Cosmic chronometers: Is spaceflight a catalyst for biological ageing?

Astronauts returning from space missions often exhibit health issues mirroring age-related conditions, suggesting spaceflight as a potential driver of biological ageing and age-related diseases. To unravel the underlying mechanisms of these conditions, this comprehensive review explores the impact of the space "exposome" on the twelve hallmarks of ageing. Through a meticulous analysis encompassing both space environments and terrestrial analogs, we aim to decipher how different conditions influence ageing hallmarks. Utilizing PubMed, we identified 189 studies and 60 meet screening criteria. Research on biological ageing in space has focused on genomic instability, chronic inflammation, and deregulated nutrient sensing. Spaceflight consistently induces genomic instability, linked to prolonged exposure to ionizing radiation, triggers pro-inflammatory and immune alterations, resembling conditions in isolated simulations. Nutrient sensing pathways reveal increased systemic insulin-like growth-factor-1. Microbiome studies indicate imbalances favoring opportunistic species during spaceflight. Telomere dynamics present intriguing patterns, with lengthening during missions and rapid shortening upon return. Despite a pro-ageing trend, some protective mechanisms emerge. Countermeasures, encompassing dietary adjustments, prebiotics, postbiotics, symbiotics, tailored exercises, meditation, and anti-inflammatory supplements, exhibit potential. Spaceflight's impact on ageing is intricate, with diverse findings challenging established beliefs. Multidisciplinary studies provide guidance for future research in this field.

Mitochondrial stress in the spaceflight environment

Space is a challenging environment that deregulates individual homeostasis. The main external hazards associated with spaceflight include ionizing space radiation, microgravity, isolation and confinement, distance from Earth, and hostile environment. Characterizing the biological responses to spaceflight environment is essential to validate the health risks, and to develop effective protection strategies. Mitochondria energetics is a key mechanism underpinning many physiological, ecological and evolutionary processes. Moreover, mitochondrial stress can be considered one of the fundamental features of space travel. So, we attempt to synthesize key information regarding the extensive effects of spaceflight on mitochondria. In summary, mitochondria are affected by all of the five main hazards of spaceflight at multiple levels, including their morphology, respiratory function, protein, and genetics, in various tissues and organ systems. We emphasize that investigating mitochondrial biology in spaceflight conditions should become the central focus of research on the impacts of spaceflight on human health, as this approach will help resolve numerous challenges of space health and combat several health disorders associated with mitochondrial dysfunction.

Anatomical considerations for reducing ocular emergencies during spaceflight

PURPOSE

The privatization of space travel is opening civilian spaceflight to an unprecedented number of individuals now and in the immediate future. The increase in the number and diversity of space travelers will mean increased exposure to both physiologic and pathologic changes observed during acute and prolonged microgravity.

AIMS

In this paper, we describe the anatomic, physiologic, and pharmacologic factors to consider that impact acute angle-closure glaucoma risk during spaceflight.

CONCLUSIONS

Based on these factors, we elaborate upon areas of medical considerations and provide future recommendations that may aid in reducing the risk of acute angle-closure glaucoma in the next era of spaceflight.

Prioritizing open science in space medicine: perspectives following the NASA "Transform to Open Science (TOPS)" Curriculum

The National Aeronautics and Space Administration (NASA) has recently made a long-term commitment towards fostering open science. The NASA Transform to Open Science (TOPS) initiative provides recommendations, best practices, and tools related to open science. The principles of open science include the transparent sharing of data, findings, and methods and is designed to accelerate the pace of discovery and foster collaboration. The goal of open science is to allow data, publications, software, and physical samples to be accessible to all, regardless of being a professional or an amateur. In this paper, we summarize several key points open science that were presented as part of NASA's Open Science 101 Module 1 at an in-person training event in Washington, D.C., and include how open science can be beneficial for researchers and society as a whole.

Utility of ultrasound in managing acute medical conditions in space: a scoping review

BACKGROUND

In long-distance spaceflight, the challenges of communication delays and the impracticality of rapid evacuation necessitate the management of medical emergencies by onboard physicians. Consequently, these physicians must be proficient in tools, such as ultrasound, which has proven itself a strong diagnostic imaging tool in space. Yet, there remains a notable gap in the discourse surrounding its efficacy in handling acute medical scenarios. This scoping review aims to present an updated analysis of the evidence supporting the role of ultrasound in diagnosing acute conditions within microgravity environments.

METHODS

A systematic search was executed across three bibliographic databases: PubMed, EMBASE (Embase.com), and the Web of Science Core Collection. We considered articles published up to February 25, 2023, that highlighted the application of ultrasound in diagnosing acute medical conditions in either microgravity or microgravity-simulated settings. Exclusions were made for review papers, abstracts, and in-vitro studies.

RESULTS

After removing duplicates, and filtering papers by pre-determined criteria, a total of 15 articles were identified that discuss the potential use of ultrasound in managing acute medical conditions in space. The publication date of these studies ranged from 1999 to 2020. A relatively similar proportion of these studies were conducted either on the International Space Station or in parabolic flight, with one performed in supine positioning to simulate weightlessness. The included studies discuss acute pathologies, such as abdominal emergencies, decompression sickness, deep venous thrombosis, acute lung pathologies, sinusitis, musculoskeletal trauma, genitourinary emergencies, and ocular emergencies.

CONCLUSIONS

While ultrasound has shown promise in addressing various acute conditions, significant knowledge gaps remain, especially in gastrointestinal, cardiac, vascular, and reproductive emergencies. As we venture further into space, expanding our medical expertise becomes vital to ensure astronaut safety and mission success.

Microbial isolation and characterization from two flex lines from the urine processor assembly onboard the international space station

Urine, humidity condensate, and other sources of non-potable water are processed onboard the International Space Station (ISS) by the Water Recovery System (WRS) yielding potable water. While some means of microbial control are in place, including a phosphoric acid/hexavalent chromium urine pretreatment solution, many areas within the WRS are not available for routine microbial monitoring. Due to refurbishment needs, two flex lines from the Urine Processor Assembly (UPA) within the WRS were removed and returned to Earth. The water from within these lines, as well as flush water, was microbially evaluated. Culture and culture-independent analysis revealed the presence of Burkholderia, Paraburkholderia, and Leifsonia. Fungal culture also identified Fusarium and Lecythophora. Hybrid de novo genome analysis of the five distinct Burkholderia isolates identified them as B. contaminans, while the two Paraburkholderia isolates were identified as P. fungorum. Chromate-resistance gene clusters were identified through pangenomic analysis that differentiated these genomes from previously studied isolates recovered from the point-of-use potable water dispenser and/or current NCBI references, indicating that unique populations exist within distinct niches in the WRS. Beyond genomic analysis, fixed samples directly from the lines were imaged by environmental scanning electron microscopy, which detailed networks of fungal-bacterial biofilms. This is the first evidence of biofilm formation within flex lines from the UPA onboard the ISS. For all bacteria isolated, biofilm potential was further characterized, with the B. contaminans isolates demonstrating the most considerable biofilm formation. Moreover, the genomes of the B. contaminans revealed secondary metabolite gene clusters associated with quorum sensing, biofilm formation, antifungal compounds, and hemolysins. The potential production of these gene cluster metabolites was phenotypically evaluated through biofilm, bacterial-fungal interaction, and hemolytic assays. Collectively, these data identify the UPA flex lines as a unique ecological niche and novel area of biofilm growth within the WRS. Further investigation of these organisms and their resistance profiles will enable engineering controls directed toward biofilm prevention in future space station water systems.

Hindlimb unloading, a physiological model of microgravity, modifies the murine bone marrow IgM repertoire in a similar manner as aging but less strongly

BACKGROUND

The spaceflight environment is an extreme environment that affects the immune system of approximately 50% of astronauts. With planned long-duration missions, such as the deployment of the Lunar Gateway and possible interplanetary missions, it is mandatory to determine how all components of the immune system are affected, which will allow the establishment of countermeasures to preserve astronaut health. However, despite being an important component of the immune system, antibody-mediated humoral immunity has rarely been investigated in the context of the effects of the space environment. It has previously been demonstrated that 30 days aboard the BION-M1 satellite and 21 days of hindlimb unloading (HU), a model classically used to mimic the effects of microgravity, decrease murine B lymphopoiesis. Furthermore, modifications in B lymphopoiesis reported in young mice subjected to 21 days of HU were shown to be similar to those observed in aged mice (18-22 months). Since the primary antibody repertoire composed of IgM is created by V(D) J recombination during B lymphopoiesis, the objective of this study was to assess the degree of similarity between changes in the bone marrow IgM repertoire and in the V(D)J recombination process in 2.5-month-old mice subjected to 21 days of HU and aged (18 months) mice.

