Wnt3a signaling induces murine dental follicle cells to differentiate into cementoblastic/osteoblastic cells via an osterix-dependent pathway

Spatiotemporal cellular dynamics and molecular regulation of tooth root ontogeny

Tooth root development involves intricate spatiotemporal cellular dynamics and molecular regulation. The initiation of Hertwig's epithelial root sheath (HERS) induces odontoblast differentiation and the subsequent radicular dentin deposition. Precisely controlled signaling pathways modulate the behaviors of HERS and the fates of dental mesenchymal stem cells (DMSCs). Disruptions in these pathways lead to defects in root development, such as shortened roots and furcation abnormalities. Advances in dental stem cells, biomaterials, and bioprinting show immense promise for bioengineered tooth root regeneration. However, replicating the developmental intricacies of odontogenesis has not been resolved in clinical treatment and remains a major challenge in this field. Ongoing research focusing on the mechanisms of root development, advanced biomaterials, and manufacturing techniques will enable next-generation biological root regeneration that restores the physiological structure and function of the tooth root. This review summarizes recent discoveries in the underlying mechanisms governing root ontogeny and discusses some recent key findings in developing of new biologically based dental therapies.

A Rare Skeletal Disorder, Fibrous Dysplasia: A Review of Its Pathogenesis and Therapeutic Prospects

Fibrous dysplasia (FD) is a rare, non-hereditary skeletal disorder characterized by its chronic course of non-neoplastic fibrous tissue buildup in place of healthy bone. A myriad of factors have been associated with its onset and progression. Perturbation of cell-cell signaling networks and response outputs leading to disrupted building blocks, incoherent multi-level organization, and loss of rigid structural motifs in mineralized tissues are factors that have been identified to participate in FD induction. In more recent years, novel insights into the unique biology of FD are transforming our understandings of its pathology, natural discourse of the disease, and treatment prospects. Herein, we built upon existing knowledge with recent findings to review clinical, etiologic, and histological features of FD and discussed known and potential mechanisms underlying FD manifestations. Subsequently, we ended on a note of optimism by highlighting emerging therapeutic approaches aimed at either halting or ameliorating disease progression.

Evaluation of Current Studies to Elucidate Processes in Dental Follicle Cells Driving Osteogenic Differentiation

When research on osteogenic differentiation in dental follicle cells (DFCs) began, projects focused on bone morphogenetic protein (BMP) signaling. The BMP pathway induces the transcription factor DLX3, whichh in turn induces the BMP signaling pathway via a positive feedback mechanism. However, this BMP2/DLX3 signaling pathway only seems to support the early phase of osteogenic differentiation, since simultaneous induction of BMP2 or DLX3 does not further promote differentiation. Recent data showed that inhibition of classical protein kinase C (PKCs) supports the mineralization of DFCs and that osteogenic differentiation is sensitive to changes in signaling pathways, such as protein kinase B (PKB), also known as AKT. Small changes in the lipidome seem to confirm the participation of AKT and PKC in osteogenic differentiation. In addition, metabolic processes, such as fatty acid biosynthesis, oxidative phosphorylation, or glycolysis, are essential for the osteogenic differentiation of DFCs. This review article attempts not only to bring the various factors into a coherent picture of osteogenic differentiation in DFCs, but also to relate them to recent developments in other types of osteogenic progenitor cells.

Cryptolepine Suppresses Colorectal Cancer Cell Proliferation, Stemness, and Metastatic Processes by Inhibiting WNT/β-Catenin Signaling

Colorectal cancer (CRC) is the third most frequent cancer and the second leading cause of cancer-related deaths globally. Evidence shows that over 90% of CRC cases are initiated by a deregulated Wingless Integrated Type-1 (WNT)/β-catenin signaling pathway. The WNT/β-catenin pathway also promotes CRC cell proliferation, stemness, and metastasis. Therefore, modulators of the WNT/β-catenin pathway may serve as promising regimens for CRC. This study investigated the effect of cryptolepine-a plant-derived compound-on the WNT/β-catenin pathway in CRC. Two CRC cell lines, COLO205 and DLD1, were treated with cryptolepine or XAV 939 (a WNT inhibitor) in the presence or absence of WNT3a (a WNT activator). Using a tetrazolium-based assay, cryptolepine was found to reduce cell viability in a dose- and time-dependent manner and was a more potent inhibitor of viability than XAV 939. RT-qPCR analyses showed that cryptolepine reverses WNT3a-induced expression of β-catenin, c-MYC, and WISP1, suggesting that cryptolepine inhibits WNT3a-mediated activation of WNT/β-catenin signaling. Cryptolepine also repressed WNT3a-induced OCT4 and CD133 expression and suppressed colony formation of the cells, indicating that cryptolepine inhibits the stemness of CRC cells. Additionally, cryptolepine inhibited WNT3a-induced epithelial-to-mesenchymal transition by reducing the expression of SNAI1 and TWIST1 genes. In a wound healing assay, cryptolepine was found to suppress cell migration under unstimulated and WNT3a-stimulated conditions. Moreover, cryptolepine downregulated WNT3a-induced expression of MMP2 and MMP9 genes, which are involved in cancer cell invasion. Altogether, cryptolepine suppresses CRC cell proliferation, stemness, and metastatic properties by inhibiting WNT3a-mediated activation of the WNT/β-catenin signaling pathway. These findings provide a rationale for considering cryptolepine as a potential WNT inhibitor in CRC.

Impact of genetic variations in the WNT family members and RUNX2 on dental and skeletal maturation: a cross-sectional study

BACKGROUND

This study evaluated if genetic variations in the WNT family members and RUNX2 are associated with craniofacial maturation, investigating dental and skeletal maturity in children and teenagers.

