Cbfa1 is required for epithelial-mesenchymal interactions regulating tooth development in mice

Combination of Runx2 and Cbfβ upregulates Amelotin gene expression in ameloblasts by directly interacting with cis‑enhancers during amelogenesis

Amelotin (Amtn) is a recently identified enamel protein secreted by ameloblasts at late stage of enamel development. Runt‑related transcription factor 2 (Runx2) in combination with the coactivator core‑binding factor β (Cbfβ) regulates the early stages of tooth development. The aim of the present study was to investigate the role of Runx2 in the regulation of Amtn gene expression in ameloblasts. Immunohistochemistry was performed and the results revealed that Runx2 protein was predominantly expressed in the nuclei of ameloblasts during the transition stage and the maturation stage of enamel development, whereas Cbfβ was expressed in ameloblasts from the secretory stage to the maturation stage. Reverse transcription‑quantitative polymerase chain reaction results demonstrated that Runx2 knockdown decreased Amtn expression in ameloblast‑lineage cells and co‑expression of Runx2 and Cbfβ in ameloblast lineage cells induced an upregulation in Amtn gene expression. Two putative Runx2‑binding sites within the Amtn promoter were identified using bioinformatics analysis. Results of an electrophoretic mobility shift assay and chromatin immunoprecipitation indicated that Runx2/Cbfβ bound to specific DNA sequences. Site‑directed mutagenesis of the Runx2 binding sites within the Amtn promoter resulted in decreased basal promoter activity and did not affect the overexpressed Runx2/Cbfβ. The results of the present study suggest that Runx2 upregulates Amtn gene expression via binding directly to Runx2 sites within the Amtn promoter during amelogenesis.

Role of GATA binding protein 4 (GATA4) in the regulation of tooth development via GNAI3

Transcription factor GATA4 regulates cardiac and osteoblast differentiation. However, its role in tooth development is not clear. Therefore, we generated Wnt1-Cre;GATA4^fl/fl mice, with conditional inactivation of the GATA4 gene in the dental papilla mesenchymal cells. Phenotypic analysis showed short root deformity along with reduced expressions of odonto/osteogenic markers. Proliferation (but not apoptosis) of cells around the apical area of the root was attenuated. In vitro, we knocked down GATA4 expression in stem cells of dental apical papilla (SCAPs). Proliferation, migration and odonto/osteogenic differentiation of SCAPs were affected in the shGATA4 group. Overexpression of GATA4 in SCAPs increased mineralization. Based on our previous iTRAQ results, guanine nucleotide binding proteins 3 (GNAI3) is one of the distinct proteins after GATA4 deletion. G protein signaling is involved in bone development, remodeling, and disease. In this study, both GATA4 deletion in the mouse root and knock-down in human SCAPs decreased the expression of GNAI3. Dual-luciferase and ChIP assay confirmed the direct binding of GATA4 to the GNAI3 promoter, both in vitro and in vivo. GNAI3 knock-down significantly decreased the odonto/osteogenic differentiation ability of SCAPs. We thus establish the role of GATA4 as a novel regulator of root development and elucidate its downstream molecular events.

FGF Signaling Prevents the Terminal Differentiation of Odontoblasts

Members of the fibroblast growth factor (FGF) family play essential and important roles in primary and reparative dentinogenesis, with conflicting results regarding their effects on odontoblast differentiation. Our recent studies showed that the effects of FGF2 on cells in odontoblast lineage were stage-specific and depended on the stage of cell maturity. Continuous exposure of pulp cells to FGF2 inhibited odontoblast differentiation, whereas early and limited exposure of pulp cells to FGF2 resulted in marked increases in odontoblast differentiation. The purpose of this study was to evaluate the cellular and molecular mechanisms regulating the inhibitory effects of FGF2 on odontoblast differentiation. To do so, we examined the effects of the addition of FGF2 during the differentiation/mineralization phase of the in vitro growth of pulp cultures derived from a series of green fluorescent protein reporter transgenic mice that display stage-specific activation of transgenes during odontoblast differentiation. Our results showed that this treatment first stimulated the differentiation of remaining progenitors in pulp cultures into functional odontoblasts but prevented their differentiation into mature odontoblasts. In addition, this treatment inhibited expression of markers of osteogenesis. Furthermore, we demonstrated that the inhibitory effects of FGF2 on odontoblast differentiation were mediated through activation of FGFR/MEK/Erk1/2 signaling and downregulation of bone morphogenetic protein signaling, with negative and positive roles in the expression of Dmp1 and Dspp, respectively, during the advanced stage of odontoblast differentiation.

Retinoic Acid Excess Impairs Amelogenesis Inducing Enamel Defects

Abnormalities of enamel matrix proteins deposition, mineralization, or degradation during tooth development are responsible for a spectrum of either genetic diseases termed Amelogenesis imperfecta or acquired enamel defects. To assess if environmental/nutritional factors can exacerbate enamel defects, we investigated the role of the active form of vitamin A, retinoic acid (RA). Robust expression of RA-degrading enzymes Cyp26b1 and Cyp26c1 in developing murine teeth suggested RA excess would reduce tooth hard tissue mineralization, adversely affecting enamel. We employed a protocol where RA was supplied to pregnant mice as a food supplement, at a concentration estimated to result in moderate elevations in serum RA levels. This supplementation led to severe enamel defects in adult mice born from pregnant dams, with most severe alterations observed for treatments from embryonic day (E)12.5 to E16.5. We identified the enamel matrix proteins enamelin (Enam), ameloblastin (Ambn), and odontogenic ameloblast-associated protein (Odam) as target genes affected by excess RA, exhibiting mRNA reductions of over 20-fold in lower incisors at E16.5. RA treatments also affected bone formation, reducing mineralization. Accordingly, craniofacial ossification was drastically reduced after 2 days of treatment (E14.5). Massive RNA-sequencing (RNA-seq) was performed on E14.5 and E16.5 lower incisors. Reductions in Runx2 (a key transcriptional regulator of bone and enamel differentiation) and its targets were observed at E14.5 in RA-exposed embryos. RNA-seq analysis further indicated that bone growth factors, extracellular matrix, and calcium homeostasis were perturbed. Genes mutated in human AI (ENAM, AMBN, AMELX, AMTN, KLK4) were reduced in expression at E16.5. Our observations support a model in which elevated RA signaling at fetal stages affects dental cell lineages. Thereafter enamel protein production is impaired, leading to permanent enamel alterations.

Osteoblastic differentiation and cell calcification of adamantinomatous craniopharyngioma induced by bone morphogenetic protein-2

BACKGROUND

The calcification of adamantinomatous craniopharyngioma (ACP) often creates difficulties for surgical therapy. Nevertheless, the mechanism of ACP calcification is unclear. Our previous studies demonstrated that osteoblastic factors might play important roles in ACP calcification.

OBJECTIVE

We examined the effects of recombinant human Bmp2 on ACP cell differentiation by testing osteoblastic proteins and calcium deposition.

