Activation of p38 mitogen-activated protein kinase and c-Jun-NH2-terminal kinase by BMP-2 and their implication in the stimulation of osteoblastic cell differentiation

Regulation of tenascin expression in bone

Tenascins regulate cell interaction with the surrounding pericellular matrix. Within bone, tenascins C and W influence osteoblast adhesion and differentiation, although little is known about the regulation of tenascin expression. In this study we examined the effect of osteogenic differentiation, bone morphogenetic protein (BMP) and Wnt growth factors, and mechanical loading on tenascin expression in osteogenic cells. Osteogenic differentiation increased tenascin C (TnC), and decreased tenascin W (TnW), expression. Both growth factors and mechanical loading increased both TnC and TnW expression, albeit via distinct signaling mechanisms. Both BMP-2 and Wnt5a induction of tenascin expression were mediated by MAP kinases. These data establish a role for BMP, Wnts, and mechanical loading in the regulation of tenascin expression in osteoblasts.

Potential characteristics of stem cells from human exfoliated deciduous teeth compared with bone marrow-derived mesenchymal stem cells for mineralized tissue-forming cell biology

INTRODUCTION

Tissue engineering and regenerative medicine using stem cell biology has been a promising field for treatment of local and systemic intractable diseases. Recently, stem cells from human exfoliated deciduous teeth (SHED) have been identified as a novel population of stem cells. This study focused on the characterization of SHED as compared with bone marrow-derived mesenchymal stem cells (BMMSCs).

METHODS

We investigated potential characteristics of SHED by using DNA microarray, real-time reverse transcriptase polymerase chain reaction, and immunofluorescence analysis.

RESULTS

Multiple gene expression profiles indicated that the expression of 2753 genes in SHED had changed by ≥2.0-fold as compared with that in BMMSCs. One of the most significant pathways that accelerated in SHED was that of bone morphogenetic protein (BMP) receptor signaling, which contains several cascades such as PKA, JNK, and ASK1. When the BMP signaling pathway was stimulated by BMP-2, the expression of BMP-2, BMP-4, Runx2, and DSPP was up-regulated significantly in SHED than that in BMMSCs. Furthermore, the BMP-4 protein was expressed much higher in SHED but not in BMMSCs, as confirmed by immunofluorescence.

CONCLUSIONS

By using the gene expression profiles, this study indicates that SHED is involved in the BMP signaling pathway and suggests that BMP-4 might play a crucial role in this. These results might be useful for effective cell-based tissue regeneration, including that of bone, pulp, and dentin, by applying the characteristics of SHED.

High levels of β-catenin signaling reduce osteogenic differentiation of stem cells in inflammatory microenvironments through inhibition of the noncanonical Wnt pathway

Periodontal ligament stem cells (PDLSCs), a new population of mesenchymal stem cells (MSCs), have been isolated from the periodontal ligament (PDL). The capacity of multipotency and self-renewal makes them an excellent cell source for bone regeneration and repair. However, their bone-regeneration ability could be awakened in inflammatory microenvironments, which may be the result of changes in their differentiation potential. Recently, genetic evidences has shown that the Wnt pathway plays an important role in bone homeostasis. In this study we have determined the specific role of β-catenin in osteogenic differentiation of PDLSCs obtained from inflammatory microenvironments (P-PDLSCs). The inflammatory microenvironment, while inhibiting osteogenic differentiation potential, promotes proliferation of MSCs. A higher the level of β-catenin in P-PDLSCs than in H-PDLSCs (PDLSCs obtained from a healthy microenvironment) resulted in the same disparity in canonical Wnt signaling pathway activation between each cell type. Here we show that activation of β-catenin suppresses the noncanonical Wnt/Ca(2+) pathway, leading to increased proliferation but reduced osteogenic differentiation of P-PDLSCs. Downregulation of the levels of β-catenin by treatment with dickkopf-1 (DKK-1) leads to activation of the noncanonical Wnt/Ca(2+) pathway, which, in turn, results in the promotion of osteogenic differentiation in P-PDLSCs. Interestingly, β-catenin can affect both the canonical Wnt/β-catenin pathway and the noncanonical Wnt/Ca(2+) pathway. Our data indicate that β-catenin plays a central role in regulating osteogenic differentiation of MSCs in inflammatory microenvironments. Given the important role of Wnt signaling in osteogenic differentiation, it is possible that agents that can modify this pathway may be of value in bone regeneration by MSCs in chronic inflammatory microenvironments.

Divergent activities of osteogenic BMP2, and tenogenic BMP12 and BMP13 independent of receptor binding affinities

Ectopic expression of recombinant human bone morphogenetic protein 2 (rhBMP2) induces osteogenesis, while ectopic expression of rhBMP12 and rhBMP13 induces the formation of tendon-like tissue. Despite their different in vivo activities, all three ligands bound to the type I bone morphogenic protein receptors (BMPRs), activin receptor-like kinase (ALK)-3 and ALK6, and to the type II BMPRs, activin receptor type-2A, activin receptor type-2B, and BMPR2, with similar affinities. Treatment of C3H10T1/2 cells with rhBMP2 activated SMAD signaling and induced expression of osteoblast markers including osteocalcin mRNA (Ocn). In contrast, treatment with rhBMP12 or rhBMP13 resulted in a dose-dependent induction of a tendon-specific gene (Thbs4) expression with no detectable activation of SMAD 1, 5, and 8. Differential regulation of Thbs4 and Ocn has potential utility as an in vitro biomarker for induction of tenogenic signaling. Such an assay also permits the ability to distinguish between the activities of different BMPs and may prove useful in studies on the molecular mechanisms of BMP tenogenic activity.

Bone morphogenic protein: an elixir for bone grafting--a review

Bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor beta superfamily. This literature review focuses on the molecular biology of BMPs, their mechanism of action, and subsequent applications. It also discusses uses of BMPs in the fields of dentistry and orthopedics, research on methods of delivering BMPs, and their role in tissue regeneration. BMP has positive effects on bone grafts, and their calculated and timely use with other growth factors can provide extraordinary results in fractured or nonhealing bones. Use of BMP introduces new applications in the field of implantology and bone grafting. This review touches on a few unknown facts about BMP and this ever-changing field of research to improve human life.

Activation of c-Jun NH(2)-terminal kinase 1 increases cellular responsiveness to BMP-2 and decreases binding of inhibitory Smad6 to the type 1 BMP receptor

Bone morphogenetic protein 2 (BMP-2) plays a critical role in the differentiation of precursor cells and has been approved for clinical application to induce new bone formation. To date, unexpectedly high doses of recombinant BMP-2 have been required to induce bone healing in humans. Thus, enhancing cellular responsiveness to BMP-2 potentially has critically important clinical implications. BMP responsiveness may be modulated in part by cross-talk with other signaling pathways, including mitogen-activated protein kinases (MAPKs). c-Jun NH(2)-terminal kinase (JNK) is a MAPK that has been reported to be required for late-stage differentiation of preosteoblasts and BMP-2-induced differentiation of preosteoblasts and pleuripotent cells. In this study we determined that MC3T3-E1-clone 24 cells (MC-24) can be induced by BMP-2 to differentiate into mineralizing osteoblast cultures. Using this inducible system, we employed both JNK loss-of-function and gain-of-function reagents to make three key observations: (1) JNK is required for phosphorylation of Smad1 by BMP-2 and subsequent activation of Smad1 signaling and osteoblast differentiation, (2) JNK1, but not JNK2, is required for BMP-2-induced formation of mineralized nodules, and (3) JNK1 activation decreases binding of inhibitory Smad6 to the type I BMP receptor (BMPR-I) and reciprocally increases binding of Smad1, both observations that would increase responsiveness to BMP-2. Understanding this and other pathways that lead to increased cellular responsiveness to BMPs could greatly aid more cost-effective and safe clinical delivery of these important molecules.

