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

p75NTR promotes tooth rhythmic mineralization via upregulation of BMAL1/CLOCK

The circadian clock plays a critical role in dentomaxillofacial development. Tooth biomineralization is characterized by the circadian clock; however, the mechanisms underlying the coordination of circadian rhythms with tooth development and biomineralization remain unclear. The p75 neurotrophin receptor (p75NTR) is a clock factor that regulates the oscillatory components of the circadian rhythm. This study aims to investigate the impact of p75NTR on the rhythmic mineralization of teeth and elucidate its underlying molecular mechanisms. We generated p75NTR knockout mice to examine the effects of p75NTR deficiency on tooth mineralization. Ectomesenchymal stem cells (EMSCs), derived from mouse tooth germs, were used for in vitro experiments. Results showed a reduction in tooth mineral density and daily mineralization rate in p75NTR knockout mice. Deletion of p75NTR decreased the expression of DMP1, DSPP, RUNX2, and ALP in tooth germ. Odontogenic differentiation and mineralization of EMSCs were activated by p75NTR. Histological results demonstrated predominant detection of p75NTR protein in odontoblasts and stratum intermedium cells during rapid formation phases of dental hard tissue. The mRNA expression of p75NTR exhibited circadian variations in tooth germs and EMSCs, consistent with the expression patterns of the core clock genes Bmal1 and Clock. The upregulation of BMAL1/CLOCK expression by p75NTR positively regulated the mineralization ability of EMSCs, whereas BMAL1 and CLOCK exerted a negative feedback regulation on p75NTR by inhibiting its promoter activity. Our findings suggest that p75NTR is necessary to maintain normal tooth biomineralization. Odontogenic differentiation and mineralization of EMSCs is regulated by the p75NTR-BMAL1/CLOCK signaling axis. These findings offer valuable insights into the associations between circadian rhythms, tooth development, and biomineralization.

The odontoblastic differentiation of dental mesenchymal stem cells: molecular regulation mechanism and related genetic syndromes

Dental mesenchymal stem cells (DMSCs) are multipotent progenitor cells that can differentiate into multiple lineages including odontoblasts, osteoblasts, chondrocytes, neural cells, myocytes, cardiomyocytes, adipocytes, endothelial cells, melanocytes, and hepatocytes. Odontoblastic differentiation of DMSCs is pivotal in dentinogenesis, a delicate and dynamic process regulated at the molecular level by signaling pathways, transcription factors, and posttranscriptional and epigenetic regulation. Mutations or dysregulation of related genes may contribute to genetic diseases with dentin defects caused by impaired odontoblastic differentiation, including tricho-dento-osseous (TDO) syndrome, X-linked hypophosphatemic rickets (XLH), Raine syndrome (RS), hypophosphatasia (HPP), Schimke immuno-osseous dysplasia (SIOD), and Elsahy-Waters syndrome (EWS). Herein, recent progress in the molecular regulation of the odontoblastic differentiation of DMSCs is summarized. In addition, genetic syndromes associated with disorders of odontoblastic differentiation of DMSCs are discussed. An improved understanding of the molecular regulation and related genetic syndromes may help clinicians better understand the etiology and pathogenesis of dentin lesions in systematic diseases and identify novel treatment targets.

The functional effects of Piezo channels in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are widely used in cell therapy, tissue engineering, and regenerative medicine because of their self-renewal, pluripotency, and immunomodulatory properties. The microenvironment in which MSCs are located significantly affects their physiological functions. The microenvironment directly or indirectly affects cell behavior through biophysical, biochemical, or other means. Among them, the mechanical signals provided to MSCs by the microenvironment have a particularly pronounced effect on their physiological functions and can affect osteogenic differentiation, chondrogenic differentiation, and senescence in MSCs. Mechanosensitive ion channels such as Piezo1 and Piezo2 are important in transducing mechanical signals, and these channels are widely distributed in sites such as skin, bladder, kidney, lung, sensory neurons, and dorsal root ganglia. Although there have been numerous studies on Piezo channels in MSCs in recent years, the function of Piezo channels in MSCs is still not well understood, and there has been no summary of their relationship to illustrate which physiological functions of MSCs are affected by Piezo channels and the possible underlying mechanisms. Therefore, based on the members, structures, and functions of Piezo ion channels and the fundamental information of MSCs, this paper focused on summarizing the advances in Piezo channels in MSCs from various tissue sources to provide new ideas for future research and practical applications of Piezo channels and MSCs.

Maxillary lateral incisor agenesis is associated with maxillary form: a geometric morphometric analysis

BACKGROUND AND OBJECTIVE

Agenesis of the maxillary lateral incisor occurs in up to 4% of all individuals and requires multidisciplinary treatment. Its developmental origins, however, are not fully understood. Earlier studies documented genetic factors contributing to agenesis but also an association with craniofacial morphology. In this study, we assessed the association between maxillary morphology and lateral incisor agenesis by a geometric morphometric approach to disentangle the roles of developmental plasticity and genetic factors.

MATERIALS AND METHODS

We quantified the maxillary alveolar ridge by 19 two-dimensional landmarks on cross-sectional images of 101 computed tomography scans. We compared the shape and size of the alveolar ridge across patients with unilateral or bilateral agenesis of maxillary lateral incisors and patients with extracted or in situ incisors.

RESULTS

The maxillary alveolar ridge was clearly narrower in patients with agenesis or an extracted incisor compared to the control group, whereas the contralateral side of the unilateral agenesis had an intermediate width. Despite massive individual variation, the ventral curvature of the alveolar ridge was, on average, more pronounced in the bilateral agenesis group compared to unilateral agenesis and tooth extraction.

CONCLUSIONS

This suggests that pleiotropic genetic and epigenetic factors influence both tooth development and cranial growth, but an inappropriately sized or shaped alveolar process may also inhibit normal formation or development of the tooth bud, thus leading to dental agenesis.

CLINICAL RELEVANCE

Our results indicate that bilateral agenesis of the lateral incisor tends to be associated with a higher need of bone augmentation prior to implant placement than unilateral agenesis.

IPO7 Promotes Odontoblastic Differentiation and Inhibits Osteoblastic Differentiation Through Regulation of RUNX2 Expression and Translocation

RUNX2, an important transcriptional factor for both odontoblastic and osteoblastic differentiation, is upregulated during osteoblastic differentiation, but downregulated during late odontoblastic differentiation. However, the specific mechanism of the different RUNX2 expression in bone and dentin remains largely unknown. Importin 7 (IPO7), a member of the karyopherin β-superfamily, mediates nucleocytoplasmic transport of proteins. In this study, we found that IPO7 was increasingly expressed from pre-odontoblasts to mature odontoblasts. IPO7 expression was increased with odontoblastic differentiation of mouse dental papilla cells (mDPCs) and knockdown of IPO7-inhibited cell differentiation. While in MC3T3-E1 cells, IPO7 was decreased during osteoblastic differentiation and knockdown of IPO7-promoted cell differentiation. In mPDCs, IPO7 was able to bind with some odontoblastic transcription factors, and imported them into the nucleus, but not with RUNX2. Furthermore, IPO7 inhibited the total RUNX2 expression by promoting HDAC6 nuclear localization during odontoblastic differentiation. However, in MC3T3-E1 cells, IPO7 inhibited the nuclear distribution of RUNX2 but did not affect the total protein level of RUNX2. In conclusion, we found that IPO7 promotes odontoblastic differentiation and inhibits osteoblastic differentiation through regulating RUNX2 expression and translocation differently.

