Simulated weightlessness changes the cytoskeleton and extracellular matrix proteins in papillary thyroid carcinoma cells

The Expression of Cell Cycle Cyclins in a Human Megakaryoblast Cell Line Exposed to Simulated Microgravity

The study of the physiological and pathophysiological processes under extreme conditions facilitates a better understanding of the state of a healthy organism and can also shed light on the pathogenesis of diseases. In recent years, it has become evident that gravitational stress affects both the whole organism and individual cells. We have previously demonstrated that simulated microgravity inhibits proliferation, induces apoptosis, changes morphology, and alters the surface marker expression of megakaryoblast cell line MEG-01. In the present work, we investigate the expression of cell cycle cyclins in MEG-01 cells. We performed several experiments for 24 h, 72 h, 96 h and 168 h. Flow cytometry and Western blot analysis demonstrated that the main change in the levels of cyclins expression occurs under conditions of simulated microgravity after 96 h. Thus, the level of cyclin A expression showed an increase in the RPM group during the first 4 days, followed by a decrease, which, together with the peak of cyclin D, may indicate inhibition of the cell cycle in the G2 phase, before mitosis. In addition, based on the data obtained by PCR analysis, we were also able to see that both cyclin A and cyclin B expression showed a peak at 72 h, followed by a gradual decrease at 96 h. STED microscopy data also confirmed that the main change in cyclin expression of MEG-01 cells occurs at 96 h, under simulated microgravity conditions, compared to static control. These results suggested that the cell cycle disruption induced by RPM-simulated microgravity in MEG-01 cells may be associated with the altered expression of the main regulators of the cell cycle. Thus, these data implicate the development of cellular stress in MEG-01 cells, which may be important for proliferating human cells exposed to microgravity in real space.

Exploring the influence of microgravity on chemotherapeutic drug response in cancer: Unveiling new perspectives

Microgravity, an altered gravity condition prevailing in space, has been reported to have a profound impact on human health. Researchers are very keen to comprehensively investigate the impact of microgravity and its intricate involvement in inducing physiological changes. Evidenced transformations were observed in the internal architecture including cytoskeletal organization and cell membrane morphology. These alterations can significantly influence cellular function, signalling pathways and overall cellular behaviour. Further, microgravity has been reported to alter in the expression profile of genes and metabolic pathways related to cellular processes, signalling cascades and structural proteins in cancer cells contributing to the overall changes in the cellular architecture. To investigate the effect of microgravity on cellular and molecular levels numerous ground-based simulation systems employing both in vitro and in vivo models are used. Recently, researchers have explored the possibility of leveraging microgravity to potentially modulate cancer cells against chemotherapy. These findings hold promise for both understanding fundamental processes and could potentially lead to the development of more effective, personalized and innovative approaches in therapeutic advancements against cancer.

PTH 1-34 reduced apoptosis of MLO-Y4 osteocyte-like cells by activating autophagy and inhibiting ER stress under RPM conditions

Osteocytes, as mechanosensitive cells residing within bone tissue, hold a pivotal role in averting the occurrence and progression of osteoporosis. The apoptosis of osteocytes induced by unloading is one of the contributing factors to osteoporosis, although the underlying molecular mechanisms have not been fully elucidated. PTH 1-34 is known to promote bone formation and inhibit bone loss by targeting osteoblasts and osteocytes. However, it is not known whether PTH 1-34 can inhibit osteocyte apoptosis under unloading conditions and the molecular mechanisms involved. In this study, we employed a Random Positioning Machine (RPM) to emulate unloading conditions and cultured MLO-Y4 osteocyte-like cells, in order to unravel the mechanisms through which PTH 1-34 constrains osteocyte apoptosis amidst unloading circumstances. Our findings revealed that PTH 1-34 activated autophagy while suppressing endoplasmic reticulum stress by curtailing the generation of reactive oxygen species (ROS) in MLO-Y4 osteocyte-like cells during unloading conditions. By shedding light on the osteoporosis triggered by skeletal unloading, this study contributes vital insights that may pave the way for the development of pharmacological interventions.

Simulated microgravity induces DNA damage concurrent with impairment of DNA repair and activation of cell-type specific DNA damage response in microglial and glioblastoma cells

Long-term spaceflights affect the structural changes in brain, alter motor or cognitive function and associated development of neuro-optic syndrome in astronauts. Studies addressing the impact of microgravity on brain cells are very limited. Herein, we employed microglial (CHME3) and glioblastoma (U87MG and A172) cells to study their molecular and functional adaptations under simulated microgravity (SMG) exposure. A reduction in cell viability and proliferation with decreased levels of PCNA were observed in these cells. SMG caused extensive DNA damage with an increase in γH2A.X (ser139) phosphorylation and differential activation/expression of DNA damage response (DDR) proteins including ATM, ATR, Chk1, Chk2 and p53 in all the three cell lines. Unlike CHME3, the ATM/Chk2-dependent DDR pathway was activated in glioblastoma cells suggesting a marked difference in the adaptation between normal and cancer cells to SMG. Five different classes of DNA repair pathways including BER, NER, MMR, NHEJ and HR were suppressed in both cell lines with the notable exception of NHEJ (Ku70/80 and DNA-PK) activation in U87MG cells. SMG induced mitochondrial apoptosis with increased expression of Bax, cleaved caspase-3 and cleaved poly-(ADP-ribose) polymerase, and reduced Bcl-2 level. SMG triggered apoptosis simultaneously via ERK1/2 and AKT activation, and inhibition of GSK3β activity which was reversed by MEK1 and PI3K inhibitors. Taken together, our study revealed that microgravity is a strong stressor to trigger DNA damage and apoptosis through activation of ERK1/2 and AKT, and impairment of DNA repair capacity, albeit with a cell-type difference in DDR and NHEJ regulation, in microglial and glioblastoma cells.

Morphologic and genomic changes of thyroid cancer cell lines exposed to conditions of simulated microgravity

Microgravity in space impacts human health. In particular, thyroid cancer, which has a high incidence rate, has been the subject of numerous studies with respect to microgravity. However, most studies have focused on Western follicular thyroid cancer cell lines, while data regarding the effects of microgravity on Asian cell lines are lacking. Therefore, we aimed to investigate the effect of simulated ground-based microgravity on two Korean thyroid cancer cell lines, namely SNU-790 and SNU-80. We found that both cell lines formed multicellular spheroids under simulated microgravity. Gene expression analysis revealed that in SNU-790 cells, histone-related genes were upregulated and microRNA-related genes were downregulated. Meanwhile, in SNU-80 cells, genes related to the cellular response to hypoxia were downregulated. These findings contribute to a better understanding of the effects of microgravity on thyroid cancer cells. Further validation studies and clinical significance analyses are needed to fully understand the implications of these findings.

Simulated Microgravity Influences Immunity-Related Biomarkers in Lung Cancer

Microgravity is a novel strategy that may serve as a complementary tool to develop future cancer therapies. In lung cancer, the influence of microgravity on cellular processes and the migratory capacity of cells is well addressed. However, its effect on the mechanisms that drive lung cancer progression remains in their infancy. In this study, 13 differentially expressed genes were shown to be associated with the prognosis of lung cancer under simulated microgravity (SMG). Using gene set enrichment analysis, these genes are enriched in humoral immunity pathways. In lieu, alveolar basal-epithelial (A549) cells were exposed to SMG via a 2D clinostat system in vitro. In addition to morphology change and decrease in proliferation rate, SMG reverted the epithelial-to-mesenchymal transition (EMT) phenotype of A549, a key mechanism in cancer progression. This was evidenced by increased epithelial E-cadherin expression and decreased mesenchymal N-cadherin expression, hence exhibiting a less metastatic state. Interestingly, we observed increased expression of FCGBP, BPIFB, F5, CST1, and CFB and their correlation to EMT under SMG, rendering them potential tumor suppressor biomarkers. Together, these findings reveal new opportunities to establish novel therapeutic strategies for lung cancer treatment.

