Mineralized nodule formation by human dental papilla cells in culture

Dexamethasone and zinc loaded polymeric nanoparticles reinforce and remineralize coronal dentin. A morpho-histological and dynamic-biomechanical study

OBJECTIVE

To investigate the effect of novel polymeric nanoparticles (NPs) doped with dexamethasone (Dex) on viscoelasticity, crystallinity and ultra-nanostructure of the formed hydroxyapatite after NPs dentin infiltration.

METHODS

Undoped-NPs, Dex-doped NPs (Dex-NPs) and zinc-doped-Dex-NPs (Zn-Dex-NPs) were tested at dentin, after 24 h and 21 d. A control group without NPs was included. Coronal dentin surfaces were studied by nano-dynamic mechanical analysis measurements, atomic force microscopy, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p < 0.05).

RESULTS

At 21 d of storage time, both groups doped with Dex exhibited the highest complex, storage and loss moduli among groups. Zn-Dex-NPs and Dex-NPs promoted the highest and lowest tan delta values, respectively. Dex-NPs contributed to increase the fibril diameters of dentin collagen over time. Dentin surfaces treated with Zn-Dex-NPs attained the lowest nano-roughness values, provoked the highest crystallinity, and produced the longest and shortest crystallite and grain size. These new crystals organized with randomly oriented lattices. Dex-NPs induced the highest microstrain. Crystalline and amorphous matter was present in the mineral precipitates of all groups, but Zn and Dex loaded NPs helped to increase crystallinity.

SIGNIFICANCE

Dentin treated with Zn-Dex-NPs improved crystallographic and atomic order, providing structural stability, high mechanical performance and tissue maturation. Amorphous content was also present, so high hydroxyapatite solubility, bioactivity and remineralizing activity due to the high ion-rich environment took place in the infiltrated dentin.

Changes of mitochondrial respiratory function during odontogenic differentiation of rat dental papilla cells

Dental papilla cells (DPCs) belong to precursor cells differentiating to odontoblasts and play an important role in dentin formation and reproduction. This study aimed to explore the changes and and involvement of mitochondrial respiratory function during odontogenic differentiation. Primary DPCs were obtained from first molar dental papilla of neonatal rats and cultured in odontogenic medium for 7, 14, 21 days. DPCs, which expressed mesenchymal surface markers CD29, CD44 and CD90, had the capacity for self-renewal and multipotent differentiation. Odontoblastic induction increased mineralized matrix formation in a time-dependent manner, which was accompanied by elevated alkaline phosphatase (ALP), dentin sialophosphoprotein and dentin matrix protein 1 expression at mRNA and protein levels. Notably, odontogenic medium led to an increase in adenosine-5'-triphosphate content and mitochondrial membrane potential, whereas a decrease in intercellular reactive oxygen species production and NAD⁺/NADH ratio. Furthermore, odontogenic differentiation was significantly suppressed by treatment with rotenone, an inhibitor of mitochondrial respiratory chain. These results demonstrate that enhanced mitochondrial function is crucial for odontogenic differentiation of DPCs.

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.

Osteogenic differentiation of human dental papilla mesenchymal cells

We isolated dental papilla from impacted human molar and proliferated adherent fibroblastic cells after collagenase treatment of the papilla. The cells were negative for hematopoietic markers but positive for CD29, CD44, CD90, CD105, and CD166. When the cells were further cultured in the presence of beta-glycerophosphate, ascorbic acid, and dexamethasone for 14 days, mineralized areas together with osteogenic differentiation evidenced by high alkaline phosphatase activity and osteocalcin contents were observed. The differentiation was confirmed at both protein and gene expression levels. The cells can also be cryopreserved and, after thawing, could show in vivo bone-forming capability. These results indicate that mesenchymal type cells localize in dental papilla and that the cells can be culture expanded/utilized for bone tissue engineering.

Effects of Proinflammatory Cytokines on the Expression of Mineralization Markers and Heme Oxygenase-1 in Human Pulp Cells

The roles of IL-1alpha and TNF-alpha in early pulp inflammation were investigated by determining the alkaline phosphatase (ALP) activity, the osteonectin (ON), osteocalcin (OC), bone sialoprotein (BSP), and heme oxygenase-1 (HO-1) expression using an immunoblot method. Primary cultured dental pulp cells were treated with IL-1alpha, TNF-alpha, or both for 3, 7, and 14 days. The pulp cells treated with IL-1alpha for 3 days showed elevated ALP activity and increased ON, OC, and HO-1 expression, whereas TNF-alpha treatment did not increase the ALP activity and no BSP was expressed until day 14. The pulp cells treated with both IL-1alpha and TNF-alpha for 3 days showed increased HO-1 expression compared with that of the control. These data suggest that IL-1alpha and TNF-alpha produced in the early inflammatory reaction have different functions in human pulp cells. IL-1alpha induces ALP, ON, and OC in tooth mineralization and it may play a role in the cytoprotection of pulp cells via HO-1 expression, while long-term treatment of TNF-alpha may inhibit the tooth mineralization.

