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

Single-cell RNA-seq of in vitro expanded cells from cranial neural crest reveals a rare odontogenic sub-population

Ecto-mesenchymal cells of mammalian tooth germ develops from cranial neural crest cells. These cells are recognised as a promising source for tooth development and regeneration. Despite the high heterogeneity of the neural crest, the cellular landscape of in vitro cultured cranial neural crest cells (CNCCs) for odontogenesis remains unclear. In this study, we used large-scale single-cell RNA sequencing to analyse the cellular landscape of in vitro cultured mouse CNCCs for odontogenesis. We revealed distinct cell trajectories from primary cells to passage 5 and identified a rare Alx3+/Barx1+ sub-population in primary CNCCs that differentiated into two odontogenic clusters characterised by the up-regulation of Pax9/Bmp3 and Lhx6/Dmp1. We successfully induced whole tooth-like structures containing enamel, dentin, and pulp under the mouse renal capsule using in vitro cultured cells from both cranial and trunk neural crests with induction rates of 26.7% and 22.1%, respectively. Importantly, we confirmed only cells sorted from odontogenic path can induce tooth-like structures. Cell cycle and DNA replication genes were concomitantly upregulated in the cultured NCCs of the tooth induction groups. Our data provide valuable insights into the cell heterogeneity of in vitro cultured CNCCs and their potential as a source for tooth regeneration.

p75NTR promotes tooth rhythmic mineralization via upregulation of BMAL1/CLOCK

The circadian clock plays a critical role in dentomaxillofacial development. Tooth biomineralization is characterized by the circadian clock; however, the mechanisms underlying the coordination of circadian rhythms with tooth development and biomineralization remain unclear. The p75 neurotrophin receptor (p75NTR) is a clock factor that regulates the oscillatory components of the circadian rhythm. This study aims to investigate the impact of p75NTR on the rhythmic mineralization of teeth and elucidate its underlying molecular mechanisms. We generated p75NTR knockout mice to examine the effects of p75NTR deficiency on tooth mineralization. Ectomesenchymal stem cells (EMSCs), derived from mouse tooth germs, were used for in vitro experiments. Results showed a reduction in tooth mineral density and daily mineralization rate in p75NTR knockout mice. Deletion of p75NTR decreased the expression of DMP1, DSPP, RUNX2, and ALP in tooth germ. Odontogenic differentiation and mineralization of EMSCs were activated by p75NTR. Histological results demonstrated predominant detection of p75NTR protein in odontoblasts and stratum intermedium cells during rapid formation phases of dental hard tissue. The mRNA expression of p75NTR exhibited circadian variations in tooth germs and EMSCs, consistent with the expression patterns of the core clock genes Bmal1 and Clock. The upregulation of BMAL1/CLOCK expression by p75NTR positively regulated the mineralization ability of EMSCs, whereas BMAL1 and CLOCK exerted a negative feedback regulation on p75NTR by inhibiting its promoter activity. Our findings suggest that p75NTR is necessary to maintain normal tooth biomineralization. Odontogenic differentiation and mineralization of EMSCs is regulated by the p75NTR-BMAL1/CLOCK signaling axis. These findings offer valuable insights into the associations between circadian rhythms, tooth development, and biomineralization.

Single cell RNA sequencing reveals mesenchymal heterogeneity and critical functions of Cd271 in tooth development

BACKGROUND

Accumulating evidence suggests that the maxillary process, to which cranial crest cells migrate, is essential to tooth development. Emerging studies indicate that Cd271 plays an essential role in odontogenesis. However, the underlying mechanisms have yet to be elucidated.

AIM

To establish the functionally heterogeneous population in the maxillary process, elucidate the effects of Cd271 deficiency on gene expression differences.

METHODS

p75NTR knockout (Cd271^-/-) mice (from American Jackson laboratory) were used to collect the maxillofacial process tissue of p75NTR knockout mice, and the wild-type maxillofacial process of the same pregnant mouse wild was used as control. After single cell suspension, the cDNA was prepared by loading the single cell suspension into the 10x Genomics Chromium system to be sequenced by NovaSeq6000 sequencing system. Finally, the sequencing data in Fastq format were obtained. The FastQC software is used to evaluate the quality of data and CellRanger analyzed the data. The gene expression matrix is read by R software, and Seurat is used to control and standardize the data, reduce the dimension and cluster. We search for marker genes for subgroup annotation by consulting literature and database; explore the effect of p75NTR knockout on mesenchymal stem cells (MSCs) gene expression and cell proportion by cell subgrouping, differential gene analysis, enrichment analysis and protein-protein interaction network analysis; understand the interaction between MSCs cells and the differentiation trajectory and gene change characteristics of p75NTR knockout MSCs by cell communication analysis and pseudo-time analysis. Last we verified the findings single cell sequencing in vitro.

