Differentiation of Dental Pulp Stem Cells into Regular-Shaped Dentin-Pulp Complex Induced by Tooth Germ Cell Conditioned Medium

Tissue engineering: state of the art in oral rehabilitation

More than 85% of the global population requires repair or replacement of a craniofacial structure. These defects range from simple tooth decay to radical oncologic craniofacial resection. Regeneration of oral and craniofacial tissues presents a formidable challenge that requires synthesis of basic science, clinical science and engineering technology. Identification of appropriate scaffolds, cell sources and spatial and temporal signals (the tissue engineering triad) is necessary to optimize development of a single tissue, hybrid organ or interface. Furthermore, combining the understanding of the interactions between molecules of the extracellular matrix and attached cells with an understanding of the gene expression needed to induce differentiation and tissue growth will provide the design basis for translating basic science into rationally developed components of this tissue engineering triad. Dental tissue engineers are interested in regeneration of teeth, oral mucosa, salivary glands, bone and periodontium. Many of these oral structures are hybrid tissues. For example, engineering the periodontium requires growth of alveolar bone, cementum and the periodontal ligament. Recapitulation of biological development of hybrid tissues and interfaces presents a challenge that exceeds that of engineering just a single tissue. Advances made in dental interface engineering will allow these tissues to serve as model systems for engineering other tissues or organs of the body. This review will begin by covering basic tissue engineering principles and strategic design of functional biomaterials. We will then explore the impact of biomaterials design on the status of craniofacial tissue engineering and current challenges and opportunities in dental tissue engineering.

The biological effect of dentin noncollagenous proteins (DNCPs) on the human periodontal ligament stem cells (HPDLSCs) in vitro and in vivo

It was recognized that periodontal progenitor cells penetrate disintegrated Hertwig's epithelial root sheath, and contact with root dentin give rise to periodontium formation. Clinically, direct contact of the conditioned or denuded root surfaces with periodontal cells seems to be a prerequisite for periodontal regeneration. In this study, we investigated the biological effect of dentin noncollagenous proteins (DNCPs) on the human periodontal ligament stem cells (HPDLSCs) in vitro and in vivo. Chemical-conditioned root dentin (CCRD) was prepared by process of partly demineralization and deproteinization. Treated HPDLSCs with DNCPs showed increased proliferation and adhesion ability. Induced HPDLSCs presented several features of cementoblast differentiation, as indicated by morphologic changes, enhanced alkaline phosphatase (ALP) activity, increased matrix mineralization, and upregulated expression of mineralization-associated genes. Incubation of treated HPDLSC aggregate in vivo revealed that cementum-like tissues formed along the CCRD surface with fibrous tissue adjacent to or inserted into it, but untreated HPDLSCs cannot form similar structure. To our knowledge, this is the first study to apply active proteins derived from dentin with periodontal stem cells to construct periodontal structure, which may shed light on human periodontal tissue regeneration.

Dental pulp stem cells: what, where, how?

INTRODUCTION

It is now accepted that progenitor/stem cells reside within the post-natal dental pulp. Studies have identified several niches of multipotent mesenchymal progenitor cells, known as dental pulp stem cells, which have a high proliferative potential for self-renewal. These progenitor stem cells are now recognized as being vital to the dentine regeneration process following injury. Understanding the nature of these progenitor/stem cell populations in the pulp is important in determining their potentialities and development of isolation or recruitment strategies for use in regeneration and tissue engineering. Characterization of these cells, and determination of their potentialities in terms of specificity of regenerative response, may help direct new clinical treatment modalities. Such novel treatments may involve controlled direct recruitment of the cells in situ and possible seeding of stem cells at sites of injury for regeneration or use of the stem cells with appropriate scaffolds for tissue engineering solutions. Such approaches may provide an innovative and novel biologically based new generation of clinical materials and/or treatments for dental disease.

AIM

This study aimed to review the body of knowledge relating to stem cells and to consider the possibility of these cell populations, and related technology, in future clinical applications.

Dental pulp stem cells: a promising tool for bone regeneration

Human tissues are different in term of regenerative properties. Stem cells are a promising tool for tissue regeneration, thanks to their particular characteristics of proliferation, differentiation and plasticity. Several "loci" or "niches" within the adult human body are colonized by a significant number of stem cells. However, access to these potential collection sites often is a limiting point. The interaction with biomaterials is a further point that needs to be considered for the therapeutic use of stem cells. Dental pulp stem cells (DPSCs) have been demonstrated to answer all of these issues: access to the collection site of these cells is easy and produces very low morbidity; extraction of stem cells from pulp tissue is highly efficiency; they have an extensive differentiation ability; and the demonstrated interactivity with biomaterials makes them ideal for tissue reconstruction. SBP-DPSCs are a multipotent stem cell subpopulation of DPSCs which are able to differentiate into osteoblasts, synthesizing 3D woven bone tissue chips in vitro and that are capable to synergically differentiate into osteoblasts and endotheliocytes. Several studied have been performed on DPSCs and they mainly found that these cells are multipotent stromal cells that can be safety cryopreserved, used with several scaffolds, that can extensively proliferate, have a long lifespan and build in vivo an adult bone with Havers channels and an appropriate vascularization. A definitive proof of their ability to produce dentin has not been yet done. Interestingly, they seem to possess immunoprivileges as they can be grafted into allogenic tissues and seem to exert anti-inflammatory abilities, like many other mesenchymal stem cells. The easy management of dental pulp stem cells make them feasible for use in clinical trials on human patients.

