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

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.

Allogeneic cell therapy bioprocess economics and optimization: single-use cell expansion technologies

For allogeneic cell therapies to reach their therapeutic potential, challenges related to achieving scalable and robust manufacturing processes will need to be addressed. A particular challenge is producing lot-sizes capable of meeting commercial demands of up to 10(9) cells/dose for large patient numbers due to the current limitations of expansion technologies. This article describes the application of a decisional tool to identify the most cost-effective expansion technologies for different scales of production as well as current gaps in the technology capabilities for allogeneic cell therapy manufacture. The tool integrates bioprocess economics with optimization to assess the economic competitiveness of planar and microcarrier-based cell expansion technologies. Visualization methods were used to identify the production scales where planar technologies will cease to be cost-effective and where microcarrier-based bioreactors become the only option. The tool outputs also predict that for the industry to be sustainable for high demand scenarios, significant increases will likely be needed in the performance capabilities of microcarrier-based systems. These data are presented using a technology S-curve as well as windows of operation to identify the combination of cell productivities and scale of single-use bioreactors required to meet future lot sizes. The modeling insights can be used to identify where future R&D investment should be focused to improve the performance of the most promising technologies so that they become a robust and scalable option that enables the cell therapy industry reach commercially relevant lot sizes. The tool outputs can facilitate decision-making very early on in development and be used to predict, and better manage, the risk of process changes needed as products proceed through the development pathway.

Simulated microgravity combined with polyglycolic acid scaffold culture conditions improves the function of pancreatic islets

The in vitro culture of pancreatic islets reduces their immunogenicity and prolongs their availability for transplantation. Both simulated microgravity (sMG) and a polyglycolic acid scaffold (PGA) are believed to confer advantages to cell culture. Here, we evaluated the effects of sMG combined with a PGA on the viability, insulin-producing activity and morphological alterations of pancreatic islets. Under PGA-sMG conditions, the purity of the islets was ≥85%, and the islets had a higher survival rate and an increased ability to secrete insulin compared with islets cultured alone in the static, sMG, or PGA conditions. In addition, morphological analysis under scanning electron microscopy (SEM) revealed that the PGA-sMG treatment preserved the integral structure of the islets and facilitated islet adhesion to the scaffolds. These results suggest that PGA-sMG coculture has the potential to improve the viability and function of islets in vitro and provides a promising method for islet transplantation.

RhoA mediates defective stem cell function and heterotopic ossification in dystrophic muscle of mice

Heterotopic ossification (HO) and fatty infiltration (FI) often occur in diseased skeletal muscle and have been previously described in various animal models of Duchenne muscular dystrophy (DMD); however, the pathological mechanisms remain largely unknown. Dystrophin-deficient mdx mice and dystrophin/utrophin double-knockout (dKO) mice are mouse models of DMD; however, mdx mice display a strong muscle regeneration capacity, while dKO mice exhibit a much more severe phenotype, which is similar to patients with DMD. Our results revealed that more extensive HO, but not FI, occurred in the skeletal muscle of dKO mice versus mdx mice, and RhoA activation specifically occurred at the sites of HO. Moreover, the gene expression of RhoA, BMPs, and several inflammatory factors were significantly up-regulated in muscle stem cells isolated from dKO mice; while inactivation of RhoA in the cells with RhoA/ROCK inhibitor Y-27632 led to reduced osteogenic potential and improved myogenic potential. Finally, inactivation of RhoA signaling in the dKO mice with Y-27632 improved muscle regeneration and reduced the expression of BMPs, inflammation, HO, and intramyocellular lipid accumulation in both skeletal and cardiac muscle. Our results revealed that RhoA represents a major molecular switch in the regulation of HO and muscle regeneration in dystrophic skeletal muscle of mice.

Induction of EMT-like response by BMP4 via up-regulation of lysyl oxidase is required for adipocyte lineage commitment

The developmental pathway that gives rise to mature adipocytes involves commitment and terminal differentiation. Our previous findings indicate that BMP4 (bone morphogenetic protein 4) induces nearly complete commitment of C3H10T1/2 pluripotent stem cells to the adipocyte lineage and knockdown of lysyl oxidase (Lox) disrupts this commitment process. Here, we found that an epithelial-mesenchymal transition (EMT)-like response is required for adipocyte lineage commitment and that Lox is indispensable for this process. When C3H10T1/2 cells were treated with BMP4, Vim and Cdh2 showed up-regulated expression while Cdh1 and Ocln were down-regulated along with enhanced cell migration, which are EMT-like responses. Silencing of Lox in BMP4-treated C3H10T1/2 cells induced a mesenchymal-epithelial transition (MET)-like response associated with the repression of mesenchymal markers, induction of epithelial markers and decreased cell migration. Importantly, blocking the EMT-like response by knocking down Cdh2 or over-expression of Cdh1 impairs adipocyte lineage commitment. EMT is regulated by distinct transcription factors such as Snai1, Snai2 and Twist. In this study, we also found that only Twist was down-regulated after Lox silencing in C3H10T1/2 cells treated with BMP4. This study provides new insights into adipocyte lineage commitment.

LIM kinase 1 deficient mice have reduced bone mass

The cytoskeleton determines cell shape and is involved in cell motility. It also plays a role in differentiation and in modulating specialized cellular functions. LIM kinase 1 (LIMK1) participates in cytoskeletal remodeling by phosphorylating and inactivating the actin-severing protein, cofilin. Severing F-actin to release G-actin monomers is required for actin cytoskeletal remodeling. Although less well established, LIMK1 may also influence the cell cycle and modulate metalloproteinase activity. Since the role of LIMK1 in bone cell biology has not been reported, the skeletal phenotype of LIMK1(-/-) mice was examined. LIMK1(-/-) mice had significantly reduced trabecular bone mass when analyzed by microCT (p<0.01). Histomorphometric analyses demonstrated a 31% reduction in the number of osteoblasts (p=0.0003) and a 23% reduction in osteoid surface (p=0.0005). The number of osteoclasts was no different in control and knock out animals. Consistent with the in vivo findings in osteoblasts, the number of osteoblast colony forming units in LIMK1(-/-) bone marrow was reduced by nearly 50%. Further, osteoblasts isolated from LIMK1(-/-) mice showed significantly reduced rates of mineralization in vitro. Osteoclasts from LIMK1(-/-) mice evidenced more rapid cytoskeletal remodeling in response to treatment with CSF1. In keeping with this latter finding, basal levels of phospho-cofilin were reduced in LIMK1(-/-) osteoclasts. LIMK1(-/-) osteoclasts also resorbed dentine slices to a greater extent in vitro and were more active in a pit assay. These data support the hypothesis that LIMK1 is required for normal osteoblast differentiation. In addition, its absence leads to increased cytoskeletal remodeling and bone resorption in osteoclasts.

