Microgravity and Cell Adherence

Changes in interstitial fluid flow, mass transport and the bone cell response in microgravity and normogravity

In recent years, our scientific interest in spaceflight has grown exponentially and resulted in a thriving area of research, with hundreds of astronauts spending months of their time in space. A recent shift toward pursuing territories farther afield, aiming at near-Earth asteroids, the Moon, and Mars combined with the anticipated availability of commercial flights to space in the near future, warrants continued understanding of the human physiological processes and response mechanisms when in this extreme environment. Acute skeletal loss, more severe than any bone loss seen on Earth, has significant implications for deep space exploration, and it remains elusive as to why there is such a magnitude of difference between bone loss on Earth and loss in microgravity. The removal of gravity eliminates a critical primary mechano-stimulus, and when combined with exposure to both galactic and solar cosmic radiation, healthy human tissue function can be negatively affected. An additional effect found in microgravity, and one with limited insight, involves changes in dynamic fluid flow. Fluids provide the most fundamental way to transport chemical and biochemical elements within our bodies and apply an essential mechano-stimulus to cells. Furthermore, the cell cytoplasm is not a simple liquid, and fluid transport phenomena together with viscoelastic deformation of the cytoskeleton play key roles in cell function. In microgravity, flow behavior changes drastically, and the impact on cells within the porous system of bone and the influence of an expanding level of adiposity are not well understood. This review explores the role of interstitial fluid motion and solute transport in porous bone under two different conditions: normogravity and microgravity.

Passive limitation of surface contamination by perFluoroDecylTrichloroSilane coatings in the ISS during the MATISS experiments

Future long-duration human spaceflight will require developments to limit biocontamination of surface habitats. The MATISS (Microbial Aerosol Tethering on Innovative Surfaces in the international Space Station) experiments allowed for exposing surface treatments in the ISS (International Space Station) using a sample-holder developed to this end. Three campaigns of FDTS (perFluoroDecylTrichloroSilane) surface exposures were performed over monthly durations during distinct periods. Tile scanning optical microscopy (×3 and ×30 magnifications) showed a relatively clean environment with a few particles on the surface (0.8 to 7 particles per mm²). The varied densities and shapes in the coarse area fraction (50-1500 µm²) indicated different sources of contamination in the long term, while the bacteriomorph shapes of the fine area fraction (0.5-15 µm²) were consistent with microbial contamination. The surface contamination rates correlate to astronauts' occupancy rates on board. Asymmetric particles density profiles formed throughout time along the air-flow. The higher density values were located near the flow entry for the coarse particles, while the opposite was the case for the fine particles, probably indicating the hydrophobic interaction of particles with the FDTS surface.

Proteomic analysis of the effects of simulated microgravity in human gastric mucosal cells

Microgravity is an ecological factor that affects the environment of the body. In this study, quantitative isobaric labeling (tandem mass tag) method was used to study the changes in human gastric mucosal cells under simulated microgravity for the first time. Comparative proteomic analysis identified 394 (202 upregulated and 192 downregulated) and 542 (286 upregulated and 256 downregulated) proteins differentially regulated by simulated microgravity after 3 and 7 days, respectively. Then the identified proteins were subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses for further exploration. The results of the analysis showed that the ribosomes of gastric mucosal cells were significantly impacted after exposure to simulated microgravity for 3 days, and the cells appeared to be in a state of stress and inflammation. Exposure to simulated microgravity for 7 days significantly affected the mitochondria of the cells, oxidative stress became more evident, while inflammation and weakened connections were observed in the cells. The results of this study highlighted the temporal response trend of gastric mucosal cells to the stressor of microgravity at the two time points of 3 and 7 days. These findings will provide insights into the development of methods to protect the gastric mucosa during space flight.

