Update on the effects of microgravity on the musculoskeletal system

Light-based 3D bioprinting techniques for illuminating the advances of vascular tissue engineering

Vascular tissue engineering faces significant challenges in creating in vitro vascular disease models, implantable vascular grafts, and vascularized tissue/organ constructs due to limitations in manufacturing precision, structural complexity, replicating the composited architecture, and mimicking the mechanical properties of natural vessels. Light-based 3D bioprinting, leveraging the unique advantages of light including high resolution, rapid curing, multi-material adaptability, and tunable photochemistry, offers transformative solutions to these obstacles. With the emergence of diverse light-based 3D bioprinting techniques and innovative strategies, the advances in vascular tissue engineering have been significantly accelerated. This review provides an overview of the human vascular system and its physiological functions, followed by an in-depth discussion of advancements in light-based 3D bioprinting, including light-dominated and light-assisted techniques. We explore the application of these technologies in vascular tissue engineering for creating in vitro vascular disease models recapitulating key pathological features, implantable blood vessel grafts, and tissue analogs with the integration of capillary-like vasculatures. Finally, we provide readers with insights into the future perspectives of light-based 3D bioprinting to revolutionize vascular tissue engineering.

Formaldehyde initiates memory and motor impairments under weightlessness condition

During space flight, prolonged weightlessness stress exerts a range of detrimental impacts on the physiology and psychology of astronauts. These manifestations encompass depressive symptoms, anxiety, and impairments in both short-term memory and motor functions, albeit the precise underlying mechanisms remain elusive. Recent studies have revealed that hindlimb unloading (HU) animal models, which simulate space weightlessness, exhibited a disorder in memory and motor function associated with endogenous formaldehyde (FA) accumulation in the hippocampus and cerebellum, disruption of brain extracellular space (ECS), and blockage of interstitial fluid (ISF) drainage. Notably, the impairment of the blood-brain barrier (BBB) caused by space weightlessness elicits the infiltration of albumin and hemoglobin from the blood vessels into the brain ECS. However, excessive FA has the potential to form cross-links between these two proteins and amyloid-beta (Aβ), thereby obstructing ECS and inducing neuron death. Moreover, FA can inhibit N-methyl-D-aspartate (NMDA) currents by crosslinking NR1 and NR2B subunits, thus impairing memory. Additionally, FA has the ability to modulate the levels of certain microRNAs (miRNAs) such as miRNA-29b, which can affect the expression of aquaporin-4 (AQP4) so as to regulate ECS structure and ISF drainage. Especially, the accumulation of FA may inactivate the ataxia telangiectasia-mutated (ATM) protein kinase by forming cross-linking, a process that is associated with ataxia. Hence, this review presents that weightlessness stress-derived FA may potentially serve as a crucial catalyst in the deterioration of memory and motor abilities in the context of microgravity.

Profiling muscle transcriptome in mice exposed to microgravity using gene set enrichment analysis

Space exploration's advancement toward long-duration missions prompts intensified research on physiological effects. Despite adaptive physiological stability in some variables, persistent changes affect genome integrity, immune response, and cognitive function. Our study, utilizing multi-omics data from GeneLab, provides crucial insights investigating muscle atrophy during space mission. Leveraging NASA GeneLab's data resources, we apply systems biology-based analyses, facilitating comprehensive understanding and enabling meta-analysis. Through transcriptomics, we establish a reference profile of biological processes underlying muscle atrophy, crucial for intervention development. We emphasize the often-overlooked role of glycosylation in muscle atrophy. Our research sheds light on fundamental molecular mechanisms, bridging gaps between space research and terrestrial conditions. This study underscores the importance of interdisciplinary collaboration and data-sharing initiatives like GeneLab in advancing space medicine research.

The MyoGravity project to study real microgravity effects on human muscle precursor cells and tissue

Microgravity (µG) experienced during space flights promotes adaptation in several astronauts' organs and tissues, with skeletal muscles being the most affected. In response to reduced gravitational loading, muscles (especially, lower limb and antigravity muscles) undergo progressive mass loss and alteration in metabolism, myofiber size, and composition. Skeletal muscle precursor cells (MPCs), also known as satellite cells, are responsible for the growth and maintenance of muscle mass in adult life as well as for muscle regeneration following damage and may have a major role in µG-induced muscle wasting. Despite the great relevance for astronaut health, very few data are available about the effects of real µG on human muscles. Based on the MyoGravity project, this study aimed to analyze: (i) the cellular and transcriptional alterations induced by real µG in human MPCs (huMPCs) and (ii) the response of human skeletal muscle to normal gravitational loading after prolonged exposure to µG. We evaluated the transcriptomic changes induced by µG on board the International Space Station (ISS) in differentiating huMPCs isolated from Vastus lateralis muscle biopsies of a pre-flight astronaut and an age- and sex-matched volunteer, in comparison with the same cells cultured on the ground in standard gravity (1×g) conditions. We found that huMPCs differentiated under real µG conditions showed: (i) upregulation of genes related to cell adhesion, plasma membrane components, and ion transport; (ii) strong downregulation of genes related to the muscle contraction machinery and sarcomere organization; and (iii) downregulation of muscle-specific microRNAs (myomiRs). Moreover, we had the unique opportunity to analyze huMPCs and skeletal muscle tissue of the same astronaut before and 30 h after a long-duration space flight on board the ISS. Prolonged exposure to real µG strongly affected the biology and functionality of the astronaut's satellite cells, which showed a dramatic reduction of responsiveness to activating stimuli and proliferation rate, morphological changes, and almost inability to fuse into myotubes. RNA-Seq analysis of post- vs. pre-flight muscle tissue showed that genes involved in muscle structure and remodeling are promptly activated after landing following a long-duration space mission. Conversely, genes involved in the myelination process or synapse and neuromuscular junction organization appeared downregulated. Although we have investigated only one astronaut, these results point to a prompt readaptation of the skeletal muscle mechanical components to the normal gravitational loading, but the inability to rapidly recover the physiological muscle myelination/innervation pattern after landing from a long-duration space flight. Together with the persistent functional deficit observed in the astronaut's satellite cells after prolonged exposure to real µG, these results lead us to hypothesize that a condition of inefficient regeneration is likely to occur in the muscles of post-flight astronauts following damage.

Icariin promotes cell adhesion for osteogenesis in bone marrow stromal cells via binding to integrin α5β1

BACKGROUND AND PURPOSE

Icariin, an 8-prenylated flavonoid glycoside, is an anabolic agent that could exert rapid estrogenic actions via ligand-independent activation of estrogen receptor alpha (ERα) in osteoblastic cells to promote osteogenesis. However, relatively little is known about its direct cellular target, its protective effects, and cell adhesion activities in bone marrow stromal cells (BMSCs) against microgravity. In the present study, the effects of icariin on osteogenesis and cell adhesion under microgravity were examined with the involvement of integrin receptor α5β1, connexin 43, and CAMs.

STUDY DESIGN AND METHODS

Icariin was orally administered to 6-month-old ovariectomized (OVX) Sprague-Dawley (SD) rats for 3 months through daily intake of phytoestrogen-free rodent diets containing icariin at 2 different dosages (50 and 500 ppm). BMSCs were harvested for experiments and RNA-sequencing analysis to examine the mechanism of action of icariin and its direct cellular target in stimulating osteogenesis.

RESULTS

The results revealed that icariin induced the expression of cell adhesion molecules (CAMs) and protected against microgravity-induced disruption of actin cytoskeleton and the loss of osteogenic activities in BMSCs through the activation of connexin-43 (Cx43) and Ras homolog family member A (RhoA) and Rac family small GTPase 1 (Rac1)-mediated signaling pathways. Computerized molecular docking techniques and the competitive solid-phase binding ELISA assay confirmed that icariin could be a direct ligand of integrin alpha 5 beta 1 (α5β1), and it could also increase the protein expression of integrin α5β1 for mechanosensing.

CONCLUSION

Our findings suggest that icariin could directly activate cell adhesion signaling by binding to integrin α5β1, which opens up new avenues for the development of integrin α5β1 ligand as an agent to protect against unloading-induced bone loss.

