RhoA and cytoskeletal disruption mediate reduced osteoblastogenesis and enhanced adipogenesis of human mesenchymal stem cells in modeled microgravity

The effects of microgravity on stem cells and the new insights it brings to tissue engineering and regenerative medicine

Conventional two-dimensional (2D) cell culture techniques may undergo modifications in the future, as life scientists have widely acknowledged the ability of three-dimensional (3D) in vitro culture systems to accurately simulate in vivo biology. In recent years, researchers have discovered that microgravity devices can address many challenges associated with 3D cell culture. Stem cells, being pluripotent cells, are regarded as a promising resource for regenerative medicine. Recent studies have demonstrated that 3D culture in microgravity devices can effectively guide stem cells towards differentiation and facilitate the formation of functional tissue, thereby exhibiting advantages within the field of tissue engineering and regenerative medicine. Furthermore, We delineate the impact of microgravity on the biological behavior of various types of stem cells, while elucidating the underlying mechanisms governing these alterations. These findings offer exciting prospects for diverse applications.

Gene co-expression patterns in Atlantic salmon adipose tissue provide a molecular link among seasonal changes, energy balance and age at maturity

Sexual maturation in many fishes requires a major physiological change that involves a rapid transition between energy storage and usage. In Atlantic salmon, this transition for the initiation of maturation is tightly controlled by seasonality and requires a high-energy status. Lipid metabolism is at the heart of this transition since lipids are the main energy storing molecules. The balance between lipogenesis (lipid accumulation) and lipolysis (lipid use) determines energy status transitions. A genomic region containing a transcription co-factor of the Hippo pathway, vgll3, is the main determinant of maturation timing in Atlantic salmon. Interestingly, vgll3 acts as an inhibitor of adipogenesis in mice and its genotypes are potentially associated with seasonal heterochrony in lipid storage and usage in juvenile Atlantic salmon. Here, we explored changes in expression of more than 300 genes directly involved in the processes of adipogenesis, lipogenesis and lipolysis, as well as the Hippo pathway in the adipose tissue of immature and mature Atlantic salmon with distinct vgll3 genotypes. We found molecular evidence consistent with a scenario in which immature males with different vgll3 genotypes exhibit contrasting seasonal dynamics in their lipid profiles. We also identified components of the Hippo signalling pathway as potential major drivers of vgll3 genotype-specific differences in adipose tissue gene expression. This study demonstrates the importance of adipose gene expression patterns for directly linking environmental changes with energy balance and age at maturity through genetic factors bridging lipid metabolism, seasonality and sexual maturation.

Reorganization of the mouse oocyte' cytoskeleton after cultivation under simulated weightlessness

Female germ cells provide the structural basis for the development of a new organism, while the main molecular mechanisms of the impact of weightlessness on the cell remain unknown. The aim of this work was to determine the relative content and distribution of the main proteins of microtubules and microfilaments, to assess the relative RNA content of genes in mouse oocytes after short-term exposure to simulated microgravity, and to determine the potential for embryo development up to the 3-cell stage. Before starting the study, BALB/c mice were divided into two groups. One group received water and standard food without any modifications. Before exposure to simulated microgravity, the oocytes of these animals were randomly divided into two groups - c and µg. The second group of animals additionally received essential phospholipids containing at least 80% phosphatidylcholines, per os for 6 weeks before the start of the experiment at a dosage of 350 mg/kg of the animal's body to modify the lipid composition of the oocyte membrane. The obtained oocytes of these animals were also randomly divided into two groups - ce and µge. To determine the protein distribution and its relative content, immunofluorescence analysis was performed, and the RNA content of genes was assessed using real-time PCR with reverse transcription. After cultivation under simulated microgravity, beta-actin and acetylated alpha-tubulin are redistributed from the cortical layer to the central part of the oocyte, and the relative content of acetylated alpha-tubulin and tubulin isoforms decreases. At the same time, the mRNA content of most genes encoding cytoskeletal proteins was significantly higher in comparison with the control level. The use of essential phospholipids led to a decrease in the content of cellular cholesterol in the oocyte and leveled changes in the content and redistribution of acetylated alpha-tubulin and beta-actin after cultivation under simulated microgravity. In addition, after in vitro fertilization and further cultivation under simulated weightlessness, we observed a decrease in the number of embryos that passed the stage of the 2-cell embryo, but while taking essential phospholipids, the number of embryos that reached the 3-cell stage did not differ from the control group. The results obtained show changes in the content and redistribution of cytoskeletal proteins in the oocyte, which may be involved in the process of pronucleus migration, the formation of the fission spindle and the contractile ring under simulated weightlessness, which may be important for normal fertilization and cleavage of the future embryo.

The myosin and RhoGAP MYO9B influences osteocyte dendrite growth and responses to mechanical stimuli

Introduction: Myosin IXB (MYO9B) is an unconventional myosin with RhoGAP activity and thus is a regulator of actin cytoskeletal organization. MYO9B was previously shown to be necessary for skeletal growth and health and to play a role in actin-based functions of both osteoblasts and osteoclasts. However, its role in responses to mechanical stimulation of bone cells has not yet been described. Therefore, experiments were undertaken to determine the role of MYO9B in bone cell responses to mechanical stress both in vitro and in vivo. Methods: MYO9B expression was knocked down in osteoblast and osteocyte cell lines using RNA interference and the resulting cells were subjected to mechanical stresses including cyclic tensile strain, fluid shear stress, and plating on different substrates (no substrate vs. monomeric or polymerized collagen type I). Osteocytic cells were also subjected to MYO9B regulation through Slit-Robo signaling. Further, wild-type or Myo9b -/- mice were subjected to a regimen of whole-body vibration (WBV) and changes in bone quality were assessed by micro-CT. Results: Unlike control cells, MYO9B-deficient osteoblastic cells subjected to uniaxial cyclic tensile strain were unable to orient their actin stress fibers perpendicular to the strain. Osteocytic cells in which MYO9B was knocked down exhibited elongated dendrites but were unable to respond normally to treatments that increase dendrite length such as fluid shear stress and Slit-Robo signaling. Osteocytic responses to mechanical stimuli were also found to be dependent on the polymerization state of collagen type I substrates. Wild-type mice responded to WBV with increased bone tissue mineral density values while Myo9b -/- mice responded with bone loss. Discussion: These results demonstrate that MYO9B plays a key role in mechanical stress-induced responses of bone cells in vitro and in vivo.

Exercise improved bone health in aging mice: a role of SIRT1 in regulating autophagy and osteogenic differentiation of BMSCs

Introduction

This study was designed to investigate the effect of running exercise on improving bone health in aging mice and explore the role of the SIRT1 in regulating autophagy and osteogenic differentiation of Bone marrow Mesenchymal Stem Cells (BMSCs).

Methods

Twelve-month-old male C57BL/6J mice were used in this study as the aging model and were assigned to treadmill running exercise for eight weeks. Non-exercise male C57BL/6J mice of the same old were used as aging control and five-month-old mice were used as young controls. BMSCs were isolated from mice and subjected to mechanical stretching stimulation in vitro.

Results

The results showed that aging mice had lower bone mass, bone mineral density (BMD), and autophagy than young mice, while running exercise improved BMD and bone mass as well as upregulated autophagy in bone cells. Mechanical loading increased osteogenic differentiation and autophagy in BMSCs, and knockdown of SIRT1 in BMSCs demonstrated that SIRT1-regulated autophagy involved the mechanical loading activation of osteogenic differentiation.

Conclusion

Taken together, this study revealed that exercise improved bone health during aging by activating bone formation, which can be attributed to osteogenic differentiation of BMSCs through the activation of SIRT1-mediated autophagy. The mechanisms underlying this effect may involve mechanical loading.

