Depletion of SNRNP200 inhibits the osteo-/dentinogenic differentiation and cell proliferation potential of stem cells from the apical papilla

BACKGROUND

Tissue regeneration mediated by mesenchymal stem cells (MSCs) is deemed a desirable way to repair teeth and craniomaxillofacial tissue defects. Nevertheless, the molecular mechanisms about cell proliferation and committed differentiation of MSCs remain obscure. Previous researches have proved that lysine demethylase 2A (KDM2A) performed significant function in the regulation of MSC proliferation and differentiation. SNRNP200, as a co-binding factor of KDM2A, its potential effect in regulating MSCs' function is still unclear. Therefore, stem cells from the apical papilla (SCAPs) were used to investigate the function of SNRNP200 in this research.

METHODS

The alkaline phosphatase (ALP) activity assay, Alizarin Red staining, and osteogenesis-related gene expressions were used to examine osteo-/dentinogenic differentiation potential. Carboxyfluorescein diacetate, succinimidyl ester (CFSE) and cell cycle analysis were applied to detect the cell proliferation. Western blot analysis was used to evaluate the expressions of cell cycle-related proteins.

RESULTS

Depletion of SNRNP200 caused an obvious decrease of ALP activity, mineralization formation and the expressions of osteo-/dentinogenic genes including RUNX2, DSPP, DMP1 and BSP. Meanwhile, CFSE and cell cycle assays revealed that knock-down of SNRNP200 inhibited the cell proliferation and blocked cell cycle at the G2/M and S phase in SCAPs. In addition, it was found that depletion of SNRNP200 up-regulated p21 and p53, and down-regulated the CDK1, CyclinB, CyclinE and CDK2.

CONCLUSIONS

Depletion of SNRNP200 repressed osteo-/dentinogenic differentiation potentials and restrained cell proliferation through blocking cell cycle progression at the G2/M and S phase, further revealing that SNRNP200 has crucial effects on preserving the proliferation and differentiation potentials of dental tissue-derived MSCs.

The role of Rho-GEF Trio in regulating tooth root development through the p38 MAPK pathway

Trio, the Rho guanine nucleotide exchange factor (Rho-GEF), plays diverse roles in cell migration, cell axon guidance and cytoskeleton reorganization. Conserved during evolution, Trio encodes two guanine nucleotide exchange factor domains (GEFs) and activates small GTPases. The Rho-family small GTPases RhoA and Rac1, which are target molecules of Trio, have been described to engage in craniofacial development and tooth formation. However, the exact role of Trio in tooth development remains elusive. In this study, we generated Wnt1-cre;Trio^fl/fl mice to address the potential function of Trio in tooth development. Wnt1-cre;Trio^fl/fl mice showed short root deformity as well as decreased expression of odontogenic makers such as RUNX2, OSX, OCN, and OPN. In vitro, Trio was silenced in human stem cells of dental papilla (SCAPs). Compared with the control group, the proliferation and migration ability in the experimental group was disrupted. After knocking down Trio in SCAPs, the cells showed phenotypes of poor odontogenic differentiation and weak mineralized nodules. To study the underlying mechanism, we investigated the p38 MAPK pathway and found that loss of Trio blocked the cascade transduction of p38 MAPK signaling. In conclusion, we identified Trio as a novel coordinator in regulating root development and clarified its relevant molecular events.

