Hey1 basic helix-loop-helix protein plays an important role in mediating BMP9-induced osteogenic differentiation of mesenchymal progenitor cells

Characterization of the essential role of bone morphogenetic protein 9 (BMP9) in osteogenic differentiation of mesenchymal stem cells (MSCs) through RNA interference

Mesenchymal stem cells (MSCs) are multipotent stem cells and capable of differentiating into multiple cell types including osteoblastic, chondrogenic and adipogenic lineages. We previously identified BMP9 as one of the most potent BMPs that induce osteoblastic differentiation of MSCs although exact molecular mechanism through which BMP9 regulates osteogenic differentiation remains to be fully understood. Here, we seek to develop a recombinant adenovirus system to optimally silence mouse BMP9 and then characterize the important role of BMP9 in osteogenic differentiation of MSCs. Using two different siRNA bioinformatic prediction programs, we design five siRNAs targeting mouse BMP9 (or simB9), which are expressed under the control of the converging H1 and U6 promoters in recombinant adenovirus vectors. We demonstrate that two of the five siRNAs, simB9-4 and simB9-7, exhibit the highest efficiency on silencing exogenous mouse BMP9 in MSCs. Furthermore, simB9-4 and simB9-7 act synergistically in inhibiting BMP9-induced expression of osteogenic markers, matrix mineralization and ectopic bone formation from MSCs. Thus, our findings demonstrate the important role of BMP9 in osteogenic differentiation of MSCs. The characterized simB9 siRNAs may be used as an important tool to investigate the molecular mechanism behind BMP9 osteogenic signaling. Our results also indicate that recombinant adenovirus-mediated expression of siRNAs is efficient and sustained, and thus may be used as an effective delivery vehicle of siRNA therapeutics.

Mesenchymal Chondrosarcoma: a Review with Emphasis on its Fusion-Driven Biology

Mesenchymal chondrosarcoma is a rare but deadly form of chondrosarcoma that typically affects adolescents and young adults. While curative intent is possible for patients with localized disease, few options exist for patients in the unresectable/metastatic setting. Thus, it is imperative to understand the fusion-driven biology of this rare malignant neoplasm so as to lead to the future development of better therapeutics for this disease. This manuscript will briefly review the clinical and pathologic features of mesenchymal chondrosarcoma followed by an appraisal of existing data linked to the fusions, HEY1-NCOA2 and IRF2BP2-CDX1, and the associated downstream pathways.

Osteoconduction of Unrestricted Somatic Stem Cells on an Electrospun Polylactic-Co-Glycolic Acid Scaffold Coated with Nanohydroxyapatite

The limitation of traditional bone grafts could be overcome by applying engineered bone constructs, which are mainly produced by seeding suitable stem cells on appropriate scaffolds. So far, bone marrow-derived stromal cells have been the most applied cells in bone tissue engineering, but current data show that unrestricted somatic stem cells (USSCs) from human cord blood might actually be a better stem cell source due to the accessibility and noninvasive procedure of collection. In this study, we cultured USSCs on a plasma-treated electrospun polylactic-co-glycolic acid (PLGA) scaffold coated with nanohydroxyapatite (nHA). Adhesion and proliferation of USSCs on PLGA/nHA were assessed by scanning electron microscopy and MTT assay. Osteogenic differentiation of USSCs into osteoblast lineage cells was evaluated via alkaline phosphatase (ALP) activity and real-time polymerase chain reaction. Our observation showed that USSCs attached and proliferated on PLGA/nHA. Osteogenic differentiation was confirmed by increased ALP activity and OSTEONECTIN expression in USSCs on PLGA/nHA after the 1st week of the osteogenic period. Therefore, using USSCs on electrospun PLGA/nHA is a promising approach in bone tissue engineering.

Circulating bone morphogenetic protein-9 in relation to metabolic syndrome and insulin resistance

Our objective is to determine circulating Bone morphogenetic protein-9(BMP-9) levels in subjects with Metabolic Syndrome (MetS) and examine the relationship between BMP-9 and conventional markers for MetS and insulin resistance (IR). A total of 362 newly diagnosed patients with MetS along with healthy controls were recruited for this cross-sectional study. Circulating BMP-9 levels were measured by ELISA. Circulating BMP-9 levels were significantly lower in MetS patients compared to those of the healthy controls. BMP-9 was associated negatively with Waist hip ratio (WHR), fasting blood glucose (FBG), 2-hour blood glucose after glucose overload (2h-OGTT), HbA1c, triglyceride (TG) levels and HOMA-IR and positively with free fatty acid (FFA) and HDL after control for age and sex. In a multiple linear regression, BMP-9 was independently associated with type 2 diabetes mellitus (T2DM), HOMA-IR and FFA. Binary logistic regression showed that plasma BMP-9 concentrations were significantly associated with MetS even after controlling for anthropometric variables and lipid profiles. In addition, circulating BMP-9 levels reduced progressively with an increasing number of MetS components. The best cutoff values for circulating BMP-9 to predict MetS was 56.6 ng/L. Circulating BMP-9 levels were associated with the key components of MetS and IR.

Loss of polarity alters proliferation and differentiation in low-grade endometrial cancers by disrupting Notch signaling

Cell adhesion and apicobasal polarity together maintain epithelial tissue organization and homeostasis. Loss of adhesion has been described as a prerequisite for the epithelial to mesenchymal transition. However, what role misregulation of apicobasal polarity promotes tumor initiation and/or early progression remains unclear. We find that human low-grade endometrial cancers are associated with disrupted localization of the apical polarity protein Par3 and Ezrin while, the adhesion molecule E-cadherin remains unchanged, accompanied by decreased Notch signaling, and altered Notch receptor localization. Depletion of Par3 or Ezrin, in a cell-based model, results in loss of epithelial architecture, differentiation, increased proliferation, migration and decreased Notch signaling. Re-expression of Par3 in endometrial cancer cell lines with disrupted Par3 protein levels blocks proliferation and reduces migration in a Notch dependent manner. These data uncover a function for apicobasal polarity independent of cell adhesion in regulating Notch-mediated differentiation signals in endometrial epithelial cells.

CRISPR/Cas9-mediated reversibly immortalized mouse bone marrow stromal stem cells (BMSCs) retain multipotent features of mesenchymal stem cells (MSCs)

Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells that can undergo self-renewal and differentiate into multi-lineages. Bone marrow stromal stem cells (BMSCs) represent one of the most commonly-used MSCs. In order to overcome the technical challenge of maintaining primary BMSCs in long-term culture, here we seek to establish reversibly immortalized mouse BMSCs (imBMSCs). By exploiting CRISPR/Cas9-based homology-directed-repair (HDR) mechanism, we target SV40T to mouse Rosa26 locus and efficiently immortalize mouse BMSCs (i.e., imBMSCs). We also immortalize BMSCs with retroviral vector SSR #41 and establish imBMSC41 as a control line. Both imBMSCs and imBMSC41 exhibit long-term proliferative capability although imBMSC41 cells have a higher proliferation rate. SV40T mRNA expression is 130% higher in imBMSC41 than that in imBMSCs. However, FLP expression leads to 86% reduction of SV40T expression in imBMSCs, compared with 63% in imBMSC41 cells. Quantitative genomic PCR analysis indicates that the average copy number of SV40T and hygromycin is 1.05 for imBMSCs and 2.07 for imBMSC41, respectively. Moreover, FLP expression removes 92% of SV40T in imBMSCs at the genome DNA level, compared with 58% of that in imBMSC41 cells, indicating CRISPR/Cas9 HDR-mediated immortalization of BMSCs can be more effectively reversed than that of retrovirus-mediated random integrations. Nonetheless, both imBMSCs and imBMSC41 lines express MSC markers and are highly responsive to BMP9-induced osteogenic, chondrogenic and adipogenic differentiation in vitro and in vivo. Thus, the engineered imBMSCs can be used as a promising alternative source of primary MSCs for basic and translational research in the fields of MSC biology and regenerative medicine.