RESULTS

We identified 21 cell clusters, and we re-clustered these into three subclusters. Importantly, we revealed the cell–cell communication networks between clusters. We clarified that Cd271 was significantly associated with the regulation of mineralization.

CONCLUSION

This study provides comprehensive mechanistic insights into the maxillary- process-derived MSCs and demonstrates that Cd271 is significantly associated with the odontogenesis in mesenchymal populations.

Isolation and characterization of apical papilla cells from root end of human third molar and their differentiation into cementoblast cells: an in vitro study

BACKGROUND

Periodontal regeneration, treatment of periodontal-related diseases and improving the function of implants are global therapeutic challenges. The differentiation of human stem cells from apical papilla into cementoblasts may provide a strategy for periodontitis treatment. This study aimed to evaluate the differentiation of primary human stem cells apical papilla (hSCAPs) to cementoblast cells.

MATERIAL AND METHODS

SCAPs cells were isolated from human third molar and then incubated for 21 days in a differentiation microenvironment. Alkaline phosphatase (ALP) and Alizarin red S staining assays were performed to evaluate the calcium deposition and formation of hydroxyapatite in the cultured hSCAPs microenvironment. Real-time polymerase chain reaction (RT-PCR) assay was performed for cementum protein 1 (CEMP1), collagen type I (COL1), F-Spondin (SPON1), osteocalcin (OCN), and osteopontin (OPN) as specific markers of cementoblasts and their progenitors.

RESULTS

ALP phosphatase activity in day 21 of treatment demonstrated a significant increase in ALP compared to the control. Alizarin red S staining assay showed that the differentiated hSCAPs offered a great amount of calcium deposition nodules compared to the control. The increased expression level of CEMP1, OCN, OPN, COL1 and Spon1 was observed in days 7, 14 and 21 compared to the control, while greatest expression level was observed in day 21.

CONCLUSION

In conclusion, the differentiation microenviroment is convenient and useful for promoting the differentiation of hSCAPs into cementoblast.

Dental applications of induced pluripotent stem cells and their derivatives

Periodontal tissue regeneration is the ideal tactic for treating periodontitis. Tooth regeneration is the potential strategy to restore the lost teeth. With infinite self-renewal, broad differentiation potential, and less ethical issues than embryonic stem cells, induced pluripotent stem cells (iPSCs) are promising cell resource for periodontal and tooth regeneration. This review summarized the optimized technologies of generating iPSC lines and application of iPSC derivatives, which reduce the risk of tumorigenicity. Given that iPSCs may have epigenetic memory from the donor tissue and tend to differentiate into lineages along with the donor cells, iPSCs derived from dental tissues may benefit for personalized dental application. Neural crest cells (NCCs) and mesenchymal stem or stomal cells (MSCs) are lineage-specific progenitor cells derived from iPSCs and can differentiate into multilineage cell types. This review introduced the updated technologies of inducing iPSC-derived NCCs and iPSC-derived MSCs and their application in periodontal and tooth regeneration. Given the complexity of periodontal tissues and teeth, it is crucial to elucidate the integrated mechanisms of all constitutive cells and the spatio-temporal interactions among them to generate structural periodontal tissues and functional teeth. Thus, more sophisticated studies in vitro and in vivo and even preclinical investigations need to be conducted.

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.

P75 neurotrophin receptor positively regulates the odontogenic/osteogenic differentiation of ectomesenchymal stem cells via nuclear factor kappa-B signaling pathway

