Odontogenic potential of bone marrow mesenchymal stem cells

An in-vitro study investigating the effect of air-abrasion bioactive glasses on dental adhesion, cytotoxicity and odontogenic gene expression

OBJECTIVE

To assess the microtensile bond strength (MTBS) and interfacial characteristics of universal adhesives applied on dentine air-abraded using different powders. The analysis includes the cytotoxicity of the powders and their effect on odontogenic gene expression.

METHODS

Sound human dentine specimens were air-abraded using bioglass 45S5 (BAG), polycarboxylated zinc-doped bioglass (SEL), alumina (AL) and submitted to SEM analysis. Resin composite was bonded to air-abraded or smear layer-covered dentine (SML) using an experimental (EXP) or a commercial adhesive (ABU) in etch&rinse (ER) or self-etch (SE) modes. Specimens were stored in artificial saliva (AS) and subjected to MTBS testing after 24 h and 10 months. Interfacial nanoleakage assessment was accomplished using confocal microscopy. The cytotoxicity of the powders was assessed, also the total RNA was extracted and the expression of odontogenic genes was evaluated through RT-PCR.

RESULTS

After prolonged AS storage, specimens in the control (SML) and AL groups showed a significant drop in MTBS (p > 0.05), with degradation evident within the bonding interface. Specimens in BAG or SEL air-abraded dentine groups showed no significant difference, with resin-dentine interfaces devoid of important degradation. The metabolic activity of pulp stem cells was not affected by the tested powders. SEL and BAG had no effect on the expression of odontoblast differentiation markers. However, AL particles interfered with the expression of the odontogenic markers.

SIGNIFICANCE

The use of bioactive glass air-abrasion may prevent severe degradation at the resin-dentine interface. Unlike alumina, bioactive glasses do not interfere with the normal metabolic activity of pulp stem cells and their differentiation to odontoblasts.

Increasing Odontoblast-like Differentiation from Dental Pulp Stem Cells through Increase of β-Catenin/p-GSK-3β Expression by Low-Frequency Electromagnetic Field

Odontoblasts produce proteins that form the dentinal extracellular matrix, which can protect the dental pulp from external stimuli and is required for tooth regeneration. This study showed that a pulsed electromagnetic field (PEMF) can regulate cell metabolism and induce cell differentiation. This study determined the frequency of PEMF that is effective for odontoblast differentiation. Human dental pulp stem cells (hDPSCs) were cultured in odontoblast differentiation medium containing dexamethasone, BMP2, TGF-β1, and FGF-2, and then exposed to 10 mT intensity of PEMF at 40, 60, 70, and 150 Hz for 15 min/day. The MTT assay, LDH assay, flow cytometry, protein and gene expression, and immunofluorescence were performed to check if hDPSCs differentiated into odontoblast-like cells. The hDPSCs showed frequency-dependent differences in protein and gene expression. The mesenchymal stem cell markers were reduced to a greater extent at 60 and 70 Hz than at other frequencies, and odontoblast-related markers, particularly β-catenin, p-GSK-3β, and p-p38, were increased at 60 and 70 Hz. Exposure to 10 mT intensity of PEMF at 70 Hz influenced the differentiation of hDPSCs considerably. Taken together, PEMF treatment can promote differentiation of hDPSCs into odontoblast-like cells by increasing p-GSK-3β and β-catenin expression.

The colocalizations of pulp neural stem cells markers with dentin matrix protein-1, dentin sialoprotein and dentin phosphoprotein in human denticle (pulp stone) lining cells

BACKGROUND

The primary dentin, secondary dentin, and reactive tertiary dentin are formed by terminal differentiated odontoblasts, whereas atubular reparative tertiary dentin is formed by odontoblast-like cells. Odontoblast-like cells differentiate from pulpal stem cells, which express the neural stem cell markers nestin, S100β, Sox10, and P0. The denticle (pulp stone) is an unique mineralized extracellular matrix that frequently occurs in association with the neurovascular structures in the dental pulp. However, to date, the cellular origin of denticles in human dental pulp is unclear. In addition, the non-collagenous extracellular dentin matrix proteins dentin matrix protein 1 (DMP1), dentin sialoprotein (DSP), and dentin phosphoprotein (DPP) have been well characterized in the dentin matrix, whereas their role in the formation and mineralization of the denticle matrix remains to be clarified.