Spaceflight-induced contractile and mitochondrial dysfunction in an automated heart-on-a-chip platform

With current plans for manned missions to Mars and beyond, the need to better understand, prevent, and counteract the harmful effects of long-duration spaceflight on the body is becoming increasingly important. In this study, an automated heart-on-a-chip platform was flown to the International Space Station on a 1-mo mission during which contractile cardiac function was monitored in real-time. Upon return to Earth, engineered human heart tissues (EHTs) were further analyzed with ultrastructural imaging and RNA sequencing to investigate the impact of prolonged microgravity on cardiomyocyte function and health. Spaceflight EHTs exhibited significantly reduced twitch forces, increased incidences of arrhythmias, and increased signs of sarcomere disruption and mitochondrial damage. Transcriptomic analyses showed an up-regulation of genes and pathways associated with metabolic disorders, heart failure, oxidative stress, and inflammation, while genes related to contractility and calcium signaling showed significant down-regulation. Finally, in silico modeling revealed a potential link between oxidative stress and mitochondrial dysfunction that corresponded with RNA sequencing results. This represents an in vitro model to faithfully reproduce the adverse effects of spaceflight on three-dimensional (3D)-engineered heart tissue.

Gene-environmental influence of space and microgravity on red blood cells with sickle cell disease

A fundamental question in human biology and for hematological disease is how do complex gene-environment interactions lead to individual disease outcome? This is no less the case for sickle cell disease (SCD), a monogenic disorder of Mendelian inheritance, both clinical course, severity, and treatment response, is variable amongst affected individuals. New insight and discovery often lie between the intersection of seemingly disparate disciplines. Recently, opportunities for space medicine have flourished and have offered a new paradigm for study. Two recent Nature papers have shown that hemolysis and oxidative stress play key mechanistic roles in erythrocyte pathogenesis during spaceflight. This paper reviews existing genetic and environmental modifiers of the sickle cell disease phenotype. It reviews evidence for erythrocyte pathology in microgravity environments and demonstrates why this may be relevant for the unique gene-environment interaction of the SCD phenotype. It also introduces the hematology and scientific community to methodological tools for evaluation in space and microgravity research. The increasing understanding of space biology may yield insight into gene-environment influences and new treatment paradigms in SCD and other hematological disease phenotypes.

Dynamic cellular responses to gravitational forces: Exploring the impact on white blood cell(s)

In recent years, the allure of space exploration and human spaceflight has surged, yet the effects of microgravity on the human body remain a significant concern. Immune and red blood cells rely on hematic or lymphatic streams as their primary means of transportation, posing notable challenges under microgravity conditions. This study sheds light on the intricate dynamics of cell behavior when suspended in bio-fluid under varying gravitational forces. Utilizing the dissipative particle dynamics approach, blood and white blood cells were modeled, with gravity applied as an external force along the vertical axis, ranging from 0 to 2 g in parameter sweeps. The results revealed discernible alterations in the cell shape and spatial alignment in response to gravity, quantified through metrics such as elongation and deformation indices, pitch angle, and normalized center of mass. Statistical analysis using the Mann-Whitney U test underscored clear distinctions between microgravity (<1 g) and hypergravity (>1 g) samples compared to normal gravity (1 g). Furthermore, the examination of forces exerted on the solid, including drag, shear stress, and solid forces, unveiled a reduction in the magnitude as the gravitational force increased. Additional analysis through dimensionless numbers unveiled the dominance of capillary and gravitational forces, which impacted cell velocity, leading to closer proximity to the wall and heightened viscous interaction with surrounding fluid particles. These interactions prompted shape alterations and reduced white blood cell area while increasing red blood cells. This study represents an effort in comprehending the effects of gravity on blood cells, offering insights into the intricate interplay between cellular dynamics and gravitational forces.

Exercise Training Attenuates the Muscle Mitochondria Genomic Response to Bed Rest

PURPOSE

Exercise training during the National Aeronautics and Space Administration 70-d bed rest study effectively counteracted the decline in aerobic capacity, muscle mass, strength, and endurance. We aimed to characterize the genomic response of the participants' vastus lateralis on day 64 of bed rest with and without exercise countermeasures.

METHODS

Twenty-two healthy young males were randomized into three groups: 1) bed rest only ( n = 7), 2) bed rest + aerobic (6 d·wk -1 ) and resistance training (3 d·wk -1 ) on standard equipment ( n = 7), and 3) bed rest + aerobic and resistance training using a flywheel device ( n = 8). The vastus lateralis gene and microRNA microarrays were analyzed using GeneSpring GX 14.9.1 (Agilent Technologies, Palo Alto, CA).

RESULTS

Bed rest significantly altered the expression of 2113 annotated genes in at least one out of the three study groups (fold change (FC) > 1.2; P < 0.05). Interaction analysis revealed that exercise attenuated the bed rest effect of 511 annotated genes (FC = 1.2, P < 0.05). In the bed rest only group, a predominant downregulation of genes was observed, whereas in the two exercise groups, there was a notable attenuation or reversal of this effect, with no significant differences between the two exercise modalities. Enrichment analysis identified functional categories and gene pathways, many of them related to the mitochondria. In addition, bed rest significantly altered the expression of 35 microRNAs (FC > 1.2, P < 0.05) with no difference between the three groups. Twelve are known to regulate some of the mitochondrial-related genes that were altered following bed rest.

CONCLUSIONS

Mitochondrial gene expression was a significant component of the molecular response to long-term bed rest. Although exercise attenuated the FC in the downregulation of many genes, it did not completely counteract all the molecular consequences.

Skeletal muscle-on-a-chip in microgravity as a platform for regeneration modeling and drug screening

Microgravity has been shown to lead to both muscle atrophy and impaired muscle regeneration. The purpose was to study the efficacy of microgravity to model impaired muscle regeneration in an engineered muscle platform and then to demonstrate the feasibility of performing drug screening in this model. Engineered human muscle was launched to the International Space Station National Laboratory, where the effect of microgravity exposure for 7 days was examined by transcriptomics and proteomics approaches. Gene set enrichment analysis of engineered muscle cultured in microgravity, compared to normal gravity conditions, highlighted a metabolic shift toward lipid and fatty acid metabolism, along with increased apoptotic gene expression. The addition of pro-regenerative drugs, insulin-like growth factor-1 (IGF-1) and a 15-hydroxyprostaglandin dehydrogenase inhibitor (15-PGDH-i), partially inhibited the effects of microgravity. In summary, microgravity mimics aspects of impaired myogenesis, and the addition of these drugs could partially inhibit the effects induced by microgravity.

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.

Special Issue: 'Advances in Space Biology'

As we enter a new era of space exploration, space biology is at the forefront of both robotic and human space programs [...].

Considerations for oral and dental tissues in holistic care during long-haul space flights

The health of astronauts during and after the return from long-haul space missions is paramount. There is plethora of research in the literature about the medical side of astronauts' health, however, the dental and oral health of the space crew seem to be overlooked with limited information in the literature about the effects of the space environment and microgravity on the oral and dental tissues. In this article, we shed some light on the latest available research related to space dentistry and provide some hypotheses that could guide the directions of future research and help maintain the oral health of space crews. We also promote for the importance of regenerative medicine and dentistry as well highlight the opportunities available in the expanding field of bioprinting/biomanufacturing through utilizing the effects of microgravity on stem cells culture techniques. Finally, we provide recommendations for adopting a multidisciplinary approach for oral healthcare during long-haul space flights.

Effects of Simulated Microgravity on Rat Reproductive System: Potential Benefits of Vitamin D3 Intervention

Gravity in space can have a negative impact on the reproductive system. Given that the reproductive system is one of vitamin D's objectives, this study will use a simulated microgravity model to evaluate its impact on the rat reproductive system.Twenty-two male Wistar rats were allocated into four groups at random. Under microgravity circumstances, the rats were housed in both special and standard cages. Each group was then separated into two subgroups, one of which received vitamin D3 and the other did not. Blood was drawn twice to determine blood levels of vitamin D3, LH, FSH, and testosterone. Rat testes were isolated for histological analysis, as well as a piece of epididymis for sperm count and morphological examination.Microgravity had a detrimental effect on testicular tissue, resulting in lower serum levels of LH and testosterone (p-value < 0.001). Spermatogenesis was largely inhibited under microgravity. During microgravity conditions, however, vitamin D3 had a good effect on testicular structure, and the total number of sperm. Simulated microgravity affects the male reproductive system, compromising testicular morphology, sperm parameters, and hormonal balance. However, this study shows that vitamin D3 supplementation can act as a preventative strategy, minimizing the negative consequences of microgravity. The beneficial effect of vitamin D3 on testicular health and sperm quality implies that it may be useful in protecting male reproductive function in space-related situations.

