Hypergravity speeds up the development of T-lymphocyte motility

Human neural network activity reacts to gravity changes in vitro

During spaceflight, humans experience a variety of physiological changes due to deviations from familiar earth conditions. Specifically, the lack of gravity is responsible for many effects observed in returning astronauts. These impairments can include structural as well as functional changes of the brain and a decline in cognitive performance. However, the underlying physiological mechanisms remain elusive. Alterations in neuronal activity play a central role in mental disorders and altered neuronal transmission may also lead to diminished human performance in space. Thus, understanding the influence of altered gravity at the cellular and network level is of high importance. Previous electrophysiological experiments using patch clamp techniques and calcium indicators have shown that neuronal activity is influenced by altered gravity. By using multi-electrode array (MEA) technology, we advanced the electrophysiological investigation covering single-cell to network level responses during exposure to decreased (micro-) or increased (hyper-) gravity conditions. We continuously recorded in real-time the spontaneous activity of human induced pluripotent stem cell (hiPSC)-derived neural networks in vitro. The MEA device was integrated into a custom-built environmental chamber to expose the system with neuronal cultures to up to 6 g of hypergravity on the Short-Arm Human Centrifuge at the DLR Cologne, Germany. The flexibility of the experimental hardware set-up facilitated additional MEA electrophysiology experiments under 4.7 s of high-quality microgravity (10–6 to 10–5 g) in the Bremen drop tower, Germany. Hypergravity led to significant changes in activity. During the microgravity phase, the mean action potential frequency across the neural networks was significantly enhanced, whereas different subgroups of neurons showed distinct behaviors, such as increased or decreased firing activity. Our data clearly demonstrate that gravity as an environmental stimulus triggers changes in neuronal activity. Neuronal networks especially reacted to acute changes in mechanical loading (hypergravity) or de-loading (microgravity). The current study clearly shows the gravity-dependent response of neuronal networks endorsing the importance of further investigations of neuronal activity and its adaptive responses to micro- and hypergravity. Our approach provided the basis for the identification of responsible mechanisms and the development of countermeasures with potential implications on manned space missions.

Implications of Lymphatic Transport to Lymph Nodes in Immunity and Immunotherapy

Adaptive immune response consists of many highly regulated, multistep cascades that protect against infection while preserving the health of autologous tissue. The proper initiation, maintenance, and resolution of such responses require the precise coordination of molecular and cellular signaling over multiple time and length scales orchestrated by lymphatic transport. In order to investigate these functions and manipulate them for therapy, a comprehensive understanding of how lymphatics influence immune physiology is needed. This review presents the current mechanistic understanding of the role of the lymphatic vasculature in regulating biomolecule and cellular transport from the interstitium, peripheral tissue immune surveillance, the lymph node stroma and microvasculature, and circulating lymphocyte homing to lymph nodes. This review also discusses the ramifications of lymphatic transport in immunity as well as tolerance and concludes with examples of how lymphatic-mediated targeting of lymph nodes has been exploited for immunotherapy applications.

Exposure to hypergravity increases serum interleukin-5 and pulmonary infiltration in mice with allergic asthma

Objective

We evaluated the effect of acute hypergravity (HG) on the immune response in a murine model of allergic asthma.

Material and methods

Twenty-eight BALB/c mice were used. Group A (control group, n = 7) mice were sensitized and challenged with normal saline. Group B (control HG exposure group, n = 7) mice were sensitized, challenged with saline, and exposed to acute HG (+10 Gz) for 4 hours. Group C (asthma group, n = 7) mice were challenged with intraperitoneal and intranasal ovalbumin (OVA) to induce asthma. Group D (asthma HG exposure group, n = 7) mice were exposed to HG for 4 hours after the induction of asthma. We estimated the total and OVA-specific serum IgE, serum titers of various cytokines, and the number of eosinophils, neutrophils, and lymphocytes in bronchoalveolar lavage (BAL) fluid. Histopathology of the lung was also evaluated.

Results

The serum level of interleukin (IL)-5 was significantly higher in Group D (12.9 ±4.9 pg/ml) compared to that in Group C (4.7 ±6.5 pg/ml, p = 0.017). In BAL fluid, the number of neutrophils was significantly increased in Group D compared to Group C (p = 0.014). Group D demonstrated a higher infiltration of inflammatory cells (9973.8 ±1642.7 cells/mm²) compared to Group C (7666.3 ±586.5 cells/mm², p = 0.017). This tendency of increase in infiltration was not significant in non-asthmatic animals (Group A: 4488.8 ±176.1 cells/mm² vs. Group B: 4946.3 ±513.7 cells/mm², p > 0.05).

Conclusions

Acute HG exacerbated the allergic response by increasing serum IL-5 levels and promoting pulmonary infiltration of inflammatory cells.

