Human Health during Space Travel: State-of-the-Art Review

New insights into the impact of bed rest on lumbopelvic muscles: a computer-vision model approach to measure fat fraction changes

Space agencies plan crewed missions to the Moon and Mars. However, microgravity-induced lumbopelvic deconditioning, characterized by an increased fat fraction (FF) due to reduced physical activity, poses a significant challenge to spine health. This study investigates the spatial distribution of FF in the lumbopelvic muscles to identify the most affected regions by deconditioning, utilizing a computer-vision model and a tile-based approach to assess FF changes. Twenty-four healthy individuals (8 F) were recruited, and automatic segmentation of the lumbopelvic muscles was applied before and after 59 days of head-down tilt bed rest (HDTBR + 59) and 13 days of reconditioning (R + 13). Axial Dixon sequence images were acquired from 3 T magnetic resonance imaging. FF in the lumbar multifidus (LM), lumbar erector spinae (LES), quadratus lumborum, psoas major, gluteus maximus (GMax), gluteus medius (GMed), and gluteus minimus (GMin) muscles from the upper margin of L1 vertebra to the inferior border of GMax muscle were automatically derived using a computer-vision model. Lumbar muscles were segmented into eight tiles (superficial and deep, lateral to medial), and gluteal muscles into regions (anterior/superior for GMed and GMin, superior/inferior for GMax). At HDTBR + 59, the deep centrolateral region at L5/S1 for LM (18.7 ± 15.7%, P < 0.001; d = 0.97) and the deep medial region at Upper L4 for LES (5.4 ± 5.9%, P < 0.001; d = 0.34) showed the largest increase in FF compared with baseline data collection. These regions did not recover at R + 13 (P < 0.05; d ≥ 0.25). These findings highlight the need to target deep fascicles of LM and LES in countermeasure strategies to mitigate microgravity-induced lumbopelvic deconditioning, optimizing spine health, and performance.NEW & NOTEWORTHY This study reveals novel insights into fat fraction changes in lumbopelvic muscles after 60 days of head-down bed rest and 13 days of reconditioning. Lipids increased in the deep regions of the lumbar multifidus (LM) and lumbar erector spinae (LES), particularly at lower vertebral levels, and persisted after reconditioning. These findings highlight the need to target deep fascicles of LM and LES in future countermeasures to mitigate microgravity-induced deconditioning and optimize spine health.

Hypothesis on the outflow of optic nerve cerebrospinal fluid in spaceflight associated neuro ocular syndrome

Spaceflight-associated neuro-ocular syndrome (SANS) has been well documented in astronauts. However, its pathogenesis is not fully understood. New findings indicate the impaired outflow of the optic nerve cerebrospinal fluid may participate or contribute to some changes in SANS. In this perspective, we generated a hypothesis that the outflow of cerebrospinal fluid through the optic nerve sheath may be impaired under micro-gravity and then may potentially lead to SANS-related alterations.

X-ray-induced acoustic computed tomography: 3D X-ray absorption imaging from a single view

Computed tomography (CT) scanners are essential for modern imaging but require around 600 projections from various angles. We present x-ray-induced acoustic computed tomography (XACT), a method that uses radiation-induced acoustic waves for three-dimensional (3D) x-ray imaging. These spherical acoustic waves travel through tissue at 1.5 × 103 meters per second, much slower than x-rays, allowing ultrasound detectors to capture them and generate 3D images without mechanical scanning. We validate this theory by performing 3D numerical reconstructions of a human breast from a single x-ray projection and experimentally determining 3D structures of objects at different depths. Achieving resolutions of 0.4 millimeters in the XZ plane and 3.5 millimeters in the XY plane at a depth of 16 millimeters, XACT demonstrates the ability to produce 3D images from one x-ray projection, reducing radiation exposure and enabling gantry-free imaging. XACT shows great promise for biomedical and nondestructive testing applications, potentially replacing conventional CT.

