Induction of three-dimensional assembly and increase in apoptosis of human endothelial cells by simulated microgravity: impact of vascular endothelial growth factor

Endothelial cells play a crucial role in the pathogenesis of many diseases and are highly sensitive to low gravity conditions. Using a three-dimensional random positioning machine (clinostat) we investigated effects of simulated weightlessness on the human EA.hy926 cell line (4, 12, 24, 48 and 72 h) and addressed the impact of exposure to VEGF (10 ng/ml). Simulated microgravity resulted in an increase in extracellular matrix proteins (ECMP) and altered cytoskeletal components such as microtubules (alpha-tubulin) and intermediate filaments (cytokeratin). Within the initial 4 h, both simulated microgravity and VEGF, alone, enhanced the expression of ECMP (collagen type I, fibronectin, osteopontin, laminin) and flk-1 protein. Synergistic effects between microgravity and VEGF were not seen. After 12 h, microgravity further enhanced all proteins mentioned above. Moreover, clinorotated endothelial cells showed morphological and biochemical signs of apoptosis after 4 h, which were further increased after 72 h. VEGF significantly attenuated apoptosis as demonstrated by DAPI staining, TUNEL flow cytometry and electron microscopy. Caspase-3, Bax, Fas, and 85-kDa apoptosis-related cleavage fragments were clearly reduced by VEGF. After 72 h, most surviving endothelial cells had assembled to three-dimensional tubular structures. Simulated weightlessness induced apoptosis and increased the amount of ECMP. VEGF develops a cell-protective influence on endothelial cells exposed to simulated microgravity.

Key gravity‐sensitive signaling pathways drive T‐cell activation

Returning astronauts have experienced altered immune function and increased vulnerability to infection during spaceflights dating back to Apollo and Skylab. Lack of immune response in microgravity occurs at the cellular level. We analyzed differential gene expression to find gravity-dependent genes and pathways. We found inhibited induction of 91 genes in the simulated freefall environment of the random positioning machine. Altered induction of 10 genes regulated by key signaling pathways was verified using real-time RT-PCR. We discovered that impaired induction of early genes regulated primarily by transcription factors NF-kappaB, CREB, ELK, AP-1, and STAT after crosslinking the T-cell receptor contributes to T-cell dysfunction in altered gravity environments. We have previously shown that PKA and PKC are key early regulators in T-cell activation. Since the majority of the genes were regulated by NF-kappaB, CREB, and AP-1, we studied the pathways that regulated these transcription factors. We found that the PKA pathway was down-regulated in vg. In contrast, PI3-K, PKC, and its upstream regulator pLAT were not significantly down-regulated by vectorless gravity. Since NF-kappaB, AP-1, and CREB are all regulated by PKA and are transcription factors predicted by microarray analysis to be involved in the altered gene expression in vectorless gravity, the data suggest that PKA is a key player in the loss of T-cell activation in altered gravity.

Modeled microgravity affects motility and cytoskeletal structures

The hypothesis to be tested is that reduced cell-cell interactions between T cells and monocytes are one of the reasons for the observed depression of the "in vitro" activation of human lymphocytes in microgravity. Locomotion is essential for cell-cell contacts. Lymphocytes in suspension are highly motile in microgravity, whereas no data are available so far on the motility of adherent monocytes. It can be argued that an impaired locomotion of monocytes and cytoskeletal changes, both linked to cell contacts, could be responsible for their reduced interaction with T lymphocytes. This study is aimed at revealing how locomotion as well as cytoskeletal structures of adherent monocytes are modified under modeled microgravity conditions using the Random Positioning Machine (RPM, Dutch-Space) as earth based model of spaceflight.

The effect of space flight on human cellular immunity

T-lymphocyte responsiveness to mitogens is depressed by an average of 56% in humans (129 subjects) tested during and after space flight. Although there is not yet conclusive evidence of a clinical significance of the test, it is clear that factors of space flight like stress, closed environment and cosmic radiation may affect immune responsiveness. The data obtained from space crews may be compared to the depression seen in subjects undergoing heavy physical stress of head down tilt bedrest. Recently, delayed hypersensitivity [correction of hypersensivity] response was tested on crews of the US space shuttle and of the orbital station MIR by means of a commercially available "skin test". Again, the response was lower in 14 of the 15 subjects tested. In two cases, a strong in flight depression could be related to heavy physical and psychological stress experienced in flight. The data available today are not sufficient to draw conclusions on the hazard of infectious diseases during and after space flight. Although the changes observed never harmed the health of astronauts, immunological changes must be seriously investigated and understood in view of long-duration flights on space stations in an Earth orbit and to other planets like Mars and the Moon.

Effect of gravity on lymphocyte proliferation

Reports on postflight examination of lymphocytes from crew members of soviet and american spaceships show a depression of reactivity towards mitogens in vitro. The purpose of this communication is to present experimental evidence that gravity can interfere with lymphocyte activation. Lymphocytes were incubated in the presence of concanavalin A in a centrifuge at 2 and 4 g for four days. This environment causes a significant acceleration of the response to the mitogen. In addition, remarkable differences in the ultrastructure of cells grown at 1 g and 4 g are observed by electron microscopy. This investigation is related to the experiment "Effect of weightlessness on lymphocyte proliferation" experiment which will be performed during the first Spacelab mission.

