Comparison of stem cell behaviors between indigenous high and low-CD24 percentage expressing cells of stem cells from apical papilla (SCAPs)

Noncanonical Wnt5a Signaling Suppresses Hippo/TAZ-Mediated Osteogenesis Partly Through the Canonical Wnt Pathway in SCAPs

Purpose

Stem cells from the apical papilla (SCAPs) are promising seed cells for tissue regeneration medicine and possess the osteogenic differentiation potential. Wnt5a, a typical ligand of the noncanonical Wnt pathway, exhibits diverse roles in the regulation of osteogenesis. The transcriptional co-activator with PDZ-binding motif (TAZ, WWTR1) is a core regulator in the Hippo pathway and regulates stem behavior including osteogenic differentiation. This study aims to examine how Wnt5a regulates SCAPs osteogenesis and explore the precise mechanistic relationship between Wnt5a and TAZ.

Methods

SCAPs were isolated from developing apical papilla tissue of extracted human immature third molars in vitro. ALP staining, ALP activity and Alizarin red staining were used to evaluate osteogenic capacity. Osteogenic-related factors were assessed by qRT-PCR or Western blotting. Additionally, the receptor tyrosine kinase-like orphan receptor 2 (ROR2) was detected by immunocytofluorescence staining and silenced by small interfering RNA to verify the function of Wnt5a/ROR2 in TAZ-mediated osteogenesis. And we constructed TAZ-overexpression and β-catenin-overexpression SCAPs generated by lentivirus to explore the precise mechanistic relationship between Wnt5a and TAZ.

Results

Wnt5a (100ng/mL) significantly suppressed ALP activity, mineralization nodules formation, expression of osteogenic-related factors. Meanwhile, it decreased the expression of TAZ mRNA and protein. TAZ overexpression promoted osteogenesis of SCAPs while Wnt5a could block TAZ-mediated osteogenesis. Furthermore, ROR2 siRNA (siROR2) was found to upregulate TAZ and canonical Wnt pathway signaling related molecules such as β-catenin, GSK3β and p-GSK3β. The suppression of Wnt5a/ROR2 on osteogenesis was significantly reversed by β-catenin overexpression through Wnt5a/ROR2/β-catenin/TAZ pathway.

Conclusion

Taken together, the present study demonstrates that Wnt5a suppresses TAZ-mediated osteogenesis of SCAPs and there may be a Wnt5a/ROR2/β-catenin/TAZ pathway regulating osteogenesis of SCAPs. Moreover, Wnt5a could be a candidate for regulators in tissue regeneration.

A pilot study on biological characteristics of human CD24(+) stem cells from the apical papilla

BACKGROUND/PURPOSE

CD24 is a specific cell surface marker for undifferentiated dental stem cells from apical papilla (SCAPs) seen only during root development, before the tooth emerges through gum. But the comprehensive role of CD24 in the SCAPs is unclear. This study aims to clarify the exact roles of CD24 in SCAPs.

MATERIALS AND METHODS

SCAPs were divided into CD24 (+)-SCAPs (high percentage CD24) and CD24 (-)-SCAPs (low percentage CD24) via flow cytometry. The proliferation, migration and osteogenic/adipogenic differentiation of the two groups were detected, RT-PCR was performed to detect the expression of osteogenic/adipogenic related genes and thegene expression were analyzed.

RESULTS

The proliferative and migratory ability of CD24 (-)-SCAPs were significantly stronger than that of CD24 (+)-SCAPs. Although, the mineralization process and the osteogenic genes expression were not significantly difference in the two groups. Both CD24 (+)-SCAPs and CD24 (-)-SCAPs differentiated into adipocytes. The adipogenic differentiation in CD24 (+)-SCAPs was better than that in CD24 (-)-SCAPs, after 3 weeks of adipogenic induction. However, the expression of adipogenic related gene, PPAR γ2 mRNA in CD24 (+)-SCAPs was lower than that in CD24 (-)-SCAPs after 1 week of adipogenic induction. But the trend changed for the opposite after 3 weeks.

CONCLUSION

The study proposes that CD24 has a regulatory effect on the adipogenic differentiation of SCAPs, and this may be attained by targeting the PPAR γ2 mRNA. Concurrently, it was found that CD24 plays an inhibitory role in the proliferation and migration of SCAPs, which may minimize the manifestation of diseases caused by an abnormal cell growth.