Real and Simulated Microgravity: Focus on Mammalian Extracellular Matrix

The lack of gravitational loading is a pivotal risk factor during space flights. Biomedical studies indicate that because of the prolonged effect of microgravity, humans experience bone mass loss, muscle atrophy, cardiovascular insufficiency, and sensory motor coordination disorders. These findings demonstrate the essential role of gravity in human health quality. The physiological and pathophysiological mechanisms of an acute response to microgravity at various levels (molecular, cellular, tissue, and physiological) and subsequent adaptation are intensively studied. Under the permanent gravity of the Earth, multicellular organisms have developed a multi-component tissue mechanosensitive system which includes cellular (nucleo- and cytoskeleton) and extracellular (extracellular matrix, ECM) “mechanosensory” elements. These compartments are coordinated due to specialized integrin-based protein complexes, forming a distinctive mechanosensitive unit. Under the lack of continuous gravitational loading, this unit becomes a substrate for adaptation processes, acting as a gravisensitive unit. Since the space flight conditions limit large-scale research in space, simulation models on Earth are of particular importance for elucidating the mechanisms that provide a response to microgravity. This review describes current state of art concerning mammalian ECM as a gravisensitive unit component under real and simulated microgravity and discusses the directions of further research in this field.

Testing 3D printed biological platform for advancing simulated microgravity and space mechanobiology research

The advancement of microgravity simulators is helping many researchers better understanding the impact of the mechanically unloaded space environment on cellular function and disfunction. However, performing microgravity experiments on Earth, using simulators such as the Random Positioning Machine, introduces some unique practical challenges, including air bubble formation and leakage of growth medium from tissue culture flask and plates, all of which limit research progress. Here, we developed an easy-to-use hybrid biological platform designed with the precision of 3D printing technologies combined with PDMS microfluidic fabrication processes to facilitate reliable and reproducible microgravity cellular experiments. The system has been characterized for applications in the contest of brain cancer research by exposing glioblastoma and endothelial cells to 24 h of simulated microgravity condition to investigate the triggered mechanosensing pathways involved in cellular adaptation to the new environment. The platform demonstrated compatibility with different biological assays, i.e., proliferation, viability, morphology, protein expression and imaging of molecular structures, showing advantages over the conventional usage of culture flask. Our results indicated that both cell types are susceptible when the gravitational vector is disrupted, confirming the impact that microgravity has on both cancer and healthy cells functionality. In particular, we observed deactivation of Yap-1 molecule in glioblastoma cells and the remodeling of VE-Cadherin junctional protein in endothelial cells. The study provides support for the application of the proposed biological platform for advancing space mechanobiology research, also highlighting perspectives and strategies for developing next generation of brain cancer molecular therapies, including targeted drug delivery strategies.

The Fight against Cancer by Microgravity: The Multicellular Spheroid as a Metastasis Model

Cancer is a disease exhibiting uncontrollable cell growth and spreading to other parts of the organism. It is a heavy, worldwide burden for mankind with high morbidity and mortality. Therefore, groundbreaking research and innovations are necessary. Research in space under microgravity (µg) conditions is a novel approach with the potential to fight cancer and develop future cancer therapies. Space travel is accompanied by adverse effects on our health, and there is a need to counteract these health problems. On the cellular level, studies have shown that real (r-) and simulated (s-) µg impact survival, apoptosis, proliferation, migration, and adhesion as well as the cytoskeleton, the extracellular matrix, focal adhesion, and growth factors in cancer cells. Moreover, the µg-environment induces in vitro 3D tumor models (multicellular spheroids and organoids) with a high potential for preclinical drug targeting, cancer drug development, and studying the processes of cancer progression and metastasis on a molecular level. This review focuses on the effects of r- and s-µg on different types of cells deriving from thyroid, breast, lung, skin, and prostate cancer, as well as tumors of the gastrointestinal tract. In addition, we summarize the current knowledge of the impact of µg on cancerous stem cells. The information demonstrates that µg has become an important new technology for increasing current knowledge of cancer biology.

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.

Simulated microgravity triggers DNA damage and mitochondria-mediated apoptosis through ROS generation in human promyelocytic leukemic cells

The weightlessness or microgravity, a physical factor in space, may adversely affect the health of the space travellers or astronauts. The knowledge about the effect of microgravity on human cancer cells is very limited and poorly understood. Here, we employed rotary cell culture system (RCCS) to induce simulated microgravity (SMG) and examined its effects on human promyelocytic leukemic HL-60 cells. These cells were grown in normal gravity condition (1g) for control purpose. The 72 h exposure of cells to SMG decreased cell proliferation and viability which were accompanied by the reduced expression of PCNA and phosphorylated ERK1/2 and AKT proteins. SMG increased the DNA damage as well as the expression of DNA damage sensing proteins including ATM, ATR, Chk1, Chk2 and γH2A.X. The expression of AP1, XRCC1 and APEX1 regulating BER, XPC regulating NER and MLH1 and PMS2 regulating MMR were downregulated. However, SMG increased the expression of Ku70/80, DNA-PK and Rad51, regulating NHEJ and HR. SMG induced apoptosis and increased the levels of cleaved-poly-(ADP-ribose) polymerase and cleaved-caspase-3. An increase in Bax/Bcl-2 ratio and dissipation of mitochondrial membrane potential were also observed. SMG enhanced reactive oxygen species (ROS) formation which led to the enhanced DNA damage and apoptotic cell death. Overall, SMG induced ROS, DNA damage and differential expression of DNA repair genes, and altered the overall DNA repair capacity which may activate ATM/ATR-Chk1/2 and Ku70/80 and DNA-PK-mediated apoptotic cell death.

Testing Lab-on-a-Chip Technology for Culturing Human Melanoma Cells under Simulated Microgravity

The dynamic development of the space industry makes space flights more accessible and opens up new opportunities for biological research to better understand cell physiology under real microgravity. Whereas specialized studies in space remain out of our reach, preliminary experiments can be performed on Earth under simulated microgravity (sµg). Based on this concept, we used a 3D-clinostat (3D-C) to analyze the effect of short exposure to sµg on human keratinocytes HaCaT and melanoma cells A375 cultured on all-glass Lab-on-a-Chip (LOC). Our preliminary studies included viability evaluation, mitochondrial and caspase activity, and proliferation assay, enabling us to determine the effect of sµg on human cells. By comparing the results concerning cells cultured on LOCs and standard culture dishes, we were able to confirm the biocompatibility of all-glass LOCs and their potential application in microgravity research on selected human cell lines. Our studies revealed that HaCaT and A375 cells are susceptible to simulated microgravity; however, we observed an increased caspase activity and a decrease of proliferation in cancer cells cultured on LOCs in comparison to standard cell cultures. These results are an excellent basis to conduct further research on the possible application of LOCs systems in cancer research in space.

Mechanical Regulation of Apoptosis in the Cardiovascular System

Apoptosis is a highly conserved physiological process of programmed cell death which is critical for proper organism development, tissue maintenance, and overall organism homeostasis. Proper regulation of cell removal is crucial, as both excessive and reduced apoptotic rates can lead to the onset of a variety of diseases. Apoptosis can be induced in cells in response to biochemical, electrical, and mechanical stimuli. Here, we review literature on specific mechanical stimuli that regulate apoptosis and the current understanding of how mechanotransduction plays a role in apoptotic signaling. We focus on how insufficient or excessive mechanical forces may induce apoptosis in the cardiovascular system and thus contribute to cardiovascular disease. Although studies have demonstrated that a broad range of mechanical stimuli initiate and/or potentiate apoptosis, they are predominantly correlative, and no mechanisms have been established. In this review, we attempt to establish a unifying mechanism for how various mechanical stimuli initiate a single cellular response, i.e. apoptosis. We hypothesize that the cytoskeleton plays a central role in this process as it does in determining myriad cell behaviors in response to mechanical inputs. We also describe potential approaches of using mechanomedicines to treat various diseases by altering apoptotic rates in specific cells. The goal of this review is to summarize the current state of the mechanobiology field and suggest potential avenues where future research can explore.