A review of the physiological effects of microgravity and innovative formulation for space travelers

During the space travel mission, astronauts' physiological and psychological behavior will alter, and they will start consuming terrestrial drug products. However, factors such as microgravity, radiation exposure, temperature, humidity, strong vibrations, space debris, and other issues encountered, the drug product undergo instability This instability combined with physiological changes will affect the shelf life and diminish the pharmacokinetic and pharmacodynamic profile of the drug product. Consequently, the physicochemical changes will produce a toxic degradation product and a lesser potency dosage form which may result in reduced or no therapeutic action, so the astronaut consumes an additional dose to remain healthy. On long-duration missions like Mars, the drug product cannot be replaced, and the astronaut may relay on the available medications. Sometimes, radiation-induced impurities in the drug product will cause severe problems for the astronaut. So, this review article highlights the current state of various space-related factors affecting the drug product and provides a comprehensive summary of the physiological changes which primarly focus on absorption, distribution, metabolism, and excretion (ADME). Along with that, we insist some of the strategies like novel formulations, space medicine manufacturing from plants, and 3D printed medicine for astronauts in longer-duration missions. Such developments are anticipated to significantly contribute to new developments with applications in both human space exploration and on terrestrial healthcare.

Development and characterization of a low intensity vibrational system for microgravity studies

Extended-duration human spaceflight necessitates a better understanding of the physiological impacts of microgravity. While the ground-based microgravity simulations identified low intensity vibration (LIV) as a possible countermeasure, how cells may respond to LIV under real microgravity remain unexplored. In this way, adaptation of LIV bioreactors for space remains limited, resulting in a significant gap in microgravity research. In this study, we introduce an LIV bioreactor designed specifically for the usage in the International Space Station. Our research covers the bioreactor's design process and evaluation of the short-term viability of cells encapsulated in hydrogel-laden 3D printed scaffolds under 0.7 g, 90 Hz LIV. An LIV bioreactor compatible with the operation requirements of space missions provides a robust platform to study cellular effects of LIV under real microgravity conditions.

Proteomic and ubiquitinome analysis reveal that microgravity affects glucose metabolism of mouse hearts by remodeling non-degradative ubiquitination

Long-term exposure to a microgravity environment leads to structural and functional changes in hearts of astronauts. Although several studies have reported mechanisms of cardiac damage under microgravity conditions, comprehensive research on changes at the protein level in these hearts is still lacking. In this study, proteomic analysis of microgravity-exposed hearts identified 156 differentially expressed proteins, and ubiquitinomic analysis of these hearts identified 169 proteins with differential ubiquitination modifications. Integrated ubiquitinomic and proteomic analysis revealed that differential proteomic changes caused by transcription affect the immune response in microgravity-exposed hearts. Additionally, changes in ubiquitination modifications under microgravity conditions excessively activated certain kinases, such as hexokinase and phosphofructokinase, leading to cardiac metabolic disorders. These findings provide new insights into the mechanisms of cardiac damage under microgravity conditions.

Effects of simulated space conditions on CD4+ T cells: a multi modal analysis

Introduction

The immune system is an intricate network of cellular components that safeguards against pathogens and aberrant cells, with CD4+ T cells playing a central role in this process. Human space travel presents unique health challenges, such as heavy ion ionizing radiation, microgravity, and psychological stress, which can collectively impede immune function. The aim of this research was to examine the consequences of simulated space stressors on CD4+ T cell activation, cytokine production, and gene expression.

Methods

CD4+ T cells were obtained from healthy individuals and subjected to Fe ion particle radiation, Photon irradiation, simulated microgravity, and hydrocortisone, either individually or in different combinations. Cytokine levels for Th1 and Th2 cells were determined using multiplex Luminex assays, and RNA sequencing was used to investigate gene expression patterns and identify essential genes and pathways impacted by these stressors.

Results

Simulated microgravity exposure resulted in an apparent Th1 to Th2 shift, evidenced on the level of cytokine secretion as well as altered gene expression. RNA sequencing analysis showed that several gene pathways were altered, particularly in response to Fe ions irradiation and simulated microgravity exposures. Individually, each space stressor caused differential gene expression, while the combination of stressors revealed complex interactions.