Dragon's Blood Regulates Rac1-WAVE2-Arp2/3 Signaling Pathway to Protect Rat Intestinal Epithelial Barrier Dysfunction Induced by Simulated Microgravity

Dragon’s Blood is a red resin from Dracaena cochinchinensis (Lour.) S.C. Chen (Yunnan, China). As a traditional Chinese medicinal herb, it has shown protective effects on intestinal disorders. Microgravity could alter intestinal homeostasis. However, the potential herbal drugs for preventing intestine epithelial barrier (IEB) dysfunction under microgravity are not available. This study aimed to investigate the effects of Dragon’s Blood (DB) on microgravity-induced IEB injury and explore its underlying mechanism. A rat tail-suspension model was used to simulate microgravity (SMG). Histomorphology, ultrastructure, permeability, and expression of junction proteins in jejunum, ileum, and colon of SMG rats were determined. Proteomic analysis was used to identify differentially expressed proteins (DEPs) in rat ileum mucosa altered by DB. The potential mechanism of DB to protect IEB dysfunction was validated by western blotting. The effects of several components in DB were evaluated in SMG-treated Caco-2 cells. DB protected against IEB disruption by repairing microvilli and crypts, inhibiting inflammatory factors, lowering the permeability and upregulating the expression of tight and adherens junction proteins in the ileum of SMG rats. Proteomic analysis showed that DB regulated 1080 DEPs in rat ileum mucosa. DEPs were significantly annotated in cell–cell adhesion, focal adhesion, and cytoskeleton regulation. DB increased the expression of Rac1-WAVE2-Arp2/3 pathway proteins and F-actin to G-actin ratio, which promoted the formation of focal adhesions. Loureirin C in DB showed a protective effect on epithelial barrier injury in SMG-treated Caco-2 cells. DB could protect against IEB dysfunction induced by SMG, and its mechanism is associated with the formation of focal adhesions mediated by the Rac1-WAVE2-Arp2/3 pathway, which benefits intestinal epithelial cell migration and barrier repair.

Implications of microgravity-induced cell signaling alterations upon cancer cell growth, invasiveness, metastatic potential, and control by host immunity

The human endeavor to venture beyond the orbit of Earth is challenged by both continuous space radiation and microgravity-induced immune dysfunction. If cancers were to develop in astronauts, it is unclear how these abnormal cells would grow and progress in the microgravity environment. It is unknown if the astronaut's immune response would be able to control or eradicate cancer. A better molecular understanding of how the mechanical force of gravity affects the cell as well as the aggressiveness of cancers and the functionality of host immunity is needed. This review will summarize findings related to microgravity-mediated alterations in the cell cytoskeleton, cell-cell, and cell-extracellular matrix interactions including cadherins, immunoglobulin superfamily of adhesion molecules, selectins, and integrins and related cell signaling. The effects of spaceflight and simulated microgravity on cell viability, cancer cell growth, invasiveness, angiogenesis, metastasis as well as immune cell functions and the subsequent signaling pathways involved will be discussed. Microgravity-induced alterations in function and signaling of the major anti-cancer immune populations will be examined including natural killer cells, dendritic cells, CD4⁺ T cells, and CD8⁺ T cells. Further studies regarding the molecular events impacted by microgravity in both cancer and immune cells will greatly increase the development of therapies to restrict tumor growth and enhance cancer-specific responses for both astronauts and patients on Earth.

Survival Pathways Are Differently Affected by Microgravity in Normal and Cancerous Breast Cells

Metazoan living cells exposed to microgravity undergo dramatic changes in morphological and biological properties, which ultimately lead to apoptosis and phenotype reprogramming. However, apoptosis can occur at very different rates depending on the experimental model, and in some cases, cells seem to be paradoxically protected from programmed cell death during weightlessness. These controversial results can be explained by considering the notion that the behavior of adherent cells dramatically diverges in respect to that of detached cells, organized into organoids-like, floating structures. We investigated both normal (MCF10A) and cancerous (MCF-7) breast cells and found that appreciable apoptosis occurs only after 72 h in MCF-7 cells growing in organoid-like structures, in which major modifications of cytoskeleton components were observed. Indeed, preserving cell attachment to the substrate allows cells to upregulate distinct Akt- and ERK-dependent pathways in MCF-7 and MCF-10A cells, respectively. These findings show that survival strategies may differ between cell types but cannot provide sufficient protection against weightlessness-induced apoptosis alone if adhesion to the substrate is perturbed.