Skeletal (stromal) stem cells: an update on intracellular signaling pathways controlling osteoblast differentiation

Safflower yellow promotes angiogenesis through p-VHL/ HIF-1α/VEGF signaling pathway in the process of osteogenic differentiation

OBJECTIVE

Safflower yellow (SY) is an active component ofCarthamus tinctorius L. that is widely used in orthopedics. This study aimed to evaluate the role of SY in angiogenesis and osteogenic differentiation.

METHODS

The migration and in vitro angiogenesis of SY (4.5, 9.0, 18 μg/ml)-treated human umbilical vein endothelial cells (HUVEC-12) were assessed by transwell and tube formation assay, respectively. Osteogenic differentiation ability was detected by alkaline phosphatase (ALP) and Alizarin Red S staining. The mRNA and protein expressions of related markers were determined by RT-qPCR and Western blot.

RESULTS

The migration and tube formation ability of HUVEC-12 were promoted by SY. Furthermore, SY facilitated the angiogenesis and osteogenic differentiation in the co-culture of HUVEC-12 and BMSCs by increasing hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), Angiopoietin-2 (Ang-2), ALP, runt-related transcription factor 2 (Runx2) and osteopontin-1 (OPN-1) levels. Inhibition of HIF-1α expression by 3-(5-hydroxymethl-2-furyl)-1-benzylindazole (YC-1), restrained SY-induced proliferation, migration and angiogenesis of HUVEC-12 and the increased protein levels of VEGF, Ang-2, ALP, Runx2 and OPN-1. Finally, WD repeat and SOCS box-containing protein-1 (WSB-1)/Von Hippel-Lindau protein (p-VHL) pathway was involved in the beneficial effect of SY.

CONCLUSION

SY promotes osteogenic differentiation via enhancing angiogenesis by regulating pVHL/HIF-1α/VEGF signaling pathway.

Knockdown of FOXA2 enhances the osteogenic differentiation of bone marrow-derived mesenchymal stem cells partly via activation of the ERK signalling pathway

Forkhead box protein A2 (FOXA2) is a core transcription factor that controls cell differentiation and may have an important role in bone metabolism. However, the role of FOXA2 during osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) remains largely unknown. In this study, decreased expression of FOXA2 was observed during osteogenic differentiation of rat BMSCs (rBMSCs). FOXA2 knockdown significantly increased osteoblast-specific gene expression, the number of mineral deposits and alkaline phosphatase activity, whereas FOXA2 overexpression inhibited osteogenesis-specific activities. Moreover, extracellular signal-regulated protein kinase (ERK) signalling was upregulated following knockdown of FOXA2. The enhanced osteogenesis due to FOXA2 knockdown was partially rescued by an ERK inhibitor. Using a rat tibial defect model, a rBMSC sheet containing knocked down FOXA2 significantly improved bone healing. Collectively, these findings indicated that FOXA2 had an essential role in osteogenic differentiation of BMSCs, partly by activation of the ERK signalling pathway.

Expression of the ectodomain-releasing protease ADAM17 is directly regulated by the osteosarcoma and bone-related transcription factor RUNX2

Osteoblast differentiation is controlled by transcription factor RUNX2 which temporally activates or represses several bone-related genes, including those encoding extracellular matrix proteins or factors that control cell-cell, and cell-matrix interactions. Cell-cell communication in the many skeletal pericellular micro-niches is critical for bone development and involves paracrine secretion of growth factors and morphogens. This paracrine signaling is in part regulated by "A Disintegrin And Metalloproteinase" (ADAM) proteins. These cell membrane-associated metalloproteinases support proteolytic release ("shedding") of protein ectodomains residing at the cell surface. We analyzed microarray and RNA-sequencing data for Adam genes and show that Adam17, Adam10, and Adam9 are stimulated during BMP2 mediated induction of osteogenic differentiation and are robustly expressed in human osteoblastic cells. ADAM17, which was initially identified as a tumor necrosis factor alpha (TNFα) converting enzyme also called (TACE), regulates TNFα-signaling pathway, which inhibits osteoblast differentiation. We demonstrate that Adam17 expression is suppressed by RUNX2 during osteoblast differentiation through the proximal Adam17 promoter region (-0.4 kb) containing two functional RUNX2 binding motifs. Adam17 downregulation during osteoblast differentiation is paralleled by increased RUNX2 expression, cytoplasmic-nuclear translocation and enhanced binding to the Adam17 proximal promoter. Forced expression of Adam17 reduces Runx2 and Alpl expression, indicating that Adam17 may negatively modulate osteoblast differentiation. These findings suggest a novel regulatory mechanism involving a reciprocal Runx2-Adam17 negative feedback loop to regulate progression through osteoblast differentiation. Our results suggest that RUNX2 may control paracrine signaling through regulation of ectodomain shedding at the cell surface of osteoblasts by directly suppressing Adam17 expression.