Upregulation of Amy1 in the salivary glands of mice exposed to a lunar gravity environment using the multiple artificial gravity research system

Introduction: Space is a unique environment characterized by isolation from community life and exposure to circadian misalignment, microgravity, and space radiation. These multiple differences from those experienced on the earth may cause systemic and local tissue stress. Autonomic nerves, including sympathetic and parasympathetic nerves, regulate functions in multiple organs. Saliva is secreted from the salivary gland, which is regulated by autonomic nerves, and plays several important roles in the oral cavity and digestive processes. The balance of the autonomic nervous system in the seromucous glands, such as the submandibular glands, precisely controls serous and mucous saliva. Psychological stress, radiation damage, and other triggers can cause an imbalance in salivary secretion systems. A previous study reported that amylase is a stress marker in behavioral medicine and space flight crews; however, the detailed mechanisms underlying amylase regulation in the space environment are still unknown. Methods: In this study, we aimed to elucidate how lunar gravity (1/6 g) changes mRNA expression patterns in the salivary gland. Using a multiple artificial gravity research system during space flight in the International Space Station, we studied the effects of two different gravitational levels, lunar and Earth gravity, on the submandibular glands of mice. All mice survived, returned to Earth from space, and their submandibular glands were collected 2 days after landing. Results: We found that lunar gravity induced the expression of the salivary amylase gene Amy1; however, no increase in Aqp5 and Ano1, which regulate water secretion, was observed. In addition, genes involved in the exocrine system, such as vesicle-associated membrane protein 8 (Vamp8) and small G proteins, including Rap1 and Rab families, were upregulated under lunar gravity. Conclusion: These results imply that lunar gravity upregulates salivary amylase secretion via Rap/Rab signaling and exocytosis via Vamp8. Our study highlights Amy1 as a potential candidate marker for stress regulation in salivary glands in the lunar gravity environment.

Effect of Spaceflight and Microgravity on the Musculoskeletal System: A Review

With National Aeronautics and Space Administration's plans for longer distance, longer duration spaceflights such as missions to Mars and the surge in popularity of space tourism, the need to better understand the effects of spaceflight on the musculoskeletal system has never been more present. However, there is a paucity of information on how spaceflight affects orthopaedic health. This review surveys existing literature and discusses the effect of spaceflight on each aspect of the musculoskeletal system. Spaceflight reduces bone mineral density at rapid rates because of multiple mechanisms. While this seems to be recoverable upon re-exposure to gravity, concern for fracture in spaceflight remains as microgravity impairs bone strength and fracture healing. Muscles, tendons, and entheses similarly undergo microgravity adaptation. These changes result in decreased muscle mass, increased tendon laxity, and decreased enthesis stiffness, thus decreasing the strength of the muscle-tendon-enthesis unit with variable recovery upon gravity re-exposure. Spaceflight also affects joint health; unloading of the joints facilitates changes that thin and atrophy cartilage similar to arthritic phenotypes. These changes are likely recoverable upon return to gravity with exercise. Multiple questions remain regarding effects of longer duration flights on health and implications of these findings on terrestrial medicine, which should be the target of future research.

Spatially resolved multiomics on the neuronal effects induced by spaceflight in mice

Impairment of the central nervous system (CNS) poses a significant health risk for astronauts during long-duration space missions. In this study, we employed an innovative approach by integrating single-cell multiomics (transcriptomics and chromatin accessibility) with spatial transcriptomics to elucidate the impact of spaceflight on the mouse brain in female mice. Our comparative analysis between ground control and spaceflight-exposed animals revealed significant alterations in essential brain processes including neurogenesis, synaptogenesis and synaptic transmission, particularly affecting the cortex, hippocampus, striatum and neuroendocrine structures. Additionally, we observed astrocyte activation and signs of immune dysfunction. At the pathway level, some spaceflight-induced changes in the brain exhibit similarities with neurodegenerative disorders, marked by oxidative stress and protein misfolding. Our integrated spatial multiomics approach serves as a stepping stone towards understanding spaceflight-induced CNS impairments at the level of individual brain regions and cell types, and provides a basis for comparison in future spaceflight studies. For broader scientific impact, all datasets from this study are available through an interactive data portal, as well as the National Aeronautics and Space Administration (NASA) Open Science Data Repository (OSDR).

Custom-made 3D-printed boot as a model of disuse-induced atrophy in murine skeletal muscle

Skeletal muscle atrophy is characterized by a decrease in muscle mass and strength caused by an imbalance in protein synthesis and degradation. This process naturally occurs upon reduced or absent physical activity, often related to illness, forced bed rest, or unhealthy lifestyles. Currently, no treatment is available for atrophy, and it can only be prevented by overloading exercise, causing severe problems for patients who cannot exercise due to chronic diseases, disabilities, or being bedridden. The two murine models commonly used to induce muscle atrophy are hindlimb suspension and ankle joint immobilization, both of which come with criticalities. The lack of treatments and the relevance of this atrophic process require a unilateral, safe, and robust model to induce muscle atrophy. In this work, we designed and developed a 3D-printed cast to be used for the study of disuse skeletal muscle atrophy. Applying two halves of the cast is non-invasive, producing little to no swelling or skin damage. The application of the cast induces, in 2-weeks immobilized leg, the activation of atrophy-related genes, causing a muscle weight loss up to 25% in the gastrocnemius muscle, and 31% in the soleus muscle of the immobilized leg compared to the control leg. The cross-sectional area of the fibers is decreased by 31% and 34% respectively, with a peculiar effect on fiber types. In the immobilized gastrocnemius, absolute muscle force is reduced by 38%, while normalized force is reduced by 16%. The contralateral leg did not show signs of overload or hypertrophy when compared to free roaming littermates, offering a good internal control over the immobilized limb. Upon removing the cast, the mice effectively recovered mass and force in 3 weeks.

Nitrosative Stress in Astronaut Skeletal Muscle in Spaceflight

Long-duration mission (LDM) astronauts from the International Space Station (ISS) (>180 ISS days) revealed a close-to-normal sarcolemmal nitric oxide synthase type-1 (NOS1) immunoexpression in myofibers together with biochemical and quantitative qPCR changes in deep calf soleus muscle. Nitro-DIGE analyses identified functional proteins (structural, metabolic, mitochondrial) that were over-nitrosylated post- vs. preflight. In a short-duration mission (SDM) astronaut (9 ISS days), s-nitrosylation of a nodal protein of the glycolytic flux, specific proteins in tricarboxylic acid (TCA) cycle, respiratory chain, and over-nitrosylation of creatine kinase M-types as signs of impaired ATP production and muscle contraction proteins were seen. S-nitrosylation of serotransferrin (TF) or carbonic anhydrase 3 (CA3b and 3c) represented signs of acute response microgravity muscle maladaptation. LDM nitrosoprofiles reflected recovery of mitochondrial activity, contraction proteins, and iron transporter TF as signs of muscle adaptation to microgravity. Nitrosated antioxidant proteins, alcohol dehydrogenase 5/S-nitrosoglutathione reductase (ADH5/GSNOR), and selenoprotein thioredoxin reductase 1 (TXNRD1) levels indicated signs of altered redox homeostasis and reduced protection from nitrosative stress in spaceflight. This work presents a novel spaceflight-generated dataset on s-nitrosylated muscle protein signatures from astronauts that helps both to better understand the structural and molecular networks associated to muscular nitrosative stress and to design countermeasures to dysfunction and impaired performance control in human spaceflight missions.