Sulphur dioxide and fluoride co-exposure induce incisor hypomineralization and amelogenin upregulation via YAP/RUNX2 signaling pathway

Sulphur dioxide (SO₂) and fluoride are among the most common environmental pollutants affecting human health, and both co-exist in areas predominantly consuming coal. It is vital to analyse the combined toxicity of SO₂ and fluoride, and their effects on health and the underlying mechanisms of their co-exposure have not yet been adequately assessed. In the present study, we used ICR mice and LS8 cells to investigate the toxicity of SO₂ and fluoride exposure to the enamel, alone or in combination. Factorial design analysis was used to reveal the combined toxicity in vitro and in vivo. Co-exposure to SO₂ and fluoride exacerbated enamel injury, resulting in more severe hypomineralization of incisor, and enamel structure disorders in mice, and could induce the accumulation of protein residue in the matrix of the enamel. Amelogenin expression was increased upon exposure to SO₂ and fluoride, but enamel matrix proteases were not affected. Consistent with our in vivo results, co-exposure of SO₂ and fluoride aggravated amelogenin expression in LS8 cells, and increased the YAP and RUNX2 levels. Co-exposure to SO₂ and fluoride resulted in greater toxicity than individual exposure, both in vitro and in vivo, indicating that residents of areas exposed to SO₂ and fluoride may have an increased risk of developing enamel damage.

Identification of Novel Regulator Involved in Differentiation of Mouse iPS Cells into Odontoblast-like Cells

Odontoblasts differentiate from dental papilla stem cells, but the genetic changes that occur during this process remain unclear. The aim of this study was to investigate gene expression patterns during differentiation of mouse iPS cells into odontoblast-like cells. Mouse iPS cells were cultured on a collagen type-1 scaffold with bone morphogenetic protein 4 (BMP4) and retinoic acid (RA). The results of immunofluorescence studies for dentin sialoprotein, dentin matrix protein 1 (DMP1), and nestin were positive. A qRT-PCR analysis revealed that mRNA expression levels of neural crest marker sex determining region Y box (Sox)-10, dentin sialophosphoprotein (Dspp), and Dmp1 were up-regulated, but that mRNA expression levels of the mineralization markers bone sialoprotein and osteocalcin were down-regulated. Microarray analysis showed that 2,597 entities were up-regulated and 1,327 down-regulated among a total of 15,330 investigated. Sox11 was among the up-regulated genes identified. The Sox11 mRNA expression level with odontoblast induction after day 11 was higher than that after day 2 (p<0.05). Gene knockdown using small interference RNA (siRNA) silencing was used to characterize the function of Sox11. The Dspp mRNA expression level in Sox11 siRNA-treated cells was significantly lower than that in the control (p<0.05). These results suggest that BMP4 and RA induce mouse iPS cells to differentiate into odontoblast-like cells. The differentiation efficiency is not high, however, and many stem cells remain. The results also suggest that Sox11 is an important factor in odontoblastic differentiation.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Role of the Demethylase AlkB Homolog H5 in the Promotion of Dentinogenesis

Dentinogenesis is a key process in tooth formation and is regulated by a series of pre- and post-transcriptional regulations. N6-methyl-adenosine (m⁶A), which is the most prevalent internal chemical modification that can be removed by the RNA demethylase AlkB homolog H5 (ALKBH5), has recently been reported to be involved in several biological processes. However, the exact function of ALKBH5-mediated m⁶A modification in tooth development remains unclear. Here, we showed that Alkbh5 was expressed in pre-odontoblasts, polarizing odontoblasts, and secretory odontoblasts. Alkbh5 overexpression in the mouse dental papilla cell line mDPC6T promoted odontoblastic differentiation. Conditional knockout of Alkbh5 in Dmp1-expressing odontoblasts led to a decrease in number of odontoblasts and increased pre-dentin formation. Mechanistically, RNA sequencing and m⁶A sequencing of Alkbh5-overexpressing mDPC6T cells revealed that Alkbh5 promoted odontoblast differentiation by prolonging the half-life of Runx2 transcripts in an m⁶A-dependent manner and by activating the phosphatidylinositol 3-kinase/protein kinase B pathway. Notably, the loss of Alkbh5 expression in odontoblasts impaired tertiary dentin formation in vivo. These results suggested that the RNA demethylase ALKBH5 plays a role in dentinogenesis.

Multiple roles of Runt-related transcription factor-2 in tooth eruption: bone formation and resorption

OBJECTIVE

The aim was to provide a comprehensive review of the current knowledge of the multiple roles of Runt-related transcription factor-2 (RUNX2) in regulating tooth eruption, focusing on the molecular mechanisms regarding tooth eruption mediated by RUNX2.

DESIGN

Relevant literatures in PubMed, Medline, and Scopus database were searched, and a narrative review was performed. The multiple roles of RUNX2 in regulating tooth eruption was reviewed and discussed.

RESULTS

Aberrant RUNX2 expression leads to disturbed or failed tooth eruption. Tooth eruption involves both the process of bone formation and bone resorption. RUNX2 promotes osteogenesis around the radicular portion of the dental follicle that provides the biological force for tooth eruption through inducing the expression of osteogenesis-related genes in dental follicle cells/osteoblasts. On the other hand, through indirect and direct pathways, RUNX2 regulates osteoclastogenesis and the formation of the eruption pathway.

CONCLUSION

RUNX2 exerts a pivotal and complex influence in regulating tooth eruption. This review provides a better understanding of the function of RUNX2 in tooth eruption, which is beneficial to illuminate the precise molecular mechanism of osteogenesis and bone resorption, aiding the development of effective therapy for the failure of tooth eruption.

Minimal Intervention Dentistry: Biocompatibility and Mechanism of Action of Products for Chemical-Mechanical Removal of Carious Tissue

Conventional method for removal of carious tissue using low speed drills usually induce noise and vibration, in addition to thermal and pressure effects that can be harmful to the pulp tissue and cause fear in children. Therefore, several alternative methods are being developed to try to minimize the unpleasant perception of the patient during caries removal. Chemical-mechanical removal of carious tissue goal is to selectively remove the carious lesion, which reduces the amount of bacteria inside the cavity without removing the tissue susceptible to remineralization. This method is also able to minimize the tactile perception by the patient during the manipulation of the lesion compared to the conventional method, and, therefore, it has been widely accepted among phobic patients, children and special needs patients. Due to the close relationship between dentin and pulp tissue, all injuries imposed on this dentin may have repercussions on the underlying pulp connective tissue. The morphological aspects of remaining dentin favor the diffusion of chemical components of dental materials, which can be toxic to the pulp tissue or even negatively interfere in the reparative process. Thus, considering the proximity between the applied material and the underlying pulp tissue, especially in deep cavities, there is a need to assess the biological behavior of dental materials against pulp cells, since aggressions to the pulp tissue can be caused not only by metabolites from microorganisms involved in dental caries but also by components that are released from these products. This subject was explored in this narrative literature review.