METHODS

Radiographs from pre-orthodontic treatment of Brazilian patients (7 to 17 years-old) were used to assess dental (panoramic radiographs) and skeletal maturity (cephalometric radiographs). The chronological age (CA) was calculated based on the date of birth and the time the radiographs were performed. For the dental maturity analysis, the Demirjian (1973) method was used and a delta [dental age - chronological age (DA-CA)] was calculated. For the skeletal maturity analysis, the Baccetti et al. (2005) method was used and the patients were classified as "delayed skeletal maturation", "advanced skeletal maturation" or "normal skeletal maturation". DNA isolated from buccal cells was used for genotyping of two genetic variations in WNT family genes: rs708111 (G > A) in WNT3A and rs1533767 (G > A) in WNT11; and two genetic variations in RUNX2: rs1200425 (G > A) and rs59983488 (G > T). A statistical analysis was performed and values of p < 0.05 indicated a significant difference.

RESULTS

There were no associations between dental maturity and genotypes (p > 0.05). In the skeletal maturity analysis, the allele A in the rs708111 (WNT3A) was statistically more frequent in patients with delayed skeletal maturation (Prevalence Ratio = 1.6; 95% Confidence Interval = 1.00 to 2.54; p-value = 0.042).

CONCLUSIONS

The rs708111 in the WNT3A gene impacts on skeletal maturation.

PTHrP Modulates the Proliferation and Osteogenic Differentiation of Craniofacial Fibrous Dysplasia-Derived BMSCs

Fibrous dysplasia (FD) is a skeletal stem cell disease caused by mutations in the guanine nucleotide-binding protein, alpha-stimulating activity polypeptide (GNAS) gene, which results in the abnormal accumulation of cyclic adenosine monophosphate (cAMP) and hyperactivation of downstream signaling pathways. Parathyroid hormone-related protein (PTHrP) is secreted by the osteoblast lineage and is involved in various physiological and pathological activities of bone. However, the association between the abnormal expression of PTHrP and FD, as well as its underlying mechanism, remains unclear. In this study, we discovered that FD patient-derived bone marrow stromal cells (FD BMSCs) expressed significantly higher levels of PTHrP during osteogenic differentiation and exhibited greater proliferation capacity but impaired osteogenic ability compared to normal control patient-derived BMSCs (NC BMSCs). Continuous exogenous PTHrP exposure on the NC BMSCs promoted the FD phenotype in both in vitro and in vivo experiments. Through the PTHrP/cAMP/PKA axis, PTHrP could partially influence the proliferation and osteogenesis capacity of FD BMSCs via the overactivation of the Wnt/β-Catenin signaling pathway. Furthermore, PTHrP not only directly modulated cAMP/PKA/CREB transduction but was also demonstrated as a transcriptional target of CREB. This study provides novel insight into the possible pathogenesis involved in the FD phenotype and enhances the understanding of its molecular signaling pathways, offering theoretical evidence for the feasibility of potential therapeutic targets for FD.

Micro/nano-topography promotes osteogenic differentiation of bone marrow stem cells by regulating periostin expression

Micro/nano-topography (MNT) is an important factor affecting cell response. Earlier studies using titania (TiO₂) nanotube as a model of MNT found that they mediated the differentiation of BMSCs into osteoblasts, but the mechanisms are not fully understood. Surprisingly, Periostin (Postn), a secreted protein involved in extracellular matrix (ECM) construction and promoting osteogenic differentiation of bone marrow stem cells (BMSCs), was previously observed to significantly up-regulated on TiO₂ nanotube. We proposed that Postn may act as a MNT signal transduction role. In this study, we investigated the effect of MNT on Postn, and the influence of Postn on osteogenic differentiation-related genes through focal adhesion and downstream signals. It was found that, titanium (Ti) plates carrying TiO₂ nanotubes with diameters of ∼100 nm (TNT-100) significantly up-regulated the expression of Postn compared with flat Ti. Furthermore, Postn activated the downstream focal adhesion kinase (FAK) signal pathway and β-catenin into the nucleus by interacting with integrin αV. Surprisingly, TNT-100 up-regulated the transcription level of Wnt3a, which was independent of the up-regulation of Postn. This new Postn signaling pathway may provide more insights into the signal transduction mechanism of MNT and development of biomaterials with improved osteogenic properties.

Carbon Monoxide-Releasing Molecule-3 Enhances Osteogenic Differentiation of Rat Bone Marrow Mesenchymal Stem Cells via miR-195-5p/Wnt3a Pathway

Purpose

Bone marrow-derived mesenchymal stem cells (BMSCs) are hopeful in promoting bone regeneration as their pluripotency in differentiation. Our previous study showed that carbon monoxide-releasing molecule-3 (CORM-3) increased the osteogenic differentiation of rat BMSCs in vitro. However, the mechanism remained unclear. MicroRNAs (miRNAs) play a very important role in modulating the osteogenic differentiation of BMSCs. Therefore, we researched the miRNAs involved in CORM-3-stimulated osteogenic differentiation.

Methods

The CORM-3-stimulated osteogenic differentiation of rat BMSCs was further studied in vivo. Based on the gene sequencing experiment, the rat BMSCs were transfected with miR-195-5p mimics and inhibitor, pcDNA3.1-Wnt3a and Wnt3a siRNA. The osteogenic differentiation of rat BMSCs was measured by quantitative real-time polymerase chain reaction, Western blot and alizarin red staining. Additionally, the targeting relationship between miR-195-5p and Wnt3a was confirmed by the dual-luciferase assay.

Results

MiR-195-5p was down-expressed during the CORM-3-stimulated osteogenic differentiation of rat BMSCs. CORM-3-stimulated osteogenic differentiation of rat BMSCs was inhibited with miR-195-5p overexpression, evidenced by significantly reduced mRNA and protein expressions of runt-related transcription factor 2 and osteopontin, and matrix mineralization demonstrated. On the contrary, the osteogenic differentiation was enhanced with inhibition of miR-195-5p. CORM-3-stimulated osteogenic differentiation of rat BMSCs was increased by overexpression of Wnt3a, while the opposite was observed in the Wnt3a-deficient cells. Moreover, the decreased osteogenic differentiation capacity by increased expression of miR-195-5p was rescued by Wnt3a overexpression, showing miR-195-5p directly targeted Wnt3a.

