An osteopontin-integrin interaction plays a critical role in directing adipogenesis and osteogenesis by mesenchymal stem cells

Bacteria-laden microgels as autonomous three-dimensional environments for stem cell engineering

A one-step microfluidic system is developed in this study which enables the encapsulation of stem cells and genetically engineered non-pathogenic bacteria into a so-called three-dimensional (3D) pearl lace-like microgel of alginate with high level of monodispersity and cell viability. The alginate-based microgel constitutes living materials that control stem cell differentiation in either an autonomous or heteronomous manner. The bacteria (Lactococcus lactis) encapsulated within the construct surface display adhesion fragments (III7-10 fragment of human fibronectin) for integrin binding while secreting growth factors (recombinant human bone morphogenetic protein-2) to induce osteogenic differentiation of human bone marrow-derived mesenchymal stem cells. We concentrate on interlinked pearl lace microgels that enabled us to prototype a low-cost 3D bioprinting platform with highly tunable properties.

Obesity-Induced Methylation of Osteopontin Contributes to Adipogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells

Obesity is a major risk factor for many chronic diseases, including diabetes, fatty livers, and cancer. Expansion of the adipose mass has been shown to be related to adipogenic differentiation of adipose-derived mesenchymal stem cells (ASCs). However, the underlying mechanism of this effect has yet to be elucidated. We found that osteopontin (OPN) is downregulated in ASCs and adipose tissues of obese mice and overweight human beings because of methylation on its promoter, indicating that OPN may affect the development of obesity. Silencing of OPN in wild-type ASCs promotes adipogenic differentiation, while reexpression of OPN reduced adipogenic differentiation in OPN^−/− ASCs. The role of extracellular OPN in ASC differentiation was further demonstrated by supplementation and neutralization of OPN. Additionally, OPN suppresses adipogenic differentiation in ASCs through the C/EBP pathways. Consistent with these in vitro results, by intravenous injection of OPN-expressing adenovirus to the mice, we found OPN can delay the development of obesity and improve insulin sensitivity. Therefore, our study demonstrates an important role of OPN in regulating the development of obesity, indicating OPN might be a novel target to attenuate obesity and its complications.

Impact of aging on bone, marrow and their interactions

Hematopoiesis in land dwelling vertebrates and marine mammals occurs within the bone marrow, continually providing mature progeny over the course of an organism's lifetime. This conserved dependency highlights the critical relationship between these two organs, yet the skeletal and hematopoietic systems are often thought of as separate. In fact, data are beginning to show that skeletal disease pathogenesis influences hematopoiesis and viceversa, offering novel opportunities to approach disease affecting bone and blood. With a growing global population of aged individuals, interest has focused on cell autonomous changes in hematopoietic and skeletal systems that result in dysfunction. The purpose of this review is to summarize the literature on aging effects in both fields, and provide critical examples of organ cross-talk in the aging process.

Secretome analysis of human bone marrow derived mesenchymal stromal cells

As an essential cellular component of the bone marrow (BM) microenvironment mesenchymal stromal cells (MSC) play a pivotal role for the physiological regulation of hematopoiesis, in particular through the secretion of cytokines and chemokines. Mass spectrometry (MS) facilitates the identification and quantification of a large amount of secreted proteins (secretome), but can be hampered by the false-positive identification of contaminating proteins released from dead cells or derived from cell medium. To reduce the likelihood of contaminations we applied an approach combining secretome and proteome analysis to characterize the physiological secretome of BM derived human MSC. Our analysis revealed a secretome consisting of 315 proteins. Pathway analyses of these proteins revealed a high abundance of proteins related to cell growth and/or maintenance, signal transduction and cell communication thereby representing key biological functions of BM derived MSC on protein level. Within the MSC secretome we identified several cytokines and growth factors such as VEGFC, TGF-β1, TGF-β2 and GDF6 which are known to be involved in the physiological regulation of hematopoiesis. By comparing the peptide patterns of secretomes and cell lysates 17 proteins were identified as candidates for proteolytic processing. Taken together, our combined MS work-flow reduced the likelihood of contaminations and enabled us to carve out a specific overview about the composition of the secretome from human BM derived MSC. This methodological approach and the specific secretome signature of BM derived MSC may serve as basis for future comparative analyses of the interplay of MSC and HSPC in patients with hematological malignancies.

Integrin alpha11 is an Osteolectin receptor and is required for the maintenance of adult skeletal bone mass

We previously discovered a new osteogenic growth factor that is required to maintain adult skeletal bone mass, Osteolectin/Clec11a. Osteolectin acts on Leptin Receptor⁺ (LepR⁺) skeletal stem cells and other osteogenic progenitors in bone marrow to promote their differentiation into osteoblasts. Here we identify a receptor for Osteolectin, integrin α11, which is expressed by LepR⁺ cells and osteoblasts. α11β1 integrin binds Osteolectin with nanomolar affinity and is required for the osteogenic response to Osteolectin. Deletion of Itga11 (which encodes α11) from mouse and human bone marrow stromal cells impaired osteogenic differentiation and blocked their response to Osteolectin. Like Osteolectin deficient mice, Lepr-cre; Itga11^fl/fl mice appeared grossly normal but exhibited reduced osteogenesis and accelerated bone loss during adulthood. Osteolectin binding to α11β1 promoted Wnt pathway activation, which was necessary for the osteogenic response to Osteolectin. This reveals a new mechanism for maintenance of adult bone mass: Wnt pathway activation by Osteolectin/α11β1 signaling.

Throughout our lives, our bones undergo constant remodeling. Cells called osteoclasts break down old bone and cells called osteoblasts lay down new. Normally, the two cell types work in balance but if the rate of breakdown outpaces new bone formation the skeleton can become weak. This weakness leads to a condition called osteoporosis, in which people suffer from fragile bones. Osteoporosis is hard to reverse, in part because our ability to encourage new bone to form is limited.

In 2016, researchers discovered a protein called osteolectin, which promotes new bone formation during adulthood by helping skeletal stem cells transform into bone cells. But so far, it has been unclear how osteolectin achieves this. To investigate this further, Shen et al. – including some researchers involved in the 2016 study – marked osteolectin with a molecular tag and tested what it bound on the surface of mouse and human bone marrow cells.

The experiments revealed that osteolectin binds to a specific receptor protein called α11 integrin, which can only be found on skeletal stem cells and the osteoblasts they give rise to. Once osteolectin binds to the receptor, it activates a signaling pathway that induces the stem cells to develop into osteoblasts. Mice that lacked either osteolectin or α11 integrin produced less bone and lost bone tissue faster as adults.

Osteolectin could potentially be useful in the treatment of osteoporosis or broken bones. Since only skeletal stem cells and osteoblasts cells produce α11 integrin, osteolectin would specifically target these cells without affecting cells that do not form bones. A next step will be to assess how well osteolectin compares to existing treatments for fragile bones.

Chemokine-like receptor 1 deficiency leads to lower bone mass in male mice

The adipokine Chemerin and its receptor, chemokine-like receptor 1 (CMKLR1), are associated with osteoblastogenic differentiation of mesenchymal stem cells (MSCs) and osteoclastogenic differentiation of osteoclast precursors in vitro, suggesting that CMKLR1 would affect the bone mineral density (BMD). However, the role of CMKLR1 on BMD in vivo remains unknown. Here, using CMKLR1 knockout mouse model, we unveiled that CMKLR1 effected the amount of Leydig cells in testis and regulated androgen-dependent bone maintenance in male mice, which exhibited lower serum testosterone levels, thereby reducing the trabecular bone mass. Correspondingly, the mRNA expression of testosterone synthesis enzymes in testis decreased. The bone tissue also showed decreased mRNAs expression of osteogenic markers and increased mRNA levels for osteoclast markers. Furthermore, by in vitro differentiation models, we found CMKLR1-deficiency could break the balance between osteoblastogenesis and osteoclastogenesis that caused a shift from osteogenic to adipogenic differentiation in MSCs and enhanced osteoclast formation. In addition, bone mass increase in CMKLR1 KO male mice can be promoted by treatment with 5α-dihydrotestosterone (DHT), and the inactivation of CMKLR1 in male wild-type (WT) mice with antagonist treatment can lead to low bone mass. Taken together, these data indicate that CMKLR1 positively regulates bone metabolism through mediating testosterone production and the balance between osteoblast and osteoclast formation.

