Leveraging Spaceflight to Advance Cardiovascular Research on Earth

The Detrimental Effects of Bedrest: Premature Cardiovascular Aging and Dysfunction

Bedrest as an experimental paradigm or as an in-patient stay for medical reasons has negative consequences for cardiovascular health. The effects of severe inactivity parallel many of the changes experienced with natural aging but over a much shorter duration. Cardiac function is reduced, arteries stiffen, neural reflex responses are impaired, and metabolic and oxidative stress responses impose burden on the heart and vascular systems. The effect of these changes is revealed in studies of integrative function. Aerobic fitness progressively deteriorates with bedrest and tolerance of upright posture is rapidly impaired. In this review we consider the similarities of aging and bedrest-induced cardiovascular deconditioning. We concur with many recent clinical recommendations that early and regular mobility with upright posture will reduce likelihood of hospital-associated disability related to bedrest.

Long-term simulated microgravity fosters carotid aging-like changes via Piezo1

AIMS

Elucidating the impacts of long-term spaceflight on cardiovascular health is urgently needed in face of the rapid development of human space exploration. Recent reports including the NASA Twins Study on vascular deconditioning and aging of astronauts in spaceflight are controversial. The aims of this study were to elucidate whether long-term microgravity promotes vascular aging and the underlying mechanisms.

METHODS AND RESULTS

Hindlimb unloading (HU) by tail suspension was used to simulate microgravity in rats and mice. The dynamic changes of carotid stiffness in rats during 8 weeks of HU were determined. Simulated microgravity led to carotid artery aging-like changes as evidenced by increased stiffness, thickness, fibrosis, and elevated senescence biomarkers in the HU rats. Specific deletion of the mechanotransducer Piezo1 in vascular smooth muscles significantly blunted these aging-like changes in mice. Mechanistically, mechanical stretch-induced activation of Piezo1 elevated microRNA-582-5p in vascular smooth muscle cells, with resultant enhanced synthetic cell phenotype and increased collagen deposition via PTEN/PI3K/Akt signalling. Importantly, inhibition of miRNA-582-5p alleviated carotid fibrosis and stiffness not only in HU rats but also in aged rats.

CONCLUSIONS

Long-term simulated microgravity induces carotid aging-like changes via the mechanotransducer Piezo1-initiated and miRNA-mediated mechanism.

Thiamine-modified metabolic reprogramming of human pluripotent stem cell-derived cardiomyocyte under space microgravity

During spaceflight, the cardiovascular system undergoes remarkable adaptation to microgravity and faces the risk of cardiac remodeling. Therefore, the effects and mechanisms of microgravity on cardiac morphology, physiology, metabolism, and cellular biology need to be further investigated. Since China started constructing the China Space Station (CSS) in 2021, we have taken advantage of the Shenzhou-13 capsule to send human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) to the Tianhe core module of the CSS. In this study, hPSC-CMs subjected to space microgravity showed decreased beating rate and abnormal intracellular calcium cycling. Metabolomic and transcriptomic analyses revealed a battery of metabolic remodeling of hPSC-CMs in spaceflight, especially thiamine metabolism. The microgravity condition blocked the thiamine intake in hPSC-CMs. The decline of thiamine utilization under microgravity or by its antagonistic analog amprolium affected the process of the tricarboxylic acid cycle. It decreased ATP production, which led to cytoskeletal remodeling and calcium homeostasis imbalance in hPSC-CMs. More importantly, in vitro and in vivo studies suggest that thiamine supplementation could reverse the adaptive changes induced by simulated microgravity. This study represents the first astrobiological study on the China Space Station and lays a solid foundation for further aerospace biomedical research. These data indicate that intervention of thiamine-modified metabolic reprogramming in human cardiomyocytes during spaceflight might be a feasible countermeasure against microgravity.

Simulated microgravity improves maturation of cardiomyocytes derived from human induced pluripotent stem cells

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) possess tremendous potential for basic research and translational application. However, these cells structurally and functionally resemble fetal cardiomyocytes, which is a major limitation of these cells. Microgravity can significantly alter cell behavior and function. Here we investigated the effect of simulated microgravity on hiPSC-CM maturation. Following culture under simulated microgravity in a random positioning machine for 7 days, 3D hiPSC-CMs had increased mitochondrial content as detected by a mitochondrial protein and mitochondrial DNA to nuclear DNA ratio. The cells also had increased mitochondrial membrane potential. Consistently, simulated microgravity increased mitochondrial respiration in 3D hiPSC-CMs, as indicated by higher levels of maximal respiration and ATP content, suggesting improved metabolic maturation in simulated microgravity cultures compared with cultures under normal gravity. Cells from simulated microgravity cultures also had improved Ca2+ transient parameters, a functional characteristic of more mature cardiomyocytes. In addition, these cells had improved structural properties associated with more mature cardiomyocytes, including increased sarcomere length, z-disc length, nuclear diameter, and nuclear eccentricity. These findings indicate that microgravity enhances the maturation of hiPSC-CMs at the structural, metabolic, and functional levels.