Notch signaling negatively regulates BMP9-induced osteogenic differentiation of mesenchymal progenitor cells by inhibiting JunB expression

Although interaction between BMP and Notch signaling has been demonstrated to be crucial for osteogenic differentiation of mesenchymal stem cells (MSCs), the precise molecular mechanism remains unknown. Here, we show that Notch intracellular domain (NICD) overexpression inhibits BMP9-induced C3H10T1/2 cell osteogenesis in vivo and in vitro. Our results show that activated Notch signaling results in down-regulation of Runx2 and early osteogenesis differentiation factors, without affecting p-Smad1/5/8 expression, and that blocking Notch signaling with DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) significantly increases p-Smad1/5/8 expression. Interestingly, Notch signaling also regulates the cell cycle by increasing PCNA (proliferation cell nuclear antigen) and CyclinD1 expression. Furthermore, similar results were obtained by ectopic bone formation and histological analyses, indicating that Notch signaling activation significantly inhibits BMP9-induced MSC osteogenic, cartilage and adipogenic differentiation. Moreover, we are the first to show that Notch regulates by suppressing JunB synthesis and that the negative effect of Notch is partially reversed by treatment with the JunB activator TPA (12-O-tetradeca-noylphorbol-13-acetate). Our findings demonstrate that Notch signaling significantly enhances cell proliferation but inhibits MSC osteogenic differentiation induced by BMP9 via JunB protein suppression rather than by BMP/Smad signaling regulation.

The NOTCH4-HEY1 Pathway Induces Epithelial-Mesenchymal Transition in Head and Neck Squamous Cell Carcinoma

Purpose: Recently, several comprehensive genomic analyses demonstrated NOTCH1 and NOTCH3 mutations in head and neck squamous cell carcinoma (HNSCC) in approximately 20% of cases. Similar to other types of cancers, these studies also indicate that the NOTCH pathway is closely related to HNSCC progression. However, the role of NOTCH4 in HNSCC is less well understood.Experimental Design: We analyzed NOTCH4 pathway and downstream gene expression in the TCGA data set. To explore the functional role of NOTCH4, we performed in vitro proliferation, cisplatin viability, apoptosis, and cell-cycle assays. We also compared the relationships among NOTCH4, HEY1, and epithelial-mesenchymal transition (EMT)-related genes using the TCGA data set and in vitro assays.Results:HEY1 is specifically upregulated in HNSCC compared with normal tissues in the TCGA data set. NOTCH4 is more significantly related to HEY1 activation in HNSCC in comparison with other NOTCH receptors. NOTCH4 promotes cell proliferation, cisplatin resistance, inhibition of apoptosis, and cell-cycle dysregulation. Furthermore, NOTCH4 and HEY1 upregulation resulted in decreased E-cadherin expression and increased Vimentin, Fibronectin, TWIST1, and SOX2 expression. NOTCH4 and HEY1 expression was associated with an EMT phenotype as well as increased invasion and cell migration.Conclusions: In HNSCC, the NOTCH4-HEY1 pathway is specifically upregulated, induces proliferation and cisplatin resistance, and promotes EMT. Clin Cancer Res; 24(3); 619-33. ©2017 AACR.

Hey1 functions as a positive regulator of odontogenic differentiation in odontoblast‑lineage cells

Substantial evidence has indicated that Notch and bone morphogenetic protein (BMP) signaling may regulate odontoblastic differentiation. Hairy/enhancer‑of‑split related with YRPW motif 1 (Hey1), a downstream target gene of Notch and BMP signaling, is expressed in dental pulp tissues and has been demonstrated to be responsible for osteoblast mineralization. The aim of this study was to investigate the effects of Hey1 on odontoblast differentiation. The results of the study demonstrated that Hey1 expression in odontoblast‑lineage cells (OLCs) was upregulated by stimulation of osteoblastic/odontoblastic differentiation medium containing ascorbic acid, β‑glycerol phosphate and dexamethasone. Furthermore, stable Hey1‑overexpressing cells expressed higher levels of dentin sialophosphoprotein (DSPP) and exhibited higher mineralization capabilities following stimulation by differentiation medium. Furthermore, RNA interference‑mediated knockdown of Hey1 downregulated the expression levels of DSPP in OLCs stimulated by differentiation medium. Taken together, the findings indicate that Hey1 may be a positive regulator of odontoblastic differentiation. The present study broadens the understanding of odontoblast differentiation and biomineralization.

RUNX3 plays an important role in mediating the BMP9-induced osteogenic differentiation of mesenchymal stem cells

Although bone morphogenetic protein 9 (BMP9) is highly capable of promoting the osteogenic differentiation of mesenchymal stem cells (MSCs) both in vitro and in vivo, the molecular mechanisms involved remain to be fully elucidated. Runt-related transcription factor (RUNX)3 is an essential regulator of osteoblast/chondrocyte maturation. However, the exact role of RUNX3 in BMP9 osteoinductive activity is unknown. In this study, we sought to investigate the functional role of RUNX3 in the BMP9-induced osteogenic differentiation of MSCs. We found that BMP9 upregulated the endogenous expression of RUNX3 in MSCs. The overexpression or/and knockdown of RUNX3 both increased the levels of alkaline phosphatase (ALP) a marker of BMP9-induced early osteogenic differentiation. Nevertheless, matrix mineralization, a marker of BMP9-induced late osteogenic differentiation was enhanced by the overexpression of RUNX3, whereas it was inhibited by the knockdown of RUNX3. The BMP9-induced expression of osteogenic pivotal transcription factors [inhibitor of differentiation (Id)3, distal-less homeobox 5 (DLX5) and RUNX2)] was further increased by the overexpression of RUNX3; however, it was reduced by the knockdown of RUNX3. However, the expression levels of Id1 and Id2 were both enhanced by the overexpression or/and knockdown of RUNX3. The BMP9-induced phosphorylation of Smad1/5/8 was increased with the overexpression of RUNX3, and yet was decreased with the knockdown of RUNX3. Collectively, our findings suggest that RUNX3 is an essential modulator of the BMP9-induced osteoblast lineage differentiation of MSCs.

Notch pathway is active during osteogenic differentiation of human bone marrow mesenchymal stem cells induced by pulsed electromagnetic fields

Pulsed electromagnetic fields (PEMFs) have been used to treat bone diseases, particularly nonunion healing. Although it is known that PEMFs promote the osteogenic differentiation of human mesenchymal stem cells (hMSCs), to date PEMF molecular mechanisms remain not clearly elucidated. The Notch signalling is a highly conserved pathway that regulates cell fate decisions and skeletal development. The aim of this study was to investigate if the known PEMF-induced osteogenic effects may involve the modulation of the Notch pathway. To this purpose, during in vitro osteogenic differentiation of bone marrow hMSCs in the absence and in the presence of PEMFs, osteogenic markers (alkaline phosphatase activity, osteocalcin and matrix mineralization), the messenger ribonucleic acid expression of osteogenic transcription factors (Runx2, Dlx5, Osterix) as well as of Notch receptors (Notch1-4), their ligands (Jagged1, Dll1 and Dll4) and nuclear target genes (Hes1, Hes5, Hey1, Hey2) were investigated. PEMFs stimulated all osteogenic markers and increased the expression of Notch4, Dll4, Hey1, Hes1 and Hes5 in osteogenic medium compared to control. In the presence of DAPT and SAHM1, used as Notch pathway inhibitors, the expression of the osteogenic markers, including Runx2, Dlx5, Osterix, as well as Hes1 and Hes5 were significantly inhibited, both in unexposed and PEMF-exposed hMSCs. These results suggest that activation of Notch pathway is required for PEMFs-stimulated osteogenic differentiation. These new findings may be useful to improve autologous cell-based regeneration of bone defects in orthopaedics.

lncRNA H19 mediates BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) through Notch signaling

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can undergo self-renewal and differentiate into multiple lineages. Osteogenic differentiation from MSCs is a well-orchestrated process and regulated by multiple signaling pathways. We previously demonstrated that BMP9 is one of the most potent osteogenic factors. However, molecular mechanism through which BMP9 governs osteoblastic differentiation remains to be fully understood. Increasing evidence indicates noncoding RNAs (ncRNAs) may play important regulatory roles in many physiological and/or pathologic processes. In this study, we investigate the role of lncRNA H19 in BMP9-regulated osteogenic differentiation of MSCs. We demonstrated that H19 was sharply upregulated at the early stage of BMP9 stimulation of MSCs, followed by a rapid decease and gradual return to basal level. This process was correlated with BMP9-induced expression of osteogenic markers. Interestingly, either constitutive H19 expression or silencing H19 expression in MSCs significantly impaired BMP9-induced osteogenic differentiation in vitro and in vivo, which was effectively rescued by the activation of Notch signaling. Either constitutive H19 expression or silencing H19 expression led to the increased expression of a group of miRNAs that are predicted to target Notch ligands and receptors. Thus, these results indicate that lncRNA H19 functions as an important mediator of BMP9 signaling by modulating Notch signaling-targeting miRNAs. Our findings suggest that the well-coordinated biphasic expression of lncRNA H19 may be essential in BMP9-induced osteogenic differentiation of MSCs, and that dysregulated H19 expression may impair normal osteogenesis, leading to pathogenic processes, such as bone tumor development.