Rescuing mesenchymal stem cell regenerative properties on hydrogel substrates post serial expansion

The use of human mesenchymal stem/stromal cells (hMSCs) in most clinical trials requires millions of cells/kg, necessitating ex vivo expansion typically on stiff substrates (tissue culture polystyrene [TCPS]), which induces osteogenesis and replicative senescence. Here, we quantified how serial expansion on TCPS influences proliferation, expression of hMSC-specific surface markers, mechanosensing, and secretome. Results show decreased proliferation and surface marker expression after five passages (P5) and decreased mechanosensing ability and cytokine production at later passages (P11-P12). Next, we investigated the capacity of poly(ethylene glycol) hydrogel matrices (E ~ 1 kPa) to rescue hMSC regenerative properties. Hydrogels reversed the reduction in cell surface marker expression observed at P5 on TCPS and increased secretion of cytokines for P11 hMSCs. Collectively, these results show that TCPS expansion significantly changes functional properties of hMSCs. However, some changes can be rescued by using hydrogels, suggesting that tailoring material properties could improve in vitro expansion methods.

Bone remodeling-inspired dual delivery electrospun nanofibers for promoting bone regeneration

Developing a highly bioactive bone tissue engineering scaffold that can modulate the bone remodeling process for promoting bone regeneration is a great challenge. In order to tackle this issue, inspired by the balance between bone resorption and formation in the bone remodeling process, here we developed a mesoporous silicate nanoparticle (MSN)-based electrospun polycaprolactone (PCL)/gelatin nanofibrous scaffold to achieve dual delivery of alendronate (ALN) and silicate for a synergetic effect in modulating bone remodeling, where ALN inhibited the bone-resorbing process via preventing guanosine triphosphate-related protein expression, and silicate promoted the bone-forming process via improving vascularization and bone calcification. The scaffold was successfully prepared by encapsulation of ALN into MSNs (ALN@MSNs) and co-electrospinning of an acetic acid-mediated PCL/gelatin homogeneous solution with well-dispersed ALN@MSNs. The results of ALN and Si element release profiles indicated that the ALN@MSN-loaded nanofibers achieved dual release of ALN and silicate (produced due to the hydrolysis of MSNs) simultaneously. The bone repair data from a rat critical-sized cranial defect model revealed that the developed strategy accelerated the healing time from 12 weeks to 4 weeks, almost three times faster, while the other nanofiber groups only had limited bone regeneration at 4 weeks. In addition, we used interactive double-factor analysis of variance for the data of bone volume and maturity to evaluate the synergetic effect of ALN and silicate in promoting bone regeneration, and the result clearly proved our original design and hypothesis. In summary, the presented bone remodeling-inspired electrospun nanofibers with dual delivery of ALN and silicate may be highly promising for bone repair in the clinic.

Osteopontin Expression in Cardiomyocytes Is Increased in Pediatric Patients With Sepsis or Pneumonia

Sepsis and pneumonia are major causes of death in the United States, and their pathophysiology includes infection with inflammation and immune dysfunction. Both sepsis and pneumonia cause cardiovascular dysfunction. The expression of Osteopontin (OPN) in cardiomyocytes of patients with sepsis or pneumonia, and its role the induced cardiac dysfunction have not been thoroughly investigated. OPN is a matricellular protein synthesized by multiple diseased tissues and cells including cardiomyocytes. Here, we studied the expression of OPN protein using immunofluorescence in human myocardial autopsy tissues from pediatric and mid age or elderly patients with sepsis and/or pneumonia. Fourteen human myocardial tissues from six pediatric patients and eight mid-age or elderly patients were studied. Immunofluorescence was used to investigate the expression of OPN in paraffin-embedded heart sections co-stained with the myocyte markers Actin Alpha 1 (ACTA1) and Myosin Light Chain 2 (MLC2). A quantitative analysis was performed to determine the number of ACTA1 and MLC2 positive cardiomyocytes that express OPN. The results showed that OPN expression was significantly increased in cardiomyocytes in the hearts from pediatric patients with sepsis and/or pneumonia (N = 3) relative to pediatric patients without sepsis/pneumonia (N = 3), or adult to elderly patients with sepsis/pneumonia (N = 5). Among the older septic hearts, higher levels of cardiomyocyte OPN expression was seen only in conjunction with severe coronary arterial occlusion. This is the first study to document increased OPN expression in cardiomyocytes of pediatric subjects with sepsis or pneumonia. Our findings highlight a potentially important role for OPN in sepsis- or pneumonia-mediated cardiac dysfunction in pediatric patients.

Elevated extracellular calcium ions promote proliferation and migration of mesenchymal stem cells via increasing osteopontin expression

Supplementation of mesenchymal stem cells (MSCs) at sites of bone resorption is required for bone homeostasis because of the non-proliferation and short lifespan properties of the osteoblasts. Calcium ions (Ca2+) are released from the bone surfaces during osteoclast-mediated bone resorption. However, how elevated extracellular Ca2+ concentrations would alter MSCs behavior in the proximal sites of bone resorption is largely unknown. In this study, we investigated the effect of extracellular Ca2+ on MSCs phenotype depending on Ca2+ concentrations. We found that the elevated extracellular Ca2+ promoted cell proliferation and matrix mineralization of MSCs. In addition, MSCs induced the expression and secretion of osteopontin (OPN), which enhanced MSCs migration under the elevated extracellular Ca2+ conditions. We developed in vitro osteoclast-mediated bone resorption conditions using mouse calvaria bone slices and demonstrated Ca2+ is released from bone resorption surfaces. We also showed that the MSCs phenotype, including cell proliferation and migration, changed when the cells were treated with a bone resorption-conditioned medium. These findings suggest that the dynamic changes in Ca2+ concentrations in the microenvironments of bone remodeling surfaces modulate MSCs phenotype and thereby contribute to bone regeneration.

Fra-2 Expression in Osteoblasts Regulates Systemic Inflammation and Lung Injury through Osteopontin

Inflammatory responses require mobilization of innate immune cells from the bone marrow. The functionality of this process depends on the state of the bone marrow microenvironment. We therefore hypothesized that molecular changes in osteoblasts, which are essential stromal cells of the bone marrow microenvironment, influence the inflammatory response. Here, we show that osteoblast-specific expression of the AP-1 transcription factor Fra-2 (Fra-2^Ob-tet) induced a systemic inflammatory state with infiltration of neutrophils and proinflammatory macrophages into the spleen and liver as well as increased levels of proinflammatory cytokines, such as interleukin-1β (IL-1β), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF). By in vivo inhibition of osteopontin (OPN) in Fra-2^Ob-tet mice, we demonstrated that this process was dependent on OPN expression, which mediates alterations of the bone marrow niche. OPN expression was transcriptionally enhanced by Fra-2 and stimulated mesenchymal stem cell (MSC) expansion. Furthermore, in a murine lung injury model, Fra-2^Ob-tet mice showed increased inflammatory responses and more severe disease features via an enhanced and sustained inflammatory response to lipopolysaccharide (LPS). Our findings demonstrate for the first time that molecular changes in osteoblasts influence the susceptibility to inflammation by altering evasion of innate immune cells from the bone marrow space.

Bioinstructive Naringin-Loaded Micelles for Guiding Stem Cell Osteodifferentiation

Naringin is a naturally occurring flavanone with recognized neuroprotective, cardioprotective, anti-inflammatory, and antiosteoporotic properties. Herein, the delivery of Naringin-loaded methoxy-poly(ethylene glycol)-maleimide-thiol-poly(l-lactide) (mPEGMSPLA) diblock polymeric micelles to human adipose-derived stem cells (hASCs) with the aim to augment its pro-osteogenic effect in these cells is reported for the first time. The synthesis of the diblock copolymer is performed via Michael-type addition reaction between hydrophilic methoxy-poly(ethylene glycol)-maleimide (mPEGMAL) and hydrophobic thiol-poly(l-lactide) (PLASH) and confirmed by 1 H NMR and attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectroscopy. The resulting mPEGMSPLA copolymer self-assembles into monodispersed polymeric micelles (≈84.4 ± 2 nm) and presents a high Naringin encapsulation efficiency (87.8 ± 4%), with a sustained release profile at physiological pH. Alongside, in vitro data reveal that upon internalization into hASC 2D cultures, Naringin nanomicellar formulations attain a higher pro-osteogenic effect than that of free drug. Notably, these bioactive carriers also induce superior osteopontin expression and increase matrix mineralization in these cells over free drug administration. Overall, such findings support for the first time the use of polymeric nanomicelles for Naringin delivery into hASCs as a valid approach for modulating stem cell osteogenic differentiation.

The multiple functions and mechanisms of osteopontin

Osteopontin (OPN) is a highly phosphorylated glycophosphoprotein having acidic characteristics and rich in aspartic acid. OPN, a multifunctional protein, has important functions on cardiovascular diseases, cancer, diabetes and kidney stone diseases and in the process of inflammation, biomineralization, cell viability and wound healing. Osteopontin acts on organisms by playing a key role in secretion levels of interleukin-10 (IL-10), interleukin-12 (IL-12), interleukin-3 (IL-3), interferon-γ (IFN-γ), integrin αvB3, nuclear factor kappa B (NF-kB), macrophage and T cells, regulating the osteoclast function and affecting CD44 receptors. The aim of the present review is to address majority of different functions of OPN protein which are known, suspected or suggested through the data obtained about this protein yet.

