Remission for Loss of Odontogenic Potential in a New Micromilieu In Vitro

Generating Tooth Organoids Using Defined Bioorthogonally Cross-Linked Hydrogels

Generating teeth in vitro requires mimicking tooth developmental processes. Biomaterials are essential to support 3D tooth organoid formation, but their properties must be finely tuned to achieve the required biomimicry for tooth development. For the first time, we used bioorthogonally cross-linked hydrogels as defined 3D matrixes for tooth developmental engineering, and we highlighted how their properties play a pivotal role in enabling 3D tooth organoid formation in vitro. We prepared hydrogels by mixing gelatin precursors modified either with tetrazine (Tz) or norbornene (Nb) moieties. We tuned the hydrogel properties (E = 2-7 kPa; G' = 500-1500 Pa) by varying the gelatin concentration (8% vs 12% w/V) and stoichiometric ratio (Tz:Nb = 1 vs 0.5). We encapsulated dental epithelial-mesenchymal cell pellets in a library of hydrogels and identified a hydrogel formulation that enabled successful growth kinetics and morphogenesis of tooth germs, introducing a defined tunable platform for tooth organoid engineering and modeling.

Decoding a gene expression program that accompanies the phenotype of sporadic and Basal Cell Nevus Syndrome-associated odontogenic keratocyst

BACKGROUND

Odontogenic keratocyst (OKC) is characterized by local aggressive behavior and a high recurrence rate, as well as the potential to develop in association with the Basal Cell Nevus Syndrome (BCNS). The aim of this study was to decode the gene expression program accompanying OKC phenotype.

METHODS

150-bp paired-end RNA-sequencing was applied on 6 sporadic and 6 BSCN-associated whole-tissue OKC samples in comparison to 6 dental follicles, coupled to bioinformatics and complemented by immunohistochemistry.

RESULTS

2,654 and 2,427 differentially expressed genes were captured to characterize the transcriptome of sporadic and BCNS-associated OKCs, respectively. Gene ontologies (GOs) related to "epidermis/skin development" and "keratinocyte/epidermal cell differentiation" were enriched among the upregulated genes (KRT10, NCCRP1, TP63, GRHL3, SOX21), while "extracellular matrix (ECM) organization" (ITGA5, LOXL2) and "odontogenesis" (MSX1, LHX8) GOs were overrepresented among the downregulated genes in OKC. Interestingly, upregulation of various embryonic stem cells (ESCs) markers (EPHA1, SCNN1A) and genes committed in cellular reprogramming (SOX2, KLF4, OVOL1, IRF6, TACSTD2, CDH1) was found in OKC. These findings were highly shared between sporadic and BCNS-associated OKCs. Immunohistochemistry verified SOX2, KLF4, OVOL1, IRF6, TACSTD2/TROP2, CDH1/E-cadherin, and p63 expression predominantly in the OKC suprabasal epithelial layers.

CONCLUSION

The OKC transcriptomic profile is characterized by a prominent epidermal and dental epithelial fate, a repressed dental mesenchyme fate combined with deregulated ECM organization, and enhanced stemness gene signatures. Thus, we propose a developed epidermis-like phenotype in the OKC suprabasal epithelial cells, established in parallel to a significant upregulation of marker genes related to ESCs and cellular reprogramming. This article is protected by copyright. All rights reserved.

Effects of KnockOut Serum Replacement on Differentiation of Mouse-Induced Pluripotent Stem Cells into Odontoblasts

Serum serves as a source of rich nutrients during in vitro cell culture, facilitating cell adhesion, growth, and differentiation. When culturing stem cells for transplantation, however, it must be remembered that such culture medium may contain substances potentially harmful to the proposed recipient and may even induce cellular damage. The purpose of this study was to determine whether KnockOut Serum Replacement (KSR), a chemically defined medium supplement, enhanced in vitro differentiation of induced pluripotent stem cells into odontoblasts. Cranial neural crest cells, precursors of odontoblasts, were generated from mouse-induced pluripotent stem cells. They were then cultured in serum-free Dulbecco's modified Eagle's/F12 medium containing fibroblast growth factor 8 with or without KSR. The cells cultured with KSR showed strong proliferation, acquired a spindle-like morphology, and connected with the surrounding cells. KnockOut Serum Replacement also boosted expression of odontoblast markers as measured by qRT-PCR, and increased dentin sialoprotein as assessed by immunostaining. These results confirmed that mouse-induced pluripotent stem cells differentiated into odontoblasts under serum-free conditions, and that KSR enhanced the efficiency of this process.

