Differentiation of Dental Pulp Stem Cells into Regular-Shaped Dentin-Pulp Complex Induced by Tooth Germ Cell Conditioned Medium

Current Trends, Advances, and Challenges of Tissue Engineering-Based Approaches of Tooth Regeneration: A Review of the Literature

INTRODUCTION

Tooth loss is a significant health issue. Currently, this situation is often treated with the use of synthetic materials such as implants and prostheses. However, these treatment modalities do not fully meet patients' biological and mechanical needs and have limited longevity. Regenerative medicine focuses on the restoration of patients' natural tissues via tissue engineering techniques instead of rehabilitating with artificial appliances. Therefore, a tissue-engineered tooth regeneration strategy seems like a promising option to treat tooth loss.

OBJECTIVE

This review aims to demonstrate recent advances in tooth regeneration strategies and discoveries about underlying mechanisms and pathways of tooth formation.

RESULTS AND DISCUSSION

Whole tooth regeneration, tooth root formation, and dentin-pulp organoid generation have been achieved by using different seed cells and various materials for scaffold production. Bioactive agents are critical elements for the induction of cells into odontoblast or ameloblast lineage. Some substantial pathways enrolled in tooth development have been figured out, helping researchers design their experiments more effectively and aligned with the natural process of tooth formation.

CONCLUSION

According to current knowledge, tooth regeneration is possible in case of proper selection of stem cells, appropriate design and manufacturing of a biocompatible scaffold, and meticulous application of bioactive agents for odontogenic induction. Understanding innate odontogenesis pathways play a crucial role in accurately planning regenerative therapeutic interventions in order to reproduce teeth.

Promotion effect of apical tooth germ cell-conditioned medium on osteoblastic differentiation of periodontal ligament stem cells through regulating miR-146a-5p

BACKGROUND

MicroRNAs (miRNAs) play an important role in gene regulation that controls stem cells differentiation. Periodontal ligament stem cells (PDLSCs) could differentiate into osteo-/cementoblast-like cells that secretes cementum-like matrix both in vitro and in vivo. Whether miRNAs play key roles in osteoblastic differentiation of PDLSCs triggered by a special microenviroment remains elusive. In this study, we aimed to investigate potential miRNA expression changes in osteoblastic differentiation of PDLSCs by the induction of apical tooth germ cell-conditioned medium (APTG-CM).

METHODS AND RESULTS

First, we analyzed the ability of APTG-CM to osteogenically differentiate PDLSCs. The results exhibited an enhanced mineralization ability, higher ALP activity and increased expression of osteogenic genes in APTG-CM-induced PDLSCs. Second, we used miRNA sequencing to analyze the miRNA expression profile of PDLSCs derived from three donors under 21-day induction or non-induction of APTG-CM. MiR-146a-5p was found to be up-regulated miRNA in induced PDLSCs and validated by RT-qPCR. Third, we used lentivirus-up/down system to verify the role of miR-146a-5p in the regulation of osteoblastic differentiation of PDLSCs.

CONCLUSIONS

In conclusion, our results demonstrated that miR-146a-5p was involved in the promotion effect of APTG-CM on osteoblastic differentiation of PDLSCs, and suggested that miR-146a-5p might be a novel way in deciding the direction of PDLSCs differentiation.

A Compilation of Study Models for Dental Pulp Regeneration

Efforts to heal damaged pulp tissue through tissue engineering have produced positive results in pilot trials. However, the differentiation between real regeneration and mere repair is not possible through clinical measures. Therefore, preclinical study models are still of great importance, both to gain insights into treatment outcomes on tissue and cell levels and to develop further concepts for dental pulp regeneration. This review aims at compiling information about different in vitro and in vivo ectopic, semiorthotopic, and orthotopic models. In this context, the differences between monolayer and three-dimensional cell cultures are discussed, a semiorthotopic transplantation model is introduced as an in vivo model for dental pulp regeneration, and finally, different animal models used for in vivo orthotopic investigations are presented.

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.

Dental stem cell-conditioned medium for tissue regeneration: Optimization of production and storage

BACKGROUND

Mesenchymal stem cells (MSC) effects on tissue regeneration are mainly mediated by their secreted substances (secretome), inducing their paracrine activity. This Conditioned medium (CM), including soluble factors (proteins, nucleic acids, lipids) and extracellular vesicles is emerging as a potential alternative to cell therapy. However, the manufacturing of CM suffers from variable procedures and protocols leading to varying results between studies. Besides, there is no well-defined optimized procedure targeting specific applications in regenerative medicine.

AIM

To focus on conditioned medium produced from dental MSC (DMSC-CM), we reviewed the current parameters and manufacturing protocols, in order to propose a standardization and optimization of these manufacturing procedures.

METHODS

We have selected all publications investigating the effects of dental MSC secretome in in vitro and in vivo models of tissue regeneration, in accordance with the PRISMA guidelines.

RESULTS

A total of 351 results were identified. And based on the inclusion criteria described above, 118 unique articles were included in the systematic review. DMSC-CM production was considered at three stages: before CM recovery (cell sources for CM), during CM production (culture conditions) and after production (CM treatment).

CONCLUSION

No clear consensus could be recovered as evidence-based methods, but we were able to describe the most commonly used protocols: donors under 30 years of age, dental pulp stem cells and exfoliated deciduous tooth stem cells with cell passage between 1 and 5, at a confluence of 70% to 80%. CM were often collected during 48 h, and stored at -80 °C. It is important to point out that the preconditioning environment had a significant impact on DMSC-CM content and efficiency.

Dentin-Pulp Complex Tissue Regeneration via Three-Dimensional Cell Sheet Layering

The dentin-pulp complex is a unique structure in teeth that contains both hard and soft tissues. Generally, deep caries and trauma cause damage to the dentin-pulp complex, and if left untreated, this damage will progress to irreversible pulpitis. The aim of this study was to fabricate a layered cell sheet composed of rat dental pulp (DP) cells and odontogenic differentiation of pulp (OD) cells and to investigate the ability to regenerate the dentin-pulp complex in a scaffold tooth. We fabricated two single cell sheets composed of DP cells (DP cell sheet) or OD cells (OD cell sheet) and a layered cell sheet made by layering both cells. The characteristics of the fabricated cell sheets were analyzed using light microscopy, scanning electron microscope (SEM), hematoxylin-eosin (HE) staining, and immunohistochemistry (IHC). Furthermore, the cell sheets were transplanted into the subrenal capsule of immunocompromised mice for 8 weeks. After this, the regenerative capacity to form dentin-like tissue was evaluated using micro-computed tomography (micro-CT), HE staining, and IHC. The findings of SEM and IHC confirmed that layered cell sheets fabricated by stacking OD cells and DP cells maintained their cytological characteristics. Micro-CT of layered cell sheet transplants revealed a mineralized capping of the access cavity in the crown area, similar to that of natural dentin. In contrast, the OD cell sheet group demonstrated the formation of irregular fragments of mineralized tissue in the pulp cavity, and the DP cell sheet did not develop any hard tissue. Moreover, bone volume/tissue volume (BV/TV) showed a significant increase in hard tissue formation in the layered cell sheet group compared with that in the single cell sheet group (p < 0.05). HE staining also showed a combination of soft and hard tissue formation in the layered cell sheet group. Furthermore, IHC confirmed that the dentin-like tissue generated from the layered cell sheet expressed characteristic markers of dentin but not bone equivalent to that of a natural tooth. In conclusion, this study demonstrates the feasibility of regenerating dentin-pulp complex using a bioengineered tissue designed to simulate the anatomical structure. Impact statement The dentin-pulp complex can be destroyed by deep caries and trauma, which may cause pulpitis and progress to irreversible pulpitis, apical periodontitis, and even tooth loss. Current treatments cannot maintain pulp health, and teeth can become brittle. We developed a three-dimensional (3D) layered cell sheet using dental pulp cells and odontogenic differentiation of pulp cells for dentin-pulp complex regeneration. Our layered cell sheet enables the regeneration of an organized 3D dentin-pulp-like structure comparable with that of natural teeth. This layered cell sheet technology may contribute to dentin-pulp complex regeneration and provide a novel method for complex tissue engineering.

