Explore the vast range of titles available.

Exposure to microgravity during spaceflight induces the alterations in endothelial cell function associated with post-flight cardiovascular deconditioning. PIEZO1 is a major mechanosensitive ion channel that regulates endothelial cell function. In this study, we used a two-dimensional clinostat to investigate the expression of PIEZO1 and its regulatory mechanism on human umbilical vein endothelial cells (HUVECs) under simulated microgravity. Utilizing quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis, we observed that PIEZO1 expression was significantly increased in response to simulated microgravity. Moreover, we found microgravity promoted endothelial cells migration by increasing expression of PIEZO1. Proteomics analysis highlighted the importance of C-X-C chemokine receptor type 4(CXCR4) as a main target molecule of PIEZO1 in HUVECs. CXCR4 protein level was increased with simulated microgravity and decreased with PIEZO1 knock down. The mechanistic study showed that PIEZO1 enhances CXCR4 expression via Ca2+ influx. In addition, CXCR4 could promote endothelial cell migration under simulated microgravity. Taken together, these results suggest that the upregulation of PIEZO1 in response to simulated microgravity regulates endothelial cell migration due to enhancing CXCR4 expression via Ca2+ influx.

Microgravity or low gravity environment of space can be simulated on Earth by using clinorotation with appropriate speed of rotation. Previous reports show that microgravity environment (real or simulated) affects growth, chlorophyll content and photosynthetic performance in different plants. However, most of the reports showed variation in results. Earlier studies carried out on simulated microgravity (SMG) using clinorotation in our laboratory showed increase in growth, chlorophyll content and various yield attributes in case of laboratory and field grown rice. Subsequent studies were carried out on mungbean seedlings. In the present work, comparative aspects of these studies are reported. Results of the present study showed increase in growth, chlorophyll content and chlorophyll fluorescence parameters in SMG samples as compared to control samples in rice and mungbean seedlings. Interestingly, percentage of enhancement in growth, chlorophyll content and chlorophyll fluorescence parameters of SMG samples is significantly higher in rice (monocotyledonous) seedlings as compared to mungbean (dicotyledonous).

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood. Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism. Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth’s surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein CsPIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots. Our results suggest that roots become hydrotropically sensitive in μG, and CsPIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity.

Muscle and skeleton structures are considered most susceptible to negative factors of spaceflights, namely microgravity. Three-dimensional clinorotation is a ground-based simulation of microgravity. It provides an opportunity to elucidate the effects of microgravity at the cellular level. The extracellular matrix (ECM) content, transcriptional profiles of genes encoding ECM and remodelling molecules, and secretory profiles were investigated in a heterotypic primary culture of bone marrow cells after 14 days of 3D clinorotation. Simulated microgravity negatively affected stromal lineage cells, responsible for bone tissue formation. This was evidenced by the reduced ECM volume and stromal cell numbers, including multipotent mesenchymal stromal cells (MSCs). ECM genes encoding proteins responsible for matrix stiffness and cell-ECM contacts were downregulated. In a heterotypic population of bone marrow cells, the upregulation of genes encoding ECM degrading molecules and the formation of a paracrine profile that can stimulate ECM degradation, may be mechanisms of osteodegenerative events that develop in real spaceflight.

Astronauts exposed to a gravity-free environment experience cardiovascular deconditioning that causes post-spaceflight orthostatic intolerance and other pathological conditions. Endothelial dysfunction is an important factor responsible for this alteration. Our previous study showed enhanced autophagy in endothelial cells under simulated microgravity. The present study explored the cytoprotective role of autophagy under microgravity in human umbilical vein endothelial cells (HUVECs). We found that clinorotation for 48 h induced apoptosis and endoplasmic reticulum (ER) stress in HUVECs. ER stress and the unfolded protein response (UPR) partially contributed to apoptosis under clinorotation. Autophagy partially reduced ER stress and restored UPR signaling by autophagic clearance of ubiquitin-protein aggregates, thereby reducing apoptosis. In addition, the ER stress antagonist 4-phenylbutyric acid upregulated autophagy in HUVECs. Taken together, these findings indicate that autophagy plays a protective role against apoptosis under clinorotation by clearing protein aggregates and partially restoring the UPR.

Plant cell cultures are precious tools for investigating the response of plants to altered gravity at the cellular level. In the present study, the effects of clinorotation on the growth and cell cycle progression of cultured Nicotiana tabacum cells were investigated. Exposure to 2D-clinostat for 12 h increased the percentage of the cells in the G1 phase from 80 to 83.2%, while significantly reduced the percentage of those cells at the G2/M transition, compared to their corresponding control cells. When the duration of exposure was extended, the rate of cells transition to the M phase increased, ultimately promoted the exponential growth phase after 168 h. During the first 24 h of clinorotation, a significant rise in the levels of simple sugars within the cells was observed. The ferric-reducing antioxidant power (FRAP) of tobacco cells exhibited a downward trajectory that continued until 48 h. This research showed the influence of clinorotation on plant cells dependent on the exposure duration. The cells exhibited signs of stress after a short exposure, possibly due to high levels of soluble sugars that could impede cell advancement in the G1 phase by negatively affecting radical scavenging capacity (RSC). Upon extending the exposure duration to 168 h, the cells were adapted to the altered gravity conditions and improved their growth, probably due to a rise in auxin and gibberellin production. The results suggest cultured cells are a viable candidate, for examining plants in long-term space missions.Key messageThe improvement of growth of plant cultured cells after longer treatment with altered gravity suggests them suitable candidates for investigation on plant response mechanisms to gravity in long-term space missions.

