Hard tissue-forming potential of stem/progenitor cells in human dental follicle and dental papilla

Curcumin attenuates replicative senescence in human dental follicle cells and restores their osteogenic differentiation

OBJECTIVE

This study aimed to examine the therapeutic effects of curcumin against replicative senescence in dental follicle cells (DFCs).

METHODS

Human DFCs were cultured in Dulbecco's Modified Eagle Medium with growth supplements. Replicative senescence in DFCs at different passages was assessed using β-galactosidase activity assay. Cell proliferation and size of DFCs at different passages were determined by CCK-8 kit and microscopy method, respectively. In addition, curcumin's effect on replicative senescence, cell proliferation, and size of DFCs at different passages was analyzed. Using western-blot analysis and siRNA-mediated gene silencing, we determined the molecular mechanisms involved in curcumin's effect against replicative senescence and osteogenic differentiation in DFCs at different passages.

RESULTS

We observed decreased proliferation and increased cell size and replicative senescence in cultured human DFCs at higher passages. Intriguingly, despite not showing any effect on cell size, curcumin (50 μM) significantly restored proliferation ability in DFCs and inhibited their replicative senescence. Concerning mechanisms, we found that curcumin inhibits replicative senescence in DFCs via down-regulation of senescence markers (P16 & P21) and restoration of proliferation markers (E2F1 & P53). Additionally, curcumin also rescued the osteogenic differentiation potential in higher-passage DFCs via restoration of osteogenic markers RUNX2 and OPN.

CONCLUSION

Our findings reveal for the first time that curcumin could act as a potential anti-senescence therapeutic for DFCs via regulation of proliferation, senescence, and osteogenic differentiation markers.

DNA protein kinase promotes cellular senescence in dental follicle cells

OBJECTIVE

Short telomeres and genomic DNA damage are causes of cellular senescence in dental follicle cells (DFCs).

DESIGN

This study examined the role of the DNA damage response (DDR) during cellular senescence of DFCs by β-galactosidase activity and DNA damage by comet assay. Expression of genes/proteins was determined by Western Blots and reverse transcription-quantitative polymerase chain reaction, while glycolysis was enzymatically estimated. Cell cycle stages and reactive oxygen species (ROS) were investigated by flow cytometry.

RESULTS

During the induction of cellular senescence gene expression of DDR genes were down-regulated, while DNA double-strand breaks occurred at the same time. Furthermore, inhibition of DNA protein kinase (DNA-PK) reduced senescence and ROS, both of which are associated with cellular senescence. In contrast, while these data suggest that inhibition of DDR is associated with the induction of cellular senescence, inhibition of DNA-PK did not result in renewal of DFCs, as inhibition resulted in typical features of depleted cells such as increased cell size and reduced cell proliferation rate. DNA-PK repression inhibited both osteogenic differentiation potential and glycolysis, which are typical features of cellular exhaustion. Moreover, DNA-PK affects cellular senescence via activation of AKT1 (protein kinase B).

CONCLUSION

Our results suggest that DNA-PK promotes cellular senescence, but DFCs may control the induction of cellular senescence via down-regulation of DDR genes. However, we also showed that inhibition of DNA-PK cannot renew senescent DFCs.

Advances in tooth agenesis and tooth regeneration

The lack of treatment options for congenital (0.1%) and partial (10%) tooth anomalies highlights the need to develop innovative strategies. Over two decades of dedicated research have led to breakthroughs in the treatment of congenital and acquired tooth loss. We revealed that by inactivating USAG-1, congenital tooth agenesis can be successfully ameliorated during early tooth development and that the inactivation promotes late-stage tooth morphogenesis in double knockout mice. Furthermore, Anti- USAG-1 antibody treatment in mice is effective in tooth regeneration and can be a breakthrough in treating tooth anomalies in humans. With approximately 0.1% of the population suffering from congenital tooth agenesis and 10% of children worldwide suffering from partial tooth loss, early diagnosis will improve outcomes and the quality of life of patients. Understanding the role of pathogenic USAG-1 variants, their interacting gene partners, and their protein functions will help develop critical biomarkers. Advances in next-generation sequencing, mass spectrometry, and imaging technologies will assist in developing companion and predictive biomarkers to help identify patients who will benefit from tooth regeneration.

Stem cells and common biomaterials in dentistry: a review study

Stem cells exist as normal cells in embryonic and adult tissues. In recent years, scientists have spared efforts to determine the role of stem cells in treating many diseases. Stem cells can self-regenerate and transform into some somatic cells. They would also have a special position in the future in various clinical fields, drug discovery, and other scientific research. Accordingly, the detection of safe and low-cost methods to obtain such cells is one of the main objectives of research. Jaw, face, and mouth tissues are the rich sources of stem cells, which more accessible than other stem cells, so stem cell and tissue engineering treatments in dentistry have received much clinical attention in recent years. This review study examines three essential elements of tissue engineering in dentistry and clinical practice, including stem cells derived from the intra- and extra-oral sources, growth factors, and scaffolds.