METHODS

The expression of osteoblastic factors including osteopontin (OPN), Runx2, and osterix in Bmp2-treated ACP cells was examined by western blot and/or real time PCR. ALP activity and calcium deposition after Bmp2 induction were also tested.

RESULTS

Bmp2 significantly amplified the expression of Runx2, Osterix and OPN, as well as ALP activity. Both of these effects could be repressed by noggin treatment. Bmp2 also significantly induced the calcification of ACP, and noggin inhibited this calcium deposition.

CONCLUSION

Our study demonstrated for the first time that ACP cells could differentiate into an osteoblastic lineage via induction by Bmp2. The mechanism of ACP calcification likely involves osteoblastic differentiation modulated by Bmp2. Further studies targeting Bmp2 cascades could result in novel therapeutic interventions for recurrent ACP.

Opg, Rank, and Rankl in Tooth Development: Co-ordination of Odontogenesis and Osteogenesis

Osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK), and RANK ligand (RANKL) are mediators of various cellular interactions, including bone metabolism. We analyzed expression of these three genes during murine odontogenesis from epithelial thickening to cytodifferentiation stages. Opg showed expression in the thickening and bud epithelium. Expression of Opg and Rank was observed in both the internal and the external enamel epithelium as well as in the dental papilla mesenchyme. Although Rankl expression was not detected in tooth epithelium or mesenchyme, it was expressed in pre-osteogenic mesenchymal cells close to developing tooth germs. All three genes were detected in developing dentary bone at P0. The addition of exogenous OPG to explant cultures of tooth primordia produced a delay in tooth development that resulted in reduced mineralization. We propose that the spatiotemporal expression of these molecules in early tooth and bone primordia cells has a role in co-ordinating bone and tooth development.

Antagonistic Functions of USAG-1 and RUNX2 during Tooth Development

Supernumerary teeth and tooth agenesis are common morphological anomalies in humans. We previously obtained evidence that supernumerary maxillary incisors form as a result of the successive development of the rudimentary maxillary incisor tooth germ in Usag-1 null mice. The development of tooth germs is arrested in Runx2 null mice, and such mice also exhibit lingual epithelial buds associated with the upper molars and incisors. The aim of this study is to investigate the potential crosstalk between Usag-1 and Runx2 during tooth development. In the present study, three interesting phenomena were observed in double null Usag-1^-/-/Runx2^-/- mice: the prevalence of supernumerary teeth was lower than in Usag-1 null mice; tooth development progressed further compared than in Runx2 null mice; and the frequency of molar lingual buds was lower than in Runx2 null mice. Therefore, we suggest that RUNX2 and USAG-1 act in an antagonistic manner. The lingual bud was completely filled with odontogenic epithelial Sox2-positive cells in the Usag-1^+/+/Runx2^-/- mice, whereas almost no odontogenic epithelial Sox2-positive cells contributed to supernumerary tooth formation in the rudimentary maxillary incisors of the Usag-1^-/-/Runx2^+/+ mice. Our findings suggest that RUNX2 directly or indirectly prevents the differentiation and/or proliferation of odontogenic epithelial Sox2-positive cells. We hypothesize that RUNX2 inhibits the bone morphogenetic protein (BMP) and/or Wnt signaling pathways regulated by USAG-1, whereas RUNX2 expression is induced by BMP signaling independently of USAG-1.

αE-catenin inhibits YAP/TAZ activity to regulate signalling centre formation during tooth development

Embryonic signalling centres are specialized clusters of non-proliferating cells that direct the development of many organs. However, the mechanisms that establish these essential structures in mammals are not well understood. Here we report, using the murine incisor as a model, that αE-catenin is essential for inhibiting nuclear YAP localization and cell proliferation. This function of αE-catenin is required for formation of the tooth signalling centre, the enamel knot (EK), which maintains dental mesenchymal condensation and epithelial invagination. EK formation depends primarily on the signalling function of αE-catenin through YAP and its homologue TAZ, as opposed to its adhesive function, and combined deletion of Yap and Taz rescues the EK defects caused by loss of αE-catenin. These findings point to a developmental mechanism by which αE-catenin restricts YAP/TAZ activity to establish a group of non-dividing and specialized cells that constitute a signalling centre.

It is unclear which signals regulate the establishment of the tooth signalling centre, the enamel knot (EK). Here, the authors show that EK formation depends on αE-catenin, which acts to restrict the Hippo pathway transcription factors Yes-associated protein (YAP) and TAZ.

Phenotypic Changes in Dentition of Runx2 Homozygote-null Mutant Mice

Genetic and molecular studies in humans and mice indicate that Runx2 (Cbfa1) is a critical transcriptional regulator of bone and tooth formation. Heterozygous mutations in Runx2 cause cleidocranial dysplasia (CCD), an inherited disorder in humans and mice characterized by skeletal defects, supernumerary teeth, and delayed eruption. Mice lacking the Runx2 gene die at birth and lack bone and tooth development. Our extended phenotypic studies of Runx2 mutants showed that developing teeth fail to advance beyond the bud stage and that mandibular molar organs were more severely affected than maxillary molar organs. Runx2 (−/−) tooth organs, when transplanted beneath the kidney capsules of nude mice, failed to progress in development. Tooth epithelial-mesenchymal recombinations using Runx2 (+/+) and (−/−) tissues indicate that the defect in mesenchyme cannot be rescued by normal dental epithelium. Finally, our molecular analyses showed differential effects of the absence of Runx2 on tooth extracellular matrix (ECM) gene expression. These data support the hypothesis that Runx2 is one of the key mesenchymal factors that influences tooth morphogenesis and the subsequent differentiation of ameloblasts and odontoblasts.

Expression of Runx1, -2 and -3 during tooth, palate and craniofacial bone development

We describe the expression of three Runt-related RUNX genes (previously termed AML, Cbfa, or Pebp2alpha) Runx1 and Runx3 during the development of teeth and other craniofacial tissues and compare them to Runx2 expression reported earlier. All three genes were expressed in mesenchymal condensates. Runx1 was expressed in several cartilage primordia earlier than Runx3, and Runx2 was intense in all mesenchymal condensations of bones and teeth. Only Runx1 was expressed in epithelia, and in tooth germs transcripts were detected in outer dental epithelium. Runx1 was also intensely expressed in the midline epithelium of palatal shelves. In early tooth morphogenesis Runx3 was coexpressed with Runx2 in a thin layer of mesenchymal cells underlying dental epithelium. Unlike Runx2, Runx3 was expressed in odontoblasts. However, Runx3 mutant mice did not show obvious tooth phenotype or deviations of Runx1 and Runx2 expression patterns in the tooth.