Hypergravity Activates a Pro-Angiogenic Homeostatic Response by Human Capillary Endothelial Cells

Capillary endothelial cells are responsible for homeostatic responses to organismic and environmental stimulations. When malfunctioning, they may cause disease. Exposure to microgravity is known to have negative effects on astronauts’ physiology, the endothelium being a particularly sensitive organ. Microgravity-related dysfunctions are striking similar to the consequences of sedentary life, bed rest, and ageing on Earth. Among different countermeasures implemented to minimize the effects of microgravity, a promising one is artificial gravity. We examined the effects of hypergravity on human microvascular endothelial cells of dermal capillary origin (HMEC-1) treated at 4 g for 15 min, and at 20 g for 15 min, 3 and 6 h. We evaluated cell morphology, gene expression and 2D motility and function. We found a profound rearrangement of the cytoskeleton network, dose-dependent increase of Focal Adhesion kinase (FAK) phosphorylation and Yes-associated protein 1 (YAP1) expression, suggesting cell stiffening and increased proneness to motility. Transcriptome analysis showed expression changes of genes associated with cardiovascular homeostasis, nitric oxide production, angiogenesis, and inflammation. Hypergravity-treated cells also showed significantly improved motility and function (2D migration and tube formation). These results, expanding our knowledge about the homeostatic response of capillary endothelial cells, show that adaptation to hypergravity has opposite effect compared to microgravity on the same cell type.

Modeling the Impact of Microgravity at the Cellular Level: Implications for Human Disease

A lack of gravity experienced during space flight has been shown to have profound effects on human physiology including muscle atrophy, reductions in bone density and immune function, and endocrine disorders. At present, these physiological changes present major obstacles to long-term space missions. What is not clear is which pathophysiological disruptions reflect changes at the cellular level versus changes that occur due to the impact of weightlessness on the entire body. This review focuses on current research investigating the impact of microgravity at the cellular level including cellular morphology, proliferation, and adhesion. As direct research in space is currently cost prohibitive, we describe here the use of microgravity simulators for studies at the cellular level. Such instruments provide valuable tools for cost-effective research to better discern the impact of weightlessness on cellular function. Despite recent advances in understanding the relationship between extracellular forces and cell behavior, very little is understood about cellular biology and mechanotransduction under microgravity conditions. This review will examine recent insights into the impact of simulated microgravity on cell biology and how this technology may provide new insight into advancing our understanding of mechanically driven biology and disease.

Simulated Microgravity Influences VEGF, MAPK, and PAM Signaling in Prostate Cancer Cells

Prostate cancer is one of the leading causes of cancer mortality in men worldwide. An unusual but unique environment for studying tumor cell processes is provided by microgravity, either in space or simulated by ground-based devices like a random positioning machine (RPM). In this study, prostate adenocarcinoma-derived PC-3 cells were cultivated on an RPM for time periods of 3 and 5 days. We investigated the genes associated with the cytoskeleton, focal adhesions, extracellular matrix, growth, survival, angiogenesis, and metastasis. The gene expression of signaling factors of the vascular endothelial growth factor (VEGF), mitogen-activated protein kinase (MAPK), and PI3K/AKT/mTOR (PAM) pathways was investigated using qPCR. We performed immunofluorescence to study the cytoskeleton, histological staining to examine the morphology, and a time-resolved immunofluorometric assay to analyze the cell culture supernatants. When PC-3 cells were exposed to simulated microgravity (s-µg), some cells remained growing as adherent cells (AD), while most cells detached from the cell culture flask bottom and formed multicellular spheroids (MCS). After 3-day RPM exposure, PC-3 cells revealed significant downregulation of the VEGF, SRC1, AKT, MTOR, and COL1A1 gene expression in MCS, whereas FLT1, RAF1, MEK1, ERK1, FAK1, RICTOR, ACTB, TUBB, and TLN1 mRNAs were not significantly changed. ERK2 and TLN1 were elevated in AD, and FLK1, LAMA3, COL4A5, FN1, VCL, CDH1, and NGAL mRNAs were significantly upregulated in AD and MCS after 3 days. After a 5-day culture in s-µg, the PC-3 cells showed significant downregulations of VEGF mRNA in AD and MCS, and FN1, CDH1, and LAMA3 in AD and SCR1 in MCS. In addition, we measured significant upregulations in FLT1, AKT, ERK1, ERK2, LCN2, COL1A1, TUBB, and VCL mRNAs in AD and MCS, and increases in FLK1, FN1, and COL4A5 in MCS as well as LAMB2, CDH1, RAF1, MEK1, SRC1, and MTOR mRNAs in AD. FAK1 and RICTOR were not altered by s-µg. In parallel, the secretion rate of VEGFA and NGAL proteins decreased. Cytoskeletal alterations (F-actin) were visible, as well as a deposition of collagen in the MCS. In conclusion, RPM-exposure of PC-3 cells induced changes in their morphology, cytoskeleton, and extracellular matrix protein synthesis, as well as in their focal adhesion complex and growth behavior. The significant upregulation of genes belonging to the PAM pathway indicated their involvement in the cellular changes occurring in microgravity.

Changes in the Surface Expression of Intercellular Adhesion Molecule 3, the Induction of Apoptosis, and the Inhibition of Cell-Cycle Progression of Human Multidrug-Resistant Jurkat/A4 Cells Exposed to a Random Positioning Machine

Experiments from flight- and ground-based model systems suggest that unexpected alterations of the human lymphoblastoid cell line Jurkat, as well as effects on cell growth, metabolism, and apoptosis, can occur in altered gravity conditions. Using a desktop random positioning machine (RPM), we investigated the effects of simulated microgravity on Jurkat cells and their multidrug-resistant subline, Jurkat/A4 cells. The viability of Jurkat/A4 cells decreased after simulated microgravity in contrast with the Jurkat cells. At the same time, the viability between the experimental Jurkat cells and control Jurkat cells was not significantly different. Of note, Jurkat cells appeared as less susceptible to apoptosis than their multidrug-resistant clone Jurkat/A4 cells, whereas cell-cycle analysis showed that the percentage of Jurkat/A4 cells in the S-phase was increased after 72 and 96 h of RPM-simulated microgravity relative to their static counterparts. The differences in Jurkat cells at all phases between static and simulated microgravity were not significant. The surface expression of the intercellular adhesion molecule 3 (ICAM-3)-also known as cluster of differentiation (CD)50-protein was changed for Jurkat/A4 cells following exposure to the RPM. Changes in cell morphology were observed in the Jurkat/A4 cells after 96 h of RPM-simulated microgravity. Thus, we concluded that Jurkat/A4 cells are more sensitive to RPM-simulated microgravity as compared with the parental Jurkat cell line. We also suggest that intercellular adhesion molecule 3 may be an important adhesion molecule involved in the induction of leukocyte apoptosis. The Jurkat/A4 cells with an acquired multidrug resistance phenotype could be a useful model for studying the effects of simulated microgravity and testing anticancer drugs.

Effect of Unloading Condition on the Healing Process and Effectiveness of Platelet Rich Plasma as a Countermeasure: Study on In Vivo and In Vitro Wound Healing Models

Wound healing is a very complex process that allows organisms to survive injuries. It is strictly regulated by a number of biochemical and physical factors, mechanical forces included. Studying wound healing in space is interesting for two main reasons: (i) defining tools, procedures, and protocols to manage serious wounds and burns eventually occurring in future long-lasting space exploration missions, without the possibility of timely medical evacuation to Earth; (ii) understanding the role of gravity and mechanical factors in the healing process and scarring, thus contributing to unravelling the mechanisms underlying the switching between perfect regeneration and imperfect repair with scarring. In the study presented here, a new in vivo sutured wound healing model in the leech (Hirudo medicinalis) has been used to evaluate the effect of unloading conditions on the healing process and the effectiveness of platelet rich plasma (PRP) as a countermeasure. The results reveal that microgravity caused a healing delay and structural alterations in the repair tissue, which were prevented by PRP treatment. Moreover, investigating the effects of microgravity and PRP on an in vitro wound healing model, it was found that PRP is able to counteract the microgravity-induced impairment in fibroblast migration to the wound site. This could be one of the mechanisms underlying the effectiveness of PRP in preventing healing impairment in unloading conditions.

