The effect of simulated microgravity on osteoblasts is independent of the induction of apoptosis

Pharmacological inhibition of endoplasmic reticulum stress mitigates osteoporosis in a mouse model of hindlimb suspension

Hindlimb suspension (HLS) mice exhibit osteoporosis of the hindlimb bones and may be an excellent model to test pharmacological interventions. We investigated the effects of inhibiting endoplasmic reticulum (ER) stress with 4-phenyl butyrate (4-PBA) on the morphology, physicochemical properties, and bone turnover markers of hindlimbs in HLS mice. We randomly divided 21 male C57BL/6J mice into three groups, ground-based controls, untreated HLS group and 4-PBA treated group (HLS+4PBA) (100mg/kg/day, intraperitoneal) for 21 days. We investigated histopathology, micro-CT imaging, Raman spectroscopic analysis, and gene expression. Untreated HLS mice exhibited reduced osteocyte density, multinucleated osteoclast-like cells, adipocyte infiltration, and reduced trabecular striations on micro-CT than the control group. Raman spectroscopy revealed higher levels of ER stress, hydroxyproline, non-collagenous proteins, phenylalanine, tyrosine, and CH2Wag as well as a reduction in proteoglycans and adenine. Furthermore, bone alkaline phosphatase and osteocalcin were downregulated, while Cathepsin K, TRAP, and sclerostin were upregulated. Treatment with 4-PBA partially restored normal bone histology, increased collagen crosslinking, and mineralization, promoted anti-inflammatory markers, and downregulated bone resorption markers. Our findings suggest that mitigating ER stress with 4-PBA could be a therapeutic intervention to offset osteoporosis in conditions mimicking hindlimb suspension.

Microgravity and Musculoskeletal Health: What Strategies Should Be Used for a Great Challenge?

Space colonization represents the most insidious challenge for mankind, as numerous obstacles affect the success of space missions. Specifically, the absence of gravitational forces leads to systemic physiological alterations, with particular emphasis on the musculoskeletal system. Indeed, astronauts exposed to spaceflight are known to report a significant impairment of bone microarchitecture and muscle mass, conditions clinically defined as osteoporosis and sarcopenia. In this context, space medicine assumes a crucial position, as the development of strategies to prevent and/or counteract weightlessness-induced alterations appears to be necessary. Furthermore, the opportunity to study the biological effects induced by weightlessness could provide valuable information regarding adaptations to spaceflight and suggest potential treatments that can preserve musculoskeletal health under microgravity conditions. Noteworthy, improving knowledge about the latest scientific findings in this field of research is crucial, as is thoroughly investigating the mechanisms underlying biological adaptations to microgravity and searching for innovative solutions to counter spaceflight-induced damage. Therefore, this narrative study review, performed using the MEDLINE and Google Scholar databases, aims to summarize the most recent evidence regarding the effects of real and simulated microgravity on the musculoskeletal system and to discuss the effectiveness of the main defence strategies used in both real and experimental settings.

Long-term osteogenic differentiation of human bone marrow stromal cells in simulated microgravity: novel proteins sighted

Microgravity-induced bone loss is a major concern for space travelers. Ground-based microgravity simulators are crucial to study the effect of microgravity exposure on biological systems and to address the limitations posed by restricted access to real space. In this work, for the first time, we adopt a multidisciplinary approach to characterize the morphological, biochemical, and molecular changes underlying the response of human bone marrow stromal cells to long-term simulated microgravity exposure during osteogenic differentiation. Our results show that osteogenic differentiation is reduced while energy metabolism is promoted. We found novel proteins were dysregulated under simulated microgravity, including CSC1-like protein, involved in the mechanotransduction of pressure signals, and PTPN11, SLC44A1 and MME which are involved in osteoblast differentiation pathways and which may become the focus of future translational projects. The investigation of cell proteome highlighted how simulated microgravity affects a relatively low number of proteins compared to time and/or osteogenic factors and has allowed us to reconstruct a hypothetical pipeline for cell response to simulated microgravity. Further investigation focused on the application of nanomaterials may help to increase understanding of how to treat or minimize the effects of microgravity.

