J Cell Physiol. 2010 Jul 12.

S A T, S S, D K.

Department of Periodontics and Oral Medicine, University of Michigan; Ann Arbor, MI USA;

J Endod. 2010 Jul;36(7):1139-44. Epub 2010 Apr 10.

Hirata TM, Ishkitiev N, Yaegaki K, Calenic B, Ishikawa H, Nakahara T, Mitev V, Tanaka T, Haapasalo M.

Department of Oral Health, Nippon Dental University, School of Life Dentistry at Tokyo, Tokyo, Japan.

Arch Oral Biol. 2010 Jul 12.

Iida K, Takeda-Kawaguchi T, Tezuka Y, Kunisada T, Shibata T, Tezuka KI.

Department of Oral and Maxillofacial Science, Gifu University Graduate School of Medicine, 1-1 Yanagido, Gifu City, Gifu 501-1194, Japan.

Stem Cell Res Ther. 2010 Mar 15;1(1):5.

Yamaza T, Kentaro A, Chen C, Liu Y, Shi Y, Gronthos S, Wang S, Shi S.

Center for Craniofacial Molecular Biology, University of Southern California School of Dentistry, 2250 Alcazar Street, CSA 103, Los Angeles, CA 90033, USA. yamazata@dent.kyushu-u.ac.jp.

J Biol Regul Homeost Agents. 2010 Apr-Jun;24(2):167-75.

Mori G, Centonze M, Brunetti G, Ballini A, Oranger A, Mori C, Lo Muzio L, Tetè S, Ciccolella F, Colucci S, Grano M, Grassi FR.

Department of Biomedical Science, University of Foggia Medical School, Foggia, Italy. g.mori@unifg.it

Regen Med. 2010 May 14.

Alongi DJ, Yamaza T, Song Y, Fouad AF, Romberg EE, Shi S, Tuan RS, Huang GT.

University of Maryland, College of Dental Surgery, MD, USA; and Boston University School of Dental Medicine, Department of Endodontics, Boston, MA 02118, USA.

Cell Tissue Res. 2010 Mar 23.

Chadipiralla K, Yochim JM, Bahuleyan B, Huang CY, Garcia-Godoy F, Murray PE, Stelnicki EJ.

Craniofacial Research Laboratory, College of Dental Medicine, Nova Southeastern University, Fort Lauderdale, Fla., USA.

Huang CY, Pelaez D, Bendala JD, Garcia-Godoy F, Cheung HS.

Department of Biomedical Engineering, University of Miami, Coral Gables, FL, USA.

Yalvac ME, Rizvanov AA, Kilic E, Sahin F, Mukhamedyarov MA, Islamov RR, Palotás A.

Department of Genetics and BioEngineering, College of Engineering and Architecture, Yeditepe University, Istanbul, Turkey.

Zou D, Zhao J, Ding W, Xia L, Jang X, Huang Y.

School of Stomatology, Tongji University, Shanghai 200072, China; Department of Stomatology, Shanghai East Hospital Affiliated to Tongji University, No.150 JiMO Road, Shanghai City 200011, China.

J Endod. 2009 Nov;35(11):1536-42. Epub 2009 Sep 20.

Nakamura S, Yamada Y, Katagiri W, Sugito T, Ito K, Ueda M.

Department of Oral and Maxillofacial Surgery, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan.

Kádár K, Porcsalmy B, Király M, Molnár B, Jobbágy-Ovári G, Somogyi E, Hermann P, Gera I, Varga G.

Semmelweis Egyetem Orálbiológiai Tanszék, Budapest.

Nakashima M, Iohara K, Sugiyama M.

Department of Oral Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Aichi 474-8522, Japan.

Columbia University, Dentistry, New York, New York, United States; xy2137@columbia.edu.

Generation of induced pluripotent stem (iPS) cells holds a great promise for regenerative medicine and other aspects of clinical applications. Many types of cells have been successfully reprogrammed into iPS cells in the mouse system, however, reprogramming human cells have been more difficult. To date, human dermal fibroblasts are the most accessible and feasible cell source for iPS generation. Dental tissues derived from ectomesenchyme harbor mesenchymal-like stem/progenitor cells and some of the tissues have been treated as biomedical wastes, e.g., exfoliated primary teeth and extracted third molars. We asked whether stem/progenitor cells from discarded dental tissues can be reprogrammed into iPS cells. The four factors Lin28/Nanog/Oct4/Sox2 or c-Myc/Klf4/Oct4/Sox2 carried by viral vectors were used to reprogram three different dental stem/progenitor cells: stem cells from exfoliated deciduous teeth (SHED), stem cells from apical papilla (SCAP) and dental pulp stem cells (DPSCs). We showed that all three can be reprogrammed into iPS cells and appeared to be at a higher rate than fibroblasts. They exhibited a morphology indistinguishable from human embryonic stem (hES) cells in cultures and expressed hES cell markers SSEA-4, TRA-1-60, TRA-1-80, TRA-2-49, Nanog, Oct4 and Sox2. They formed embryoid bodies in vitro and teratomas in vivo containing tissues of all three germ layers. We conclude that cells of ectomesenchymal origin serve as an excellent alternative source for generating iPS cells.