RESULTS

We found that in 21 days, HU induced changes in the IgM repertoire that were approximately 3-fold less than those in aged mice, which is a rapid effect. Bone remodeling and epigenetics likely mediate these changes. Indeed, we previously demonstrated a significant decrease in tibial morphometric parameters from day 6 of HU and a progressive reduction in these parameters until day 21 of HU, and it has been shown that age and microgravity induce epigenetic changes.

CONCLUSION

These data reveal novel immune changes that are akin to advanced aging and underline the importance of studying the effects of spaceflight on antibody-mediated humoral immunity.

Identification of gravity-responsive proteins in the femur of spaceflight mice using a quantitative proteomic approach

Although the microgravity (μ-g) environment that astronauts encounter during spaceflight can cause severe acute bone loss, the molecular mechanism of this bone loss remains unclear. To investigate the gravity-response proteins involved in bone metabolism, it is important to comprehensively determine which proteins exhibit differential abundance associated with mechanical stimuli. However, comprehensive proteomic analysis using small bone samples is difficult because protein extraction in mineralized bone tissue is inefficient. Here, we established a high-sensitivity analysis system for mouse bone proteins using data-independent acquisition mass spectrometry. This system successfully detected 40 proteins in the femoral diaphysis showing differential abundance between mice raised in a μ-g environment, where the bone mass was reduced by gravity unloading, and mice raised in an artificial 1-gravity environment on the International Space Station. Additionally, 22 proteins, including noncollagenous bone matrix proteins, showed similar abundance between the two groups in the mandible, where bone mass was unaltered due to mastication stimuli, suggesting that these proteins are responsive to mechanical stimuli. One of these proteins, SPARCL1, is suggested to promote osteoclastogenesis induced by receptor activator of nuclear factor-κB ligand. We expect these findings to lead to new insights into the mechanisms of bone metabolism induced by mechanical stimuli. SIGNIFICANCE: We aimed to investigate the gravity-response proteins involved in bone metabolism. To this end, we established a comprehensive analysis system for mouse bone proteins using data-independent acquisition mass spectrometry, which is particularly useful in comprehensively analyzing the bone proteome using small sample volumes. In addition, a comprehensive proteomic analysis of the femoral diaphysis and mandible, which exhibit different degrees of bone loss in mice raised on the International Space Station, identified proteins that respond to mechanical stimuli. SPARCL1, a mechanical stimulus-responsive protein, was consequently suggested to be involved in osteoclast differentiation associated with bone remodeling. Our findings represent an important step toward elucidating the molecular mechanism of bone metabolism induced by mechanical stimuli.

Artificial gravity during a spaceflight analog alters brain sensory connectivity

Spaceflight has numerous untoward effects on human physiology. Various countermeasures are under investigation including artificial gravity (AG). Here, we investigated whether AG alters resting-state brain functional connectivity changes during head-down tilt bed rest (HDBR), a spaceflight analog. Participants underwent 60 days of HDBR. Two groups received daily AG administered either continuously (cAG) or intermittently (iAG). A control group received no AG. We assessed resting-state functional connectivity before, during, and after HDBR. We also measured balance and mobility changes from pre- to post-HDBR. We examined how functional connectivity changes throughout HDBR and whether AG is associated with differential effects. We found differential connectivity changes by group between posterior parietal cortex and multiple somatosensory regions. The control group exhibited increased functional connectivity between these regions throughout HDBR whereas the cAG group showed decreased functional connectivity. This finding suggests that AG alters somatosensory reweighting during HDBR. We also observed brain-behavioral correlations that differed significantly by group. Control group participants who showed increased connectivity between the putamen and somatosensory cortex exhibited greater mobility declines post-HDBR. For the cAG group, increased connectivity between these regions was associated with little to no mobility declines post-HDBR. This suggests that when somatosensory stimulation is provided via AG, functional connectivity increases between the putamen and somatosensory cortex are compensatory in nature, resulting in reduced mobility declines. Given these findings, AG may be an effective countermeasure for the reduced somatosensory stimulation that occurs in both microgravity and HDBR.

Database of space life investigations and information on spaceflight plant biology

Extensive spaceflight life investigations (SLIs) have revealed observable space effects on plants, particularly their growth, nutrition yield, and secondary metabolite production. Knowledge of these effects not only facilitates space agricultural and biopharmaceutical technology development but also provides unique perspectives to ground-based investigations. SLIs are specialized experimental protocols and notable biological phenomena. These require specialized databases, leading to the development of the NASA Science Data Archive, Erasmus Experiment Archive, and NASA GeneLab. The increasing interests of SLIs across diverse fields demand resources with comprehensive content, convenient search facilities, and friendly information presentation. A new database SpaceLID (Space Life Investigation Database http://bidd.group/spacelid/ ) was developed with detailed menu search tools and categorized contents about the phenomena, protocols, and outcomes of 459 SLIs (including 106 plant investigations) of 92 species, where 236 SLIs and 57 plant investigations are uncovered by the existing databases. The usefulness of SpaceLID as an SLI information source is illustrated by the literature-reported analysis of metabolite, nutrition, and symbiosis variations of spaceflight plants. In conclusion, this study extensively investigated the impact of the space environment on plant biology, utilizing SpaceLID as an information source and examining various plant species, including Arabidopsis thaliana, Brassica rapa L., and Glycyrrhiza uralensis Fisch. The findings provide valuable insights into the effects of space conditions on plant physiology and metabolism.

Could exposure to spaceflight cause mutations in genes that affect male fertility?

Recently, a study reported that upon analyzing blood samples from 14 astronauts that flew Space Transportation System missions between 1998 and 2001, 34 somatic nonsynonymous single nucleotide variants were detected in 17 CH-driver genes. Of interest is that the cohort consisted of relatively young astronauts, 85% of which were males of reproductive age. Having investigated the genes with nonsynonymous substitutes from the literature, it was found that twelve of these 17 genes appear to play essential roles in male reproduction. Changes in telomere length and gene regulation were also reported in another study conducted on an astronaut during a long duration stay on the International Space Station. Realizing the impact of spaceflight on gene sequence with potential influence on male fertility, it is important that more studies are conducted in this field. Specifically, in light of ultimately colonizing space, multi-generational survival is crucial and strategies to mitigate or counteract such effects should be explored.

Microgravity alters the expressions of DNA repair genes and their regulatory miRNAs in space-flown Caenorhabditis elegans

During spaceflight, multiple unique hazardous factors, particularly microgravity and space radiation, can induce different types of DNA damage, which pose a constant threat to genomic integrity and stability of living organisms. Although organisms have evolved different kinds of conserved DNA repair pathways to eliminate this DNA damage on Earth, the impact of space microgravity on the expressions of these DNA repair genes and their regulatory miRNAs has not been fully explored. In this study, we integrated all existing datasets, including both transcriptional and miRNA microarrays in wild-type (WT) Caenorhabditis elegans that were exposed to the treatments of spaceflight (SF), spaceflight control with a 1g centrifugal device (SC), and ground control (GC) in three space experiments with the periods of 4, 8 and 16.5 days. The results of principal component analysis showed the gene expression patterns for five major DNA repair pathways (i.e., non-homologous end joining (NHEJ), homologous recombination (HR), mismatch repair (MMR), nucleotide excision repair (NER), and base excision repair (BER)) were well separated and clustered between SF/GC and SC/GC treatments after three spaceflights. In the 16.5-days space experiment, we also selected the datasets of dys-1 mutant and ced-1 mutant of C. elegans, which respectively presented microgravity-insensitivity and radiosensitivity. Compared to the WT C. elegans flown in the 16.5-days spaceflight, the separation distances between SF and SC samples were significantly reduced in the dys-1 mutant, while greatly enhanced in the ced-1 mutant for five DNA repair pathways. By comparing the results of differential expression analysis in SF/GC versus SC/GC samples, we found the DNA repair genes annotated in the pathways of BER and NER were prominently down-regulated under microgravity during both the 4- and 8-days spaceflights. While, under microgravity, the genes annotated in MMR were dominatingly up-regulated during the 4-days spaceflight, and those annotated in HR were mainly up-regulated during the 8-days spaceflight. And, most of the DNA repair genes annotated in the pathways of BER, NER, MMR, and HR were up-regulated under microgravity during the 16.5-days spaceflight. Using miRNA-mRNA integrated analysis, we determined the regulatory networks of differentially expressed DNA repair genes and their regulatory miRNAs in WT C. elegans after three spaceflights. Compared to GC conditions, the differentially expressed miRNAs were analyzed under SF and SC treatments of three spaceflights, and some altered miRNAs that responded to SF and SC could regulate the expressions of corresponding DNA repair genes annotated in different DNA repair pathways. In summary, these findings indicate that microgravity can significantly alter the expression patterns of DNA repair genes and their regulatory miRNAs in space-flown C. elegans. The alterations of the expressions of DNA repair genes and the dominating DNA repair pathways under microgravity are possibly related to the spaceflight period. In addition, the key miRNAs are identified as the post-transcriptional regulators to regulate the expressions of various DNA repair genes under microgravity. These altered miRNAs that responded to microgravity can be implicated in regulating diverse DNA repair processes in space-flown C. elegans.