Towards a New 3Rs Era in the construction of 3D cell culture models simulating tumor microenvironment

Three-dimensional cell culture technology (3DCC) sits between two-dimensional cell culture (2DCC) and animal models and is widely used in oncology research. Compared to 2DCC, 3DCC allows cells to grow in a three-dimensional space, better simulating the in vivo growth environment of tumors, including hypoxia, nutrient concentration gradients, micro angiogenesis mimicism, and the interaction between tumor cells and the tumor microenvironment matrix. 3DCC has unparalleled advantages when compared to animal models, being more controllable, operable, and convenient. This review summarizes the comparison between 2DCC and 3DCC, as well as recent advances in different methods to obtain 3D models and their respective advantages and disadvantages.

The Effects of Combined Exposure to Simulated Microgravity, Ionizing Radiation, and Cortisol on the In Vitro Wound Healing Process

Human spaceflight is associated with several health-related issues as a result of long-term exposure to microgravity, ionizing radiation, and higher levels of psychological stress. Frequent reported skin problems in space include rashes, itches, and a delayed wound healing. Access to space is restricted by financial and logistical issues; as a consequence, experimental sample sizes are often small, which limits the generalization of the results. Earth-based simulation models can be used to investigate cellular responses as a result of exposure to certain spaceflight stressors. Here, we describe the development of an in vitro model of the simulated spaceflight environment, which we used to investigate the combined effect of simulated microgravity using the random positioning machine (RPM), ionizing radiation, and stress hormones on the wound-healing capacity of human dermal fibroblasts. Fibroblasts were exposed to cortisol, after which they were irradiated with different radiation qualities (including X-rays, protons, carbon ions, and iron ions) followed by exposure to simulated microgravity using a random positioning machine (RPM). Data related to the inflammatory, proliferation, and remodeling phase of wound healing has been collected. Results show that spaceflight stressors can interfere with the wound healing process at any phase. Moreover, several interactions between the different spaceflight stressors were found. This highlights the complexity that needs to be taken into account when studying the effect of spaceflight stressors on certain biological processes and for the aim of countermeasures development.

Strontium-Incorporated Carbon Nitride Nanosheets Modulate Intracellular Tension for Reinforced Bone Regeneration

Strontium-containing agents have been demonstrated to elicit both bone anabolic and antiosteoporotic effects, showing great potential for the treatment of bone loss. However, an increased incidence of strontium-induced side effects restricts their clinical applications. Herein, oxidized carbon nitride nanosheets (CN) are delicately used to incorporate Sr²⁺ for the first time to achieve high osteogenic efficacy. The lamellar structure and enriched nitrogen species of CN provide them with a high surface area-to-volume ratio and abundant anchoring sites for Sr²⁺ incorporation. Importantly, Sr²⁺-incorporated CN (CNS) could synergistically promote osteoblast differentiation and bone regeneration at a single, very low Sr²⁺ dose. Mechanically, CNS could activate the FAK/RhoA signaling pathway to modulate the intracellular tension that stimulates osteoblasts differentiation. The present study will provide a new paradigm to enhance the efficacy of osteogenic metal ions by using lamellar nanocarriers.

Single Cell in a Gravity Field

The exploration of deep space or other bodies of the solar system, associated with a long stay in microgravity or altered gravity, requires the development of fundamentally new methods of protecting the human body. Most of the negative changes in micro- or hypergravity occur at the cellular level; however, the mechanism of reception of the altered gravity and transduction of this signal, leading to the formation of an adaptive pattern of the cell, is still poorly understood. At the same time, most of the negative changes that occur in early embryos when the force of gravity changes almost disappear by the time the new organism is born. This review is devoted to the responses of early embryos and stem cells, as well as terminally differentiated germ cells, to changes in gravity. An attempt was made to generalize the data presented in the literature and propose a possible unified mechanism for the reception by a single cell of an increase and decrease in gravity based on various deformations of the cortical cytoskeleton.

Sperm of Fruit Fly Drosophila melanogaster under Space Flight

Studies of reproductive function under long-term space flight conditions are of interest in planning the exploration of deep space. Motility, including the use of various inhibitors, cellular respiration, and the content of cytoskeletal proteins were studied, assessing the level of expression of the corresponding genes in spermatozoa of Drosophila melanogaster, which were in space flight conditions for 12 days. The experiment was carried out twice on board the Russian Segment of the International Space Station. Sperm motility speed after space flight, and subsequently 16 h after landing, is reduced relative to the control by 20% (p < 0.05). In comparison with the simulation experiment, we showed that this occurs as a result of the action of overloads and readaptation to the Earth’s gravity. At the same time, cellular respiration, the content of proteins of the respiratory chain, and the expression of their genes do not change. We used kinase inhibitor 6-(dimethylamino)purine (6-DMAP) and phosphatase inhibitors; 6-DMAP restored the reduced the speed of spermatozoa in the flight group to that of the control. These results can be useful in developing a strategy for protecting reproductive health during the development of other bodies in the solar system.

Adaptation and Changes in Actin Dynamics and Cell Motility as Early Responses of Cultured Mammalian Cells to Altered Gravitational Vector

Cultured mammalian cells have been shown to respond to microgravity (μG), but the molecular mechanism is still unknown. The study we report here is focused on molecular and cellular events that occur within a short period of time, which may be related to gravity sensing by cells. Our assumption is that the gravity-sensing mechanism is activated as soon as cells are exposed to any new gravitational environment. To study the molecular events, we exposed cells to simulated μG (SμG) for 15 min, 30 min, 1 h, 2 h, 4 h, and 8 h using a three-dimensional clinostat and made cell lysates, which were then analyzed by reverse phase protein arrays (RPPAs) using a panel of 453 different antibodies. By comparing the RPPA data from cells cultured at 1G with those of cells under SμG, we identified a total of 35 proteomic changes in the SμG samples and found that 20 of these changes took place, mostly transiently, within 30 min. In the 4 h and 8 h samples, there were only two RPPA changes, suggesting that the physiology of these cells is practically indistinguishable from that of cells cultured at 1 G. Among the proteins involved in the early proteomic changes were those that regulate cell motility and cytoskeletal organization. To see whether changes in gravitational environment indeed activate cell motility, we flipped the culture dish upside down (directional change in gravity vector) and studied cell migration and actin cytoskeletal organization. We found that compared with cells grown right-side up, upside-down cells transiently lost stress fibers and rapidly developed lamellipodia, which was supported by increased activity of Ras-related C3 botulinum toxin substrate 1 (Rac1). The upside-down cells also increased their migratory activity. It is possible that these early molecular and cellular events play roles in gravity sensing by mammalian cells. Our study also indicated that these early responses are transient, suggesting that cells appear to adapt physiologically to a new gravitational environment.

Insight Into Rho Kinase Isoforms in Obesity and Energy Homeostasis

Obesity and associated complications increasingly jeopardize global health and contribute to the rapidly rising prevalence of type 2 diabetes mellitus and obesity-related diseases. Developing novel methods for the prevention and treatment of excess body adipose tissue expansion can make a significant contribution to public health. Rho kinase is a Rho-associated coiled-coil-containing protein kinase (Rho kinase or ROCK). The ROCK family including ROCK1 and ROCK2 has recently emerged as a potential therapeutic target for the treatment of metabolic disorders. Up-regulated ROCK activity has been involved in the pathogenesis of all aspects of metabolic syndrome including obesity, insulin resistance, dyslipidemia and hypertension. The RhoA/ROCK-mediated actin cytoskeleton dynamics have been implicated in both white and beige adipogenesis. Studies using ROCK pan-inhibitors in animal models of obesity, diabetes, and associated complications have demonstrated beneficial outcomes. Studies via genetically modified animal models further established isoform-specific roles of ROCK in the pathogenesis of metabolic disorders including obesity. However, most reported studies have been focused on ROCK1 activity during the past decade. Due to the progress in developing ROCK2-selective inhibitors in recent years, a growing body of evidence indicates more attention should be devoted towards understanding ROCK2 isoform function in metabolism. Hence, studying individual ROCK isoforms to reveal their specific roles and principal mechanisms in white and beige adipogenesis, insulin sensitivity, energy balancing regulation, and obesity development will facilitate significant breakthroughs for systemic treatment with isoform-selective inhibitors. In this review, we give an overview of ROCK functions in the pathogenesis of obesity and insulin resistance with a particular focus on the current understanding of ROCK isoform signaling in white and beige adipogenesis, obesity and thermogenesis in adipose tissue and other major metabolic organs involved in energy homeostasis regulation.