Petrovic V, Stefanovic V.

University of Nis School of Medicine, Nis, Serbia. vlada@medfak.ni.ac.rs

Karaöz E, Dogan BN, Aksoy A, Gacar G, Akyüz S, Ayhan S, Genç ZS, Yürüker S, Duruksu G, Demircan PC, Sariboyaci AE.

Stem Cell and Gene Therapy Research and Applied Center, Kocaeli University, 41380, Kocaeli, Turkey, ekaraoz@hotmail.com.

Huang AH, Chen YK, Lin LM, Shieh TY, Chan AW.

Grace Dental Clinic, School of Dentistry, Kaosiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan. andersonh@seed.net.tw

Mesenchymal Stem Cell Group, CSCR University of Adelaide, Adelaide, South Australia, Australia.

The human central nervous system has limited capacity for regeneration. Stem cell-based therapies may overcome this through cellular mechanisms of neural replacement and/or through molecular mechanisms, whereby secreted factors induce change in the host tissue. To investigate these mechanisms, we used a readily accessible human cell population, dental pulp progenitor/stem cells (DPSCs) that can differentiate into functionally active neurons given the appropriate environmental cues. We hypothesized that implanted DPSCs secrete factors that coordinate axon guidance within a receptive host nervous system. An avian embryonic model system was adapted to investigate axon guidance in vivo after transplantation of adult human DPSCs. Chemoattraction of avian trigeminal ganglion axons toward implanted DPSCs was mediated via the chemokine, CXCL12, also known as stromal cell-derived factor-1, and its receptor, CXCR4. These findings provide the first direct evidence that DPSCs may induce neuroplasticity within a receptive host nervous system. STEM CELLS 2009;27:2229-2237.

Department of Conservative Dentistry and Endodontics, K.D. Dental College and Hospital, Mathura, India. vipin_endodontist@yahoo.co.in

Tooth derived cells are readily accessible and provide an easy and minimally invasive way to obtain and store stem cells for future use. Banking ones own tooth-derived stem cells is a reasonable and simple alternative to harvesting stem cells from other tissues. Obtaining stem cells from human exfoliated deciduous teeth (SHED) is simple and convenient, with little or no trauma. Every child loses primary teeth, which creates the perfect opportunity to recover and store this convenient source of stem cells--should they be needed to treat future injuries or ailments and presents a far better alternative to simply discarding the teeth or storing them as mementos from the past. Furthermore, using ones own stem cells poses few, if any, risks for developing immune reactions or rejection following transplantation and also eliminates the potential of contracting disease from donor cells. Stem cells can also be recovered from developing wisdom teeth and permanent teeth. Individuals have different opportunities at different stages of their life to bank these valuable cells. It is best to recover stem cells when a child is young and healthy and the cells are strong and proliferative. The purpose of this review is to discuss the present scenario as well as the technical details of tooth banking as related to SHED cells.

Department of Oral and Maxillofacial Surgery, Graduate School of Medicine, Kyoto University, Shogoin, Sakyo-ku, Kyoto, Japan.

PURPOSE: Postnatal stem cells have been isolated from various tissues, including bone marrow, neural tissue, skin, retina, and dental epithelium. Recently, adult stem cells have been isolated from human dental pulp. Postnatal stem cells have been isolated from a variety of tissues. Previously, it was generally accepted that the differentiation potential of postnatal stem cells was lineage restricted. MATERIALS AND METHODS: Normal impacted third molars were collected from adults and normal exfoliated deciduous teeth (SHED; stem cells from human exfoliated deciduous teeth) by single-colony selection and magnetic activated cell sorting. RESULTS: BMP-2 treatment groups produced alkaline phosphatase in the cells and also produced and secreted osteocalcin in the culture medium, and were capable of inducing an upregulated expression of Osteocalcin or Sox9, Col 2, and Col X by reverse transcriptase polymerase chain reaction (RT-PCR). For adipogenic differentiation, there is potential for SHED and dental pulp stem cells (DPSC) to express 2 adipocyte-specific transcripts, PPARgamma2 and LPL, in vitro, as do bone marrow mesenchymal stem cells by RT-PCR. CONCLUSION: This study demonstrated that pluripotential cells isolated from the pulp of human teeth expanded in vitro and differentiated into osteoblasts, chondrocytes, and adipocytes. DPSC and SHED are not only derived from a very accessible tissue resource but also capable of providing enough cells for potential clinical applications.

University of Maryland, College of Dental Surgery, Dental School, Department of Endodontics, Prosthodontics and Operative Dentistry, 650 West Baltimore St., Baltimore, MD 21201, USA. ghuang@umaryland.edu

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 postnatal 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.

Methods: Cell cultures were isolated from milk tooth and third molar pulp and were grown in DMEM supplemented with 10 % FBS. Cells were characterized for expressing stem cell markers CD117, CD44H, Oct3/4 by immunofluorescency and flow-cytometry. After 3 to 5 passages we added to the media 20 ng/ml hepatocyte growth factor (HGF) for 5 days for hepatic commitment. For hepatic differentiation the cells were cultured in DMEM, 20 ng/ml HGF, 10 nM dexamethasone, insulin-transferrin-selenium X, 10 ng/ml oncostatin and 2% FBS for 15 days.

