Establishment of primary cultures of pulp cells from bovine permanent incisors

Effects of Sr2+, BO33-, and SiO32- on Differentiation of Human Dental Pulp Stem Cells into Odontoblast-Like Cells

This study aimed to clarify the effects of strontium (Sr2+), borate (BO33-), and silicate (SiO32-) on cell proliferative capacity, the induction of differentiation into odontoblast-like cells (OLCs), and substrate formation of human dental pulp stem cells (hDPSCs). Sr2+, BO33-, and SiO32- solutions were added to the hDPSC culture medium at three different concentrations, totaling nine experimental groups. The effects of these ions on hDPSC proliferation, calcification, and collagen formation after 14, 21, and 28 days of culture were evaluated using a cell proliferation assay, a quantitative alkaline phosphatase (ALP) activity assay, and Alizarin Red S and Sirius Red staining, respectively. Furthermore, the effects of these ions on hDPSC differentiation into OLCs were assessed via quantitative polymerase chain reaction and immunocytochemistry. Sr2+ and SiO32- increased the expression of odontoblast markers; i.e., nestin, dentin matrix protein-1, dentin sialophosphoprotein, and ALP genes, compared with the control group. BO33- increased the ALP gene expression and activity. The results of this study suggested that Sr2+, BO33-, and SiO32- may induce hDPSC differentiation into OLCs.

Biodentine but not MTA induce DSPP expression of dental pulp cells with different severity of LPS-induced inflammation

OBJECTIVES

To explore the inflammatory and differentiation response in inflamed dental pulp cells (DPCs) induced by lipopolysaccharide (LPS) under different conditions with Biodentine and mineral trioxide aggregate (MTA) treatment.

MATERIALS AND METHODS

DPCs were treated with 0.001-1 µg/mL LPS for different periods to induce inflammation. Normal and inflamed DPCs were further treated with 0.14 mg/mL Biodentine or 0.13 mg/mL MTA for different periods. mRNA expression level of IL-6, IL-8 and ALP were analysed by qPCR. DSPP protein expression was detected by western blot. The data were analysed by the Mann-Whitney test, unpaired t test or two-way ANOVA.

RESULTS

After treatment for different times and with different concentrations of LPS, different severity of pulp inflammation was revealed by the expressions of IL-6 and IL-8. Higher concentrations of LPS induced higher IL-6 and IL-8 expressions, and these expressions first increased and then decreased (p < 0.0001). At 96 and 192 h, Biodentine significantly suppressed IL-6 expression in both normal and inflamed DPCs (p < 0.05). At 48 and 96 h, Biodentine suppressed ALP expression in both normal and inflamed DPCs (p < 0.05). At 48 and 96 h, Biodentine induced DSPP expressions in both normal and inflamed DPCs (p < 0.05).

CONCLUSION

Biodentine enhanced more DSPP differentiation of both normal and inflamed DPCs under different treatment durations than MTA.

CLINICAL RELEVANCE

The prognosis of vital pulp therapy may depend on the severity of pulp inflammation which is difficult to be determined in clinical settings. Therefore, Biodentine may enhance odontogenic differentiation in different severity of pulp inflammation imply its clinical indications.

A Compilation of Study Models for Dental Pulp Regeneration

Efforts to heal damaged pulp tissue through tissue engineering have produced positive results in pilot trials. However, the differentiation between real regeneration and mere repair is not possible through clinical measures. Therefore, preclinical study models are still of great importance, both to gain insights into treatment outcomes on tissue and cell levels and to develop further concepts for dental pulp regeneration. This review aims at compiling information about different in vitro and in vivo ectopic, semiorthotopic, and orthotopic models. In this context, the differences between monolayer and three-dimensional cell cultures are discussed, a semiorthotopic transplantation model is introduced as an in vivo model for dental pulp regeneration, and finally, different animal models used for in vivo orthotopic investigations are presented.

The biocompatibility and mineralization potential of mineral trioxide aggregate containing calcium fluoride-An in vitro study

BACKGROUND/PURPOSE

MTA is used to induce hard tissue regeneration in various procedures. This study evaluated the biocompatibility and mineralization potential of mineral trioxide aggregate (MTA) containing calcium fluoride (CaF2). To verify if the change of components affected physical properties, the setting time, solubility, and surface roughness were measured.

MATERIALS AND METHODS

Human dental pulp cells (HDPCs) were treated with powder and set MTA containing CaF2 (0, 1, 5, and 10 wt %). The proliferation of HDPCs was investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The mineralization potential of HDPCs was investigated with the relative gene expression of alkaline phosphatase (ALP), collagen type I (ColI), osteocalcin (OCN), and runt-related transcription factor 2 (Runx2) using real-time reverse transcription polymerase chain reaction (RT-PCR). For investigating the physical properties, setting time and solubility were tested. Surface profiles of material were analyzed by a non-contact surface profiler and a scanning electron microscope (SEM).

RESULTS

MTA-5% CaF2 mixtures increased the proliferation and the mineralization-related gene expression of HDPCs to a greater degree than pure MTA. The addition of CaF2 to MTA delayed the setting, but the difference was only significant in the MTA-10% CaF2. Solubility and surface roughness was not altered.

CONCLUSION

The addition of more than 5% CaF2 can be considered to increase the regeneration potential of pulp cells without adverse effects on physical property.

Osteogenic and odontogenic differentiation potential of dental pulp stem cells isolated from inflamed dental pulp tissues (I-DPSCs) by two different methods

Objective: The objective of the present study is to isolate stem cells from inflamed dental pulp tissues (I-DPSCs) and study the characteristic such as surface markers, osteo/odontogenic differentiation potential between the outgrowth (OG) and enzymatic digestion (COL) methods.Materials and methods: I-DPSCs harvested by both methods were analysed for Mesenchymal Stem Cell marker expression by flow cytometry. The metabolic activity of the isolated cells was assessed by MTT assay. The Alkaline Phosphatase (ALP) and Alizarin red staining was done to analyse the osteogenic potential of isolated cells. The osteo/odontogenic differentiation was done by checking the expression of Dentine Matrix Protein 1 (DMP1), Dentine Sialophosphoprotein (DSPP), ALP and Bone Gamma-Carboxyglutamate Protein (BGLAP) by Real time PCR.Results: The isolated cells were positive for MSC markers such as CD-90, CD-105 and CD-73 and negative for CD-14, CD-45 and STRO-1. MTT assay indicated that the I-DPSCs from OG method showed higher metabolic activity than cells from COL. However, the osteo/odontogenic differentiation was in favour of cells isolated by COL method.Conclusion: Although the cell metabolic rate was more in OG, the osteo/odontogenic differentiation was higher in COL, suggesting that the isolation method and culture conditions do affect the differentiation capacity of isolated cells.