In vitro differentiation and mineralization of human dental pulp cells induced by dentin extract

In this study, the progenitor cells isolated from the human dental pulp were used to study the effects of ethylenediaminetetraacetic acid-soluble dentin extract (DE) on their differentiation and mineralization to better understand tissue injury and repair in the tooth. Mineralization of the matrix was increasingly evident at 14, 21, and 28 d after treatment with a mineralization supplement (MS) (ascorbic acid [AA], beta-glycerophosphate [beta-GP]) and MS + DE. Real-time polymerase chain reaction results showed type I collagen upregulation after the addition of MS + DE at 7 d. Alkaline phosphatase was downregulated after the mineralization became obvious at 14 d. Bone sialoprotein was shown to be upregulated in the mineralized cell groups at all time points and dentin sialophosphoprotein after 7 d. Core binding factor a 1 was upregulated by the treatment of MS and DE at 7, 14, and 21 d. These results indicated that the MS of AA, beta-GP, and DE synergistically induced cell differentiation of pulp progenitor cells into odontoblast-like cells and induced in vitro mineralization.

Effects of transforming growth factor β1 (TGFβ-1) and dentin non-collagenous proteins (DNCP) on human embryonic ectomesenchymal cells in a three-dimensional culture system

Cranial neural crest-derived ectomesenchymal cells represent a population of pluripotent stem cells giving rise to many of the various oro-facial and dental tissues. The factors determining the terminal fate of these cells are still unclear. The potentiality of human embryonic ectomesenchymal cells from the first branchial arch have been investigated when isolated and grown in a three-dimensional (3D)-collagen gel culture system in the presence of dentin matrix-derived non-collagenous proteins (DNCP) and TGFbeta-1. Functional differentiation of cells showing some characteristics of odontoblast-like cells could be observed when the cells were cultured with DNCP+TGFbeta-1 or DNCP, however, only cytological differentiation was observed during culture with TGFbeta-1 alone. The characteristics of these cells was assessed by morphological appearance, expression of the odontoblast phenotype marker dentin sialophosphoprotein (DSPP), increased alkaline phosphatase levels and formation of mineralised nodules in vitro. The results indicate that these embryonic cells from the first branchial arch are capable of responding to the inductive stimulus of DNCP or DNCP+TGFbeta-1 when isolated and grown in the 3D collagen gel culture system. The capacity of the isolated cells to differentiate into mineralizing cells showing some characteristics of odontoblast-like cells under these growth conditions highlights the potential of such approaches for tissue engineering strategies for hard-tissue regeneration after injury.

Effects of doxorubicin on human dental pulp cells in vitro

There is substantial information concerning the effects of continuous exposure to supratherapeutic or therapeutic concentrations of doxorubicin on human molar pulpal cells; the effects of continuous exposure to subtherapeutic concentrations of this agent are undetermined. To this end, we studied the proliferation of human fibroblasts and pulpal cells and their pattern of mineralized nodule deposition in vitro. Cell proliferation was assessed at 1, 3, 5, and 7 days from populations with either no exposure (control) or exposure to 10(-6)-10(-9) mol/L doxorubicin. Mineralized nodule deposition and calcium-45 incorporation were assessed at 7 and 21 days of culture. Data were compared by factorial ANOVA and a post-hoc Tukey test. 10(-6) and 10(-7) mol/L doxorubicin significantly reduced the total number of viable pulpal cells in cultures from days 1 to 3 (p < 0.05); doxorubicin 10(-6)-10(-9) mol/L significantly inhibited cell proliferation (p < 0.05) and DNA synthesis 5 days after plating (p < 0.001). After 21 days, doxorubicin 10(-6)-10(-8) mol/L significantly decreased calcium-45 incorporation into pulpal cultures (p < 0.001); all dilutions significantly reduced the number of mineralized nodules within the 21-day pulpal cultures (p < 0.05). In addition, all dilutions of doxorubicin significantly inhibited fibroblast cell proliferation and incorporation of [(3)H]thymidine. In contrast, the fibroblast cultures did not produce mineralized nodules, suggesting that the mineralized nodules within the pulpal cell cultures did not result from dystrophic calcification. Thus, exposure to subtheraputic doxorubicin concentrations has potential adverse effects on mineralized tissue formation within the pulp, which could affect the rates of reparative dentin deposition within the tooth pulps of patients receiving this chemotherapeutic agent.