Results: Both mesenchymal cell lines were proven to be positive for pluripotent cell markers CD117, CD44H, Oct3/4. After hepatic induction both cell types changed from spindle shaped, fibroblast like to polygonal, parenchimal-like morphology. The alpha feto-protein and albumin expression were found during the differentiating process by immunofluorescency and ELISA. Mesenchymal cells were expanded in vitro and maintained in an undifferentiated state for more than 50 population doublings. Thus the cells differentiated into cells with morphological, phenotypic, and functional characteristics of hepatocytes.

Yalvac ME, Ramazanoglu M, Rizvanov AA, Sahin F, Bayrak OF, Salli U, Palotás A, Kose GT.

Department of Genetics and BioEngineering, College of Engineering and Architecture, Yeditepe University, Kayisdagi, Istanbul, Turkey.

Department of Oral Pathology, College of Dental Medicine, Kaohsiung Medical University, Taiwan.

INTRODUCTION: Human dental pulp stem/stromal cells (hDPSCs) in adults are primarily derived from the pulp tissues of permanent third molar teeth in existing literatures, whereas no reports exist, to our knowledge, on deriving hDPSCs from a tooth without the need for surgical procedure. The aim of this study was to raise a novel idea to source hDPSCs from complicated crown-fractured teeth requiring root canal therapy. METHODS: hDPSCs were harvested from the pulp tissues for two complicated crown-fractured teeth requiring root canal therapy, retaining the teeth for subsequent prosthodontic rehabilitation, in a 41-year-old woman who had suffered a motorcycle accident. Pulp tissue from the left lower deciduous canine of a healthy 10-year-old boy (the positive control) was also removed because of high mobility and cultured for hDPSCs. RESULTS: The hDPSCs derived from the two complicated crown-fractured teeth and the deciduous tooth were able to differentiate into adipogenic, chondrogenic, and osteogenic lineages and also expressed stem cells markers and differentiation markers, which indicated their stem cell origin and differentiation capability. In addition, hDPSCs from both the complicated crown-fractured teeth and the deciduous tooth showed high expression for bone marrow stem cell markers including CD29, CD90, and CD105 and exhibited very low expression of markers specific for hematopoietic cells such as CD14, CD34, and CD45. CONCLUSIONS: This report describes the successful isolation and characterization of hDPSCs from the pulp tissue of complicated crown-fractured teeth without tooth extraction. Therefore, pulp exposed in complicated crown-fractured teeth might represent a valuable source of personal hDPSCs.

Institute of Human Genetics, University of Regensburg, Regensburg, Germany. christian.morsczeck@klinik.uni-regensburg.de

Complex human tissues harbour stem cells and/or precursor cells, which are responsible for tissue development or repair. Recently, dental tissues such as periodontal ligament (PDL), dental papilla or dental follicle have been identified as easily accessible sources of undifferentiated cells. The dental stem cell biology might provide meaningful insights into the development of dental tissues and cellular differentiation processes. Dental stem cells could also be feasible tools for dental tissue engineering. Constructing complex structures like a periodontium, which provides the functional connection between a tooth or an implant and the surrounding jaw, could effectively improve modern dentistry. Dental precursor cells are attractive for novel approaches to treat diseases like periodontitis, dental caries or to improve dental pulp healing and the regeneration of craniofacial bone and teeth. These cells are easily accessible and, in contrast to bone-marrow-derived mesenchymal stem cells, are more closely related to dental tissues. This review gives a short overview of stem cells of dental origin.

Oral Biology, The School of Dentistry, The University of Birmingham, St. Chads Queensway, Birmingham B4 6NN, UK.

OBJECTIVE: Primary pulp cell cultures are frequently used to study cellular responses, odontogenic potential and stem cell responses. Their isolation and expansion via a range of technical approaches are widely reported. The purpose of this study was to investigate the influence of isolation approach and extended expansion on cell phenotype and behaviour. DESIGN: To determine viable cell isolation, enzymatic dissociation was performed on rodent incisor pulps using collagenase, trypsin, hyaluronidase and ficin. Extended expansion culture of released cells was performed in DMEM and alpha-MEM media. Cultures were subsequently analysed for gene expression, cell proliferation, cell morphology and differentiation capacity up to passage 20. RESULTS: Data indicated that incubation of extirpated and mechanically minced rodent pulpal tissue with 0.25% Trypsin:EDTA and subsequent culture in alpha-MEM medium provided optimal conditions for maximal cell growth and expansion. Under these conditions, extended culture decreased cellular proliferative capacity up to passage 7, whilst higher passages demonstrated recovered growth rates. In general gene expression analysis of osteogenic and dentinogenic associated markers decreased with increasing passage number. Notably expression of TGFbetas-1, -2 and -3 increased up to passage 10 as did the stem cell and pericyte/myofibroblast markers, CD74, Neuroserpin and alpha-SMA. Analysis of molecular phenotypes indicated little difference in lineage differentiation capacity between earlier and later passages. CONCLUSIONS: The present study characterizes conditions for primary pulp cell isolation and expansion and indicates that both earlier and later passages maintain differentiation capacity. Continued passage however may result in selection for cells with a pericyte/myofibroblast phenotype.