Comparison of two digestion strategies on characteristics and differentiation potential of human dental pulp stem cells

OBJECTIVE

This study aimed to compare the behavior of dental pulp stem cells (DPSCs) after isolation using solutions containing either collagenase/dispase or collagenase alone.

DESIGN

DPSCs were isolated by two digestion methods (collagenase/dispase or collagenase alone) from human third molars. Immunophenotypic features were confirmed by flow cytometry for cell markers STRO-1, cluster of differentiation (CD) 146, CD45, and collagen type-I. The proliferation potential of cells was evaluated by 5-bromo-2'-deoxyuridine (brdU) incorporation assay, and finally they were assessed for multi-lineage differentiation potential. Data were analyzed using one-way analysis of variance and independent t-tests.

RESULTS

DPSCs isolated by either method showed similar levels of STRO-1, CD45, and collagen type-I and similar incorporation of brdU (P > 0.05). However, DPSCs obtained by collagenase I/dispase treatment had significantly higher numbers of CD146⁺ cells and osteogenic and chondrogenic capacities compared to those obtained by treatment with collagenase I alone (P < 0.05). On the other hand, more STRO-1+/CD164-DPSCs were found in the collagenase alone group with higher adipogenic potential.

CONCLUSIONS

Different enzyme solutions gave rise to different populations of DPSCs. Dispase enhanced isolation of CD146⁺ DPSCs probably by disrupting the basement membranes of blood vessels and releasing DPCSs embedded in the perivascular niche. Furthermore, the differentiation potential of DPSCs was influenced by the change in enzyme solution.

Efficacy of Human Platelet Rich Fibrin Exudate vs Fetal Bovine Serum on Proliferation and Differentiation of Dental Pulp Stem Cells

Background and Objectives

The imperative role of dental pulp stem cells (DPSCs) in regenerative therapy demands an in-vitro expansion which must deal with the safety and ethical problems associated with fetal bovine serum (FBS). The primary aim of this study was to compare the effects of human platelet rich fibrin (hPRF) exudate Vs FBS on proliferation and osteodifferentiation of human dental pulp stem cells (hDPSCs). The secondary one was to determine the optimum concentration of hPRF exudate inducing hDPSCs proliferation and osteodifferentiation.

Methods

The direct method was used to prepare hPRF exudate. hDPSCs were isolated from impacted mandibular third molars of twelve donors by the outgrowth method. For cell viability and proliferation rate testing, 96 well plates were used and the assay was done in duplicate and the trial repeated four times under the same conditions. Six wells were used to contain 10% FBS, serum free media, 1%, 5%, 10% and 20% concentrations of hPRF exudates, respectively. The proliferation assay was carried out by MTS tetrazolium cell proliferation assay kit and Elisa reader. The study design for osteodifferentiation protocol was exactly as the proliferation one and instead the assay was carried out by alizarin red with Elisa reader.

Results

Compared to 10% FBS, 10% hPRF exudate was the optimum concentration for hDPSCs proliferation, while 1% hPRF exudate was the optimum concentration for osteodifferentiation of hDPSCs.

Conclusions

Avoiding the risk of zoonosis which may be occurred with FBS, it is recommended to use 10% hPRF exudate for proliferation and 1% for osteodifferentiation.

Enhanced regeneration potential of mobilized dental pulp stem cells from immature teeth

OBJECTIVES

We have previously demonstrated that dental pulp stem cells (DPSCs) isolated from mature teeth by granulocyte colony-stimulating factor (G-CSF)-induced mobilization method can enhance angiogenesis/vasculogenesis and improve pulp regeneration when compared with colony-derived DPSCs. However, the efficacy of this method in immature teeth with root-formative stage has never been investigated. Therefore, the aim of this study was to examine the stemness, biological characteristics, and regeneration potential in mobilized DPSCs compared with colony-derived DPSCs from immature teeth.

MATERIALS AND METHODS

Mobilized DPSCs isolated from immature teeth were compared to colony-derived DPSCs using methods including flow cytometry, migration assays, mRNA expression of angiogenic/neurotrophic factor, and induced differentiation assays. They were also compared in trophic effects of the secretome. Regeneration potential was further compared in an ectopic tooth transplantation model.

RESULTS

Mobilized DPSCs had higher migration ability and expressed more angiogenic/neurotrophic factors than DPSCs. The mobilized DPSC secretome produced a higher stimulatory effect on migration, immunomodulation, anti-apoptosis, endothelial differentiation, and neurite extension. In addition, vascularization and pulp regeneration potential were higher in mobilized DPSCs than in DPSCs.

CONCLUSIONS

G-CSF-induced mobilization method enhances regeneration potential of colony-derived DPSCs from immature teeth.

Dentin Regeneration by Dental Pulp Stem Cell Therapy with Recombinant Human Bone Morphogenetic Protein 2

Regenerative medicine is based on stem cells, signals, and scaffolds. Dental pulp tissue has the potential to regenerate dentin in response to noxious stimuli, such as caries. The progenitor/stem cells are responsible for this regeneration. Thus, stem cell therapy has considerable promise in dentin regeneration. Culture of porcine pulp cells, as a three-dimensional pellet, promoted odontoblast differentiation compared with monolayers. The expression of dentin sialophosphoprotein (Dspp) and enamelysin/matrix metalloproteinase 20 (MMP20) mRNA confirmed the differentiation of pulp cells into odontoblasts and was stimulated by the morphogenetic signal, bone morphogenetic protein 2 (BMP2). Based on the in vitro experiments, an in vivo evaluation of pulp progenitor/stem cells in the dog was performed. The autogenous transplantation of the BMP2-treated pellet culture onto the amputated pulp stimulated reparative dentin formation. In conclusion, BMP2 can direct pulp progenitor/stem cell differentiation into odontoblasts and result in dentin formation.

Effects of Extracellular pH on Dental Pulp Cells In Vitro

INTRODUCTION

The proliferation and migration of dental pulp stem cells (DPSCs), a population comprised of dental pulp cells (DPCs), are important processes for pulp tissue repair. Dental pulp is exposed to changes in extracellular pH under various conditions, such as acidosis and exposure to caries-associated bacteria or a pulp capping agent. The objective of this study was to investigate the effects of extracellular pH on DPC proliferation and migration in vitro.

METHODS

To evaluate the proliferation potency of DPCs in various extracellular pH conditions, 2 × 10(4) cells were seeded into 35-mm dishes. The following day, we changed to NaHCO3-free medium, which was adjusted to different extracellular pH levels.