Regulation of transforming growth factor-β1-stimulation of Runx2 acetylation for matrix metalloproteinase 13 expression in osteoblastic cells

Transforming growth factor beta 1 (TGF-β1) functions as a coupling factor between bone development and resorption. Matrix metalloproteinase 13 (MMP13) is important in bone remodeling, and skeletal dysplasia is caused by a deficiency in MMP13 expre-ssion. Runx2, a transcription factor is essential for bone development, and MMP13 is one of its target genes. TGF-β1 promoted Runx2 phosphorylation, which was necessary for MMP13 production in osteoblastic cells, as we previously shown. Since the phosphorylation of some proteins causes them to be degraded by the ubiquitin/proteasome pathway, we hypothesized that TGF-β1 might stabilize the phosphorylated Runx2 protein for its activity by other post-translational modification (PTM). This study demonstrated that TGF-β1-stimulated Runx2 acetylation in rat osteoblastic cells. p300, a histone acetyltransferase interacted with Runx2, and it promoted Runx2 acetylation upon TGF-β1-treatment in these cells. Knockdown of p300 decreased the TGF-β1-stimulated Runx2 acetylation and MMP13 expression in rat osteoblastic cells. TGF-β1-treatment stimulated the acetylated Runx2 bound at the MMP13 promoter, and knockdown of p300 reduced this effect in these cells. Overall, our studies identified the transcriptional regulation of MMP13 by TGF-β1 via Runx2 acetylation in rat osteoblastic cells, and these findings contribute to the knowledge of events presiding bone metabolism.

The Association Between Runx Signaling and Craniofacial Development and Disease

PURPOSE OF REVIEW

The Runx family genes (Runx1, Runx2, Runx3, and Cbfb) are important transcriptional regulators in the development of various tissues. We herein highlight the roles of the Runx family genes in morphogenesis in the craniofacial regions and in the pathogenesis of congenital morphological problems in these regions.

RECENT FINDINGS

A recent analysis using conditional Runx mutant animals and a human genetic study identified the novel roles of Runx genes in the development of the tooth, salivary glands, and the palate. In an animal study, Runx1/Cbfb signaling was found to regulate the Lgr5 expression and maintain the stem cells in the dental epithelium in the growing incisors. Aberrant Runx1/Cbfb signaling induced male-specific involution of the convoluted granular cell differentiation of the submandibular gland. In palatogenesis, Runx1/Cbfb signaling regulated the Tgfb3 expression in the fusing palatal epithelium through Stat3 activation. The combination of a human genetic study and a phenotype analysis of mutant animals revealed the various roles of Runx genes in the development of the tooth, palate, and salivary glands. Runx genes have functional redundancy in various tissues, which still hinder the roles of Runx genes in morphogenesis. Future studies may reveal the novel roles of Runx signaling.

Cleidocranial dysplasia and novel RUNX2 variants: dental, craniofacial, and osseous manifestations

Cleidocranial dysplasia (CCD) is a skeletal disorder affecting cranial sutures, teeth, and clavicles, and is associated with the RUNX2 mutations. Although numerous patients have been described, a direct genotype–phenotype correlation for RUNX2 has been difficult to establish. Further cases must be studied to understand the clinical and genetic spectra of CCD.

YBX1 Promotes the Inclusion of RUNX2 Alternative Exon 5 in Dental Pulp Stem Cells

Background and Objectives

RUNX2 plays an essential role during the odontoblast differentiation of dental pulp stem cells (DPSCs). RUNX2 Exon 5 is an alternative exon and essential for RUNX2 transcriptional activity. This study aimed to investigate the regulatory mechanisms of RUNX2 exon 5 alternative splicing in human DPSCs.

Methods and Results

The regulatory motifs of RUNX2 exon 5 were analyzed using the online SpliceAid program. The alternative splicing of RUNX2 exon 5 in DPSCs during mineralization-induced differentiation was analyzed by RT-PCR. To explore the effect of splicing factor YBX1 on exon 5 alternative splicing, gaining or losing function of YBX1 was performed by transfection of YBX1 overexpression plasmid or anti-YBX1 siRNA in DPSCs. Human RUNX2 exon 5 is evolutionarily conserved and alternatively spliced in DPSCs. There are three potential YBX1 binding motifs in RUNX2 exon 5. The inclusion of RUNX2 exon 5 and YBX1 expression level increased significantly during mineralization- induced differentiation in DPSCs. Overexpression of YBX1 significantly increased the inclusion of RUNX2 exon 5 in DPSCs. In contrast, silence of YBX1 significantly reduced the inclusion of exon 5 and the corresponding RUNX2 protein expression level. Knockdown of YBX1 reduced the expression of alkaline phosphatase (ALP) and osteocalcin (OC) and the mineralization ability of DPSCs, while overexpression of YBX1 increased the expression of ALP and OC and the mineralization ability of DPSCs.

Conclusions

Human RUNX2 exon 5 is conserved evolutionarily and alternatively spliced in DPSCs. Splicing factor YBX1 promotes the inclusion of RUNX2 exon 5 and improves the mineralization ability of DPSCs.

Genome-scale actions of master regulators directing skeletal development

The mammalian skeleton develops through two distinct modes of ossification: intramembranous ossification and endochondral ossification. During the process of skeletal development, SRY-box containing gene 9 (Sox9), runt-related transcription factor 2 (Runx2), and Sp7 work as master transcription factors (TFs) or transcriptional regulators, underlying cell fate specification of the two distinct populations: bone-forming osteoblasts and cartilage-forming chondrocytes. In the past two decades, core transcriptional circuits underlying skeletal development have been identified mainly through mouse genetics and biochemical approaches. Recently emerging next-generation sequencer (NGS)-based studies have provided genome-scale views on the gene regulatory landscape programmed by the master TFs/transcriptional regulators. With particular focus on Sox9, Runx2, and Sp7, this review aims to discuss the gene regulatory landscape in skeletal development, which has been identified by genome-scale data, and provide future perspectives in this field.

Exploring the Association Between Genetic Polymorphisms in Genes Involved in Craniofacial Development and Isolated Tooth Agenesis

Tooth agenesis is a common congenital anomaly in humans and is more common in oral cleft patients than in the general population. Many previous studies suggested that oral cleft and tooth agenesis share a similar genetic background. Therefore, this study explored the association between isolated tooth agenesis and genetic polymorphisms in genes that are crucial for craniofacial and tooth development. Panoramic radiographs, anamnesis, and genomic DNA from 273 patients were included. Patients were classified as tooth agenesis present, when at least one permanent tooth was congenitally missing. Patients with syndromes and oral cleft were excluded. Only unrelated patients were included. The genetic polymorphisms in BMP2 (rs235768 and rs1005464), BMP4 (rs17563), RUNX2 (rs59983488 and rs1200425), and SMAD6 (rs3934908 and rs2119261) were genotyped by real-time polymerase chain reaction. Genotype and allele distributions were compared between the tooth agenesis phenotypes and controls by Chi-square test. Haplotype and diplotype analysis were also performed, in addition to multivariate analysis (alpha of 0.05). A total of 86 tooth agenesis cases and 187 controls were evaluated. For the rs235768 in BMP2, patients carrying TT genotype have higher chance to present tooth agenesis [p < 0.001; prevalence ratio (PR) = 8.29; 95% confidence interval (CI) = 4.26–16.10]. The TT genotype in rs3934908 (SMAD6) was associated with higher chance to present third molar agenesis (p = 0.023; PR = 3.25; 95% CI = 1.17–8.99). BMP2 was also associated in haplotype and diplotype analysis with tooth agenesis. In conclusion, genetic polymorphisms in BMP2 and SMAD6 were associated with isolated tooth agenesis.