Nutraceuticals Synergistically Promote Osteogenesis in Cultured 7F2 Osteoblasts and Mitigate Inhibition of Differentiation and Maturation in Simulated Microgravity

Microgravity is known to impact bone health, similar to mechanical unloading on Earth. In the absence of countermeasures, bone formation and mineral deposition are strongly inhibited in Space. There is an unmet need to identify nutritional countermeasures. Curcumin and carnosic acid are phytonutrients with anticancer, anti-inflammatory, and antioxidative effects and may exhibit osteogenic properties. Zinc is a trace element essential for bone formation. We hypothesized that these nutraceuticals could counteract the microgravity-induced inhibition of osteogenic differentiation and function. To test this hypothesis, we cultured 7F2 murine osteoblasts in simulated microgravity (SMG) in a Random Positioning Machine in the presence and absence of curcumin, carnosic acid, and zinc and evaluated cell proliferation, function, and differentiation. SMG enhanced cell proliferation in osteogenic medium. The nutraceuticals partially reversed the inhibitory effects of SMG on alkaline phosphatase (ALP) activity and did not alter the SMG-induced reduction in the expression of osteogenic marker genes in osteogenic medium, while they promoted osteoblast proliferation and ALP activity in the absence of traditional osteogenic media. We further observed a synergistic effect of the intermix of the phytonutrients on ALP activity. Intermixes of phytonutrients may serve as convenient and effective nutritional countermeasures against bone loss in space.

TM9SF4 is a novel regulator in lineage commitment of bone marrow mesenchymal stem cells to either osteoblasts or adipocytes

BACKGROUND

Osteoporosis is a common bone disease in elderly population caused by imbalanced bone formation and bone resorption. Mesenchymal stem cells (MSCs) are responsible for maintaining this bone homeostasis. The phenotype of transmembrane 9 superfamily 4 (TM9SF4) knockout mice suggests a relationship between TM9SF4 proteins and bone homeostasis. But the effect of TM9SF4 in osteology has never been reported. In the present study, we investigated the function of TM9SF4 in MSC differentiation commitment, as well as its role in osteoporosis.

METHODS

Primary bone marrow MSCs, isolated from TM9SF4 wildtype (TM9SF4^+/+) and knockout (TM9SF4^-/-) mice, were induced to differentiate into osteoblasts or adipocytes, respectively. The osteogenesis was examined by qRT-PCR detection of osteogenic markers, ALP staining and Alizarin Red S staining. The adipogenesis was tested by qRT-PCR quantification of adipogenic markers and Oil Red O staining. The cytoskeletal organization of MSCs was observed under confocal microscope. The osteoporotic model was induced by ovariectomy in TM9SF4^+/+ and TM9SF4^-/- mice, followed by Toluidine blue and H&E staining to assess lipid accumulation in trabecular bones, as well as micro-computed tomography scanning and immunohistochemistry staining for bone mass density assessment. The experiments on signaling pathways were conducted using qRT-PCR, Western blot and Alizarin Red S staining.

RESULTS

We determined the role of TM9SF4 in MSC differentiation and found that TM9SF4^-/- MSCs had higher potential to differentiate into osteoblasts and lower capability into adipocytes, without affecting osteoclastogenesis in vitro. In ovariectomy-induced osteoporotic model, TM9SF4^-/- mice retained higher bone mass and less lipid accumulation in trabecular bones, indicating an important role of TM9SF4 in the regulation of osteoporosis. Mechanistically, TM9SF4-depleted cells showed elongated actin fibers, which may act through mTORC2/Akt/β-catenin pathway to promote their commitment into osteoblasts. Furthermore, TM9SF4-depleted cells showed higher activity of canonical Wnt pathway, suggesting the participation of Wnt/β-catenin during TM9SF4-regulated osteogenesis.

CONCLUSIONS

Our study demonstrates TM9SF4 as a novel regulator for MSC lineage commitment. Depletion of TM9SF4 preferentially drives MSCs into osteoblasts instead of adipocytes. Furthermore, TM9SF4^-/- mice show delayed bone loss and reduced lipid accumulation during ovariectomy-induced osteoporosis. Our results indicate TM9SF4 as a promising target for the future clinical osteoporotic treatment.

At the nuclear envelope of bone mechanobiology

The nuclear envelope and nucleoskeleton are emerging as signaling centers that regulate how physical information from the extracellular matrix is biochemically transduced into the nucleus, affecting chromatin and controlling cell function. Bone is a mechanically driven tissue that relies on physical information to maintain its physiological function and structure. Disorder that present with musculoskeletal and cardiac symptoms, such as Emery-Dreifuss muscular dystrophies and progeria, correlate with mutations in nuclear envelope proteins including Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, Lamin A/C, and emerin. However, the role of nuclear envelope mechanobiology on bone function remains underexplored. The mesenchymal stem cell (MSC) model is perhaps the most studied relationship between bone regulation and nuclear envelope function. MSCs maintain the musculoskeletal system by differentiating into multiple cell types including osteocytes and adipocytes, thus supporting the bone's ability to respond to mechanical challenge. In this review, we will focus on how MSC function is regulated by mechanical challenges both in vitro and in vivo within the context of bone function specifically focusing on integrin, β-catenin and YAP/TAZ signaling. The importance of the nuclear envelope will be explored within the context of musculoskeletal diseases related to nuclear envelope protein mutations and nuclear envelope regulation of signaling pathways relevant to bone mechanobiology in vitro and in vivo.

Increased Mesenchymal Stem Cell Functionalization in Three-Dimensional Manufacturing Settings for Enhanced Therapeutic Applications

Mesenchymal stem/stromal cell (MSC) exist within their in vivo niches as part of heterogeneous cell populations, exhibiting variable stemness potential and supportive functionalities. Conventional extensive 2D in vitro MSC expansion, aimed at obtaining clinically relevant therapeutic cell numbers, results in detrimental effects on both cellular characteristics (e.g., phenotypic changes and senescence) and functions (e.g., differentiation capacity and immunomodulatory effects). These deleterious effects, added to the inherent inter-donor variability, negatively affect the standardization and reproducibility of MSC therapeutic potential. The resulting manufacturing challenges that drive the qualitative variability of MSC-based products is evident in various clinical trials where MSC therapeutic efficacy is moderate or, in some cases, totally insufficient. To circumvent these limitations, various in vitro/ex vivo techniques have been applied to manufacturing protocols to induce specific features, attributes, and functions in expanding cells. Exposure to inflammatory cues (cell priming) is one of them, however, with untoward effects such as transient expression of HLA-DR preventing allogeneic therapeutic schemes. MSC functionalization can be also achieved by in vitro 3D culturing techniques, in an effort to more closely recapitulate the in vivo MSC niche. The resulting spheroid structures provide spatial cell organization with increased cell–cell interactions, stable, or even enhanced phenotypic profiles, and increased trophic and immunomodulatory functionalities. In that context, MSC 3D spheroids have shown enhanced “medicinal signaling” activities and increased homing and survival capacities upon transplantation in vivo. Importantly, MSC spheroids have been applied in various preclinical animal models including wound healing, bone and osteochondral defects, and cardiovascular diseases showing safety and efficacy in vivo. Therefore, the incorporation of 3D MSC culturing approach into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved without requiring ex vivo stimulatory regimes. In the present review, we discuss the MSC functionalization in 3D settings and how this strategy can contribute to an improved MSC-based product for safer and more effective therapeutic applications.

