Stability of gene expression in human T cells in different gravity environments is clustered in chromosomal region 11p15.4

NASA GeneLab derived microarray studies of Mus musculus and Homo sapiens organisms in altered gravitational conditions

One of the greatest challenges of humanity for deep space exploration is to fully understand how altered gravitational conditions affect human physiology. It is evident that the spaceflight environment causes multiple alterations to musculoskeletal, cardiovascular, immune and central nervous systems, to name a few known effects. To better characterize these biological effects, we compare gene expression datasets from microarray studies found in NASA GeneLab, part of the NASA Open Science Data Repository. In this review, we summarize these archived results for various tissues, emphasizing key genes which are highly reproducible in different mice or human experiments. Such exhaustive mining shows the potential of NASA Open Science data to identify and validate mechanisms taking place when mammalian organisms are exposed to microgravity or other spaceflight conditions. Our comparative meta-analysis findings highlight certain degrees of overlap and reproducibility in genes identified as differentially expressed within musculoskeletal tissues in each species across a variety of altered gravity conditions. However, the level of overlap between species was found to be significantly limited, partly attributed to the limited availability of human samples.

Increased H3K9me3 and F-Actin Reorganization in the Rapid Adaptive Response to Hypergravity in Human T Lymphocytes

Our study explored the impact of hypergravity on human T cells, which experience additional acceleration forces beyond Earth's gravity due to various factors, such as pulsatile blood flow, and technology, such as high-performance aircraft flights or spaceflights. We investigated the histone modifications Histone 3 lysine 4 and 9 trimethylation (H3K4me3 and H3K9me3, respectively), as well as the structural and cytoskeletal organization of Jurkat T cells in response to hypergravity. Histone modifications play a crucial role in gene regulation, chromatin organization and DNA repair. In response to hypergravity, we found only minimal changes of H3K4me3 and a rapid increase in H3K9me3, which was sustained for up to 15 min and then returned to control levels after 1 h. Furthermore, rapid changes in F-actin fluorescence were observed within seconds of hypergravity exposure, indicating filament depolymerization and cytoskeletal restructuring, which subsequently recovered after 1 h of hypergravity. Our study demonstrated the rapid, dynamic and adaptive cellular response to hypergravity, particularly in terms of histone modifications and cytoskeletal changes. These responses are likely necessary for maintaining genome stability and structural integrity under hypergravity conditions as they are constantly occurring in the human body during blood cell circulation.

Simulated Microgravity Exposure Induces Antioxidant Barrier Deregulation and Mitochondria Enlargement in TCam-2 Cell Spheroids

One of the hallmarks of microgravity-induced effects in several cellular models is represented by the alteration of oxidative balance with the consequent accumulation of reactive oxygen species (ROS). It is well known that male germ cells are sensitive to oxidative stress and to changes in gravitational force, even though published data on germ cell models are scarce. We previously studied the effects of simulated microgravity (s-microgravity) on a 2D cultured TCam-2 seminoma-derived cell line, considered the only human cell line available to study in vitro mitotically active human male germ cells. In this study, we used a corresponding TCam-2 3D cell culture model that mimics cell-cell contacts in organ tissue to test the possible effects induced by s-microgravity exposure. TCam-2 cell spheroids were cultured for 24 h under unitary gravity (Ctr) or s-microgravity conditions, the latter obtained using a random positioning machine (RPM). A significant increase in intracellular ROS and mitochondria superoxide anion levels was observed after RPM exposure. In line with these results, a trend of protein and lipid oxidation increase and increased pCAMKII expression levels were observed after RPM exposure. The ultrastructural analysis via transmission electron microscopy revealed that RPM-exposed mitochondria appeared enlarged and, even if seldom, disrupted. Notably, even the expression of the main enzymes involved in the redox homeostasis appears modulated by RPM exposure in a compensatory way, with GPX1, NCF1, and CYBB being downregulated, whereas NOX4 and HMOX1 are upregulated. Interestingly, HMOX1 is involved in the heme catabolism of mitochondria cytochromes, and therefore the positive modulation of this marker can be associated with the observed mitochondria alteration. Altogether, these data demonstrate TCam-2 spheroid sensitivity to acute s-microgravity exposure and indicate the capability of these cells to trigger compensatory mechanisms that allow them to overcome the exposure to altered gravitational force.