The Effects of Simulated and Real Microgravity on Vascular Smooth Muscle Cells

As considerations are being made for the limitations and safety of long-term human spaceflight, the vasculature is important given its connection to and impact on numerous organ systems. As a major constituent of blood vessels, vascular smooth muscle cells are of interest due to their influence over vascular tone and function. Additionally, vascular smooth muscle cells are responsive to pressure and flow changes. Therefore, alterations in these parameters under conditions of microgravity can be functionally disruptive. As such, here we review and discuss the existing literature that assesses the effects of microgravity, both actual and simulated, on smooth muscle cells. This includes the various methods for achieving or simulating microgravity, the animal models or cells used, and the various durations of microgravity assessed. We also discuss the various reported findings in the field, which include changes to cell proliferation, gene expression and phenotypic shifts, and renin-angiotensin-aldosterone system (RAAS), nitric oxide synthase (NOS), and Ca2+ signaling. Additionally, we briefly summarize the literature on smooth muscle tissue engineering in microgravity as well as considerations of radiation as another key component of spaceflight to contextualize spaceflight experiments, which by their nature include radiation exposure. Finally, we provide general recommendations based on the existing literature's focus and limitations.

Simulated spaceflight-induced cardiac remodeling is modulated by gut microbial-derived trimethylamine N-oxide

Spaceflight is physically demanding and can negatively affect astronauts' health. It has been shown that the human gut microbiota and cardiac function are affected by spaceflight and simulated spaceflight. This study investigated the effects of the gut microbiota on simulated spaceflight-induced cardiac remodeling using 10° of head-down bed rest (HDBR) in rhesus macaques and 30° of hindlimb unloading (HU) in mice. The gut microbiota, fecal metabolites, and cardiac remodeling were markedly affected by HDBR in macaques and HU in mice, cardiac remodeling in control mice was affected by the gut microbiota of HU mice and that of HU mice was protected by the gut microbiota of control mice, and there was a correlation between cardiac remodeling and the gut microbial-derived metabolite trimethylamine N-oxide. These findings suggest that spaceflight can affect cardiac remodeling by modulating the gut microbiota and fecal metabolites.

Space microgravity increases expression of genes associated with proliferation and differentiation in human cardiac spheres

Efficient generation of cardiomyocytes from human-induced pluripotent stem cells (hiPSCs) is important for their application in basic and translational studies. Space microgravity can significantly change cell activities and function. Previously, we reported upregulation of genes associated with cardiac proliferation in cardiac progenitors derived from hiPSCs that were exposed to space microgravity for 3 days. Here we investigated the effect of long-term exposure of hiPSC-cardiac progenitors to space microgravity on global gene expression. Cryopreserved 3D hiPSC-cardiac progenitors were sent to the International Space Station (ISS) and cultured for 3 weeks under ISS microgravity and ISS 1 G conditions. RNA-sequencing analyses revealed upregulation of genes associated with cardiac differentiation, proliferation, and cardiac structure/function and downregulation of genes associated with extracellular matrix regulation in the ISS microgravity cultures compared with the ISS 1 G cultures. Gene ontology analysis and Kyoto Encyclopedia of Genes and Genomes mapping identified the upregulation of biological processes, molecular function, cellular components, and pathways associated with cell cycle, cardiac differentiation, and cardiac function. Taking together, these results suggest that space microgravity has a beneficial effect on the differentiation and growth of cardiac progenitors.

Public-private partnerships in fostering outer space innovations

As public and private institutions recognize the role of space exploration as a catalyst for economic growth, various areas of innovation are expected to emerge as drivers of the space economy. These include space transportation, in-space manufacturing, bioproduction, in-space agriculture, nuclear launch, and propulsion systems, as well as satellite services and their maintenance. However, the current nature of space as an open-access resource and global commons presents a systemic risk for exuberant competition for space goods and services, which may result in a "tragedy of the commons" dilemma. In the race among countries to capture the value of space exploration, NASA, American research universities, and private companies can avoid any coordination failures by collaborating in a public-private research and development partnership (PPRDP) structure. We present such a structure founded upon the principles of polycentric autonomous governance, which incorporate a decentralized autonomous organization framework and specialized research clusters. By advancing an alignment of incentives among the specified participatory members, PPRDPs can play a pivotal role in stimulating open-source research by creating positive knowledge spillover effects and agglomeration externalities as well as embracing the nonlinear decomposition paradigm that may blur the distinction between basic and applied research.