Asperosaponin VI, a saponin component from Dipsacus asper wall, induces osteoblast differentiation through bone morphogenetic protein-2/p38 and extracellular signal-regulated kinase 1/2 pathway

Osteoporosis is a reduction in skeletal mass because of the loss of osteoblastic activity or an increase in osteoclastic activity. The survival of osteoblast cells plays a crucial role in the development of osteoporosis. Asperosaponin VI (ASA VI) is a kind of saponin in the medicinal herb Dipsacus asper Wall which has long been used as an antiosteoporosis drug. The assay of cell proliferation, alkaline phosphatase (ALP) activity and measurement of mineralized matrix, showed that ASA VI exhibited a significant induction of proliferation, differentiation and mineralization in MC3T3-E1 and primary osteoblastic cells. Induction of differentiation by ASA VI was associated with increased bone morphogenetic protein-2 (BMP-2), indicating that BMP-2 is essential in ASA VI to mediate osteoblast maturation and differentiation. In addition, ASA VI may induce differentiation by increasing the activity of p38 and ERK1/2. In conclusion, ASA VI may induce osteoblast maturation and differentiation, and then increase bone formation via increasing BMP-2 synthesis, and activating p38 and ERK1/2.

Noncanonical BMP signaling regulates cyclooxygenase-2 transcription

Activation of p38 MAPK has been shown to be relevant for a number of bone morphogenetic protein (BMP) physiological effects. We report here the involvement of noncanonical phosphorylated mothers against decapentaplegic (Smad) signaling in the transcriptional induction of Cox2 (Ptgs2) by BMP-2 in mesenchymal cells and organotypic calvarial cultures. We demonstrate that different regulatory elements are required for regulation of Cox2 expression by BMP-2: Runt-related transcription factor-2 and cAMP response element sites are essential, whereas a GC-rich Smad binding element is important for full responsiveness. Efficient transcriptional activation requires cooperation between transcription factors because mutation of any element results in a strong decrease of BMP-2 responsiveness. BMP-2 activation of p38 leads to increased recruitment of activating transcription factor-2, Runx2, Smad, and coactivators such as p300 at the responsive sites in the Cox2 proximal promoter. We demonstrate, by either pharmacological or genetic analysis, that maximal BMP-2 effects on Cox2 and JunB expression require the function of p38 and its downstream effector mitogen/stress-activated kinase 1. Altogether our results strongly suggest that cooperative effects between canonical and noncanonical BMP signaling allow the fine-tuning of BMP transcriptional responses on specific target genes.

Na-doped β-tricalcium phosphate: physico-chemical and in vitro biological properties

Synthetic calcium phosphate ceramics as β-tricalcium phosphate (Ca(3)(PO(4))(2); β-TCP) are currently successfully used in human bone surgery. The aim of this work was to evaluate the influence of the presence of sodium ion in β-TCP on its mechanical and biological properties. Five Na-doped-β-TCP [Ca(10.5-x/2)Na(x)(PO(4))(7), 0 ≤ x ≤ 1] microporous pellets were prepared via solid phase synthesis, and their physico-chemical data (lattice compacity, density, porosity, compressive strength, infrared spectra) denote an increase of the mechanical properties and a decrease of the solubility when the sodium content is raised. On the other hand, the in vitro study of MC3T3-E1 cell activity (morphology, MTS assay and ALP activity) shows that the incorporation of sodium does not modify the bioactivity of the β-TCP. These results strongly suggest that Na-doped-β-TCP appear to be good candidates for their use as bone substitutes.

CB2 cannabinoid receptor targets mitogenic Gi protein-cyclin D1 axis in osteoblasts

CB2 is a Gi protein-coupled receptor activated by endo- and phytocannabinoids, thus inhibiting stimulated adenylyl cyclase activity. CB2 is expressed in bone cells and Cb2 null mice show a marked age-related bone loss. CB2-specific agonists both attenuate and rescue ovariectomy-induced bone loss. Activation of CB2 stimulates osteoblast proliferation and bone marrow derived colony-forming units osteoblastic. Here we show that selective and nonselective CB2 agonists are mitogenic in MC3T3 E1 and newborn mouse calvarial osteoblastic cultures. The CB2 mitogenic signaling depends critically on the stimulation of Erk1/2 phosphorylation and de novo synthesis of MAP kinase-activated protein kinase 2 (Mapkapk2) mRNA and protein. Further downstream, CB2 activation enhances CREB transcriptional activity and cyclin D1 mRNA expression. The CB2-induced stimulation of CREB and cyclin D1 is inhibitable by pertussis toxin, the MEK-Erk1/2 inhibitors PD098059 and U0126, and Mapkapk2 siRNA. These data demonstrate that in osteoblasts CB2 targets a Gi protein-cyclin D1 mitogenic axis. Erk1/2 phosphorylation and Mapkapk2 protein synthesis are critical intermediates in this axis.

8-Prenylkaempferol accelerates osteoblast maturation through bone morphogenetic protein-2/p38 pathway to activate Runx2 transcription

AIMS

In this study, we investigated the effect of 8-prenylkaempferol (8-PK), a prenyl-flavonoid isolated from Sophora flavescens, on osteoblast differentiation and maturation.

MAIN METHODS

MC3T3-E1 cells were exposed to 8-PK and the cytotoxicity was assayed. Osteoblast differentiation and maturation were evaluated by analyzing alkaline phosphatase (ALP) activity and cell mineralization, respectively. RT-PCR and Western blot were executed to determine the effects of 8-PK on osteoblast differentiation-related gene expression and signaling pathway.

KEY FINDINGS

8-PK significantly promoted ALP activity, up-regulated mRNA expressions of osteocalcin, osteopontin, and type I collagen, and induced bone nodules formation. Induction of differentiation by 8-PK was associated with increased bone morphogenetic protein (BMP)-2 expression, and sequentially up-regulated the phosphorylations of Smad1/5/8 and p38, and increased the nuclear translocation of runt-related transcription factor 2 (Runx2). Addition of BMP-2 antagonist noggin blocked 8-PK and recombinant mouse BMP-2-induced ALP activity, reconfirming that BMP-2 production is required in 8-PK-mediated osteoblast differentiation. Noggin also abrogated 8-PK evoked phosphorylations of Smad1/5/8 and p38, suggesting that BMP-2 signaling is required for p38 activation in 8-PK-treated cells. Application of p38 inhibitor SB203580 repressed not only 8-PK-mediated activation of ALP, but also the nuclear translocation of Runx2 and bone nodules formation.

SIGNIFICANCE

The present results suggested that BMP-2/p38/Runx2 pathways were involved in 8-PK-induced differentiation/maturation of MC3T3-E1 osteoblasts and firstly demonstrated that 8-PK might be a promising agent for inducing osteogenesis.

Gold nanoparticles promote osteogenic differentiation of mesenchymal stem cells through p38 MAPK pathway

Understanding the interaction mechanisms between nanomaterials and biological cells is important for the control and manipulation of these interactions for biomedical applications. In this study, we investigated the cellular effects of gold nanoparticles (AuNPs) on the differentiation of mesenchymal stem cells (MSCs) and the associated molecular mechanisms. The results showed that AuNPs promoted the differentiation of MSCs toward osteoblast cells over adipocyte cells by inducing an enhanced osteogenic transcriptional profile and an attenuated adipogenic transcriptional profile. AuNPs exerted the effects by interacting with the cell membrane and binding with proteins in the cytoplasm, causing mechanical stress on the MSCs to activate p38 mitogen-activated protein kinase pathway (MAPK) signaling pathway, which regulates the expression of relevant genes to induce osteogenic differentiation and inhibit adipogenic differentiation.