RESULTS

After 120 hours, DPCs cultured in media from a pH of 3.5 to 5.5 showed cell death, those cultured in conditions from a pH of 6.5 to 7.5 showed growth arrest or cell death, and those grown at a pH of 9.5 showed mild proliferation. The migratory activity of living DPCs was not affected by extracellular pH. For histologic analysis, human teeth possessing a small abscess in the coronal pulp chamber were sliced for histologic analysis. Proliferating cell nuclear antigen (PCNA) immunolocalization was used as an index of cell proliferation for the sections and cultured cells. Acidic extracellular pH conditions resulted in reduced numbers of PCNA-positive DPCs in the dishes. As for pulp tissue affected by a small abscess, a PCNA-negative pulp cell layer was observed in close proximity to the infectious lesion.

CONCLUSIONS

Together, these results suggest that an acidic extracellular pH condition is associated with DPC growth arrest or cell death.

Injection of Dental Pulp Stem Cells Promotes Healing of Damaged Bladder Tissue in a Rat Model of Chemically Induced Cystitis

Dental pulp stem cells (DPSCs) are reported as sources of mesenchymal stem cells (MSCs). MSCs are used as cell therapy options for various diseases. The present study examined the healing effects of DPSC injection on damaged bladder tissue in a chemically induced cystitis rat model. Cystitis was induced by hydrochloride injection into the bladder of female F344/NSlc rats. On the following day, DPSCs suspended in phosphate-buffered saline (PBS) were injected into the bladder and maintained for 1 h (DPSC injection group), while PBS alone was injected as the standard for comparison (PBS injection group). After 2 days following injection, considerable submucosal edema, vascular structure destruction, hemorrhage, and inflammatory cell invasion were observed both in the DPSC and PBS injection groups, with no difference in their degree of submucosal edema and hemorrhage. Six days after injection, vascular structure regeneration was observed in both groups; however, unlike the DPSC injection group, the PBS injection group showed traces of submucosal edema and hemorrhage. These results correlated with tissue concentrations of myeloperoxidase (MPO) and the inflammatory cytokines IL-1β, IL-6, and TNF-α. Furthermore, the intercontraction interval was prolonged, and the frequency of nociceptive behaviors was reduced in the DPSC injection group compared with the PBS injection group. DPSCs were found on the bladder epithelium until day 3 after injection. In the DPSC-conditioned media (CM), the trophic factors FGF-2, VEGF, and the C-C and C-X-C families of chemokines were detected. The results of DPSC injection into the cystitis rat model suggested that the injected cells promote the healing of the damaged bladder tissue by exerting various trophic effects while localizing on the bladder epithelium and that MSC injection is a potential novel therapy for interstitial cystitis/painful bladder syndrome.

The efficiency of the in vitro osteo/dentinogenic differentiation of human dental pulp cells, periodontal ligament cells and gingival fibroblasts

Although the primary cell cultures from dental pulp and other oral tissue are frequently used to study osteogenic potential and stem cell responses, few systematic and comparative studies on stemness for the dentinogenic differentiation of these cells have been conducted. In the present study, to investigate the stemness of oral primary cells during extended culture, human adult dental pulp cells (hDPCs), periodontal ligament stem cells (hPDLSCs) and gingival fibroblasts (hGFs) were obtained and cultured from pulp tissue, periodontal ligaments, and marginal and attached gingival tissue of extracted third molars, respectively. As shown by fluorescence-activated cell sorting analysis and immunophenotyping, the mesenchymal stem cell markers, CD44, CD73, CD90, CD146 and CD166, were highly expressed in early passage hDPCs, hPDLSCs and hGFs. However, when the cells were treated with osteogenic additives, mineralization markedly increased in the hDPCs and hPDLSCs, but not in the hGFs. Moreover, the expression of dentinogenic markers, such as dentin sialophosphoprotein and dentin matrix protein-1, appeared to decrease during extended culture past passage number 8 of the hDPCs and hPDLSCs. These data suggest that hDPCs and hPDLSCs may have differentiation potential during the early passages, and that their progenitor potential is diminished during extended culture. The hGFs did not show differentiation capability during culture, even though they contained general mesenchymal stem cell surface proteins. The transcriptional expression of dentinogenic markers in hDPCs was not affected by co-culture with hPDLSCs and/or hGFs.

Isolation of a stable subpopulation of mobilized dental pulp stem cells (MDPSCs) with high proliferation, migration, and regeneration potential is independent of age

Insights into the understanding of the influence of the age of MSCs on their cellular responses and regenerative potential are critical for stem cell therapy in the clinic. We have isolated dental pulp stem cells (DPSCs) subsets based on their migratory response to granulocyte-colony stimulating factor (G-CSF) (MDPSCs) from young and aged donors. The aged MDPSCs were efficiently enriched in stem cells, expressing high levels of trophic factors with high proliferation, migration and anti-apoptotic effects compared to young MDPSCs. In contrast, significant differences in those properties were detected between aged and young colony-derived DPSCs. Unlike DPSCs, MDPSCs showed a small age-dependent increase in senescence-associated β-galactosidase (SA-β-gal) production and senescence markers including p16, p21, Interleukin (IL)-1β, -6, -8, and Groα in long-term culture. There was no difference between aged and young MDPSCs in telomerase activity. The regenerative potential of aged MDPSCs was similar to that of young MDPSCs in an ischemic hindlimb model and an ectopic tooth root model. These results demonstrated that the stem cell properties and the high regenerative potential of MDPSCs are independent of age, demonstrating an immense utility for clinical applications by autologous cell transplantation in dental pulp regeneration and ischemic diseases.

The use of granulocyte-colony stimulating factor induced mobilization for isolation of dental pulp stem cells with high regenerative potential

Human dental pulp stem cells (DPSCs) contain subsets of progenitor/stem cells with high angiogenic, neurogenic and regenerative potential useful for cell therapy. It is essential to develop a safe and efficacious method to isolate the clinical-grade DPSCs subsets from a small amount of pulp tissue without using conventional flow cytometry. Thus, a method for isolation of DPSCs subsets based on their migratory response to optimized concentration of 100 ng/ml of granulocyte-colony stimulating factor (G-CSF) was determined in this study. The DPSCs mobilized by G-CSF (MDPSCs) were enriched for CD105, C-X-C chemokine receptor type 4 (CXCR-4) and G-CSF receptor (G-CSFR) positive cells, demonstrating stem cell properties including high proliferation rate and stability. The absence of abnormalities/aberrations in karyotype and lack of tumor formation after transplantation in an immunodeficient mouse were demonstrated. The conditioned medium of MDPSCs exhibited anti-apoptotic activity, enhanced migration and immunomodulatory properties. Furthermore, transplantation of MDPSCs accelerated vasculogenesis in an ischemic hindlimb model and augmented regenerated pulp tissue in an ectopic tooth root model compared to that of colony-derived DPSCs, indicating higher regenerative potential of MDPSCs. In conclusion, this isolation method for DPSCs subsets is safe and efficacious, having utility for potential clinical applications to autologous cell transplantation.