CGFe and TGF-β1 enhance viability and osteogenic differentiation of human dental pulp stem cells through the MAPK pathway

The present study aimed to evaluate the effects of concentrated growth factor exudate (CGFe) and TGF-β1 on the viability and osteogenic differentiation of human dental pulp stem cells (hDPSCs). CGFe was prepared from the peripheral blood of healthy donors (obtained with informed consent). STRO-1⁺ hDPSCs were isolated from dental pulp tissues and treated in four groups: i) Control; ii) TGF-β1 (1 ng/ml); iii) 100% CGFe; and iv) TGF-β1 (1 ng/ml) + 100% CGFe group. hDPSC viability was measured via MTT assay. The osteogenic differentiation of hDPSCs was quantified via alkaline phosphatase (ALP) activity, western blotting and reverse transcription-quantitative PCR assays. CGFe and TGF-β1 enhanced hDPSC viability, upregulated ALP activity, upregulated the expression of phosphorylated (p)-ERK1/2, p-JNK and p-p38 in hDPSCs, and promoted transcription and protein expression of osteogenic-related genes (bone sialoprotein, Runt-related transcription factor 2 and osteocalcin) in hDPSCs. The present study demonstrated that CGFe and TGF-β1 facilitated the viability and osteogenic differentiation of hDPSCs potentially through activation of the MAPK signaling pathway.

Scaffold-based developmental tissue engineering strategies for ectodermal organ regeneration

Tissue engineering (TE) is a multidisciplinary research field aiming at the regeneration, restoration, or replacement of damaged tissues and organs. Classical TE approaches combine scaffolds, cells and soluble factors to fabricate constructs mimicking the native tissue to be regenerated. However, to date, limited success in clinical translations has been achieved by classical TE approaches, because of the lack of satisfactory biomorphological and biofunctional features of the obtained constructs. Developmental TE has emerged as a novel TE paradigm to obtain tissues and organs with correct biomorphology and biofunctionality by mimicking the morphogenetic processes leading to the tissue/organ generation in the embryo. Ectodermal appendages, for instance, develop in vivo by sequential interactions between epithelium and mesenchyme, in a process known as secondary induction. A fine artificial replication of these complex interactions can potentially lead to the fabrication of the tissues/organs to be regenerated. Successful developmental TE applications have been reported, in vitro and in vivo, for ectodermal appendages such as teeth, hair follicles and glands. Developmental TE strategies require an accurate selection of cell sources, scaffolds and cell culture configurations to allow for the correct replication of the in vivo morphogenetic cues. Herein, we describe and discuss the emergence of this TE paradigm by reviewing the achievements obtained so far in developmental TE 3D scaffolds for teeth, hair follicles, and salivary and lacrimal glands, with particular focus on the selection of biomaterials and cell culture configurations.

Differences in osteogenic and odontogenic differentiation potential of DPSCs and SHED

OBJECTIVE

Dental pulp stem cells (DPSCs) and stem cells from human exfoliated deciduous teeth (SHED) are types of human dental tissue-derived mesenchymal stem cells (MSCs) that have emerged as an interesting and promising source of stem cells in the field of tissue engineering. The aim of this work is to isolate stem cells from DPSCs and SHED, cultivate them in vitro and compare their odontogenic differentiation potential.

METHODS

DPSCs and SHED were extracted from molars, premolars and canines of six healthy subjects aged 5-29 years. The cells were characterized, using flow cytometry, for mesenchymal stem cell surface markers. MTT colorimetric assay was applied to assess cell viability. Alizarin red staining, alkaline phosphatase (ALP) activity, quantitative real-time PCR (qRT-PCR) and western blot were carried out to determine DPSCs and SHED osteogenic/odontogenic differentiation.

RESULTS

DPSCs express higher STRO-1 and CD44 levels compared to SHED. Moreover, the cells differentiate and acquire columnar shape with a level of calcium deposition and mineralization that is the same between DPSCs and SHED. ALP activity, ALP, COLI, DMP-1, DSPP, OC, and RUNX2 (osteogenic/odontogenic differentiation markers) expression levels were higher in DPSCs.

CONCLUSIONS

DPSCs and SHED express MSCs markers. Although both cell types had calcium deposits, DPSCs presented a higher ALP activity level. In addition, DPSCs showed higher levels of osteogenic and odontogenic differentiation markers such as COLI, DSPP, OC, RUNX2, and DMP-1. These results suggest that DPSCs are closer to the phenotype of odontoblasts than SHED and may improve the efficacy of human dental tissue-derived mesenchymal stem cells therapeutic protocols.

'CLINICAL SIGNIFICANCE'

DPSCs are closer than t SHED to the phenotype of odontoblasts. This would be helpful to enable better therapeutic decisions when applying MSCs-based therapy in the field of dentistry.

Fabrication of Dentin-Pulp-Like Organoids Using Dental-Pulp Stem Cells

We developed a novel dentin-pulp-like organoid. It has both stem-cell and odontoblast characteristics using a mesenchymal cell lineage of human dental-pulp stem cells (hDPSCs). The mixture of hDPSCs and Matrigel was transferred into the maintenance medium (MM) and divided into four different groups according to how long they were maintained in the odontogenic differentiation medium (ODM). All organoids were harvested at 21 days and analyzed to find the optimal differentiation condition. To assess the re-fabrication of dentin-pulp-like organoid, after dissociation of the organoids, it was successfully regenerated. Additionally, its biological activity was confirmed by analyzing changes of relevant gene expression and performing a histology analysis after adding Biodentine^® into the ODM. The organoid was cultured for 11 days in the ODM (ODM 11) had the most features of both stem cells and differentiated cells (odontoblasts) as confirmed by relevant gene expression and histology analyses. Micro-computed tomography and an electron microscope also showed mineralization and odontoblastic differentiation. Finally, ODM 11 demonstrated a biologically active response to Biodentine^® treatment. In conclusion, for the first time, we report the fabrication of a dentin-pulp-like organoid using mesenchymal stem cells. This organoid has potential as a future therapeutic strategy for tooth regeneration.

Regulating substrate mechanics to achieve odontogenic differentiation for dental pulp stem cells on TiO2 filled and unfilled polyisoprene

We have shown that materials other than hydrogels commonly used in tissue engineering can be effective in enabling differentiation of dental pulp stem cells (DPSC). Here we demonstrate that a hydrophobic elastomer, polyisoprene (PI), a component of Gutta-percha, normally used to obturate the tooth canal, can also be used to initiate differentiation of the pulp. We showed that PI substrates without additional coating promote cell adhesion and differentiation, while their moduli can be easily adjusted either by varying the coating thickness or incorporation of inorganic particles. DPSC plated on those PI substrates were shown, using SPM and hysitron indentation, to adjust their moduli to conform to differentially small changes in the substrate modulus. In addition, optical tweezers were used to separately measure the membrane and cytoplasm moduli of DPSC, with and without Rho kinase inhibitor. The results indicated that the changes in modulus were attributed predominantly to changes within the cytoplasm, rather than the cell membrane. CLSM was used to identify cell morphology. Differentiation, as determined by qRT-PCR, of the upregulation of OCN, and COL1α1 as well as biomineralization, characterized by SEM/EDAX, was observed on hard PI substrates in the absence of induction factors, i.e. dexamethasone, with moduli 3-4 MPa, regardless of preparation. SEM showed that even though biomineralization was deposited on both spun cast thin PI and filled thick PI substrates, the minerals were aggregated into large clusters on thin PI, and uniformly distributed on filled thick PI, where it was templated within banded collagen fibers. STATEMENT OF SIGNIFICANCE: This manuscript demonstrates the potential of polyisoprene (PI), an elastomeric polymer, for use in tissue engineering. We show how dental pulp stem cells adjust their moduli continuously to match infinitesimally small changes in substrate mechanics, till a critical threshold is reached when they will differentiate. The lineage of differentiation then becomes a sensitive function of both mechanics and morphology for a given chemical composition. Since PI is a major component of Gutta-percha, the FDA approved material commonly used for obturating the root canal, this work suggests that it can easily be adapted for in vivo use in dental regeneration.

