Simulated Microgravity Condition Alters the Gene Expression of some ECM and Adhesion Molecules in Adipose Derived Stem Cells

Microgravity Effects and Aging Physiology: Similar Changes or Common Mechanisms?

Despite the use of countermeasures (including intense physical activity), cosmonauts and astronauts develop muscle atony and atrophy, cardiovascular system failure, osteopenia, etc. All these changes, reminiscent of age-related physiological changes, occur in a healthy person in microgravity quite quickly - within a few months. Adaptation to the lost of gravity leads to the symptoms of aging, which are compensated after returning to Earth. The prospect of interplanetary flights raises the question of gravity thresholds, below which the main physiological systems will decrease their functional potential, similar to aging, and affect life expectancy. An important role in the aging process belongs to the body's cellular reserve - progenitor cells, which are involved in physiological remodeling and regenerative/reparative processes of all physiological systems. With age, progenitor cell count and their regenerative potential decreases. Moreover, their paracrine profile becomes pro-inflammatory during replicative senescence, disrupting tissue homeostasis. Mesenchymal stem/stromal cells (MSCs) are mechanosensitive, and therefore deprivation of gravitational stimulus causes serious changes in their functional status. The review compares the cellular effects of microgravity and changes developing in senescent cells, including stromal precursors.

S100A8 accelerates wound healing by promoting adipose stem cell proliferation and suppressing inflammation

Adipose-derived stem cells (ADSCs) are stem cells with multidirectional differentiation potential isolated from adipose tissue. They have the same immunomodulatory effect as bone marrow mesenchymal stem cells in wound repair and immune regulation as bone marrow. The mechanism of action of ADSCs in skin wound repair has not been elucidated. S100A8 is a calcium and zinc binding protein, but its role in skin wound healing is rarely reported. We herein show that S100A8 overexpression significantly promoted ADSC proliferation and differentiation, whereas S100A8 knockdown yielded the opposite results. A skin injury model with bone exposure was created in rats by surgically removing the skin from the head and exposing the skull. The wounds were treated with S100A8-overexpressing or S100A8-knockdown ADSCs, and wound healing was monitored. The serum levels of the inflammation-related factors tumor necrosis factor-α and interleukin-6 were decreased significantly after S100A8 overexpression, while the angiogenic factor vascular endothelial growth factor and connective tissue generating factor showed the opposite trend. Histological staining revealed that granulation tissue neovascularization was more pronounced in wounds treated with S100A8-overexpressing ADSCs than that in the control group. We conclude that S100A8 promotes the proliferation of ADSCs and inhibits inflammation to improve skin wound healing.

3D cell culture based on artificial cells and hydrogel under microgravity for bottom-up microtissue constructs

The use of hydrogel as a filling medium to recombine dispersed microencapsulated cells to form an embedded gel-cell microcapsule complex is a new idea based on bottom-up tissue construction, which is benefit for cell distribution and of great significance for tissue construction research in vitro. In this experiment, sodium alginate and chitosan were used as the main materials, rat normal liver cell BRL-3A was used as the model cell to prepare “artificial cells”. Silkworm pupa was used as raw material to extract silk fibroin solution, which was prepared by ultrasound to be the silk fibroin gel; silk fibroin hydrogel-microencapsulated hepatocyte embedded complex was then prepared by using silk fibroin gel as filling medium; the complex was cultured under three modes (static, shaking, and 3D microgravity), and the tissue forming ability of rat hepatocytes was investigated. The results showed that the microgravity culture condition can enhance the cell proliferation and promote the formation of cell colonies in the microcapsules; silk fibroin can form an embedded gel-cell microcapsule complex with microencapsulated cells, which provided mechanical support for the structure of the composite. We hope that this bottom-up construction system will have potential applications in the fields of cell culture and tissue construction.

Three-Dimensional Growth of Prostate Cancer Cells Exposed to Simulated Microgravity