Discussion

The research findings underscore the substantial influence of the space exposome on immune function, particularly in the regulation of T cell responses. Future work should focus expanding the limited knowledge in this field. Comprehending these modifications will be essential for devising effective strategies to safeguard the health of astronauts during extended space missions.

Conclusion

The effects of simulated space stressors on CD4+ T cell function are substantial, implying that space travel poses a potential threat to immune health. Additional research is necessary to investigate the intricate relationship between space stressors and to develop effective countermeasures to mitigate these consequences.

Changing the gravity vector direction by inverted culture enhances radiation-induced cell damage

In recent years, it has become clear that the cytotoxicity of γ-irradiation of cells is increased under microgravity conditions. However, there has been no study of the effect of the gravity vector direction, rather than the magnitude, on γ-ray-induced cytotoxicity. Therefore, in this study, we inverted cultures of human bronchial epithelium BEAS-2B cells and human lung cancer A549 cells in order to change the gravity vector direction by 180° with respect to the cells and observed the cellular response to radiation in this state. We found that cells in inverted culture showed increased irradiation-induced production of reactive oxygen species and decreased expression of the antioxidant protein thioredoxin-1 compared to cells in normal culture. Furthermore, the DNA damage response was delayed in γ-irradiated cells in inverted culture, and the number of unrepaired DNA sites was increased, compared to irradiated cells in normal culture. γ-Ray-induced cell death and the number of G2-M arrested cells were increased in inverted culture, in accordance with the decreased capacity for DNA repair. Our findings suggest that the gravity vector direction, as well as its magnitude, alters the cellular response to radiation.

Differential Functional Changes in Visual Performance during Acute Exposure to Microgravity Analogue and Their Potential Links with Spaceflight-Associated Neuro-Ocular Syndrome

BACKGROUND

Spaceflight-Associated Neuro-Ocular Syndrome (SANS) is a complex pathology threatening the health of astronauts, with incompletely understood causes and no current specific functional diagnostic or screening test. We investigated the use of the differential performance of the visual system (central vs. perimacular visual function) as a candidate marker of SANS-related pathology in a ground-based microgravity analogue.

METHODS

We used a simple reaction time (SRT) task to visual stimuli, presented in the central and perimacular field of view, as a measure of the overall performance of the visual function, during acute settings (first 10 min) of vertical, bed rest (BR), -6°, and -15° head-down tilt (HDT) presentations in healthy participants (n = 8). We built dose-response models linking the gravitational component to SRT distribution parameters in the central vs. perimacular areas.

RESULTS

Acute exposure to microgravity induces detectable changes between SRT distributions in the perimacular vs. central retina (increased mean, standard deviation, and tau component of the ex-Gaussian function) in HDT compared with vertical presentation.

CONCLUSIONS

Functional testing of the perimacular retina might be beneficial for the earlier detection of SANS-related ailments in addition to regular testing of the central vision. Future diagnostic tests should consider the investigation of the extra-macular areas, particularly towards the optic disc.

Effects of Electroencephalogram Neurofeedback Intervention on Blood C-Reactive Protein Levels in Astronauts Attending 2-Week Long Analog Moon Mission

The human organism is affected by multiple stressors every single day, especially during extremely demanding activities. It needs a method to regulate itself better. One of the stressors that is affecting humans is social isolation. The state of prolonged isolation happens during space missions. In this study, 40 analog astronauts attended a two-week-long mission. The experimental group had EEG neurofeedback training intervention performed on a daily basis, while the control group remained isolated without neurofeedback. The results let us take this non-invasive intervention under consideration, while debating the methods to lower the physiological stress reaction in humans that are exposed to extremely hard circumstances. Although not statistically significant, the trends observed give us direction towards other research to confirm EEG neurofeedback as a method to lower cell stress response levels.