Microgravity-Related Changes in Bone Density and Treatment Options: A Systematic Review

Space travelers are exposed to microgravity (µg), which induces enhanced bone loss compared to the age-related bone loss on Earth. Microgravity promotes an increased bone turnover, and this obstructs space exploration. This bone loss can be slowed down by exercise on treadmills or resistive apparatus. The objective of this systematic review is to provide a current overview of the state of the art of the field of bone loss in space and possible treatment options thereof. A total of 482 unique studies were searched through PubMed and Scopus, and 37 studies met the eligibility criteria. The studies showed that, despite increased bone formation during µg, the increase in bone resorption was greater. Different types of exercise and pharmacological treatments with bisphosphonates, RANKL antibody (receptor activator of nuclear factor κβ ligand antibody), proteasome inhibitor, pan-caspase inhibitor, and interleukin-6 monoclonal antibody decrease bone resorption and promote bone formation. Additionally, recombinant irisin, cell-free fat extract, cyclic mechanical stretch-treated bone mesenchymal stem cell-derived exosomes, and strontium-containing hydroxyapatite nanoparticles also show some positive effects on bone loss.

Impairment of 7F2 osteoblast function by simulated partial gravity in a Random Positioning Machine

The multifaceted adverse effects of reduced gravity pose a significant challenge to human spaceflight. Previous studies have shown that bone formation by osteoblasts decreases under microgravity conditions, both real and simulated. However, the effects of partial gravity on osteoblasts’ function are less well understood. Utilizing the software-driven newer version of the Random Positioning Machine (RPM^SW), we simulated levels of partial gravity relevant to future manned space missions: Mars (0.38 G), Moon (0.16 G), and microgravity (Micro, ~10⁻³ G). Short-term (6 days) culture yielded a dose-dependent reduction in proliferation and the enzymatic activity of alkaline phosphatase (ALP), while long-term studies (21 days) showed a distinct dose-dependent inhibition of mineralization. By contrast, expression levels of key osteogenic genes (Alkaline phosphatase, Runt-related Transcription Factor 2, Sparc/osteonectin) exhibited a threshold behavior: gene expression was significantly inhibited when the cells were exposed to Mars-simulating partial gravity, and this was not reduced further when the cells were cultured under simulated Moon or microgravity conditions. Our data suggest that impairment of cell function with decreasing simulated gravity levels is graded and that the threshold profile observed for reduced gene expression is distinct from the dose dependence observed for cell proliferation, ALP activity, and mineral deposition. Our study is of relevance, given the dearth of research into the effects of Lunar and Martian gravity for forthcoming space exploration.

The effects of microgravity on bone structure and function

Humans are spending an increasing amount of time in space, where exposure to conditions of microgravity causes 1–2% bone loss per month in astronauts. Through data collected from astronauts, as well as animal and cellular experiments conducted in space, it is evident that microgravity induces skeletal deconditioning in weight-bearing bones. This review identifies contentions in current literature describing the effect of microgravity on non-weight-bearing bones, different bone compartments, as well as the skeletal recovery process in human and animal spaceflight data. Experiments in space are not readily available, and experimental designs are often limited due to logistical and technical reasons. This review introduces a plethora of on-ground research that elucidate the intricate process of bone loss, utilising technology that simulates microgravity. Observations from these studies are largely congruent to data obtained from spaceflight experiments, while offering more insights behind the molecular mechanisms leading to microgravity-induced bone loss. These insights are discussed herein, as well as how that knowledge has contributed to studies of current therapeutic agents. This review also points out discrepancies in existing data, highlighting knowledge gaps in our current understanding. Further dissection of the exact mechanisms of microgravity-induced bone loss will enable the development of more effective preventative and therapeutic measures to protect against bone loss, both in space and possibly on ground.

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.

Update on the effects of microgravity on the musculoskeletal system

With the reignited push for manned spaceflight and the development of companies focused on commercializing spaceflight, increased human ventures into space are inevitable. However, this venture would not be without risk. The lower gravitational force, known as microgravity, that would be experienced during spaceflight significantly disrupts many physiological systems. One of the most notably affected systems is the musculoskeletal system, where exposure to microgravity causes both bone and skeletal muscle loss, both of which have significant clinical implications. In this review, we focus on recent advancements in our understanding of how exposure to microgravity affects the musculoskeletal system. We will focus on the catabolic effects microgravity exposure has on both bone and skeletal muscle cells, as well as their respective progenitor stem cells. Additionally, we report on the mechanisms that underlie bone and muscle tissue loss resulting from exposure to microgravity and then discuss current countermeasures being evaluated. We reveal the gaps in the current knowledge and expound upon how current research is filling these gaps while also identifying new avenues of study as we continue to pursue manned spaceflight.