RUNX2 Mutation Impairs 1α,25-Dihydroxyvitamin D3 mediated Osteoclastogenesis in Dental Follicle Cells

Cleidocranial dysplasia (CCD), a skeletal disorder characterized by delayed permanent tooth eruption and other dental abnormalities, is caused by heterozygous RUNX2 mutations. As an osteoblast-specific transcription factor, RUNX2 plays a role in bone remodeling, tooth formation and tooth eruption. To investigate the crosstalk between RUNX2 and 1α,25-dihydroxyvitamin D3 (1α,25-(OH)₂D₃) in human dental follicle cells (hDFCs) during osteoclast formation, we established a co-culture system of hDFCs from CCD patient and healthy donors with peripheral blood mononuclear cells (PBMCs). Expression of the osteoclast-associated genes and the number of TRAP⁺ cells were reduced in CCD hDFCs, indicating its suppressed osteoclast-inductive ability, which was reflected by the downregulated RANKL/OPG ratio. In addition, 1α,25-(OH)₂D₃-stimulation elevated the expression of osteoclast-related genes, as well as RANKL mRNA levels and RANKL/OPG ratios in control hDFCs. Conversely, RUNX2 mutation abolished this 1α,25-(OH)₂D₃-induced RANKL gene activation and osteoclast formation in CCD hDFCs. Therefore, RUNX2 haploinsufficiency impairs dental follicle-induced osteoclast formation capacity through RANKL/OPG signaling, which may be partially responsible for delayed permanent tooth eruption in CCD patients. Furthermore, this abnormality was not rescued by 1α,25-(OH)₂D₃ application because 1α,25-(OH)₂D₃-induced RANKL activation in hDFCs is mediated principally via the RUNX2-dependent pathway.

Site-specific function and regulation of Osterix in tooth root formation

Congenital diseases of tooth roots, in terms of developmental abnormalities of short and thin root phenotypes, can lead to loss of teeth. A more complete understanding of the genetic molecular pathways and biological processes controlling tooth root formation is required. Recent studies have revealed that Osterix (Osx), a key mesenchymal transcriptional factor participating in both the processes of osteogenesis and odontogenesis, plays a vital role underlying the mechanisms of developmental differences between root and crown. During tooth development, Osx expression has been identified from late embryonic to postnatal stages when the tooth root develops, particularly in odontoblasts and cementoblasts to promote their differentiation and mineralization. Furthermore, the site-specific function of Osx in tooth root formation has been confirmed, because odontoblastic Osx-conditional knockout mice demonstrate primarily short and thin root phenotypes with no apparent abnormalities in the crown (Journal of Bone and Mineral Research 30, 2014 and 742, Journal of Dental Research 94, 2015 and 430). These findings suggest that Osx functions to promote odontoblast and cementoblast differentiation and root elongation only in root, but not in crown formation. Mechanistic research shows regulatory networks of Osx expression, which can be controlled through manipulating the epithelial BMP signalling, mesenchymal Runx2 expression and cellular phosphorylation levels, indicating feasible routes of promoting Osx expression postnatally (Journal of Cellular Biochemistry 114, 2013 and 975). In this regard, a promising approach might be available to regenerate the congenitally diseased root and that regenerative therapy would be the best choice for patients with developmental tooth diseases.

Establishment of Immortalized Mouse Bmp2 Knock-Out Dental Papilla Mesenchymal Cells Necessary for Study of Odontoblastic Differentiation and Odontogenesis

Bmp2 is essential for dentin formation. Bmp2 cKO mice exhibited similar phenotype to dentinogenesis imperfecta, showing dental pulp exposure, hypomineralized dentin, and delayed odontoblast differentiation. As it is relatively difficult to obtain lot of primary Bmp2 cKO dental papilla mesenchymal cells and to maintain a long-term culture of these primary cells, availability of immortalized deleted Bmp2 dental papilla mesenchymal cells is critical for studying the underlying mechanism of Bmp2 signal in odontogenesis. In this study, our goal was to generate an immortalized deleted Bmp2 dental papilla mesenchymal (iBmp2(ko/ko)dp) cell line by introducing Cre recombinase and green fluorescent protein (GFP) into the immortalized mouse floxed Bmp2 dental papilla mesenchymal (iBmp2(fx/fx)dp) cells. iBmp2(ko/ko)dp cells were confirmed by GFP and PCR. The deleted Bmp2 cells exhibited slow cell proliferation rate and cell growth was arrested in G2 phase. Expression of tooth-related marker genes and cell differentiation were decreased in the deleted cells. Importantly, extracellular matrix remodeling was impaired in the iBmp2(ko/ko)dp cells as reflected by the decreased Mmp-9 expression. In addition, with exogenous Bmp2 induction, these cell differentiation and mineralization were rescued as well as extracellular matrix remodeling was enhanced. Therefore, we for the first time described establishment of iBmp(ko/ko) cells that are useful for study of mechanisms in regulating dental papilla mesenchymal cell lineages.

Bmp2 and Bmp4 accelerate alveolar bone development

Alveolar bone remodeling is a continuous process that takes place during development and in response to various physiological and pathological stimuli. However, detailed knowledge regarding the underlying mechanisms involved in alveolar bone development is still lacking. This study aims at improving our understanding of alveolar bone formation and the role of bone morphogenetic proteins (Bmps) in this process. Mice at embryonic (E) day 13.5 to postnatal (PN) day 15.5 were selected to observe the process of alveolar bone development. Alveolar bone development was found to be morphologically observable at E14.5. Molar teeth isolated from mice at PN7.5 were pretreated with Bmp2, Bmp4, Noggin, or BSA, and grafted subcutaneously into mice. The subcutaneously implanted tooth germs formed alveolar bone indicating the role of the dental follicle in alveolar bone development. Alveolar bone formation was increased after pretreatment with Bmp2 and Bmp4, but not with Noggin. Gene expression levels in dental follicle cells from murine molars were also determined by real-time RT-PCR. The expression levels of Runx2, Bsp, and Ocn were significantly higher in dental follicle cells cultured with Bmp2 or Bmp4, and significantly lower in those cultured with Noggin when compared with that of the BSA controls. Our results suggest that the dental follicle participates in alveolar bone formation and Bmp2/4 appears to accelerate alveolar bone development.

COUP-TFII Stimulates Dentin Sialophosphoprotein Expression and Mineralization in Odontoblasts

Chicken ovalbumin upstream promoter transcription factor 2 (COUP-TFII), an orphan nuclear receptor belonging to the steroid-thyroid hormone receptor superfamily, plays an important role in cell fate determination of various tissues. However, the specific role of COUP-TFII in tooth development has not yet been elucidated. In the present study, we aimed to explore the role of COUP-TFII in dentin sialophosphoprotein (DSPP) expression and matrix mineralization in odontoblast-lineage cells. In primary human dental pulp cells (HDPCs) and murine dental papilla-derived cells (MDPC-23) cultured in a mineralizing medium, the expression of COUP-TFII was induced along with the increased odontoblast-specific dentin matrix protein-1 (DMP-1) and DSPP expression. Endogenous expression of COUP-TFII in maxillary second molar germs of rats showed an increasing tendency as development of the tooth progressed. Also, COUP-TFII protein was detected in greater quantity in the odontoblastic layer of second molar germs than in that of third molar germs of rats. Overexpression of COUP-TFII using an adenoviral system upregulated the expression of odontoblast-specific genes with increased alkaline phosphatase activity and matrix mineralization in odontoblast-lineage cells. In contrast, knockdown of COUP-TFII using small interfering RNA decreased the expression of odontoblast-specific genes, which reduced matrix mineralization. Mechanistic studies revealed that COUP-TFII increased DSPP transcription by direct binding on the DSPP promoter. In addition, COUP-TFII physically interacted with the homeodomain transcription factor Msx2 and antagonistically regulated the Msx2 effect on DSPP promoter activity. Taken together, these results suggest that COUP-TFII has a stimulatory role in DSPP expression and matrix mineralization in odontoblast-lineage cells.