BackgroundLong-term space missions will necessarily require producing viable seeds to be used for plant cultivation over time under altered gravity conditions. Pollen is known to play a key role in determining seed and fruit production over seed-to-seed cycles, but very few studies have evaluated pollen functionality under altered gravity.MethodsWe performed ground-based experiments to test how simulated microgravity can affect the directional growth of pollen tubes as a potential bottleneck in seed and fruit sets. The effect of clinorotation was assessed in the pollen of Solanum lycopersicum L. cv. ‘Micro-Tom’ and Brassica rapa L. var. silvestris , both eligible for cultivation in space. Pollen tube length and tortuosity were compared under 1 g and simulated microgravity with a uniaxial clinostat.ResultsThe main results highlighted that simulated microgravity significantly increased pollen tube length and tortuosity compared to 1 g conditions. Further, clinorotation prompted a differential effect on pollen germination between S. lycopersicum and B. rapa . A more in-depth analysis evaluating the effect of gravity on the directional growth of pollen tubes excluded gravitropic responses as responsible for the tube tip position reached after germination.DiscussionThis research provides new insights into how altered gravity can interfere with plant reproduction and, in particular, microgametophyte functionality. Our findings represent a basis for further studies aimed at understanding the effect of real microgravity on plant reproduction and developing countermeasures to ensure seed-to-seed cultivation in long-term space missions and achieve self-sufficiency in food supplies from Earth.

Although the BMPR-SMAD-RUNX2 signaling pathway plays widely recognized roles in BMP-induced osteogenesis, factors regulating this pathway remain to be defined. In this study, we used simulated microgravity models, which represent mechanical unloading conditions, to detect miRNAs that function in osteoblast differentiation. We found that miR-494 was persistently increased in C2C12 cells subjected to clinorotation conditions and in osteoblasts isolated from tail-suspended rats. Experiments showed that the overexpression of miR-494 correlated with a marked reduction in osteoblast differentiation genes and a decrease in osteogenesis in BMP2-induced osteogenetic differentiation. In contrast, the inhibition of miR-494 promoted BMP2-induced osteogenesis and partially rescued osteoblast differentiation disorder under simulated microgravity conditions. Mechanism studies revealed that miR-494 directly targeted BMPR2 and RUNX2, both of which play vital roles in the BMPR-SMAD-RUNX2 signaling pathway. More importantly, we demonstrated a positive feedback loop between miR-494 and MYOD, a critical transcription factor for myogenesis, indicating that miR-494 may participate in deciding cell fate of the multipotent mesenchymal stem cells (MSCs). Collectively, our study reveals an important role for miR-494 in regulating osteogenesis, the identification of which not only clarifies a regulator of BMP2-induced osteoblast differentiation, but also offers a possible strategy for preventing bone loss under microgravity conditions.

Root gravitropism affects root hydrotropism. The interference intensity of root gravitropism with root hydrotropism differs among plant species. However, these differences have not been well compared within a single plant species. In this study, we compared root hydrotropism in various natural variants of Arabidopsis under stationary conditions. As a result, we detected a range of root hydrotropism under stationary conditions among natural Arabidopsis variants. Comparison of root gravitropism and root hydrotropism among several Arabidopsis natural variants classified natural variants that decreased root hydrotropism into two types; namely one type that expresses root gravitropism and root hydrotropism weaker than Col-0, and the other type that expresses weaker root hydrotropism than Col-0 but expresses similar root gravitropism with Col-0. However, root hydrotropism of all examined Arabidopsis natural variants was facilitated by clinorotation. These results suggested that the interference of root gravitropism with root hydrotropism is conserved among Arabidopsis natural variants, although the intensity of root gravitropism interference with root hydrotropism differs.

Bacterial behavior has been studied under microgravity conditions, but very little is known about it under lunar and Martian gravitational regimes. An Earth-based approach was designed and implemented using inclined clinostats and an in-house-developed code to determine the optimal clinorotation angular speed for bacterial liquid cultures of 5 RPM. With this setup, growth dynamics, phenotypic changes, and sensitivity to antibiotics (minimum inhibitory concentration (MIC) of two different classes of antibiotics) for three Escherichia coli strains (including uropathogenic) were examined under simulated micro-, lunar, and Martian gravities. The results included increased growth under simulated micro- and lunar gravities for some strains, and higher concentrations of antibiotics needed under simulated lunar gravity with respect to simulated micro- and Martian gravities. Clinostat-produced results can be considered suggestive but not determinative of what might be expected in altered gravity, as there is still a need to systematically verify these simulation devices’ ability to accurately replicate phenomena observed in space. Nevertheless, this approach serves as a baseline to start interrogating key cellular and molecular aspects relevant to microbial processes on the lunar and Martian surfaces.