Bone morphogenetic proteins: a critical review

Bone Morphogenetic Proteins (BMPs) are potent growth factors belonging to the Transforming Growth Factor Beta superfamily. To date over 20 members have been identified in humans with varying functions during processes such as embryogenesis, skeletal formation, hematopoiesis and neurogenesis. Though their functions have been identified, less is known regarding levels of regulation at the extracellular matrix, membrane surface, and receptor activation. Further, current models of activation lack the integration of these regulatory mechanisms. This review focuses on the different levels of regulation, ranging from the release of BMPs into the extracellular components to receptor activation for different BMPs. It also highlights areas in research that is lacking or contradictory.

Induction of interleukin-6 expression by bone morphogenetic protein-6 in macrophages requires both SMAD and p38 signaling pathways

Unlike the prototype transforming growth factor-β (TGF-β), bone morphogenetic protein-6 (BMP-6) activates macrophages. Here, we report that BMP-6 induces the expression of IL-6 in macrophages. Using overexpression and knockdown experiments, we demonstrate that BMP receptor type II and activin-like kinase-2 are necessary for IL-6 induction by BMP-6. At the intracellular level, both Smad and p38 signaling pathways are required for the induction of IL-6. The cross-talk between the two pathways occurs at the level of transcription factor GATA4 and Smad 1/4. These results, taken together, demonstrate a novel BMP-6 signaling mechanism in which both the Smad and non-Smad pathways directly interact to activate the transcription of a target gene.

The identification of a heparin binding domain peptide from bone morphogenetic protein-4 and its role on osteogenesis

The presence of heparin binding has been become crucial in exerting growth factor related tissue formation. Receptor-mediated osteoblastic differentiation by bone morphogenetic protein (BMP)-4 and supportive function of its heparin binding has been proposed, direct role of the heparin binding site of BMP-4 on osteogenesis has not yet been fully investigated. If the binding site itself plays role on osteogenesis, the site domain can be useful in bone formation in combination with biomaterial. Herein, we synthesized a peptide sequence corresponding to residues 15-24 of BMP-4 (HBD, RKKNPNCRRH), as potential heparin binding sequence. The HBD peptide-induced ostoegenic differentiation by activating extracellular signal-regulated kinase (ERK1/2), one of the key regulators in hMSC. Also, treatment of cultured hMSCs with heparinase blocked both HBD peptide-induced osteogenic differentiation and GAG chain detection while abolishing the increased phospho-ERK level. These results suggest that the identified heparin binding domain peptide (HBD) stimulated osteoblastic differentiation via interaction with heparin and the ERK signaling. In vivo results further demonstrated that HBD, as a form of complex with alginate gel, was able to induce bone formation in the bone defect.

Protective effect of quercitrin against hydrogen peroxide-induced dysfunction in osteoblastic MC3T3-E1 cells

The protective effect of quercitrin on the response of osteoblastic MC3T3-E1 cells to oxidative stress was evaluated. Osteoblasts were incubated with H(2)O(2) and/or quercitrin, and markers of osteoblast function and oxidative damage were examined. Quercitrin treatment reversed the cytotoxic effect of H(2)O(2) significantly (P<0.05). This effect was blocked by ICI182780 and LY294002, suggesting that quercitrin's effect might be involved in estrogen action and results from PI3K mediated signaling pathway. Pretreatment of quercitrin increased collagen content, alkaline phosphatase (ALP) activity, and calcium deposition of osteoblasts compared with H(2)O(2) treated cells and these effects were blocked by ERKs and p38 mitogen-activated protein kinases (MAPKs) inhibitors such as PD98059 and SB203580, respectively. These suggest that quercitrin-induced protective effect against osteoblast dysfunction by oxidative stress is associated with increased activation of ERKs and p38 MAPK. Pretreatment with quercitrin also reduced the increase in bone-resorbing factor, receptor activator of nuclear factor-kB ligand (RANKL) and oxidative damage markers (malondialdehyde, protein carbonyl, and nitrotyrosine) induced by H(2)O(2). These results suggest that quercitrin may be protective against H(2)O(2)-induced dysfunction in osteoblasts.

Effect of phosphatidyl inositol 3-kinase, extracellular signal-regulated kinases 1/2, and p38 mitogen-activated protein kinase inhibition on osteogenic differentiation of muscle-derived stem cells

Skeletal muscle-derived stem cells (MDSCs) can undergo osteogenesis when treated with bone morphogenetic proteins (BMPs), making them a potential cell source for bone tissue engineering. The signaling pathways that regulate BMP4-induced osteogenesis in MDSCs are not well understood, although they may provide a means to better regulate differentiation during bone regeneration. The objective of this study was to characterize the signaling pathways involved in the BMP4-induced osteogenesis of MDSCs. Cells were treated with BMP4 and specific inhibitors to the extracellular signal-regulated kinases 1/2 (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and phosphatidyl inositol 3-kinase (PI3K) pathways (PD98059, SB203580, and Ly294002, respectively). Cellular proliferation, expression of osteoblast-related genes, alkaline phosphatase (ALP) activity, and tissue mineralization were measured to determine the role of each pathway in the osteogenic differentiation of MDSCs. Inhibition of the ERK1/2 pathway increased ALP activity and mineralization, whereas inhibition of the p38 MAPK pathway decreased osteogenesis, suggesting opposing roles of these pathways in the BMP4-induced osteogenesis of MDSCs. Inhibition of the PI3K pathway significantly increased mineralization by MDSCs. These findings highlight the involvement of the ERK1/2, p38 MAPK, and PI3K pathways in opposing capacities in MDSC differentiation and warrant further investigation, as it may identify novel therapeutic targets for the development of stem cell-based therapies for bone tissue engineering.

Immunolocalization of TAK1, TAB1, and p38 in the developing rat molar

In tooth development, transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) are involved in cell differentiation and matrix protein production. TGF-β and BMP have two signaling pathways: the Smad pathway and the non-Smad pathway. However, only a few studies have focused on the non-Smad pathway in tooth development. TGF-β-activated kinase 1 (TAK1) is activated by TGF-β or BMP and binds to TAK1-binding protein (TAB1), activating p38 or c-Jun N-terminal kinase (JNK), forming the non-Smad signaling pathway. In this study, we examined the distribution of these kinases, TGF-β receptor 1 (TGF-β-R1), BMP receptor-1B (BMPR-1B) and Smad4 in cells of the rat molar germ histochemically, in order to investigate the signaling pathway in each type of cell. Immunostaining for TGF-β-R1, BMPR-1B, Smad4, TAK1, TAB1 and phosphorylated-p38 (p-p38) showed similar reactions. In the cervical loop, reactions were clearer than in other enamel epithelium. In the inner enamel epithelium, signal increased with differentiation into ameloblasts, became strongest in the secretory stage, and decreased rapidly in the maturation stage. Signal also increased upon differentiation from preodontoblasts to odontoblasts. In Hertwig's epithelial sheath, with the exception of BMPR-1B, reactions were stronger in the later stage, showing more enamel protein secretion than in the early stage. However, no clear reaction corresponding to phosphorylated-JNK was observed in any type of cell. These results suggest that TGF-β or BMP is involved in the induction of differentiation of inner enamel epithelium cells into ameloblasts, and preodontoblast differentiation into odontoblasts, the regulation of cervical loop cell proliferation, the elongation or regulation of the epithelial sheath, and the secretion of enamel protein and dentin matrix protein through the non-Smad signaling pathway via TAK1, TAB1 and p38 as well as Smad signaling pathways in the rat molar germ.