A single-cell interactome of human tooth germ from growing third molar elucidates signaling networks regulating dental development

Background

Development of dental tissue is regulated by extensive cell crosstalk based on various signaling molecules, such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) pathways. However, an intact network of the intercellular regulation is still lacking.

Result

To gain an unbiased and comprehensive view of this dental cell interactome, we applied single-cell RNA-seq on immature human tooth germ of the growing third molar, discovered refined cell subtypes, and applied multiple network analysis to identify the central signaling pathways. We found that immune cells made up over 80% of all tooth germ cells, which exhibited profound regulation on dental cells via Transforming growth factor-β, Tumor necrosis factor (TNF) and Interleukin-1. During osteoblast differentiation, expression of genes related to extracellular matrix and mineralization was continuously elevated by signals from BMP and FGF family. As for the self-renewal of apical papilla stem cell, BMP-FGFR1-MSX1 pathway directly regulated the G0-to-S cell cycle transition. We also confirmed that Colony Stimulating Factor 1 secreted from pericyte and TNF Superfamily Member 11 secreted from osteoblast regulated a large proportion of genes related to osteoclast transformation from macrophage and monocyte.

Conclusions

We constructed the intercellular signaling networks that regulated the essential developmental process of human tooth, which served as a foundation for future dental regeneration engineering and the understanding of oral pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00691-5.

Characteristics, Classification, and Application of Stem Cells Derived from Human Teeth

Since mesenchymal stem cells derived from human teeth are characterized as having the properties of excellent proliferation, multilineage differentiation, and immune regulation. Dental stem cells exhibit fibroblast-like microscopic appearance and express mesenchymal markers, embryonic markers, and vascular markers but do not express hematopoietic markers. Dental stem cells are a mixed population with different sensitive markers, characteristics, and therapeutic effects. Single or combined surface markers are not only helpful for understanding the subpopulation of mixed stem cell populations according to cell function but also for improving the stable treatment effect of dental stem cells. Focusing on the discovery and characterization of stem cells isolated from human teeth over the past 20 years, this review outlines the effect of marker sorting on cell proliferation and differentiation ability and the assessment of the clinical application potential. Classified dental stem cells from markers and functional molecules can solve the problem of heterogeneity and ensure the efficacy of cell therapy strategies including dentistry, neurologic diseases, bone repair, and tissue engineering.

Epigallocatechin-3-Gallate Promotes Osteo-/Odontogenic Differentiation of Stem Cells from the Apical Papilla through Activating the BMP-Smad Signaling Pathway

Stem cells from apical papilla (SCAPs) are desirable sources of dentin regeneration. Epigallocatechin-3-gallate (EGCG), a natural component of green tea, shows potential in promoting the osteogenic differentiation of bone mesenchymal stem cells. However, whether EGCG regulates the odontogenic differentiation of SCAPs and how this occurs remain unknown. SCAPs from immature human third molars (16–20 years, n = 5) were treated with a medium containing different concentrations of EGCG or bone morphogenic protein 2 (BMP2), with or without LDN193189 (an inhibitor of the canonical BMP pathway). Cell proliferation and migration were analyzed using a CCK-8 assay and wound-healing assay, respectively. Osteo-/odontogenic differentiation was evaluated via alkaline phosphatase staining, alizarin red S staining, and the expression of osteo-/odontogenic markers using qPCR and Western blotting. We found that EGCG (1 or 10 μM) promoted the proliferation of SCAPs, increased alkaline phosphatase activity and mineral deposition, and upregulated the expression of osteo-/odontogenic markers including dentin sialophosphoprotein (Dspp), dentin matrix protein-1 (Dmp-1), bone sialoprotein (Bsp), and Type I collagen (Col1), along with the elevated expression of BMP2 and phosphorylation level of Smad1/5/9 (p < 0.01). EGCG at concentrations below 10 μM had no significant influence on cell migration. Moreover, EGCG-induced osteo-/odontogenic differentiation was significantly attenuated via LDN193189 treatment (p < 0.01). Furthermore, EGCG showed the ability to promote mineralization comparable with that of recombinant BMP2. Our study demonstrated that EGCG promotes the osteo-/odontogenic differentiation of SCAPs through the BMP–Smad signaling pathway.