Signal transduction in T lymphocites under simulated microgravity conditions: involvement of PKC isoforms

Previous data obtained from experiments either in space or in clinostats have shown that: a) human T lymphocytes activation is strongly inhibited; b) the distribution of protein kinase C (PKC) in human leukocytes is altered; c) expression of IL-2 and IL-2-R-alpha is altered. In this study we focus our attention on different isoforms of PKC to determine whether microgravity directly affects the activity and subcellular distribution of PKC. This work was carried out with Con A and anti-CD 28 activated human T cells in simulated microgravity conditions in the Random Positioning Machine (RPM). The cellular fractions (nuclear, cytosolic and membrane) extracted were subjected to Western blotting and RT-PCR analysis.

Preliminary study of gene expression levels in human T-cells exposed to cosmic radiations

Several experiments demonstrated the influence of microgravity on mitogenic activation of T cells at molecular level. To discriminate between effects of microgravity and cosmic radiations, in this work we studied the effects of high cosmic radiations on the genetic expression in human T cells boarded in a stratospheric balloon (BIRBA-1 mission, 22 hours of flight). The genetic expression was analyzed by the cDNA microarray hybridization technology, which allows the comparative and simultaneous estimate of hundreds of mRNAs Activated cells react to the ionizing stress by activating genes involved in cell cycle check-point, oxidative stress response, heat shock proteins production or by repressing genes involved in antigen recognition.

Gravitational unloading induces osteoclast-like differentiation of FLG 29.1 cells

FLG 29.1 cells, cultured at 1xg, are able to switch on a differentiating process only when they are suitably induced by chemical factors. On the contrary, when FLG 29.1 cells are cultured in conditions of gravitational unloading, simulated by a Random Positioning Machine, the switching on of the differentiation process occurs in the absence of any added differentiating agent or any stimulating factor. The phenotypic characterization of the cells and quantitative measures of their bone resorption activity are consistent with a differentiation process through the osteoclastic pathway.

Bioprocessing in space: human cells attach to beads in microgravity

Attachment to a substrate and survival of human embryonic kidney (HEK) cells have been tested in an incubator installed in the flight-deck of the Space Shuttle 'Challenger' during its eighth mission. HEK cells are producing the enzyme urokinase and are presently investigated as candidates for electrophoretic separation in an apparatus developed and manufactured by McDonnell Douglas. Attachment of HEK cells to a substrate is mandatory for survival and production of urokinase after electrophoretic separation. Analysis of the samples shows that cells adhere, spread and survive in microgravity (< 10(-3) x g) conditions as well as the ground controls at 1 x g. This result represents an important step towards further bioprocessing in space.

Research on Biolab, a multi-user facility for APM

A study carried out by a team of seven scientists appointed by ESA resulted in the design of a biological laboratory "Biolab" for Columbus APM. The basis for the study were four pre-Phase A studies performed by industry on the assumption that 15 racks would be available to biology and biotechnology in the APM. Due to the constraints newly imposed by the Columbus project, only five racks are now allocated. The tasks of the Biolab scientific team were: (i) to define the scientific objectives of biological research in Columbus; (ii) to review the requirements of the industrial studies; and (iii) to design a multi-purpose facility compatible with the present constraints and satisfying the requirements of the biological investigations considered in the four studies. The Biolab team was able to define a facility capable of accommodating in five racks the following biological objects: small plants (up to 40 cm), insects like drosophila, frog eggs, single cells from animals, bacteria, slime molds and protozoa, as well as human physiology, but restricted to general diagnostic needs. The Biolab facility includes instruments and devices providing the capacity of holding and/or growing the organisms as well as to perform basic experimentation and a minimum essential diagnostic inflight. Within the growth unit the growth chambers/incubators are exchangeable, permitting the use of growth chambers of different sizes. The temperature will be adjustable to the requirements of the objects under investigation, i.e. either 20 or 37 degrees C. Thus a considerable level of flexibility will permit to investigate a broad spectrum of living systems.

Gravitational effects on mammalian cells

In this paper we present first the results of our most recent investigations on gravitational effects on the activation of human lymphocytes: by immunoenzymatic staining and by using concanavalin A (Con A) coated to red blood cells (RBC) we demonstrate that the increase of activation measured at 10xg is due to a simultaneous activation of T- and B-lymphocytes whereas at 1xg only T-cells are stimulated. Conversely, activation of T-cells by chemical modification of the membrane with sodium periodate is depressed at 10xg. Secondly, experiments performed in the centrifuge as well as in the clinostat with Friend, K-562, and hybridoma cells show that each cell line develops its own adaptation reaction to gravitational stress.

Cultivation of single cells in space

The purpose of this review is to present an updated and comprehensive analysis of the experiments with single cells performed in space. Especially the results of the investigations performed in Biorack on the D-1 mission clearly show that important cellular functions are changing in microgravity. Cell proliferation, differentiation, metabolism, membrane properties, and cytoplasmic streaming underwent significant alteration during exposure to space flight conditions in a variety of single cells cultures spanning from bacteria to mammalian cells. These findings open new and interesting perspectives to basic and applied research in microgravity. The focus of this paper is on the cultivation of mammalian cells in space laboratories and on the related instrumentation. While Biorack is a useful and efficient instrument for simple studies in Spacelab, the development of new facilities like incubators with automated fixation devices as well as of more complex bioreactors is strongly recommended.