Dorsomorphin and LDN-193189 inhibit BMP-mediated Smad, p38 and Akt signalling in C2C12 cells

Bone morphogenetic proteins (BMPs) are key regulators of cell fate decisions during embryogenesis and tissue homeostasis. BMPs signal through a coordinated assembly of two types of transmembrane serine/threonine kinase receptors to induce Smad1/5/8 plus non-Smad pathways, such as MAPK and Akt. The recent discovery of BMP receptor inhibitors opened new avenues to study specific BMP signalling and to delineate this effect from TGF-β and Activin signalling. Here we present comprehensive and quantitative analyses on both canonical and non-Smad mediated BMP signalling under Dorsomorphin (DM) and LDN-193189 (LDN) treatment conditions. We demonstrate for the first time, that both compounds affect not only the Smad but also the non-Smad signalling pathways induced by either BMP2, BMP6 or GDF5. The activation of p38, ERK1/2 and Akt in C2C12 cells was inhibited by DM and LDN. In addition "off-target" effects on all branches of BMP non-Smad signalling are presented. From this we conclude that the inhibition of BMP receptors by DM and more efficiently by LDN-193189 affects all known BMP induced signalling cascades.

p38 regulates expression of osteoblast-specific genes by phosphorylation of osterix

Osterix, a zinc finger transcription factor, is specifically expressed in osteoblasts and osteocytes of all developing bones. Because no bone formation occurs in Osx-null mice, Osterix is thought to be an essential regulator of osteoblast differentiation. We report that, in several mesenchymal and osteoblastic cell types, BMP-2 induces an increase in expression of the two isoforms of Osterix arising from two alternative promoters. We identified a consensus Sp1 sequence (GGGCGG) as Osterix binding regions in the fibromodulin and the bone sialoprotein promoters in vitro and in vivo. Furthermore, we show that Osterix is a novel substrate for p38 MAPK in vitro and in vivo and that Ser-73 and Ser-77 are the regulatory sites phosphorylated by p38. Our data also demonstrate that Osterix is able to increase recruitment of p300 and Brg1 to the promoters of its target genes fibromodulin and bone sialoprotein in vivo and that it directly associates with these cofactors through protein-protein interactions. Phosphorylation of Osterix at Ser-73/77 increased its ability to recruit p300 and SWI/SNF to either fibromodulin or bone sialoprotein promoters. We therefore propose that Osterix binds to Sp1 sequences on target gene promoters and that its phosphorylation by p38 enhances recruitment of coactivators to form transcriptionally active complexes.

Gallium modulates osteoclastic bone resorption in vitro without affecting osteoblasts

BACKGROUND AND PURPOSE

Gallium (Ga) has been shown to be effective in the treatment of disorders associated with accelerated bone loss, including cancer-related hypercalcemia and Paget's disease. These clinical applications suggest that Ga could reduce bone resorption. However, few studies have studied the effects of Ga on osteoclastic resorption. Here, we have explored the effects of Ga on bone cells in vitro.

EXPERIMENTAL APPROACH

In different osteoclastic models [osteoclasts isolated from long bones of neonatal rabbits (RBC), murine RAW 264.7 cells and human CD14-positive cells], we have performed resorption activity tests, staining for tartrate resistant acid phosphatase (TRAP), real-time polymerase chain reaction analysis, viability and apoptotic assays. We also evaluated the effect of Ga on osteoblasts in terms of proliferation, viability and activity by using an osteoblastic cell line (MC3T3-E1) and primary mouse osteoblasts.

KEY RESULTS

Gallium dose-dependently (0-100 microM) inhibited the in vitro resorption activity of RBC and induced a significant decrease in the expression level of transcripts coding for osteoclastic markers in RAW 264.7 cells. Ga also dramatically reduced the formation of TRAP-positive multinucleated cells. Ga down-regulated in a dose-dependant manner the expression of the transcription factor NFATc1. However, Ga did not affect the viability or activity of primary and MC3T3-E1 osteoblasts.

CONCLUSIONS AND IMPLICATIONS

Gallium exhibits a dose-dependent anti-osteoclastic effect by reducing in vitro osteoclastic resorption, differentiation and formation without negatively affecting osteoblasts. We provide evidence that this inhibitory mechanism involves down-regulation of NFATc1 expression, a master regulator of RANK-induced osteoclastic differentiation.

Neighbor of Brca1 gene (Nbr1) functions as a negative regulator of postnatal osteoblastic bone formation and p38 MAPK activity

The neighbor of Brca1 gene (Nbr1) functions as an autophagy receptor involved in targeting ubiquitinated proteins for degradation. It also has a dual role as a scaffold protein to regulate growth-factor receptor and downstream signaling pathways. We show that genetic truncation of murine Nbr1 leads to an age-dependent increase in bone mass and bone mineral density through increased osteoblast differentiation and activity. At 6 mo of age, despite normal body size, homozygous mutant animals (Nbr1(tr/tr)) have approximately 50% more bone than littermate controls. Truncated Nbr1 (trNbr1) co-localizes with p62, a structurally similar interacting scaffold protein, and the autophagosome marker LC3 in osteoblasts, but unlike the full-length protein, trNbr1 fails to complex with activated p38 MAPK. Nbr1(tr/tr) osteoblasts and osteoclasts show increased activation of p38 MAPK, and significantly, pharmacological inhibition of the p38 MAPK pathway in vitro abrogates the increased osteoblast differentiation of Nbr1(tr/tr) cells. Nbr1 truncation also leads to increased p62 protein expression. We show a role for Nbr1 in bone remodeling, where loss of function leads to perturbation of p62 levels and hyperactivation of p38 MAPK that favors osteoblastogenesis.

Physcion-8-O-beta-D-glucopyranoside enhances the commitment of mouse mesenchymal progenitors into osteoblasts and their differentiation: Possible involvement of signaling pathways to activate BMP gene expression

Here, we show the involvement of signaling pathways to induce the gene expression of bone morphogenetic protein (BMP) in the osteogenic activity of physcion-8-O-beta-D-glucopyranoside (physcion-Glu); it stimulated osteoblast differentiation in mouse osteoblast MC3T3-E1 subclone 4 cells and induced BMP-2 gene expression and activation of Akt and ERK/MAP kinases. Physcion-Glu-induced BMP-2 expression and mineralization were attenuated by LY294002, an inhibitor of PI3K that lies upstream of Akt and MAP kinases, suggesting that physcion-Glu induces osteoblast differentiation via PI3K-Akt/MAP kinase signaling pathways, which play important roles in inducing BMP-2 gene expression. Physcion-Glu also enhanced BMP-2-induced commitment of mouse bi-potential mesenchymal precursor C2C12 cells into osteoblasts while inducing the transcription of several osteogenic BMP isoforms, such as BMP-2, -4, -7, and -9. Osteogenic synergy between BMP-2 and physcion-Glu was supported by the fact that noggin inhibited BMP-2 and physcion-Glu-induced alkaline phosphatase expression and activity. Considering that physcion-Glu induced Runx2 activity and the nuclear translocation of p-Smad, physcion-Glu could act by enhancing the BMP signaling pathway that induces Smad activation and translocation to activate Runx2. In conclusion, physcion-Glu could enhance the commitment of mesenchymal progenitors into osteoblasts and their differentiation by activating signaling pathways to induce BMP gene expression.

Effect of BMP-9 and its derived peptide on the differentiation of human white preadipocytes

Several studies have shown that bone morphogenetic proteins (BMPs) can influence adipogenic and osteogenic cell lineages. We have shown that a peptide derived from BMP-9 (pBMP-9) at 400 ng/ml inhibits the proliferation of preosteoblasts and induces differentiation. We have now determined the effects of pBMP-9 (400 ng/ml) and equimolar concentrations of BMP-2 (100 ng/ml), BMP-9 (84.6 ng/ml) and pBMP-9 (9.04 ng/ml) on human white preadipocytes (HWP). pBMP-9 dose dependently reduced the proliferation of HWP without affecting the number of apoptotic cells. Incubation of the cells for 1 h with BMP-2, BMP-9 or pBMP-9 activated the Smad1/5/8 pathway, while incubation for 7 days in adipocyte differentiation (AD) serum-free medium containing ciglitazone and equimolar concentrations of BMP-2, BMP-9 or pBMP-9 enhanced the levels of mRNA of the adipogenic markers aP2 and adipoQ and increased the number of lipid vesicles. Thus, pBMP-9, like BMP-9, can increase the AD of HWP in AD serum-free medium.