Conclusion

These results demonstrate that CORM-3 promoted osteogenic differentiation of rat BMSCs via miR-195-5p/Wnt3a, which bodes well for the application of CORM-3 in the treatment of periodontal disease and other bone-defect diseases.

Bmal1 promotes cementoblast differentiation and cementum mineralization via Wnt/β-catenin signaling

Remodeling of the cementum plays a crucial role in periodontal regenerative therapy, while the precise mechanism of cementogenesis has yet been adequately understood. Recent studies have indicated the connection between osteogenic differentiation and Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein-1 (Bmal1). Besides, Wnt/β-catenin signaling is proven to be an essential regulator in cementogenesis. In this study, we found a robust expression of Bmal1 in cementoblasts in the mandibular first molar of mice by immunohistochemical staining. To further explore the role of Bmal1 in cementogenesis, we examined the expression pattern of Bmal1 in OCCM-30, an immortalized murine cementoblast cell line by qRT-PCR and western blot. Our data demonstrated the upregulation of Bmal1 at both mRNA and protein levels during differentiation. Additionally, stable knockdown of Bmal1 in OCCM-30 cells resulted in downregulation of osteogenic markers such as alkaline phosphatase (Alp), osteopontin (Opn), and osteocalcin (Ocn), and reduced formation of mineralized nodules. Moreover, qRT-PCR and western blot results exhibited that the expression of β-catenin was attenuated by Bmal1 deficiency. We also found that the mRNA levels of Tcf1 and Lef1, the target transcription factors of β-catenin, were reduced by Bmal1 deficiency. In conclusion, this study preliminarily confirms that Bmal1 promotes cementoblast differentiation and cementum mineralization via Wnt/β-catenin signaling, which contributes to a potential strategy in periodontal regenerative therapy.

Wnt Signaling in Periodontal Disease

Periodontitis is a multifactorial and chronic condition associated with the formation of a dysbiotic biofilm, leading to a pro-inflammatory environment that can modulate cell signaling. The Wnt pathway plays fundamental roles during homeostasis and disease, and emerging evidence suggests its involvement in the maintenance of the periodontium and the development of periodontitis. Here, we summarize the role of the Wnt/β-catenin and non-canonical Wnt signaling pathways in periodontitis. The accumulated data suggests specific roles for each branch of the Wnt pathway. Wnt5a emerges as a critical player promoting periodontal ligament remodeling and impairing regenerative responses modulated by the Wnt/β-catenin pathway, such as alveolar bone formation. Collectively, the evidence suggests that achieving a proper balance between the Wnt/β-catenin and non-canonical pathways, rather than their independent modulation, might contribute to controlling the progression and severity of the periodontal disease.

The Role of Wnt Signaling in Postnatal Tooth Root Development

Appropriate tooth root formation and tooth eruption are critical for achieving and maintaining good oral health and quality of life. Tooth eruption is the process through which teeth emerge from their intraosseous position to their functional position in the oral cavity. This temporospatial process occurs simultaneously with tooth root formation through a cascade of interactions between the epithelial and adjoining mesenchymal cells. Here, we will review the role of the Wnt system in postnatal tooth root development. This signaling pathway orchestrates the process of tooth root formation and tooth eruption in conjunction with several other major signaling pathways. The Wnt signaling pathway is comprised of the canonical, or Wnt/β-catenin, and the non-Canonical signaling pathway. The expression of multiple Wnt ligands and their downstream transcription factors including β-catenin is found in the cells in the epithelia and mesenchyme starting from the initiation stage of tooth development. The inhibition of canonical Wnt signaling in an early stage arrests odontogenesis. Wnt transcription factors continue to be present in dental follicle cells, the progenitor cells responsible for differentiation into cells constituting the tooth root and the periodontal tissue apparatus. This expression occurs concurrently with osteogenesis and cementogenesis. The conditional ablation of β-catenin in osteoblast and odontoblast causes the malformation of the root dentin and cementum. On the contrary, the overexpression of β-catenin led to shorter molar roots with thin and hypo-mineralized dentin, along with the failure of tooth eruption. Therefore, the proper expression of Wnt signaling during dental development is crucial for regulating the proliferation, differentiation, as well as epithelial-mesenchymal interaction essential for tooth root formation and tooth eruption.

Function of Dental Follicle Progenitor/Stem Cells and Their Potential in Regenerative Medicine: From Mechanisms to Applications

Dental follicle progenitor/stem cells (DFPCs) are a group of dental mesenchyme stem cells that lie in the dental follicle and play a critical role in tooth development and maintaining function. Originating from neural crest, DFPCs harbor a multipotential differentiation capacity. More importantly, they have superiorities, including the easy accessibility and abundant sources, active self-renewal ability and noncontroversial sources compared with other stem cells, making them an attractive candidate in the field of tissue engineering. Recent advances highlight the excellent properties of DFPCs in regeneration of orofacial tissues, including alveolar bone repair, periodontium regeneration and bio-root complex formation. Furthermore, they play a unique role in maintaining a favorable microenvironment for stem cells, immunomodulation and nervous related tissue regeneration. This review is intended to summarize the current knowledge of DFPCs, including their stem cell properties, physiological functions and clinical application potential. A deep understanding of DFPCs can thus inspire novel perspectives in regenerative medicine in the future.

Dental-Derived Mesenchymal Stem Cells: State of the Art

Mesenchymal stem cells (MSCs) could be identified in mammalian teeth. Currently, dental-derived MSCs (DMSCs) has become a collective term for all the MSCs isolated from dental pulp, periodontal ligament, dental follicle, apical papilla, and even gingiva. These DMSCs possess similar multipotent potential as bone marrow-derived MSCs, including differentiation into cells that have the characteristics of odontoblasts, cementoblasts, osteoblasts, chondrocytes, myocytes, epithelial cells, neural cells, hepatocytes, and adipocytes. Besides, DMSCs also have powerful immunomodulatory functions, which enable them to orchestrate the surrounding immune microenvironment. These properties enable DMSCs to have a promising approach in injury repair, tissue regeneration, and treatment of various diseases. This review outlines the most recent advances in DMSCs' functions and applications and enlightens how these advances are paving the path for DMSC-based therapies.