Sequencing analysis of exons 5 and 6 in RUNX2 in non-syndromic patients with supernumerary tooth in Kelantan, Malaysia

OBJECTIVE

The aim of this study is to do a sequencing analysis of RUNX2 in non-syndromic patients with supernumerary tooth.

MATERIALS AND METHODS

Fifty-three patients with supernumerary tooth were identified retrospectively from 1,275 radiographic reviews who attended the Hospital Universiti Sains Malaysia (USM) Dental Clinic. Informed consent was obtained from the patients prior to the study. Blood samples were collected from 41 patients and DNA extractions were performed out of which 10 samples were chosen randomly for PCR amplification using designated primers for RUNX2 followed by DNA sequencing analysis.

RESULTS

This study involved 28 male patients (68.3%) and 13 female patients (31.7%) with a gender ratio of 2.2:1 and mean age of 15.9 ± 6.2 years. DNA extraction yielded ~ 40 ng/μl of concentrated DNA, and each DNA sample had more than 1500 bp of DNA length. The purity ranged between 1.8 and 2.0. DNA sequencing analysis did not reveal any mutations in exons 5 and 6 of RUNX2.

CONCLUSION

This study did not reveal any mutations in exons 5 and 6 of RUNX2 in non-syndromic patients with supernumerary tooth.

CLINICAL RELEVANCE

Analysis of mutations in RUNX2 is important to enhance the understanding of tooth development in humans.

Odontogenesis-related candidate genes involved in variations of permanent teeth size

OBJECTIVE

The aim of the study was to evaluate the association between genetic polymorphisms in RUNX2, BMP4, BMP2, TGFβ1, EGF, and SMAD6 and variations in permanent tooth size (TS).

MATERIALS AND METHODS

This cross-sectional study evaluated 110 individuals' dental casts to determine the maximum tooth crown size of all fully erupted permanent teeth (third molars were excluded) in the mesiodistal (MD) and buccolingual (BL) dimensions. Genomic DNA was obtained from the epithelial cells of the oral mucosa to evaluate the genetic polymorphisms in RUNX2 (rs59983488 and rs1200425), BMP4 (rs17563), BMP2 (rs235768 and rs1005464), TGFβ1 (rs1800470), EGF (rs4444903), and SMAD6 (rs2119261 and rs3934908) through real-time PCR. The data were submitted to statistical analysis with a significance level of 0.05.

RESULTS

The genetic polymorphisms rs59983488, rs1200425, rs17563, rs235768, rs1005464, rs1800470, and rs4444903 were associated with MD and BL TS of the upper and lower arches (p < 0.05). The polymorphism rs2119261 was associated with variation in TS only in the upper arch (p < 0.05). The rs3934908 was not associated with any TS measurement (p > 0.05).

CONCLUSIONS

In summary, this study reports novel associations between variation in permanent TS and genetic polymorphisms in RUNX2, BMP4, BMP2, TGFβ1, EGF, and SMAD6 indicating a possible role of these genes in dental morphology.

CLINICAL RELEVANCE

Polymorphisms in odontogenesis-related genes may be involved in dental morphology enabling a prediction of permanent TS variability. The knowledge regarding genes involved in TS might impact the personalized dental treatment, considering that patients' genetic profile would soon be introduced into clinical practice to improve patient management.

Estrogen deficiency affects tooth formation and gene expression in the odontogenic region of female rats

BACKGROUND

There is some evidence that estrogen regulates the expression of several genes in different cells, including dental cells. Therefore, the aim of this study was to investigate the role of estrogen deficiency during tooth development regarding tooth structure morphology and its impact on the expression of odontogenesis-related genes.

METHODS

A total of 40 female Wistar rats was divided into OVX (estrogen deficiency) and Sham (control) groups. Bilateral ovariectomy was performed in the OVX group, while Sham surgery was performed in the control group at the age of 21 days. At an age of 56 days, 16 rats were euthanized for gene expression analyses of Bmp4, Smad6, Tgfb1 and Runx2. At the age of 63 days, the remaining rats were euthanized for histological and morphometric analyses of teeth. The mandibles of the rats were submitted to μCT analysis. Tooth structures (enamel, dentin and dental pulp) were analyzed. T test was used to compare the mean differences between groups (p<0.05).

RESULTS

In the μCT analysis, enamel and dentin thickness were significantly increased in the control group (p<0.0001). Pulp dimensions were significantly larger in the OVX group (p<0.0001). A reduction of tooth structures in the OVX group was confirmed in HE staining. Smad6 was differentially expressed in the OVX group (p=0.04).

CONCLUSION

Estrogen deficiency affects gene expression in the odontogenic region and tooth structure morphology.

Anti-USAG-1 therapy for tooth regeneration through enhanced BMP signaling

Uterine sensitization-associated gene-1 (USAG-1) deficiency leads to enhanced bone morphogenetic protein (BMP) signaling, leading to supernumerary teeth formation. Furthermore, antibodies interfering with binding of USAG-1 to BMP, but not lipoprotein receptor-related protein 5/6 (LRP5/6), accelerate tooth development. Since USAG-1 inhibits Wnt and BMP signals, the essential factors for tooth development, via direct binding to BMP and Wnt coreceptor LRP5/6, we hypothesized that USAG-1 plays key regulatory roles in suppressing tooth development. However, the involvement of USAG-1 in various types of congenital tooth agenesis remains unknown. Here, we show that blocking USAG-1 function through USAG-1 knockout or anti-USAG-1 antibody administration relieves congenital tooth agenesis caused by various genetic abnormalities in mice. Our results demonstrate that USAG-1 controls the number of teeth by inhibiting development of potential tooth germs in wild-type or mutant mice missing teeth. Anti-USAG-1 antibody administration is, therefore, a promising approach for tooth regeneration therapy.

Zeb1 Promotes Odontoblast Differentiation in a Stage-Dependent Manner

A comprehensive study of odontoblastic differentiation is essential to understand the process of tooth development and to achieve the ability of tooth regeneration in the future. Zinc finger E-box-binding homeobox 1 (Zeb1) is a transcription factor expressed in various neural crest-derived tissues, including the mesenchyme of the tooth germ. However, its role in odontoblastic differentiation remains unknown. In this study, we found the expression of Zeb1 gradually increased during odontoblast differentiation in vivo, as well as during induced differentiation of cultured primary murine dental papilla cells (mDPCs) in vitro. In addition, the differentiation of mDPCs was repressed in Zeb1-silenced cells. We used RNA sequencing (RNA-seq) to identify the transcriptome-wide targets of Zeb1 and used assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to explore the direct targets of Zeb1 in both the early stage (embryonic day 16.5; E16.5) and the late stage (postnatal day 0; PN0) of tooth development. We identified the motifs of transcription factors enriched in Zeb1-dependent accessible chromatin regions and observed that only in the early stage of mDPCs could Zeb1 significantly change the accessibility of chromatin regions. In vivo and in vitro experiments confirmed that silencing of Zeb1 at E16.5 inhibited dentinogenesis. Analysis of RNA-seq and ATAC-seq resulted in the identification of Runx2, a gene directly regulated by Zeb1 during early odontoblast differentiation. Zeb1 enhances the expression of Runx2 by binding to its cis-elements, and ZEB1 interacts with RUNX2. In the late stage of tooth development, we found that ZEB1 could directly bind to and increase the enhancer activity of an element upstream of Dspp and promote dentinogenesis. In this study, for the first time, we revealed that ZEB1 promoted odontoblast differentiation in the early stage by altering chromatin accessibility of cis-elements near genes such as Runx2, while in the late stage, it directly enhanced Dspp transcription, thereby performing a dual role.

