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

Exploring the impact of oral bacteria remnants on stem cells from the Apical papilla: mineralization potential and inflammatory response

Introduction

Bacterial persistence is considered one of the main causal factors for regenerative endodontic treatment (RET) failure in immature permanent teeth. This interference is claimed to be caused by the interaction of bacteria that reside in the root canal with the stem cells that are one of the essentials for RET. The aim of the study was to investigate whether prolonged exposure of stem cells from the apical papilla (SCAP) to bacterial remnants of Fusobacterium nucleatum, Actinomyces gerensceriae, Slackia exigua, Enterococcus faecalis, Peptostreptococcaceae yurii, commonly found in infected traumatized root canals, and the probiotic bacteria Lactobacillus gasseri and Limosilactobacillus reuteri, can alter SCAP's inflammatory response and mineralization potential.

Methods

To assess the effect of bacterial remnants on SCAP, we used UV-C-inactivated bacteria (as cell wall-associated virulence factors) and bacterial DNA. Histochemical staining using Osteoimage Mineralization Assay and Alizarin Red analysis was performed to study SCAP mineralization, while inflammatory and osteo/odontogenic-related responses of SCAPs were assessed with Multiplex ELISA.

Results

We showed that mineralization promotion was greater with UV C-inactivated bacteria compared to bacterial DNA. Immunofluorescence analysis detected that the early mineralization marker alkaline phosphatase (ALP) was increased by the level of E. coli lipopolysaccharide (LPS) positive control in the case of UV-C-inactivated bacteria; meanwhile, DNA treatment decreased the level of ALP compared to the positive control. SCAP's secretome assessed with Multiplex ELISA showed the upregulation of pro-inflammatory factors IL-6, IL-8, GM-CSF, IL-1b, neurotrophic factor BDNF, and angiogenic factor VEGF, induced by UV-C-killed bacteria.

Discussion

The results suggest that long term stimulation (for 21 days) of SCAP with UV-C-inactivated bacteria stimulate their mineralization and inflammatory response, while DNA influence has no such effect, which opens up new ideas about the nature of RET failure.

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.

Stem Cells from the Apical Papilla (SCAPs): Past, Present, Prospects, and Challenges

Dental diseases occurring on young permanent teeth usually lead to the premature arrest of tooth root development. Sustained tooth root elongation is necessary to achieve the goal of long-term preservation of affected teeth. To this end, stem cell-based regenerative endodontic treatment has been regarded as one of the most promising strategies for treating young permanent teeth with pulp and periapical infections. Endogenous stem cells residing in the apical papilla, named stem cells from the apical papilla (SCAPs), have been intensively investigated due to their critical roles in pulp regeneration and root redevelopment. The present review summarizes advances in the field of SCAPs studies and discusses the challenges that need to be further addressed.

Dentin regeneration based on tooth tissue engineering: A review

Missing or damaged teeth due to caries, genetic disorders, oral cancer, or infection may contribute to physical and mental impairment that reduces the quality of life. Despite major progress in dental tissue repair and those replacing missing teeth with prostheses, clinical treatments are not yet entirely satisfactory, as they do not regenerate tissues with natural teeth features. Therefore, much of the focus has centered on tissue engineering (TE) based on dental stem/progenitor cells to create bioengineered dental tissues. Many in vitro and in vivo studies have shown the use of cells in regenerating sections of a tooth or a whole tooth. Tooth tissue engineering (TTE), as a promising method for dental tissue regeneration, can form durable biological substitutes for soft and mineralized dental tissues. The cell-based TE approach, which directly seeds cells and bioactive components onto the biodegradable scaffolds, is currently the most potential method. Three essential components of this strategy are cells, scaffolds, and growth factors (GFs). This study investigates dentin regeneration after an injury such as caries using TE and stem/progenitor cell-based strategies. We begin by discussing about the biological structure of a dentin and dentinogenesis. The engineering of teeth requires knowledge of the processes that underlie the growth of an organ or tissue. Then, the three fundamental requirements for dentin regeneration, namely cell sources, GFs, and scaffolds are covered in the current study, which may ultimately lead to new insights in this field.

Comparative characterization and analysis of telomere length in stem cells derived from deciduous and permanent teeth

Background

Understanding the influence of age on growth kinetics and telomere length in dental stem cells is essential for the successful development of cell therapies. Hence, the present study compared the basic cellular and phenotypical characteristics of stem cells from human exfoliated deciduous teeth (SHEDs) and dental pulp stem cells (DPSCs) of permanent teeth and their telomere lengths using quantitative real-time polymerase chain reaction.

Materials and Methods

The study is an in vitro original research article. Primary cultures of SHED and DPSCs (n = 6 each) were successfully established in vitro, and the parameters analyzed were the morphology, viability, proliferation rate, population doubling time (PDT), phenotypic markers expression, and the relative telomere lengths. Data were analyzed by analysis of variance and P < 0.05 was considered statistically significant.