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

The advent of extended-duration human spaceflight demands a better comprehension of the physiological impacts of microgravity. One primary concern is the adverse impact on the musculoskeletal system, including muscle atrophy and bone density reduction. Ground-based microgravity simulations have provided insights, with vibrational bioreactors emerging as potential mitigators of these negative effects. Despite the potential they have, the adaptation of vibrational bioreactors for space remains unfulfilled, resulting in a significant gap in microgravity research. This paper introduces the first automated low-intensity vibrational (LIV) bioreactor designed specifically for the International Space Station (ISS) environment. Our research covers the bioreactor's design and characterization, the selection of an optimal linear guide for consistent 1-axis acceleration, a thorough analysis of its thermal and diffusion dynamics, and the pioneering use of BioMed Clear resin for enhanced scaffold design. This advancement sets the stage for more authentic space-based biological studies, vital for ensuring the safety of future space explorations.

Organs in orbit: how tissue chip technology benefits from microgravity, a perspective

Tissue chips have become one of the most potent research tools in the biomedical field. In contrast to conventional research methods, such as 2D cell culture and animal models, tissue chips more directly represent human physiological systems. This allows researchers to study therapeutic outcomes to a high degree of similarity to actual human subjects. Additionally, as rocket technology has advanced and become more accessible, researchers are using the unique properties offered by microgravity to meet specific challenges of modeling tissues on Earth; these include large organoids with sophisticated structures and models to better study aging and disease. This perspective explores the manufacturing and research applications of microgravity tissue chip technology, specifically investigating the musculoskeletal, cardiovascular, and nervous systems.

Human-like acceleration and deceleration control of a robot astronaut floating in a space station

The acceleration and deceleration (AD) motions are the basic motion modes of robot astronauts moving in a space station. Controlling the locomotion of the robot astronaut is very challenging due to the strong nonlinearity of its complex multi-body dynamics in a gravity-free environment. However, after training, humans can move well in space stations by pushing the bulkhead, and the motion mechanism of humans is a good reference for robot astronauts. The contribution of this study is modeling the human AD motion in a microgravity environment and proposing a human-like control method for robot astronauts moving in space stations. Specifically, the movement and contact force data of the human body during AD motion were collected on an air-floating platform. Through human AD modeling analysis, the mechanism of human motion is discovered, and semi-sinusoidal primitives of contact forces are proposed for AD motion. Then, a dynamic guidance model of human AD motion is built to complete motion planning under contact constraints, which is used as the expected model for the AD control of robot astronauts. Benefiting from the force primitives, accurate and safe planning of human-like AD motion can be completed. The characteristics and mechanism of human AD motion have been analyzed from the perspective of optimization. Lastly, based on the proposed dynamic guidance model, the AD motion policy is mapped to the robot astronaut system via a system control method based on the equivalent mapping of dynamic responses (force, velocity and pose). Through comparative analysis with real human motion data and simulation results under different conditions, the proposed AD control method can achieve human-like motion efficiently and stably. Even when confronted with errors in the robot's contact velocities and inertia parameters, the method can significantly reduce the motion errors while ensuring stability.

Muscle stiffness indicating mission crew health in space

Muscle function is compromised by gravitational unloading in space affecting overall musculoskeletal health. Astronauts perform daily exercise programmes to mitigate these effects but knowing which muscles to target would optimise effectiveness. Accurate inflight assessment to inform exercise programmes is critical due to lack of technologies suitable for spaceflight. Changes in mechanical properties indicate muscle health status and can be measured rapidly and non-invasively using novel technology. A hand-held MyotonPRO device enabled monitoring of muscle health for the first time in spaceflight (> 180 days). Greater/maintained stiffness indicated countermeasures were effective. Tissue stiffness was preserved in the majority of muscles (neck, shoulder, back, thigh) but Tibialis Anterior (foot lever muscle) stiffness decreased inflight vs. preflight (p < 0.0001; mean difference 149 N/m) in all 12 crewmembers. The calf muscles showed opposing effects, Gastrocnemius increasing in stiffness Soleus decreasing. Selective stiffness decrements indicate lack of preservation despite daily inflight countermeasures. This calls for more targeted exercises for lower leg muscles with vital roles as ankle joint stabilizers and in gait. Muscle stiffness is a digital biomarker for risk monitoring during future planetary explorations (Moon, Mars), for healthcare management in challenging environments or clinical disorders in people on Earth, to enable effective tailored exercise programmes.

How are cell and tissue structure and function influenced by gravity and what are the gravity perception mechanisms?

Progress in mechanobiology allowed us to better understand the important role of mechanical forces in the regulation of biological processes. Space research in the field of life sciences clearly showed that gravity plays a crucial role in biological processes. The space environment offers the unique opportunity to carry out experiments without gravity, helping us not only to understand the effects of gravitational alterations on biological systems but also the mechanisms underlying mechanoperception and cell/tissue response to mechanical and gravitational stresses. Despite the progress made so far, for future space exploration programs it is necessary to increase our knowledge on the mechanotransduction processes as well as on the molecular mechanisms underlying microgravity-induced cell and tissue alterations. This white paper reports the suggestions and recommendations of the SciSpacE Science Community for the elaboration of the section of the European Space Agency roadmap "Biology in Space and Analogue Environments" focusing on "How are cells and tissues influenced by gravity and what are the gravity perception mechanisms?" The knowledge gaps that prevent the Science Community from fully answering this question and the activities proposed to fill them are discussed.

Modeled microgravity unravels the roles of mechanical forces in renal progenitor cell physiology

BACKGROUND

The glomerulus is a highly complex system, composed of different interdependent cell types that are subjected to various mechanical stimuli. These stimuli regulate multiple cellular functions, and changes in these functions may contribute to tissue damage and disease progression. To date, our understanding of the mechanobiology of glomerular cells is limited, with most research focused on the adaptive response of podocytes. However, it is crucial to recognize the interdependence between podocytes and parietal epithelial cells, in particular with the progenitor subset, as it plays a critical role in various manifestations of glomerular diseases. This highlights the necessity to implement the analysis of the effects of mechanical stress on renal progenitor cells.

METHODS

Microgravity, modeled by Rotary Cell Culture System, has been employed as a system to investigate how renal progenitor cells respond to alterations in the mechanical cues within their microenvironment. Changes in cell phenotype, cytoskeleton organization, cell proliferation, cell adhesion and cell capacity for differentiation into podocytes were analyzed.

RESULTS

In modeled microgravity conditions, renal progenitor cells showed altered cytoskeleton and focal adhesion organization associated with a reduction in cell proliferation, cell adhesion and spreading capacity. Moreover, mechanical forces appeared to be essential for renal progenitor differentiation into podocytes. Indeed, when renal progenitors were exposed to a differentiative agent in modeled microgravity conditions, it impaired the acquisition of a complex podocyte-like F-actin cytoskeleton and the expression of specific podocyte markers, such as nephrin and nestin. Importantly, the stabilization of the cytoskeleton with a calcineurin inhibitor, cyclosporine A, rescued the differentiation of renal progenitor cells into podocytes in modeled microgravity conditions.

CONCLUSIONS

Alterations in the organization of the renal progenitor cytoskeleton due to unloading conditions negatively affect the regenerative capacity of these cells. These findings strengthen the concept that changes in mechanical cues can initiate a pathophysiological process in the glomerulus, not only altering podocyte actin cytoskeleton, but also extending the detrimental effect to the renal progenitor population. This underscores the significance of the cytoskeleton as a druggable target for kidney diseases.