SALL1 regulates commitment of odontoblast lineages by interacting with RUNX2 to remodel open chromatin regions

Mouse dental papilla cells (mDPCs) derive from cranial neural crest cells and maintain mesenchymal stem cell characteristics. The differentiation of neural crest cells into odontoblasts is orchestrated by transcription factors regulating the expression of genes whose enhancers are initially inaccessible. However, the identity of the transcription factors driving the emergence of odontoblast lineages remains elusive. In this study, we identified SALL1, a transcription factor that was particularly expressed in preodontoblasts, polarizing odontoblasts, and secretory odontoblasts in vivo. Knockdown of Sall1 in mDPCs inhibited their odontoblastic differentiation. In order to identify the regulatory network of Sall1, RNA sequencing and an assay for transposase-accessible chromatin with high-throughput sequencing were performed to analyze the genome-wide direct regulatory targets of SALL1. We found that inhibition of Sall1 expression could decrease the accessibility of some chromatin regions associated with odontoblast lineages at embryonic day 16.5, whereas these regions remained unaffected at postnatal day 0.5, suggesting that SALL1 regulates the fate of mDPCs by remodeling open chromatin regions at the early bell stage. Specifically, we found that SALL1 could directly increase the accessibility of cis-regulatory elements near Tgf-β2 and within the Runx2 locus. Moreover, coimmunoprecipitation and proximal ligation assays showed that SALL1 could establish functional interactions with RUNX2. Taken together, our results demonstrated that SALL1 positively regulates the commitment of odontoblast lineages by interacting with RUNX2 and directly activating Tgf-β2 at an early stage.

Development of tooth regenerative medicine strategies by controlling the number of teeth using targeted molecular therapy

Analysis of various genetically modified mice, with supernumerary teeth, has revealed the following two intrinsic molecular mechanisms that increase the number of teeth. One plausible explanation for supernumerary tooth formation is the rescue of tooth rudiments. Topical application of candidate molecules could lead to whole tooth formation under suitable conditions. Congenital tooth agenesis is caused by the cessation of tooth development due to the deletion of the causative gene and suppression of its function. The arrest of tooth development in Runx2 knockout mice, a mouse model of congenital tooth agenesis, is rescued in double knockout mice of Runx2 and Usag-1. The Usag-1 knockout mouse is a supernumerary model mouse. Targeted molecular therapy could be used to generate teeth in patients with congenital tooth agenesis by stimulating arrested tooth germs. The third dentition begins to develop when the second successional lamina is formed from the developing permanent tooth in humans and usually regresses apoptotically. Targeted molecular therapy, therefore, seems to be a suitable approach in whole-tooth regeneration by the stimulation of the third dentition. A second mechanism of supernumerary teeth formation involves the contribution of odontogenic epithelial stem cells in adults. Cebpb has been shown to be involved in maintaining the stemness of odontogenic epithelial stem cells and suppressing epithelial-mesenchymal transition. Odontogenic epithelial stem cells are differentiated from one of the tissue stem cells, enamel epithelial stem cells, and odontogenic mesenchymal cells are formed from odontogenic epithelial cells by epithelial-mesenchymal transition. Both odontogenic epithelial cells and odontogenic mesenchymal cells required to form teeth from enamel epithelial stem cells were directly induced to form excess teeth in adults. An approach for the development of targeted therapeutics has been the local application of monoclonal neutralizing antibody/siRNA with cationic gelatin for USAG-1 or small molecule for Cebpb.

iMatrix-511 Stimulates the Proliferation and Differentiation of MDPC-23 Cells into Odontoblastlike Phenotype

INTRODUCTION

iMatrix-511 is a novel integrin-binding fragment derived from laminin-511. Previous studies showed its superiority as a culture substrate for xeno-free culture and maintenance of pluripotency in stem cells. However, its effects in the dental field remain largely unknown. The aim of the present study was to unravel the in vitro effects of iMatrix-511 in comparison with vitronectin (VN).

METHODS

Biochemical assays were performed in vitro in MDPC-23 cells. The optimal coating density for 2 proteins was determined using the cell counting kit-8. To evaluate cell proliferation to both proteins, MDPC-23 cells were directly seeded onto the iMatrix-511 or VN-modified polystyrene and analyzed by the cell counting kit-8. The phenotype of cells seeded on iMatrix-511 and VN was characterized. Phenotypic characterization included real-time reverse-transcription polymerase chain reaction and alizarin red staining.

RESULTS

The optimal coating density for iMatrix-511 and VN was determined to be 1 μg/cm² and 0.25 μg/cm², respectively. Cells cultured on iMatrix-511 showed higher cell proliferative activity than the noncoated control and VN on days 1, 2, and 4. Cell morphology observation revealed MDPC-23 cells attach preferentially to iMatrix-511 and start to spread as early as 1 hour after inoculation. MDPC-23 cells exhibited more potent odontogenic differentiation on iMatrix-511 than the control and VN as shown by the marked enhancement of dentin matrix protein 1 and dentin sialophosphoprotein messenger RNA expression. Although both proteins showed more mineralized nodule formation than the control, iMatrix-511 remained to be the one that elicited stronger calcific deposition.

CONCLUSIONS

iMatrix-511 supported the proliferation and acquisition of odontogenic cell phenotype in vitro, rendering this novel material a potential candidate for dentin regeneration.

Trps1 transcription factor regulates mineralization of dental tissues and proliferation of tooth organ cells

Mutations of the TRPS1 gene cause trichorhinophalangeal syndrome (TRPS), a skeletal dysplasia with dental abnormalities. TRPS dental phenotypes suggest that TRPS1 regulates multiple aspects of odontogenesis, including the tooth number and size. Previous studies delineating Trps1 expression throughout embryonic tooth development in mice detected strong Trps1 expression in dental mesenchyme, preodontoblasts, and dental follicles, suggesting that TRPS dental phenotypes result from abnormalities in early developmental processes. In this study, Trps1^+/- and Trps1^-/- mice were analyzed to determine consequences of Trps1 deficiency on odontogenesis. We focused on the aspects of tooth formation that are disturbed in TRPS and on potential molecular abnormalities underlying TRPS dental phenotypes. Microcomputed tomography analyses of molars were used to determine tooth size, crown shape, and mineralization of dental tissues. These analyses uncovered that disruption of one Trps1 allele is sufficient to impair mineralization of dentin in both male and female mice. Enamel mineral density was decreased only in males, while mineralization of the root dental tissues was decreased only in females. In addition, significantly smaller teeth were detected in Trps1^+/- females. Histomorphometric analyses of tooth organs showed reduced anterior-posterior diameter in Trps1^-/- mice. BrdU-incorporation assay detected reduced proliferation of mesenchymal and epithelial cells in Trps1^-/- tooth organs. Immunohistochemistry for Runx2 and Osx osteogenic transcription factors revealed changes in their spatial distribution in Trps1^-/- tooth organs and uncovered cell-type specific requirements of Trps1 for Osx expression. In conclusion, this study has demonstrated that Trps1 is a positive regulator of cell proliferation in both dental mesenchyme and epithelium, suggesting that the microdontia in TRPS is likely due to decreased cell proliferation in developing tooth organs. Furthermore, the reduced mineralization observed in Trps1^+/- mice may provide some explanation for the extensive dental caries reported in TRPS patients.