Transcriptional Response in Human Jurkat T Lymphocytes to a near Physiological Hypergravity Environment and to One Common in Routine Cell Culture Protocols

Cellular effects of hypergravity have been described in many studies. We investigated the transcriptional dynamics in Jurkat T cells between 20 s and 60 min of 9 g hypergravity and characterized a highly dynamic biphasic time course of gene expression response with a transition point between rapid adaptation and long-term response at approximately 7 min. Upregulated genes were shifted towards the center of the nuclei, whereby downregulated genes were shifted towards the periphery. Upregulated gene expression was mostly located on chromosomes 16-22. Protein-coding transcripts formed the majority with more than 90% of all differentially expressed genes and followed a continuous trend of downregulation, whereas retained introns demonstrated a biphasic time-course. The gene expression pattern of hypergravity response was not comparable with other stress factors such as oxidative stress, heat shock or inflammation. Furthermore, we tested a routine centrifugation protocol that is widely used to harvest cells for subsequent RNA analysis and detected a huge impact on the transcriptome compared to non-centrifuged samples, which did not return to baseline within 15 min. Thus, we recommend carefully studying the response of any cell types used for any experiments regarding the hypergravity time and levels applied during cell culture procedures and analysis.

Rapid Downregulation of H3K4me3 Binding to Immunoregulatory Genes in Altered Gravity in Primary Human M1 Macrophages

The sensitivity of human immune system cells to gravity changes has been investigated in numerous studies. Human macrophages mediate innate and thus rapid immune defense on the one hand and activate T- and B-cell-based adaptive immune response on the other hand. In this process they finally act as immunoeffector cells, and are essential for tissue regeneration and remodeling. Recently, we demonstrated in the human Jurkat T cell line that genes are differentially regulated in cluster structures under altered gravity. In order to study an in vivo near system of immunologically relevant human cells under physically real microgravity, we performed parabolic flight experiments with primary human M1 macrophages under highly standardized conditions and performed chromatin immunoprecipitation DNA sequencing (ChIP-Seq) for whole-genome epigenetic detection of the DNA-binding loci of the main transcription complex RNA polymerase II and the transcription-associated epigenetic chromatin modification H3K4me3. We identified an overall downregulation of H3K4me3 binding loci in altered gravity, which were unequally distributed inter- and intrachromosomally throughout the genome. Three-quarters of all affected loci were located on the p arm of the chromosomes chr5, chr6, chr9, and chr19. The genomic distribution of the downregulated H3K4me3 loci corresponds to a substantial extent to immunoregulatory genes. In microgravity, analysis of RNA polymerase II binding showed increased binding to multiple loci at coding sequences but decreased binding to central noncoding regions. Detection of altered DNA binding of RNA polymerase II provided direct evidence that gravity changes can lead to altered transcription. Based on this study, we hypothesize that the rapid transcriptional response to changing gravitational forces is specifically encoded in the epigenetic organization of chromatin.

Assoziation schneller Reaktionen der Genexpression mit Änderungen der 3D-Chromatinkonformation in veränderter Schwerkraft

Die molekularen Prinzipien bei der Transduktion von Schwerkraftänderungen in zelluläre Antwort- und Anpassungsprozesse sind bisher weitgehend unbekannt. Wir konnten in humanen Jurkat-T-Zellen zeigen, dass Gene bei veränderter Schwerkraft in Clusterstrukturen („gravity-responsive chromosomal regions“, GRCRs) differenziell reguliert werden. Durch Kombination mit Hochdurchsatz-Chromatin-Konformationsanalysen (Hi-C) konnte eine hochsignifikante Assoziation von GRCRs mit strukturellen 3D-Chromatinveränderungen identifiziert werden, die vor allem auf den kleinen Chromosomen (chr16–chr22) kolokalisieren. Wir fanden weiterhin Hinweise auf einen mechanistischen Zusammenhang zwischen Spleißprozessen und differenzieller Genexpression bei veränderter Schwerkraft. Somit haben wir erste Belege dafür gefunden, dass Änderungen der Schwerkraft in den Zellkern übertragen werden und dort 3D-Chromosomen-Konformationsänderungen hervorrufen, die mit einer schnellen Transkriptionsantwort verbunden sind. Wir vermuten, dass die schnelle genomische Antwort auf veränderte Gravitationskräfte in der Organisation des Chromatins spezifisch codiert ist.