Dynamic cell culture system: a new cell cultivation instrument for biological experiments in space

The prototype of a miniaturized cell cultivation instrument for animal cell culture experiments aboard Spacelab is presented (Dynamic cell culture system: DCCS). The cell chamber is completely filled and has a working volume of 200 microliters. Medium exchange is achieved with a self-powered osmotic pump (flowrate 1 microliter h-1). The reservoir volume of culture medium is 230 microliters. The system is neither mechanically stirred nor equipped with sensors. Hamster kidney (Hak) cells growing on Cytodex 3 microcarriers were used to test the biological performance of the DCCS. Growth characteristics in the DCCS, as judged by maximal cell density, glucose consumption, lactic acid secretion and pH, were similar to those in cell culture tubes.

Tissue engineering in space

The purpose of this paper is to present the status of that part of the [Microgravity Application Program] project related to the study of cartilage formation from pig chondrocytes. The work carried out so far followed two lines: (i) chondrocytes were incubated for up to three weeks in the RPM; (ii) a module developed for in-vitro cartilage formation will be tested in a sounding rocket flight (MASER 9, November 2001).

Performance of a miniaturized bioreactor in space flight: microtechnology at the service of space biology

We describe here the performance and the use of microtechnology in a miniaturized bioreactor developed for the continuous cultivation of yeast cells, Saccharomyces cerevisiae, in microgravity. This bioreactor has been used on two Shuttle missions, where its functionality was successfully demonstrated. In the future, bioreactors will become a key element for long-term experiments, and would also be applied in the cultivation of mammalian cells or tissues for medical applications.

From cell biology to biotechnology in space

In this article I discuss the main results of our research in space biology from the simple early investigations with human lymphocytes in the early eighties until the projects in tissue engineering of the next decade on the international space station ISS. The discovery that T lymphocyte activation is nearly totally depressed in vitro in 0 g conditions showed that mammalian single cells are sensitive to the gravitational environment. Such finding had important implications in basic research, medicine and biotechnology. Low gravity can be used as a tool to investigate complicated and still obscure biological process from a new perspective not available to earth-bound laboratories. Low gravity may also favor certain bioprocesses involving the growth of tissues and thus lead to commercial and medical applications. However, shortage of crew time and of other resources, lack of sophisticated instrumentation, safety constraints pose serious limits to biological endeavors in space laboratories.

Gravitational effects on the response to different stimulatory signals in T cells

The purpose of this paper is to present new data on the in vitro activation of purified T cells with three different mitogenic agents in conditions simulating low-gravity.

Stress-compensation by a food supplement based on yeast plasmolysate in mitogen-activated T lymphocytes under simulated low-gravity

T lymphocyte function is strongly depressed in vitro and in vivo under low-g conditions in space as well as simulated in clinostat. Here we describe the effect of a food supplement based on yeast plasmolysate on T cells activated in vitro with Concanavalin A and cultured in a random positioning machine. The mitotic index was measured by 3H-thymidine incorporation into DNA, the expression of activation markers CD25, CD69 and HLA-DR on the cell surface by cytofluorimetry and the secretion of the IL-2R by an enzyme immunoassay. Our data indicate that the food supplement used is capable to modulate T lymphocyte function. The addition of the food supplement increased the expression of activation markers in activated and non-activated cells. Cultivation under low-gravity conditions reduced the expression of the activation markers, but this expression was partly restored or even increased upon addition of yeast plasmolysate. On the other hand, cell proliferation and secretion of soluble IL-2 receptor was reduced after addition of the food supplement in all samples.

Human immune cells as space travelers

Experiments in space have shown that T lymphocyte function is altered in more than 50% of space crew members. There is strong evidence that such effect is due to stress rather than to weightlessness per se. However the health of astronauts was never threatened so far. Experiments in-vitro with cultures of human peripheral blood lymphocytes (not from astronauts) have shown that T cell function is dramatically reduced. Recent work with the random positioning machine, a new instrument to simulate conditions similar to microgravity, indicate that there are direct gravitational effects on the genetic expression of interleukin-2 and of its receptor in T lymphocytes.

Microtechnology in space bioreactors

Space biology is a young and rapidly developing discipline comprising basic research and biotechnology. In the next decades it will play a prominent role in the International Space Station (ISS). Therefore, there is an increasing demand for sophisticated instrumentation to satisfy the requirements of the future projects in space biology. Bioreactors will be needed to supply fresh living material (cells and tissues) either to study still obscure basic biological mechanisms or to develop profitable bioprocesses which will take advantage of the peculiar microgravity conditions. Since more than twenty years, the Space Biology Group of the ETHZ is carrying out research projects in space (Space Shuttle/Spacelab, MIR Station, satellites, and sounding rockets) that involve also the development of space-qualified instrumentation. In the last ten years we have developed, in collaboration with Mecanex SA, Nyon, and the Institute of Microtechnology of the University of Neuchatel, a space bioreactor for the continuous culture of yeast cells under controlled conditions. Sensors, pH control, nutrients pump and fluid flowmeter are based on state-of-the-art silicon technology. After two successful space flights, a further improved version is presently prepared for a flight in the year 2000.