CKIP-1 suppresses odontoblastic differentiation of dental pulp stem cells via BMP2 pathway and can interact with NRP1

AIM

Casein kinase 2 interacting protein-1 (CKIP-1) is a recently discovered intracellular regulator of bone formation, muscle cell differentiation, and tumor cell proliferation. Our study aims to identify the inhibition of BMP2-Smad1/5 signaling by CKIP-1 in odontoblastic differentiation of human dental pulp stem cells (DPSCs).

MATERIALS AND METHODS

DPSCs infected CKIP-1 siRNA or transfected CKIP-1 full-length plasmid were cultured in odontoblastic differentiation medium or added noggin (200 ng/mL) for 21 days. We examined the effects of CKIP-1 on odontoblastic differentiation, mineralized nodules formation, and interaction by western blot, real-time polymerase chain reaction (RT-PCR), alkaline phosphatase (ALP) staining, alizarin red S staining, and immunoprecipitation.

RESULTS

Firstly, we have demonstrated that CKIP-1 expression markedly decreased time-dependently along with cell odontoblastic differentiation. Indeed, the silence of CKIP-1 upregulated odontoblastic differentiation via BMP2-Smad1/5 signaling, while CKIP-1 over-expression had a negative effect on odontoblastic differentiation of DPSCs. Furthermore, CKIP-1 could interact with Neuropilin-1 (NRP1).

CONCLUSIONS

This work provides data that advocates a novel perception on odontoblastic differentiation of DPSCs. Therefore, inhibiting the expression of CKIP-1 may be of great significance to the development of dental caries.

Platelet‑rich fibrin exudate promotes the proliferation and osteogenic differentiation of human periodontal ligament cells in vitro

The purpose of the present study was to evaluate the effects of platelet-rich fibrin (PRF) exudate on the proliferation, osteogenic differentiation and mineralization of human periodontal ligament cells (hPDLCs) in vitro. In the present study PRF was obtained with permission, from the peripheral blood of healthy donors and PRF exudates were collected on the 7th day of incubation. hPDLCs were obtained from healthy premolars, cultured by a tissue explant method and identified with anti-vimentin and anti-cytokeratin antibodies. PRF exudates were added to hPDLCs in different concentrations to evaluate cell proliferation and osteogenic differentiation. The proliferation of hPDLCs was measured using a colorimetric assay. Osteogenic differentiation and mineralization were determined by Alizarin red staining, alkaline phosphatase activity (ALP), western blotting and reverse transcription-quantitative polymerase chain reaction. Cell proliferation was enhanced by addition of the PRF exudate, which also promoted the formation of mineralized matrix nodules and upregulated ALP activity and osteoblast-associated levels of osteocalcin, runt-related transcription factor and osterix gene expression. As these stimulatory effects occurred in a dose-dependent manner, it was concluded that high concentrations of the PRF exudate served an essential role in the proliferation, osteogenic differentiation and mineralization of hPDLCs in vitro. The present study demonstrated that PRF exudate enhanced hPDLC proliferation, induced the osteoblastic differentiation of hPDLCs into mineralized tissue-formation cells in vitro, and may therefore provide potential benefits for periodontal tissue engineering; contributing to the primary processes of periodontal tissue regeneration. From the perspective of both economics and biology, PRF has greater clinical benefits than analogous growth factors.

Ex vivo evaluation of intravitreal mesenchymal stromal cell viability using bioluminescence imaging

Background

Bone marrow-derived mesenchymal stromal cell (MSC) therapy is a promising treatment for several degenerative ocular diseases; however, no reproducible method of monitoring these cells into the eye has been established. The aim of this study was to describe successful bioluminescence imaging (BLI) to detect viable luciferase-expressing MSC in the eye.

Methods

Human donor MSC in culture were transduced with 50 μl luciferase lentiviral vector (three viral particles/cell) prior to intraocular injection. Twenty-one right eyes of 21 rabbits were evaluated through BLI after receiving 1 × 10⁶ luciferase-expressing MSC intravitreally. Contralateral eyes were injected with vehicle (phosphate-buffered saline (PBS)) and were used as controls. At seven different time points (1 h to 60 days), d-luciferin (40 mg/ml, 300 μl PBS) was injected in subsets of six enucleated eyes for evaluation of radiance decay through BLI analysis. CD90 and CD73 immunofluorescence was studied in selected eyes.

Results

Eyes injected with MSC showed high BLI radiance immediately after d-luciferin injection and progressive decay until 60 days. Mean BLI radiance measures from eyes with luciferase-expressing MSC were significantly higher than controls from 8 h to 30 days. At the thirtieth day, positive CD90- and CD73-expressing cells were observed only in the vitreous cavity of eyes injected with MSC.

Conclusions

Viable MSC were identified in the vitreous cavity 1 month after a single injection. Our results confirmed BLI as a useful and reliable method to detect MSC injected into the eye globe.

Hsa-let-7c controls the committed differentiation of IGF-1-treated mesenchymal stem cells derived from dental pulps by targeting IGF-1R via the MAPK pathways

The putative tumor suppressor microRNA let-7c is extensively associated with the biological properties of cancer cells. However, the potential involvement of let-7c in the differentiation of mesenchymal stem cells has not been fully explored. In this study, we investigated the influence of hsa-let-7c (let-7c) on the proliferation and differentiation of human dental pulp-derived mesenchymal stem cells (DPMSCs) treated with insulin-like growth factor 1 (IGF-1) via flow cytometry, CCK-8 assays, alizarin red staining, real-time RT-PCR, and western blotting. In general, the proliferative capabilities and cell viability of DPMSCs were not significantly affected by the overexpression or deletion of let-7c. However, overexpression of let-7c significantly inhibited the expression of IGF-1 receptor (IGF-1R) and downregulated the osteo/odontogenic differentiation of DPMSCs, as indicated by decreased levels of several osteo/odontogenic markers (osteocalcin, osterix, runt-related transcription factor 2, dentin sialophosphoprotein, dentin sialoprotein, alkaline phosphatase, type 1 collagen, and dentin matrix protein 1) in IGF-1-treated DPMSCs. Inversely, deletion of let-7c resulted in increased IGF-1R levels and enhanced osteo/odontogenic differentiation. Furthermore, the ERK, JNK, and P38 MAPK pathways were significantly inhibited following the overexpression of let-7c in DPMSCs. Deletion of let-7c promoted the activation of the JNK and P38 MAPK pathways. Our cumulative findings indicate that Let-7c can inhibit the osteo/odontogenic differentiation of IGF-1-treated DPMSCs by targeting IGF-1R via the JNK/P38 MAPK signaling pathways.

Stiffness regulates the proliferation and osteogenic/odontogenic differentiation of human dental pulp stem cells via the WNT signalling pathway

OBJECTIVES

Researches showed that stiffness of the extracellular matrix can affect the differentiation of many stem cells. Dental pulp stem cells (DPSCs) are a promising type of adult stem cell. However, we know little about whether and how the behaviour of DPSCs is influenced by stiffness.

MATERIALS AND METHODS

We carried out a study that cultured DPSCs on tunable elasticity polydimethylsiloxane substrates to investigate the influence on morphology, proliferation, osteogenic/odontogenic differentiation and its possible mechanism.