Collapsin Response Mediator Protein 1, a Novel Marker Protein for Differentiated Odontoblasts

We previously reported that the terminal differentiation of odontoblasts was inhibited in Runx2 transgenic {Tg(Col1a1-Runx2)} mice under the control of the 2.3-kb Col1a1 promoter. Odontoblasts in Tg(Col1a1-Runx2) mice lose their characteristic long cellular processes, and show marked reductions in the protein levels of markers for odontoblasts, such as dentin sialophosphoprotein, nestin, and microtubule-associated protein tau (Mapt). We herein demonstrated that collapsin response mediator protein 1 (CRMP1), a neuronal phosphoprotein that participates in various aspects of neuronal development, was specifically expressed in the differentiated odontoblasts of wild-type, but not Tg(Col1a1-Runx2) tooth germs by comparing expression profiles in wild-type and Tg(Col1a1-Runx2) mouse molars using microarray and immunohistochemical analyses. CRMP1 expression was detected at a slightly later differentiation stage in odontoblasts than type 1 collagen, nestin, and Mapt expression, which was observed from the onset of dentinogenesis. Among these proteins, CRMP1 was the most specifically localized in odontoblasts in the tooth germ. In erupted molars, odontoblast-specific CRMP1 expression decreased with age. These results indicate that CRMP1 is a novel marker protein for differentiated odontoblasts in mouse tooth germs, and suggest that CRMP1 participates in the morphogenesis of functioning odontoblasts.

Persistent Wnt/β-catenin signaling in mouse epithelium induces the ectopic Dspp expression in cheek mesenchyme

Tooth development is accomplished by a series of epithelial-mesenchyme interactions. Epithelial Wnt/β-catenin signaling is sufficient to initiate tooth development by activating Shh, Bmps, Fgfs and Wnts in dental epithelium, which in turn, triggered the expression of odontogenic genes in the underlying mesenchyme. Although constitutive activation of Wnt/β-catenin signaling in oral ectoderm resulted in the continuous tooth formation throughout the life span, if the epithelial Wnt/β-catenin signaling could induce the mesenchyme other than oral mesenchyme still required to be elucidated. In this study, we found that in the K14-cre; Ctnnb1^ex3f mice, the markers of dental epithelium, such as Pitx2, Shh, Bmp2, Fgf4, and Fgf8, were not only activated in the oral ectoderm, but also in the cheek epithelium. Surprisingly, the underlying cheek mesenchymal cells were elongated and expressed Dspp. Further investigations detected that the expression of Msx1 and Runx2 extended from oral to cheek mesenchyme. These findings suggested that epithelial Wnt/β-catenin signaling was capable of inducing Dspp expression in non-dental mesenchyme. Moreover, Dspp expression in the K14-cre; Ctnnb1^ex3f oral mesenchyme was activated earlier than that in the wild type littermates. In contrast, although the elongated oral epithelial cells were detected in the K14-cre; Ctnnb1^ex3f mice, the Amelogenin expression was suppressed. The differential effects of the persistent epithelial Wnt/β-catenin signaling on ameloblast and odontoblast differentiation might result from the altered BMP signaling. In summary, our findings suggested that the epithelial Wnt/β-catenin signaling could induce craniofacial mesenchyme into odontogenic program and promote odontoblast differentiation.

An ancient Turing-like patterning mechanism regulates skin denticle development in sharks

Vertebrates have a vast array of epithelial appendages, including scales, feathers, and hair. The developmental patterning of these diverse structures can be theoretically explained by Alan Turing's reaction-diffusion system. However, the role of this system in epithelial appendage patterning of early diverging lineages (compared to tetrapods), such as the cartilaginous fishes, is poorly understood. We investigate patterning of the unique tooth-like skin denticles of sharks, which closely relates to their hydrodynamic and protective functions. We demonstrate through simulation models that a Turing-like mechanism can explain shark denticle patterning and verify this system using gene expression analysis and gene pathway inhibition experiments. This mechanism bears remarkable similarity to avian feather patterning, suggesting deep homology of the system. We propose that a diverse range of vertebrate appendages, from shark denticles to avian feathers and mammalian hair, use this ancient and conserved system, with slight genetic modulation accounting for broad variations in patterning.

Biological interactions of a calcium silicate based cement (Biodentine™) with Stem Cells from Human Exfoliated Deciduous teeth

OBJECTIVE

To investigate the biological interactions of a calcium silicate based cement (Biodentine™) with Stem Cells from Human Exfoliated Deciduous teeth (SHED), focusing on viability/proliferation, odontogenic differentiation, biomineralization and elemental release/exchange.

METHODS

Biodentine™ specimens were used directly or for eluate preparation at serial dilutions (1:1-1:64). SHED cultures were established from deciduous teeth of healthy children. Viability/proliferation and morphological characteristics were evaluated by live/dead fluorescent staining, MTT assay and Scanning Electron Microscopy. Odontogenic differentiation by qRT-PCR, biomineralization by Alizarin red S staining, while ion elution by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES).

RESULTS

SHED effectively attached within the crystalline surface of Biodentine™ specimens acquiring a spindle-shaped phenotype. Statistically significant stimulation of cell proliferation was induced at day 3 by eluates in dilutions from 1:16 to 1:64. Differential, concentration- and time-dependent expression patterns of odontogenic genes were observed under non-inductive and inductive (osteogenic) conditions, with significant up-regulation of DSPP and Runx2 at higher dilutions and a peak in expression of BMP-2, BGLAP and MSX-2 at 1:8 dilution on day 7. Progressive increase in mineralized tissue formation was observed with increasing dilutions of Biodentine™ eluates. ICP-OES indicated that Biodentine™ absorbed Ca, Mg and P ions from culture medium, while releasing Si and Sr ions from its backbone.

SIGNIFICANCE

Biodentine™ interacts through elemental release/uptake with the cellular microenvironment, triggering odontogenic differentiation and biomineralization in a concentration-dependent manner. These results reveal a promising strategy for application of the calcium silicate based cement (Biodentine™) for vital pulp therapies of deciduous teeth in Paediatric Dentistry.

The Nfic-osterix pathway regulates ameloblast differentiation and enamel formation

Enamel makes up the outermost layer of the crown and its hardness protects other dental tissues from various stimuli. Enamel cannot be regenerated once damaged because ameloblasts are lost during the tooth eruption. Since the ameloblast differentiation mechanism is still unknown, further research is essential for developing treatments for defective or damaged enamel. Previously, we have reported that osteoblast differentiation and bone formation were regulated through the runt-related transcription factor 2 (Runx2)-nuclear factor 1-C (Nfic)-osterix (Osx) pathway where Nfic directly controls Osx expression. This pathway regulates odontoblast differentiation and dentin formation as well. The aim of this study was to investigate if the same pathway is applicable for ameloblast differentiation. Structural enamel defects with disorganized ameloblasts and decreased proliferation activity of the cervical loop were observed in Nfic^-/- mice incisors. Expression of the ameloblast differentiation markers was also downregulated significantly in Nfic^-/- mice. Real-time PCR analyses suggested that Runx2, Nfic, and Osx regulate the expression of ameloblast differentiation markers, where Runx2 is upstream of Nfic, and Nfic controls Osx expression. Therefore, we suggest the Runx2-Nfic-Osx pathway as one of the key factors that regulate ameloblast differentiation.