Bringing Interventional Radiology to Mars!

At present, astronauts on space missions can get medical assistant from Earth. In the future, deep space missions such as missions to Mars will delay communication with physicians on Earth, making it impossible to get immediate support in urgent medical situations. On the spaceship, a polyvalent physician-astronaut could mainly perform small surgery and traumatology procedures. Interventional Radiology (IR) allows minimally invasive interventions and requires small devices. In these conditions of space constrains, IR presents significant benefits. To guarantee the technical realization of specific medical interventions during deep space missions, a team composed of interventional radiologists and space engineers, is developing the IR toolbox. The development of the toolbox intents to minimize the volume/weight of medical devices and to ensure the safety requirements for the crew. New scenarios of IR interventions have been developed to adapt the interventions to the spatial context, making possible the treatment of pathologies that are otherwise, on Earth, optimally treated surgically. Interventional radiology has a major role to play in the management of acute medical problems which may occur in the future story of deep space missions to the Moon, and further to Mars.

Effects of a microgravity SkinSuit on lumbar geometry and kinematics

PURPOSE

Astronauts returning from long ISS missions have demonstrated an increased incidence of lumbar disc herniation accompanied by biomechanical and morphological changes associated with spine elongation. This research describes a ground-based study of the effects of an axial compression countermeasure Mk VI SkinSuit designed to reload the spine and reduce these changes before return to terrestrial gravity.

METHODS

Twenty healthy male volunteers aged 21-36 without back pain participated. Each lay overnight on a Hyper Buoyancy Flotation (HBF) bed for 12 h on two occasions 6 weeks apart. On the second occasion participants donned a Mk VI SkinSuit designed to axially load the spine at 0.2 Gz during the last 4 h of flotation. Immediately after each exposure, participants received recumbent MRI and flexion-extension quantitative fluoroscopy scans of their lumbar spines, measuring differences between spine geometry and intervertebral kinematics with and without the SkinSuit. This was followed by the same procedure whilst weight bearing. Paired comparisons were performed for all measurements.

RESULTS

Following Mk VI SkinSuit use, participants evidenced more flexion RoM at L3-4 (p = 0.01) and L4-5 (p = 0.003), more translation at L3-4 (p = 0.02), lower dynamic disc height at L5-S1 (p = 0.002), lower lumbar spine length (p = 0.01) and greater lordosis (p = 0.0001) than without the Mk VI SkinSuit. Disc cross-sectional area and volume were not significantly affected.

CONCLUSION

The MkVI SkinSuit restores lumbar mobility and lordosis following 4 h of wearing during hyper buoyancy flotation in a healthy control population and may be an effective countermeasure for post space flight lumbar disc herniation.

Contemporary review of dermatologic conditions in space flight and future implications for long-duration exploration missions

BACKGROUND

Future planned exploration missions to outer space will almost surely require the longest periods of continuous space exposure by the human body yet. As the most external organ, the skin seems the most vulnerable to injury. Therefore, discussion of the dermatological implications of such extended-duration missions is critical.

OBJECTIVES

In order to help future missions understand the risks of spaceflight on the human skin, this review aims to consolidate data from the current literature pertaining to the space environment and its physiologic effects on skin, describe all reported dermatologic manifestations in spaceflight, and extrapolate this information to longer-duration mission.

METHODS AND MATERIALS

The authors searched PubMed and Google Scholar using keywords and Mesh terms. The publications that were found to be relevant to the objectives were included and described.

RESULTS

The space environment causes changes in the skin at the cellular level by thinning the epidermis, altering wound healing, and dysregulating the immune system. Clinically, dermatological conditions represented the most common medical issues occurring in spaceflight. We predict that as exploration missions increase in duration, astronauts will experience further physiological changes and an increased rate and severity of adverse events.

CONCLUSION

Maximizing astronaut safety requires a continued knowledge of the human body's response to space, as well as consideration and prediction of future events. Dermatologic effects of space missions comprise the majority of health-related issues arising on missions to outer space, and these issues are likely to become more prominent with increasing time spent in space. Improvements in hygiene may mitigate some of these conditions.

Effect of Active Muscles on Astronaut Kinematics and Injury Risk for Piloted Lunar Landing and Launch While Standing

While astronauts may pilot future lunar landers in a standing posture, the response of the human body under lunar launch and landing-related dynamic loading conditions is not well understood. It is important to consider the effects of active muscles under these loading conditions as muscles stabilize posture while standing. In the present study, astronaut response for a piloted lunar mission in a standing posture was simulated using an active human body model (HBM) with a closed-loop joint-angle based proportional integral derivative controller muscle activation strategy and compared with a passive HBM to understand the effects of active muscles on astronaut body kinematics and injury risk. While head, neck, and lumbar spine injury risk were relatively unaffected by active muscles, the lower extremity injury risk and the head and arm kinematics were significantly changed. Active muscle prevented knee-buckling and spinal slouching and lowered tibia injury risk in the active vs. passive model (revised tibia index: 0.02-0.40 vs. 0.01-0.58; acceptable tolerance: 0.43). Head displacement was higher in the active vs. passive model (11.6 vs. 9.0 cm forward, 6.3 vs. 7.0 cm backward, 7.9 vs. 7.3 cm downward, 3.7 vs. 2.4 cm lateral). Lower arm movement was seen with the active vs. passive model (23 vs. 35 cm backward, 12 vs. 20 cm downward). Overall simulations suggest that the passive model may overpredict injury risk in astronauts for spaceflight loading conditions, which can be improved using the model with active musculature.

Sedentary behavior and the biological hallmarks of aging

While the benefits of physical exercise for a healthy aging are well-recognized, a growing body of evidence shows that sedentary behavior has deleterious health effects independently, to some extent, of physical activity levels. Yet, the increasing prevalence of sedentariness constitutes a major public health issue that contributes to premature aging but the potential cellular mechanisms through which prolonged immobilization may accelerate biological aging remain unestablished. This narrative review summarizes the impact of sedentary behavior using different models of extreme sedentary behaviors including bedrest, unilateral limb suspension and space travel studies, on the hallmarks of aging such as genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. We further highlight the remaining knowledge gaps that need more research in order to promote healthspan extension and to provide future contributions to the field of geroscience.

Simulated Astronaut Kinematics and Injury Risk for Piloted Lunar Landings and Launches While Standing

During future lunar missions, astronauts may be required to pilot vehicles while standing, and the associated kinematic and injury response is not well understood. In this study, we used human body modeling to predict unsuited astronaut kinematics and injury risk for piloted lunar launches and landings in the standing posture. Three pulses (2-5 g; 10-150 ms rise times) were applied in 10 directions (vertical; ± 10-degree offsets) for a total of 30 simulations. Across all simulations, motion envelopes were computed to quantify displacement of the astronaut's head (max 9.0 cm forward, 7.0 cm backward, 2.1 cm upward, 7.3 cm downward, 2.4 cm lateral) and arms (max 25 cm forward, 35 cm backward, 15 cm upward, 20 cm downward, 20 cm lateral). All head, neck, lumbar, and lower extremity injury metrics were within NASA's tolerance limits, except tibia compression forces (0-1543 N upper tibia; 0-1482 N lower tibia; tolerance-1350 N) and revised tibia index (0.04-0.58 upper tibia; 0.03-0.48 lower tibia; tolerance-0.43) for the 2.7 g/150 ms pulse. Pulse magnitude and duration contributed over 80% to the injury metric values, whereas loading direction contributed less than 3%. Overall, these simulations suggest piloting a lunar lander vehicle in the standing posture presents a tibia injury risk which is potentially outside NASA's acceptance limits and warrants further investigation.