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.

A single-cell atlas of human teeth

Teeth exert fundamental functions related to mastication and speech. Despite their great biomedical importance, an overall picture of their cellular and molecular composition is still missing. In this study, we have mapped the transcriptional landscape of the various cell populations that compose human teeth at single-cell resolution, and we analyzed in deeper detail their stem cell populations and their microenvironment. Our study identified great cellular heterogeneity in the dental pulp and the periodontium. Unexpectedly, we found that the molecular signatures of the stem cell populations were very similar, while their respective microenvironments strongly diverged. Our findings suggest that the microenvironmental specificity is a potential source for functional differences between highly similar stem cells located in the various tooth compartments and open new perspectives toward cell-based dental therapeutic approaches.

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Dental atlas of the pulp and periodontal tissues of human teeth

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Identification of three common MSC subclusters between dental pulp and periodontium

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Dental pulp and periodontal MSCs are similar, and their niches diverge

A Current Overview of Scaffold-Based Bone Regeneration Strategies with Dental Stem Cells

Bone defects due to trauma or diseases still pose a clinical challenge to be resolved in the current tissue engineering approaches. As an alternative to traditional methods to restore bone defects, such as autografts, bone tissue engineering aims to achieve new bone formation via novel biomaterials used in combination with multipotent stem cells and bioactive molecules. Mesenchymal stem cells (MSCs) can be successfully isolated from various dental tissues at different stages of development including dental pulp, apical papilla, dental follicle, tooth germ, deciduous teeth, periodontal ligament and gingiva. A wide range of biomaterials including polymers, ceramics and composites have been investigated for their potential as an ideal bone scaffold material. This article reviews the properties and the manufacturing methods of biomaterials used in bone tissue engineering, and provides an overview of bone tissue regeneration approaches of scaffold and dental stem cell combinations as well as their limitations.

MicroRNA-204 regulates osteogenic induction in dental follicle cells

The dental follicle is an ectomesenchymal tissue surrounding developing tooth germ that contains osteoblastic-lineage-committed stem/progenitor cells. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression during stem cell growth, proliferation, and differentiation. The aim of this study was to investigate the key regulators of miRNA during osteogenic differentiation in human dental follicle cells (hDFC). We analyzed miRNA expression profiles in hDFC during osteoblastic differentiation. Expression of miR-204 was decreased in hDFC during osteogenic induction on microarray analysis. Real-time and RT-PCR analysis also showed that the expression of miR-204 was decreased in all three hDFC during osteogenic differentiation. To investigate whether miR-204 has an effect on osteogenic differentiation, miR-204 was predicted to target alkaline phosphatase (ALP), secreted protein acidic and rich in cysteine (SPARC), and Runx2 in the in the 3'-UTRs by in silico analysis. When miR-204 was transfected into hDFC, the activity of ALP and protein levels of SPARC and Runx2 were decreased. mRNA levels of ALP, SPARC and Runx2 were also decreased by miR-204 transfection. Our data suggest that miR-204 negatively regulates the osteogenic differentiation of hDFC by targeting the bone-specific transcription factor Runx2, the mineralization maker ALP and the bone extracellular matrix protein SPARC.

Current Perspectives on Tooth Implantation, Attachment, and Replacement in Amniota

Teeth and dentitions contain many morphological characters which give them a particularly important weight in comparative anatomy, systematics, physiology and ecology. As teeth are organs that contain the hardest mineralized tissues vertebrates can produce, their fossil remains are abundant and the study of their anatomy in fossil specimens is of major importance in evolutionary biology. Comparative anatomy has long favored studies of dental characters rather than features associated with tooth attachment and implantation. Here we review a large part of the historical and modern work on the attachment, implantation and replacement of teeth in Amniota. We propose synthetic definitions or redefinitions of most commonly used terms, some of which have led to confusion and conflation of terminology. In particular, there has long been much conflation between dental implantation that strictly concerns the geometrical aspects of the tooth-bone interface, and the nature of the dental attachment, which mostly concerns the histological features occurring at this interface. A second aim of this work was to evaluate the diversity of tooth attachment, implantation and replacement in extant and extinct amniotes in order to derive hypothetical evolutionary trends in these different dental traits over time. Continuous dental replacement prevails within amniotes, replacement being drastically modified only in Mammalia and when dental implantation is acrodont. By comparison, dental implantation frequently and rapidly changes at various taxonomic scales and is often homoplastic. This contrasts with the conservatism in the identity of the tooth attachment tissues (cementum, periodontal ligament, and alveolar bone), which were already present in the earliest known amniotes. Because the study of dental attachment requires invasive histological investigations, this trait is least documented and therefore its evolutionary history is currently poorly understood. Finally, it is essential to go on collecting data from all groups of amniotes in order to better understand and consequently better define dental characters.

