Insight into the maintenance of odontogenic potential in mouse dental mesenchymal cells based on transcriptomic analysis

Induction of periodontal ligament-derived mesenchymal stromal cell-like cells from human induced pluripotent stem cells

Introduction

Periodontal disease is a common oral infection which affects the tooth-supportive tissues directly. Considering the limitation of present regenerative treatments for severe periodontal cases, cytotherapies have been gradually introduced. Human periodontal ligament-derived mesenchymal stromal cells (hPDLMSCs), while identified as one of the promising cell sources for periodontal regenerative therapy, still hold some problems in the clinical application especially their limited life span. To solve the problems, human induced pluripotent stem cells (hiPSCs) are taken into consideration as a robust supply for hPDLMSCs.

Methods

The induction of hPDLMSCs was performed based on the generation of neural crest-like cells (NCLCs) from hiPSCs. Fibronectin and laminin were tested as coating materials for NCLCs differentiation when following previous protocol, and the characteristics of induced cells were identified by flow cytometry and RT-qPCR for evaluating the induction efficiency. Subsequently, selected dental ectoderm signaling-related cytokines were applied for hPDLMSCs induction for 14 days, and dental mesenchyme-related genes, dental follicle-related genes and hPDL-related genes were tested by RT-qPCR for the evaluation of differentiation.

Results

Compared to the 58% in laminin-coated condition, fibronectin-coated condition had a higher induction efficiency of CD271high cells as 86% after 8-day induction, while the mesenchymal potential of induced NCLCs was similar between two coating materials.It was shown that the gene expressions of dental mesenchyme, dental follicles and hPDL cells were significantly enhanced with the stimulation of the combination with fibroblast growth factor 8b (FGF8b), FGF2, and bone morphogenetic protein 4 (BMP4).

Conclusion

FN coating was more effective in NCLCs induction, and the FGF8b+FGF2+BMP4 growth factor cocktail was effective in hPDLMSC-like cell generation. These findings underscored the likely regenerative potential of hiPSCs as an applicable and promising curative strategy for periodontal diseases.

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

INTRODUCTION

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

OBJECTIVE

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

RESULTS AND DISCUSSION

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

CONCLUSION

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

Identification of novel candidate genes implicated in odontogenic potential in the developing mouse tooth germ using transcriptome analysis

BACKGROUND

In tooth bioengineering for replacement therapy of missing teeth, the utilized cells must possess an inductive signal-forming ability to initiate odontogenesis. This ability is called odontogenic potential. In mice, the odontogenic potential signal is known to be translocated from the epithelium to the mesenchyme at the early bud stage in the developing molar tooth germ. However, the identity of the molecular constituents of this process remains unclear.

OBJECTIVE

The purpose of this study is to determine the molecular identity of odontogenic potential and to provide a new perspective in the field of tooth development research.

METHODS

In this study, whole transcriptome profiles of the mouse molar tooth germ epithelium and mesenchyme were investigated using the RNA sequencing (RNA-seq) technique. The analyzed transcriptomes corresponded to two developmental stages, embryonic day 11.5 (E11.5) and 14.5 (E14.5), which represent the odontogenic potential shifts.

RESULTS

We identified differentially expressed genes (DEGs), which were specifically overexpressed in both the E11.5 epithelium and E14.5 mesenchyme, but not expressed in their respective counterparts. Of the 55 DEGs identified, the top three most expressed transcription factor genes (transcription factor AP-2 beta isoform 3 [TFAP2B], developing brain homeobox protein 2 [DBX2], and insulin gene enhancer protein ISL-1 [ISL1]) and three tooth development-related genes (transcription factor HES-5 [HES5], platelet-derived growth factor D precursor [PDGFD], semaphrin-3 A precursor [SEMA3A]) were selected and validated by quantitative RT-PCR. Using immunofluorescence staining, the TFAP2B protein expression was found to be localized only at the E11.5 epithelium and E14.5 mesenchyme.

CONCLUSIONS

Thus, our empirical findings in the present study may provide a new perspective into the characterization of the molecules responsible for the odontogenic potential and may have an implication in the cell-based whole tooth regeneration strategy.