METHODS

To characterize the formation of denticle, healthy human third molars (n = 59) were completely sectioned and evaluated by HE staining in different layers at 720 µm intervals. From these samples, molars with (n = 5) and without denticles (n = 8) were selected. Using consecutive cryo-sections from a layer containing denticles of different sizes, we examined DMP1, DSP, and DPP in denticle lining cells and tested their co-localizations with the glial stem cell markers nestin, S100β, Sox10, and P0 by quantitative and double staining methods.

RESULTS

DMP1, DSP and DPP were found in odontoblasts, whereas denticle lining cells were positive only for DMP1 and DSP but not for DPP. Nestin was detected in both odontoblasts and denticle lining cells. S100β, Sox10, and P0 were co-localized with DMP1 and DSP in different subpopulations of denticle lining cells.

CONCLUSIONS

The co-localization of S100β, Sox10, and P0 with DMP1 and DSP in denticle lining cells suggest that denticle lining cells are originated from glial and/or endoneurial mesenchymal stem cells which are involved in biomineralization of denticle matrix by secretion of DMP1 and DSP. Since denticles are atubular compared to primary, secondary, reactionary tertiary dentin and denticle formed by odontoblasts, our results suggest that DPP could be one of the proteins involved in the complex regulation of dentinal tubule formation.

Early Odontogenic Differentiation of Dental Pulp Stem Cells Treated with Nanohydroxyapatite-Silica-Glass Ionomer Cement

This study aimed to investigate the effects of nanohydroxyapatite–silica–glass ionomer cement (nanoHA–silica–GIC) on the differentiation of dental pulp stem cells (DPSCs) into odontogenic lineage. DPSCs were cultured in complete Minimum Essential Medium Eagle—Alpha Modification (α-MEM) with or without nanoHA–silica–GIC extract and conventional glass ionomer cement (cGIC) extract. Odontogenic differentiation of DPSCs was evaluated by real-time reverse transcription polymerase chain reaction (rRT–PCR) for odontogenic markers: dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP1), osteocalcin (OCN), osteopontin (OPN), alkaline phosphatase (ALP), collagen type I (COL1A1), and runt-related transcription factor 2 (RUNX2) on day 1, 7, 10, 14, and 21, which were normalized to the house keeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Untreated DPSCs were used as a control throughout the study. The expressions of DSPP and DMP1 were higher on days 7 and 10, that of OCN on day 10, those of OPN and ALP on day 14, and that of RUNX2 on day 1; COL1A1 exhibited a time-dependent increase from day 7 to day 14. Despite the above time-dependent variations, the expressions were comparable at a concentration of 6.25 mg/mL between the nanoHA–silica–GIC and cGIC groups. This offers empirical support that nanoHA–silica–GIC plays a role in the odontogenic differentiation of DPSCs.

Contribution of Bone Marrow-derived Cells to Reparative Dentinogenesis Using Bone Marrow Transplantation Model

INTRODUCTION

The aim of this study was to analyze the contribution of bone marrow-derived cells (BMDCs) to reparative dentinogenesis using bone marrow transplantation (BMT) and pulp capping as an in vivo model.

METHODS

A chimeric mouse model was created through the injection of BMDCs expressing green fluorescent protein (GFP+ BMDCs) from C57BL/6 GFP+ transgenic donor mice into irradiated C57BL/6 wild-type recipient mice (GFP- mice). These GFP- chimeric mice (containing transplanted GFP+ BMDCs) were subjected to microscopic pulp exposure and capping with white mineral trioxide aggregate (n = 18) or Biodentine (Septodont, St Maur-des-Fossés, France) (n = 18) in the maxillary first molar. Maxillary arches from GFP- chimeric mice (with the capped tooth) were isolated and histologically processed 5 (n = 9) and 7 (n = 9) weeks after BMT. Confocal laser microscopy and immunohistochemical analysis were performed to assess the presence of GFP+ BMDCs and the expression of dentin sialoprotein, an odontoblast marker, for those cells contributing to reparative dentinogenesis in the dental pulp.

