The role of bone morphogenetic proteins 2 and 4 in mouse dentinogenesis

BMP signaling in the development and regeneration of tooth roots: from mechanisms to applications

Short root anomaly (SRA), along with caries, periodontitis, and trauma, can cause tooth loss, affecting the physical and mental health of patients. Dental implants have become widely utilized for tooth restoration; however, they exhibit certain limitations compared to natural tooth roots. Tissue engineering-mediated root regeneration offers a strategy to sustain a tooth with a physiologically more natural function by regenerating the bioengineered tooth root (bio-root) based on the bionic principle. While the process of tooth root development has been reported in previous studies, the specific molecular mechanisms remain unclear. The Bone Morphogenetic Proteins (BMPs) family is an essential factor regulating cellular activities and is involved in almost all tissue development. Recent studies have focused on exploring the mechanism of BMP signaling in tooth root development by using transgenic animal models and developing better tissue engineering strategies for bio-root regeneration. This article reviews the unique roles of BMP signaling in tooth root development and regeneration.

The BMP and FGF pathways reciprocally regulate odontoblast differentiation

PURPOSE

Previous studies demonstrated that the exposure of primary dental pulp (DP) cultures to fibroblast growth factor 2 (FGF2) between days 3-7 exerted significant and long-lasting stimulatory effects on odontoblast differentiation and Dspp expression. These effects involved the increased expression of components of bone morphogenetic protein (BMP) signaling and were reverted by a BMP inhibitor noggin. FGF2 also transiently stimulated osteoblast differentiation and the expression of Ibsp and Dmp1. The present study aimed to further explore interactions between BMP and FGF signaling during odontoblast and osteoblast differentiation in DP cultures.

MATERIALS AND METHODS

Cultures were established using DP tissue isolated from non-transgenic and fluorescent reporter (DSPP-Cerulean, BSP-GFP, and DMP1-mCherry) transgenic mice and exposed to BMP2, FGF2, SU5402 (an FGF receptor inhibitor), and noggin between days 3-7. Mineralization, gene expression, fluorescent protein expression, and odontoblast formation were examined using xylenol orange, quantitative PCR, fluorometric analysis, and immunocytochemistry, respectively.

RESULTS

BMP2 activated SMAD1/5/8 but not ERK1/2 signaling, whereas FGF2 exerted opposite effects. BMP2 did not affect mineralization, the expression of Ibsp and Dmp1, and the percentage of DSPP-Cerulean+ odontoblasts but significantly increased Dspp and DSPP-Cerulean. In cultures exposed to BMP2 and FGF2, respectively, both SU5402 and noggin led to long-lasting decreases in Dspp and DSPP-Cerulean and transient decreases in Dmp1 and DMP1-mCherry without affecting Ibsp and BSP-GFP.

CONCLUSION

BMP2 and FGF2 exerted reciprocal stimulatory effects on odontoblast differentiation, whereas their effects on osteoblast differentiation were mediated independently. These data will further elucidate the perspectives of using BMP2 and FGF2 for dentin regeneration/repair.

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.

Assessing the prevalence of S-shaped root canal and associated genes in humans

BACKGROUND

Multiple signaling molecules have been shown to play crucial roles in dental root development. Therefore, we aimed to investigate the prevalence of S-shaped roots and also to investigate, if single nucleotide polymorphisms (SNPs) in BMP2, BMP4 and SMAD6 are associated with this phenotype in humans.

METHODS

This is a cross-sectional phenotype-genotype association study that used radiographs to determine the phenotypes and DNA to investigate SNPs in candidate genes. During the radiographic exam, teeth presenting root canal(s) doubly curved were considered S-shaped roots. SNPs in BMP2 (rs1005464 and rs235768), BMP4 (rs17563) and SMAD6 (rs2119261 and rs3934908) were blindly genotyped by real-time PCR using TaqMan assay. The relative and absolute frequency of S-shaped roots were calculated. Chi-square test was used to compare the genotype distributions between control and S-shaped groups.