Impact of daily artificial gravity on autonomic cardiovascular control following 60-day head-down tilt bed rest

Impaired cardiovascular autonomic control following space flight or immobilization may limit the ability to cope with additional hemodynamic stimuli. Head-down tilt bedrest is an established terrestrial analog for space flight and offers the opportunity to test potential countermeasures for autonomic cardiovascular deconditioning. Previous studies revealed a possible benefit of daily artificial gravity on cardiovascular autonomic control following head-down tilt bedrest, but there is a need for efficiency in a long-term study before an artificial gravity facility would be brought to space. We hypothesized that artificial gravity through short-arm centrifugation attenuates functional adaptions of autonomic function during head-down tilt bed rest. 24 healthy persons (8 women, 33.4 ± 9.3 years, 24.3 ± 2.1 kg/m2) participated in the 60-day head-down tilt bed rest (AGBRESA) study. They were assigned to three groups, 30 min/day continuous, or 6(5 min intermittent short-arm centrifugation, or a control group. We assessed autonomic cardiovascular control in the supine position and in 5 minutes 80° head-up tilt position before and immediately after bed rest. We computed heart rate variability (HRV) in the time (rmssd) and frequency domain, blood pressure variability, and baroreflex sensitivity (BRS). RR interval corrected rmssd was reduced supine (p = 0.0358) and during HUT (p = 0.0161). Heart rate variability in the high-frequency band (hf-RRI; p = 0.0004) and BRS (p < 0.0001) decreased, whereas blood pressure variability in the low-frequency band (lf-SBP, p = 0.0008) increased following bedrest in all groups. We did not detect significant interactions between bedrest and interventions. We conclude that up to daily 30 min of artificial gravity on a short-arm centrifuge with 1Gz at the center of mass do not suffice to prevent changes in autonomic cardiovascular control following 60-day of 6° head-down tilt bed rest. Clinical Trial Registration: https://drks.de/search/en/trial/DRKS00015677, identifier, DRKS00015677.

Discovery of Salidroside as a Novel Non-Coding RNA Modulator to Delay Cellular Senescence and Promote BK-Dependent Apoptosis in Cerebrovascular Smooth Muscle Cells of Simulated Microgravity Rats

Cardiovascular aging has been reported to accelerate in spaceflights, which is a great potential risk to astronauts' health and performance. However, current exercise routines are not sufficient to reverse the adverse effects of microgravity exposure. Recently, salidroside (SAL), a valuable medicinal herb, has been demonstrated to display an important role for prevention and treatment in cardiovascular and other diseases. In the present work, Sprague-Dawley rats with four-week tail-suspension hindlimb-unloading were used to simulate microgravity effects on the cardiovascular system. We found that intragastrical administration of SAL not only significantly decreased the expressions of senescence biomarkers, such as P65 and P16, but also obviously increased the expressions of BK-dependent apoptotic genes, including the large-conductance calcium-activated K+ channel (BK), Bax, Bcl-2, and cleaved caspase-3, in vascular smooth muscle cells (VSMCs) in vivo and in vitro. In addition, relative non-coding RNAs were screened, and a luciferase assay identified that SAL increased apoptosis by activating LncRNA-FLORPAR, inhibiting miR-193, and then triggering the activity of the BK-α subunit. Our work indicated that SAL is a novel non-coding RNA modulator for regulating the LncRNA-FLORPAR sponging miR-193 pathway, which significantly promoted BK-dependent apoptosis and delayed cerebrovascular aging-like remodeling during simulated microgravity exposure. Our findings may provide a new approach to prevent cardiovascular aging in future spaceflights.

Methods for assessing change in brain plasticity at night and psychological resilience during daytime between repeated long-duration space missions

This study was designed to examine the feasibility of analyzing heart rate variability (HRV) data from repeat-flier astronauts at matching days on two separate missions to assess any effect of repeated missions on brain plasticity and psychological resilience, as conjectured by Demertzi. As an example, on the second mission of a healthy astronaut studied about 20 days after launch, sleep duration lengthened, sleep quality improved, and spectral power (ms²) co-varying with activity of the salience network (SN) increased at night. HF-component (0.15-0.50 Hz) increased by 61.55%, and HF-band (0.30-0.40 Hz) by 92.60%. Spectral power of HRV indices during daytime, which correlate negatively with psychological resilience, decreased, HF-component by 22.18% and HF-band by 37.26%. LF-component and LF-band, reflecting activity of the default mode network, did not change significantly. During the second mission, 24-h acrophases of HRV endpoints did not change but the 12-h acrophase of TF-HRV did (P < 0.0001), perhaps consolidating the circadian system to help adapt to space by taking advantage of brain plasticity at night and psychological resilience during daytime. While this N-of-1 study prevents drawing definitive conclusions, the methodology used herein to monitor markers of brain plasticity could pave the way for further studies that could add to the present results.