Signal transduction in T lymphocytes--a comparison of the data from space, the free fall machine and the random positioning machine

In this paper we discuss the effect of microgravity on T cells and we present the data of studies with two new machines for 0 g simulations. Several experiments in space show that mitogenic T cell activation is lost at 0 g. Immunocytochemistry indicates that such effect is associated with changes of the cytoskeleton. Biochemical studies suggest that the lack of expression of the interleukin-2 receptor is one of the major causes of the loss of activity. In fact, interleukin-2 is the third signal required for full activation. In order to deepen our investigations we are now working with the free-fall machine, FFM, invented by D. Mesland, and with the random positioning machine, RPM, or three-dimensional clinostat, developed by T. Hoson. The FFM produces periods of free-fall lasting approximately 800 ms followed by bounces of 15-30 g lasting 45-60 ms. The RPM eliminates the effect of gravity by rotating biological specimen randomly around two orthogonal axes. While the FFM failed to reproduce the results obtained with T lymphocytes in space, the data from the RPM are in good agreement with those in real microgravity. In fact, the inhibition of the mitotic index in the RPM is 89% compared to static controls. The RPM (as the FFM) can carry markedly larger specimen than the fast rotating clinostat and thus allows to conduct comprehensive studies to select suitable biological objects for further investigations in space.

Influence of microgravity on mitogen binding and cytoskeleton in Jurkat cells

The effects of microgravity on Jurkat cells--a T-lymphoid cell line--was studied on a sounding rocket flight. An automated pre-programmed instrument permitted the injection of fluorescent labelled concanavalin A (Con A), culture medium and/or fixative at given times. An in-flight 1 g centrifuge allowed the comparison of the data obtained in microgravity with a 1 g control having the same history related to launch and re-entry. After flight, the cells fixed either at the onset of microgravity or after a or 12 minute incubation time with fluorescent concanavalin A were labelled for vimentin and actin and analysed by fluorescence microscopy. Binding of Con A to Jurkat cells is not influenced by microgravity, whereas patching of the Con A receptors is significantly lower. A significant higher number of cells show changes in the structure of vimentin in microgravity. Most evident is the appearance of large bundles, significantly increased in the microgravity samples. No changes are found in the structure of actin and in the colocalisation of actin on the inner side of the cell membrane with the Con A receptors after binding of the mitogen.

Simulated microgravity inhibits the genetic expression of interleukin-2 and its receptor in mitogen-activated T lymphocytes

Experiments conducted in space in the last two decades have shown that T lymphocyte activation in vitro is remarkably reduced in microgravity. The data indicate that a failure of the expression of the interleukin-2 receptor (measured as protein secreted in the supernatant) is responsible of the loss of activity. To test such hypothesis we have studied the genetic expression of interleukin-2 and of its receptor in concanavalin A-activated lymphocytes with the RT-PCR technology. Microgravity conditions were simulated in the fast rotating clinostat and in the random positioning machine. The latter is an instrument introduced recently to study gravitational effects on single cells. Our data clearly show that the expression of both IL-2 and IL-2Ralpha genes is significantly inhibited in simulated O X g. Thus full activation is prevented.

Cellular adhesion in neoplastic and syngeneic normal cells under altered gravitational conditions

The major objective of several experiments performed in space in the last 15 years was to establish whether single cells are sensitive to gravity. It was found in certain cells that reduced gravity leads to profound changes of a number of physiological functions like genetic expression, cell proliferation, signal transduction and cytoskeleton structure. In cell biology studies microgravity can be simulated on Earth in the clinostat. Nearly all data on experiments in the clinostat are related to cells cultured in suspension and, therefore, to adhesion-independent cells. In contrast, several biological phenomena as neoplastic transformation, cell differentiation, in-vitro cellular aging, contact inhibition and cellular adhesion require mainly cellular systems that are adhesion-dependent. The purpose of this work was: a) to study the behaviour of two rat cell strains (neoplastic SGS/4A and syngeneic fibroblasts FG) in order to test whether adhesion-dependent cells are suitable for clinorotation and b) to investigate cell-cell and cell-substratum adhesion in these cells kept under simulated low-g in the fast rotating clinostat and in hypergravity at l0g in the centrifuge.

Microgravity simulations with human lymphocytes in the free fall machine and in the random positioning machine

The purpose of this paper is to present the results obtained in our laboratory with both instruments, the FFM [free fall machine] and the RPM [random positioning machine], to compare them with the data from earlier experiments with human lymphocytes conducted in the FRC [fast rotating clinostat] and in space. Furthermore, the suitability of the FFM and RPM for research in gravitational cell biology is discussed.

