Inductive effects of dexamethasone on the gene expression of Cbfa1, Osterix and bone matrix proteins during differentiation of cultured primary rat osteoblasts

A novel strategy for calcium magnesium phosphate/carboxymethyl chitosan composite bone cements with enhanced physicochemical properties, excellent cytocompatibility and osteogenic differentiation

Artificial bone substitutes for bone repair and reconstruction still face enormous challenges. Previous studies have shown that calcium magnesium phosphate cements (CMPCs) possess an excellent bioactive surface, but its clinical application is restricted due to short setting time. This study aimed to develop new CMPC/carboxymethyl chitosan (CMCS) comg of mixed powders of active MgO, calcined MgO and calcium dihydrogen phosphate monohydrate. With this novel strategy, it can adjust the setting time and improve the compressive strength. The results confirmed that CMPC/CMCS composite bone cements were successfully developed with a controllable setting time (18-70 min) and high compressive strength (87 MPa). In addition, the composite bone cements could gradually degrade in PBS with weight loss up to 32% at 28 d. They also promoted the proliferation of pre-osteoblasts, and induced osteogenic differentiation. The findings indicate that CMPC/CMCS composite bone cements hold great promise as a new type of bone repair material in further and in-depth studies.

Osteogenically committed hUCMSCs-derived exosomes promote the recovery of critical-sized bone defects with enhanced osteogenic properties

Low viability of seed cells and the concern about biosafety restrict the application of cell-based tissue-engineered bone (TEB). Exosomes that bear similar bioactivities to donor cells display strong stability and low immunogenicity. Human umbilical cord mesenchymal stem cells-derived exosomes (hUCMSCs-Exos) show therapeutic efficacy in various diseases. However, little is known whether hUCMSCs-Exos can be used to construct TEB to repair bone defects. Herein, PM-Exos and OM-Exos were separately harvested from hUCMSCs which were cultured in proliferation medium (PM) or osteogenic induction medium (OM). A series of in-vitro studies were performed to evaluate the bioactivities of human bone marrow mesenchymal stem cells (hBMSCs) when co-cultured with PM-Exos or OM-Exos. Differential microRNAs (miRNAs) between PM-Exos and OM-Exos were sequenced and analyzed. Furthermore, PM-Exos and OM-Exos were incorporated in 3D printed tricalcium phosphate scaffolds to build TEBs for the repair of critical-sized calvarial bone defects in rats. Results showed that PM-Exos and OM-Exos bore similar morphology and size. They expressed representative surface markers of exosomes and could be internalized by hBMSCs to promote cellular migration and proliferation. OM-Exos outweighed PM-Exos in accelerating the osteogenic differentiation of hBMSCs, which might be attributed to the differentially expressed miRNAs. Furthermore, OM-Exos sustainably released from the scaffolds, and the resultant TEB showed a better reparative outcome than that of the PM-Exos group. Our study found that exosomes isolated from osteogenically committed hUCMSCs prominently facilitated the osteogenic differentiation of hBMSCs. TEB grafts functionalized by OM-Exos bear a promising application potential for the repair of large bone defects.

Mechanical properties, and in vitro biocompatibility assessment of biomimetic dual layered keratin/ hydroxyapatite scaffolds

A novel biomimetic dual layered keratin/hydroxyapatite (keratin/HA) scaffold was designed using iterative freeze-drying technique. The prepared scaffolds were studied using several analytical techniques to better understand the biological, structural, and mechanical properties. The developed multilayered, interconnected, porous keratin scaffold with different hydroxyapatite (HA) content in the outer and inner layer, mimics the inherent gradient structure of alveolar bone. SEM studies showed an interconnected porous architecture of the prepared scaffolds with seamless integration between the upper and lower layers. The incorporation of HA improved the mechanical properties keratin/HA scaffolds. The keratin/HA scaffolds exhibited superior mechanical properties in terms of Young's modulus and compressive strength in comparison to pure keratin scaffolds. The biocompatibility studies suggested that both keratin and keratin/HA scaffolds were cyto-compatible, in terms of cell proliferation. Furthermore, it showed that both the tested materials can served as an ideal substrate for the differentiation of Saos-2 cells, leading to mineralization of the extracellular matrix. In summary, ionic liquid based green technique was employed for keratin extraction to fabricate keratin/HA scaffolds and our detailed in vitro investigations suggest the great potential for these composite scaffolds for bone tissue engineering in future.

Synergistic effect of FGF-2 and TGF-β1 on the mineralization of human umbilical cord perivascular cells

OBJECTIVE

Human umbilical cord perivascular cells (HUCPVCs) are derived from the human umbilical cord perivascular tissue and are expected to replace mesenchymal stromal cells in the future. We investigated the synergistic effects of fibroblast growth factor 2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1) on HUCPVC mineralization.

DESIGN

We prepared HUCPVCs with (FGF(+)HUCPVCs) or without FGF-2 (FGF(-)HUCPVCs) in the presence of activated vitamin D3, a bone morphogenic protein inhibitor, and TGF-β1. We examined the cell proliferative capacity, expression of various hard tissue-forming cell gene markers, and mineralization induction ability and identified the crystalline phases of the mineralized nodules.

RESULTS

FGF(+)HUCPVCs exhibited higher intracellular alkaline phosphatase (ALP) gene expression and ALP activity, and their cell proliferation rate was higher than that of FGF(-)HUCPVCs. The expression levels of osteoblast marker genes increased in FGF(+)HUCPVCs, whereas those of elastic fiber and muscle cell markers increased in FGF(-)HUCPVCs. The expression of genes related to matrix vesicle-mediated mineralization was increased in FGF(+)HUCPVCs. While FGF(-)HUCPVCs displayed myofibroblast-like properties and could not induce mineralization, FGF(+)HUCPVCs demonstrated the ability to produce mineralized nodules. The resulting mineralized nodules consisted of hydroxyapatite as the major phase and minor amounts of octacalcium phosphate. The mineralized nodules exhibited the morphological characteristics of bone hydroxyapatite, composed of fibrous hydroxyapatite nanorods and polycrystalline sheets.

CONCLUSION

We found that FGF-2 synergizes with TGF-β1 and is a key factor in the differentiation of HUCPVCs into osteoblast-like cells. Thus, HUCPVCs can potentially serve as a new stem cell source for future bone regeneration and dental treatments.

In Vitro Evaluation of the Effects of Hyaluronic Acid and an Aminoacidic Pool on Human Osteoblasts

The treatment of bone injuries must be timely and effective to improve the chances of full recovery. In this respect, a mix of hyaluronic acid and an amino acidic pool has been marketed to promote soft tissue healing, fastening recovery times. Several studies have reported the in vitro and in vivo influence of hyaluronic acid and amino acids on fibroblasts and keratinocytes, highlighting the enhancement of cell proliferation, motility and cytokines synthesis. Even though the effectiveness of this combination of molecules on bone repair has been described in vivo, to the best of our knowledge, its in vitro effects on osteoblasts still need to be investigated. Therefore, this work describes for the first time osteoblast metabolism, proliferation and in vitro differentiation in the presence of hyaluronic acid and amino acids, aiming at understanding the mechanisms underlying their effectiveness in injured tissue repair. The reported results demonstrate the enhancement of osteoblasts’ metabolic activity and the fastening of cell cycle progression. Furthermore, gene expression studies show a significant increase in differentiation markers, i.e., osteoprotegerin and osteonectin. Finally, alkaline phosphatase activity is also boosted by the combination of hyaluronic acid and aminoacids, confirming the ability of in vitro cultured cells to properly differentiate through the osteogenic lineage.

Long-term osteogenic differentiation of human bone marrow stromal cells in simulated microgravity: novel proteins sighted

Microgravity-induced bone loss is a major concern for space travelers. Ground-based microgravity simulators are crucial to study the effect of microgravity exposure on biological systems and to address the limitations posed by restricted access to real space. In this work, for the first time, we adopt a multidisciplinary approach to characterize the morphological, biochemical, and molecular changes underlying the response of human bone marrow stromal cells to long-term simulated microgravity exposure during osteogenic differentiation. Our results show that osteogenic differentiation is reduced while energy metabolism is promoted. We found novel proteins were dysregulated under simulated microgravity, including CSC1-like protein, involved in the mechanotransduction of pressure signals, and PTPN11, SLC44A1 and MME which are involved in osteoblast differentiation pathways and which may become the focus of future translational projects. The investigation of cell proteome highlighted how simulated microgravity affects a relatively low number of proteins compared to time and/or osteogenic factors and has allowed us to reconstruct a hypothetical pipeline for cell response to simulated microgravity. Further investigation focused on the application of nanomaterials may help to increase understanding of how to treat or minimize the effects of microgravity.