Results

SHED and DPSCs exhibited a small spindle-shaped fibroblast-like morphology with >90% viability. The proliferation assay showed that the cells had a typical growth pattern. The PDT values of SHED and DPSCs were 29.03 ± 9.71 h and 32.05 ± 9.76 h, respectively. Both cells were positive for surface markers CD29, CD44, and CD90. However, they were negative for CD45 and human leukocyte antigen DR. Although the differences in relative telomere lengths between the individual cell lines of SHED and DPSCs were observed, no significant (P > 0.05) variations were found for the mean T/S ratios of both the cells.

Conclusion

SHED and DPSCs displayed similar morphology, proliferation rates, and phenotypic features. The relative telomere lengths were slightly shorter in DPSCs than SHED, but the values were not significantly different. Thus, SHED and DPSCs can be considered as recognized sources for regenerative applications in dentistry.

Effects of inflammation in dental pulp cell differentiation and reparative response

The responsiveness of the dentin-pulp complex is possible due to the stimulation of dental pulp cells, which begin to synthesize and secrete dentin matrix. The inflammatory process generated by harmful stimuli should be understood as a natural event of the immune response, resulting in the recruitment of hematopoietic cells, which cross the endothelial barrier and reach the site affected by the injury in order to eliminate the damage and provide an appropriate environment for the restoration of homeostasis. The repair process occurs in the presence of adequate blood supply, absence of infection, and with the participation of pro-inflammatory cytokines, growth factors, extracellular matrix components, and other biologically active molecules. Prostaglandins and leukotrienes are bioactive molecules derived from the metabolism of arachidonic acid, as a result of a variable range of cellular stimuli. The aim of this review is to describe the process of formation and biomineralization of the dentin-pulp complex and how pro-inflammatory events can modify this response, with emphasis on the lipid mediators prostaglandins and leukotrienes derived from arachidonic acid metabolism.

Effect of lentivirus-mediated BMP2 from autologous tooth on the proliferative and osteogenic capacity of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Periodontitis is a chronic progressive inflammation that invades periodontal supporting tissues, in which periodontal tissue regeneration engineering offers new hope for prevention and treatment, including seed cells, scaffolds, and growth factors. In recent years, scholars have shown that autologous teeth can be used as new bone tissue repair materials for periodontal regeneration and bone tissue repair. The aim of this study was to establish a human periodontal ligament cell line that expresses the human bone morphogenetic protein 2 gene (BMP2) in a stable manner using lentiviral mediation in order to explore the effect of BMP2 from autologous tooth on the proliferative and osteogenic capacity of human periodontal ligament cells (hPDLCs).

MATERIALS AND METHODS

Human periodontal ligament cells were cultured, subcultured, and identified, and then homologous recombinant lentivirus plasmid plv-BMP2 was constructed and transfected into the third passage (P₃ ) hPDLCs. After that, the effect of BMP2 on its proliferation was detected by CCK-8, at the same time, the osteogenic induction of hPDLCs was carried out at 7, 14, and 21 days, and then the effect of BMP2 on its osteogenic ability was detected by alizarin red staining, alkaline phosphatase activity determination, and the mRNA expression levels of osteogenic-related genes using real-time fluorescence quantitative PCR, including alkaline phosphatase, runt-related transcription factor 2, bone sialoprotein, osteocalcin, osteopontin, and collagen I. Finally, spss26.0 software was used for statistical processing.

RESULTS

The results showed that cells transfected with the homologous recombinant lentiviral plasmid pLV-BMP2 had a similar morphology to normal hPDLCs, showing a typical radial arrangement; the cell proliferative capacity of the pLV-BMP2 group as measured by CCK-8 was enhanced compared with the control group and the pLV-puro group (p < .05); alizarin red staining and alkaline phosphatase activity assay showed that the osteogenic ability of pLV-BMP2 was significantly enhanced compared with the control and pLV-puro groups (p < .01), and the findings of real-time fluorescence-based quantitative PCR showed high expression of osteogenic-related genes in pLV-BMP2 group (p < .01).

CONCLUSION

In conclusion, a stable periodontal ligament cell line overexpressing BMP2 was successfully established by a lentivirus-mediated method, which proved that BMP2 has a strong ability to promote the proliferation and osteogenesis of hPDLCs, thereby providing an opportunity for the study of periodontal tissue regeneration as well as providing an experimental basis for the application of autologous teeth as a new type of bone repair material for periodontal therapy and even for maxillofacial bone tissue repair.