The combined effects of simulated microgravity and X-ray radiation on MC3T3-E1 cells and rat femurs

Microgravity is well-known to induce Osteopenia. However, the combined effects of microgravity and radiation that commonly exist in space have not been broadly elucidated. This research investigates the combined effects on MC3T3-E1 cells and rat femurs. In MC3T3-E1 cells, simulated microgravity and X-ray radiation, alone or combination, show decreased cell activity, increased apoptosis rates by flow cytometric analysis, and decreased Runx2 and increased Caspase-3 mRNA and protein expressions. In rat femurs, simulated microgravity and X-ray radiation, alone or combination, show increased bone loss by micro-CT test and Masson staining, decreased serum BALP levels and Runx2 mRNA expressions, and increased serum CTX-1 levels and Caspase-3 mRNA expressions. The strongest effect is observed in the combined group in MC3T3-E1 cells and rat femurs. These findings suggest that the combination of microgravity and radiation exacerbates the effects of either treatment alone on MC3T3-E1 cells and rat femurs.

Novel method for evaluating the health condition of mice in space through a video downlink

Clarification of the criteria for managing animal health is essential to increase the reliability of experiments and ensure transparency in animal welfare. For experiments performed in space, there is no consensus on how to care for animals owing to technical issues, launch mass limitation, and human resources. Some biological processes in mammals, such as musculoskeletal or immune processes, are altered in the space environment, and mice in space can be used to simulate morbid states, such as senescence acceleration. Thus, there is a need to establish a novel evaluation method and evaluation criteria to monitor animal health. Here, we report a novel method to evaluate the health of mice in space through a video downlink in a series of space experiments using the Multiple Artificial-gravity Research System (MARS). This method was found to be more useful in evaluating animal health in space than observations and body weight changes of the same live mice following their return to Earth. We also developed criteria to evaluate health status via a video downlink. These criteria, with “Fur condition” and “Respiratory” as key items, provided information on the daily changes in the health status of mice and helped to identify malfunctions at an early stage. Our method and criteria led to the success of our missions, and they will help establish appropriate rules for space experiments in the future.

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

Gene Expression in Osteoblasts and Osteoclasts Under Microgravity Conditions: A Systematic Review

Background

Microgravity (μG) negatively influences bone metabolism by affecting normal osteoblast and osteoclast function. μG effects on bone metabolism has been an extensive field of study in recent years, due to the challenges presented by space flight.

Methods

We systematically reviewed research data from genomic studies performed in real or simulat-ed μG, on osteoblast and osteoclast cells. Our search yielded 50 studies, of which 39 concerned cells of the osteoblast family and 11 osteoclast precursors.

Results

Osteoblastic cells under μG show a decreased differentiation phenotype, proved by diminished expression levels of Alkaline Phosphatase (ALP) and Osteocalcin (OCN) but no apoptosis. Receptor Activator of NF-κB Ligand (RANKL)/ Osteoprotegerine (OPG) ratio is elevated in favor of RANKL in a time-dependent manner, and further RANKL production is caused by upregulation of Interleukin-6 (IL-6) and the inflammation pathway. Extracellular signals and changes in the gravitational environment are perceived by mechanosensitive proteins of the cytoskeleton and converted to intracellular signals through the Mitogen Activated Protein Kinase pathway (MAPK). This is followed by changes in the ex-pression of nuclear transcription factors of the Activator Protein-1 (AP-1) family and in turn of the NF-κB, thus affecting osteoblast differentiation, cell cycle, proliferation and maturation. Pre-osteoclastic cells show increased expression of the marker proteins such as Tryptophan Regulated Attenuation Protein (TRAP), cathepsin K, Matrix Metalloproteinase-9 (MMP-9) under μG conditions and become sensitized to RANKL.