Small tissue chips with big opportunities for space medicine

The spaceflight environment, including microgravity and radiation, may have considerable effects on the health and performance of astronauts, especially for long-duration and Martian missions. Conventional on-ground and in-space experimental approaches have been employed to investigate the comprehensive biological effects of the spaceflight environment. As a class of recently emerging bioengineered in vitro models, tissue chips are characterized by a small footprint, potential automation, and the recapitulation of tissue-level physiology, thus promising to help provide molecular and cellular insights into space medicine. Here, we briefly review the technical advantages of tissue chips and discuss specific on-chip physiological recapitulations. Several tissue chips have been launched into space, and more are poised to come through multi-agency collaborations, implying an increasingly important role of tissue chips in space medicine.

Biomechanics of healthy subjects during exercise on a simulated vibration isolation and stabilization system

With long-term space flights being planned for the Moon and Mars, proper countermeasures must be taken to facilitate human health in microgravity environments. Exercise is a vital countermeasure used to prevent bone and muscle loss, among other health interests. Future exploration missions encourage creating an exercise device that is both compact and can be used to properly execute exercise by the astronauts. Current design considerations include interfacing an exercise device with a vibration isolation and stabilization (VIS) system, which is necessary for protecting the spacecraft and sensitive experiments from harmful vibrations developed during repetitive exercise. This human factor study assesses the feasibility of a VIS system exercise device by using the Computer Assistive Rehabilitation Environment (CAREN) to simulate characteristics of the system. The CAREN includes a 6 degree of freedom (DOF) platform, force plates and a motion capture system. An algorithm was developed using the D-Flow software to move the platform in 1 and 2 DOF sinusoidal responses. Multiple sinusoidal frequencies for platform motion during subject exercise were evaluated. Four subjects completed squat and row exercises on the CAREN while their motion was recorded. Kinematic and kinetic data were collected from each subject. Trials were executed with 1-2 DOF motion in heave and pitch. Results conclude that subjects completed exercises with adequate range of motion (ROM) and ground reaction forces (GRF) during each trial. Certain environments, such as movement at a slower frequency (0.10 Hz) and movement of heave and pitch at differing frequencies, caused loss of balance indicated by grabbing of the handrail in some subjects and difficulty in synchronization between the subjects and the platform. This indicates that VIS system design should focus on frequency of movements centering around subjects' natural exercise frequencies if possible. This study serves as a proof of concept for using CAREN and programming tool D-Flow to simulate platform movement on VIS system design. Further experimentation will test more detailed designs, including active and passive systems that will move based on real-time subject data.

Express: Cognition in Zero Gravity: Effects of Non-Terrestrial Gravity on Human Behaviour

As humanity prepares for deep space exploration, understanding the impact of spaceflight on bodily physiology is critical. While the effects of non-terrestrial gravity on the body are well established, little is known about its impact on human behaviour and cognition. Astronauts often describe dramatic alterations in sensorimotor functioning, including orientation, postural control and balance. Changes in cognitive functioning as well as in socio-affective processing have also been observed. Here we have reviewed the key literature and explored the impact of non-terrestrial gravity across three key functional domains: sensorimotor, cognition, and socio-affective processing. We have proposed a neuroanatomical model to account for the effects of non-terrestrial gravity in these domains. Understanding the impact of non-terrestrial gravity on human behaviour has never been more timely and it will help mitigate against risks in both commercial and non-commercial spaceflight.

Phenotypic, genomic, and transcriptomic changes in an Acinetobacter baumannii strain after spaceflight in China's Tiangong-2 space laboratory

Acinetobacter baumannii is an opportunistic pathogen often found in patients with low immunity. It causes nosocomial infections, which are difficult to treat. This bacterium can rapidly mutate, developing resistance to antimicrobials and adapting to environmental stress, thereby increasing its survival. Understanding such adaptive mechanisms will be beneficial for controlling the spread of A. baumannii. Astrobiology studies have demonstrated that microbiomes from astronauts and manned spaceflight environments show resistance to stress and antibiotics. Astronauts also encounter low immunity during spaceflight missions. The extreme conditions of spaceflight provide a unique research platform for studying how opportunistic pathogens such as A. baumannii adapt to conditions such as microgravity and mutate during spaceflight. In this study, we compared phenotypic variations and analyzed genomic and transcriptomic variations in A. baumannii strains exposed to three different conditions: ST1 (64 days on Tiangong-2 space laboratory), GT1 (ground control), and Aba (original strain). Biofilm formation ability of the ST1 strain increased after 64 days of spaceflight. In addition, high-throughput sequencing revealed that some differentially expressed genes were upregulated in the ST1 strain compared to the GT1 strain. These results provide insights into the environmental adaptation of this widespread pathogen.

Alternative splicing diversifies the skeletal muscle transcriptome during prolonged spaceflight

BACKGROUND

As the interest in manned spaceflight increases, so does the requirement to understand the transcriptomic mechanisms that underlay the detrimental physiological adaptations of skeletal muscle to microgravity. While microgravity-induced differential gene expression (DGE) has been extensively investigated, the contribution of differential alternative splicing (DAS) to the plasticity and functional status of the skeletal muscle transcriptome has not been studied in an animal model. Therefore, by evaluating both DGE and DAS across spaceflight, we set out to provide the first comprehensive characterization of the transcriptomic landscape of skeletal muscle during exposure to microgravity.

METHODS

RNA-sequencing, immunohistochemistry, and morphological analyses were conducted utilizing total RNA and tissue sections isolated from the gastrocnemius and quadriceps muscles of 30-week-old female BALB/c mice exposed to microgravity or ground control conditions for 9 weeks.

RESULTS

In response to microgravity, the skeletal muscle transcriptome was remodeled via both DGE and DAS. Importantly, while DGE showed variable gene network enrichment, DAS was enriched in structural and functional gene networks of skeletal muscle, resulting in the expression of alternatively spliced transcript isoforms that have been associated with the physiological changes to skeletal muscle in microgravity, including muscle atrophy and altered fiber type function. Finally, RNA-binding proteins, which are required for regulation of pre-mRNA splicing, were themselves differentially spliced but not differentially expressed, an upstream event that is speculated to account for the downstream splicing changes identified in target skeletal muscle genes.

CONCLUSIONS

Our work serves as the first investigation of coordinate changes in DGE and DAS in large limb muscles across spaceflight. It opens up a new opportunity to understand (i) the molecular mechanisms by which splice variants of skeletal muscle genes regulate the physiological adaptations of skeletal muscle to microgravity and (ii) how small molecule splicing regulator therapies might thwart muscle atrophy and alterations to fiber type function during prolonged spaceflight.

Responses of neuromuscular properties to unloading and potential countermeasures during space exploration missions

We reviewed the responses of the neuromuscular properties of mainly the soleus and possible mechanisms. Sensory nervous activity in response to passive shortening and/or active contraction, associated with plantar-flexion or dorsi-flexion of the ankle joints, may play an essential role in the regulation of muscle properties. Passive shortening of the muscle fibers and sarcomeres inhibits the development of tension, electromyogram (EMG), and afferent neurogram. Remodeling of the sarcomeres, which decreases the total sarcomere number in a single muscle fiber causing recovery of the length in each sarcomere, is induced in the soleus following chronic unloading. Although EMG activity and tension development in each sarcomere are increased, the total tension produced by the whole muscle is still less owing to the lower sarcomere number. Therefore, muscle atrophy continues to progress. Moreover, walking or slow running by rear-foot strike landing with the application of greater ground reaction force, which stimulates soleus mobilization, could be an effective countermeasure. Periodic, but not chronic, passive stretching of the soleus may also be effective.