Deletion of Osr2 Partially Rescues Tooth Development in Runx2 Mutant Mice

Tooth organogenesis depends on genetically programmed sequential and reciprocal inductive interactions between the dental epithelium and neural crest-derived mesenchyme. Previous studies showed that the Msx1 and Runx2 transcription factors are required for activation of odontogenic signals, including Bmp4 and Fgf3, in the early tooth mesenchyme to drive tooth morphogenesis through the bud-to-cap transition and that Runx2 acts downstream of Msx1 to activate Fgf3 expression. Recent studies identified Osr2 as a repressor of tooth development and showed that inactivation of Osr2 rescued molar tooth morphogenesis in the Msx1(-/-) mutant mice as well as in mice with neural crest-specific inactivation of Bmp4. Here we show that Runx2 expression is expanded in the tooth bud mesenchyme in Osr2(-/-) mutant mouse embryos and is partially restored in the tooth mesenchyme in Msx1(-/-)Osr2(-/-) mutants in comparison with Msx1(-/-) and wild-type embryos. Whereas mandibular molar development arrested at the bud stage and maxillary molar development arrested at the bud-to-cap transition in Runx2(-/-) mutant mice, both mandibular and maxillary molar tooth germs progressed to the early bell stage, with rescued expression of Msx1 and Bmp4 in the dental papilla as well as expression of Bmp4, p21, and Shh in the primary enamel knot in the Osr2(-/-)Runx2(-/-) compound mutants. In contrast to the Msx1(-/-)Osr2(-/-) compound mutants, which exhibit nearly normal first molar morphogenesis, the Osr2(-/-)Runx2(-/-) compound mutant embryos failed to activate the expression of Fgf3 and Fgf10 in the dental papilla and exhibited significant deficit in cell proliferation in both the dental epithelium and mesenchyme in comparison with the control embryos. These data indicate that Runx2 synergizes with Msx1 to drive tooth morphogenesis through the bud-to-cap transition and that Runx2 controls continued tooth growth and morphogenesis beyond the cap stage through activation of Fgf3 and Fgf10 expression in the dental papilla.

Towards unraveling the human tooth transcriptome: the dentome

The goal of the study was to characterize the transcriptome profiles of human ameloblasts and odontoblasts, evaluate molecular pathways and advance our knowledge of the human "dentome". Laser capture microdissection was used to isolate odontoblasts and ameloblasts from human tooth buds (15-20week gestational age) from 4 fetuses. RNA was examined using Agilent 41k whole genome arrays at 2 different stages of enamel formation, presecretory and secretory. Probe detection was considered against the array negative control to control for background noise. Differential expression was examined using Significance Analysis of Microarrays (SAM) 4.0 between different cell types and developmental stages with a false discovery rate of 20%. Pathway analysis was conducted using Ingenuity Pathway Analysis software. We found that during primary tooth formation, odontoblasts expressed 14,802 genes, presecretory ameloblasts 15,179 genes and secretory ameloblasts 14,526 genes. Genes known to be active during tooth development for each cell type (eg COL1A1, AMELX) were shown to be expressed by our approach. Exploring further into the list of differentially expressed genes between the motile odontoblasts and non-motile presecretory ameloblasts we found several genes of interest that could be involved in cell movement (FN1, LUM, ASTN1). Furthermore, our analysis indicated that the Phospholipase C and ERK5 pathways, that are important for cell movement, were activated in the motile odontoblasts. In addition our pathway analysis identified WNT3A and TGFB1 as important upstream contributors. Recent studies implicate these genes in the development of Schimke immuno-osseous dysplasia. The utility of laser capture microdissection can be a valuable tool in the examination of specific tissues or cell populations present in human tooth buds. Advancing our knowledge of the human dentome and related molecular pathways provides new insights into the complex mechanisms regulating odontogenesis and biomineralization. This knowledge could prove useful in future studies of odontogenic related pathologies.

Resveratrol prevents osteoporosis in ovariectomized rats by regulating microRNA-338-3p

Osteoporosis is a disease characterized by loss of bone mass and degeneration of the microstructure of bone. Resveratrol (3,5,4-tri-hydroxystilbene; RESV) may delay the onset of a variety of age-related diseases. In the present study, an ovariectomized female rat model was used to detect the changes in microRNAs (miRNAs/miRs) following RESV treatment. Subsequently, the target genes of miRNA were predicted using TargetScan software and determined using a dual-luciferase reporter assay. Finally, the role of miR-338-3p in the proliferation and differentiation of human osteoblast (HOB) cells was confirmed. The predominant finding of the present study was the identification of an intact mechanism of the effect of RESV in osteoporosis treatment. The results suggested that RESV suppresses miR-338-3p, followed by an increase in the expression of runt-related transcription factor 2 in HOB cells.

Thymosin beta 4 is associated with RUNX2 expression through the Smad and Akt signaling pathways in mouse dental epithelial cells

In previous studies by our group, we reported that thymosin beta 4 (Tb4) is closely associated with the initiation and development of the tooth germ, and can induce the expression of runt-related transcription factor 2 (RUNX2) during the development of the tooth germ. RUNX2 regulates the expression of odontogenesis-related genes, such as amelogenin, X-linked (Amelx), ameloblastin (Ambn) and enamelin (Enam), as well as the differentiation of osteoblasts during bone formation. However, the mechanisms through which Tb4 induces the expression of RUNX2 remain unknown. In the present study, we employed a mouse dental epithelial cell line, mDE6, with the aim to elucidate these mechanisms. The mDE6 cells expressed odontogenesis-related genes, such as Runx2, Amelx, Ambn and Enam, and formed calcified matrices upon the induction of calcification, thus showing characteristics of odontogenic epithelial cells. The expression of odontogenesis-related genes, and the calcification of the mDE6 cells were reduced by the inhibition of phosphorylated Smad1/5 (p-Smad1/5) and phosphorylated Akt (p-Akt) proteins. Furthermore, we used siRNA against Tb4 to determine whether RUNX2 expression and calcification are associated with Tb4 expression in the mDE6 cells. The protein expression of p-Smad1/5 and p-Akt in the mDE6 cells was reduced by treatment with Tb4-siRNA. These results suggest that Tb4 is associated with RUNX2 expression through the Smad and PI3K-Akt signaling pathways, and with calcification through RUNX2 expression in the mDE6 cells. This study provides putative information concerning the signaling pathway through which Tb4 induces RUNX2 expression, which may help to understand the regulation of tooth development and tooth regeneration.