Enhanced self-renewal of human pluripotent stem cells by simulated microgravity

A systematic study on the biological effects of simulated microgravity (sµg) on human pluripotent stem cells (hPSC) is still lacking. Here, we used a fast-rotating 2-D clinostat to investigate the sµg effect on proliferation, self-renewal, and cell cycle regulation of hPSCs. We observed significant upregulation of protein translation of pluripotent transcription factors in hPSC cultured in sµg compared to cells cultured in 1g conditions. In addition to a significant increase in expression of telomere elongation genes. Differentiation experiments showed that hPSC cultured in sµg condition were less susceptible to differentiation compared to cells in 1g conditions. These results suggest that sµg enhances hPSC self-renewal. Our study revealed that sµg enhanced the cell proliferation of hPSCs by regulating the expression of cell cycle-associated kinases. RNA-seq analysis indicated that in sµg condition the expression of differentiation and development pathways are downregulated, while multiple components of the ubiquitin proteasome system are upregulated, contributing to an enhanced self-renewal of hPSCs. These effects of sµg were not replicated in human fibroblasts. Taken together, our results highlight pathways and mechanisms in hPSCs vulnerable to microgravity that imposes significant impacts on human health and performance, physiology, and cellular and molecular processes.

Post-Transcriptional Dynamics is Involved in Rapid Adaptation to Hypergravity in Jurkat T Cells

The transcriptome of human immune cells rapidly reacts to altered gravity in a highly dynamic way. We could show in previous experiments that transcriptional patterns show profound adaption after seconds to minutes of altered gravity. To gain further insight into these transcriptional alteration and adaption dynamics, we conducted a highly standardized RNA-Seq experiment with human Jurkat T cells exposed to 9xg hypergravity for 3 and 15 min, respectively. We investigated the frequency with which individual exons were used during transcription and discovered that differential exon usage broadly appeared after 3 min and became less pronounced after 15 min. Additionally, we observed a shift in the transcript pool from coding towards non-coding transcripts. Thus, adaption of gravity-sensitive differentially expressed genes followed a dynamic transcriptional rebound effect. The general dynamics were compatible with previous studies on the transcriptional effects of short hypergravity on human immune cells and suggest that initial up-regulatory changes mostly result from increased elongation rates. The shift correlated with a general downregulation of the affected genes. All chromosome bands carried homogenous numbers of gravity-sensitive genes but showed a specific tendency towards up- or downregulation. Altered gravity affected transcriptional regulation throughout the entire genome, whereby the direction of differential expression was strongly dependent on the structural location in the genome. A correlation analysis with potential mediators of the early transcriptional response identified a link between initially upregulated genes with certain transcription factors. Based on these findings, we have been able to further develop our model of the transcriptional response to altered gravity.

Mechano-Immunomodulation in Space: Mechanisms Involving Microgravity-Induced Changes in T Cells

Of the most prevalent issues surrounding long-term spaceflight, the sustainability of human life and the maintenance of homeostasis in an extreme environment are of utmost concern. It has been observed that the human immune system is dysregulated in space as a result of gravitational unloading at the cellular level, leading to potential complications in astronaut health. A plethora of studies demonstrate intracellular changes that occur due to microgravity; however, these ultimately fall short of identifying the underlying mechanisms and dysfunctions that cause such changes. This comprehensive review covers the changes in human adaptive immunity due to microgravity. Specifically, there is a focus on uncovering the gravisensitive steps in T cell signaling pathways. Changes in gravitational force may lead to interrupted immune signaling cascades at specific junctions, particularly membrane and surface receptor-proximal molecules. Holistically studying the interplay of signaling with morphological changes in cytoskeleton and other cell components may yield answers to what in the T cell specifically experiences the consequences of microgravity. Fully understanding the nature of this problem is essential in order to develop proper countermeasures before long-term space flight is conducted.