Cortical thickness of primary motor and vestibular brain regions predicts recovery from fall and balance directly after spaceflight

Motor adaptations to the microgravity environment during spaceflight allow astronauts to perform adequately in this unique environment. Upon return to Earth, this adaptation is no longer appropriate and can be disruptive for mission critical tasks. Here, we measured if metrics derived from MRI scans collected from astronauts can predict motor performance post-flight. Structural and diffusion MRI scans from 14 astronauts collected before launch, and motor measures (balance performance, speed of recovery from fall, and tandem walk step accuracy) collected pre-flight and post-flight were analyzed. Regional measures of gray matter volume (motor cortex, paracentral lobule, cerebellum), myelin density (motor cortex, paracentral lobule, corticospinal tract), and white matter microstructure (corticospinal tract) were derived as a-priori predictors. Additional whole-brain analyses of cortical thickness, cerebellar gray matter, and cortical myelin were also tested for associations with post-flight and pre-to-post-flight motor performance. The pre-selected regional measures were not significantly associated with motor behavior. However, whole-brain analyses showed that paracentral and precentral gyri thickness significantly predicted recovery from fall post-spaceflight. Thickness of vestibular and sensorimotor regions, including the posterior insula and the superior temporal gyrus, predicted balance performance post-flight and pre-to-post-flight decrements. Greater cortical thickness pre-flight predicted better performance post-flight. Regional thickness of somatosensory, motor, and vestibular brain regions has some predictive value for post-flight motor performance in astronauts, which may be used for the identification of training and countermeasure strategies targeted for maintaining operational task performance.

Mice display learning and behavioral deficits after a 30-day spaceflight on Bion-M1 satellite

Profound effects of spaceflight on the physiology of humans and non-human animals are well-documented but incompletely explored. Current goals to undertake interplanetary missions increase the urgency to learn more about adaptation to prolonged spaceflight and readaptation to Earth-normal conditions, especially with the inclusion of radiation exposures greater than those confronted in traditional, orbital flights. The 30-day-long Bion M-1 biosatellite flight was conducted at a relatively high orbit, exposing the mice to greater doses of radiation in addition to microgravity, a combination of factors relevant to Mars missions. Results of the present studies with mice provide insights into the consequences on brain function of long-duration spaceflight. After landing, mice showed profound deficits in vestibular responses during aerial drop tests. Spaceflown mice displayed reduced grip strength, rotarod performance, and voluntary wheel running, each, which improved gradually but incompletely over the 7-days of post-flight testing. Continuous monitoring in the animals' home cage activity, in combination with open-field and other tests of motor performance, revealed indices of altered affect, expressed as hyperactivity, potentiated thigmotaxis, and avoidance of open areas which, together, presented a syndrome of persistent anxiety-like behavior. A learned, operant response acquired before spaceflight was retained, whereas the acquisition of a new task was impaired after the flight. We integrate these observations with other results from Bion-M1's program, identifying deficits in musculoskeletal and cardiovascular systems, as well as in the brain and spinal cord, including altered gene expression patterns and the accompanying neurochemical changes that could underlie our behavioral findings.

Biomechanical changes in the lumbar spine following spaceflight and factors associated with postspaceflight disc herniation

BACKGROUND CONTEXT

For chronic low back pain, the causal mechanisms between pathological features from imaging and patient symptoms are unclear. For instance, disc herniations can often be present without symptoms. There remains a need for improved knowledge of the pathophysiological mechanisms that explore spinal tissue damage and clinical manifestations of pain and disability. Spaceflight and astronaut health provides a rare opportunity to study potential low back pain mechanisms longitudinally. Spaceflight disrupts diurnal loading on the spine and several lines of evidence indicate that astronauts are at a heightened risk for low back pain and disc herniation following spaceflight.

PURPOSE

To examine the relationship between prolonged exposure to microgravity and the elevated incidence of postflight disc herniation, we conducted a longitudinal study to track the spinal health of twelve NASA astronauts before and after approximately 6 months in space. We hypothesize that the incidence of postflight disc herniation and low back complaints associates with spaceflight-included muscle atrophy and pre-existing spinal pathology.

STUDY DESIGN

This is a prospective longitudinal study.

PATIENT SAMPLE

Our sample included a cohort of twelve astronaut crewmembers.

OUTCOME MEASURES

From 3T MRI, we quantified disc water content (ms), disc degeneration (Pfirrmann grade), vertebral endplate irregularities, facet arthropathy and/ fluid, high intensity zones, disc herniation, multifidus total cross-sectional area (cm²), multifidus lean muscle cross-sectional area (cm²), and muscle quality/composition (%). From quantitative fluoroscopy we quantified, maximum flexion-extension ROM (°), maximum lateral bending ROM (°), and maximum translation (%). Lastly, patient outcomes and clinical notes were used for identifying postflight symptoms associated with disc herniations from 3T MRI.

METHODS

Advanced imaging data from 3T MRI were collected at three separate time points in relation to spending six months in space: (1) within a year before launch ("pre-flight"), (2) within a week after return to Earth ("post-flight"), and (3) between 1 and 2 months after return to Earth ("recovery"). Fluoroscopy of segmental kinematics was collected at preflight and postflight timepoints. We assessed the effect of spaceflight and postflight recovery on longitudinal changes in spinal structure and function, as well as differences between crew members who did and did not present a symptomatic disc herniation following spaceflight.

RESULTS

Half of our astronauts (n=6) experienced new symptoms associated with a new or previously asymptomatic lumbar disc protrusion or extrusion following spaceflight. We observed decreased multifidus muscle quality following spaceflight in the lower lumbar spine, with a reduced percentage of lean muscle at L4L5 (-6.2%, p=.009) and L5S1 (-7.0%, p=.006) associated with the incidence of new disc herniation. Additionally, we observed reduced lumbar segment flexion-extension ROM for L2L3 (-17.2%, p=.006) and L3L4 (-20.5%, p=.02) following spaceflight, and furthermore that reduced ROM among the upper three lumbar segments (-24.1%, p=.01) associated with the incidence of disc herniation. Existing endplate pathology was most prevalent in the upper lumbar spine and associated with reduced segmental ROM (-20.5%, p=.02).

CONCLUSIONS

In conclusion from a 10-year study investigating the effects of spaceflight on the lumbar spine and risk for disc herniation, we found the incidence of lumbar disc herniation following spaceflight associates with compromised multifidus muscle quality and spinal segment kinematics, as well as pre-existing spinal endplate irregularities. These findings suggest differential effects of spinal stiffness and muscle loss in the upper versus lower lumbar spine regions that may specifically provoke risk for symptomatic disc herniation in the lower lumbar spine following spaceflight. Results from this study provide a unique longitudinal assessment of mechanisms and possible risk factors for developing disc herniations and related low back pain. Furthermore, these findings will help inform physiologic countermeasures to maintain spinal health in astronauts during long-duration missions in space.

Mimic microgravity effect on muscle transcriptome under ionizing radiation

Spaceflight imposes the risk of skeletal muscle atrophy for astronauts. Two main factors of a spaceflight that results in deleterious effects are microgravity and cosmic rays in outer space. To study spaceflight-induced muscle atrophy with ground-based models, we performed two models of microgravity, tail suspension and denervation, in a low dose radiation environment and studied transcriptional changes in rat soleus muscle using microarrays. Soleus muscle from rats in the denervation group had greater expression changes compared to that found in rats from the tail suspension group. However, there was a very similar pattern of expression of differentially expressed genes (DEGs) in both models. In total, we identified 144 differentially expressed genes common in both models. Our study yielded two main findings. First, a large number of genes involved in energy metabolism were transcriptionally suppressed including those involved in fatty acid transport and beta-oxidation, and oxidative phosphorylation. Second, slow-twitch contractile protein encoding genes were down-regulated while there was an up-regulation in the fast-twitch type transcription. These results were consistent with other spaceflight studies on the effects on muscle cells, hence showed the potential of our ground-based models in studying spaceflight effects. The genes that might be involved in spaceflight effects will serve as candidate genes for future studies in understanding the mechanism of spaceflight-induced muscle atrophy and result in the development of effective countermeasures.

Spaceflight studies identify a gene encoding an intermediate filament involved in tropism pathways

We performed a series of experiments to study the interaction between phototropism and gravitropism in Arabidopsis thaliana as part of the Seedling Growth Project on the International Space Station. Red-light-based and blue-light-based phototropism were examined in microgravity and at 1g, a control that was produced by an on-board centrifuge. At the end of the experiments, seedlings were frozen and brought back to Earth for gene profiling studies via RNASeq methods. In this paper, we focus on five genes identified in these space studies by their differential expression in space: one involved in auxin transport and four others encoding genes for: a methyltransferase subunit, a transmembrane protein, a transcription factor for endodermis formation, and a cytoskeletal element (an intermediate filament protein). Time course studies using mutant strains of these five genes were performed for blue-light and red-light phototropism studies as well as for gravitropism assays on ground. Interestingly, all five of the genes had some effects on all the tropisms under the conditions studied. In addition, RT-PCR analyses examined expression of the five genes in wild-type seedlings during blue-light-based phototropism. Previous studies have supported a role of both microfilaments and microtubules in tropism pathways. However, the most interesting finding of the present space studies is that NFL, a gene encoding an intermediate filament protein, plays a role in phototropism and gravitropism, which opens the possibility that this cytoskeletal element modulates signal transduction in plants.