Complication After Extraction of Natal Teeth with Continued Growth of a Dental Papilla

The purposes of this case report were to describe a growing two-cm gingival mass that developed after natal teeth were extracted in a four-month-old female patient, present a review of the literature on the growth of a gingival mass after the extraction of natal teeth, and illustrate the clinical and histological features that differentiate this condition from other types of gingival masses in infants. Histological examination of the excised mass revealed that it contained tooth-like hard tissue (regular and irregular dentin) that intermingled with bone, dental pulp, and fibrous tissue. We found eight cases from 1962 to 2009 in which a soft-tissue mass with dentin-like hard tissue or a tooth-like structure had developed after the extraction of natal teeth. Based on clinical and histological findings, we deduced that the mass was the result of abnormal growth of a residual dental papilla, including mesenchymal stem cells. Consequently, dentists, obstetricians, gynecologists, and pediatricians should be aware of this potential complication and observe caution before they extract natal teeth.

c-kit positive cells and networks in tooth germs of human midterm fetuses

Numerous studies have attempted to characterize the dental pulp stem cells. However, studies performed on prenatal human tissues have not been performed to evaluate the in situ characterization and topography of progenitor cells. We aimed to perform such a study using of antibodies for CD117/c-kit and multiplex antibody for Ki67+ caspase 3. Antibodies were applied on samples dissected from five human midterm fetuses. Positive CD117/c-kit labeling was found in mesenchymal derived tissues, such as the dental follicle and the dental papilla. The epithelial tissues, that is, dental lamina, enamel organ and oral epithelia, also displayed isolated progenitor cells which were CD117/c-kit positive. Interestingly, CD117/c-kit positive cells of mesenchymal derived tissues extended multiple prolongations building networks; the most consistent of such networks were those of the dental follicle and the perivascular networks of the dental papilla. However, the mantle of the dental papilla was also positive for CD117/c-kit positive stromal networks. The CD117/c-kit cell populations building networks appeared mostly with a Ki67 negative phenotype. The results suggest that CD117/c-kit progenitor cells of the prenatal tooth germ tissues might be involved in intercellular signaling.

Immortalized mouse dental papilla mesenchymal cells preserve odontoblastic phenotype and respond to bone morphogenetic protein 2

Odontogenesis is the result of the reciprocal interactions between epithelial–mesenchymal cells leading to terminally differentiated odontoblasts. This process from dental papilla mesenchymal cells to odontoblasts is regulated by a complex signaling pathway. When isolated from the developing tooth germs, odontoblasts quickly lose their potential to maintain the odontoblast-specific phenotype. Therefore, generation of an odontoblast-like cell line would be a good surrogate model for studying the dental mesenchymal cell differentiation into odontoblasts and the molecular events of dentin formation. In this study, immortalized dental papilla mesenchymal cell lines were generated from the first mouse mandibular molars at postnatal day 3 using pSV40. These transformed cells were characterized by RT-PCR, immunohistochemistry, Western blot, and analyzed for alkaline phosphatase activity and mineralization nodule formation. One of these immortalized cell lines, iMDP-3, displayed a high proliferation rate, but retained the genotypic and phenotypic characteristics similar to primary cells as determined by expression of tooth-specific markers and demonstrated the ability to differentiate and form mineralized nodules. Furthermore, iMDP-3 cells had high transfection efficiency as well as were inducible and responded to BMP2 stimulation. We conclude that the establishment of the stable murine dental papilla mesenchymal cell line might be used for studying the mechanisms of dental cell differentiation and dentin formation.

[Combined crown lengthening surgery with restorative therapy for inducing papilla growth: a case report]

A young lady with unsatisfied restorations of upper anterior teeth and swollen gum wanted to improve aesthetics. Oral examination showed that 12-22 were provisional crowns with normal occlusion, poorly gingival contour and gummy smile. The gingiva was red, light swollen and bleeding on probing. X-ray showed the roots of 11, 21 were short and the alveolar bone absorbed. After the periodontal initial treatment, an ideal location of gingival margin was determined. Then, an esthetic periodontal surgery was performed to recover the biology width and the gingival margin was fitted with the anterior teeth. The temporary restorations were made twice to guide the gingiva growth by changing the shape of the restorations and moving up the contact points of the restorations. The ceramic crowns were completed 3 months after the operation. The gummy smile disappeared and the gingival margin was filled well with the upper anterior ceramic crowns. The 14-month follow-up presented a satisfied effect. Crown lengthening surgery combined restorative therapy could lead papilla to grow well. This process is beneficial for the future treatment plan and clinical esthetic evaluation.