Signal transduction in primary human T lymphocytes in altered gravity - results of the MASER-12 suborbital space flight mission

We investigated the influence of altered gravity on key proteins of T cell activation during the MASER-12 ballistic suborbital rocket mission of the European Space Agency (ESA) and the Swedish Space Cooperation (SSC) at ESRANGE Space Center (Kiruna, Sweden). We quantified components of the T cell receptor, the membrane proximal signaling, MAPK-signaling, IL-2R, histone modifications and the cytoskeleton in non-activated and in ConA/CD28-activated primary human T lymphocytes. The hypergravity phase during the launch resulted in a downregulation of the IL-2 and CD3 receptor and reduction of tyrosine phosphorylation, p44/42-MAPK phosphorylation and histone H3 acetylation, whereas LAT phosphorylation was increased. Compared to the baseline situation at the point of entry into the microgravity phase, CD3 and IL-2 receptor expression at the surface of non-activated T cells were reduced after 6 min microgravity. Importantly, p44/42-MAPK-phosphorylation was also reduced after 6 min microgravity compared to the 1g ground controls, but also in direct comparison between the in-flight μg and the 1g group. In activated T cells, the reduced CD3 and IL-2 receptor expression at the baseline situation recovered significantly during in-flight 1g conditions, but not during microgravity conditions. Beta-tubulin increased significantly after onset of microgravity until the end of the microgravity phase, but not in the in-flight 1g condition. This study suggests that key proteins of T cell signal modules are not severely disturbed in microgravity. Instead, it can be supposed that the strong T cell inhibiting signal occurs downstream from membrane proximal signaling, such as at the transcriptional level as described recently. However, the MASER-12 experiment could identify signal molecules, which are sensitive to altered gravity, and indicates that gravity is obviously not only a requirement for transcriptional processes as described before, but also for specific phosphorylation / dephosphorylation of signal molecules and surface receptor dynamics.

On the nature and shape of tubulin trails: implications on microtubule self-organization

Microtubules, major elements of the cell skeleton are, most of the time, well organized in vivo, but they can also show self-organizing behaviors in time and/or space in purified solutions in vitro. Theoretical studies and models based on the concepts of collective dynamics in complex systems, reaction-diffusion processes and emergent phenomena were proposed to explain some of these behaviors. In the particular case of microtubule spatial self-organization, it has been advanced that microtubules could behave like ants, self-organizing by 'talking to each other' by way of hypothetic (because never observed) concentrated chemical trails of tubulin that are expected to be released by their disassembling ends. Deterministic models based on this idea yielded indeed like-looking spatio-temporal self-organizing behaviors. Nevertheless the question remains of whether microscopic tubulin trails produced by individual or bundles of several microtubules are intense enough to allow microtubule self-organization at a macroscopic level. In the present work, by simulating the diffusion of tubulin in microtubule solutions at the microscopic scale, we measure the shape and intensity of tubulin trails and discuss about the assumption of microtubule self-organization due to the production of chemical trails by disassembling microtubules. We show that the tubulin trails produced by individual microtubules or small microtubule arrays are very weak and not elongated even at very high reactive rates. Although the variations of concentration due to such trails are not significant compared to natural fluctuations of the concentration of tubuline in the chemical environment, the study shows that heterogeneities of biochemical composition can form due to microtubule disassembly. They could become significant when produced by numerous microtubule ends located in the same place. Their possible formation could play a role in certain conditions of reaction. In particular, it gives a mesoscopic basis to explain the collective dynamics observed in excitable microtubule solutions showing the propagation of concentration waves of microtubules at the millimeter scale, although we doubt that individual microtubules or bundles can behave like molecular ants.

Signal transduction in cells of the immune system in microgravity

Life on Earth developed in the presence and under the constant influence of gravity. Gravity has been present during the entire evolution, from the first organic molecule to mammals and humans. Modern research revealed clearly that gravity is important, probably indispensable for the function of living systems, from unicellular organisms to men. Thus, gravity research is no more or less a fundamental question about the conditions of life on Earth. Since the first space missions and supported thereafter by a multitude of space and ground-based experiments, it is well known that immune cell function is severely suppressed in microgravity, which renders the cells of the immune system an ideal model organism to investigate the influence of gravity on the cellular and molecular level. Here we review the current knowledge about the question, if and how cellular signal transduction depends on the existence of gravity, with special focus on cells of the immune system. Since immune cell function is fundamental to keep the organism under imnological surveillance during the defence against pathogens, to investigate the effects and possible molecular mechanisms of altered gravity is indispensable for long-term space flights to Earth Moon or Mars. Thus, understanding the impact of gravity on cellular functions on Earth will provide not only important informations about the development of life on Earth, but also for therapeutic and preventive strategies to cope successfully with medical problems during space exploration.