Are Skeletal Muscle Changes during Prolonged Space Flights Similar to Those Experienced by Frail and Sarcopenic Older Adults?

An Update on Neuroaging on Earth and in Spaceflight

Over 400 articles on the pathophysiology of brain aging, neuroaging, and neurodegeneration were reviewed, with a focus on epigenetic mechanisms and numerous non-coding RNAs. In particular, this review the accent is on microRNAs, the discovery of whose pivotal role in gene regulation was recognized by the 2024 Nobel Prize in Physiology or Medicine. Aging is not a gradual process that can be easily modeled and described. Instead, multiple temporal processes occur during aging, and they can lead to mosaic changes that are not uniform in pace. The rate of change depends on a combination of external and internal factors and can be boosted in accelerated aging. The rate can decrease in decelerated aging due to individual structural and functional reserves created by cognitive, physical training, or pharmacological interventions. Neuroaging can be caused by genetic changes, epigenetic modifications, oxidative stress, inflammation, lifestyle, and environmental factors, which are especially noticeable in space environments where adaptive changes can trigger aging-like processes. Numerous candidate molecular biomarkers specific to neuroaging need to be validated to develop diagnostics and countermeasures.

Resistance exercise training improves disuse-induced skeletal muscle atrophy in humans: a meta-analysis of randomized controlled trials

BACKGROUND

This meta-analysis aimed to determine whether resistance exercise training (RET) can attenuate the loss of muscle volume and function in anti-gravitational muscles, especially quadriceps and calf muscles, during immobilization/disuse conditions.

METHODS

A comprehensive literature search was conducted to identify randomized controlled trials comparing RET vs. no exercise during immobilization/disuse. Searches were conducted in databases including Web of Science, PubMed, EBOSCO, and Cochrane Library, without imposing a time limit until 20 March, 2023. Studies reporting outcomes related to muscle volume, MVC, peak power, concentric peak force, eccentric peak force, isometric MVC torque of knee extension, isometric MVC torque of knee flexion were included. Data were pooled using random-effects models.

RESULTS

Eleven randomized controlled trials were finally included. RET elicited substantial benefits for preserving quadriceps muscle volume (n = 5, MD = 252.56, 95% CI = 151.92, 353.21, p < 0.001). RET demonstrated a statistically significant preventive effect on the reduction of MVC in both quadriceps (n = 4, MD = 338.59, 95% CI = 247.49, 429.69, p < 0.001) and calf muscles (n = 3, MD = 478.59, 95% CI = 160.42, 796.77, p < 0.01). Peak power of quadriceps muscles (n = 4, MD = 166.08, 95% CI = 28.44, 303.73, p < 0.05) and calf muscles (n = 2, MD = 176.58, 95% CI = 102.36, 250.79, p < 0.001) were elevated after RET intervention. RET significantly ameliorated the weakening of both concentric and eccentric peak force in quadriceps (concentric: n = 2, MD = 470.95, 95% CI = 355.45, 586.44, p < 0.001; eccentric: n = 1, MD = 351.51, 95% CI = 254.43, 448.58, p < 0.001) and calf muscles (concentric: n = 2, MD = 867.52, 95% CI = 548.18, 1186.86, p < 0.001; eccentric: n = 1, MD = 899.86, 95% CI = 558.17, 1241.55, p < 0.001). Additionally, the diminishing of isometric MVC torques of knee extension (n = 6, MD = 41.85, 95% CI = 20.93, 62.77, p < 0.001) and knee flexion (n = 4, MD = 13.20, 95% CI = 8.12, 18.77, p < 0.001) were enhanced significantly after RET intervention.

CONCLUSIONS

RET effectively minimized deterioration of muscle volume and muscle function during immobilization/disuse, particularly in anti-gravitational muscles. RET should be recommended to maintain muscle and neuromuscular health for spaceflight, bed rest, immobilization/disuse conditions. Further research is needed to explore the effects of RET in more diverse populations and under various disuse conditions. More high-quality research will be required to demonstrate the aforementioned benefits conclusively.