The Effect of LncRNA H19 on Human Dental Pulp Cells Through Tumor Growth Factor-β1 (TGF-β1)/Smad Signaling Pathway

The pulp tissue is located in the pulp cavity of tooth and has the ability of nutrition, feeling, and defense. Human dental pulp cells (hDPCs) are the main cells of pulp with the ability to self-renew and multi-directional differentiation. LncRNA H19 is involved in the regulation of human dental pulp stem cells, but the specific mechanism has not been elucidated. hDPCs were isolated and cultured in vitro to measure vimentin expression by immunohistochemistry (IHC). hDPCs were randomly assigned into control group, negative control (NC) group and lncRNA H19 overexpression group followed by measuring lncRNA H19, DSPP, and DMP-1 mRNA expression, cell proliferation, ALP activity, BMP-2 expression by ELISA, TGF-β1, Smad2, and Smad4 expression by Western blot. hDPCs were positive for vimentin staining and confirmed to be derived from mesenchymal. Transfection of pcDNA3.1-LncRNA H19 plasmid significantly increased LncRNA H19 expression, promoted cell proliferation, enhanced ALP activity, upregulated DSPP and DMP-1, elevated BMP-2 expression in cell supernatant, as well as promoted TGF-β1, Smad2, and Smad4 expressions compared with control (P < 0.05). In conclusion, lncRNA H19 facilitates hDPCs differentiation into odontoblasts by promoting cell proliferation and increasing BMP-2 secretion via regulating TGF-β1/Smad signaling pathway.

Dynamically Bioresponsive DNA Hydrogel Incorporated with Dual-Functional Stem Cells from Apical Papilla-Derived Exosomes Promotes Diabetic Bone Regeneration

The regeneration of bone defects in patients with diabetes mellitus (DM) is remarkably impaired by hyperglycemia and over-expressed proinflammatory cytokines, proteinases (such as matrix metalloproteinases, MMPs), etc. In view of the fact that exosomes represent a promising nanomaterial, herein, we reported the excellent capacity of stem cells from apical papilla-derived exosomes (SCAP-Exo) to facilitate angiogenesis and osteogenesis whether in normal or diabetic conditions in vitro. Then, a bioresponsive polyethylene glycol (PEG)/DNA hybrid hydrogel was developed to support a controllable release of SCAP-Exo for diabetic bone defects. This system could be triggered by the elevated pathological cue (MMP-9) in response to the dynamic diabetic microenvironment. It was further confirmed that the administration of the injectable SCAP-Exo-loaded PEG/DNA hybrid hydrogel into the mandibular bone defect of diabetic rats demonstrated a great therapeutic effect on promoting vascularized bone regeneration. In addition, the miRNA sequencing suggested that the mechanism of dual-functional SCAP-Exo might be related to highly expressed miRNA-126-5p and miRNA-150-5p. Consequently, our study provides valuable insights into the design of promising bioresponsive exosome-delivery systems to improve bone regeneration in diabetic patients.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

CDR1as regulated by hnRNPM maintains stemness of periodontal ligament stem cells via miR-7/KLF4

CDR1as is a well‐identified circular RNA with regulatory roles in a variety of physiological processes. However, the effects of CDR1as on stemness of periodontal ligament stem cells (PDLSCs) and the underlying mechanisms remain unclear. In this study, we detect CDR1as in human PDLSCs, and subsequently demonstrate that CDR1as maintains PDLSC stemness. Knockdown of CDR1as decreases the expression levels of stemness‐related genes and impairs the cell's multi‐differentiation and cell migration abilities, while overexpression of CDR1as increases the expression levels of stemness‐related genes and enhances these abilities. Furthermore, our results indicate that the RNA‐binding protein hnRNPM directly interacts with CDR1as and regulates its expression in PDLSCs. In addition, we show that CDR1as promotes the expression of stemness‐related genes in PDLSCs by inhibiting miR‐7‐mediated suppression of KLF4 expression. Collectively, our results demonstrate that CDR1as participates in the molecular circuitry that regulates PDLSC stemness.

Effects of Platelet-Rich Plasma on Proliferation, Viability, and Odontogenic Differentiation of Neural Crest Stem-Like Cells Derived from Human Dental Apical Papilla

Objective

This study is aimed at evaluating the effects of platelet-rich plasma (PRP) on proliferation, viability, and odontogenic differentiation of neural crest stem-like cells (NCSCs) derived from human dental apical papilla.

Materials and Methods

Cells from apical papillae were obtained and then induced to form neural spheres. The expression of NCSC markers p75NTR and HNK-1 in neural sphere cells was detected by immunofluorescence staining. Human PRP was prepared by a 2-step centrifugation method and activated by CaCl₂ and thrombin. The concentrations of PDGF-BB and TGF-β1 in whole blood and PRP were measured by an ELISA kit. PRP in five different concentrations (0%, 2.5%, 5%, 10%, and 25%) was applied to culture NCSCs. On the 1^st, 3^rd, 5^th, and 7^th days, cell proliferation was evaluated by CCK8. Cell viability was tested by a live/dead staining kit. mRNA and protein expression of DSPP and BMP4 were analyzed by RT-qPCR and western blot, respectively. Statistical analysis was performed by a one-way analysis of variance (ANOVA) test or t-test.

