Bone morphogenetic proteins, extracellular matrix, and mitogen-activated protein kinase signaling pathways are required for osteoblast-specific gene expression and differentiation in MC3T3-E1 cells

The roles of bone morphogenetic proteins and their signaling in the osteogenesis of adipose-derived stem cells

Large-size bone defects can severely compromise both aesthetics and musculoskeletal functions. Adipose-derived stem cells (ASCs)-based bone tissue engineering has recently become a promising treatment strategy for the above situation. As robust osteoinductive cytokines, bone morphogenetic proteins (BMPs) are commonly used to promote the osteogenesis of ASCs. In this process, BMP signaling plays a pivotal role. However, it remains ambiguous how the pleiotrophic BMPs are involved in the commitment of ASCs along osteogenesis instead of other lineages, such as adipogenesis. BMP receptor type-IB, extracellular signal-regulated kinase, and Wnt5a appear to be the main switches controlling the in vitro osteogenic commitment of ASCs. Tumor necrosis factor-alpha, an acute inflammatory cytokine, is reported to play an important role in mediating osteogenic commitment of ASCs in vivo. In addition, various active agents and methods have been used to enhance and accelerate the osteogenesis of ASCs through promoting BMP signaling. In this review, we summarize the current knowledge on the roles of BMPs and their signaling in the osteogenesis of ASCs in vitro and in vivo.

Fibronectin and vitronectin promote human fetal osteoblast cell attachment and proliferation on nanoporous titanium surfaces

Improvements in osteoconduction of implant biomaterials require focusing on the bone-implant interface, which is a complex multifactorial system. Surface topography of implants plays a crucial role at this interface. Nanostructured surfaces have been shown to promote serum protein adsorption and osteoblast adhesion when compared to micro-structured surfaces for bone-implant materials. We studied the influence of the serum proteins fibronectin and vitronectin on the attachment and proliferation of osteoblasts onto nanostructured titania surfaces. Human fetal osteoblastic cells hFOB 1.19 were used as model osteoblasts and were grown on nanoporous TiO2 templates, using Ti6AI4V and commercially pure Ti substrates as controls. Results show a significant increase in cell proliferation'on nanoporous TiO2 over flat substrates. Initial cell attachment data exhibited a significant effect by either fibronectin or vitronectin on cell adhesion at the surface of any of the tested materials. In addition, the extent of cell adhesion was significantly different between the nanoporous TiO2 and both Ti6AI4V and commercially pure Ti substrates, with the first showing the highest surface coverage. There was no significant difference on osteoblast attachment or proliferation between the presence of fibronectin or vitronectin using any of the material substrates. Taken together, these results suggest that the increase in osteoblast attachment and proliferation shown on the nanoporous TiO2 is due to an increase in the adsorption of fibronectin and vitronectin because of the higher surface area and to an enhanced protein unfolding, which allows access to osteoblast binding motifs within these proteins.

Osteogenic differentiation of human adipose-derived stem cells can be accelerated by controlling the frequency of continuous ultrasound

OBJECTIVES

The purpose of this study was to demonstrate that the effects of continuous ultrasound on the osteogenic differentiation of human adipose-derived stem cells (hASCs) are dependent on the frequency in vitro.

METHODS

Before stimulation, we characterized the hASCs using cluster of differentiation marker profiles and tridifferentiation. Then we selected effective frequencies in the range of 0.5 to 1.5 MHz (with a peak negative pressure of 52 kPa), which upregulated runt-related transcription factor 2 messenger RNA expression. Next, the effects of ultrasound at the selected frequencies on the osteogenic differentiation were evaluated at the protein level. Alkaline phosphatase activity and the formation of mineralized nodules were measured. We additionally identified the cellular mechanisms underlying the effects of ultrasound stimulation using Western blotting.

RESULTS

The hASCs showed general cluster of differentiation marker profiles of stem cells and confirmed their potentials to yield adipogenic, chondrogenic, and osteogenic differentiation. Frequencies of 0.5, 1.0, and 1.5 MHz were selected for higher runt-related transcription factor 2 expression in the range of 0.5 to 1.5 MHz. Among the 3 groups, alkaline phosphatase activity and the formation of mineralized nodules were increased in cells exposed to 1.5-MHz ultrasound compared with cells exposed to 0.5-or 1.0-MHz ultrasound and nontreated control cells. We additionally confirmed that this acceleration of osteogenic differentiation was related to p38 and protein kinase B signaling pathways.

CONCLUSIONS

In this study, we found that, in the selected range, 1.5 MHz was the most effective frequency for inducing the osteogenic differentiation of hASCs.

BMP-2 differentially modulates FGF-2 isoform effects in osteoblasts from newborn transgenic mice

We previously generated separate lines of transgenic mice that specifically overexpress either the Fibroblast growth factor (FGF)-2 low-molecular-mass isoform (Tg(LMW)) or the high-mass isoforms (Tg(HMW)) in the osteoblast lineage. Vector/control (Tg(Vector)) mice were also made. Here we report the use of isolated calvarial osteoblasts (COBs) from those mice to investigate whether the FGF-2 protein isoforms differentially modulate bone formation in vitro. Our hypothesis states that FGF-2 isoforms specifically modulate bone morphogenetic protein 2 (BMP-2) function and subsequently bone differentiation genes and their related signaling pathways. We found a significant increase in alkaline phosphatase-positive colonies in Tg(LMW) COBs compared with Tg(Vector) controls. BMP-2 treatment significantly increased mineralized colonies in Tg(Vector) and Tg(LMW) COBs. BMP-2 caused a further significant increase in mineralized colonies in Tg(LMW) COBs compared with Tg(Vector) COBs but did not increase alkaline phosphatase-positive colonies in Tg(HMW) COBs. Time-course studies showed that BMP-2 caused a sustained increase in phosphorylated mothers against decapentaplegic-1/5/8 (Smad/1/5/8), runt-related transcription factor-2 (Runx-2), and osterix protein in Tg(LMW) COBs. BMP-2 caused a sustained increase in phospho-p38 MAPK in Tg(Vector) but only a transient increase in Tg(LMW) and Tg(HMW) COBs. BMP-2 caused a transient increase in phospho-p44/42 MAPK in Tg(Vector) COBs and no increase in Tg(LMW) COBs, but a sustained increase was found in Tg(HMW) COBs. Basal expression of FGF receptor 1 protein was significantly increased in Tg(LMW) COBs relative to Tg(Vector) COBs, and although BMP-2 caused a transient increase in FGF receptor 1 expression in Tg(Vector) COBs and Tg(HMW) COBs, there was no further increase Tg(LMW) COBs. Interestingly, although basal expression of FGF receptor 2 was similar in COBs from all genotypes, BMP-2 treatment caused a sustained increase in Tg(LMW) COBs but decreased FGF receptor 2 in Tg(Vector) COBs and Tg(HMW) COBs.