Gravitational Force-Induced 3D Chromosomal Conformational Changes Are Associated with Rapid Transcriptional Response in Human T Cells

The mechanisms underlying gravity perception in mammalian cells are unknown. We have recently discovered that the transcriptome of cells in the immune system, which is the most affected system during a spaceflight, responds rapidly and broadly to altered gravity. To pinpoint potential underlying mechanisms, we compared gene expression and three-dimensional (3D) chromosomal conformational changes in human Jurkat T cells during the short-term gravitational changes in parabolic flight and suborbital ballistic rocket flight experiments. We found that differential gene expression in gravity-responsive chromosomal regions, but not differentially regulated single genes, are highly conserved between different real altered gravity comparisons. These coupled gene expression effects in chromosomal regions could be explained by underlying chromatin structures. Based on a high-throughput chromatin conformation capture (Hi-C) analysis in altered gravity, we found that small chromosomes (chr16–22, with the exception of chr18) showed increased intra- and interchromosomal interactions in altered gravity, whereby large chromosomes showed decreased interactions. Finally, we detected a nonrandom overlap between Hi-C-identified chromosomal interacting regions and gravity-responsive chromosomal regions (GRCRs). We therefore demonstrate the first evidence that gravitational force-induced 3D chromosomal conformational changes are associated with rapid transcriptional response in human T cells. We propose a general model of cellular sensitivity to gravitational forces, where gravitational forces acting on the cellular membrane are rapidly and mechanically transduced through the cytoskeleton into the nucleus, moving chromosome territories to new conformation states and their genes into more expressive or repressive environments, finally resulting in region-specific differential gene expression.

Rapid Transient Transcriptional Adaptation to Hypergravity in Jurkat T Cells Revealed by Comparative Analysis of Microarray and RNA-Seq Data

Cellular responses to micro- and hypergravity are rapid and complex and appear within the first few seconds of exposure. Transcriptomic analyses are a valuable tool to analyze these genome-wide cellular alterations. For a better understanding of the cellular dynamics upon altered gravity exposure, it is important to compare different time points. However, since most of the experiments are designed as endpoint measurements, the combination of cross-experiment meta-studies is inevitable. Microarray and RNA-Seq analyses are two of the main methods to study transcriptomics. In the field of altered gravity research, both methods are frequently used. However, the generation of these data sets is difficult and time-consuming and therefore the number of available data sets in this research field is limited. In this study, we investigated the comparability of microarray and RNA-Seq data and applied the results to a comparison of the transcriptomics dynamics between the hypergravity conditions during two real flight platforms and a centrifuge experiment to identify temporal adaptation processes. We performed a comparative study on an Affymetrix HTA2.0 microarray and a paired-end RNA-Seq data set originating from the same Jurkat T cell RNA samples from a short-term hypergravity experiment. The overall agreeability was high, with better sensitivity of the RNA-Seq analysis. The microarray data set showed weaknesses on the level of single upregulated genes, likely due to its normalization approach. On an aggregated level of biotypes, chromosomal distribution, and gene sets, both technologies performed equally well. The microarray showed better performance on the detection of altered gravity-related splicing events. We found that all initially altered transcripts fully adapted after 15 min to hypergravity and concluded that the altered gene expression response to hypergravity is transient and fully reversible. Based on the combined multiple-platform meta-analysis, we could demonstrate rapid transcriptional adaptation to hypergravity, the differential expression of the ATPase subunits ATP6V1A and ATP6V1D, and the cluster of differentiation (CD) molecules CD1E, CD2AP, CD46, CD47, CD53, CD69, CD96, CD164, and CD226 in hypergravity. We could experimentally demonstrate that it is possible to develop methodological evidence for the meta-analysis of individual data.

May the Force Be with You (Or Not): The Immune System under Microgravity

All terrestrial organisms have evolved and adapted to thrive under Earth's gravitational force. Due to the increase of crewed space flights in recent years, it is vital to understand how the lack of gravitational forces affects organisms. It is known that astronauts who have been exposed to microgravity suffer from an array of pathological conditions including an impaired immune system, which is one of the most negatively affected by microgravity. However, at the cellular level a gap in knowledge exists, limiting our ability to understand immune impairment in space. This review highlights the most significant work done over the past 10 years detailing the effects of microgravity on cellular aspects of the immune system.