Pulp Regeneration Concepts for Nonvital Teeth: From Tissue Engineering to Clinical Approaches

Following the basis of tissue engineering (Cells-Scaffold-Bioactive molecules), regenerative endodontic has emerged as a new concept of dental treatment. Clinical procedures have been proposed by endodontic practitioners willing to promote regenerative therapy. Preserving pulp vitality was a first approach. Later procedures aimed to regenerate a vascularized pulp in necrotic root canals. However, there is still no protocol allowing an effective regeneration of necrotic pulp tissue either in immature or mature teeth. This review explores in vitro and preclinical concepts developed during the last decade, especially the potential use of stem cells, bioactive molecules, and scaffolds, and makes a comparison with the goals achieved so far in clinical practice. Regeneration of pulp-like tissue has been shown in various experimental conditions. However, the appropriate techniques are currently in a developmental stage. The ideal combination of scaffolds and growth factors to obtain a complete regeneration of the pulp-dentin complex is still unknown. The use of stem cells, especially from pulp origin, sounds promising for pulp regeneration therapy, but it has not been applied so far for clinical endodontics, in case of necrotic teeth. The gap observed between the hope raised from in vitro experiments and the reality of endodontic treatments suggests that clinical success may be achieved without external stem cell application. Therefore, procedures using the concept of cell homing, through evoked bleeding that permit to recreate a living tissue that mimics the original pulp has been proposed. Perspectives for pulp tissue engineering in the near future include a better control of clinical parameters and pragmatic approach of the experimental results (autologous stem cells from cell homing, controlled release of growth factors). In the coming years, this therapeutic strategy will probably become a clinical reality, even for mature necrotic teeth.

Are Hertwig's epithelial root sheath cells necessary for periodontal formation by dental follicle cells?

OBJECTIVE

The role of Hertwig's epithelial root sheath (HERS) cells in periodontal formation has been controversial. This study aimed to further clarify whether HERS cells participate in formation of the periodontium, and the necessity of HERS cells in differentiation of dental follicle cells (DFCs) for periodontal regeneration.

DESIGN

HERS cells and DFCs were isolated and identified from post-natal 7-day Sprauge-Dawley rats. In vitro, direct co-culture of HERS cells and DFCs as well as the individual culture of HERS and DFCs were performed and followed by alizarin red staining and the quantitative real-time polymerase chain reaction analysis. For in vivo evaluation, the inactivated dentin matrix (iTDM) was fabricated. HERS cells and DFCs were seeded in combination or alone on iTDM and then transplanted into the rat omentum. Scanning electron microscope and further histological analysis were carried out.

RESULTS

In vitro, mineral-like nodules were found in the culture of HERS cells alone or HERS + DFCs either by alizarin red staining or scanning electronic microscope. The mineralization and fiber-forming relevant mRNA expressions, such as bone sialoprotein, osteopontin, collagen I and collagen III in HERS + DFCs were significantly higher than that of the HERS or DFCs alone group. After transplantation in vivo, cementum and periodontal ligament-like tissues were formed in groups of HERS + DFCs and HERS alone, while no evident hard tissues and attached fibers were found in DFCs alone.

CONCLUSIONS

Hertwig's epithelial root sheath cells directly participate in the formation of the periodontium, and they are essential for the differentiation of dental follicle cells to form periodontal structures. The combination use of Hertwig's epithelial root sheath cells and dental follicle cells is a promising approach for periodontal regeneration.

Advanced 3D Models Cultured to Investigate Mesenchymal Stromal Cells of the Human Dental Follicle