RESULTS

Soft substrates changed the cell morphology and inhibited the proliferation of DPSCs. Expression of markers related to osteogenic/odontogenic differentiation was significantly increased as the substrate stiffness increased, including ALP (alkaline phosphatase), OCN (osteocalcin), OPN (osteopontin), RUNX-2 (runt-related transcription factor-2), BMP-2 (bone morphogenetic protein-2), DSPP (dentin sialophosphoprotein) and DMP-1 (dentin matrix protein-1). Mechanical properties promote the function of DPSCs related to the Wnt signalling pathway.

CONCLUSIONS

Our results showed that mechanical factors can regulate the proliferation and differentiation of DPSCs via the WNT signalling pathway. This provides theoretical basis to optimize dental or bone tissue regeneration through increasing stiffness of extracelluar matrix.

Secretome profiles of immortalized dental follicle cells using iTRAQ-based proteomic analysis

Secretomes produced by mesenchymal stromal cells (MSCs) were considered to be therapeutic potential. However, harvesting enough primary MSCs from tissue was time-consuming and costly, which impeded the application of MSCs secretomes. This study was to immortalize MSCs and compare the secretomes profile of immortalized and original MSCs. Human dental follicle cells (DFCs) were isolated and immortalized using pMPH86. The secretome profile of immortalized DFCs (iDFCs) was investigated and compared using iTRAQ labeling combined with mass spectrometry (MS) quantitative proteomics. The MS data was analyzed using ProteinPilotTM software, and then bioinformatic analysis of identified proteins was done. A total of 2092 secreted proteins were detected in conditioned media of iDFCs. Compared with primary DFCs, 253 differently expressed proteins were found in iDFCs secretome (142 up-regulated and 111 down-regulated). Intensive bioinformatic analysis revealed that the majority of secreted proteins were involved in cellular process, metabolic process, biological regulation, cellular component organization or biogenesis, immune system process, developmental process, response to stimulus and signaling. Proteomic profile of cell secretome wasn't largely affected after immortalization converted by this piggyBac immortalization system. The secretome of iDFCs may be a good candidate of primary DFCs for regenerative medicine.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

Composite cell sheet for periodontal regeneration: crosstalk between different types of MSCs in cell sheet facilitates complex periodontal-like tissue regeneration

Background

Tissue-engineering strategies based on mesenchymal stem cells (MSCs) and cell sheets have been widely used for periodontal tissue regeneration. However, given the complexity in periodontal structure, the regeneration methods using a single species of MSC could not fulfill the requirement for periodontal regeneration.

Methods

We researched the interaction between the periodontal ligament stem cells (PDLSCs) and jaw bone marrow-derived mesenchymal stem cells (JBMMSCs), and constructed a composite cell sheet comprising both of the above MSCs to regenerate complex periodontium-like structures in nude mice.

Results

Our results show that by co-culturing PDLSCs and JBMMSCs, the expressions of bone and extracellular matrix (ECM)-related genes and proteins were significantly improved in both MSCs. Further investigations showed that, compared to the cell sheet using PDLSCs or JBMMSCs, the composite stem cell sheet (CSCS), which comprises these two MSCs, expressed higher levels of bone- and ECM-related genes and proteins, and generated a composite structure more similar to the native periodontal tissue physiologically in vivo.

Conclusions

In conclusion, our results demonstrate that the crosstalk between PDLSCs and JBMMSCs in cell sheets facilitate regeneration of complex periodontium-like structures, providing a promising new strategy for physiological and functional regeneration of periodontal tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0417-x) contains supplementary material, which is available to authorized users.

RETRACTED: New findings for dentin sialophosphoprotein studies: Applications of purified odontoblast-like cells derived from stem cells

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Authors. After the retraction of the article [Hiyama T, Ozeki N, Mogi M, Yamaguchi H, Kawai R, Nakata K, Kondo A, Nakamura H. 2013. Matrix Metalloproteinase-3 in Odontoblastic Cells Derived from Ips Cells: Unique Proliferation Response as Odontoblastic Cells Derived from ES Cells. PLoS ONE 8(12): e83563. doi:10.1371/journal.pone.0083563] which contained fabricated/falsified data, the authors attempted to confirm original data for the results presented in their related publications. As a result, they reached a conclusion that there were no original data for the results presented in several their publications. This article was written on the basis of the seven publications retracted or to be retracted and it is no longer reliable. Reference 24: N. Ozeki, M. Mogi, R. Kawai, H. Yamaguchi, T. Hiyama, K. Nakata, H. Nakamura Mouse-induced pluripotent stem cells differentiate into odontoblast-like cells with induction of altered adhesive and migratory phenotype of integrin PLoS One, 8 (2013), p. e80026 Reference 25:R. Kawai, N. Ozeki, H. Yamaguchi, T. Tanaka, K. Nakata, M. Mogi, H. Nakamura Mouse ES cells have a potential to differentiate into odontoblast-like cells using hanging drop method Oral Dis, 20 (2014), pp. 395-403 Reference 26:N. Ozeki, M. Mogi, H. Yamaguchi, T. Hiyama, R. Kawai, N. Hase, K. Nakata, H. Nakamura, R.H. Kramer Differentiation of human skeletal muscle stem cells into odontoblasts is dependent on induction of alpha1 integrin expression J Biol Chem, 289 (2014), pp. 14380-14391 Reference 42:N. Ozeki, N. Hase, R. Kawai, H. Yamaguchi, T. Hiyama, A. Kondo, K. Nakata, M. Mogi Unique proliferation response in odontoblastic cells derived from human skeletal muscle stem cells by cytokine-induced matrix metalloproteinase-3 Exp Cell Res, 331 (2015), pp. 105-114 Reference 43: N. Ozeki, N. Hase, H. Yamaguchi, T. Hiyama, R. Kawai, A. Kondo, K. Nakata, M. Mogi Polyphosphate induces matrix metalloproteinase-3-mediated proliferation of odontoblast-like cells derived from induced pluripotent stem cells Exp Cell Res, 333 (2015), pp. 303-315 Reference 44: N. Ozeki, R. Kawai, N. Hase, T. Hiyama, H. Yamaguchi, A. Kondo, K. Nakata, M. Mogi Alpha2 integrin, extracellular matrix metalloproteinase inducer, and matrix metalloproteinase-3 act sequentially to induce differentiation of mouse embryonic stem cells into odontoblast-like Exp Cell Res, 331 (2015), pp. 21-37 Reference 45: N. Ozeki, M. Mogi, N. Hase, T. Hiyama, H. Yamaguchi, R. Kawai, A. Kondo, T. Matsumoto, K. Nakata Autophagy-related gene 5 and Wnt5 signaling pathway requires differentiation of embryonic stem cells into odontoblast-like cells Exp Cell Res, 341 (2016), pp. 92-104 All of the authors except Nobuaki Ozeki have agreed to retract the article. Nobuaki Ozeki, the corresponding author and the first author of the article, left Aichi Gakuin University in March 2018, and does not respond to co-authors inquiries. The authors deeply regret this error and any inconvenience it may have caused.

PDGFRβ+/c-kit+ pulp cells are odontoblastic progenitors capable of producing dentin-like structure in vitro and in vivo

Background

Successful pulp regeneration depends on identification of pulp stem cells capable of differentiation under odontoblastic lineage and producing pulp-dentinal like structure. Recent studies demonstrate that platelet-derived growth factor (PDGF) plays an important role in damage repair and tissue regeneration. The aim of this study was to identify a subpopulation of dental pulp cells responsive to PDGF and with dentin regeneration potential.

Methods

Pulp tissues were isolated from 12 freshly extracted human impacted third molars. Pulp cells were sorted by their expression of PDGFRβ and stem cell marker genes via flow cytometry. For the selected cells, proliferation was analyzed by a colorimetric cell proliferation assay, differentiation was assessed by real time PCR detection the expression of odontoblast marker genes, and mineralization was evaluated by Alizarin Red S staining. GFP marked PDGFRβ⁺/c-kit⁺ pulp cells were transplanted into emptied root canals of nude rat lower left incisors. Pulp-dentinal regeneration was examined by immunohistochemistry.