Rodent incisor and molar dental follicles show distinct characteristics in tooth eruption

OBJECTIVE

Rodent incisors and molars show different eruption patterns. Dental follicles and their interaction with dental epithelia play key roles in tooth eruption. However, little is known about the differences between incisor dental follicle (IF) and molar dental follicle (MF) during tooth eruption of rodents. This study aimed to investigate the differences between IF and MF during tooth eruption under induction with cervical-loop cells (CLC) and Hertwig's epithelial root sheath (HERS) cells of rats.

MATERIALS AND METHODS

CLC, HERS, IF, MF cells were isolated from 10 postnatal day 7 rats and identified by immunofluorescence staining. CLC or HERS cells-derived conditioned medium (CM) was obtained to induce IF and MF cells. Cell proliferation, mineralization, gene and protein expression related to tooth eruption were detected, and histological analysis was also performed.

RESULTS

The osteogenic differentiation and mineralization abilities of IF cells were stronger than those of MF cells. Both CLC and HERS cells-derived CM enhanced these abilities of IF cells, whereas they showed the opposite effect on MF cells. At 7, 10, and 15 d after birth, IF cells expressed more OPG and less RANKL than MF cells.

CONCLUSIONS

IF and MF cells present distinct characteristics in tooth eruption, CLC and HERS cells have significant inductive effects on them.

Role of Wnt5a in periodontal tissue development, maintenance, and periodontitis: Implications for periodontal regeneration (Review)

The periodontium is a highly dynamic microenvironment constantly adapting to changing external conditions. In the processes of periodontal tissue formation and remodeling, certain molecules may serve an essential role in maintaining periodontal homeostasis. Wnt family member 5a (Wnt5a), as a member of the Wnt family, has been identified to have extensive biological roles in development and disease, predominantly through the non‑canonical Wnt signaling pathway or through interplay with the canonical Wnt signaling pathway. An increasing number of studies has also demonstrated that it serves crucial roles in periodontal tissues. Wnt5a participates in the development of periodontal tissues, maintains a non‑mineralized state of periodontal ligament, and regulates bone homeostasis. In addition, Wnt5a is involved in the pathogenesis of periodontitis. Recently, it has been shown to serve a positive role in the regeneration of integrated periodontal complex. The present review article focuses on recent research studies of Wnt5a and its functions in development, maintenance, and pathological disorders of periodontal tissues, as well as its potential effect on periodontal regeneration.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.

Evaluation of Preosteoblast MC3T3-E1 Cells Cultured on a Microporous Titanium Membrane Fabricated Using a Precise Mechanical Punching Process

The surface topography of Titanium (Ti) combined toughness and biocompatibility affects the attachment and migration of cells. Limited information of morphological characteristics, formed by precise machining in micron order, is currently available on the Ti that could promote osteoconduction. In the present study, a pure Ti membrane was pierced with precise 25 μm square holes at 75 μm intervals and appear burrs at the edge of aperture. We defined the surface without burrs as the “Head side” and that with burrs as the “Tail side”. The effects of the machining microtopography on the proliferation and differentiation of the preosteoblasts (MC3T3-E1 cells) were investigated. The cells were more likely to migrate to, and accumulate in, the aperture of holes on the head side, but grew uniformly regardless of holes on the tail side. The topography on the both surfaces increased osteopontin gene expression levels. Osteocalcin expression levels were higher on the head side than one on the blank scaffold and tail side (p < 0.05). The osteocalcin protein expression levels were higher on the tail side than on the head side after 21 days of cultivation, and were comparable to the proportion of the calcified area (p < 0.05). These results demonstrate the capacity of a novel microporous Ti membrane fabricated using a precise mechanical punching process to promote cell proliferation and activity.

Effects of Cellular Senescence on Dental Follicle Cells

The dental follicle is part of the tooth germ, and isolated stem cells from this tissue (dental follicle cells; DFCs) are considered, for example, for regenerative medicine and immunotherapies. However somatic stem cells can also improve pharmaceutical research. Cell proliferation is limited by the induction of senescence, which, while reducing the therapeutic potential of DFCs for cell therapy, can also be used to study aging processes at the cellular level that can be used to test anti-aging pharmaceuticals. Unfortunately, very little is known about cellular senescence in DFCs. This review presents current knowledge about cellular senescence in DFCs.

Isolation and characterization of dental follicle-derived Hertwig's epithelial root sheath cells

OBJECTIVES

The aim of this study was the isolation and characterization of dental follicle-derived Hertwig's epithelial root sheath cells (DF-HERSCs).

MATERIALS AND METHODS

DF-HERSCs were isolated from dental follicle (DF)-derived single-cell suspensions. Their epithelial phenotypes were analyzed by Western blotting, polymerase chain reaction (PCR), and quantitative polymerase chain reaction (qPCR). Epithelial-mesenchymal transition (EMT) was induced in DF-HERSCs by treatment with transforming growth factor-β (TGF-β) or fetal bovine serum (FBS)-added medium. Characteristics of DF-HERSCs were compared with normal human oral keratinocytes (NHOKs) and normal human epidermal keratinocytes (NHEKs). Osteogenic differentiation and mineralization of DF-HERSCs were analyzed by alkaline phosphatase (ALP) and Alizarin red staining. All experiments were conducted in triplicate.

RESULTS

Primary DF-HERSCs were isolated from DF. Epithelial phenotypes of DF-HERSCs were confirmed by morphological and Western blot analysis. PCR results demonstrated that the origin of DF-HERSCs was neither endothelial nor hematopoietic. Enamel matrix derivative (EMD)-associated genes were not expressed in DF-HERSCs. Treatment with TGF-β and FBS-added medium triggered the progression of EMT in DF-HERSCs. The acquired potency of differentiation and mineralization was shown in EMT-progressed DF-HERSCs.