Achieving stem cell imaging and osteogenic differentiation by using nitrogen doped graphene quantum dots

Nitrogen doped graphene quantum dots (N-GQDs) were synthesized to explore and extend their potential applications in biomedical field. The hemocompatibility and cytotoxity of the obtained N-GQDs were primarily assessed at concentrations ranging from 10 to 100 μg/ml. From the results, it was found that the proliferation of rat Bone Mesenchymal Stem Cells (rBMSCs) was depressed to a certain extent after incubating with the high concentration (100 μg/ml) of N-GQDs. The nanoscale size and superior dispersibility endow N-GQDs with good cell permeability. Meanwhile, owing to their intrinsic photoluminescence characteristic, the N-GQDs can be used to label cells with high uniformity and light stability in absence of chemical dyes. More importantly, the up-regulated expression of alkaline phosphate (ALP), extracellular matrix, osteopontin (OPN) and osteocalcin (OCN) in rBMSCs cultured with N-GQDs, indicating N-GQDs have the abilities to promote rBMSCs osteogenic differentiation. This work would help give a new insight into the advantages of N-GQDs and pave the way for application of N-GQDs in regenerative medicine fields.

Adaptive Regulation of Osteopontin Production by Dendritic Cells Through the Bidirectional Interaction With Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) exert immunosuppressive effects on immune cells including dendritic cells (DCs). However, many details of the bidirectional interaction of MSCs with DCs are still unsolved and information on key molecules by which DCs can modulate MSC functions is limited. Here, we report that osteopontin (OPN), a cytokine involved in homeostatic and pathophysiologic responses, is constitutively expressed by DCs and regulated in the DC/MSC cocultures depending on the activation state of MSCs. Resting MSCs promoted OPN production, whereas the production of OPN was suppressed when MSCs were activated by proinflammatory cytokines (i.e., TNF-α, IL-6, and IL-1β). OPN induction required cell-to-cell contact, mediated at least in part, by β1 integrin (CD29). Conversely, activated MSCs inhibited the release of OPN via the production of soluble factors with a major role played by Prostaglandin E₂ (PGE₂). Accordingly, pretreatment with indomethacin significantly abrogated the MSC-mediated suppression of OPN while the direct addition of exogenous PGE₂ inhibited OPN production by DCs. Furthermore, DC-conditioned medium promoted osteogenic differentiation of MSCs with a concomitant inhibition of adipogenesis. These effects were paralleled by the repression of the adipogenic markers PPARγ, adiponectin, and FABP4, and induction of the osteogenic markers alkaline phosphatase, RUNX2, and of the bone-anabolic chemokine CCL5. Notably, blocking OPN activity with RGD peptides or with an antibody against CD29, one of the OPN receptors, prevented the effects of DC-conditioned medium on MSC differentiation and CCL5 induction. Because MSCs have a key role in maintenance of bone marrow (BM) hematopoietic stem cell niche through reciprocal regulation with immune cells, we investigated the possible MSC/DC interaction in human BM by immunohistochemistry. Although DCs (CD1c⁺) are a small percentage of BM cells, we demonstrated colocalization of CD271⁺ MSCs with CD1c⁺ DCs in normal and myelodysplastic BM. OPN reactivity was observed in occasional CD1c⁺ cells in the proximity of CD271⁺ MSCs. Altogether, these results candidate OPN as a signal modulated by MSCs according to their activation status and involved in DC regulation of MSC differentiation.

Osteoactivin inhibits dexamethasone-induced osteoporosis through up-regulating integrin β1 and activate ERK pathway

BACKGROUNDS

Dexamethasone (Dex) is widely used in autoimmune diseases and inflammation treatment. A sever side effect of prolonged exposure to Dex is increased risk of osteoporosis (OP) or even femoral head necrosis, which would cause much suffer to patients. To reveal the mechanism behind this phenomenon, provide therapeutic guidance and potential target, we analyzed the inhibitory mechanism of Dex on osteogenesis of rat-BMSC.

METHODS

Rat BMSC were obtained and characterized with FACS analysis. Osteogenesis and adipogenesis abilities were detected with Oil-O-Red staining, Alizarin Red staining and ALP activity analysis. These BMSC were then treated with Dex in combination with recombinant OA or not and detected for osteogenesis related gene expression with qRT-PCR. Protein interaction and expression were detected by Co-Immunoprecipitation and western blot.

RESULTS

Osteoactivin (OA) could promote integrin β 1 expression and interact with this protein physically, leading to ERK activation and promoting osteogenesis related genes' expression including Runx2, Col1a and OCN in BMSC. Dex, however, could block expression of several upstream genes of OA and decrease OA mRNA and protein level, and eventually suppress integrin β1-ERK activation and lead to decreased osteogenesis, which could finally develop into OP.

CONCLUSION

Recombinant OA treated BMSC exerted better osteogenesis potency even with Dex administration. This is because additional OA in medium counter-acts with Dex's influence and rescued osteoblast differentiation via up-regulating integrin β1 and activate ERK/MAPK pathway which promotes osteogenesis. Hence, OA/integrin β1 could serve as potential therapeutic target for OP.

The Role of Semipurified Fractions Isolated from Quercus infectoria on Bone Metabolism by Using hFOB 1.19 Human Fetal Osteoblast Cell Model

Background. Quercus infectoria (QI) is a plant used in traditional medicines in Asia. The plant was reported to contain various active phytochemical compounds that have potential to stimulate bone formation. However, the precise mechanism of the stimulation effect of QI on osteoblast has not been elucidated. The present study was carried out to isolate QI semipurified fractions from aqueous QI extract and to delineate the molecular mechanism of QI semipurified fraction that enhanced bone formation by using hFOB1.19 human fetal osteoblast cell model. Methods. Isolation of QI semipurified fractions was established by means of column chromatography and thin layer chromatography. Established QI semipurified fractions were identified using Liquid Chromatography-Mass Spectrometry (LC-MS). Cells were treated with derived QI semipurified fractions and investigated for mineralization deposition and protein expression level of BMP-2, Runx2, and OPN by ELISA followed gene expression analysis of BMP-2 and Runx2 by RT-PCR. Results. Column chromatography isolation and purification yield Fractions A, B, and C. LC-MS analysis reveals the presence of polyphenols in each fraction. Results show that QI semipurified fractions increased the activity and upregulated the gene expression of BMP-2 and Runx2 at day 1, day 3, and day 7. OPN activity increased in cells treated with QI semipurified fractions at day 1 and day 3. Meanwhile, at day 7, expression of OPN decreased in activity. Furthermore, the study showed that combination of Fractions A, B, and C with osteoporotic drug (pamidronate) further increased the activity and upregulated the gene expression of BMP-2 and Runx2. Conclusions. These findings demonstrated that polyphenols from semipurified fractions of QI enhanced bone formation through expression of the investigated bone-related marker that is its potential role when combined with readily available osteoporotic drug.

Modulation of Correlated Segment Fluctuations in IDPs upon Complex Formation as an Allosteric Regulatory Mechanism

Molecular recognition of and by intrinsically disordered proteins (IDPs) is an intriguing and still largely elusive phenomenon. Typically, protein recognition involving IDPs requires either folding upon binding or, alternatively, the formation of "fuzzy complexes." Here we show via correlation analyses of paramagnetic relaxation enhancement data unprecedented and striking alterations of the concerted fluctuations within the conformational ensemble of IDPs upon ligand binding. We study the binding of α-synuclein to calmodulin, a ubiquitous calcium-binding protein, and the binding of the extracellular matrix IDP osteopontin to heparin, a mimic of the extracellular matrix ligand hyaluronic acid. In both cases, binding leads to reduction of correlated long-range motions in these two IDPs and thus indicates a loosening of structural compaction upon binding. Most importantly, however, the simultaneous presence of correlated and anti-correlated fluctuations in IDPs suggests the prevalence of "energetic frustration" and provides an explanation for the puzzling observation of disordered allostery in IDPs.

Alcohol exposure decreases osteopontin expression during fracture healing and osteopontin-mediated mesenchymal stem cell migration in vitro

BACKGROUND

Alcohol consumption is a risk factor for impaired fracture healing, though the mechanism(s) by which this occurs are not well understood. Our laboratory has previously shown that episodic alcohol exposure of rodents negatively affects fracture callus development, callus biomechanics, and cellular signaling which regulates stem cell differentiation. Here, we examine whether alcohol alters chemokine expression and/or signaling activity in the mouse fracture callus during early fracture healing.