Microgravity Accelerates Skeletal Muscle Degeneration: Functional and Transcriptomic Insights from a Muscle Lab-on-Chip Model Onboard the ISS

Microgravity accelerates skeletal muscle degeneration, mimicking aging, yet its effects on human muscle cell function and signaling remain underexplored. Using a muscle lab-on-chip model onboard the International Space Station, we examined how microgravity and electrically stimulated contractions influence muscle biology and age-related muscle changes. Our 3D bioengineered muscle model, cultured for 21 days (12 days in microgravity), included myobundles from young, active and older, sedentary individuals, with and without electrically stimulated contraction. Real-time data collected within an autonomous Space Tango CubeLab™ showed reduced contraction magnitude in microgravity. Global transcriptomic analysis revealed increased gene expression and particularly mitochondrial-related gene expression in microgravity for the electrically stimulated younger myobundles, while the older myobundles were less responsive. Moreover, a comparative analysis using a skeletal muscle aging gene expression database revealed that certain age-induced genes showed changes in expression in myobundles from the younger cohort when exposed to microgravity, whereas these genes remained unchanged in myobundles from the older cohort. Younger, electrically stimulated myobundles in microgravity exhibited higher expression of 45 aging genes involved in key aging pathways related to inflammation and immune function, mitochondrial dysfunction, and cellular stress; and decreased expression of 41 aging genes associated with inflammation, and cell growth. This study highlights a unique age-related molecular signature in muscle cells exposed to microgravity and underscores electrical stimulation as a potential countermeasure. These insights advance understanding of skeletal muscle aging and microgravity-induced degeneration, informing strategies for mitigating age-related muscle atrophy in space and on Earth.

A second space age spanning omics, platforms and medicine across orbits

The recent acceleration of commercial, private and multi-national spaceflight has created an unprecedented level of activity in low Earth orbit, concomitant with the largest-ever number of crewed missions entering space and preparations for exploration-class (lasting longer than one year) missions. Such rapid advancement into space from many new companies, countries and space-related entities has enabled a 'second space age'. This era is also poised to leverage, for the first time, modern tools and methods of molecular biology and precision medicine, thus enabling precision aerospace medicine for the crews. The applications of these biomedical technologies and algorithms are diverse, and encompass multi-omic, single-cell and spatial biology tools to investigate human and microbial responses to spaceflight. Additionally, they extend to the development of new imaging techniques, real-time cognitive assessments, physiological monitoring and personalized risk profiles tailored for astronauts. Furthermore, these technologies enable advancements in pharmacogenomics, as well as the identification of novel spaceflight biomarkers and the development of corresponding countermeasures. In this Perspective, we highlight some of the recent biomedical research from the National Aeronautics and Space Administration, Japan Aerospace Exploration Agency, European Space Agency and other space agencies, and detail the entrance of the commercial spaceflight sector (including SpaceX, Blue Origin, Axiom and Sierra Space) into aerospace medicine and space biology, the first aerospace medicine biobank, and various upcoming missions that will utilize these tools to ensure a permanent human presence beyond low Earth orbit, venturing out to other planets and moons.

Satellite-Based On-Orbit Printing of 3D Tumor Models

Space three dimension (3D） bioprinting provides a precise and bionic tumor model for evaluating the compound effect of the space environment on tumors, thereby providing insight into the progress of the disease and potential treatments. However, space 3D bioprinting faces several challenges, including prelaunch uncertainty, possible liquid leakage, long-term culture in space, automatic equipment control, data acquisition, and transmission. Here, a novel satellite-based 3D bioprinting device with high structural strength, small volume, and low weight (<6 kg) is developed. A microgel-based biphasic thermosensitive bioink and suspension medium that supports the on-orbit printing and in situ culture of complex tumor models is developed. An intelligent control algorithm that enables the automatic control of 3D printing, autofocusing, fluorescence imaging, and data transfer back to the ground is developed. To the authors' knowledge, this is the first time that on-orbit printing of tumor models is achieved in space with stable morphology and moderate viability via a satellite. It is found that 3D tumor models are more sensitive to antitumor drugs in space than on Earth. This study opens up a new avenue for 3D bioprinting in space and offers new possibilities for future research in space life science and medicine.