Chrysin promotes osteogenic differentiation via ERK/MAPK activation

The effect of the anti-inflammatory flavonoid chrysin on osteogenesis was determined in preosteoblast MC3T3-E1 cells. Results demonstrated that chrysin could induce osteogenic differentiation in the absence of other osteogenic agents. Chrysin treatment promoted the expression of transcription factors (Runx2 and Osx) and bone formation marker genes (Col1A1, OCN, and OPN) as well as enhanced the formation of mineralized nodules. During osteogenic differentiation, chrysin preferentially activated ERK1/2, but not JNK nor the p38 MAPKs. Further experiments with inhibitors revealed the co-treatment of U0126, PD98059, or ICI182780 (a general ER antagonist) with chrysin effectively abrogated the chrysin-induced osteogenesis and ERK1/2 activation. Thus, the effect of chrysin on osteogenesis is ERK1/2-dependent and involves ER. Therefore, chrysin has the significant potential to enhance osteogenesis for osteoporosis prevention and treatment.

Actin microfilament mediates osteoblast Cbfa1 responsiveness to BMP2 under simulated microgravity

Microgravity decreases osteoblastic activity, induces actin microfilament disruption and inhibits the responsiveness of osteoblast to cytokines, but the mechanisms remains enigmatic. The F-actin cytoskeleton has previously been implicated in manifold changes of cell shape, function and signaling observed under microgravity. Here we investigate the involvement of microfilament in mediating the effects of microgravity and BMP2 induction on Cbfa1 activity. For this purpose we constructed a fluorescent reporter cell line (OSE-MG63) of Cbfa1 activity by stably transfecting MG63 cells with a reporter consisting of six tandem copies of OSE2 and a minimal mOG2 promoter upstream of enhanced green fluorescent protein (EGFP). The fluorescence intensity of OSE-MG63 showed responsiveness to bone-related cytokines (IGF-I, vitamin D3 and BMP2) and presented an accordant tendency with alkaline phosphatase (ALP) activity. Using OSE-MG63 reporter fluorescence, we performed a semi-quantitative analysis of Cbfa1 activity after treatment with simulated microgravity, microfilament-disrupting agent (cytochalasin B, CB), microfilament-stabilizing agent (Jasplakinolide, JAS) or any combination thereof. In parallel, ALP activity, DNA binding activity of Cbfa1 to OSE2 (ChIP), F-actin structure (immunofluorescence) and EGFP mRNA expression (RT-qPCR) were analyzed. Simulated microgravity inhibited Cbfa1 activity, affected the responsiveness of Cbfa1 to cytokine BMP2, and caused a thinning and dispersed distribution of microfilament. Under normal gravity, CB significantly attenuated BMP2 induction to Cbfa1 activity as well as DNA binding activity of Cbfa1 to OSE2. The addition of JAS reversed the inhibitory effects of microgravity on the responsiveness of Cbfa1 to BMP2. Our study demonstrates that disrupting the microfilament organization by CB or simulated microgravity attenuates the responsiveness of Cbfa1 to BMP2. A stabilization of the microfilament organization by JAS reverses this inhibition. Taken together, these results suggest that actin microfilament participates in BMP2’s induction to Cbfa1 activity and that their disruption might be an important contributor to microgravity’s inhibition on BMP2’s osteogenic induction.

Affinity-selected heparan sulfate for bone repair

Bone morphogenetic protein (BMP)-2 is a potent bone healing compound produced at sites of bone trauma. Here we present a therapeutic strategy to harness the activity of endogenously produced BMP-2 by delivery of an affinity-matched heparan sulfate (HS) glycos aminoglycan biomaterial that increases the bioavailability, bioactivity and half-life of this growth factor. We have developed a robust, cost effective, peptide-based affinity platform to isolate a unique BMP-2 binding HS variant from commercially available preparations of HS, so removing the manufacturing bottleneck for their translation into the clinic. This affinity-matched HS enhanced BMP-2-induced osteogenesis through improved BMP-2 kinetics and receptor modulation, prolonged pSMAD signaling and reduced interactions with its antagonist noggin. When co-delivered with a collagen implant, the HS was as potent as exogenous BMP-2 for the healing of critical-sized bone defects in rabbits. This affinity platform can be readily tuned to isolate HS variants targeted ata range of clinically-relevant growth and adhesive factors.

Epigenetic regulation of BMP2 by 1,25-dihydroxyvitamin D3 through DNA methylation and histone modification

Genetic hypercalciuric stone-forming (GHS) rats have increased intestinal Ca absorption, decreased renal tubule Ca reabsorption and low bone mass, all of which are mediated at least in part by elevated tissue levels of the vitamin D receptor (VDR). Both 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and bone morphogenetic protein 2 (BMP2) are critical for normal maintenance of bone metabolism and bone formation, respectively. The complex nature of bone cell regulation suggests a potential interaction of these two important regulators in GHS rats. In the present study, BMP2 expression is suppressed by the VDR-1,25(OH)2D3 complex in Bone Marrow Stromal Cells (BMSCs) from GHS and SD rat and in UMR-106 cell line. We used chromatin immunoprecipitation (ChIP) assays to identify VDR binding to only one of several potential binding sites within the BMP2 promoter regions. This negative region also mediates suppressor reporter gene activity. The molecular mechanisms underlying the down-regulation of BMP2 by 1,25(OH)2D3 were studied in vitro in BMSCs and UMR-106 cells using the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (DAC) and the histone deacetylase inhibitor trichostatin A (TSA). Both DAC and TSA activate BMP2 expression in combination with 1,25(OH)2D3. Bisulfite DNA pyrosequencing reveals 1,25(OH)2D3 to completely hypermethylate a single CpG site in the same BMP2 promoter region identified by the ChIP and reporter gene assays. ChIP assays also show that 1,25(OH)2D3 can increase the repressive histone mark H3K9me2 and reduce the acetylation of histone H3 at the same BMP2 promoter region. Taken together, our results indicate that 1,25(OH)2D3 binding to VDR down-regulates BMP2 gene expression in BMSCs and osteoblast-like UMR-106 cells by binding to the BMP2 promoter region. The mechanism of this 1,25(OH)2D3-induced transcriptional repression of BMP2 involves DNA methylation and histone modification. The study provides novel evidence that 1,25(OH)2D3 represses bone formation through down-regulating BMP2 expression both in vivo and in vitro.

Increased preosteoblast adhesion and osteogenic gene expression on TiO2 nanotubes modified with KRSR

TiO2 anodized nanotubelayers are potentially useful for orthopedic and dental implants because they promotes bone formation. Peptide sequences, such as lysine-arginine-serine-arginine (KRSR), are often used to modify biomaterial surfaces for the selective adhesion of bone cells. The objective of this study was to functionalize TiO2 nanotube layers with KRSR to examine the responses of mouse preosteoblasts (MC3T3-E1) to this new material in vitro. SEM, AFM, XPS were used to characterize the materials. Immunofluorescence staining, SEM, ALP, RT-PCR, Wb analysis were used to detect the preosteoblast adhesion, spreading and osteogenic differentiation. KRSR peptides could be immobilized on the TiO2 nanotube layers by silane coupling. Immobilized KRSR increased preosteoblast adhesion and spreading on TiO2 nanotube layers. Moreover, osteogenic differentiation increased on the KRSR-modified TiO2 nanotube layers. KRSR-modified TiO2 nanotube layers have satisfactory biological properties and should be further investigated as medical implant materials.