RESULTS

Confocal laser microscopic analyses evidenced the presence of GFP+ BMDCs in close association with reparative dentin synthesized at the site of pulp exposure in GFP- mice 5 and 7 weeks after BMT. Immunohistochemical analysis revealed that GFP+ BMDCs in close association with reparative dentin expressed DSP, suggesting the contribution of nonresident GFP+ BMDCs to reparative dentinogenesis.

CONCLUSIONS

These data suggest the presence of nonresident BMDCs in reparative dentinogenesis and its contribution to dental pulp regeneration in the pulp healing process.

Hematopoietic Stem Cells as a Novel Source of Dental Tissue Cells

While earlier studies have suggested that cells positive for hematopoietic markers can be found in dental tissues, it has yet to be confirmed. To conclusively demonstrate this, we utilized a unique transgenic model in which all hematopoietic cells are green fluorescent protein⁺ (GFP⁺). Pulp, periodontal ligament (PDL) and alveolar bone (AvB) cell culture analysis demonstrated numerous GFP⁺ cells, which were also CD45⁺ (indicating hematopoietic origin) and co-expressed markers of cellular populations in pulp (dentin matrix protein-1, dentin sialophosphoprotein, alpha smooth muscle actin [ASMA], osteocalcin), in PDL (periostin, ASMA, vimentin, osteocalcin) and in AvB (Runx-2, bone sialoprotein, alkaline phosphatase, osteocalcin). Transplantation of clonal population derived from a single GFP⁺ hematopoietic stem cell (HSC), into lethally irradiated recipient mice, demonstrated numerous GFP⁺ cells within dental tissues of recipient mice, which also stained for markers of cell populations in pulp, PDL and AvB (used above), indicating that transplanted HSCs can differentiate into cells in dental tissues. These hematopoietic-derived cells deposited collagen and can differentiate in osteogenic media, indicating that they are functional. Thus, our studies demonstrate, for the first time, that cells in pulp, PDL and AvB can have a hematopoietic origin, thereby opening new avenues of therapy for dental diseases and injuries.

Required Time for Migration of Bone Marrow-derived Cells to Dental Pulp after Bone Marrow Transplantation

INTRODUCTION

This study aimed to evaluate the time required for bone marrow-derived cells (BMDCs) from transgenic green fluorescent protein (GFP)+ donor mice (GFP+ mice) to migrate into the dental pulp of wild-type GFP- recipient mice (GFP- mice) by using bone marrow transplantation (BMT) as an in vivo model for tracking BMDCs from GFP+ mice (GFP+ BMDCs).

METHODS

GFP+ BMDCs were injected into irradiated GFP- mice. Maxillary arches, tibiae, and femora from GFP- mice were isolated and processed at 24 hours, 48 hours, 4, 7, and 14 days, and 7 weeks after BMT. Confocal laser microscopy analyses were performed to assess the presence of GFP+ BMDCs in the dental pulp, and flow cytometry of BM was performed to confirm the efficiency of engraftment of GFP+ BMDCs.

RESULTS

Confocal laser microscopy analyses evidenced the presence of GFP+ BMDCs in the dental pulp of GFP- mice from 14 days to 7 weeks after BMT. There was no presence of GFP+ BMDCs at 24 hours, 48 hours, 4 days, and 7 days. Flow cytometry of the BM of GFP- mice demonstrated a constant increase in the presence of GFP+ BMDCs at 24 hours, 48 hours, and 4 days after BMT, which stabilized from 7 days to 7 weeks.

CONCLUSIONS

The study demonstrated the presence of GFP+ BMDCs in the dental pulp from 14 days to 7 weeks after BMT and the feasibility of using GFP+ animals and BMT as an in vivo model for tracking GFP+ BMDCs.

Bone marrow mesenchymal stem cells combine with Treated dentin matrix to build biological root

Treated dentin matrix (TDM) as a kind of scaffolding material has been proved odontogenic induction ability on dental-derived stem cells. Given the limited resources of dental stem cells, it is necessary to seek new seed cell which easily obtained. Jaw bone marrow mesenchymal stem cell (JBMMSC) as non-dental-derived stem cell relates to the development of teeth and jaws which suggest us JBMMSCs could act as a new seed cell for tooth tissue engineering. To assess the odontogenic and osteogenic potential of JBMMSCs, cells were induced by TDM extraction in vitro and combined with TDM in vivo. Results were analyzed by PCR, Western Blotting and histology. PCR and Western Blotting showed odontogenic and osteogenic makers were significantly enhanced in varying degrees after induced by TDM extraction in vitro. In vivo, JBMMSCs expressed both odontogenic and osteogenic-related protein, and the latter showed stronger positive expression. Furthermore, histological examination of the harvested grafts was observed the formation of bone-like tissue. Therefore, osteogenic differentiation ability of JBMMSCs were enhanced significantly after being inducted by TDM which illustrates that non-odontogenic derived stem cells are still promising seed cells in tooth root tissue engineering.

