Requirement of Smad4-mediated signaling in odontoblast differentiation and dentin matrix formation

Mitigation of BMP-induced inflammation in craniofacial bone regeneration and improvement of bone parameters by dietary hesperidin

Based on anti-inflammatory and osteogenic properties of hesperidin (HE), we hypothesized its systemic administration could be a cost-effective method of improving BMP-induced bone regeneration. Sprague-Dawley rats were allocated into 4 groups (n = 10/group): a 5-mm critical-sized mandible defect + collagen scaffold or, scaffold + 1 µg of BMP2 with and without dietary HE at 100 mg/kg. HE was administered by oral gavage 4 weeks prior to surgeries until euthanasia at day 7 or 14 post-surgery. The healing tissue within the defect collected at day 7 was subjected to gene expression analysis. Mandibles harvested at day 14 were subjected to microcomputed tomography and histology. HE + BMP2-treated rats had a statistically significant decrease in expression of inflammatory genes compared to BMP2 alone. The high-dose BMP2 alone caused cystic-like regeneration with incomplete defect closure. HE + BMP2 showed virtually complete bone fusion. Collagen fibril birefringence pattern (red color) under polarized light indicated high organization in BMP2-induced newly formed bone (NFB) in HE-supplemented group (p < 0.05). Clear changes in osteocyte lacunae as well as a statistically significant increase in osteoclasts were found around NFB in HE-treated rats. A significant increase in trabecular volume and thickness, and trabecular and cortical density was found in femurs of HE-supplemented rats (p < 0.05). Our findings show, for the first time, that dietary HE has a remarkable modulatory role in the function of locally delivered high-dose BMP2 in bone regeneration possibly via control of inflammation, osteogenesis, changes in osteocyte and osteoclast function and collagen maturation in regenerated and native bone. In conclusion, HE had a significant skeletal bone sparing effect and the ability to provide a more effective BMP-induced craniofacial regeneration.

Loss of Stat3 in Osterix+ cells impairs dental hard tissues development

BACKGROUND

Mutations in the signal transducers and activators of transcription 3 (STAT3) gene result in hyper-IgE syndrome(HIES), a rare immunodeficiency that causes abnormalities in immune system, bones and teeth. However, the role of Stat3 in development of dental hard tissues was yet to investigate.

METHODS

In this study, a transgenic mouse of conditional knockout of Stat3 in dental mesenchymal cells (Osx-Cre; Stat3^fl/fl, Stat3 CKO) was made. The differences of postnatal tooth development between control and Stat3 CKO mice were compared by histology, µCT and scanning electron microscopy.

RESULT

Compared with the control, Stat3 CKO mice were presented with remarkable abnormal tooth phenotypes characterized by short root and thin dentin in molars and incisors. The enamel defects were also found on mandibular incisors. showed that Ki67-positive cells significantly decreased in dental mesenchymal of Stat3 CKO mice. In addition, β-catenin signaling was reduced in Hertwig's epithelial root sheath (HERS) and odontoblasts of Stat3 CKO mice.

CONCLUSIONS

Our results suggested that Stat3 played an important role in dental hard tissues development, and Stat3 may regulate dentin and tooth root development through the β-catenin signaling pathway.

Ecological Speciation Promoted by Divergent Regulation of Functional Genes Within African Cichlid Fishes

Rapid ecological speciation along depth gradients has taken place repeatedly in freshwater fishes, yet molecular mechanisms facilitating such diversification are typically unclear. In Lake Masoko, an African crater lake, the cichlid Astatotilapia calliptera has diverged into shallow-littoral and deep-benthic ecomorphs with strikingly different jaw structures within the last 1,000 years. Using genome-wide transcriptome data, we explore two major regulatory transcriptional mechanisms, expression and splicing-QTL variants, and examine their contributions to differential gene expression underpinning functional phenotypes. We identified 7,550 genes with significant differential expression between ecomorphs, of which 5.4% were regulated by cis-regulatory expression QTLs, and 9.2% were regulated by cis-regulatory splicing QTLs. We also found strong signals of divergent selection on differentially expressed genes associated with craniofacial development. These results suggest that large-scale transcriptome modification plays an important role during early-stage speciation. We conclude that regulatory variants are important targets of selection driving ecologically relevant divergence in gene expression during adaptive diversification.