Microtubule-associated protein tau (Mapt) is expressed in terminally differentiated odontoblasts and severely down-regulated in morphologically disturbed odontoblasts of Runx2 transgenic mice

Runx2 is an essential transcription factor for osteoblast and odontoblast differentiation and the terminal differentiation of chondrocytes. We have previously shown that the terminal differentiation of odontoblasts is inhibited in Runx2 transgenic {Tg(Col1a1-Runx2)} mice under the control of the 2.3-kb Col1a1 promoter, which directs the transgene expression to osteoblasts and odontoblasts. Odontoblasts show severe reductions in Dspp and nestin expression and lose their characteristic polarized morphology, including a long process extending to dentin, in Tg(Col1a1-Runx2) mice. We study the molecular mechanism of odontoblast morphogenesis by comparing gene expression in the molars of wild-type and Tg(Col1a1-Runx2) mice, focusing on cytoskeleton-related genes. Using microarray, we found that the gene expression of microtubule-associated protein tau (Mapt), a neuronal phosphoprotein with important roles in neuronal biology and microtubule dynamics and assembly, was high in wild-type molars but severely reduced in Tg(Col1a1-Runx2) molars. Immunohistochemical analysis revealed that Mapt was specifically expressed in terminally differentiated odontoblasts including their processes in wild-type molars but its expression was barely detectable in Tg(Col1a1-Runx2) molars. Double-staining of Mapt and Runx2 showed their reciprocal expression in odontoblasts. Mapt and tubulin co-localized in odontoblasts in wild-type molars. Immunoelectron microscopic analysis demonstrated Mapt lying around α-tubulin-positive filamentous structures in odontoblast processes. Thus, Mapt is a useful marker for terminally differentiated odontoblasts and might play an important role in odontoblast morphogenesis.

Abnormal Differentiation of Dental Pulp Cells in Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is a skeletal dysplasia caused by heterozygous mutations of RUNX2, a gene that is essential for the mineralization of bone and tooth. We isolated primary dental pulp cells from a 10-y-old patient and tested their proliferative capacity, alkaline phosphatase activity, and ability to form mineralized nodules, in comparison with those from 7 healthy children. All these measures were reduced in primary dental pulp cells from the CCD patient. The expression of the osteoblast/odontoblast-associated genes RUNX2, ALP, OCN, and DSPP was also found to be significantly decreased in the primary dental pulp cells of the CCD patient. The osteoclast-related markers TRAP, CTSK, CTR, and MMP9 were decreased in primary dental pulp cells cocultured with human peripheral blood mononuclear cells. Moreover, the expression of RANKL and the ratio of RANKL/OPG were both reduced in the cells from the CCD patient, indicating that the RUNX2 mutation interfered with the bone-remodeling pathway and decreased the capacity of primary dental pulp cells to support osteoclast differentiation. These effects may be partly responsible for the defects in tooth development and the retention of primary teeth that is typical of CCD.

Osterix regulates tooth root formation in a site-specific manner

Bone and dentin share similar biochemical compositions and physiological properties. Dentin, a major tooth component, is formed by odontoblasts; in contrast, bone is produced by osteoblasts. Osterix (Osx), a zinc finger-containing transcription factor, has been identified as an essential regulator of osteoblast differentiation and bone formation. However, it has been difficult to establish whether Osx functions in odontoblast differentiation and dentin formation. To understand the role of Osx in dentin formation, we analyzed mice in which Osx was subjected to tissue-specific ablation under the control of either the Col1a1 or the OC promoter. Two independent Osx conditional knockout mice exhibited similar molar abnormalities. Although no phenotype was found in the crowns of these teeth, both mutant lines exhibited short molar roots due to impaired root elongation. Furthermore, the interradicular dentin in these mice showed severe hypoplastic features, which were likely caused by disruptions in odontoblast differentiation and dentin formation. These phenotypes were closely related to the temporospatial expression pattern of Osx during tooth development. These findings indicate that Osx is required for root formation by regulating odontoblast differentiation, maturation, and root elongation. Cumulatively, our data strongly indicate that Osx is a site-specific regulator in tooth root formation.

Odontogenic differentiation of human dental pulp cells induced by silicate-based bioceramics via activation of P38/MEPE pathway

Ca₇Si₂P₂O₁₆ bioceramic significantly enhanced odontogenic protein expression (ALP activity and staining) of hDPCs.

17beta-estradiol promotes the odonto/osteogenic differentiation of stem cells from apical papilla via mitogen-activated protein kinase pathway

Introduction

Estrogen plays an important role in the osteogenic differentiation of mesenchymal stem cells, while stem cells from apical papilla (SCAP) can contribute to the formation of dentin/bone-like tissues. To date, the effects of estrogen on the differentiation of SCAP remain unclear.

Methods

SCAP was isolated and treated with 10^-7 M 17beta-estradiol (E2). The odonto/osteogenic potency and the involvement of mitogen-activated protein kinase (MAPK) signaling pathway were subsequently investigated by using methyl-thiazolyl-tetrazolium (MTT) assay, and other methods.

Results

MTT and flow cytometry results demonstrated that E2 treatment had no effect on the proliferation of SCAP in vitro, while alkaline phosphatase (ALP) assay and alizarin red staining showed that E2 can significantly promote ALP activity and mineralization ability in SCAP. Real-time reverse transcription polymerase chain reaction (RT-PCR) and western blot assay revealed that the odonto/osteogenic markers (ALP, DMP1/DMP1, DSPP/DSP, RUNX2/RUNX2, OSX/OSX and OCN/OCN) were significantly upregulated in E2-treated SCAP. In addition, the expression of phosphor-p38 and phosphor-JNK in these stem cells was enhanced by E2 treatment, as was the expression of the nuclear downstream transcription factors including phosphor-Sp1, phosphor-Elk-1, phosphor-c-Jun and phosphor-c-Fos, indicating the activation of MAPK signaling pathway during the odonto/osteogenic differentiation of E2-treated SCAP. Conversely, the differentiation of E2-treated SCAP was inhibited in the presence of MAPK specific inhibitors.

Conclusions

The ondonto/osteogenic differentiation of SCAP is enhanced by 10^-7 M 17beta-estradiol via the activation of MAPK signaling pathway.