Secreted Clusterin protein inhibits osteoblast differentiation of bone marrow mesenchymal stem cells by suppressing ERK1/2 signaling pathway

Secreted Clusterin (sCLU, also known as Apolipoprotein J) is an anti-apoptotic glycoprotein involved in the regulation of cell proliferation, lipid transport, extracellular tissue remodeling and apoptosis. sCLU is expressed and secreted by mouse bone marrow-derived skeletal (stromal or mesenchymal) stem cells (mBMSCs), but its functional role in MSC biology is not known. In this study, we demonstrated that Clusterin mRNA expression and protein secretion in conditioned medium increased during adipocyte differentiation and decreased during osteoblast differentiation of mBMSCs. Treatment of mBMSC cultures with recombinant sCLU protein increased cell proliferation and exerted an inhibitory effect on the osteoblast differentiation while stimulated adipocyte differentiation in a dose-dependent manner. siRNA-mediated silencing of Clu expression in mBMSCs reduced adipocyte differentiation and stimulated osteoblast differentiation of mBMSCs. Furthermore, the inhibitory effect of sCLU on the osteoblast differentiation of mBMSCs was mediated by the suppression of extracellular signal-regulated kinase (ERK1/2) phosphorylation. In conclusion, we identified sCLU as a regulator of mBMSCs lineage commitment to osteoblasts versus adipocytes through a mechanism mediated by ERK1/2 signaling. Inhibiting sCLU is a possible therapeutic approach for enhancing osteoblast differentiation and consequently bone formation.

Porous Polyethylene Coated with Functionalized Hydroxyapatite Particles as a Bone Reconstruction Material

In this study, porous polyethylene scaffolds were examined as bone substitutes in vitro and in vivo in critical-sized calvarial bone defects in transgenic Sprague-Dawley rats. A microscopic examination revealed that the pores appeared to be interconnected across the material, making them suitable for cell growth. The creep recovery behavior of porous polyethylene at different loads indicated that the creep strain had two main portions. In both portions, strain increased with increased applied load and temperature. In terms of the thermographic behavior of the material, remarkable changes in melting temperature and heat fusion were revealed with increased the heating rates. The tensile strength results showed that the material was sensitive to the strain rate and that there was adequate mechanical strength to support cell growth. The in vitro cell culture results showed that human bone marrow mesenchymal stem cells attached to the porous polyethylene scaffold. Calcium sulfate–hydroxyapatite (CS–HA) coating of the scaffold not only improved attachment but also increased the proliferation of human bone marrow mesenchymal stem cells. In vivo, histological analysis showed that the study groups had active bone remodeling at the border of the defect. Bone regeneration at the border was also evident, which confirmed that the polyethylene acted as an osteoconductive bone graft. Furthermore, bone formation inside the pores of the coated polyethylene was also noted, which would enhance the process of osteointegration.

Directing osteogenic differentiation of BMSCs by cell-secreted decellularized extracellular matrixes from different cell types

Cell-secreted decellularized extracellular matrixes (D-ECM) are promising for conferring bioactivity and directing cell fate to facilitate tissue regeneration.

The Potential of microRNAs for Stem Cell-based Therapy for Degenerative Skeletal Diseases

Purpose of Review

Degenerative skeletal disorders including osteoarthritis (OA) and osteoporosis (OP) are the result of attenuation of tissue regeneration and lead to painful conditions with limited treatment options. Preventative measures to limit the onset of OA and OP remain a significant unmet clinical need. MicroRNAs (miRNAs) are known to be involved in the differentiation of stem cells, and in combination with stem cell therapy could induce skeletal regeneration and potentially prevent OA and OP onset.