Serum multi-omics analysis in hindlimb unloading mice model: Insights into systemic molecular changes and potential diagnostic and therapeutic biomarkers

Microgravity, in space travel and prolonged bed rest conditions, induces cardiovascular deconditioning along with skeletal muscle mass loss and weakness. The findings of microgravity research may also aid in the understanding and treatment of human health conditions on Earth such as muscle atrophy, and cardiovascular diseases. Due to the paucity of biomarkers and the unknown underlying mechanisms of cardiovascular and skeletal muscle deconditioning in these environments, there are insufficient diagnostic and preventative measures. In this study, we employed hindlimb unloading (HU) mouse model, which mimics astronauts in space and bedridden patients, to first evaluate cardiovascular and skeletal muscle function, followed by proteomics and metabolomics LC-MS/MS-based analysis using serum samples. Three weeks of unloading caused changes in the function of the cardiovascular system in c57/Bl6 mice, as seen by a decrease in mean arterial pressure and heart weight. Unloading for three weeks also changed skeletal muscle function, causing a loss in grip strength in HU mice and atrophy of skeletal muscle indicated by a reduction in muscle mass. These modifications were partially reversed by a two-week recovery period of reloading condition, emphasizing the significance of the recovery process. Proteomics analysis revealed 12 dysregulated proteins among the groups, such as phospholipid transfer protein, Carbonic anhydrase 3, Parvalbumin alpha, Major urinary protein 20 (Mup20), Thrombospondin-1, and Apolipoprotein C-IV. On the other hand, metabolomics analysis showed altered metabolites among the groups such as inosine, hypoxanthine, xanthosine, sphinganine, l-valine, 3,4-Dihydroxyphenylglycol, and l-Glutamic acid. The joint data analysis revealed that HU conditions mainly impacted pathways such as ABC transporters, complement and coagulation cascades, nitrogen metabolism, and purine metabolism. Overall, our results indicate that microgravity environment induces significant alterations in the function, proteins, and metabolites of these mice. These observations suggest the potential utilization of these proteins and metabolites as novel biomarkers for assessing and mitigating cardiovascular and skeletal muscle deconditioning associated with such conditions.

The Interconnection Between Muscle and Bone: A Common Clinical Management Pathway

Often observed with aging, the loss of skeletal muscle (sarcopenia) and bone (osteoporosis) mass, strength, and quality, is associated with reduced physical function contributing to falls and fractures. Such events can lead to a loss of independence and poorer quality of life. Physical inactivity (mechanical unloading), especially in older adults, has detrimental effects on the mass and quality of bone as well as muscle, while increases in activity (mechanical loading) have positive effects. Emerging evidence suggests that the relationship between bone and muscle is driven, at least in part, by bone-muscle crosstalk. Bone and muscle are closely linked anatomically, mechanically, and biochemically, and both have the capacity to function with paracrine and endocrine-like action. However, the exact mechanisms involved in this crosstalk remain only partially explored. Given older adults with lower bone mass are more likely to present with impaired muscle function, and vice versa, strategies capable of targeting both bone and muscle are critical. Exercise is the primary evidence-based prevention strategy capable of simultaneously improving muscle and bone health. Unfortunately, holistic treatment plans including exercise in conjunction with other allied health services to prevent or treat musculoskeletal disease remain underutilized. With a focus on sarcopenia and osteoporosis, the aim of this review is to (i) briefly describe the mechanical and biochemical interactions between bone and muscle; (ii) provide a summary of therapeutic strategies, specifically exercise, nutrition and pharmacological approaches; and (iii) highlight a holistic clinical pathway for the assessment and management of sarcopenia and osteoporosis.

Genetic variation influences the skeletal response to hindlimb unloading in the eight founder strains of the diversity outbred mouse population

During disuse, mechanical unloading causes extensive bone loss, decreasing bone volume and strength. Variations in bone mass and risk of osteoporosis are influenced by genetics; however, it remains unclear how genetic variation affects the skeletal response to unloading. We previously found that genetic variation affects the musculoskeletal response to 3 weeks of immobilization in the 8 Jackson Laboratory J:DO founder strains: C57Bl/6J, A/J, 129S1/SvImJ, NOD/ShiLtJ, NZO/HlLtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ. Hindlimb unloading (HLU) is the best model for simulating local and systemic contributors of disuse and therefore may have a greater impact on bones than immobilization. We hypothesized that genetic variation would affect the response to HLU across the eight founder strains. Mice of each founder strain were placed in HLU for 3 weeks, and the femurs and tibias were analyzed. There were significant HLU and mouse strain interactions on body weight, femur trabecular BV/TV, and femur ultimate force. This indicates that unloading only caused significant catabolic effects in some mouse strains. C57BL/6 J mice were most affected by unloading while other strains were more protected. There were significant HLU and mouse strain interactions on gene expression of genes encoding bone metabolism genes in the tibia. This indicates that unloading only caused significant effects on bone metabolism genes in some mouse strains. Different mouse strains respond to HLU differently, and this can be explained by genetic differences. These results suggest the outbred J:DO mice will be a powerful model for examining the effects of genetics on the skeletal response to HLU.

Microgravity triggers ferroptosis and accelerates senescence in the MG-63 cell model of osteoblastic cells

In space, cells sustain strong modifications of their mechanical environment. Mechanosensitive molecules at the cell membrane regulate mechanotransduction pathways that induce adaptive responses through the regulation of gene expression, post-translational modifications, protein interactions or intracellular trafficking, among others. In the current study, human osteoblastic cells were cultured on the ISS in microgravity and at 1 g in a centrifuge, as onboard controls. RNAseq analyses showed that microgravity inhibits cell proliferation and DNA repair, stimulates inflammatory pathways and induces ferroptosis and senescence, two pathways related to ageing. Morphological hallmarks of senescence, such as reduced nuclear size and changes in chromatin architecture, proliferation marker distribution, tubulin acetylation and lysosomal transport were identified by immunofluorescence microscopy, reinforcing the hypothesis of induction of cell senescence in microgravity during space flight. These processes could be attributed, at least in part, to the regulation of YAP1 and its downstream effectors NUPR1 and CKAP2L.

Explainable machine learning identifies multi-omics signatures of muscle response to spaceflight in mice

The adverse effects of microgravity exposure on mammalian physiology during spaceflight necessitate a deep understanding of the underlying mechanisms to develop effective countermeasures. One such concern is muscle atrophy, which is partly attributed to the dysregulation of calcium levels due to abnormalities in SERCA pump functioning. To identify potential biomarkers for this condition, multi-omics data and physiological data available on the NASA Open Science Data Repository (osdr.nasa.gov) were used, and machine learning methods were employed. Specifically, we used multi-omics (transcriptomic, proteomic, and DNA methylation) data and calcium reuptake data collected from C57BL/6 J mouse soleus and tibialis anterior tissues during several 30+ day-long missions on the international space station. The QLattice symbolic regression algorithm was introduced to generate highly explainable models that predict either experimental conditions or calcium reuptake levels based on multi-omics features. The list of candidate models established by QLattice was used to identify key features contributing to the predictive capability of these models, with Acyp1 and Rps7 proteins found to be the most predictive biomarkers related to the resilience of the tibialis anterior muscle in space. These findings could serve as targets for future interventions aiming to reduce the extent of muscle atrophy during space travel.

Genetic diversity modulates the physical and transcriptomic response of skeletal muscle to simulated microgravity in male mice

Developments in long-term space exploration necessitate advancements in countermeasures against microgravity-induced skeletal muscle loss. Astronaut data shows considerable variation in muscle loss in response to microgravity. Previous experiments suggest that genetic background influences the skeletal muscle response to unloading, but no in-depth analysis of genetic expression has been performed. Here, we placed eight, male, inbred founder strains of the diversity outbred mice (129S1/SvImJ, A/J, C57BL/6J, CAST/EiJ, NOD/ShiLtJ, NZO/HILtJ, PWK/PhJ, and WSB/EiJ) in simulated microgravity (SM) via hindlimb unloading for three weeks. Body weight, muscle morphology, muscle strength, protein synthesis marker expression, and RNA expression were collected. A/J and CAST/EiJ mice were most susceptible to SM-induced muscle loss, whereas NOD/ShiLtJ mice were the most protected. In response to SM, A/J and CAST/EiJ mice experienced reductions in body weight, muscle mass, muscle volume, and muscle cross-sectional area. A/J mice had the highest number of differentially expressed genes (68) and associated gene ontologies (328). Downregulation of immunological gene ontologies and genes encoding anabolic immune factors suggest that immune dysregulation contributes to the response of A/J mice to SM. Several muscle properties showed significant interactions between SM and mouse strain and a high degree of heritability. These data imply that genetic background plays a role in the degree of muscle loss in SM and that more individualized programs should be developed for astronauts to protect their skeletal muscles against microgravity on long-term missions.