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.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

Integrated analysis of lncRNA-mRNA networks associated with an SLA titanium surface reveals the potential role of HIF1A-AS1 in bone remodeling

Microstructured titanium surface implants, such as typical sandblasted and acid-etched (SLA) titanium implants, are widely used to promote bone apposition in prosthetic treatment by dental implants following tooth loss. Although there are multiple factors associated with the superior osseointegration of an SLA titanium surface, the molecular mechanisms of long noncoding RNAs (lncRNAs) are still unclear. In this study, we characterized smooth (SMO) and SLA surfaces, and compared the osteoinduction of these surfaces using human bone marrow-derived mesenchymal stem cells (hBMSCs) in vitro and implants in a rat model in vivo. Then, we used microarrays and bioinformatics analysis to investigate the differential expression profiles of mRNAs and lncRNAs on SMO and SLA titanium surfaces. An lncRNA–mRNA network was constructed, which showed an interaction between lncRNA HIF1A antisense RNA 1 (HIF1A-AS1) and vascular endothelial growth factor. We further found that knockdown of HIF1A-AS1 significantly decreased osteogenic differentiation of hBMSCs. This study screened SLA-induced lncRNAs using a systemic strategy and showed that lncRNA HIF1A-AS1 plays a role in promotion of new bone formation in the peri-implant area, providing a novel insight for future surface modifications of implants.

Long non-coding RNA HIF1A-AS1 plays a role in SLA titanium surface-induced osteogenic differentiation of hBMSCs by regulating p38 MAPK.

Tooth Repair and Regeneration

PURPOSE OF REVIEW

Current dental treatments are based on conservative approaches, using inorganic materials and appliances.This report explores and discusses the newest achievements in the field of "regenerative dentistry," based on the concept of biological repair as an alternative to the current conservative approach.

RECENT FINDINGS

The review covers and critically analyzes three main approaches of tooth repair: the re-mineralization of the enamel, the biological repair of dentin, and whole tooth engineering.

SUMMARY

The development of a concept of biological repair based on the role of the Wnt signaling pathway in reparative dentin formation offers a new translational approach into development of future clinical dental treatments.In the field of bio-tooth engineering, the current focus of the researchers remains the establishment of odontogenic cell-sources that would be viable and easily accessible for future bio-tooth engineering.

Time series clustering of mRNA and lncRNA expression during osteogenic differentiation of periodontal ligament stem cells

Background

Long noncoding RNAs (lncRNAs) are regulatory molecules that participate in biological processes such as stem cell differentiation. Periodontal ligament stem cells (PDLSCs) exhibit great potential for the regeneration of periodontal tissue and the formation of new bone. However, although several lncRNAs have been found to be involved in the osteogenic differentiation of PDLSCs, the temporal transcriptomic landscapes of mRNAs and lncRNAs need to be mapped to obtain a complete picture of osteoblast differentiation. In this study, we aimed to characterize the time-course expression patterns of lncRNAs during the osteogenic differentiation of PDLSCs and to identify the lncRNAs that are related to osteoblastic differentiation.

Methods

We cultured PDLSCs in an osteogenic medium for 3, 7, or 14 days. We then used RNA sequencing (RNA-seq) to analyze the expression of the coding and non-coding transcripts in the PDLSCs during osteogenic differentiation. We also utilized short time-series expression miner (STEM) to describe the temporal patterns of the mRNAs and lncRNAs. We then performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses to assess the biological relevance of genes in each profile, and used quantitative real-time PCR (qRT-PCR) to validate the differentially expressed mRNAs and lncRNAs that were associated with osteoblast differentiation. Lastly, we performed a knock down of two lncRNAs, MEG8, and MIR22HG, and evaluated the expression of osteogenic markers.