Cell mechanosensitivity: mechanical properties and interaction with gravitational field

This paper addressed the possible mechanisms of primary reception of a mechanical stimulus by different cells. Data concerning the stiffness of muscle and nonmuscle cells as measured by atomic force microscopy are provided. The changes in the mechanical properties of cells that occur under changed external mechanical tension are presented, and the initial stages of mechanical signal transduction are considered. The possible mechanism of perception of different external mechanical signals by cells is suggested.

Characterizing the effects of VPA, VC and RCCS on rabbit keratocytes onto decellularized bovine cornea

To investigate the morphological and growth characteristics of rabbit keratocytes when cultured on decellularized cornea under simulate microgravity (SMG) rotary cell culture system (RCCS) and static culture or in plastic culture supplemented with small molecules of valproic acid (VPA) and vitamin C (VC). Bovine corneas were firstly decellularized with Triton X-100 and NH(4)OH and through short-term freezing process. Then cell count kit-8 (CCK-8) and flow cytometry were used to test the effects of VPA and VC on the proliferation, cell cycle and apoptosis of rabbit keratocytes. Hematoxylin-eosin (H&E) staining and scanning electron microscopy (SEM) imaging showed that cells were eliminated in the decellularized bovine corneas. The proliferation of cultured keratocytes was promoted by VPA and VC in the cell proliferation assay. VPA and VC moderately decreased the number of apoptotic cells and obviously promoted cell-cycle entrance of keratocytes. Rabbit keratocytes in plastic displayed spindle shape and rare interconnected with or without VPA and VC. Cells revealed dendritic morphology and reticular cellular connections when cultured on the carriers of decellularized corneas supplemented with VPA and VC even in the presence of 10% fetal bovine serum (FBS). When cultured in RCCS supplemented with VPA, VC and 10% FBS, keratocytes displayed round shape with many prominences and were more prone to grow into the pores of carriers with aggregation. Reverse transcription-polymerase chain reaction (RT-PCR) analysis proved that the keratocytes cultured on decellularized bovine cornea under SMG with VPA and VC expressed keratocan and lumican. Keratocytes cultured on plastic expressed lumican but not keratocan. Immunofluorescence identification revealed that cells in all groups were positively immunostained for vimentin. Keratocytes on decellularized bovine cornea under SMG or in static culture were positively immunostained for keratocan and lumican. Thus, we reasonably made a conclusion that the combination of VPA, VC, RCCS and decellularized corneal carriers provide a good condition for keratocytes to well grow. Keratocytes can be manipulated to be aggregates or physiological morphological growth in vitro, which are important for the research of corneal stem cells and corneal tissue engineering.

Mineralization content alters osteogenic responses of bone marrow stromal cells on hydroxyapatite/polycaprolactone composite nanofiber scaffolds

Synthetic tissue scaffolds have a high potential impact for patients experiencing osteogenesis imperfecta. Using electrospinning, tissue scaffolds composed of hydroxyapatite/polycaprolactone (HAp/PCL) composite nanofibers were fabricated with two different HAp concentrations—1% and 10% of the solid scaffold weight. After physico-chemical scaffold characterization, rat bone marrow stromal cells were cultured on the composite scaffolds in maintenance medium and then in osteogenic medium. Quantitative PCR, colorimetric assays, immunofluorescent labeling, and electron microscopy measured osteogenic cell responses to the HAp/PCL scaffolds. In maintenance conditions, both Hap/PCL scaffolds and control scaffolds supported cell colonization through seven days with minor differences. In osteogenic conditions, the 10% HAp scaffolds exhibited significantly increased ALP assay levels at week 3, consistent with previous reports. However, qPCR analysis demonstrated an overall decrease in bone matrix-associated genes on Hap/PCL scaffolds. Osteopontin and osteocalcin immunofluorescent microscopy revealed a trend that both mineralized scaffolds had greater amounts of both proteins, though qPCR results indicated the opposite trend for osteopontin. Additionally, type I collagen expression decreased on HAp scaffolds. These results indicate that cells are sensitive to minor changes in mineral content within nanofibers, even at just 1% w/w, and elucidating the sensing mechanism may lead to optimized osteogenic scaffold designs.

Cytoskeletal and focal adhesion influences on mesenchymal stem cell shape, mechanical properties, and differentiation down osteogenic, adipogenic, and chondrogenic pathways

Mesenchymal stem cells (MSCs) hold great potential for regenerative medicine and tissue-engineering applications. They have multipotent differentiation capabilities and have been shown to differentiate down various lineages, including osteoblasts, adipocytes, chondrocytes, myocytes, and possibly neurons. The majority of approaches to control the MSC fate have been via the use of chemical factors in the form of growth factors within the culture medium. More recently, it has been understood that mechanical forces play a significant role in regulating MSC fate. We and others have shown that mechanical stimuli can control MSC lineage specification. The cytoskeleton is known to play a large role in mechanotransduction, and a growing number of studies are showing that it can also contribute to MSC differentiation. This review analyzes the significant contribution of actin and integrin distribution, and the smaller role of microtubules, in regulating MSC fate. Osteogenic differentiation is more prevalent in MSCs with a stiff, spread actin cytoskeleton and greater numbers of focal adhesions. Both adipogenic differentiation and chondrogenic differentiation are encouraged when MSCs have a spherical morphology associated with a dispersed actin cytoskeleton with few focal adhesions. Different mechanical stimuli can be implemented to alter these cytoskeletal patterns and encourage MSC differentiation to the desired lineage.

Mechanical regulation of signaling pathways in bone

A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.