Recent Findings

The combination of stem cells and miRNA has been successful at regenerating the bone and cartilage in vivo. MiRNAs, including miR-146b known to be involved in chondrogenic differentiation, could provide innovative targets for stem cell-based therapy, for the repair of articular cartilage defects forestalling the onset of OA or in the generation of a stem cell-based therapy for OP.

Summary

This review discusses the combination of skeletal stem cells (SSCs) and candidate miRNAs for application in a cell-based therapy approach for skeletal regenerative medicine.

Evidence based anti-osteoporosis effects of Periplaneta americana L on osteoblasts, osteoclasts, vascular endothelial cells and bone marrow derived mesenchymal stem cells

Background

Kangfuxin (KFX) is the ethanol extract of Periplaneta americana L, which has been widely used in the Traditional Chinese Medicine for the repair and regeneration of injured organ and tissues with long history. This study is to investigate the influence of KFX in the various cellular activities and evaluate the anti-osteoporosis potential of KFX.

Methods

The influence of the KFX in the cellular activities, including: 1) migration, osteocalcin secretion of osteoblasts; 2) apoptosis of osteoclasts; 3) migration and tube formation of human umbilical vein endothelial cell (HUVEC); and 4) proliferation, cell cycle regulation and migration of bone marrow mesenchymal stem cells (BMSCs), were investigated systematically.

Results

KFX was shown to significantly 1) Promote of the migration of osteoblasts, HUVEC, and BMSCs; 2) Increase the secretion of osteocalcin and mineralization of osteoblasts; 3) Accelerate the apoptosis of osteoclasts; 4) Stimulate the proliferation and regulate the cell cycle of BMSCs.

Conclusion

Taken together, these results provide the evidence for the osteogenesis, anti-osteoporosis and angiogenesis effects of KFX, with the mechanism of activating the bone formation through stimulating the osteoblasts and HUVECs, as well as inhibiting the bone absorption by inhibiting the osteoclasts activities. The KFX was definitely shown a promising bone turnover agent with great potential for anti-osteoporosis treatment.

Magnesium Chloride promotes Osteogenesis through Notch signaling activation and expansion of Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) are osteoblasts progenitors and a variety of studies suggest that they may play an important role for the health in the field of bone regeneration. Magnesium supplementation is gaining importance as adjuvant treatment to improve osteogenesis, although the mechanisms involving this process are not well understood. The objective of this study was to investigate the effects of magnesium on MSC differentiation. Here we show that in rat bone marrow MSC, magnesium chloride increases MSC proliferation in a dose-dependent manner promoting osteogenic differentiation and mineralization. These effects are reduced by 2-APB administration, an inhibitor of magnesium channel TRPM7. Of note, magnesium supplementation did not increase the canonical Wnt/β-catenin pathway, although it promoted the activation of Notch1 signaling, which was also decreased by addition of 2-APB. Electron microscopy showed higher proliferation, organization and maturation of osteoblasts in bone decellularized scaffolds after magnesium addition. In summary, our results demonstrate that magnesium chloride enhances MSC proliferation by Notch1 signaling activation and induces osteogenic differentiation, shedding light on the understanding of the role of magnesium during bone regeneration.