Palate morphogenesis: current understanding and future directions

In the past, most scientists conducted their inquiries of nature via inductivism, the patient accumulation of "pieces of information" in the pious hope that the sum of the parts would clarify the whole. Increasingly, modern biology employs the tools of bioinformatics and systems biology in attempts to reveal the "big picture." Most successful laboratories engaged in the pursuit of the secrets of embryonic development, particularly those whose research focus is craniofacial development, pursue a middle road where research efforts embrace, rather than abandon, what some have called the "pedestrian" qualities of inductivism, while increasingly employing modern data mining technologies. The secondary palate has provided an excellent paradigm that has enabled examination of a wide variety of developmental processes. Examination of cellular signal transduction, as it directs embryogenesis, has proven exceptionally revealing with regard to clarification of the "facts" of palatal ontogeny-at least the facts as we currently understand them. Herein, we review the most basic fundamentals of orofacial embryology and discuss how functioning of TGFbeta, BMP, Shh, and Wnt signal transduction pathways contributes to palatal morphogenesis. Our current understanding of palate medial edge epithelial differentiation is also examined. We conclude with a discussion of how the rapidly expanding field of epigenetics, particularly regulation of gene expression by miRNAs and DNA methylation, is critical to control of cell and tissue differentiation, and how examination of these epigenetic processes has already begun to provide a better understanding of, and greater appreciation for, the complexities of palatal morphogenesis.

Role of PI3K on the regulation of BMP2-induced beta-Catenin activation in human bone marrow stem cells

Bone morphogenetic protein 2 (BMP2), a very potent bone-inducing agent, promotes the differentiation of bone marrow stem cells (BMSCs) to osteoblasts. However, the potency of BMP2 action is variable and its perturbed dynamic signaling pathways in human BMSCs has not been fully elucidated. In this study, we used a combination of stable isotope labeling by amino acids during cell culture (SILAC) and liquid-chromatography electrospray ionization mass spectrometry (LC-ESI-MS/MS) technology to reveal the BMP2 action in BMSC. In this quantitative proteomic analysis, 414 of 449 proteins were successfully quantified with 79.2% peptide quantification efficiency. Interestingly, beta-Catenin was identified in BMP2-stimulated heavy isotope-labeled cells, and further analysis confirmed that BMP2 increased beta-Catenin mRNA and protein levels. The increment effects of BMP2 on the beta-Catenin expression levels and its translocation to nucleus were diminished by blocking the PI3K signal pathway. In addition, BMP2-induced beta-Catenin activity and ALP activity were blocked by PI3K inhibition. Thus, our quantitative proteomics analysis and further biochemical investigations showed that BMP2 modulates beta-Catenin signaling via PI3K pathway and that this pathway plays roles in BMP2-induced osteoblast differentiation of hBMSCs.

Tanshinone IIA enhances BMP-2-stimulated commitment of C2C12 cells into osteoblasts via p38 activation

In this study, we demonstrate a stimulatory effect of tanshinone IIA isolated from the root of Salvia miltiorrhiza on the commitment of bi-potential mesenchymal precursor C2C12 cells into osteoblasts in the presence of bone morphogenetic protein (BMP)-2. At low concentrations, tanshinone IIA enhanced BMP-2-stimulated induction of alkaline phosphatase (ALP), an early phase biomarker of osteoblast differentiation, and mRNA expression of BMPs. ALP induction was inhibited by the BMP antagonist noggin, suggesting that tanshinone IIA enhances the osteogenic activity of BMP signaling. Furthermore, considering the tanshinone IIA-mediated enhancement of BMP-2-stimulated Smad-Runx2 activities, tanshinone IIA could enhance the osteogenic activity of BMP-2 via acceleration of Smad-Runx2 activation. Additionally, pharmacologic inhibition studies suggest the possible involvement of p38 in the action of tanshinone IIA. The p38 inhibitor SB202190 strongly and dose-dependently inhibited tanshinone IIA-enhanced ALP induction. SB202190 also dose-dependently inhibited the tanshinone IIA-induced p38 activation and combined tanshinone IIA-BMP-2-induced Smad activation. In conclusion, tanshinone IIA enhances the commitment of C2C12 cells into osteoblasts and their differentiation through synergistic cross talk between tanshinone IIA-induced p38 activation and BMP-2-induced Smad activation. These activations could subsequently induce the activation of Runx2, which induces osteogenesis via regulation of the osteogenic factors BMP and ALP expression.

COMP-Ang1, a chimeric form of Angiopoietin 1, enhances BMP2-induced osteoblast differentiation and bone formation

INTRODUCTION

Angiogenesis is closely associated with bone formation, especially endochondral ossification. Angiopoietin 1 (Ang1) is a specific growth factor functioning to generate a stable and matured vasculature through the Tie2 receptor/PI3K/AKT pathway. Recently cartilage oligomeric matrix protein (COMP)-Ang1, an Ang1 variant which is more potent than native Ang1 in phosphorylating Tie2 receptor and AKT, was developed. This study was designed to examine the effects of angiogenic COMP-Ang1 on BMP2-induced osteoblast differentiation and bone formation.

METHODS

Expression of endogenous Ang-1 and its binding receptor Tie 2 mRNA was examined in osteoblast-like cells and primary mouse calvarial cells by RT-PCR analysis, and was also monitored during osteoblast differentiation induced by BMP-2 and/or ascorbic acid and beta-glycerophosphate. Effects of COMP-Ang-1 on osteoblast differentiation and mineralization were evaluated by alkaline phosphatase (ALP) activity and osteocalcin (OC) production, and Alizarin red stain. For a molecular mechanism, Western blot and OG2 and 6xOSE promoter assays were done. For in vivo evaluation, adenoviral (Ad) vectors containing COMP-Ang-1 or BMP-2 gene were administered into thigh muscle of mice, and after 2 weeks bone formation was analyzed by micro-computed tomography and histology. Angiogenic event of COMP-Ang1 was confirmed by immunofluorescence analysis with anti-CD31 antibody.

RESULTS

Expression of Tie2 receptor was significantly increased in the course of osteoblast differentiation. Treatment or overexpression of COMP-Ang1 enhanced BMP2-induced ALP activity, OC production, and mineral deposition in a dose-dependent manner. In addition, COMP-Ang1 synergistically increased OG2 and 6xOSE promoter activities of BMP2, and sustained p38, Smad and AKT phosphorylation of BMP2. Notably, in vivo intramuscular injection of COMP-Ang1 dose-dependently enhanced BMP2-induced ectopic bone formation with increases in CD31 reactivity.

CONCLUSIONS

These results suggest that COMP-Ang1 synergistically enhanced osteoblast differentiation and bone formation through potentiating BMP2 signaling pathways and angiogenesis. Combination of BMP2 and COMP-Ang1 should be clinically useful for therapeutic application to fracture and destructive bone diseases.