MKP1-dependent PTH modulation of bone matrix mineralization in female mice is osteoblast maturation stage specific and involves P-ERK and P-p38 MAPKs

Limited information is available on the role of MAPK phosphatase 1 (MKP1) signaling in osteoblasts. We have recently reported distinct roles for MKP1 during osteoblast proliferation, differentiation, and skeletal responsiveness to parathyroid hormone (PTH). As MKP1 regulates the phosphorylation status of MAPKs, we investigated the involvement of P-ERK and P-p38 MAPKs in MKP1 knockout (KO) early and mature osteoblasts with respect to mineralization and PTH response. Calvarial osteoblasts from 9-14-week-old WT and MKP1 KO male and female mice were examined. Western blot analysis revealed downregulation and sustained expressions of P-ERK and P-p38 with PTH treatment in differentiated osteoblasts derived from KO males and females respectively. Exposure of early osteoblasts to p38 inhibitor, SB203580 (S), markedly inhibited mineralization in WT and KO osteoblasts from both genders as determined by von Kossa assay. In osteoblasts from males, ERK inhibitor U0126 (U), not p38 inhibitor (S), prevented the inhibitory effects of PTH on mineralization in early or mature osteoblasts. In osteoblasts from KO females, PTH sustained mineralization in early osteoblasts and decreased mineralization in mature cells. This effect of PTH was attenuated by S in early osteoblasts and by U in mature KO cells. Changes in matrix Gla protein expression with PTH in KO osteoblasts did not correlate with mineralization, indicative of MKP1-dependent additional mechanisms essential for PTH action on osteoblast mineralization. We conclude that PTH regulation of osteoblast mineralization in female mice is maturation stage specific and involves MKP1 modulation of P-ERK and P-p38 MAPKs.

Scaffold-free microtissues: differences from monolayer cultures and their potential in bone tissue engineering

OBJECTIVES

Cell-based therapies for bone augmentation after tooth loss and for the treatment of periodontal defects improve healing defects. Usually, osteogenic cells or stem cells are cultivated in 2D primary cultures, before they are combined with scaffold materials, even though this means a loss of the endogenous 3D microenvironment for the cells. Moreover, the use of single-cell suspensions for the inoculation of scaffolds or for the direct application into an area of interest has the disadvantages of low initial cell numbers and susceptibility to unwanted cellular distribution, respectively.

MATERIALS AND METHODS

We addressed the question whether an alternative to monolayer cultures, namely 3D microtissues, has the potential to improve osteogenic tissue engineering and its clinical outcome.

RESULTS

By contrast, to monolayer cultures, osteogenic differentiation of 3D microtissues is enhanced by mimicking in vivo conditions. It seems that the osteogenic differentiation in microtissues is enhanced by strong integrin-extracellular matrix interaction and by stronger autocrine BMP2 signaling. Moreover, microtissues are less prone to wash out by body fluids and allow the precise administration of large cell numbers.

CONCLUSION

Microtissue cultures have closer characteristics with cells in vivo and their enhanced osteogenic differentiation makes scaffold-free microtissues a promising concept in osteogenic tissue engineering.

CLINICAL RELEVANCE

Microtissues are particularly suitable for tissue engineering because they improve seeding efficiency of biomaterials by increasing the cell load of a scaffold. This results in accelerated osteogenic tissue formation and could contribute to earlier implant stability in mandibular bone augmentation.

A comparative study on morphochemical properties and osteogenic cell differentiation within bone graft and coral graft culture systems

The objective of this study was to compare the morphological and chemical composition of bone graft (BG) and coral graft (CG) as well as their osteogenic differentiation potential using rabbit mesenchymal stem cells (rMSCs) in vitro. SEM analysis of BG and CG revealed that the pores in these grafts were interconnected, and their micro-CT confirmed pore sizes in the range of 107-315 µm and 103-514 µm with a total porosity of 92% and 94%, respectively. EDS analysis indicated that the level of calcium in CG was relatively higher than that in BG. FTIR of BG and CG confirmed the presence of functional groups corresponding to carbonyl, aromatic, alkyl, and alkane groups. XRD results revealed that the phase content of the inorganic layer comprised highly crystalline form of calcium carbonate and carbon. Atomic force microscopy analysis showed CG had better surface roughness compared to BG. In addition, significantly higher levels of osteogenic differentiation markers, namely, alkaline phosphatase (ALP), Osteocalcin (OC) levels, and Osteonectin and Runx2, Integrin gene expression were detected in the CG cultures, when compared with those in the BG cultures. In conclusion, our results demonstrate that the osteogenic differentiation of rMSCs is relatively superior in coral graft than in bone graft culture system.

Simplified microenvironments and reduced cell culture size influence the cell differentiation outcome in cellular microarrays

Cellular microarrays present a promising tool for multiplex evaluation of the signalling effect of substrate-immobilized factors on cellular differentiation. In this paper, we compare the early myoblast-to-osteoblast cell commitment steps in response to a growth factor stimulus using standard well plate differentiation assays or cellular microarrays. Our results show that restraints on the cell culture size, inherent to cellular microarrays, impair the differentiation outcome. Also, while cells growing on spots with immobilised BMP-2 are early biased towards the osteoblast fate, longer periods of cell culturing in the microarrays result in cell proliferation and blockage of osteoblast differentiation. The results presented here raise concerns about the efficiency of cell differentiation when the cell culture dimensions are reduced to a simplified microspot environment. Also, these results suggest that further efforts should be devoted to increasing the complexity of the microspots composition, aiming to replace signalling cues missing in this system.

Influence of select extracellular matrix proteins on mesenchymal stem cell osteogenic commitment in three-dimensional contexts

Growth factors have been shown to be powerful mediators of mesenchymal stem cell (MSC) osteogenic differentiation. However, their use in tissue engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically promote MSC osteogenic differentiation in the absence of exogenous growth factors via the manipulation of scaffold material properties would be beneficial. The current work examines the influence of select extracellular matrix (ECM) proteins on MSC osteogenesis toward the goal of developing scaffolds with intrinsically osteoinductive properties. Fibrinogen (FG), fibronectin (FN) and laminin-1 (LN) were chosen for evaluation due to their known roles in bone morphogenesis or bone fracture healing. These proteins were conjugated into poly(ethylene glycol) diacrylate (PEGDA) hydrogels and their effects on encapsulated 10T½ MSCs were evaluated. Specifically, following 1week of culture, mid-term markers of various MSC lineages were examined in order to assess the strength and specificity of the observed osteogenic responses. PEG-LN gels demonstrated increased levels of the osteogenic transcription factor osterix relative to day 0 levels. In addition, PEG-FG and PEG-LN gels were associated with increased deposition of bone ECM protein osteocalcin relative to PEG-FN gels and day 0. Importantly, the osteogenic response associated with FG and LN appeared to be specific in that markers for chondrocytic, smooth muscle cell and adipocytic lineages were not similarly elevated relative to day 0 in these gels. To gain insight into the integrin dynamics underlying the observed differentiation results, initial integrin adhesion and temporal alterations in cell integrin profiles were evaluated. The associated results suggest that α(2), α(v) and α(6) integrin subunits may play key roles in integrin-mediated osteogenesis.