Development and Characterization of Alkaline Phosphatase-Positive Human Umbilical Cord Perivascular Cells

Human umbilical cord perivascular cells (HUCPVCs), harvested from human umbilical cord perivascular tissue, show potential for future use as an alternative to mesenchymal stromal cells. Here, we present the results for the characterization of the properties alkaline phosphatase-positive HUCPVCs (ALP(+)-HUCPVCs). These ALP(+)-HUCPVCs were created from HUCPVCs in this study by culturing in the presence of activated vitamin D3, an inhibitor of bone morphogenetic protein signaling and transforming growth factor-beta1 (TGF-β1). The morphological characteristics, cell proliferation, gene expression, and mineralization-inducing ability of ALP(+)-HUCPVCs were investigated at the morphological, biological, and genetic levels. ALP(+)-HUCPVCs possess high ALP gene expression and activity in cells and a slow rate of cell growth. The morphology of ALP(+)-HUCPVCs is fibroblast-like, with an increase in actin filaments containing alpha-smooth muscle actin. In addition to ALP expression, the gene expression levels of type I collagen, osteopontin, elastin, fibrillin-1, and cluster of differentiation 90 are increased in ALP(+)-HUCPVCs. ALP(+)-HUCPVCs do not have the ability to induce mineralization nodules, which may be due to the restriction of phosphate uptake into matrix vesicles. Moreover, ALP(+)-HUCPVCs may produce anti-mineralization substances. We conclude that ALP(+)-HUCPVCs induced from HUCPVCs by a TGF-β1 stimulation possess myofibroblast-like properties that have little mineralization-inducing ability.

Gene expression profiling on effect of aspirin on osteogenic differentiation of periodontal ligament stem cells

Periodontal ligament (PDL) contains a unique population of mesenchymal stem cells (MSCs), also known as PDL stem cells (PDLSCs). The regenerative properties of PDLSCs hold great potential for its use in stem cells based therapy, particularly for periodontal or bone regeneration. The present study investigated the global gene expression profile in PDLSCs during osteogenic differentiation. MSCs from PDL were isolated from normal permanent human teeth (n = 3). Microarray analysis was used to study the effects of ASA (200, 500, and 1000 μM) on the gene expression profiles in PDLSCs during osteogenic differentiation. Microarray study revealed that ASA was able to modulate PDLSCs gene expression profile. At 200 µM, 315 genes were dysregulated genes (DE), involving 151 upregulated and 164 downregulated genes. At 500 µM, 794 genes were DE, involving of 364 upregulated and 430 downregulated genes. At 1000 µM, the number of DE genes increased to 2035, of which 735 were upregulated and 1300 were downregulated. Bioinformatics analyses of the gene expression data revealed that the majority of DE genes (for 500 and 1000 µM ASA treatment) are involved in osteogenic differentiation. The gene network analysis was carried out using Ingenuity Pathway Analysis (IPA) software, and this revealed that the number of gene groups involved in cell adhesion and extracellular matrix components were increased. This study indicated that ASA could enhance PDLSCs functions and provide evidence for the potential use of ASA with PDLSCs for regenerative dentistry applications, particularly in the areas of periodontal health and regeneration. Periodontal ligament stem cells (PDLSCs) Aspirin (ASA) Microarray Osteogenic.

Lycii radicis cortex inhibits glucocorticoid‑induced bone loss by downregulating Runx2 and BMP‑2 expression

Lycii radicis cortex (LRC) has been used to regulate high blood pressure, body temperature, pain and bone disorders in East Asia. Glucocorticoids (GCs), also known as steroids, are potent immunity regulators widely used in the treatment of inflammatory diseases. However, despite their effectiveness, GC usage is strictly controlled due to severe side‑effects, such as osteoporosis. However, further research is required as to date, at least to the best of our knowledge, there is no appropriate model to overcome secondary osteoporosis as a side‑effect of GC use. Thus, the aim of the present study was to establish an experimental model of osteoporosis induced by GC. Furthermore, the present study aimed to establish the research methodology for medical evaluations of the effectiveness and side‑effects of GCs. A secondary osteoporosis animal model was established, and the animals were divided into two groups as follows: The allergic contact dermatitis (ACD)‑induced group and the non‑ACD‑induced group. In the ACD‑induced group, a GC topical application group was compared with a GC subcutaneous injection group. The results revealed that the presence of ACD affected the induction of GC‑mediated osteoporosis. Therefore, the group exhibiting induced ACD that was treated with a topical application of GC was selected for examining the side‑effects of GCs. The effects of LRC on secondary osteoporosis were confirmed in vivo and in vitro. The results indicated that LRC regulated dexamethasone‑induced osteoblast apoptotic markers, including caspase‑6, caspase‑9, X‑linked inhibitor of apoptosis, apoptosis inhibitor 1 and apoptosis inhibitor 2, and increased the expression of osteoblast differentiation‑related genes, such as Runt‑related transcription factor 2 and bone morphogenetic protein 2 in the MC3T3E‑1 cell line. LRC also significantly reduced GC‑induced osteoporosis and exerted anti‑inflammatory effects in vivo. In addition, LRC inhibited the reduction of calbindin‑D28k in the kidney. Overall, the results of the present study suggest that the use of LRC alleviates GC‑induced secondary osteoporosis.

Surface topography and free energy regulate osteogenesis of stem cells: effects of shape-controlled gold nanoparticles

The surface free energy of a biomaterial plays an important role in the early stages of cell-biomaterial interactions, profoundly influencing protein adsorption, interfacial water accessibility, and cell attachment on the biomaterial surface. Although multiple approaches have been developed to engineer the surface free energy of biomaterials, systematically tuning their surface free energy without altering other physicochemical properties remains challenging. In this study, we constructed an array of chemically-equivalent surfaces with comparable apparent roughness through assembly of gold nanoparticles adopting various geometrically-distinct shapes but all capped with the same surface ligand, (1-hexadecyl)trimethylammonium chloride, on cell culture substrates. We found that bone marrow stem cells exhibited distinct osteogenic differentiation behaviours when interacting with different types of substrates comprising shape-controlled gold nanoparticles. Our results reveal that bone marrow stem cells are capable of sensing differences in the nanoscale topographical features, which underscores the role of the surface free energy of nanostructured biomaterials in regulating cell responses. The study was approved by Institutional Animal Care and Use Committee, School of Medicine, University of South Carolina.

BMP2-dependent gene regulatory network analysis reveals Klf4 as a novel transcription factor of osteoblast differentiation

Transcription factors (TFs) regulate the expression of target genes, inducing changes in cell morphology or activities needed for cell fate determination and differentiation. The BMP signaling pathway is widely regarded as one of the most important pathways in vertebrate skeletal biology, of which BMP2 is a potent inducer, governing the osteoblast differentiation of bone marrow stromal cells (BMSCs). However, the mechanism by which BMP2 initiates its downstream transcription factor cascade and determines the direction of differentiation remains largely unknown. In this study, we used RNA-seq, ATAC-seq, and animal models to characterize the BMP2-dependent gene regulatory network governing osteoblast lineage commitment. Sp7-Cre; Bmp2fx/fx mice (BMP2-cKO) were generated and exhibited decreased bone density and lower osteoblast number (n > 6). In vitro experiments showed that BMP2-cKO mouse bone marrow stromal cells (mBMSCs) had an impact on osteoblast differentiation and deficient cell proliferation. Osteogenic medium induced mBMSCs from BMP2-cKO mice and control were subjected to RNA-seq and ATAC-seq analysis to reveal differentially expressed TFs, along with their target open chromatin regions. Combined with H3K27Ac CUT&Tag during osteoblast differentiation, we identified 2338 BMP2-dependent osteoblast-specific active enhancers. Motif enrichment assay revealed that over 80% of these elements were directly targeted by RUNX2, DLX5, MEF2C, OASIS, and KLF4. We deactivated Klf4 in the Sp7 + lineage to validate the role of KLF4 in osteoblast differentiation of mBMSCs. Compared to the wild-type, Sp7-Cre; Klf4fx/+ mice (KLF4-Het) were smaller in size and had abnormal incisors resembling BMP2-cKO mice. Additionally, KLF4-Het mice had fewer osteoblasts and decreased osteogenic ability. RNA-seq and ATAC-seq revealed that KLF4 mainly "co-bound" with RUNX2 to regulate downstream genes. Given the significant overlap between KLF4- and BMP2-dependent NFRs and enriched motifs, our findings outline a comprehensive BMP2-dependent gene regulatory network specifically governing osteoblast differentiation of the Sp7 + lineage, in which Klf4 is a novel transcription factor.