Exchange protein activated by cyclic adenosine monophosphate regulates the switch between adipogenesis and osteogenesis of human mesenchymal stem cells through increasing the activation of phosphatidylinositol 3-kinase

Epac, exchange protein activated by cyclic adenosine monophosphate (cAMP), could regulate the trans-differentiation between adipogenesis and osteogenesis of human mesenchymal stem cells (hMSCs). Epac activated by 8-pCPT-2'-O-Me-cAMP, a cAMP analog preferentially activating Epac, resulted in the increase of adipogenic gene expression and the decrease of osteogenic gene expression. The pro-adipogenic and anti-osteogenic effect of 8-pCPT-2'-O-Me-cAMP was attributed to that 8-pCPT-2'-O-Me-cAMP led to the activation of protein kinase B (PKB) and cAMP response element-binding protein (CREB) as well as the inhibition of Ras homolog gene family member A (RhoA), focal adhesion kinase (FAK), extracellular-signal-regulated kinase (ERK) and runt-related transcription factor 2 (Runx2) activities. Inhibition of Epac by a dominant-negative form of Epac1 resulted in the decrease of phosphatidylinositol 3-kinase (PI3K), PKB and CREB activities as well as down-regulation of peroxisome proliferator activated receptor-γ (PPARγ) expression. Inhibition of PI3K by a specific inhibitor or inhibition of Arf and Rho GAP adapter protein 3 (ARAP3, a phosphatidylinositol (PtdIns)(3,4,5)P(3) binding protein) by ARAP3 siRNA led to the recovery of RhoA and FAK activities. RhoA-V14, a constitutively active form of RhoA, could activate the MEK/ERK/Runx2 signaling. Therefore, we conclude that PI3K activated by Epac leads to the activation of PKB/CREB signaling and the up-regulation of PPARγ expression, which in turn activate the transcription of adipogenic genes; whereas osteogenesis is driven by Rho/FAK/MEK/ERK/Runx2 signaling, which can be inhibited by Epac via PI3K. These results should be helpful to provide new targets for treatment of osteoporosis and related bone-wasting diseases.

Mesenchymal stem cells as a potent cell source for bone regeneration

While small bone defects heal spontaneously, large bone defects need surgical intervention for bone transplantation. Autologous bone grafts are the best and safest strategy for bone repair. An alternative method is to use allogenic bone graft. Both methods have limitations, particularly when bone defects are of a critical size. In these cases, bone constructs created by tissue engineering technologies are of utmost importance. Cells are one main component in the manufacture of bone construct. A few cell types, including embryonic stem cells (ESCs), adult osteoblast, and adult stem cells, can be used for this purpose. Mesenchymal stem cells (MSCs), as adult stem cells, possess characteristics that make them good candidate for bone repair. This paper discusses different aspects of MSCs that render them an appropriate cell type for clinical use to promote bone regeneration.

Using cell and organ culture models to analyze responses of bone cells to mechanical stimulation

Bone cells of the osteoblastic lineage are responsive to the local mechanical environment. Through integration of a number of possible loading-induced regulatory stimuli, osteocyte, osteoblast, and osteoclast behaviour is organized to fashion a skeletal element of sufficient strength and toughness to resist fracture and crack propagation. Early pre-osteogenic responses had been determined in vivo and this led to the development of bone organ culture models to elucidate other pre-osteogenic responses where osteocytes and osteoblasts retain the natural orientation, connections and attachments to their native extracellular matrix. The application of physiological mechanical loads to bone in these organ culture models generates the regulatory stimuli. As a consequence, these experiments can be used to illustrate the distinctive mechanisms by which osteocytes and osteoblasts respond to mechanical loads and also differences in these responses, suggesting co-ordinated and cooperatively between cell populations. Organ explant cultures are awkward to maintain, and have a limited life, but length of culture times are improving. Monolayer cultures are much easier to maintain and permit the application of a particular mechanical stimulation to be studied in isolation; mainly direct mechanical strain or fluid shear strains. These allow for the response of a single cell type to the applied mechanical stimulation to be monitored precisely.The techniques that can be used to apply mechanical strain to bone and bone cells have not advanced greatly since the first edition. The output from such experiments has, however, increased substantially and their importance is now more broadly accepted. This suggests a growing use of these approaches and an increasing awareness of the importance of the mechanical environment in controlling normal bone cell behaviour. We expand the text to include additions and modifications made to the straining apparatus and update the research cited to support this growing role of cell and organ culture models to analyze responses of bone cells to mechanical stimulation.

Bone morphogenetic protein-2-induced signaling and osteogenesis is regulated by cell shape, RhoA/ROCK, and cytoskeletal tension

Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be mediated by different cytokines such as the bone morphogenetic proteins (BMPs). Here, we report that cell adhesion to extracellular matrix (ECM), and its effects on cell shape and cytoskeletal mechanics, regulates BMP-induced signaling and osteogenic differentiation of hMSCs. Using micropatterned substrates to progressively restrict cell spreading and flattening against ECM, we demonstrated that BMP-induced osteogenesis is progressively antagonized with decreased cell spreading. BMP triggered rapid and sustained RhoA/Rho-associated protein kinase (ROCK) activity and contractile tension only in spread cells, and this signaling was required for BMP-induced osteogenesis. Exploring the molecular basis for this effect, we found that restricting cell spreading, reducing ROCK signaling, or inhibiting cytoskeletal tension prevented BMP-induced SMA/mothers against decapentaplegic (SMAD)1 c-terminal phosphorylation, SMAD1 dimerization with SMAD4, and SMAD1 translocation into the nucleus. Together, these findings demonstrate the direct involvement of cell spreading and RhoA/ROCK-mediated cytoskeletal tension generation in BMP-induced signaling and early stages of in vitro osteogenesis, and highlight the essential interplay between biochemical and mechanical cues in stem cell differentiation.

Simulated microgravity using a rotary cell culture system promotes chondrogenesis of human adipose-derived mesenchymal stem cells via the p38 MAPK pathway

Mesenchymal stem cells (MSCs) are multi-potent, and the chondrogenesis of MSCs is affected by mechanical stimulation. The aim of this study was to investigate, using a rotary cell culture system (RCCS) bioreactor, the effects of microgravity on the chondrogenic differentiation of human adipose-derived MSCs (ADSCs), which were cultured in pellets with or without the chondrogenic growth factor TGF-β1. In addition, we evaluated the role of the p38 MAPK pathway in this process. The real-time PCR and histological results show that microgravity has a synergistic effect on chondrogenesis with TGF-β1. The p38 MAPK pathway was activated by TGF-β1 alone and was further stimulated by microgravity. Inhibition of p38 activity with SB203580 suppressed chondrocyte-specific gene expression and matrix production. These findings suggest that the p38 MAPK signal acts as an essential mediator in the microgravity-induced chondrogenesis of ADSCs.