The prolyl hydroxylase inhibitor dimethyloxalylglycine enhances dentin sialophoshoprotein expression through VEGF-induced Runx2 stabilization

Prolyl hydroxylase (PHD) inhibitors are suggested as therapeutic agents for tissue regeneration based on their ability to induce pro-angiogenic responses. In this study, we examined the effect of the PHD inhibitor dimethyloxalylglycine (DMOG) on odontoblast maturation and sought to determine the underlying mechanism using MDPC-23 odontoblast-like cells. DMOG significantly enhanced matrix mineralization, confirmed by alizarin red staining and by measurement of the calcium content. DMOG dose-dependently increased alkaline phosphatase activity and the expressions of dentin sialophosphoprotein (Dspp) and osteocalcin. To determine the underlying events leading to DMOG-induced Dspp expression, we analyzed the effect of DMOG on Runx2. Knockdown of Runx2 using siRNAs decreased Dspp expression and prevented DMOG-induced Dspp expression. DMOG enhanced the transcriptional activity and level of Runx2 protein but not Runx2 transcript, and this enhancement was linked to the inhibitory effects of DMOG on the degradation of Runx2 protein. The vascular endothelial growth factor (VEGF) siRNAs profoundly decreased the Runx2 protein levels and inhibited the DMOG-increased Runx2 protein. Recombinant VEGF protein treatment significantly and dose-dependently increased the transcriptional activity and level of the Runx2 protein but not Runx2 transcript. Dspp expression was also enhanced by VEGF. Last, we examined the involvement of the Erk mitogen-activated protein kinase and Pin1 pathway in VEGF-enhanced Runx2 because this pathway can regulate the stability and activity of the Runx2 protein. VEGF stimulated Erk activation, and the inhibitors of Erk and Pin1 hampered VEGF-enhanced Runx2 protein. Taken together, the results of this study provide evidence that DMOG can enhance Dspp expression through VEGF-induced stabilization of Runx2 protein, and thus, suggest that DMOG can be used as a therapeutic tool for enhancing odontoblast maturation in dental procedures.

Oxytalan-positive peripheral ossifying fibromas express runt-related transcription factor 2, bone morphogenetic protein-2, and cementum attachment protein. An immunohistochemical study

BACKGROUND

The peripheral ossifying fibroma (POF) represents one of the most common lesions of the periodontal tissues that may originate from the gingival soft tissues, the periosteum, or the periodontal ligament.

AIM

To investigate the immunohistochemical expression of runt-related transcription factor 2 (Runx-2), bone morphogenetic protein-2 (BMP-2), and cementum attachment protein (CAP) in oxytalan-positive POF, to establish the use of POF as an in vivo model for the study of the periodontal ligament.

MATERIALS AND METHODS

Thirty tumors that presented clinical and histologic features of POF, as well as oxytalan fibers, were included in the study. Immunohistochemical expression of Runx-2, BMP-2, and CAP was evaluated by light microscopy.

RESULTS

Runx-2, BMP-2, and CAP were abundantly expressed by POFs; 22 of 30 tumors expressed positive staining for Runx-2, twenty-six tumors for BMP-2, and twenty-five tumors for CAP. The expression of Runx-2 was abundant in POFs where bone was histologically present (P = 0.04) and of BMP-2 in POFs where dystrophic calcifications were present (P = 0.03).

CONCLUSION

It is suggested that oxytalan-positive POFs, purportedly originating from the periodontal ligament, express molecules that are specific to bone and cementum (Runx-2, BMP-2), or cementum only (CAP). Thus, the cell populations present in the lesion belong to the mineralized-tissue-forming cell lineages, the cementoblastic or osteoblastic lineage.

Dentin sialophosphoprotein: a regulatory protein for dental pulp stem cell identity and fate

The dentin sialophosphoprotein (dspp) transcript is expressed during tooth development as a DSPP precursor protein, which then undergoes cleavage to form mature dentin sialoprotein (DSP) and phosphophoryn (PP) proteins. Previous studies using DSPP-knockout (KO) mice have reported that these animals have hypomineralized teeth, thin dentin, and a large dental pulp chamber, similar to those from patients with dentinogenesis imperfecta III. However, there is no information about factors that regulate dental pulp stem cell lineage fate, a critical early event in the odontoblast-dentin mineralization scheme. To reveal the role of DSPP in odontoblast lineage differentiation during tooth development, we systematically examined teeth from wild-type (wt) and DSPP-KO C57BL/6 mice between the ages of postnatal day 1 and 3 months. We found developmental abnormalities not previously reported, such as circular dentin formation within dental pulp cells and altered odontoblast differentiation in DSPP-KO mice, even as early as 1 day after birth. Surprisingly, we also identified chondrocyte-like cells in the dental pulp from KO-mice teeth. Thus, these studies that compare wt and DSPP-KO mice suggest that the expression of DSPP precursor protein is required for normal odontoblast lineage differentiation and that the absence of DSPP allows dental pulp cells to differentiate into chondrocyte-like cells, which could negatively impact pulpal wound healing and tissue regeneration.

Signaling pathways involved in osteogenesis and their application for bone regenerative medicine

Bone regeneration is a well organized but complex physiological process, in which different cell types and their activated signaling pathways are involved. In bone regeneration and remodeling processes, mesenchymal stem cells (MSCs) have a crucial role, and their differentiation during these processes is regulated by specific signaling molecules (growth factors/cytokines and hormones) and their activated intracellular networks. Especially the utilization of the molecular machinery seems crucial to consider prior to developing bone implants, bone-substitute materials, and cell-based constructs for bone regeneration. The aim of this review is to provide an overview of the signaling mechanisms involved in bone regeneration and remodeling and the osteogenic potential of MSCs to become a key cellular resource for such regeneration and remodeling processes. Additionally, an overview of possibilities to beneficially exploit cell signaling processes to optimize bone regeneration is provided.

Specificity protein 7 is not essential for tooth morphogenesis

Tooth formation is a multifaceted process involving numerous interactions between oral epithelium and neural crest derived ecto-mesenchyme from morphogenesis to cyto-differentiation. The precise molecular regulator that drives the cyto-differentiation and dynamic cross-talk between the two cell types has yet to be fully understood. Runx2 along with its downstream target Sp7 are essential transcription factors for development of the mineralizing cell types. Global knockout of the Runx2 gene results in an arrest of tooth morphogenesis at the late bud stage. Like Runx2, Sp7-null mutants exhibit peri-natal lethality and are completely devoid of alveolar bone. However, the role of Sp7 in tooth development remains elusive. Here, we report the effects of Sp7 deletion on tooth formation. Surprisingly, tooth morphogenesis progresses normally until the mid bell stage in Sp7-homozygous mutants. Incisors and multi-cusped first and second molars were noted in both littermates. Thus, formation of alveolar bone is not a prerequisite for tooth morphogenesis. Tooth organs of Sp7-null however, were significantly smaller in size when compared to WT. Differentiation of both ameloblasts and odontoblasts was disrupted in Sp7-null mice. Only premature and disorganized ameloblasts and odontoblasts were noted in mutant mice. These data indicate that Sp7 is not required for tooth morphogenesis but is obligatory for the functional maturation of both ameloblasts and odontoblasts.

A feedback loop between RUNX2 and the E3 ligase SMURF1 in regulation of differentiation of human dental pulp stem cells

INTRODUCTION

Runt-related transcription factor 2 (RUNX2) is a transcription factor that is indispensable for bone and tooth development. Smad ubiquitylation regulatory factor-1 (SMURF1) promotes RUNX2 degradation and negatively regulates osteoblast differentiation, whereas RUNX2 activates SMURF1 transcription in osteoblasts. However, the relationship between RUNX2 and SMURF1 in tooth development is unknown. This study aimed to evaluate the potential relationship between RUNX2 and SMURF1 in human dental pulp stem cells (hDPSCs).