RESULTS

Among the 578 subjects, 61 (10.6%) presented at least one tooth with an S-shaped root. The most commonly affected type of tooth was the premolar. rs1005464 in BMP2 was statistically associated with an S-shaped root (p=0.036). rs235768 in BMP2 was associated with an S-shaped root also in mandibular teeth (p=0.017). A statistical significance was observed for the rs3934908 in SMAD6 (p=0.049) for S-shaped root in the mandible. In the analysis stratified according to the type of tooth, rs235768 in BMP2 was associated with S-shaped roots in premolars (p=0.029).

CONCLUSION

The prevalence of S-shaped roots is 10.6% in permanent teeth. SNPs in BMP2 and SMAD6 could be involved in a higher chance to present S-shaped roots.

Loss of BMP2 and BMP4 Signaling in the Dental Epithelium Causes Defective Enamel Maturation and Aberrant Development of Ameloblasts

BMP signaling is crucial for differentiation of secretory ameloblasts, the cells that secrete enamel matrix. However, whether BMP signaling is required for differentiation of maturation-stage ameloblasts (MA), which are instrumental for enamel maturation into hard tissue, is hitherto unknown. To address this, we used an in vivo genetic approach which revealed that combined deactivation of the Bmp2 and Bmp4 genes in the murine dental epithelium causes development of dysmorphic and dysfunctional MA. These fail to exhibit a ruffled apical plasma membrane and to reabsorb enamel matrix proteins, leading to enamel defects mimicking hypomaturation amelogenesis imperfecta. Furthermore, subsets of mutant MA underwent pathological single or collective cell migration away from the ameloblast layer, forming cysts and/or exuberant tumor-like and gland-like structures. Massive apoptosis in the adjacent stratum intermedium and the abnormal cell-cell contacts and cell-matrix adhesion of MA may contribute to this aberrant behavior. The mutant MA also exhibited severely diminished tissue non-specific alkaline phosphatase activity, revealing that this enzyme’s activity in MA crucially depends on BMP2 and BMP4 inputs. Our findings show that combined BMP2 and BMP4 signaling is crucial for survival of the stratum intermedium and for proper development and function of MA to ensure normal enamel maturation.

Crucial Roles of microRNA-16-5p and microRNA-27b-3p in Ameloblast Differentiation Through Regulation of Genes Associated With Amelogenesis Imperfecta

Amelogenesis imperfecta is a congenital disorder within a heterogeneous group of conditions characterized by enamel hypoplasia. Patients suffer from early tooth loss, social embarrassment, eating difficulties, and pain due to an abnormally thin, soft, fragile, and discolored enamel with poor aesthetics and functionality. The etiology of amelogenesis imperfecta is complicated by genetic interactions. To identify mouse amelogenesis imperfecta-related genes (mAIGenes) and their respective phenotypes, we conducted a systematic literature review and database search and found and curated 70 mAIGenes across all of the databases. Our pathway enrichment analysis indicated that these genes were enriched in tooth development-associated pathways, forming four distinct groups. To explore how these genes are regulated and affect the phenotype, we predicted microRNA (miRNA)-gene interaction pairs using our bioinformatics pipeline. Our miRNA regulatory network analysis pinpointed that miR-16-5p, miR-27b-3p, and miR-23a/b-3p were hub miRNAs. The function of these hub miRNAs was evaluated through ameloblast differentiation assays with/without the candidate miRNA mimics using cultured mouse ameloblast cells. Our results revealed that overexpression of miR-16-5p and miR-27b-3p, but not miR-23a/b-3p, significantly inhibited ameloblast differentiation through regulation of mAIGenes. Thus, our study shows that miR-16-5p and miR-27b-3p are candidate pathogenic miRNAs for amelogenesis imperfecta.

Single nucleotide polymorphisms in runt-related transcription factor 2 and bone morphogenetic protein 2 impact on their maxillary and mandibular gene expression in different craniofacial patterns - A comparative study

Introduction:

This study aimed to evaluate if single nucleotide polymorphisms (SNPs) in runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein 2 (BMP2) are associated with different craniofacial patterns. Furthermore, we also investigated if RUNX2 and BMP2 expression in the maxilla and mandible are differently expressed according to facial phenotypes and influenced by the SNPs in their encoding genes. Orthognathic patients were included.