Chromatin Accessibility Predetermines Odontoblast Terminal Differentiation

Embryonic development and stem cell differentiation are orchestrated by changes in sequential binding of regulatory transcriptional factors to their motifs. These processes are invariably accompanied by the alternations in chromatin accessibility, conformation, and histone modification. Odontoblast lineage originates from cranial neural crest cells and is crucial in dentinogenesis. Our previous work revealed several transcription factors (TFs) that promote odontoblast differentiation. However, it remains elusive as to whether chromatin accessibility affects odontoblast terminal differentiation. Herein, integration of single-cell RNA-seq and bulk RNA-seq revealed that in vitro odontoblast differentiation using dental papilla cells at E18.5 was comparable to the crown odontoblast differentiation trajectory of OC (osteocalcin)-positive odontogenic lineage. Before in vitro odontoblast differentiation, ATAC-seq and H3K27Ac CUT and Tag experiments demonstrated high accessibility of chromatin regions adjacent to genes associated with odontogenic potential. However, following odontoblastic induction, regions near mineralization-related genes became accessible. Integration of RNA-seq and ATAC-seq results further revealed that the expression levels of these genes were correlated with the accessibility of nearby chromatin. Time-course ATAC-seq experiments further demonstrated that odontoblast terminal differentiation was correlated with the occupation of the basic region/leucine zipper motif (bZIP) TF family, whereby we validated the positive role of ATF5 in vitro. Collectively, this study reports a global mapping of open chromatin regulatory elements during dentinogenesis and illustrates how these regions are regulated via dynamic binding of different TF families, resulting in odontoblast terminal differentiation. The findings also shed light on understanding the genetic regulation of dentin regeneration using dental mesenchymal stem cells.

DNCP induces the differentiation of induced pluripotent stem cells into odontoblasts by activating the Smad/p-Smad and p38/p-p38 signaling pathways

In recent years, stem cells have been studied for treating tooth loss. The present study aimed to investigate the roles of dentin non-collagen protein (DNCP)-associated microenvironments in the differentiation of induced pluripotent stem cells (iPSCs) into dentin cells. iPSCs were cultured and identified by examining octamer-binding transcription-factor-4 (Oct-4) and sex-determining region-Y-2 (Sox-2) expression. iPSCs were differentiated by culturing DNCP-associated microenvironments (containing specific growth factors), and they were divided into control, DNCP, DNCP+bone morphogenetic proteins (BMPs) and DNCP+Noggin (a BMP inhibitor) groups. Msh homeobox 1 (Msx-1), dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP-1) mRNA expression was evaluated using reverse transcription-quantitative PCR. The levels of p38, phosphorylated (p)-p38, Smad and p-Smad were determined by western blotting. Upon treatment with mouse embryonic fibroblasts, iPSCs-dependent embryoid bodies (EBs) were successfully generated. iPSCs exhibited increased Oct-4 and Sox-2 expression. Differentiated iPSCs had higher expression levels of DSPP, DMP-1 and Msx-1 in the DNCP group compared with those in the control group (P<0.05). Noggin treatment significantly downregulated, while BMPs administration significantly increased the expression levels of DSPP, DMP-1 and Msx-1 compared with those of the DNCP group (P<0.05). The ratios of p-p38/p38 and p-Smad/Smad were significantly higher in the DNCP group compared with those in the control group (P<0.05). Noggin and BMPs significantly decreased ratios of p-p38/p38, compared with those of the DNCP group (P<0.05). In conclusion, DNCP induced the differentiation of iPSCs into odontoblasts by activating the Smad/p-Smad and p38/p-p38 signaling pathways.