Nanofiber-based delivery of bioactive agents and stem cells to bone sites

Biodegradable nanofibers are important scaffolding materials for bone regeneration. In this paper, the basic concepts and recent advances of self-assembly, electrospinning and thermally induced phase separation techniques that are widely used to generate nanofibrous scaffolds are reviewed. In addition, surface functionalization and bioactive factor delivery within these nanofibrous scaffolds to enhance bone regeneration are also discussed. Moreover, recent progresses in applying these nanofiber-based scaffolds to deliver stem cells for bone regeneration are presented. Along with the significant advances, challenges and obstacles in the field as well as the future perspective are discussed.

Osteogenic potency of a 3-dimensional scaffold-free bonelike sphere of periodontal ligament stem cells in vitro

OBJECTIVE

The present study aimed to investigate the osteogenic potency of scaffold-free 3-dimensional (3D) spheres of periodontal ligament stem cells (PDLSCs).

STUDY DESIGN

The osteogenic potency of PDLSC spheres was determined by the ability to form mineralization and to express key osteogenesis-associated genes. The alkaline phosphatase (ALP) activity and the protein content of PDLSC spheres were also measured.

RESULTS

The 3D sphere developed its osteogenic potency in a time-dependent manner, containing approximately 10-fold higher mineralization, 5-fold higher protein content, and 4-fold greater ALP activity than those in the controls. The expression of key osteogenic genes was also upregulated in the 3D PDLSC spheres. Cellular outgrowth was observed when reintroduced into 2D culture.

CONCLUSIONS

PDLSCs were able to undergo osteogenic differentiation in a scaffold-free 3D culture, producing bonelike mineralization in vitro. This suggests, at least in vitro, the osteogenic potency of the 3D PDLSC spheres.

Bioreactor strategy in bone tissue engineering: pre-culture and osteogenic differentiation under two flow configurations

Since robust osteogenic differentiation and mineralization are integral to the engineering of bone constructs, understanding the impact of the cellular microenvironments on human mesenchymal stem cell (hMSCs) osteogenic differentiation is crucial to optimize bioreactor strategy. Two perfusion flow conditions were utilized in order to understand the impact of the flow configuration on hMSC construct development during both pre-culture (PC) in growth media and its subsequent osteogenic induction (OI). The media in the in-house perfusion bioreactor was controlled to perfuse either around (termed parallel flow [PF]) the construct surfaces or penetrate through the construct (termed transverse flow [TF]) for 7 days of the PC followed by 7 days of the OI. The flow configuration during the PC not only changed growth kinetics but also influenced cell distribution and potency of osteogenic differentiation and mineralization during the subsequent OI. While shear stress resulted from the TF stimulated cell proliferation during PC, the convective removal of de novo extracellular matrix (ECM) proteins and growth factors (GFs) reduced cell proliferation on OI. In contrast, the effective retention of de novo ECM proteins and GFs in the PC constructs under the PF maintained cell proliferation under the OI but resulted in localized cell aggregations, which influenced their osteogenic differentiation. The results revealed the contrasting roles of the convective flow as a mechanical stimulus, the redistribution of the cells and macromolecules in 3D constructs, and their divergent impacts on cellular events, leading to bone construct formation. The results suggest that the modulation of the flow configuration in the perfusion bioreactor is an effective strategy that regulates the construct properties and maximizes the functional outcome.

Scaffold-free microtissues: differences from monolayer cultures and their potential in bone tissue engineering

Objectives

The paper’s aim is to review dentin hypersensitivity (DHS), discussing pain mechanisms and aetiology.

Materials and methods

Literature was reviewed using search engines with MESH terms, DH pain mechanisms and aetiology (including abrasion, erosion and periodontal disease).

Results

The many hypotheses proposed for DHS attest to our lack of knowledge in understanding neurophysiologic mechanisms, the most widely accepted being the hydrodynamic theory. Dentin tubules must be patent from the oral environment to the pulp. Dentin exposure, usually at the cervical margin, is due to a variety of processes involving gingival recession or loss of enamel, predisposing factors being periodontal disease and treatment, limited alveolar bone, thin biotype, erosion and abrasion.

Conclusions

The current pain mechanism of DHS is thought to be the hydrodynamic theory. The initiation and progression of DHS are influenced by characteristics of the teeth and periodontium as well as the oral environment and external influences. Risk factors are numerous often acting synergistically and always influenced by individual susceptibility.

Clinical relevance

Whilst the pain mechanism of DHS is not well understood, clinicians need to be mindful of the aetiology and risk factors in order to manage patients’ pain and expectations and prevent further dentin exposure with subsequent sensitivity.

c-Jun N-terminal kinase 1 negatively regulates osteoblastic differentiation induced by BMP2 via phosphorylation of Runx2 at Ser104

Runx2 plays a crucial role in osteoblastic differentiation, which can be upregulated by bone morphogenetic proteins 2 (BMP2). Mitogen-activated protein kinase (MAPK) cascades, such as extracellular signal-regulated kinase (ERK) and p38, have been reported to be activated by BMP2 to increase Runx2 activity. The role of cjun-N-terminal kinase (JNK), the other kinase of MAPK, in osteoblastic differentiation has not been well elucidated. In this study, we first showed that JNK1 is activated by BMP2 in multipotent C2C12 and preosteoblastic MC3T3-E1 cell lines. We then showed that early and late osteoblastic differentiation, represented by ALP expression and mineralization, respectively, are significantly enhanced by JNK1 loss-of-function, such as treatment of JNK inhibitor, knockdown of JNK1 and ectopic expression of a dominant negative JNK1 (DN-JNK1). Consistently, BMP2-induced osteoblastic differentiation is reduced by JNK1 gain-of-function, such as enforced expression of a constitutively active JNK1 (CA-JNK1). Most importantly, we showed that Runx2 is required for JNK1-mediated inhibition of osteoblastic differentiation, and identified Ser104 of Runx2 is the site phosphorylated by JNK1 upon BMP2 stimulation. Finally, we found that overexpression of the mutant Runx2 (Ser104Ala) stimulates osteoblastic differentiation of C2C12 and MC3T3-E1 cells to the extent similar to that achieved by overexpression of wild-type (WT) Runx2 plus JNK inhibitor treatment. Taken together, these data indicate that JNK1 negatively regulates BMP2-induced osteoblastic differentiation through phosphorylation of Runx2 at Ser104. In addition, unraveling these mechanisms may help to develop new strategies in enhancing osteoblastic differentiation and bone formation.