Results

When PDLSCs were differentiated to osteoblasts, mRNAs associated with bone remodeling, cell differentiation, and cell apoptosis were upregulated while genes associated with cell proliferation were downregulated. lncRNAs showed stage-specific expression, and more than 200 lncRNAs were differentially expressed between the undifferentiated and osteogenically differentiated PDLSCs. Using STEM, we identified 25 temporal gene expression profiles, among which 14 mRNA and eight lncRNA profiles were statistically significant. We found that genes in pattern 12 were associated with osteoblast differentiation. The expression patterns of osteogenic mRNAs (COL6A1, VCAN, RRBP1, and CREB3L1) and lncRNAs (MEG8 and MIR22HG) were consistent between the qRT-PCR and RNA-seq results. Moreover, the knockdown of MEG8 and MIR22HG significantly decreased the expression of osteogenic markers (runt-related transcription factor 2 and osteocalcin).

Discussion

During the osteogenic differentiation of PDLSCs, both mRNAs and lncRNAs showed stage-specific expression. lncRNAs MEG8 and MIR22HG showed a high correlation with osteoblastogenesis. Our results can be used to gain a more comprehensive understanding of the molecular events regulating osteoblast differentiation and the identification of functional lncRNAs in PDLSCs.

The Circular RNA Landscape of Periodontal Ligament Stem Cells During Osteogenesis

BACKGROUND

The present study aims to investigate the distinct expression pattern of circular RNAs (circRNAs) in periodontal ligament stem cells (PDLSCs) during osteogenesis.

METHODS

PDLSCs were isolated and cultured in osteogenic medium. Total RNA was extracted from cells at day 0 (D0), day 3 (D3), day 7 (D7), and day 14 (D14) and submitted to RNA-sequencing to detect expression profiles of circRNAs, messenger RNAs (mRNAs), and microRNAs (miRNAs). Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to validate expression of circRNAs and miRNAs. Differential expression analysis and gene ontology analysis were performed. A circRNA-miRNA-mRNA network was constructed to reveal the potential regulatory role of circRNAs.

RESULTS

A total of 12,693 circRNA transcripts were detected, and circRNAs displayed stage-specific expression. Expression of four well-known circRNAs was validated by qRT-PCR. In total, 118 circRNAs were differentially expressed at D3, 128 circRNAs were differentially expressed at D7, and 139 circRNAs were differentially expressed at D14 compared with D0. Host genes of differentially expressed circRNAs were enriched in cytoplasmic or membrane-bound vesicles and extracellular matrix, indicating their potential roles in modulating biogenesis of extracellular vesicles. Moreover, mRNAs that were potentially regulated by circRNAs were enriched in bone-formation-associated processes, including extracellular matrix organization, cell differentiation, and bone morphogenetic protein signaling pathway.

CONCLUSION

Expression profiles of circRNAs were significantly altered during osteogenic differentiation of PDLSCs, providing a clue for future studies on the role of circRNAs in osteoblast differentiation.

Mesenchymal Cell Community Effect in Whole Tooth Bioengineering

In vitro expanded cell populations can contribute to bioengineered tooth formation but only as cells that respond to tooth-inductive signals. Since the success of whole tooth bioengineering is predicated on the availability of large numbers of cells, in vitro cell expansion of tooth-inducing cell populations is an essential requirement for further development of this approach. We set out to investigate if the failure of cultured mesenchyme cells to form bioengineered teeth might be rescued by the presence of uncultured cells. To test this, we deployed a cell-mixing approach to evaluate the contributions of cell populations to bioengineered tooth formation. Using genetically labeled cells, we are able to identify the formation of tooth pulp cells and odontoblasts in bioengineered teeth. We show that although cultured embryonic dental mesenchyme cells are unable to induce tooth formation, they can contribute to tooth induction and formation if combined with noncultured cells. Moreover, we show that teeth can form from cell mixtures that include embryonic cells and populations of postnatal dental pulp cells; however, these cells are unable to contribute to the formation of pulp cells or odontoblasts, and at ratios of 1:1, they inhibit tooth formation. These results indicate that although in vitro cell expansion of embryonic tooth mesenchymal cells renders them unable to induce tooth formation, they do not lose their ability to contribute to tooth formation and differentiate into odontoblasts. Postnatal pulp cells, however, lose all tooth-inducing and tooth-forming capacity following in vitro expansion, and at ratios >1:3 postnatal:embryonic cells, they inhibit the ability of embryonic dental mesenchyme cells to induce tooth formation.