CD146 (MCAM) in human cs-DLK1-/cs-CD34+ adipose stromal/progenitor cells

To precisely characterize CD146 in adipose stromal/progenitor cells (ASCs) we sorted the stromal vascular faction (SVF) of human abdominal subcutaneous white adipose tissue (sWAT) according to cell surface (cs) expression of CD146, DLK1 and CD34. This test identified three main SVF cell populations: ~50% cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs, ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146⁺ and ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146^- cells. All cells contained intracellular CD146. Whole mount fluorescent IHC staining of small vessels detected CD146⁺ endothelial cells (CD31⁺/CD34⁺/CD146⁺) and pericytes (CD31^-/CD34^-/CD146⁺ ASCs). The cells in the outer adventitial layer showed the typical ASC morphology, were strongly CD34⁺ and contained low amounts of intracellular CD146 protein (CD31^-/CD34⁺/CD146⁺). Additionally, we detected wavy CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells. CD34^dim/CD146⁺ cells were slightly more bulky than CD34^-/CD146⁺ cells. Both CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells were detached from the inner pericyte layer and protruded into the outer adventitial layer. Cultured early passage ASCs contained low levels of CD146 mRNA, which was expressed in two different splicing variants, at a relatively high amount of the CD146-long form and at a relatively low amount of the CD146-short form. ASCs contained low levels of CD146 protein, which consisted predominantly long form and a small amount of short form. The CD146 protein was highly stable, and the majority of the protein was localized in the Golgi apparatus. In conclusion, the present study contributes to a better understanding of the spatial localization of CD34⁺/CD146⁺ and CD34^-/CD146⁺ cells in the adipose niche of sWAT and identifies CD146 as intracellular protein in cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs.

Distinctive expression pattern of cystathionine-β-synthase and cystathionine-γ-lyase identifies mesenchymal stromal cells transition to mineralizing osteoblasts

Mesenchymal stromal cells (MSCs) are key players in the repair or regeneration of the damaged bone tissue. However, heterogeneity exists between MSCs derived from different donors in their bone formation ability both in vitro and in vivo. The identification of markers defining MSCs with different functional phenotypes is fundamental to maximize their clinical potential. In our previous in vivo study, impaired expression in MSCs of cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE), the two key enzymes in the catabolic pathway of homocysteine, was associated to decreased bone formation and to the onset of osteoporosis in mice. Here, we investigated whether osteogenic differentiation of human MSCs (hMSCs) modulates the expression of CBS and CSE. The expression of CBS and CSE was also assessed during chondrogenesis to confirm the specificity of their expression during osteogenesis. hMSCs displayed a heterogeneous mineralizing capacity between donors (70% of the samples mineralized, while 30% did not mineralize). Inducible expression of CBS and CSE was found to be associated with a mineralizing phenotype in hMSCs. In particular, up-regulation of CSE was restricted to hMSCs undergoing mineralization. During chondrogenesis, CBS was significantly up-regulated while CSE expression was not affected. Ex-vivo findings confirmed that mature h-osteoblasts (hOBs) show consistently higher expression of CBS and CSE than hMSCs. Our data provide the first evidence that the expression of CBS and CSE in hMSCs closely correlates with the transition of hMSCs toward the osteoblastic phenotype and that CSE may constitute a novel marker of osteogenic differentiation.

MicroRNA-4739 regulates osteogenic and adipocytic differentiation of immortalized human bone marrow stromal cells via targeting LRP3

Understanding the regulatory networks underlying lineage differentiation and fate determination of human bone marrow stromal cells (hBMSC) is a prerequisite for their therapeutic use. The goal of the current study was to unravel the novel role of the low-density lipoprotein receptor-related protein 3 (LRP3) in regulating the osteogenic and adipogenic differentiation of immortalized hBMSCs. Gene expression profiling revealed significantly higher LRP3 levels in the highly osteogenic hBMSC clone imCL1 than in the less osteogenic clone imCL2, as well as a significant upregulation of LRP3 during the osteogenic induction of the imCL1 clone. Data from functional and gene expression assays demonstrated the role of LRP3 as a molecular switch promoting hBMSC lineage differentiation into osteoblasts and inhibiting differentiation into adipocytes. Interestingly, microRNA (miRNA) expression profiling identified miR-4739 as the most under-represented miRNA (-36.11 fold) in imCL1 compared to imCL2. The TargetScan prediction algorithm, combined with functional and biochemical assays, identified LRP3 mRNA as a novel target of miR-4739, with a single potential binding site for miR-4739 located in the LRP3 3' UTR. Regulation of LRP3 expression by miR-4739 was subsequently confirmed by qRT-PCR, western blotting, and luciferase assays. Over-expression of miR-4739 mimicked the effects of LRP3 knockdown on promoting adipogenic and suppressing osteogenic differentiation of hBMSCs. Hence, we report for the first time a novel biological role for the LRP3/hsa-miR-4739 axis in balancing osteogenic and adipocytic differentiation of hBMSCs. Our data support the potential utilization of miRNA-based therapies in regenerative medicine.