Department of Histology and Medical Embryology, University of Rome "La Sapienza", Rome, Italy.

Abstract Numerous stem cell niches are present in the different tissues and organs of the adult human body. Among these tissues, dental pulp, entrapped within the 'sealed niche' of the pulp chamber, is an extremely rich site for collecting stem cells. In this study, we demonstrate that the isolation of human dental pulp stem cells by the explants culture method (hD-DPSCs) allows the recovery of a population of dental mesenchymal stem cells that exhibit an elevated proliferation potential. Moreover, we highlight that hD-DPSCs are not only capable of differentiating into osteoblasts and chondrocytes but are also able to switch their genetic programme when co-cultured with murine myoblasts. High levels of MyoD expression were detected, indicating that muscle-specific genes in dental pulp cells can be turned on through myogenic fusion, confirming thus their multipotency. A perivascular niche may be the potential source of hD-DPSCs, as suggested by the consistent Ca(2+) release from these cells in response to endothelin-1 (ET-1) treatment, which is also able to significantly increase cell proliferation. Moreover, response to ET-1 has been found to be superior in hD-DPSCs than in DPSCs, probably due to the isolation method that promotes release of stem/progenitor cells from perivascular structures. The ability to isolate, expand and direct the differentiation of hD-DPSCs into several lineages, mainly towards myogenesis, offers an opportunity for the study of events associated with cell commitment and differentiation. Therefore, hD-DPSCs display enhanced differentiation abilities when compared to DPSCs, and this might be of relevance for their use in therapy.

Department of Biological Science, College of Natural Sciences, Wonkwang University, Iksan, Jeonbuk 570-749, Republic of Korea.

Human dental pulp-derived stem cells (hDPSCs) have been considered alternative sources of adult stem cells because of their potential to differentiate into multiple cell lineages. This study investigated the possible role of gangliosides in the neural differentiation of hDPSCs. When hDPSCs were cultured under neural differentiation conditions, expression of neural cell maker genes such as Nestin, MAP-2, and NeuN was detected. Immunostaining and high-performance thin-layer chromatography analysis showed that an increase in ganglioside biosynthesis was associated with neural differentiation of hDPSCs. Specifically, a significant increase in GD3 and GD1a expression was observed during neural differentiation. To confirm the role of gangliosides in neural differentiation, ganglioside biosynthesis was inhibited in hDPSCs by knockdown of UDP-glucose ceramide glucosyltransferase (Ugcg), which prevented differentiation into neural cells. These results suggest that gangliosides may play a role in the neural differentiation process of hDPSCs.

Tzu Chi Stem Cells Centre, Tzu Chi General Hospital, Hualien, Taiwan.

Background aims We have isolated human neuronal stem cells from exfoliated third molars (wisdom teeth) using a simple and efficient method. The cultured neuronal stem cells (designated tNSC) expressed embryonic and adult stem cell markers, markers for chemotatic factor and its corresponding ligand, as well as neuron proteins. The tNSC expressed genes of Nurr1, NF-M and nestin. They were used to treat middle cerebral artery occlusion (MCAO) surgery-inflicted Sprague-Dawley (SD) rats to assess their therapeutic potential for stroke therapy. Methods. For each tNSC cell line, a normal human impacted wisdom tooth was collected from a donor with consent. The tooth was cleaned thoroughly with normal saline. The molar was vigorously shaken or vortexed for 30 min in a 50-mL conical tube with 15-20 mL normal saline. The mixture of dental pulp was collected by centrifugation and cultured in a 25-cm(2) tissue culture flask with 4-5 mL Medium 199 supplemented with 5-10% fetal calf serum. The tNSC harvested from tissue culture, at a concentration of 1-2x10(5), were suspended in 3 microL saline solution and injected into the right dorsolateral striatum of experimental animals inflicted with MCAO. Results. Behavioral measurements of the tNSC-treated SD rats showed a significant recovery from neurologic dysfunction after MCAO treatment. In contrast, a sham group of SD rats failed to recover from the surgery. Immunohistochemistry analysis of brain sections of the tNSC-treated SD rats showed survival of the transplanted cells. Conclusions. These results suggest that adult neuronal stem cells may be procured from third molars, and tNSC thus cultivated have potential for treatment of stroke-inflicted rats.

Department of Oral Biology, Semmelweis University, Budapest, Hungary.

The plasticity of dental pulp stem cells (DPSCs) has been demonstrated by several studies showing that they appear to self-maintain through several passages, giving rise to a variety of cells. The aim of the present study was to differentiate DPSCs to mature neuronal cells showing functional evidence of voltage gated ion channel activities in vitro. First, DPSC cultures were seeded on poly-l-lysine coated surfaces and pretreated for 48h with a medium containing basic fibroblast growth factor and the demethylating agent 5-azacytidine. Then neural induction was performed by the simultaneous activation of protein kinase C and the cyclic adenosine monophosphate pathway. Finally, maturation of the induced cells was achieved by continuous treatment with neurotrophin-3, dibutyryl cyclic AMP, and other supplementary components. Non-induced DPSCs already expressed vimentin, nestin, N-tubulin, neurogenin-2 and neurofilament-M. The inductive treatment resulted in decreased vimentin, nestin, N-tubulin and increased neurogenin-2, neuron-specific enolase, neurofilament-M and glial fibrillary acidic protein expression. By the end of the maturation period, all investigated genes were expressed at higher levels than in undifferentiated controls except vimentin and nestin. Patch clamp analysis revealed the functional activity of both voltage-dependent sodium and potassium channels in the differentiated cells. Our results demonstrate that although most surviving cells show neuronal morphology and express neuronal markers, there is a functional heterogeneity among the differentiated cells obtained by the in vitro differentiation protocol described herein. Nevertheless, this study clearly indicates that the dental pulp contains a cell population that is capable of neural commitment by our three step neuroinductive protocol.