Metabolic Dynamics in Short- and Long-Term Microgravity in Human Primary Macrophages

Microgravity acts on cellular systems on several levels. Cells of the immune system especially react rapidly to changes in gravity. In this study, we performed a correlative metabolomics analysis on short-term and long-term microgravity effects on primary human macrophages. We could detect an increased amino acid concentration after five minutes of altered gravity, that was inverted after 11 days of microgravity. The amino acids that reacted the most to changes in gravity were tightly clustered. The observed effects indicated protein degradation processes in microgravity. Further, glucogenic and ketogenic amino acids were further degraded to Glucose and Ketoleucine. The latter is robustly accumulated in short-term and long-term microgravity but not in hypergravity. We detected highly dynamic and also robust adaptative metabolic changes in altered gravity. Metabolomic studies could contribute significantly to the understanding of gravity-induced integrative effects in human cells.

Gravitational Influence on Human Living Systems and the Evolution of Species on Earth

Gravity constituted the only constant environmental parameter, during the evolutionary period of living matter on Earth. However, whether gravity has affected the evolution of species, and its impact is still ongoing. The topic has not been investigated in depth, as this would require frequent and long-term experimentations in space or an environment of altered gravity. In addition, each organism should be studied throughout numerous generations to determine the profound biological changes in evolution. Here, we review the significant abnormalities presented in the cardiovascular, immune, vestibular and musculoskeletal systems, due to altered gravity conditions. We also review the impact that gravity played in the anatomy of snakes and amphibians, during their evolution. Overall, it appears that gravity does not only curve the space–time continuum but the biological continuum, as well.

Feasibility, potency, and safety of growing human mesenchymal stem cells in space for clinical application

Growing stem cells on Earth is very challenging and limited to a few population doublings. The standard two-dimensional (2D) culture environment is an unnatural condition for cell growth. Therefore, culturing stem cells aboard the International Space Station (ISS) under a microgravity environment may provide a more natural three-dimensional environment for stem cell expansion and organ development. In this study, human-derived mesenchymal stem cells (MSCs) grown in space were evaluated to determine their potential use for future clinical applications on Earth and during long-term spaceflight. MSCs were flown in Plate Habitats for transportation to the ISS. The MSCs were imaged every 24-48 h and harvested at 7 and 14 days. Conditioned media samples were frozen at -80 °C and cells were either cryopreserved in 5% dimethyl sulfoxide, RNAprotect, or paraformaldehyde. After return to Earth, MSCs were characterized to establish their identity and cell cycle status. In addition, cell proliferation, differentiation, cytokines, and growth factors' secretion were assessed. To evaluate the risk of malignant transformation, the space-grown MSCs were subjected to chromosomal, DNA damage, and tumorigenicity assays. We found that microgravity had significant impact on the MSC capacity to secrete cytokines and growth factors. They appeared to be more potent in terms of immunosuppressive capacity compared to their identical ground control. Chromosomal, DNA damage, and tumorigenicity assays showed no evidence of malignant transformation. Therefore, it is feasible and potentially safe to grow MSCs aboard the ISS for potential future clinical applications.

Antioxidant Strategy to Prevent Simulated Microgravity-Induced Effects on Bone Osteoblasts

The effects induced by microgravity on human body functions have been widely described, in particular those on skeletal muscle and bone tissues. This study aims to implement information on the possible countermeasures necessary to neutralize the oxidative imbalance induced by microgravity on osteoblastic cells. Using the model of murine MC3T3-E1 osteoblast cells, cellular morphology, proliferation, and metabolism were investigated during exposure to simulated microgravity on a random positioning machine in the absence or presence of an antioxidant—the 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox). Our results confirm that simulated microgravity-induced morphological and metabolic alterations characterized by increased levels of reactive oxygen species and a slowdown of the proliferative rate. Interestingly, the use of Trolox inhibited the simulated microgravity-induced effects. Indeed, the antioxidant-neutralizing oxidants preserved cell cytoskeletal architecture and restored cell proliferation rate and metabolism. The use of appropriate antioxidant countermeasures could prevent the modifications and damage induced by microgravity on osteoblastic cells and consequently on bone homeostasis.