METHODS

A mouse model for alcohol-impaired tibia fracture healing was utilized. Early fracture callus was examined for alcohol-effects on tissue composition, expression of chemokines involved in MSC migration to the fracture site, and biomechanics. The effects of alcohol on MSC migration and cell adhesion receptors were examined in an in vitro system.

RESULTS

Mice exposed to alcohol showed decreased evidence of external callus formation, decreased callus-related osteopontin (OPN) expression levels, and decreased biomechanical stiffness. Alcohol exposure decreased rOPN-mediated MSC migration and integrin β1 receptor expression in vitro.

CONCLUSIONS

The effects of alcohol exposure demonstrated here on fracture callus-associated OPN expression, rOPN-mediated MSC migration in vitro, and MSC integrin β1 receptor expression in vitro have not been previously reported. Understanding the effects of alcohol exposure on the early stages of fracture repair may allow timely initiation of treatment to mitigate the long-term complications of delayed healing and/or fracture non-union.

Serum levels of osteopontin predict major adverse cardiovascular events in patients with severe carotid artery stenosis

BACKGROUND

Inflammatory mediators in the blood stream and within plaques are key determinants in atherogenesis. Here, we investigated serum osteopontin (OPN) as a potential predictor of poor outcome in patients with severe carotid atherosclerosis.

METHODS

Carotid plaques and serum were collected from patients asymptomatic (n=185) or symptomatic (n=40) for ischemic stroke. Plaques were stained for lipids, smooth muscle cells, neutrophils, M1 and M2 macrophage subsets and matrix metallopropteinase-9 (MMP-9). Serum levels of OPN and interleukin-6 (IL-6) were determined by colorimetric enzyme-linked immunosorbent assays.

RESULTS

Symptomatic patients showed a two-fold increase in serum OPN levels. In both symptomatic and asymptomatic patients, OPN levels positively correlated with intraplaque count of neutrophils, total macrophages, and MMP-9 content. In asymptomatic patients, OPN levels also positively correlated with lipids and M1 macrophage subsets. Receiver operating characteristic curve analysis identified serum OPN concentration of 70ng/ml as the best cut-off value to predict major adverse cardiovascular events (MACEs). Patients with high OPN levels had more vulnerable plaque phenotype and reduced levels of HDL-cholesterol and IL-6 as compared to low OPN levels. Kaplan-Meier curve confirmed that patients with OPN levels >70ng/ml had more MACEs at a 24-month follow-up. In the multivariate survival analysis, OPN levels >70ng/ml predicted MACEs, independently of age, gender, and symptomatic status.

CONCLUSION

High circulating OPN levels were strongly correlated with vulnerability parameters within plaques and predict MACEs in patients with severe carotid artery stenosis. Although confirmation is needed from larger trials, OPN could be a promising clinical tool to assess atherosclerotic outcomes.

Tuning surface properties of bone biomaterials to manipulate osteoblastic cell adhesion and the signaling pathways for the enhancement of early osseointegration

Osteoblast cell adhesion is the initial step of early osseointegration responding to bone material implants. Enhancing the osteoblastic cell adhesion has become one of the prime aims when optimizing the surface properties of bone biomaterials. The traditional strategy focuses in improving the physical attachment of osteoblastic cells onto the surfaces of biomaterials. However, instead of a simple cell physical attachment, the osteoblastic cell adhesion has been revealed to be a sophisticated system. Despite the well-documented effect of bone biomaterial surface modifications on adhesion, few studies have focused on the underlying molecular mechanisms. Physicochemical signals from biomaterials can be transduced into intracellular signaling network and further initiate the early response cascade towards the implants, which includes cell survival, migration, proliferation, and differentiation. Adhesion is vital in determining the early osseointegration between host bone tissue and implanted bone biomaterials via regulating involving signaling pathways. Therefore, the modulation of early adhesion behavior should not simply target in physical attachment, but emphasize in the manipulation of downstream signaling pathways, to regulate early osseointegration. This review firstly summarized the basic biological principles of osteoblastic cell adhesion process and the activated downstream cell signaling pathways. The effects of different biomaterial physicochemical properties on osteoblastic cell adhesion were then reviewed. This review provided up-to-date research outcomes in the adhesion behavior of osteoblastic cells on bone biomaterials with different physicochemical properties. The strategy is optimised from traditionally focusing in physical cell adhesion to the proposed strategy that manipulating cell adhesion and the downstream signaling network for the enhancement of early osseointegration.

Fish bone peptide promotes osteogenic differentiation of MC3T3-E1 pre-osteoblasts through upregulation of MAPKs and Smad pathways activated BMP-2 receptor

Fish bone, a by-product of fishery processing, is composed of protein, calcium, and other minerals. The objective of this study was to investigate the effects of a bioactive peptide isolated from the bone of the marine fish, Johnius belengerii, on the osteoblastic differentiation of MC3T3-E1 pre-osteoblasts. Post consecutive purification by liquid chromatography, a potent osteogenic peptide, composed of 3 amino acids, Lys-Ser-Ala (KSA, MW: 304.17 Da), was identified. The purified peptide promoted cell proliferation, alkaline phosphatase activity, mineral deposition, and expression levels of phenotypic markers of osteoblastic differentiation in MC3T3-E1 pre-osteoblast. The purified peptide induced phosphorylation of mitogen-activated protein kinases, including p38 mitogen-activated protein kinase, extracellular regulated kinase, and c-Jun N-terminal kinase as well as Smads. As attested by molecular modelling study, the purified peptide interacted with the core interface residues in bone morphogenetic protein receptors with high affinity. Thus, the purified peptide could serve as a potential pharmacological substance for controlling bone metabolism.

Evaluation of estrogenic potential by herbal formula, HPC 03 for in vitro and in vivo

HPC 03 is herbal formula that consists of extracts from Angelica gigas, Cnidium officinale Makino and Cinnamomum cassia Presl. The present study evaluated the estrogenic potential of HPC 03 by using in vitro and in vivo models. The regulatory mechanisms of HPC 03 in estrogen-dependent MCF-7 cells were assessed. HPC 03 induced the proliferation of estrogen receptor-positive MCF-7 cells, and the proliferation was blocked by the addition of the estrogen antagonist tamoxifen. The estrogen receptor_α/β luciferase activities were significantly increased by HPC 03 treatment, which also increased the mRNA expression of the estrogen-responsive genes Psen2, Pgr and Ctsd Also, we evaluated the ameliorative effects of HPC 03 on menopausal symptoms in ovariectomized rats. HPC 03 treatment in OVX rats significantly affected the uterine weight, increased the expression of estrogen-responsive genes Pgr and Psen2 in uterus, increased bone mineral density loss in the femur and inhibited body weight increase. Serum E2, collagen type 1 and osteocalcin were significantly increased, while serum LH, FSH and ALP were decreased compared with OVX rats. HPC 03 may be a promising candidate for the treatment of menopause, but further research is necessary to determine whether the observed effects also occur in humans.

C4orf7 modulates osteogenesis and adipogenesis of human periodontal ligament cells

Periodontal ligament cells (PDLCs), which have potential for multilineage differentiation, are candidates for use in regeneration of periodontal tissue defects; however, our understanding of the mechanisms underlying the lineage commitment of PDLCs remains limited. C4orf7, which is specifically expressed in the periodontal ligament (PDL) tissue, may be crucial in deciding the fate of PDLCs and regulating the periodontal bone balance. In this study, we examined the expression of C4orf7 in PDL tissue, using immunohistochemical staining. We transfected PDLCs with lentiviral vectors expressing C4orf7 and examined the effect of C4orf7 on the balance of PDLC osteogenic and osteoclastogenic differentiation. Osteogenic induction resulted in the downregulation of mRNA and protein expression levels of the osteogenic/cementoblastic markers: ALP, RUNX2, COL1, OPN, OPG, OSX, IBSP, CAP, and CEMP1. Transfected cells also exhibited an increased RANKL/OPG ratio, which is an indicator of osteoclastogenic differentiation. ALP activity assays and Alizarin red staining confirmed the negative effect of C4orf7 on PDLC osteogenic differentiation. Finally, we investigated the effect of C4orf7 on the lineage commitment of PDLCs to adipocytes. We observed increased expression levels of PPARγ2, GLUT4, ZFP423, FABP4, and LPL mRNAs, as well as a gradual accumulation of lipid droplets in the C4orf7-overexpressing group compared with controls. In summary, our data confirm that C4orf7 has an important role in the regulation of periodontal bone remodeling through promotion of the adipogenic/osteoclastogenic, and inhibition of the osteogenic/cementoblastic, differentiation of PDLCs. Therefore, C4orf7 is a potential therapeutic target for the treatment of periodontal disease and other bone metabolic disorders.