Gravity sensing in plant and animal cells

Gravity determines shape of body tissue and affects the functions of life, both in plants and animals. The cellular response to gravity is an active process of mechanotransduction. Although plants and animals share some common mechanisms of gravity sensing in spite of their distant phylogenetic origin, each species has its own mechanism to sense and respond to gravity. In this review, we discuss current understanding regarding the mechanisms of cellular gravity sensing in plants and animals. Understanding gravisensing also contributes to life on Earth, e.g., understanding osteoporosis and muscle atrophy. Furthermore, in the current age of Mars exploration, understanding cellular responses to gravity will form the foundation of living in space.

The individual and combined effects of spaceflight radiation and microgravity on biologic systems and functional outcomes

Both microgravity and radiation exposure in the spaceflight environment have been identified as hazards to astronaut health and performance. Substantial study has been focused on understanding the biology and risks associated with prolonged exposure to microgravity, and the hazards presented by radiation from galactic cosmic rays (GCR) and solar particle events (SPEs) outside of low earth orbit (LEO). To date, the majority of the ground-based analogues (e.g., rodent or cell culture studies) that investigate the biology of and risks associated with spaceflight hazards will focus on an individual hazard in isolation. However, astronauts will face these challenges simultaneously Combined hazard studies are necessary for understanding the risks astronauts face as they travel outside of LEO, and are also critical for countermeasure development. The focus of this review is to describe biologic and functional outcomes from ground-based analogue models for microgravity and radiation, specifically highlighting the combined effects of radiation and reduced weight-bearing from rodent ground-based tail suspension via hind limb unloading (HLU) and partial weight-bearing (PWB) models, although in vitro and spaceflight results are discussed as appropriate. The review focuses on the skeletal, ocular, central nervous system (CNS), cardiovascular, and stem cells responses.

Steering cell behavior through mechanobiology in 3D: A regenerative medicine perspective

Mechanobiology, translating mechanical signals into biological ones, greatly affects cellular behavior. Steering cellular behavior for cell-based regenerative medicine approaches requires a thorough understanding of the orchestrating molecular mechanisms, among which mechanotransducive ones are being more and more elucidated. Because of their wide use and highly mechanotransduction dependent differentiation, this review focuses on mesenchymal stromal cells (MSCs), while also briefly relating the discussed results to other cell types. While the mechanotransduction pathways are relatively well-studied in 2D, much remains unknown of the role and regulation of these pathways in 3D. Ultimately, cells need to be cultured in a 3D environment to create functional de novo tissue. In this review, we explore the literature on the roles of different material properties on cellular behavior and mechanobiology in 2D and 3D. For example, while stiffness plays a dominant role in 2D MSCs differentiation, it seems to be of subordinate importance in 3D MSCs differentiation, where matrix remodeling seems to be key. Also, the role and regulation of some of the main mechanotransduction players are discussed, focusing on MSCs. We have only just begun to fundamentally understand MSCs and other stem cells behavior in 3D and more fundamental research is required to advance biomaterials able to replicate the stem cell niche and control cell activity. This better understanding will contribute to smarter tissue engineering scaffold design and the advancement of regenerative medicine.

Good Manufacturing Practice-Grade of Megakaryocytes Produced by a Novel Ex Vivo Culturing Platform

Ex vivo (EV)‐derived megakaryocytes (MKs) have shown great promise as a substitute for platelets in transfusion medicine to alleviate a severe shortage of donor‐platelets. Challenges remain that include poor efficiency, a limited scale of production, and undefined short‐term storage conditions of EV‐derived MKs. This study aims to develop a high‐efficiency system for large‐scale production of Good Manufacturing Practice (GMP)‐grade MKs and determine the short‐term storage condition for the MKs. A roller‐bottle culture system was introduced to produce GMP‐grade MKs from small‐molecule/cytokine cocktail expanded hematopoietic stem cells. Various buffer systems and temperatures for the short‐term storage of MKs were assessed by cell viability, biomarker expression, and DNA ploidy levels. MKs stored for 24 hours were transplanted into sublethally irradiated nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice to confirm their platelet‐releasing and tissue‐homing ability in vivo. A yield of ~ 2.5 × 10⁴ CD41a⁺/CD42b⁺ MKs with purity of ~ 80% was achieved from one original cord blood CD34⁺ cell. Compared with the static culture, the roller‐bottle culture system significantly enhanced megakaryopoiesis, as shown by the cell size, DNA ploidy, and megakaryopoiesis‐related gene expression. The optimal storage condition for the MKs was defined as normal saline with 10% human serum albumin at 22℃. Stored MKs were capable of rapidly producing functional platelets and largely distributing in the lungs of NOD/SCID mice. The novel development of efficient production and storage system for GMP‐grade MKs represents a significant step toward application of these MKs in the clinic.

Mechanosensitivity of Cells and Its Role in the Regulation of Physiological Functions and the Implementation of Physiotherapeutic Effects (Review)

Regulatory signals in the body are not limited to chemical and electrical ones. There is another type of important signals for cells: those are mechanical signals (coming from the environment or arising from within the body), which have been less known in the literature. The review summarizes new information on the mechanosensitivity of various cells of connective tissue and nervous system. Participation of mechanical stimuli in the regulation of growth, development, differentiation, and functioning of tissues is described. The data focus on bone remodeling, wound healing, neurite growth, and the formation of neural networks. Mechanotransduction, cellular organelles, and mechanosensitive molecules involved in these processes are discussed as well as the role of the extracellular matrix. The importance of mechanical characteristics of cells in the pathogenesis of diseases is highlighted. Finally, the possible role of mechanosensitivity in mediating the physiotherapeutic effects is addressed.

Effect of simulated microgravity conditions of hindlimb unloading on mice hematopoietic and mesenchymal stromal cells

Conditions in space, such as microgravity, may affect the hematopoietic and bone marrow‐derived mesenchymal stromal cells (BM‐MSCs) of astronauts. However, to date, few detailed phenotype change data about the different type of hematopoietic cells have reported. In this study, C57BL/6 mice were randomly divided into two groups: a control group (control) and a hindlimb suspension group (treated). After four weeks of hindlimb suspension, we found that this simulated microgravity (sµg) condition could increase the percentage of monocytes and macrophages and decrease the percentage of B lymphocytes and mature red cells in bone marrow. The percentage of B lymphocytes in the spleen and the red blood cell count in peripheral blood also decreased, consistent with the response of bone marrow. The cytoskeleton in the BM‐MSCs was disrupted. The expression levels of hematopoietic‐related genes, such as fms‐like tyrosine kinase‐3 ligand, granulocyte‐macrophage colony stimulating factor, interleukin‐3, and adipogenic differentiation associated genes, leptin and proliferator‐activated receptor γ type 2, were upregulated under sµg conditions. These results indicated that simulating microgravity can affect the phenotype of certain types of hematopoietic cells and the morphology and gene expression pattern of BM‐MSCs.