Results

PDGFRβ⁺/c-kit⁺ pulp cells proliferated significantly faster than whole pulp cells. In mineralization media, PDGFRβ⁺/c-kit⁺ pulp cells were able to develop under odontoblastic linage as demonstrated by a progressively increased expression of DMP1, DSPP, and osteocalcin. BMP2 seemed to enhance whereas PDGF-BB seemed to inhibit odontoblastic differentiation and mineralization of PDGFRβ⁺/c-kit⁺ pulp cells. In vivo root canal transplantation study revealed globular dentin and pulp-like tissue formation by PDGFRβ⁺/c-kit⁺ cells.

Conclusions

PDGFRβ⁺/c-kit⁺ pulp cells appear to have pulp stem cell potential capable of producing dentinal like structure in vitro and in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12903-016-0307-8) contains supplementary material, which is available to authorized users.

Stem Cells of Dental Origin: Current Research Trends and Key Milestones towards Clinical Application

Dental Mesenchymal Stem Cells (MSCs), including Dental Pulp Stem Cells (DPSCs), Stem Cells from Human Exfoliated Deciduous teeth (SHED), and Stem Cells From Apical Papilla (SCAP), have been extensively studied using highly sophisticated in vitro and in vivo systems, yielding substantially improved understanding of their intriguing biological properties. Their capacity to reconstitute various dental and nondental tissues and the inherent angiogenic, neurogenic, and immunomodulatory properties of their secretome have been a subject of meticulous and costly research by various groups over the past decade. Key milestone achievements have exemplified their clinical utility in Regenerative Dentistry, as surrogate therapeutic modules for conventional biomaterial-based approaches, offering regeneration of damaged oral tissues instead of simply “filling the gaps.” Thus, the essential next step to validate these immense advances is the implementation of well-designed clinical trials paving the way for exploiting these fascinating research achievements for patient well-being: the ultimate aim of this ground breaking technology. This review paper presents a concise overview of the major biological properties of the human dental MSCs, critical for the translational pathway “from bench to clinic.”

Indirect co-culture of stem cells from human exfoliated deciduous teeth and oral cells in a microfluidic platform

Oral epithelial-mesenchymal interactions play a key role in tooth development and assist differentiation of dental pulp. Many epithelial and mesenchymal factors in the microenvironment influence dental pulp stem cells to differentiate and regenerate. To investigate the interaction between oral cells during differentiation, we designed a microfluidic device system for indirect co-culture. The system has several advantages, such as consumption of low reagent volume, high-throughput treatment of reagents, and faster mineralization analysis. In this study, stem cells from human exfoliated deciduous teeth were treated with media cultured with human gingival fibroblasts or periodontal ligament stem cells. When human exfoliated deciduous teeth was incubated in media cultured in human gingival fibroblasts and human periodontal ligament stem cells under the concentration gradient constructed by the microfluidic system, no remarkable change in human exfoliated deciduous teeth mineralization efficiency was detected. However, osteoblast gene expression levels in human exfoliated deciduous teeth incubated with human gingival fibroblasts media decreased compared to those in human exfoliated deciduous teeth treated with human periodontal ligament stem cells media, suggesting that indirect co-culture of human exfoliated deciduous with human gingival fibroblasts may inhibit osteogenic cytodifferentiation. This microfluidic culture device allows a co-culture system set-up for sequential treatment with co-culture media and differentiation additives and facilitated the mineralization assay in a micro-culture scale.

Nanomaterials for Tissue Engineering In Dentistry

The tissue engineering (TE) of dental oral tissue is facing significant changes in clinical treatments in dentistry. TE is based on a stem cell, signaling molecule, and scaffold triad that must be known and calibrated with attention to specific sectors in dentistry. This review article shows a summary of micro- and nanomorphological characteristics of dental tissues, of stem cells available in the oral region, of signaling molecules usable in TE, and of scaffolds available to guide partial or total reconstruction of hard, soft, periodontal, and bone tissues. Some scaffoldless techniques used in TE are also presented. Then actual and future roles of nanotechnologies about TE in dentistry are presented.

Odontoblastic inductive potential of epithelial cells derived from human deciduous dental pulp

For the dentin regeneration, dental epithelial cells are indispensible and must possess odontoblastic induction capability. Epithelial cell-like stem cells were recently identified in human deciduous dental pulp (DPESCs). However, their cellular characteristics remain poorly defined. The purpose of this study was to characterize DPESCs compared to HAT-7 ameloblastic cells. Expression levels of ameloblast-specific markers [odontogenic ameloblast-associated protein (Odam), matrix metalloproteinase (Mmp)-20, amelogenin, and ameloblastin] were detected in DPESCs. Co-culturing odontoblastic MDPC-23 cells with DPESCs increased expression of odontoblast differentiation markers (Dmp1 and Dspp) from days 4 to 10, while the expression of bone sialoprotein rapidly decreased. MDPC-23 cells cultured in DPESC-conditioned medium (CM) showed increased Dspp promoter activity compared with control MDPC-23 cultures. Mineralization was first observed in the CM groups from day 4 and proceeded rapidly until day 14, whereas mineralized nodules were found from day 7 in control media-cultured cells. In conclusion, DPESCs in human deciduous pulp possess ameloblast-like characteristics and differentiation properties, and substances derived from DPESCs promote odontoblastic differentiation. Thus, our results indicate that DPESCs can be a realistic epithelial source for use in odontoblastic induction and dentin formation of dental mesenchymal cells.

Current Advance and Future Prospects of Tissue Engineering Approach to Dentin/Pulp Regenerative Therapy

Recent advances in biomaterial science and tissue engineering technology have greatly spurred the development of regenerative endodontics. This has led to a paradigm shift in endodontic treatment from simply filling the root canal systems with biologically inert materials to restoring the infected dental pulp with functional replacement tissues. Currently, cell transplantation has gained increasing attention as a scientifically valid method for dentin-pulp complex regeneration. This multidisciplinary approach which involves the interplay of three key elements of tissue engineering—stem cells, scaffolds, and signaling molecules—has produced an impressive number of favorable outcomes in preclinical animal studies. Nevertheless, many practical hurdles need to be overcome prior to its application in clinical settings. Apart from the potential health risks of immunological rejection and pathogenic transmission, the lack of a well-established banking system for the isolation and storage of dental-derived stem cells is the most pressing issue that awaits resolution and the properties of supportive scaffold materials vary across different studies and remain inconsistent. This review critically examines the classic triad of tissue engineering utilized in current regenerative endodontics and summarizes the possible techniques developed for dentin/pulp regeneration.

Odontogenic Differentiation of Human Dental Pulp Stem Cells on Hydrogel Scaffolds Derived from Decellularized Bone Extracellular Matrix and Collagen Type I

OBJECTIVES

The aim of this study was to evaluate the level of odontogenic differentiation of dental pulp stem cells (DPSCs) on hydrogel scaffolds derived from bone extracellular matrix (bECM) in comparison to those seeded on collagen I (Col-I), one of the main components of dental pulp ECM.

METHODS

DPSCs isolated from human third molars were characterized for surface marker expression and odontogenic potential prior to seeding into bECM or Col-I hydrogel scaffolds. The cells were then seeded onto bECM and Col-I hydrogel scaffolds and cultured under basal conditions or with odontogenic and growth factor (GF) supplements. DPSCs cultivated on tissue culture polystyrene (TCPS) with and without supplements were used as controls. Gene expression of dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP-1) and matrix extracellular phosphoglycoprotein (MEPE) was evaluated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and mineral deposition was observed by Von Kossa staining.