Altered osteogenic commitment of human mesenchymal stem cells by ERM protein-dependent modulation of cellular biomechanics

Cellular mechanics is known to play an important role in many cellular functions including adhesion, migration, proliferation, and differentiation. Human mesenchymal stem cells (hMSCs) demonstrate unique mechanical properties distinct from fully differentiated cells. This observation suggests that the stem cell mechanics may be modulated to regulate the hMSCs' lineage commitment. Specifically, ERM (ezrin, radixin, moesin) proteins are known to mediate the membrane-cytoskeleton adhesion, cell elasticity, actin cytoskeleton organization, and therefore could serve as potential targets for modulation of the cellular mechanics. Combining silencing RNA, atomic force microscopy, and laser optical tweezers, the role of the ERM proteins involved in the regulation of stem cell biomechanics and osteogenic differentiation was quantitatively determined. Transient ERM knockdown by RNAi causes disassembly of actin stress fibers and focal adhesions, a decrease in the cell stiffness, and membrane separation from the cytoskeleton. The silencing RNA treatment not only induced mechanical changes in stem cells but impaired biochemically-directed osteogenic differentiation. The intact actin cytoskeleton and focal adhesions of hMSCs appear critical for the osteogenic induction. Thus, ERM knockdown modulates the dynamics of cell mechanical changes during hMSC differentiation and regulates the expression of tissue specific molecular markers. These findings are of particular interest for modulation of the cellular biomechanics to control hMSCs' activities and fate in tissue engineering, regenerative medicine, and other stem cell-based therapeutic applications.

Regulation of osteogenetic differentiation of mesenchymal stem cells by two axial rotational culture

It is crucial to understand how gravitational force affects the osteogenic differentiation of mesenchymal stem cells (MSCs), and these fundamental aspects hold promise for the development of a novel model of MSC regulation for cell proliferation and differentiation. The objective of this study was to investigate how significantly gravitational dispersion affects the spontaneously induced osteogenic differentiation of MSCs. Expression of surface antigen was measured by flow cytometry prior to two axial rotational cultures. About 12,500 hMSC cells were spread on culture wells of 1.8 cm(2) surface area and incubated for 7 days at 5% CO(2). The culture medium, 10% FCS/DMEM containing 3 ng/ml bFGF, was replaced every 3 days. Four wells then were placed in a 50-ml centrifugal tube filled with 10% FCS/DMEM without bFGF. The centrifugal tube was attached to the center of the rotor, and two axial rotational cultures were started at 10 rpm each of both rotational speeds. It was confirmed that the hMSCs used in this study expressed typical surface antigens as well as a multipotent differentiation ability for either osteogenic or adipogenic differentiation. Spontaneous expression of alkaline phosphatase (Alp) mRNA following the conventional static culture (1G condition) was suppressed by two axial rotational cultures for 7 days (p < 0.05). A separate study indicated that the cell count number eventually increased from 24,700 ± 6,400 to 78,400 ± 18,700 (p < 0.05). In addition, suppressed Alp mRNA was recovered after an additional 7-day culture under static conditions. This result indicated that dispersion of gravity is a promising modality to regulate osteogenic differentiation of hMSCs.

How and why does the proteome respond to microgravity?

For medical and biotechnological reasons, it is important to study mammalian cells, animals, bacteria and plants exposed to simulated and real microgravity. It is necessary to detect the cellular changes that cause the medical problems often observed in astronauts, cosmonauts or animals returning from prolonged space missions. In order for in vitro tissue engineering under microgravity conditions to succeed, the features of the cell that change need to be known. In this article, we summarize current knowledge about the effects of microgravity on the proteome in different cell types. Many studies suggest that the effects of microgravity on major cell functions depend on the responding cell type. Here, we discuss and speculate how and why the proteome responds to microgravity, focusing on proteomic discoveries and their future potential.

Differential proteome analysis of bone marrow mesenchymal stem cells from adolescent idiopathic scoliosis patients

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine. The cause and pathogenesis of scoliosis and the accompanying generalized osteopenia remain unclear despite decades of extensive research. In this study, we utilized two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry (MS) to analyze the differential proteome of bone marrow mesenchymal stem cells (BM-MSCs) from AIS patients. In total, 41 significantly altered protein spots were detected, of which 34 spots were identified by MALDI-TOF/TOF analysis and found to represent 25 distinct gene products. Among these proteins, five related to bone growth and development, including pyruvate kinase M2, annexin A2, heat shock 27 kDa protein, γ-actin, and β-actin, were found to be dysregulated and therefore selected for further validation by Western blot analysis. At the protein level, our results supported the previous hypothesis that decreased osteogenic differentiation ability of MSCs is one of the mechanisms leading to osteopenia in AIS. In summary, we analyzed the differential BM-MSCs proteome of AIS patients for the first time, which may help to elucidate the underlying molecular mechanisms of bone loss in AIS and also increase understanding of the etiology and pathogenesis of AIS.

Physical properties of mesenchymal stem cells are coordinated by the perinuclear actin cap

Mesenchymal stem cells (MSCs) have been extensively investigated for their applications in regenerative medicine. Successful use of MSCs in cell-based therapies will rely on the ability to effectively identify their properties and functions with a relatively non-destructive methodology. In this study, we measured the surface stiffness and thickness of rat MSCs with atomic force microscopy and clarified their relation at a single-cell level. The role of the perinuclear actin cap in regulating the thickness, stiffness, and proliferative activity of these cells was also determined by using several actin cytoskeleton-modifying reagents. This study has helped elucidate a possible link between the physical properties and the physiological function of the MSCs, and the corresponding regulatory role of the actin cytoskeleton.

Matrix stiffness regulation of integrin-mediated mechanotransduction during osteogenic differentiation of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) cultured on extracellular matrices with different stiffness have been shown to possess diverse lineage commitment owing to the extracellular mechanical stimuli sensed by the cells. The aim of this study was to further delineate how matrix stiffness affects intracellular signaling through the mechanotransducers Rho kinase (ROCK) and focal adhesion kinase (FAK) and subsequently regulates the osteogenic phenotype of MSCs. MSCs were cultured in osteogenic medium on tunable polyacrylamide hydrogels coated with type I collagen with elasticities corresponding to Young's modulus of 7.0 ± 1.2 and 42.1 ± 3.2 kPa. Osteogenic differentiation was increased on stiffer matrices, as evident by type I collagen, osteocalcin, and Runx2 gene expressions and alizarin red S staining for mineralization. Western blot analysis demonstrated an increase in kinase activities of ROCK, FAK, and ERK1/2 on stiffer matrices. Inhibition of FAK, an important mediator of osteogenic differentiation, and inhibition of ROCK, a known mechanotransducer of matrix stiffness during osteogenesis, resulted in decreased expression of osteogenic markers during osteogenic induction. In addition, FAK affects osteogenic differentiation through ERK1/2, whereas ROCK regulates both FAK and ERK1/2. Furthermore, α(2)-integrin was upregulated on stiffer matrices during osteogenic induction, and its knockdown by siRNA downregulated the osteogenic phenotype through ROCK, FAK, and ERK1/2. Taken together, our results provide evidence that the matrix rigidity affects the osteogenic outcome of MSCs through mechanotransduction events that are mediated by α(2)-integrin.