Optimizing In Vitro Osteogenesis in Canine Autologous and Induced Pluripotent Stem Cell-Derived Mesenchymal Stromal Cells with Dexamethasone and BMP-2

A growing body of work suggests that canine mesenchymal stromal cells (cMSCs) require additional agonists such as bone morphogenic protein-2 (BMP-2) for consistent in vitro osteogenic differentiation. BMP-2 is costly and may challenge the translational relevance of the canine model. Dexamethasone enhances osteogenic differentiation of human MSCs (hMSCs) and is widely utilized in osteogenic protocols. The aim of this study was to determine the effect of BMP-2 and dexamethasone on early- and late-stage osteogenesis of autologous and induced pluripotent stem cell (iPS)-derived cMSCs. Two preparations of marrow-derived cMSCs were selected to represent exceptionally or marginally osteogenic autologous cMSCs. iPS-derived cMSCs were generated from canine fibroblasts. All preparations were evaluated using alkaline phosphatase (ALP) activity, Alizarin Red staining of osteogenic monolayers, and quantitative polymerase chain reaction. Data were reported as mean ± standard deviation and compared using one- or two-way analysis of variance and Tukey or Sidak post hoc tests. Significance was established at P < 0.05. In early-stage assays, dexamethasone decreased ALP activity for all cMSCs in the presence of BMP-2. In late-stage assays, inclusion of dexamethasone and BMP-2 at Day 1 of culture produced robust monolayer mineralization for autologous cMSCs. Delivering 100 nM dexamethasone at Day 1 improved mineralization and reduced the BMP-2 concentrations required to achieve mineralization of the marginal cMSCs. For iPS-cMSCs, dexamethasone was inhibitory to both ALP activity and monolayer mineralization. There was increased expression of osteocalcin and osterix with BMP-2 in autologous cMSCs but a more modest expression occurred in iPS cMSCs. While autologous and iPS-derived cMSCs respond similarly in early-stage osteogenic assays, they exhibit unique responses to dexamethasone and BMP-2 in late-stage mineralization assays. This study demonstrates that dexamethasone and BMP-2 can be titrated in a time- and concentration-dependent manner to enhance osteogenesis of autologous cMSC preparations. These results will prove useful for investigators performing translational studies with cMSCs while providing insight into iPS-derived cMSC osteogenesis.

Vertebral Bone Marrow-Derived Mesenchymal Stromal Cells from Osteoporotic and Healthy Patients Possess Similar Differentiation Properties In Vitro

Osteoporosis is a disease characterized by low bone mass and an increased risk of fractures. Although several cellular players leading to osteoporosis have been identified, the role of mesenchymal stromal cells (MSC) is still not fully elaborated. The aim of this study was, therefore, to isolate and characterize MSCs from vertebral body of healthy non-osteoporotic and osteoporotic patients, with a particular focus on their osteogenic differentiation potential. Isolated MSCs were characterized by their osteogenic, adipogenic, and chondrogenic differentiation, as well as surface marker expression, proliferation behavior, and immunomodulatory capacity. The mineralization process was confirmed using Alizarin Red S and alkaline phosphatase (ALP) stains and further evaluated by determining ALP activity, mineral deposition, and free phosphate ion release. MSCs from both healthy and osteoporotic patients showed common fibroblast-like morphology and similar proliferation behavior. They expressed the typical MSC surface markers and possessed immunomodulatory capacity. Both groups demonstrated solid trilineage differentiation potential; osteogenic differentiation was further confirmed by increased ALP activity, deposition of inorganic crystals, phosphate ion release, and expression of osteoblast marker genes. Overall, MSCs from osteoporotic and non-osteoporotic patients showed neither a difference in general MSC features nor in the detailed analysis regarding osteogenic differentiation. These data suggest that vertebral body MSCs from osteoporotic patients were not impaired; rather, they possessed full osteogenic potential compared to MSCs from non-osteoporotic patients.

Autophagy was involved in tumor necrosis factor-α-inhibited osteogenic differentiation of murine calvarial osteoblasts through Wnt/β-catenin pathway

Periodontitis is an inflammatory disease with a high incidence characterized by irreversible destruction of alveolar bone. This study aimed to investigate the effect of tumor necrosis factor-α (TNF-α) on osteogenic differentiation and its molecular mechanism. TNF-α inhibited osteogenic differentiation as revealed by the lower accumulation of osteoblastic genes like runt-related transcription factor (Runx2), alkaline phosphatase (ALP), osteoprotegerin (OPG), and osteocalcin (OCN). Moreover, TNF-α down-regulated the expressions of LC3II, ATG7, and beclin 1 (BECN1); suggesting that autophagy was inhibited during the process of osteogenic differentiation. Consistently, Wnt/β-catenin signaling pathway members such as low-density lipoprotein receptor-related protein 5 (LRP5), β-catenin, and phosphorylated-β-catenin (p-β-catenin) were reduced by TNF-α. Furthermore, the inhibitory effect of TNF-α on osteogenic differentiation and the Wnt/β-catenin signaling pathway could be abated by autophagy inducers but exacerbated by autophagy inhibitors. The most intriguing finding of all was that TNF-α inhibited osteoblastic differentiation and the Wnt/β-catenin signaling pathway by down-regulating autophagy, and autophagy positively regulated the Wnt/β-catenin pathway and thus influenced osteoblastic differentiation. Our study provides a theoretical basis for autophagy-inducer therapy for the alveolar bone loss caused by periodontitis.

MGF-19E peptide promoted proliferation, differentiation and mineralization of MC3T3-E1 cell and promoted bone defect healing

The repair of segmental bone defects and bone fractures is a clinical challenge involving high risk and postsurgical morbidity. Bone injury and partial bone tumor resection via traditional bone grafting result in high complications. Growth factors have been proposed as alternatives to promote bone repair and formation and circumvent these limitations. In this study, we classified different lengths of mechano growth factor (MGF) E peptides in different species and analyzed their effects on MC3T3-E1 cell proliferation, cell cycle, alkaline phosphatase (ALP) activity, differentiation-related factor expression, and cell mineralization. A rabbit bone injury model was constructed, and the repair function of MGF E peptide was verified by injecting the candidate MGF E peptide. We analyzed 52 different MGF-E peptides and classified them into the following four categories: T-MGF-25E, M-MGF-25E, T-MGF-19E, and M-MGF-19E. These peptides were synthesized for further study. T-MGF-19E peptide obviously promoted cell proliferation by regulating cell cycle after MGF E peptide treatment at 72 h. T-MGF-25E and T-MGF-19E peptide significantly promoted the differentiation of osteoblasts on day 14, and M-MGF-25E peptide promoted cell differentiation on day 7. T-MGF-19E, T-MGF-25E, and M-MGF-19E significantly promoted osteoblast mineralization, with T-MGF19E showing the most significant effect. These results implied that T-MGF19E peptide could remarkably promote MC3T3-E1 cell proliferation, differentiation, and mineralization. The rabbit bone defect model showed that the low-dose T-MGF-19E peptide significantly promoted bone injury healing, suggesting its promoting effect on the healing of bone injury.