Osteogenesis Catalyzed by Titanium-Supported Silver Nanoparticles

Silver nanoparticles (Ag NPs) were widely explored for antimicrobial applications, whereas the translation into drugs and implantable antibacterial devices provoked serious concerns about their potential cytotoxicity. Herein, Ag NPs with diameters ranging from 4 to 19 nm were in situ fabricated and immobilized on titanium by using a plasma immersion ion implantation process. The particles have a population-dependent capability in activating the integrin α5 orchestrated MAPK/ERK signal cascade of osteoblast differentiation in rat bone marrow stem cells (BMSCs), and promoting osteointegration of titanium. It was demonstrated that the titanium-supported Ag NPs played an important role in motivating integrin α5 through triggering the galvanic hydrogen evolution reactions, which was found in positive correlation with the distribution density of the immobilized Ag NPs. Since cellular uptake is a key factor determining the cytotoxic performance of Ag NPs, the extracellular effects of immobilized Ag NPs on promoting osteogenesis provided new insights into the safe application of nanomaterials, and into designing and developing renewed antibacterial devices with selective toxicity.

miR-203 inhibits the traumatic heterotopic ossification by targeting Runx2

Emerging evidence has indicated that dysregulated microRNAs (miRNAs) have an important role in bone formation. However, the pathophysiological role of miRNAs in traumatic heterotopic ossification (HO) remains to be elucidated. Using gene expression profile analyses and subsequent confirmation with real-time PCR assays, we identified the decreased expression of miRNA-203 (miR-203) and increased expression of Runx2 as responses to the development of traumatic HO. We found that miR-203 expression was markedly higher in primary and recurrent HO tissues than in normal bones. The upregulation of miR-203 significantly decreased the level of Runx2 expression, whereas miR-203 downregulation increased Runx2 expression. Mutation of the putative miR-203-binding sites in Runx2 mRNA abolished miR-203-mediated repression of Runx2 3'-untranslated region luciferase reporter activity, indicating that Runx2 is an important target of miR-203 in osteoblasts. We also found that miR-203 is negatively correlated with osteoblast differentiation. Furthermore, in vitro osteoblast activity and matrix mineralization were promoted by antagomir-203 and decreased by agomir-203. We showed that miR-203 suppresses osteoblast activity by inhibiting the β-catenin and extracellular signal-regulated kinase pathways. Moreover, using a tenotomy mouse HO model, we found an inhibitory role of miR-203 in regulating HO in vivo; pretreatment with antagomiR-203 increased the development of HO. These data suggest that miR-203 has a crucial role in suppressing HO by directly targeting Runx2 and that the therapeutic overexpression of miR-203 may be a potential strategy for treating traumatic HO.

Transgelin is a TGFβ-inducible gene that regulates osteoblastic and adipogenic differentiation of human skeletal stem cells through actin cytoskeleston organization

Regenerative medicine is a novel approach for treating conditions in which enhanced bone regeneration is required. We identified transgelin (TAGLN), a transforming growth factor beta (TGFβ)-inducible gene, as an upregulated gene during in vitro osteoblastic and adipocytic differentiation of human bone marrow-derived stromal (skeletal) stem cells (hMSC). siRNA-mediated gene silencing of TAGLN impaired lineage differentiation into osteoblasts and adipocytes but enhanced cell proliferation. Additional functional studies revealed that TAGLN deficiency impaired hMSC cell motility and in vitro transwell cell migration. On the other hand, TAGLN overexpression reduced hMSC cell proliferation, but enhanced cell migration, osteoblastic and adipocytic differentiation, and in vivo bone formation. In addition, deficiency or overexpression of TAGLN in hMSC was associated with significant changes in cellular and nuclear morphology and cytoplasmic organelle composition as demonstrated by high content imaging and transmission electron microscopy that revealed pronounced alterations in the distribution of the actin filament and changes in cytoskeletal organization. Molecular signature of TAGLN-deficient hMSC showed that several genes and genetic pathways associated with cell differentiation, including regulation of actin cytoskeleton and focal adhesion pathways, were downregulated. Our data demonstrate that TAGLN has a role in generating committed progenitor cells from undifferentiated hMSC by regulating cytoskeleton organization. Targeting TAGLN is a plausible approach to enrich for committed hMSC cells needed for regenerative medicine application.