Results

Dental apical papilla cells formed neural spheres, from which cells displayed positive expression of p75NTR and HNK-1. The concentrations of PDGF-BB and TGF-β1 in PRP were about 3.5-fold higher than those in whole blood. 5% and 10% PRP significantly promoted proliferation of NCSCs, while 25% and 50% PRP inhibited cell proliferation from Day 3 to Day 7. Low-concentration (2.5%, 5%, and 10%) PRP slightly improved viability of NCSCs on Day 7. On the other hand, high-concentration (25% and 50%) PRP significantly inhibited viability of NCSCs from Day 3 to Day 7. RT-qPCR and western blot results indicated that 10% PRP could promote odontogenic differentiation of NCSCs on Day 7. mRNA and protein expression of DSPP and BMP4 were significantly upregulated in the 10% PRP group compared to those in the control group (P < 0.05).

Conclusions

PRP is a simply acquirable blood derivative which contains high concentration of growth factors like PDGF-BB and TGF-β1. PRP in a proper concentration could promote proliferation, viability, and odontogenic differentiation of NCSCs derived from human dental apical papilla.

GATA Binding Protein 4 Regulates Tooth Root Dentin Development via FBP1

Tooth development is a complex process that is regulated precisely by several signalling pathways and transcription factors. GATA-binding protein 4 (GATA4) is a DNA binding transcription factor, and our previous study showed that GATA4 is a novel regulator of root development. However, it remains unclear whether GATA4 is necessary for odontoblast differentiation and dentin formation. Here, we evaluated the phenotypic changes of Wnt1-Cre;GATA4^fl/fl mice. The mutant mice showed defective dentin and short root deformity. The odontoblasts lost polarity instead of exhibiting a shorter height and flattened morphology. Moreover, the expression of several molecules, such as DSPP, COL-1, DCN, and PCNA, were downregulated during mutant tooth development. In vivo, we injected lentivirus to overexpress GATA4 in mice root. The dentin formation and the expression of odonto/osteogenic markers (DSPP, COL-1, DCN) were enhanced in the GATA4 overexpression group. During the in vitro study, the ability of proliferation, migration and odonto/osteogenic differentiation was declined by GATA4 knockdown approach in human dental pulp stem cells (DPSCs). The expression of odonto/osteogenic markers (DSPP, BMP4, RUNX2, OSX, OPN, OCN) was reduced in the shGATA4 group, while overexpressing GATA4 in DPSCs promoted mineralization. Furthermore, an immunoprecipitation-mass spectrometry procedure was used to confirm the interaction between GATA4 and Fructose-1, 6-bisphosphatase 1 (FBP1). We used gain and lose-of-function to delineated the role of GATA4 in regulating FBP1 expression. Knocking down GATA4 in DPSCs resulted in decreased glucose consumption and lactate production. We used small hairpin RNA targeting FBP1 to reduce the expression of FBP1 in DPSCs, which significantly increased glucose consumption and lactate production. Together, the results suggested that GATA4 is important for root formation and odontoblast polarity, as it promotes the growth and differentiation of dental mesenchymal cells around the root and affects the glucose metabolism of DPSCs via the negative regulation of FBP1.

Matin M. Odontoblast-like Cytodifferentiation of Dental Stem Cells: A Review

Dental problems are common in human populations. Traditional treatments are focused on managing caries, soft tissue impairments, functional defects, poor aesthetics, digestive disorders and alveolar bone resorption. During the last two decades, basic and clinical researches on adult stem cells have established a potential therapeutic concept in tissue regeneration. Among major cells responsible for tooth development, odontoblasts play a key role in the formation of organic and inorganic constituents of dental tissue. A premier stride in the development of novel stem cell-based strategies for the treatment of reversible and irreversible pulpitis is odontoblast regeneration. Among different candidate cell sources for odontoblastic regeneration, use of dental adult stem cells is a preferred option because of their great ability to differentiate into odontoblasts and also their minimally invasive isolation procedure. This review emphasizes on articles that report successful odontoblast-like differentiation of dental mesenchymal stem cells which in turn provide a background for dentin-pulp complex cell therapies, using genetic or chemical manipulation. The series of experiments both in vitro and in vivo asserted that dental mesenchymal stem cells can efficiently differentiate into functional odontoblast-like cells. However, the review shows there are drawbacks in present methods. Future research should focus on optimizing protocols on odontoblast differentiation of dental stem cells by simultaneously introducing different genes with mutual synergy, combined with chemical or recombinant protein introduction.

Magnesium-enriched microenvironment promotes odontogenic differentiation in human dental pulp stem cells by activating ERK/BMP2/Smads signaling

Background

Magnesium (Mg²⁺)-enriched microenvironment promotes odontogenic differentiation in human dental pulp stem cells (DPSCs), but the regulatory mechanisms remain undefined. The aim of this work was to assess magnesium’s function in the above process and to explore the associated signaling pathway.