Dexamethasone stimulates differentiation of odontoblast-like cells in human dental pulp cultures

Regenerative dental pulp strategies require the identification of precursors able to differentiate into odontoblast-like cells that secrete reparative dentin after injury. Pericytes have the ability to give rise to osteoblasts, chondrocytes, and adipocytes, a feature that has led to the suggestion that odontoblast-like cells could derive from these perivascular cells. In order to gain new insights into this hypothesis, we investigated the effects of dexamethasone (Dex), a synthetic glucocorticoid employed to induce osteogenic differentiation in vitro, in a previously reported model of human dental pulp cultures containing pericytes as identified by their expression of smooth muscle actin (SMA) and their specific ultrastructural morphology. Our data indicated that Dex (10(-8) M) significantly inhibited cell proliferation and markedly reduced the proportion of SMA-positive cells. Conversely, Dex strongly stimulated alkaline phosphatase (ALP) activity and induced the expression of the transcript encoding the major odontoblastic marker, dentin sialophosphoprotein. Nevertheless, parathyroid hormone/parathyroid hormone-related peptide receptor, core-binding factor a1/osf 2, osteonectin, and lipoprotein lipase mRNA levels were not modified by Dex treatment. Dex also increased the proportion of cells expressing STRO-1, a marker of multipotential mesenchymal progenitor cells. These observations indicate that glucocorticoids regulate the commitment of progenitors derived from dental pulp cells to form odontoblast-like cells, while reducing the proportion of SMA-positive cells. These results provide new perspectives in deciphering the cellular and molecular mechanisms leading to reparative dentinogenesis.

Cultured human and rat tooth papilla cells induce hair follicle regeneration and fiber growth

The mesenchymal-epithelial interactions that characterize the early stages of tooth and hair follicle morphogenesis share certain similarities, and there is increasing evidence that mesenchymal cells derived from both mature structures retain interactive and stem cell-like properties. This study aimed to gauge the cross-appendage inductive capabilities of cultured tooth dental papilla (or pulp) cells from different species and ages of donor. Adult human and juvenile rat tooth papilla cells were implanted into surgically inactivated hair follicles within two different microenvironments. The human cells interacted with follicle epithelium to regenerate new end bulbs and create multiple differentiated hair fibers. Rodent tooth dental cells also induced new epithelial matrix structures and stimulated de novo hair formation. However, in many instances they also elicited mineralization and bone formation, a phenomenon that appeared to relate to their donor's age; the type of tooth of origin; and the host environment. Taken together, this study reveals that cultured dental papilla cells from postnatal mammals (adult, juvenile, and newborn) retain inductive molecular signals that must be common to both hair and teeth follicles. It highlights the stem cell-like qualities and morphogenetic abilities of tooth and hair follicle cells from mature humans, and their capacity for cross-appendage and interspecies communication and interaction. Besides the developmental implications, the present findings have relevance for stem cell biology, hair growth, tissue repair, and other biotechnologies. Moreover, the critical importance of considering the local microenvironment in which different cells/tissues are naturally or experimentally engineered is firmly demonstrated.

Site-specific effect of ascorbic acid deficiency on the structure and function of odontoblasts in the teeth of osteogenic disorder rat in vivo

The influence of chronic L-ascorbic acid (AsA) deficiency on dentinogenesis was examined in Osteogenic Disorder Shionogi (ODS) rat, which bear inborn lack of L-gulonolactone oxidase. Weanling male rats were kept on AsA-free diet for 4 weeks until all suffered from scurvy. Control rats were given AsA in drinking water. The dentin of molars and incisors of the scorbutic rats was thinner than that in control, except for the crown-analogue (enamel-related) of incisors. Predentin in scorbutic molars showed irregular thickness, and was almost lacking in roots. In the root-analogue (cementum-related) region of scorbutic incisors, dentin displayed metachromatic incremental lines, and the thickened predentin contained collagen fibrils of irregular diameter. The odontoblasts facing the affected regions contained dilated rough endoplasmic reticulum cisternae. In the crown-analogue of scorbutic incisors, however, dentin, predentin, and odontoblasts were comparable to those of controls. These data indicate that AsA deficiency differentially affects the synthetic and/or secretory activity of odontoblasts in ODS rat teeth in a site-specific manner. The regional differences implicate the presence of putative local factor(s) in the crown-analogue of incisors that might have compensated for AsA deficiency. The odontoblasts in the crown-analogue of incisors may have different requirements for AsA from those in molars and the root-analogue of incisors.