CONCLUSIONS

DF contains putative populations of HERSC, named DF-HERSC. DF-HERSCs shared common characteristics with NHOKs and NHEKs.

Dental Follicle Cells: Roles in Development and Beyond

Dental follicle cells (DFCs) are a group of mesenchymal progenitor cells surrounding the tooth germ, responsible for cementum, periodontal ligament, and alveolar bone formation in tooth development. Cascades of signaling pathways and transcriptional factors in DFCs are involved in directing tooth eruption and tooth root morphogenesis. Substantial researches have been made to decipher multiple aspects of DFCs, including multilineage differentiation, senescence, and immunomodulatory ability. DFCs were proved to be multipotent progenitors with decent amplification, immunosuppressed and acquisition ability. They are able to differentiate into osteoblasts/cementoblasts, adipocytes, neuron-like cells, and so forth. The excellent properties of DFCs facilitated clinical application, as exemplified by bone tissue engineering, tooth root regeneration, and periodontium regeneration. Except for the oral and maxillofacial regeneration, DFCs were also expected to be applied in other tissues such as spinal cord defects (SCD), cardiomyocyte destruction. This article reviewed roles of DFCs in tooth development, their properties, and clinical application potentials, thus providing a novel guidance for tissue engineering.

Histone demethylase KDM4A regulates adipogenic and osteogenic differentiation via epigenetic regulation of C/EBPα and canonical Wnt signaling

Epigenetic modifications play a central role in cell differentiation and development. In the current study, we have recognized lysine demethylase 4A (KDM4A) as a novel epigenetic regulator of osteoblast and adipocyte differentiation. Kdm4a expression was upregulated during osteogenesis and adipogenesis of primary marrow stromal cells and established stromal ST2 line. Overexpression of wild-type Kdm4a promoted adipogenic differentiation and blocked osteogenic differentiation of the progenitor cells. This effect was largely alleviated when the catalytically dead mutation was made. Conversely, depletion or inactivation of Kdm4a in undifferentiated progenitor cells inhibited the formation of adipocytes and promoted the differentiation of osteoblasts. Mechanism explorations showed that overexpression of Kdm4a upregulated the expression of secreted frizzled-related protein 4 (Sfrp4) and CCAAT/enhancer-binding protein α (C/ebpα). Chromatin immunoprecipitation assay demonstrated that KDM4A directly bound the promoters of Sfrp4 and C/ebpα, removed the histone methylation mark H3K9me3, and reduced DNA methylation levels of CpG in promoter regions of C/ebpα and Sfrp4. Furthermore, overexpression of Kdm4a inactivated canonical Wnt signaling. Moreover, activation of canonical Wnt signaling through silencing of Sfrp4 in ST2 attenuated the inhibition of osteogenic differentiation and the enhancement of adipogenic differentiation by KDM4A. These data have identified KDM4A as a novel regulator of osteoblast and adipocyte differentiation and suggest KDM4A inhibition as a potential therapeutic target for treating metabolic disorders such as osteoporosis.

M2 Macrophages Enhance the Cementoblastic Differentiation of Periodontal Ligament Stem Cells via the Akt and JNK Pathways

Although macrophage (Mφ) polarization has been demonstrated to play crucial roles in cellular osteogenesis across the cascade of events in periodontal regeneration, how polarized Mφ phenotypes influence the cementoblastic differentiation of periodontal ligament stem cells (PDLSCs) remains unknown. In the present study, human monocyte leukemic cells (THP-1) were induced into M0, M1, and M2 subsets, and the influences of these polarized Mφs on the cementoblastic differentiation of PDLSCs were assessed in both conditioned medium-based and Transwell-based coculture systems. Furthermore, the potential pathways and cyto-/chemokines involved in Mφ-mediated cementoblastic differentiation were screened and identified. In both systems, M2 subsets increased cementoblastic differentiation-related gene/protein expression levels in cocultured PDLSCs, induced more PDLSCs to differentiate into polygonal and square cells, and enhanced alkaline phosphatase activity in PDLSCs. Furthermore, Akt and c-Jun N-terminal Kinase (JNK) signaling was identified as a potential pathway involved in M2 Mφ-enhanced PDLSC cementoblastic differentiation, and cyto-/chemokines (interleukin (IL)-10 and vascular endothelial growth factor [VEGF]) secreted by M2 Mφs were found to be key players that promoted cell cementoblastic differentiation by activating Akt signaling. Our data indicate for the first time that Mφs are key modulators during PDLSC cementoblastic differentiation and are hence very important for the regeneration of multiple periodontal tissues, including the cementum. Although the Akt and JNK pathways are involved in M2 Mφ-enhanced cementoblastic differentiation, only the Akt pathway can be activated via a cyto-/chemokine-associated mechanism, suggesting that players other than cyto-/chemokines also participate in the M2-mediated cementoblastic differentiation of PDLSCs. Stem Cells 2019;37:1567-1580.

NFIC promotes the vitality and osteogenic differentiation of rat dental follicle cells

Nuclear factor I-C (NFIC) plays critical roles in the regulation of tooth development by influencing the biological behaviors of stem cells in the dental germ. This study aimed to investigate the effect of NFIC on the vitality and osteogenic/cementogenic differentiation of rat dental follicle cells (DFCs). DFCs were isolated from dental follicles in the first molars of neonatal rats. DFCs expressed mesenchymal stromal cell markers CD29, CD44 and CD90 and had capabilities for self-renewal and multipotent differentiation. Overexpression of NFIC promoted the proliferation of DFCs without markedly influencing the apoptosis of DFCs. Moreover, NFIC increased alkaline phosphatase (ALP) activity in DFCs and upregulated the mRNA levels of osteogenic-related markers, namely, collagen type I (Col I), Runt-related transcription factor 2 (Runx2) and ALP, as well as β-catenin. In contrast, silencing NFIC by siRNA increased the apoptosis of DFCs and downregulated the expression of osteogenic-related markers. In conclusion, these results suggested that upregulation of NFIC may promote the proliferation and osteogenic/cementogenic differentiation of DFCs.