Apical tooth germ cell-conditioned medium enhances the differentiation of periodontal ligament stem cells into cementum/periodontal ligament-like tissues

BACKGROUND AND OBJECTIVE

Limitations of current periodontal regeneration modalities in both predictability and extent of healing response, especially on new cementum and attachment formation, underscore the importance of restoring or providing a microenvironment that is capable of promoting the differentiation of periodontal ligament stem cells (PDLSCs) towards cementoblast-like cells and the formation of cementum/periodontal ligament-like tissues. The aim of this study was to investigate the biological effect of conditioned medium from developing apical tooth germ cells (APTG-CM) on the differentiation and cementogenesis of PDLSCs both in vitro and in vivo.

MATERIAL AND METHODS

Using the limiting dilution technique, single-colony-derived human PDLSCs were isolated and expanded to obtain homogeneous populations of PDLSCs. Morphological appearance, cell cycle analysis, bromodeoxyuridine incorporation, alkaline phosphatase (ALP) activity, mineralization behavior, gene expression of cementoblast phenotype and in vivo differentiation capacities of PDLSCs co-cultured with APTG-CM were evaluated.

RESULTS

The induced PDLSCs exhibited several characteristics of cementoblast lineages, as indicated by the morphological changes, increased proliferation, high ALP activity, and the expression of cementum-related genes and calcified nodule formation in vitro. When transplanted into immunocompromised mice, the induced PDLSCs showed tissue-regenerative capacity to produce cementum/periodontal ligament-like structures, characterized by a layer of cementum-like mineralized tissues and associated periodontal ligament-like collagen fibers connecting with the newly formed cementum-like deposits, whereas control, untreated PDLSCs transplants mainly formed connective tissues.

CONCLUSION

Our findings suggest that APTG-CM is able to provide a cementogenic microenvironment and induce differentiation of PDLSCs along the cementoblastic lineage. This has important implications for periodontal engineering.

N-acetylcysteine protects dental pulp stromal cells from HEMA-induced apoptosis by inducing differentiation of the cells

Resin-based materials are now widely used in dental restorations. Although the use of these materials is aesthetically appealing to patients, it carries the risk of local and systemic adverse effects. The potential risks are direct damage to the cells and induction of immune-based hypersensitivity reactions. Dental pulp stromal cells (DPSCs) and oral keratinocytes are the major cell types which may come in contact with dental resins such as 2-hydroxyethyl methacrylate (HEMA) after dental restorations. Here we show that N-acetylcysteine (NAC) inhibits HEMA-induced apoptotic cell death and restores the function of DPSCs and oral epithelial cells. NAC inhibits HEMA-mediated toxicity through induction of differentiation in DPSCs, because the genes for dentin sialoprotein, osteopontin (OPN), osteocalcin, and alkaline phosphatase, which are induced during differentiation, are also induced by NAC. Unlike NAC, vitamins E and C, which are known antioxidant compounds, failed to prevent either HEMA-mediated cell death or the decrease in VEGF secretion by human DPSCs. More importantly, when added either alone or in combination with HEMA, vitamin E and vitamin C did not increase the gene expression for OPN, and in addition vitamin E inhibited the protective effect of NAC on DPSCs. NAC inhibited the HEMA-mediated decrease in NF-kappaB activity, thus providing a survival mechanism for the cells. Overall, the studies reported in this paper indicate that undifferentiated DPSCs have exquisite sensitivity to HEMA-induced cell death, and their differentiation in response to NAC resulted in an increased NF-kappaB activity, which might have provided the basis for their increased protection from HEMA-mediated functional loss and cell death.

[Stem cells of dental pulp]

Any clinician dreams to obtain the regeneration of the destroyed organ for his patient. In the human being, the regeneration of complex structures is not possible, except the liver and the bone marrow, which can be regenerated because of the presence of adult stem cells in these tissues. The stem cells have two principal properties: they ensure their self-renewal and they have the ability to differentiate into several cellular types. Using specific markers allowing the identification of the stem cells in bone marrow, stem cells were observed in dental pulp tissues. Although the origin, the identification, and the localization of these stem cells of dental pulp remain under consideration, the optimism in research on stem cells permits to believe that the knowledge on dental stem cells will lead to their use in therapeutics.

Odontogenic capability: bone marrow stromal stem cells versus dental pulp stem cells

BACKGROUND INFORMATION

Although adult bone-marrow-derived cell populations have been used to make teeth when recombined with embryonic oral epithelium, the differences between dental and non-dental stem-cell-mediated odontogenesis remain an open question.

RESULTS

STRO-1(+) (stromal precursor cell marker) DPSCs (dental pulp stem cells) and BMSSCs (bone marrow stromal stem cells) were isolated from rat dental pulp and bone marrow respectively by magnetic-activated cell-sorting techniques. Their odontogenic capacity was compared under the same inductive microenvironment produced by ABCs (apical bud cells) from 2-day-old rat incisors. Co-cultured DPSCs/ABCs in vitro showed more active odontogenic differentiation ability than mixed BMSSCs/ABCs, as indicated by the accelerated matrix mineralization, up-regulated alkaline phosphatase activity, cell-cycle modification, and the expression of tooth-specific proteins and genes. After cultured for 14 days in the renal capsules of rat hosts, recombined DPSC/ABC pellets formed typical tooth-shaped tissues with balanced amelogenesis and dentinogenesis, whereas BMSSC/ABC recombinants developed into atypical dentin-pulp complexes without enamel formation. DPSC and BMSSC pellets in vivo produced osteodentin-like structures and fibrous connective tissues respectively.

CONCLUSIONS

DPSCs presented more striking odontogenic capability than BMSSCs under the induction of postnatal ABCs. This report provides critical insights into the selection of candidate cells for tooth regeneration between dental and non-dental stem cell populations.