Gut matters in microgravity: potential link of gut microbiota and its metabolites to cardiovascular and musculoskeletal well-being

The gut microbiota and its secreted metabolites play a significant role in cardiovascular and musculoskeletal health and diseases. The dysregulation of the intestinal microbiota poses a significant threat to cardiovascular and skeletal muscle well-being. Nonetheless, the precise molecular mechanisms underlying these changes remain unclear. Furthermore, microgravity presents several challenges to cardiovascular and musculoskeletal health compromising muscle strength, endothelial dysfunction, and metabolic changes. The purpose of this review is to critically examine the role of gut microbiota metabolites on cardiovascular and skeletal muscle functions and dysfunctions. It also explores the molecular mechanisms that drive microgravity-induced deconditioning in both cardiovascular and skeletal muscle. Key findings in this review highlight that several alterations in gut microbiota and secreted metabolites in microgravity mirror characteristics seen in cardiovascular and skeletal muscle diseases. Those alterations include increased levels of Firmicutes/Bacteroidetes (F/B) ratio, elevated lipopolysaccharide levels (LPS), increased in para-cresol (p-cresol) and secondary metabolites, along with reduction in bile acids and Akkermansia muciniphila bacteria. Highlighting the potential, modulating gut microbiota in microgravity conditions could play a significant role in mitigating cardiovascular and skeletal muscle diseases not only during space flight but also in prolonged bed rest scenarios here on Earth.

Exploring New Horizons: Advancements in Cartilage Tissue Engineering Under Space Microgravity

Novel investigations of how microgravity affects cellular and tissue development have recently been made possible by the multidisciplinary fusion of tissue engineering and space science. This review examines the intersection of cartilage tissue engineering (CTE) and space science, focusing on how microgravity affects cartilage development. Space microgravity induces distinct physiological changes in chondrocytes, including a 20-30% increase in cell diameter, a 1.5- to 2-fold increase in proliferation rates, and up to 3-fold increases in chondrogenic markers such as SOX9 and collagen type II. These cellular alterations impact extracellular matrix composition and tissue structure. Space-optimized bioreactors using dynamic culture methods replicate physiological conditions and enhance tissue growth, but the absence of gravity raises concerns about the mechanical properties of engineered cartilage. Key research areas include the role of growth factors in cartilage development under microgravity, biocompatibility and degradation of scaffold materials in space, and in situ experiments on space stations. This review highlights the opportunities and challenges in leveraging microgravity for CTE advancements, emphasizing the need for continued research to harness space environments for therapeutic applications in cartilage regeneration. The multidisciplinary fusion of tissue engineering and space science opens novel avenues for understanding and improving cartilage tissue engineering, with significant implications for the future of biomedical applications in space and on Earth.

Machine learning workflow for edge computed arrhythmia detection in exploration class missions

Deep-space missions require preventative care methods based on predictive models for identifying in-space pathologies. Deploying such models requires flexible edge computing, which Open Neural Network Exchange (ONNX) formats enable by optimizing inference directly on wearable edge devices. This work demonstrates an innovative approach to point-of-care machine learning model pipelines by combining this capacity with an advanced self-optimizing training scheme to classify periods of Normal Sinus Rhythm (NSR), Atrial Fibrillation (AFIB), and Atrial Flutter (AFL). 742 h of electrocardiogram (ECG) recordings were pre-processed into 30-second normalized samples where variable mode decomposition purged muscle artifacts and instrumentation noise. Seventeen heart rate variability and morphological ECG features were extracted by convoluting peak detection with Gaussian distributions and delineating QRS complexes using discrete wavelet transforms. The decision tree classifier's features, parameters, and hyperparameters were self-optimized through stratified triple nested cross-validation ranked on F1-scoring against cardiologist labeling. The selected model achieved a macro F1-score of 0.899 with 0.993 for NSR, 0.938 for AFIB, and 0.767 for AFL. The most important features included median P-wave amplitudes, PRR20, and mean heart rates. The ONNX-translated pipeline took 9.2 s/sample. This combination of our self-optimizing scheme and deployment use case of ONNX demonstrated overall accurate operational tachycardia detection.