RESULTS

When DPSCs were cultured on bECM hydrogels, the mRNA expression levels of DSPP, DMP-1 and MEPE genes were significantly upregulated with respect to those cultured on Col-I scaffolds or TCPS in the absence of extra odontogenic inducers. In addition, more mineral deposition was observed on bECM hydrogel scaffolds as demonstrated by Von Kossa staining. Moreover, DSPP, DMP-1 and MEPE mRNA expressions of DPSCs cultured on bECM hydrogels were further upregulated by the addition of GFs or osteo/odontogenic medium compared to Col-I treated cells in the same culture conditions.

SIGNIFICANCE

These results demonstrate the potential of the bECM hydrogel scaffolds to stimulate odontogenic differentiation of DPSCs.

In Vivo Experiments with Dental Pulp Stem Cells for Pulp-Dentin Complex Regeneration

In recent years, many studies have examined the pulp-dentin complex regeneration with DPSCs. While it is important to perform research on cells, scaffolds, and growth factors, it is also critical to develop animal models for preclinical trials. The development of a reproducible animal model of transplantation is essential for obtaining precise and accurate data in vivo. The efficacy of pulp regeneration should be assessed qualitatively and quantitatively using animal models. This review article sought to introduce in vivo experiments that have evaluated the potential of dental pulp stem cells for pulp-dentin complex regeneration. According to a review of various researches about DPSCs, the majority of studies have used subcutaneous mouse and dog teeth for animal models. There is no way to know which animal model will reproduce the clinical environment. If an animal model is developed which is easier to use and is useful in more situations than the currently popular models, it will be a substantial aid to studies examining pulp-dentin complex regeneration.

In vitro cementoblast-like differentiation of postmigratory neural crest-derived p75(+) stem cells with dental follicle cell conditioned medium

Cranial neural crest-derived cells (CNCCs) play important role in epithelial-mesenchymal interactions during tooth morphogenesis. However, the heterogeneity of CNCCs and their tendency to spontaneously differentiate along smooth muscle or osteoblast lineages in vitro limit further understanding of their biological properties. We studied the differentiation properties of isolated rat embryonic postmigratory CNCCs, expressing p75 neurotrophin receptor (p75NTR). These p75NTR positive (p75(+)) CNCCs, isolated using fluorescence activated cell sorter, exhibited fibroblast-like morphology and characteristics of mesenchymal stem cells. Incubation of p75(+) CNCCs in dental follicle cell conditioned medium (DFCCM) combined with dentin non-collagenous proteins (dNCPs), altered their morphological features to cementoblast-like appearance. These cells also showed low proliferative activity, high ALP activity and significantly increased calcified nodule formation. Markers related to mineralization or specific to cementoblast lineage were highly expressed in dNCPs/DFCCM-treated p75(+) cells, suggesting their differentiation along cementoblast-like lineage. p75(+) stem cells selected from postmigratory CNCCs represent a pure stem cell population and could be used as a stem cell model for in vitro studies due to their intrinsic ability to differentiate to neuronal cells and transform from neuroectoderm to ectomesenchyme. They can provide a potential stem cell resource for tooth engineering studies and help to further investigate mechanisms of epithelial-mesenchymal interactions in tooth morphogenesis.

Biomineralization on enzymatically cross-linked gelatin hydrogels in the absence of dexamethasone

A mechanical stimulus and chemical induction by dexamethasone have been important factors in dental pulp stem cell (DPSC) differentiation and biomineralization. We have demonstrated that the enzymatically crosslinked gelatin hydrogels are extremely effective substrates for DPSC differentiation towards odontoblasts. DPSCs were seeded on the crosslinked hard (∼8 kPa) and soft (∼0.15 kPa) gelatin hydrogels for 35 days with and without dexamethasone. Odontogenic differentiation markers such as OCN, ALP and DSPP were upregulated after 35 days of culture on crosslinked hydrogels with and without dexamethasone. SEM and Alizarin red staining of the crosslinked hydrogels showed a biomineralized sheet of hydroxyapatite deposits laid by the DPSCs on the top surface and inside the hydrogel. We found that the DPSC differentiation and biomineralization were independent of the hydrogel stiffness and dexamethasone. We hypothesize that this biomineralization was indeed triggered by the surface chemistry of the crosslinked gelatin hydrogels since we did not observe any biomineralization on the uncrosslinked gelatin or mTG. We also showed that the DPSCs, when removed from hard hydrogel surfaces and re-seeded on a TCPS, retained their odontogenic lineage and showed a permanent mineralization effect. Our results show the potential of enzymatically crosslinked gelatin hydrogels as scaffolds for dentin regeneration.

Complete pulpodentin complex regeneration by modulating the stiffness of biomimetic matrix

Dental caries is one of the most prevalent chronic diseases in all populations. The regeneration of dentin-pulp tissues (pulpodentin) using a scaffold-based tissue engineering strategy is a promising approach to replacing damaged dental structures and restoring their biological functions. However, the current scaffolding design for pulpodentin regeneration does not take into account the distinct difference between pulp and dentin, therefore, is incapable of regenerating a complete tooth-like pulpodentin complex. In this study, we determined that scaffolding stiffness is a crucial biophysical cue to modulate dental pulp stem cell (DPSC) differentiation. The DPSCs on a high-stiffness three-dimensional (3D) nanofibrous gelatin (NF-gelatin) scaffold had more organized cytoskeletons and a larger spreading area than on a low-stiffness NF-gelatin scaffold. In the same differentiation medium, a high-stiffness NF-gelatin facilitated DPSC differentiation to form a mineralized tissue, while a low-stiffness NF-gelatin promoted a soft pulp-like tissue formation from the DPSCs. A facile method was then developed to integrate the low- and high-stiffness gelatin matrices into a single scaffold (S-scaffold) for pulpodentin complex regeneration. A 4-week in vitro experiment showed that biomineralization took place only in the high-stiffness peripheral area and formed a ring-like structure surrounding the non-mineralized central area of the DPSC/S-scaffold construct. A complete pulpodentin complex similar to natural pulpodentin was successfully regenerated after subcutaneous implantation of the DPSC/S-scaffold in nude mice for 4weeks. Histological staining showed a significant amount of extracellular matrix (ECM) formation in the newly formed pulpodentin complex, and a number of blood vessels were observed in the pulp tissue. Taken together, this work shows that modulating the stiffness of the NF-gelatin scaffold is a successful approach to regenerating a complete tooth-like pulpodentin complex.

Human Umbilical Cord Mesenchymal Stem Cells: A New Therapeutic Option for Tooth Regeneration

Tooth regeneration is considered to be an optimistic approach to replace current treatments for tooth loss. It is important to determine the most suitable seed cells for tooth regeneration. Recently, human umbilical cord mesenchymal stem cells (hUCMSCs) have been regarded as a promising candidate for tissue regeneration. However, it has not been reported whether hUCMSCs can be employed in tooth regeneration. Here, we report that hUCMSCs can be induced into odontoblast-like cells in vitro and in vivo. Induced hUCMSCs expressed dentin-related proteins including dentin sialoprotein (DSP) and dentin matrix protein-1 (DMP-1), and their gene expression levels were similar to those in native pulp tissue cells. Moreover, DSP- and DMP-1-positive calcifications were observed after implantation of hUCMSCs in vivo. These findings reveal that hUCMSCs have an odontogenic differentiation potency to differentiate to odontoblast-like cells with characteristic deposition of dentin-like matrix in vivo. This study clearly demonstrates hUCMSCs as an alternative therapeutic cell source for tooth regeneration.

Cell viability and proliferation capability of long-term human dental pulp stem cell cultures

BACKGROUND AIMS

Evaluation of cell viability is one of the most important steps of the quality control process for therapeutic use of cells. The aim of this study was to evaluate the long-term cell viability profile of human dental pulp stem cell (hDPSC) subcultures (beyond 10 passages) to determine which of these passages are suitable for clinical use and to identify the cell death processes that may occur in the last passages.