Conclusion

Suppressing the expression of fusion genes such as syncytine-A which acts independently of RANKL, could be possible future therapeutic targets for microgravity side effects.

Melatonin Suppresses Autophagy Induced by Clinostat in Preosteoblast MC3T3-E1 Cells

Microgravity exposure can cause cardiovascular and immune disorders, muscle atrophy, osteoporosis, and loss of blood and plasma volume. A clinostat device is an effective ground-based tool for simulating microgravity. This study investigated how melatonin suppresses autophagy caused by simulated microgravity in preosteoblast MC3T3-E1 cells. In preosteoblast MC3T3-E1 cells, clinostat rotation induced a significant time-dependent increase in the levels of the autophagosomal marker microtubule-associated protein light chain (LC3), suggesting that autophagy is induced by clinostat rotation in these cells. Melatonin treatment (100, 200 nM) significantly attenuated the clinostat-induced increases in LC3 II protein, and immunofluorescence staining revealed decreased levels of both LC3 and lysosomal-associated membrane protein 2 (Lamp2), indicating a decrease in autophagosomes. The levels of phosphorylation of mammalian target of rapamycin (p-mTOR) (Ser2448), phosphorylation of extracellular signal-regulated kinase (p-ERK), and phosphorylation of serine-threonine protein kinase (p-Akt) (Ser473) were significantly reduced by clinostat rotation. However, their expression levels were significantly recovered by melatonin treatment. Also, expression of the Bcl-2, truncated Bid, Cu/Zn- superoxide dismutase (SOD), and Mn-SOD proteins were significantly increased by melatonin treatment, whereas levels of Bax and catalase were decreased. The endoplasmic reticulum (ER) stress marker GRP78/BiP, IRE1α, and p-PERK proteins were significantly reduced by melatonin treatment. Treatment with the competitive melatonin receptor antagonist luzindole blocked melatonin-induced decreases in LC3 II levels. These results demonstrate that melatonin suppresses clinostat-induced autophagy through increasing the phosphorylation of the ERK/Akt/mTOR proteins. Consequently, melatonin appears to be a potential therapeutic agent for regulating microgravity-related bone loss or osteoporosis.

A mesoscale study of the degradation of bone structural properties in modeled microgravity conditions

One of the most important alterations that occur in man and experimental animals during spaceflight concerns the skeletal system, and entails important bone loss and degradation of mechanical properties. In the present work we investigate ex vivo the long-term effects of weightlessness (simulated microgravity) on bone tissue, by comparing the mesoscale structural properties of weight-bearing rat tibial epiphyseal cancellous structures of healthy animals (ground controls) with those of identical bone explants maintained ex vivo in the Rotary Cell Culture System (RCCS) bioreactor, used to model, on ground, microgravity conditions. Bone structures were reconstructed by synchrotron radiation micro-CT, morphometric analyses were performed, and the apparent elastic properties were computed by means of a numerical model based on the Cell Method. Two novel results were achieved in this study. First of all, the skeletal modifications found in bone explants after 3-4 weeks of culture in the RCCS bioreactor are in perfect agreement with those observed in vivo after a long-term spaceflight (Mice Drawer System mission, 2009), thus confirming the relevance of our model in reproducing the effects of microgravity on whole bone tissue. Secondly, but not less importantly, our study points out that the degradation in bone structural performance (apparent mechanical properties) must be considered in order to achieve an accurate representation of trabecular bone modifications not only in osteoporotic bone diseases, but also in the microgravity-induced bone alterations. In conclusion, our findings, by proving that the association of the RCCS bioreactor-based culture method, used to model microgravity conditions, with numerical simulations able to quantify bone quality, represents the first ground-based reliable model for investigating, ex vivo, some of the spaceflight effects on bone tissue, and open new perspectives to basic research and clinical applications.