Considering clonal hematopoiesis of indeterminate potential in space radiation risk analysis for hematologic cancers and cardiovascular disease

BACKGROUND

Expanding human presence in space through long-duration exploration missions and commercial space operations warrants improvements in approaches for quantifying crew space radiation health risks. Currently, risk assessment models for radiogenic cancer and cardiovascular disease consider age, sex, and tobacco use, but do not incorporate other modifiable (e.g., body weight, physical activity, diet, environment) and non-modifiable individual risk factors (e.g., genetics, medical history, race/ethnicity, family history) that may greatly influence crew health both in-mission and long-term. For example, clonal hematopoiesis of indeterminate potential (CHIP) is a relatively common age-related condition that is an emerging risk factor for a variety of diseases including cardiovascular disease and cancer. CHIP carrier status may therefore exacerbate health risks associated with space radiation exposure.

METHODS

In the present study, published CHIP hazard ratios were used to modify background hazard rates for coronary heart disease, stroke, and hematologic cancers in the National Aeronautics and Space Administration space radiation risk assessment model. The risk of radiation exposure-induced death for these endpoints was projected for a future Mars exploration mission scenario.

RESULTS

Here we show appreciable increases in the lifetime risk of exposure-induced death for hematologic malignancies, coronary heart disease, and stroke, which are observed as a function of age after radiation exposure for male and female crew members that are directly attributable to the elevated health risks for CHIP carriers.

CONCLUSIONS

We discuss the importance of evaluating individual risk factors such as CHIP as part of a comprehensive space radiation risk assessment strategy aimed at effective risk communication and disease surveillance for astronauts embarking on future exploration missions.

Potential Biomarkers of Resilience to Microgravity Hazards in Astronauts

Space exploration exposes astronauts to the unique environment of microgravity, which poses significant health challenges. Identifying biomarkers that can predict an individual's resilience to the stressors of microgravity holds great promise for optimizing astronaut selection and developing personalized countermeasures. This narrative review examines the principal health risks associated with microgravity and explores potential biomarkers indicative of resilience. The biomarkers being evaluated represent a broad spectrum of physiological domains, including musculoskeletal, neurological, immunological, gastrointestinal, cardiovascular, and cutaneous systems. Earth-based microgravity analogs, such as dry immersion and head-down tilt bed rest, may provide valuable platforms to validate candidate biomarkers. However, biomarker sensitivity and specificity must be further evaluated to ensure efficacy and reliability. Establishing a panel of biomarkers predictive of resilience to microgravity-induced health risks would significantly enhance astronaut health and mission success, especially for long-duration exploration missions. Insights gained may also translate to health conditions on Earth characterized by reduced physical activity and mechanical loading.

Palmer Station, Antarctica: A ground-based spaceflight analog suitable for validation of biomedical countermeasures for deep space missions

Astronauts are known to exhibit a variety of immunological alterations during spaceflight including changes in leukocyte distribution and plasma cytokine concentrations, a reduction in T-cell function, and subclinical reactivation of latent herpesviruses. These alterations are most likely due to mission-associated stressors including circadian misalignment, microgravity, isolation, altered nutrition, and increased exposure to cosmic radiation. Some of these stressors may also occur in terrestrial situations. This study sought to determine if crewmembers performing winterover deployment at Palmer Station, Antarctica, displayed similar immune alterations. The larger goal was to validate a ground analog suitable for the evaluation of countermeasures designed to protect astronauts during future deep space missions. For this pilot study, plasma, saliva, hair, and health surveys were collected from Palmer Station, Antarctica, winterover participants at baseline, and at five winterover timepoints. Twenty-six subjects consented to participate over the course of two seasons. Initial sample processing was performed at Palmer, and eventually stabilized samples were returned to the Johnson Space Center for analysis. A white blood cell differential was performed (real time) using a fingerstick blood sample to determine alterations in basic leukocyte subsets throughout the winterover. Plasma and saliva samples were analyzed for 30 and 13 cytokines, respectively. Saliva was analyzed for cortisol concentration and three latent herpesviruses (DNA by qPCR), EBV, HSV1, and VZV. Voluntary surveys related to general health and adverse clinical events were distributed to participants. It is noteworthy that due to logistical constraints caused by COVID-19, the baseline samples for each season were collected in Punta Arenas, Chile, after long international travel and during isolation. Therefore, the Palmer pre-mission samples may not reflect a true normal 'baseline'. Minimal alterations were observed in leukocyte distribution during winterover. The mean percentage of monocyte concentration elevated at one timepoint. Plasma G-CSF, IL1RA, MCP-1, MIP-1β, TNFα, and VEGF were decreased during at least one winterover timepoint, whereas RANTES was significantly increased. No statistically significant changes were observed in mean saliva cytokine concentrations. Salivary cortisol was substantially elevated throughout the entire winterover compared to baseline. Compared to shedding levels observed in healthy controls (23%), the percentage of participants who shed EBV was higher throughout all winterover timepoints (52-60%). Five subjects shed HSV1 during at least one timepoint throughout the season compared to no subjects shedding during pre-deployment. Finally, VZV reactivation, common in astronauts but exceptionally rare in ground-based stress analogs, was observed in one subject during pre-deployment and a different subject at WO2 and WO3. These pilot data, somewhat influenced by the COVID-19 pandemic, do suggest that participants at Palmer Station undergo immunological alterations similar to, but likely in reduced magnitude, as those observed in astronauts. We suggest that winterover at Palmer Station may be a suitable test analog for spaceflight biomedical countermeasures designed to mitigate clinical risks for deep space missions.

