How are cell and tissue structure and function influenced by gravity and what are the gravity perception mechanisms?

Progress in mechanobiology allowed us to better understand the important role of mechanical forces in the regulation of biological processes. Space research in the field of life sciences clearly showed that gravity plays a crucial role in biological processes. The space environment offers the unique opportunity to carry out experiments without gravity, helping us not only to understand the effects of gravitational alterations on biological systems but also the mechanisms underlying mechanoperception and cell/tissue response to mechanical and gravitational stresses. Despite the progress made so far, for future space exploration programs it is necessary to increase our knowledge on the mechanotransduction processes as well as on the molecular mechanisms underlying microgravity-induced cell and tissue alterations. This white paper reports the suggestions and recommendations of the SciSpacE Science Community for the elaboration of the section of the European Space Agency roadmap "Biology in Space and Analogue Environments" focusing on "How are cells and tissues influenced by gravity and what are the gravity perception mechanisms?" The knowledge gaps that prevent the Science Community from fully answering this question and the activities proposed to fill them are discussed.

How do gravity alterations affect animal and human systems at a cellular/tissue level?

The present white paper concerns the indications and recommendations of the SciSpacE Science Community to make progress in filling the gaps of knowledge that prevent us from answering the question: "How Do Gravity Alterations Affect Animal and Human Systems at a Cellular/Tissue Level?" This is one of the five major scientific issues of the ESA roadmap "Biology in Space and Analogue Environments". Despite the many studies conducted so far on spaceflight adaptation mechanisms and related pathophysiological alterations observed in astronauts, we are not yet able to elaborate a synthetic integrated model of the many changes occurring at different system and functional levels. Consequently, it is difficult to develop credible models for predicting long-term consequences of human adaptation to the space environment, as well as to implement medical support plans for long-term missions and a strategy for preventing the possible health risks due to prolonged exposure to spaceflight beyond the low Earth orbit (LEO). The research activities suggested by the scientific community have the aim to overcome these problems by striving to connect biological and physiological aspects in a more holistic view of space adaptation effects.

Microbially-Enhanced Vanadium Mining and Bioremediation Under Micro- and Mars Gravity on the International Space Station.

As humans explore and settle in space, they will need to mine elements to support industries such as manufacturing and construction. In preparation for the establishment of permanent human settlements across the Solar System, we conducted the ESA BioRock experiment on board the International Space Station to investigate whether biological mining could be accomplished under extraterrestrial gravity conditions. We tested the hypothesis that the gravity (g) level influenced the efficacy with which biomining could be achieved from basalt, an abundant material on the Moon and Mars, by quantifying bioleaching by three different microorganisms under microgravity, simulated Mars and Earth gravitational conditions. One element of interest in mining is vanadium (V), which is added to steel to fabricate high strength, corrosion-resistant structural materials for buildings, transportation, tools and other applications. The results showed that Sphingomonas desiccabilis and Bacillus subtilis enhanced the leaching of vanadium under the three gravity conditions compared to sterile controls by 184.92 to 283.22%, respectively. Gravity did not have a significant effect on mean leaching, thus showing the potential for biomining on Solar System objects with diverse gravitational conditions. Our results demonstrate the potential to use microorganisms to conduct elemental mining and other bioindustrial processes in space locations with non-1 × g gravity. These same principles apply to extraterrestrial bioremediation and elemental recycling beyond Earth.

Space station biomining experiment demonstrates rare earth element extraction in microgravity and Mars gravity.

Microorganisms are employed to mine economically important elements from rocks, including the rare earth elements (REEs), used in electronic industries and alloy production. We carried out a mining experiment on the International Space Station to test hypotheses on the bioleaching of REEs from basaltic rock in microgravity and simulated Mars and Earth gravities using three microorganisms and a purposely designed biomining reactor. Sphingomonas desiccabilis enhanced mean leached concentrations of REEs compared to non-biological controls in all gravity conditions. No significant difference in final yields was observed between gravity conditions, showing the efficacy of the process under different gravity regimens. Bacillus subtilis exhibited a reduction in bioleaching efficacy and Cupriavidus metallidurans showed no difference compared to non-biological controls, showing the microbial specificity of the process, as on Earth. These data demonstrate the potential for space biomining and the principles of a reactor to advance human industry and mining beyond Earth.

Rapid adaptation to microgravity in mammalian macrophage cells.

Despite the observed severe effects of microgravity on mammalian cells, many astronauts have completed long term stays in space without suffering from severe health problems. This raises questions about the cellular capacity for adaptation to a new gravitational environment. The International Space Station (ISS) experiment TRIPLE LUX A, performed in the BIOLAB laboratory of the ISS COLUMBUS module, allowed for the first time the direct measurement of a cellular function in real time and on orbit. We measured the oxidative burst reaction in mammalian macrophages (NR8383 rat alveolar macrophages) exposed to a centrifuge regime of internal 0 g and 1 g controls and step-wise increase or decrease of the gravitational force in four independent experiments. Surprisingly, we found that these macrophages adapted to microgravity in an ultra-fast manner within seconds, after an immediate inhibitory effect on the oxidative burst reaction. For the first time, we provided direct evidence of cellular sensitivity to gravity, through real-time on orbit measurements and by using an experimental system, in which all factors except gravity were constant. The surprisingly ultra-fast adaptation to microgravity indicates that mammalian macrophages are equipped with a highly efficient adaptation potential to a low gravity environment. This opens new avenues for the exploration of adaptation of mammalian cells to gravitational changes.

Effects of fatty acids on endothelial cells: inflammation and monocyte adhesion.