Hybrid-spheroids incorporating ECM like engineered fragmented fibers potentiate stem cell function by improved cell/cell and cell/ECM interactions

Extracellular matrix (ECM) microenvironment is critical for the viability, stemness, and differentiation of stem cells. In this study, we developed hybrid-spheroids of human turbinate mesenchymal stem cells (hTMSCs) by using extracellular matrix (ECM) mimicking fragmented fibers (FFs) for improvement of the viability and functions of hTMSCs. We prepared FFs with average size of 68.26 µm by partial aminolysis of poly L-lactide (PLLA) fibrous sheet (FS), which was coated with polydopamine for improved cell adhesion. The proliferation of hTMSCs within the hybrid-spheroids mixed with fragmented fibers was significantly increased as compared to that from the cell-only group. Cells and fragmented fibers were homogenously distributed with the presence of pore like empty spaces in the structure. LOX-1 staining revealed that the hybrid-spheroids improved the cell viability, which was potentially due to enhanced transport of oxygen through void space generated by engineered ECM. Transmission electron microscopy (TEM) analysis confirmed that cells within the hybrid-spheroid formed strong cell junctions and contacts with fragmented fibers. The expression of cell junction proteins including connexin 43 and E-cadherin was significantly upregulated in hybrid-spheroids by 16.53 ± 0.04 and 28.26 ± 0.11-fold greater than that from cell-only group. Similarly, expression of integrin α_2, α₅, and β₁ was significantly enhanced at the same group by 25.72 ± 0.13, 27.48 ± 0.49, and 592.78 ± 0.06-fold, respectively. In addition, stemness markers including Oct-4, Nanog, and Sox2 were significantly upregulated in hybrid-spheroids by 96.56 ± 0.06, 158.95 ± 0.06, and 115.46 ± 0.47-fold, respectively, relative to the cell-only group. Additionally, hTMSCs within the hybrid-spheroids showed significantly greater osteogenic differentiation under osteogenic media conditions. Taken together, our hybrid-spheroids can be an ideal approach for stem cell expansion and serve as a potential carrier for bone regeneration.

STATEMENT OF SIGNIFICANCE

Cells are spatially arranged within extracellular matrix (ECM) and cell/ECM interactions are crucial for cellular functions. Here, we developed a hybrid-spheroid system incorporating engineered ECM prepared from fragmented electrospun fibers to tune stem cell functions. Conventionally prepared cell spheroids with large diameters (>200 µm) is often prone to hypoxia. In contrast, the hybrid-spheroids significantly enhanced viability and proliferation of human turbinate mesenchymal stem cells (hTMSCs) as compared to spheroid prepared from cell only. Under these conditions, the presence of fragmented fibers also improved maintenance of stemness of hTMSCs for longer time cultured in growth media and demonstrated significantly greater osteogenic differentiation under osteogenic media conditions. Thus, the hybrid-spheroids can be used as a delivery carrier for stem cell based therapy or a 3D culture model for in vitro assay.

Role of the protease corin in chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the potency to differentiate into chondrocytes, osteocytes and adipocytes. Corin is a cardiac protease that activates the natriuretic peptides, thereby regulating blood volume and pressure. In addition to the heart, corin gene upregulation was reported in bone marrow- and adipose tissue-derived MSCs that underwent osteogenic differentiation. To date, the biological significance of corin expression in MSC differentiation remains unknown. In this study we isolated and cultured human bone marrow-derived MSCs that were capable of undergoing chondrogenic, osteogenic and adipogenic lineage differentiation. By reverse transcription polymerase chain reaction (RT-PCR) and immunostaining, we found that corin expression was upregulated when these MSCs underwent chondrogenic, osteogenic and adipogenic differentiation. The upregulation of corin expression was most significant in the cells undergoing chondrogenic lineage differentiation. Silencing corin gene expression by small hairpin RNA in the MSCs inhibited chondrogenic, but not osteogenic and adipogenic, differentiation. These results suggest a novel function of corin in MSC differentiation and chondrocyte development.

Integrin-Linked Kinase Regulates Bone Formation by Controlling Cytoskeletal Organization and Modulating BMP and Wnt Signaling in Osteoprogenitors

Cell-matrix interactions constitute a fundamental aspect of skeletal cell biology and play essential roles in bone homeostasis. These interactions are primarily mediated by transmembrane integrin receptors, which mediate cell adhesion and transduce signals from the extracellular matrix to intracellular responses via various downstream effectors, including integrin-linked kinase (ILK). ILK functions as adaptor protein at focal adhesion sites, linking integrins to the actin cytoskeleton, and has been reported to act as a kinase phosphorylating signaling molecules such as GSK-3β and Akt. Thereby, ILK plays important roles in cellular attachment, motility, proliferation and survival. To assess the in vivo role of ILK signaling in osteoprogenitors and the osteoblast lineage cells descending thereof, we generated conditional knockout mice using the Osx-Cre:GFP driver strain. Mice lacking functional ILK in osterix-expressing cells and their derivatives showed no apparent developmental or growth phenotype, but by 5 weeks of age they displayed a significantly reduced trabecular bone mass, which persisted into adulthood in male mice. Histomorphometry and serum analysis indicated no alterations in osteoclast formation and activity, but provided evidence that osteoblast function was impaired, resulting in reduced bone mineralization and increased accumulation of unmineralized osteoid. In vitro analyses further substantiated that absence of ILK in osteogenic cells was associated with compromised collagen matrix production and mineralization. Mechanistically, we found evidence for both impaired cytoskeletal functioning and reduced signal transduction in osteoblasts lacking ILK. Indeed, loss of ILK in primary osteogenic cells impaired F-actin organization, cellular adhesion, spreading, and migration, indicative of defective coupling of cell-matrix interactions to the cytoskeleton. In addition, BMP/Smad and Wnt/β-catenin signaling was reduced in the absence of ILK. Taken together, these data demonstrate the importance of integrin-mediated cell-matrix interactions and ILK signaling in osteoprogenitors in the control of osteoblast functioning during juvenile bone mass acquisition and adult bone remodeling and homeostasis. © 2017 American Society for Bone and Mineral Research.

TRIB3 inhibits proliferation and promotes osteogenesis in hBMSCs by regulating the ERK1/2 signaling pathway

Osteogenic differentiation in human bone marrow-derived mesenchymal stem cells (hBMSCs) is regulated by various factors, including bone morphogenetic proteins (BMPs), Notch, growth hormones and mitogen-activated protein kinases (MAPKs). Tribbles homolog 3 (TRIB3), a pseudokinase, plays an important role in cancer cells and adipocytes. However, TRIB3 function in osteogenic differentiation is unknown, although it is involved in regulating signaling pathways associated with osteogenic differentiation. Here, we found that TRIB3 was highly expressed during osteogenic differentiation in hBMSCs. Inhibition of focal adhesion kinase (FAK) or phosphatidylinositol 3-kinase (PI3K) resulted in a significant decrease in TRIB3 expression, and expression of TRIB3 was restored by increasing insulin-like growth factor-1 (IGF-1) via activating phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling. TRIB3 knock-down enhanced proliferation and decreased osteogenic differentiation at the middle stage of differentiation, and these effects were reversed by inhibiting the activation of extracellular signal-regulated kinase (ERK)-1/2. In conclusion, TRIB3 plays an important role in proliferation and osteogenic differentiation by regulating ERK1/2 activity at the middle stage of differentiation, and expression of TRIB3 is regulated by FAK in a PI3K/AKT-dependent manner.

Osteopontin -- a promising biomarker for cancer therapy

Osteopontin (OPN), a multifunctional protein, has emerged as a potentially valuable biomarker for diagnosing and treating cancers. Recent research focuses on its involvement in tumor biology including the cell proliferation, survival, angiogenesis, invasion, and metastasis. Understanding the molecular mechanisms and pharmacological effects of OPN in cancer development could lead to new targets for improving cancer diagnosis and treatment. This review explains how the structurally conserved domains of OPN are associated with OPN signaling mediators and CD44, and how the conserved OPN domains determine biological functions. The authors have reviewed representative works of OPN expression in breast cancer and colorectal cancer to elucidate the relationship between OPN and cancer/tumor biology. It has also been shown that the prognostic sensitivity in non-small cell lung cancer, hepatocellular carcinoma, gastric cancer, and ovarian cancer improved compared to the individual marker when OPN was analyzed in conjunction with other markers. The therapeutic approaches based on OPN inhibitors are discussed to illustrate recent research progress. Previous clinical data has indicated that OPN has played a unique role in cancer development, but further investigation is required to understand the underlying mechanism. More clinical trials are also required to examine the applicability and efficacy of OPN inhibitors in cancer therapy.