Neobavaisoflavone stimulates osteogenesis via p38-mediated up-regulation of transcription factors and osteoid genes expression in MC3T3-E1 cells

Neobavaisoflavone (NBIF) is an isoflavone isolated from Psoralea corylifolia L, a plant claimed to have osteogenic activity and used to treat bone fractures, osteomalacia and osteoporosis. The present results showed that NBIF concentration-dependently promoted osteogenesis in MC3T3-E1cells, demonstrated by notable enhancement of alkaline phosphatase (ALP) activity, increase of bone-specific matrix proteins expression including type I collagen (Col-I), osteocalcin (OCN) and bone sialoprotein (BSP), and formation of bone nodules. However, cell proliferation in the presence of NBIF was not affected. Results also demonstrated that NBIF up-regulated the expression of runt-related transcription factor 2 (Runx2) and Osterix (Osx), the bone-specific transcription factors participating in regulation of bone marker genes expression. Application of p38 inhibitor SB203580 repressed not only NBIF-induced activation of ALP, the expression of Col-I, OCN and BSP, but also the matrix proteins mineralization. Western blot analysis further revealed that NBIF increased the phosphorylated level of p38 concentration-dependently. Additionally, inhibition of p38 abolished the stimulatory effect of NBIF on the expression of Runx2 and Osx. Taken together, the osteogenic activity of NBIF might probably act through activation of p38-dependent signaling pathway to up-regulate the mRNA levels of Runx2 and Osx then stimulate bone matrix proteins expression. The beneficial effect of NBIF on mineralization demonstrated that NBIF represented as an active component existed in P. corylifolia and might be a potential anabolic agent to treat bone loss-associated diseases.

Exchange protein activated by cyclic adenosine monophosphate regulates the switch between adipogenesis and osteogenesis of human mesenchymal stem cells through increasing the activation of phosphatidylinositol 3-kinase

Epac, exchange protein activated by cyclic adenosine monophosphate (cAMP), could regulate the trans-differentiation between adipogenesis and osteogenesis of human mesenchymal stem cells (hMSCs). Epac activated by 8-pCPT-2'-O-Me-cAMP, a cAMP analog preferentially activating Epac, resulted in the increase of adipogenic gene expression and the decrease of osteogenic gene expression. The pro-adipogenic and anti-osteogenic effect of 8-pCPT-2'-O-Me-cAMP was attributed to that 8-pCPT-2'-O-Me-cAMP led to the activation of protein kinase B (PKB) and cAMP response element-binding protein (CREB) as well as the inhibition of Ras homolog gene family member A (RhoA), focal adhesion kinase (FAK), extracellular-signal-regulated kinase (ERK) and runt-related transcription factor 2 (Runx2) activities. Inhibition of Epac by a dominant-negative form of Epac1 resulted in the decrease of phosphatidylinositol 3-kinase (PI3K), PKB and CREB activities as well as down-regulation of peroxisome proliferator activated receptor-γ (PPARγ) expression. Inhibition of PI3K by a specific inhibitor or inhibition of Arf and Rho GAP adapter protein 3 (ARAP3, a phosphatidylinositol (PtdIns)(3,4,5)P(3) binding protein) by ARAP3 siRNA led to the recovery of RhoA and FAK activities. RhoA-V14, a constitutively active form of RhoA, could activate the MEK/ERK/Runx2 signaling. Therefore, we conclude that PI3K activated by Epac leads to the activation of PKB/CREB signaling and the up-regulation of PPARγ expression, which in turn activate the transcription of adipogenic genes; whereas osteogenesis is driven by Rho/FAK/MEK/ERK/Runx2 signaling, which can be inhibited by Epac via PI3K. These results should be helpful to provide new targets for treatment of osteoporosis and related bone-wasting diseases.

Interactions between extracellular signal-regulated kinase 1/2 and p38 MAP kinase pathways in the control of RUNX2 phosphorylation and transcriptional activity

RUNX2, a key transcription factor for osteoblast differentiation, is regulated by ERK1/2 and p38 MAP kinase-mediated phosphorylation. However, the specific contribution of each kinase to RUNX2-dependent transcription is not known. Here we investigate ERK and p38 regulation of RUNX2 using a unique P-RUNX2-specific antibody. Both MAP kinases stimulated RUNX2 Ser319 phosphorylation and transcriptional activity. However, a clear preference for ERK1 versus p38α/β was found when the ability of these MAPKs to phosphorylate and activate RUNX2 was compared. Similarly, ERK1 preferentially bound to a consensus MAPK binding site on RUNX2 that was essential for the activity of either kinase. To assess the relative contribution of ERK1/2 and p38 to osteoblast gene expression, MC3T3-E1 preosteoblast cells were grown in control or ascorbic acid (AA)-containing medium ± BMP2/7. AA-induced gene expression, which requires collagen matrix synthesis, was associated with parallel increases in P-ERK and RUNX2-S319-P in the absence of any changes in P-p38. This response was blocked by ERK, but not p38, inhibition. Significantly, in the presence of AA, BMP2/7 synergistically stimulated RUNX2 S319 phosphorylation and transcriptional activity without affecting total RUNX2 and this response was totally dependent on ERK/MAPK activity. In contrast, although p38 inhibition partially blocked BMP-dependent transcription, it did not affect RUNX2 S319 phosphorylation, suggesting the involvement of other phosphorylation sites and/or transcription factors in this response. Based on this work, we conclude that extracellular matrix and BMP regulation of RUNX2 phosphorylation and transcriptional activity in osteoblasts is predominantly mediated by ERK rather than p38 MAPKs.

Effects of recombinant dentin sialoprotein in dental pulp cells

Dentin sialophosphoprotein (DSPP) is critical for dentin mineralization. However, the function of dentin sialoprotein (DSP), the cleaved product of DSPP, remains unclear. This study aimed to investigate the signal transduction pathways and effects of recombinant human DSP (rh-DSP) on proliferation, migration, and odontoblastic differentiation in human dental pulp cells (HDPCs). The exogenous addition of rh-DSP enhanced the proliferation and migration of HDPCs in dose- and time-dependent manners. rh-DSP markedly increased ALP activity, calcium nodule formation, and levels of odontoblastic marker mRNA. rh-DSP increased BMP-2 expression and Smad1/5/8 phosphorylation, which was blocked by the BMP antagonist, noggin. Furthermore, rh-DSP phosphorylated extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), Akt, and IκB-α, and induced the nuclear translocation of the NF-κB p65 subunit. Analysis of these data demonstrates a novel signaling function of rh-DSP for the promotion of growth, migration, and differentiation in HDPCS via the BMP/Smad, JNK, ERK, MAPK, and NF-κB signaling pathways, suggesting that rh-DSP may have therapeutic utility in dentin regeneration or dental pulp tissue engineering.