METHODS

Four different cell viability assays were combined to determine the average cell viability levels at each cell passage: trypan blue exclusion test, water-soluble tetrazolium 1 (WST-1), LIVE/DEAD Viability/Cytotoxicity Kit and electron probe x-ray microanalysis (EPXMA). Apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and caspase 4 and BCL7C Western blotting, and cell proliferation was analyzed by WST-1 and proliferating cell nuclear antigen protein detection.

RESULTS

hDPSCs showed high average cell viability levels from passages 11-14, with adequate cytoplasmic and mitochondrial functionality at these subcultures. A non-significant trend to decreased cell proliferation was found from passages 16-20. EPXMA and TUNEL analyses suggested that a pre-apoptotic process could be activated from passages 15-20 (P < 0.001), with a correlation with caspase 4 and BCL7C expression.

CONCLUSIONS

hDPSCs corresponding to passages 11-14 show adequate cell function, proliferation and viability. These cells could be considered as potentially useful for clinical applications.

Lithium chloride promotes the odontoblast differentiation of hair follicle neural crest cells by activating Wnt/β-catenin signaling

The Wnt/β-catenin signalling pathway contributes to the maintenance of pluripotency and partial reprogramming of stem cells. Postnatal neural crest cells (NCCs) can differentiate into odontoblast-like cells due to their multi-potential property, but further endeavors need to be made to promote odontogenic differentiation of hair follicle neural crest cells (hfNCCs). This study investigated whether the Wnt pathway activator lithium chloride (LiCl) promotes odontoblast differentiation of hfNCCs. Change of proliferation, β-catenin and pluripotency markers of hfNCCs were examined after treatment with LiCl. An in vitro odontoblast differentiation model of hfNCCs was built using dental cell conditioned media (DC-CM). The effects of LiCl on odontoblast differentiation of hfNCCs showed that proliferation and expression of β-catenin in the cytosolic and nuclear compartments were increased in the LiCl-treated hfNCCs, and the pluripotency marks, Oct4, Klf4, Sox2 and Nanog, were more highly expressed in the LiCl-treated group than in the control group. The odontoblast markers such as DSP, DMP1 and Runx2, could be detected in hfNCCs induced by DC-CM, but in LiCl -treated group all three markers had stronger expression. Expression of β-catenin in the nuclear of LiCl-treated hfNCCs induced by DC-CM was higher than in the other groups. The data indicate that the Wnt pathway activator LiCl can promote proliferation and odontoblast differentiation of hfNCCs, and chemical approaches are of benefit in obtaining more desirable seed cell types for cell-based therapies.

Proliferation and odontogenic differentiation of BMP2 gene‑transfected stem cells from human tooth apical papilla: an in vitro study

Stem cells from the apical papilla (SCAP) have odontogenic potential, which plays a pivotal role in the root dentin development of permanent teeth. Human bone morphogenetic protein 2 (BMP2) is a well-known gene that participates in regulating the odontogenic differentiation of dental tissue-derived stem cells. However, little is known regarding the effects of the BMP2 gene on the proliferation and odontogenic differentiation of SCAP. This study aimed to evaluate the odontogenic differentiation potential of lentiviral-mediated BMP2 gene-transfected human SCAP (SCAP/BMP2) in vitro. SCAP were isolated by enzymatic dissociation of human teeth apical papillae. The multipotential of SCAP was verified by their osteogenic and adipogenic differentiation characteristics. The phenotype of SCAP was evaluated by flow cytometry (FCM). The proliferation status of the blank vector-transfected SCAP (SCAP/Vector) and SCAP/BMP2 was analyzed by a cell counting kit-8 (CCK-8). Odontogenic genes, including alkaline phosphatase (ALP), osteocalcin (OCN), dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1) of the two groups of cells were evaluated by quantitative polymerase chain reaction (qPCR). ALP staining and alizarin red (AR) staining of the cells was performed on the 16th day after transfection. In vitro results of CCK-8, qPCR, ALP and AR staining demonstrated that: i) SCAP/BMP2 had a comparable proliferation rate to SCAP/Vector; ii) SCAP/BMP2 presented significantly better potential to differentiate into odontoblasts compared to SCAP/Vector by upregulating ALP, OCN, DSPP and DMP1 genes; iii) more ALP granules and mineralized deposits were formed by SCAP/BMP2 as compared to SCAP/Vector. The results suggested that lentiviral-mediated BMP2 gene transfection enhances the odontogenic differentiation capacity of human SCAP in vitro.

Bone marrow stromal cell paracrine factors direct osteo/odontogenic differentiation of dental pulp cells

Growth factors play an important role in osteo/odontogenic differentiation of human dental pulp cells (hDPCs). The aim of this in vitro study was to compare the biological effects of recombinant human growth differentiation factor 5 (rhGDF-5) alone and a cocktail of soluble growth factors (conditioned medium) released from human bone marrow mesenchymal stem cells (hBMMSCs) on the morphology, proliferation and osteo/odontogenic differentiation potential of hDPCs. Passage 4 hDPCs were harvested for culture in four different media: (a) DMEM with 10% FBS, (b) odontogenic induction medium (OM), (c) OM plus 500 ng/mL rhGDF-5, and (d) OM plus conditioned medium (CM). Morphological changes at 48 and 120 h were determined by crystal violet staining. The proliferation rates at 3, 24, 48, and 120 h were assayed by MTT. Using real-time reverse transcription-polymerase chain reaction (RT-PCR), the mRNA levels of dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP1), collagen type I (Col 1), Runt-related transcription factor 2 (Cbfa1/Runx2), alkaline phosphatase (ALP), osteocalcin (OC), β3 tubulin (TUBB3), glial cell-derived neurotrophic factor (GDNF), angiopoietin-1 (Ang1), and vascular endothelial growth factor A (VEGFA), were determined at 2, 5, and 9 days. Protein expression of dental sialoprotein (DSP), DMP1, OC, and TUBB3 was recorded at 5 days, using western blot and immunocytochemistry. The effect of the different culture media on mineralization was determined by ALP staining at day 5 and Alizarin red S staining at days 7 and 14. In response to the different culture media, the shape of the hDPCs varied from spindled to polygonal and cuboidal. CM inhibited the cellular proliferation rate, while rhGDF-5 had no effect at early time points, but promoted cellular proliferation at 120 h of culture. In the CM group, the mRNA levels of Cbfa1/Runx2, Col 1, ALP, VEGFA, Ang1, and TUBB3 decreased and the levels of GDNF and OC increased. The mRNA levels of DSPP and DMP1 were inconsistent at the time points evaluated. The staining assays also demonstrated that compared with the other groups, the CM group exhibited lower expression of ALP and higher mineralization levels. Protein expression of DSP, DMP1, OC, and TUBB3 was pronounced by the CM-treated cells. It is concluded that under these in vitro conditions, CM released from hBMMSCs have a greater osteo/odontogenic inductive effect on hDPCs than rhGDF-5.

Intrafibrillar-silicified collagen scaffolds enhance the osteogenic capacity of human dental pulp stem cells

OBJECTIVES

The present study investigated the effects of intrafibrillar-silicified collagen scaffolds (ISCS) on the osteogenic differentiation of human dental pulp stem cells (hDPSCs) in vitro and in vivo.

METHODS

The hDPSCs were co-cultured with ISCS or nonsilicified collagen scaffolds (NCS) in control medium (CM) or osteogenic differentiation medium (ODM). Cell cycle and cell apoptosis were analyzed with flow cytometry to measure the viability of hDPSCs. Reverse transcription-polymerase chain reaction (RT-PCR) and western blotting were used to evaluate the expression levels of osteogenic marker genes and proteins of hDPSCs. Alkaline phosphatase (ALP) staining and alizarin red S assay were used to evaluate the ALP activity of hDPSCs and their calcium deposition potential. In addition, hDPSCs and scaffolds were implanted subcutaneously in nude mice for 8 weeks. Harvested tissues were immunohistochemically stained for osteocalcin (OCN) expression from hDPSCs, and stained with alizarin red S for examination of their calcium deposition in vivo.

