Ablation of FAM20C caused short root defects via suppressing the BMP signaling pathway in mice

Short root defects are prone to cause various periodontal diseases and lead to tooth loss in some serious cases. Studies about the mechanisms governing the development of the root are needed for a better understanding of the pathogenesis of short root defects. The protein family with sequence similarity 20 group C (FAM20C) is a Golgi casein kinase that has been well studied in the development of tooth crown formation. However, whether FAM20C plays a role in the development of tooth root is still unknown. Thus, we generated Sox2-Cre;Fam20cfl/fl (cKO) mice, in which Fam20c was ablated in both the dental epithelium and dental mesenchyme, and found that the cKO mice showed severe short root defects mainly by inhibiting the development of dental mesenchyme in the root region. In this investigation, we found morphological changes and differentiation defects, with reduced expression of dentin sialophosphoprotein (DSPP) in odontoblasts of the root region in cKO mice. Furthermore, the proliferation rate of apical papillary cells was reduced in the root of cKO mice. In addition, the levels of bone morphogenetic protein 4 (BMP4) and phospho-Smad1/5/8, and that of Osterix and Krüppel-like factor 4 (KLF4), two downstream target molecules of the BMP signaling pathway, were significantly reduced in the root of cKO mice. These results indicate that FAM20C plays an essential role in the development of the root by regulating the BMP signaling pathway.

Fam20C overexpression in odontoblasts regulates dentin formation and odontoblast differentiation

FAM20C phosphorylates secretory proteins at S-x-E/pS motifs, and previous studies of Fam20C-dificient mice revealed that FAM20C played essential roles in bone and tooth formation. Inactivation of FAM20C in mice led to hypophosphatemia that masks direct effect of FAM20C in these tissues, and consequently the direct role of FAM20C remains unknown. Our previous study reported that osteoblast/odontoblast-specific Fam20C transgenic (Fam20C-Tg) mice had normal serum phosphate levels and that osteoblastic FAM20C-mediated phosphorylation regulated bone formation and resorption. Here, we investigated the direct role of FAM20C in dentin using Fam20C-Tg mice. The tooth of Fam20C-Tg mice contained numerous highly phosphorylated proteins, including SIBLINGs, compared to that of wild-type mice. In Fam20C-Tg mice, coronal dentin volume decreased and mineral density unchanged at early age, while the volume unchanged and the mineral density elevated at maturity. In these mice, radicular dentin volume and mineral density decreased at all ages, and histologically, the radicular dentin had wider predentin and abnormal apical-side dentin with embedded cells and argyrophilic canaliculi. Immunohistochemical analyses revealed that abnormal apical-side dentin had bone and dentin matrix properties accompanied with osteoblast-lineage cells. Further, in Fam20C-Tg mice, DSPP content which is important for dentin formation, was reduced in dentin, especially radicular dentin, which might lead to defects mainly in radicular dentin. Renal subcapsular transplantations of tooth germ revealed that newly formed radicular dentin replicated apical abnormal dentin of Fam20C-Tg mice, corroborating that FAM20C overexpression indeed caused the abnormal dentin. Our findings indicate that odontoblastic FAM20C-mediated phosphorylation in the tooth regulates dentin formation and odontoblast differentiation.

CHIP inhibits odontoblast differentiation through promoting DLX3 polyubiquitylation and degradation

Dentin is the major hard tissue of teeth formed by differentiated odontoblasts. How odontoblast differentiation is regulated remains enigmatic. Here, we report that the E3 ubiquitin ligase CHIP is highly expressed in undifferentiated dental mesenchymal cells and downregulated after differentiation of odontoblasts. Ectopic expression of CHIP inhibits odontoblastic differentiation of mouse dental papilla cells, whereas knockdown of endogenous CHIP has opposite effects. Chip (Stub1) knockout mice display increased formation of dentin and enhanced expression of odontoblast differentiation markers. Mechanistically, CHIP interacts with and induces K63 polyubiquitylation of the transcription factor DLX3, leading to its proteasomal degradation. Knockdown of DLX3 reverses the enhanced odontoblastic differentiation caused by knockdown of CHIP. These results suggest that CHIP inhibits odontoblast differentiation by targeting its tooth-specific substrate DLX3. Furthermore, our results indicate that CHIP competes with another E3 ubiquitin ligase, MDM2, that promotes odontoblast differentiation by monoubiquitylating DLX3. Our findings suggest that the two E3 ubiquitin ligases CHIP and MDM2 reciprocally regulate DLX3 activity by catalyzing distinct types of ubiquitylation, and reveal an important mechanism by which differentiation of odontoblasts is delicately regulated by divergent post-translational modifications.