The human dental follicle (hDF) contains the developing tooth and is involved in regulating tooth maturation and eruption. To investigate the mesenchymal stromal cells of the dental follicle, 2 three-dimensional (3D) culture models were used, based on a dynamic bioreactor: the Rotary Cell Culture System (RCCS™) and the 3D culture of precursor cells isolated from follicular tissue (human dental follicle cells [hDFCs]). The hDFCs were obtained from impacted third molars of 20 patients. Two 3D culture models were tested. In the first model, intact hDF explants were cultured in 3D conditions, preserving the original tissue architecture; they were studied using histomorphological and molecular analyses. The second model involved the 3D culture of hDFCs, which were characterized to evaluate their multipotency in terms of differentiation capability. Of the biomarkers known to characterize hDFCs, hDF precursors were selected for our study. The immunophenotype and in situ immunocytochemistry were evaluated for markers CD44, CD90, CD146, CD105, CD31, CD34, and CD45 Ag. The results show that the conditions provided by the RCCS preserve the original organizational architecture of the cells. The 3D conditions of the model enhanced differentiation in response to adipogenic, osteogenic, and chondrogenic inductive growth media. The immunophenotype and the immunocytochemistry showed generally high expression of CD90, CD44, and CD105, while CD146 expression was more restricted to ∼30% of cells. No expression was observed for CD31, CD34, and CD45 Ags. Two 3D tissue- and cell-based ex vivo models of the hDF supported the long-term maintenance of hDF-specific cell phenotypes and their ability to recapitulate typical cellular differentiation states. As such, these ex vivo models could be used to study the physiopathology of human odontogenesis. In addition, in a therapeutic context, they could be used to examine the role of specific chemical signals (e.g., new therapeutic agents) in the processes of dental tissue repair and regeneration.

Stem Cells of Dental Origin: Current Research Trends and Key Milestones towards Clinical Application

Dental Mesenchymal Stem Cells (MSCs), including Dental Pulp Stem Cells (DPSCs), Stem Cells from Human Exfoliated Deciduous teeth (SHED), and Stem Cells From Apical Papilla (SCAP), have been extensively studied using highly sophisticated in vitro and in vivo systems, yielding substantially improved understanding of their intriguing biological properties. Their capacity to reconstitute various dental and nondental tissues and the inherent angiogenic, neurogenic, and immunomodulatory properties of their secretome have been a subject of meticulous and costly research by various groups over the past decade. Key milestone achievements have exemplified their clinical utility in Regenerative Dentistry, as surrogate therapeutic modules for conventional biomaterial-based approaches, offering regeneration of damaged oral tissues instead of simply “filling the gaps.” Thus, the essential next step to validate these immense advances is the implementation of well-designed clinical trials paving the way for exploiting these fascinating research achievements for patient well-being: the ultimate aim of this ground breaking technology. This review paper presents a concise overview of the major biological properties of the human dental MSCs, critical for the translational pathway “from bench to clinic.”

Evaluation of bone regeneration potential of dental follicle stem cells for treatment of craniofacial defects

BACKGROUND AIMS

Stem cell-based tissue regeneration offers potential for treatment of craniofacial bone defects. The dental follicle, a loose connective tissue surrounding the unerupted tooth, has been shown to contain progenitor/stem cells. Dental follicle stem cells (DFSCs) have strong osteogenesis capability, which makes them suitable for repairing skeletal defects. The objective of this study was to evaluate bone regeneration capability of DFSCs loaded into polycaprolactone (PCL) scaffold for treatment of craniofacial defects.

METHODS

DFSCs were isolated from the first mandibular molars of postnatal Sprague-Dawley rats and seeded into the PCL scaffold. Cell attachment and cell viability on the scaffold were examined with the use of scanning electron microscopy and alamar blue reduction assay. For in vivo transplantation, critical-size defects were created on the skulls of 5-month-old immunocompetent rats, and the cell-scaffold constructs were transplanted into the defects.

RESULTS

Skulls were collected at 4 and 8 weeks after transplantation, and bone regeneration in the defects was evaluated with the use of micro-computed tomography and histological analysis. Scanning electron microscopy and Alamar blue assay demonstrated attachment and proliferation of DFSCs in the PCL scaffold. Bone regeneration was observed in the defects treated with DFSC transplantation but not in the controls without DFSC transplant. Transplanting DFSC-PCL with or without osteogenic induction before transplantation achieved approximately 50% bone regeneration at 8 weeks. Formation of woven bone was observed in the DFSC-PCL treatment group. Similar results were seen when osteogenic-induced DFSC-PCL was transplanted to the critical-size defects.

CONCLUSIONS

This study demonstrated that transplantation of DFSCs seeded into PCL scaffolds can be used to repair craniofacial defects.

Dental Stem Cells in Pulp Regeneration: Near Future or Long Road Ahead?

Although regenerative endodontic procedures have yielded an impressive body of favorable outcomes, the treatment of necrotic immature permanent teeth in particular remains to be a challenge. Recent advances in dental stem cell (DSC) research have gained increasing insight in their regenerative potential and prospective use in the formation of viable dental tissues. Numerous studies have already reported successful dental pulp regeneration following application of dental pulp stem cells, stem cells from the apical papilla, or dental follicle precursor cells in different in vivo models. Next to responsive cells, dental tissue engineering also requires the support of an appropriate scaffold material, ranging from naturally occurring polymers to treated dentin matrix components. However, the routine use and banking of DSCs still holds some major challenges, such as culture-associated differences, patient-related variability, and the effects of culture medium additives. Only in-depth evaluation of these problems and the implementation of standardized models and protocols will effectively lead to better alternatives for patients who no longer benefit from current treatment protocols.