Conducting Plant Experiments in Space and on the Moon

The growth and development of plants during spaceflight have important implications for both basic and applied research supported by NASA and other international space agencies. While there have been many reviews of plant space biology, this chapter attempts to fill a gap in the literature on the actual process and methods of performing plant research in the spaceflight environment. One of the authors (JZK) has been a principal investigator on eight spaceflight projects. These experiences include using the U.S. Space Shuttle, the former Russian Space Station Mir, and the International Space Station, utilizing the Space Shuttle and Space X as launch vehicles. While there are several ways to fly an experiment into space and to obtain a spaceflight opportunity, this review focuses on using the NASA peer-reviewed sciences approach to get an experiment manifested for flight. Three narratives for the implementation of plant space biology experiments are considered from rapid turn around of a few months to a project with new hardware development that lasted 6 years. The many challenges of spaceflight research include logistical and resource constraints such as crew time, power, cold stowage, data downlinks, among others. Additional issues considered are working at NASA centers, hardware development, safety concerns, and the engineering versus science culture in space agencies. The difficulties of publishing the results from spaceflight research based on such factors as the lack of controls, limited sample size, and the indirect effects of the spaceflight environment also are summarized. Lessons learned from these spaceflight experiences are discussed in the context of improvements for future space-based research projects with plants. We also will consider new opportunities for Moon-based research via NASA's Artemis lunar exploration program.

Plant Gravitropism: From Mechanistic Insights into Plant Function on Earth to Plants Colonizing Other Worlds

Gravitropism, the growth of roots and shoots toward or away from the direction of gravity, has been studied for centuries. Such studies have not only led to a better understanding of the gravitropic process itself, but also paved new paths leading to deeper mechanistic insights into a wide range of research areas. These include hormone biology, cell signal transduction, regulation of gene expression, plant evolution, and plant interactions with a variety of environmental stimuli. In addition to contributions to basic knowledge about how plants function, there is accumulating evidence that gravitropism confers adaptive advantages to crops, particularly under marginal agricultural soils. Therefore, gravitropism is emerging as a breeding target for enhancing agricultural productivity. Moreover, research on gravitropism has spawned several studies on plant growth in microgravity that have enabled researchers to uncouple the effects of gravity from other tropisms. Although rapid progress on understanding gravitropism witnessed during the past decade continues to be driven by traditional molecular, physiological, and cell biological tools, these tools have been enriched by technological innovations in next-generation omics platforms and microgravity analog facilities. In this chapter, we review the field of gravitropism by highlighting recent landmark studies that have provided unique insights into this classic research topic while also discussing potential contributions to agriculture on Earth and beyond.

Diagnosing an Opportunistic Fungal Pathogen on Spaceflight-Grown Plants Using the MinION Sequencing Platform

Sustainable agriculture in microgravity is integral to future long-term human space exploration. To ensure the efficient and sustainable cultivation of plants in space, a contingency plan to monitor plant health and mitigate plant diseases is necessary. Yet, neither methods nor tools currently exist to evaluate the plant microbial interactions or to diagnose potential plant diseases in space-based bioregenerative life support systems. In this study, we show how the MinION sequencing platform can be used to diagnose the opportunistic pathogen Fusarium oxysporum sensu lato, a fungal infection on Zinnia hybrida (zinnia) plants that were grown on the International Space Station (ISS) in 2015-2016. Genomic DNA from the infected plant material (root and leaf tissues) retrieved from the ISS were extracted and sequenced. In addition, pure cultures of Burkholderia contaminans, F. oxysporum sensu lato, and Fusarium sporotrichioides were used as controls to test the specificity of the bioinformatics pipeline developed. The results show that the MinION platform can be used to accurately differentiate between fusaria species and strengthens the case for using the platform as a rapid plant disease diagnostic tool in space.

Arabidopsis Growth and Dissection on Polyethersulfone (PES) Membranes for Gravitropic Studies

Polyethersulfone (PES) membranes provide a versatile tool for gravity-related plant studies. Benefits of this system include straightforward setup, no need for specialized equipment, long-term seed viability between plating and hydration/growth, and adaptability to diverse protocols and downstream analyses. Methods outlined here include seed sterilization, planting, growth, and dissection that will transition directly into any RNA extraction protocol.

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.

Microgravity-induced alterations of mouse bones are compartment- and site-specific and vary with age

The age at which astronauts experience microgravity is a critical consideration for skeletal health and similarly has clinical relevance for musculoskeletal disuse on Earth. While astronauts are extensively studied for bone and other physiological changes, rodent studies enable direct evaluation of skeletal changes with microgravity. Yet, mouse spaceflight studies have predominately evaluated tissues from young, growing mice. We evaluated bone microarchitecture in tibiae and femurs from Young (9-week-old) and Mature (32-weeks-old) female, C57BL/6N mice flown in microgravity for ~2 and ~3 weeks, respectively. Microgravity-induced changes were both compartment- and site-specific. Changes were greater in trabecular versus cortical bone in Mature mice exposed to microgravity (-40.0% Tb. BV/TV vs -4.4% Ct. BV/TV), and bone loss was greater in the proximal tibia as compared to the distal femur. Trabecular thickness in Young mice increased by +25.0% on Earth and no significant difference following microgravity. In Mature mice exposed to microgravity, trabecular thickness rapidly decreased (-24.5%) while no change was detected in age-matched mice that were maintained on Earth. Mature mice exposed to microgravity experienced greater bone loss than Young mice with net skeletal growth. Moreover, machine learning classification models confirmed that microgravity exposure-driven decrements in trabecular microarchitecture and cortical structure occurred disproportionately in Mature than in Young mice. Our results suggest that age of disuse onset may have clinical implications in osteoporotic or other at-risk populations on Earth and may contribute to understanding bone loss patterns in astronauts.

Brains in space: the importance of understanding the impact of long-duration spaceflight on spatial cognition and its neural circuitry

Fifty years after the first humans stepped on the Moon, space faring nations have entered a new era of space exploration. NASA’s reference mission to Mars is expected to comprise 1100 days. Deep space exploratory class missions could even span decades. They will be the most challenging and dangerous expeditions in the history of human spaceflight and will expose crew members to unprecedented health and performance risks. The development of adverse cognitive or behavioral conditions and psychiatric disorders during those missions is considered a critical and unmitigated risk factor. Here, we argue that spatial cognition, i.e., the ability to encode representations about self-to-object relations and integrate this information into a spatial map of the environment, and their neural bases will be highly vulnerable during those expeditions. Empirical evidence from animal studies shows that social isolation, immobilization, and altered gravity can have profound effects on brain plasticity associated with spatial navigation. We provide examples from historic spaceflight missions, spaceflight analogs, and extreme environments suggesting that spatial cognition and its neural circuitry could be impaired during long-duration spaceflight, and identify recommendations and future steps to mitigate these risks.

Index of Reflectivity of Ultrasound Radio Frequency Signal from the Carotid Artery Wall Increases in Astronauts after a 6 mo Spaceflight

The objective was to quantify the index of reflectivity of the common carotid artery and surrounding structures, before and after 6 mo of microgravity. Our hypothesis was that structural changes in the insonated target would increase its index of reflectivity. The neck anterior muscle and common carotid artery (walls and lumen) were visualized by echography (17 MHz linear probe), and the radiofrequency signal along each vertical line was displayed. The limits of the radiofrequency data corresponding to each target (muscle, vessel wall) were determined from the B-mode image and radiofrequency trace. Each target's index of reflectivity was calculated as the proportion of backscattered energy to the whole backscattered energy along the line. After 6 mo in flight, the index of reflectivity increased significantly for both common carotid walls, while it remained unchanged for the neck muscle, carotid intima and lumen. The index of reflectivity provided additional information beyond traditional B-mode imaging.