Differential Effects of Escherichia coli- Versus Porphyromonas gingivalis-derived Lipopolysaccharides on Dental Pulp Stem Cell Differentiation in Scaffold-free Engineered Tissues

INTRODUCTION

To leverage the therapeutic capabilities of dental pulp stem cells (DPSCs) for regenerative endodontic applications, a better understanding of their innate defense and reparative processes is needed. Lipopolysaccharide (LPS) is a major virulent factor of gram-negative bacteria and contributor to endodontic infections. We have developed 3-dimensional scaffold-free DPSC tissues that self-organize into dentin-pulp organoids comprising a mineralized dentin-like tissue on the periphery and an unmineralized pulp-like core. In this study, scaffold-free DPSC constructs were used as controllable experimental models to study the DPSC response to bacterial challenge.

METHODS

Scaffold-free constructs were engineered using DPSCs isolated from human third molars. To simulate bacterial exposure, DPSC constructs were exposed to either Porphyromonas gingivalis-derived LPS or Escherichia coli-derived LPS. The effects of LPS on DPSC differentiation, proliferation, and apoptosis were evaluated.

RESULTS

Engineered tissues lacking LPS treatment self-organized into dentin-pulp organoids. LPS treatment did not negatively affect DPSC proliferation or apoptosis in the engineered tissues. Both E. coli LPS and P. gingivalis LPS inhibited the up-regulation of RUNX2 messenger RNA expression and reduced the expression of the odontoblast-associated proteins (P < .05), suggesting that LPS is inhibiting odontoblastic differentiation. However, only E. coli LPS treatment significantly reduced mineral deposition in the DPSC (P < .05) constructs, indicating that E. coli LPS but not P. gingivalis LPS reduced functional differentiation of DPSCs and prevented DPSCs from self-organizing into a dentin-pulp complex-like structure.

CONCLUSIONS

This study establishes scaffold-free DPSC constructs as models of oral disease. Furthermore, it emphasizes the diversity of LPS derived from different bacterial species and highlights the necessity of using LPS derived from clinically relevant bacteria in basic science investigations.

Odontoblast differentiation is regulated by an interplay between primary cilia and the canonical Wnt pathway

Primary cilium is a protruding cellular organelle that has various physiological functions, especially in sensory reception. While an avalanche of reports on primary cilia have been published, the function of primary cilia in dental cells remains to be investigated. In this study, we focused on the function of primary cilia in dentin-producing odontoblasts. Odontoblasts, like most other cell types, possess primary cilia, which disappear upon the knockdown of intraflagellar transport protein 88. In cilia-depleted cells, the expression of dentin sialoprotein, an odontoblastic marker, was elevated, while the deposition of minerals was slowed. This was recapitulated by the activation of canonical Wnt pathway, also decreased the ratio of ciliated cells. In dental pulp cells, as they differentiated into odontoblasts, the ratio of ciliated cells was increased, whereas the canonical Wnt signaling activity was repressed. Our results collectively underscore the roles of primary cilia in regulating odontoblastic differentiation through canonical Wnt signaling. This study implies the existence of a feedback loop between primary cilia and the canonical Wnt pathway.

LncRNA CALB2 sponges miR-30b-3p to promote odontoblast differentiation of human dental pulp stem cells via up-regulating RUNX2

Illuminating the mechanisms of odontoblast differentiation of human dental pulp stem cells (hDPSCs) is the key to find therapeutic clues to promote odontogenesis. LncRNAs play a regulatory role in odontoblast differentiation. Here, we identified a novel lncRNA, named lncRNA CALB2. It was up-regulated in odontoblast-differentiated hDPSCs and potentially interacted with miR-30b-3p and RUNX2. Via gain- and loss-of-function approaches, we found lncRNA CALB2 significantly promoted the odontoblast differentiation of hDPSCs. Then, dual luciferase reporter assay and RNA immunoprecipitation assay revealed that both lncRNA CALB2 and RUNX2 mRNA could directly bind to miR-30b-3p via the same binding sites. Interestingly, miR-30b-3p in hDPSCs was down-regulated and RUNX2 was up-regulated during odontoblast differentiation. Moreover, lncRNA CALB2 knockdown significantly reduced the protein level of RUNX2, DSPP and DMP-1, while miR-30b-3p inhibitor rescued the reduction. Furthermore, miR-30b-3p exerted an inhibitory effect on odontoblast differentiation, which could be reversed by lncRNA CALB2. Collectively, these findings indicate that the newly identified lncRNA CALB2 acts as a miR-30b-3p sponge to regulate RUNX2 expression, thus promoting the odontoblast differentiation of hDPSCs. LncRNA CALB2/miR-30b-3p/RUNX2 axis could be a novel therapeutic target for accelerating odontogenesis.