Murine preosteoblast differentiation induced by a peptide derived from bone morphogenetic proteins-9

Bone morphogenetic proteins (BMPs) increase the differentiation of osteoblasts implicated in bone formation and repair. In a previous study, we demonstrated that a peptide derived from BMP-9 (pBMP-9) at 400 ng/mL inhibited murine preosteoblasts MC3T3-E1 proliferation. Here, we compared the effects of equimolar concentrations of BMP-2 (50 ng/mL), BMP-9 (42.3 ng/mL), and pBMP-9 (4.52 ng/mL) on the differentiation of MC3T3-E1 in a serum-free medium. Like BMP-2, BMP-9 and pBMP-9 activated the Smad pathway. In contrary to BMP-2, the Smad phosphorylation induced by BMP-9 and pBMP-9 is not prevented by noggin, an extracellular antagonist of BMP-2. Further, BMP-9 and pBMP-9 increased, dose dependently, alkaline phosphatase activity, an early marker of osteoblast differentiation, after 1 day. Quantitative real-time polymerase chain reaction analysis demonstrated that BMP-2, BMP-9, and pBMP-9 (4.52 or 400 ng/mL) all activated the transcription of Runx2, Osterix, type I collagen alpha1 chain, and Osteocalcin genes within day 6. Alizarin red S quantification demonstrated that pBMP-9 (400 ng/mL) and pBMP-9 (4.52 ng/mL) allowed a slight deposition of Ca(2+) in the extracellular matrix of cells within 12 and 18 days, respectively. Therefore, pBMP-9 might be a promising replacement for costly BMP in tissue engineering applications that require a well-defined serum-free medium.

Osteoarthritic cartilage chondrocytes alter subchondral bone osteoblast differentiation via MAPK signalling pathway involving ERK1/2

Osteoarthritic subchondral bone is characterized by abnormal bone density and enhanced production of bone turnover markers, an indication of osteoblast dysfunction. Several studies have proposed that pathological changes in articular cartilage influence the subchondral bone changes, which are typical of the progression of osteoarthritis; however, direct evidence of this has yet to be reported. The aim of the present study was to investigate what effects articular cartilage cells, isolated from normal and osteoarthritic joints, may have on the subchondral bone osteoblast phenotype, and also the potential involvement of the mitogen activated protein kinase (MAPK) signalling pathway during this process. Our results suggest that chondrocytes isolated from a normal joint inhibited osteoblast differentiation, whereas chondrocytes isolated from an osteoarthritic joint enhanced osteoblast differentiation, both via a direct and indirect cell interaction mechanisms. Furthermore, the interaction of subchondral bone osteoblasts with osteoarthritic chondrocyte conditioned media appeared to significantly activate ERK1/2 phosphorylation. On the other hand, conditioned media from normal articular chondrocytes did not affect ERK1/2 phosphorylation. Inhibition of the MAPK-ERK1/2 pathways reversed the phenotype changes of subchondral bone osteoblast, which would otherwise be induced by the conditioned media from osteoarthritic chondrocytes. In conclusion, our findings provide evidence that osteoarthritic chondrocytes affect subchondral bone osteoblast metabolism via an ERK1/2 dependent pathway.

N-methyl pyrrolidone as a potent bone morphogenetic protein enhancer for bone tissue regeneration

In medicine, N-methyl pyrrolidone (NMP) has a long track record as a constituent in medical devices approved by the Food and Drug Administration and thus can be considered as a safe and biologically inactive small chemical. In the present study, we report on the newly discovered pharmaceutical property of NMP in enhancing bone regeneration in a rabbit calvarial defect model in vivo. At the cellular level, the pharmaceutical effect of NMP was confirmed, in particular, in combination with bone morphogenetic protein (BMP)-2, because NMP increased early and late markers for maturation of preosteoblasts and human bone marrow-derived stem cells in vitro. When we used the multipotent cell line C2C12 without autologous BMP expression, NMP alone had no effect on alkaline phosphatase activity, a marker for osteogenic transdifferentiation. Nevertheless, in combination with low BMP-2 doses, alkaline phosphatase activity was more than eight times as great. Thus, the pharmaceutical NMP mode of action is that of an enhancer of BMP activity. The dependency of the effects of NMP on BMP was confirmed in preosteoblasts because noggin, an extracellular BMP inhibitor, suppressed NMP-induced increases in early markers for osteoblast maturation in vitro. At the molecular level, NMP was shown to have no effect on the binding of BMP-2 to the ectodomain of the high-affinity BMP receptor IA. However, NMP further increased the phosphorylation of p38 and Smad1,5,8 induced by BMP-2. Thus, the small chemical NMP enhances BMP activity by increasing the kinase activity of the BMP receptor complex for Smad1,5,8 and p38 and could be employed as a potent drug for bone tissue regeneration and engineering.

Differential effects of hypoxia on osteochondrogenic potential of human adipose-derived stem cells

Human adipose tissue-derived stem cells (hATSC) have been contemplated as reparative cells for cartilage engineering. Chondrogenic differentiation of hATSC can be induced by an enriched culture medium and a three-dimensional environment. Given that bone is vascularized and cartilage is not, oxygen tension has been suggested as a regulatory factor for osteochondrogenic differentiation. Our work aimed at determining whether hypoxia affects the osteochondrogenic potential of hATSC. hATSC were cultured in chondrogenic or osteogenic medium for 28 days, in pellets or monolayers, and under 5% or 20% oxygen tension. Cell differentiation was monitored by real-time PCR (COL2A1, aggrecan, Runx2, and osteocalcin). The chondrogenic differentiation was further evaluated by Alcian blue and immunohistological staining for glycosaminoglycans (GAGs) and type II collagen, respectively. Osteogenic differentiation was also assessed by the staining of mineralized matrix (Alizarin Red) and measurement of alkaline phosphatase (ALP) activity. The expression of chondrogenic markers was upregulated when hATSC were exposed to hypoxia in chondrogenic medium. Conversely, osteocalcin expression, mineralization, and ALP activity were severely reduced under hypoxic conditions even in the presence of osteogenic medium. Our data strongly suggest that hypoxia favors the chondrogenic differentiation of hATSC as evidenced by the expression of the chondrogenic markers, whereas it could alter their osteogenic potential. Our results highlight the differential regulatory role of hypoxia on the chondrogenic and osteogenic differentiation processes of hATSC. These data could help us exploit the potential of tissue engineering and stem cells to replace or restore the function of osteoarticular tissues.

The pro-form of BMP-2 interferes with BMP-2 signalling by competing with BMP-2 for IA receptor binding

Pro-forms of growth factors have received increasing attention since it was shown that they can affect both the maturation and functions of mature growth factors. Here, we assessed the biological function of the pro-form of bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor beta (TGFbeta)/BMP superfamily. The role of the 263 amino acids of the pro-peptide is currently unclear. In order to obtain an insight into the function of the pro-form (proBMP-2), the ability of proBMP-2 to induce alkaline phosphatase (AP), a marker enzyme for cells differentiating into osteoblasts, was tested. Interestingly, in contrast to mature BMP-2, proBMP-2 did not lead to induction of AP. Instead, proBMP-2 inhibited the induction of AP by BMP-2. This result raised the question of whether proBMP-2 may compete with mature BMP-2 for receptor binding. ProBMP-2 was found to bind to the purified extracellular ligand binding domain (ECD) of BMPR-IA, a high-affinity receptor for mature BMP-2, with a similar affinity as mature BMP-2. Binding of proBMP-2 to BMPR-IA was confirmed in cell culture by cross-linking proBMP-2 to BMPR-IA presented on the cell surface. In contrast to this finding, proBMP-2 did not bind to the ECD of BMPR-II. ProBMP-2 also differed from BMP-2 in its capacity to induce p38 and Smad phosphorylation. The data presented here suggest that the pro-domain of BMP-2 can alter the signalling properties of the growth factor by modulating the ability of the mature part to interact with the receptors.