Bisphosphonate conjugation enhances the bone-specificity of NELL-1-based systemic therapy for spaceflight-induced bone loss in mice

Microgravity-induced bone loss results in a 1% bone mineral density loss monthly and can be a mission critical factor in long-duration spaceflight. Biomolecular therapies with dual osteogenic and anti-resorptive functions are promising for treating extreme osteoporosis. We previously confirmed that NELL-like molecule-1 (NELL-1) is crucial for bone density maintenance. We further PEGylated NELL-1 (NELL-polyethylene glycol, or NELL-PEG) to increase systemic delivery half-life from 5.5 to 15.5 h. In this study, we used a bio-inert bisphosphonate (BP) moiety to chemically engineer NELL-PEG into BP-NELL-PEG and specifically target bone tissues. We found conjugation with BP improved hydroxyapatite (HA) binding and protein stability of NELL-PEG while preserving NELL-1's osteogenicity in vitro. Furthermore, BP-NELL-PEG showed superior in vivo bone specificity without observable pathology in liver, spleen, lungs, brain, heart, muscles, or ovaries of mice. Finally, we tested BP-NELL-PEG through spaceflight exposure onboard the International Space Station (ISS) at maximal animal capacity (n = 40) in a long-term (9 week) osteoporosis therapeutic study and found that BP-NELL-PEG significantly increased bone formation in flight and ground control mice without obvious adverse health effects. Our results highlight BP-NELL-PEG as a promising therapeutic to mitigate extreme bone loss from long-duration microgravity exposure and musculoskeletal degeneration on Earth, especially when resistance training is not possible due to incapacity (e.g., bone fracture, stroke).

Human skeletal muscle tissue chip autonomous payload reveals changes in fiber type and metabolic gene expression due to spaceflight

Microphysiological systems provide the opportunity to model accelerated changes at the human tissue level in the extreme space environment. Spaceflight-induced muscle atrophy experienced by astronauts shares similar physiological changes to muscle wasting in older adults, known as sarcopenia. These shared attributes provide a rationale for investigating molecular changes in muscle cells exposed to spaceflight that may mimic the underlying pathophysiology of sarcopenia. We report the results from three-dimensional myobundles derived from muscle biopsies from young and older adults, integrated into an autonomous CubeLab™, and flown to the International Space Station (ISS) aboard SpaceX CRS-21 as part of the NIH/NASA funded Tissue Chips in Space program. Global transcriptomic RNA-Seq analyses comparing the myobundles in space and on the ground revealed downregulation of shared transcripts related to myoblast proliferation and muscle differentiation. The analyses also revealed downregulated differentially expressed gene pathways related to muscle metabolism unique to myobundles derived from the older cohort exposed to the space environment compared to ground controls. Gene classes related to inflammatory pathways were downregulated in flight samples cultured from the younger cohort compared to ground controls. Our muscle tissue chip platform provides an approach to studying the cell autonomous effects of spaceflight on muscle cell biology that may not be appreciated on the whole organ or organism level and sets the stage for continued data collection from muscle tissue chip experimentation in microgravity. We also report on the challenges and opportunities for conducting autonomous tissue-on-chip CubeLabTM payloads on the ISS.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Effects of simulated microgravity and vibration on osteoblast and osteoclast activity in cultured zebrafish scales

Zebrafish cultured scales have been used effectively to study cellular and molecular responses of bone cells. In order to expose zebrafish scales to simulated microgravity (SMG) and/or vibration, we first determined via apoptosis staining whether cells of the scale survive in culture for two days and hence, we restricted our analyses to two-day durations. Next, we measured the effects of SMG and vibration on cell death, osteoclast tartrate-resistant acid phosphatase, and osteoblast alkaline phosphatase activity and on the number of Runx2a positive cells. We found that during the SMG treatment, osteoclast tartrate-resistant acid phosphatase activity increased on average, while the number of Runx2a positive cells decreased significantly. In contrast, SMG exposure caused a decrease in osteoblast activity. The vibration treatment showed an increase, on average, in the osteoblast alkaline phosphatase activity. This study demonstrates the effect of SMG and vibration on zebrafish scales and the effects of SMG on bone cells. We also show that zebrafish scales can be used to examine the effects of SMG on bone maintenance.

Bioreactor Technologies for Enhanced Organoid Culture

An organoid is a 3D organization of cells that can recapitulate some of the structure and function of native tissue. Recent work has seen organoids gain prominence as a valuable model for studying tissue development, drug discovery, and potential clinical applications. The requirements for the successful culture of organoids in vitro differ significantly from those of traditional monolayer cell cultures. The generation and maturation of high-fidelity organoids entails developing and optimizing environmental conditions to provide the optimal cues for growth and 3D maturation, such as oxygenation, mechanical and fluidic activation, nutrition gradients, etc. To this end, we discuss the four main categories of bioreactors used for organoid culture: stirred bioreactors (SBR), microfluidic bioreactors (MFB), rotating wall vessels (RWV), and electrically stimulating (ES) bioreactors. We aim to lay out the state-of-the-art of both commercial and in-house developed bioreactor systems, their benefits to the culture of organoids derived from various cells and tissues, and the limitations of bioreactor technology, including sterilization, accessibility, and suitability and ease of use for long-term culture. Finally, we discuss future directions for improvements to existing bioreactor technology and how they may be used to enhance organoid culture for specific applications.

Space Environment Impacts Homeostasis: Exposure to Spaceflight Alters Mammary Gland Transportome Genes

Membrane transporters and ion channels that play an indispensable role in metabolite trafficking have evolved to operate in Earth's gravity. Dysregulation of the transportome expression profile at normogravity not only affects homeostasis along with drug uptake and distribution but also plays a key role in the pathogenesis of diverse localized to systemic diseases including cancer. The profound physiological and biochemical perturbations experienced by astronauts during space expeditions are well-documented. However, there is a paucity of information on the effect of the space environment on the transportome profile at an organ level. Thus, the goal of this study was to analyze the effect of spaceflight on ion channels and membrane substrate transporter genes in the periparturient rat mammary gland. Comparative gene expression analysis revealed an upregulation (p < 0.01) of amino acid, Ca²⁺, K⁺, Na⁺, Zn²⁺, Cl^-, PO₄^3-, glucose, citrate, pyruvate, succinate, cholesterol, and water transporter genes in rats exposed to spaceflight. Genes associated with the trafficking of proton-coupled amino acids, Mg²⁺, Fe²⁺, voltage-gated K⁺-Na⁺, cation-coupled chloride, as well as Na⁺/Ca²⁺ and ATP-Mg/Pi exchangers were suppressed (p < 0.01) in these spaceflight-exposed rats. These findings suggest that an altered transportome profile contributes to the metabolic modulations observed in the rats exposed to the space environment.

Bioprinting in Microgravity

Bioprinting as an extension of 3D printing offers capabilities for printing tissues and organs for application in biomedical engineering. Conducting bioprinting in space, where the gravity is zero, can enable new frontiers in tissue engineering. Fabrication of soft tissues, which usually collapse under their own weight, can be accelerated in microgravity conditions as the external forces are eliminated. Furthermore, human colonization in space can be supported by providing critical needs of life and ecosystems by 3D bioprinting without relying on cargos from Earth, e.g., by development and long-term employment of living engineered filters (such as sea sponges-known as critical for initiating and maintaining an ecosystem). This review covers bioprinting methods in microgravity along with providing an analysis on the process of shipping bioprinters to space and presenting a perspective on the prospects of zero-gravity bioprinting.

Impacts of microgravity on amino acid metabolism during spaceflight

Spaceflight exerts an extreme and unique influence on human physiology as astronauts are subjected to long-term or short-term exposure to microgravity. During spaceflight, a multitude of physiological changes, including the loss of skeletal muscle mass, bone resorption, oxidative stress, and impaired blood flow, occur, which can affect astronaut health and the likelihood of mission success. In vivo and in vitro metabolite studies suggest that amino acids are among the most affected nutrients and metabolites by microgravity (a weightless condition due to very weak gravitational forces). Moreover, exposure to microgravity alters gut microbial composition, immune function, musculoskeletal health, and consequently amino acid metabolism. Appropriate knowledge of daily protein consumption, with a focus on specific functional amino acids, may offer insight into potential combative and/or therapeutic effects of amino acid consumption in astronauts and space travelers. This will further aid in the successful development of long-term manned space mission and permanent space habitats.