Methods

DPSCs underwent culture in odontogenic medium with the addition of 0, 1, 5, or 10 mM MgCl₂. Intracellular Mg²⁺ levels in DPSCs were evaluated flow cytometrically using Mag-Fluo-4-AM. Mg²⁺-entry was inhibited by TRPM7 inhibitor 2-aminoethoxydiphenyl borate (2-APB). RNA-Sequencing was carried out for assessing transcriptome alterations in DPSCs during odontogenic differentiation associated with high extracellular Mg²⁺. KEGG pathway analysis was performed to determine pathways related to the retrieved differentially expressed genes (DEGs). Immunoblot was performed for assessing magnesium’s role and exploring ERK/BMP2/Smads signaling.

Results

Mg²⁺-enriched microenvironment promoted odontogenic differentiation in DPSCs via intracellular Mg²⁺ increase. Consistently, the positive effect of high extracellular Mg²⁺ on odontogenic differentiation in DPSCs was blocked by 2-APB, which reduced Mg²⁺ entry. RNA-sequencing identified 734 DEGs related to odontogenic differentiation in DPSCs in the presence of high extracellular Mg²⁺. These DEGs participated in many cascades such as MAPK and TGF-β pathways. Consistently, ERK and BMP2/Smads pathways were activated in DPSCs treated with high extracellular Mg²⁺. In agreement, ERK signaling inhibition by U0126 blunted the effect of high extracellular Mg²⁺ on mineralization and odontogenic differentiation in DPSCs. Interestingly, BMP2, BMPR1, and phosphorylated Smad1/5/9 were significantly decreased by U0126, indicating that BMP2/Smads acted as downstream of ERK.

Conclusions

Mg²⁺-enriched microenvironment promotes odontogenic differentiation in DPSCs by activating ERK/BMP2/Smads signaling via intracellular Mg²⁺ increase. This study revealed that Mg²⁺-enriched microenvironment could be used as a new strategy for dental pulp regeneration.

Prostaglandin E2 Induces Expression of Mineralization Genes by Undifferentiated Dental Pulp Cells

Abstract Prostaglandin E2 (PGE2) is a lipid mediator usually released during inflammation. This study aimed to investigate the potential of soluble or microsphere-loaded PGE2 on inducing differentiation of dental pulp stem cells. PGE2-loaded microspheres (MS) were prepared using an oil-in-water emulsion solvent extraction-evaporation process and were characterized. Mouse dental pulp stem cells (OD-21) were stimulated with soluble or PGE2-loaded MS (0.01 and 0.1 µM). Cell viability was determined by MTT colorimetric assay. Ibsp, Bmp2 and Runx2 expression was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) after 3, 6, and 24 h. The results showed that the soluble PGE2 reduced dental pulp stem cells viability after 24 h of stimulation whereas PGE2-loaded MS did not. Soluble PGE2 up-regulated Ibsp and Bmp2 at 3 h, differently from PGE2-loaded MS. On the other hand, PGE2-MS induced Bmp2 and Runx2 at 6 h and Ibsp at 24 h. In conclusion, our in vitro results show that PGE2, soluble or loaded in MS are not cytotoxic and modulateIbsp,Bmp2, andRunx2gene expression in cultured OD-21 cells.

Stem Cells from the Apical Papilla: A Promising Source for Stem Cell-Based Therapy

Stem cells are biological cells that can self-renew and can differentiate into multiple cell lineages. Stem cell-based therapy is emerging as a promising alternative therapeutic option for various disorders. Mesenchymal stem cells (MSCs) are multipotent adult stem cells that are isolated from various tissues and can be used as an alternative to embryonic stem cells. Stem cells from the apical papilla (SCAPs) are a novel population of MSCs residing in the apical papilla of immature permanent teeth. SCAPs present the characteristics of expression of MSCs markers, self-renewal, proliferation, migration, differentiation, and immunosuppression, which support the application of SCAPs in stem cell-based therapy, including the immunotherapy and the regeneration of dental tissues, bone, neural, and vascular tissues. In view of these properties and therapeutic potential, SCAPs can be considered as promising candidates for stem cell-based therapy. Thus the aim of our review was to summarize the current knowledge of SCAPs considering isolation, characterization, and multilineage differentiation. The prospects for their use in stem cell-based therapy were also discussed.

Heparin is biocompatible and can induce differentiation of human dental pulp cells

AIM

To investigate the biocompatibility, osteogenic bioactivity and mRNA expression of the osteo/odontogenic markers bone morphogenetic protein 2 (BMP-2), osteocalcin (OC) and alkaline phosphatase (ALP), induced by heparin in human dental pulp cells (hDPCs).