RUNX1 Plays an Important Role in Mediating BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells Line C3H10T1/2, Murine Multi-Lineage Cells Lines C2C12 and MEFs

As one of the least studied bone morphogenetic proteins (BMPs), BMP9 is highly capable of promoting osteogenic differentiation. However, the underlying mechanism involved remains largely unknown. Recent studies have demonstrated that RUNX1 (runt-related transcription factor 1) is essential in osteoblast/chondrocyte maturation. In this study, we investigated the function of RUNX1 in BMP9-induced osteogenic of murine mesenchymal stem cell line (C3H10T1/2) and murine multi-lineage cell lines (C2C12 and MEFs). Our data showed that BMP9 promoted the endogenous expression of RUNX1 in C3H10T1/2, C2C12 and MEFs. Moreover, RUNX1 was probably a direct target of BMP9/Smad signaling. BMP9-induced osteogenic differentiation was enhanced by overexpression of RUNX1, whereas inhibited by knockdown RUNX1 in C3H10T1/2, C2C12 and MEFs. Further mechanism studies demonstrated that RUNX1 might affect BMP9-induced phosphorylation of Smad1/5/8, but not the phosphorylation of p38 and ERK1/2.Our results suggest that RUNX1 may be an essential modulator in BMP9- induced osteogenic differentiation of MSCs (Mesenchymal stem cells).

Gelatin-Derived Graphene-Silicate Hybrid Materials Are Biocompatible and Synergistically Promote BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells

Graphene-based materials are used in many fields but have found only limited applications in biomedicine, including bone tissue engineering. Here, we demonstrate that novel hybrid materials consisting of gelatin-derived graphene and silicate nanosheets of Laponite (GL) are biocompatible and promote osteogenic differentiation of mesenchymal stem cells (MSCs). Homogeneous cell attachment, long-term proliferation, and osteogenic differentiation of MSCs on a GL-scaffold were confirmed using optical microscopy and scanning electron microscopy. GL-powders made by pulverizing the GL-scaffold were shown to promote bone morphogenetic protein (BMP9)-induced osteogenic differentiation. GL-powders increased the alkaline phosphatase (ALP) activity in immortalized mouse embryonic fibroblasts but decreased the ALP activity in more-differentiated immortalized mouse adipose-derived cells. Note, however, that GL-powders promoted BMP9-induced calcium mineral deposits in both MSC lines, as assessed using qualitative and quantitative alizarin red assays. Furthermore, the expression of chondro-osteogenic regulator markers such as Runx2, Sox9, osteopontin, and osteocalcin was upregulated by the GL-powder, independent of BMP9 stimulation; although the powder synergistically upregulated the BMP9-induced Osterix expression, the adipogenic marker PPARγ was unaffected. Furthermore, in vivo stem cell implantation experiments demonstrated that GL-powder could significantly enhance the BMP9-induced ectopic bone formation from MSCs. Collectively, our results strongly suggest that the GL hybrid materials promote BMP9-induced osteogenic differentiation of MSCs and hold promise for the development of bone tissue engineering platforms.

BMP9 induces osteogenesis and adipogenesis in the immortalized human cranial suture progenitors from the patent sutures of craniosynostosis patients

The cranial suture complex is a heterogeneous tissue consisting of osteogenic progenitor cells and mesenchymal stem cells (MSCs) from bone marrow and suture mesenchyme. The fusion of cranial sutures is a highly coordinated and tightly regulated process during development. Craniosynostosis is a congenital malformation caused by premature fusion of cranial sutures. While the progenitor cells derived from the cranial suture complex should prove valuable for studying the molecular mechanisms underlying suture development and pathogenic premature suture fusion, primary human cranial suture progenitors (SuPs) have limited life span and gradually lose osteoblastic ability over passages. To overcome technical challenges in maintaining sufficient and long-term culture of SuPs for suture biology studies, we establish and characterize the reversibly immortalized human cranial suture progenitors (iSuPs). Using a reversible immortalization system expressing SV40 T flanked with FRT sites, we demonstrate that primary human suture progenitor cells derived from the patent sutures of craniosynostosis patients can be efficiently immortalized. The iSuPs maintain long-term proliferative activity, express most of the consensus MSC markers and can differentiate into osteogenic and adipogenic lineages upon BMP9 stimulation in vitro and in vivo. The removal of SV40 T antigen by FLP recombinase results in a decrease in cell proliferation and an increase in the endogenous osteogenic and adipogenic capability in the iSuPs. Therefore, the iSuPs should be a valuable resource to study suture development, intramembranous ossification and the pathogenesis of craniosynostosis, as well as to explore cranial bone tissue engineering.

Regulation of Bone Metabolism

Bone is formed through the processes of endochondral and intramembranous ossification. In endochondral ossification primary mesenchymal cells differentiate to chondrocytes and then are progressively substituted by bone, while in intramembranous ossification mesenchymal stem cells (MSCs) differentiate directly into osteoblasts to form bone. The steps of osteogenic proliferation, differentiation, and bone homeostasis are controlled by various markers and signaling pathways. Bone needs to be remodeled to maintain integrity with osteoblasts, which are bone-forming cells, and osteoclasts, which are bone-degrading cells.In this review we considered the major factors and signaling pathways in bone formation; these include fibroblast growth factors (FGFs), bone morphogenetic proteins (BMPs), wingless-type (Wnt) genes, runt-related transcription factor 2 (RUNX2) and osteoblast-specific transcription factor (osterix or OSX).

Osseous differentiation of human fat tissue grafts: From tissue engineering to tissue differentiation

Conventional bone tissue engineering approaches require isolation and in vitro propagation of autologous cells, followed by seeding on a variety of scaffolds. Those protracted procedures impede the clinical applications. Here we report the transdifferentiation of human fat tissue fragments retrieved from subcutaneous fat into tissue with bone characteristics in vitro without prior cell isolation and propagation. 3D collagen-I cultures of human fat tissue were cultivated either in growth medium or in osteogenic medium (OM) with or without addition of Bone Morphogenetic Proteins (BMPs) BMP-2, BMP-7 or BMP-9. Ca²⁺ depositions were observed after two weeks of osteogenic induction which visibly increased when either type of BMP was added. mRNA levels of alkaline phosphatase (ALP) and osteocalcin (OCN) increased when cultured in OM alone but addition of BMP-2, BMP-7 or BMP-9 caused significantly higher expression levels of ALP and OCN. Immunofluorescent staining for OCN, osteopontin and sclerostin supported the observed real-time-PCR data. BMP-9 was the most effective osteogenic inducer in this system. Our findings reveal that tissue regeneration can be remarkably simplified by omitting prior cell isolation and propagation, therefore removing significant obstacles on the way to clinical applications of much needed regeneration treatments.

Acute Phosphate Restriction Impairs Bone Formation and Increases Marrow Adipose Tissue in Growing Mice

Phosphate plays a critical role in chondrocyte maturation and skeletal mineralization. Studies examining the consequences of dietary phosphate restriction in growing mice demonstrated not only the development of rickets, but also a dramatic decrease in bone accompanied by increased marrow adipose tissue (MAT). Thus studies were undertaken to determine the effects of dietary phosphate restriction on bone formation and bone marrow stromal cell (BMSC) differentiation. Acute phosphate restriction of 28-day-old mice profoundly inhibited bone formation within 48 hours. It also resulted in increased mRNA expression of the early osteolineage markers Sox9 and Runt-related transcription factor 2 (Runx2), accompanied by decreased expression of the late osteolineage markers Osterix and Osteocalcin in BMSCs and osteoblasts, suggesting that phosphate restriction arrests osteoblast differentiation between Runx2 and Osterix. Increased expression of PPARγ and CEBPα, key regulators of adipogenic differentiation, was observed within 1 week of dietary phosphate restriction and was followed by a 13-fold increase in MAT at 3 weeks of phosphate restriction. In vitro phosphate restriction did not alter BMSC osteogenic or adipogenic colony formation, implicating aberrant paracrine or endocrine signaling in the in vivo phenotype. Because BMP signaling regulates the transition between Runx2 and Osterix, this pathway was interrogated. A dramatic decrease in pSmad1/5/9 immunoreactivity was observed in the osteoblasts of phosphate-restricted mice on day 31 (d31) and d35. This was accompanied by attenuated expression of the BMP target genes Id1, KLF10, and Foxc2, the latter of which promotes osteogenic and angiogenic differentiation while impairing adipogenesis. A decrease in expression of the Notch target gene Hey1, a BMP-regulated gene that governs angiogenesis, was also observed in phosphate-restricted mice, in association with decreased metaphyseal marrow vasculature. Whereas circulating phosphate levels are known to control growth plate maturation and skeletal mineralization, these studies reveal novel consequences of phosphate restriction in the regulation of bone formation and osteoblast differentiation. © 2016 American Society for Bone and Mineral Research.