Osterix is regulated by Erk1/2 during osteoblast differentiation

Osterix (Osx) is a novel zinc finger-containing transcription factor that is essential for osteoblast differentiation and bone formation in bone homeostasis. The mitogen-activated protein (MAP) kinases are a group of evolutionarily conserved proline-directed protein serine/threonine kinases that are activated in response to a variety of extracellular stimuli and mediate signal transduction from the cell surface to the nucleus. Erk1/2 plays essential roles in osteoblast differentiation and in supporting osteoclastogenesis, but the precise molecular signaling mechanisms between Osterix and Erk1/2 are not known. We therefore focused on the relationship between Osterix and Erk1/2 during osteoblast differentiation because BMP signaling induces Erk activation in osteoblasts. We investigated the role of the MAPK pathway in regulating protein levels and transcriptional functions of Osterix. We found that Erk activation by overexpression of constitutively active MEK increased the mRNA and protein levels of Osterix and enhanced the transcriptional activity of Osterix, whereas U0126, an inhibitor of MEK, suppressed the protein levels of Osterix and the transcriptional activity. Also, overexpression of constitutively active MEK stabilized Osterix protein. These results suggest that Erk1/2 regulates a major transcription factor, Osterix, during osteoblast differentiation by increasing its protein stability and transcriptional activity.

Differentiation of mesenchymal stem cells in heparin-containing hydrogels via coculture with osteoblasts

The therapeutic potency of delivered mesenchymal stem cells (MSCs) in tissue engineering applications may be improved by priming cells toward a differentiated state via coculture with native, differentiated cells prior to implantation; however, there is a lack of understanding in what may be the most efficacious method. The objective of this study was to investigate the role of negatively-charged heparin in priming hydrogel-encapsulated MSCs toward the osteoblastic lineage during coculture with a monolayer of osteoblasts in the absence of dexamethasone. MSCs encapsulated with higher amounts of heparin and cocultured with osteoblasts exhibited an over 36-fold increase in alkaline phosphatase activity and 13-fold increase in calcium accumulation by day 21, compared to MSCs cocultured with MSCs at the same heparin content. Moreover, hydrogels with higher amounts of heparin and cocultured with osteoblasts exhibited enhanced mineralization on the edges, suggesting that heparin may be important in sequestering osteoblast-secreted soluble factors, particularly on the surfaces of hydrogels. The ability of heparin to selectively interact with soluble positively-charged proteins from the surroundings was confirmed through protein labeling and microscopy. These results suggest that heparin-containing hydrogels as part of a coculture system can be utilized as a versatile platform to study and enhance priming of MSCs toward various cell types for a wide variety of regenerative medicine-based therapies.

Pediatric Craniofacial Surgery: A Review for the Multidisciplinary Team

Pediatric craniofacial surgery is a specialty that grew dramatically in the 20th century and continues to evolve today. Out of the efforts to correct facial deformities encountered during World War II, the techniques of modern craniofacial surgery developed. An analysis of the relevant literature allowed the authors to explore this historical progression.

Current advances in technology, tissue engineering, and molecular biology have further refined pediatric craniofacial surgery. The development of distraction osteogenesis and the progressive study of craniosynostosis provide remarkable examples of this momentum. The growing study of genetics, biotechnology, the influence of growth factors, and stem cell research provide additional avenues of innovation for the future. The following article is intended to reveal a greater understanding of pediatric craniofacial surgery by examining the past, present, and possible future direction. It is intended both for the surgeon, as well as for the nonsurgical individual specialists vital to the multidisciplinary craniofacial team.

The effects of acellular amniotic membrane matrix on osteogenic differentiation and ERK1/2 signaling in human dental apical papilla cells

The amniotic membrane (AM) has been widely used in the field of tissue engineering because of the favorable biological properties for scaffolding material. However, little is known about the effects of an acellular AM matrix on the osteogenic differentiation of mesenchymal stem cells. In this study, it was found that both basement membrane side and collagenous stroma side of the acellular AM matrix were capable of providing a preferential environment for driving the osteogenic differentiation of human dental apical papilla cells (APCs) with proven stem cell characteristics. Acellular AM matrix potentiated the induction effect of osteogenic supplements (OS) such as ascorbic acid, β-glycerophosphate, and dexamethasone and enhanced the osteogenic differentiation of APCs, as seen by increased core-binding factor alpha 1 (Cbfa-1) phosphorylation, alkaline phosphatase activity, mRNA expression of osteogenic marker genes, and mineralized matrix deposition. Even in the absence of soluble OS, acellular AM matrix also could exert the substrate-induced effect on initiating APCs' differentiation. Especially, the collagenous stroma side was more effective than the basement membrane side. Moreover, the AM-induced effect was significantly inhibited by U0126, an inhibitor of extracellular signaling-regulated kinase 1/2 (ERK1/2) signaling. Taken together, the osteogenic differentiation promoting effect on APCs is AM-specific, which provides potential applications of acellular AM matrix in bone/tooth tissue engineering.

Modification of Smad1 linker modulates BMP-mediated osteogenesis of adult human MSC

We examined whether bone morphogenetic protein (BMP)-mediated osteogenesis of adult human mesenchymal stem cells (MSCs) is regulated by extracellular signal-regulated kinase phosphorylation of Smad1. Adenoviral constructs carrying either unmodified human Smad1 or Smad1 mutated in the linker region to preclude extracellular signal-regulated kinase phosphorylation were expressed in human and rodent cells. Unlike unmodified Smad1, expression of mutated Smad1 facilitated BMP-stimulated expression of osteoblast markers in human MSC but had no effect on either rat MSC or mouse pre-osteoblastic MC3T3-E1 cells. Expression of mutated Smad1 in adult human MSC cultures also resulted in increased nuclear accumulation of BMP-activated Smads and elevated gene transcripts characteristic of differentiating osteoblasts. These results may partly explain the poor efficacy of BMP in some human bone therapies and indicate an important mechanism regulating BMP-mediated bone formation in adults.

Unveiling novel genes upregulated by both rhBMP2 and rhBMP7 during early osteoblastic transdifferentiation of C2C12 cells

FINDINGS

We set out to analyse the gene expression profile of pre-osteoblastic C2C12 cells during osteodifferentiation induced by both rhBMP2 and rhBMP7 using DNA microarrays. Induced and repressed genes were intercepted, resulting in 1,318 induced genes and 704 repressed genes by both rhBMP2 and rhBMP7. We selected and validated, by RT-qPCR, 24 genes which were upregulated by rhBMP2 and rhBMP7; of these, 13 are related to transcription (Runx2, Dlx1, Dlx2, Dlx5, Id1, Id2, Id3, Fkhr1, Osx, Hoxc8, Glis1, Glis3 and Cfdp1), four are associated with cell signalling pathways (Lrp6, Dvl1, Ecsit and PKCδ) and seven are associated with the extracellular matrix (Ltbp2, Grn, Postn, Plod1, BMP1, Htra1 and IGFBP-rP10). The novel identified genes include: Hoxc8, Glis1, Glis3, Ecsit, PKCδ, LrP6, Dvl1, Grn, BMP1, Ltbp2, Plod1, Htra1 and IGFBP-rP10.