Dental tissue repair: novel models for tissue regeneration strategies

Studies have shown that dentin matrices contain reservoirs of bioactive molecules capable of directing tissue repair. Elucidating the release mechanisms of such endogenous growth factors will enhance our understanding of dentinpulp regeneration and support the development of novel treatment modalities to enhance dentin repair following trauma and disease. Current clinical practice using new materials which are perceived to maintain pulpal viability require biological evidence to assess their therapeutic benefit and there is a need for better effective methods of assessing therapeutic approaches to improving dentin regeneration at the cellular and tissue level. Experimental modelling of dentin regeneration is hampered by the lack of suitable models. In vivo and in vitro studies have yielded considerable information on the processes taking place, but are limited, due to the cost, ethics and lack of cell/matrix interactions. Novel organotypic models, whereby cells and tissues are cultured in situ may provide a more suitable model system to facilitate dental tissue engineering and regeneration.

In vitro effects of ascorbic acid and β-glycerophosphate on human gingival fibroblast cells

Ascorbic acid (AA) and β-glycerophosphate (βG) are considered in vitro osteogenic factors important to the differentiation of osteoblastic progenitor and dental pulp cells into mineralized tissue-forming cells. So, the present study investigated in vitro if these mineralizing inducible factors (AA and βG) could influence differentiation of human gingival fibroblasts when compared with human pulp cells and osteogenic cells derived from rat calvaria cultured. The expression of osteopontin (OPN) and osteoadherin (OSAD) was analyzed by indirect immunofluorescence, immunocytochemistry as well as Western-blotting. In addition, the main ultrastructural aspects were also investigated. No mineralized matrix formation occurred on gingival fibroblasts induced with AA+βG. On these cells, no expression of OPN and OSAD was observed when compared with pulp cells, pulp cells induced with AA+βG as well as osteogenic cells. Ultrastructure analysis additionally showed that gingival fibroblasts exhibited typical fibroblast morphology with no nodule formation. The present findings showed that AA and βG could not promote a mineralized cell differentiation of human gingival fibroblasts and confirm that human dental pulp cells, as the osteogenic cells, are capable to form a mineralized extracellular.

Dentinogenic potential of human adult dental pulp cells during the extended primary culture

Despite the frequent use of primary dental pulp cells in dental regenerative research, few systematic studies of stemness for osteogenic and dentinogenic differentiation of human adult pulp cells have been reported. To investigate the stemness of human adult dental pulp cells, pulp tissues were obtained from extracted third molars and used as a source of pulp cells. In FACS analysis and immunophenotyping, the general mesenchymal stem cell markers CD44, CD90, and CD146 were highly expressed in early passages of the pulp cell culture. The stem cell population was dramatically decreased in an expansion culture of human dental pulp cells. When pulp cells were treated with additives such as β-glycerophosphate, ascorbic acid, and dexamethasone, nodule formation was facilitated and mineralization occurred within 2 weeks. Expression of osteogenic markers such as alkaline phosphatase, osteocalcin, and osteonectin was relatively low in undifferentiated cells, but increased significantly under differentiation conditions in whole passages. Dentinogenic markers such as dentin sialophosphoprotein and dentin matrix protein-1 appeared to decrease in their expression with increasing passage number; however, peak levels of expression occurred at around passage 5. These data suggested that stem cells with differentiation potential might exist in the dental pulp primary culture, and that their phenotypes were changed during expansion culture over 8-9 passages. Under these conditions, a dentinogenic population of pulp cells occurred in limited early passages, whereas osteogenic cells occurred throughout the whole passage range.

Differentiation potential of dental papilla, dental pulp, and apical papilla progenitor cells

INTRODUCTION

Regenerative endodontic procedures use the differentiation potential of embryonic and adult pulp progenitor cell populations to reconstitute dental structures.

METHODS

An in-depth search of the literature was accomplished to review biologic knowledge from basic research on tooth morphogenesis and differentiation, root development, dentin-pulp regeneration, pulp revascularization and apexification, experimental and clinical studies on the dentinogenic differentiation potential of progenitor cells in the embryonic dental papilla, dental pulp, and associated mesenchymal tissues of the developing root.

RESULTS

Odontogenic potential is determined during early tooth morphogenesis in the odontogenic mesenchyme. Progenitor cells from the odontogenic mesenchyme give rise to primary dentin-forming cells (odontoblasts) in the presence of stage-specific enamel epithelium and/or basement membrane and tertiary dentin-forming cells (odontoblast-like cells) in experimental conditions. The specificity of odontogenic mesenchymal cells to form tertiary dentin might be related to the repertoire of signaling pathways operated by the temporospatial pattern of epithelial-mesenchymal interactions during tooth formation. Dental papilla cells isolated from tooth germs before the onset of odontoblast differentiation have not shown any competence to become odontoblasts in the absence of enamel epithelium. On the other hand, the specificity of progenitor cells in the mesenchymal cell populations of the developing root apex remains to be determined.

CONCLUSIONS

It seems evident that the dental pulp might be only used as a source of progenitor cells with dentinogenic competence for the regeneration of the dentin-pulp complex. The nature of dental or apical papilla progenitor cells in terms of their specificity for dentin regeneration has to be first characterized.

Odontoblast marker gene expression is enhanced by a CC-chemokine family protein MIP-3alpha in human mesenchymal stem cells

OBJECTIVE

Macrophage inflammatory protein-3 alpha (MIP-3alpha) is a major CC-chemokine family protein, which serves as a differentiation factor for mesenchymal cells, including osteoblasts and dental pulp cells. The purpose of this study was to investigate the influence of MIP-3alpha on human mesenchymal stem cell differentiation in vitro.

DESIGN

Human mesenchymal stem cells were maintained in Dulbecco's modified Eagle's medium in the presence or absence of MIP-3alpha and the presence or absence of osteogenic factors (dexamethasone, beta-glycerophoshate and ascorbic acid). Alkaline phosphatase (ALP) activity was measured, and expression of odontoblast and osteoblast markers were examined by RT-PCR and Western blotting.