Genome-wide gene expression profiles of dental follicle stem cells

OBJECTIVE

Dental stem cells (SCs) will be increasingly used for bone regeneration in the future. Recently, dental follicle cells (DFCs) from retained human third molars have been isolated and characterized as osteogenic progenitors. Although these results are promising for regenerative dentistry, molecular processes during osteogenic differentiation are not yet well understood.

MATERIALS AND METHODS

This study compared DFCs before and during osteogenic differentiation. ALP activity was measured and cells were stained with alizarin red. Real-time RT-PCRs for osteogenic markers were done. The genome-wide expression profile was evaluated using a microarray.

RESULTS

DFCs showed strong mineralization and increased expression of osteogenic marker genes during osteogenic differentiation. A microarray analysis showed regulated genes before and in the process of osteogenic differentiation (day 7). Several regulated genes in DFCs were associated with skeletal development. Bioinformatic analysis revealed a number of factors associated with dental follicle osteogenic differentiation. Osteogenic differentiation affected expression levels of the transcriptional regulators FOXC2 and ZNF219.

CONCLUSION

In conclusion, the results yielded new objectives for further studies on transcription factors like FOXC2 or ETV1 and their role in dental SCs during osteogenic differentiation.

Cartilage tissue engineering on macroporous scaffolds using human tooth germ stem cells

The main objective was to study cartilage regeneration through differentiation of human tooth germ stem cells (HTGSCs) into chondrocytes on different three-dimensional (3D) scaffolds (PCL, PLLA and PCL-PLLA). Scaffold topographies were studied by scanning electron microscopy and it was found that the scaffolds had interconnected macroporous structures. HTGSCs were isolated from impacted third molar tooth germs of young adult patients and grown for 3 weeks on the scaffolds in chondrogenic differentiation medium. Cell proliferation on the scaffolds was determined by MTS assay and it was observed that all scaffolds supported cell proliferation. Immunostaining was carried out for morphological and differentiation analyses. Immunohistochemical analyses revealed that the cells attached onto the scaffolds and deposited cartilage-specific extracellular matrix (ECM). Real-time PCR was performed to determine the expression levels of cartilage-specific genes. After 21 days of incubation in cartilage differentiation medium, expression of collagen type II increased only in the cells seeded onto PCL-PLLA blend scaffolds. Similarly, aggrecan expression was the highest on PCL-PLLA scaffolds after 3 weeks. These results suggest that all the scaffolds, and especially PCL-PLLA, were suitable for chondrogenic differentiation of HTGSCs. Copyright © 2015 John Wiley & Sons, Ltd.

Today prospects for tissue engineering therapeutic approach in dentistry

In dental practice there is an increasing need for predictable therapeutic protocols able to regenerate tissues that, due to inflammatory or traumatic events, may suffer from loss of their function. One of the topics arising major interest in the research applied to regenerative medicine is represented by tissue engineering and, in particular, by stem cells. The study of stem cells in dentistry over the years has shown an exponential increase in literature. Adult mesenchymal stem cells have recently been isolated and characterized from tooth-related tissues and they might represent, in the near future, a new gold standard in the regeneration of all oral tissues. The aim of our review is to provide an overview on the topic reporting the current knowledge for each class of dental stem cells and to identify their potential clinical applications as therapeutic tool in various branches of dentistry.

c-kit positive cells and networks in tooth germs of human midterm fetuses

Numerous studies have attempted to characterize the dental pulp stem cells. However, studies performed on prenatal human tissues have not been performed to evaluate the in situ characterization and topography of progenitor cells. We aimed to perform such a study using of antibodies for CD117/c-kit and multiplex antibody for Ki67+ caspase 3. Antibodies were applied on samples dissected from five human midterm fetuses. Positive CD117/c-kit labeling was found in mesenchymal derived tissues, such as the dental follicle and the dental papilla. The epithelial tissues, that is, dental lamina, enamel organ and oral epithelia, also displayed isolated progenitor cells which were CD117/c-kit positive. Interestingly, CD117/c-kit positive cells of mesenchymal derived tissues extended multiple prolongations building networks; the most consistent of such networks were those of the dental follicle and the perivascular networks of the dental papilla. However, the mantle of the dental papilla was also positive for CD117/c-kit positive stromal networks. The CD117/c-kit cell populations building networks appeared mostly with a Ki67 negative phenotype. The results suggest that CD117/c-kit progenitor cells of the prenatal tooth germ tissues might be involved in intercellular signaling.