Effects of lipopolysaccharide on proliferation, migration and osteogenic differentiation of apical papilla cells from early and late stage of root development

The aim of this study was to investigate the effects of lipopolysaccharide on cell proliferation, migration and osteogenic differentiation of apical papilla cells from early and late stage of root development. After challenging with various lipopolysaccharide concentrations to apical papilla cells from both stages of root development for 168 h, cell proliferation and migration were investigated. Osteogenic differentiation was examined by Alizarin red staining, and gene expressions of bone/cementum or dentin-related genes were examined by polymerase chain reaction. Lipopolysaccharide did not affect cell proliferation and migration in both groups. Lipopolysaccharide at 1 and 5 µg mL^-1 increased Alizarin red staining in apical papilla cells from early-stage but not the late-stage cells. Bone sialoprotein (bone/cementum marker) gene expression increased in both early and late stage of root development at 5 µg mL^-1 . These results might explain bone/cementum generation in regenerative endodontic procedures.

Intermittent Administration of Parathyroid Hormone Enhances Odonto/Osteogenic Differentiation of Stem Cells from the Apical Papilla via JNK and P38 MAPK Pathways

Objective

Parathyroid hormone (PTH) is considered to be essential during the tooth development. Stem cells from the apical papilla (SCAPs) are responsible for dentine formation. However, the interaction between PTH and SCAPs remains unclear. This study was aimed at investigating the effects of PTH on odonto/osteogenic differentiation capacity of SCAPs and elucidating the underlying molecular mechanisms. Materials and Methods. Here, SCAPs were isolated and identified in vitro. Effects of PTH on the proliferation of SCAPs were determined by Cell Counting Kit-8 (CCK-8), flow cytometry (FCM), and EdU. Alkaline phosphatase (ALP) activity, alizarin red staining, Western blot, and RT-PCR were carried out to detect the odonto/osteogenic differentiation of PTH-treated SCAPs as well as the participation of the MAPK signaling pathway.

Results

An ALP activity assay determined that 10^-8 mol/L PTH was the optimal concentration for the induction of SCAPs with no significant influence on the proliferation of SCAPs as indicated by CCK-8, FCM, and EdU. The expression of odonto/osteogenic markers was significantly upregulated in mRNA levels and protein levels. Moreover, intermittent treatment of PTH also increased phosphorylation of JNK and P38, and the differentiation was suppressed following the inhibition of JNK and P38 MAPK pathways.

Conclusion

PTH can regulate the odonto/osteogenic differentiation of SCAPs via JNK and P38 MAPK pathways.

Mesenchymal stem cells and biologic factors leading to bone formation

BACKGROUND

Physiological bone formation and bone regeneration occurring during bone repair can be considered distinct but similar processes. Mesenchymal stem cells (MSC) and associated biologic factors are crucial to both bone formation and bone regeneration.

AIM

To perform a narrative review of the current literature regarding the role of MSC and biologic factors in bone formation with the aim of discussing the clinical relevance of in vitro and in vivo animal studies.

METHODS

The literature was searched for studies on MSC and biologic factors associated with the formation of bone in the mandible and maxilla. The search specifically targeted studies on key aspects of how stem cells and biologic factors are important in bone formation and how this might be relevant to bone regeneration. The results are summarized in a narrative review format.

RESULTS

Different types of MSC and many biologic factors are associated with bone formation in the maxilla and mandible.

CONCLUSION

Bone formation and regeneration involve very complex and highly regulated cellular and molecular processes. By studying these processes, new clinical opportunities will arise for therapeutic bone regenerative treatments.

Isolation and Culture of Human Stem Cells from Apical Papilla under Low Oxygen Concentration Highlight Original Properties

Stem cells isolated from the apical papilla of wisdom teeth (SCAPs) are an attractive model for tissue repair due to their availability, high proliferation rate and potential to differentiate in vitro towards mesodermal and neurogenic lineages. Adult stem cells, such as SCAPs, develop in stem cell niches in which the oxygen concentration [O₂] is low (3–8% compared with 21% of ambient air). In this work, we evaluate the impact of low [O₂] on the physiology of SCAPs isolated and processed in parallel at 21% or 3% O₂ without any hyperoxic shock in ambient air during the experiment performed at 3% O₂. We demonstrate that SCAPs display a higher proliferation capacity at 3% O₂ than in ambient air with elevated expression levels of two cell surface antigens: the alpha-6 integrin subunit (CD49f) and the embryonic stem cell marker (SSEA4). We show that the mesodermal differentiation potential of SCAPs is conserved at early passage in both [O₂], but is partly lost at late passage and low [O₂], conditions in which SCAPs proliferate efficiently without any sign of apoptosis. Unexpectedly, we show that autophagic flux is active in SCAPs irrespective of [O₂] and that this process remains high in cells even after prolonged exposure to 3% O₂.