RESULTS

MIP-3alpha alone did not increase ALP activity, as compared to controls. The combination of MIP-3alpha and osteogenic factors increased ALP activity beyond increases observed with osteogenic factors alone. mRNA expression of the odontoblast marker dspp was only detectable when MIP-3alpha was added together with osteogenic factors at day 7 in three out of four samples. DSP protein level was increased only in the samples treated with both MIP-3alpha and osteogenic factors until day 5. In contrast, MIP-3alpha did not influence levels of the osteoblast markers CBFA1 or BSP.

CONCLUSIONS

The present study demonstrated that MIP-3alpha enhanced gene expression and protein levels of odontoblast-related genes, without affecting levels of the osteogenic proteins CBFA1 or BSP.

Stem cells and the dental pulp: potential roles in dentine regeneration and repair

The dentine-pulp complex displays exquisite regenerative potential in response to injury. The postnatal dental pulp contains a variety of potential progenitor/stem cells, which may participate in dental regeneration. A population of multipotent mesenchymal progenitor cells known as dental pulp stem cells with high proliferative potential for self-renewal has been described and may be important to the regenerative capacity of the tissue. The nature of the progenitor/stem cell populations in the pulp is of importance in understanding their potentialities and development of isolation or recruitment strategies, and allowing exploitation of their use in regeneration and tissue engineering. Various strategies will be required to ensure not only effective isolation of these cells, but also controlled signalling of their differentiation and regulation of secretory behaviour. Characterization of these cells and determination of their potentialities in terms of specificity of regenerative response will form the foundation for development of new clinical treatment modalities, whether involving directed recruitment of the cells and 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 will provide an innovative and novel biologically based new generation of clinical treatments for dental disease.

Pulp cell cultures obtained with two different methods for in vitro cytotoxicity tests

AIM

To describe two different protocols for obtaining primary pulp cell cultures, one derived from explants and the other following dissociation into single cell suspension by enzyme digestion.

METHODS

Human pulp tissue was obtained from three healthy premolars. The harvested pulp tissue was prepared for culture using physical methods (one of the premolars) and enzyme, type XI collagenase, (the two remaining premolars).

RESULTS

In the case of explant based culture, only limited growth was observed in some cases. However, by enzyme digestion, after two weeks cell growth was evident, and differences in cell type were observed according to the tooth involved.

CONCLUSION

It has been possible to obtain abundant biological material using an enzyme digestion-based protocol for testing purposes, with low experimental variability, as all cells originated from the same individual.

Formation of odontoblast-like cells from cultured human dental pulp cells on dentin in vitro

Recent characterization of human dental pulp stem cells has shed new light on the understanding of the odontoblastic lineage. The purpose of the study was to characterize human adult dental pulp cells isolated and cultured in vitro and to examine the cell differentiation potential grown on dentin. We observed that some pulp cells isolated with an enzyme-digestion approach proliferated at a similar rate as the immortal cell line NIH 3T3. Population doubling time (PDt) for pulp cells at passage 3 was 22.6 +/- 0.5 hours and for NIH 3T3 was 23.1 +/- 2.3 hours. The pulp cells formed mineral nodules stimulated with dexamethasone or dexamethasone plus 1,25-dihydroxyvitamin D3. Pulp cells, after being seeded onto mechanically and chemically treated dentin surface, appeared to establish an odontoblast-like morphology with a cytoplasmic process extending into a dentinal tubule revealed by scanning electron microscopy analysis. Our data demonstrated the formation of cells with odontoblastic morphologies on existing dentin, suggesting that isolated human pulp stem cells may differentiate into odontoblasts on dentin in vitro.

Differential inducibility of human and porcine dental pulp-derived cells into odontoblasts

A robust method for generating odontoblasts from cultured dental pulp cells has not been established. In this study, efficient methods for deriving odontoblasts from cultured human and porcine dental pulp-derived cells were investigated with special attention to species differences. Cultured human cells showed relatively low alkaline phosphatase (ALP) activity in the presence of dexamethasone (Dex) and beta-glycerophosphate (beta-Gly). In contrast, the addition of 1,25-dihydroxyvitaminD(3) (VitD3) significantly increased the ALP activity. In porcine cells, beta-Gly alone or a combination of Dex and beta-Gly significantly increased ALP activity; however, addition of VitD3 reduced this activity. RT-PCR and Western blotting analysis revealed that the combination of three induction reagents on human cells significantly upregulates the expression of osteocalcin mRNA, and dentin sialoprotein. We propose that the combination of Dex, beta-Gly, and VitD3 is critical for differentiation of human dental pulp-derived cells into odontoblasts. In addition, the inducibility of dental pulp-derived cells presented remarkable species differences.

Establishment and characterization of an immortomouse-derived odontoblast-like cell line to evaluate the effect of insulin-like growth factors on odontoblast differentiation

Insulin-like growth factors (IGF-I and IGF-II) play important roles in regulating growth and differentiation of many different organs including teeth. The presence of these factors in the developing tooth has been demonstrated. In vitro studies using tooth explants grown in the presence of IGFs suggest that they promote differentiation of ameloblast and odontoblasts cells. This is achieved by inducing or repressing gene expression associated with these cells. Since some of the genes involved in tooth differentiation are expressed by both cells, to determine the effect of IGF on odontoblast cell differentiation we first need a cell line in which a controlled environment can be created. In this study, we report the establishment and characterization of an Immortomouse-derived odontoblast-like cell line. This conditional cell line can grow indefinitely under permissive conditions in the presence of INF-gamma at 33 degrees C, differentiate into odontoblast-like cells and produce a mineralized extracellular matrix when the INF-gamma is removed and cell maintained at 39 degrees C. Addition of exogenous IGFs to the media results in an accelerated production of a mineralized matrix. This is the result of increased transcription of genes associated with bone mineralization while down regulating genes associated with dentin formation like DSPP. This data suggest that IGFs induce dental papillae mesenchyme cells to produce a bone-like mineralized extracellular matrix.