Sites of Cre-recombinase activity in mouse lines targeting skeletal cells

The Cre/Lox system is a powerful tool in the biologist's toolbox, allowing loss-of-function and gain-of-function studies, as well as lineage tracing, through gene recombination in a tissue-specific and inducible manner. Evidence indicates, however, that Cre transgenic lines have a far more nuanced and broader pattern of Cre activity than initially thought, exhibiting "off-target" activity in tissues/cells other than the ones they were originally designed to target. With the goal of facilitating the comparison and selection of optimal Cre lines to be used for the study of gene function, we have summarized in a single manuscript the major sites and timing of Cre activity of the main Cre lines available to target bone mesenchymal stem cells, chondrocytes, osteoblasts, osteocytes, tenocytes, and osteoclasts, along with their reported sites of "off-target" Cre activity. We also discuss characteristics, advantages, and limitations of these Cre lines for users to avoid common risks related to overinterpretation or misinterpretation based on the assumption of strict cell-type specificity or unaccounted effect of the Cre transgene or Cre inducers. © 2021 American Society for Bone and Mineral Research (ASBMR).

Fluoride Alters Signaling Pathways Associated with the Initiation of Dentin Mineralization in Enamel Fluorosis Susceptible Mice

Fluoride can alter the formation of mineralized tissues, including enamel, dentin, and bone. Dentin fluorosis occurs in tandem with enamel fluorosis. However, the pathogenesis of dentin fluorosis and its mechanisms are poorly understood. In this study, we report the effects of fluoride on the initiation of dentin matrix formation and odontoblast function. Mice from two enamel fluorosis susceptible strains (A/J and C57BL/6J) were given either 0 or 50 ppm fluoride in drinking water for 4 weeks. In both mouse strains, there was no overall change in dentin thickness, but fluoride treatment resulted in a significant increase in the thickness of the predentin layer. The lightly mineralized layer (LL), which lies at the border between predentin and fully mineralized dentin and is associated with dentin phosphoprotein (DPP), was absent in fluoride exposed mice. Consistent with a possible reduction of DPP, fluoride-treated mice showed reduced immunostaining for dentin sialoprotein (DSP). Fluoride reduced RUNX2, the transcription regulator of dentin sialophosphoprotein (DSPP), that is cleaved to form both DPP and DSP. In fluoride-treated mouse odontoblasts, the effect of fluoride was further seen in the upstream of RUNX2 as the reduced nuclear translocation of β-catenin and phosphorylated p65/NFκB. In vitro, MD10-F2 pre-odontoblast cells showed inhibition of the Dspp mRNA level in the presence of 10 μM fluoride, and qPCR analysis showed a significantly downregulated level of mRNAs for RUNX2, β-catenin, and Wnt10b. These findings indicate that in mice, systemic exposure to excess fluoride resulted in reduced Wnt/β-catenin signaling in differentiating odontoblasts to downregulate DSPP production via RUNX2.

Dentinal Lesions in Dogs with Dental Calculus

Histopathological changes in tooth structures in dogs with calculus have not been described. The aim of this study was to evaluate the frequency of various histopathological changes in the dentine of teeth that had been surgically extracted from dogs with calculus. Data including breed, sex, age, reason for tooth extraction and dental history were obtained for each animal. A total of 158 teeth (45 incisors, 31 canines, 35 premolars and 47 molars) with calculus were extracted from 74 dogs of various ages and breeds. The teeth were decalcified, processed in paraffin wax and stained with haematoxylin and eosin for histopathological analysis. Of the 158 analysed teeth, 71 had dentinal changes, including 45 with external resorption cavities, 11 with osteodentine, six with internal resorption cavities, four with tertiary dentine, four with dentinal degeneration or fragmentation, and one with predentine degeneration or fragmentation. Canine teeth were the least commonly affected. Areas of dentinal degeneration or fragmentation unrelated to resorption cavities were only seen in the incisor and molar teeth. Dentinal changes and their frequencies were similar among the incisor, premolar and molar teeth. The presence or extension of dental calculus was not associated with the type or frequency of dentinal changes.