AFM studies of cellular mechanics during osteogenic differentiation of human amniotic fluid-derived stem cells

Amniotic fluid-derived stem cells (AFSCs) are becoming an important source of cells for regenerative medicine given with apparent advantages of accessibility, renewal capacity and multipotentiality. In this study, the mechanical properties of human amniotic fluid-derived stem cells (hAFSCs), such as the average Young's modulus, were determined by atomic force microscopy (3.97 ± 0.53 kPa for hAFSCs vs. 1.52 ± 0.63 kPa for fully differentiated osteoblasts). These differences in cell elasticity result primarily from differential actin cytoskeleton organization in these two cell types. Furthermore, ultrastructures, nanostructural details on the surface of cell, were visualized by atomic force microscopy (AFM). It was clearly shown that surface of osteoblasts were covered by mineralized particles, and the histogram of particles size showed that most of the particles on the surface of osteoblasts distributed from 200 to 400 nm in diameter, while the diameter of hAFSCs particles ranged from 100 to 200 nm. In contrast, there were some dips on the surface of hAFSCs, and particles were smaller than that of osteoblasts. Additionally, as osteogenic differentiation of hAFSCs progressed, more and more stress fibers were replaced by a thinner actin network which is characteristic of mature osteoblasts. These results can improve our understanding of the mechanical properties of hAFSCs during osteogenic differentiation. AFM can be used as a powerful tool for detecting ultrastructures and mechanical properties.

Human mesenchymal stem cells are sensitive to abnormal gravity and exhibit classic apoptotic features

The aim of the present study was to investigate the effects of abnormal gravity on human mesenchymal stem cells (hMSCs). Strong magnetic field and magnetic field gradient generate a magnetic force that can add to or subtract from the gravitational force. In this study, this is defined as a high-magneto-gravitational environment (HMGE). The HMGE provides three apparent gravity levels, i.e. hypogravity (μg), hypergravity (2g) and normal gravity with strong magnetic field (1g) conditions. After hMSCs were subject to HMGE for 12 h, the proliferation, morphology, structure and apoptosis were investigated. Results showed that the proliferation of hMSCs was inhibited under μg condition. The abnormal gravity induced morphologic characteristics of apoptosis cells, such as cell shrinkage, membrane blebbing, nuclear chromatin condensation and margination, decreased cell viability, and increased caspase-3/7 activity. The rate of apoptosis under μg condition is up to 56.95%. The F-actin stress fibers and microtubules were disrupted under abnormal gravity condition. Under μg-condition, the expression of p53 at mRNA and protein levels was up-regulated more than 9- and 6 folds, respectively. The Pifithrin-α, an specific inhibitor of p53, inhibited the apoptosis and prevented the disruption of cytoskeleton induced by abnormal gravity. These results implied that hMSCs were sensitive to abnormal gravity and exhibited classic apoptotic features, which might be associated with p53 signaling.

Functional Cells Cultured on Microcarriers for Use in Regenerative Medicine Research

Microcarriers have been successfully used for many years for growing anchorage-dependent cells and as a means of delivering cells for tissue repair. When cultured on microcarriers, the number of anchorage-dependent cells, including primary cells, can easily be scaled up and controlled to generate the quantities of cells necessary for therapeutic applications. Recently, stem cell technology has been recognized as a powerful tool in regenerative medicine, but adequate numbers of stem cells that retain their differentiation potential are still difficult to obtain. For anchorage-dependent stem cells, however, microcarrier-based suspension culture using various types of microcarriers has proven to be a good alternative for effective ex vivo expansion. In this article, we review studies reporting the expansion, differentiation, or transplantation of functional anchorage-dependent cells that were expanded with the microcarrier culture system. Thus, the implementation of technological advances in biodegradable microcarriers, the bead-to-bead transfer process, and appropriate stem cell media may soon foster the ability to produce the numbers of stem cells necessary for cell-based therapies and/or tissue engineering.

Effects of microgravity modeled by large gradient high magnetic field on the osteogenic initiation of human mesenchymal stem cells

Microgravity (MG) leads to a decrease in osteogenic potential of human bone marrow-derived mesenchymal stem cells (hMSCs). In the present study, we used large gradient high magnetic field (LGHMF) produced by a superconducting magnet to model MG (LGHMF-MG) and analyzed the effects of LGHMF-MG on survival, cytoskeleton and osteogenic potential of hMSCs. Results showed that the LGHMF-MG treatment for 6 h disrupted the cytoskeleton of hMSCs, and the LGHMF-MG treatment for 24 h led to cell death. LGHMF-MG treatments for 6 h in early stages of osteogenic induction (the pre-treatment before osteogenic induction, the beginning-treatment in the beginning-stage of osteogenic induction and the middle-treatment in the middle-stage of osteogenic induction) resulted in suppression on osteogenesis of hMSCs. The suppression intensity was reduced gradually as the treatment stage of LGHMF-MG was postponed. The LGHMF-MG treatment for 6 h in the ending-stage of osteogenic induction (the ending-treatment) had no obvious effect on osteogenesis of hMSCs. These results indicated that LGHMF-MG should affect the initiation of osteogenesis. Finally, the possible mechanism for the inhibition effect of LGHMF-MG on osteogenesis of hMSCs is discussed.

Modeled microgravity and hindlimb unloading sensitize osteoclast precursors to RANKL-mediated osteoclastogenesis

Mechanical forces are essential to maintain skeletal integrity, and microgravity exposure leads to bone loss. The underlying molecular mechanisms leading to the changes in osteoblasts and osteoclast differentiation and function remain to be fully elucidated. Because of the infrequency of spaceflights and payload constraints, establishing in vitro and in vivo systems that mimic microgravity conditions becomes necessary. We have established a simulated microgravity (modeled microgravity, MMG) system to study the changes induced in osteoclast precursors. We observed that MMG, on its own, was unable to induce osteoclastogenesis of osteoclast precursors; however, 24 h of MMG activates osteoclastogenesis-related signaling molecules ERK, p38, PLCγ2, and NFATc1. Receptor activator of NFkB ligand (RANKL) (with or without M-CSF) stimulation for 3-4 days in gravity of cells that had been exposed to MMG for 24 h enhanced the formation of very large tartrate-resistant acid phosphatase (TRAP)-positive multinucleated (>30 nuclei) osteoclasts accompanied by an upregulation of the osteoclast marker genes TRAP and cathepsin K. To validate the in vitro system, we studied the hindlimb unloading (HLU) system using BALB/c mice and observed a decrease in BMD of femurs and a loss of 3D microstructure of both cortical and trabecular bone as determined by micro-CT. There was a marked stimulation of osteoclastogenesis as determined by the total number of TRAP-positive multinucleated osteoclasts formed and also an increase in RANKL-stimulated osteoclastogenesis from precursors removed from the tibias of mice after 28 days of HLU. In contrast to earlier reported findings, we did not observe any histomorphometric changes in the bone formation parameters. Thus, the foregoing observations indicate that microgravity sensitizes osteoclast precursors for increased differentiation. The in vitro model system described here is potentially a valid system for testing drugs for preventing microgravity-induced bone loss by targeting the molecular events occurring in microgravity-induced enhanced osteoclastogenesis.