Application of cell-sheet engineering for new formation of cementum around dental implants

Periodontal disease involves the chronic inflammation of tooth supporting periodontal tissues. As the disease progresses, it manifests destruction of periodontal tissues and eventual tooth loss. The regeneration of lost periodontal tissue has been one of the most important subjects in periodontal research. Since their discovery, periodontal ligament stem cells (PDLSCs), have been transplanted into periodontal bony defects to examine their regenerative potential. Periodontal defects were successfully regenerated using PDLSC sheets, which were fabricated by cell sheet engineering in animal models, and for which clinical human trials are underway. To expand the utility of PDLSC sheet, we attempted to construct periodontal tissues around titanium implants with the goal of facilitating the prevention of peri-implantitis. In so doing, we found newly formed cementum-periodontal ligament (PDL) structures on the implant surface. In this mini review, we summarize the literature regarding cell-based periodontal regeneration using PDLSCs, as well as previous trials aimed at forming periodontal tissues around dental implants. Moreover, the recent findings in cementogenesis are reviewed from the perspective of the formation of further stable periodontal attachment structure on dental implant. This mini review aims to summarize the current status of the creation of novel periodontal tissue-bearing dental implants, and to consider its future direction.

Cyclic Stretch Force Induces Periodontal Ligament Cells to Secrete Exosomes That Suppress IL-1β Production Through the Inhibition of the NF-κB Signaling Pathway in Macrophages

In the oral mechanical environment, periodontal ligament cells (PDL cells) contribute to maintaining periodontal tissue homeostasis. Recent studies showed that exosomes, which are small vesicles secreted by various types of cells, play a pivotal role in cell-to-cell communication in biological processes. We examined the secretion of exosomes from PDL cells stimulated with cyclic stretch and their role in the inflammatory response of macrophages using the human macrophage cell line THP-1 and human primary monocytes/macrophages. We prepared supernatants from human PDL cells (PDL-sup) stimulated with cyclic stretch. The treatment of macrophages with PDL-sup, but not PDL-sup from unstimulated PDL cells, inhibited the production of IL-1β in LPS/nigericin-stimulated macrophages. The pretreatment of PDL cells with GW4869, an inhibitor of exosome secretion, or siRNA for Rab27B, which controls exosome secretion, abrogated the inhibitory effects of PDL-sup. A transmission electron microscopy analysis demonstrated the existence of exosomes with diameters ranging between 30 and 100 nm in PDL-sup, suggesting that exosomes in PDL-sup contribute to this inhibition. An immunofluorescence microscopy analysis revealed that exosomes labeled with PKH67, a fluorescent dye, were incorporated by macrophages as early as 2 h after the addition of exosomes. Purified exosomes inhibited IL-1β production in LPS/nigericin-stimulated macrophages and the nuclear translocation of NF-κB as well as NF-κB p65 DNA-binding activity in LPS-stimulated macrophages, suggesting that exosomes suppress IL-1β production by inhibiting the NF-κB signaling pathway. Our results indicate that PDL cells in mechanical environments contribute to the maintenance of periodontal immune/inflammatory homeostasis by releasing exosomes.

WNT5A supports viability of senescent human dental follicle cells

The osteogenic differentiation of dental follicle cells (DFCs) is inhibited by the onset of cellular senescence, but the cause for this is largely unknown. Recently it was shown that WNT5a, which is an inductor of the non-canonical WNT pathway, stimulates both cellular senescence and osteogenic differentiation of different cell types. In this study, we investigated the role of WNT5a for viability and osteogenic differentiation in human DFCs after the induction of cellular senescence. DFCs were cultivated until the induction of cellular senescence. The induction of cellular senescence was confirmed by β-galactosidase staining, estimation of population doubling time, and slightly telomere length shortening. After induction of cellular senescence, the expression of WNT5A and the potential to induce the osteogenic differentiation decreased. Inhibition of WNT5A by specific siRNAs had significant effect on the viability of DFCs. Cell proliferation was reduced, whereas both cellular senescence and cell death were increased in DFCs. However, an inhibition of WNT5A did only slightly effect the osteogenic differentiation of DFCs. Our results suggest that WNT5A supports viability during both cell proliferation and osteogenic differentiation of DFCs.

[The role of bone morphogenetic protein signaling pathway in tooth root development]

The bone morphogenetic protein (BMP) family is an important factor in the regulation of cell ular life activities and in the development of almost all tissues. BMP-mediated signaling plays an important role in tooth root development, which is a part of tooth development. Epithelial and mesenchymal interactions are involved in tooth root development, but the BMP signaling pathway has a different effect on tooth root development in epithelial and mesenchymal. This review summarizes the advances of BMP signaling in tooth root development.

Nkd2 promotes the differentiation of dental follicle stem/progenitor cells into osteoblasts

Dental follicle stem/progenitor cells have the potential to undergo osteogenesis. naked cuticle homolog 2 (Nkd2) is a signal-inducible feedback antagonist of the canonical Wnt signaling pathway. The purpose of the present study was to investigate the function of Nkd2 in the differentiation of dental follicle stem/progenitor cells (DFSCs) into osteoblasts. Immunohistochemistry, reverse transcription-quantitative polymerase chain reaction and western blotting were employed to detect Nkd2 expression in rat DFSCs. In addition, rat DFSCs (rDFSCs) were transfected with small interfering RNAs to examine the effect of Nkd2 on the differentiation of these cells into osteoblasts. Furthermore, the function of Nkd2 in the Wnt/β-catenin pathway in rDFSCs was investigated using β-catenin/T-cell factor luciferase activity assays and western blotting. It was revealed that the expression of Nkd2 was upregulated during the differentiation of rDFSCs into osteoblasts. Furthermore, osteoblast differentiation ability and Wnt/β-catenin pathway activity were significantly decreased in Nkd2-silenced rDFSCs compared with the si-NC group (P<0.05 and P<0.001, respectively). The results suggest that Nkd2 promotes the differentiation of rDFSCs into osteoblasts through Wnt/β-catenin signaling.