Development and functional analysis of an anticancer T-cell medicine with immune checkpoint inhibitory ability

Adoptive cell therapy using patients' own T-cells is expected to be an ideal cancer treatment strategy with excellent antitumor effects and low side effects. However, this therapy targeting solid tumors is unlikely to be effective because tumor tissues have an environment that suppresses T-cell function. In particular, interaction between programmed death-1 (PD-1) and its ligand (PD-L1) inhibits T-cell activation by which T-cells eliminate tumor cells. Here, we attempted to develop T-cells that can exert potent antitumor activity even in tumor tissues by genetically modifying them to express the anti-PD-L1 membrane-anchoring type single chain variable fragment (M-scFv) that can inhibit PD-L1/PD-1 interaction. Anti-PD-L1 M-scFv could be expressed on T-cells while maintaining PD-L1-binding ability. Although T-cell proliferation induced by CD3 stimulation was decreased depending on the PD-L1 stimulation intensity, M-scFv-expressing T-cells showed high proliferative activity even in the presence of PD-L1 by avoiding the PD-L1/PD-1-mediated suppression. Furthermore, M-scFv-expressing T-cells showed higher cytotoxic activity against PD-L1^high tumor cells than that of mock T-cells. The effect of PD-L1/PD-1 blockade was more pronounced when the therapeutic target was low-antigenic tumor cells with low major histocompatibility complex expression, presenting only the shared antigen. These results indicated that anti-PD-L1 M-scFv expression was functional in avoiding T-cell dysfunction by PD-L1/PD-1 interaction. Our concept of anti-PD-L1 M-scFv-expressing T-cells is thus expected to improve the efficacy of T-cell therapy and contribute to simplify the treatment system and reduce treatment costs compared with the combination therapy of T-cells and antibodies.

Changes in the Surface Expression of Intercellular Adhesion Molecule 3, the Induction of Apoptosis, and the Inhibition of Cell-Cycle Progression of Human Multidrug-Resistant Jurkat/A4 Cells Exposed to a Random Positioning Machine

Experiments from flight- and ground-based model systems suggest that unexpected alterations of the human lymphoblastoid cell line Jurkat, as well as effects on cell growth, metabolism, and apoptosis, can occur in altered gravity conditions. Using a desktop random positioning machine (RPM), we investigated the effects of simulated microgravity on Jurkat cells and their multidrug-resistant subline, Jurkat/A4 cells. The viability of Jurkat/A4 cells decreased after simulated microgravity in contrast with the Jurkat cells. At the same time, the viability between the experimental Jurkat cells and control Jurkat cells was not significantly different. Of note, Jurkat cells appeared as less susceptible to apoptosis than their multidrug-resistant clone Jurkat/A4 cells, whereas cell-cycle analysis showed that the percentage of Jurkat/A4 cells in the S-phase was increased after 72 and 96 h of RPM-simulated microgravity relative to their static counterparts. The differences in Jurkat cells at all phases between static and simulated microgravity were not significant. The surface expression of the intercellular adhesion molecule 3 (ICAM-3)-also known as cluster of differentiation (CD)50-protein was changed for Jurkat/A4 cells following exposure to the RPM. Changes in cell morphology were observed in the Jurkat/A4 cells after 96 h of RPM-simulated microgravity. Thus, we concluded that Jurkat/A4 cells are more sensitive to RPM-simulated microgravity as compared with the parental Jurkat cell line. We also suggest that intercellular adhesion molecule 3 may be an important adhesion molecule involved in the induction of leukocyte apoptosis. The Jurkat/A4 cells with an acquired multidrug resistance phenotype could be a useful model for studying the effects of simulated microgravity and testing anticancer drugs.

Rapid Cellular Perception of Gravitational Forces in Human Jurkat T Cells and Transduction into Gene Expression Regulation