Neurosurgery and spinal adaptations in spaceflight: A literature review

BACKGROUND

Spaceflight places astronauts in multiple environments capable of inducing pathological changes. Alterations in the spine have a significant impact on astronauts' health during and after spaceflight. Low back pain is an established and common intra-flight complaint. Intervertebral disc herniation occurs at higher rates in this population and poses significant morbidity. Morphological changes within intervertebral discs, vertebral bodies, and spinal postural muscles affect overall spine function and astronaut performance. There remains a paucity of research related to spaceflight-induced pathologies, and currently available reviews concern the central nervous system broadly while lacking emphasis on spinal function.

OBJECTIVE

Our aim was to review and summarize available data regarding changes in spinal health with exposure to spaceflight, especially focusing on effects of microgravity. The authors also present promising diagnostic and treatment approaches wherein the neurosurgeon could positively impact astronauts' health and post-flight outcomes.

MATERIALS AND METHODS

Articles included in this review were identified via search engine using MEDLINE, PubMed, Cochrane Review, Google Scholar, and references within other relevant articles. Search criteria included "spine and spaceflight", "vertebral column and spaceflight", "vertebral disc and spaceflight", and "muscle atrophy and spaceflight", with results limited to articles written in English from 1961 to 2020. References of selected articles were included as appropriate.

RESULTS

Fifty-six articles were included in this review. Compositional changes at the intervertebral discs, vertebral bone, and paraspinal muscles contribute to undesirable effects on astronaut spinal function in space and contribute to post-flight pathologies. Risk of intervertebral disc herniation increases, especially during post-flight recovery. Vertebral bone degeneration in microgravity may increase risk for herniation and fracture. Paraspinal muscle atrophy contributes to low back pain, poorer spine health, and reduced stability.

CONCLUSION

Anatomical changes in microgravity contribute to the development of spinal pathologies. Microgravity impacts sensory neurovestibular function, neuromuscular output, genetic expression, among other systems. Future developments in imaging and therapeutic interventions may better analyze these changes and offer targeted therapeutic interventions to decrease the burden of pain and other diseases of the spine in this population.

Effects of Spaceflight on Human Skin

During both short- and long-duration spaceflight, several health problems can occur, including those of the skin. Astronauts in space and after returning to earth experience erythematous, burning, itchy, dry, sensitive, and thinning skin. Other skin problems, such as infections, abrasions, lacerations, delayed wound healing, and accelerated skin aging, are also common. Human skin is an ecosystem composed of a wide range of habitats for bacteria, fungi, and viruses called microbiome, which not only show a strong skin site-specific preference but also serve as microbial fingerprints that are highly unique to individuals. These human skin-associated microorganisms make a substantial contribution to the microbial ecosystems that inhabit the closed environments in space. On the other hand, human skin microbiome is also subject to change during spaceflight, which may lead to skin infections or the flare up of skin diseases. This review highlights some of the interactions between the space environment and the skin.

The role of nutrition in space exploration: Implications for sensorimotor, cognition, behavior and the cerebral changes due to the exposure to radiation, altered gravity, and isolation/confinement hazards of spaceflight

Multi-year crewed space exploration missions are now on the horizon; therefore, it is important that we understand and mitigate the physiological effects of spaceflight. The spaceflight hazards-radiation, isolation, confinement, and altered gravity-have the potential to contribute to neuroinflammation and produce long-term cognitive and behavioral effects-while the fifth hazard, distance from earth, limits capabilities to mitigate these risks. Accumulated evidence suggests that nutrition has an important role in optimizing cognition and reducing the risk of neurodegenerative diseases caused by neuroinflammation. Here we review the nutritional perspective of how these spaceflight hazards affect the astronaut's brain, behavior, performance, and sensorimotor function. We also assess potential nutrient/nutritional countermeasures that could prevent or mitigate spaceflight risks and ensure that crewmembers remain healthy and perform well during their missions. Just as history has taught us the importance of nutrition in terrestrial exploration, we must understand the role of nutrition in the development and mitigation of spaceflight risks before humans can successfully explore beyond low-Earth orbit.

Generating waist area-dependent ground reaction forces for long-duration spaceflight

Prolonged microgravity exposure greatly weakens the bones and muscles of astronauts. This is a critical biomechanical issue for astronauts as they may be more prone to bone fractures. To combat this issue, lower body negative pressure (LBNP) is a concept that generates artificial gravitational forces that may help strengthen bones and muscles during long-term spaceflight. Negative pressure, defined as below ambient pressure, is applied within a chamber that encompasses the lower half of the body. By increasing the negative pressure, more ground reaction forces (GRFs) are generated beneath the subject's feet. We hypothesize that increasing the cross-sectional area (CSA) of the subject's waist will generate greater GRFs beneath the subject's feet. Six healthy subjects volunteered to participate under two different experimental conditions: 1) original CSA of their waist and 2) larger CSA of their waist. In both conditions the subjects were suspended in a supine position (simulated microgravity) along with a weight scale beneath their feet. Negative pressures ranged from zero to 50 mmHg, increasing in increments of 5 mmHg. At -50 mmHg, original CSAs generated 1.18 ± 0.31 (mean ± SD) of their normal bodyweight. Subjects generated about one bodyweight at -45 mmHg using their original waist CSA. At -50 mmHg, larger CSAs generated 1.46 ± 0.31 of their normal bodyweight. Subjects generated about one bodyweight at -35 mmHg using their larger waist CSA. These data support our hypothesis. This novel technique may apply less stress to the cardiovascular system and conserve power for exercise in the spacecraft.

The effects of exposure to microgravity and reconditioning of the lumbar multifidus and anterolateral abdominal muscles: implications for people with LBP

BACKGROUND CONTEXT

One of the primary changes in the neuromuscular system in response to microgravity is skeletal muscle atrophy, which occurs especially in muscles that maintain posture while being upright on Earth. Reduced size of paraspinal and abdominal muscles has been documented after spaceflight. Exercises are undertaken on the International Space Station (ISS) during and following space flight to remediate these effects. Understanding the adaptations which occur in trunk muscles in response to microgravity could inform the development of specific countermeasures, which may have applications for people with conditions on Earth such as low back pain (LBP).

PURPOSE

The aim of this study was to examine the changes in muscle size and function of the lumbar multifidus (MF) and anterolateral abdominal muscles (1) in response to exposure to 6 months of microgravity on the ISS and (2) in response to a 15-day reconditioning program on Earth.

DESIGN

Prospective longitudinal series.

PATIENT SAMPLE

Data were collected from five astronauts who undertook seven long-duration missions on the ISS.

OUTCOME MEASURES

For the MF muscle, measures included cross-sectional area (CSA) and linear measures to assess voluntary isometric contractions at vertebral levels L2 to L5. For the abdominal muscles, the thickness of the transversus abdominis (TrA), obliquus internus abdominis (IO) and obliquus externus abdominis (EO) muscles at rest and on contraction were measured.

METHODS

Ultrasound imaging of trunk muscles was conducted at four timepoints (preflight, postflight, mid-reconditioning, and post reconditioning). Data were analyzed using multilevel linear models to estimate the change in muscle parameters of interest across three time periods.

RESULTS

Beta-coefficients (estimates of the expected change in the measure across the specified time period, adjusted for the baseline measurement) indicated that the CSA of the MF muscles decreased significantly at all lumbar vertebral levels (except L2) in response to exposure to microgravity (L3=12.6%; L4=6.1%, L5=10.3%; p<.001), and CSAs at L3-L5 vertebral levels increased in the reconditioning period (p<.001). The thickness of the TrA decreased by 34.1% (p<.017), IO decreased by 15.4% (p=.04), and the combination of anterolateral abdominal muscles decreased by 16.2% (p<.001) between pre- and postflight assessment and increased (TrA<0.008; combined p=.035) during the postreconditioning period. Results showed decreased contraction of the MF muscles at the L2 (from 12.8% to 3.4%; p=.007) and L3 (from 12.2% to 5%; p=.032) vertebral levels following exposure to microgravity which increased (L2, p=.046) after the postreconditioning period. Comparison with preflight measures indicated that there were no residual changes in muscle size and function after the postreconditioning period, apart from CSA of MF at L2, which remained 15.3% larger than preflight values (p<.001).