Signal transduction in T lymphocytes in microgravity

More than 120 experiments conducted in space in the last 15 years have shown that dramatic changes are occurring in several types of single cells during their exposure to microgravity. One focus of today's research on cells in space is on signal transduction, especially those steps involving the cytoskeleton and cell-cell interactions. Signal transduction is often altered in microgravity as well as in hypergravity. This leads to changes in cell proliferation, genetic expression and differentiation. Interesting examples are leukocytes, HeLa cells, epidermoid cells and osteoblastic cells. Signalling pathways were studied in T lymphocytes in microgravity by several investigators after the discovery that mitogenic activation in vitro is virtually nil at 0g. T cells are a good model to study signal transduction because three extracellular signals (mitogen, IL-1 and IL-2) are required for full activation, and two classical pathways (via proteins G and PKC) are activated within the cell. In addition, low molecular weight GTP-binding proteins (Ras and Rap) are interacting with the cytoskeleton. The data at 0g support the notion that the expression of IL-2 receptor is inhibited at 0g, while mitogen binding and the transmission of IL-1 by accessory cells occur normally. In addition, alterations of the cytoskeleton suggest that the interaction with Rap proteins is disturbed. Data obtained with phorbol esters indicate that the function of PKC is changed in microgravity. Similar conclusions are drawn from the results with epidermoid cells A431.

Activation and proliferation of lymphocytes and other mammalian cells in microgravity

The experimental findings reviewed in this chapter support the following conclusions: Proliferation. Human T-lymphocytes, associated with monocytes as accessory cells, show dramatic changes in the centrifuge, in the clinostat and in space. In free-floating cells the mitogenic response is depressed by 90% in microgravity, whereas in cells attached to a substratum activation is enhanced by 100% compared to 1-G ground and inflight controls. The duration of phase G1 of the mitotic cycle of HeLa cells is reduced in hypergravity, resulting in an increased proliferation rate. Other systems like Friend cells and WI38 human embryonic lung cells do not show significant changes. Genetic expression and signal transduction. T-lymphocytes and monocytes show important changes in the expression of cytokines like interleukin-1, interleukin-2, interferon-gamma and tumor necrosis factor. The data from space experiments in Spacelab, Space Shuttle mid-deck, and Biokosmos have helped to clarify certain aspects of the mechanism of T-cell activation. Epidermoid A431 cells show changes in the genetic expression of the proto-oncogenes c-fos and c-jun in the clinostat and in sounding rockets. Membrane function, in particular the binding of ligates as first messengers of a signal, is not changed in most of the cell systems in microgravity. Morphology and Mortility. Free cells, lymphocytes in particular, are able to move and form aggregates in microgravity, indicating that cell-cell contacts and cell communications do take place in microgravity. Dramatic morphological and ultrastructural changes are not detected in cells cultured in microgravity. Important experiments with single mammalian cells, including immune cells, were carried out recently in three Spacelab flights, (SL-J, D-2, and IML-2 in 1992, 1993, and 1994, respectively). The results of the D-2 mission have been published in ref. 75; those of the IML-2 mission in ref. 76. Finally, many cell biology experiments in space have suffered in the past from a lack of adequate controls (like 1-G centrifuges) and of proper experimental conditions (like well-controlled temperature). In this respect the availability of Biorack, outfitted with proper incubators with 1-G control centrifuge as well as a glovebox with a microscope, is a great advantage. It is also desirable that cell biology experiments in space are accompanied or even preceded by a program of ground-based investigations in the fast rotating clinostat and in the centrifuge, and that preparatory experiments be done in parabolic flights and sounding rockets, whenever possible. Proper publication of the results of space experiments is another important need. A great number of data have been published in proceedings and reports that are not available to the broad scientific community. To guarantee the credibility and the international recognition of space biology it is important that the results be published in international, peer reviewed journals.

Preservation of viable biological samples for experiments in space laboratories

Standard viable preservation methods for biological samples using low temperatures have been investigated concerning their storage capabilities under higher temperature levels than usual. For a representative set of organism classes (plants, mammalian cells, arthropods and aquatic invertebrates), the minimum appropriate storage conditions have been identified by screening storage temperatures at -196 degrees, -80 degrees, -20 degrees, +4 degrees, +20 degrees/25 degrees C for periods from 2 days to 4 weeks. For storage below 0 degree C, as a typical cryopreservative, dimethylsulfoxide (DMSO) was used. For some samples, the addition of trehalose (as cryopreservative) and the use of a nitrogen atmosphere were investigated. After storage, the material was tested for vitality. The findings demonstrated that acceptable preservation can be achieved under higher storage temperatures than are typically applied. Small, dense cultured plant cells survive for 21 d when moderately cooled (+4 degrees to -20 degrees C); addition of trehalose enhances viability at -20 degrees C. For mammalian cells, the results show that human lymphocytes can be preserved for 3 d at 25 degrees C, 7 d at 4 degrees C and 28 d at -80 degrees C. Friend leukaemia virus transformed cells can be stored for 3 d at 25 degrees C, 14 d at 4 degrees C and 28 d at -80 degrees C. Hybridoma cells can be kept 7 d at 4 degrees C and 28 d at -20 degrees C or -80 degrees C. Model arthropod systems are well preserved for 2 weeks if maintained at lower temperatures that vary depending on the species and/or stage of development; e.g., 12 degrees C for Drosophila imagoes and 4-6 degrees C for Artemia nauplii. For aquatic invertebrates such as sea urchins, embryonic and larval stages can be preserved for several weeks at +6 degrees C, whereas sperm and eggs can best be stored at + 4 degrees C for up to 5 d at maximum. These results enhance the range of feasible space experiments with biological systems. Moreover, for typical terrestrial preservation methods, considerable modification potential is identified.