p75NTR, a neural crest stem cell marker, is continuously expressed in mesenchymal cells during tooth development. Importantly, high expression of p75NTR in the late bell stage implicates its involvement in odontogenesis and mineralization. However, the regulatory mechanisms underlying p75NTR involvement in odonto/osteogenic differentiation remain unclear. Here, we investigate the effect and potential mechanisms underlying p75NTR involvement in odonto/osteogenic differentiation. We dissected EMSCs from the first branchial arches of mice embryo and compared the proliferation and migration of p75NTR+/+ and p75NTR-/-EMSCs by transwell, scratch and cell counting kit 8(CCK8)assays. The differentiation ability and the involvement of nuclear factor kappa-B (NF-κB) pathway were investigated through alkaline phosphatase and immunofluorescence assay, real-time PCR, and western blot. During induction of dental epithelium conditioned medium, p75NTR+/+ EMSCs exhibited deeper Alkaline phosphatase (ALP) staining and higher expression of odonto/osteogenic genes/proteins (e.g., dentin sialoprotein (DSPP) than p75NTR+/+ EMSCs. Moreover, p75NTR+/+ EMSCs exhibited higher nuclear P65 expression than p75NTR-/-EMSCs. Inhibition of NF-κB pathway with Bay11-7082 in p75NTR+/+EMSCs substantially decreased DSPP expression level. However, activation of NF-κB pathway with Bay11-7082 in p75NTR-/-EMSCs enhanced DSPP expression level. Thus, p75NTR possibly plays a paramount role in the proliferation and differentiation of EMSCs via NF-κB pathway.

[Mage-D1 binding to activated p75NTR positively regulates mineralization of rat ectomesenchymal stem cells in vitro]

OBJECTIVE

To detect the binding of Mage-D1 with activated p75NTR and explore their role in regulating mineralization of ectomesenchymal stem cells (EMSCs).

METHODS

EMSCs were isolated from the tooth germs of embryonic SD rats (19.5 days of gestation) by tissue explant culture and were identified for surface markers using flow cytometry. The cultured cells were divided into blank control group, 100 ng/mL nerve growth factor (NGF) stimulation group, and lentivirus-mediated Mage-D1 interference (SH-Mage-D1) group. Proximity ligation assay was used to detect the binding of Mage-D1 with activated p75NTR in the EMSCs, and the binding strength was compared among the 3 groups. Alizarin red staining and ALP staining were used to observe mineralization of the induced cells. The expressions of ALP, Runx2, OCN, BSP, OPN, Msx1 and Dlx1 at both the mRNA and protein levels were detected using RT-PCR and Western blotting.

RESULTS

The isolated EMSCs expressed high levels of cell surface markers CD44, CD90, CD29, CD146, and CD105 with a low expression of CD45. The results of proximity ligation assay showed that the binding of Mage-D1 with activated p75NTR in the cells increased over time, and the binding strength was significantly greater in NFG-treated cells than in the cells in the other two groups (P < 0.05). Alizarin red staining and ALP staining of the induced cells showed that the changes in the mineralization nodules were consistent with those of ALP activity. The cells treated with 100 ng/mL NGF exhibited significantly increased expressions of ALP, Runx2, OCN, BSP, OPN, Col1, Msx1 and Dlx1 as compared with the cells in the other two groups (P < 0.05).

CONCLUSION

Mage-D1 directly binds to activated p75NTR in embryonic rat EMSCs to positively regulate the mineralization of the EMSCs.

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

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

p75NTR-/- mice exhibit an alveolar bone loss phenotype and inhibited PI3K/Akt/β-catenin pathway

OBJECTIVES

The aim of this study was to investigate the role of p75 neurotrophin receptor (p75NTR) in regulating the mouse alveolar bone development and the mineralization potential of murine ectomesenchymal stem cells (EMSCs). Moreover, we tried to explore the underlying mechanisms associated with the PI3K/Akt/β-catenin pathway.

MATERIALS AND METHODS

p75NTR knockout (p75NTR-/- ) mice and wild-type (WT) littermates were used. E12.5d p75NTR-/- and WT EMSCs were isolated in the same pregnant p75NTR-/+ mice from embryonic maxillofacial processes separately. Mouse alveolar bone mass was evaluated using micro-CT. Differential osteogenic differentiation pathways between p75NTR-/- and WT EMSCs were analysed by RNA-sequencing. The PI3K inhibitor LY294002 and PI3K agonist 740Y-P were used to regulate the PI3K/Akt pathway in EMSCs. p75NTR overexpression lentiviruses, p75NTR knock-down lentiviruses and recombined mouse NGF were used to transfect cells.

RESULTS

The alveolar bone mass was found reduced in the p75NTR knockout mouse comparing to the WT mouse. During mineralization induction, p75NTR-/- EMSCs displayed decreased osteogenic capacity and downregulated PI3K/Akt/β-catenin signalling. The PI3K/Akt/β-catenin pathway positively regulates the potential of differential mineralization in EMSCs. The promotive effect of p75NTR overexpression can be attenuated by LY294002, while the inhibitory effect of p75NTR knock-down on Runx2 and Col1 expression can be reversed by 740Y-P.