A rice bran phytochemical, cyanidin 3-glucoside, inhibits the progression of PC3 prostate cancer cell

Prostate cancer is one of the high incidences and the most invasive cancer that is also highly resistant to chemotherapy. Currently, several natural products have been considering using as the supplements for anti-cancer therapy. This study aims to identify the potential active anti-cancer ingredients in the bran extracts of the native Thai rice (Luempua cultivar). Rice bran fraction enriched in anthocyanins was successively isolated and processed until the major purified compound obtained. The sub-fractions and the purified, rice bran, cyanidin 3-glucoside (RBC3G), were studied for biological effects (cell viability, migration, and invasion assays) on human prostatic cancer (PC3) cells using immunohistochemical-staining and immuno-blotting approaches. The sub-fractions and the purified RBC3G inhibited epithelial mesenchymal transition (EMT) characteristics of PC3 cells by blocking the expression of several cytoskeletal associate proteins in a concentration dependent manner, leading to decreasing of the cancer cell motility. RBC3G reduced the expression of Smad/Snail signaling molecules but enhanced the expression of cell surface protein, E-cadherin, leading to a delay tumor transformation. The RBC3G also inhibited matrix metalloproteinase-9 and nuclear factor-kappa B expression levels and the enzymes activity in PC3 cells, leading to a slow cell migration/invasion process. The results suggested that RBC3G blunt and/or delay the progressive cancer cell behaviors by inhibit EMT through Smad signaling pathway(s) mediating Snail/E-cadherin expression.

Geometrical Structure of Honeycomb TCP to Control Dental Pulp-Derived Cell Differentiation

Recently, dental pulp has been attracting attention as a promising source of multipotent mesenchymal stem cells (MSCs) for various clinical applications of regeneration fields. To date, we have succeeded in establishing rat dental pulp-derived cells showing the characteristics of odontoblasts under in vitro conditions. We named them Tooth matrix-forming, GFP rat-derived Cells (TGC). However, though TGC form massive dentin-like hard tissues under in vivo conditions, this does not lead to the induction of polar odontoblasts. Focusing on the importance of the geometrical structure of an artificial biomaterial to induce cell differentiation and hard tissue formation, we previously have succeeded in developing a new biomaterial, honeycomb tricalcium phosphate (TCP) scaffold with through-holes of various diameters. In this study, to induce polar odontoblasts, TGC were induced to form odontoblasts using honeycomb TCP that had various hole diameters (75, 300, and 500 μm) as a scaffold. The results showed that honeycomb TCP with 300-μm hole diameters (300TCP) differentiated TGC into polar odontoblasts that were DSP positive. Therefore, our study indicates that 300TCP is an appropriate artificial biomaterial for dentin regeneration.

Smad4-dependent transforming growth factor-β family signaling regulates the differentiation of dental epithelial cells in adult mouse incisors

Teeth consist of two major tissues, enamel and dentin, which are formed during development by epithelial and mesenchymal cells, respectively. Rodent incisors are useful experimental models for studying the molecular mechanisms of tooth formation because they are simultaneously growing in not only embryos but also adults. Members of the transforming growth factor-β (TGF-β) family regulate epithelial-mesenchymal interactions through an essential coactivator, Smad4. In the present study, we established Smad4 conditional knockout (cKO) mice and examined phenotypes in adult incisors. Smad4 cKO mice died with severe anemia within one month. Phosphorylated Smad1/5/9 and Smad2/3 were detected in epithelial cells in both control and Smad4 cKO mice. Disorganized and hypoplastic epithelial cells, such as ameloblasts, were observed in Smad4 cKO mice. Moreover, alkaline phosphatase expression and iron accumulation were reduced in dental epithelial cells in Smad4 cKO mice. These findings suggest that TGF-β family signaling through Smad4 is required for the differentiation and functions of dental epithelial cells in adult mouse incisors.

Comparison of osteogenic and dentinogenic potentials of mice incisor and molar pulps in vitro

OBJECTIVE

In the present study, we compared the in vitro osteogenic and dentinogenic potential of pulp cells from incisors and molars.

DESIGN

Primary pulp cultures were established from DSPP-Cerulean/DMP1-Cherry and BSP-GFPtpz reporter mouse lines and processed for various assays.