Oestrogen receptor α regulates the odonto/osteogenic differentiation of stem cells from apical papilla via ERK and JNK MAPK pathways

OBJECTIVES

Oestrogen receptor (ER) is a common nucleus receptor that is essential for the regulation of cell growth, proliferation and differentiation. This study was to examine whether ERα can affect the proliferation and odonto/osteogenic differentiation of stem cells from apical papilla (SCAPs).

MATERIALS AND METHODS

Stem cells from apical papillas were isolated, purified and then transfected with ERα lentiviruses. The proliferation capacity was investigated by cell counting kit-8 (CCK-8) assay and flow cytometry. The odonto/osteogenic differentiation ability was analysed by alkaline phosphatase (ALP) activity, alizarin red staining, western blot assay (WB) and real-time RT-PCR. MAPK pathway and its downstream transcriptional factors were explored by WB assay.

RESULTS

As indicated by CCK-8 assay and flow cytometry, ERα had no significant effect on the proliferation of SCAPs. When ERα was overexpressed, the ALP activity and the formation of calcified nodules were significantly enhanced in SCAPs. Moreover, the odonto/osteogenic markers (DMP1/DMP1, DSPP/DSP, RUNX2/RUNX2, OCN/OCN) in SCAPs were significantly up-regulated at both mRNA and protein levels. On the contrary, the odonto/osteogenic differentiation ability of SCAPs was remarkably inhibited after suppression of ERα. Mechanistically, the protein levels of phosphorylated ERK and JNK significantly increased after ERα overexpression. Moreover, some downstream transcriptional factors of MAPK pathway were simultaneously activated by ERα overexpression.

CONCLUSIONS

Together, the data accumulated here indicated that ERα can enhance the odonto/osteogenic differentiation of SCAPs via ERK and JNK MAPK pathways.

Ablation of Runx2 in Ameloblasts Suppresses Enamel Maturation in Tooth Development

Runt-related transcription factor 2 (Runx2) is involved in the early stage of tooth development. However, only few studies have reported the role of Runx2 in enamel development, which may be attributed to that Runx2 full knockout mice cannot survive after birth. In the present study, we successfully established a Runx2-deficient mouse model using a conditional knockout (cKO) method. We observed a significant reduction in the degree of mineralization and the decreased size of enamel rods in cKO mice. Histological analysis showed the retained enamel proteins in enamel layer at maturation stage in cKO molars. Further analysis by qRT-PCR revealed that the expressions of genes encoding enamel structure proteins, such as amelogenin (AMELX), ameloblastin (AMBN) and enamelin (ENAM), were increased in cKO enamel organs. On the other hand, the expression of kallikrein-related peptidase-4 (KLK4) at the mRNA and protein levels was dramatically decreased from late secretory stage to maturation stage in cKO enamel organs, while the expression of matrix metalloproteinase-20 (MMP-20) was not significantly altered. Finally, immunohistochemistry indicated that the uptake of amelogenins by ameloblasts was significantly decreased in cKO mice. Taken together, Runx2 played critical roles in controlling enamel maturation by increasing synthesis of KLK4 and decreasing synthesis of AMELX, AMBN and ENAM.

A three-generation family with metaphyseal dysplasia, maxillary hypoplasia and brachydactyly (MDMHB) due to intragenic RUNX2 duplication

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly (MDMHB) is an autosomal-dominant skeletal dysplasia characterised by metaphyseal flaring of the long bones, enlargement of the medial halves of the clavicles, maxillary hypoplasia, brachydactyly, dental anomalies and mild osteoporosis. To date, only one large French Canadian family and a Finnish woman have been reported with the condition. In both, intragenic duplication encompassing exons 3-5 of the RUNX2 gene was identified. We describe a new, three-generation family with clinical features of MDMHB and an intragenic tandem duplication of RUNX2 exons 3-6. Dental problems were the primary presenting feature in all four affected individuals. We compare the features in our family to those previously reported in MDMHB, review the natural history of this condition and highlight the importance of considering an underlying skeletal dysplasia in patients presenting with significant dental problems and other suggestive features, including disproportionate short stature and/or digital anomalies.

Specificity Protein 7 Is Required for Proliferation and Differentiation of Ameloblasts and Odontoblasts

The Sp7/Osterix transcription factor is essential for bone development. Mutations of the Sp7 gene in humans are associated with craniofacial anomalies and osteogenesis imperfecta. However, the role of Sp7 in embryonic tooth development remains unknown. Here we identified the functional requirement of Sp7 for dentin synthesis and tooth development. Sp7-null mice exhibit craniofacial dysmorphogenesis and are completely void of alveolar bone. Surprisingly, initial tooth morphogenesis progressed normally in Sp7-null mice. Thus the formation of alveolar bone is not a prerequisite for tooth morphogenesis. Sp7 is required for mineralization of palatal tissue but is not essential for palatal fusion. The reduced proliferative capacity of Sp7-deficient ectomesenchyme results in small and misshapen teeth with randomly arranged cuboidal preodontoblasts and preameloblasts. Sp7 promotes functional maturation and polarization of odontoblasts. Markers of mature odontoblast (Col1a, Oc, Dspp, Dmp1) and ameloblast (Enam, Amelx, Mmp20, Amtn, Klk4) are barely expressed in incisors and molar tissues of Sp7-null mice. Consequently, dentin and enamel matrix are absent in the Sp7-null littermates. Interestingly, the Sp7 expression is restricted to cells of the dental mesenchyme indicating the effect on oral epithelium-derived ameloblasts is cell-nonautonomous. Abundant expression of Fgf3 and Fgf8 ligand was noted in the developing tooth of wild-type mice. Both ligands were remarkably absent in the Sp7-null incisor and molar, suggesting cross-signaling between mesenchyme and epithelium is disrupted. Finally, promoter-reporter assays revealed that Sp7 directly controls the expression of Fgf-ligands. Together, our data demonstrate that Sp7 is obligatory for the differentiation of both ameloblasts and odontoblasts but not for the initial tooth morphogenesis. © 2018 American Society for Bone and Mineral Research.

Oro-dental phenotype in patients with RUNX2 duplication

Runt-related transcription factor 2 (RUNX2) is well-known for its role in bone development and tooth morphogenesis. Most RUNX2 mutations described in the literature result in loss-of-function mutations of RUNX2 responsible for cleidocranial dysplasia, an autosomal dominant disorder. We describe here the oro-dental phenotype of four patients of a unique family with a 285 kb duplication including the entire sequence of RUNX2, likely responsible for three functional copies of the gene, leading to an increased RUNX2 dosage. Several dental anomalies of number (hypodontia or oligodontia), morphology (microdontia, radiculomegaly, taurodontism or dens invaginatus) and tooth position (rotation) were found in these patients.