Epigenetic marks define the lineage and differentiation potential of two distinct neural crest-derived intermediate odontogenic progenitor populations

Epigenetic mechanisms, such as histone modifications, play an active role in the differentiation and lineage commitment of mesenchymal stem cells. In the present study, epigenetic states and differentiation profiles of two odontogenic neural crest-derived intermediate progenitor populations were compared: dental pulp (DP) and dental follicle (DF). ChIP on chip assays revealed substantial H3K27me3-mediated repression of odontoblast lineage genes DSPP and dentin matrix protein 1 (DMP1) in DF cells, but not in DP cells. Mineralization inductive conditions caused steep increases of mineralization and patterning gene expression levels in DP cells when compared to DF cells. In contrast, mineralization induction resulted in a highly dynamic histone modification response in DF cells, while there was only a subdued effect in DP cells. Both DF and DP progenitors featured H3K4me3-active marks on the promoters of early mineralization genes RUNX2, MSX2, and DLX5, while OSX, IBSP, and BGLAP promoters were enriched for H3K9me3 or H3K27me3. Compared to DF cells, DP cells expressed higher levels of three pluripotency-associated genes, OCT4, NANOG, and SOX2. Finally, gene ontology comparison of bivalent marks unique for DP and DF cells highlighted cell-cell attachment genes in DP cells and neurogenesis genes in DF cells. In conclusion, the present study indicates that the DF intermediate odontogenic neural crest lineage is distinguished from its DP counterpart by epigenetic repression of DSPP and DMP1 genes and through dynamic histone enrichment responses to mineralization induction. Findings presented here highlight the crucial role of epigenetic regulatory mechanisms in the terminal differentiation of odontogenic neural crest lineages.

Melatonin influences proliferation and differentiation of rat dental papilla cells in vitro and dentine formation in vivo by altering mitochondrial activity

Melatonin mediates a variety of biological processes ranging from the control of circadian rhythms to immune regulation. Melatonin also influences bone formation and osteointegration of dental implants. However, the effects of melatonin on dentine formation have not been examined. This study investigated the effects of melatonin on the proliferation and differentiation of rat dental papilla cells (rDPCs) in vitro and dentine formation in vivo. We found that melatonin (0, 10(-12) , 10(-10) ,10(-8)  m) induced a dose-dependent reduction in rDPCs proliferation, increased alkaline phosphatase (ALP) activity, the expression of dentine sialoprotein (DSP), and mineralized matrix formation in vitro. In vivo melatonin (50 mg/kg, BW, i.p.) inhibited dentine formation. Melatonin (10(-8 ) m) suppressed the activity of complex I and IV in the basal medium (OS-) and enhanced the activity of complex I and complex IV in osteogenic medium (OS+). These results demonstrate that melatonin suppresses the proliferation and promotes differentiation of rDPCs, the mechanisms of which may be related to activity of mitochondrial complex I and complex IV.

Biological Characteristics of Dental Stem Cells for Tissue Engineering

Scientists have recently focused their attention on adult stem cells as new and more effective treatments for different diseases and disabilities. In fact, it is known that stem cells are capable of renewing themselves and that they can generate multiple cell types. Today, there is new evidence that stem cells are present in far more tissues and organs than once thought and that these cells are capable of developing into more kinds of cells than previously imagined. In this chapter, we focus the attention on teeth as source of stem cells. In particular, we describe the characteristic of the different types of dental stem cells and their use in tissue engineering.

Tooth bioengineering leads the next generation of dentistry

BACKGROUND

As a result of numerous rapid and exciting developments in tissue engineering technology, scientists are able to regenerate a fully functional tooth in animal models, from a bioengineered tooth germ. Advances in technology, together with our understanding of the mechanisms of tooth development and studies dealing with dentally derived stem cells, have led to significant progress in the field of tooth regeneration.

AIM AND DESIGN

This review focuses on some of the recent advances in tooth bioengineering technology, the signalling pathways in tooth development, and in dental stem cell biology. These factors are highlighted in respect of our current knowledge of tooth regeneration.

RESULTS AND CONCLUSION

An understanding of these new approaches in tooth regeneration should help to prepare clinicians to use this new and somewhat revolutionary therapy while also enabling them to partake in future clinical trials. Tooth bioengineering promises to be at the forefront of the next generation of dental treatments.