BACKGROUND

BMPs (bone morphogenetic proteins) are members of the TGFβ (transforming growth factor-β) super-family of proteins, which regulate growth and differentiation of different cell types in various tissues, and play a critical role in the differentiation of mesenchymal cells into osteoblasts. In particular, rhBMP2 and rhBMP7 promote osteoinduction in vitro and in vivo, and both proteins are therapeutically applied in orthopaedics and dentistry.

CONCLUSION

Using DNA microarrays and RT-qPCR, we identified both previously known and novel genes which are upregulated by rhBMP2 and rhBMP7 during the onset of osteoblastic transdifferentiation of pre-myoblastic C2C12 cells. Subsequent studies of these genes in C2C12 and mesenchymal or pre-osteoblastic cells should reveal more details about their role during this type of cellular differentiation induced by BMP2 or BMP7. These studies are relevant to better understanding the molecular mechanisms underlying osteoblastic differentiation and bone repair.

Integrin-associated tyrosine kinase FAK affects Cbfa1 expression

Following cell adhesion, focal adhesion kinase (FAK) autophosphorylates on tyrosine and regulates intracellular signaling cascades that regulate cell growth and differentiation. The hypothesis of this study was FAK mediates osteoblast differentiation dependent Cbfa1 expression. Slowly mineralizing UI and rapidly mineralizing UMR-106-01 BSP osteoblasts formed focal adhesions; however, the level of FAK in UI focal adhesions was less than that seen in BSP cells. UI cultures had less FAK expression (p < 0.05) along with elevated levels of FAK phosphotyrosine in comparison to rapidly mineralizing BSP cultures. Mineralization decreased in a dose-dependent manner in response to Herbimycin A, a tyrosine kinase inhibitor. Overexpression of FAK in UI cells led to a fourfold increase in Cbfa1 gene expression (p < 0.02), and an increase in Cbfa1 protein expression. These results suggest that the integrin-associated tyrosine kinase FAK contributes to the regulation of the osteoblast differentiation in part through the regulation of Cbfa1 expression.

Effects of miR-335-5p in modulating osteogenic differentiation by specifically downregulating Wnt antagonist DKK1

Dickkopf-related protein 1 (DKK1) is essential to maintain skeletal homeostasis as an inhibitor of Wnt signaling and osteogenic differentiation. The purpose of this study was to investigate the molecular mechanisms underlying the developmental stage-specific regulation of the DKK1 protein level. We performed a series of studies including luciferase reporter assays, micro-RNA microarray, site-specific mutations, and gain- and loss-of-function analyses. We found that the DKK1 protein level was regulated via DKK1 3' UTR by miRNA control, which was restricted to osteoblast-lineage cells. As a result of decreased DKK1 protein level by miR-335-5p, Wnt signaling was enhanced, as indicated by elevated GSK-3β phosphorylation and increased β-catenin transcriptional activity. The effects of miR-335-5p were reversed by anti-miR-335-5p treatment, which downregulated endogenous miR-335-5p. In vivo studies showed high expression levels of miR-335-5p in osteoblasts and hypertrophic chondrocytes of mouse embryos, indicating a pivotal role of miR-335-5p in regulating bone development. In conclusion, miR-335-5p activates Wnt signaling and promotes osteogenic differentiation by downregulating DKK1. This cell- and development-specific regulation is essential and mandatory for the initiation and progression of osteogenic differentiation. miR-335-5p proves to be a potential and useful targeting molecule for promoting bone formation and regeneration.

Effects of Cissus quadrangularis on the proliferation, differentiation and matrix mineralization of human osteoblast like SaOS-2 cells

Osteoporosis is a public health problem which is associated with significant morbidity and mortality. The repair of bone defect is still a big challenge for orthopedic surgeons. Traditional use of Cissus quadrangularis (C. quadrangularis) in the treatment of bone disorders has been documented. The present study was employed to delineate the effects of ethanolic extract of C. quadrangularis on the proliferation, differentiation and matrix mineralization of human osteoblast like SaOS-2 cells. Lactate dehydrogenase assayed in the conditioned medium of control and C. quadrangularis treated cells did not differ significantly indicating that ethanolic extract of C. quadrangularis is nontoxic to osteoblastic cells. [(3)H] Thymidine incorporation assay revealed that C. quadrangularis treatment has increased the DNA synthesis of human osteoblastic SaOS-2 cells indicating increased proliferation of these cells. The data on alizarin red and ALP staining revealed increased matrix mineralization of human osteoblast like SaOS-2 cells. The study also revealed that the anabolic actions of ethanolic extract of C. quadrangularis in human osteoblast like cells are mediated through increased mRNA and protein expression of Runx2, a key transcription factor involved in the regulation of bone matrix proteins. Chromatin immunoprecipitation analysis revealed increased transcriptional activity of Runx2 on the promoter of osteocalcin after C. quadrangularis treatment. These results indicate positive regulation of C. quadrangularis on the proliferation, differentiation, and matrix mineralization of human osteoblast like SaOS-2 cells.

Ugonin K promotes osteoblastic differentiation and mineralization by activation of p38 MAPK- and ERK-mediated expression of Runx2 and osterix

Ugonin K is a flavonoid isolated from the roots of Helminthostachys zeylanica, a folk medicine used to strengthen bone mass and cure bone fracture. It is of interest to determine whether ugonin K has beneficial effect on osteoblast maturation. In this study, MC3T3-E1 osteoblasts were treated with ugonin K. Cell differentiation and mineralization were identified by alkaline phosphatase (ALP) activity and Alizarin red S staining, respectively. RT-PCR and Western blot were used to analyze osteoblast-associated gene expression and signaling pathways. Our results showed that ugonin K significantly induced the increase of ALP activity, expressions of bone sialoprotein (BSP) and osteocalcin (OCN), and mineralization. The mRNA expressions of the transcription factors Runx2 and osterix were also up-regulated by ugonin K. Ugonin K increased the phosphorylated level of p38 and ERK, respectively. In the presence of SB203580, ugonin K induced expressions of Runx2 and osterix, ALP activity, BSP level and bone nodule formation were all completely inhibited, but ugonin K induced OCN expression was not affected. On the other hand, ugonin K-induced ALP activity and mineralization were mildly attenuated by PD98059, but the over-expressed Runx2, osterix, BSP and OCN also were significantly repressed by PD98059. These suggested that both p38 and ERK participate in regulating ugonin K evoked osteogenesis but p38 seemed to play a more important role. Take together, the potential anabolic effect of ugonin K on bone might act through activations of p38- and ERK-mediated Runx2 and osterix expressions to induce the synthesis of osteoids and formation of bone nodule.