Notch signaling represses hypoxia-inducible factor-1α-induced activation of Wnt/β-catenin signaling in osteoblasts under cobalt-mimicked hypoxia

The modification of Wnt and Notch signaling pathways by hypoxia, and its association with osteoblast proliferation and apoptosis remain to be fully elucidated. To investigate Wnt-Notch crosstalk, and its role in hypoxia-induced osteoblast proliferation and apoptosis regulation, the present study investigated the effects of cobalt-mimicked hypoxia on the mouse pre-osteoblast-like cell line, MC3T3-E1, when the Notch signals were repressed using a γ-secretase inhibitor DAPT. The data showed that the cobalt-mimicked hypoxia suppressed cell proliferation under normal conditions, but increased cell proliferation under conditions of Notch repression, in a concentration-dependent manner. The results of western blot and reverse transcription-quantitative polymerase chain reaction analyses showed that the cobalt treatment increased the levels of activated β-catenin protein and the expression levels of the target genes, axis inhibition protein 2 and myelocytomatosis oncogene, under DAPT-induced Notch repression. However, no significant changes were found in the expression levels of the Notch intracellular domain protein or the Notch target gene, hes1. In a β-catenin gene-knockdown experiment, the proliferation of the MC3T3-E1 cells under hypoxia were decreased by DAPT treatment, and knockdown of the expression of hypoxia-inducible factor-1α (HIF-1α) suppressed the cobalt-induced increase in Wnt target gene levels. No significant difference in cell proliferation rate was found following DAPT treatment when the expression of HIF-1α was knocked down. The results of the present study showed the opposing effects of Wnt and Notch signaling under cobalt-mimicked hypoxia, which were partially regulated by HIF-1α, The results also showed that osteoblast proliferation was dependent on Wnt-Notch signal crosstalk.

Epigenetic Library Screen Identifies Abexinostat as Novel Regulator of Adipocytic and Osteoblastic Differentiation of Human Skeletal (Mesenchymal) Stem Cells

: The epigenetic mechanisms promoting lineage-specific commitment of human skeletal (mesenchymal or stromal) stem cells (hMSCs) into adipocytes or osteoblasts are still not fully understood. Herein, we performed an epigenetic library functional screen and identified several novel compounds, including abexinostat, which promoted adipocytic and osteoblastic differentiation of hMSCs. Using gene expression microarrays, chromatin immunoprecipitation for H3K9Ac combined with high-throughput DNA sequencing (ChIP-seq), and bioinformatics, we identified several key genes involved in regulating stem cell proliferation and differentiation that were targeted by abexinostat. Concordantly, ChIP-quantitative polymerase chain reaction revealed marked increase in H3K9Ac epigenetic mark on the promoter region of AdipoQ, FABP4, PPARγ, KLF15, CEBPA, SP7, and ALPL in abexinostat-treated hMSCs. Pharmacological inhibition of focal adhesion kinase (PF-573228) or insulin-like growth factor-1R/insulin receptor (NVP-AEW51) signaling exhibited significant inhibition of abexinostat-mediated adipocytic differentiation, whereas inhibition of WNT (XAV939) or transforming growth factor-β (SB505124) signaling abrogated abexinostat-mediated osteogenic differentiation of hMSCs. Our findings provide insight into the understanding of the relationship between the epigenetic effect of histone deacetylase inhibitors, transcription factors, and differentiation pathways governing adipocyte and osteoblast differentiation. Manipulating such pathways allows a novel use for epigenetic compounds in hMSC-based therapies and tissue engineering.

SIGNIFICANCE

This unbiased epigenetic library functional screen identified several novel compounds, including abexinostat, that promoted adipocytic and osteoblastic differentiation of human skeletal (mesenchymal or stromal) stem cells (hMSCs). These data provide new insight into the understanding of the relationship between the epigenetic effect of histone deacetylase inhibitors, transcription factors, and differentiation pathways controlling adipocyte and osteoblast differentiation of hMSCs. Manipulating such pathways allows a novel use for epigenetic compounds in hMSC-based therapies for tissue engineering, bone disease, obesity, and metabolic-disorders.