Alpha ketoglutarate exerts a pro-osteogenic effect in osteoblast cell lines through activation of JNK and mTOR/S6K1/S6 signaling pathways

Although numerous in vivo studies have suggested that alpha-ketoglutarate (AKG), i.e. the key intermediate in the Krebs cycle, may have an anabolic effect on bone tissue, the direct influence of AKG on osteoblasts and the underlying mechanism of its action have not been investigated so far. The aim of this study was to assess the impact of AKG (disodium salt dihydrate) on osteogenesis in vitro and identification of some signaling mechanisms involved in this activity. The human and mouse normal osteoblast cell lines hFOB 1.19 and MC3T3-E1 were used in this study. The results showed that AKG did not increase the proliferation of osteoblasts; however, it upregulated the expression of transcription factors RUNX2 and Osterix, the mRNA and protein levels of osteoblast differentiation markers (alkaline phosphatase, type I collagen, bone sialoprotein II, osteopontin, osteocalcin), and the mineralization levels in the hFOB 1.19 and MC3T3-E1 cell cultures. Moreover, AKG increased JNK, mTOR, S6K1, and S6 phosphorylation and decreased ERK1/2 phosphorylation in both osteoblast cell lines. The JNK inhibitor and rapamycin, but not the ERK inhibitor, abolished the AKG-promoted osteoblast differentiation. Using immunofluorescence staining, qRT-PCR, and Western blot analysis, we detected the presence of an AKG receptor GPR99 activated by alpha ketoglutaric acid in the tested osteoblast cell lines. However, AKG salt did not activate GPR99. Our findings suggest that AKG salt activates the JNK and mTOR/S6K1/S6 signaling pathways to promote differentiation of osteoblasts, independently of GPR99 activation. We can conclude that AKG salts might be promising candidates for bone anabolic drugs used for prevention or/and treatment of osteoporosis.

Synergistic Osteogenesis of Biocompatible Reduced Graphene Oxide with Methyl Vanillate in BMSCs

Methyl vanillate (MV), a recently characterized small molecule, can promote the Wnt/β-catenin signaling pathway and induce osteoblast differentiation both in vitro and in vivo. On the other hand, graphene-based materials have been introduced into the field of biomedical sciences in the past decade, and graphene oxide (GO), which serves as an efficient nanocarrier for drug delivery, has attracted great attention for its biomedical applications in tissue engineering. This study aimed to develop a biocompatible gelatin-reduced graphene oxide (GOG) for MV delivery so as to realize the effective osteogenesis for bone repair. First, GOG was prepared, and its morphology as well as properties were then characterized using scanning electron microscope (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA), respectively. In addition, the endocytosis of GOG in bone marrow stromal cells (BMSCs) was also investigated with the treatment of Rhodamine 6G (R6G)-labeled GOG. Our results found that GOG could be easily absorbed by cells and was distributed in both nucleus and cytoplasm, thus suggesting the favorable biocompatibility of GOG. Moreover, the effect of MV on osteogenesis was also tested, the results of which indicated that MV could promote BMSC osteogenesis in a concentration-dependent manner, and significant enhancement could be achieved at the concentration of 1 μg/mL. In addition, the complex containing different concentrations of GOG and an optimal concentration of MV was used to investigate the synergistic effect between GOG and MV on pro-osteogenesis. The results revealed that the weight ratio of MV/GOG of 1:1000 could attain remarkably enhanced osteoinduction in BMSCs, as evaluated by alkaline phosphatase (ALP) assay, alizarin red S (ARS) staining, immunofluorescence staining, and gene expression of related osteogenic markers. Taken together, these data had provided strong evidence that the complex of MV and GOG could induce osteogenesis, which was promising for bone tissue engineering.

Square prism micropillars on poly(methyl methacrylate) surfaces modulate the morphology and differentiation of human dental pulp mesenchymal stem cells

Use of soluble factors is the most common strategy to induce osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro, but it may raise potential side effects in vivo. The topographies of the substrate surfaces affect cell behavior, and this could be a promising approach to guide stem cell differentiation. Micropillars have been reported to modulate cellular and subcellular shape, and it is particularly interesting to investigate whether these changes in cell morphology can modulate gene expression and lineage commitment without chemical induction. In this study, poly(methyl methacrylate) (PMMA) films were decorated with square prism micropillars with different lateral dimensions (4, 8 and 16 μm), and the surface wettability of the substrates was altered by oxygen plasma treatment. Both, pattern dimensions and hydrophilicity, were found to affect the attachment, proliferation, and most importantly, gene expression of human dental pulp mesenchymal stem cells (DPSCs). Decreasing the pillar width and interpillar spacing of the square prism pillars enhanced cell attachment, cell elongation, and deformation of nuclei, but reduced early proliferation rate. Surfaces with 4 or 8 μm wide pillars/gaps upregulated the expression of early bone-marker genes and mineralization over 28 days of culture. Exposure to oxygen plasma increased wettability and promoted cell attachment and proliferation but delayed osteogenesis. Our findings showed that surface topography and chemistry are very useful tools in controlling cell behavior on substrates and they can also help create better implants. The most important finding is that hydrophobic micropillars on polymeric substrate surfaces can be exploited in inducing osteogenic differentiation of MSCs without any differentiation supplements.

Square prism micropillars improve osteogenicity of poly(methyl methacrylate) surfaces

Osteogenicity and osteointegration of materials is one of the key elements of the success of bone implants. Poly(methyl methacrylate) (PMMA) is the basic compound of bone cement and has been widely investigated for other orthopedic applications, but its poor osteointegration and the subsequent loosening of implant material limits its widespread use as bone implants. Micropillar features on substrate surfaces were recently reported to modulate cell behavior through alteration of cell morphology and promotion of osteogenesis. Utilization of this pillar-decorated topography may be an effective approach to enhance osteogenicity of polymeric surfaces. The aim of this study was to investigate the effect of cell morphology on the micropillar features on attachment, proliferation, and osteogenic activity of human osteoblast-like cells. A series of solvent cast PMMA films decorated with 8 µm high square prism micropillars with pillar width and interpillar distances of 4, 8 and 16 µm were prepared from photolithographic templates, and primary human osteoblast-like cells (hOB) isolated from bone fragments were cultured on them. Micropillars increased cell attachment and early proliferation rate compared to unpatterned surfaces, and triggered distinct morphological changes in cell body and nucleus. Surfaces with pillar dimensions and gap width of 4 µm presented the best osteogenic activity. Expression of osteogenic marker genes was upregulated by micropillars, and cells formed bone nodule-like aggregates rich in bone matrix proteins and calcium phosphate. These results indicated that micropillar features enhance osteogenic activity on PMMA films, possibly by triggering morphological changes that promote the osteogenic phenotype of the cells.

Dexamethasone-Activated MSCs Release MVs for Stimulating Osteogenic Response

The extracellular microvesicles (MVs) are attracting much attention because they are found to be the key paracrine mediator participating in tissue regeneration. Dexamethasone (DXM) is widely accepted as an important regulator in tailoring the differentiation potential of mesenchymal stem cells (MSCs). However, the effect of DXM on the paracrine signaling of MSCs remains unknown. To this point, we aimed to explore the role of DXM in regulating the paracrine activity of MSCs through evaluating the release and function of MSC-MVs, based on their physicochemical characteristics and support on osteogenic response. Results showed that DXM had no evident impact on the release of MSC-MVs but played a pivotal role in regulating the function of MSC-MVs. MVs obtained from the DXM-stimulated MSCs (DXM-MVs) increased MC3T3 cell proliferation and migration and upregulated Runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and osteopontin (OPN) expression. The repair efficiency of DXM-MVs for femur defects was further investigated in an established rat model. It was found that DXM-MVs accelerated the healing process of bone formation in the defect area. Thus, we conclude that using DXM as stimuli to obtain functional MSCs-MVs could become a valuable tool for promoting bone regeneration.

The osteogenesis-promoting effects of alpha-lipoic acid against glucocorticoid-induced osteoporosis through the NOX4, NF-kappaB, JNK and PI3K/AKT pathways

Recently, accumulating evidence has indicated that glucocorticoid-induced osteoporosis (GIOP) is closely related to oxidative stress and apoptosis. Alpha-lipoic acid (LA), a naturally endogenous anti-oxidant, possesses anti-oxidative and anti-apoptosis activities, implicating LA as a therapeutic agent for the treatment of GIOP. In this study, the osteogenesis-promoting effects of LA against GIOP were investigated and the mechanisms were further probed. Here, the results showed that LA inhibited oxidative stress, suppressed apoptosis and improved osteopenia by promoting the expression of osteogenesis markers, including ALP, COL-I, OCN, BMP-2, RUNX2 and OSX. Further study revealed that the osteogenesis-promoting effects of LA likely occur via the regulation of the NOX4, NF-kappaB, JNK and PI3K/AKT pathways. The present study indicated that LA may prevent GIOP and promote osteogenesis and might be a candidate for the treatment of GIOP.