Cellular processes are influenced in many ways by changes in gravitational force. In previous studies, we were able to demonstrate, in various cellular systems and research platforms that reactions and adaptation processes occur very rapidly after the onset of altered gravity. In this study we systematically compared differentially expressed gene transcript clusters (TCs) in human Jurkat T cells in microgravity provided by a suborbital ballistic rocket with vector-averaged gravity (vag) provided by a 2D clinostat. Additionally, we included 9× g centrifuge experiments and rigorous controls for excluding other factors of influence than gravity. We found that 11 TCs were significantly altered in 5 min of flight-induced and vector-averaged gravity. Among the annotated clusters were G3BP1, KPNB1, NUDT3, SFT2D2, and POMK. Our results revealed that less than 1% of all examined TCs show the same response in vag and flight-induced microgravity, while 38% of differentially regulated TCs identified during the hypergravity phase of the suborbital ballistic rocket flight could be verified with a 9× g ground centrifuge. In the 2D clinostat system, doing one full rotation per second, vector effects of the gravitational force are only nullified if the sensing mechanism requires 1 s or longer. Due to the fact that vag with an integration period of 1 s was not able to reproduce the results obtained in flight-induced microgravity, we conclude that the initial trigger of gene expression response to microgravity requires less than 1 s reaction time. Additionally, we discovered extensive gene expression differences caused by simple handling of the cell suspension in control experiments, which underlines the need for rigorous standardization regarding mechanical forces during cell culture experiments in general.

Real-Time 3D High-Resolution Microscopy of Human Cells on the International Space Station

Here we report the successful first operation of FLUMIAS-DEA, a miniaturized high-resolution 3D fluorescence microscope on the International Space Station (ISS) by imaging two scientific samples in a temperature-constant system, one sample with fixed cells and one sample with living human cells. The FLUMIAS-DEA microscope combines features of a high-resolution 3D fluorescence microscope based on structured illumination microscope (SIM) technology with hardware designs to meet the requirements of a space instrument. We successfully demonstrated that the FLUMIAS technology was able to acquire, transmit, and store high-resolution 3D fluorescence images from fixed and living cells, allowing quantitative and dynamic analysis of subcellular structures, e.g., the cytoskeleton. The capability of real-time analysis methods on ISS will dramatically extend our knowledge about the dynamics of cellular reactions and adaptations to the space environment, which is not only an option, but a requirement of evidence-based medical risk assessment, monitoring and countermeasure development for exploration class missions.

Physiological Responses of Jurkat Lymphocytes to Simulated Microgravity Conditions

The presence of microgravity conditions deeply affects the human body functions at the systemic, organ and cellular levels. This study aimed to investigate the effects induced by simulated-microgravity on non-stimulated Jurkat lymphocytes, an immune cell phenotype considered as a biosensor of the body responses, in order to depict at the cellular level the effects of such a peculiar condition. Jurkat cells were grown at 1 g or on random positioning machine simulating microgravity. On these cells we performed: morphological, cell cycle and proliferation analyses using cytofluorimetric and staining protocols—intracellular Ca²⁺, reactive oxygen species (ROS), mitochondria membrane potential and O₂⁻ measurements using fluorescent probes—aconitase and mitochondria activity, glucose and lactate content using colorimetric assays. After the first exposure days, the cells showed a more homogeneous roundish shape, an increased proliferation rate, metabolic and detoxifying activity resulted in decreased intracellular Ca²⁺ and ROS. In the late exposure time, the cells adapted to the new environmental condition. Our non-activated proliferating Jurkat cells, even if responsive to altered external forces, adapted to the new environmental condition showing a healthy status. In order to define the cellular mechanism(s) triggered by microgravity, developing standardized experimental approaches and controlled cell culture and simulator conditions is strongly recommended.

Expression of Hypoxia-Inducible Factor 1α (HIF-1α) and Genes of Related Pathways in Altered Gravity

Immune system deterioration in space represents a major risk, which has to be mitigated for exploration-class missions into the solar system. Altered gravitational forces have been shown to regulate adaptation processes in cells of the immune system, which are important for appropriate risk management, monitoring and development of countermeasures. T lymphocytes and cells of the monocyte-macrophage system are highly migratory cell types that frequently encounter a wide range of oxygen tensions in human tissues and in hypoxic areas, even under homeostatic conditions. Hypoxia-inducible factor 1 and 2 (HIF's) might have an important role in activation of T cells and cells of the monocyte-macrophages system. Thus, we investigated the regulation of HIF-dependent and, therefore, hypoxia-signaling systems in both cell types in altered gravity and performed transcript and protein analysis from parabolic flight and suborbital ballistic rocket experiments. We found that HIF-1α and HIF-1-dependent transcripts were differently regulated in altered gravity, whereas HIF-1α-dependent gene expression adapted after 5 min microgravity. Inter-platform comparisons identified PDK1 as highly responsive to gravitational changes in human U937 myelomonocytic cells and in Jurkat T cells. We suggest HIF-1 as a potential pharmacological target for counteracting immune system deterioration during space flight.