RESULTS

The ISCS had no adverse effect on hDPSCs, promoted their proliferation, and significantly up-regulated the expression of osteogenesis-related genes and proteins. The hDPSCs co-cultured with ISCS in ODM exhibited the highest ALP activity and calcium deposition in vitro. The ISCS promoted the OCN expression and calcium deposition of hDPSCs after ectopic transplantation in vivo.

CONCLUSIONS

Intrafibrillar-silicified collagen scaffolds significantly promoted the proliferation, osteogenic differentiation and mineralization of hDPSCs, when compared with NCS. This study demonstrates combining the use of hDPSCs and ISCS to promote bone-like tissue formation is a promising approach for clinical bone repair and regeneration.

Differentiation of human skeletal muscle stem cells into odontoblasts is dependent on induction of α1 integrin expression

Skeletal muscle stem cells represent an abundant source of autologous cells with potential for regenerative medicine that can be directed to differentiate into multiple lineages including osteoblasts and adipocytes. In the current study, we found that α7 integrin-positive human skeletal muscle stem cells (α7(+)hSMSCs) could differentiate into the odontoblast lineage under specific inductive conditions in response to bone morphogenetic protein-4 (BMP-4). Cell aggregates of FACS-harvested α7(+)hSMSCs were treated in suspension with retinoic acid followed by culture on a gelatin scaffold in the presence of BMP-4. Following this protocol, α7(+)hSMSCs were induced to down-regulate myogenic genes (MYOD and α7 integrin) and up-regulate odontogenic markers including dentin sialophosphoprotein, matrix metalloproteinase-20 (enamelysin), dentin sialoprotein, and alkaline phosphatase but not osteoblastic genes (osteopontin and osteocalcin). Following retinoic acid and gelatin scaffold/BMP-4 treatment, there was a coordinated switch in the integrin expression profile that paralleled odontoblastic differentiation where α1β1 integrin was strongly up-regulated with the attenuation of muscle-specific α7β1 integrin expression. Interestingly, using siRNA knockdown strategies revealed that the differentiation-related expression of the α1 integrin receptor positively regulates the expression of the odontoblastic markers dentin sialophosphoprotein and matrix metalloproteinase-20. These results strongly suggest that the differentiation of α7(+)hSMSCs along the odontogenic lineage is dependent on the concurrent expression of α1 integrin.

Three-dimensional spheroid culture promotes odonto/osteoblastic differentiation of dental pulp cells

OBJECTIVE

Three-dimensional (3D) spheroid culture is a method for creating 3D aggregations of cells and their extracellular matrix without a scaffold mimicking the actual tissues. The aim of this study was to evaluate the effects of 3D spheroid culture on the phenotype of immortalized mouse dental papilla cells (MDPs) that have the ability to differentiate into odontoblasts.

METHODS

We cultured MDPs for 1, 3, 7, and 14 days in 96-well low-attachment culture plates for 3D spheroid culture or flat-bottomed plates for two-dimensional (2D) monolayer culture. Cell proliferation and apoptosis were detected by immunohistochemical staining of Ki67 and cleaved caspase-3, respectively. Hypoxia was measured by the hypoxia probe LOX-1. Odonto/osteoblastic differentiation marker gene expression was evaluated by quantitative PCR. We also determined mineralized nodule formation, alkaline phosphatase (ALP) activity, and dentine matrix protein-1 (DMP1) expression. Vinculin and integrin signalling-related proteins were detected immunohistochemically.

RESULTS

Odonto/osteoblastic marker gene expression and mineralized nodule formation were significantly up-regulated in 3D spheroid-cultured MDPs compared with those in 2D monolayer-cultured MDPs (p<0.05). Histologically, 3D spheroid colonies consisted of two compartments: a cell-dense peripheral zone and cell-sparse core zone. Proliferating cells with high ALP activity and DMP1 expression were found mainly in the peripheral zone that also showed strong expression of vinculin and integrin signalling-related proteins. In contrast, apoptotic and hypoxic cells were detected in the core zone.

CONCLUSION

3D spheroid culture promotes odonto/osteoblastic differentiation of MDPs, which may be mediated by integrin signalling.

Mineral trioxide aggregate enhances the odonto/osteogenic capacity of stem cells from inflammatory dental pulps via NF-κB pathway

OBJECTIVE

This study was designed to investigate the effects of mineral trioxide aggregate (MTA) on the osteo/odontogenic differentiation of inflammatory dental pulp stem cells (iDPSCs).

MATERIALS AND METHODS

inflammatory DPSCs were isolated from the inflammatory pulps of rat incisors and cocultured with MTA-conditioned medium. MTT assay and flow cytometry were performed to evaluate the proliferation of iDPSCs. Alkaline phosphatase (ALP) activity, alizarin red staining, real-time RT-PCR, and Western blot assay were used to investigate the differentiation capacity as well as the involvement of NF-κB pathway in iDPSCs.

RESULTS

Mineral trioxide aggregate-treated iDPSCs demonstrated the higher ALP activity and formed more mineralized nodules than the untreated group. The odonto/osteoblastic markers (Alp, Runx2/RUNX2, Osx/OSX, Ocn/OCN, and Dspp/DSP, respectively) in MTA-treated iDPSCs were significantly upregulated as compared with untreated iDPSCs. Mechanistically, cytoplastic phos-P65 and nuclear P65 in MTA-treated iDPSCs were significantly increased in a time-dependent manner. Moreover, the inhibition of NF-κB pathway suppressed the MTA-induced odonto/osteoblastic differentiation of iDPSCs, as indicated by decreased ALP levels, weakened mineralization capacity and downregulated levels of odonto/osteoblastic genes (Osx, Ocn, and Dspp).

CONCLUSIONS

Mineral trioxide aggregate enhances the odonto/osteogenic capacity of DPSCs from inflammatory sites via activating the NF-κB pathway.

Dental pulp stem cells from traumatically exposed pulps exhibited an enhanced osteogenic potential and weakened odontogenic capacity

OBJECTIVES

Traumatic pulp exposure can bring about some permanent damages to tooth tissues including dental pulps. This study was designed to evaluate the effects of traumatic pulp exposure on the osteo/odontogenic capacity of dental pulp stem cells (DPSCs).

METHODS

Rat incisors were artificially fractured and dental pulps were exposed to the oral environment for 48 h. Then, multi-colony-derived DPSCs from the injured pulps (iDPSCs) were isolated. Their osteo/odontogenic differentiation and the involvement of NF-κB pathway were subsequently investigated.

RESULTS

iDPSCs presented a lower proliferative capacity than normal DPSCs (nDPSCs), as indicated by MTT and FCM assay. ALP levels in iDPSCs were significantly higher (P<0.01) than those in nDPSCs. Alizarin red staining revealed that iDPSCs exhibited an increased capacity of calcium deposition. Moreover, iDPSCs expressed stronger osteogenic markers (Runx2/RUNX2 and Ocn/OCN) and less odontogenic gene/protein (Dspp/DSP) than nDPSCs in vitro. In vivo transplantation showed that nDPSCs implants generated the typical dentine-pulp complex while all iDPSCs pellets formed the osteodentin-like tissues which were immunopositive for OCN. Mechanistically, iDPSCs expressed the higher levels of cytoplasmic phosphorylated IκBα/P65 and nuclear P65 than nDPSCs, indicating an active cellular NF-κB pathway in iDPSCs. After the inhibition of NF-κB pathway, the osteogenic potential in iDPSCs was significantly down-regulated while odontogenic differentiation was up-regulated, as indicated by the decreased Alp/Runx2/Ocn and uprised Dspp expression.

CONCLUSIONS

Pulp exposure for 48 h decreased the odontogenic capacity and enhanced the osteogenic potential of DPSCs via the NF-κB signalling pathway.