Movements and interactions of leukocytes in microgravity

The mitogenic activation of human lymphocytes resuspended in vitro is dramatically reduced in microgravity. As cell-cell contacts are one of the elements essential for activation, the behaviour of human leukocytes (mainly lymphocytes and monocytes as accessory cells) in the presence of the mitogen concanavalin A was studied in the centrifuge microscope NIZEMI at 0 x g. Aggregates (formed by intercellular bindings of membrane glycoproteins via the tetravalent alpha-glucoside ligand concanavalin A) were found at 0 x g as well as at 1 x g already 12 h after the addition of the mitogen. In general, the aggregates observed at 0 x g after an incubation time of 46 and 78 h were smaller than the corresponding aggregates in the ground control. The findings are of primary importance since they confirm the indirect evidence we had from earlier Spacelab experiments and demonstrate that cell-cell contacts are occurring also in microgravity. In addition, single cells in 0 x g show a significant higher locomotion velocity than the cells at 1 x g. The fact that the locomotion capability is not decreased during the 78-h incubation with concanavalin A provides further evidence that the cells are not proceeding through the cell cycle.

Cultivation of Saccharomyces cerevisiae in a bioreactor in microgravity

Yeast cells were cultured for 8 d in a newly developed bioreactor during the Spacelab IML-2 mission. Two bioreactors, one stirred and one without stirring, were installed in the Biorack facility in space. Two control units were installed in the Biorack module at the Kennedy Space Center. Samples were drawn on mission day 3, 5, 6, 7 and 8 and preserved either by freezing or chemically fixed for post-flight analysis. The values of pH, pH regulation, temperature and redox potential were transmitted on-line to the ground station throughout the mission. The performance of the bioreactor was satisfactory except for a partial failure of the medium micropump. Despite the failure of the pump, the data support the following conclusions: There is a significant difference in the distribution of the bud scars between cells cultured at 0 x g and at 1 x g. The percentage of randomly distributed bud scars was significantly higher in the flight (17%) than in the ground control cells (5%). No remarkable differences were noted in the cell cycle, ultrastructure, cell proliferation, cell volume, ethanol production and glucose consumption.

Activation signals of T lymphocytes in microgravity

Human peripheral blood lymphocytes and monocytes were activated with concanavalin A with or without exogenous recombinant interleukin 1 (IL-1) alone or IL-1 + interleukin 2 (IL-2) under microgravity conditions to test the hypothesis that lack of production of IL-1 by monocytes is the cause of the near total loss of activation observed earlier on several Spacelab flights. The 60 min failure of the on-board 1 x g reference centrifuge at the time of the addition of the activator renders the in-flight data at 1 x g unreliable. However, the data from a previous experiment on SLS-1 show that there is no difference between the results from the in-flight 1 x g centrifuge and 1 x g on ground. The comparison between the data of the cultures at 0 x g in space and of the synchronous control at 1 x g on ground show that exogenous IL-1 and IL-2 do not prevent the loss of activity (measured as the mitotic index) at 0 x g; production of interferon-gamma, however, is partially restored. In contrast to a previous experiment in space, the production of IL-1 is not inhibited.

Gravitational physiology of human immune cells: a review of in vivo, ex vivo and in vitro studies

The study of the function of immune cells in microgravity has been studied for more than 20 years in several laboratories. It is clear today that the immune system is depressed in more than 50% of the astronauts during and after space flight and that the activation of T lymphocytes by mitogens in vitro changes dramatically. This article gives an overview of the gravitational studies conducted by our laboratory in Spacelab, in MIR station, in sounding rockets and on the ground in the clinostat and the centrifuge. Three experimental approaches are followed in our work: (i) Ex vivo studies are performed with blood samples drawn from astronauts; (ii) in vivo studies are based on the application of seven antigens to the skin of the astronauts; (iii) in vitro studies are carried out with immune cells purified from the blood of healthy donors (not astronauts). The data from our in vivo and ex vivo studies are in agreement with those of other laboratories and show that the immunological function is depressed in the majority of astronauts as a consequence of the stress of space flight rather than by a direct influence of gravity on the cell. Immune depression may become a critical hazard on long duration flights on space stations or to other planets. In vitro experiments show that cultures of free-floating lymphocytes and monocytes undergo a dramatic depression of activation by the mitogen concanavalin A, while activation is more than doubled when the cells are attached to microcarrier beads. Such effects may be attributed to both direct and indirect effects of gravitational unloading on basic biological mechanisms of the cell. While the in vitro data are very important to clarify certain aspects of the biological mechanism of T cells activation, they are not descriptive of the changes of the immunological function of the astronauts.

Development of a miniature bioreactor for continuous culture in a space laboratory

A new type of miniature bioreactor for continuous culture of yeast cells in space laboratories has been developed. Silicon microtechnology has permitted the integration of numerous functions and systems in a volume of 87 x 63 x 63 mm3 and a weight of 610 g. The 100 ml of fresh medium can be delivered at variable flow rates to the cultivation chamber (volume 3 ml) by means of a micropump. The culture is agitated by a magnetic stirrer. Microsensors monitor pH, temperature and redox potential. The decrease of pH occurring during the cultivation of Saccharomyces cerevisiae is compensated electrochemically. A window allows the inspection of the culture status. Samples of up to 1 ml can be drawn through a silicone rubber septum. The data measured by the sensors are transmitted on-line to the ground station during operations in space. The bioreactor had to fulfil several requirements related to the safety regulation of the space agencies. In particular, new materials had to be selected and tested for their biocompatibility. The instrument has now passed all space and biological qualification tests and will be used in an experiment selected by ESA for the International Microgravity Laboratory-2 Mission in Spacelab in July 1994. This paper gives the results of the functional and biological tests and a detailed description of the instrument.