Primary cilia act as microgravity sensors by depolymerizing microtubules to inhibit osteoblastic differentiation and mineralization

Microgravity-induced bone deterioration is a major challenge in long-term spaceflights since the underlying mechanisms remain elusive. Previously, we reported that primary cilia of osteoblasts gradually disappeared in microgravity conditions, and cilia abrogation was necessary for the inhibition of osteogenesis induced by microgravity. However, the precise roles of primary cilia have not been fully elucidated. Here, we report that microgravity depolymerizes the microtubule network of rat calvarial osteoblasts (ROBs) reversibly but has no effect on the architecture of actin filaments. Preventing primary ciliogenesis by chloral hydrate or a small interfering RNA sequence (siRNA) targeting intraflagellar transport protein 88 (IFT88) effectively relieves microgravity-induced microtubule depolymerization, whereas the stabilization of microtubules using pharmacological approaches cannot prevent the disappearance of primary cilia in microgravity conditions. Furthermore, quantification of the number of microtubules emerging from the ciliary base body shows that microgravity significantly decreases the number of basal microtubules, which is dependent on the existence of primary cilia. Finally, microgravity-induced repression of the differentiation, maturation, and mineralization of ROBs is abrogated by the stabilization of cytoplasmic microtubules. Taken together, these data suggest that primary cilia-dependent depolymerization of microtubules is responsible for the inhibition of osteogenesis induced by microgravity. Our study provides a new perspective regarding the mechanism of microgravity-induced bone loss, supporting the previously established role of primary cilia as a sensor in bone metabolism.

β-Catenin Preserves the Stem State of Murine Bone Marrow Stromal Cells Through Activation of EZH2

During bone marrow stromal cell (BMSC) differentiation, both Wnt signaling and the development of a rigid cytoskeleton promote commitment to the osteoblastic over adipogenic lineage. β-catenin plays a critical role in the Wnt signaling pathway to facilitate downstream effects on gene expression. We show that β-catenin was additive with cytoskeletal signals to prevent adipogenesis, and β-catenin knockdown promoted adipogenesis even when the actin cytoskeleton was depolymerized. β-catenin also prevented osteoblast commitment in a cytoskeletal-independent manner, with β-catenin knockdown enhancing lineage commitment. Chromatin immunoprecipitation (ChIP)-sequencing demonstrated binding of β-catenin to the promoter of enhancer of zeste homolog 2 (EZH2), a key component of the polycomb repressive complex 2 (PRC2) complex that catalyzes histone methylation. Knockdown of β-catenin reduced EZH2 protein levels and decreased methylated histone 3 (H3K27me3) at osteogenic loci. Further, when EZH2 was inhibited, β-catenin's anti-differentiation effects were lost. These results indicate that regulating EZH2 activity is key to β-catenin's effects on BMSCs to preserve multipotentiality. © 2020 American Society for Bone and Mineral Research.

Targeted Proteomic Analysis of Small GTPases in Murine Adipogenesis

Small GTPases are essential signaling molecules for regulating glucose uptake in adipose tissues upon insulin stimulation, and this regulation maintains an appropriate range of glycemia. The involvement of small GTPases in adipogenesis, however, has not been systemically investigated. In this study, we applied a high-throughput scheduled multiple-reaction monitoring (MRM) method, along with the use of synthetic stable isotope-labeled peptides, to identify differentially expressed small GTPase proteins during adipogenesis of cultured murine cells. We were able to quantify the relative levels of expression of 55 and 49 small GTPases accompanied by adipogenic differentiation in 3T3-L1 and C3H10T1/2 cells, respectively. When compared with analysis conducted in the data-dependent acquisition (DDA) mode, the MRM-based proteomic platform substantially increased the coverage of the small GTPase proteome. Western blot analysis further corroborated the MRM quantification results for selected small GTPases. Interestingly, overall a significant number of small GTPases were down-regulated during adipogenesis. Among them, the expression levels of Rab32 protein were consistently lower in differentiated adipocytes than the corresponding undifferentiated precursors in both cell lines. Overexpression of Rab32 in 3T3-L1 and C3H10T1/2 cells prior to adipogenesis induction suppressed their differentiation. Together, this is the first comprehensive analysis of the alterations in small GTPase proteome during adipogenesis, and we reveal a previously unrecognized role of Rab32 in adipogenic differentiation.

RANKL/RANK/OPG Pathway: A Mechanism Involved in Exercise-Induced Bone Remodeling

Bones as an alive organ consist of about 70% mineral and 30% organic component. About 200 million people are suffering from osteopenia and osteoporosis around the world. There are multiple ways of protecting bone from endogenous and exogenous risk factors. Planned physical activity is another useful way for protecting bone health. It has been investigated that arranged exercise would effectively regulate bone metabolism. Until now, a number of systems have discovered how exercise could help bone health. Previous studies reported different mechanisms of the effect of exercise on bone health by modulation of bone remodeling. However, the regulation of RANKL/RANK/OPG pathway in exercise and physical performance as one of the most important remodeling systems is not considered comprehensive in previous evidence. Therefore, the aim of this review is to clarify exercise influence on bone modeling and remodeling, with a concentration on its role in regulating RANKL/RANK/OPG pathway.

Spaceflight-Induced Bone Tissue Changes that Affect Bone Quality and Increase Fracture Risk

PURPOSE OF REVIEW

Bone mineral density and systemic factors are used to assess skeletal health in astronauts. Yet, even in a general population, these measures fail to accurately predict when any individual will fracture. This review considers how long-duration human spaceflight requires evaluation of additional bone structural and material quality measures that contribute to microgravity-induced skeletal fragility.

RECENT FINDINGS

In both humans and small animal models following spaceflight, bone mass is compromised via reduced bone formation and elevated resorption levels. Concurrently, bone structural quality (e.g., trabecular microarchitecture) is diminished and the quality of bone material is reduced via impaired tissue mineralization, maturation, and maintenance (e.g., mediated by osteocytes). Bone structural and material quality are both affected by microgravity and may, together, jeopardize astronaut operational readiness and lead to increased fracture risk upon return to gravitational loading. Future studies need to directly evaluate how bone quality combines with diminished bone mass to influence bone strength and toughness (e.g., resistance to fracture). Bone quality assessment promises to identify novel biomarkers and therapeutic targets.

Knockdown of formin mDia2 alters lamin B1 levels and increases osteogenesis in stem cells

Nuclear actin plays a critical role in mediating mesenchymal stem cell (MSC) fate commitment. In marrow-derived MSCs, the principal diaphanous-related formin Diaph3 (mDia2) is present in the nucleus and regulates intranuclear actin polymerization, whereas Diaph1 (mDia1) is localized to the cytoplasm and controls cytoplasmic actin polymerization. We here show that mDia2 can be used as a tool to query actin-lamin nucleoskeletal structure. Silencing mDia2 affected the nucleoskeletal lamin scaffold, altering nuclear morphology without affecting cytoplasmic actin cytoskeleton, and promoted MSC differentiation. Attempting to target intranuclear actin polymerization by silencing mDia2 led to a profound loss in lamin B1 nuclear envelope structure and integrity, increased nuclear height, and reduced nuclear stiffness without compensatory changes in other actin nucleation factors. Loss of mDia2 with the associated loss in lamin B1 promoted Runx2 transcription and robust osteogenic differentiation and suppressed adipogenic differentiation. Hence, mDia2 is a potent tool to query intranuclear actin-lamin nucleoskeletal structure, and its presence serves to retain multipotent stromal cells in an undifferentiated state.

Stem Cell Culture Under Simulated Microgravity

Challenging environment of space causes several pivotal alterations in living systems, especially due to microgravity. The possibility of simulating microgravity by ground-based systems provides research opportunities that may lead to the understanding of in vitro biological effects of microgravity by eliminating the challenges inherent to spaceflight experiments. Stem cells are one of the most prominent cell types, due to their self-renewal and differentiation capabilities. Research on stem cells under simulated microgravity has generated many important findings, enlightening the impact of microgravity on molecular and cellular processes of stem cells with varying potencies. Simulation techniques including clinostat, random positioning machine, rotating wall vessel and magnetic levitation-based systems have improved our knowledge on the effects of microgravity on morphology, migration, proliferation and differentiation of stem cells. Clarification of the mechanisms underlying such changes offers exciting potential for various applications such as identification of putative therapeutic targets to modulate stem cell function and stem cell based regenerative medicine.