The Role of C-X-C Chemokine Receptor Type 4 (CXCR4) in Cell Adherence and Spheroid Formation of Human Ewing's Sarcoma Cells under Simulated Microgravity

We studied the behavior of Ewing's Sarcoma cells of the line A673 under simulated microgravity (s-µg). These cells express two prominent markers-the oncogene EWS/FLI1 and the chemokine receptor CXCR4, which is used as a target of treatment in several types of cancer. The cells were exposed to s-µg in a random-positioning machine (RPM) for 24 h in the absence and presence of the CXCR4 inhibitor AMD3100. Then, their morphology and cytoskeleton were examined. The expression of selected mutually interacting genes was measured by qRT-PCR and protein accumulation was determined by western blotting. After 24 h incubation on the RPM, a splitting of the A673 cell population in adherent and spheroid cells was observed. Compared to 1 g control cells, EWS/FLI1 was significantly upregulated in the adherent cells and in the spheroids, while CXCR4 and CD44 expression were significantly enhanced in spheroids only. Transcription of CAV-1 was upregulated and DKK2 and VEGF-A were down-regulated in both, adherent in spheroid cells, respectively. Regarding, protein accumulation EWS/FLI1 was enhanced in adherent cells only, but CD44 decreased in spheroids and adherent cells. Inhibition of CXCR4 did not change spheroid count, or structure. Under s-µg, the tumor marker EWS/FLI1 is intensified, while targeting CXCR4, which influences adhesion proteins, did not affect spheroid formation.

Morphological and Molecular Changes in Juvenile Normal Human Fibroblasts Exposed to Simulated Microgravity

The literature suggests morphological alterations and molecular biological changes within the cellular milieu of human cells, exposed to microgravity (µg), as many cell types assemble to multicellular spheroids (MCS). In this study we investigated juvenile normal human dermal fibroblasts (NHDF) grown in simulated µg (s-µg) on a random positioning machine (RPM), aiming to study changes in cell morphology, cytoskeleton, extracellular matrix (ECM), focal adhesion and growth factors. On the RPM, NHDF formed an adherent monolayer and compact MCS. For the two cell populations we found a differential regulation of fibronectin, laminin, collagen-IV, aggrecan, osteopontin, TIMP-1, integrin-β₁, caveolin-1, E-cadherin, talin-1, vimentin, α-SM actin, TGF-β₁, IL-8, MCP-1, MMP-1, and MMP-14 both on the transcriptional and/or translational level. Immunofluorescence staining revealed only slight structural changes in cytoskeletal components. Flow cytometry showed various membrane-bound proteins with considerable variations. In silico analyses of the regulated proteins revealed an interaction network, contributing to MCS growth via signals mediated by integrin-β₁, E-cadherin, caveolin-1 and talin-1. In conclusion, s-µg-conditions induced changes in the cytoskeleton, ECM, focal adhesion and growth behavior of NHDF and we identified for the first time factors involved in fibroblast 3D-assembly. This new knowledge might be of importance in tissue engineering, wound healing and cancer metastasis.

Fighting Thyroid Cancer with Microgravity Research

Microgravity in space or simulated by special ground-based devices provides an unusual but unique environment to study and influence tumour cell processes. By investigating thyroid cancer cells in microgravity for nearly 20 years, researchers got insights into tumour biology that had not been possible under normal laboratory conditions: adherently growing cancer cells detach from their surface and form three-dimensional structures. The cells included in these multicellular spheroids (MCS) were not only altered but behave also differently to those grown in flat sheets in normal gravity, more closely mimicking the conditions in the human body. Therefore, MCS became an invaluable model for studying metastasis and developing new cancer treatment strategies via drug targeting. Microgravity intervenes deeply in processes such as apoptosis and in structural changes involving the cytoskeleton and the extracellular matrix, which influence cell growth. Most interestingly, follicular thyroid cancer cells grown under microgravity conditions were shifted towards a less-malignant phenotype. Results from microgravity research can be used to rethink conventional cancer research and may help to pinpoint the cellular changes that cause cancer. This in turn could lead to novel therapies that will enhance the quality of life for patients or potentially develop new preventive countermeasures.

Semantic Analysis of Posttranslational Modification of Proteins Accumulated in Thyroid Cancer Cells Exposed to Simulated Microgravity

When monolayers of tissue cancer cells of various origins are exposed to real or simulated microgravity, many cells leave the monolayer and assemble to three-dimensional (3D) aggregates (spheroids). In order to define the cellular machinery leading to this change in growth behavior of FTC-133 human thyroid cancer cells and MCF-7 breast cancer cells, we recently performed proteome analyses on these cell lines and determined the proteins’ accumulation in monolayer cells grown under 1g-conditions as well as in the cells of spheroids assembled under simulated microgravity during three and 14 days, respectively. At that time, an influence of the increment or decrement of some of the more than 5000 proteins detected in each cell line was investigated. In this study, we focused on posttranslational modifications (PTMs) of proteins. For this purpose, we selected candidates from the list of the proteins detected in the two preceding proteome analyses, which showed significant accumulation in spheroid cells as compared to 1g monolayer cells. Then we searched for those PTMs of the selected proteins, which according to the literature have already been determined experimentally. Using the Semantic Protocol and RDF Query Language (SPARQL), various databases were examined. Most efficient was the search in the latest version of the dbPTM database. In total, we found 72 different classes of PTMs comprising mainly phosphorylation, glycosylation, ubiquitination and acetylation. Most interestingly, in 35 of the 69 proteins, N6 residues of lysine are modifiable.

Microgravity-Induced Alterations of Inflammation-Related Mechanotransduction in Endothelial Cells on Board SJ-10 Satellite

Endothelial cells (ECs) are mechanosensitive cells undergoing morphological and functional changes in space. Ground-based study has provided a body of evidences about how ECs can respond to the effect of simulated microgravity, however, these results need to be confirmed by spaceflight experiments in real microgravity. In this work, we cultured EA.hy926 ECs on board the SJ-10 Recoverable Scientific Satellite for 3 and 10 days, and analyzed the effects of space microgravity on the ECs. Space microgravity suppressed the glucose metabolism, modulated the expression of cellular adhesive molecules such as ICAM-1, VCAM-1, and CD44, and depressed the pro-angiogenesis and pro-inflammation cytokine secretion. Meanwhile, it also induced the depolymerization of actin filaments and microtubules, promoted the vimentin accumulation, restrained the collagen I and fibronectin deposition, regulated the mechanotransduction through focal adhesion kinase and Rho GTPases, and enhanced the exosome-mediated mRNA transfer. Unlike the effect of simulated microgravity, neither three-dimensional growth nor enhanced nitric oxide production was observed in our experimental settings. This work furthers the understandings in the effects and mechanisms of space microgravity on ECs, and provides useful information for future spaceflight experimental design.