Cell pellets from dental papillae can reexhibit dental morphogenesis and dentinogenesis

We isolated dental papilla mesenchymal cells (DPMCs) from different rat incisor germs at the late bell stage and incubated them as cell pellets in polypropylene tubes. In vitro pellet culture of DPMCs presented several crucial characteristics of odontoblasts, as indicated by accelerated mineralization, positive immunostaining for dentin sialophosphoprotein and dentin matrix protein 1, and expression of dentin sialophosphoprotein mRNA. The allotransplantation of these pellets into renal capsules was also performed. Despite the absence of dental epithelial components, dissociated DPMCs with a complete loss of positional information rapidly underwent dentinogenesis and morphogenesis, and formed a cusp-like dentin-pulp complex containing distinctive odontoblasts, predentin, dentin, and dentinal tubules. These results imply that DPMCs at the late bell stage can reexhibit the dental morphogenesis and dentinogenesis by themselves, and epithelial-mesenchymal interactions at this stage may not be indispensable. Furthermore, different DPMC populations from the similar stage may keep the same developmental pattern.

Influence of interimplant distance on gingival papilla formation and bone resorption: clinical-radiographic study in dogs

PURPOSE

The purpose of this study was to evaluate in dogs the area between implants after prosthetic restoration within 5 mm distance between the contact point (CP) between crowns and the bone crest (BC).

MATERIALS AND METHODS

The mandibular premolars of 6 dogs were extracted bilaterally. After 12 weeks of healing, each dog received 8 implants. On each side, 2 implants were separated by 2 mm (group 1) and 2 by 3 mm (group 2). After a healing period (3 months), the implants were restored with temporary acrylic resin prostheses and after 4 more weeks, with definitive metallic prostheses. After 8 weeks, the distance between the CP and the papilla (P) was measured. The distance between a line extending from the CP and the gingival height at the distal extension of the prosthesis (DE) was also measured. Digital radiographic images were obtained for evaluation of the CP-BC and BC-P distances and the analysis of bone resorption adjacent to the implant surfaces.

RESULTS

The median CP-P distances were 1.75 mm and 1.98 mm for groups 1 and 2, respectively; the median CP-DE distances were 2.60 and 2.69, respectively. The mean CP-BC distances were 5.64 mm and 6.45 mm, for groups 1 and 2, respectively; mean BC-P distances were 3.07 mm and 3.55 mm, respectively.

DISCUSSION AND CONCLUSIONS

The differences in distances of 2 and 3 mm between implants did not present significant differences in the formation of papillae or in crestal resorption. The CP-BC distances for prostheses should be different from those of natural teeth because in natural teeth, the biologic width is already present, and in the case of implant-supported prostheses, it will develop following second-stage surgery.

The induction of enamel and dentin complexes by subcutaneous implantation of reconstructed human and murine tooth germ elements

Tooth induction by xenogenic graft of reconstructed human tooth germ components has never been attempted. Here we report our first attempt at a transplantation of human tooth germ components, heterologously recombined with mouse dental epithelia, into immunocompromised animals. Human third molar tooth germs enucleated from young patients as prophylactic treatment for orthodontic reasons were collected. The whole or minced human dental papilla was reconstructed with human- or mouse molar enamel epithelium, and transplanted in the dorsal aspect of C.B-17/Icr-scid Jcl mice. The transplant of human dental papilla reconstructed with human enamel epithelium formed thin dentin and immature enamel layers by 3 to 4 weeks, but remained extremely small in quantity due to a shortage of epithelial components in the graft. The addition of E16 mouse molar enamel organs (n=10-12) to each graft augmented the formation of tooth germ-like structures, but the differentiation of mouse molar ameloblasts was suppressed. However, once a solid layer of mineralized dentin was established, mouse ameloblasts accelerated their differentiation, and completed the enamel matrix formation and maturation within the following 4 weeks, whereas human ameloblasts, which had interacted with human dental papilla, remained in the stage of matrix formation during the same period. These data imply that, in reconstructed transplants, the differentiation of mouse dental epithelia is restrained by putative suppressive factors derived from human dental papilla until they are separated by mineralized dentin layers that serve as a diffusion barrier. The mouse enamel organ nevertheless retains its own phenotypic characteristics and intrinsic timing of cell differentiation and function.