METHODS

RUNX2 or SMURF1 expression was silenced in hDPSCs by lentiviral transduction of short hairpin RNA . The relationship between RUNX2 and SMURF1 expression was analyzed using quantitative polymerase chain reaction, Western blotting, dual luciferase reporter assays, and chromatin immunoprecipitation. The effect of the interplay between RUNX2 and SMURF1 on the odontoblastic differentiation of hDPSCs was examined in SMURF1-deficient hDPSCs.

RESULTS

The inhibition of SMURF1 in hDPSCs significantly increased RUNX2 at the protein level that was associated with decreased RUNX2 ubiquitination but did not affect RUNX2 messenger RNA expression. On the other hand, depletion of RUNX2 in hDPSCs decreased SMURF1 at both the protein and messenger RNA levels. A RUNX2-binding motif at -308 bp of the SMURF1 promoter functioned in RUNX2-mediated SMURF1 expression. Moreover, the expression levels of RUNX2 were associated with SMURF1 levels during odontoblastic differentiation. Significantly, the knockdown of SMURF1 up-regulated RUNX2 expression and down-regulated dentin sialophosphoprotein and dental matrix protein-1 expression in odontoblastic differentiation.

CONCLUSIONS

These results reveal the regulatory circuit between RUNX2 and SMURF1 controls RUNX2 expression and regulates odntoblastic differentiation in hDPSCs.

Bobby Sox homology regulates odontoblast differentiation of human dental pulp stem cells/progenitors

BACKGROUND

Transcription factors have been implicated in regulating the differentiation of odontoblasts from dental pulp stem cells/progenitors (DPSCs/progenitors), but their regulatory network is not completely understood.

RESULT

New transcription factors that control the odontoblast differentiation of human DPSCs/progenitors were analyzed using a microarray. The result revealed bobby sox homolog (BBX) to be expressed most strongly during odontoblast differentiation. Validation using RT-PCR also revealed the strong expression of BBX during the odontoblast differentiation of DPSCs/progenitors. BBX expression was also detected in adult molar odontoblasts and other tissues, including the heart, kidney, testis, and bone marrow. To understand the role of BBX in odontoblast differentiation, BBX variant 1 and 2 cDNA were cloned and overexpressed in DPSCs/progenitors. The results showed that the overexpression of BBX cDNA in DPSCs/progenitors induced substantial mineralization and expression of the odontoblast marker genes, such as ALP, OPN, BSP, DMP1, and DSPP. The knockdown of BBX using shRNA, however, did not affect mineralization, but the expression of ALP and DSPP was decreased substantially. Meanwhile overexpression or knockdown of BBX did not modulate proliferation of DPSCs/progenitors.

CONCLUSION

Our results suggest that BBX plays an important role during the odontoblast differentiation of human DPSCs/progenitors.

Cbfβ deletion in mice recapitulates cleidocranial dysplasia and reveals multiple functions of Cbfβ required for skeletal development

The pathogenesis of cleidocranial dysplasia (CCD) as well as the specific role of core binding factor β (Cbfβ) and the Runt-related transcription factor (RUNX)/Cbfβ complex in postnatal skeletogenesis remain unclear. We demonstrate that Cbfβ ablation in osteoblast precursors, differentiating chondrocytes, osteoblasts, and odontoblasts via Osterix-Cre, results in severe craniofacial dysplasia, skeletal dysplasia, abnormal teeth, and a phenotype recapitulating the clinical features of CCD. Cbfβ(f/f)Osterix-Cre mice have fewer proliferative and hypertrophic chondrocytes, fewer osteoblasts, and almost absent trabecular bone, indicating that Cbfβ may maintain trabecular bone formation through its function in hypertrophic chondrocytes and osteoblasts. Cbfβ(f/f)Collagen, type 1, alpha 1 (Col1α1)-Cre mice show decreased bone mineralization and skeletal deformities, but no radical deformities in teeth, mandibles, or cartilage, indicating that osteoblast lineage-specific ablation of Cbfβ results in milder bone defects and less resemblance to CCD. Activating transcription factor 4 (Atf4) and Osterix protein levels in both mutant mice are dramatically reduced. ChIP assays show that Cbfβ directly associates with the promoter regions of Atf4 and Osterix. Our data further demonstrate that Cbfβ highly up-regulates the expression of Atf4 at the transcriptional regulation level. Overall, our genetic dissection approach revealed that Cbfβ plays an indispensable role in postnatal skeletal development and homeostasis in various skeletal cell types, at least partially by up-regulating the expression of Atf4 and Osterix. It also revealed that CCD may result from functional defects of the Runx2/Cbfβ heterodimeric complex in various skeletal cells. These insights into the role of Cbfβ in postnatal skeletogenesis and CCD pathogenesis may assist in the development of new therapies for CCD and osteoporosis.

Functionalized scaffolds to control dental pulp stem cell fate

Emerging understanding about interactions between stem cells, scaffolds, and morphogenic factors has accelerated translational research in the field of dental pulp tissue engineering. Dental pulp stem cells constitute a subpopulation of cells endowed with self-renewal and multipotency. Dental pulp stem cells seeded in biodegradable scaffolds and exposed to dentin-derived morphogenic factors give rise to a pulplike tissue capable of generating new dentin. Notably, dentin-derived proteins are sufficient to induce dental pulp stem cell differentiation into odontoblasts. Ongoing work is focused on developing ways of mobilizing dentin-derived proteins and disinfecting the root canal of necrotic teeth without compromising the morphogenic potential of these signaling molecules. On the other hand, dentin by itself does not appear to be capable of inducing endothelial differentiation of dental pulp stem cells despite the well-known presence of angiogenic factors in dentin. This is particularly relevant in the context of dental pulp tissue engineering in full root canals in which access to blood supply is limited to the apical foramina. To address this challenge, scientists are looking at ways to use the scaffold as a controlled-release device for angiogenic factors. The aim of this article was to present and discuss current strategies to functionalize injectable scaffolds and customize them for dental pulp tissue engineering. The long-term goal of this work is to develop stem cell-based therapies that enable the engineering of functional dental pulps capable of generating new tubular dentin in humans.

Does the calcification of adamantinomatous craniopharyngioma resemble the calcium deposition of osteogenesis/odontogenesis?

AIMS

Calcification in adamantinomatous craniopharyngioma (ACP) is troublesome for surgical intervention. The aim of this study was to examine the osteogenic proteins that play important roles in the calcium deposition of the odontogenic/osteogenic tissues in craniopharyngioma.

METHODS AND RESULTS

Craniopharyngiomas (n = 89) were investigated for the presence and expression pattern of the osteoinductive/odontoinductive factor bone morphogenetic protein-2 (Bmp2) and two osteoblastic differentiation makers, Runt-related transcription factor-2 (Runx2) and Osterix, using immunohistochemistry and Western blotting. Our results showed that Bmp2, Runx2 and Osterix levels increased in cases with high calcification and correlated positively with the degree of calcification in ACP, whereas they showed little or no expression in squamous papillary craniopharyngioma. In ACP, Bmp2 was expressed primarily in the stellate reticulum and whorl-like array cells; Runx2 and Osterix tended to be expressed in calcification-related epithelia, including whorl-like array cells and epithelia in/around wet keratin and calcification lesions.