Medical Astro-Microbiology: Current Role and Future Challenges

The second and third decades of the twenty-first century are marked by a flourishing of space technology which may soon realise human aspirations of a permanent multiplanetary presence. The prevention, control and management of infection with microbial pathogens is likely to play a key role in how successful human space aspirations will become. This review considers the emerging field of medical astro-microbiology. It examines the current evidence regarding the risk of infection during spaceflight via host susceptibility, alterations to the host's microbiome as well as exposure to other crew members and spacecraft's microbiomes. It also considers the relevance of the hygiene hypothesis in this regard. It then reviews the current evidence related to infection risk associated with microbial adaptability in spaceflight conditions. There is a particular focus on the International Space Station (ISS), as one of the only two  crewed objects in low Earth orbit. It discusses the effects of spaceflight related stressors on viruses and the infection risks associated with latent viral reactivation and increased viral shedding during spaceflight. It then examines the effects of the same stressors on bacteria, particularly in relation to changes in virulence and drug resistance. It also considers our current understanding of fungal adaptability in spaceflight. The global public health and environmental risks associated with a possible re-introduction to Earth of invasive species are also briefly discussed. Finally, this review examines the largely unknown microbiology and infection implications of celestial body habitation with an emphasis placed on Mars. Overall, this review summarises much of our current understanding of medical astro-microbiology and identifies significant knowledge gaps.

Graphical Abstract

How controlled motion alters the biophysical properties of musculoskeletal tissue architecture

INTRODUCTION

Movement is fundamental to the normal behaviour of the hand, not only for day-to-day activity, but also for fundamental processes like development, tissue homeostasis and repair. Controlled motion is a concept that hand therapists apply to their patients daily for functional gains, yet the scientific understanding of how this works is poorly understood.

PURPOSE OF THE ARTICLE

To review the biology of the tissues in the hand that respond to movement and provide a basic science understanding of how it can be manipulated to facilitate better functionThe review outlines the concept of controlled motion and actions across the scales of tissue architecture, highlighting the the role of movement forces in tissue development, homeostasis and repair. The biophysical behaviour of mechanosensitve tissues of the hand such as skin, tendon, bone and cartilage are discussed.

CONCLUSION

Controlled motion during early healing is a form of controlled stress and can be harnessed to generate appropriate reparative tissues. Understanding the temporal and spatial biology of tissue repair allows therapists to tailor therapies that allow optimal recovery based around progressive biophysical stimuli by movement.

Validation of Human Skeletal Muscle Tissue Chip Autonomous Platform to Model Age-Related Muscle Wasting in Microgravity

Microgravity-induced muscle atrophy experienced by astronauts shares similar physiological changes to muscle wasting experienced by older adults, known as sarcopenia. These shared attributes provide a rationale for investigating microgravity-induced molecular changes in human bioengineered muscle cells that may also mimic the progressive underlying pathophysiology of sarcopenia. Here, we report the results of an experiment that incorporated three-dimensional myobundles derived from muscle biopsies from young and older adults, that were integrated into an autonomous CubeLabâ"¢, and flown to the International Space Station (ISS) aboard SpaceX CRS-21 in December 2020 as part of the NIH/NASA funded Tissue Chips in Space program. Global transcriptomic RNA-Seq analysis comparing the myobundles in space and on the ground revealed downregulation of shared transcripts related to myoblast proliferation and muscle differentiation for those in space. The analysis also revealed differentially expressed gene pathways related to muscle metabolism unique to myobundles derived from the older cohort exposed to the space environment compared to ground controls. Gene classes related to inflammatory pathways were uniquely modulated in flight samples cultured from the younger cohort compared to ground controls. Our muscle tissue chip platform provides a novel approach to studying the cell autonomous effects of microgravity on muscle cell biology that may not be appreciated on the whole organ or organism level and sets the stage for continued data collection from muscle tissue chip experimentation in microgravity. Thus, we also report on the challenges and opportunities for conducting autonomous tissue-on-chip CubeLab TM payloads on the ISS.

Space habitats for bioengineering and surgical repair: addressing the requirement for reconstructive and research tissues during deep-space missions

Numerous technical scenarios have been developed to facilitate a human return to the Moon, and as a testbed for a subsequent mission to Mars. Crews appointed with constructing and establishing planetary bases will require a superior level of physical ability to cope with the operational demands. However, the challenging environments of nearby planets (e.g. geological, atmospheric, gravitational conditions) as well as the lengthy journeys through microgravity, will lead to progressive tissue degradation and an increased susceptibility to injury. The isolation, distance and inability to evacuate in an emergency will require autonomous medical support, as well as a range of facilities and specialised equipment to repair tissue damage on-site. Here, we discuss the design requirements of such a facility, in the form of a habitat that would concomitantly allow tissue substitute production, maintenance and surgical implantation, with an emphasis on connective tissues. The requirements for the individual modules and their operation are identified. Several concepts are assessed, including the presence of adjacent wet lab and medical modules supporting the gradual implementation of regenerative biomaterials and acellular tissue substitutes, leading to eventual tissue grafts and, in subsequent decades, potential tissues/organ-like structures. The latter, currently in early phases of development, are assessed particularly for researching the effects of extreme conditions on representative analogues for astronaut health support. Technical solutions are discussed for bioengineering in an isolated planetary environment with hypogravity, from fluid-gel bath suspended manufacture to cryostorage, cell sourcing and on-site resource utilisation for laboratory infrastructure. Surgical considerations are also discussed.

EuniceScope: Low-Cost Imaging Platform for Studying Microgravity Cell Biology

Microgravity is proven to impact a wide range of human physiology, from stimulating stem cell differentiation to confounding cell health in bones, skeletal muscles, and blood cells. The research in this arena is progressively intensified by the increasing promises of human spaceflights. Considering the limited access to spaceflight, ground-based microgravity-simulating platforms have been indispensable for microgravity-biology research. However, they are generally complex, costly, hard to replicate and reconfigure - hampering the broad adoption of microgravity biology and astrobiology. To address these limitations, we developed a low-cost reconfigurable 3D-printed microscope coined EuniceScope to allow the democratization of astrobiology, especially for educational use. EuniceScope is a compact 2D clinostat system integrated with a modularized brightfield microscope, built upon 3D-printed toolbox. We demonstrated that this compact system offers plausible imaging quality and microgravity-simulating performance. Its high degree of reconfigurability thus holds great promise in the wide dissemination of microgravity-cell-biology research in the broader community, including Science, technology, engineering, and mathematics (STEM) educational and scientific community in the future.

Space Omics and Tissue Response in Astronaut Skeletal Muscle after Short and Long Duration Missions

The molecular mechanisms of skeletal muscle adaptation to spaceflight are as yet not fully investigated and well understood. The MUSCLE BIOPSY study analyzed pre and postflight deep calf muscle biopsies (m. soleus) obtained from five male International Space Station (ISS) astronauts. Moderate rates of myofiber atrophy were found in long-duration mission (LDM) astronauts (~180 days in space) performing routine inflight exercise as countermeasure (CM) compared to a short-duration mission (SDM) astronaut (11 days in space, little or no inflight CM) for reference control. Conventional H&E scout histology showed enlarged intramuscular connective tissue gaps between myofiber groups in LDM post vs. preflight. Immunoexpression signals of extracellular matrix (ECM) molecules, collagen 4 and 6, COL4 and 6, and perlecan were reduced while matrix-metalloproteinase, MMP2, biomarker remained unchanged in LDM post vs. preflight suggesting connective tissue remodeling. Large scale proteomics (space omics) identified two canonical protein pathways associated to muscle weakness (necroptosis, GP6 signaling/COL6) in SDM and four key pathways (Fatty acid β-oxidation, integrin-linked kinase ILK, Rho A GTPase RHO, dilated cardiomyopathy signaling) explicitly in LDM. The levels of structural ECM organization proteins COL6A1/A3, fibrillin 1, FBN1, and lumican, LUM, increased in postflight SDM vs. LDM. Proteins from tricarboxylic acid, TCA cycle, mitochondrial respiratory chain, and lipid metabolism mostly recovered in LDM vs. SDM. High levels of calcium signaling proteins, ryanodine receptor 1, RyR1, calsequestrin 1/2, CASQ1/2, annexin A2, ANXA2, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1) pump, ATP2A, were signatures of SDM, and decreased levels of oxidative stress peroxiredoxin 1, PRDX1, thioredoxin-dependent peroxide reductase, PRDX3, or superoxide dismutase [Mn] 2, SOD2, signatures of LDM postflight. Results help to better understand the spatiotemporal molecular adaptation of skeletal muscle and provide a large scale database of skeletal muscle from human spaceflight for the better design of effective CM protocols in future human deep space exploration.