Notch: A multi-functional integrating system of microenvironmental signals

The Notch signaling cascade is an evolutionarily ancient system that allows cells to interact with their microenvironmental neighbors through direct cell-cell interactions, thereby directing a variety of developmental processes. Recent research is discovering that Notch signaling is also responsive to a broad variety of stimuli beyond cell-cell interactions, including: ECM composition, crosstalk with other signaling systems, shear stress, hypoxia, and hyperglycemia. Given this emerging understanding of Notch responsiveness to microenvironmental conditions, it appears that the classical view of Notch as a mechanism enabling cell-cell interactions, is only a part of a broader function to integrate microenvironmental cues. In this review, we summarize and discuss published data supporting the idea that the full function of Notch signaling is to serve as an integrator of microenvironmental signals thus allowing cells to sense and respond to a multitude of conditions around them.

Wnt and BMP Signaling Crosstalk in Regulating Dental Stem Cells: Implications in Dental Tissue Engineering

Tooth is a complex hard tissue organ and consists of multiple cell types that are regulated by important signaling pathways such as Wnt and BMP signaling. Serious injuries and/or loss of tooth or periodontal tissues may significantly impact aesthetic appearance, essential oral functions and the quality of life. Regenerative dentistry holds great promise in treating oral/dental disorders. The past decade has witnessed a rapid expansion of our understanding of the biological features of dental stem cells, along with the signaling mechanisms governing stem cell self-renewal and differentiation. In this review, we first summarize the biological characteristics of seven types of dental stem cells, including dental pulp stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, periodontal ligament stem cells, alveolar bone-derived mesenchymal stem cells (MSCs), and MSCs from gingiva. We then focus on how these stem cells are regulated by bone morphogenetic protein (BMP) and/or Wnt signaling by examining the interplays between these pathways. Lastly, we analyze the current status of dental tissue engineering strategies that utilize oral/dental stem cells by harnessing the interplays between BMP and Wnt pathways. We also highlight the challenges that must be addressed before the dental stem cells may reach any clinical applications. Thus, we can expect to witness significant progresses to be made in regenerative dentistry in the coming decade.

Bone morphogenetic protein 9 (BMP9) induces effective bone formation from reversibly immortalized multipotent adipose-derived (iMAD) mesenchymal stem cells

Regenerative medicine and bone tissue engineering using mesenchymal stem cells (MSCs) hold great promise as an effective approach to bone and skeletal reconstruction. While adipose tissue harbors MSC-like progenitors, or multipotent adipose-derived cells (MADs), it is important to identify and characterize potential biological factors that can effectively induce osteogenic differentiation of MADs. To overcome the time-consuming and technically challenging process of isolating and culturing primary MADs, here we establish and characterize the reversibly immortalized mouse multipotent adipose-derived cells (iMADs). The isolated mouse primary inguinal MAD cells are reversibly immortalized via the retrovirus-mediated expression of SV40 T antigen flanked with FRT sites. The iMADs are shown to express most common MSC markers. FLP-mediated removal of SV40 T antigen effectively reduces the proliferative activity and cell survival of iMADs, indicating the immortalization is reversible. Using the highly osteogenic BMP9, we find that the iMADs are highly responsive to BMP9 stimulation, express multiple lineage regulators, and undergo osteogenic differentiation in vitro upon BMP9 stimulation. Furthermore, we demonstrate that BMP9-stimulated iMADs form robust ectopic bone with a thermoresponsive biodegradable scaffold material. Collectively, our results demonstrate that the reversibly immortalized iMADs exhibit the characteristics of multipotent MSCs and are highly responsive to BMP9-induced osteogenic differentiation. Thus, the iMADs should provide a valuable resource for the study of MAD biology, which would ultimately enable us to develop novel and efficacious strategies for MAD-based bone tissue engineering.

Adenovirus-mediated expression of vascular endothelial growth factor-a potentiates bone morphogenetic protein9-induced osteogenic differentiation and bone formation

Mesenchymal stem cells (MSCs) are suitable seed cells for bone tissue engineering because they can self-renew and undergo differentiation into osteogenic, adipogenic, chondrogenic, or myogenic lineages. Vascular endothelial growth factor-a (VEGF-a), an angiogenic factor, is also involved in osteogenesis and bone repair. However, the effects of VEGF-a on osteogenic MSCs differentiation remain unknown. It was previously reported that bone morphogenetic protein9 (BMP9) is one of the most important osteogenic BMPs. Here, we investigated the effects of VEGF-a on BMP9-induced osteogenesis with mouse embryo fibroblasts (MEFs). We found that endogenous VEGF-a expression was undetectable in MSCs. Adenovirus-mediated expression of VEGF-a in MEFs potentiated BMP9-induced early and late osteogenic markers, including alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). In stem cell implantation assays, VEGF-a augmented BMP9-induced ectopic bone formation. VEGF-a in combination with BMP9 effectively increased the bone volume and osteogenic activity. However, the synergistic effect was efficiently abolished by the phosphoinositide 3-kinase (PI3K)/AKT inhibitor LY294002. These results demonstrated that BMP9 may crosstalk with VEGF-a through the PI3K/AKT signaling pathway to induce osteogenic differentiation in MEFs. Thus, our findings demonstrate the effects of VEGF-a on BMP9-induced bone formation and provide a new potential strategy for treating nonunion fractures, large segmental bony defects, and/or osteoporotic fractures.

KSHV-Mediated Angiogenesis in Tumor Progression

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), is a malignant human oncovirus belonging to the gamma herpesvirus family. HHV-8 is closely linked to the pathogenesis of Kaposi's sarcoma (KS) and two other B-cell lymphoproliferative diseases: primary effusion lymphoma (PEL) and a plasmablastic variant of multicentric Castleman's disease (MCD). KS is an invasive tumor of endothelial cells most commonly found in untreated HIV-AIDS or immuno-compromised individuals. KS tumors are highly vascularized and have abnormal, excessive neo-angiogenesis, inflammation, and proliferation of infected endothelial cells. KSHV directly induces angiogenesis in an autocrine and paracrine fashion through a complex interplay of various viral and cellular pro-angiogenic and inflammatory factors. KS is believed to originate due to a combination of KSHV's efficient strategies for evading host immune systems and several pro-angiogenic and pro-inflammatory stimuli. In addition, KSHV infection of endothelial cells produces a wide array of viral oncoproteins with transforming capabilities that regulate multiple host-signaling pathways involved in the activation of angiogenesis. It is likely that the cellular-signaling pathways of angiogenesis and lymph-angiogenesis modulate the rate of tumorigenesis induction by KSHV. This review summarizes the current knowledge on regulating KSHV-mediated angiogenesis by integrating the findings reported thus far on the roles of host and viral genes in oncogenesis, recent developments in cell-culture/animal-model systems, and various anti-angiogenic therapies for treating KSHV-related lymphoproliferative disorders.

A thermoresponsive polydiolcitrate-gelatin scaffold and delivery system mediates effective bone formation from BMP9-transduced mesenchymal stem cells

Successful bone tissue engineering requires at the minimum sufficient osteoblast progenitors, efficient osteoinductive factors, and biocompatible scaffolding materials. We previously demonstrated that bone morphogenetic protein 9 (BMP9) is one of the most potent factors in inducing osteogenic differentiation of mesenchymal stem cells (MSCs). Here, we investigated the potential use of a biodegradable citrate-based thermosensitive macromolecule, poly(polyethyleneglycol citrate-co-N-isopropylacrylamide) (PPCN) mixed with gelatin (PPCNG) as a scaffold for the delivery of BMP9-stimulated MSCs to promote localized bone formation. The addition of gelatin to PPCN effectively enhanced the cell adhesion and survival properties of MSCs entrapped within the gel in 3D culture. Using the BMP9-transduced MSC line immortalized mouse embryonic fibroblasts (iMEFs), we found that PPCNG facilitated BMP9-induced osteogenic differentiation of iMEFs in vivo and promoted the formation of well-ossified and vascularized trabecular bone-like structures in a mouse model of ectopic bone formation. Histologic evaluation revealed that vascularization of the bony masses retrieved from the iMEFs  +  PPCNG group was significantly more pronounced than that of the direct cell injection group. Accordingly, vascular endothelial growth factor (VEGF) expression was shown to be significantly higher in the bony masses recovered from the iMEFs  +  PPCNG group. Taken together, our results suggest that PPCNG may serve as a novel biodegradable and injectable scaffold and carrier for gene and cell-based bone tissue engineering.