Materials and Methods:

Lateral cephalometric radiographs were used to classify facial phenotypes based on Steiner's ANB and Ricketts’ NBa-PtGn angles. Bone samples from 21 patients collected during orthognathic surgery were used for the gene expression assays. DNA from 129 patients was used for genotyping the SNPs rs59983488 and rs1200425 in RUNX2 and rs235768 and rs1005464 in BMP2. The established alpha was 5%.

Results:

A statistically significant difference was observed in the relative BMP2 expression in the mandible between Class I and III participants (P = 0.042). Homozygous GG (rs59983488) had higher RUNX2 expression (P = 0.036) in the mandible. In maxilla, GG (rs1200425) had a higher BMP2 expression (P = 0.038).

Discussion:

In conclusion, BMP2 is expressed differently in the mandible of Class I and Class III participants. Genetic polymorphisms in RUNX2 and BMP2 are associated with their relative gene expression.

Investigation of Genetic Polymorphisms in BMP2, BMP4, SMAD6, and RUNX2 and Persistent Apical Periodontitis

INTRODUCTION

This study aimed to evaluate the interplay among single-nucleotide polymorphisms (SNPs) in the encoding genes BMP2, BMP4, SMAD6, and RUNX2 in persistent apical periodontitis (PAP).

METHODS

In this multicentric study, 272 patients diagnosed with pulp necrosis with apical periodontitis before root canal therapy who attended regular follow-up visits for at least 1 year were screened. Periapical radiographs and clinical aspects were evaluated, and the participants were classified as PAP (n = 110) or repaired (n = 162). Genomic DNA was used for the genotyping of the following SNPs: rs1005464 and rs235768 in bone morphogenetic protein 2 (BMP2), rs17563 in bone morphogenetic protein 4 (BMP4), rs2119261 and rs3934908 in SMAD family member 6 (SMAD6), and rs59983488 and rs1200425 in runt-related transcription factor 2 (RUNX2). The chi-square test was used to compare genotype distributions between groups. The multifactor dimensionality reduction method was applied to identify SNP-SNP interactions. The alpha for all the analysis was 5%.

RESULTS

The multifactor dimensionality reduction suggested the rs235768 in BMP2 and rs59983488 in RUNX2 as the best SNP-SNP interaction model (cross-validation = 10/10, testing balanced accuracy = 0.584, P = .026) followed by rs17563 in BMP4 and rs2119261 in SMAD6 (cross validation = 10/10, testing balanced accuracy = 0.580, P = .031). In the rs235768 in BMP2 and rs59983488 in RUNX2 model, the high-risk genotype was TT + TT (odds ratio = 4.36; 95% confidence interval, 0.44-42.1). In model rs17563 in BMP4 and rs2119261 in SMAD6, GG + TT (odds ratio = 2.63; 95% confidence interval, 0.71-11.9) was the high-risk genotype.

CONCLUSIONS

The interactions between rs235768 in BMP2 and rs59983488 in RUNX2 and between rs17563 in BMP4 and rs2119261 in SMAD6 are associated with PAP, suggesting that an interplay of these SNPs is involved in the higher risk of developing PAP.

Developmental Roles of FUSE Binding Protein 1 (Fubp1) in Tooth Morphogenesis

FUSE binding protein 1 (Fubp1), a regulator of the c-Myc transcription factor and a DNA/RNA-binding protein, plays important roles in the regulation of gene transcription and cellular physiology. In this study, to reveal the precise developmental function of Fubp1, we examined the detailed expression pattern and developmental function of Fubp1 during tooth morphogenesis by RT-qPCR, in situ hybridization, and knock-down study using in vitro organ cultivation methods. In embryogenesis, Fubp1 is obviously expressed in the enamel organ and condensed mesenchyme, known to be important for proper tooth formation. Knocking down Fubp1 at E14 for two days, showed the altered expression patterns of tooth development related signalling molecules, including Bmps and Fgf4. In addition, transient knock-down of Fubp1 at E14 revealed changes in the localization patterns of c-Myc and cell proliferation in epithelium and mesenchyme, related with altered tooth morphogenesis. These results also showed the decreased amelogenin and dentin sialophosphoprotein expressions and disrupted enamel rod and interrod formation in one- and three-week renal transplanted teeth respectively. Thus, our results suggested that Fubp1 plays a modulating role during dentinogenesis and amelogenesis by regulating the expression pattern of signalling molecules to achieve the proper structural formation of hard tissue matrices and crown morphogenesis in mice molar development.