γ-Secretase inhibitor reverts the Notch signaling attenuation of osteogenic differentiation in aged bone marrow mesenchymal stem cells

The age-related changes in cell viability and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) play pivotal roles in the fracture healing process, especially in geriatric individuals. This study was designed to explore the age-related changes in murine BMSCs and the regulation of osteogenic differentiation in aged BMSCs in vitro. Notch signaling pathway took part in the regulation of osteogensis, while the relationship between Notch and the osteogenic differentiation in aged BMSCs has not been reported yet. BMSCs harvested from the bone marrow of young, adult, and aged C57BL/6 mice were cultured in osteogenic and adipogenic differentiation media. Histochemical staining results indicated that the osteogenic ability of BMSCs gradually decreased with aging, whereas the adipogenic ability increased. Cell activity assays showed that the proliferative and migrated capacity did not decline with aging significantly. According to real-time PCR and Western blotting results, the aged cells exhibited higher Notch signaling expression level than the younger ones did. After the aged BMSCs being treated with γ-secretase inhibitor, however, Notch activity was changed and the aging-imparied osteogenic ability reverted to a normal level. This study demonstrated that the decreased bone formation capacity in aged BMSCs had relationship with the transdifferentiation between osteogenesis and adipogenesis, which would be regulated by Notch signaling pathway and the attenuated osteogenesis in aged BMSCs could be promoted when the inhibition of Notch pathway.

Genome-Wide Chromatin Landscape Transitions Identify Novel Pathways in Early Commitment to Osteoblast Differentiation

Bone continuously undergoes remodeling by a tightly regulated process that involves osteoblast differentiation from Mesenchymal Stem Cells (MSC). However, commitment of MSC to osteoblastic lineage is a poorly understood process. Chromatin organization functions as a molecular gatekeeper of DNA functions. Detection of sites that are hypersensitive to Dnase I has been used for detailed examination of changes in response to hormones and differentiation cues. To investigate the early steps in commitment of MSC to osteoblasts, we used a model human temperature-sensitive cell line, hFOB. When shifted to non-permissive temperature, these cells undergo "spontaneous" differentiation that takes several weeks, a process that is greatly accelerated by osteogenic induction media. We performed Dnase I hypersensitivity assays combined with deep sequencing to identify genome-wide potential regulatory events in cells undergoing early steps of commitment to osteoblasts. Massive reorganization of chromatin occurred within hours of differentiation. Whereas ~30% of unique DHS sites were located in the promoters, the majority was outside of the promoters, designated as enhancers. Many of them were at novel genomic sites and need to be confirmed experimentally. We developed a novel method for identification of cellular networks based solely on DHS enhancers signature correlated to gene expression. The analysis of enhancers that were unique to differentiating cells led to identification of bone developmental program encompassing 147 genes that directly or indirectly participate in osteogenesis. Identification of these pathways provided an unprecedented view of genomic regulation during early steps of differentiation and changes related to WNT, AP-1 and other pathways may have therapeutic implications.

miR-140-5p regulates adipocyte differentiation by targeting transforming growth factor-β signaling

Recent emerging studies of miRNAs in adipocyte commitment provide new insights to understand the molecular basis of adipogenesis. The current study indicated that miR-140-5p was altered in primary cultured marrow stromal cells and established progenitor lines after adipogenic and/or osteogenic treatment. miR-140-5p was increased in adipose tissue in db/db obese mice vs. lean mice. Supplementing miR-140-5p activity induced stromal cell ST2 and preadipocyte 3T3-L1 to differentiate into mature adipocytes. Conversely, inhibition of the endogenous miR-140-5p repressed ST2 and 3T3-L1 to fully differentiate. By contrast, knockdown of the endogenous miR-140-5p enhanced osteoblast differentiation. Transforming growth factor-β receptor I (Tgfbr1) was shown to be a direct target of miR-140-5p. Supplementing miR-140-5p in ST2 reduced the level of TGFBR1 protein, while suppression of endogenous miR-140-5p increased TGFBR1. Overexpression of Tgfbr1 inhibited, whereas knockdown of Tgfbr1 promoted adipogenic differentiation of ST2 cells. Further investigation of mechanisms that control miR-140-5p expression revealed that C/EBPα induced transcriptional activity of the miR-140-5p promoter. Removal of the putative response element of C/EBP from the promoter abolished the enhancement of the promoter activity by C/EBPα, suggesting that C/EBPα transcriptionally controls miR-140-5p expression. Taken together, our study provides evidences that miR-140-5p regulates adipocyte differentiation through a C/EBP/miR-140-5p/TGFBR1 regulatory feedback loop.