Simulated Microgravity Reduces Focal Adhesions and Alters Cytoskeleton and Nuclear Positioning Leading to Enhanced Apoptosis via Suppressing FAK/RhoA-Mediated mTORC1/NF-κB and ERK1/2 Pathways

Simulated-microgravity (SMG) promotes cell-apoptosis. We demonstrated that SMG inhibited cell proliferation/metastasis via FAK/RhoA-regulated mTORC1 pathway. Since mTORC1, NF-κB, and ERK1/2 signaling are important in cell apoptosis, we examined whether SMG-enhanced apoptosis is regulated via these signals controlled by FAK/RhoA in BL6-10 melanoma cells under clinostat-modelled SMG-condition. We show that SMG promotes cell-apoptosis, alters cytoskeleton, reduces focal adhesions (FAs), and suppresses FAK/RhoA signaling. SMG down-regulates expression of mTORC1-related Raptor, pS6K, pEIF4E, pNF-κB, and pNF-κB-regulated Bcl2, and induces relocalization of pNF-κB from the nucleus to the cytoplasm. In addition, SMG also inhibits expression of nuclear envelope proteins (NEPs) lamin-A, emerin, sun1, and nesprin-3, which control nuclear positioning, and suppresses nuclear positioning-regulated pERK1/2 signaling. Moreover, rapamycin, the mTORC1 inhibitor, also enhances apoptosis in cells under 1 g condition via suppressing the mTORC1/NF-κB pathway. Furthermore, the FAK/RhoA activator, toxin cytotoxic necrotizing factor-1 (CNF1), reduces cell apoptosis, restores the cytoskeleton, FAs, NEPs, and nuclear positioning, and converts all of the above SMG-induced changes in molecular signaling in cells under SMG. Therefore, our data demonstrate that SMG reduces FAs and alters the cytoskeleton and nuclear positioning, leading to enhanced cell apoptosis via suppressing the FAK/RhoA-regulated mTORC1/NF-κB and ERK1/2 pathways. The FAK/RhoA regulatory network may, thus, become a new target for the development of novel therapeutics for humans under spaceflight conditions with stressed physiological challenges, and for other human diseases.

Simulated microgravity inhibits cell focal adhesions leading to reduced melanoma cell proliferation and metastasis via FAK/RhoA-regulated mTORC1 and AMPK pathways

Simulated microgravity (SMG) was reported to affect tumor cell proliferation and metastasis. However, the underlying mechanism is elusive. In this study, we demonstrate that clinostat-modelled SMG reduces BL6-10 melanoma cell proliferation, adhesion and invasiveness in vitro and decreases tumor lung metastasis in vivo. It down-regulates metastasis-related integrin α6β4, MMP9 and Met72 molecules. SMG significantly reduces formation of focal adhesions and activation of focal adhesion kinase (FAK) and Rho family proteins (RhoA, Rac1 and Cdc42) and of mTORC1 kinase, but activates AMPK and ULK1 kinases. We demonstrate that SMG inhibits NADH induction and glycolysis, but induces mitochondrial biogenesis. Interestingly, administration of a RhoA activator, the cytotoxic necrotizing factor-1 (CNF1) effectively converts SMG-triggered alterations and effects on mitochondria biogenesis or glycolysis. CNF1 also converts the SMG-altered cell proliferation and tumor metastasis. In contrast, mTORC inhibitor, rapamycin, produces opposite responses and mimics SMG-induced effects in cells at normal gravity. Taken together, our observations indicate that SMG inhibits focal adhesions, leading to inhibition of signaling FAK and RhoA, and the mTORC1 pathway, which results in activation of the AMPK pathway and reduced melanoma cell proliferation and metastasis. Overall, our findings shed a new light on effects of microgravity on cell biology and human health.

Biological responses of osteocytic connexin 43 hemichannels to simulated microgravity

Connexin 43 (Cx43) hemichannels and gap junctions in osteocytes are responsive to mechanical loading, which is important for bone formation and remodeling. However, the mechanism of these Cx43-forming channels in the process of mechanical unloading is still not very clear. In this study, unloading caused by weightlessness was simulated by using a random position machine (RPM). Osteocytic MLO-Y4 cells were subjected to 2 h of RPM treatment, and levels of Cx43 mRNA and total and cell surface expressed protein were determined by quantitative real-time PCR, western blotting, and biotinylation analysis. Although mRNA was elevated by RPM, total protein level of Cx43 was not altered; however, surface biotinylated Cx43 was significantly reduced. Interestingly, RPM promoted the retention of Cx43 in the Golgi apparatus detected by co-immunofluorescence with antibodies against Cx43 and 58 K Golgi marker protein. Dye uptake assay showed that hemichannels were induced open after RPM for 2 h. Consistently, prostaglandin E₂ release was increased and this increase was completely attenuated with the treatment of a Cx43 hemichannel blocking antibody. Together, this study demonstrates increased activity of Cx43 hemichannels to RPM, and active Cx43 hemichannels with prostaglandin E₂ release are likely to module biological function under simulated weightless conditions. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1195-1202, 2017.

Cytoskeletal stability and metabolic alterations in primary human macrophages in long-term microgravity

The immune system is one of the most affected systems of the human body during space flight. The cells of the immune system are exceptionally sensitive to microgravity. Thus, serious concerns arise, whether space flight associated weakening of the immune system ultimately precludes the expansion of human presence beyond the Earth's orbit. For human space flight, it is an urgent need to understand the cellular and molecular mechanisms by which altered gravity influences and changes the functions of immune cells. The CELLBOX-PRIME (= CellBox-Primary Human Macrophages in Microgravity Environment) experiment investigated for the first time microgravity-associated long-term alterations in primary human macrophages, one of the most important effector cells of the immune system. The experiment was conducted in the U.S. National Laboratory on board of the International Space Station ISS using the NanoRacks laboratory and Biorack type I standard CELLBOX EUE type IV containers. Upload and download were performed with the SpaceX CRS-3 and the Dragon spaceship on April 18th, 2014 / May 18th, 2014. Surprisingly, primary human macrophages exhibited neither quantitative nor structural changes of the actin and vimentin cytoskeleton after 11 days in microgravity when compared to 1g controls. Neither CD18 or CD14 surface expression were altered in microgravity, however ICAM-1 expression was reduced. The analysis of 74 metabolites in the cell culture supernatant by GC-TOF-MS, revealed eight metabolites with significantly different quantities when compared to 1g controls. In particular, the significant increase of free fucose in the cell culture supernatant was associated with a significant decrease of cell surface-bound fucose. The reduced ICAM-1 expression and the loss of cell surface-bound fucose may contribute to functional impairments, e.g. the activation of T cells, migration and activation of the innate immune response. We assume that the surprisingly small and non-significant cytoskeletal alterations represent a stable "steady state" after adaptive processes are initiated in the new microgravity environment. Due to the utmost importance of the human macrophage system for the elimination of pathogens and the clearance of apoptotic cells, its apparent robustness to a low gravity environment is crucial for human health and performance during long-term space missions.

Simulated Microgravity Disrupts Cytoskeleton Organization and Increases Apoptosis of Rat Neural Crest Stem Cells Via Upregulating CXCR4 Expression and RhoA-ROCK1-p38 MAPK-p53 Signaling

Neural crest stem cells (NCSCs) are a population of multipotent stem cells that are distributed broadly in many tissues and organs and are capable of differentiating into a variety of cell types that are dispersed throughout three germ layers. We are interested in studying the effects of simulated microgravity on the survival and self-renewal of NCSCs. NCSCs extracted from the hair follicle bulge region of the rat whisker pad were cultured in vitro, respectively, in a 2D adherent environment and a 3D suspension environment using the rotatory cell culture system (RCCS) to simulate microgravity. We found that rat NCSCs (rNCSCs) cultured in the RCCS for 24 h showed disrupted organization of filamentous actin, increased globular actin level, formation of plasma membrane blebbing and neurite-like artifact, as well as decreased levels of cortactin and vimentin. Interestingly, ∼70% of RCCS-cultured rNCSCs co-expressed cleaved (active) caspase-3 and neuronal markers microtubule-associated protein 2 (MAP2) and Tuj1 instead of NCSC markers, suggesting stress-induced formation of neurite-like artifact in rNCSCs. In addition, rNCSCs showed increased C-X-C chemokine receptor 4 (CXCR4) expression, RhoA GTPase activation, Rho-associated kinase 1 (ROCK1) and p38 mitogen-activated protein kinase (MAPK) phosphorylation, and p53 expression in the nucleus. Incubation of rNCSCs with the Gα protein inhibitor pertussis toxin or CXCR4 siRNA during RCCS-culturing prevented cytoskeleton disorganization and plasma membrane blebbing, and it suppressed apoptosis of rNCSCs. Taken together, we demonstrate for the first time that simulated microgravity disrupts cytoskeleton organization and increases apoptosis of rNCSCs via upregulating CXCR4 expression and the RhoA-ROCK1-p38 MAPK-p53 signaling pathway.