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 [...].

Aging and putative frailty biomarkers are altered by spaceflight

Human space exploration poses inherent risks to astronauts' health, leading to molecular changes that can significantly impact their well-being. These alterations encompass genomic instability, mitochondrial dysfunction, increased inflammation, homeostatic dysregulation, and various epigenomic changes. Remarkably, these changes bear similarities to those observed during the aging process on Earth. However, our understanding of the connection between these molecular shifts and disease development in space remains limited. Frailty syndrome, a clinical syndrome associated with biological aging, has not been comprehensively investigated during spaceflight. To bridge this knowledge gap, we leveraged murine data obtained from NASA's GeneLab, along with astronaut data gathered from the JAXA and Inspiration4 missions. Our objective was to assess the presence of biological markers and pathways related to frailty, aging, and sarcopenia within the spaceflight context. Through our analysis, we identified notable changes in gene expression patterns that may be indicative of the development of a frailty-like condition during space missions. These findings suggest that the parallels between spaceflight and the aging process may extend to encompass frailty as well. Consequently, further investigations exploring the utility of a frailty index in monitoring astronaut health appear to be warranted.

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.

Circadian regulation in aging: Implications for spaceflight and life on earth

Alterations in the circadian system are characteristic of aging on Earth. With the decline in physiological processes due to aging, several health concerns including vision loss, cardiovascular disorders, cognitive impairments, and muscle mass loss arise in elderly populations. Similar health risks are reported as "red flag" risks among astronauts during and after a long-term Space exploration journey. However, little is known about the common molecular alterations underlying terrestrial aging and space-related aging in astronauts, and controversial conclusions have been recently reported. In light of the regulatory role of the circadian clock in the maintenance of human health, we review here the overlapping role of the circadian clock both on aging on Earth and spaceflight with a focus on the four most affected systems: visual, cardiovascular, central nervous, and musculoskeletal systems. In this review, we briefly introduce the regulatory role of the circadian clock in specific cellular processes followed by alterations in those processes due to aging. We next summarize the known molecular alterations associated with spaceflight, highlighting involved clock-regulated genes in space flown Drosophila, nematodes, small mammals, and astronauts. Finally, we discuss common genes that are altered in terms of their expression due to aging on Earth and spaceflight. Altogether, the data elaborated in this review strengthen our hypothesis regarding the timely need to include circadian dysregulation as an emerging hallmark of aging on Earth and beyond.

Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles

The progressive loss of skeletal muscle mass and concomitant reduction in contractile strength plays a central role in frailty syndrome. Age-related neuronal impairments are closely associated with sarcopenia in the elderly, which is characterized by severe muscular atrophy that can considerably lessen the overall quality of life at old age. Mass-spectrometry-based proteomic surveys of senescent human skeletal muscles, as well as animal models of sarcopenia, have decisively improved our understanding of the molecular and cellular consequences of muscular atrophy and associated fiber-type shifting during aging. This review outlines the mass spectrometric identification of proteome-wide changes in atrophying skeletal muscles, with a focus on contractile proteins as potential markers of changes in fiber-type distribution patterns. The observed trend of fast-to-slow transitions in individual human skeletal muscles during the aging process is most likely linked to a preferential susceptibility of fast-twitching muscle fibers to muscular atrophy. Studies with senescent animal models, including mostly aged rodent skeletal muscles, have confirmed fiber-type shifting. The proteomic analysis of fast versus slow isoforms of key contractile proteins, such as myosin heavy chains, myosin light chains, actins, troponins and tropomyosins, suggests them as suitable bioanalytical tools of fiber-type transitions during aging.