Mesenchymal Stem Cell Group, Division of Haematology, Institute of Medical and Veterinary Science/Hanson Institute, CSCR University of Adelaide, Adelaide 5000, SA, Australia.

The human central nervous system has limited capacity for regeneration. Stem cell-based therapies may overcome this through cellular mechanisms of neural replacement and/or through molecular mechanisms, whereby secreted factors induce change in the host tissue. A readily accessible human cell population to investigate these mechanisms are dental pulp progenitor/stem cells (DPSC) that can differentiate into functionally active neurons given the appropriate environmental cues. We hypothesized that implanted DPSC secrete factors that coordinate axon guidance within a receptive host nervous system. An avian embryonic model system was adapted to investigate axon guidance in vivo following transplantation of adult human DPSC. Chemo-attraction of avian trigeminal ganglion axons towards implanted DPSC was mediated via the chemokine, CXCL12, also known as stromal cell derived factor-1, and its receptor, CXCR4. These findings provide the first direct evidence that DPSC may induce neuroplasticity within a receptive host nervous system.

Laboratory of Molecular Genetics and Stem Cell Differentiation, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Republic of Korea.

It is well known that interactions between epithelial components and mesenchymal components are essential for tooth development. Therefore, it has been postulated that both types of stem cells might be involved in the regeneration of dental hard tissues. Recently, mesenchymal dental pulp stem cells that have odontogenic potential were identified from human dental pulp. However, the existence of epithelial cells has never been reported in human dental pulp. In the present study, we isolated and characterized epithelial cell-like cells from human deciduous dental pulp. They had characteristic epithelial morphology and expressed epithelial markers. Moreover, they expressed epithelial stem cell-related genes such as ABCG2, Bmi-1, DeltaNp63, and p75. Taken together, our findings suggest that epithelial stem cell-like cells might exist in human deciduous dental pulp and might play a role as an epithelial component for the repair or regeneration of teeth.

Department of Restorative Dentistry, Harvard School of Medicine, Boston, MA 02115, USA. bjsakdee@post.harvard.edu

INTRODUCTION: Postnatal human dental pulp is a potentially promising source of progenitor cells. Sustaining and amplifying progenitor cell populations would be beneficial for basic science research with application in pulpal regeneration. Hypoxia has been observed to promote the undifferentiated cell state in various stem cell populations. The purpose of this study was to examine human dental pulp cells (DPCs) proliferation in normoxia and hypoxia. METHODS: Dental pulp cells were obtained from third molars of adult patients and cultured in alpha modification of Eagle's medium culture medium with 10% fetal bovine serum. For cell proliferation, DPCs were divided into two groups: (1) DPCs incubated in normoxic conditions (20% oxygen tension) and (2) DPC incubated in hypoxic conditions (3% oxygen tension). Cell proliferation assays were performed every 2 to 3 days from day 3 to day 14 by trypsinization and quantification of cells with a hemacytometer. Fluorescence-activated cell sorting analysis was completed to investigate stem cell markers, CD133, and STRO-1. RESULTS: DPCs proliferated significantly more in hypoxia than in normoxia (ie, two-fold throughout the experiment, p < 0.0001). The primitive stem cell marker, CD133, decreased in hypoxia, whereas the osteoprogenitor marker, STRO-1, increased by 8.5-fold. CONCLUSIONS: This study suggested that hypoxia is an effective treatment to amplify numbers of progenitor cells from human dental pulp.

Mineralised Tissue Research Group, Tissue Engineering and Regenerative Dentistry, School of Dentistry Cardiff University, Cardiff, UK. sloanaj@cardiff.ac.uk

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.

Tissue Engineering and Reparative Dentistry, School of Dentistry, Cardiff University, Cardiff, UK. waddingtonrj@cardiff.ac.uk

The present study compared the cellular characteristics of progenitor stem cell populations present in adult dental pulp, isolated by different methods utilizing 2 different features of stem cell biology. One population expressing high levels of beta1 integrin was isolated by preferential selection of adherent cells to fibronectin over 20 min. In an alternative approach, cells expressing the embryonic neural crest cell marker, low-affinity nerve growth factor receptor (LANGFR), were selected by magnetic-activated cell sorting. For each method, clonal cell lines were established and expanded in culture. One clone derived via the respective methods was examined for embryonic/progenitor cell markers by immunocytochemistry and RT-PCR. Both clonal populations demonstrated the expression of stro-1 and stained positive for vimentin, demonstrating mesenchymal lineage. Of note, cells selected for LANGFR cells demonstrated the additional expression of CD105 and Notch 2. For both clonal populations, expanded cultures demonstrated the ability to differentiate into osteoblasts, adipocytes and chondrocytes. These results would suggest the potential isolation of 2 progenitor cell populations exhibiting different cellular characteristics in terms of their embryonic nature. The potential for both cell populations to derive from a common origin is discussed. Copyright 2008 S. Karger AG, Basel.