Dental and Craniofacial Characteristics in Patients With 14Q22.1-Q22.2 Deletion: A Case Series

This case series is a follow-up report focusing on dental and facial characteristics in patients with a rare microdeletion in chromosome 14q22.1-q22.2. Usually, these patients have severe ocular, brain, and digital abnormalities. However, this case series shows that clinical presentation can be mild. Four relatives spanning 3 generations were diagnosed with a familial autosomal dominant 2.79 Mb microdeletion in chromosome 14q22.1-q22.2. Genetic screening was done by the Bacterial Artificial Chromosome array-comparative genome hybridization and was confirmed by the fluorescence in situ hybridization technique. Dental and craniofacial data were collected from medical files, clinical examinations, clinical photos, panoramic and cephalometric radiographs, and dental casts. Written informed consent for scientific use was obtained for all family members. No larger syndrome could be identified. All cases had similar facial red flag characteristics, consisting of a long face with retrognathia and open mouth relation, associated oral clefts in varying degrees, depressed nasal bridge, delayed tooth development, hypertelorism, and low-set angular ears. The dental casts showed a distal molar occlusion and a lack of space in the dental arches. Developmental delay was noted together with limb defects such as poly- and syndactyly. Microphthalmia and hearing loss were present in the most severe cases. This rare congenital disorder, associated with facial dysmorphia, oral clefts, and tooth agenesis, can remain undiagnosed until adulthood. A family history of short stature, developmental delay, poly- or syndactyly, and micropthalmia are suggestive features. Similar reports help to raise awareness among dental practitioners, leading to an early genetic diagnosis.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

MSX1 is differentially expressed in the deepest impacted maxillary third molars

An impacted third molar is one of the most common dental abnormalities. Among the reasons for impaction the most common are: insufficient space, time of eruption, improper position of the tooth bud, and genetic disruptions. To investigate if runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), and msh homeobox 1 (MSX1) are differently expressed depending on the position of the molar, we studied 32 patients who had been referred for surgical removal. An orthopantomogram was used to separate them according to Winter's, and Pell & Gregory's, classifications. Bone samples were harvested during the operation for gene expression assay. The Kruskal-Wallis, Dunn's post hoc, and Spearman's correlation, tests were used to assess the significance of differences. No correlations were found in expression of the genes, and no differences between expression in maxillary and mandibular third molars, nor were they expressed differently according to Winter's or Pell and Gregory's classifications or in relation to impaction of the mandibular ramus. However, MSX1 was expressed differently when account was taken of the depth of impaction in maxillary third molars (p = 0.029), but there was no difference in expression of RUNX2, BMP2, and MSX1 for the Pell and Gregory classification of depth of impaction (p > 0.05). We conclude that MSX1 is expressed differently depending on the depth of maxillary impaction phenotypes.

Expression and distribution of bone morphogenetic protein 4 and its antagonist Noggin in the skin of Kazakh sheep (Ovis aries) with a white and brown coat color

The natural coat color is an important trait of vertebrate animals. For example, the coat color can help avoid harm to human beings caused by chemical dyeing, and it has economic significance for domestic animals. The bone morphogenetic protein 4 (BMP4) and its antagonist Noggin can regulate pigmentation and the generation of coat color in mice; thus, they may also regulate the coat color of Kazakh sheep. To gain mechanistic insight into this possibility, we determined the relative expression levels of BMP4 and Noggin in the skin of white and brown Kazakh sheep by quantitative real-time polymerase chain reaction (qPCR) and western blotting analysis. The localization of BMP4 and Noggin were detected by immunohistochemistry (IHC). The results of qPCR and western blot analysis demonstrated that the relative expression levels of BMP4 and Noggin in the skin of brown Kazakh sheep were significantly higher than those in white Kazakh sheep. Our IHC results showed that the BMP4 protein was expressed in the epidermis and root sheath of the Kazakh sheep skin. The Noggin protein was expressed in the epidermis, root sheath, hair shaft, and dermal papilla of the Kazakh sheep skin. These results provide a theoretical basis for additional studies regarding the association and mechanism of BMP4 and Noggin in coat-color formation in Kazakh sheep. These results may provide new methods for developing treatment strategies for pigmentation disorders and diseases.