Lost in Space? Unmasking the T Cell Reaction to Simulated Space Stressors

The space environment will expose astronauts to stressors like ionizing radiation, altered gravity fields and elevated cortisol levels, which pose a health risk. Understanding how the interplay between these stressors changes T cells' response is important to better characterize space-related immune dysfunction. We have exposed stimulated Jurkat cells to simulated space stressors (1 Gy, carbon ions/1 Gy photons, 1 µM hydrocortisone (HC), Mars, moon, and microgravity) in a single or combined manner. Pro-inflammatory cytokine IL-2 was measured in the supernatant of Jurkat cells and at the mRNA level. Results show that alone, HC, Mars gravity and microgravity significantly decrease IL-2 presence in the supernatant. 1 Gy carbon ion irradiation showed a smaller impact on IL-2 levels than photon irradiation. Combining exposure to different simulated space stressors seems to have less immunosuppressive effects. Gene expression was less impacted at the time-point collected. These findings showcase a complex T cell response to different conditions and suggest the importance of elevated cortisol levels in the context of space flight, also highlighting the need to use simulated partial gravity technologies to better understand the immune system's response to the space environment.

Oral Health in Zero Gravity: A Comprehensive Review of Orofacial Effects and Countermeasures in Spaceflights

Space is a complex and challenging setting encompassing the region beyond Earth's atmosphere where astronauts and spacecraft operate. The unique conditions of spaceflights, particularly microgravity and radiation, pose significant challenges to astronaut health, including the orofacial region. It has effects on saliva production, microbial composition, and oral hygiene practices, which influence oral health status, such as increased risk of dental caries, gum diseases, oral discomfort, temporomandibular joint dysfunctions, sialoliths, pain and dysesthesia in the teeth and oral mucosa, masticatory muscle atrophy, and oral cancer which can be detrimental during prolonged missions. Hence, a comprehensive approach to dental care in space is imperative to ensure astronauts' well-being and overall health as we strive to extend our presence beyond Earth. This literature review paper sheds light on the intricate effects of space on the orofacial region and delves into the unique challenges astronauts face in upholding optimal oral health while in space. It explores the current state of dentistry in space and discusses advancements and strategies that aim to maintain optimal oral health for astronauts during extended space missions.

Managing Hemostasis in Space

Human space travel requires exposure to weightlessness, ionizing radiation, isolation, and austerity. A recent report of internal jugular vein thrombosis in astronauts in low Earth orbit confirms that these exposures also affect vascular biology to influence diseases of thrombosis and hemostasis. This brief review summarizes the known influences of space travel on inflammation, blood coagulation, and the cardiovascular system and conceptualizes how they might combine to affect thrombosis and hemostasis. In the event of a major thrombotic or bleeding emergency, it is anticipated that the unique physiological influences of the space environment and logistical limitations of providing medical care in space would require a response that is unique from our current experience. We also look towards the future to discuss lessons learned from our current experiences on Earth and in space.