Characterization of Notch Signaling During Osteogenic Differentiation in Human Osteosarcoma Cell Line MG63

Osteogenic differentiation is a multi-step process controlled by a complex molecular framework. Notch is an evolutionarily conserved intercellular signaling pathway playing a prominent role in cell fate and differentiation, although the mechanisms by which this pathway regulates osteogenesis remain controversial. This study aimed to investigate, in vitro, the involvement of Notch pathway during all the developmental stages of osteogenic differentiation in human osteosarcoma cell line MG63. Cells were cultured in basal condition (control) and in osteoinductive medium (OM). Notch inhibitors were also added in OM to block Notch pathway. During osteogenic differentiation, early (alkaline phosphatase activity and collagen type I) and late osteogenic markers (osteocalcin levels and matrix mineralization), as well as the gene expression of the main osteogenic transcription factors (Runx2, Osterix, and Dlx5) increased. Time dependent changes in the expression of specific Notch receptors were identified in OM versus control with a significant reduction in the expression of Notch1 and Notch3 receptors in the early phase of differentiation, and an increase of Notch2 and Notch4 receptors in the late phase. Among Notch nuclear target genes, Hey1 expression was significantly higher in OM than control, while Hes5 expression decreased. Osteogenic markers were reduced and Hey1 was significantly inhibited by Notch inhibitors, suggesting a role for Notch through the canonical pathway. In conclusion, Notch pathway might be involved with a dual role in osteogenesis of MG63, through the activation of Notch2, Notch4, and Hey1, inducing osteoblast differentiation and the depression of Notch1, Notch3, and Hes5, maintaining an undifferentiated status. J. Cell. Physiol. 231: 2652-2663, 2016. © 2016 Wiley Periodicals, Inc.

LPS-stimulated inflammation inhibits BMP-9-induced osteoblastic differentiation through crosstalk between BMP/MAPK and Smad signaling

Inflammation is a common situation during bone healing and is recognized to inhibit osteogenic differentiation and bone formation. However, the effect of inflammation on BMP-9-induced osteoblastic differentiation remains unclear. In the present study, we found that an inflammatory environment triggered by lipopolysaccharide (LPS) in vitro suppressed BMP-9-induced osteogenic differentiation. In addition, LPS decreased BMP-9-induced phosphorylation of Smad1/5/8 and showed obvious inhibitory effects on BMP-9-induced Smad signaling. We then confirmed that LPS and BMP-9 can activate p38MAPK and ERK1/2 signaling, and that LPS stimulation reduces BMP-9-induced Runx2 expression through the activation of p38MAPK and ERK1/2 signaling. Finally, we determined that blockade of MAPK signaling by specific inhibitors reverses the inhibitory effect of LPS on BMP-9-induced osteogenic differentiation, and that MAPK acts as a mediator of the negative regulatory role of LPS in BMP-9-induced activation of Smad signaling. Based on these results, we conclude that the LPS-mediated inflammatory environment inhibits BMP-9-induced osteogenic differentiation, via crosstalk between BMP/MAPK and Smad signaling. The elucidation of these mechanisms may hasten the development of new strategies and improve the osteoinductive efficacy of BMP-9 in the clinic, resulting in enhanced osteoblastic differentiation and bone formation.

The Prodomain-Containing BMP9 Produced from a Stable Line Effectively Regulates the Differentiation of Mesenchymal Stem Cells

BACKGROUND

BMPs play important roles in regulating stem cell proliferation and differentiation. Using adenovirus-mediated expression of the 14 types of BMPs we demonstrated that BMP9 is one of the most potent BMPs in inducing osteogenic differentiation of mesenchymal stem cells (MSCs), which was undetected in the early studies using recombinant BMP9 proteins. Endogenous BMPs are expressed as a precursor protein that contains an N-terminal signal peptide, a prodomain and a C-terminal mature peptide. Most commercially available recombinant BMP9 proteins are purified from the cells expressing the mature peptide. It is unclear how effectively these recombinant BMP9 proteins functionally recapitulate endogenous BMP9.

METHODS

A stable cell line expressing the full coding region of mouse BMP9 was established in HEK-293 cells by using the piggyBac transposon system. The biological activities and stability of the conditioned medium generated from the stable line were analyzed.

RESULTS

The stable HEK-293 line expresses a high level of mouse BMP9. BMP9 conditioned medium (BMP9-cm) was shown to effectively induce osteogenic differentiation of MSCs, to activate BMP-R specific Smad signaling, and to up-regulate downstream target genes in MSCs. The biological activity of BMP9-cm is at least comparable with that induced by AdBMP9 in vitro. Furthermore, BMP9-cm exhibits an excellent stability profile as its biological activity is not affected by long-term storage at -80ºC, repeated thawing cycles, and extended storage at 4ºC.

CONCLUSIONS

We have established a producer line that stably expresses a high level of active BMP9 protein. Such producer line should be a valuable resource for generating biologically active BMP9 protein for studying BMP9 signaling mechanism and functions.

Mechanism of BMP9 promotes growth of osteosarcoma mediated by the Notch signaling pathway

Bone morphogenetic protein 9 (BMP9), also known as growth differentiation factor 2, plays a key role in promoting osteosarcoma growth. However, the underlying mechanism remains to be determined. The aim of the present study was to determine the mechanism of BMP9 promoting the growth of osteosarcoma mediated by the Notch signaling pathway. Osteosarcoma cell lines, 143B and MG63, were used for the in vitro experiments. Cell proliferation, cell migration and cell cycle transformation were monitored under various settings. The control and experimental groups used in the present study were BMP9 adenovirus (AdBMP9), a recombinant adenovirus expressing the dominant-negative mutant of Notch1 (AdR-dnNotch1), AdBMP9+AdR-dnNotch1 and AdBMP9+compound E (blocker of the Notch signaling pathway). The results showed that Notch ligands DLL1, JAG1 and JAG2, as well as Notch receptors Notch1, Notch2 and Notch3 were markedly expressed in the two cell lines. Cell proliferation and migration ability increased in the AdBMP9 group and were higher than that in the AdBMP9+AdR-dn Notch1 and AdBMP9+compound E group. Cell proliferation and migration in the AdR-dnNothc1 group was lower than that in the AdBMP9 group, although the differences were not statistically significant (P>0.05). The cell cycle ratio in the S/G2 phase increased significantly in the AdBMP9 group and was higher than that in the AdBMP9+AdR-dnNotch1 and AdBMP9+compound E groups. By contrast, the ratio of the cell cycle in S/G2 phase in the AdR-dnNotch1 group was lower than that in the AdBMP9 group. The differences were not statistically significant (P>0.05). In conclusion, the results showed that the Notch signaling pathway plays an important role in mediating the growth of osteosarcoma promoted by BMP9.

Synergistic Effects of BMP9 and miR-548d-5p on Promoting Osteogenic Differentiation of Mesenchymal Stem Cells

Various stimulators have been reported to promote MSC osteogenic differentiation via different pathways such as bone morphogenetic protein 9 (BMP9) through influencing COX-2 and miR-548d-5p through targeting peroxisome proliferator-activated receptor-γ (PPARγ). Whether synergistic effects between BMP9 and miR-548d-5p existed in promoting osteogenesis from MSCs was unclear. In the study, the potential synergistic effects of BMP9 and miR-548d-5p on human MSC differentiation were investigated. Osteogenic differentiation of MSCs treated with BMP9 or miR-548d-5p was detected with multimodality of methods. The results demonstrated that BMP9 and miR-548d-5p significantly influenced COX-2 and PPARγ, respectively. BMP9 also influenced the expression of PPARγ, but no significant effect of miR-548d-5p on COX-2 was observed. When BMP9 and miR-548d-5p were combined, more potent effects on both COX-2 and PPARγ were observed than BMP9 or miR-548d-5p alone. Consistently, osteogenic analysis at different timepoints demonstrated that osteogenic genes, ALP activity, calcium deposition, OPN protein, and matrix mineralization were remarkably upregulated by BMP9/miR-548d-5p compared with BMP9 or miR-548d-5p alone, indicating the synergetic effects of BMP9 and miR-548d-5p on osteogenic differentiation of MSCs. Our study demonstrated that regulating different osteogenic regulators may be an effective strategy to promote bone tissue regeneration for bone defects.