CONCLUSION

Deletion of p75NTR reduced alveolar bone mass in mice. P75NTR positively regulated the osteogenic differentiation of EMSCs via enhancing the PI3K/Akt/β-catenin pathway.

The role and potential mechanism of p75NTR in mineralization via in vivo p75NTR knockout mice and in vitro ectomesenchymal stem cells

OBJECTIVE

The aim of this study is to investigate the role and potential mechanism of p75NTR in mineralization in vivo using p75NTR-knockout mice and in vitro using ectomesenchymal stem cells (EMSCs).

MATERIALS AND METHODS

Femur bone mass and daily incisor mineralization speed were assessed in an in vivo p75NTR-knockout mouse model. The molecular signatures alkaline phosphatase (ALP), collagen type 1 (Col1), melanoma-associated antigen (Mage)-D1, bone sialoprotein (BSP), osteocalcin (OCN), osteopontin (OPN), distal-less homeobox 1 (Dlx1) and Msh homeobox 1 (Msx1) were examined in vitro in EMSCs isolated from p75NTR+/+ and p75NTRExIII-/- mice.

RESULTS

p75NTR-knockout mice were smaller in body size than heterozygous and wild-type mice. Micro-computed tomography and structural quantification showed that the osteogenic ability of p75NTRExIII -knockout mice was significantly decreased compared with that of wild-type mice (P < .05). Weaker ALP and alizarin red staining and reduced expression of ALP, Col1, Runx2, BSP, OCN and OPN were also observed in p75NTRExIII-/- EMSCs. Moreover, the distance between calcein fluorescence bands in p75NTRExIII -knockout mice was significantly smaller than that in wild type and heterozygous mice (P < .05), indicating the lower daily mineralization speed of incisors in p75NTRExIII -knockout mice. Further investigation revealed a positive correlation between p75NTR and Mage-D1, Dlx1, and Msx1.

CONCLUSION

p75NTR not only promotes osteogenic differentiation and tissue mineralization, but also shows a possible relationship with the circadian rhythm of dental hard tissue formation.

Regrowing a tooth: in vitro and in vivo approaches

Biologically oriented regenerative dentistry in an attempt to regrow a functional tooth by harnessing the natural healing capabilities of dental tissues has become a recent trend challenging the current dental practice on repairing the damaged or missing tooth. In this review, we outline the conceptual development on the in situ revitalization of the tooth replacement capability lost during evolution, the updated progress in stem-cell-based in vivo repair of the damaged tooth, and the recent endeavors for in vitro generation of an implantable bioengineered tooth germ. Thereafter, we summarize the major challenges that need to be overcome in order to provide the rationale and directions for the success of fully functional tooth regeneration in the near future.

LNGFR targets the Wnt/β-catenin pathway and promotes the osteogenic differentiation in rat ectomesenchymal stem cells

Considerable evidence has shown that the Wnt/β-catenin pathway is involved in osteogenic differentiation in various stem cells. However, the role of Wnt/β-catenin pathway in regulating the osteogenic differentiation of rat ectomesenchymal stem cells (EMSCs), which are considered to be the progenitors of dental mesenchymal stem cells, remains unknown. In this study, we demonstrated that nuclear β-catenin was upregulated during EMSC osteogenic differentiation. The Wnt signalling inhibitor IWR-1-endo inhibited EMSC osteogenic differentiation, while the Wnt signalling agonist SKL2001 promoted it. Moreover, nuclear β-catenin was further upregulated by the overexpression of low-affinity nerve growth factor receptor (LNGFR) during EMSC osteogenic differentiation. Further experiments demonstrated that LNGFR overexpression enhanced EMSC osteogenic differentiation, while LNGFR silencing decreased it. Additionally, IWR-1-endo attenuated LNGFR-enhanced EMSC osteogenic differentiation. Collectively, our data reveal that LNGFR targets the Wnt/β-catenin pathway and positively regulates EMSC osteogenic differentiation, suggesting that Wnt/β-catenin pathway may be involved in the development of teeth and that the targeting Wnt/β-catenin pathway may have great potential for applications in dental tissue engineering regeneration.