Cellular immunity in cosmonauts during long duration spaceflight on board the orbital MIR station

To investigate the effect of spaceflight on cell mediated immunity we tested delayed-type hypersensitivity (DTH) in 5 cosmonauts on three missions in the orbital space station MIR. DTH was determined by the intradermal application of seven antigens and a control using the standardized Multitest Mérieux. This multiple prick puncture test was applied prior to, during, and following missions, which lasted for up to 177 d. In four of the five cosmonauts, reaction scores of DTH-responses below the warning level were noted during flight (two subjects) or following landing (two subjects). In-flight reductions of DTH-responses were possibly induced by a series of stressful extravehicular activities and recovered to normal levels after landing. The results confirm earlier observations of a decreased lymphocyte function following spaceflights determined by means of mitogenic responsiveness of lymphocytes. Thus, the notion of a possibly impaired cell-mediated immunity under stress in association with spaceflight gains further support.

Theories and models of the biology of the cell in space--an introduction

The World Space Congress 1992 took place after two Spacelab flights with important biological payloads on board, the SLS-1 (June 1991) and IML-1 (January 1992) missions respectively. Interesting experiments were carried out in 1991 also on the Shuttle middeck and on the sounding rocket MASER 4. The highlights of the investigations on these missions together with the results of relevant ground-based research were presented at the symposium.

The effect of hypogravity and hypergravity on cells of the immune system

This article reviews the gravity effects discovered in T lymphocytes and other cells of the immune system. The strong depression of mitogenic activation first observed in an experiment conducted in Spacelab 1 in 1983 triggered several other investigations in space and on the ground in the clinostat and in the centrifuge in the past 10 years. During this period, great progress was made in our knowledge of the complex mechanism of T cell activation as well as the technology to analyze the lymphokines produced during stimulation. Nevertheless, several aspects of the steps leading to activation are not yet clear. Studies in hypogravity and hypergravity may contribute to answering some of the questions. A recent investigation in the U.S. Spacelab SLS-1, based on a new technology in which leukocytes are attached to microcarrier beads, showed that the strong inhibition of activation in microgravity is due to a malfunction of monocytes acting as accessory cells. In fact, interleukin-1 production is nearly nil in resuspended monocytes, whereas T cell activation is doubled in attached cells. In hypergravity, but not at 1g, concanavalin A bound to erythrocytes activates B lymphocytes in addition to T cells. The activation of Jurkat cells is also severely impaired in space. These recent results have raised new questions that have to be answered in experiments to be conducted in space and on Earth in this decade. The experimental system, based on the mitogenic activation of T lymphocytes and accessory cells attached to microcarriers, offers an optimum model for studying basic biological mechanisms of the cell to assess the immunological fitness of humans in space and to test the feasibility of bioprocesses in space as well as on Earth.

Mitogenic signal transduction in T lymphocytes in microgravity

The activation by concanavalin A Con A of human peripheral blood lymphocytes (PBLs) in the presence of monocytes as accessory cells was investigated in cultures exposed to microgravity conditions in Spacelab. Activation of T cells was measured as incorporation of [3H]thymidine into DNA, secretion of interleukin-2 (IL-2), and interferon-gamma, and expression of IL-2 receptors. Whereas, as discovered in earlier experiments, the activation of resuspended T cells is strongly inhibited, activation of cells attached to microcarrier beads is more than doubled in microgravity. The results suggest that the depression of the activation in resuspended cells may be attributed to a malfunction of monocytes acting as accessory cells. In fact, although the ultrastructure of resuspended monocytes is not altered in microgravity, the secretion of IL-1 is strongly inhibited. Our data suggest that (1) IL-2 is produced independently of IL-1, (2) IL-1 production is triggered only when monocytes (and lymphocytes?) adhere to microcarriers, (3) the expression of IL-2 receptors depends on IL-1, and (4) provided sufficient IL-1 is available, activation is enhanced in microgravity. Finally, cultures of resuspended PBLs and monocytes in microgravity constitute a complete and natural system in which monocytes are not operational. This may be useful for studies of the role of accessory cells and cell-cell interactions in T lymphocyte activation.

Cultivation of hamster kidney cells in a dynamic cell culture system in space (Spacelab IML-1 Mission)

Cell proliferation, tissue plasminogen activator (t-PA) production and metabolic changes of Hamster Kidney cells (HaK) grown on microcarriers in an automatic Dynamic Cell Culture System (DCCS) were determined on the first International Microgravity Mission (IML-1) Spacelab (22-30 January 1992). The DCCS was designed for two cell culture chambers (volume: 200 microliters each), one operating as a hatch system, the other as a perfusion system. Medium exchange was achieved with an osmotic pump (flow rate 1 microliter h-1). Two major items were investigated: the biological performance of the DCCS in space and the effect of microgravity on HaK cells. The results obtained demonstrated that (1) the DCCS can be used for biological experiments on long term Spacelab missions. In fact, higher cell densities and higher concentration of glucose but lower concentration of lactate in the perfusion chambers than in the batch chambers were measured. The concentration of t-PA, glutamine and ammonia was similar in all chambers. (2) Microgravity had no effect on cell growth and metabolism of HaK cells.