Spheroid Culture System Methods and Applications for Mesenchymal Stem Cells

Owing to the importance of stem cell culture systems in clinical applications, researchers have extensively studied them to optimize the culture conditions and increase efficiency of cell culture. A spheroid culture system provides a similar physicochemical environment in vivo by facilitating cell–cell and cell–matrix interaction to overcome the limitations of traditional monolayer cell culture. In suspension culture, aggregates of adjacent cells form a spheroid shape having wide utility in tumor and cancer research, therapeutic transplantation, drug screening, and clinical study, as well as organic culture. There are various spheroid culture methods such as hanging drop, gel embedding, magnetic levitation, and spinner culture. Lately, efforts are being made to apply the spheroid culture system to the study of drug delivery platforms and co-cultures, and to regulate differentiation and pluripotency. To study spheroid cell culture, various kinds of biomaterials are used as building forms of hydrogel, film, particle, and bead, depending upon the requirement. However, spheroid cell culture system has limitations such as hypoxia and necrosis in the spheroid core. In addition, studies should focus on methods to dissociate cells from spheroid into single cells.

Fluorescence Imaging of Actin Turnover Parses Early Stem Cell Lineage Divergence and Senescence

This study describes a new approach to discern early divergence in stem cell lineage progression via temporal dynamics of the cytoskeletal protein, F-actin. The approach involves real-time labeling of human mesenchymal stem cells (MSCs) and longitudinal tracking of the turnover dynamics of a fluorogenic F-actin specific probe, SiR-actin (SA). Cells cultured in media with distinct lineage factors and labeled with SA showed lineage specific reduction in the actin turnover shortly after adipogenic (few minutes) and chondrogenic (3–4 hours) commitment in contrast to osteogenic and basal cultured conditions. Next, composite staining of SA along with the competing F-actin specific fluorescent conjugate, phalloidin, and high-content image analysis of the complementary labels showed clear phenotypic parsing of the sub-populations as early as 1-hour post-induction across all three lineages. Lastly, the potential of SA-based actin turnover analysis to distinguish cellular aging was explored. In-vitro aged cells were found to have reduced actin turnover within 1-hour of simultaneous analysis in comparison to cells of earlier passage. In summary, SiR-actin fluorescent reporter imaging offers a new platform to sensitively monitor emergent lineage phenotypes during differentiation and aging and resolve some of the earliest evident differences in actin turnover dynamics.

Testes and duct deferens of mice during space flight: cytoskeleton structure, sperm-specific proteins and epigenetic events

To analyze the effect of gravity on the structure of germinal tissues, we examined tissues of the testes and duct deferens of mice that were exposed to space flight conditions for 21–24 days (experiment Rodent Research-4, SpaceX-10 mission, February 2017, USA). We evaluated the levels of cytoskeletal proteins, sperm-specific proteins, and epigenetic events; in particular, we evaluated levels of 5-hydroxymethylcytosine and of enzymes that regulate DNA methylation/demethylation. We did not detect changes in the levels of cytoskeletal proteins, sperm-specific proteins, DNA-methylases, DNA demethylases, DNA acetylases, or histone deacetylases. However, there were changes at the gene expression level. In particular, there was an increase in the demethylase Tet2 and a decrease in the histone deacetylase Hdac1. These gene expression changes may be of key importance during the early period of readaptation since they could lead to an increase in the expression of target genes.

PLEXIN-B2 promotes the osteogenic differentiation of human bone marrow mesenchymal stem cells via activation of the RhoA signaling pathway

Plexin-B2 (PLXNB2), a transmembrane protein is found in various tissues. Recent studies have indicated the presence of PLXNB2 in large quantity in the growth plates of Sprague-Dawley rats and are believed to be potentially involved in their skeletal development. This study endeavored to analyze the effect of PLXNB2 on the osteogenic differentiation of BMSCs by using gene overexpression and knockdown assays. The results of our study revealed that PLXNB2 was upregulated during BMSCs differentiation into an osteoblastic lineage. By determining the expression levels of specific markers and mineral deposition, the study established that PLXNB2 promotes the osteogenic differentiation of human BMSCs through the activation of the RhoA signaling pathway. In conclusion, the study identified PLXNB2 as a novel regulator that enhanced the osteogenic differentiation of human BMSCs. The enhancing effect of PLXNB2 on osteogenesis of human BMSCs was mediated through activation of RhoA signaling. The results of our study imply that pharmacological targeting of PLXNB2 may initiate a possible improvement in bone formation.

DNA Methylation of Mouse Testes, Cardiac and Lung Tissue During Long-Term Microgravity Simulation

Under microgravity, the gene expression levels vary in different types of cells; however, the reasons for this have not been sufficiently studied. The aim of this work was to evaluate the methylation of CpG islands in the promoter regions of the genes encoding some cytoskeletal proteins, the total methylation and 5 hmC levels, and the levels of enzymes that regulate these processes in the testes, heart, and lungs in mice after a 30-day microgravity modeling by antiorthostatic suspension and after a subsequent 12-hour recovery as well as in the corresponding control group and identical groups treated with essential phospholipids. The obtained results indicate that under modeling microgravity in the examined tissues a decrease of cytoskeletal gene expression (mainly in the heart and lungs tissues) correlated with an increase in the CpG islands methylation and an increase of the expression (mainly in the testes tissue) - with a decrease of the CpG-methylation, despite of the fact that in the examined tissues took place a decrease of the content methylases and demethylases. But the deacetylase HDAC1 content increased in the heart and lungs tissues and decreased in the testes, letting us suggest its participation in the regulation of the methylation level under microgravity conditions.

Microgravity-induced hepatogenic differentiation of rBMSCs on board the SJ-10 satellite

Bone marrow-derived mesenchymal stem cells (BMSCs) are able to differentiate into functional hepatocytelike cells, which are expected to serve as a potential cell source in regenerative medicine, tissue engineering, and clinical treatment of liver injury. Little is known about whether and how space microgravity is able to direct the hepatogenic differentiation of BMSCs in the actual space microenvironment. In this study, we examined the effects of space microgravity on BMSC hepatogenic differentiation on board the SJ-10 Recoverable Scientific Satellite. Rat BMSCs were cultured and induced in hepatogenic induction medium for 3 and 10 d in custom-made space cell culture hardware. Cell growth was monitored periodically in orbit, and the fixed cells and collected supernatants were retrieved back to the Earth for further analyses. Data indicated that space microgravity improves the differentiating capability of the cells by up-regulating hepatocyte-specific albumin and cytokeratin 18. The resulting cells tended to be maturated, with an in-orbit period of up to 10 d. In space, mechanosensitive molecules of β1-integrin, β-actin, α-tubulin, and Ras homolog gene family member A presented enhanced expression, whereas those of cell-surface glycoprotein CD44, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, vinculin, cell division control protein 42 homolog, and Rho-associated coiled-coil kinase yielded reduced expression. Also observed in space were the depolymerization of actin filaments and the accumulation of microtubules and vimentin through the altered expression and location of focal adhesion complexes, Rho guanosine 5'-triphosphatases, as well as the enhanced exosome-mediated mRNA transfer. This work furthers the understanding of the underlying mechanisms of space microgravity in directing hepatogenic differentiation of BMSCs.-Lü, D., Sun, S., Zhang, F., Luo, C., Zheng, L., Wu, Y., Li, N., Zhang, C., Wang, C., Chen, Q., Long, M. Microgravity-induced hepatogenic differentiation of rBMSCs on board the SJ-10 satellite.