EGFR signaling suppresses osteoblast differentiation and inhibits expression of master osteoblastic transcription factors Runx2 and Osterix

The epidermal growth factor receptor (EGFR) and its ligands regulate key processes of cell biology, such as proliferation, survival, differentiation, migration, and tumorigenesis. We previously showed that, EGFR signaling pathway is an important bone regulator and it primarily plays an anabolic role in bone metabolism. In this study, we demonstrated that EGF-like ligands strongly inhibited osteoblast differentiation and mineralization in several lines of osteoblastic cells. Real-time RT-PCR and promoter reporter assays revealed that EGF-like ligands suppressed the expression of both early and late bone marker genes at the transcriptional level in the differentiating osteoblasts via an EGFR-dependent manner. This inhibitory effect of EGFR signaling was not dependent on its mitogenic activity. Furthermore, we demonstrated that EGFR signaling reduced the expression of two major osteoblastic transcription factors Runx2 (type II) and Osterix in osteoblast differentiating cells. EGFR-induced decrease in Runx2 transcriptional activity was confirmed by Runx2 reporter and chromatin immunoprecipitation assays. EGFR signaling increased the protein amounts of transcription co-repressors HDAC4 and 6 and over-expression of HDAC4 decreased Runx2 amount in differentiating osteoblasts, implying that HDACs contribute to the down-regulation of Runx2 by EGFR. Moreover, activation of EGFR in undifferentiated osteoprogenitors attenuated the expression of early bone markers and Osterix and decreased Runx2 protein amounts. Together with our previous data, that EGFR stimulates osteoprogenitor proliferation and that blocking EGFR activity in osteoblast lineage cells results in fewer osteoprogenitors and an osteopenic phenotype, we conclude that EGFR signaling is important for maintaining osteoprogenitor population at an undifferentiated stage.

Maohuoside A promotes osteogenesis of rat mesenchymal stem cells via BMP and MAPK signaling pathways

Osteoporosis is becoming a more prevalent health problem with the aging of the population around the world. Epimedium koreanum Nakai is one of the most used herbs in East Asia for curing osteoporosis, with its major ingredient, icariin, mostly explored by researchers. In this article, maohuoside A (MHA), a single isolated compound from the herb, was identified to be more potent than icariin in promoting osteogenesis of rat bone marrow-derived mesenchymal stem cells (rMSCs) (increasing by 16.6, 33.3, and 15.8% on D3, D7, and D11, respectively). Alkaline phosphatase (ALP) assay and calcium content measurement were assigned to quantify the promoted osteogenesis and alizarin red S (ARS) staining was conducted to visualize it. Quantitative real-time PCR (Q-PCR) was assayed to evaluate the mRNA expression of marker genes in osteogenesis and master regulators in BMP pathway. Moreover, PD98059 (PD) and SB203580 (SB), inhibitor of ERK1/2 and p38 MAPK pathway, were administered to assess the involvement of MAPK pathway in the promotion process. In conclusion, MHA pronouncedly enhanced the osteogenesis of rMSC, plausibly via the BMP and MAPK signaling pathways.

Zinc deprivation inhibits extracellular matrix calcification through decreased synthesis of matrix proteins in osteoblasts

SCOPE

Zinc is implicated as an activator for bone formation, however, its influence on bone calcification has not been reported. This study examined how zinc regulates the bone matrix calcification in osteoblasts.

METHODS AND RESULTS

Two osteoblastic MC3T3-E1 cell subclones (SC 4 and SC 24 as high and low osteogenic differentiation, respectively) were cultured in normal osteogenic (OSM), Zinc deficient (Zn-, 1 μM), or adequate (Zn+, 15 μM) media up to 20 days. Cells (SC 4) were also supplemented with (50 μg/mL) or no ascorbic acid (AA) in combination with Zinc treatment. Zn- decreased collagen synthesis and matrix accumulation. Although AA is essential for collagen formation, its supplementation could not compensate for Zinc deficiency-induced detrimental effects on extracellular matrix mineralization. Zn- also decreased the medium and cell layer alkaline phosphatase ALP activity. This decreased ALP activity might cause the decrease of Pi accumulation in response to Zn-, as measured by von Kossa staining. Ca deposition in cell layers, measured by Alizarin red S staining, was also decreased by Zn(-) .

CONCLUSION

Our findings suggest that zinc deprivation inhibits extracellular matrix calcification in osteoblasts by decreasing the synthesis and activity of matrix proteins, type I collagen and ALP, and decreasing Ca and Pi accumulation. Therefore zinc deficiency can be considered as risk factor for poor extracellular matrix calcification.

Time series gene expression profiling and temporal regulatory pathway analysis of BMP6 induced osteoblast differentiation and mineralization

Background

BMP6 mediated osteoblast differentiation plays a key role in skeletal development and bone disease. Unfortunately, the signaling pathways regulated by BMP6 are largely uncharacterized due to both a lack of data and the complexity of the response.

Results

To better characterize the signaling pathways responsive to BMP6, we conducted a time series microarray study to track BMP6 induced osteoblast differentiation and mineralization. These temporal data were analyzed using a customized gene set analysis approach to identify temporally coherent sets of genes that act downstream of BMP6. Our analysis identified BMP6 regulation of previously reported pathways, such as the TGF-beta pathway. We also identified previously unknown connections between BMP6 and pathways such as Notch signaling and the MYB and BAF57 regulatory modules. In addition, we identify a super-network of pathways that are sequentially activated following BMP6 induction.

Conclusion

In this work, we carried out a microarray-based temporal regulatory pathway analysis of BMP6 induced osteoblast differentiation and mineralization using GAGE method. This novel temporal analysis is more informative and powerful than the classical static pathway analysis in that: (1) it captures the interconnections between signaling pathways or functional modules and demonstrates the even higher level organization of molecular biological systems; (2) it describes the temporal perturbation patterns of each pathway or module and their dynamic roles in osteoblast differentiation. The same set of experimental and computational strategies employed in our work could be useful for studying other complex biological processes.

Suppression of Runx2 protein degradation by fibrous engineered matrix

The fibre structure of engineered matrix that mimic the morphology of type I collagen has exhibited good biological performance for bone regeneration. However, the mechanism by which synthetic fibres promote osteoblast differentiation has yet to be determined. In this study, we demonstrate that fibre structure of an engineered matrix suppresses the degradation of Runx2, a master transcription factor that can turn on to osteoblast differentiation. MC3T3-E1 pre-osteoblasts grown on a fibrous collagen matrix sustained a higher level of Runx2 protein than those on tissue culture dishes or on a collagenase-treated, non-fibrous collagen matrix. The ubiquitin-dependent degradation of Runx2 was profoundly decreased in cells grown on the fibrous collagen matrix. The forced expression of Smurf1, an ubiquitin ligase responsible for Runx2 degradation, abrogated the collagen fibre-induced increase of Runx2. We also prepared a polystyrene fibre matrix, and confirmed that the fibre matrix stabilised the Runx2 protein in MC3T3-E1. Furthermore, we genetically modified C2C12 myoblasts with Runx2, cultured the cells on polystyrene fibre matrix, and observed that the fibre matrix stabilised and sustained exogenous Runx2, which led to the promotion of osteoblast differentiation. Our findings in this study provide evidence that the fibre structure of an engineered matrix contributes to osteoblast differentiation by stabilising the Runx2 protein.

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.