Prostate cancer metastasis has an enormous impact on the mortality of cancer patients. Factors involved in cancer progression and metastasis are known to be key players in microgravity (µg)-driven three-dimensional (3D) cancer spheroid formation. We investigated PC-3 prostate cancer cells for 30 min, 2, 4 and 24 h on the random positioning machine (RPM), a device simulating µg on Earth. After a 24 h RPM-exposure, the cells could be divided into two groups: one grew as 3D multicellular spheroids (MCS), the other one as adherent monolayer (AD). No signs of apoptosis were visible. Among others, we focused on cytokines involved in the events of metastasis and MCS formation. After 24 h of exposure, in the MCS group we measured an increase in ACTB, MSN, COL1A1, LAMA3, FN1, TIMP1, FLT1, EGFR1, IL1A, IL6, CXCL8, and HIF1A mRNA expression, and in the AD group an elevation of LAMA3, COL1A1, FN1, MMP9, VEGFA, IL6, and CXCL8 mRNAs compared to samples subjected to 1 g conditions. Significant downregulations in AD cells were detected in the mRNA levels of TUBB, KRT8, IL1B, IL7, PIK3CB, AKT1 and MTOR after 24 h. The release of collagen-1α1 and fibronectin protein in the supernatant was decreased, whereas the secretion of IL-6 was elevated in 24 h RPM samples. The secretion of IL-1α, IL-1β, IL-7, IL-2, IL-8, IL-17, TNF-α, laminin, MMP-2, TIMP-1, osteopontin and EGF was not significantly altered after 24 h compared to 1 g conditions. The release of soluble factors was significantly reduced after 2 h (IL-1α, IL-2, IL-7, IL-8, IL-17, TNF-α, collagen-1α1, MMP-2, osteopontin) and elevated after 4 h (IL-1β, IL-2, IL-6, IL-7, IL-8, TNF-α, laminin) in RPM samples. Taken together, simulated µg induced 3D growth of PC-3 cancer cells combined with a differential expression of the cytokines IL-1α, IL-1β, IL-6 and IL-8, supporting their involvement in growth and progression of prostate cancer cells.

Microgravity Effects on the Matrisome

Gravity is fundamental factor determining all processes of development and vital activity on Earth. During evolution, a complex mechanism of response to gravity alterations was formed in multicellular organisms. It includes the "gravisensors" in extracellular and intracellular spaces. Inside the cells, the cytoskeleton molecules are the principal gravity-sensitive structures, and outside the cells these are extracellular matrix (ECM) components. The cooperation between the intracellular and extracellular compartments is implemented through specialized protein structures, integrins. The gravity-sensitive complex is a kind of molecular hub that coordinates the functions of various tissues and organs in the gravitational environment. The functioning of this system is of particular importance under extremal conditions, such as spaceflight microgravity. This review covers the current understanding of ECM and associated molecules as the matrisome, the features of the above components in connective tissues, and the role of the latter in the cell and tissue responses to the gravity alterations. Special attention is paid to contemporary methodological approaches to the matrisome composition analysis under real space flights and ground-based simulation of its effects on Earth.

Role of Apoptosis in Wound Healing and Apoptosis Alterations in Microgravity

Functioning as the outermost self-renewing protective layer of the human organism, skin protects against a multitude of harmful biological and physical stimuli. Consisting of ectodermal, mesenchymal, and neural crest-derived cell lineages, tissue homeostasis, and signal transduction are finely tuned through the interplay of various pathways. A health problem of astronauts in space is skin deterioration. Until today, wound healing has not been considered as a severe health concern for crew members. This can change with deep space exploration missions and commercial spaceflights together with space tourism. Albeit the molecular process of wound healing is not fully elucidated yet, there have been established significant conceptual gains and new scientific methods. Apoptosis, e.g., programmed cell death, enables orchestrated development and cell removal in wounded or infected tissue. Experimental designs utilizing microgravity allow new insights into the role of apoptosis in wound healing. Furthermore, impaired wound healing in unloading conditions would depict a significant challenge in human-crewed exploration space missions. In this review, we provide an overview of alterations in the behavior of cutaneous cell lineages under microgravity in regard to the impact of apoptosis in wound healing. We discuss the current knowledge about wound healing in space and simulated microgravity with respect to apoptosis and available therapeutic strategies.

Simulated Microgravity Remodels Extracellular Matrix of Osteocommitted Mesenchymal Stromal Cells

The extracellular matrix (ECM) is the principal structure of bone tissue. Long-term spaceflights lead to osteopenia, which may be a result of the changes in composition as well as remodeling of the ECM by osteogenic cells. To elucidate the cellular effects of microgravity, human mesenchymal stromal cells (MSCs) and their osteocommitted progeny were exposed to simulated microgravity (SMG) for 10 days using random positioning machine (RPM). After RPM exposure, an imbalance of MSC collagen/non-collagen ratio at the expense of a decreased level of collagenous proteins was detected. At the same time, the secretion of proteases (cathepsin A, cathepsin D, MMP3) was increased. No significant effects of SMG on the expression of stromal markers and cell adhesion molecules on the MSC surface were noted. Upregulation of COL11A1, CTNND1, TIMP3, and TNC and downregulation of HAS1, ITGA3, ITGB1, LAMA3, MMP1, and MMP11 were detected in RPM exposed MSCs. ECM-associated transcriptomic changes were more pronounced in osteocommitted progeny. Thus, 10 days of SMG provokes a decrease in the collagenous components of ECM, probably due to the decrease in collagen synthesis and activation of proteases. The presented data demonstrate that ECM-associated molecules of both native and osteocommitted MSCs may be involved in bone matrix reorganization during spaceflight.

