not to baseline values. A target network analysis identified genes of the p53 signaling pathway and the cell cycle highly enriched among the targets of the four microRNAs. Our findings suggest cellular adaption to gravitational changes at the post-transcriptional level. Based on our results, we suggest a change in cell cycle regulation as potential explanation for adaptational changes observed in space missions.

Approaching Gravity as a Continuum Using the Rat Partial Weight-Bearing Model

For decades, scientists have relied on animals to understand the risks and consequences of space travel. Animals remain key to study the physiological alterations during spaceflight and provide crucial information about microgravity-induced changes. While spaceflights may appear common, they remain costly and, coupled with limited cargo areas, do not allow for large sample sizes onboard. In 1979, a model of hindlimb unloading (HU) was successfully created to mimic microgravity and has been used extensively since its creation. Four decades later, the first model of mouse partial weight-bearing (PWB) was developed, aiming at mimicking partial gravity environments. Return to the Lunar surface for astronauts is now imminent and prompted the need for an animal model closer to human physiology; hence in 2018, our laboratory created a new model of PWB for adult rats. In this review, we will focus on the rat model of PWB, from its conception to the current state of knowledge. Additionally, we will address how this new model, used in conjunction with HU, will help implement new paradigms allowing scientists to anticipate the physiological alterations and needs of astronauts. Finally, we will discuss the outstanding questions and future perspectives in space research and propose potential solutions using the rat PWB model.

Serum Metabolomics Associating With Circulating MicroRNA Profiles Reveal the Role of miR-383-5p in Rat Hippocampus Under Simulated Microgravity

Microgravity impacts various aspects of human health. Yet the mechanisms of spaceflight-induced health problems are not elucidated. Here, we mapped the fusion systemic analysis of the serum metabolome and the circulating microRNAome in a hindlimb unloading rat model to simulate microgravity. The response of serum metabolites and microRNAs to simulated microgravity was striking. Integrated pathway analysis of altered serum metabolites and target genes of the significantly altered circulating miRNAs with Integrated Molecular Pathway-Level Analysis (IMPaLA) software was mainly suggestive of modulation of neurofunctional signaling pathways. Particularly, we revealed significantly increased miR-383-5p and decreased aquaporin 4 (AQP4) in the hippocampus. Using rabies virus glycoprotein-modified exosomes, delivery of miR-383-5p inhibited the expression of AQP4 not only in rat C6 glioma cells in vitro but also in the hippocampus in vivo. Using bioinformatics to map the crosstalk between the circulating metabolome and miRNAome could offer opportunities to understand complex biological systems under microgravity. Our present results suggested that the change of miR-383-5p level and its regulation of target gene AQP4 was one of the potential molecular mechanisms of microgravity-induced cognitive impairment in the hippocampus.

Integrated RNA-seq Analysis Indicates Asynchrony in Clock Genes between Tissues under Spaceflight

Rodent models have been widely used as analogs for estimating spaceflight-relevant molecular mechanisms in human tissues. NASA GeneLab provides access to numerous spaceflight omics datasets that can potentially generate novel insights and hypotheses about fundamental space biology when analyzed in new and integrated fashions. Here, we performed a pilot study to elucidate space biological mechanisms across tissues by reanalyzing mouse RNA-sequencing spaceflight data archived on NASA GeneLab. Our results showed that clock gene expressions in spaceflight mice were altered compared with those in ground control mice. Furthermore, the results suggested that spaceflight promotes asynchrony of clock gene expressions between peripheral tissues. Abnormal circadian rhythms are associated not only with jet lag and sleep disorders but also with cancer, lifestyle-related diseases, and mental disorders. Overall, our findings highlight the importance of elucidating the causes of circadian rhythm disruptions using the unique approach of space biology research to one day potentially develop countermeasures that benefit humans on Earth and in space.

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.

Dexamethasone Inhibits Spheroid Formation of Thyroid Cancer Cells Exposed to Simulated Microgravity

Detachment and the formation of spheroids under microgravity conditions can be observed with various types of intrinsically adherent human cells. In particular, for cancer cells this process mimics metastasis and may provide insights into cancer biology and progression that can be used to identify new drug/target combinations for future therapies. By using the synthetic glucocorticoid dexamethasone (DEX), we were able to suppress spheroid formation in a culture of follicular thyroid cancer (FTC)-133 cells that were exposed to altered gravity conditions on a random positioning machine. DEX inhibited the growth of three-dimensional cell aggregates in a dose-dependent manner. In the first approach, we analyzed the expression of several factors that are known to be involved in key processes of cancer progression such as autocrine signaling, proliferation, epithelial–mesenchymal transition, and anoikis. Wnt/β-catenin signaling and expression patterns of important genes in cancer cell growth and survival, which were further suggested to play a role in three-dimensional aggregation, such as NFKB2, VEGFA, CTGF, CAV1, BCL2(L1), or SNAI1, were clearly affected by DEX. Our data suggest the presence of a more complex regulation network of tumor spheroid formation involving additional signal pathways or individual key players that are also influenced by DEX.

GeneLab Database Analyses Suggest Long-Term Impact of Space Radiation on the Cardiovascular System by the Activation of FYN Through Reactive Oxygen Species

Space radiation has recently been considered a risk factor for astronauts’ cardiac health. As an example, for the case of how to query and identify datasets within NASA’s GeneLab database and demonstrate the database utility, we used an unbiased systems biology method for identifying key genes/drivers for the contribution of space radiation on the cardiovascular system. This knowledge can contribute to designing appropriate experiments targeting these specific pathways. Microarray data from cardiomyocytes of male C57BL/6 mice followed-up for 28 days after exposure to 900 mGy of 1 GeV proton or 150 mGy of 1 GeV/n ⁵⁶Fe were compared to human endothelial cells (HUVECs) cultured for 7 days on the International Space Station (ISS). We observed common molecular pathways between simulated space radiation and HUVECs flown on the ISS. The analysis suggests FYN is the central driver/hub for the cardiovascular response to space radiation: the known oxidative stress induced immediately following radiation would only be transient and would upregulate FYN, which in turn would reduce reactive oxygen species (ROS) levels, protecting the cardiovascular system. The transcriptomic signature of exposure to protons was also much closer to the spaceflight signature than ⁵⁶Fe’s signature. To our knowledge, this is the first time GeneLab datasets were utilized to provide potential biological indications that the majority of ions on the ISS are protons, clearly illustrating the power of omics analysis. More generally, this work also demonstrates how to combine animal radiation studies done on the ground and spaceflight studies to evaluate human risk in space.