Characteristics and osteogenic differentiation of stem/progenitor cells in the human dental follicle analyzed by gene expression profiling

The dental follicle is an ectomesenchymal tissue that surrounds developing tooth germ and that contains osteoblastic-lineage-committed stem/progenitor cells. We examined the osteogenic potential of human dental follicle cells (hDFC) by microarray analysis. We first compared the characteristics of hDFC with those of human bone marrow mesenchymal stem cells (hMSC). Like hMSC, hDFC expressed stem cell markers such as STRO-1 and Notch-1 and differentiated not only into the osteoblastic lineage, but also into the adipogenic lineage. We analyzed the gene expression profiles of hDFC and hMSC that were not differentiated toward the osteogenic lineage. The expression of cell markers and growth factor receptors by hDFC and hMSC was similar, whereas the expression pattern of homeobox genes differed between hDFC and hMSC. Next, we investigated gene expression in hDFC during osteogenic differentiation. Gene expression profiles were analyzed in hDFC cultured in osteogenic induction medium (OIM) or in growth medium (GM) for 3 and 10 days. Many genes whose expression was regulated under these conditions were functionally categorized as "transcription" genes. Osteogenic markers were up-regulated in hDFC during osteogenic differentiation, whereas neurogenic markers were down-regulated. The genes whose expression was regulated in hDFC during osteogenic differentiation were further analyzed by ingenuity pathway analysis and real-time polymerase chain reaction. Bone morphogenetic protein and transforming growth factor-β signaling pathways were activated in hDFC cultured in OIM for 3 days. This study indicates that the dental follicle contains stem cells and/or osteoblastic progenitor cells and is a potential cellular resource for bone regeneration therapy.

Stem cells in dentistry--part I: stem cell sources

Stem cells can self-renew and produce different cell types, thus providing new strategies to regenerate missing tissues and treat diseases. In the field of dentistry, adult mesenchymal stem/stromal cells (MSCs) have been identified in several oral and maxillofacial tissues, which suggests that the oral tissues are a rich source of stem cells, and oral stem and mucosal cells are expected to provide an ideal source for genetically reprogrammed cells such as induced pluripotent stem (iPS) cells. Furthermore, oral tissues are expected to be not only a source but also a therapeutic target for stem cells, as stem cell and tissue engineering therapies in dentistry continue to attract increasing clinical interest. Part I of this review outlines various types of intra- and extra-oral tissue-derived stem cells with regard to clinical availability and applications in dentistry. Additionally, appropriate sources of stem cells for regenerative dentistry are discussed with regard to differentiation capacity, accessibility and possible immunomodulatory properties.

Tooth root regeneration using dental follicle cell sheets in combination with a dentin matrix - based scaffold

Stem cell mediated tissue engineering has been acknowledged as a prospective strategy for repairing and replacing damaged and lost tissues. However, the low survival rate of implanted stem cells proves to be a major challenge in the management of transplantation failures. While previous studies have indicated the effectiveness of tissue engineered cell sheets in improving the survival rate of implanted cells, we have recently demonstrated the use of treated dentin matrix (TDM) as a biological scaffold and dental follicle cells (DFCs) as the seeding cells for dentinogenesis and tooth root construction. This study proposes a strategy utilizing TDM with human dental follicle cell sheets (DFCSs) for root regeneration. The biological characteristics and changes of human DFCSs under the effect of TDM were studied with scanning electron microscopy, transmission electron microscopy, immunofluorescence microscopy, immunohistochemistry and quantitative real-time PCR. DFCSs combined with TDM were implanted subcutaneously into the dorsum of mice. Histological examination of the harvested grafts revealed a whirlpool-like alignment of the DFCs in multiple layers that were positive for COLI, integrinβ1, fibronectin and alkaline phosphatase (ALP), suggestive of the formation of a rich extracellular matrix. DFCSs, under the effect of TDM, highly expressed DMP-1 and bone sialoprotein (BSP), indicating their potential for odontogenesis and osteogenesis. Importantly, in vivo, TDM could induce and support DFCSs to develop new dentin-pulp like tissues and cementum-periodontal complexes that were positive for markers such as DSP, nestin and VIII factors, COLI and cementum attachment protein (CAP), implying successful root regeneration. Therefore, DFCSs combined with TDM may prove to be a better strategy for the construction of tooth root, and is a prospective approach that could be utilized for the treatment of root or tooth defect or loss in future.

The effects of acellular amniotic membrane matrix on osteogenic differentiation and ERK1/2 signaling in human dental apical papilla cells

The amniotic membrane (AM) has been widely used in the field of tissue engineering because of the favorable biological properties for scaffolding material. However, little is known about the effects of an acellular AM matrix on the osteogenic differentiation of mesenchymal stem cells. In this study, it was found that both basement membrane side and collagenous stroma side of the acellular AM matrix were capable of providing a preferential environment for driving the osteogenic differentiation of human dental apical papilla cells (APCs) with proven stem cell characteristics. Acellular AM matrix potentiated the induction effect of osteogenic supplements (OS) such as ascorbic acid, β-glycerophosphate, and dexamethasone and enhanced the osteogenic differentiation of APCs, as seen by increased core-binding factor alpha 1 (Cbfa-1) phosphorylation, alkaline phosphatase activity, mRNA expression of osteogenic marker genes, and mineralized matrix deposition. Even in the absence of soluble OS, acellular AM matrix also could exert the substrate-induced effect on initiating APCs' differentiation. Especially, the collagenous stroma side was more effective than the basement membrane side. Moreover, the AM-induced effect was significantly inhibited by U0126, an inhibitor of extracellular signaling-regulated kinase 1/2 (ERK1/2) signaling. Taken together, the osteogenic differentiation promoting effect on APCs is AM-specific, which provides potential applications of acellular AM matrix in bone/tooth tissue engineering.