miR-21 synergizes with BMP9 in osteogenic differentiation by activating the BMP9/Smad signaling pathway in murine multilineage cells

Bone morphogenetic proteins (BMPs), particularly BMP9, have been shown to promote the osteogenic differentiation of murine multilineage cells (MMCs) and to promote bone formation in bone diseases; however, the mechanisms involved remain poorly understood. MicroRNAs (miRNAs or miRs) have been proven to regulate mesenchymal stem cell (MSC) differentiation. In this study, we identified a novel mechanism that unravels the functional axis of a key miRNA (miR-21) which contributes to BMP9-induced osteogenic differentiation. We screened differentially expressed miRNAs in MMCs during BMP9-induced osteogenic differentiation and found that miR-21 was significantly upregulated by BMP9 during the osteogenesis of MMCs. Furthermore, miR-21 was confirmed to promote the osteogenic differentiation of the MMCs by suppressing Smad7, which negatively regulates the osteogenic differentiation of MMCs. The upregulation of miR-21 may promote the osteogenic differentiation of MMCs in synergy with BMP9. The findings of our study revealed a novel function of miR-21, and suggest that the overexpression of miR-21 contributes to bone formation by promoting BMP9-induced osteogenic differentiation. Our data may provide a molecular basis for the development of novel therapeutic strategies to treat bone diseases, such as osteoporosis and other inflammatory bone diseases.

CA-074Me compound inhibits osteoclastogenesis via suppression of the NFATc1 and c-FOS signaling pathways

The osteoclast is an integral cell of bone resorption. Since osteolytic disorders hinge on the function and dysfunction of the osteoclast, understanding osteoclast biology is fundamental to designing new therapies that curb osteolytic disorders. The identification and study of lysosomal proteases, such as cathepsins, have shed light on mechanisms of bone resorption. For example, Cathepsin K has already been identified as a collagen degradation protease produced by mature osteoclasts with high activity in the acidic osteoclast resorption pits. Delving into the mechanisms of cathepsins and other osteoclast related compounds provides new targets to explore in osteoclast biology. Through our anti-osteoclastogenic compound screening experiments we encountered a modified version of the Cathepsin B inhibitor CA-074: the cell membrane-permeable CA-074Me (L-3-trans-(Propylcarbamoyl) oxirane-2-carbonyl]-L-isoleucyl-L-proline Methyl Ester). Here we confirm that CA-074Me inhibits osteoclastogenesis in vivo and in vitro in a dose-dependent manner. However, Cathepsin B knockout mice exhibited unaltered osteoclastogenesis, suggesting a more complicated mechanism of action than Cathepsin B inhibition. We found that CA-074Me exerts its osteoclastogenic effect within 24 h of osteoclastogenesis stimulation by suppression of c-FOS and NFATc1 pathways.

TqPCR: A Touchdown qPCR Assay with Significantly Improved Detection Sensitivity and Amplification Efficiency of SYBR Green qPCR

The advent of fluorescence-based quantitative real-time PCR (qPCR) has revolutionized the quantification of gene expression analysis in many fields, including life sciences, agriculture, forensic science, molecular diagnostics, and medicine. While SYBR Green-based qPCR is the most commonly-used platform due to its inexpensive nature and robust chemistry, quantifying the expression of genes with low abundance or RNA samples extracted from highly restricted or limited sources can be challenging because the detection sensitivity of SYBR Green-based qPCR is limited. Here, we develop a novel and effective touchdown qPCR (TqPCR) protocol by incorporating a 4-cycle touchdown stage prior to the quantification amplification stage. Using the same cDNA templates, we find that TqPCR can reduce the average Cq values for Gapdh, Rps13, and Hprt1 reference genes by 4.45, 5.47, and 4.94 cycles, respectively, when compared with conventional qPCR; the overall average Cq value reduction for the three reference genes together is 4.95. We further find that TqPCR can improve PCR amplification efficiency and thus increase detection sensitivity. When the quantification of Wnt3A-induced target gene expression in mesenchymal stem cells is analyzed, we find that, while both conventional qPCR and TqPCR can detect the up-regulation of the relatively abundant target Axin2, only TqPCR can detect the up-regulation of the lowly-expressed targets Oct4 and Gbx2. Finally, we demonstrate that the MRQ2 and MRQ3 primer pairs derived from mouse reference gene Tbp can be used to validate the RNA/cDNA integrity of qPCR samples. Taken together, our results strongly suggest that TqPCR may increase detection sensitivity and PCR amplification efficiency. Overall, TqPCR should be advantageous over conventional qPCR in expression quantification, especially when the transcripts of interest are lowly expressed, and/or the availability of total RNA is highly restricted or limited.

TrAmplification of Human Dental Follicle Cells by piggyBac Transposon - Mediated Reversible Immortalization System

Dental follicle cells (DFCs) are the precursor cells of periodontium. Under certain differentiation conditions, DFCs can be induced to differentiate into chondrogenic, osteogenic and adipogenic cells. However, DFCs has limited lifespan in vitro, so it's difficult to harvest enough cells for basic research and translational application. pMPH86 is a piggyBac transposon-mediated vector which contains SV40 T-Ag cassette that can be removed by flippase recognition target (FRT) recombinase. Here we demonstrated the pMPH86 can effectively amplify human DFCs through reversible immortalization. The immortalized DFCs (iDFCs) exhibit higher proliferate activity, which can be reversed to its original level before immortalization when deimmortalized by FLP recombinase. The iDFCs and deimmortalized DFCs (dDFCs) express most DFC markers and maintain multiple differentiation potential in vitro as they can be induced by BMP9 to differentiate into chondrogenic, osteogenic and adipogenic cells evidenced by gene expression and protein marker. We also proved telomerase activity of iDFCs are significantly increased and maintained at a high level, while the telomerase activity of primary DFCs was relatively low and decreased with every passage. After SV40 T-Ag was removed to deimmortalize the cells, telomerase activity was reduced to its original level before immortalization and decreased with passages just the same as primary DFCs. These results suggest that piggyBac immortalization system could be a potential strategy to amplify primary cells, which is critical for regenerative research and further clinical application.

Hairy/enhancer-of-split related with YRPW motif protein 1 promotes osteosarcoma metastasis via matrix metallopeptidase 9 expression

BACKGROUND

Activation of the Notch pathway has been reported in various types of cancers. However, the role of the hairy/enhancer-of-split related with YRPW motif protein 1 (HEY1) in osteosarcoma is unknown. We examined the function of HEY1 in osteosarcoma.

METHODS

Expression of HEY1 was studied in human osteosarcoma. The effects of HEY1 in osteosarcoma were evaluated in vitro and in a xenograft model. Moreover, we examined the function of matrix metallopeptidase 9 (MMP9) as a downstream effector of HEY1.

RESULTS

HEY1 was upregulated in human osteosarcoma. Knockdown of HEY1 inhibited the invasion of osteosarcoma cell lines. In contrast, the forced expression of HEY1 increased the invasion of mesenchymal stem cell. In addition, lung metastases were significantly inhibited by the knockdown of HEY1. We found that MMP9 was a downstream effector of HEY1 that promotes the invasion of osteosarcoma cells. Knockdown of HEY1 decreased the expression of MMP9. Addition of MMP9 rescued the invasion of osteosarcoma cells that had been rendered less invasive by knockdown of HEY1 expression.

CONCLUSIONS

Our findings suggested that HEY1 augmented the metastasis of osteosarcoma via upregulation of MMP9 expression. Therefore, inhibition of HEY1 may be a novel therapeutic strategy for preventing osteosarcoma metastasis.

Sustained high level transgene expression in mammalian cells mediated by the optimized piggyBac transposon system

Sustained, high level transgene expression in mammalian cells is desired in many cases for studying gene functions. Traditionally, stable transgene expression has been accomplished by using retroviral or lentiviral vectors. However, such viral vector-mediated transgene expression is often at low levels and can be reduced over time due to low copy numbers and/or chromatin remodeling repression. The piggyBac transposon has emerged as a promising non-viral vector system for efficient gene transfer into mammalian cells. Despite its inherent advantages over lentiviral and retroviral systems, piggyBac system has not been widely used, at least in part due to their limited manipulation flexibilities. Here, we seek to optimize piggyBac-mediated transgene expression and generate a more efficient, user-friendly piggyBac system. By engineering a panel of versatile piggyBac vectors and constructing recombinant adenoviruses expressing piggyBac transposase (PBase), we demonstrate that adenovirus-mediated PBase expression significantly enhances the integration efficiency and expression level of transgenes in mesenchymal stem cells and osteosarcoma cells, compared to that obtained from co-transfection of the CMV-PBase plasmid. We further determine the drug selection timeline to achieve optimal stable transgene expression. Moreover, we demonstrate that the transgene copy number of piggyBac-mediated integration is approximately 10 times higher than that mediated by retroviral vectors. Using the engineered tandem expression vector, we show that three transgenes can be simultaneously expressed in a single vector with high efficiency. Thus, these results strongly suggest that the optimized piggyBac system is a valuable tool for making stable cell lines with sustained, high transgene expression.