RESULTS

Our results showed marked differences in dentinogenic and osteogenic potentials of primary cultures from unerupted molars and incisors isolated from 5 to 7 days old pups. While primary cultures from both incisors and molars differentiated into odontoblasts and osteoblasts, cultures from molars differentiated into more DSPP-Cerulean + cells (∼5.5 %) compared to incisor cultures (∼0.7 %) at Day 14 and appear to be more committed to the odontogenic lineage. On the other hand, cultures from incisors show more differentiation into BSP-GFPtpz + cells (∼25 %) compared to molar cultures (∼16 %) and were more committed to the osteogenic lineage. Data were analyzed by Student's t-test and statistical significance was set at P ≤ 0.05.

CONCLUSION

Since in the dental pulp, MSCs are the primary source of progenitors capable of giving rise to osteoblasts and odontoblasts, our results provide evidence for differences in the commitment of MSCs in molars and incisors to the odontogenic and osteogenic lineages, respectively.

Distribution of glutamate receptor, ionotropic, kainate 1 and neuropeptide calcitonin gene-related peptide mRNAs during formation of the embryonic and postnatal mouse molar in the maxilla

The neuropeptide calcitonin gene-related peptide (CGRP) is a well-characterized neurotransmitter. Glutamate receptor, ionotropic, kainate 1 (Grik1) has also been demonstrated to generate high-affinity kainate receptors. However, little is known about the roles of CGRP and Grik1 during the developmental formation of teeth. In this study, we endeavoured to analyse the expression and localization of CGRP and Grik1 mRNAs using in situ hybridization on the mouse maxilla during development from the embryonic stage (E18.5) to after birth (P10, P15 and P20). We found that hybridization with an anti-sense probe for CGRP clearly localized in the maxilla at E18.5 in contrast to that of P15 and P20. Hybridization with an anti-sense probe for CGRP was not detected in the dental pulp of molars in the maxilla at P10, which is in contrast to Grik1 mRNA at the same developmental stage. Hybridization with an anti-sense probe for Grik1 mRNA was detected in the basal region of the dental pulp of molars at P10 and P15. Finally, these markers were not detected in molars in the mouse maxilla at P20. The ratio of positive cells for the hybridization signals of Grik1and CGRP in the dental pulp decreased from E18.5 (p<0.001). These features in CGRP and Grik1r mRNAs may indicate roles of function during tooth development between embryonic and postnatal stages with root formation and erupted movements.

ALK5 is essential for tooth germ differentiation during tooth development

The TGFβ superfamily of proteins participates in tooth development. TGFβ1 and TGFβ3 regulate odontoblast differentiation and dentin extracellular matrix synthesis. Although the expression of TGFβ family member ligands is well-characterized during mammalian tooth development, less is known about the TGFβ receptor, which is a heteromeric complex consisting of a type I and type II receptors. The molecular mechanism of ALK5 (TGFβR1) in the dental mesenchyme is not clear. We investigated the role of ALK5 in tooth germ mesenchymal cells (TGMCs) from the lower first molar tooth germs of day 15.5 embryonic mice. Human recombinant TGFβ3 protein or an ALK5 inhibitor (SD208) was added to the cells. Cell proliferation was inhibited by SD208 and promoted by TGFβ3. We found that SD208 inhibited TGMCs osteogenesis and dentinogenesis. Both canonical and noncanonical TGFβ signaling pathways participated in the process. TAK1, P-TAK1, p38 and P-p38 showed greater expression and SMAD4 showed less expression when ALK5 was inhibited. Our findings contribute to understanding the role of TGFβ signaling for the differentiation of mesenchymal stem cells derived from dental germ and suggest possible targets for optimizing the use of stem cells of dental origin for tissue regeneration.