CONCLUSIONS

Our study indicated, for the first time, that osteogenic factor Bmp2 may play an important role in the calcification of ACP via autocrine or paracrine mechanisms. Given the presence of osteogenic markers (Runx2 and Osterix), craniopharyngioma cells could differentiate into an osteoblast-like lineage, and the process of craniopharyngioma calcification resembles that which occurs in osteogenesis/odontogenesis.

Domain of dentine sialoprotein mediates proliferation and differentiation of human periodontal ligament stem cells

Classic embryological studies have documented the inductive role of root dentin on adjacent periodontal ligament differentiation.  The biochemical composition of root dentin includes collagens and cleavage products of dentin sialophosphoprotein (DSPP), such as dentin sialoprotein (DSP).  The high abundance of DSP in root dentin prompted us to ask the question whether DSP or peptides derived thereof would serve as potent biological matrix components to induce periodontal progenitors to further differentiate into periodontal ligament cells. Here, we test the hypothesis that domain of DSP influences cell fate. In situ hybridization and immunohistochemical analyses showed that the COOH-terminal DSP domain is expressed in mouse periodontium at various stages of root development. The recombinant COOH-terminal DSP fragment (rC-DSP) enhanced attachment and migration of human periodontal ligament stem cells (PDLSC), human primary PDL cells without cell toxicity. rC-DSP induced PDLSC cell proliferation as well as differentiation and mineralization of PDLSC and PDL cells by formation of mineralized tissue and ALPase activity. Effect of rC-DSP on cell proliferation and differentiation was to promote gene expression of tooth/bone-relate markers, transcription factors and growth factors. The results for the first time showed that rC-DSP may be one of the components of cell niche for stimulating stem/progenitor cell proliferation and differentiation and a natural scaffold for periodontal regeneration application.

FGF signaling sustains the odontogenic fate of dental mesenchyme by suppressing β-catenin signaling

Odontoblasts and osteoblasts develop from multipotent craniofacial neural crest cells during tooth and jawbone development, but the mechanisms that specify and sustain their respective fates remain largely unknown. In this study we used early mouse molar and incisor tooth germs that possess distinct tooth-forming capability after dissociation and reaggregation in vitro to investigate the mechanism that sustains odontogenic fate of dental mesenchyme during tooth development. We found that after dissociation and reaggregation, incisor, but not molar, mesenchyme exhibits a strong osteogenic potency associated with robustly elevated β-catenin signaling activity in a cell-autonomous manner, leading to failed tooth formation in the reaggregates. Application of FGF3 to incisor reaggregates inhibits β-catenin signaling activity and rescues tooth formation. The lack of FGF retention on the cell surface of incisor mesenchyme appears to account for the differential osteogenic potency between incisor and molar, which can be further attributed to the differential expression of syndecan 1 and NDST genes. We further demonstrate that FGF signaling inhibits intracellular β-catenin signaling by activating the PI3K/Akt pathway to regulate the subcellular localization of active GSK3β in dental mesenchymal cells. Our results reveal a novel function for FGF signaling in ensuring the proper fate of dental mesenchyme by regulating β-catenin signaling activity during tooth development.

Immortalized mouse dental papilla mesenchymal cells preserve odontoblastic phenotype and respond to bone morphogenetic protein 2

Odontogenesis is the result of the reciprocal interactions between epithelial–mesenchymal cells leading to terminally differentiated odontoblasts. This process from dental papilla mesenchymal cells to odontoblasts is regulated by a complex signaling pathway. When isolated from the developing tooth germs, odontoblasts quickly lose their potential to maintain the odontoblast-specific phenotype. Therefore, generation of an odontoblast-like cell line would be a good surrogate model for studying the dental mesenchymal cell differentiation into odontoblasts and the molecular events of dentin formation. In this study, immortalized dental papilla mesenchymal cell lines were generated from the first mouse mandibular molars at postnatal day 3 using pSV40. These transformed cells were characterized by RT-PCR, immunohistochemistry, Western blot, and analyzed for alkaline phosphatase activity and mineralization nodule formation. One of these immortalized cell lines, iMDP-3, displayed a high proliferation rate, but retained the genotypic and phenotypic characteristics similar to primary cells as determined by expression of tooth-specific markers and demonstrated the ability to differentiate and form mineralized nodules. Furthermore, iMDP-3 cells had high transfection efficiency as well as were inducible and responded to BMP2 stimulation. We conclude that the establishment of the stable murine dental papilla mesenchymal cell line might be used for studying the mechanisms of dental cell differentiation and dentin formation.

Transcriptional regulatory cascades in Runx2-dependent bone development

The development of the musculoskeletal system is a complex process that involves very precise control of bone formation and growth as well as remodeling during postnatal life. Although the understanding of the transcriptional mechanisms of osteogenesis has increased considerably, the molecular regulatory basis, especially the gene regulatory network of osteogenic differentiation, is still poorly understood. This review provides the reader with an overview of the key transcription factors that govern bone formation, highlighting their function and regulation linked to Runt-related transcription factor 2 (Runx2). Runx2 as the master transcription factor of osteoblast differentiation, Twist, Msh homeobox 2 (Msx2), and promyelocytic leukemia zinc-finger protein (PLZF) acting upstream of Runx2, Osterix (Osx) acting downstream of Runx2, and activating transcription factor 4 (ATF4) and zinc-finger protein 521 (ZFP521) acting as cofactors of Runx2 are discussed, and their relevance for tissue engineering is presented. References are provided for more in-depth personal study.

Msx1 and Tbx2 antagonistically regulate Bmp4 expression during the bud-to-cap stage transition in tooth development

Bmp4 expression is tightly regulated during embryonic tooth development, with early expression in the dental epithelial placode leading to later expression in the dental mesenchyme. Msx1 is among several transcription factors that are induced by epithelial Bmp4 and that, in turn, are necessary for the induction and maintenance of dental mesenchymal Bmp4 expression. Thus, Msx1(-/-) teeth arrest at early bud stage and show loss of Bmp4 expression in the mesenchyme. Ectopic expression of Bmp4 rescues this bud stage arrest. We have identified Tbx2 expression in the dental mesenchyme at bud stage and show that this can be induced by epithelial Bmp4. We also show that endogenous Tbx2 and Msx1 can physically interact in mouse C3H10T1/2 cells. In order to ascertain a functional relationship between Msx1 and Tbx2 in tooth development, we crossed Tbx2 and Msx1 mutant mice. Our data show that the bud stage tooth arrest in Msx1(-/-) mice is partially rescued in Msx1(-/-);Tbx2(+/-) compound mutants. This rescue is accompanied by formation of the enamel knot (EK) and by restoration of mesenchymal Bmp4 expression. Finally, knockdown of Tbx2 in C3H10T1/2 cells results in an increase in Bmp4 expression. Together, these data identify a novel role for Tbx2 in tooth development and suggest that, following their induction by epithelial Bmp4, Msx1 and Tbx2 in turn antagonistically regulate odontogenic activity that leads to EK formation and to mesenchymal Bmp4 expression at the key bud-to-cap stage transition.