Simulated microgravity affects stroma-dependent ex vivo myelopoiesis

Microgravity is known negatively affect physiology of living beings, including hematopoiesis. Dysregulation of hematopoietic cells and supporting stroma relationships in bone marrow niche may be in charge. We compared the efficacy of ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs) in presence of native or osteocommitted MSCs under simulated microgravity (Smg) using Random Positioning Machine (RPM). In comparison with 1 g, a decrease of MSC-associated HSPCs and an increase of floating HSPCs was observed after 7 days of Smg exposure. Among floating HSPCs, primitive progenitors were presented by late CD34⁺/133^-. Total CFUs as well as erythroid (BFU-E) and granulocytic (CFU-G) numbers were lower. MSC-associated primitive HSPCs demonstrated increased proportion of late CD34⁺/133^- in expense of early CD34^-/133⁺. Osteo-MSCs preferentially supported late primitive CD34⁺ and more committed HSPCs as followed from increase of CFUs, and CD235a⁺ erythroid progenitors. Under Smg, an increased VEGF, eotaxin, and GRO-a levels, and a decrease in RANTES were found in the osteo-MSC-HSPC co-cultures. IL-6,-8, -13, G-CSF, GRO-a, MCP-3, MIP-1b, VEGF increased in co-culture with osteo-MSCs vs intact MSCs. Based on the findings, the misbalance between primitive/committed HSPCs and a decrease in hematopoiesis-supportive activity of osteocommitted cells are supposed to underline hematopoietic disorders during space flights.

Investigating the effects of chronic low-dose radiation exposure in the liver of a hypothermic zebrafish model

Mankind's quest for a manned mission to Mars is placing increased emphasis on the development of innovative radio-protective countermeasures for long-term space travel. Hibernation confers radio-protective effects in hibernating animals, and this has led to the investigation of synthetic torpor to mitigate the deleterious effects of chronic low-dose-rate radiation exposure. Here we describe an induced torpor model we developed using the zebrafish. We explored the effects of radiation exposure on this model with a focus on the liver. Transcriptomic and behavioural analyses were performed. Radiation exposure resulted in transcriptomic perturbations in lipid metabolism and absorption, wound healing, immune response, and fibrogenic pathways. Induced torpor reduced metabolism and increased pro-survival, anti-apoptotic, and DNA repair pathways. Coupled with radiation exposure, induced torpor led to a stress response but also revealed maintenance of DNA repair mechanisms, pro-survival and anti-apoptotic signals. To further characterise our model of induced torpor, the zebrafish model was compared with hepatic transcriptomic data from hibernating grizzly bears (Ursus arctos horribilis) and active controls revealing conserved responses in gene expression associated with anti-apoptotic processes, DNA damage repair, cell survival, proliferation, and antioxidant response. Similarly, the radiation group was compared with space-flown mice revealing shared changes in lipid metabolism.

A Compact Imaging Platform for Conducting C. elegans Phenotypic Assays on Earth and in Spaceflight

The model organism Caenorhabditis elegans is used in a variety of applications ranging from fundamental biological studies, to drug screening, to disease modeling, and to space-biology investigations. These applications rely on conducting whole-organism phenotypic assays involving animal behavior and locomotion. In this study, we report a 3D printed compact imaging platform (CIP) that is integrated with a smart-device camera for the whole-organism phenotyping of C. elegans. The CIP has no external optical elements and does not require mechanical focusing, simplifying the optical configuration. The small footprint of the system powered with a standard USB provides capabilities ranging from plug-and-play, to parallel operation, and to housing it in incubators for temperature control. We demonstrate on Earth the compatibility of the CIP with different C. elegans substrates, including agar plates, liquid droplets on glass slides and microfluidic chips. We validate the system with behavioral and thrashing assays and show that the phenotypic readouts are in good agreement with the literature data. We conduct a pilot study with mutants and show that the phenotypic data collected from the CIP distinguishes these mutants. Finally, we discuss how the simplicity and versatility offered by CIP makes it amenable to future C. elegans investigations on the International Space Station, where science experiments are constrained by system size, payload weight and crew time. Overall, the compactness, portability and ease-of-use makes the CIP desirable for research and educational outreach applications on Earth and in space.

Movement in low gravity environments (MoLo) programme-The MoLo-L.O.O.P. study protocol

BACKGROUND

Exposure to prolonged periods in microgravity is associated with deconditioning of the musculoskeletal system due to chronic changes in mechanical stimulation. Given astronauts will operate on the Lunar surface for extended periods of time, it is critical to quantify both external (e.g., ground reaction forces) and internal (e.g., joint reaction forces) loads of relevant movements performed during Lunar missions. Such knowledge is key to predict musculoskeletal deconditioning and determine appropriate exercise countermeasures associated with extended exposure to hypogravity.

OBJECTIVES

The aim of this paper is to define an experimental protocol and methodology suitable to estimate in high-fidelity hypogravity conditions the lower limb internal joint reaction forces. State-of-the-art movement kinetics, kinematics, muscle activation and muscle-tendon unit behaviour during locomotor and plyometric movements will be collected and used as inputs (Objective 1), with musculoskeletal modelling and an optimisation framework used to estimate lower limb internal joint loading (Objective 2).

METHODS

Twenty-six healthy participants will be recruited for this cross-sectional study. Participants will walk, skip and run, at speeds ranging between 0.56-3.6 m/s, and perform plyometric movement trials at each gravity level (1, 0.7, 0.5, 0.38, 0.27 and 0.16g) in a randomized order. Through the collection of state-of-the-art kinetics, kinematics, muscle activation and muscle-tendon behaviour, a musculoskeletal modelling framework will be used to estimate lower limb joint reaction forces via tracking simulations.

CONCLUSION

The results of this study will provide first estimations of internal musculoskeletal loads associated with human movement performed in a range of hypogravity levels. Thus, our unique data will be a key step towards modelling the musculoskeletal deconditioning associated with long term habitation on the Lunar surface, and thereby aiding the design of Lunar exercise countermeasures and mitigation strategies.

Changes in interstitial fluid flow, mass transport and the bone cell response in microgravity and normogravity

In recent years, our scientific interest in spaceflight has grown exponentially and resulted in a thriving area of research, with hundreds of astronauts spending months of their time in space. A recent shift toward pursuing territories farther afield, aiming at near-Earth asteroids, the Moon, and Mars combined with the anticipated availability of commercial flights to space in the near future, warrants continued understanding of the human physiological processes and response mechanisms when in this extreme environment. Acute skeletal loss, more severe than any bone loss seen on Earth, has significant implications for deep space exploration, and it remains elusive as to why there is such a magnitude of difference between bone loss on Earth and loss in microgravity. The removal of gravity eliminates a critical primary mechano-stimulus, and when combined with exposure to both galactic and solar cosmic radiation, healthy human tissue function can be negatively affected. An additional effect found in microgravity, and one with limited insight, involves changes in dynamic fluid flow. Fluids provide the most fundamental way to transport chemical and biochemical elements within our bodies and apply an essential mechano-stimulus to cells. Furthermore, the cell cytoplasm is not a simple liquid, and fluid transport phenomena together with viscoelastic deformation of the cytoskeleton play key roles in cell function. In microgravity, flow behavior changes drastically, and the impact on cells within the porous system of bone and the influence of an expanding level of adiposity are not well understood. This review explores the role of interstitial fluid motion and solute transport in porous bone under two different conditions: normogravity and microgravity.