METHODOLOGY

hDPCs were exposed to the heparin, and cell viability was assessed by 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide (MTT), and cell death was evaluated by flow cytometry. Osteogenic bioactivity was evaluated by the alkaline phosphatase (ALP) assay, and the detection of calcium deposits by alizarin red staining (ARS). The gene expression of BMP-2, OC and ALP was quantified with real-time PCR. Statistical analysis was performed with ANOVA and Bonferroni or Tukey post-test and t-test (α = 0.05).

RESULTS

Heparin had no cytotoxic effect and did not induce apoptosis. After 3 days, heparin had significantly higher ALP activity in comparison with the control (P < 0.05). Heparin had a significant (P < 0.05) stimulatory effect on the formation of mineralized nodules. BMP-2 and OC mRNA expressions were significantly higher in cells exposed to heparin than control group after 1 day (P < 0.05).

CONCLUSIONS

Heparin was biocompatible in hDPCs, induced osteogenic bioactivity and enhanced mRNA expression of osteo/odontogenic markers BMP-2 and OC. These results suggest that heparin has potential to induce osteo/odontogenic cell differentiation of hDPCs.

Guanine and nucleotide binding protein 3 promotes odonto/osteogenic differentiation of apical papilla stem cells via JNK and ERK signaling pathways

Odonto/osteogenic differentiation of stem cells from the apical papilla (SCAPs) is a key process in tooth root formation and development. However, the molecular mechanisms underlying this process remain largely unknown. In the present study, it was identified that guanine and nucleotide binding protein 3 (GNAI3) was at least in part responsible for the odonto/osteogenic differentiation of SCAPs. GNAI3 was markedly induced in mouse tooth root development in vivo and in human SCAPs mineralization in vitro. Notably, knockdown of GNAI3 by lentiviral vectors expressing short-hairpin RNAs against GNAI3 significantly inhibited the proliferation, cell cycle progression and migration of SCAPs, as well as odonto/osteogenic differentiation of SCAPs in vitro, suggesting that GNAI3 may play an essential role in tooth root development. The promotive role of GNAI3 in odonto/osteogenic differentiation was further confirmed by downregulation of odonto/osteogenic makers in GNAI3-deficient SCAPs. In addition, knockdown of GNAI3 effectively suppressed activity of c-Jun N-terminal kinase (JNK) and extracellular-signal regulated kinase (ERK) signaling pathways that was induced during SCAPs differentiation, suggesting that GNAI3 promotes SCAPs mineralization at least partially via JNK/ERK signaling. Taken together, the present results implicate GNAI3 as a critical regulator of odonto/osteogenic differentiation of SCAPs in tooth root development, and suggest a possible role of GNAI3 in regeneration processes in dentin or other tissues.

Foxc2 and BMP2 Induce Osteogenic/Odontogenic Differentiation and Mineralization of Human Stem Cells from Apical Papilla

As a transcription factor regulated by bone morphogenetic protein 2 (BMP2), Forkhead c2 (Foxc2) plays a pivot role in osteogenesis/odontogenesis. However, the role of Foxc2 and BMP2 in regulating osteo-/odontogenic differentiation and mineralization of stem cells from apical papilla (SCAP) is still uncertain. In this research, overexpression of Foxc2 gene significantly improved the proliferation of SCAP four days and eight days after transfection, but overexpression of both Foxc2 and BMP2 genes significantly inhibited the proliferation of SCAP eight days after transfection. RT-qPCR and western blot results indicated that SCAP-Foxc2-BMP2 significantly upregulated osteo-/odontogenic genes and proteins at most of the time points in SCAP after transfection. Moreover, SCAP-Foxc2-BMP2 formed notably more alkaline phosphatase-positive and alizarin red-positive mineralized nodules than other three group cells sixteen days after transfection. In conclusion, our findings revealed that Foxc2 and BMP2 synergistically promoted osteo-/odontogenic differentiation and mineralization of SCAP in vitro.

Stem Cells From the Apical Papilla (SCAP) as a Tool for Endogenous Tissue Regeneration

Stem cells extracted from developing tissues possibly exhibit not only unique but also superior traits against their developed counterparts. Indeed, stem cells from the apical papilla (SCAP); a unique group of dental stem cells related to developing roots have been shown to be a promising tool for regenerative endodontic procedures and regeneration in general. Studies have characterized the phenotypic traits as well as other regenerative potentials of these cells. Specific sub-populations have been highlighted as well as their neurogenic and angiogenic properties. Nevertheless, in light of the previously discussed features and potential applications of SCAP, there is still much to understand and a lot of information to unravel. The current review will discuss the role of specific markers for detection of different functional populations of SCAP; including CD146 and STRO-1, as well as their true multilineage differentiation potential. In particular, the role of the secretome in association with paracrine signaling in inflammatory microenvironments is also tackled. Additionally, the role of SCAP both in vitro and in vivo during regenerative approaches and in response to different growth factors and biologic scaffolds is highlighted. Finally, this review will shed light on current knowledge regarding the clinical translational potential of SCAP and elucidate possible areas for future research applications.