Bone marrow-derived stromal cells are more beneficial cell sources for tooth regeneration compared with adipose-derived stromal cells

Tooth loss is presently a global epidemic and tooth regeneration is thought to be a feasible and ideal treatment approach. Choice of cell source is a primary concern in tooth regeneration. In this study, the odontogenic differentiation potential of two non-dental-derived stem cells, adipose-derived stromal cells (ADSCs) and bone marrow-derived stromal cells (BMSCs), were evaluated both in vitro and in vivo. ADSCs and BMSCs were induced in vitro in the presence of tooth germ cell-conditioned medium (TGC-CM) prior to implantation into the omentum majus of rats, in combination with inactivated dentin matrix (IDM). Real-time quantitative polymerase chain reaction (RT-qPCR) was used to detect the mRNA expression levels of odontogenic-related genes. Immunofluorescence and immunohistochemical assays were used to detect the protein levels of odontogenic-specific genes, such as DSP and DMP-1 both in vitro and in vivo. The results suggest that both ADSCs and BMSCs have odontogenic differentiation potential. However, the odontogenic potential of BMSCs was greater compared with ADSCs, showing that BMSCs are a more appropriate cell source for tooth regeneration.

Human Umbilical Cord Mesenchymal Stem Cells: A New Therapeutic Option for Tooth Regeneration

Tooth regeneration is considered to be an optimistic approach to replace current treatments for tooth loss. It is important to determine the most suitable seed cells for tooth regeneration. Recently, human umbilical cord mesenchymal stem cells (hUCMSCs) have been regarded as a promising candidate for tissue regeneration. However, it has not been reported whether hUCMSCs can be employed in tooth regeneration. Here, we report that hUCMSCs can be induced into odontoblast-like cells in vitro and in vivo. Induced hUCMSCs expressed dentin-related proteins including dentin sialoprotein (DSP) and dentin matrix protein-1 (DMP-1), and their gene expression levels were similar to those in native pulp tissue cells. Moreover, DSP- and DMP-1-positive calcifications were observed after implantation of hUCMSCs in vivo. These findings reveal that hUCMSCs have an odontogenic differentiation potency to differentiate to odontoblast-like cells with characteristic deposition of dentin-like matrix in vivo. This study clearly demonstrates hUCMSCs as an alternative therapeutic cell source for tooth regeneration.

Regeneration of dentin–pulp-like tissue using an injectable tissue engineering technique

An injectable tissue engineering technique to regenerate dentin–pulp complex.

The effects of osterix on the proliferation and odontoblastic differentiation of human dental papilla cells

INTRODUCTION

Dental papilla cells (DPCs) are precursors of odontoblasts and have the potential to differentiate into odontoblasts. Osteoblasts and odontoblasts have many common characteristics. Osterix (Osx) is essential for osteoblast differentiation. However, no information is available for the effects of Osx on the odontoblastic differentiation of DPCs. The purpose of this study was to investigate the effects of Osx on the proliferation and odontoblastic differentiation of DPCs.

METHODS

An immortalized human dental papilla cell (hDPC) line was used. Osx was stably overexpressed or knocked down in hDPCs with infection of lentiviral particles to determine its biological effects on hDPCs. The proliferation of cells was measured by the 5-ethynyl-2'-deoxyuridine incorporation assay and direct cell counting. Expressions of dentin sialophosphoprotein, nestin, dentin matrix protein 1, and alkaline phosphatase were detected by real-time polymerase chain reaction to determine the odontoblastic differentiation of cells. The mineralization ability of cells was evaluated by von Kossa staining and alkaline phosphatase activity assay.