A Reciprocal Interaction between β-Catenin and Osterix in Cementogenesis

Although accumulating evidence indicates that both β-catenin and osterix (Osx) are essential for bone and tooth development, few studies have investigated the interaction of these two key proteins in the context of cementogenesis. In this study, we used transgenic mice with constitutively active β-catenin and inactive Osx in the dental mesenchyme to address this question. We found that cementoblasts with constitutively active β-catenin require Osx to produce excessive cellular cementum, and that ablation of Osx prevents this abnormal accumulation. Importantly, cementoblasts transduced with retrovirus expressing constitutively active β-catenin exhibited upregulation of Osx expression through direct binding to the promoter region of Osx. Osx regulates Lef1 expression and consequently could regulate T-cell factor/lymphoid enhancer factor (Tcf/Lef) binding activity in Wnt/β-catenin signaling. However, the loss of Tcf/Lef binding activity by Osx ablation was not rescued by transduction of retrovirus expressing constitutively active β-catenin or ectopic Lef1 overexpression. These results suggest that the Tcf/Lef binding activity of Wnt/β-catenin signaling is Osx-dependent during cementogenesis. Moreover, Osx differentially regulates the expression of various Tcf family members, suggesting that Osx regulates cementogenesis by utilizing various Tcf/Lef-dependent mechanisms. This is the first report to show that downstream Osx signaling through Tcf/Lefs is critical for cementogenesis.

Intermittent parathyroid hormone (PTH) promotes cementogenesis and alleviates the catabolic effects of mechanical strain in cementoblasts

Background

External root resorption, commonly starting from cementum, is a severe side effect of orthodontic treatment. In this pathological process and repairing course followed, cementoblasts play a significant role. Previous studies implicated that parathyroid hormone (PTH) could act on committed osteoblast precursors to promote differentiation, and inhibit apoptosis. But little was known about the role of PTH in cementoblasts. The purpose of this study was to investigate the effects of intermittent PTH on cementoblasts and its influence after mechanical strain treatment.

Results

Higher levels of cementogenesis- and differentiation-related biomarkers (bone sialoprotein (BSP), osteocalcin (OCN), Collagen type I (COL1) and Osterix (Osx)) were shown in 1–3 cycles of intermittent PTH treated groups than the control group. Additionally, intermittent PTH increased alkaline phosphatase (ALP) activity and mineralized nodules formation, as measured by ALP staining, quantitative ALP assay, Alizarin red S staining and quantitative calcium assay. The morphology of OCCM-30 cells changed after mechanical strain exertion. Expression of BSP, ALP, OCN, osteopontin (OPN) and Osx was restrained after 18 h mechanical strain. Furthermore, intermittent PTH significantly increased the expression of cementogenesis- and differentiation-related biomarkers in mechanical strain treated OCCM-30 cells.

Conclusions

Taken together, these data suggested that intermittent PTH promoted cementum formation through activating cementogenesis- and differentiation-related biomarkers, and attenuated the catabolic effects of mechanical strain in immortalized cementoblasts OCCM-30.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0133-0) contains supplementary material, which is available to authorized users.

Angled Growth of the Dental Lamina Is Accompanied by Asymmetrical Expression of the WNT Pathway Receptor Frizzled 6

Frizzled 6 (FZD6) belongs to a family of proteins that serve as receptors in the WNT signaling pathway. FZD6 plays an important role in the establishment of planar cell polarity in many embryonic processes such as convergent extension during gastrulation, neural tube closure, or hair patterning. Based on its role during hair development, we hypothesized that FZD6 may have similar expression pattern and function in the dental lamina, which is also a distinct epithelial protrusion growing characteristically angled into the mesenchyme. Diphyodont minipig was selected as a model species because its dentition closely resemble human ones with successional generation of teeth initiated from the dental lamina. We revealed asymmetrical expression of FZD6 in the dental lamina of early as well as late stages during its regression with stronger expression located on the labial side of the dental lamina. During lamina regression, FZD6-positive cells were found in its superficial part and the signal coincided with the upregulation of molecules involved in epithelial-mesenchymal transition and increased migratory potential of epithelial cells. FZD6-expression was also turned on during differentiation of cells producing hard tissues, in which mature odontoblasts, ameloblasts, or surrounding osteoblasts were FZD6-positive. On the other hand, the tip of successional lamina and its lingual part, in which progenitor cells are located, exhibited FZD6-negativity. In conclusion, asymmetrical expression of FZD6 correlates with the growth directionality and side-specific morphological differences in the dental lamina of diphyodont species. Based on observed expression pattern, we propose that the dental lamina is other epithelial tissue, where planar cell polarity signaling is involved during its asymmetrical growth.

Periodontal ligament stem/progenitor cells with protein-releasing scaffolds for cementum formation and integration on dentin surface

Purpose/Aim: Cementogenesis is a critical step in periodontal tissue regeneration given the essential role of cementum in anchoring teeth to the alveolar bone. This study is designed to achieve integrated cementum formation on the root surfaces of human teeth using growth factor-releasing scaffolds with periodontal ligament stem/progenitor cells (PDLSCs).

MATERIALS AND METHODS

Human PDLSCs were sorted by CD146 expression, and characterized using CFU-F assay and induced multi-lineage differentiation. Polycaprolactone scaffolds were fabricated using 3D printing, embedded with poly(lactic-co-glycolic acids) (PLGA) microspheres encapsulating connective tissue growth factor (CTGF), bone morphogenetic protein-2 (BMP-2), or bone morphogenetic protein-7 (BMP-7). After removing cementum on human tooth roots, PDLSC-seeded scaffolds were placed on the exposed dentin surface. After 6-week culture with cementogenic/osteogenic medium, cementum formation and integration were evaluated by histomorphometric analysis, immunofluorescence, and qRT-PCR.