Osteogenic differentiation system based on biopolymer nanoparticles for stem cells in simulated microgravity

An efficient long-term intracellular growth factor release system in simulated microgravity for osteogenic differentiation was prepared based on polylactic acid (PLA) and polyhydroxyalkanoate (PHA) nanoparticles for loading of bone morphogenetic protein 2 (BMP2) and bone morphogenetic protein 7 (BMP7) (defined as sB2-PLA-NP and sB7-PHA-NP), respectively, associated with osteogenic differentiation of human adipose derived stem cells (hADSCs). On account of soybean lecithin (SL) as biosurfactants, sB2-PLA-NPs and sB7-PHA-NPs had a high encapsulation efficiency (>80%) of BMPs and uniform small size (<100 nm), and showed different slow-release to provide BMP2 in early stage and BMP7 in late stages of osteogenic differentiation within 20 days, due to degradation rate of PLA and PHA in cells. After uptake into hADSCs, by comparison with single sB2-PLA-NP or sB7-PHA-NP, the Mixture NPs, compound of sB2-PLA-NP and sB7-PHA-NP with a mass ratio of 1:1, can well-promote ALP activity, expression of OPN and upregulated related osteo-genes. Directed osteo-differentiation of Mixture NPs was similar to result of sustained free-BMP2 and BMP7-supplying (sFree-B2&B7) in simulated microgravity, which demonstrated the reliability and stability of Mixture NPs as a long-term osteogenic differentiation system in space medicine and biology in future.

The Impact of Spaceflight and Simulated Microgravity on Cell Adhesion

Microgravity induces a number of significant physiological changes in the cardiovascular, nervous, immune systems, as well as the bone tissue of astronauts. Changes in cell adhesion properties are one aspect affected during long-term spaceflights in mammalian cells. Cellular adhesion behaviors can be divided into cell-cell and cell-matrix adhesion. These behaviors trigger cell-cell recognition, conjugation, migration, cytoskeletal rearrangement, and signal transduction. Cellular adhesion molecule (CAM) is a general term for macromolecules that mediate the contact and binding between cells or between cells and the extracellular matrix (ECM). In this review, we summarize the four major classes of adhesion molecules that regulate cell adhesion, including integrins, immunoglobulin superfamily (Ig-SF), cadherins, and selectin. Moreover, we discuss the effects of spaceflight and simulated microgravity on the adhesion of endothelial cells, immune cells, tumor cells, stem cells, osteoblasts, muscle cells, and other types of cells. Further studies on the effects of microgravity on cell adhesion and the corresponding physiological behaviors may help increase the safety and improve the health of astronauts in space.

Insight in Adhesion Protein Sialylation and Microgravity Dependent Cell Adhesion-An Omics Network Approach

The adhesion behavior of human tissue cells changes in vitro, when gravity forces affecting these cells are modified. To understand the mechanisms underlying these changes, proteins involved in cell-cell or cell-extracellular matrix adhesion, their expression, accumulation, localization, and posttranslational modification (PTM) regarding changes during exposure to microgravity were investigated. As the sialylation of adhesion proteins is influencing cell adhesion on Earth in vitro and in vivo, we analyzed the sialylation of cell adhesion molecules detected by omics studies on cells, which change their adhesion behavior when exposed to microgravity. Using a knowledge graph created from experimental omics data and semantic searches across several reference databases, we studied the sialylation of adhesion proteins glycosylated at their extracellular domains with regards to its sensitivity to microgravity. This way, experimental omics data networked with the current knowledge about the binding of sialic acids to cell adhesion proteins, its regulation, and interactions in between those proteins provided insights into the mechanisms behind our experimental findings, suggesting that balancing the sialylation against the de-sialylation of the terminal ends of the adhesion proteins' glycans influences their binding activity. This sheds light on the transition from two- to three-dimensional growth observed in microgravity, mirroring cell migration and cancer metastasis in vivo.