RESULTS

Overexpression of Osx retarded the proliferation of hDPCs, whereas knockdown of Osx increased the cell proliferation. Overexpression of Osx promoted the odontoblastic differentiation of hDPCs by up-regulating odontoblastic differentiation genes and increased the mineralization ability of hDPCs. Knockdown of Osx down-regulated odontoblastic differentiation genes and decreased the mineralization ability of hDPCs.

CONCLUSIONS

Osx might function as a potential regulator for the proliferation and odontoblastic differentiation of hDPCs.

Adult stem cell-based apexogenesis

Generally, the dental pulp needs to be removed when it is infected, and root canal therapy (RCT) is usually required in which infected dental pulp is replaced with inorganic materials (paste and gutta percha). This treatment approach ultimately brings about a dead tooth. However, pulp vitality is extremely important to the tooth itself, since it provides nutrition and acts as a biosensor to detect the potential pathogenic stimuli. Despite the reported clinical success rate, RCT-treated teeth are destined to be devitalized, brittle and susceptible to postoperative fracture. Recently, the advances and achievements in the field of stem cell biology and regenerative medicine have inspired novel biological approaches to apexogenesis in young patients suffering from pulpitis or periapical periodontitis. This review mainly focuses on the benchtop and clinical regeneration of root apex mediated by adult stem cells. Moreover, current strategies for infected pulp therapy are also discussed here.

Differentiation of mesenchymal stem cells from human umbilical cord tissue into odontoblast-like cells using the conditioned medium of tooth germ cells in vitro

The easily accessible mesenchymal stem cells in the Wharton's jelly of human umbilical cord tissue (hUCMSCs) have excellent proliferation and differentiation potential, but it remains unclear whether hUCMSCs can differentiate into odontoblasts. In this study, mesenchymal stem cells were isolated from the Wharton's jelly of human umbilical cord tissue using the simple method of tissue blocks culture attachment. UCMSC surface marker expression was then evaluated for the isolated cells using flow cytometry. The third-passage hUCMSCs induced by conditioned medium from developing tooth germ cells (TGC-CM) displayed high alkaline phosphatase (ALP) levels (P < 0.001), an enhanced ability to proliferate (P < 0.05), and the presence of mineralized nodules. These effects were not observed in cells treated with regular medium. After induction of hUCMSCs, the results of reverse transcriptional polymerase chain reaction (PCR) indicated that the dentin sialophosphoprotein (DSPP) and dentin matrix protein 1 (DMP1) genes were significantly tested. Additionally, dentin sialoprotein (DSP) and DMP1 demonstrated significant levels of staining in an immunofluorescence analysis. In contrast, the control cells failed to display the characteristics of odontoblasts. Taken together, these results suggest that hUCMSCs can be induced to differentiate into odontoblast-like cells with TGC-CM and provide a novel strategy for tooth regeneration research.

Effect of dentine matrix proteins on human endometrial adult stem-like cells: in vitro regeneration of odontoblasts cells

OBJECTIVE

Human endometrium has enormous regenerative capacity due to the presence of endometrial stem cells. The present study sought to assess the possibility of differentiation of these cells into odontoblast-like cells by in vitro induction.

METHODS

Endometrial stem-like cells were obtained using enzymatic digestion of the biopsy samples of the endometrium after hysterectomy and cultured in Dulbecco's Modified Eagle's Medium (DMEM) which contained dentine non-collagenous proteins (dNCPs). The results were evaluated using the following assays: analysis of morphology, enzymatic assay for measuring alkaline phosphatase activity, Alizarin Red staining to detect in vitro formation of mineralized nodules, immunofluorescence for detection of dentine sialoprotein (DSP) and dentine-matrix protein (DMP1), and Western blotting for DMP1 expression.

RESULTS

Following induction, endometrial stem-like cells demonstrated high alkaline phosphatase activity, and expression of DSP and DMP1 confirmed the odontoblast phenotype. DMP1 level increased in samples treated with dNCPs.

CONCLUSIONS

Study results indicated that odontoblastic differentiation of endometrial stem cells can be induced by extracellular matrix proteins (e.g. dNCPs). The capacity of endometrial stem-like cells to differentiate into odontoblast-like cells under specific conditions gives new insights into the mechanism of odontogenesis and highlights the potential of such approaches for further research on dental tissue regeneration.