Side population cells isolated from porcine dental pulp tissue with self-renewal and multipotency for dentinogenesis, chondrogenesis, adipogenesis, and neurogenesis

Dental pulp has the potential to form dentin as a regenerative response to caries. This regeneration is mediated by stem/progenitor cells. Thus, stem cell therapy might be of potential utility in induction of reparative dentin. We isolated side population (SP) cells from dental pulp based on the exclusion of the DNA binding dye Hoechst 33342 by flow cytometry and compared its self-renewal capacities and multipotency with non-SP cells and primary pulp cells. The cumulative cell number of the SP cells was greater than the non-SP cells and primary pulp cells. Bmi1 was continuously expressed in SP cells, suggesting longer proliferative lifespan and self-renewal capacity of SP cells. Next, the maintenance of the multilineage differentiation potential of pulp SP cells was investigated. Expression of type II collagen and aggrecan confirmed chondrogenic conversion (30%) of SP cells. SP cells expressed peroxisome proliferator-activated receptor gamma and adaptor protein 2, showing adipogenic conversion. Expression of mRNA and proteins of neurofilament and neuromodulin confirmed neurogenic conversion (90%). These results demonstrate that pulp SP cells maintain multilineage differentiation potential. We further examined whether bone morphogenetic protein 2 (BMP2) could induce differentiation of pulp SP cells into odontoblasts. BMP2 stimulated the expression of dentin sialophosphoprotein (Dspp) and enamelysin in three-dimensional pellet cultures. Autogenous transplantation of the Bmp2-supplemented SP cells on the amputated pulp stimulated the reparative dentin formation. Thus, adult pulp contains SP cells, which are enriched for stem cell properties and useful for cell therapy with BMP2 for dentin regeneration.

Ultrastructural and immunocytochemical characterization of immortalized odontoblast MO6-G3

AIM

To investigate an immortalized murine odontoblast cell line as a potential alternative for experimental studies on dentinogenesis.

METHODOLOGY

The MO6-G3 cell line was investigated morphologically over 3, 7, 11 and 42 days of culture, using histochemical localization of dentine sialoprotein (DSP), alkaline phosphatase (AP), type I collagen and actin filaments, histoenzymatic staining and biochemical investigation of AP and finally, transmission and scanning electron microscopy.

RESULTS

Scanning electron micrographs showed elongated cells. Accordingly, a polarized organization of odontoblasts was observed by transmission electron microscopy, identifying distinct subcellular compartments as described in vivo. The secretion apparatus, which includes cisternae of rough endoplasmic reticulum, Golgi apparatus saccules and secretion vesicles and granules, was longitudinally organized in the supranuclear compartment ending distally in the secretory pole. A cellular process was observed. The investigation of the cytoskeleton network revealed that actin microfilaments were organized in parallel stress fibre oriented depending on the longitudinal axis of the cytoplasm. Immunofluorescent labelling showed a continuous expression of type I collagen, DSP and AP. A unipolar distribution characterized intracellular DSP immunoreactivity. Histoenzymology revealed AP active sites increasing from 3 to 11 days albeit with a moderate level of activity comparatively to the in vivo situation in dental cells.

CONCLUSION

This cell line MO6-G3 not only showed the criteria of odontoblast phenotype as previously reported but also the characteristic morphodifferentiation pattern of polarized odontoblasts at the cellular level but with an apparent random distribution.

Isolated rat dental pulp cell culture and transplantation with an alginate scaffold

Many studies have been conducted on tissue stem cells in the field of regenerative medicine, and cultured dental pulp mesenchymal cells have been reported to secrete dentin matrix. In the present study we used alginate as a scaffold to transplant subcultured rat dental-pulp-derived cells subcutaneously into the back of nude mice. We found that when beta-glycerophosphate was added to the culture medium, the mRNA of the dentin sialophosphoprotein (DSPP) gene coding dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) was expressed, and an increase in alkaline phosphatase, an early marker of odontoblast differentiation, was also demonstrated. Six weeks after implantation, subcutaneous formation of radiopaque calcified bodies was observed in situ. Immunohistochemical and fine structure studies identified expression of type I collagen, type III collagen, and DSP in the mineralizing transplants, and isolated odontoblast-like cells began to form dentin-like hard tissue formation. Scattered autolyzing apoptotic cells were also observed in the transplants. The study showed that subcultured rat dental-pulp-derived cells actively differentiate into odontoblast-like cells and induce calcification in an alginate scaffold.

Human dental pulp cell culture and cell transplantation with an alginate scaffold

Many studies on tissue stem cells have been conducted in the field of regenerative medicine, and some studies have indicated that cultured dental pulp mesenchymal cells secrete dentin matrix. In the present study we used alginate as a scaffold to transplant subcultured human dental pulp cells subcutaneously into the backs of nude mice. We found that when beta-glycerophosphate was added to the culture medium, dentin sialophosphoprotein mRNA coding dentin sialoprotein (DSP) was expressed. An increase in alkaline phosphatase, which is an early marker for odontoblast differentiation, was also demonstrated. At 6 weeks after implantation the subcutaneous formation of radio-opaque calcified bodies was observed in situ. Immunohistochemical and fine structure studies identified expression of type I collagen, type III collagen, and DSP in the mineralizing transplants. Isolated odontoblast-like cells initiated dentin-like hard tissue formation and scattered autolyzing apoptotic cells were also observed in the transplants. The study showed that subcultured dental pulp cells actively differentiate into odontoblast-like cells and induce calcification in an alginate scaffold.

In vitro characterization of human dental pulp cells: various isolation methods and culturing environments

Our purpose was to characterize human dental pulp cells isolated by various methods and to examine the behavior of cells grown under various conditions for the purpose of pulp/dentin tissue engineering and regeneration. We compared the growth of human pulp cells isolated by either enzyme digestion or the outgrowth method. Expression of dentin sialophosphoprotein, Cbfa1, and two types of collagen (I and III) in these cells was examined by Western blot or reverse transcription/polymerase chain reaction. Growth of pulp cells on dentin and in collagen gel was also characterized. We found that different isolation methods give rise to different populations or lineages of pulp cells during in vitro passage based on their collagen gene expression patterns. Cells isolated by enzymedigestion had a higher proliferation rate than those isolated by outgrowth. Pulp cells did not proliferate or grew minimally on chemically and mechanically treated dentin surface and appeared to establish an odontoblast-like morphology with a cytoplasmic process extending into a dentinal tubule as revealed by scanning electron microscopy. The contraction of the collagen matrix caused by pulp cells was dramatic: down to 34% on day 14. Our data indicate that (1) the choice of the pulp cell isolation method may affect the distribution of the obtained cell populations, (2) a treated dentin surface might still promote odontoblast differentiation, and (3) a collagen matrix may not be a suitable scaffold for pulp tissue regeneration because of the marked contraction caused by pulp cells in the matrix. The present study thus provides important information and a basis for further investigations pre-requisite to establishing pulp tissue engineering/regeneration protocols.