Disorders of bone remodeling

The skeleton provides mechanical support for stature and locomotion, protects vital organs, and controls mineral homeostasis. A healthy skeleton must be maintained by constant bone modeling to carry out these crucial functions throughout life. Bone remodeling involves the removal of old or damaged bone by osteoclasts (bone resorption) and the subsequent replacement of new bone formed by osteoblasts (bone formation). Normal bone remodeling requires a tight coupling of bone resorption to bone formation to guarantee no alteration in bone mass or quality after each remodeling cycle. However, this important physiological process can be derailed by a variety of factors, including menopause-associated hormonal changes, age-related factors, changes in physical activity, drugs, and secondary diseases, which lead to the development of various bone disorders in both women and men. We review the major diseases of bone remodeling, emphasizing our current understanding of the underlying pathophysiological mechanisms.

The effect of simulated microgravity on human mesenchymal stem cells cultured in an osteogenic differentiation system: a bioinformatics study

One proposed strategy for bone regeneration involves ex vivo tissue engineering, accomplished using bone-forming cells, biodegradable scaffolds, and dynamic culture systems, with the goal of three-dimensional tissue formation. Rotating wall vessel bioreactors generate simulated microgravity conditions ex vivo, which lead to cell aggregation. Human mesenchymal stem cells (hMSCs) have been extensively investigated and shown to possess the potential to differentiate into several cell lineages. The goal of the present study was to evaluate the effect of simulated microgravity on all genes expressed in hMSCs, with the underlying hypothesis that many important pathways are affected during culture within a rotating wall vessel system. Gene expression was analyzed using a whole genome microarray and clustering with the aid of the National Institutes of Health's Database for Annotation, Visualization and Integrated Discovery database and gene ontology analysis. Our analysis showed 882 genes that were downregulated and 505 genes that were upregulated after exposure to simulated microgravity. Gene ontology clustering revealed a wide variety of affected genes with respect to cell compartment, biological process, and signaling pathway clusters. The data sets showed significant decreases in osteogenic and chondrogenic gene expression and an increase in adipogenic gene expression, indicating that ex vivo adipose tissue engineering may benefit from simulated microgravity. This finding was supported by an adipogenic differentiation assay. These data are essential for further understanding of ex vivo tissue engineering using hMSCs.

Involvement of cytoskeleton-associated proteins in the commitment of C3H10T1/2 pluripotent stem cells to adipocyte lineage induced by BMP2/4

The developmental pathway that gives rise to mature adipocytes involves two distinct stages: commitment and terminal differentiation. Although the important proteins/factors contributing to terminal adipocyte differentiation have been well defined, the proteins/factors in the commitment of mesenchymal stem cells to the adipocyte lineage cells have not. In this study, we applied proteomics analysis profiling to characterize differences between uncommitted C3H10T1/2 pluripotent stem cells and those that have been committed to the adipocyte lineage by BMP4 or BMP2 with the goal to identify such proteins/factors and to understand the molecular mechanisms that govern the earliest stages of adipocyte lineage commitment. Eight proteins were found to be up-regulated by BMP2, and 27 proteins were up-regulated by BMP4, whereas five unique proteins were up-regulated at least 10-fold by both BMP2/4, including three cytoskeleton-associated proteins (i.e. lysyl oxidase (LOX), translationally controlled tumor protein 1 (TPT1), and αB-crystallin). Western blotting further confirmed the induction of the expression of these cytoskeleton-associated proteins in the committed C3H10T1/2 induced by BMP2/4. Importantly, knockdown of LOX expression totally prevented the commitment, whereas knockdown of TPT1 and αB-crystallin expression partially inhibited the commitment. Several published reports suggest that cell shape can influence the differentiation of partially committed precursors of adipocytes, osteoblasts, and chondrocytes. We observed a dramatic change of cell shape during the commitment process, and we showed that knockdown of these cytoskeleton-associated proteins prevented the cell shape change and restored F-actin organization into stress fibers and inhibited the commitment to the adipocyte lineage. Our studies indicate that these differentially expressed cytoskeleton-associate proteins might determine the fate of mesenchymal stem cells to commit to the adipocyte lineage through cell shape regulation.

Cytoskeletal disassembly and cell rounding promotes adipogenesis from ES cells

Biomechanical signals such as cell shape and spreading play an important role in controlling stem cell commitment. Cell shape, adhesion and spreading are also affected by calreticulin, a multifunctional calcium-binding protein, which influences several cellular processes, including adipogenesis. Here we show that cytoskeletal disruption in mouse embryonic stem cells using cytochalasin D or nocodazole promotes adipogenesis. While cytochalasin D disrupts stress fibres and inhibits focal adhesion formation, nocodazole depolymerises microtubules and promotes focal adhesion formation. Furthermore, cytochalasin D increases the levels of both total and activated calcium/calmodulin-dependent protein kinase II, whereas nocodazole decreases it. Nevertheless, both treatments significantly increase the adipogenic potential of embryonic stem cells in vitro. Both cytochalasin D and nocodazole exposure caused cell rounding suggesting that it is cell shape that causes the switch towards the adipogenic programme. Calreticulin-containing embryonic stem cells, under baseline conditions, show low adipogenic potential, have low activity of signalling via calcium/calmodulin-dependent protein kinase II and display normal adhesive properties and cellular spreading in comparison to the highly adipogenic but poorly spread calreticulin-deficient ES cells. We conclude that forced cell rounding via cytoskeletal disruption overrides the effects of calreticulin, an ER chaperone, thus negatively regulating adipogenesis via focal adhesion-mediated cell spreading.

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.

Mechanisms of gravitational sensitivity of osteogenic precursor cells

This report is a detailed review of the current data on the mechanic and gravitational sensitivity of osteoblasts and osteogenic precursor cells in vitro. It summarizes the numerous responses of cells with an osteoblastic phenotype and osteogenic precursor cells and especially their responses to the alteration of their mechanic or gravitational surroundings. The review also discusses the osteogenic cell's pathways of signal transduction and the mechanisms of gravitational sensitivity. It was shown that the earliest multipotent stromal precursor cells of an adult organism's bone marrow can sense changes of intensity in a gravitational or mechanic field in model conditions, which may play a certain role in the development of osteopenia in microgravity.