Application of induced pluripotent stem cells in generation of a tissue-engineered tooth-like structure

Stem cells, such as adult stem cells or embryonic stem cells, are the most important seed cells employed in tooth tissue engineering. Even though dental-derived stem cells are a good source of seed cells for such procedures, they are not often used in clinical applications because of the limited supply. Induced pluripotent stem (iPS) cells, with their high proliferation and differentiation ability, are now considered a promising alternative. The objectives of this study were to assess the role of iPS cells in tooth tissue engineering. We used real-time polymerase chain reaction to confirm that mouse iPS (miPS) cells can be induced to express both odontogenic and osteogenic gene profiles. We then established a tooth germ model and transplanted the recombinant tooth germ into a mouse subrenal capsule for 4 weeks to reproduce early-tooth organogenesis. After 4 weeks, hematoxylin and eosin staining results showed newly formed bone-like and dental pulp-like areas. Further immunohistochemical staining confirmed that osteopontin was present in the apical part of the tooth-like structure. These results demonstrate that miPS cells have the potential to differentiate into odontogenic cells, confirming that they could be a new source of seed cells for use in tooth tissue engineering.

A comparison between adipose tissue and dental pulp as sources of MSCs for tooth regeneration

In this study, several in vivo and in vitro comparisons were performed to test the possibility of using adipose-derived stem cells (ADSCs), a more convenient cell source than dental pulp stem cells (DPSCs), in tooth regeneration. Using an efficient, non-engineering implantation method, we first demonstrated that both implants of ADSCs and DPSCs were able to grow self-assembled new teeth in adult rabbit extraction sockets with high success rate. The stem cells were necessary because the implants grew no tooth without them. A stepwise comparison showed that the regenerated teeth from these two types of adult stem cells were living with nerves and vascular system and remarkably similar to a normal tooth in many details. Further strictly controlled, side-by-side comparisons between the two types of stem cells also showed that the expression patterns of gene markers and the broad differentiation potentials induced by specific methods in vitro were very similar. Although a few differences were found, they did not affect the tested tooth regeneration in vivo or differentiation in vitro. Furthermore, rabbit ADSCs had a higher growth rate and a better senescence resistance in culture. All these findings suggest that ADSCs, one of the richest adult stem cells in mammals, are very similar and useful as DPSCs for regenerative dentistry.

Comparative analysis of in vitro osteo/odontogenic differentiation potential of human dental pulp stem cells (DPSCs) and stem cells from the apical papilla (SCAP)

OBJECTIVE

The aim of this study was to compare the in vitro osteo/odontogenic differentiation potential of mesenchymal stem cells (MSCs) derived from the dental pulp (dental pulp stem cells - DPSCs) or the apical papilla (stem cells from the apical papilla - SCAP) of permanent developing teeth.

DESIGN

DPSCs and SCAP cultures were established from impacted third molars of young healthy donors at the stage of root development. Cultures were analysed for stem cell markers, including STRO-1, CD146, CD34 and CD45 using flow cytometry. Cells were then induced for osteo/odontogenic differentiation by media containing dexamethasone, KH(2)PO(4) and β-glycerophosphate. Cultures were analysed for morphology, growth characteristics, mineralization potential (Alizarin Red method) and differentiation markers (dentine sialophosphoprotein-DSPP, bone sialoprotein-BSP, osteocalcin-OCN, alkaline phosphatase-ALP), using immunocytochemistry and reverse transcriptase-polymerase chain reaction.

RESULTS

All DPSCs and SCAP cultures were positive for STRO-1, CD146 and CD34, in percentages varying according to cell type and donor, but negative for CD45. Both types of MSCs displayed an active potential for cellular migration, organization and mineralization, producing 3D mineralized structures. These structures progressively expressed differentiation markers, including DSPP, BSP, OCN, ALP, having the characteristics of osteodentin. SCAP, however, showed a significantly higher proliferation rate and mineralization potential, which might be of significance for their use in bone/dental tissue engineering.

CONCLUSIONS

This study provides evidence that different types of dental MSCs can be used in tissue engineering/regeneration protocols as an approachable stem cell source for osteo/odontogenic differentiation and biomineralization that could be further applied for stem cell-based clinical therapies.