Identifications of novel mechanisms in breast cancer cells involving duct-like multicellular spheroid formation after exposure to the Random Positioning Machine

Many cell types form three-dimensional aggregates (MCS; multicellular spheroids), when they are cultured under microgravity. MCS often resemble the organ, from which the cells have been derived. In this study we investigated human MCF-7 breast cancer cells after a 2 h-, 4 h-, 16 h-, 24 h- and 5d-exposure to a Random Positioning Machine (RPM) simulating microgravity. At 24 h few small compact MCS were detectable, whereas after 5d many MCS were floating in the supernatant above the cells, remaining adherently (AD). The MCS resembled the ducts formed in vivo by human epithelial breast cells. In order to clarify the underlying mechanisms, we harvested MCS and AD cells separately from each RPM-culture and measured the expression of 29 selected genes with a known involvement in MCS formation. qPCR analyses indicated that cytoskeletal genes were unaltered in short-term samples. IL8, VEGFA, and FLT1 were upregulated in 2 h/4 h AD-cultures. The ACTB, TUBB, EZR, RDX, FN1, VEGFA, FLK1 Casp9, Casp3, PRKCA mRNAs were downregulated in 5d-MCS-samples. ESR1 was upregulated in AD, and PGR1 in both phenotypes after 5d. A pathway analysis revealed that the corresponding gene products are involved in organization and regulation of the cell shape, in cell tip formation and membrane to membrane docking.

Simulated Microgravity Using a Rotary Culture System Compromises the In Vitro Development of Mouse Preantral Follicles

Background

Growing cells in simulated weightlessness condition might be a highly promising new technique to maintain or generate tissue constructs in a scaffold-free manner. There is limited evidence that microgravity condition may affect development of ovarian follicles. The objective of the present study was to investigate the effects of simulated microgravity on the in vitro development of mouse preantral follicles.

Methods and Results

Ovarian tissue from 14-day-old mice, or preantral follicles mechanically isolated from 14-day-old mouse ovaries were cultured at a simulated microgravity condition generated using a rotating wall vessel apparatus. Follicle survival was assessed quantitatively using H&E staining. Follicle diameter and oocyte diameter were measured under an inverted microscope. Ultrastructure of oocytes was evaluated using transmission electron microscopy. We observed that simulated microgravity compromised follicle survival in vitro, downregulated PCNA and GDF-9 expressions, and caused ultrastructural abnormalities in oocytes.

Conclusion

This study showed for the first time that three-dimensional culture condition generated by simulated microgravity is detrimental to the initial stage development of mouse preantral follicles in vitro. The experimental setup provides a model to further investigate the mechanisms involved in the in vitro developmental processes of oocytes/granulosa cells under the microgravity condition.

Simulated Microgravity Promotes Cell Apoptosis Through Suppressing Uev1A/TICAM/TRAF/NF-κB-Regulated Anti-Apoptosis and p53/PCNA- and ATM/ATR-Chk1/2-Controlled DNA-Damage Response Pathways

Microgravity has been known to induce cell death. However, its underlying mechanism is less studied. In this study, BL6-10 melanoma cells were cultured in flasks under simulated microgravity (SMG). We examined cell apoptosis, and assessed expression of genes associated with apoptosis and genes regulating apoptosis in cells under SMG. We demonstrate that SMG induces cell morphological changes and microtubule alterations by confocal microscopy, and enhances apoptosis by flow cytometry, which was associated with up- and down-regulation of pro-apoptotic and anti-apoptotic genes, respectively. Moreover, up- and down-regulation of pro-apoptotic (Caspases 3, 7, 8) and anti-apoptotic (Bcl2 and Bnip3) molecules was confirmed by Western blotting analysis. Western blot analysis also indicates that SMG causes inhibition of an apoptosis suppressor, pNF-κB-p65, which is complemented by the predominant localization of NF-κB-p65 in the cytoplasm. SMG also reduces expression of molecules regulating the NF-κB pathway including Uev1A, TICAM, TRAF2, and TRAF6. Interestingly, 10 DNA repair genes are down-regulated in cells exposed to SMG, among which down-regulation of Parp, Ercc8, Rad23, Rad51, and Ku70 was confirmed by Western blotting analysis. In addition, we demonstrate a significant inhibition of molecules involved in the DNA-damage response, such as p53, PCNA, ATM/ATR, and Chk1/2. Taken together, our work reveals that SMG promotes the apoptotic response through a combined modulation of the Uev1A/TICAM/TRAF/NF-κB-regulated apoptosis and the p53/PCNA- and ATM/ATR-Chk1/2-controlled DNA-damage response pathways. Thus, our investigation provides novel information, which may help us to determine the cause of negative alterations in human physiology occurring at spaceflight environment. J. Cell. Biochem. 117: 2138-2148, 2016. © 2016 Wiley Periodicals, Inc.

RNA sequencing identifies crucial genes in papillary thyroid carcinoma (PTC) progression

PURPOSE

The study aims to uncover molecular mechanisms of PTC (papillary thyroid carcinoma) progression and provide therapeutic biomarkers.

METHODS

The paired tumor and control tissues were obtained from 5 PTC patients. RNA was extracted and cDNA libraries were constructed. RNA-sequencing (RNA-seq) was performed on the Illumina HiSeq2000 platform using paired-end method. After preprocessing of the RNA-seq data, gene expression value was calculated by RPKM. Then the differentially expressed genes (DEGs) were identified with edgeR. Functional enrichment and protein-protein interaction (PPI) network analyses were conducted for the DEGs. Module analysis of the PPI network was also performed. Transcription factors (TFs) of DEGs were predicted.

RESULTS

A cohort of 496 up-regulated DEGs mainly correlating with the ECM degradation pathways, and 440 down-regulated DEGs predominantly enriching in transmembrane transport process were identified. Hub nodes in the PPI network were RRM2 and a set of collagens (COL1A1, COL3A1 and COL5A1), which were also remarkable in module 3 and module 5, respectively. Genes in module 3 were associated with cell cycle pathways, while in module 5 were related to ECM degradation pathways. PLAU, PSG1 and EGR2 were the crucial TFs with higher transcriptional activity in PTC than in control.

CONCLUSION

Several genes including COL1A1, COL3A1, RRM2, PLAU, and EGR2 might be used as biomarkers of PTC therapy. Among them, COL1A1 and COL3A1 might exert their functions via involving in ECM degradation pathway, while RRM2 through cell cycle pathway. PLAU might be an active TF, whereas EGR2 might be a tumor suppressor.

Mechanisms of three-dimensional growth of thyroid cells during long-term simulated microgravity

Three-dimensional multicellular spheroids (MCS) of human cells are important in cancer research. We investigated possible mechanisms of MCS formation of thyroid cells. Both, normal Nthy-ori 3–1 thyroid cells and the poorly differentiated follicular thyroid cancer cells FTC-133 formed MCS within 7 and 14 days of culturing on a Random Positioning Machine (RPM), while a part of the cells continued to grow adherently in each culture. The FTC-133 cancer cells formed larger and numerous MCS than the normal cells. In order to explain the different behaviour, we analyzed the gene expression of IL6, IL7, IL8, IL17, OPN, NGAL, VEGFA and enzymes associated cytoskeletal or membrane proteins (ACTB, TUBB, PFN1, CPNE1, TGM2, CD44, FLT1, FLK1, PKB, PKC, ERK1/2, Casp9, Col1A1) as well as the amount of secreted proteins (IL-6, IL-7, IL-8, IL-17, OPN, NGAL, VEGFA). Several of these components changed during RPM-exposure in each cell line. Striking differences between normal and malignant cells were observed in regards to the expression of genes of NGAL, VEGFA, OPN, IL6 and IL17 and to the secretion of VEGFA, IL-17, and IL-6. These results suggest several gravi-sensitive growth or angiogenesis factors being involved in 3D formation of thyroid cells cultured under simulated microgravity.