Involvement of small G protein RhoB in the regulation of proliferation, adhesion and migration by dexamethasone in osteoblastic cells

Long-term exposure to therapeutic doses of glucocorticoids (GCs) results in bone remodeling, which frequently causes osteoporosis and fracture healing retardation because of the abnormality of osteoblastic proliferation and differentiation. The mechanisms of GCs’ effect on osteoblasts are largely unknown. In this present study, we found that dexamethasone (Dex) could induce the expression of the small G protein, RhoB, in mRNA and protein levels in the osteoblast-derived osteosarcoma cell lines MG-63. The up-regulation of RhoB mRNA by Dex mainly occurs at posttranscriptional level by increasing its mRNA stability through PI-3K/Akt and p38 mitogen-activated protein kinase signaling pathways. Over-expression of RhoB in MG-63 cells magnified while down-regulation of RhoB level by RNA interference impaired Dex-induced growth inhibition but not differentiation. What’s more, over-expression of RhoB mimicked the effect of Dex on cell adhesion and migration. And interfering RhoB expression partially suppressed Dex-induced pro-adhesion and anti-migration in MG-63 cells. In conclusion, these results indicate that RhoB plays an important role in the pathological effect of Dex on osteoblastic growth and migration, which is a part of the mechanisms of GCs’ adverse effect on bone remodeling.

3D bioprinting of GelMA scaffolds triggers mineral deposition by primary human osteoblasts

Due to its relatively low level of antigenicity and high durability, titanium has successfully been used as the major material for biological implants. However, because the typical interface between titanium and tissue precludes adequate transmission of load into the surrounding bone, over time, load-bearing implants tend to loosen and revision surgeries are required. Osseointegration of titanium implants requires presentation of both biological and mechanical cues that promote attachment of and trigger mineral deposition by osteoblasts. While many factors contribute to differentiation, the relative importance of the various cues is unclear. To substantially improve osseointegration of titanium implants, we generated a gelatin methacryloyl (GelMA) scaffold, using an extrusion-based 3D bioprinter, which can be directly printed on and grafted to the titanium implant surface. We demonstrate that this scaffold is able to trigger mineral deposition of both MG63 osteoblasts and primary normal human osteoblasts in the absence of any exogenous osteogenic factors. Films of the same formulation failed to promote mineral deposition suggesting that the three dimensional scaffold was able to tip the balance in favor of differentiation despite other potentially unfavorable differentiation cues of the material. We further show that these GelMA lattices can be directly grafted to titanium alloy and are secure in vitro over a period of seven weeks. When grafted within a groove system, the GelMA hydrogel is protected from shearing forces in a marrow implantation model. This prepares the way for osteogenic coatings to be directly manufactured on the implant surface and packaged for surgery.

Glucocorticoid receptor and Histone deacetylase 6 mediate the differential effect of dexamethasone during osteogenesis of mesenchymal stromal cells (MSCs)

Lineage commitment and differentiation of mesenchymal stromal cells (MSCs) into osteoblasts in vitro is enhanced by a potent synthetic form of glucocorticoid (GC), dexamethasone (Dex). Paradoxically, when used chronically in patients, GCs exert negative effects on bone, a phenomenon known as glucocorticoid-induced osteoporosis in clinical practice. The mechanism on how GC differentially affects bone precursor cells to become mature osteoblasts during osteogenesis remains elusive. In this study, the dose and temporal regulation of Dex on MSC differentiation into osteoblasts were investigated. We found that continuous Dex treatment led to a net reduction of the maturation potential of differentiating osteoblasts. This phenomenon correlated with a decrease in glucocorticoid receptor (GR) expression, hastened degradation, and impaired sub cellular localization. Similarly, Histone Deacetylase 6 (HDAC6) expression was found to be regulated by Dex, co-localized with GR and this GR-HDAC6 complex occupied the promoter region of the osteoblast late marker osteocalcin (OCN). Combinatorial inhibition of HDAC6 and GR enhanced OCN expression. Together, the cross-talk between the Dex effector molecule GR and the inhibitory molecule HDAC6 provided mechanistic explanation of the bimodal effect of Dex during osteogenic differentiation of MSCs. These findings may provide new directions of research to combat glucocorticoid-induced osteoporosis.

The Characteristics Of Human Bone-Derived Cells (HBDCS) during osteogenesis in vitro

BACKGROUND

The primary human bone-derived cell culture technique is used as a model to study human osteogenesis. Compared to cell line cultures, primary osteoprogenitor and osteoblast cultures provide more complex information about osteogenesis, bone remodeling and regeneration than cell line cultures.

METHODS

In this study, we isolated human bone-derived cells (HBDCs) and promoted their differentiation into osteoblasts. The following parameters were evaluated: cell number and viability, total protein expression, alkaline phosphatase activity, collagenous matrix production and osteogenic genes expression, i.e., gene coding for type I collagen and alkaline phosphatase.

RESULTS

It was proved the results show that HBDCs intensively proliferate during the first 7 days of culture followed by differentiation accompanied by an increase in alkaline phosphatase activity. Moreover, it was observed that during the differentiation of HBDCs, the expression of integrin β1 increased.

CONCLUSIONS

The process was also accompanied by changes in cell shape and rearrangement of the actin cytoskeleton and focal contacts containing FAK and the integrin β1 subunit. We suggest that the β1 integrin subunit may be a suitable new target in studies of the differentiation of primary human osteoblasts in culture.

In vitro Osteogenic impulse effect of Dexamethasone on periodontal ligament stem cells

Periodontium is a complex organ composed of mineralized epithelial and connective tissue. Dexamethasone could stimulate proliferation of osteoblast and fibroblasts. This study aimed to assess the osteogenic effect of dexamethasone on periodental ligament (PDL) stem cells. PDL stem cells were collected from periodontal ligament tissue of root of extracted premolar of young and healthy people. The stem cells were cultured in α-MEM Medium in three groups, one group with basic medium contains (α- MEM and FBS 10 % and 50 mmol of β_ gelisrophosphat and L_ ascorbic acid µg/ml), the second group: basic medium with dexamethasone and the third one: basic medium without any osteogenic stimulant. Mineralization of cellular layer was analyzed with Alizarin red stain method. Osteogenic analysis was done by Alkaline phosphates and calcium test. These analysis indicated that the amount of intra-cellular calcium and alkaline phosphates in the Dexamethasone group was far more than the control and basic group (P<0.05). The results of Alizarin red stain indicated more mineralization of cultured cells in Dexamethasone group (P<0.05). The study results showed that Dexamethasone has significant osteogenic effect on PDL stem cells and further studies are recommended to evaluate its effect on treatment of bone disorders.

Denosumab could be a Potential Inhibitor of Valvular Interstitial Cells Calcification in vitro

OBJECTIVE

Denosumab is a fully human monoclonal antibody and novel antiresorptive agent that works by binding receptor activator of nuclear factor kappa-β ligand (RANKL) and inhibiting the signaling cascade that causes osteoclast maturation, activity, and survival. We aimed to elucidate the effect of Denosumab in the process of spontaneous and induced calcification in an in vitro porcine valvular interstitial cells (VICs) model.

MATERIALS AND METHODS

VICs were extracted from fresh porcine hearts by serial collagenase digestion. Spontaneous calcification of VICs was increased in vitro by adding Na₃PO₄ (3 mM, pH 7.4) and different concentrations (0.1, 1 and 10 ng/ml) of transforming growth factor beta (TGFß). The degree of calcification before and after treatment with Denosumab was estimated by Alizarin Red staining for calcium deposition, and Sirius Red staining for collagen. Colorimetric techniques were used to determine calcium and collagen deposition quantitatively. For statistical analysis we used SPSS and Microsoft Office Excel 2013.

RESULTS

Porcine aortic VICs in vitro were induced to calcify by the addition of either 3 mM Na₃PO₄, showing a 5.2 fold increase by 14 days (P<0.001), or 3 mM Na₃PO₄ + 10 ng/ml of TGFβ, showing a 7 fold increase by Day 14 (P<0.001). Denosumab inhibited induced calcification by 3 mM Na₃PO₄ and 3 mM Na₃PO₄ with the addition of TGFß at either 0.1, 1 or 10 ng/ml to basal levels only at a concentration of 50 μg/ml (P<0.001).

CONCLUSION

This study has proved that Denosumab could be a potential inhibitor of the calcification of VICs in vitro. A fuller understanding of the actions of Denosumab may identify a novel therapeutic strategy for clinical intervention against aortic valve calcification and aortic stenosis.