Bone morphogenetic proteins in dentin regeneration for potential use in endodontic therapy

The human dentition is indispensable for nutrition and physiology. The teeth have evolved for mastication of food. Caries is a common dental problem in which the dentin matrix is damaged. When the caries is deep and the dental pulp is exposed, the pulp has to be removed in many cases, resulting ultimately in loss of the tooth. Therefore, the regeneration of dentin-pulp complex is the long-term goal of operative dentistry and endodontics. The key elements of dentin regeneration are stem cells, morphogens such as bone morphogenetic proteins (BMPs) and a scaffold of extracellular matrix. The dental pulp has stem/progenitor cells that have the potential to differentiate into dentin-forming odontoblasts in response to BMPs. Pulpal wound healing consists of stem/progenitor cells release from dental pulp niche after noxious stimuli such as caries, migration to the injured site, proliferation and differentiation into odontoblasts. There are two main strategies for pulp therapy to regenerate dentin: (1) in vivo method of enhancing the natural healing potential of pulp tissue by application of BMP proteins or BMP genes, (2) ex vivo method of isolation of stem/progenitor cells, differentiation with BMP proteins or BMP genes and transplantation to the tooth. This review summarizes recent advances in application of BMPs for dentin regeneration and possible use in endodotic therapy.

Stimulation of reparative dentin formation by ex vivo gene therapy using dental pulp stem cells electrotransfected with growth/differentiation factor 11 (Gdf11)

Dental pulp progenitor/stem cells have the capacity to differentiate into odontoblasts and they provide a potential for dentin repair and regeneration by gene therapy. To develop a successful ex vivo gene therapy to induce reparative dentin formation rapidly and effectively after treatment of caries, we developed a three-dimensional pellet culture system of pulp cells electrotransfected with growth/differentiation factor 11 (Gdf11). The viability after electrotransfection was more than 85%, and the efficiency was about 70% as determined by flow cytometry. After 10 days of culture, the total amount of type I and type III collagen was 3-fold higher in the pEGFP-Gdf11-transfected pellet than in the control. Real-time RT-PCR analysis demonstrated that the expression of markers of odontoblast differentiation (alkaline phosphatase, dentin matrix protein 1 [Dmp1], dentin sialophosphoprotein [Dspp], enamelysin, and phosphate-regulating gene with homologies to endopeptidases on X-chromosome [Phex]) was increased in the pEGFP-Gdf11-transfected pellet compared with the control on day 14. On the basis of this in vitro evaluation, an in vivo investigation in the dog was performed. Autogenous transplantation of Gdf11-transfected cells cultured as a pellet on amputated pulp stimulated reparative dentin formation. Thus, Gdf11 gene therapy may be potentially used in endodontic treatment in dentistry.

CELLS AND EXTRACELLULAR MATRICES OF DENTIN AND PULP: A BIOLOGICAL BASIS FOR REPAIR AND TISSUE ENGINEERING

Odontoblasts produce most of the extracellular matrix (ECM) components found in dentin and implicated in dentin mineralization. Major differences in the pulp ECM explain why pulp is normally a non-mineralized tissue. In vitro or in vivo, some dentin ECM molecules act as crystal nucleators and contribute to crystal growth, whereas others are mineralization inhibitors. After treatment of caries lesions of moderate progression, odontoblasts and cells from the sub-odontoblastic Höhl's layer are implicated in the formation of reactionary dentin. Healing of deeper lesions in contact with the pulp results in the formation of reparative dentin by pulp cells. The response to direct pulp-capping with materials such as calcium hydroxide is the formation of a dentinal bridge, resulting from the recruitment and proliferation of undifferentiated cells, which may be either stem cells or dedifferentiated and transdifferentiated mature cells. Once differentiated, the cells synthesize a matrix that undergoes mineralization. Animal models have been used to test the capacity of potentially bioactive molecules to promote pulp repair following their implantation into the pulp. ECM molecules induce either the formation of dentinal bridges or large areas of mineralization in the coronal pulp. They may also stimulate the total closure of the pulp in the root canal. In conclusion, some molecules found in dentin extracellular matrix may have potential in dental therapy as bioactive agents for pulp repair or tissue engineering.

A novel gene, GliH1, with homology to the Gli zinc finger domain not required for mouse development

The Sonic hedgehog (Shh)-Gli signaling pathway regulates development of many organs, including teeth. We cloned a novel gene encoding a transcription factor that contains a zinc finger domain with highest homology to the Gli family of proteins (61-64% amino acid sequence identity) from incisor pulp. Consistent with this sequence conservation, gel mobility shift assays demonstrated that this new Gli homologous protein, GliH1, could bind previously characterized Gli DNA binding sites. Furthermore, transfection assays in dental pulp cells showed that whereas Gli1 induces a nearly 50-fold increase in activity of a luciferase reporter containing Gli DNA binding sites, coexpression of Gli1 with Gli3 and/or GliH1 results in inhibition of the Gli1-stimulated luciferase activity. In situ hybridization analysis of mouse embryos demonstrated that GliH1 expression is initiated later than the three Gli genes and has a more restricted expression pattern. GliH1 is first detected diffusely in the limb buds at 10.0 days post coitus and later is expressed in the branchial arches, craniofacial interface, ventral part of the tail, whisker follicles and hair, intervertebral discs, teeth, eyes and kidney. LacZ was inserted into the GliH1 allele in embryonic stem cells to produce mice lacking GliH1 function. While this produced indicator mice for GliH1-expression, analysis of mutant mice revealed no discernible phenotype or required function for GliH1. A search of the Celera Genomics and associated databases identified possible gene sequences encoding a zinc finger domain with approximately 90% homology to that of GliH1, indicating there is a family of GliH genes and raising the possibility of overlapping functions during development.

Induction of dental pulp stem cell differentiation into odontoblasts by electroporation-mediated gene delivery of growth/differentiation factor 11 (Gdf11)

The long-term goal of dental treatment is to preserve teeth and prolong their function. In dental caries an efficient method is to cap the exposed dental pulp and conserve the pulp tissue with reparative dentin. We examined whether growth/differentiation factor 11 (GDF11), a morphogen could enhance the healing potential of pulp tissue to induce differentiation of pulp stem cells into odontoblasts by electroporation-mediated gene delivery. Recombinant human GDF11 induced the expression of dentin sialoprotein (Dsp), a differentiation marker for odontoblasts, in mouse dental papilla mesenchyme in organ culture. The Gdf11 cDNA plasmid which was transferred into mesenchymal cells derived from mouse dental papilla by electroporation, induced the expression of Dsp. The in vivo transfer of Gdf11 by electroporation stimulated the reparative dentin formation during pulpal wound healing in canine teeth. These results provide the scientific basis and rationale for gene therapy for endodontic treatments in oral medicine and dentistry.