Distinct effects of platelet-rich plasma and BMP13 on rotator cuff tendon injury healing in a rat model

BACKGROUND

Although platelet-rich plasma (PRP) is used clinically to augment tendon healing, bone morphogenetic protein-13 (BMP13) may provide a better therapeutic avenue to improve early tendon healing and repair.

HYPOTHESIS

Exogenous expression of BMP13 in tenocytes will up-regulate genes involved in tendon healing. Direct delivery of adenovirus-mediated BMP13 (AdBMP13) into the injured rat supraspinatus tendon will increase biomechanical properties.

STUDY DESIGN

Controlled laboratory study.

METHODS

Exogenous expression of BMP13 and the major growth factors in PRP (transforming growth factor-β1 [TGF-β1], vascular endothelial growth factor-A [VEGF-A], and platelet-derived growth factor-BB [PDGF-BB]) was accomplished by using recombinant adenoviral vectors. The expression of tendon- and matrix-associated genes in growth factor-treated tenocytes was analyzed by use of semiquantitative reverse-transcription polymerase chain reaction. A total of 32 rats with supraspinatus defect were divided into 4 groups and injected with adenovirus-containing green fluorescent protein (AdGFP; negative control), PRP, AdBMP13, or PRP+AdBMP13. All rats were sacrificed at 2 weeks after surgery, and tendons were harvested for biomechanical testing and histologic analysis.

RESULTS

BMP13 up-regulated type III collagen expression compared with AdGFP control and PRP growth factors (P < .01). BMP13 and PRP growth factors each up-regulated fibronectin expression (P < .01). There was an increase in stress to failure in each of the 3 treatment groups (P < .05 for PRP; P < .01 for AdBMP13 or PRP+AdBMP13) compared with AdGFP control. AdBMP13 demonstrated higher stress to failure than did the PRPs (P < .01). The addition of PRP did not increase the BMP13-enhanced stress to failure or stiffness. The biomechanical results were further supported by histologic analysis of the retrieved samples.

CONCLUSION

Exogenous expression of BMP13 enhances tendon healing more effectively than PRP as assessed by tendon- and matrix-associated gene expression, biomechanical testing, and histologic analysis.

CLINICAL RELEVANCE

While PRP is used in the clinical setting, BMP13 may be explored as a superior biofactor to improve rotator cuff tendon healing and reduce the incidence of retears.

Canonical Wnt signaling acts synergistically on BMP9-induced osteo/odontoblastic differentiation of stem cells of dental apical papilla (SCAPs)

Dental pulp/dentin regeneration using dental stem cells combined with odontogenic factors may offer great promise to treat and/or prevent premature tooth loss. Here, we investigate if BMP9 and Wnt/β-catenin act synergistically on odontogenic differentiation. Using the immortalized SCAPs (iSCAPs) isolated from mouse apical papilla tissue, we demonstrate that Wnt3A effectively induces early osteogenic marker alkaline phosphatase (ALP) in iSCAPs, which is reduced by β-catenin knockdown. While Wnt3A and BMP9 enhance each other's ability to induce ALP activity in iSCAPs, silencing β-catenin significantly diminishes BMP9-induced osteo/odontogenic differentiation. Furthermore, silencing β-catenin reduces BMP9-induced expression of osteocalcin and osteopontin and in vitro matrix mineralization of iSCAPs. In vivo stem cell implantation assay reveals that while BMP9-transduced iSCAPs induce robust ectopic bone formation, iSCAPs stimulated with both BMP9 and Wnt3A exhibit more mature and highly mineralized trabecular bone formation. However, knockdown of β-catenin in iSCAPs significantly diminishes BMP9 or BMP9/Wnt3A-induced ectopic bone formation in vivo. Thus, our results strongly suggest that β-catenin may play an important role in BMP9-induced osteo/ondontogenic signaling and that BMP9 and Wnt3A may act synergistically to induce osteo/odontoblastic differentiation of iSCAPs. It's conceivable that BMP9 and/or Wnt3A may be explored as efficacious biofactors for odontogenic regeneration and tooth engineering.

A simplified and versatile system for the simultaneous expression of multiple siRNAs in mammalian cells using Gibson DNA Assembly

RNA interference (RNAi) denotes sequence-specific mRNA degradation induced by short interfering double-stranded RNA (siRNA) and has become a revolutionary tool for functional annotation of mammalian genes, as well as for development of novel therapeutics. The practical applications of RNAi are usually achieved by expressing short hairpin RNAs (shRNAs) or siRNAs in cells. However, a major technical challenge is to simultaneously express multiple siRNAs to silence one or more genes. We previously developed pSOS system, in which siRNA duplexes are made from oligo templates driven by opposing U6 and H1 promoters. While effective, it is not equipped to express multiple siRNAs in a single vector. Gibson DNA Assembly (GDA) is an in vitro recombination system that has the capacity to assemble multiple overlapping DNA molecules in a single isothermal step. Here, we developed a GDA-based pSOK assembly system for constructing single vectors that express multiple siRNA sites. The assembly fragments were generated by PCR amplifications from the U6-H1 template vector pB2B. GDA assembly specificity was conferred by the overlapping unique siRNA sequences of insert fragments. To prove the technical feasibility, we constructed pSOK vectors that contain four siRNA sites and three siRNA sites targeting human and mouse β-catenin, respectively. The assembly reactions were efficient, and candidate clones were readily identified by PCR screening. Multiple β-catenin siRNAs effectively silenced endogenous β-catenin expression, inhibited Wnt3A-induced β-catenin/Tcf4 reporter activity and expression of Wnt/β-catenin downstream genes. Silencing β-catenin in mesenchymal stem cells inhibited Wnt3A-induced early osteogenic differentiation and significantly diminished synergistic osteogenic activity between BMP9 and Wnt3A in vitro and in vivo. These findings demonstrate that the GDA-based pSOK system has been proven simplistic, effective and versatile for simultaneous expression of multiple siRNAs. Thus, the reported pSOK system should be a valuable tool for gene function studies and development of novel therapeutics.

Cartilage oligomeric matrix protein gene multilayers inhibit osteogenic differentiation and promote chondrogenic differentiation of mesenchymal stem cells

There are still many challenges to acquire the optimal integration of biomedical materials with the surrounding tissues. Gene coatings on the surface of biomaterials may offer an effective approach to solve the problem. In order to investigate the gene multilayers mediated differentiation of mesenchymal stem cells (MSCs), gene functionalized films of hyaluronic acid (HA) and lipid-DNA complex (LDc) encoding cartilage oligomeric matrix protein (COMP) were constructed in this study via the layer-by-layer self-assembly technique. Characterizations of the HA/DNA multilayered films indicated the successful build-up process. Cells could be directly transfected by gene films and a higher expression could be obtained with the increasing bilayer number. The multilayered films were stable for a long period and DNA could be easily released in an enzymatic condition. Real-time polymerase chain reaction (RT-PCR) assay presented significantly higher (p < 0.01) COMP expression of MSCs cultured with HA/COMP multilayered films. Compared with control groups, the osteogenic gene expression levels of MSCs with HA/COMP multilayered films were down-regulated while the chondrogenic gene expression levels were up-regulated. Similarly, the alkaline phosphatase (ALP) staining and Alizarin red S staining of MSCs with HA/COMP films were weakened while the alcian blue staining was enhanced. These results demonstrated that HA/COMP multilayered films could inhibit osteogenic differentiation and promote chondrogenic differentiation of MSCs, which might provide new insight for physiological ligament-bone healing.