Effect of Polyhydroxybutyrate/Chitosan/Bioglass nanofiber scaffold on proliferation and differentiation of stem cells from human exfoliated deciduous teeth into odontoblast-like cells

Scaffolds and their characteristics play a central role in tissue engineering. The purpose of this study was to determine the effects of Polyhydroxybutyrate (PHB)/Chitosan/nano-bioglass (nBG) nanofiber scaffold made using the electrospinning method, on the proliferation and differentiation of stem cells obtained from human exfoliated deciduous teeth into odontoblast-like cells. In this experimental study, the pulps of the molten deciduous teeth were isolated, thereafter, the stem cells from human exfoliated deciduous teeth (SHED) were extracted and then the 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the cell viability percentage. The expression of some stem cell genes was studied by flowcytometry. These cells were then subjected to odontoblast by using the bone morphogenetic proteins-2 (BMP2) growth factor in the differentiation medium and for the expression of their specific genes. Primers of collagen type-I, dentin sialophosphoprotein (DSPP) and alkaline phosphatase (ALP) were used and the percentage of differentiation to odontoblast cells in induction scaffolds was investigated using real-time PCR and immunohistochemistry methods. The results revealed a 6-fold increase in the expression of DSPP genes and collagen type-I, and a 2-fold increase in the expression of ALP in scaffold with BMP2 group compared to the scaffold as control group which according to the immunohistochemical test results, showed the extracted SHED to have been differentiated into dentin odontoblast-like cells. As a result, this scaffold can be used as a suitable substrate to apply in dentin tissue engineering.

Hey1 functions as a positive regulator of odontogenic differentiation in odontoblast‑lineage cells

Substantial evidence has indicated that Notch and bone morphogenetic protein (BMP) signaling may regulate odontoblastic differentiation. Hairy/enhancer‑of‑split related with YRPW motif 1 (Hey1), a downstream target gene of Notch and BMP signaling, is expressed in dental pulp tissues and has been demonstrated to be responsible for osteoblast mineralization. The aim of this study was to investigate the effects of Hey1 on odontoblast differentiation. The results of the study demonstrated that Hey1 expression in odontoblast‑lineage cells (OLCs) was upregulated by stimulation of osteoblastic/odontoblastic differentiation medium containing ascorbic acid, β‑glycerol phosphate and dexamethasone. Furthermore, stable Hey1‑overexpressing cells expressed higher levels of dentin sialophosphoprotein (DSPP) and exhibited higher mineralization capabilities following stimulation by differentiation medium. Furthermore, RNA interference‑mediated knockdown of Hey1 downregulated the expression levels of DSPP in OLCs stimulated by differentiation medium. Taken together, the findings indicate that Hey1 may be a positive regulator of odontoblastic differentiation. The present study broadens the understanding of odontoblast differentiation and biomineralization.

Role of GATA binding protein 4 (GATA4) in the regulation of tooth development via GNAI3

Transcription factor GATA4 regulates cardiac and osteoblast differentiation. However, its role in tooth development is not clear. Therefore, we generated Wnt1-Cre;GATA4^fl/fl mice, with conditional inactivation of the GATA4 gene in the dental papilla mesenchymal cells. Phenotypic analysis showed short root deformity along with reduced expressions of odonto/osteogenic markers. Proliferation (but not apoptosis) of cells around the apical area of the root was attenuated. In vitro, we knocked down GATA4 expression in stem cells of dental apical papilla (SCAPs). Proliferation, migration and odonto/osteogenic differentiation of SCAPs were affected in the shGATA4 group. Overexpression of GATA4 in SCAPs increased mineralization. Based on our previous iTRAQ results, guanine nucleotide binding proteins 3 (GNAI3) is one of the distinct proteins after GATA4 deletion. G protein signaling is involved in bone development, remodeling, and disease. In this study, both GATA4 deletion in the mouse root and knock-down in human SCAPs decreased the expression of GNAI3. Dual-luciferase and ChIP assay confirmed the direct binding of GATA4 to the GNAI3 promoter, both in vitro and in vivo. GNAI3 knock-down significantly decreased the odonto/osteogenic differentiation ability of SCAPs. We thus establish the role of GATA4 as a novel regulator of root development and elucidate its downstream molecular events.

Paradigm Shift from Stem Cells to Cell-Free Regenerative Endodontic Procedures: A Critical Review

Regenerative endodontic procedures of immature teeth with necrotic pulp have become a part of therapeutic endodontic spectrum and are considered as an alternative to calcium hydroxide or mineral trioxide aggregate apexification. In last decade, numerous case reports and series with usage of cell-free approaches known as revascularization, revitalization, or maturogenesis have been published. This cell-free approach prevails in clinical regenerative endodontics because of its relative ease of performance, lower financial demands, and absence of complications such as tumorigenesis of used stem cells. In this article, the integral steps of cell-free treatment approaches such as source of stem cells, possible endogenous scaffolds, sources of growth factors, and width of apical foramen in the context of sufficient disinfection of root canal system and outcome of treatment are discussed. Despite not being a fully established treatment protocol, the achieved outcomes are promising regardless of it having a reparative character than a regenerative one.