Two- versus three-dimensional in vitro differentiation of human pulp cells into odontoblastic cells

The spatial organization of the pulp cells may modify the cytodifferentiation process. The purpose of this study was to compare the two- versus three-dimensional cell culture systems for differentiation of human odontoblastic cells in vitro. Pulpal cores from freshly extracted human third molars were cultured in vitro in a perfusion device on two types of membranes: polyester membrane (two-dimensional [2D] cell culture) and nylon mesh (three-dimensional [3D] cell culture). The cells were incubated with minimum essential medium containing (a) substitute serum, (b) 10% fetal calf serum (FCS), (c) 10% fetal calf serum + 2 mM beta-glycerophosphate (beta GP), and (d) 10% fetal calf serum + transforming growth factor (TGF) beta 1. Immunohistochemistry was used to evaluate the expression of collagen I, osteonectin, and nestin. Small differences were observed between 2D and 3D cell culture systems. This was particularly evident in the 10% FCS group. beta-Glycerophosphate in the 3D system seems to stimulate the osteogenic cell phenotype, as a considerable induction of osteonectin is observed.

Alkaline phosphatase activity in normal and inflamed dental pulps

Alkaline phosphatase (ALP) seems to be important in the formation of mineralized tissues. High levels of ALP have been demonstrated in dental pulp cells. In the present study ALP activity was analyzed in normal healthy human dental pulps, in reversible pulpitis, and in irreversible pulpitis. Enzymatic ALP control values for the normal healthy pulps were 110.96+/-20.93. In the reversible pulpitis specimens the ALP activity increased almost eight times to 853.6+/-148.27. In the irreversible pulpitis specimens the values decreased sharply to 137.15+/-21.28 and were roughly equivalent to those seen in normal healthy pulps. The differences between the groups (control vs. reversible pulpitis and reversible pulpitis vs. irreversible pulpitis) were statistically significant. These results could point to a role of ALP in the initial pulp response after injury.

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.

Human dentin production in vitro

The main hard tissues of teeth are composed of dentin and enamel, synthesized by the mesenchyme-derived odontoblasts and the epithelial-derived ameloblasts, respectively. Odontoblasts are highly differentiated post-mitotic cells secreting the organic matrix of dentin throughout the life of the animal. Pathological conditions such as carious lesions and dental injuries are often lethal to the odontoblasts, which are then replaced by other pulp cells. These cells are able to differentiate into odontoblast-like cells and produce a reparative dentin. In this study we reproduced this physiological event in an in vitro culture system using pulps of human third molars. Pulp cells cultured in presence of beta-glycerophosphate formed mineralization nodules, which grew all over the culture period. The immunohistochemical study revealed that, as odontoblasts, pulp cells contributing to the nodule formation express type I collagen, osteonectin, and nestin. By the exception of nestin, these proteins are also detected in the nodules. The composition of the nodules was also analyzed by Fourier transform infrared microspectroscopy. The spectra obtained showed that both the organic and the mineral composition of the nodules have the characteristics of the human dentin and differ from those of enamel and bone. Taken together, these results show that both the molecular and the mineral characteristics of the human dentin matrix are respected in the in vitro culture conditions.

Nestin expression in embryonic and adult human teeth under normal and pathological conditions

Nestin is an intermediate filament most related to neurofilaments and expressed predominantly in the developing nervous system and muscles. In the present study we examined the in vivo distribution of nestin in human teeth during embryonic development and in permanent teeth under normal and pathological conditions. The results show that nestin is first expressed at the bell stage and that its distribution is restricted in pulpal cells located at the cusp area of the fetal teeth. In young permanent teeth, nestin is found only in functional odontoblasts, which produce the hard tissue matrix of dentin. Expression is progressively down-regulated and nestin is absent from older permanent teeth. In carious and injured teeth, nestin expression is up-regulated in a selective manner in odontoblasts surrounding the injury site, showing a link between tissue repair competence and nestin up-regulation under pathological conditions. In an in vitro assay system of human dental pulp explants, nestin is up-regulated after local application of bone morphogenic protein-4. A similar effect is seen in cultures of primary pulp cells during their differentiation into odontoblasts. Taken together, these results suggest that nestin plays a potential role in odontoblast differentiation during normal and pathological conditions and that bone morphogenic protein-4 is involved in nestin up-regulation.