Dental Pulp Stem Cells: Isolation, Characterization, Expansion, and Odontoblast Differentiation for Tissue Engineering

Tissue engineering is an interdisciplinary area offering a promising approach by the use of stem cells combined with scaffolds and signaling factors for regeneration of damaged or lost tissues. Incorporation of a sufficient number of cells which do not elicit the immunoreaction in the body is a pivotal element for successful tissue formation using this method. Stem cells exhibiting strong capacity to self-renew and differentiate into different cell types are considered as a potent cell source. Among various cell sources, dental pulp stem cells (DPSCs) are widely under investigation due to the fact that they are simply obtainable from extracted third molars or orthodontically extracted teeth and show an excellent potential for clinical application and also their harvesting method is minimally invasive. DPSCs are odontogenic progenitor cells with clonogenic abilities, rapid proliferation rates, and multiple differentiation potentials. Here, we describe protocols that allow 1) the isolation of DPSCs from a single tooth; 2) the characterization of human mesenchymal stem cells markers of DPSCs by flow cytometry; 3) the culture growth of DPSCs in 2D (in cell culture flasks) and 3D (by 3D printing of cell-laden constructs); and 4) the in vivo evaluation of differentiation potential of DPSCs.

Oligomeric proanthocyanidins released from dentin induce regenerative dental pulp cell response

Proanthocyanidins (PACs) are plant-derived, multifunctional compounds that possess high interactivity with extracellular matrix (ECM) components. The documented affinity of PACs for type-I collagen is directly correlated with their structural features and degree of polymerization. In this investigation, centrifugal partition chromatography (CPC) was used to sequentially deplete less active monomeric and polymeric PACs from a crude Pinus massoniana bark extract to create refined mixtures enriched in oligomeric PACs. The ability of these oligomeric PACs to modify the mechanical properties of the dentin collagen matrix and their biocompatibility with dental pulp cells (DPCs) was evaluated in an innovative biomimetic environment. The refined mixtures displayed high interactivity with dentin collagen as demonstrated by a significant increase (>5-fold) in the modulus of elasticity of the dentin matrix. In a simplified model of the dentin-DPC complex, DPCs embedded within their native ECM in the presence of PAC-treated dentin exhibited increased proliferation. Quantitative gene expression analyses indicated that exposure to PAC-treated dentin increased the expression of key biomineralization and odontogenic differentiation regulators, including RUNX2, BMP2, OCN, and DSPP. LC-MS/MS analysis revealed that PACs two to four units long (dimers, trimers, and tetramers) were being released from dentin into media, influencing cell behavior. Overall, the results suggested that PAC dimers, trimers, and tetramers are not only biocompatible, but enhance the differentiation of DPCs towards a phenotype that favors biomineralization. PAC-enriched refined mixtures can influence the field of biomaterials and regeneration by serving as renewable, non-cytotoxic agents that can increase the mechanical properties of biomaterials.

STATEMENT OF SIGNIFICANCE

Pine bark extract is a renewable source of structurally diverse proanthocyanidins (PACs), multifunctional compounds whose interaction with collagen can be tailored to specific purposes by enrichment of selected PACs from the complex mixture. Oligomeric PACs were enriched from the extract and were shown here to sustain desired tissue modification and were thus assessed for cellular response in a model of the dentin-pulp interface. This model was developed to mimic leaching of potentially reactive compounds into pulp tissue. Dental pulp cells exposed to PAC-treated dentin showed increased proliferation and expression of genes necessary for extracellular matrix deposition and biomineralization, processes crucial for forming new dentin. Thus, collagen-interactive PACs may also enhance tissue regeneration and have broad impact in tissue engineering.

Role of MIZ-1 in AMELX gene expression

Amelogenin (AMELX) is the main component of the developing tooth enamel matrix and is essential for enamel thickness and structure. However, little is known about its transcriptional regulation. Using gene expression analysis, we found that MIZ-1, a potent transcriptional activator of CDKN1A, is expressed during odontoblastic differentiation of hDPSCs (human dental pulp stem cells), and is essential for odontoblast differentiation and mineralization. We also investigated how MIZ-1 regulates gene expression of AMELX. Oligonucleotide-pull down assays showed that MIZ-1 binds to an MRE (MIZ-1 binding element) of the AMELX proximal promoter region (bp, −170 to −25). Combined, our ChIP, transient transcription assays, and promoter mutagenesis revealed that MIZ-1 directly binds to the MRE of the Amelx promoter recruits p300 and induces Amelx gene transcription. Finally, we show that the zinc finger protein MIZ-1 is an essential transcriptional activator of Amelx, which is critical in odontogenesis and matrix mineralization in the developing tooth.

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MIZ-1is expressed during odontoblast differentiation.

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MIZ-1 activates transcription of theAmelxgene.

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MIZ-1 binds to the proximal promoter MRE (bp, −70 to −49).

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MIZ-1 is a critical factor of odontogenesis and matrix mineralization of hDPSCs.