The Regulatory Effects of Long Noncoding RNA-ANCR on Dental Tissue-Derived Stem Cells

Long noncoding RNAs (lncRNA) have been recognized as important regulators in diverse biological processes, such as transcriptional regulation, stem cell proliferation, and differentiation. Previous study has demonstrated that lncRNA-ANCR (antidifferentiation ncRNA) plays a key role in regulating the proliferation and osteogenic differentiation of periodontal ligament stem cells (PDLSCs). However, little is known about the role of ANCR in regulating other types of dental tissue-derived stem cells (DTSCs) behaviours (including proliferation and multiple-potential of differentiation). In this study, we investigated the regulatory effects of lncRNA-ANCR on the proliferation and differentiation (including osteogenic, adipogenic, and neurogenic differentiation) of DTSCs, including dental pulp stem cells (DPSCs), PDLSCs, and stem cells from the apical papilla (SCAP) by downregulation of lncRNA-ANCR. We found that downregulation of ANCR exerted little effect on proliferation of DPSCs and SCAP but promoted the osteogenic, adipogenic, and neurogenic differentiation of DTSCs. These data provide an insight into the regulatory effects of long noncoding RNA-ANCR on DTSCs and indicate that ANCR is a very important regulatory factor in stem cell differentiation.

Osteo-/odontogenic differentiation of BMP2 and VEGF gene-co-transfected human stem cells from apical papilla

Stem cells from apical papilla (SCAP) possess clear osteo-/odontogenic differentiation capabilities, and are regarded as the major cellular source for root dentin development. Bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factor (VEGF) serve pivotal roles in the modulation of tooth development and dentin formation. However, the synergistic effects of BMP2 and VEGF on osteo-/odontogenic differentiation of SCAP remain unclear. The current study aimed to investigate the proliferative and osteo-/odontogenic differentiating capabilities of BMP2 and VEGF gene-co-transfected SCAP (SCAP-BMP2-VEGF) in vitro. The basic characteristics of the isolated SCAP were identified by the induction of multipotent differentiation and by flow cytometry. Lentiviral vector-mediated gene transfection was conducted with SCAP in order to construct blank vector-transfected SCAP (SCAP-green fluorescent protein), BMP2 gene-transfected SCAP (SCAP-BMP2), VEGF gene-transfected SCAP (SCAP-VEGF) and SCAP-BMP2-VEGF. The Cell Counting Kit 8 assay was used to analyze the proliferative capacities of the four groups of cells. The expression of osteo-/odontogenic genes and proteins in the cells were evaluated by reverse transcription-quantitative polymerase chain reaction and western blotting. The mineralized nodules formed by the four group cells were visualized by alkaline phosphatase (ALP) staining. Among the four groups of cells, SCAP-VEGF was demonstrated to exhibit increased proliferation, and SCAP-BMP2-VEGF exhibited reduced proliferation during eight days observation. SCAP-BMP2-VEGF exhibited significantly increased expression levels of ALP, osteocalcin, dentin sialophosphoprotein, dentin matrix acidic phosphoprotein gene 1 and dentin sialoprotein than the other three groups at the majority of the time points. Furthermore, the SCAP-BMP2-VEGF group exhibited a significantly greater number of ALP-positive mineralized nodules than the other groups following 16 days culture in vitro. In conclusion, lentiviral vector-mediated BMP2 and VEGF gene co-transfection significantly activated the osteo-/odontogenic differentiation of human SCAP.

Tooth-derived stem cells: Update and perspectives

Tissue engineering is an emerging field of science that focuses on creating suitable conditions for the regeneration of tissues. The basic components for tissue engineering involve an interactive triad of scaffolds, signaling molecules, and cells. In this context, stem cells (SCs) present the characteristics of self-renewal and differentiation capacity, which make them promising candidates for tissue engineering. Although they present some common markers, such as cluster of differentiation (CD)105, CD146 and STRO-1, SCs derived from various tissues have different patterns in relation to proliferation, clonogenicity, and differentiation abilities in vitro and in vivo. Tooth-derived tissues have been proposed as an accessible source to obtain SCs with limited morbidity, and various tooth-derived SCs (TDSCs) have been isolated and characterized, such as dental pulp SCs, SCs from human exfoliated deciduous teeth, periodontal ligament SCs, dental follicle progenitor cells, SCs from apical papilla, and periodontal ligament of deciduous teeth SCs. However, heterogeneity among these populations has been observed, and the best method to select the most appropriate TDSCs for regeneration approaches has not yet been established. The objective of this review is to outline the current knowledge concerning the various types of TDSCs, and discuss the perspectives for their use in regenerative approaches.