Tooth Bioengineering and Regenerative Dentistry

Over the past 100 y, tremendous progress has been made in the fields of dental tissue engineering and regenerative dental medicine, collectively known as translational dentistry. Translational dentistry has benefited from the more mature field of tissue engineering and regenerative medicine (TERM), established on the belief that biocompatible scaffolds, cells, and growth factors could be used to create functional, living replacement tissues and organs. TERM, created and pioneered by an interdisciplinary group of clinicians, biomedical engineers, and basic research scientists, works to create bioengineered replacement tissues that provide at least enough function for patients to survive until donor organs are available and, at best, fully functional replacement organs. Ultimately, the goal of both TERM and regenerative dentistry is to bring new and more effective therapies to the clinic to treat those in need. Very recently, the National Institutes of Health/National Institute of Dental and Craniofacial Research invested $24 million over a 3-y period to create dental oral and craniofacial translational resource centers to facilitate the development of more effective therapies to treat edentulism and other dental-related diseases over the next decade. This exciting era in regenerative dentistry, particularly for whole-tooth tissue engineering, builds on many key successes over the past 100 y that have contributed toward our current knowledge and understanding of signaling pathways directing natural tooth and dental tissue development-the foundation for current strategies to engineer functional, living replacement dental tissues and whole teeth. Here we use a historical perspective to present key findings and pivotal advances made in the field of translational dentistry over the past 100 y. We will first describe how this process has evolved over the past 100 y and then hypothesize on what to expect over the next century.

Effects of oleanolic acid acetate on bone formation in an experimental periodontitis model in mice

OBJECTIVE

We evaluated the role of oleanolic acid acetate (OAA), a triterpenoid commonly used in the treatment of liver disorders, inflammatory diseases, and metastasis, in bone formation after tooth loss by periodontitis.

BACKGROUND

Periodontitis causes the sequential degradation of the alveolar bone and associated structures, resulting in tooth loss. Several studies have attempted to regenerate the bone for implantation following tooth loss.

METHODS

Maxillary left second molar was extracted from 8-week-old male mice following induction of periodontitis by ligature for 5 days. The extraction socket was treated with 50 ng/µL OAA for 1, 2, and 3 weeks. Detailed morphological changes were examined using Masson's trichrome staining, and the precise localization patterns of various signaling molecules, including CD31, F4/80, interleukin (IL)-6, and osteocalcin, were observed. The volume of bone formation was examined by Micro-CT. Osteoclasts were enumerated using tartrate-resistant acid phosphatase (TRAP) staining. For molecular dissection of signaling molecules, we employed the hanging-drop in vitro cultivation method at E14 for 1 day and examined the expression pattern of transforming growth factor (TGF)-β superfamily and Wnt signaling genes.

RESULTS

Histomorphometrical examinations showed facilitated bone formation in the extraction socket following OAA treatment. In addition, OAA-treated specimens showed the altered localization patterns of inflammatory and bone formation-related signaling molecules including CD31, F4/80, IL-6, and osteocalcin. Also, embryonic tooth germ mesenchymal tissue cultivation with OAA treatment showed the significant altered expression patterns of signaling molecules such as transforming growth factor (TGF)-β superfamily and Wnt signaling.

CONCLUSIONS

Oleanolic acid acetate induces bone formation and remodeling through proper modulation of osteoblast, osteoclast, and inflammation with regulations of TGF-β and Wnt signaling.

Generation of tooth-periodontium complex structures using high-odontogenic potential dental epithelium derived from mouse embryonic stem cells

BACKGROUND

A number of studies have shown that tooth-like structures can be regenerated using induced pluripotent stem cells and mouse embryonic stem (mES) cells. However, few studies have reported the regeneration of tooth-periodontium complex structures, which are more suitable for clinical tooth transplantation. We established an optimized approach to induce high-odontogenic potential dental epithelium derived from mES cells by temporally controlling bone morphogenic protein 4 (BMP4) function and regenerated tooth-periodontium complex structures in vivo.

METHODS

First, immunofluorescence and quantitative reverse transcription-polymerase chain reaction were used to identify the watershed of skin and the oral ectoderm. LDN193189 was then used to inhibit the BMP4 receptor around the watershed, followed by the addition of exogenous BMP4 to promote BMP4 function. The generated dental epithelium was confirmed by western blot analysis and immunofluorescence. The generated epithelium was ultimately combined with embryonic day 14.5 mouse mesenchyme and transplanted into the renal capsules of nude mice. After 4 weeks, the tooth-periodontium complex structure was examined by micro-computed tomography (CT) and hematoxylin and eosin (H&E) staining.

RESULTS

Our study found that the turning point of oral ectoderm differentiation occurred around day 3 after the embryoid body was transferred to a common culture plate. Ameloblastin-positive dental epithelial cells were detected following the temporal regulation of BMP4. Tooth-periodontium complex structures, which included teeth, a periodontal membrane, and alveolar bone, were formed when this epithelium was combined with mouse dental mesenchyme and transplanted into the renal capsules of nude mice. Micro-CT and H&E staining revealed that the generated tooth-periodontium complex structures shared a similar histological structure with normal mouse teeth.

CONCLUSIONS

An optimized induction method was established to promote the differentiation of mES cells into dental epithelium by temporally controlling the function of BMP4. A novel tooth-periodontium complex structure was generated using the epithelium.