Identification of proteins involved in inhibition of spheroid formation under microgravity

Many types of cells transit in vitro from a two- to a three-dimensional growth, when they are exposed to microgravity. The underlying mechanisms are not yet understood. Hence, we investigated the impact of microgravity on protein content and growth behavior. For this purpose, the human thyroid cancer cells FTC-133 were seeded either in recently developed cell containers that can endure enhanced physical forces and perform media changes and cell harvesting automatically or in T-25 culture flasks. All cells were cultured for five days at 1g. Afterwards, a part of the cell containers were flown to the International Space Station, while another part was kept on the ground. T-25 flasks were mounted on and next to a Random Positioning Machine. The cells were cultured for 12 days under the various conditions, before they were fixed with RNAlater. All fixed cultures showed monolayers, but three-dimensional aggregates were not detected. In a subsequent protein analysis, 180 proteins were identified by mass spectrometry. These proteins did not indicate significant differences between cells exposed to microgravity and their 1g controls. However, they suggest that an enhanced production of proteins related to the extracellular matrix could detain the cells from spheroid formation, while profilin-1 is phosphorylated.

Life is three dimensional-as in vitro cancer cultures should be

For many decades, fundamental cancer research has relied on two-dimensional in vitro cell culture models. However, these provide a poor representation of the complex three-dimensional (3D) architecture of living tissues. The more recent 3D culture systems, which range from ridged scaffolds to semiliquid gels, resemble their natural counterparts more closely. The arrangement of the cells in 3D systems allows better cell-cell interaction and facilitates extracellular matrix secretion, with concomitant effects on gene and protein expression and cellular behavior. Many studies have reported differences between 3D and 2D systems as regards responses to therapeutic agents and pivotal cellular processes such as cell differentiation, morphology, and signaling pathways, demonstrating the importance of 3D culturing for various cancer cell lines.

Regulation of ICAM-1 in cells of the monocyte/macrophage system in microgravity

Cells of the immune system are highly sensitive to altered gravity, and the monocyte as well as the macrophage function is proven to be impaired under microgravity conditions. In our study, we investigated the surface expression of ICAM-1 protein and expression of ICAM-1 mRNA in cells of the monocyte/macrophage system in microgravity during clinostat, parabolic flight, sounding rocket, and orbital experiments. In murine BV-2 microglial cells, we detected a downregulation of ICAM-1 expression in clinorotation experiments and a rapid and reversible downregulation in the microgravity phase of parabolic flight experiments. In contrast, ICAM-1 expression increased in macrophage-like differentiated human U937 cells during the microgravity phase of parabolic flights and in long-term microgravity provided by a 2D clinostat or during the orbital SIMBOX/Shenzhou-8 mission. In nondifferentiated U937 cells, no effect of microgravity on ICAM-1 expression could be observed during parabolic flight experiments. We conclude that disturbed immune function in microgravity could be a consequence of ICAM-1 modulation in the monocyte/macrophage system, which in turn could have a strong impact on the interaction with T lymphocytes and cell migration. Thus, ICAM-1 can be considered as a rapid-reacting and sustained gravity-regulated molecule in mammalian cells.

Daily application of low magnitude mechanical stimulus inhibits the growth of MDA-MB-231 breast cancer cells in vitro

INTRODUCTION

Mechanical loads can regulate cell proliferation and differentiation at various stages of development and homeostasis. However, the extension of this regulatory effect of mechanical loads on cancer cells is largely unknown. Increased physical compliance is one of the key features of cancer cells, which may hamper the transmission of mechanical loads to these cells within tumor microenvironment. Here we tested whether brief daily application of an external low magnitude mechanical stimulus (LMMS), would impede the growth of MDA-MB-231 aggressive type breast cancer cells in vitro for 3 wks of growth.

METHODS

The signal was applied in oscillatory form at 90 Hz and 0.15 g, a regimen that would induce mechanical loads on MDA-MB-231 cells via inertial properties of cells rather than matrix deformations. Experimental cells were exposed to LMMS 15 min/day, 5 days/week in ambient conditions while control cells were sham loaded. Cell proliferation, viability, cycle, apoptosis, morphology and migration were tested via Trypan Blue dye exclusion, MTT, PI, Annexin V, Calcein-AM and phalloidin stains and scratch wound assays.

RESULTS

Compared to sham controls, daily application of LMMS reduced the number and viability of cancerous MDA-MB-231 cells significantly after first week in the culture, while non-cancerous MCF10A cells were found to be unaffected. Flow cytomety analyses suggested that the observed decrease for the cancer cells in the LMMS group was due to a cell cycle arrest rather than apoptosis. LMMS further reduced cancer cell circularity and increased cytoskeletal actin in MDA-MB-231 cells.

CONCLUSION

Combined, results suggest that direct application of mechanical loads negatively regulate the proliferation of aggressive type cancer cells. If confirmed, this non-invasive approach may be integrated to the efforts for the prevention and/or treatment of cancer.

Phenotypic switch induced by simulated microgravity on MDA-MB-231 breast cancer cells

Microgravity exerts dramatic effects on cell morphology and functions, by disrupting cytoskeleton and adhesion structures, as well as by interfering with biochemical pathways and gene expression. Impairment of cells behavior has both practical and theoretical significance, given that investigations of mechanisms involved in microgravity-mediated effects may shed light on how biophysical constraints cooperate in shaping complex living systems. By exposing breast cancer MDA-MB-231 cells to simulated microgravity (~0.001 g), we observed the emergence of two morphological phenotypes, characterized by distinct membrane fractal values, surface area, and roundness. Moreover, the two phenotypes display different aggregation profiles and adherent behavior on the substrate. These morphological differences are mirrored by the concomitant dramatic functional changes in cell processes (proliferation and apoptosis) and signaling pathways (ERK, AKT, and Survivin). Furthermore, cytoskeleton undergoes a dramatic reorganization, eventually leading to a very different configuration between the two populations. These findings could be considered adaptive and reversible features, given that, by culturing microgravity-exposed cells into a normal gravity field, cells are enabled to recover their original phenotype. Overall these data outline the fundamental role gravity plays in shaping form and function in living systems.

The impact of simulated and real microgravity on bone cells and mesenchymal stem cells

How microgravity affects the biology of human cells and the formation of 3D cell cultures in real and simulated microgravity (r- and s-µg) is currently a hot topic in biomedicine. In r- and s-µg, various cell types were found to form 3D structures. This review will focus on the current knowledge of tissue engineering in space and on Earth using systems such as the random positioning machine (RPM), the 2D-clinostat, or the NASA-developed rotating wall vessel bioreactor (RWV) to create tissue from bone, tumor, and mesenchymal stem cells. To understand the development of 3D structures, in vitro experiments using s-µg devices can provide valuable information about modulations in signal-transduction, cell adhesion, or extracellular matrix induced by altered gravity conditions. These systems also facilitate the analysis of the impact of growth factors, hormones, or drugs on these tissue-like constructs. Progress has been made in bone tissue engineering using the RWV, and multicellular tumor spheroids (MCTS), formed in both r- and s-µg, have been reported and were analyzed in depth. Currently, these MCTS are available for drug testing and proteomic investigations. This review provides an overview of the influence of µg on the aforementioned cells and an outlook for future perspectives in tissue engineering.

Growing tissues in real and simulated microgravity: new methods for tissue engineering

Tissue engineering in simulated (s-) and real microgravity (r-μg) is currently a topic in Space medicine contributing to biomedical sciences and their applications on Earth. The principal aim of this review is to highlight the advances and accomplishments in the field of tissue engineering that could be achieved by culturing cells in Space or by devices created to simulate microgravity on Earth. Understanding the biology of three-dimensional (3D) multicellular structures is very important for a more complete appreciation of in vivo tissue function and advancing in vitro tissue engineering efforts. Various cells exposed to r-μg in Space or to s-μg created by a random positioning machine, a 2D-clinostat, or a rotating wall vessel bioreactor grew in the form of 3D tissues. Hence, these methods represent a new strategy for tissue engineering of a variety of tissues, such as regenerated cartilage, artificial vessel constructs, and other organ tissues as well as multicellular cancer spheroids. These aggregates are used to study molecular mechanisms involved in angiogenesis, cancer development, and biology and for pharmacological testing of, for example, chemotherapeutic drugs or inhibitors of neoangiogenesis. Moreover, they are useful for studying multicellular responses in toxicology and radiation biology, or for performing coculture experiments. The future will show whether these tissue-engineered constructs can be used for medical transplantations. Unveiling the mechanisms of microgravity-dependent molecular and cellular changes is an up-to-date requirement for improving Space medicine and developing new treatment strategies that can be translated to in vivo models while reducing the use of laboratory animals.