Controlling cellular biomechanics of human mesenchymal stem cells

The therapeutic efficacy of human mesenchymal stem cells (hMSCs) depends on proper characterization and control of their unique biological, mechanical and physicochemical properties. For example, cellular biomechanics and environmental mechanical cues have been shown to critically influence cell commitment to a particular lineage. We characterized biomechanical properties of hMSCs including cytoskeleton elasticity and plasma membrane/cytoskeleton coupling. As expected, during osteogenic differentiation of hMSCs, the cellular biomechanics is remodeled, and such remodeling precedes up-regulation of the osteogenic markers. Further, application of an electrical stimulation modulates the cellular biomechanics and therefore may be used to facilitate stem cell differentiation for stem cell-based tissue engineering.

Mechanism of platelet functional changes and effects of anti-platelet agents on in vivo hemostasis under different gravity conditions

Serious thrombotic and hemorrhagic problems or even fatalities evoked by either microgravity or hypergravity occur commonly in the world. We recently reported that platelet functions are inhibited in microgravity environments and activated under high-G conditions, which reveals the pathogenesis for gravity change-related hemorrhagic and thrombotic diseases. However, the mechanisms of platelet functional variations under different gravity conditions remain unclear. In this study we show that the amount of filamin A coimmunoprecipitated with GPIbalpha was enhanced in platelets exposed to modeled microgravity and, in contrast, was reduced in 8 G-exposed platelets. Hypergravity induced actin filament formation and redistribution, whereas actin filaments were reduced in platelets treated with modeled microgravity. Furthermore, intracellular Ca2+ levels were elevated by hypergravity. Pretreatment of platelets with the cell-permeable Ca2+ chelator BAPTA-AM had no effect on cytoskeleton reorganization induced by hypergravity but significantly reduced platelet aggregation induced by ristocetin/hypergravity. Two anti-platelet agents, aspirin and tirofiban, effectively reversed the shortened tail bleeding time and reduced the death rate of mice exposed to hypergravity. Furthermore, the increased P-selectin surface expression was obviously reduced in platelets from mice treated with aspirin/hypergravity compared with those from mice treated with hypergravity alone. These data suggest that the actin cytoskeleton reorganization and intracellular Ca2+ level play key roles in the regulation of platelet functions in different gravitational environments. The results with anti-platelet agents not only further confirm the activation of platelets in vivo but also suggest a therapeutic potential for hypergravity-induced thrombotic diseases.

Mechanical behavior of human mesenchymal stem cells during adipogenic and osteogenic differentiation

Human mesenchymal stem cells (hMSCs) have gained widespread attention in the field of tissue engineering but not much is known about the changes of mechanical properties during the process of cell lineage commitment and the mechanisms of these behaviors. It is believed that exploring the inter-relations between stem cells mechanical properties and lineage commitment will shed light on the mechanobiology aspect of differentiation. hMSCs were cultured in adipogenic and osteogenic mediums and the elastic moduli were monitored using micropipette aspiration. It was found that hMSCs undergoing osteogenesis have an instantaneous Young's modulus of 890 +/- 219 Pa and an equilibrium Young's modulus of 224 +/- 40 Pa, each is about 2-fold higher than the control group. Interestingly, cells cultured in adipogenic medium exhibited a slight increase in the cellular modulus followed by a decrease relative to that of the control group. Gene expression study was employed to gain insights into this phenomenon. Concomitant up regulation of actin binding filamin A (FLNa) and gamma-Tubulin with the cellular elastic modulus indicated their important role in mechanical regulation during hMSCs differentiation. Statistical results showed that cell shape and cell area changed with cellular mechanical properties, which means that cell morphology has a close relation with cell elastic modulus in the initial stage of differentiation. Collectively, these results provide a quantitative description of hMSCs mechanical behavior during the process of differentiation as well as the possible accompanying mechanism at the biomolecular level.

Fasudil hydrochloride induces osteoblastic differentiation of stromal cell lines, C3H10T1/2 and ST2, via bone morphogenetic protein-2 expression

Rho-kinase (ROK), downstream of the mevalonate pathway, is detrimental to vessels, and suppressing its activity is a target for the treatment of human disease such as coronary artery disease and pulmonary hypertension. Recent studies have shown that ROK has a crucial role in bone metabolism. However, the role of ROK in stromal cells is still unclear. The present study was undertaken to investigate the effect of a ROK inhibitor, fasudil hydrochloride, on stromal cell lines, C3H10T1/2 and ST2. In both cells, Fasudil significantly stimulated alkaline phosphatase activity and enhanced cell mineralization. Moreover, fasudil significantly increased the mRNA expression of collagen-I, osteocalcin, and bone morphogenetic protein-2 (BMP-2). Supplementation of noggin, a BMP-2 antagonist, significantly reversed the fasudil-induced collagen-I and osteocalcin mRNA expression in both cells. These findings suggest that fasudil induces the osteoblastic differentiation of stromal cells via enhancing BMP-2 expression, and that this drug might be beneficial for not only atherosclerosis but also osteoporosis by promoting bone formation.

Genetics of osteoporosis: accelerating pace in gene identification and validation

Osteoporosis is characterized by low bone mineral density and structural deterioration of bone tissue, leading to an increased risk of fractures. It is the most common metabolic bone disorder worldwide, affecting one in three women and one in eight men over the age of 50. In the past 15 years, a large number of genes have been reported as being associated with osteoporosis. However, only in the past 4 years we have witnessed an accelerated pace in identifying and validating osteoporosis susceptibility loci. This increase in pace is mostly due to large-scale association studies, meta-analyses, and genome-wide association studies of both single nucleotide polymorphisms and copy number variations. A comprehensive review of these developments revealed that, to date, at least 15 genes (VDR, ESR1, ESR2, LRP5, LRP4, SOST, GRP177, OPG, RANK, RANKL, COLIA1, SPP1, ITGA1, SP7, and SOX6) can be reasonably assigned as confirmed osteoporosis susceptibility genes, whereas, another >30 genes are promising candidate genes. Notably, confirmed and promising genes are clustered in three biological pathways, the estrogen endocrine pathway, the Wnt/beta-catenin signaling pathway, and the RANKL/RANK/OPG pathway. New biological pathways will certainly emerge when more osteoporosis genes are identified and validated. These genetic findings may provide new routes toward improved therapeutic and preventive interventions of this complex disease.