Hematopoietic-to-mesenchymal transition of adipose tissue macrophages is regulated by integrin β1 and fabricated fibrin matrices

Some bona fide adult adipocytes arise de novo from a bone marrow-derived myeloid lineage. These studies further demonstrate that adipose tissue stroma contains a resident population of myeloid cells capable of adipocyte and multilineage mesenchymal differentiation. These resident myeloid cells lack hematopoietic markers and express mesenchymal and progenitor cell markers. Because bone marrow mesenchymal progenitor cells have not been shown to enter the circulation, we hypothesized that myeloid cells acquire mesenchymal differentiation capacity in adipose tissue. We fabricated a 3-dimensional fibrin matrix culture system to define the adipose differentiation potential of adipose tissue-resident myeloid subpopulations, including macrophages, granulocytes and dendritic cells. Our data show that multilineage mesenchymal potential was limited to adipose tissue macrophages, characterized by the acquisition of adipocyte, osteoblast, chondrocyte and skeletal muscle myocyte phenotypes. Fibrin hydrogel matrices stimulated macrophage loss of hematopoietic cell lineage determinants and the expression of mesenchymal and progenitor cell markers, including integrin β1. Ablation of integrin β1 in macrophages inhibited adipocyte specification. Therefore, some bona fide adipocytes are specifically derived from adipose tissue-resident macrophages via an integrin β1-dependent hematopoietic-to-mesenchymal transition, whereby they become capable of multipotent mesenchymal differentiation. The requirement for integrin β1 highlights this molecule as a potential target for controlling the production of marrow-derived adipocytes and their contribution to adipose tissue development and function.

Investigation of bioeffects of G protein-coupled receptor 1 on bone turnover in male mice

Maintenance of healthy bone quality and quantity requires a well-coordinated balance between bone formation by osteoblasts and bone resorption by osteoclasts. Chemerin is a novel adipokine with known functions such as regulating immunity and energy homeostasis through activation of chemokine-like receptor 1 (CMKLR1). G protein-coupled receptor 1 (GPR1) is the second mammalian chemerin receptor with similar binding affinity as CMKLR1. In male GPR1^-/- mice, a phenotype with significantly low bone mineral density was observed. We hypothesise that GPR1 might participate the process of bone remodelling. In this study, we investigated the role of GPR1 in regulating bone mass maintenance in male mice, and for the first time, revealed that GPR1^-/- male mice manifested seriously trabecular bone loss and lower serum testosterone levels compared to the wild type animals. Accordingly, the mRNA expression of biomarkers related to both osteoblast [collagen type I alpha 2 (Col1A2), osteocalcin (OCN)] and osteoclast [tartrate-resistant acid phosphatase (TRAP), Cathepsin K, NFATc1] were significantly decreased or increased in GPR1^-/- mice relative to the wild type, respectively. However, other osteogenic markers, Osterix and ALP levels, were increased. Microcomputed tomography scanning and histological analyses proved that there was a myriad of trabecular bone loss in GPR1^-/- mice. In the meantime, GPR1^-/- mice presented a significant decrease in serum testosterone level. Taken together, these findings suggested that chemerin-GPR1 signalling might be directly or indirectly communicated with testosterone synthesis on bone turnover regulation. Further detailed studies are required to unveil how chemerin-GPR1 participates in bone metabolism. The translational potential of this article: More studies and knowledge about GPR1 regulating function in bone turnover might supply a novel therapeutic target for osteoporosis in the future.

Osteopontin: its potential role in cancer of children and young adults

Objective: Osteopontin (OPN) is aglyco-phosphoprotein, involved in tissue remodeling, inflammation and boneresorption. In various adult neoplasms OPN was shown to correlate with cancer progression, invasiveness and metastasis. Aim: to define the role of OPN in malignancies of children and young adults. Material and methods: a structured PubMed and Google Scholar literature analysis based on reports published in English between I'1995 and XII'2015. Results: 14 studies (four on hematological malignancies, four on bone tumors, three on CNS tumors, two on dendritic proliferative diseases and one on renal tumors) were identified. Higher levels of serum and cerebro-spinal fluid OPN protein, and high expressions of OPN mRNA and SPP1 gene were present in more aggressive and advanced childhood malignancies. In children with acute lymphoblastic leukemia with CNS involvement and with atypical teratoid/rhabdoid tumor (AT/RT) and medulloblastoma, the serum and CSF OPN levels reflected tumor bulk and response to therapy, while in children with AT/RT and multisystem Langerhans cell histiocytosis with high-risk organs involvement, high OPN serum levels correlated with poorer survival. To the contrary, in osteosarcoma, high OPN mRNA and SPP1 gene expressions correlated with better survival and good response to chemotherapy. Conclusions: The literature review suggests that OPN may play important roles in the development and progression of selected cancers of children and young adults, including acute lymphoblastic leukemia, malignant gliomas, AT/RT and Langerhans cell histiocytosis. However, limited number of published studies prevents from definite concluding on the clinical utility of OPN as a marker of diagnosis, prognosis and treatment monitoring in these pediatric cancers. Further studies performed in more numerous groups of patients with particular types of cancers of children and young adults are warranted.

The potential role of Osteopontin in the maintenance of commensal bacteria homeostasis in the intestine

Osteopontin (Opn), a multifunctional extracellular matrix protein, is implicated in the pathogenesis of various inflammatory disorders. Under physiologic conditions, its expression is restricted to certain tissues including bone and kidney tubule. However, cellular activation during disease development induces Opn expression in various immune cells. In this study, using Opn-EGFP knock-in (KI) mice we found that CD8α⁺ T cells in the intestinal tissues, including Peyer’s patch, lamina propria and epithelium, express Opn under steady state conditions. Therefore, we examined the role of Opn-expressing CD8α⁺ T cells in intestinal homeostasis. Interestingly, Opn knockout (KO) mice had altered fecal microflora concordant with a reduction of TCRγδ⁺ intraepithelial lymphocytes (IELs). Consistent with this result, both treatment with anti-Opn blocking antibody and deficiency of Opn resulted in decreased survival of TCRγδ⁺ and TCRαβ⁺ IELs. This data suggests that a possibility that Opn may function as a survival factor for IELs in the intestinal tissue. Collectively, these data suggest the possibility that Opn might regulate the homeostasis of intestinal microflora through maintenance of TCRγδ⁺ IELs, possibly by support of IEL survival.

Differential long noncoding RNA/mRNA expression profiling and functional network analysis during osteogenic differentiation of human bone marrow mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) are the most promising cell types for bone regeneration and repair due to their osteogenic potential. MSC differentiation is precisely regulated and orchestrated by the mechanical and molecular signals from the extracellular environment, involving complex pathways regulated at both the transcriptional and post-transcriptional levels. However, the potential role of long noncoding RNA (lncRNA) in the osteogenic differentiation of human MSCs remains largely unclear.

METHODS

Here, we undertook the survey of differential coding and noncoding transcript expression profiling and functional network analysis during osteogenic differentiation of human bone marrow mesenchymal stem cells (BMSCs) using human whole transcriptome microarray. The key pathways, mRNAs, and lncRNAs controlling osteogenic differentiation of BMSCs were identified by further bioinformatic analysis. The role of lncRNA in the osteogenic differentiation of MSCs was verified by lncRNA overexpression or knockdown methods.

RESULTS

A total of 1269 coding transcripts with 648 genes significantly upregulated and 621 genes downregulated, and 1408 lncRNAs with 785 lncRNAs significantly upregulated and 623 lncRNAs downregulated were detected along with osteogenic differentiation. Bioinformatic analysis identified that several pathways may be associated with osteogenic differentiation potentials of BMSCs, such as the MAPK signaling pathway, the Jak-STAT signaling pathway, the Toll-like receptor signaling pathway, and the TGF-beta signaling pathway, etc. Bioinformatic analysis also revealed 13 core regulatory genes including seven mRNAs (GPX3, TLR2, BDKRB1, FBXO5, BRCA1, MAP3K8, and SCARB1), and six lncRNAs (XR_111050, NR_024031, FR374455, FR401275, FR406817, and FR148647). Based on the analysis, we identified one lncRNA, XR_111050, that could enhance the osteogenic differentiation potentials of MSCs.

CONCLUSIONS

The potential regulatory mechanisms were identified using bioinformatic analyses. We further predicted the interactions of differentially expressed coding and noncoding genes, and identified core regulatory factors by co-expression networks during osteogenic differentiation of BMSCs. Our results could lead to a better understanding of the molecular mechanisms of genes and lncRNAs, and their cooperation underlying MSC osteogenic differentiation and bone formation. We identified that one lncRNA, XR_111050, could be a potential target for bone tissue engineering.