Space flight and the immune system

Depression of lymphocyte response to mitogens in cosmonauts after space flight was reported for the first time in the early 1970s by Soviet immunologists. Today we know that depression of lymphocyte function affects at least 50% of space crew members. Investigations on the ground on subjects undergoing physical and psychological stress indicate that stress is a major factor in immune depression of astronauts. This is despite the fact that weightlessness per se has a strong inhibitory effect on lymphocyte activation in vitro. Although the changes observed never harmed the health of astronauts, immunological changes must be seriously investigated and understood in view of long-duration flight on space stations in an Earth orbit, to other planets such as Mars and to the Moon.

Culture of hybridoma and Friend leukemia virus transformed cells in microgravity. Spacelab IML-1 mission

The behaviour of two mammalian cell lines was investigated in Biorack during the 1st Spacelab international microgravity laboratory flight (IML-1) in the ESA facility Biorack. The parameters determined were cell proliferation, biosynthesis of specific cell products, consumption of glucose, glutamine and production of ammonia and lactate respectively. Murine Friend leukemia virus-transformed cells (Friend cells) were induced to differentiate and express hemoglobin (Hg) genes upon induction with dimethylsulfoxide (DMSO). No change was observed in all metabolic parameters including the production of Hg and the number of Hg-positive cells. Electron microscopy analysis showed no difference in morphology, mean cell volume and mitotic index between the different cell samples. Murine hybridoma cells revealed an increase (+ 30-40%) of cell proliferation rate in microgravity, whereas the metabolic parameters, production of monoclonal antibodies included, were lower in the 0 g than in the 1 g controls. The results clearly show that not all mammalian cells undergo dramatic changes in microgravity and that the effects reported on human T lymphocytes represent a unique case.

Activation of microcarrier-attached lymphocytes in microgravity

A technology has been developed to achieve optimal attachment of adhesion-independent lymphocytes to microcarrier beads. The activation of T-lymphocytes by concanavalin A was tested under microgravity conditions in an experiment carried out in space during the first Spacelab Life Science Mission. Activation, measured as the synthesis of deoxyribonucleic acid (DNA) and the production of interferon-gamma, more than doubled in attached lymphocytes in microgravity. The depression of the activation discovered in previous space experiments is due to an impairment not of the lymphocyte but of the macrophage function. The system described here may be useful for radiobiological investigations on the effect of high-energy particles and for testing the efficiency of the immune system in humans during the long-duration space flight planned in the future. The biotechnological significance of the increased lymphokine production in space remains to be assessed.

Reduced lymphocyte activation in space: role of cell-substratum interactions

We investigated the effect of substratum adhesiveness on stimulated lymphocyte blastogenesis by reducing and blocking cell adhesion with poly (2-hydroxyethyl methacrylate) (poly-HEMA) in a simple on-ground system. Cells grown on medium-thick and thick poly-HEMA films were rounded in shape and displayed no signs of spreading. By contrast, on tissue culture plastic and very thin poly-HEMA films, they showed clear signs of spreading. The mitogenic response of lymphocytes grown on thick poly-HEMA films was reduced by up to 68% of the control (tissue culture plastic). Interferon-gamma production was near zero when the cells were grown on the least adhesive substratum. On uncoated plastic, activated lymphocytes subjected to high gravity (20g) exhibited an increased proliferation rate (40%) compared with 1g. By contrast, on poly-HEMA, high gravity did not improve lymphocyte responsiveness. These results show that activated lymphocytes need to anchor and spread prior to achieving an optimal proliferation response. We conclude that decreased lymphocyte adhesion could contribute to the depressed in vitro lymphocyte responsiveness found in the microgravity conditions of space flight.

Changes observed in lymphocyte behavior during gravitational unloading

The effect of microgravity has been extensively studied on human lymphocytes in several space missions. A clear distinction must be made between two kinds of experiments: (i) with cells purified from the peripheral blood of test subjects before flight and then exposed inflight to mitogens and other activators (these are called in vitro experiments), and (ii) with lymphocytes from crewmembers of space missions exposed to mitogens prior to and after flight (ex vivo experiments). The first approach can be considered as basic research in cell biology in space; the second contributes to identifying the effects of the stress of spaceflight on the immune response of astronauts. The results from in vitro experiments have clearly shown that lymphocyte activation is nearly totally depressed in microgravity. This activation depression is confirmed by investigations on Earth in the fast rotating clinostat. Conversely, activation is increased when lymphocytes are cultured at 10 g in a centrifuge. In microgravity cell adhesion may be reduced, thus partly accounting for the decreased cell activation. The results of the experiments conducted at 10 g are due to a simultaneous activation of T- and B-lymphocytes by concanavalin A. The reduced activation observed in lymphocytes from crewmembers of space missions can be ascribed to both the physical and psychological stress of spaceflight. This observation was confirmed by investigations on subjects undergoing stress on Earth.