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

Adipose- derived stem cells (ADSCs) are widely used for tissue engineering and regenerative medicine. The beneficial effects of ADSCs on wound healing have already been reported. Remodeling of extracellular matrix (ECM) is the most important physiological event during wound healing. ECM is sensitive to mechanical stresses and the expression of its components can be therefore influenced. The aim of this study was to investigate the effect of simulated microgravity on gene expression of some ECM and adhesion molecules in human ADSCs. After isolation and characterization of ADSCs, cells were exposed to simulated microgravity for 1, 3 and 7 days. Real-time PCR, fluorescence immunocytochemistry, and MTT assay were performed to evaluate the alterations of integrin subunit beta 1 (ITGB1), collagen type 3 (ColIII), matrix metalloproteinase-1 (MMP1), CD44, fibrillin (FBN1), vimentin (VIM) genes, and ColIII protein levels as well as cells viability. Microgravity simulation increased the expression of ITGB1, ColIII, MMP1, and CD44 and declined the expression of FBN1 and VIM genes. ColIII protein levels also increased. There were no significant changes in the viability of cells cultured in microgravity. Since the high expression of ECM components is known as one of the fibroblast markers, our data suggest that pretreatment of ADSCs by simulated microgravity may increase their differentiation capacity towards fibroblastic cells. Microgravity had not adversely affected the viability of ADSCs, and it is likely to be used alone or in combination with biochemical inducers for cell manipulation.

The subsequent biological effects of simulated microgravity on endothelial cell growth in HUVECs

PURPOSE

Microgravity is known to cause endothelium dysfunction in astronauts returning from spaceflight. We aimed to reveal the regulatory mechanism in alterations of human endothelial cells after simulated microgravity (SMG).

METHODS

We utilized the rotary cell culture system (RCCS-1) to explore the subsequent effects of SMG on human umbilical vein endothelial cells (HUVECs).

RESULTS

SMG-treated HUVECs appeared obvious growth inhibition after return to normal gravity, which might be attributed to a set of responses including alteration of cytoskeleton, decreased cell adhesion capacity and increased apoptosis. Expression levels of mTOR and its downstream Apaf-1 were increased during subsequent culturing after SMG. miR-22 was up-regulated and its target genes SRF and LAMC1 were down-regulated at mRNA levels. LAMC1 siRNAs reduced cell adhesion rate and inhibited stress fiber formation while SRF siRNAs caused apoptosis.

CONCLUSION

SMG has the subsequent biological effects on HUVECs, resulting in growth inhibition through mTOR signaling and miR-22-mediated mechanism.

Cardiovascular progenitor cells cultured aboard the International Space Station exhibit altered developmental and functional properties

The heart and its cellular components are profoundly altered by missions to space and injury on Earth. Further research, however, is needed to characterize and address the molecular substrates of such changes. For this reason, neonatal and adult human cardiovascular progenitor cells (CPCs) were cultured aboard the International Space Station. Upon return to Earth, we measured changes in the expression of microRNAs and of genes related to mechanotransduction, cardiogenesis, cell cycling, DNA repair, and paracrine signaling. We additionally assessed endothelial-like tube formation, cell cycling, and migratory capacity of CPCs. Changes in microRNA expression were predicted to target extracellular matrix interactions and Hippo signaling in both neonatal and adult CPCs. Genes related to mechanotransduction (YAP1, RHOA) were downregulated, while the expression of cytoskeletal genes (VIM, NES, DES, LMNB2, LMNA), non-canonical Wnt ligands (WNT5A, WNT9A), and Wnt/calcium signaling molecules (PLCG1, PRKCA) was significantly elevated in neonatal CPCs. Increased mesendodermal gene expression along with decreased expression of mesodermal derivative markers (TNNT2, VWF, and RUNX2), reduced readiness to form endothelial-like tubes, and elevated expression of Bmp and Tbx genes, were observed in neonatal CPCs. Both neonatal and adult CPCs exhibited increased expression of DNA repair genes and paracrine factors, which was supported by enhanced migration. While spaceflight affects cytoskeletal organization and migration in neonatal and adult CPCs, only neonatal CPCs experienced increased expression of early developmental markers and an enhanced proliferative potential. Efforts to recapitulate the effects of spaceflight on Earth by regulating processes described herein may be a promising avenue for cardiac repair.

From "Bench to Bedside": Current Advancement on Large-Scale Production of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the primary cell source in cell therapy and regenerative medicine due to its extraordinary self-renewing capacity and multilineage differentiation potential. Clinical trials involving MSCs are being conducted in a range of human diseases and the number of registered cases is continuously increasing. However, a wide gap exists between the number of MSCs obtainable from the donor site and the number required for implantation to damage tissues, and also between MSC scalability and MSC phenotype stability. The clinical translation of MSCs necessitates a scalable expansion bioprocess for the biomanufacturing of therapeutically qualified cells. This review presents current achievements for expansion of MSCs. Issues involving culture condition modification, bioreactor systems, as well as microcarrier and scaffold platforms for optimal MSC systems are discussed. Most importantly, the gap between current MSC expansion and clinical application, as well as outbreak directions for the future are discussed. The present systemic review will bring new insights into future large-scale MSC expansion and clinical application.

Transfection of the IHH gene into rabbit BMSCs in a simulated microgravity environment promotes chondrogenic differentiation and inhibits cartilage aging

The effect of overexpressing the Indian hedgehog (IHH) gene on the chondrogenic differentiation of rabbit bone marrow-derived mesenchymal stem cells (BMSCs) was investigated in a simulated microgravity environment. An adenovirus plasmid encoding the rabbit IHH gene was constructed in vitro and transfected into rabbit BMSCs. Two large groups were used: conventional cell culture and induction model group and simulated microgravity environment group. Each large group was further divided into blank control group, GFP transfection group, and IHH transfection group. During differentiation induction, the expression levels of cartilage-related and cartilage hypertrophy-related genes and proteins in each group were determined. In the conventional model, the IHH transfection group expressed high levels of cartilage-related factors (Coll2 and ANCN) at the early stage of differentiation induction and expressed high levels of cartilage hypertrophy-related factors (Coll10, annexin 5, and ALP) at the late stage. Under the simulated microgravity environment, the IHH transfection group expressed high levels of cartilage-related factors and low levels of cartilage hypertrophy-related factors at all stages of differentiation induction. Under the simulated microgravity environment, transfection of the IHH gene into BMSCs effectively promoted the generation of cartilage and inhibited cartilage aging and osteogenesis. Therefore, this technique is suitable for cartilage tissue engineering.