Mechanical unloading of bone in microgravity reduces mesenchymal and hematopoietic stem cell-mediated tissue regeneration

Mechanical loading of mammalian tissues is a potent promoter of tissue growth and regeneration, whilst unloading in microgravity can cause reduced tissue regeneration, possibly through effects on stem cell tissue progenitors. To test the specific hypothesis that mechanical unloading alters differentiation of bone marrow mesenchymal and hematopoietic stem cell lineages, we studied cellular and molecular aspects of how bone marrow in the mouse proximal femur responds to unloading in microgravity. Trabecular and cortical endosteal bone surfaces in the femoral head underwent significant bone resorption in microgravity, enlarging the marrow cavity. Cells isolated from the femoral head marrow compartment showed significant down-regulation of gene expression markers for early mesenchymal and hematopoietic differentiation, including FUT1(-6.72), CSF2(-3.30), CD90(-3.33), PTPRC(-2.79), and GDF15(-2.45), but not stem cell markers, such as SOX2. At the cellular level, in situ histological analysis revealed decreased megakaryocyte numbers whilst erythrocytes were increased 2.33 fold. Furthermore, erythrocytes displayed elevated fucosylation and clustering adjacent to sinuses forming the marrow-blood barrier, possibly providing a mechanistic basis for explaining spaceflight anemia. Culture of isolated bone marrow cells immediately after microgravity exposure increased the marrow progenitor's potential for mesenchymal differentiation into in-vitro mineralized bone nodules, and hematopoietic differentiation into osteoclasts, suggesting an accumulation of undifferentiated progenitors during exposure to microgravity. These results support the idea that mechanical unloading of mammalian tissues in microgravity is a strong inhibitor of tissue growth and regeneration mechanisms, acting at the level of early mesenchymal and hematopoietic stem cell differentiation.

RhoA GTPase interacts with beta-catenin signaling in clinorotated osteoblasts

Bone is a dynamic tissue under constant remodeling in response to various signals including mechanical loading. A lack of proper mechanical loading induces disuse osteoporosis that reduces bone mass and structural integrity. The β-catenin signaling together with a network of GTPases is known to play a primary role in load-driven bone formation, but little is known about potential interactions of β-catenin signaling and GTPases in bone loss. In this study, we addressed a question: Does unloading suppress an activation level of RhoA GTPase and β-catenin signaling in osteoblasts? If yes, what is the role of RhoA GTPase and actin filaments in osteoblasts in regulating β-catenin signaling? Using a fluorescence resonance energy transfer (FRET) technique with a biosensor for RhoA together with a fluorescent T cell factor/lymphoid enhancer factor (TCF/LEF) reporter, we examined the effects of clinostat-driven simulated unloading. The results revealed that both RhoA activity and TCF/LEF activity were downregulated by unloading. Reduction in RhoA activity was correlated to a decrease in cytoskeletal organization of actin filaments. Inhibition of β-catenin signaling blocked unloading-induced RhoA suppression, and dominant negative RhoA inhibited TCF/LEF suppression. On the other hand, a constitutively active RhoA enhanced unloading-induced reduction of TCF/LEF activity. The TCF/LEF suppression by unloading was enhanced by co-culture with osteocytes, but it was independent on the organization of actin filaments, myosin II activity, or a myosin light chain kinase. Collectively, the results suggest that β-catenin signaling is required for unloading-driven regulation of RhoA, and RhoA, but not actin cytoskeleton or intracellular tension, mediates the responsiveness of β-catenin signaling to unloading.

Microgravity induces pelvic bone loss through osteoclastic activity, osteocytic osteolysis, and osteoblastic cell cycle inhibition by CDKN1a/p21