Cell migration and osteo/odontogenesis stimulation of iRoot FS as a potential apical barrier material in apexification

AIM

To investigate the in vitro biological effects of a nanoparticle bioceramic material, iRoot Fast Set root repair material (iRoot FS), on the proliferation, migration and osteo/odontogenic differentiation of human stem cells from the apical papilla (hSCAP), and to further explore the mechanism involved in osteo/odontogenic induction of iRoot FS.

METHODOLOGY

hSCAP were isolated and characterized in vitro. iRoot FS conditioned medium were prepared and used to treat hSCAP, while using mineral trioxide aggregate (MTA) conditioned medium as the positive control and regular medium as the negative control. MTT assay and BrdU labelling assay were performed to determine cell proliferation. Wound healing assay and transwell assay were conducted to evaluate cell migration. The osteo/odontogenic differentiation of hSCAP was evaluated by qPCR, Western blot and Alizarin red S staining. Wnt inhibitor was used for downregulating the expression level of β-catenin of hSCAP.

RESULTS

The cell proliferation of hSACP in the iRoot FS group was not significantly different compared with the control groups. The cell migration of hSCAP in the iRoot FS group was significantly increased than the MTA and negative control groups (P < 0.01). The expression levels of osteo/odontogenic markers and mineralization nodule formation of hSCAP in the iRoot FS group were significantly elevated (P < 0.01). Furthermore, iRoot FS enhanced the osteo/odontogenic differentiation of hSCAP by activating Wnt/β-catenin signalling.

CONCLUSIONS

iRoot FS promoted the cell migration of hSCAP and enhanced their oseto/odontogenesis potential via the Wnt/β-catenin pathway without cytotoxicity. iRoot FS had satisfactory biological properties and has potential to be used as an apical barrier in apexification or as a coronal sealing material in regenerative endodontic treatment.

Regenerative Endodontics for Adult Patients

The goal of endodontics is to save teeth. Since inception, endodontic treatments are performed to obturate disinfected root canals with inert materials such as gutta-percha. Although teeth can be saved after successful endodontic treatments, they are devitalized and therefore susceptible to reinfections and fractures. The American Association of Endodontists (AAE) has made a tremendous effort to revitalize disinfected immature permanent teeth in children and adolescents with diagnoses including pulp necrosis or apical periodontitis. The American Dental Association (ADA) in 2011 issued several clinical codes for regenerative endodontic procedures or apical revascularization in necrotic immature permanent teeth in children and adolescents. These AAE and ADA initiatives have stimulated robust interest in devising a multitude of tissue engineering approaches for dental pulp and dentin regeneration. Can the concept of regenerative endodontics be extended to revitalize mature permanent teeth with diagnoses including irreversible pulpitis and/or pulp necrosis in adults? The present article was written not only to summarize emerging findings to revitalize mature permanent teeth in adult patients but also to identify challenges and strategies that focus on realizing the goal of regenerative endodontics in adults. We further present clinical cases and describe the biological basis of potential regenerative endodontic procedures in adults. This article explores the frequently asked question if regenerative endodontic therapies should be developed for dental pulp and/or dentin regeneration in adults, who consist of the great majority of endodontic patients.

Lipoxin A4 Attenuates the Inflammatory Response in Stem Cells of the Apical Papilla via ALX/FPR2

Similar to the onset phase of inflammation, its resolution is a process that unfolds in a manner that is coordinated and regulated by a panel of mediators. Lipoxin A4 (LXA₄) has been implicated as an anti-inflammatory, pro-resolving mediator. We hypothesized that LXA₄ attenuates or prevents an inflammatory response via the immunosuppressive activity of Stem Cells of the Apical Papilla (SCAP). Here, we report for the first time in vitro that in a SCAP population, lipoxin receptor ALX/FPR2 was constitutively expressed and upregulated after stimulation with lipopolysaccharide and/or TNF-α. Moreover, LXA₄ significantly enhanced proliferation, migration, and wound healing capacity of SCAP through the activation of its receptor, ALX/FPR2. Cytokine, chemokine and growth factor secretion by SCAP was inhibited in a dose dependent manner by LXA₄. Finally, LXA₄ enhanced immunomodulatory properties of SCAP towards Peripheral Blood Mononuclear Cells. These findings provide the first evidence that the LXA₄-ALX/FPR2 axis in SCAP regulates inflammatory mediators and enhances immunomodulatory properties. Such features of SCAP may also support the role of these cells in the resolution phase of inflammation and suggest a novel molecular target for ALX/FPR2 receptor to enhance a stem cell-mediated pro-resolving pathway.