Engineering craniofacial structures: facing the challenge

The human innate regenerative ability is known to be limited by the intensity of the insult together with the availability of progenitor cells, which may cause certain irreparable damage. It is only recently that the paradigm of tissue engineering found its way to the treatment of irreversibly affected body structures with the challenge of reconstructing the lost part. In the current review, we underline recent trials that target engineering of human craniofacial structures, mainly bone, cartilage, and teeth. We analyze the applied engineering strategies relative to the selection of cell types to lay down a specific targeted tissue, together with their association with an escorting scaffold for a particular engineered site, and discuss their necessity to be sustained by growth factors. Challenges and expectations for facial skeletal engineering are discussed in the context of future treatment.

Odontogenic potential of post-natal oral mucosal epithelium

A bioengineered tooth would provide a powerful alternative to currently available clinical treatments. Previous experiments have succeeded in bioengineering teeth using tooth germs from animal embryos. However, the ultimate goal is to develop a technology which enables teeth to be regenerated with the use of autologous cells. To pursue this goal, we re-associated the palatal epithelium from young mice with the odontogenic dental mesenchyme and transplanted the re-associated tissues into mouse kidney capsules. Morphologically defined teeth were formed from the re-associated cultured palatal epithelial cell sheets from mice aged up to 4 wks, but no tooth was formed when the palatal epithelium from mice after 2 days of age was directly re-associated. Our results demonstrated that post-natal non-dental oral mucosal epithelium can be used as a substitute for dental epithelium, and that epithelial cell sheet improves the ability of the oral epithelium of older mice to differentiate into dental epithelium.

Serum regulates adipogenesis of mesenchymal stem cells via MEK/ERK-dependent PPARgamma expression and phosphorylation

Mesenchymal stem cells (MSCs) provide us an excellent cellular model to uncover the molecular mechanisms underlying adipogenic differentiation of adult stem cells. PPARγ had been considered as an important molecular marker of cells undergoing adipogenic differentiation. Here, we demonstrated that expression and phosphorylation of PPARγ could be found in bone marrow–derived MSCs cultured in expansion medium without any adipogenic additives (dexamethasone, IBMX, insulin or indomethacin). Then, PPARγ was dephosphorylated in MSCs during the process of adipogenic differentiation. We then found that inhibition of MEK activation by specific inhibitor (PD98059) counteracted the PPARγ expression and phosphorylation. However, expression and phosphorylation of PPARγ did not present in MSCs cultured in medium with lower serum concentration. When these MSCs differentiated into adipocytes, no phosphorylation could be detected to accompany the expression of PPARγ. Moreover, exposure of MSCs to higher concentration of serum induced stronger PPARγ expression, and subsequently enhanced their adipogenesis. These data suggested that activation of the MEK/ERK signalling pathway by high serum concentration promoted PPARγ expression and phosphorylation, and subsequently enhanced adipogenic differentiation of MSCs.

Odontogenic differentiation of adipose-derived stem cells for tooth regeneration: necessity, possibility, and strategy

Tooth regeneration using tissue engineering concepts is a promising biological approach to solving problems of tooth loss in elderly patients. The seeding cells, however, for tooth regeneration such as odontoblasts from dental germ, stem cells from dental pulp and deciduous teeth, and ectomesenchymal cells from the first branchial arch are difficult, even impossible to harvest in clinic. Bone marrow mesenchymal stem cells have odontogenic capacity, but their differentiation abilities significantly decrease with the increasing age of the donors. Therefore, the cells mentioned above are not practical in the clinical application of tooth regeneration in the old. Adipose derived stem cells have many clinical advantages over bone marrow mesenchymal stem cells, and their differentiation potential can be maintained with aging. Here we propose the hypothesis that adipose derived stem cells could be induced into odontogenic lineage and might be used as suitable seeding cells for tooth regeneration to replace the lost tooth of elderly patients.

Human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have elicited a great clinical interest, particularly in the areas of regenerative medicine and induction of tolerance in allogeneic transplantation. Previous reports demonstrated the feasibility of transplanting MSCs, which generates new prospects in cellular therapy. Recently, injection of MSCs induced remission of steroid-resistant acute graft-versus-host disease (GVHD). This review summarizes the knowledge and possible future clinical uses of MSCs.