To date, 5 different human dental stem/progenitor cells have been isolated and characterized: dental pulp stem cells (DPSCs), stem cells from exfoliated deciduous teeth (SHED), periodontal ligament stem cells (PDLSCs), stem cells from apical papilla (SCAP), and dental follicle progenitor cells (DFPCs). These post-natal populations have mesenchymal-stem-cell-like (MSC) qualities, including the capacity for self-renewal and multilineage differentiation potential. MSCs derived from bone marrow (BMMSCs) are capable of giving rise to various lineages of cells, such as osteogenic, chondrogenic, adipogenic, myogenic, and neurogenic cells. The dental-tissue-derived stem cells are isolated from specialized tissue with potent capacities to differentiate into odontogenic cells. However, they also have the ability to give rise to other cell lineages similar to, but different in potency from, that of BMMSCs. This article will review the isolation and characterization of the properties of different dental MSC-like populations in comparison with those of other MSCs, such as BMMSCs. Important issues in stem cell biology, such as stem cell niche, homing, and immunoregulation, will also be discussed.

Mesenchymal Stem Cells Derived from Dental Tissues vs. Those from Other Sources: Their Biology and Role in Regenerative Medicine

The hidden treasure in apical papilla: the potential role in pulp/dentin regeneration and bioroot engineering.

Dental pulp tissue engineering with stem cells from exfoliated deciduous teeth.

Current approaches to the development of regenerative therapies have been influenced by our understanding of embryonic development, stem cell biology, and tissue engineering technology. The ultimate goal of regenerative therapy is to develop fully functioning bioengineered organs which work in cooperation with surrounding tissues to replace organs that were lost or damaged as a result of disease, injury, or aging. Here, we report a successful fully functioning tooth replacement in an adult mouse achieved through the transplantation of bioengineered tooth germ into the alveolar bone in the lost tooth region. We propose this technology as a model for future organ replacement therapies. The bioengineered tooth, which was erupted and occluded, had the correct tooth structure, hardness of mineralized tissues for mastication, and response to noxious stimulations such as mechanical stress and pain in cooperation with other oral and maxillofacial tissues. This study represents a substantial advance and emphasizes the potential for bioengineered organ replacement in future regenerative therapies.

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Fully functional bioengineered tooth replacement as an organ replacement therapy

Our knowledge of the principles by which organ architecture develops through complex collective cell behaviours is still limited. Recent work has shown that the shape of such complex tissues as the optic cup forms by self-organization in vitro from a homogeneous population of stem cells. Multicellular self-organization involves three basic processes that are crucial for the emergence of latent intrinsic order. Based on lessons from recent studies, cytosystems dynamics is proposed as a strategy for understanding collective multicellular behaviours, incorporating four-dimensional measurement, theoretical modelling and experimental reconstitution.

Cytosystems dynamics in self-organization of tissue architecture

To bioengineer ectodermal organs such as teeth and whisker follicles, we developed a three-dimensional organ-germ culture method. The bioengineered tooth germ generated a structurally correct tooth, after both in vitro organ culture as well as transplantation under a tooth cavity in vivo, showing penetration of blood vessels and nerve fibers. Our method provides a substantial advance in the development of bioengineered organ replacement strategies and regenerative therapies.

The development of a bioengineered organ germ method

The regenerative therapy ultimately aims to develop bioengineered organs that can replace lost or damaged organs following disease, injury or aging. Recently, we showed that the artificial organ germ, which generates a structurally correct tooth, could be reconstituted by in vitro cell manipulation (Nature Methods 4, 227-230, 2007). In this study, we revealed that neural crest-like cells, which were differentiated from pluripotent stem cells such as embryonal carcinoma (EC) cells, could develop the regenerated tooth by organ germ method with tooth germ epithelium. EC cells were stimulated with dimethyl sulfoxide (DMSO) and differentiated cells were isolated by cell sorting as DMSO-EC cells. We found that the expressions of pluripotent stem cell marker genes (Oct3/4 and Nanog) could not be detected in DMSO-EC cells. In contrast, the expressions of neural crest-marker genes (Pax3 and Slug) and of dental mesenchyme-marker genes (Msxl, Pax9 and Lhx7) increased in DMSO-EC cells, compared with those in EC cells. Furthermore, the structurally correct tooth can be generated by combining DMSO-EC cells and tooth germ epithelium, both in vitro and in vivo. Our current results indicated the possibility that pluripotent stem cells are applicable as a candidate of cell sources to develop of a bioengineered organ germ for the organ replacement in the future regenerative therapy.

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Pluripotent stem cells developed into regenerated tooth by organ germ method in combination with tooth germ-derived epithelium

It has been expected that technology for reconstitution of an entire organ from single cells for application to organ replacement strategies in regenerative therapy. In our current study, we show that the artificial organ germ, which generates a structurally correct organ, could be reconstituted by cell manipulation. Bioengineered tooth germ was reconstituted from epithelial and mesenchymal single cells, which were separated from E14.5 incisor tooth germ under stereoscopic microscope. Explants reconstituted with the compartmentalization between epithelial and mesenchymal cells at high-cell density could generate structurally correct teeth. Furthermore, individual primordia, which were dissected from the bioengineered tooth germ on day 2 of the organ culture, could generate a single tooth. These observations indicate that the initial cell density and the compartmentalization between cell types, which mimics epithelial mesenchymal cell interaction, are essential for the development of a bioengineered organ germ. Our results have a potential for the application of bioengineered organ in future regenerative therapies.

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Yasumitsu Saji

Papers

The development of a bioengineered organ germ method

Pluripotent stem cells developed into regenerated tooth by organ germ method in combination with tooth germ-derived epithelium

The reconstruction of bioengineered organ by cell manipulation