RESULTS

Periodontal ligament (PDL) cells sorted by CD146 and single-cell clones show a superior clonogenecity and multipotency as compared with heterogeneous populations. After 6 weeks, all the growth factor-delivered groups showed resurfacing of dentin with a newly formed cementum-like layer as compared with control. BMP-2 and BMP-7 showed de novo formation of tissue layers significantly thicker than all the other groups, whereas CTGF and BMP-7 resulted in significantly improved integration on the dentin surface. The de novo mineralized tissue layer seen in BMP-7-treated samples expressed cementum matrix protein 1 (CEMP1). Consistently, BMP-7 showed a significant increase in CEMP1 mRNA expression.

CONCLUSION

Our findings represent important progress in stem cell-based cementum regeneration as an essential part of periodontium regeneration.

Wnt and BMP Signaling Crosstalk in Regulating Dental Stem Cells: Implications in Dental Tissue Engineering

Tooth is a complex hard tissue organ and consists of multiple cell types that are regulated by important signaling pathways such as Wnt and BMP signaling. Serious injuries and/or loss of tooth or periodontal tissues may significantly impact aesthetic appearance, essential oral functions and the quality of life. Regenerative dentistry holds great promise in treating oral/dental disorders. The past decade has witnessed a rapid expansion of our understanding of the biological features of dental stem cells, along with the signaling mechanisms governing stem cell self-renewal and differentiation. In this review, we first summarize the biological characteristics of seven types of dental stem cells, including dental pulp stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, periodontal ligament stem cells, alveolar bone-derived mesenchymal stem cells (MSCs), and MSCs from gingiva. We then focus on how these stem cells are regulated by bone morphogenetic protein (BMP) and/or Wnt signaling by examining the interplays between these pathways. Lastly, we analyze the current status of dental tissue engineering strategies that utilize oral/dental stem cells by harnessing the interplays between BMP and Wnt pathways. We also highlight the challenges that must be addressed before the dental stem cells may reach any clinical applications. Thus, we can expect to witness significant progresses to be made in regenerative dentistry in the coming decade.

p38 MAP kinase is required for Wnt3a-mediated osterix expression independently of Wnt-LRP5/6-GSK3β signaling axis in dental follicle cells

Wnt3a is a secreted glycoprotein that activates the glycogen synthase kinase-3β (GSK3β)/β-catenin signaling pathway through low-density-lipoprotein receptor-related protein (LRP)5/6 co-receptors. Wnt3a has been implicated in periodontal development and homeostasis, as well as in cementum formation. Recently, we have reported that Wnt3a increases alkaline phosphatase expression through the induction of osterix (Osx) expression in dental follicle cells, a precursor of cementoblasts. However, the molecular mechanism by which Wnt3a induces Osx expression is still unknown. In this study, we show that Wnt3a-induced Osx expression was inhibited in the presence of p38 mitogen-activated protein kinase (MAPK) inhibitors (SB203580 and SB202190) at gene and protein levels, as assessed by real-time PCR and immunocytohistochemistry, respectively. Pretreatment of cells with Dickkopf-1, a potent canonical Wnt antagonist binding to LRP5/6 co-receptors, did not influence Wnt3a-mediated p38 MAPK phosphorylation, suggesting that Wnt3a activates p38 MAPK through LRP5/6-independent signaling. On the other hand, pretreatment with p38 MAPK inhibitors had no effects on the phosphorylated status of GSK3β and β-catenin as well as β-catenin nuclear translocation, but inhibited Wnt3a-mediated β-catenin transcriptional activity. These findings suggest that p38 MAPK modulates canonical Wnt signaling at the β-catenin transcriptional level without any crosstalk with the Wnt3a-mediated LRP5/6-GSK3β signaling axis and subsequent β-catenin nuclear translocation. These findings expand our knowledge of the mechanisms controlling periodontal development and regeneration.

Current Understanding on Role of the Wnt Signaling Pathway Effector TCF7L2 in Glucose Homeostasis

The role of the Wnt signaling pathway in metabolic homeostasis has drawn our intensive attention, especially after the genome-wide association study discovery that certain polymorphisms of its key effector TCF7L2 are strongly associated with the susceptibility to type 2 diabetes. For a decade, great efforts have been made in determining the function of TCF7L2 in various metabolic organs, which have generated both considerable achievements and disputes. In this review, I will briefly introduce the canonical Wnt signaling pathway, focusing on its effector β-catenin/TCF, including emphasizing the bidirectional feature of TCFs and β-catenin post-translational modifications. I will then summarize the observations on the association between TCF7L2 polymorphisms and type 2 diabetes risk. The main content, however, is on the intensive functional exploration of the metabolic role of TCF7L2, including the disputes generated on determining its role in the pancreas and liver with various transgenic mouse lines. Finally, I will discuss those achievements and disputes and present my future perspectives.

Role of the Wnt signaling molecules in the tooth

Wnt signaling plays a central role in many processes during embryonic development and adult homeostasis. At least 19 types of Wnt ligands, receptors, transducers, transcription factors, and antagonists have been identified in mammals. Two distinct Wnt signaling pathways, the canonical signaling pathway and the noncanonical signaling pathway, have been described. Some Wnt signaling pathway components are expressed in the dental epithelium and mesenchyme during tooth development in humans and mice. Functional studies and experimental analysis of relevant animal models confirm the effects of Wnt signaling pathway on the regulation of developing tooth formation and adult tooth homeostasis. Mutations in some Wnt signaling pathway components have been identified in syndromic and non-syndromic tooth agenesis. This review provides an overview of progress in elucidating the role of Wnt signaling pathway components in the tooth and the resulting possibilities for therapeutic development.