M-Ras is activated by bone morphogenetic protein-2 and participates in osteoblastic determination, differentiation, and transdifferentiation

The small GTPase M-Ras is highly expressed in the central nervous system and plays essential roles in neuronal differentiation. However, its other cellular and physiological functions remain to be elucidated. Here, we clarify the novel functions of M-Ras in osteogenesis. M-Ras was prominently expressed in developing mouse bones particularly in osteoblasts and hypertrophic chondrocytes. Its expression was elevated in C3H/10T1/2 (10T1/2) mesenchymal cells and in MC3T3-E1 preosteoblasts during differentiation into osteoblasts. Treatment of C2C12 skeletal muscle myoblasts with bone morphogenetic protein-2 (BMP-2) to bring about transdifferentiation into osteoblasts also induced M-Ras mRNA and protein expression. Moreover, the BMP-2 treatment activated the M-Ras protein. Stable expression of the constitutively active M-Ras(G22V) in 10T1/2 cells facilitated osteoblast differentiation. M-Ras(G22V) also induced transdifferentiation of C2C12 cells into osteoblasts. In contrast, knockdown of endogenous M-Ras by RNAi interfered with osteoblast differentiation in 10T1/2 and MC3T3-E1 cells. Osteoblast differentiation in M-Ras(G22V)-expressing C2C12 cells was inhibited by treatment with inhibitors of p38 MAP kinase (MAPK) and c-Jun N-terminal kinase (JNK) but not by inhibitors of MAPK and ERK kinase (MEK) or phosphatidylinositol 3-kinase. These results imply that M-Ras, induced and activated by BMP-2 signaling, participates in the osteoblastic determination, differentiation, and transdifferentiation under p38 MAPK and JNK regulation.

Effects of prostaglandin D2 on Na-dependent phosphate transport activity and its intracellular signaling mechanism in osteoblast-like cells

Inorganic phosphate (Pi) transport probably represents an important function of bone-forming cells in relation to extracellular matrix mineralization. In the present study, we investigated the effect of prostaglandin D2 (PGD2) on Pi transport activity and its intracellular signaling mechanism in MC3T3-E1 osteoblast-like cells. PGD2 stimulated Na-dependent Pi uptake time- and dose-dependently in MC3T3-E1 cells during their proliferative phase. A protein kinase C (PKC) inhibitor calphostin C partially suppressed the stimulatory effect of PGD2 on Pi uptake. The selective inhibitors of mitogen-activated protein (MAP) kinase pathways such as ERK, p38 and Jun kinases suppressed PGD2-induced Pi uptake. The inhibitors of phosphatidylinositol (PI) 3-kinase and S6 kinase reduced this effect of PGD2, while Akt kinase inhibitor did not. These results suggest that PGD2 stimulates Na-dependent Pi transport activity in the phase of proliferation of osteoblasts. The mechanisms responsible for this effect are activation of PKC, MAP kinases, PI 3-kinase and S6 kinase.

Critical roles of the TGF-beta type I receptor ALK5 in perichondrial formation and function, cartilage integrity, and osteoblast differentiation during growth plate development

TGF-beta has been implicated in the proliferation and differentiation of chondrocytes and osteoblasts. However, the in vivo function of TGF-beta in skeletal development is unclear. In this study, we investigated the role of TGF-beta signaling in growth plate development by creating mice with a conditional knockout of the TGF-beta type I receptor ALK5 (ALK5(CKO)) in skeletal progenitor cells using Dermo1-Cre mice. ALK5(CKO) mice had short and wide long bones, reduced bone collars, and trabecular bones. In ALK5(CKO) growth plates, chondrocytes proliferated and differentiated, but ectopic cartilaginous tissues protruded into the perichondrium. In normal growth plates, ALK5 protein was strongly expressed in perichondrial progenitor cells for osteoblasts, and in a thin chondrocyte layer located adjacent to the perichondrium in the peripheral cartilage. ALK5(CKO) growth plates had an abnormally thin perichondrial cell layer and reduced proliferation and differentiation of osteoblasts. These defects in the perichondrium likely caused the short bones and ectopic cartilaginous protrusions. Using tamoxifen-inducible Cre-ER-mediated ALK5-deficient primary calvarial cell cultures, we found that TGF-beta signaling promoted osteoprogenitor proliferation, early differentiation, and commitment to the osteoblastic lineage through the selective MAPKs and Smad2/3 pathways. These results demonstrate the important roles of TGF-beta signaling in perichondrium formation and differentiation, as well as in growth plate integrity during skeletal development.

Controlled release of bisphosphonate from a calcium phosphate biomaterial inhibits osteoclastic resorption in vitro

Calcium phosphate biomaterials such as calcium deficient apatite (CDA) have been contemplated as carrier for delivery of bisphosphonate in bone tissues. In the present work, we have investigated the in vitro biological properties of Zoledronate-loaded CDA. CDA was loaded with zoledronate according to a previously described coating process. 31P MAS NMR spectra demonstrated the effective loading of zoledronate onto CDA. Using 14C labeled zoledronate, we then demonstrated the in vitro release of zoledronate from CDA. In a first set of experiments, we confirmed that Zoledronate reduced the number of TRAP-, vitronectin receptor-, and F-actin ring-positive cells as well as the resorption activity of osteoclasts obtained from a total rabbit bone cell culture. Interestingly, Zoledronate-loaded CDA and its extractive solutions decreased the osteoclastic resorption. Finally, zoledronate-loaded CDA did not affect the viability and alkaline phosphatase activity of primary osteoblastic cells. These data demonstrate that CDA is effective for loading and release of zoledronate. The released zoledronate inhibited osteoclastic resorption without affecting osteoblasts. Our findings therefore suggest that such a drug delivery system would allow an increase in the efficiency of bisphosphonates by being locally available. Further experiments are now required to evaluate the in vivo antiresorptive activity of this concept.

cAMP enhances BMP2-signaling through PKA and MKP1-dependent mechanisms

Recent studies suggest that the elevation of intracellular cyclic adenosine monophosphate (cAMP) and the activation of the protein kinase A regulate BMP-induced osteogenesis. However, the precise mechanisms underlying the enhancing effect of cAMP on BMP2 signaling were not completely revealed. In this study we investigated the effect of elevated cAMP level and PKA activation on the BMP2-induced osteoblastic differentiation in pluripotent C2C12 cells. Alkaline phosphatase activity and its mRNA were consistently induced by BMP2 treatment. The pretreatment of C2C12 cells with Forskolin, a cAMP generating agent, dbcAMP, an analogue of cAMP, or IBMX (3-isobutyl 1-methyl xanthine), and a nonspecific inhibitor of phosphodiesterases elicited further activation of alkaline phosphatase. Furthermore, elevated intracellular cAMP level increased BMP2-induced MKP1. On the other hand, BMP2-induced Erk phosphorylation (p44/p42) and cell proliferation were suppressed in the presence of cAMP. Thus, cAMP might enhance BMP2-induced osteoblastic differentiation by a MKP1-Erk-dependent mechanism.

Effect of exposure to an extremely low frequency-electromagnetic field on the cellular collagen with respect to signaling pathways in osteoblast-like cells

The effect of exposure to extremely low frequency-electromagnetic field (ELF-EMF: 3 mT, 60 Hz) on differentiation of mouse osteoblast-like MC3T3-E1 cells was examined together with addition of insulin-like growth factor I (IGF-I). As a marker of the differentiation, the cellular collagen content was determined by the absorbance of Sirius red-stained cells measured at the wavelength of 510-520 nm with an imaging microspectroscopy. Exposure to ELF-EMF increased significantly the collagen in the cells. Treatment with PD98059, an inhibitor of extracellular signal-regulated kinase 1/2 (ERK1/2) activation, reduced the collagen in all of the cells examined on control, IGF-I addition and ELF-EMF exposure, however, PD98059 did not prevent the increase in the collagen caused by ELF-EMF exposure, and IGF-I also increased the collagen in the presence of the inhibitor. When phosphatidylinositol 3-kinase (PI3K) pathway was inhibited by LY294002, the increase in collagen induced by ELF-EMF exposure was accelerated, however, the increase in collagen observed by IGF-I addition was suppressed. Treatment with SB203580, an inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), suppressed the increase in the collagen induced by ELF-EMF exposure, whereas IGF-I addition increased the collagen in the presence of the inhibitor. These results suggested that collagen synthesis stimulated by ELF-EMF exposure was carried out by the participation of p38 MAPK pathway, and that PI3K pathway may have the role to suppress the collagen synthesis induced by ELF-EMF exposure, and that the suppression of the PI3K pathway may allow the acceleration of the collagen synthesis.