Prospect of Human Pluripotent Stem Cell-Derived Neural Crest Stem Cells in Clinical Application

Neural crest stem cells (NCSCs) represent a transient and multipotent cell population that contributes to numerous anatomical structures such as peripheral nervous system, teeth, and cornea. NCSC maldevelopment is related to various human diseases including pigmentation abnormalities, disorders affecting autonomic nervous system, and malformations of teeth, eyes, and hearts. As human pluripotent stem cells including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) can serve as an unlimited cell source to generate NCSCs, hESC/hiPSC-derived NCSCs can be a valuable tool to study the underlying mechanisms of NCSC-associated diseases, which paves the way for future therapies for these abnormalities. In addition, hESC/hiPSC-derived NCSCs with the capability of differentiating to various cell types are highly promising for clinical organ repair and regeneration. In this review, we first discuss NCSC generation methods from human pluripotent stem cells and differentiation mechanism of NCSCs. Then we focus on the clinical application potential of hESC/hiPSC-derived NCSCs on peripheral nerve injuries, corneal blindness, tooth regeneration, pathological melanogenesis, Hirschsprung disease, and cardiac repair and regeneration.

p75 neurotrophin receptor regulates differential mineralization of rat ectomesenchymal stem cells

OBJECTIVES

The aim of this study was to investigate whether p75NTR (p75 neurotrophin receptor) regulates differential mineralization capacity of rEMSCs (rat ectomesenchymal stem cells) and underlying mechanisms associated with Mage-D1 (melanoma-associated antigens-D1).

MATERIALS AND METHODS

Immunohistochemical staining of p75NTR in developing tooth germs was performed on E12.5d (embryonic 12.5 days) and E19.5d (embryonic 19.5 days). E12.5d EMSCs and E19.5d EMSCs were isolated in the same pregnant Sprague-Dawley rats from embryonic maxillofacial processes and tooth germs. p75NTR small-interfering RNA, p75NTR overexpression plasmid, Mage-D1 small-interfering RNA and recombined rat NGF were used to transfect cells.

RESULTS

p75NTR was expressed in epithelial-mesenchymal interaction areas at E12.5d and E19.5d tooth germ development stages. E19.5d EMSCs had higher p75NTR expression levels and differential mineralization capacity but lower levels of cell proliferation. Under induction by mineralized culture medium, the potential of differential mineralization had identical trends in regulation of p75NTR in EMSCs; Mage-D1 did not fluctuate and TrkA was not expressed. Binding of p75NTR and Mage-D1 were detected. Mage-D1 knockdown significantly down-regulated expression of related genes, which NGF could not rescue.

CONCLUSION

p75NTR participated in tooth germ development stages and mediated differential mineralization of EMSCs. p75NTR played a critical role in regulating the potential of differential mineralization of EMSCs. Mage-D1 seemed to act as a bridge in the underlying mechanism of effects of p75NTR.

Comparison of P75 NTR-positive and -negative etcomesenchymal stem cell odontogenic differentiation through epithelial-mesenchymal interaction

OBJECTIVES

The aim of this study was to investigate differences of odonto-differentiation between P75 -neurotrophin receptor (P75 -NTR)-positive ectomesenchymal stem cells (P75+EMSCs) and P75 -NTR-negative ectomesenchymal stem cells (P75-EMSCs), and their underlying mechanisms.

MATERIALS AND METHODS

Primary cranial neural crest-derived cells (CNC) were isolated from the first branchial arches, and P75+EMSCs and P75-EMSCs were sorted by fluorescence-activated cell sorting. Differentiation of P75+EMSCs or P75-EMSCs into odontoblast-like cells was induced by dental epithelial cells in vitro or in vivo. Differential gene expression profiles between P75+EMSCs and P75-EMSCs were analysed by microarray assay. Smad4-specific small interfering RNA and activator kartogenin were used to treat the cells, to evaluate effects of Smad4 in odonto-differentiation of P75+EMSCs or P75-EMSCs.

RESULTS

Under induction of dental epithelium conditioned medium, P75+EMSCs had more mineralized node formation and higher expression of Dmp1 and Dspp compared to P75-EMSCs. In our in vivo study, graft of P75+EMSCs recombination with dental epithelium showed higher expression of DMP1 and DSP. Knock-down of Smad4 in P75+EMSCs significantly downregulated expression of DMP1 and DSP, while activation of Smad4 in P75-EMSCs by the activator kartogenin, significantly increased DSP and DMP1 expression.

CONCLUSIONS

P75+EMSCs showed more odonto-differentiation potential than P75-EMSCs both in vivo and in vitro. Smad4 played a critical role in determination of odonto-differentiation potential of CNC-derived EMSCs.