Cell cultivation under different gravitational loads using a novel random positioning incubator

Important in biotechnology is the establishment of cell culture methods that reflect the in vivo situation accurately. One approach for reaching this goal is through 3D cell cultivation that mimics tissue or organ structures and functions. We present here a newly designed and constructed random positioning incubator (RPI) that enables 3D cell culture in simulated microgravity (0 g). In addition to growing cells in a weightlessness-like environment, our RPI enables long-duration cell cultivation under various gravitational loads, ranging from close to 0 g to almost 1 g. This allows the study of the mechanotransductional process of cells involved in the conversion of physical forces to an appropriate biochemical response. Gravity is a type of physical force with profound developmental implications in cellular systems as it modulates the resulting signaling cascades as a consequence of mechanical loading. The experiments presented here were conducted on mouse skeletal myoblasts and human lymphocytes, two types of cells that have been shown in the past to be particularly sensitive to changes in gravity. Our novel RPI will expand the horizon at which mechanobiological experiments are conducted. The scientific data gathered may not only improve the sustainment of human life in space, but also lead to the design of alternative countermeasures against diseases related to impaired mechanosensation and downstream signaling processes on earth.

The role of the cytoskeleton in sensing changes in gravity by nonspecialized cells

A large body of evidence indicates that single cells in vitro respond to changes in gravity, and that this response might play an important role for physiological changes at the organism level during spaceflight. Gravity can lead to changes in cell proliferation, differentiation, signaling, and gene expression. At first glance, gravitational forces seem too small to affect bodies with the size of a cell. Thus, the initial response to gravity is both puzzling and important for understanding physiological changes in space. This also offers a unique environment to study the mechanical response of cells. In the past 2 decades, important steps have been made in the field of mechanobiology, and we use these advances to reevaluate the response of single cells to changes in gravity. Recent studies have focused on the cytoskeleton as initial gravity sensor. Thus, we review the observed changes in the cytoskeleton in a microgravity environment, both during spaceflight and in ground-based simulation techniques. We also evaluate to what degree the current experimental evidence supports the cytoskeleton as primary gravity sensor. Finally, we consider how the cytoskeleton itself could be affected by changed gravity. To make the next step toward understanding the response of cells to altered gravity, the challenge will be to track changes quantitatively and on short timescales.

Morphological and physiological changes in mature in vitro neuronal networks towards exposure to short-, middle- or long-term simulated microgravity

One of the objectives of the current international space programmes is to investigate the possible effects of the space environment on the crew health. The aim of this work was to assess the particular effects of simulated microgravity on mature primary neuronal networks and specially their plasticity and connectivity. For this purpose, primary mouse neurons were first grown for 10 days as a dense network before being placed in the Random Positioning Machine (RPM), simulating microgravity. These cultures were then used to investigate the impact of short- (1 h), middle- (24 h) and long-term (10 days) exposure to microgravity at the level of neurite network density, cell morphology and motility as well as cytoskeleton properties in established two-dimensional mature neuronal networks. Image processing analysis of dense neuronal networks exposed to simulated microgravity and their subsequent recovery under ground conditions revealed different neuronal responses depending on the duration period of exposure. After short- and middle-term exposures to simulated microgravity, changes in neurite network, neuron morphology and viability were observed with significant alterations followed by fast recovery processes. Long exposure to simulated microgravity revealed a high adaptation of single neurons to the new gravity conditions as well as a partial adaptation of neuronal networks. This latter was concomitant to an increase of apoptosis. However, neurons and neuronal networks exposed for long-term to simulated microgravity required longer recovery time to re-adapt to the ground gravity. In conclusion, a clear modulation in neuronal plasticity was evidenced through morphological and physiological changes in primary neuronal cultures during and after simulated microgravity exposure. These changes were dependent on the duration of exposure to microgravity.

Impact of simulated microgravity on the normal developmental time line of an animal-bacteria symbiosis

The microgravity environment during space flight imposes numerous adverse effects on animal and microbial physiology. It is unclear, however, how microgravity impacts those cellular interactions between mutualistic microbes and their hosts. Here, we used the symbiosis between the host squid Euprymna scolopes and its luminescent bacterium Vibrio fischeri as a model system. We examined the impact of simulated microgravity on the timeline of bacteria-induced development in the host light organ, the site of the symbiosis. To simulate the microgravity environment, host squid and symbiosis-competent bacteria were incubated together in high-aspect ratio rotating wall vessel bioreactors and examined throughout the early stages of the bacteria-induced morphogenesis. The host innate immune response was suppressed under simulated microgravity; however, there was an acceleration of bacteria-induced apoptosis and regression in the host tissues. These results suggest that the space flight environment may alter the cellular interactions between animal hosts and their natural healthy microbiome.

Spheroid formation of human thyroid cancer cells in an automated culturing system during the Shenzhou-8 Space mission

Human follicular thyroid cancer cells were cultured in Space to investigate the impact of microgravity on 3D growth. For this purpose, we designed and constructed a cell container that can endure enhanced physical forces, is connected to fluid storage chambers, performs media changes and cell harvesting automatically and supports cell viability. The container consists of a cell suspension chamber, two reserve tanks for medium and fixative and a pump for fluid exchange. The selected materials proved durable, non-cytotoxic, and did not inactivate RNAlater. This container was operated automatically during the unmanned Shenzhou-8 Space mission. FTC-133 human follicular thyroid cancer cells were cultured in Space for 10 days. Culture medium was exchanged after 5 days in Space and the cells were fixed after 10 days. The experiment revealed a scaffold-free formation of extraordinary large three-dimensional aggregates by thyroid cancer cells with altered expression of EGF and CTGF genes under real microgravity.

Effects of ultraviolet radiation on FRTL-5 cell growth and thyroid-specific gene expression

During space missions, radiation represents a major hazard for human health and involves all body organs and tissues. Regarding thyroid function, it has been shown that ultraviolet radiation (UVC) has dose-dependent apoptotic effects on FRTL-5 cells, a normal strain of rat thyrocytes. We examined the effects of a sublethal dose of UVC on FRTL-5 cell growth and gene expression. Cells exposed to 10 J/m(2) UVC showed no differences in viability compared to control cells after 24 h, but the BrdU incorporation was reduced, indicating a cytostatic effect. Quantitative RT-PCR carried out at 24 and 48 h after irradiation demonstrated that the mRNA levels of thyroglobulin (Tg), thyroperoxidase (Tpo), and sodium/iodide symporter (Nis) were transiently decreased at 24 h in treated cells, while the mRNAs of the thyroid transcription factors TTF1, Foxe1, and Pax8 were not affected. In cells cultured with TSH-free medium, the basal transcription of Tg, Tpo, and Nis genes was equally impaired by radiation and no longer stimulated by TSH. Overall, the results demonstrate that a sub-apoptotic dose of UVC compromises not only thyrocyte proliferation but also the expression of genes involved in thyroid hormone production. These findings might contribute to explaining the histological, biochemical, and clinical features of hypothyroidism observed in both animals and humans during spaceflight, and suggest that free thyroxine levels of astronauts during prolonged space missions should be monitored.

Using space-based investigations to inform cancer research on Earth

Experiments conducted in the microgravity environment of space are not typically at the forefront of the mind of a cancer biologist. However, space provides physical conditions that are not achievable on Earth, as well as conditions that can be exploited to study mechanisms and pathways that control cell growth and function. Over the past four decades, studies have shown how exposure to microgravity alters biological processes that may be relevant to cancer. In this Review, we explore the influence of microgravity on cell biology, focusing on tumour cells grown in space together with work carried out using models in ground-based investigations.