Development and maturation of taste buds of the palatal epithelium of the rat: histological and immunohistochemical study

Palatal taste buds are intriguing partners in the mediation of taste behavior and their spatial distribution is functionally important for suckling behavior, especially in the neonatal life. Their prenatal development has not been previously elucidated in the rat, and the onset of their maturation remains rather controversial. We delineated the development and frequency distribution of the taste buds as well as the immunohistochemical expression of alpha-gustducin, a G protein closely related to the transduction of taste stimuli, in the nasoincisor papilla (NIP) and soft palate (SP) from the embryonic day 17 (E17) till the postnatal day 70 (PN70). The main findings in the present study were the development of a substantial number of taste pores in the SP of fetal rats (60.3 +/- 1.7 out of 122.8 +/- 5.5; mean +/- SD/animal at E19) and NIP of neonatal rats (9.8 +/- 1.0 out of 44.8 +/- 2.2 at PN4). alpha-gustducin-like immunoreactivity (-LI) was not expressed in the pored taste buds of either prenatal or newborn rats. The earliest expression of alpha-gustducin-LI was demonstrated at PN1 in the SP (1.5 +/- 0.5 cells/taste bud; mean +/- SD) and at PN4 in the NIP (1.4 +/- 0.5). By age the total counts of pored taste buds continuously increased and their morphological features became quite discernible. They became pear in shape, characterized by distinct pores, long subporal space, and longitudinally oriented cells. Around the second week, a remarkable transient decrease in the total number of taste buds was recorded in the oral epithelium of NIP and SP, which might be correlated with the changes of ingestive behaviors. The total counts of cells showing alpha-gustducin-LI per taste bud gradually increased till the end of our investigation (14.1 +/- 2.7 in NIP and 12.4 +/- 2.5 in SP at PN70). We conclude that substantial development of taste buds began prenatally in the SP, whereas most developed entirely postnatal in the NIP. The present study provides evidence that the existence of a taste pore which is considered an important criterion for the morphological maturation of taste buds is not enough for the onset of the taste transduction, which necessitates also mature taste cells. Moreover, the earlier maturation of palatal taste buds compared with the contiguous populations in the oral cavity evokes an evidence of their significant role in the transmission of gustatory information, especially in the early life of rat.

Basement membrane-like structures occurring on the surface of dental papilla mesenchymal cells during odontogenesis in the monkey Macaca fuscata

The aim of this study was to examine the nature of a basement membrane-like structure occurring along the surface of dental papilla cells during odontogenesis. The tooth germs of Japanese macaques (Macaca fuscata) were prepared for both ultrastructural and immunohistochemical studies. Characteristic discrete structures which resembled basement membranes were observed along the surface of the dental papilla cells, preodontoblasts, and also of the odontoblasts. Immunoperoxidase staining showed that these structures contained major basement membrane components including laminin, heparan sulfate proteoglycan, type IV collagen, as well as fibronectin. They tended to be less prominent along dental pulp fibroblasts and fully developed odontoblasts in comparison with those along the papilla cells localized close to the basement membrane of the inner enamel epithelium. Therefore, possible roles of these basement membrane-like structures would be: 1) to support the cells, 2) to momentarily secure the appropriate positions of differentiating mesenchymal cells, and 3) to regulate epithelial-mesenchymal interactions for odontoblast differentiation.