Bone is a dynamically remodeled tissue that requires gravity-mediated mechanical stimulation for maintenance of mineral content and structure. Homeostasis in bone occurs through a balance in the activities and signaling of osteoclasts, osteoblasts, and osteocytes, as well as proliferation and differentiation of their stem cell progenitors. Microgravity and unloading are known to cause osteoclast-mediated bone resorption; however, we hypothesize that osteocytic osteolysis, and cell cycle arrest during osteogenesis may also contribute to bone loss in space. To test this possibility, we exposed 16-week-old female C57BL/6J mice (n = 8) to microgravity for 15-days on the STS-131 space shuttle mission. Analysis of the pelvis by µCT shows decreases in bone volume fraction (BV/TV) of 6.29%, and bone thickness of 11.91%. TRAP-positive osteoclast-covered trabecular bone surfaces also increased in microgravity by 170% (p = 0.004), indicating osteoclastic bone degeneration. High-resolution X-ray nanoCT studies revealed signs of lacunar osteolysis, including increases in cross-sectional area (+17%, p = 0.022), perimeter (+14%, p = 0.008), and canalicular diameter (+6%, p = 0.037). Expression of matrix metalloproteinases (MMP) 1, 3, and 10 in bone, as measured by RT-qPCR, was also up-regulated in microgravity (+12.94, +2.98 and +16.85 fold respectively, p<0.01), with MMP10 localized to osteocytes, and consistent with induction of osteocytic osteolysis. Furthermore, expression of CDKN1a/p21 in bone increased 3.31 fold (p<0.01), and was localized to osteoblasts, possibly inhibiting the cell cycle during tissue regeneration as well as conferring apoptosis resistance to these cells. Finally the apoptosis inducer Trp53 was down-regulated by −1.54 fold (p<0.01), possibly associated with the quiescent survival-promoting function of CDKN1a/p21. In conclusion, our findings identify the pelvic and femoral region of the mouse skeleton as an active site of rapid bone loss in microgravity, and indicate that this loss is not limited to osteoclastic degradation. Therefore, this study offers new evidence for microgravity-induced osteocytic osteolysis, and CDKN1a/p21-mediated osteogenic cell cycle arrest.

The Mice Drawer System (MDS) experiment and the space endurance record-breaking mice

The Italian Space Agency, in line with its scientific strategies and the National Utilization Plan for the International Space Station (ISS), contracted Thales Alenia Space Italia to design and build a spaceflight payload for rodent research on ISS: the Mice Drawer System (MDS). The payload, to be integrated inside the Space Shuttle middeck during transportation and inside the Express Rack in the ISS during experiment execution, was designed to function autonomously for more than 3 months and to involve crew only for maintenance activities. In its first mission, three wild type (Wt) and three transgenic male mice over-expressing pleiotrophin under the control of a bone-specific promoter (PTN-Tg) were housed in the MDS. At the time of launch, animals were 2-months old. MDS reached the ISS on board of Shuttle Discovery Flight 17A/STS-128 on August 28(th), 2009. MDS returned to Earth on November 27(th), 2009 with Shuttle Atlantis Flight ULF3/STS-129 after 91 days, performing the longest permanence of mice in space. Unfortunately, during the MDS mission, one PTN-Tg and two Wt mice died due to health status or payload-related reasons. The remaining mice showed a normal behavior throughout the experiment and appeared in excellent health conditions at landing. During the experiment, the mice health conditions and their water and food consumption were daily checked. Upon landing mice were sacrificed, blood parameters measured and tissues dissected for subsequent analysis. To obtain as much information as possible on microgravity-induced tissue modifications, we organized a Tissue Sharing Program: 20 research groups from 6 countries participated. In order to distinguish between possible effects of the MDS housing conditions and effects due to the near-zero gravity environment, a ground replica of the flight experiment was performed at the University of Genova. Control tissues were collected also from mice maintained on Earth in standard vivarium cages.

Rotary culture promotes the proliferation of MCF-7 cells encapsulated in three-dimensional collagen-alginate hydrogels via activation of the ERK1/2-MAPK pathway

Rotary cell culture systems (RCCS) have been shown to be promising for promoting three-dimensional (3D) cell growth and assembly of cells into functional tissues. In this study, 3D tissue-like spheroids of MCF-7 cells were constructed by encapsulating the cells in the collagen-alginate hydrogel, and then cultured in a RCCS to investigate the proliferation of MCF-7 cells. The results from the MTT assay showed that the proliferation rate of MCF-7 cells cultured in the RCCS was higher than that of the static culture control group, and the results from the flow cytometry revealed that the cells in S and G2/M phase were significantly increased compared to the control group. The expression of cell proliferation antigen PCNA and cyclin D1 was also examined with the results further supporting the enhanced proliferation of MCF-7 cells by the RCCS. The results from indirect immunofluorescence revealed that the rotary culture altered neither the cytoskeleton distribution nor the assembly of mitotic spindle. By examination, it was also shown that the rotary culture induced the ERK1/2-MAPK pathway. Taken together, this study demonstrated that the rotary culture could promote the proliferation of MCF-7 cells by inducing the ERK1/2 pathway.