Spaceflight Induces Strength Decline in Caenorhabditis elegans

Background: Understanding and countering the well-established negative health consequences of spaceflight remains a primary challenge preventing safe deep space exploration. Targeted/personalized therapeutics are at the forefront of space medicine strategies, and cross-species molecular signatures now define the 'typical' spaceflight response. However, a lack of direct genotype-phenotype associations currently limits the robustness and, therefore, the therapeutic utility of putative mechanisms underpinning pathological changes in flight. Methods: We employed the worm Caenorhabditis elegans as a validated model of space biology, combined with 'NemaFlex-S' microfluidic devices for assessing animal strength production as one of the most reproducible physiological responses to spaceflight. Wild-type and dys-1 (BZ33) strains (a Duchenne muscular dystrophy (DMD) model for comparing predisposed muscle weak animals) were cultured on the International Space Station in chemically defined media before loading second-generation gravid adults into NemaFlex-S devices to assess individual animal strength. These same cultures were then frozen on orbit before returning to Earth for next-generation sequencing transcriptomic analysis. Results: Neuromuscular strength was lower in flight versus ground controls (16.6% decline, p < 0.05), with dys-1 significantly more (23% less strength, p < 0.01) affected than wild types. The transcriptional gene ontology signatures characterizing both strains of weaker animals in flight strongly corroborate previous results across species, enriched for upregulated stress response pathways and downregulated mitochondrial and cytoskeletal processes. Functional gene cluster analysis extended this to implicate decreased neuronal function, including abnormal calcium handling and acetylcholine signaling, in space-induced strength declines under the predicted control of UNC-89 and DAF-19 transcription factors. Finally, gene modules specifically altered in dys-1 animals in flight again cluster to neuronal/neuromuscular pathways, suggesting strength loss in DMD comprises a strong neuronal component that predisposes these animals to exacerbated strength loss in space. Conclusions: Highly reproducible gene signatures are strongly associated with space-induced neuromuscular strength loss across species and neuronal changes in calcium/acetylcholine signaling require further study. These results promote targeted medical efforts towards and provide an in vivo model for safely sending animals and people into deep space in the near future.

Stem Cells and Exosome Applications for Cutaneous Wound Healing: From Ground to Microgravity Environment

The increasing number of astronauts entering microgravity environments for long-term space missions has resulted in serious health problems, including accidental injury and trauma. Skin, as the largest organ and outermost layer of the human body, has the ability to self-renew and withstand a variety of harmful biological and environmental influences. Recent spaceflight experiments and simulated studies have begun to concern the effects of microgravity on the growth of skin cells and the process of cutaneous wound healing. However, the mechanisms of the adverse effects of microgravity on skin cells and potential intervention measures are still limited. Stem cells and their exosomes provide unique opportunities for the cutaneous wound healing as they have been used to improve skin repair. This review discusses the effects of microgravity on wound healing, from cell morphological changes to molecular level alterations. Furthermore, the current research on wound healing treatment utilizing stem cells and their exosomes on the ground is summarized. Finally, this review proposes promising therapeutic strategies using stem cells or exosomes for wound healing in the microgravity environment. Graphical Abstract.

3D Bioprinting in Microgravity: Opportunities, Challenges, and Possible Applications in Space

3D bioprinting has developed tremendously in the last couple of years and enables the fabrication of simple, as well as complex, tissue models. The international space agencies have recognized the unique opportunities of these technologies for manufacturing cell and tissue models for basic research in space, in particular for investigating the effects of microgravity and cosmic radiation on different types of human tissues. In addition, bioprinting is capable of producing clinically applicable tissue grafts, and its implementation in space therefore can support the autonomous medical treatment options for astronauts in future long term and far-distant space missions. The article discusses opportunities but also challenges of operating different types of bioprinters under space conditions, mainly in microgravity. While some process steps, most of which involving the handling of liquids, are challenging under microgravity, this environment can help overcome problems such as cell sedimentation in low viscous bioinks. Hopefully, this publication will motivate more researchers to engage in the topic, with publicly available bioprinting opportunities becoming available at the International Space Station (ISS) in the imminent future.