A Comparative Evaluation of Concentrated Growth Factor and Platelet-rich Fibrin on the Proliferation, Migration, and Differentiation of Human Stem Cells of the Apical Papilla

INTRODUCTION

Concentrated growth factor (CGF) is considered to be a natural biomaterial that is better than platelet-rich fibrin (PRF) in bone regeneration, but there is little information acquired in regenerative endodontics. Therefore, the purpose of this study was to evaluate their effects on the proliferation, migration, and differentiation of human stem cells of the apical papilla (SCAPs).

METHODS

CGF- and PRF-conditioned medium were prepared using the freeze-dried method. SCAPs were isolated and identified. The proliferative potential of SCAPs was investigated using the Cell Counting Kit-8 (KeyGen Biotech, Nanjing, China). The migration capacity was analyzed using transwell assays, and the mineralization ability was determined by alizarin red S staining. The expression levels of alkaline phosphatase, bone sialoprotein, dentin matrix protein 1, and dentin sialophosphoprotein were determined by quantitative polymerase chain reaction.

RESULTS

The cultured cells exhibited mesenchymal stem cell characteristics. The growth rate and migratory cell numbers of the CGF and PRF groups were significantly greater than those of the control group. The mineralized areas in the CGF and PRF groups were significantly larger than those in the control group after incubation for 7 days and 14 days. The expression levels of osteogenic/odontoblast-related genes were reduced on day 7, but they were dramatically enhanced on day 14, and the related gene expression levels in the PRF group were higher than those in the CGF group.

CONCLUSIONS

Both CGF and PRF can promote the proliferation, migration, and differentiation of SCAPs. CGF may be a promising alternative in regenerative endodontics.

Impaired bone healing at tooth extraction sites in CD24-deficient mice: A pilot study

AIM

To use a micro-computed tomography (micro-CT) to quantify bone healing at maxillary first molar extraction sites, and test the hypothesis that bone healing is impaired in CD24-knockout mice as compared with wild-type C57BL/6J mice.

MATERIALS AND METHODS

Under ketamine-xylazine general anaesthesia, mice had either extraction of the right maxillary first molar tooth or sham operation. Mice were sacrificed 1 (n = 12/group), 2 (n = 6/group) or 4 (n = 6/group) weeks postoperatively. The right maxillae was disected. Micro-CT was used to quantify differences in bone microstructural features at extrction sites, between CD24-knockout mice and wild-type mice.

RESULTS

CD24-Knockout mice displayed impaired bone healing at extraction sites that was manifested as decreased trabecular bone density, and decreased number and thickness of trabeculae.

CONCLUSIONS

This pilot study suggests that CD24 plays an important role in extraction socket bone healing and may be used as a novel biomarker of bone quality and potential therapeutic target to improve bone healing and density following alveolar bone injury.

Dental Stem Cells in Bone Tissue Engineering: Current Overview and Challenges

The treatment of bone that is impaired due to disease, trauma or tumor resection creates a challenge for both clinicians and researchers. Critical size bone defects are conventionally treated with autografts which are associated with risks such as donor site morbidity and limitations like donor shortage. Bone tissue engineering has become a promising area for the management of critical size bone defects by the employment of biocompatible materials and the discovery of novel stem cell sources. Mesenchymal stem cells (MSCs) can be isolated with ease from various dental tissues including dental pulp stem cells, stem cells from apical papilla, dental follicle stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, gingival stem cells and tooth germ derived stem cells. Outcomes of dental MSC mediated bone tissue engineering is explored in various in vivo and in vitro preclinical studies. However, there are still obscurities regarding the mechanisms underlying in MSC mediated bone regeneration and challenges in applications of dental stem cells. In this review, we summarized dental stem cell sources and their characterizations, along with currently used biomaterials for cell delivery and future perspectives for dental MSCs in the field of bone tissue engineering. Further efforts are necessary before moving to clinical trials for future applications.