Synergetic effects of hBMSCs and hPCs in osteogenic differentiation and their capacity in the repair of critical-sized femoral condyle defects

Tissue-engineered bone grafts require an osteoblastic cellular source to be utilized in bone transplantation therapy. Human bone marrow stem cells (hBMSCs) and periosteal-derived stem cells (hPCs) are the commonly used cellular sources for bone tissue engineering and are essential in fracture healing. In the present study, hBMSCs and hPCs were co-cultured from the same donors, as the cellular source. In monolayer cultivation, co-culturing hBMSCs and hPCs demonstrated more robust mineralized nodule formation and stronger alkaline phosphatase (ALP) positive staining than hBMSCs or hPCs. Three-dimensional (3-D) culturing on porous β-tricalcium phosphate (TCP) scaffolds and co-culturing of hBMSCs and hPCs significantly promoted the osteogenic specific mRNA expression of COL1α1, BMP-2, osteopontin (OPN) and osteocalcin (OC). For in vivo bone formation and neovascularization assessment, the cellular-β-TCP scaffolds were transplanted into critical-sized femoral condyle defects in rabbits. The results confirmed that co-culturing hBMSCs and hPCs accelerated bone regeneration and enhanced mature bone formation, but also facilitated central vascularization in scaffold pores. Based on these data, we recommend co-culturing hBMSCs and hPCs as a promising cellular source for bone tissue engineering applications.

Chitosan as a potential osteogenic factor compared with dexamethasone in cultured macaque dental pulp stromal cells

Chitosan, a natural biopolymer derived from chitin, is considered a promising scaffold material for bone tissue engineering. The ability of chitosan to promote the osteogenic differentiation of dental pulp stromal/stem cells (DPSCs) is unknown. We have evaluated the potential of chitosan to induce the osteogenic differentiation of macaque DPSCs in comparison with that of dexamethasone. DPSCs were cultured in mineralizing medium supplemented with 5 or 10 μg/ml chitosan or with 1 or 10 nM dexamethasone. The metabolic activity of DPSCs was measured by MTT assay. Their osteogenic differentiation was determined by the number of transcripts of RUNX2, alkaline phosphatase (ALP), and COL1A1 by using real-time polymerase chain reaction, by alizarin red staining for mineral deposition, and by the ALP activity released into the medium for their ability to support biomineralizaton. Addition of chitosan to the mineralizing medium significantly increased DPSCs metabolism after 7 and 14 days of culture (P ≤ 0.0001). Chitosan at 5 μg/ml also significantly enhanced RUNX2 and ALP mRNA but not COL1A1 mRNA; chitosan tended to increase the release of ALP hydrolytic enzyme activity into the medium during the first week. Dexamethasone upregulated the osteogenic markers tested. Mineral deposition was similar in the chitosan and dexamethasone groups and was not statistically different from that of the mineralizing control group. Thus, the potential of chitosan to stimulate DPSCs proliferation and early osteogenic differentiation is comparable with that of dexamethasone, but mineralization remains unaffected by chitosan treatment. In addition to its role as a three-dimensional scaffold for osteogenic cells in vivo, chitosan might also stimulate DPSCs proliferation and early osteogenic differentiation in vitro.

Small molecule stimulation enhances bone regeneration but not titanium implant osseointegration

The osteogenic and osseointegrative potential of a small molecule was examined to assess its usefulness in regenerative procedures. Purmorphamine was used to stimulate bone growth and repair in an in vitro cell-based assay and an in vivo chick embryo CAM-assay with and without the presence of an implant. Purmorphamine adhered to precipitated hydroxyapatite coating, could activate the sonic hedgehog pathway and thereby stimulated osteodifferentiation. Porous calcium phosphate beads were used to deliver this small molecule in vivo and showed that purmorphamine increased the trabecular bone to bone area significantly. The assay showed purmorphamine failed to induce any significant difference in osseointegration on titanium coated PTFE implants. This suggests that, while a small molecule can enhance osteogenesis and might be useful in regenerative procedures, it failed to enhance the osseointegration of a Ti coated implant, suggesting that this sort of stimulation might be useful for enhancing bone regeneration where bone loss due to disease exists, but not for enhancing early stability of an implant.

Effect of glucocorticoid-induced oxidative stress on the expression of Cbfa1

Glucocorticoids therapy is strongly limited since extended glucocorticoids can cause serious side effects, including increased susceptibility to develop the bone disease osteoporosis. Despite its side effects recognized importance to clinicians, seldom is known about how glucocorticoids directly impact bone-forming osteoblasts. Previous studies showed that dexamethasone (DEX) induces excessive production of reactive oxygen species (ROS), and causes oxidative stress in rat hippocampal slice cultures. To assess the implications and investigate the mechanisms of glucocorticoid-elicited osteoporosis, we hypothesize that DEX exposure induces oxidative stress which leads to decreased Cbfa1 mRNA expression, and predict that the antioxidant N-acetylcysteine (NAC) mitigates the damaging effects of DEX. Oxidative stress is implicated in osteoporosis. Furthermore, the osteoblast transcriptional factor Cbfa1 is reported to play a protective role against osteoporosis in postmenopausal women. Cells treated with (0.1, 1, 10μM) DEX exhibited signs of oxidative damages including depletion in total antioxidant capacity (T-AOC), increased ROS formation, and enhanced lipid peroxidation. Cbfa1 mRNA expression, by RT-PCR, was significantly reduced after exposure to (0.1, 1, 10μM) DEX. Pretreatment with the antioxidant NAC (2mM) prevented DEX-induced decrease in Cbfa1 mRNA. This study provides insight into the underlying mechanisms of high dose DEX-induced osteotoxicity. DEX (0.1, 1, 10μM) decreases the expression of Cbfa1 mRNA and inhibits differentiation and function of osteoblasts by inducing oxidative stress. The antioxidant NAC can mitigate the oxidative stress damaging effects of DEX. In addition, this study distinguishes itself by identifying Cbfa1 as a target for high dose DEX-induced osteotoxicity.

Substantial differences between human and ovine mesenchymal stem cells in response to osteogenic media: how to explain and how to manage?

It is expected that use of adult multipotential mesenchymal stem cells (MSCs) for bone tissue engineering (TE) will lead to improvement of TE products. Prior to clinical application, biocompatibility of bone TE products need to be tested in vitro and in vivo. In orthopedic research, sheep are a well-accepted model due to similarities with humans and are assumed to be predictive of human outcomes. In this study we uncover differences between human and ovine bone marrow–derived MSCs (BMSCs) and adipose tissue–derived MSCs (ADSCs) in response to osteogenic media. Osteogenic differentiation of BMSCs and ADSCs was monitored by alkaline phosphatase (ALP) activity and calcium deposition. Mineralization of ovine BMSC was achieved in medium containing NaH₂PO₄ as a source of phosphate ions (Pi), but not in medium containing β-glycerophosphate (β-GP), which is most often used. In a detailed study we found no induction of ALP activity in ovine BMSCs and ADSCs upon osteogenic stimulation, which makes β-GP an unsuitable source of phosphate ions for ovine cells. Moreover, mineralization of human ADSCs was more efficient in osteogenic medium containing NaH₂PO₄. These results indicate major differences between ovine and human MSCs and suggest that standard in vitro osteogenic differentiation techniques may not be suitable for all types of cells used in cell-based therapies. Since mineralization is a widely accepted marker of the osteogenic differentiation and maturation of cells in culture, it may lead to potentially misleading results and should be taken into account at the stage of planning and interpreting preclinical observations performed in animal models. We also present a cell culture protocol for ovine ADSCs, which do not express ALP activity and do not mineralize under routine pro-osteogenic conditions in vitro. We plan to apply it in preclinical experiments of bone tissue–engineered products performed in an ovine model.

The advantages of three-dimensional culture in a collagen hydrogel for stem cell differentiation

We evaluated the advantages of three-dimensional (3D) culture in a collagen hydrogel for stem cell differentiation, including the morphology of differentiated cells, differentiation efficiency of stem cells from aged rat and cells after passaging and freeze/thawing. Rat mesenchymal stem cells (MSCs) from young and aged rats, and MSCs after passaging and freeze/thawing were induced to differentiate into osteoblasts in 3D and 2D cultures, and histological studies were performed. Differentiation efficiency was evaluated by markers of osteoblastic differentiation including Runx2 and osterix gene expressions, osteocalcin secretion and calcium deposition. MSCs were stained positive for alkaline phosphatase in 3D and 2D cultures. However, the morphology of differentiated cells in 3D culture, which was different from that in 2D culture, was similar to that of osteoblasts in vivo. Markers of osteoblastic differentiation in MSCs from aged rats in 3D culture were higher than those in MSCs from young rats in 2D culture. Markers of osteoblastic differentiation in MSCs after passaging and freeze/thawing in 3D culture were higher than those in nonpassaged MSCs in 2D culture. These results indicate that 3D culture in a collagen hydrogel has advantages for the differentiation of MSCs into osteoblasts with a similar phenotype to that of in vivo, when using even MSCs from aged donors or after passaging and freeze/thawing.