Cell adhesion and spreading affect adipogenesis from embryonic stem cells: the role of calreticulin

Calreticulin is an endoplasmic reticulum-resident multifunctional protein, which has been shown to influence numerous cellular processes, including cell adhesion. In this study, we characterized the adhesive properties of embryonic stem cells (ESCs) lacking calreticulin and showed that adipogenesis from ESCs is directly and reciprocally controlled by the adhesive status of a cell, which in turn is modulated by calreticulin. Calreticulin-deficient ESCs are not only highly adipogenic but also show elevated calmodulin/CaMKII signaling and poor adhesiveness compared with the wild-type ESCs. Calreticulin deficiency leads to a disorganized cytoskeleton and low levels of focal adhesion-related proteins, such as vinculin, paxillin, and phosphorylated focal adhesion kinase, which cause limited focal adhesion formation and limited fibronectin deposition. Moreover, differentiation on nonadhesive substrata, which hinder cell spreading, promoted adipogenesis in the wild-type ESCs that normally have low adipogenic potential, causing a decrease in focal adhesion protein expression and an increase in calmodulin/CaMKII signaling. In contrast, inhibition of CaMKII effectively increased focal adhesion protein levels and inhibited adipogenesis in calreticulin-deficient ESCs, causing them to behave like the low adipogenic, wild-type ESCs. Thus, the adipogenic potential of ESCs is proportional to their calmodulin/CaMKII activity but is inversely related to their focal adhesion protein levels and degree of adhesiveness/spreading.

Modeled microgravity causes changes in the cytoskeleton and focal adhesions, and decreases in migration in malignant human MCF-7 cells

Because cells are sensitive to mechanical forces,microgravity might act on stress-dependent cell changes. Regulation of focal adhesions (FAs) and cytoskeletal activity plays a role in cell maintenance, cell movement,and migration. Human MCF-7 cells were exposed to modeled microgravity (MMG) to test the hypothesis that migration responsiveness to microgravity is associated with cytoskeleton and FA anomalies. MMG acts on MCF-7 cells by disorganizing cytoskeleton filaments (microfilaments and microtubules). Microfilaments in MMG did not display their typical radial array. Likewise, microtubules were disrupted in MCF-7 cells within 4 h of initiation of MMG and were partly reestablished by 48 h. FAs generated inmicrogravity were less mature than those established in controls, shown by reduced FAs number and clustering. In parallel, MMG decreased kinases activity (such as FAK,PYK2, and ILK) of FAs in MCF-7 cells. The expression of both integrinbeta1 and integrinbeta4 were downregulated by MMG. We conclude that cytoskeletal alterations and FAs changes in MMG are concomitant with cell invasion and migration retardation. We suggest that reduced migration response in MCF-7 cells following MMG is linked to changes of cytoskeleton and FAs.

Twenty bone-mineral-density loci identified by large-scale meta-analysis of genome-wide association studies

Bone mineral density (BMD) is a heritable complex trait used in the clinical diagnosis of osteoporosis and the assessment of fracture risk. We performed meta-analysis of five genome-wide association studies of femoral neck and lumbar spine BMD in 19,195 subjects of Northern European descent. We identified 20 BMD loci that reached genome-wide significance (GWS; P < 5 x 10(-8)), of which 13 map to regions not previously associated with this trait: 1p31.3 (GPR177), 2p21 (SPTBN1), 3p22 (CTNNB1), 4q21.1 (MEPE), 5q14 (MEF2C), 7p14 (STARD3NL), 7q21.3 (FLJ42280), 11p11.2 (LRP4, ARHGAP1, F2), 11p14.1 (DCDC5), 11p15 (SOX6), 16q24 (FOXL1), 17q21 (HDAC5) and 17q12 (CRHR1). The meta-analysis also confirmed at GWS level seven known BMD loci on 1p36 (ZBTB40), 6q25 (ESR1), 8q24 (TNFRSF11B), 11q13.4 (LRP5), 12q13 (SP7), 13q14 (TNFSF11) and 18q21 (TNFRSF11A). The many SNPs associated with BMD map to genes in signaling pathways with relevance to bone metabolism and highlight the complex genetic architecture that underlies osteoporosis and variation in BMD.

Excellent effect of three-dimensional culture condition on pancreatic islets

AIM

Culture of cells in simulated microgravity may be potentially beneficial to the fields of cell biology and somatic cell therapy. We aimed to examine three-dimensional culture condition on pancreatic islets.

METHODS

Islets of Langerhans were cultured in conditions of stasis, microgravity, and microgravity with a polyglycolic acid (PGA) fibrous scaffold. After 5 days in culture, islets were transplanted into the leg muscles of streptozotocin-treated diabetic Wistar rats. The blood glucose and insulin content were determined from the tail vein blood of recipients. The grafts were then frozen, dried, and coated for analysis by scanning electron microscopy.

RESULTS

Grafts cultured in the three-dimensional conditions (simulated microgravity in the presence or absence of a PGA fibrous scaffold) were capable of significantly normalizing insulin production and blood glucose concentration when compared to control grafts (p<0.017). Scanning electron microscopy showed that the transplanted islets from three-dimensional culture groups demonstrated normal morphology with extracellular matrix on the surface. Islets in the PGA group exhibited well adhesion to PGA scaffolds.

CONCLUSIONS

The three-dimensional culture conditions significantly improved the function and morphology of the grafts. The function and morphology of the grafts in the microgravity with a scaffold group was the excellent one.

Osteogenic potential and responsiveness to leptin of mesenchymal stem cells between postmenopausal women with osteoarthritis and osteoporosis

The aim of this study was to compare the osteogenic potential and responsiveness to leptin of mesenchymal stem cells (MSCs) from bone marrow between postmenopausal women with osteoarthritis (OA) and osteoporosis (OP). MSCs of the proximal femur from OA and OP donors were cultured under control and different experimental mediums. After verifying the availability of primary cells, their osteogenic potential and responsiveness to leptin were compared between two groups. Similar patterns of cell growth were shown in both OA and OP groups. However, after the sixth passage, the viability of undifferentiated cells decreased more in OP than in OA donors. Under the same osteogenic supplements condition, the mRNA expression of osteogenesis-specific genes, osteocalcin (OC) and alkaline phosphatase (ALP) were higher in OA group. Comparison of bone matrix mineralization was parallel to that of mRNA expression. The level of bone-specific ALP (BAP) was higher in cells from donors with OA, whereas osteoprotegerin (OPG) was higher in OP group. This difference in BAP expression proved to be insignificant after the administration of leptin. Although leptin upregulated the expression of OPG, a significant difference still existed between OA and OP. In conclusion, differential osteogenic potential and responsiveness to leptin of MSCs were noted between postmenopausal women with OA and OP. Differential biological behavior of MSCs seems to be partly related to the different distribution of bone mass between OA and OP populations.