Association between in vivo bone formation and ex vivo migratory capacity of human bone marrow stromal cells

Introduction

There is a clinical need for developing systemic transplantation protocols for use of human skeletal stem cells (also known bone marrow stromal stem cells) (hBMSC) in tissue regeneration. In systemic transplantation studies, only a limited number of hBMSC home to injured tissues suggesting that only a subpopulation of hBMSC possesses “homing” capacity. Thus, we tested the hypothesis that a subpopulation of hBMSC defined by ability to form heterotopic bone in vivo, is capable of homing to injured bone.

Methods

We tested ex vivo and in vivo homing capacity of a number of clonal cell populations derived from telomerized hBMSC (hBMSC-TERT) with variable ability to form heterotopic bone when implanted subcutaneously in immune deficient mice. In vitro transwell migration assay was used and the in vivo homing ability of transplanted hBMSC to bone fractures in mice was visualized by bioluminescence imaging (BLI). In order to identify the molecular phenotype associated with enhanced migration, we carried out comparative DNA microarray analysis of gene expression of hBMSC-derived high bone forming (HBF) clones versus low bone forming (LBF) clones.

Results

HBF clones were exhibited higher ex vivo transwell migration and following intravenous injection, better in vivo homing ability to bone fracture when compared to LBF clones. Comparative microarray analysis of HBF versus LBF clones identified enrichment of gene categories of chemo-attraction, adhesion and migration associated genes. Among these, platelet-derived growth factor receptor (PDGFR) α and β were highly expressed in HBF clones. Follow up studies showed that the chemoattractant effects of PDGF in vitro was more enhanced in HBF compared to LBF clones and this effect was reduced in presence of a PDGFRβ-specific inhibitor: SU-16 f. Also, PDGF exerted greater chemoattractant effect on PDGFRβ⁺ cells sorted from LBF clones compared to PDGFRβ^- cells.

Conclusion

Our data demonstrate phenotypic and molecular association between in vivo bone forming ability and migratory capacity of hBMSC. PDGFRβ can be used as a potential marker for the prospective selection of hBMSC populations with high migration and bone formation capacities suitable for clinical trials for enhancing bone regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0188-9) contains supplementary material, which is available to authorized users.

Effect of Qing'e formula on the in vitro differentiation of bone marrow-derived mesenchymal stem cells from proximal femurs of postmenopausal osteoporotic mice

BACKGROUND

Qing'e formula (QEF), prepared from an ancient Chinese recipe, was previously suggested to regulate bone metabolism and improve bone mineral density in patients with osteoporosis. To study the effects of medicated serum containing QEF on the in vitro differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) isolated from the proximal femurs of postmenopausal osteoporosis (PMOP) mice.

METHODS

Using an established mouse model of PMOP, mononuclear cells were isolated from the bone marrow present in the proximal femurs and cultured. PMOP mice were also randomly divided into four groups: the untreated group (Group A) and the groups treated with respectively low (Group B), medium (Group C), and high (Group D) concentrations of QEF. Serum was isolated from each and used to treat the cultured BMSCs in conjunction with recombinant human bone morphogenetic protein-2 (rhBMP-2). Cell morphology, proliferation rates, intracellular alkaline phosphatase (ALP) activity, and transforming growth factor-beta 1 (TGF-β1) mRNA expression were evaluated.

RESULTS

QEF-treated serum, particularly that containing moderate and high concentrations, appears to enhance the rhBMP-2-mediated changes in cell morphology, proliferation, and differentiation (determined via the expression of TGF-β1 mRNA and ALP activity) observed in the BMSCs isolated from PMOP mice.

CONCLUSIONS

QEF may play a role in the prevention and treatment of PMOP by enhancing the activity of rhBMP-2.