Osteopontin: Relation between Adipose Tissue and Bone Homeostasis

Osteopontin (OPN) is a multifunctional protein mainly associated with bone metabolism and remodeling. Besides its physiological functions, OPN is implicated in the pathogenesis of a variety of disease states, such as obesity and osteoporosis. Importantly, during the last decades obesity and osteoporosis have become among the main threats to health worldwide. Because OPN is a protein principally expressed in cells with multifaceted effects on bone morphogenesis and remodeling and because it seems to be one of the most overexpressed genes in the adipose tissue of the obese contributing to osteoporosis, this mini review will highlight recent insights about relation between adipose tissue and bone homeostasis.

Ultrastructural changes during osteogenic differentiation in mesenchymal stromal cells cultured in alginate hydrogel

Background

Osteogenic differentiation of mesenchymal stem cells has been extensively investigated with regards to different aspects, including the analysis of cell intracellular and extracellular proteome, cell gene expression pattern, and morphology. During the osteogenic differentiation, osteoblasts produce and release specific proteins, like osteocalcin and osteopontin. Simultaneously, cells produce the extracellular matrix (ECM) that resembles the bone ECM, with high quantity of calcium and phosphorus. We focused on the ultrastructural changes occurring during the osteogenic differentiation of MSC cultured in alginate hydrogel.

Results

The analysis revealed that during the osteogenic differentiation the most of cells become dead, and these dead cells contain large quantities of calcium and deposition is strictly connected with the cellular death and small membrane vesicles released by cells. Cell organelles were not present within differentiated cells, while in cells from non-osteogenic group the cellular ultrastructure was proper, with single nuclei, endoplasmic reticulum and numerous mitochondria.

Conclusion

The ECM synthesis and deposition during the osteogenic differentiation of MSC involves cellular programmed death. The small membrane vesicles become the mineralization sites of formed bone ECM.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0128-0) contains supplementary material, which is available to authorized users.

The effect of mesoporous bioglass on osteogenesis and adipogenesis of osteoporotic BMSCs

This study evaluated the effect of mesoporous bioglass (MBG) dissolution on the differentiation of bone marrow mesenchymal stem cells (BMSCs) derived from either sham control or ovariectomized (OVX) rats. MBG was fabricated by evaporation-induced self-assembly method. Cell proliferation was tested by Cell Counting Kit-8 assay, and cytoskeletal morphology was observed by fluorescence microscopy. Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) staining and activity, Alizarin Red staining, while adipogenic differentiation was assessed by Oil Red-O staining. Quantitative real-time PCR and Western blot analysis were taken to evaluate the expression of runt-related transcription factor 2 (Runx2) and proliferator-activated receptor-γ (PPARγ). We found that MBG dissolution (0, 25, 50, 100, 200 µg/mL) was nontoxic to BMSCs growth. Sham and OVX BMSCs exhibited the highest ALP activity in 50 µg/mL of MBG osteogenic dissolution, except that sham BMSCs in 100 µg/mL showed the highest ALP activity on day 14. Runx2 was significantly upregulated after 100 µg/mL of MBG stimulation in sham and OVX BMSCs for 7 and 14 days, except that 25 µg/mL showed highest upregulation effect on OVX BMSCs at day 7. PPARγ was downregulated after MBG stimulation. The protein level of Runx2 from the sham BMSCs group was significantly upregulated after lower doses (25 and 50 µg/mL) of MBG stimulation, whereas PPARγ was downregulated in the sham and OVX BMSCs group. Thus, both the osteogenic and adipogenic abilities of BMSCs were damaged under OVX condition. Moreover, lower concentration of MBG dissolution can promote osteogenesis but inhibit adipogenesis of the sham and OVX BMSCs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3004-3014, 2016.

Osteopontin is a key player for local adipose tissue macrophage proliferation in obesity

Objective

Recent findings point towards an important role of local macrophage proliferation also in obesity-induced adipose tissue inflammation that underlies insulin resistance and type 2 diabetes. Osteopontin (OPN) is an inflammatory cytokine highly upregulated in adipose tissue (AT) of obese and has repeatedly been shown to be functionally involved in adipose-tissue inflammation and metabolic sequelae. In the present work, we aimed at unveiling both the role of OPN in human monocyte and macrophage proliferation as well as the impact of OPN deficiency on local macrophage proliferation in a mouse model for diet-induced obesity.

Methods

The impact of recombinant OPN on viability, apoptosis, and proliferation was analyzed in human peripheral blood monocytes and derived macrophages. Wild type (WT) and OPN knockout mice (SPP1KO) were compared with respect to in vivo adipose tissue macrophage and in vitro bone marrow-derived macrophage (BMDM) proliferation.

Results

OPN not only enhanced survival and decreased apoptosis of human monocytes but also induced proliferation similar to macrophage colony stimulating factor (M-CSF). Even in fully differentiated monocyte-derived macrophages, OPN induced a proliferative response. Moreover, proliferation of adipose tissue macrophages in obese mice was detectable in WT but virtually absent in SPP1KO. In BMDM, OPN also induced proliferation while OPN as well as M-CSF-induced proliferation was similar in WT and SPP1KO.

Conclusions

These data confirm that monocytes and macrophages not only are responsive to OPN and migrate to sites of inflammation but also they survive and proliferate more in the presence of OPN, a mechanism also strongly confirmed in vivo. Therefore, secreted OPN appears to be an essential player in AT inflammation, not only by driving monocyte chemotaxis and macrophage differentiation but also by facilitating local proliferation of macrophages.

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Osteopontin enhances survival and decreases apoptosis of human monocytes.

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Osteopontin induces proliferation of differentiated macrophages.

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Osteopontin facilitates local adipose tissue macrophage proliferation in obesity.

AMPK promotes osteogenesis and inhibits adipogenesis through AMPK-Gfi1-OPN axis

Several metabolic, genetic and oncogenic bone diseases share the common pathological phenotype of defective bone marrow stromal cell (BMSC) differentiation. Many reports in bone science in the past several years have suggested that the skeleton also has an endocrine role. The role of AMP-activated protein kinase (AMPK) as an energy metabolism sensor and how it regulates BMSC differentiation is largely unknown. In the current study, we used AMPK agonists to activate AMPK in MC3T3-E1 cells to investigate the functional roles of AMPK in osteogenesis. However, metformin and AICAR failed to activate AMPK consistently. Therefore, we established MC3T3-E1 and 3T3-L1 cell models of AMPK α subunit overexpression through lentivirus vector, in which AMPK was overactivated. AMPK hyperactivation stimulated MC3T3-E1 cell osteogenesis and inhibited 3T3-L1 cell adipogenesis. Osteopontin (OPN) mediated AMPK regulation of osteogenesis and adipogenesis. Furthermore, we provided evidence that the transcriptional repressor growth factor independence-1 (Gfi1) was downregulated and disassociated from the OPN promoter in response to AMPK activation, resulting in the upregulation of OPN. Overexpression of wild-type and dominant-negative Gfi1 modulated MC3T3-E1 osteogenesis and 3T3-L1 adipogenesis. Further evidence suggested that AMPK enhanced ectopic bone formation of MC3T3-E1 cells through the AMPK-Gfi1-OPN axis. In conclusion, AMPK was sufficient to stimulate osteogenesis of MC3T3-E1 cells and inhibit adipogenesis of 3T3-L1 cells through the AMPK-Gfi1-OPN axis. These findings helped elucidate the molecular mechanisms underlying AMPK regulation of osteogenesis and adipogenesis.

Directing lineage specification of human mesenchymal stem cells by decoupling electrical stimulation and physical patterning on unmodified graphene

The organization and composition of the extracellular matrix (ECM) have been shown to impact the propagation of electrical signals in multiple tissue types. To date, many studies with electroactive biomaterial substrates have relied upon passive electrical stimulation of the ionic media to affect cell behavior. However, development of cell culture systems in which stimulation can be directly applied to the material - thereby isolating the signal to the cell-material interface and cell-cell contracts - would provide a more physiologically-relevant paradigm for investigating how electrical cues modulate lineage-specific stem cell differentiation. In the present study, we have employed unmodified, directly-stimulated, (un)patterned graphene as a cell culture substrate to investigate how extrinsic electrical cycling influences the differentiation of naïve human mesenchymal stem cells (hMSCs) without the bias of exogenous biochemicals. We first demonstrated that cyclic stimulation does not deteriorate the cell culture media or result in cytotoxic pH, which are critical experiments for correct interpretation of changes in cell behavior. We then measured how the expression of osteogenic and neurogenic lineage-specific markers were altered simply by exposure to electrical stimulation and/or physical patterns. Expression of the early osteogenic transcription factor RUNX2 was increased by electrical stimulation on all graphene substrates, but the mature marker osteopontin was only modulated when stimulation was combined with physical patterns. In contrast, the expression of the neurogenic markers MAP2 and β3-tubulin were enhanced in all electrical stimulation conditions, and were less responsive to the presence of patterns. These data indicate that specific combinations of non-biological inputs - material type, electrical stimulation, physical patterns - can regulate hMSC lineage specification. This study represents a substantial step in understanding how the interplay of electrophysical stimuli regulate stem cell behavior and helps to clarify the potential for graphene substrates in tissue engineering applications.