Identification and characterization of microRNAs controlled by the osteoblast-specific transcription factor Osterix

Osterix (Osx) is an osteoblast-specific transcription factor which is essential for bone formation. MicroRNAs (miRNAs) have been previously shown to be involved in osteogenesis. However, it is unclear whether Osx is involved in the regulation of miRNA expression. In this study, we have identified groups of miRNAs that are differentially expressed in calvaria of the E18.5 Osx(-/-) embryos compared to wild type embryos. The correlation between the levels of miRNAs and Osx expression was further verified in cultured M-Osx cells in which over-expression of Osx is inducible. Our results suggest that Osx down-regulates expression of a group of miRNAs including mir-133a and -204/211, but up-regulates expression of another group of miRNAs such as mir-141/200a. Mir-133a and -204/211 are known to target the master osteogenic transcription factor Runx2. Further assays suggest that Sost, which encodes the Wnt signaling antagonist Sclerostin, and alkaline phosphatase (ALP) are two additional targets of mir-204/211. Mir-141/200a has been known to target the transcription factor Dlx5. Thus, we postulate that during the process of Osx-controlled osteogenesis, Osx has the ability to coordinately modulate Runx2, Sclerostin, ALP and Dlx5 proteins at levels appropriate for optimal osteoblast differentiation and function, at least in part, through regulation of specific miRNAs. Our study shows a tight correlation between Osx and the miRNAs involved in bone formation, and provides new information about molecular mechanisms of Osx-controlled osteogenesis.

ACTH promotes chondrogenic nodule formation and induces transient elevations in intracellular calcium in rat bone marrow cell cultures via MC2-R signaling

Adrenocorticotropic hormone (ACTH) is among several melanocortin peptide hormones that are derived from proopiomelanocortin (POMC). ACTH has been found to enhance osteogenesis and chondrogenesis. We show that, in the presence of dexamethasone, ACTH dose-dependently increases chondrogenic nodule formation in bone marrow stromal cells (BMSC) from the Wistar Kyoto (WKY) rat. The nodules consist in condensed cells highly expressing alkaline phosphatase, Sox9 and type II collagen transcripts and a proteoglycan-rich matrix. Immunoblot analysis of crude membrane fractions has shown that these cells express three melanocortin receptors (MC-R), namely MC2-R, MC3-R and MC5-R and the melanocortin 2-receptor accessory protein (MRAP). To determine which of these receptors mediate ACTH-induced effects, we have used MC-R-specific peptides and the known agonist profiles of the receptors. Neither α-MSH, a strong agonist of MC5-R, nor γ2-MSH, a strong agonist of MC3-R, duplicates ACTH effects in rat BMSC. In addition, calcium flux has been examined as a mechanism for ACTH action at the MC2-R. Consistent with MC2-R and MRAP expression patterns in the BMSC cultures, ACTH-induced transient increases in intracellular calcium are increased with dexamethasone treatment. Neither α-MSH nor γ2-MSH affects calcium flux. Dexamethasone increases MC2-R and MRAP expression and POMC peptide expression and cleavage increasing the production of the lipolytic β-lipotropic hormone product. Therefore, the effects of ACTH in rat BMSC enriched for mesenchymal progenitors are consistent with an MC2-R signaling mechanism, with dexamethasone being capable of regulating components of the melanocortin system in these cells.

The p75 neurotrophin receptor regulates MC3T3-E1 osteoblastic differentiation

While the role of p75(NTR) signaling in the regulation of nerve-related cell growth and survival has been well documented, its actions in osteoblasts are poorly understood. In this study, we examined the effects of p75(NTR) on osteoblast proliferation and differentiation using the MC3T3-E1 pre-osteoblast cell line. Proliferation and osteogenic differentiation were significantly enhanced in p75(NTR)-overexpressing MC3T3-E1 cells (p75GFP-E1). In addition, expression of osteoblast-specific osteocalcin (OCN), bone sialoprotein (BSP), and osterix mRNA, ALP activity, and mineralization capacity were dramatically enhanced in p75GFP-E1 cells, compared to wild MC3T3-E1 cells (GFP-E1). To determine the binding partner of p75(NTR) in p75GFP-E1 cells during osteogenic differentiation, we examined the expression of trkA, trkB, and trkC that are known binding partners of p75(NTR), as well as NgR. Pharmacological inhibition of trk tyrosine kinase with the K252a inhibitor resulted in marked reduction in the level of ALPase under osteogenic conditions. The deletion of the GDI binding domain in the p75(NTR)-GFP construct had no effect on mineralization. Taken together, our studies demonstrated that p75(NTR) signaling through the trk tyrosine kinase pathway affects osteoblast functions by targeting osteoblast proliferation and differentiation.

TRIP-1: a regulator of osteoblast function

Transforming growth factor β (TGFβ) receptor interacting protein-1 (TRIP-1) is an intracellular protein expressed in osteoblasts with high affinity for type 5b tartrate resistant acid phosphatase (TRAP). It is suggested that through this interaction, TRIP-1 serves as a positive regulator of TGFβ signaling and osteoblast differentiation during bone remodeling. We show here that TRIP-1 is abundant in osteoblasts in vivo and in vitro. TRIP-1 mRNA and protein expression were increased at early stages and decreased at later stages during osteoblast differentiation, suggesting a predominant role during early maturation. To investigate a role during bone remodeling, primary osteoblasts were treated with different hormones and factors that are known to affect remodeling. TRIP-1 levels were decreased with dexamethasone and increased with vitamin D(3) , dihydrotestosterone (DHT), TGFβ1, and bone morphogenic protein 2 (BMP-2). Treatment with parathyroid hormone (PTH) and β-estradiol did not affect TRIP-1 levels. Transfected small interfering RNA (siRNA) against TRIP-1 inhibited osteoblast differentiation as characterized by a decrease in alkaline phosphatase staining and enzyme activity, and decrease in the expression of collagen I, alkaline phosphatase, Runx2, osteopontin, and osteocalcin. The proliferation of osteoblasts was also affected by TRIP-1 siRNA. This particular effect was defined by decreased cell number, marked reduction of cyclin D1, a 38% decrease of cells in S phase (p < 0.001) and a 97% increase of cells in the G2/M phase (p < 0.01) of the cell cycle. However, TRIP-1 siRNA did not induce an effect in apoptosis. Using a TGFβ luciferase reporter we found that knocking down TRIP-1 decreased the activation of TGFβ signaling by 40% percent (p < 0.001). In conclusion, our characterization of TRIP-1 in osteoblasts provides the first evidence of its key role as a positive regulator of osteoblast function.

Mechanisms underlying the osteo- and adipo-differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are considered a promising cell source for regenerative medicine, because they have the potential to differentiate into a variety of lineages among which the mesoderm-derived lineages such adipo- or osteogenesis are investigated best. Human MSCs can be harvested in reasonable to large amounts from several parts of the patient's body and due to this possible autologous origin, allorecognition can be avoided. In addition, even in allogenic origin-derived donor cells, hMSCs generate a local immunosuppressive microenvironment, causing only a weak immune reaction. There is an increasing need for bone replacement in patients from all ages, due to a variety of reasons such as a new recreational behavior in young adults or age-related diseases. Adipogenic differentiation is another interesting lineage, because fat tissue is considered to be a major factor triggering atherosclerosis that ultimately leads to cardiovascular diseases, the main cause of death in industrialized countries. However, understanding the differentiation process in detail is obligatory to achieve a tight control of the process for future clinical applications to avoid undesired side effects. In this review, the current findings for adipo- and osteo-differentiation are summarized together with a brief statement on first clinical trials.