Bone morphogenetic protein 2 inhibits the proliferation and growth of human colorectal cancer cells

Colorectal cancer (CRC) is one of the most deadly cancers worldwide. Significant progress has been made in understanding the molecular pathogenesis of CRC, which has led to successful early diagnosis, surgical intervention and combination chemotherapy. However, limited therapeutic options are available for metastatic and/or drug-resistant CRC. While the aberrantly activated Wnt/β-catenin pathway plays a critical initiating role in CRC development, disruption of the bone morphogenetic protein (BMP) pathway causes juvenile polyposis syndrome, suggesting that BMP signaling may play a role in CRC development. However, conflicting results have been reported concerning the possible roles of BMP signaling in sporadic colon cancer. Here, we investigated the effect of BMP2 on the proliferation, migration, invasiveness and tumor growth capability of human CRC cells. Using an adenovirus vector that overexpresses BMP2 and the piggyBac transposon-mediated stable BMP2 overexpression CRC line, we found that exogenous BMP2 effectively inhibited HCT116 cell proliferation and colony formation. BMP2 was shown to suppress colon cancer cell migration and invasiveness. Under a low serum culture condition, forced expression of BMP2 induced a significantly increased level of apoptosis in HCT116 cells. Using a xenograft tumor model, we found that forced expression of BMP2 in HCT116 cells suppressed tumor growth, accompanied by decreased cell proliferation activity. Taken together, our results strongly suggest that BMP2 plays an important inhibitory role in governing the proliferation and aggressive features of human CRC cells.

The piggyBac transposon-mediated expression of SV40 T antigen efficiently immortalizes mouse embryonic fibroblasts (MEFs)

Mouse embryonic fibroblasts (MEFs) are mesenchymal stem cell (MSC)-like multipotent progenitor cells and can undergo self-renewal and differentiate into to multiple lineages, including bone, cartilage and adipose. Primary MEFs have limited life span in culture, which thus hampers MEFs’ basic research and translational applications. To overcome this challenge, we investigate if piggyBac transposon-mediated expression of SV40 T antigen can effectively immortalize mouse MEFs and that the immortalized MEFs can maintain long-term cell proliferation without compromising their multipotency. Using the piggyBac vector MPH86 which expresses SV40 T antigen flanked with flippase (FLP) recognition target (FRT) sites, we demonstrate that mouse embryonic fibroblasts (MEFs) can be efficiently immortalized. The immortalized MEFs (piMEFs) exhibit an enhanced proliferative activity and maintain long-term cell proliferation, which can be reversed by FLP recombinase. The piMEFs express most MEF markers and retain multipotency as they can differentiate into osteogenic, chondrogenic and adipogenic lineages upon BMP9 stimulation in vitro. Stem cell implantation studies indicate that piMEFs can form bone, cartilage and adipose tissues upon BMP9 stimulation, whereas FLP-mediated removal of SV40 T antigen diminishes the ability of piMEFs to differentiate into these lineages, possibly due to the reduced expansion of progenitor populations. Our results demonstrate that piggyBac transposon-mediated expression of SV40 T can effectively immortalize MEFs and that the reversibly immortalized piMEFs not only maintain long-term cell proliferation but also retain their multipotency. Thus, the high transposition efficiency and the potential footprint-free natures may render piggyBac transposition an effective and safe strategy to immortalize progenitor cells isolated from limited tissue supplies, which is essential for basic and translational studies.

Multipotential differentiation of human urine-derived stem cells: potential for therapeutic applications in urology

We sought to biologically characterize and identify a subpopulation of urine-derived stem cells (USCs) with the capacity for multipotent differentiation. We demonstrated that single USCs can expand to a large population with 60-70 population doublings. Nine of 15 individual USC clones expressed detectable levels of telomerase and have long telomeres. These cells expressed pericyte and mesenchymal stem cell markers. Upon induction with appropriate media in vitro, USCs differentiated into bladder-associated cell types, including functional urothelial and smooth muscle cell lineages. When the differentiated USCs were seeded onto a scaffold and subcutaneously implanted into nude mice, multilayered tissue-like structures formed consisting of urothelium and smooth muscle. Additionally, USCs were able to differentiate into endothelial, osteogenic, chondrogenic, adipogenic, skeletal myogenic, and neurogenic lineages but did not form teratomas during the 1-month study despite telomerase activity. USCs may be useful in cell-based therapies and tissue engineering applications, including urogenital reconstruction.

Reversibly Immortalized Mouse Articular Chondrocytes Acquire Long-Term Proliferative Capability While Retaining Chondrogenic Phenotype

Cartilage tissue engineering holds great promise for treating cartilaginous pathologies including degenerative disorders and traumatic injuries. Effective cartilage regeneration requires an optimal combination of biomaterial scaffolds, chondrogenic seed cells, and biofactors. Obtaining sufficient chondrocytes remains a major challenge due to the limited proliferative capability of primary chondrocytes. Here we investigate if reversibly immortalized mouse articular chondrocytes (iMACs) acquire long-term proliferative capability while retaining the chondrogenic phenotype. Primary mouse articular chondrocytes (MACs) can be efficiently immortalized with a retroviral vector-expressing SV40 large T antigen flanked with Cre/loxP sites. iMACs exhibit long-term proliferation in culture, although the immortalization phenotype can be reversed by Cre recombinase. iMACs express the chondrocyte markers Col2a1 and aggrecan and produce chondroid matrix in micromass culture. iMACs form subcutaneous cartilaginous masses in athymic mice. Histologic analysis and chondroid matrix staining demonstrate that iMACs can survive, proliferate, and produce chondroid matrix. The chondrogenic growth factor BMP2 promotes iMACs to produce more mature chondroid matrix resembling mature articular cartilage. Taken together, our results demonstrate that iMACs acquire long-term proliferative capability without losing the intrinsic chondrogenic features of MACs. Thus, iMACs provide a valuable cellular platform to optimize biomaterial scaffolds for cartilage regeneration, to identify biofactors that promote the proliferation and differentiation of chondrogenic progenitors, and to elucidate the molecular mechanisms underlying chondrogenesis.

Overexpression of Ad5 precursor terminal protein accelerates recombinant adenovirus packaging and amplification in HEK-293 packaging cells

Recombinant adenoviruses are one of the most common vehicles for efficient in vitro and in vivo gene deliveries. Here, we investigate whether exogenous precursor terminal protein (pTP) expression in 293 cells improves the efficiency of adenovirus packaging and amplification. We used a piggyBac transposon-based vector and engineered a stable 293 line that expresses high level of Ad5 pTP, designated as 293pTP. Using the AdBMP6-GLuc that expresses green fluorescent protein (GFP), BMP6 and Gaussia luciferase, we found that the infectivity of AdBMP6-GLuc viral samples packaged in 293pTP cells was titrated up to 19.3 times higher than that packaged in parental 293 cells. AdBMP6-GLuc viral samples packaged in 293pTP cells exhibited significantly higher transduction efficiency in 143B and immortalized mouse embryonic fibroblast (iMEF) cells, as assessed by fluorescence-activated cell sorting analysis of GFP-positive cells, the luciferase activity assay and BMP6-induced osteogenic marker alkaline phosphatase activities in iMEFs. When adenovirus amplification efficiency was analyzed, we found that 293pTP cells infected with AdBMP6-GLuc yielded up to 12.6 times higher titer than that in parental 293 cells, especially at lower multiplicities of infection. These results strongly suggest that exogenous pTP expression may accelerate the packaging and amplification of recombinant adenoviruses. Thus, the engineered 293pTP cells should be a superior packaging line for efficient adenovirus production.

Characterization of constitutive promoters for piggyBac transposon-mediated stable transgene expression in mesenchymal stem cells (MSCs)

Multipotent mesenchymal stem cells (MSCs) can undergo self-renewal and give rise to multi-lineages under given differentiation cues. It is frequently desirable to achieve a stable and high level of transgene expression in MSCs in order to elucidate possible molecular mechanisms through which MSC self-renewal and lineage commitment are regulated. Retroviral or lentiviral vector-mediated gene expression in MSCs usually decreases over time. Here, we choose to use the piggyBac transposon system and conduct a systematic comparison of six commonly-used constitutive promoters for their abilities to drive RFP or firefly luciferase expression in somatic HEK-293 cells and MSC iMEF cells. The analyzed promoters include three viral promoters (CMV, CMV-IVS, and SV40), one housekeeping gene promoter (UbC), and two composite promoters of viral and housekeeping gene promoters (hEFH and CAG-hEFH). CMV-derived promoters are shown to drive the highest transgene expression in HEK-293 cells, which is however significantly reduced in MSCs. Conversely, the composite promoter hEFH exhibits the highest transgene expression in MSCs whereas its promoter activity is modest in HEK-293 cells. The reduced transgene expression driven by CMV promoters in MSCs may be at least in part caused by DNA methylation, or to a lesser extent histone deacetlyation. However, the hEFH promoter is not significantly affected by these epigenetic modifications. Taken together, our results demonstrate that the hEFH composite promoter may be an ideal promoter to drive long-term and high level transgene expression using the piggyBac transposon vector in progenitor cells such as MSCs.