The Characteristic Response of the Human Leukocyte Transcriptome to 60 Days of Bed Rest and to Reambulation

INTRODUCTION

We sought to isolate the microgravity effect of spaceflight from other space stressors by characterizing the leukocytes' transcriptome of participants to a 60-d bed rest study; an Earth model of microgravity.

METHODS

Twenty healthy men received a nutritional supplement or not and 10 blood samples were collected throughout three study phases: baseline data collection (BDC) (BDC-12, BDC-11), head-down tilt (HDT) bed rest (HDT1, HDT2, HDT30, HDT60), and reambulation (R1, R2, R12, R30). We measured gene expression through RNA sequencing of leukocytes, applied generalized linear models to assess differential expression followed by enrichment analysis to identify temporal changes (model 1) and to measure the impact of a nutritional supplement (model 2).

RESULTS

Baseline transcriptomes included 14,624 protein-coding transcripts and showed both high intraindividual correlations (mean Kendall coefficient, 0.91 ± 0.04) and interindividual homogeneity (0.89 ± 0.03). We identified 2415 differentially expressed protein-coding transcripts grouping into six clusters (C1-C6). At phase transitions, clusters showed either a decrease-then-increase (C3 and C5) or an increase-then-decrease (C1, C2, C6) pattern. All six clusters converged toward average expression at HDT30 and HDT60. Gene ontology terms at baseline related to immune functions while in bed rest and reambulation related to sequestration of ions, immune response, cellular stress, and mineralization. The nutritional intervention had no effect.

CONCLUSIONS

The temporal profiles of leukocytes' transcriptomes emphasized the dynamic nature of gene expression occurring during and after bed rest. Enriched biological processes among the differentially expressed genes included immune related and unrelated responses. The convergence toward no differential expression at days 30 and 60 of bed rest suggests a hypometabolic state. Current findings can guide future work on the complex responses and adaptation mechanisms to microgravity.

Transcriptomic Effects on the Mouse Heart Following 30 Days on the International Space Station

Efforts to understand the impact of spaceflight on the human body stem from growing interest in long-term space travel. Multiple organ systems are affected by microgravity and radiation, including the cardiovascular system. Previous transcriptomic studies have sought to reveal the changes in gene expression after spaceflight. However, little is known about the impact of long-term spaceflight on the mouse heart in vivo. This study focuses on the transcriptomic changes in the hearts of female C57BL/6J mice flown on the International Space Station (ISS) for 30 days. RNA was isolated from the hearts of three flight and three comparable ground control mice and RNA sequencing was performed. Our analyses showed that 1147 transcripts were significantly regulated after spaceflight. The MAPK, PI3K-Akt, and GPCR signaling pathways were predicted to be activated. Transcripts related to cytoskeleton breakdown and organization were upregulated, but no significant change in the expression of extracellular matrix (ECM) components or oxidative stress pathway-associated transcripts occurred. Our results indicate an absence of cellular senescence, and a significant upregulation of transcripts associated with the cell cycle. Transcripts related to cellular maintenance and survival were most affected by spaceflight, suggesting that cardiovascular transcriptome initiates an adaptive response to long-term spaceflight.

Effects of exercise countermeasures on multisystem function in long duration spaceflight astronauts

Exercise training is a key countermeasure used to offset spaceflight-induced multisystem deconditioning. Here, we evaluated the effects of exercise countermeasures on multisystem function in a large cohort (N = 46) of astronauts on long-duration spaceflight missions. We found that during 178 ± 48 d of spaceflight, ~600 min/wk of aerobic and resistance exercise did not fully protect against multisystem deconditioning. However, substantial inter-individual heterogeneity in multisystem response was apparent with changes from pre to postflight ranging from -30% to +5%. We estimated that up to 17% of astronauts would experience performance-limiting deconditioning if current exercise countermeasures were used on future spaceflight missions. These findings support the need for refinement of current countermeasures, adjunct interventions, or enhanced requirements for preflight physiologic and functional capacity for the protection of astronaut health and performance during exploration missions to the moon and beyond.

Cardiac function, structural, and electrical remodeling by microgravity exposure

Space medicine is key to the human exploration of outer space and pushes the boundaries of science, technology, and medicine. Because of harsh environmental conditions related to microgravity and other factors and hazards in outer space, astronauts and spaceflight participants face unique health and medical challenges, including those related to the heart. In this review, we summarize the literature regarding the effects of spaceflight on cardiac structure and function. We also provide an in-depth review of the literature regarding the effects of microgravity on cardiac calcium handling. Our review can inform future mechanistic and therapeutic studies and is applicable to other physiological states similar to microgravity such as prolonged horizontal bed rest and immobilization.