Effects of microgravity on osteoclast bone resorption and osteoblast cytoskeletal organization and adhesion

Exposure to microgravity has been associated with several physiological changes in astronauts, including an osteoporosis-like loss in bone mass. Despite many in vivo and in vitro studies in both microgravity and simulated microgravity conditions, the mechanism for bone loss is still not clear. The lack of weight-bearing forces makes microgravity an ideal physical stimulus to assess bone cell responses. In this work, we conduct a unique investigation of the effects of microgravity on bone-producing osteoblasts and, in parallel, on bone-resorbing osteoclasts. An increase in total number of discrete resorption pits is observed in osteoclasts that experienced microgravity versus ground controls. We further show that osteoblasts exposed to 5 days of microgravity have shorter and wavier microtubules (MTs), smaller and fewer focal adhesions, and thinner cortical actin and stress fibers. Space-flown osteoblasts present extended cell shapes as well as significantly more disrupted and often fragmented or condensed nuclei. The absence of gravitational forces therefore causes both an increase in bone resorption by osteoclasts, and a decrease in osteoblast cellular integrity. The observed effects on both major bone cell types likely accelerate bone loss in microgravity environments, and additionally offer a potential explanation to the development of disuse osteoporosis on Earth.

Effects of oriented substrates on cell morphology, the cell cycle, and the cytoskeleton in Ros 17/2.8 cells

Absence of gravity or microgravity influences the cellular functions of bone forming osteoblasts. The underlying mechanism, however, of cellular sensing and responding to the gravity vector is poorly understood. This work quantified the impact of vector-directional gravity on the biological responses of Ros 17/2.8 cells grown on upward-, downward- or edge-on-oriented substrates. Cell morphology and nuclear translocation, cell proliferation and the cell cycle, and cytoskeletal reorganization were found to vary significantly in the three orientations. All of the responses were duration-dependent. These results provide a new insight into understanding how osteoblasts respond to static vector-directional gravity.

Bioastronautics: the influence of microgravity on astronaut health

For thousands of years different cultures around the world have assigned their own meaning to the Universe. Through research and technology, we have begun to understand the nature and mysteries of the Cosmos. Last year marked the 40(th) anniversary of our first steps on the Moon, and within two decades it is hoped that humankind will have established a settlement on Mars. Space is a harsh environment, and technological advancements in material science, robotics, power generation, and medical equipment will be required to ensure that astronauts survive interplanetary journeys and settlements. The innovative field of bioastronautics aims to address some of the medical issues astronauts encounter during space travel. Astronauts are faced with several health risks during both short- and long-duration spaceflight due to the hostile environment presented in space. Some of these health problems include bone loss, muscle atrophy, cardiac dysrhythmias, and altered orientation. This review discusses the effects of spaceflight on living organisms, in particular, the specific effects of microgravity on the human body and possible countermeasures to these effects.

Oxygen tension regulates preosteocyte maturation and mineralization

Oxygen availability is a critical signal for proper development of many tissues, however there is limited knowledge of its role in the maturation of bone cells. To test the hypothesis that low pO2 regulates bone cell mineralization, MLO-A5 and MLO-Y4 cells were cultured in monolayer and three-dimensional alginate scaffolds in hypoxia (2% O2) or normoxia (20% O2). Hypoxia reduced mineralization and decreased alkaline phosphatase activity of preosteocyte-like MLO-A5 cells in both monolayer and alginate cultures. Similar changes in osteogenic activity were seen when the were subjected to chemical hypoxia. Likewise, Osteocyte-like MLO-Y4 cells also exhibited reduced osteogenic activity in hypoxia relative to normoxic controls. Based on these observations, it is concluded that a low pO2 decreased the mineralization potential of bone cells at both early and late stages of maturation. Since the oxemic state is transduced by the transcription factor, HIF-1alpha, experiments were performed to determine if this protein was responsible for the observed changes in mineral formation. It was noted that when HIF-1alpha was silenced, mineralization activities were not restored. Indeed, in hypoxia, in relationship to wild type controls, the mineralization potential of the knockdown cells was further reduced. Based on these findings, it is concluded that the osteogenic activity of preosteocyte-like cells is dependent on both the O2 tension and the expression of HIF-1alpha.