Institute of Human Genetics, University of Regensburg, Regensburg, Germany. christian.morsczeck@klinik.uni-regensburg.de

Complex human tissues harbour stem cells and/or precursor cells, which are responsible for tissue development or repair. Recently, dental tissues such as periodontal ligament (PDL), dental papilla or dental follicle have been identified as easily accessible sources of undifferentiated cells. The dental stem cell biology might provide meaningful insights into the development of dental tissues and cellular differentiation processes. Dental stem cells could also be feasible tools for dental tissue engineering. Constructing complex structures like a periodontium, which provides the functional connection between a tooth or an implant and the surrounding jaw, could effectively improve modern dentistry. Dental precursor cells are attractive for novel approaches to treat diseases like periodontitis, dental caries or to improve dental pulp healing and the regeneration of craniofacial bone and teeth. These cells are easily accessible and, in contrast to bone-marrow-derived mesenchymal stem cells, are more closely related to dental tissues. This review gives a short overview of stem cells of dental origin.

Dipartimento di Medicina Sperimentale, Sezione di Istologia ed Embriologia, TESLab, Secondo Ateneo di Napoli, Napoli, Italy.

Dental pulp stem cells (DPSCs) can be found within the "cell rich zone" of dental pulp. Their embryonic origin, from neural crests, explains their multipotency. Up to now, two groups have studied these cells extensively, albeit with different results. One group claims that these cells produce a "dentin-like tissue", whereas the other research group has demonstrated that these cells are capable of producing bone, both in vitro and in vivo. In addition, it has been reported that these cells can be easily cryopreserved and stored for long periods of time and still retain their multipotency and bone-producing capacity. Moreover, recent attention has been focused on tissue engineering and on the properties of these cells: several scaffolds have been used to promote 3-D tissue formation and studies have demonstrated that DPSCs show good adherence and bone tissue formation on microconcavity surface textures. In addition, adult bone tissue with good vascularization has been obtained in grafts. These results enforce the notion that DPSCs can be used successfully for tissue engineering. J. Exp. Zool. (Mol. Dev. Evol.) 310B, 2008. (c) 2008 Wiley-Liss, Inc.

Tissue Engineering and Reparative Dentistry, School of Dentistry, Cardiff University, Cardiff, UK. waddingtonrj@cardiff.ac.uk

The present study compared the cellular characteristics of progenitor stem cell populations present in adult dental pulp, isolated by different methods utilizing 2 different features of stem cell biology. One population expressing high levels of beta1 integrin was isolated by preferential selection of adherent cells to fibronectin over 20 min. In an alternative approach, cells expressing the embryonic neural crest cell marker, low-affinity nerve growth factor receptor (LANGFR), were selected by magnetic-activated cell sorting. For each method, clonal cell lines were established and expanded in culture. One clone derived via the respective methods was examined for embryonic/progenitor cell markers by immunocytochemistry and RT-PCR. Both clonal populations demonstrated the expression of stro-1 and stained positive for vimentin, demonstrating mesenchymal lineage. Of note, cells selected for LANGFR cells demonstrated the additional expression of CD105 and Notch 2. For both clonal populations, expanded cultures demonstrated the ability to differentiate into osteoblasts, adipocytes and chondrocytes. These results would suggest the potential isolation of 2 progenitor cell populations exhibiting different cellular characteristics in terms of their embryonic nature. The potential for both cell populations to derive from a common origin is discussed. Copyright 2008 S. Karger AG, Basel.

Grace Dental Clinic, Kaohsiung City, Taiwan

Until now, interest in dental pulp stem/stromal cell (DPSC) research has centered on mineralization and tooth repair. Beginning a new paradigm in DPSC research, we grafted undifferentiated, untreated DPSCs into the hippocampus of immune-suppressed mice. The rhesus DPSC (rDPSC) line used was established from the dental pulp of rhesus macaques and found to be similar to human bone marrow/mesenchymal stem cells, which express Nanog, Rex-1, Oct-4, and various cell surface antigens, and have multipotent differentiation capability. Implantation of rDPSCs into the hippocampus of mice stimulated proliferation of endogenous neural cells and resulted in the recruitment of pre-existing Nestin(+) neural progenitor cells (NPCs) and beta-tubulin-III(+) mature neurons to the site of the graft. Additionally, many cells born during the first 7 days after implantation proliferated, forming NPCs and neurons, and, to a lesser extent, underwent astrogliosis, forming astrocytes and microglia, by 30 days after implantation. Although the DPSC graft itself was short term, it had long-term effects by promoting growth factor signaling. Implantation of DPSCs enhanced the expression of ciliary neurotrophic factor, vascular endothelial growth factor, and fibroblast growth factor for up to 30 days after implantation. In conclusion, grafting rDPSCs promotes proliferation, cell recruitment, and maturation of endogenous stem/progenitor cells by modulating the local microenvironment. Our results suggest that DPSCs have a valuable, unique therapeutic potential, specifically as a stimulator and modulator of the local repair response in the central nervous system. DPSCs would be a preferable cell source for therapy due to the possibility of a "personalized" stem cell, avoiding the problems associated with host immune rejection. Disclosure of potential conflicts of interest is found at the end of this article.