The effect of the bioactive sphingolipids S1P and C1P on multipotent stromal cells--new opportunities in regenerative medicine

Sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) belong to a family of bioactive sphingolipids that act as important extracellular signaling molecules and chemoattractants. This study investigated the influence of S1P and C1P on the morphology, proliferation activity and osteogenic properties of rat multipotent stromal cells derived from bone marrow (BMSCs) and subcutaneous adipose tissue (ASCs). We show that S1P and C1P can influence mesenchymal stem cells (MSCs), each in a different manner. S1P stimulation promoted the formation of cellular aggregates of BMSCs and ASCs, while C1P had an effect on the regular growth pattern and expanded intercellular connections, thereby increasing the proliferative activity. Although osteogenic differentiation of MSCs was enhanced by the addition of S1P, the effectiveness of osteoblast differentiation was more evident in BMSCs, particularly when biochemical and molecular marker levels were considered. The results of the functional osteogenic differentiation assay, which includes an evaluation of the efficiency of extracellular matrix mineralization (SEM-EDX), revealed the formation of numerous mineral aggregates in BMSC cultures stimulated with S1P. Our data demonstrated that in an appropriate combination, the bioactive sphingolipids S1P and C1P may find wide application in regenerative medicine, particularly in bone regeneration with the use of MSCs.

Type I interferons exert anti-tumor effect via reversing immunosuppression mediated by mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are strongly immunosuppressive via producing nitric oxide (NO) and known to migrate into tumor sites to promote tumor growth, but the underlying mechanisms remain largely elusive. Here, we found that interferon alpha (IFNα)-secreting MSCs showed more dramatic inhibition effect on tumor progression than that of IFNα alone. Interestingly, IFNα-primed MSCs could also effectively suppress tumor growth. Mechanistically, we demonstrated that both IFNα and IFNβ (type I IFNs) reversed the immunosuppressive effect of MSCs on splenocyte proliferation. This effect of type I IFNs was exerted through inhibiting inducible NO synthase (iNOS) expression in IFNγ and TNFα-stimulated MSCs. Notably, only NO production was inhibited by IFNα production of other cytokines or chemokines tested was not suppressed. Furthermore, IFNα promoted the switch from signal transducer and activator of transcription 1 (Stat1) homodimers to Stat1-Stat2 heterodimers. Studies using the luciferase reporter system and chromatin immunoprecipitation assay revealed that IFNα suppressed iNOS transcription through inhibiting the binding of Stat1 to iNOS promoter. Therefore, the synergistic anti-tumor effects of type I IFNs and MSCs were achieved by inhibiting NO production. This study provides essential information for understanding the mechanisms of MSC-mediated immunosuppression and for the development of better clinical strategies using IFNs and MSCs for cancer immunotherapy.

Bone Homeostasis and Repair: Forced Into Shape

Mechanical loading is a potent anabolic regulator of bone mass, and the first line of defense for bone loss is weight-bearing exercise. Likewise, protected weight bearing is the first prescribed physical therapy following orthopedic reconstructive surgery. In both cases, enhancement of new bone formation is the goal. Our understanding of the physical cues, mechanisms of force sensation, and the subsequent cellular response will help identify novel physical and therapeutic treatments for age- and disuse-related bone loss, delayed- and nonunion fractures, and significant bony defects. This review highlights important new insights into the principles and mechanisms governing mechanical adaptation of the skeleton during homeostasis and repair and ends with a summary of clinical implications stemming from our current understanding of how bone adapts to biophysical force.

Naringin Stimulates Osteogenic Differentiation of Rat Bone Marrow Stromal Cells via Activation of the Notch Signaling Pathway

Naringin is a major flavonoid found in grapefruit and is an active compound extracted from the Chinese herbal medicine Rhizoma Drynariae. Naringin is a potent stimulator of osteogenic differentiation and has potential application in preventing bone loss. However, the signaling pathway underlying its osteogenic effect remains unclear. We hypothesized that the osteogenic activity of naringin involves the Notch signaling pathway. Rat bone marrow stromal cells (BMSCs) were cultured in osteogenic medium containing-naringin, with or without DAPT (an inhibitor of Notch signaling), the effects on ALP activity, calcium deposits, osteogenic genes (ALP, BSP, and cbfa1), adipogenic maker gene PPARγ2 levels, and Notch expression were examined. We found that naringin dose-dependently increased ALP activity and Alizarin red S staining, and treatment at the optimal concentration (50 μg/mL) increased mRNA levels of osteogenic genes and Notch1 expression, while decreasing PPARγ2 mRNA levels. Furthermore, treatment with DAPT partly reversed effects of naringin on BMSCs, as judged by decreases in naringin-induced ALP activity, calcium deposits, and osteogenic genes expression, as well as upregulation of PPARγ2 mRNA levels. These results suggest that the osteogenic effect of naringin partly involves the Notch signaling pathway.

Evaluation of nestin or osterix promoter-driven cre/loxp system in studying the biological functions of murine osteoblastic cells

OBJECTIVE

To compare Osterix and Nestin-Cre/Loxp system in studying the biological functions of murine osteoblastic cells including primary osteoblasts (OBs) and osteolineage mesenchymal progenitor cells (MPCs).

METHODS

We isolated primary osteoblasts (OBs) from neonatal Nestin-cre-R26-loxP-YFP (Nes-OBs) and Osterix-cre-R26-loxP-YFP (Osx-OBs) mice and bone marrow mesenchymal stromal cells (BMMSCs) from the adults (termed as Nes-BMMSCs and Osx-BMMSCs). Then we detected the percentage of YFP(+) subpopulation in Nes/Osx-OBs and the percentage of CD45(-)YFP(+) progenitor population in Nes/Osx-BMMSCs and sorted them out (termed as Nes/Osx-YFP(+) OBs and Nes/Osx-CD45(-)YFP(+) MPCs) by using the sorting machine. We also analyzed the expression of surface antigens on Nes/Osx-YFP(+) OBs and Nes/Osx-CD45(-)YFP(+) MPCs by Flow cytometry. PDGF-BB induced proliferation of Nes/Osx-YFP(+) OBs and Nes/Osx-CD45(-)YFP(+) MPCs was measured by H3-Thymidine incorporation assay. We then did OB maturation and mineralization assays of Nes/Osx-YFP(+) OBs and CFU and multi-lineage differentiation assays of Nes/Osx-CD45(-)YFP(+) MPCs.

RESULTS

YFP(+)% in Nes-OBs and Osx-OBs and CD45(-)YFP(+)% in Nes-BMMSCs and Osx-BMMSCs was respectively 5.56%±3.56% (n=5), 10.12%±2.7% (n=4), 1.29%±0.98% (n=13) and 16.38%±6.98% (n=17). Both Nes-YFP(+) OBs and Osx-YFP(+) OBs were positive for CD51. Nes/Osx-CD45(-)YFP(+) MPCs were positive for CD51, CD105 and Sca1, and negative for CD31 and CD45. PDGFR expression in Osx-YFP(+) OBs was a bit higher than that in Nes-YFP(+) OBs, and slightly higher in Osx-CD45(-)YFP(+) MPCs than in Nes-CD45(-)YFP(+) MPCs. Proliferation ability of Nes/Osx-YFP(+) OBs increased dramatically after stimulated with PDGF-BB for 48 h, while it was not statistically significant that PDGF-BB induced the increase of proliferation ability in either Nes-CD45(-)YFP(+) MPCs or Osx-CD45(-)YFP(+) MPCs. We observed that no significant difference of OB maturation and mineralization ability existed between Nes-YFP(+) OBs and Osx-YFP(+) OBs, and there was little difference of self-renewal and multi-lineage differentiation potential between Nes-CD45(-)YFP(+) MPCs and Osx-CD45(-)YFP(+) MPCs, either.

CONCLUSION

Both Nestin and Osterix could be selected as useful markers for the osteoblastic cells, while Osterix was a prior choice due to larger number of Osterix-expressing cells than Nestin-expressing cells in distinct subpopulations of bone-forming cells.