BACKGROUND: Diet is known to have an important impact on cardiovascular health. n-3 Fatty acids (FAs), found in high quantity in fish oil, have demonstrated beneficial effects in patients with coronary artery disease. The role of n-6 FAs remains more controversial. The objective of this study was to examine the effect of arachidonic acid (AA), an n-6 FA, and eicosapentanoic acid (EPA), an n-3 FA, on the interaction between monocytes and endothelial cells (ECs). DESIGN: We used a cellular model of ECs (EA.hy.926) and monocytes (human leukemic myelomonocytic U937). Confluent ECs were treated with AA or EPA, in the presence of tumor necrosis factor-alpha (TNF-α) or vehicle alone for either 4 or 24h. Adhesion of monocytes to the endothelial monolayer was performed. For gene expression, reverse transcription, followed by real-time quantitative polymerase chain reaction, was performed. RESULTS: There was a significant increase in adhesion of monocytes to the endothelial monolayer in the presence of n-6 FAs, both in the presence and in the absence of TNF-α at 4 and 24h. The adhesion of monocytes to the endothelial monolayer was decreased with n-3 FAs at 24h. Intercellular adhesion molecule 1, vascular cell adhesion molecule 1, E-Selectin, Interleukin 6, and TNF-α were significantly increased in ECs treated with n-6 FAs. CONCLUSIONS: We conclude that AA increases inflammation and enhances the ability of ECs to bind monocytes in vitro. EPA leads to a decrease in the ability of EA.hy.926 to bind monocytes, although the effect appears more modest. Taken together, these data indicate that the n-6 FA AA could potentiate inflammation and early events of atherosclerosis.

EXPOSE, an astrobiological exposure facility on the international space station - from proposal to flight.

Following an European Space Agency announcement of opportunity in 1996 for "Externally mounted payloads for 1st utilization phase" on the International Space Station (ISS), scientists working in the fields of astrobiology proposed experiments aiming at longterm exposure of a variety of chemical compounds and extremely resistant microorganisms to the hostile space environment. The ESA exposure facility EXPOSE was built and an operations' concept was prepared. The EXPOSE experiments were developed through an intensive pre-flight experiment verification test program. 12 years later, two sets of astrobiological experiments in two EXPOSE facilities have been successfully launched to the ISS for external exposure for up to 1.5 years. EXPOSE-E, now installed at the balcony of the European Columbus module, was launched in February 2008, while EXPOSE-R took off to the ISS in November 2008 and was installed on the external URM-D platform of the Russian Zvezda module in March 2009.

A short pulse of mechanical force induces gene expression and growth in MC3T3-E1 osteoblasts via an ERK 1/2 pathway.

Physiological mechanical loading is crucial for maintenance of bone integrity and architecture. We have calculated the strain caused by gravity stress on osteoblasts and found that 4-30g corresponds to physiological levels of 40-300 microstrain. Short-term gravity loading (15 minutes) induced a 15-fold increase in expression of growth-related immediate early gene c-fos, a 5-fold increase in egr-1, and a 3-fold increase in autocrine bFGF. The non-growth-related genes EP-1, TGF-beta, and 18s were unaffected by gravity loading. Short-term physiological loading induced extracellular signal-regulated kinase (ERK 1/2) phosphorylation in a dose-dependent manner with maximum phosphorylation saturating at mechanical loading levels of 12g (p < 0.001) with no effect on total ERK. The phosphorylation of focal adhesion kinase (FAK) was unaffected by mechanical force. g-Loading did not activate P38 MAPK or c-jun N-terminal kinase (JNK). Additionally, a gravity pulse resulted in the localization of phosphorylated ERK 1/2 to the nucleus; this did not occur in unloaded cells. The induction of c-fos was inhibited 74% by the MEK1/2 inhibitor U0126 (p < 0.001) but was not affected by MEK1 or p38 MAPK-specific inhibitors. The long-term consequence of a single 15-minute gravity pulse was a 64% increase in cell growth (p < 0.001). U0126 significantly inhibited gravity-induced growth by 50% (p < 0.001). These studies suggest that short periods of physiological mechanical stress induce immediate early gene expression and growth in MC3T3-E1 osteoblasts primarily through an ERK 1/2-mediated pathway.

Microgravity modifies protein kinase C isoform translocation in the human monocytic cell line U937 and human peripheral blood T-cells.

Individual protein kinase C (PKC) isoforms fulfill distinct roles in the regulation of the commitment to differentiation, cell cycle arrest, and apoptosis in both monocytes and T-cells. The human monocyte like cell line U937 and T-cells were exposed to microgravity, during spaceflight and the translocation (a critical step in PKC signaling) of individual isoforms to cell particulate fraction examined. PKC activating phorbol esters induced a rapid translocation of several PKC isoforms to the particulate fraction of U937 monocytes under terrestrial gravity (1 g) conditions in the laboratory. In microgravity, the translocation of PKC beta II, delta, and epsilon in response to phorbol esters was reduced in microgravity compared to 1 g, but was enhanced in weak hypergravity (1.4 g). All isoforms showed a net increase in particulate PKC following phorbol ester stimulation, except PKC delta which showed a net decrease in microgravity. In T-cells, phorbol ester induced translocation of PKC delta was reduced in microgravity, compared to 1 g, while PKC beta II translocation was not significantly different at the two g-levels. These data show that microgravity differentially alters the translocation of individual PKC isoforms in monocytes and T-cells, thus providing a partial explanation for the modifications previously observed in the activation of these cell types under microgravity.