Departamento de Estomatologia, Centro de Ciências da Saúde, Universidade Federal de Santa Catarina, Brazil. gustavocoura@hotmail.com

BACKGROUND AND OBJECTIVE: The periodontal ligament is a specialized connective tissue, derived from dental follicle and originated from neural crest cells. Recently it has been suggested, based on animal models, that periodontal ligament could be a niche for neural crest stem cells. However, there is still little knowledge on this subject. The identification of neural crest adult stem cells has received much attention based on its potential in tissue regeneration. The objective of the present work was to verify the human periodontal ligament as a niche for neural crest stem cells. MATERIAL AND METHODS: Cells from human periodontal ligament were isolated from 10 teeth of seven individuals (periodontal ligament pool group) and also from four teeth of one individual (periodontal ligament single group), after enzymatic digestion. The cells were cultured in specific inductive medium. Analyses of protein and gene expression were performed through immunocytochemistry and reverse transcription-polymerase chain reaction techniques, respectively. RESULTS: Mesodermal phenotypes (adipogeneic, osteogenic and myofibroblastic) were identified after culture in inductive medium. Immunocytochemistry analyses showed the presence of the nestin marker of neural stem cells and also markers of undifferentiated neural crest cells (HNK1, p75). When cultured in inductive medium that allowed neural differentiation, the cells showed markers for beta-tubulin III, neurofilament M, peripherin, microtubule-associated protein 2 and protein zero. The results were similar between the two study groups (the periodontal ligament pool group and the periodontal ligament single group). CONCLUSION: This research provides evidence that human periodontal ligament, in addition to its mesodermal derivatives, produces neural crest-like cells. Such features suggest a recapitulation of their embryonic state. The human periodontal ligament revealed itself as a viable alternative source for possible primitive precursors to be used in stem-cell therapies.

Department of Oral Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Aichi 474-8522, Japan.

Center of Advanced European Studies and Research, Bonn, Germany. degistirici@caesar.de

The connective tissue of the human tooth arises from cells that are derived from the cranial neural crest and, thus, are termed as "ectomesenchymal cells." Here, cells being located in a pad-like tissue adjacent to the apex of the developing tooth, which we designated the third molar pad, were separated by the microexplant technique. When outgrowing from the explant, dental neural crest-derived progenitor cells (dNC-PCs) adhered to plastic, proliferated steadily, and displayed a fibroblast-like morphology. At the mRNA level, dNC-PCs expressed neural crest marker genes like Sox9, Snail1, Snail2, Twist1, Msx2, and Dlx6. Cytofluorometric analysis indicated that cells were positive for CD49d (alpha4 integrin), CD56 (NCAM), and PDGFRalpha, while negative for CD31, CD34, CD45, and STRO-1. dNC-PCs could be differentiated into neurogenic, chondrogenic, and osteogenic lineages and were shown to produce bone matrix in athymic mice. These results demonstrate that human third molar pad possesses neural crest-derived cells that represent multipotent stem/progenitor cells. As a rather large amount of dNC-PCs could be obtained from each single third molar, cells may be used to regenerate a wide range of tissues within the craniofacial region of humans.

Department of Stomatology, Chinese PLA General Hospital and Postgraduate Military Medical School, Beijing 100853, China; Research and Development Center for Tissue Engineering, Fourth Military Medical University, Xi'an, Shaanxi 710032, China.

Two crucial growth factors, FGF2 and TGFbeta(1), were investigated in this study to determine their inductive effects on the odontoblastic differentiation of human dental pulp stem cells (DPSCs) in vitro. DPSCs were isolated by immunomagnetic bead selection using the STRO-1 antibody, and then co-cultured respectively with FGF2, TGFbeta(1) and FGF2+TGFbeta(1). The results showed that FGF2 can exert a significant effect on the cell proliferation, while TGFbeta(1) or FGF2+TGFbeta(1) can initiate an odontoblast-like differentiation of DPSCs. Moreover, FGF2 can synergistically upregulate the effects of TGFbeta(1) on the odontoblastic differentiation of DPSCs, as indicated by the increased alkaline phosphatase activity, the polarized cell appearance and secretary ultrastructural features, the formation of mineralized nodules and the gene/protein expression of dentin sialoprotein and dentin matrix protein-1. Together, FGF2 acted primarily on the cell proliferation, while TGFbeta(1) and FGF2+TGFbeta(1) mainly stimulated the odontoblastic differentiation of DPSCs. This study provides interesting progress in the odontoblastic differentiation of DPSCs induced by FGF2 and TGFbeta(1).

Department of Oral and Maxillofacial Science and.