Transcriptional Homeostasis of Oxidative Stress-Related Pathways in Altered Gravity

Whereby several types of cultured cells are sensitive to gravity, the immune system belongs to the most affected systems during spaceflight. Since reactive oxygen species/reactive nitrogen species (ROS/RNS) are serving as signals of cellular homeostasis, particularly in the cells of the immune system, we investigated the immediate effect of altered gravity on the transcription of 86 genes involved in reactive oxygen species metabolism, antioxidative systems, and cellular response to oxidative stress, using parabolic flight and suborbital ballistic rocket experiments and microarray analysis. In human myelomonocytic U937 cells, we detected a rapid response of 19.8% of all of the investigated oxidative stress-related transcripts to 1.8 g of hypergravity and 1.1% to microgravity as early as after 20 s. Nearly all (97.2%) of the initially altered transcripts adapted after 75 s of hypergravity (max. 13.5 g), and 100% adapted after 5 min of microgravity. After the almost complete adaptation of initially altered transcripts, a significant second pool of differentially expressed transcripts appeared. In contrast, we detected nearly no response of oxidative stress-related transcripts in human Jurkat T cells to altered gravity. In conclusion, we assume a very well-regulated homeostasis and transcriptional stability of oxidative stress-related pathways in altered gravity in cells of the human immune system.

Rapid coupling between gravitational forces and the transcriptome in human myelomonocytic U937 cells

The gravitational force has been constant throughout Earth's evolutionary history. Since the cell nucleus is subjected to permanent forces induced by Earth's gravity, we addressed the question, if gene expression homeostasis is constantly shaped by the gravitational force on Earth. We therefore investigated the transcriptome in force-free conditions of microgravity, determined the time frame of initial gravitational force-transduction to the transcriptome and assessed the role of cation channels. We combined a parabolic flight experiment campaign with a suborbital ballistic rocket experiment employing the human myelomonocytic cell line U937 and analyzed the whole gene transcription by microarray, using rigorous controls for exclusion of effects not related to gravitational force and cross-validation through two fully independent research campaigns. Experiments with the wide range ion channel inhibitor SKF-96365 in combination with whole transcriptome analysis were conducted to study the functional role of ion channels in the transduction of gravitational forces at an integrative level. We detected profound alterations in the transcriptome already after 20 s of microgravity or hypergravity. In microgravity, 99.43% of all initially altered transcripts adapted after 5 min. In hypergravity, 98.93% of all initially altered transcripts adapted after 75 s. Only 2.4% of all microgravity-regulated transcripts were sensitive to the cation channel inhibitor SKF-96365. Inter-platform comparison of differentially regulated transcripts revealed 57 annotated gravity-sensitive transcripts. We assume that gravitational forces are rapidly and constantly transduced into the nucleus as omnipresent condition for nuclear and chromatin structure as well as homeostasis of gene expression.

Thyroid cancer cells in space during the TEXUS-53 sounding rocket mission - The THYROID Project

Human follicular thyroid cancer cells (FTC-133) were sent to space via a sounding rocket during the TEXUS-53 mission to determine the impact of short-term microgravity on these cells. To enable cell culture and fixation in real microgravity, an automated experiment container (EC) was constructed. In order to ensure safe cell culture, cell-chambers consisting of polycarbonate (PC) material were used. They were highly biocompatible as proved by measuring cell survival using Annexin V flow cytometry. In the follow-up experiment, FTC-133 cells were sent to space via a sounding rocket and were fixed before and after the microgravity (µg) phase with RNAlater. In addition, cells were tested for reactions on hypergravity (hyper-g) as much as 18 g to determine whether worst case acceleration during launch can have an influence on the cells. We investigated genes belonging to biological processes such as cytoskeleton, cell adhesion, tumor growth, angiogenesis and apoptosis. Pathway analyses revealed central functions of VEGFA and EGF. EGF upregulates aspartate beta-hydroxylase (ASPH) which is influencing CASP3. Hyper-g induced a significant up-regulation of TUBB1, VIM, RDX, CAV1, VEGFA and BCL2. FTC-133 cells grown in an automated EC exposed to µg revealed moderate gene expression changes indicating their survival in orbit.