Conditional Knockout of Raptor/mTORC1 Results in Dentin Malformation

mTORC1 signaling plays an important role in extracellular and intracellular signals, including growth factors, nutrients, energy metabolism, and stress. However, the functional role of mTORC1 in dentinogenesis is unknown. To study the role of Raptor/mTORC1 in dentinogenesis, an Raptor^fl/fl; Osx-Cre (Rap-Osx) mouse, in which Raptor was conditionally deleted in odontoblasts and dental mesenchymal cells, was generated, and postnatal tooth development was compared between Rap-Osx mice and control littermates. Rap-Osx mice presented a phenotype known as dentinogenesis imperfecta and had smaller tooth volume, a thinner dentin layer and a larger pulp chamber. The proliferation and differentiation of odontoblasts/preodontoblasts were attenuated in mutant mice, which was likely responsible for the defects in dentinogenesis. Raptor/mTORC1-pS6K1 signaling was inactivated during tooth development in Rap-Osx mice, whereas it was activated in control mice. These results indicate that Raptor/mTORC1 plays a critical role in dentinogenesis via promoting odontoblasts/preodontoblasts proliferation and differentiation. Raptor/mTORC1 might regulate tooth development through the pS6K1 signaling pathway.

Distinctive role of ACVR1 in dentin formation: requirement for dentin thickness in molars and prevention of osteodentin formation in incisors of mice

Dentin is a major component of teeth that protects dental pulp and maintains tooth health. Bone morphogenetic protein (BMP) signaling is required for the formation of dentin. Mice lacking a BMP type I receptor, activin A receptor type 1 (ACVR1), in the neural crest display a deformed mandible. Acvr1 is known to be expressed in the dental mesenchyme. However, little is known about how BMP signaling mediated by ACVR1 regulates dentinogenesis. To explore the role of ACVR1 in dentin formation in molars and incisors in mice, Acvr1 was conditionally disrupted in Osterix-expressing cells (designated as cKO). We found that loss of Acvr1 in the dental mesenchyme led to dentin dysplasia in molars and osteodentin formation in incisors. Specifically, the cKO mice exhibited remarkable tooth phenotypes characterized by thinner dentin and thicker predentin, as well as compromised differentiation of odontoblasts in molars. We also found osteodentin formation in the coronal part of the cKO mandibular incisors, which was associated with a reduction in the expression of odontogenic gene Dsp and an increase in the expression of osteogenic gene Bsp, leading to an alteration of cell fate from odontoblasts to osteoblasts. In addition, the expressions of WNT antagonists, Dkk1 and Sost, were downregulated and B-catenin was up-regulated in the cKO incisors, while the expression levels were not changed in the cKO molars, compared with the corresponding controls. Our results indicate the distinct and critical roles of ACVR1 between incisors and molars, which is associated with alterations in the WNT signaling related molecules. This study demonstrates for the first time the physiological roles of ACVR1 during dentinogenesis.

Abrogation of Fam20c altered cell behaviors and BMP signaling of immortalized dental mesenchymal cells

FAM20C mutations compromise the mineralization of skeleton and tooth in both human and mouse. Putatively, the mineralization disorder is attributed to the elevated fibroblast growth factor 23 (FGF23), which reduced the serum phosphorus by suppressing the reabsorption of phosphorus in kidney. Besides the regulation on systemic phosphorus homeostasis, FAM20C was also implicated to regulate cell behaviors and gene expression through a cell-autonomous manner. To identify the primary effects of Fam20c on dental mesenchymal cells, mouse Fam20c-deficient dental mesenchymal cells were generated by removing the floxed alleles from the immortalized mouse Fam20c^f/f dental mesenchymal cells with Cre-expressing lentivirus. The removal of Fam20c exerted no impact on cell morphology, but suppressed the proliferation and mobility of the dental mesenchymal cells. Fam20c deficiency also significantly reduced the expression of Osterix, Runx2, type I Collagen a 1 (Col1a1), Alkaline phosphatase (Alpl) and the members of the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family, but increased Fgf23 expression. Consistently, the in vitro mineralization of Fam20c-deficient dental mesenchymal cells was severely disabled. However, supplements of the non-collagenous proteins from wild type rat dentin failed to rescue the compromised mineralization, suggesting that the roles of FAM20C in tooth mineralization are more than phosphorylating local matrices and regulating systemic phosphorus metabolism. Moreover, the down-regulated BMP signaling pathways in the Fam20c deficient dental mesenchymal cells revealed that the kinase activity of FAM20C might be required to maintain BMP signaling. In summary, our study discloses that Fam20c indeed regulates cell behaviors and cell signaling pathway in a cell-autonomous manner.