Induction and regulation of crown dentinogenesis: embryonic events as a template for dental tissue repair?

Close regulation of odontoblast differentiation and subsequent secretory activity is critical for dentinogenesis during both embryogenesis and tissue repair. Some dental papilla cells achieve commitment and specific competence, allowing them to respond to epithelially derived inductive signals during the process of odontoblast differentiation. Temporo-spatial regulation of odontoblast differentiation is dependent on matrix-mediated interactions involving the basement membrane (BM). Experimental studies have highlighted the possible roles of growth factors in these processes. Regulation of functional activity of odontoblasts allows for both ordered secretion of the primary dentin matrix and maintenance of vitality and down-regulation of secretory activity throughout secondary dentinogenesis. After injury to the mature tooth, the fate of the odontoblast can vary according to the intensity of the injury. Milder injury can result in up-regulation of functional activity leading to focal secretion of a reactionary dentin matrix, while greater injury can lead to odontoblast cell death. Induction of differentiation of a new generation of odontoblast-like cells can then lead to reparative dentinogenesis. Many similarities exist between development and repair, including matrix-mediation of the cellular processes and the apparent involvement of growth factors as signaling molecules despite the absence of epithelium during repair. While some of the molecular mediators appear to be common to these processes, the close regulation of primary dentinogenesis may be less ordered during tertiary dentinogenic responses.

A mineralizing rat dental pulp cell subline expressing collagen type I and dentin sialoprotein-phosphophoryn transcripts

A mineralizing rat dental pulp cell subclone, termed M2H4, was selected from single-cell cloning of the rat dental pulp cell line RPC-C2A by screening confluent single-cell cultures for their ability to undergo mineralization. To induce mineralization, confluent single-cell cultures were treated for 8 d with ascorbic acid followed by the addition of inorganic phosphate to a final concentration of 4 mM for an additional 3 d. Confluent M2H4 subclones were shown by immunofluorescence and electron microscopy to form collagen type I fibrils. Furthermore, using reverse transcriptase-polymerase chain reaction, this subclone was found to be capable of expressing dentin sialoprotein-phosphophoryn (DSP-PP) transcripts, an odontoblast-specific marker. Thus, this newly identified mineralizing rat M2H4 subclone possesses odontoblast-like characteristics and can serve as an in vitro model for examining the role of DSP and PP in the formation of mineralized dentin.

MC3T3-E1-conditioned medium-induced mineralization by clonal rat dental pulp cells

Dental pulp is thought to participate in supplementary mineralization, such as reparative dentin and pulp stones, but no direct proof of this has been reported. To study this process at a molecular level, we investigated the matrix mineralization of dental pulp using a clonal cell line (RPC-C2A) derived from rat incisor dental pulp. Mineralized nodules in extracellular matrix were formed by RPC-C2A cells cultured in the presence of conditioned medium (CM) from confluent osteoblastic MC3T3-E1 cells. These nodules were stained by the von Kossa method and with alizarin red S and quantified by the measurement of acid-soluble calcium deposition. This CM was most effective when collected 3-6 days after confluency and added at 50% to the culture medium. The CM-treated RPC-C2A cells showed high alkaline phosphatase activity, a high mRNA level of osteocalcin and decreases in the mRNA levels of osteopontin and osteonectin, but undetectable levels of mRNA of dentin sialophosphoprotein by Northern blot analyses. A pan-specific anti-transforming growth factor (TGF)-beta antibody and a soluble form of receptor for bone morphogenetic protein (BMP)-2/-4 did not neutralize the CM-induced mineralization. These results suggest that some soluble factor(s) other than TGF-beta or BMP-2/-4 in the CM from MC3T3-E1 cells cause differentiation of RPC-C2A cells to osteoblast-like cells.

Characterization of alpha-smooth muscle actin positive cells in mineralized human dental pulp cultures

In response to injury, pulp precursor cells can differentiate into odontoblast-like cells that produce reparative dentine. In culture, pulp cells form mineralizing nodules, but the characteristics of the cells involved in this process are still not fully known. Human pulp cells for culture were obtained from coronal pulp isolated from non-erupted molars, and were maintained in RPMI 1640 medium supplemented with fetal calf serum. Nodules were forming in all human pulp primary cultures (HPPc) and human pulp subcultures observed until their fifth passage (HPSc<5). Mineralization of the nodules was confirmed by the presence of calcium and phosphate that were quantified by X-ray microanalysis. Specific immunolabeling revealed alpha-smooth muscle actin and vimentin in both HPPc and HPSc<5 cells. Cells positive for alpha-smooth muscle actin were either isolated or gathered together in the nodules. Under transmission electron microscopy, some cells in primary pulp cultures exhibited features typical of myofibroblasts or pericytes, such as stress fibers, fibronexus, indented nuclei and gap-junctions. These cells were frequently in close contact with mineral deposits. This work demonstrates for the first time the presence of pericytes or myofibroblasts in mineralized human pulp cultures, but further investigation is required to determine their origin, role and degree of differentiation.

Immortalization of bovine dental papilla cells with simian virus 40 large t antigen

Primary cultures of dental papilla-derived cells have a limited lifespan in vitro and can be maintained only up to passage 7-9 before showing senescence, but in vitro investigations often require a large number of cells showing phenotypic characteristics of the original tissue. To overcome this shortcoming, second-passage cells established from calf molar tooth germs by enzymatic pretreatment of the dental papilla were transfected by electroporation with pSV3neo, coding for the oncogene simian virus 40 large t antigen and a neomycin-resistance gene. Under selection by G418 (neomycin), four cell clones were isolated by single cell dilution at passage 15. Integration of simian virus 40 large t antigen and expression of the gene products were determined in cell clones by polymerase chain reaction (PCR) and immunohistochemistry. Four transfected cell lines (clones B, C, D and no. 12) were maintained in culture for over 1.5 years. For cell characterization, gene expression of procollagen alpha1 (I) and osteocalcin was evaluated by reverse transcriptase (RT)-PCR with cDNA obtained from the established cell lines at passage 20. Expression of collagen type I, osteocalcin and dentine phosphoprotein was evaluated immunohistochemically at passage 20 and after 1.5 years of continuous cell culture. Gene expression and the expression of mineralized tissue-specific proteins was demonstrated with RT-PCR and immunohistochemistry within all four immortalized cell lines. Expression of dentine phosphoprotein was observed in three simian virus 40 large t antigen-transfected cell lines, suggesting the immortalization of odontoblast-like cells in vitro. Thus, transfection of bovine dental papilla-derived cells resulted in immortal cell lines exhibiting phenotypic characteristics of the original tissue.