Noggin inhibition of mouse dentinogenesis

OBJECTIVES

The Bone Morphogenetic Proteins (BMPs) direct tooth development and still express in the adult tooth. We hypothesized that inhibition of BMP function would therefore disrupt dentinogenesis by differentiated odontoblasts.

METHODS

We generated mice overexpressing the BMP-inhibitory protein Noggin in differentiated odontoblasts and osteocytes under control of a Dmp1 promoter-driven cre transgene. We compared the dentin phenotype in these mice with that in WT littermates and in mice with a Smad4 odontoblast/osteocyte knockout mediated by the same cre and therefore lacking all BMP and Tgfβ signaling in the same tissues.

RESULTS

Three-month-old first molars from both Noggin-expressing and Smad4-deleted mice showed decreased dentin volume with enlarged pulp cavities, and both displayed less organized and mineralized dentinal tubules compared to WT. The Smad4-ablated phenotype was more severe. While dentin sialophosphoprotein (DSPP) and bone sialoprotein (BSP) were decreased in the dentin of both lines, dentin matrix protein 1 (DMP1) was sharply increased in Noggin-expressing teeth.

CONCLUSIONS

The phenotypes we observed in Noggin-overexpressing and Smad4-conditional knockout teeth resemble the phenotype of Dentinogenesis Imperfecta (DGI) type III. Our results show that BMPs regulate post-natal dentinogenesis and that BMP-inhibitory proteins like Noggin play a role in that regulation. The increased severity of the Smad4 phenotype indicates that Tgfβ ligands, in addition to BMPs, play a crucial role in post-developmental dentinogenesis.

CPNE7 Induces Biological Dentin Sealing in a Dentin Hypersensitivity Model

Dentin hypersensitivity commonly occurs due to opened dentinal tubules for many reasons. In our previous study, copine 7 (CPNE7) could induce dentin formation for an indirect pulp-capping model in vivo. This study aims to investigate the formation of tertiary dentin when CPNE7 is applied to intentionally exposed dentin with nothing over it in vivo, whether it affects microleakage of the teeth, and the penetration ability of CPNE7 molecules through dentinal tubules in vitro. Cervical dentin areas of 6 maxillary incisors of 5 beagles were exposed to a class V–like lesion, and 1 side of 3 maxillary incisors was adapted with recombinant CPNE7 protein for 5 min as the experimental group. The other side was the control group, and there was no treatment of ethylenediaminetetraacetic acid (EDTA) and CPNE7 after preparation. The defects were exposed without any restorations, and all beagles were sacrificed after 4 wk. The fluid penetration of exposed dentin areas was investigated by a microleakage-testing device and confocal laser scanning microscope. Tertiary dentin formation was confirmed with histological scanning electronic microscopic analysis. Tertiary dentin formation reduces dentinal fluid flow due to occluded tubules or discontinuity with primary or secondary dentin. The in vivo hypersensitivity model with the anterior teeth of beagle dogs showed newly formed tertiary dentin at the dentin-pulp boundary in recombinant CPNE7–treated teeth when compared with the untreated control group in histologic analysis. Scanning electronic microscopic analysis revealed occluded sites with mineral deposition of intratubular dentin. In the permeability test, the mean microleakage value of the CPNE7-treated group was significantly lower than that of the control group ( P < 0.05). The tubular penetration of rhodamine B–combined CPNE7 was confirmed under confocal laser scanning microscope. CPNE7 induces formation of tertiary dentin through shallowly exposed dentinal tubules, which decreases dentin permeability.