Evaluation of the delivery of mesenchymal stem cells into the root canal space of necrotic immature teeth after clinical regenerative endodontic procedure

INTRODUCTION

Immature teeth with open apices treated with conventional nonsurgical root canal treatment often have a poor prognosis as a result of the increased risk of fracture and susceptibility to recontamination. Regenerative endodontics represents a new treatment modality that focuses on reestablishment of pulp vitality and continued root development. This clinical procedure relies on the intracanal delivery of a blood clot (scaffold), growth factors (possibly from platelets and dentin), and stem cells. However, to date, the clinical presence of stem cells in the canal space after this procedure has not been demonstrated. The purpose of this clinical study was to evaluate whether regenerative endodontic procedures are able to deliver stem cells into the canal space of immature teeth in young patients and to identify the possible tissue origin for these cells.

METHODS

After informed consent, the first appointment consisted of NaOCl irrigation and treatment with a triple antibiotic paste. One month later, the root canal space was irrigated with sterile saline, and bleeding was evoked with collection of samples on paper points. Real-time reverse-transcription polymerase chain reaction and immunocytochemistry were conducted to compare the gene transcripts and proteins found in the root canal sample with levels found in the systemic circulation.

RESULTS

Molecular analyses of blood collected from the canal system indicated the significant accumulation of transcripts for the stem cell markers CD73 and CD105 (up to 600-fold), compared with levels found in the systemic blood. Furthermore, this effect was selective because there was no change in expression of the differentiation markers ALK-P, DSPP, ZBTB16, and CD14. Histologic analyses demonstrated that the delivered cells expressed both CD105 and STRO-1, markers for a subpopulation of mesenchymal stem cells.

CONCLUSIONS

Collectively, these findings demonstrate that the evoked-bleeding step in regenerative procedures triggers the significant accumulation of undifferentiated stem cells into the canal space where these cells might contribute to the regeneration of pulpal tissues seen after antibiotic paste therapy of the immature tooth with pulpal necrosis.

Mesenchymal stem cells derived from dental tissues

Regeneration of tissues occurs naturally due to the existence of stem cells with the capacity to self-regenerate and differentiate; however, regenerative capacity decreases with age, and in many cases, regeneration is not sufficient to repair the damage produced by degenerative, ischaemic, inflammatory, or tumour-based diseases. In the last decade, advances have been made in the understanding of stem cells, the genes that control the alternative fates of quiescence and differentiation, and the niches that provide specific signals that modulate cell fate decisions. Embryonic stem-cell research is shedding light on the secrets of development. Adult stem cells (AS cells) are available from several sources. Bone marrow and connective tissue have been used in preliminary clinical trials for regenerative therapy. Recently, several types of AS cells have been isolated from teeth, including dental pulp stem cells, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, dental follicle progenitor stem cells and stem cells from apical papilla. Preliminary data suggest that these cells have the capacity to differentiate into osteoblasts, adipocytes, chondrocytes and neural cells. If confirmed, these data would support the use of these cells, which are easily obtained from extracted teeth, in dental therapies, including in regenerative endodontics, providing a new therapeutic modality.

Stem cells isolated from human dental follicles have osteogenic potential

OBJECTIVE

Stem cells isolated from human dental follicles as a potential cell source for bone-tissue engineering were examined for correcting a critical bone defect.

STUDY DESIGN

Impacted third molars were collected and single cell-derived cell populations were cultivated in growth medium. Single cell-derived cell lines were examined in terms of cell shape, gene expression patterns, differentiation capacity in vitro, and osteogenic potential in vivo.

RESULTS

Three distinct cell populations were identified with different morphologies, patterns of gene expression, and differentiation capacity. All 3 cell populations promoted bone formation when transplanted into surgically created critical-size defects in immunodeficient rat calvaria, compared with control animals without cell transplantation, although one of these populations showed a weak capacity for osteogenetic differentiation in vitro.

CONCLUSIONS

Human dental follicle can derive at least 3 unique cell populations in culture, all of which promote bone formation in vivo.