Cytoskeleton structure and total methylation of mouse cardiac and lung tissue during space flight

The purpose of this work was to evaluate the protein and mRNA expression levels of multiple cytoskeletal proteins in the cardiac and lung tissue of mice that were euthanized onboard the United States Orbital Segment of the International Space Station 37 days after the start of the SpaceX-4 mission (September 2014, USA). The results showed no changes in the cytoskeletal protein content in the cardiac and lung tissue of the mice, but there were significant changes in the mRNA expression levels of the associated genes, which may be due to an increase in total genome methylation. The mRNA expression levels of DNA methylases, the cytosine demethylases Tet1 and Tet3, histone acetylase and histone deacetylase did not change, and the mRNA expression level of cytosine demethylase Tet2 was significantly decreased.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Space microgravity drives transdifferentiation of human bone marrow-derived mesenchymal stem cells from osteogenesis to adipogenesis

Bone formation is linked with osteogenic differentiation of mesenchymal stem cells (MSCs) in the bone marrow. Microgravity in spaceflight is known to reduce bone formation. In this study, we used a real microgravity environment of the SJ-10 Recoverable Scientific Satellite to examine the effects of space microgravity on the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs). hMSCs were induced toward osteogenic differentiation for 2 and 7 d in a cell culture device mounted on the SJ-10 satellite. The satellite returned to Earth after going through space experiments in orbit for 12 d, and cell samples were harvested and analyzed for differentiation potentials. The results showed that space microgravity inhibited osteogenic differentiation and resulted in adipogenic differentiation, even under osteogenic induction conditions. Under space microgravity, the expression of 10 genes specific for osteogenesis decreased, including collagen family members, alkaline phosphatase ( ALP), and runt-related transcription factor 2 ( RUNX2), whereas the expression of 4 genes specific for adipogenesis increased, including adipsin ( CFD), leptin ( LEP), CCAAT/enhancer binding protein β ( CEBPB), and peroxisome proliferator-activated receptor-γ ( PPARG). In the analysis of signaling pathways specific for osteogenesis, we found that the expression and activity of RUNX2 was inhibited, expression of bone morphogenetic protein-2 ( BMP2) and activity of SMAD1/5/9 were decreased, and activity of focal adhesion kinase (FAK) and ERK-1/2 declined significantly under space microgravity. These data indicate that space microgravity plays a dual role by decreasing RUNX2 expression and activity through the BMP2/SMAD and integrin/FAK/ERK pathways. In addition, we found that space microgravity increased p38 MAPK and protein kinase B (AKT) activities, which are important for the promotion of adipogenic differentiation of hMSCs. Space microgravity significantly decreased the expression of Tribbles homolog 3 ( TRIB3), a repressor of adipogenic differentiation. Y15, a specific inhibitor of FAK activity, was used to inhibit the activity of FAK under normal gravity; Y15 decreased protein expression of TRIB3. Therefore, it appears that space microgravity decreased FAK activity and thereby reduced TRIB3 expression and derepressed AKT activity. Under space microgravity, the increase in p38 MAPK activity and the derepression of AKT activity seem to synchronously lead to the activation of the signaling pathway specifically promoting adipogenesis.-Zhang, C., Li, L., Jiang, Y., Wang, C., Geng, B., Wang, Y., Chen, J., Liu, F., Qiu, P., Zhai, G., Chen, P., Quan, R., Wang, J. Space microgravity drives transdifferentiation of human bone marrow-derived mesenchymal stem cells from osteogenesis to adipogenesis.

Spaceflight Activates Protein Kinase C Alpha Signaling and Modifies the Developmental Stage of Human Neonatal Cardiovascular Progenitor Cells

Spaceflight impacts cardiovascular function in astronauts; however, its impact on cardiac development and the stem cells that form the basis for cardiac repair is unknown. Accordingly, further research is needed to uncover the potential relevance of such changes to human health. Using simulated microgravity (SMG) generated by two-dimensional clinorotation and culture aboard the International Space Station (ISS), we assessed the effects of mechanical unloading on human neonatal cardiovascular progenitor cell (CPC) developmental properties and signaling. Following 6-7 days of SMG and 12 days of ISS culture, we analyzed changes in gene expression. Both environments induced the expression of genes that are typically associated with an earlier state of cardiovascular development. To understand the mechanism by which such changes occurred, we assessed the expression of mechanosensitive small RhoGTPases in SMG-cultured CPCs and observed decreased levels of RHOA and CDC42. Given the effect of these molecules on intracellular calcium levels, we evaluated changes in noncanonical Wnt/calcium signaling. After 6-7 days under SMG, CPCs exhibited elevated levels of WNT5A and PRKCA. Similarly, ISS-cultured CPCs exhibited elevated levels of calcium handling and signaling genes, which corresponded to protein kinase C alpha (PKCα), a calcium-dependent protein kinase, activation after 30 days. Akt was activated, whereas phosphorylated extracellular signal-regulated kinase levels were unchanged. To explore the effect of calcium induction in neonatal CPCs, we activated PKCα using hWnt5a treatment on Earth. Subsequently, early cardiovascular developmental marker levels were elevated. Transcripts induced by SMG and hWnt5a-treatment are expressed within the sinoatrial node, which may represent embryonic myocardium maintained in its primitive state. Calcium signaling is sensitive to mechanical unloading and directs CPC developmental properties. Further research both in space and on Earth may help refine the use of CPCs in stem cell-based therapies and highlight the molecular events of development.

Mesenchymal Stem Cells: Cell Fate Decision to Osteoblast or Adipocyte and Application in Osteoporosis Treatment

Osteoporosis is a progressive skeletal disease characterized by decreased bone mass and degraded bone microstructure, which leads to increased bone fragility and risks of bone fracture. Osteoporosis is generally age related and has become a major disease of the world. Uncovering the molecular mechanisms underlying osteoporosis and developing effective prevention and therapy methods has great significance for human health. Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into osteoblasts, adipocytes, or chondrocytes, and have become the favorite source of cell-based therapy. Evidence shows that during osteoporosis, a shift of the cell differentiation of MSCs to adipocytes rather than osteoblasts partly contributes to osteoporosis. Thus, uncovering the molecular mechanisms of the osteoblast or adipocyte differentiation of MSCs will provide more understanding of MSCs and perhaps new methods of osteoporosis treatment. The MSCs have been applied to both preclinical and clinical studies in osteoporosis treatment. Here, we review the recent advances in understanding the molecular mechanisms regulating osteoblast differentiation and adipocyte differentiation of MSCs and highlight the therapeutic application studies of MSCs in osteoporosis treatment. This will provide researchers with new insights into the development and treatment of osteoporosis.

Mechanical Activation of Adipose Tissue and Derived Mesenchymal Stem Cells: Novel Anti-Inflammatory Properties

The adipose tissue is a source of inflammatory proteins, such as TNF, IL-6, and CXCL8. Most of their production occurs in macrophages that act as scavengers of dying adipocytes. The application of an orbital mechanical force for 6-10 min at 97 g to the adipose tissue, lipoaspirated and treated according to Coleman procedures, abolishes the expression of TNF-α and stimulates the expression of the anti-inflammatory protein TNF-stimulated gene-6 (TSG-6). This protein had protective and anti-inflammatory effects when applied to animal models of rheumatic diseases. We examined biopsy, lipoaspirate, and mechanically activated fat and observed that in addition to the increased TSG-6, Sox2, Nanog, and Oct4 were also strongly augmented by mechanical activation, suggesting an effect on stromal cell stemness. Human adipose tissue-derived mesenchymal stem cells (hADSCs), produced from activated fat, grow and differentiate normally with proper cell surface markers and chromosomal integrity, but their anti-inflammatory action is far superior compared to those mesenchymal stem cells (MSCs) obtained from lipoaspirate. The expression and release of inflammatory cytokines from THP-1 cells was totally abolished in mechanically activated adipose tissue-derived hADSCs. In conclusion, we report that the orbital shaking of adipose tissue enhances its anti-inflammatory properties, and derived MSCs maintain such enhanced activity.

Mechanical Stimulation of Adipose-Derived Stem Cells for Functional Tissue Engineering of the Musculoskeletal System via Cyclic Hydrostatic Pressure, Simulated Microgravity, and Cyclic Tensile Strain

It is critical that human adipose stem cell (hASC) tissue-engineering therapies possess appropriate mechanical properties in order to restore function of the load bearing tissues of the musculoskeletal system. In an effort to elucidate the hASC response to mechanical stimulation and develop mechanically robust tissue engineered constructs, recent research has utilized a variety of mechanical loading paradigms including cyclic tensile strain, cyclic hydrostatic pressure, and mechanical unloading in simulated microgravity. This chapter describes methods for applying these mechanical stimuli to hASC to direct differentiation for functional tissue engineering of the musculoskeletal system.