Gene-Expression Analysis Identifies IGFBP2 Dysregulation in Dental Pulp Cells From Human Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant disorder affecting osteoblast differentiation, chondrocyte maturation, skeletal morphogenesis, and tooth formation. Dental phenotype in CCD include over-retained primary teeth, failed eruption of permanent teeth, and supernumerary teeth. The underlying mechanism is unclear. We previously reported one CCD patient with allelic RUNX2 deletion (CCD-011). In the current study, we determined the transcriptomic profiles of dental pulp cells from this patient compared to one sex-and-age matched non-affected individual. Next Generation RNA sequencing revealed that 60 genes were significantly dysregulated (63% upregulated and 27% downregulated). Among them, IGFBP2 (insulin-like growth factor binding protein-2) was found to be upregulated more than twofold in comparison to control cells. Stable overexpression of RUNX2 in CCD-011 pulp cells resulted in the reduction of IGFBP2. Moreover, ALPL expression was up-regulated in CCD-011 pulp cells after introduction of normal RUNX2. Promoter analysis revealed that there are four proximal putative RUNX2 binding sites in -1.5 kb IGFBP2 promoter region. Relative luciferase assay confirmed that IGFBP2 is a direct target of RUNX2. Immunohistochemistry demonstrated that IGFBP2 was expressed in odontoblasts but not ameloblasts. This report demonstrated the importance of RUNX2 in the regulation of gene profile related to dental pulp cells and provided novel insight of RUNX2 into the negative regulation of IGFBP2.

Loss of Stemness, EMT, and Supernumerary Tooth Formation in Cebpb-/-Runx2+/- Murine Incisors

Adult Cebpb KO mice incisors present amelogenin-positive epithelium pearls, enamel and dentin allopathic hyperplasia, fewer Sox2-positive cells in labial cervical loop epitheliums, and reduced Sox2 expression in enamel epithelial stem cells. Thus, Cebpb acts upstream of Sox2 to regulate stemness. In this study, Cebpb KO mice demonstrated cementum-like hard tissue in dental pulp, loss of polarity by ameloblasts, enamel matrix in ameloblastic layer, and increased expression of epithelial-mesenchymal transition (EMT) markers in a Cebpb knockdown mouse enamel epithelial stem cell line. Runx2 knockdown in the cell line presented a similar expression pattern. Therefore, the EMT enabled disengaged odontogenic epithelial stem cells to develop supernumerary teeth. Cebpb and Runx2 knockdown in the cell line revealed higher Biglycan and Decorin expression, and Decorin-positive staining in the periapical region, indicating their involvement in supernumerary tooth formation. Cebpb and Runx2 acted synergistically and played an important role in the formation of supernumerary teeth in adult incisors.

The Role of Fibroblast Growth Factors in Tooth Development and Incisor Renewal

The mineralized tissue of the tooth is composed of enamel, dentin, cementum, and alveolar bone; enamel is a calcified tissue with no living cells that originates from oral ectoderm, while the three other tissues derive from the cranial neural crest. The fibroblast growth factors (FGFs) are critical during the tooth development. Accumulating evidence has shown that the formation of dental tissues, that is, enamel, dentin, and supporting alveolar bone, as well as the development and homeostasis of the stem cells in the continuously growing mouse incisor is mediated by multiple FGF family members. This review discusses the role of FGF signaling in these mineralized tissues, trying to separate its different functions and highlighting the crosstalk between FGFs and other signaling pathways.

Role of the Inferior Alveolar Nerve in Rodent Lower Incisor Stem Cells

In developing teeth, the sequential and reciprocal interactions between epithelial and mesenchymal tissues promote stem/progenitor cell differentiation. However, the origin of the stem/progenitor cells has been the subject of considerable debate. According to recent studies, mesenchymal stem cells originate from periarterial cells and are regulated by neurons in various organs. The present study examined the role of innervation in tooth development and rodent incisor stem/progenitor cell homeostasis. Rodent incisors continuously grow throughout their lives, and the lower incisors are innervated by the inferior alveolar nerve (IAN). In this study, we resected the IAN in adult rats, and the intact contralateral side served as a nonsurgical control. Sham control rats received the same treatment as the resected rats, except for the resection process. The extent of incisor eruption was measured, and both mesenchymal and epithelial stem/progenitor cells were visualized and compared between the IAN-resected and sham-operated groups. One week after surgery, the IAN-resected incisors exhibited a chalky consistency, and the eruption rate was decreased. Micro–computed tomography and histological analyses performed 4 wk after surgery revealed osteodentin formation, disorganized ameloblast layers, and reduced enamel thickness in the IAN-resected incisors. Immunohistochemical analysis revealed a reduction in the CD90- and LRIG1-positive mesenchymal cell ratio in the IAN-resected incisors. However, the p40-positive epithelial stem/progenitor cell ratio was comparable between the 2 groups. Thus, mesenchymal stem/progenitor cell homeostasis is more related to IAN innervation than to epithelial stem/progenitor cells. Furthermore, sensory nerve innervation influences subsequent incisor growth and formation.

Exogenous nitric oxide stimulates the odontogenic differentiation of rat dental pulp stem cells

Nitric oxide (NO) is thought to play a pivotal regulatory role in dental pulp tissues under both physiological and pathological conditions. However, little is known about the NO functions in dental pulp stem cells (DPSCs). We examined the direct actions of a spontaneous NO gas-releasing donor, NOC-18, on the odontogenic capacity of rat DPSCs (rDPSCs). In the presence of NOC-18, rDPSCs were transformed into odontoblast-like cells with long cytoplasmic processes and a polarized nucleus. NOC-18 treatment increased alkaline phosphatase activity and enhanced dentin-like mineralized tissue formation and the expression levels of several odontoblast-specific genes, such as runt related factor 2, dentin matrix protein 1 and dentin sialophosphoprotein, in rDPSCs. In contrast, carboxy-PTIO, a NO scavenger, completely suppressed the odontogenic capacity of rDPSCs. This NO-promoted odontogenic differentiation was activated by tumor necrosis factor-NF-κB axis in rDPSCs. Further in vivo study demonstrated that NOC-18-application in a tooth cavity accelerated tertiary dentin formation, which was associated with early nitrotyrosine expression in the dental pulp tissues beneath the cavity. Taken together, the present findings indicate that exogenous NO directly induces the odontogenic capacity of rDPSCs, suggesting that NO donors might offer a novel host DPSC-targeting alternative to current pulp capping agents in endodontics.

Mesenchymal Wnt/β-catenin signaling limits tooth number

Tooth agenesis is one of the predominant developmental anomalies in humans, usually affecting the permanent dentition generated by sequential tooth formation and, in most cases, caused by mutations perturbing epithelial Wnt/β-catenin signaling. In addition, loss-of-function mutations in the Wnt feedback inhibitor AXIN2 lead to human tooth agenesis. We have investigated the functions of Wnt/β-catenin signaling during sequential formation of molar teeth using mouse models. Continuous initiation of new teeth, which is observed after genetic activation of Wnt/β-catenin signaling in the oral epithelium, was accompanied by enhanced expression of Wnt antagonists and a downregulation of Wnt/β-catenin signaling in the dental mesenchyme. Genetic and pharmacological activation of mesenchymal Wnt/β-catenin signaling negatively regulated sequential tooth formation, an effect partly mediated by Bmp4. Runx2, a gene whose loss-of-function mutations result in sequential formation of supernumerary teeth in the human cleidocranial dysplasia syndrome, suppressed the expression of Wnt inhibitors Axin2 and Drapc1 in dental mesenchyme. Our data indicate that increased mesenchymal Wnt signaling inhibits the sequential formation of teeth, and suggest that Axin2/Runx2 antagonistic interactions modulate the level of mesenchymal Wnt/β-catenin signaling, underlying the contrasting dental phenotypes caused by human AXIN2 and RUNX2 mutations.

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.