Mesenchymal stem cells as a potent cell source for bone regeneration

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

1α,25-Dihydroxyvitamin D3 inhibits osteoblastic differentiation of mouse periodontal fibroblasts

OBJECTIVE

Periodontal ligament (PDL) is a non-mineralized tissue connecting cementum and alveolar bone. Recent studies have suggested that periodontal fibroblasts can differentiate into mineralized tissue-forming cells such as osteoblasts and cementoblasts. We elucidated the immunolocalization of vitamin D receptor (VDR) and the effects of vitamin D(3) (VD(3)) on mouse periodontal fibroblasts to clarify the role of VDR and VD(3) in the differentiation of periodontal fibroblasts.

DESIGN

Immunohistochemical analysis using anti-VDR antibody was performed in paraffin sections of mouse mandibles at E13, E14, E17, P10, and P35. The roles of VD(3) in osteoblastic differentiation and mineralization were estimated by alkaline phosphatase (ALP) and alizarin red (AR) staining. In addition, the mRNA expression of osteoblast markers and mineralization inhibitors was examined by real-time PCR.

RESULTS

At the bud, cap and early bell stages, immunoreactivity for VDR was scarcely seen in the cells of dental follicles. Labelling was detected in the nuclei of cemetoblasts, periodontal fibroblasts and osteoblasts during root formation. VD(3) inhibited ALP activity and AR-positive mineralized nodule formation of periodontal fibroblasts in osteogenic culture medium. Real-time PCR revealed that VD(3) down-regulated the levels of osteoblast markers. In contrast, VD(3) significantly up-regulated the level of periodontal ligament associated protein (PLAP)-1, a negative regulator of osteoblastic differentiation.

CONCLUSION

These results suggest that VD(3) negatively regulates the osteoblastic differentiation of mouse periodontal fibroblasts and prevents the periodontal ligament from mineralization via increase of PLAP-1.

Uridine adenosine tetraphosphate activation of the purinergic receptor P2Y enhances in vitro vascular calcification

Purinergic signaling has a crucial role in different vascular processes. The endothelial-derived vasoconstrictor uridine adenosine tetraphosphate (Up(4)A) is a potent activator of the purinoceptor P2Y and is released under pathological conditions. Here we sought to measure purinergic effects on vascular calcification and initially found that Up(4)A plasma concentrations are increased in patients with chronic kidney disease. Exploring this further we found that exogenous Up(4)A enhanced mineral deposition under calcifying conditions ex vivo in rat and mouse aortic rings and in vitro in rat vascular smooth muscle cells. The addition of Up(4)A increased the expression of different genes specific for osteochondrogenic vascular smooth muscle cells such as Cbfa1, while decreasing the expression of SM22α, a marker specific for vascular smooth muscle cells. The influence of different P2Y antagonists on Up(4)A-mediated process indicated that P2Y(2/6) receptors may be involved. Mechanisms downstream of P2Y signaling involved phosphorylation of the mitogen-activated kinases MEK and ERK1/2. Thus, Up(4)A activation of P2Y influences phenotypic transdifferentiation of vascular smooth muscle cells to osteochondrogenic cells, suggesting that purinergic signaling may be involved in vascular calcification.

Hydroxyapatite/polylactide biphasic combination scaffold loaded with dexamethasone for bone regeneration

This study presents a novel design of a ceramic/polymer biphasic combination scaffold that mimics natural bone structures and is used as a bone graft substitute. To mimic the natural bone structures, the outside cortical-like shells were composed of porous hydroxyapatite (HA) with a hollow interior using a polymeric template-coating technique; the inner trabecular-like core consisted of porous poly(D,L-lactic acid) (PLA) that was loaded with dexamethasone (DEX) and was directly produced using a particle leaching/gas forming technique to create the inner diameter of the HA scaffold. It was observed that the HA and PLA parts of the fabricated HA/PLA biphasic scaffold contained open and interconnected pore structures, and the boundary between both parts was tightly connected without any gaps. It was found that the structure of the combination scaffold was analogous to that of natural bone based on micro-computed tomography analysis. Additionally, the dense, uniform apatite layer was formed on the surface of the HA/PLA biphasic scaffold through a biomimetic process, and DEX was successfully released from the PLA of the biphasic scaffold over a 1-month period. This release caused human embryonic palatal mesenchyme cells to proliferate, differentiate, produce ECM, and form tissue in vitro. Therefore, it was concluded that this functionally graded scaffold is similar to natural bone and represents a potential bone-substitute material.

Short-term application of dexamethasone enhances bone morphogenetic protein-7-induced ectopic bone formation in vivo

BACKGROUND

Long-term administration of glucocorticoids may lead to bone loss and osteoporosis as reported in previous experimental and clinical studies. On the other hand, several in vitro studies have demonstrated that dexamethasone treatment induces proliferation and differentiation of human and murine osteoblast precursors. Thereby, a positive interaction of dexamethasone with the osteoinductive bone morphogenetic proteins (BMPs) is reported in vitro, but in vivo studies are still missing. Thus, the aim of this study was to determine whether short-term application of dexamethasone may improve BMP-7-induced bone formation in vivo.

METHODS

Ectopic bone formation was induced in control and dexamethasone-treated mice by application of BMP-7 into the hamstring muscles. After 20 days of treatment, each ectopic bone nodule was analyzed by contact radiography, microcomputed tomography, and histomorphometry. Furthermore, mice were subjected to histomorphometric analyses of their lumbar vertebrae and proximal tibiae to assess the systemic effect of short-term dexamethasone treatment on bone metabolism.

RESULTS

Dexamethasone application significantly increased the bone volume and osteoblast number of the ectopic bone nodules compared with untreated controls. Histomorphometric analyses of the lumbar vertebrae and proximal tibiae revealed no significant differences between the control and dexamethasone-treated mice.

CONCLUSIONS

This study demonstrates that BMP-7-induced ectopic bone formation is significantly enhanced by systemic short-term application of dexamethasone. These in vivo data confirm the results of previous in vitro studies and could be of interest for further studies with the intention to improve BMP-induced bone formation by short-term application of dexamethasone.

Inorganic Polyphosphate Induces Osteoblastic Differentiation

Inorganic polyphosphate [Poly(P)] is especially prevalent in osteoblasts. We tested the hypothesis that Poly(P) stimulates osteoblastic differentiation and polyphosphate metabolism for bone formation. The osteoblast-like cell line, MC 3T3-E1, was cultured with Poly(P), and gene expression was evaluated by real-time reverse-transcription polymerase chain-reaction. Phosphatase activity and extracellular matrix mineralization were also determined. The role of Poly(P) was assessed in a beagle dog alveolar bone regeneration model. Poly(P) increased osteocalcin, osterix, bone sialoprotein, and tissue non-specific alkaline phosphatase gene expression, with a high level of end-polyphosphatase activity, resulting in low-chain-length Poly(P), inorganic pyrophosphate, and inorganic phosphate production. MC3T3-E1 cells differentiated into mature osteoblasts and showed expression of ectonucleotide pyrophosphatase phosphodiesterase 1, while mouse progressive ankylosis gene expression remained unchanged. Promotion of alveolar bone regeneration was observed in Poly(P)-treated beagle dogs. These findings suggest that Poly(P) induces osteoblastic differentiation and bone mineralization, and acts as a resource for mineralization.

Effects of vitamin E on the osteoblast differentiation

Vitamin E is thought to affect bone formation and bone remodeling. In this study, we investigated the effects of vitamin E (alpha-tocopherol and delta-tocopherol) on the osteoblasts isolated from rat calvariae. At 4 and 7 days (Day 4 and 7) after induction of osteoblastic differentiation, treatment of alpha-tocopherol (100 and 200 microM) and delta-tocopherol (2 and 20 microM) for 3 days significantly decreased alkaline phophatase activity of the cultured osteoblasts. At Day 14, however, no significant change was detected in ALP activity and expression of bone sialoprotein mRNA in the osteoblasts treated with alpha-tocopherol or delta-tocopherol for 3 days. Expression of osteocalcin mRNA was decreased by treatment of alpha-tocopherol (100 and 200 microM) and delta-tocopherol (2 and 20 microM) at Day 4 and 7. At Day 14, expression of osteocalcin mRNA was decreased only with treatment of 200 microM alpha-tocopherol. In addition, the noncalcified nodules were decreased by treatment of alpha-tocopherol (200 microM) and delta-tocopherol (20 microM) at Day 7. However, treatment of alpha-tocopherol and delta-tocopherol showed no significant change of formation of calcified nodules at Day 14. These results indicate that vitamin E inhibits differentiation of osteoblasts especially from early stage to osteoid-producing stage.