In previous studies, human dental pulp stem cells (hDPSCs) were mainly isolated from adults. In this present study, we characterized hDPSCs isolated from an earlier developmental stage to evaluate the potential usage of these cells for tissue-regenerative therapy. hDPSCs isolated at the crown-completed stage showed a higher proliferation rate than those isolated at a later stage. When the cells from either group were cultured in medium promoting differentiation toward cells of the osteo/odontoblastic lineage, both became alkaline-phosphatase-positive, produced calcified matrix, and were also capable of forming dentin-like matrix on scaffolds in vivo. However, during long-term passage, these cells underwent a change in morphology and lost their differentiation ability. The results of a DNA array experiment showed that the expression of several genes, such as WNT16, was markedly changed with an increasing number of passages, which might have caused the loss of their characteristics as hDPSCs.

Department of Pediatric Dentistry, Peking University School & Hospital of Stomatology, Beijing 100081, China.

OBJECTIVE: To isolate and culture the pulp cells from human young permanent teeth (pDPC), and to observe their biological characteristics and the expression of some specific markers, and to induce these pulp cells to differentiate into osteoblast, adipocyte, neuron and chondrocyte lineages. METHODS: Pulp cells were isolated and cultured from orthodontic extracted premolars of children. The attached cells after at least 3 passages were used for the following experiments: 1. Morphology and ultrastructure analysis; 2. Cell cycle and phenotype were analyzed by flowcytometry; 3. Growth curve were recorded; 4. pDPC were induced to differentiate into osteoblast, adipocyte, neuron in vitro, and were identified by histochemical methods and RT-PCR. RESULTS: 1. Attached pDPCs were fibroblast-like cells, which were distinguished from BMSC. 2. The cell organs in dDPCs were well developed. 3. pDPCs were highly positive for CD90, CD44, CD147, which are mesenchymal stem-cell markers, but were negative for other markers including CD34, CD38, CD45, HLA-DR. 4. pDPCs showed high growth rate. 5. pDPCs could be induced to differentiate into osteoblast, adipocyte, and neuron lineages, but not chondrocyte lineages. CONCLUSION: pDPCs were characterized by their ability to proliferate with high growth rate in vitro. The expression of some BMSC markers in these cells were observed. They showed the potential to differentiate into multiple mesenchymal lineages such as osteoblast, adipocyte, neuron lineages under specific conditions in vitro.

Departamento di Scienze Odontostomatologiche, Universitá La Sapienze, Romae, Italy.

OBJECTIVE: Bone tissue engineering is a promising approach for bone reconstruction in oral-maxillofacial surgery. This study investigates the suitability of oral skeletal tissues as convenient and accessible sources of osteogenic progenitors as an alternative to the iliac crest bone marrow. STUDY DESIGN: Samples of maxilla tuberosity (MT) and maxillary and mandibular periosteum (MP) were obtained during routine oral surgery, and donor site morbidity was assessed using a "split-mouth" approach. Cells isolated from MT (bone marrow stromal cells; MT-BMSCs) and from MP (periosteal cells; M-PCs), were analyzed for clonogenicity, phenotype, expression of osteogenic markers, and ability to form bone in vivo. RESULTS: Both MT-BMSCs and M-PCs included clonogenic cells, showed comparable phenotypic profiles, and expressed early osteogenic markers. Most importantly, both cell populations formed bone upon ectopic in vivo transplantation. CONCLUSION: MT-BMSCs and M-PCs behaved as osteoprogenitor cells in vitro and in vivo. MT and MP may be considered as suitable sources of cells for bone tissue engineering in humans.

Inserm, JPA Center, Inserm U837, Lille, cedex, France; gaelique.stevens@wanadoo.fr.

Adult tissues contain highly proliferative, clonogenic cells that meet criteria of multipotent stem cells and are potential sources for autologous reparative and reconstructive medicine. We demonstrated that human dental pulp contains self renewing human dental pulp stem cells (hDPSCs) capable of differentiating into mesenchymal-derived odontoblasts, osteoblasts, adipocytes, chondrocytes and striated muscle, and interestingly, also into non-mesenchymal melanocytes. Furthermore, we showed that hDPSC cultures include cells with the label-retaining and sphere-forming abilities, traits attributed to multipotent stem cells, and provide evidence that these might be multipotent neural crest stem cells.

Laboratory of Molecular Signaling, Department of Biologic and Materials Sciences, School of Dentistry, The University of Michigan, Ann Arbor, MI 48109, USA.

Dental pulp stem cells (DPSCs) are a unique precursor population isolated from postnatal human dental pulp and have the ability to regenerate a reparative dentin-like complex. Canonical Wnt signaling plays a critical role in tooth development and stem cell self-renewal through beta-catenin. In this study, the regulation of odontoblast-like differentiation of DPSCs by canonical Wnt signaling was examined. DPSCs were stably transduced with canonical Wnt-1 or the active form of beta-catenin, with retrovirus-mediated infection. Northern blot analysis found that Wnt-1 strongly induced the expression of matricellular protein osteopontin, and modestly enhanced the expression of type I collagen in DPSCs. Unexpectedly, Wnt-1 inhibited alkaline phosphatase (ALP) activity and the formation of mineralized nodules in DPSCs. Moreover, over-expression of beta-catenin was also sufficient to suppress the differentiation and mineralization of DPSCs. In conclusion, our results suggest that canonical Wnt signaling negatively regulates the odontoblast-like differentiation of DPSCs.