Signaling networks that control the lineage commitment and differentiation of bone cells

Osteoblasts and osteoclasts are the two major bone cells involved in the bone remodeling process. Osteoblasts are responsible for bone formation while osteoclasts are the bone-resorbing cells. The major event that triggers osteogenesis and bone remodeling is the transition of mesenchymal stem cells into differentiating osteoblast cells and monocyte/macrophage precursors into differentiating osteoclasts. Imbalance in differentiation and function of these two cell types will result in skeletal diseases such as osteoporosis, Paget's disease, rheumatoid arthritis, osteopetrosis, periodontal disease, and bone cancer metastases. Osteoblast and osteoclast commitment and differentiation are controlled by complex activities involving signal transduction and transcriptional regulation of gene expression. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of the multiple factors and signaling networks that control the differentiation process at a molecular level. This review summarizes recent advances in studies of signaling transduction pathways and transcriptional regulation of osteoblast and osteoclast cell lineage commitment and differentiation. Understanding the signaling networks that control the commitment and differentiation of bone cells will not only expand our basic understanding of the molecular mechanisms of skeletal development but will also aid our ability to develop therapeutic means of intervention in skeletal diseases.

Therapeutic potential of inhaled p38 mitogen-activated protein kinase inhibitors for inflammatory pulmonary diseases

BACKGROUND

Over the past two decades, p38 MAPK (mitogen-activated protein kinase) has been the subject of intense multidisciplinary research. p38 MAPK inhibitors have been shown to be efficacious in several disease models, including rheumatoid arthritis, psoriasis, Crohn's disease, and stroke. Recent studies support a role for p38 MAPK in the development, maintenance, and/or exacerbation of a number of pulmonary diseases, such as asthma, cystic fibrosis, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD).

OBJECTIVE

Many previous attempts to develop p38 MAPK inhibitors have failed as a result of unacceptable safety profiles. These toxicities have been varied and are believed to derive from different off-target effects.

METHOD

The above concerns can be overcome by delivering the compound locally to minimize whole-body burden, resulting in low exposure to the gastrointestinal, liver, and CNS. This review discusses the role of p38 MAPK in various inflammatory diseases, followed by the toxicity concerns associated with p38 MAPK inhibition. It also highlights the possible beneficial effect of delivering drugs via the inhalation route.

CONCLUSION

We present proof-of-principle confirming the therapeutic potential of inhaled p38 inhibitors for asthma and other inflammatory pulmonary diseases.

Bone morphogenic protein 2 activates protein kinase D to regulate histone deacetylase 7 localization and repression of Runx2

The transcriptional activity of Runx2 is determined by associations with co-repressors including histone deacetylase 7 (HDAC7). We previously found that bone morphogenic protein 2 (BMP2) induces export of HDAC7 from the nucleus. In this study we demonstrate that BMP2 specifically stimulates redistribution of HDAC7 but not HDAC 4, 5, or 6. HDAC7 subcellular redistribution in mesenchymal cells requires Crm1-mediated nuclear export, is associated with increased HDAC7 serine phosphorylation, and requires conserved serines in the HDAC7 amino terminus. The protein kinase D (PKD) inhibitor Gö6976 blocked both basal and BMP2-directed HDAC7 nuclear export. Protein kinase D1 (PKD1) associated with HDAC7 in a BMP2-enhanced manner, and a constitutively active form of PKD1 stimulated HDAC7 nuclear export. Furthermore, active PKD1 inhibited repression of Runx2-mediated transcription by HDAC7. Suppression of HDAC7 was not sufficient to rescue BMP2 induction of osteoblast marker genes in Gö6976-treated cells, indicating that PKD-dependent factors beyond attenuation of HDAC7-repressive activity are required for osteoblast differentiation. These results establish a novel pathway by which BMP signaling regulates Runx2 activity via PKD-dependent inhibition of HDAC7 transcriptional repression.

Prevention of trabecular bone loss induced by estrogen deficiency by a selective p38alpha inhibitor

Increased bone remodeling with estrogen deficiency is mediated by the production of cytokines such as TNFalpha and interleukin (IL)-1. Recent data have indicated that the p38 pathway mediates cytokines effects on enhanced bone turnover in postmenopausal osteoporosis. Thus, in this study, we investigated the effect of a selective p38alpha inhibitor, SD-282, on the prevention of bone loss induced by estrogen deficiency in an adult ovariectomized (OVX) rat model. Results indicate that oral administration of SD-282 for 8 wk dose-dependently blunted the increase in the bone resorption marker DPD/Cr induced by OVX in adult rats. Associated with this effect, SD-282 did not reduce but significantly enhanced by 2-fold the rise in the bone formation marker serum osteocalcin observed in OVX animals. In addition, SD-282 completely blocked vertebral bone loss associated with estrogen deficiency. Furthermore, a partial preventive effect was observed in long bones with reduction of trabecular bone loss and enhancement of cross-sectional area of the diaphysis. Prevention of trabecular bone loss and increased in cortical bone area were associated with improvement of biomechanical resistances. In conclusion, chronic administration of a selective p38alpha inhibitor effectively prevented trabecular bone loss and alteration of bone microarchitecture induced by estrogen deficiency. Prevention of bone loss was associated with inhibition of bone resorption with uncoupled changes in bone formation. These data strongly suggest that the p38 pathway is important for regulation of bone resorption induced by estrogen deficiency, and selective inhibitors of this pathway have potential for prevention of bone loss in postmenopausal osteoporosis.

BMP signaling dynamics in embryonic orofacial tissue

The bone morphogenetic protein (BMP) family represents a class of signaling molecules, that plays key roles in morphogenesis, cell proliferation, survival and differentiation during normal development. Members of this family are essential for the development of the mammalian orofacial region where they regulate cell proliferation, extracellular matrix synthesis, and cellular differentiation. Perturbation of any of these processes results in orofacial clefting. Embryonic orofacial tissue expresses BMP mRNAs, their cognate proteins, and BMP-specific receptors in unique temporo-spatial patterns, suggesting functional roles in orofacial development. However, specific genes that function as downstream mediators of BMP action during orofacial ontogenesis have not been well defined. In the current study, elements of the Smad component of the BMP intracellular signaling system were identified and characterized in embryonic orofacial tissue and functional activation of the Smad pathway by BMP2 and BMP4 was demonstrated. BMP2 and BMP4-initiated Smad signaling in cells derived from embryonic orofacial tissue was found to result in: (1) phosphorylation of Smads 1 and 5; (2) nuclear translocation of Smads 1, 4, and 5; (3) binding of Smads 1, 4, and 5 to a consensus Smad binding element (SBE)-containing oligonucleotide; (4) transactivation of transfected reporter constructs, containing BMP-inducible Smad response elements; and (5) increased expression at transcriptional as well as translational levels of Id3 (endogenous gene containing BMP receptor-specific Smad response elements). Collectively, these data document the existence of a functional Smad-mediated BMP signaling system in cells of the developing murine orofacial region.