CONCLUSIONS

In-flight exercise countermeasures mitigated, but did not completely prevent, changes in the size and function of the lumbar MF and anterolateral abdominal muscles. Many of the observed changes in size and control of the MF and abdominal muscles that occurred in response to prolonged exposure to microgravity paralleled those seen in people with LBP or exposed to prolonged bed rest on Earth. Daily individualized postflight reconditioning, which included both motor control training and weight-bearing exercises with an emphasis on retraining strength and endurance to re-establish normal postural alignment with respect to gravity, restored the decreased size and control of the MF (at the L3-L5 vertebral levels) and anterolateral abdominal muscles. Drawing parallels between changes which occur to the neuromuscular system in microgravity and which exercises best recover muscle size and function could help health professionals tailor improved interventions for terrestrial populations. Results suggested that the principles underpinning the exercises developed for astronauts following prolonged exposure to microgravity (emphasizing strength and endurance training to re-establish normal postural alignment and distribution of load with respect to gravity) can also be applied for people with chronic LBP, as the MF and anterolateral abdominal muscles were affected in similar ways in both populations. The results may also inform the development of new astronaut countermeasures targeting the MF and abdominal muscles.

Relevance of the Unfolded Protein Response to Spaceflight-Induced Transcriptional Reprogramming in Arabidopsis

Plants are primary producers of food and oxygen on Earth and will likewise be indispensable to the establishment of large-scale sustainable ecosystems and human survival in space. To contribute to the understanding of how plants respond to spaceflight stress, we examined the significance of the unfolded protein response (UPR), a conserved signaling cascade that responds to a number of unfavorable environmental stresses, in the model plant Arabidopsis thaliana. To do so, we performed a large-scale comparative transcriptome profiling in wild type and various UPR-defective mutants during the SpaceX-CRS12 mission to the International Space Station. We established that orbital culture substantially alters the expression of hundreds of stress-related genes compared with ground control conditions. Although expression of those genes varied in the UPR mutants on the ground, it was largely similar across the genotypes in the spaceflight condition. Our results have yielded new information on how plants respond to growth in orbit and support the hypothesis that spaceflight induces the activation of signaling pathways that compensate for the loss of UPR regulators in the control of downstream transcriptional regulatory networks.

Effects of spaceflight on cancellous and cortical bone in proximal femur in growing rats

Mechanical loading of the skeleton during normal weight bearing plays an important role in bone accrual and turnover balance. We recently evaluated bone microarchitecture in the femoral head in 5.6-week-old male Sprague Dawley rats subjected to a 4-day spaceflight aboard STS-41. Compared to weight bearing ground controls, cancellous bone volume fraction was dramatically lower in animals subjected to microgravity. The effects of spaceflight on the rat skeleton are potentially influenced by factors such as age, duration of flight, strain and sex. To test the generalizability of our initial observation, we evaluated archived proximal femora from two additional spaceflight missions: a 10-day mission (STS-57) with 7.5-week-old male Fisher 344 rats, and a 14-day mission (STS-62) with 12-week-old ovariectomized (ovx) female Fisher 344 rats. Cancellous microarchitecture and cortical thickness were assessed using x-ray microtomography/microcomputed tomography. In male rats, cancellous bone volume fraction (bone volume/tissue volume) was lower in flight animals compared to flight controls, but differences were not significant compared to baseline. In ovx female rats, cancellous bone volume fraction was lower in flight animals compared to flight controls and baseline, indicating net bone loss. Cortical thickness did not differ among groups in either experiment. In summary, findings from three separate studies support the conclusion that spaceflight results in cancellous osteopenia in femoral head of growing rats.

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Spaceflight resulted in cancellous osteopenia in femoral head of growing rats.

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Osteopenia was observed in female ovariectomized and male Fisher 344 rats.

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The femoral head should be evaluated in future spaceflight experiments.

Impact of galactic cosmic ray simulation on nutritional content of foods

Foods packaged for future deep-space exploration missions may be prepositioned ahead of astronaut arrival and will be exposed to galactic cosmic rays (GCRs) and solar radiation in deep space at higher levels and different spectrums than those found in low-Earth orbit (LEO). In this study, we have evaluated the impact of a GCR simulation (approximately 0.5 and 5 Gy doses) at the NASA Space Radiation Laboratory (NSRL) on two retort thermostabilized food products that are good sources of radiation labile nutrients (thiamin, vitamin E, or unsaturated fats). No trends or nutritional differences were found between the radiation-treated samples and the control immediately after treatment or one-year after treatment. Small changes in a few nutrients were measured following one-year of storage. Further studies may be needed to confirm these results, as the foods in this study were heterogeneous, and this may have masked meaningful changes due to pouch-to-pouch variations.

Plant responses to real and simulated microgravity

Plant biology experiments in real and simulated microgravity have significantly contributed to our understanding of physiology and behavior of plants. How do plants perceive microgravity? How that perception translates into stimulus? And in turn plant's response and adaptation to microgravity through physiological, cellular, and molecular changes have been reasonably well documented in the literature. Knowledge gained through these plant biology experiments in microgravity helped to successfully cultivate crops in space. For instance, salad crop such as red romaine lettuce grown on the International Space Station (ISS) is allowed to incorporate into the crew's supplementary diet. However, the use of plants as a sustainable bio-regenerative life support system (BLSS) to produce fresh food and O2, reduce CO2 level, recycle metabolic waste, and efficient water management for long-duration space exploration missions requires critical gap filling research. Hence, it is inevitable to reflect and review plant biology microgravity research findings time and again with a new set of data available in the literature. With that in focus, the current article discusses phenotypic, physiological, biochemical, cell cycle, cell wall changes and molecular responses of plants to microgravity both in real and simulated conditions with the latest literature.

Microgravity effects on the human brain and behavior: Dysfunction and adaptive plasticity

Emerging plans for travel to Mars and other deep space destinations make it critical for us to understand how spaceflight affects the human brain and behavior. Research over the past decade has demonstrated two co-occurring patterns of spaceflight effects on the brain and behavior: dysfunction and adaptive plasticity. Evidence indicates the spaceflight environment induces adverse effects on the brain, including intracranial fluid shifts, gray matter changes, and white matter declines. Past work also suggests that the spaceflight environment induces adaptive neural effects such as sensory reweighting and neural compensation. Here, we introduce a new conceptual framework to synthesize spaceflight effects on the brain, Spaceflight Perturbation Adaptation Coupled with Dysfunction (SPACeD). We review the literature implicating neurobehavioral dysfunction and adaptation in response to spaceflight and microgravity analogues, and we consider pre-, during-, and post-flight factors that may interact with these processes. We draw several instructive parallels with the aging literature which also suggests co-occurring neurobehavioral dysfunction and adaptive processes. We close with recommendations for future spaceflight research, including: 1) increased efforts to distinguish between dysfunctional versus adaptive effects by testing brain-behavioral correlations, and 2) greater focus on tracking recovery time courses.

Microbiome for Mars: surveying microbiome connections to healthcare with implications for long-duration human spaceflight, virtual workshop, July 13, 2020

The inaugural "Microbiome for Mars" virtual workshop took place on July 13, 2020. This event assembled leaders in microbiome research and development to discuss their work and how it may relate to long-duration human space travel. The conference focused on surveying current microbiome research, future endeavors, and how this growing field could broadly impact human health and space exploration. This report summarizes each speaker's presentation in the order presented at the workshop.

Longitudinal change in ventricular volume is accelerated in astronauts undergoing long-duration spaceflight

An 11-25% increase in total ventricular volume has been documented in astronauts following spaceflight on the ISS. Given the approximately 2-year time interval between pre- and post-flight MRI, it is unknown if ventricular enlargement simply reflects normal aging or is unique to spaceflight exposure. Therefore, we compared percent ventricular volume change per year (PVVC/yr) documented on pre- to post-flight MRI in a group of NASA ISS astronauts (n = 18, 16.7% women, mean age (SD) 48.43 (4.35) years) with two groups who underwent longitudinal MRI: (1.) healthy age- and sex-matched adults (n = 18, 16.7% women, mean age (SD) 51.26 (3.88) years), and (2.) healthy older adults (n = 79, 16.5% women, mean age (SD) 73.26 (5.34) years). The astronauts, who underwent a mean (SD) 173.4 (51.3) days in spaceflight, showed a greater increase in PVVC/yr than the control (6.86 vs 2.23%, respectively, p < .001) and older adult (4.18%, p = 0.04) groups. These results highlight that on top of physiologically ventricular volume changes due to normal aging, NASA astronauts undergoing ISS missions experience an additional 4.63% PVVC/yr and underscore the need to perform post-flight follow-up scans to determine the time course of PVVC in astronauts over time back on Earth along with monitoring to determine if the PVVC is ultimately clinically relevant.

One sentence summary

NASA astronauts who were exposed to prolonged spaceflight experienced an annual rate of ventricular expansion more than three times that expected from normal aging.