Distribution of the neural cell adhesion molecule (NCAM) during pre- and postnatal development of mouse incisors

Developmental changes in the distribution of the neural cell adhesion molecule (NCAM) were investigated in mouse incisors by means of the indirect immunofluorescence method. During the prenatal stages of development, NCAM was predominantly found in the dental follicle, but not in the dental papilla; the results were analogous to the distribution of NCAM during molar development. After birth, the expression of NCAM continued in the tissue between the enamel organ and the alveolar bone on the labial aspect. In contrast, the follicular tissue covering the lingual aspect of the incisor gradually lost NCAM immunoreactivity from its outer zone as it differentiated into the highly organized periodontal ligament. The intermediate zone of the ligament continued to express NCAM-immunoreactivity even in mice of 6 weeks of age. This pattern of NCAM expression was different from that found in molar teeth, where the organized peridontal ligament was NCAM-negative. The dental pulp, in which we previously reported that an NCAM-positive area appeared at later stages of molar tooth development, did not express NCAM immunoreactivity even at the latest stage of development covered in this study. These differences in the distribution of NCAM between the incisors and the molars might be related to the fact that rodent incisors continue to grow throughout the life of the animal.

Evidence for the role of the enamel knot as a control center in mammalian tooth cusp formation: non-dividing cells express growth stimulating Fgf-4 gene

The main morphological features of the mammalian tooth crown are cusps, but the developmental mechanisms that cause the formation of cusps are unknown. Tooth cusp formation commences at cap-stage with the appearance of the enamel knot, which is a cluster of non-dividing epithelial cells. In this study, enamel knot was first seen in embryonic mice molar teeth at the onset of cap-stage. Later in tooth development, secondary enamel knot structures were observed at the cusp tips and their appearance corresponded to the formation of individual cusp morphology. Comparisons of the pattern of cell proliferation in embryonic mouse molars and the expression of fibroblast growth factor-4 (Fgf-4) gene revealed that expression of Fgf-4 mRNA is strictly localized to the non-dividing cells of the enamel knot. However, when FGF-4 protein was introduced onto isolated dental tissues in vitro, it stimulated the proliferation of both dental epithelial and mesenchymal cells. Based on these results, we suggest that the enamel knot may control tooth morphogenesis by concurrently stimulating cusp growth (via FGF-4 synthesis) and by directing folding of cusp slopes (by not proliferating itself).

Age-related changes of the dental pulp complex and their relationship to systemic aging

The dental pulp and its associated structures, the dentin and the cementum, are discussed. Because many of the age-related pulpal changes have components considered in several of the current theories of aging, these theories are briefly reviewed. Part 2 describes the age-related changes of the dental pulp, the dentin, and the cementum (the dental pulp complex). An attempt is made to differentiate inherent aging changes from physiologic defensive changes and pathologic irritant-induced changes. Part 3 describes the relationship of age-induced changes in the dental pulp complex to components of the current aging theories together with a unified concept of the dental pulp complex aging. Part 4 considers whether dental pulp complex aging can be used as a biomarker for generalized aging. Whether age-related changes of the dental pulp complex can be altered by interventions is discussed.

Histological study on the postnatal development and sequence of eruption of the maxillary cheek-teeth of rabbits (Oryctolagus cuniculus)

The development and sequence of eruption of the maxillary cheek-teeth of rabbits were studied by histological methods. The presence of three deciduous molars which were replaced by correspondent premolars and of three permanent molars without predecessors was confirmed. The eruption of the maxillary deciduous molars was shown to begin at 4 days postnatally and that of the permanent molar at 9 days, while the eruption of the premolars occurs from 24 days on, replacing the deciduous molars which are exfoliated. The last tooth to erupt is the M3. At 32 days all the permanent cheek-teeth are erupted. The deciduous molars are completely developed at birth, root resorption starting at 4 days. On the first day the premolars are in the bell stage and in the M1 and M2 amelogenesis is taking place. After 27 days the development of the permanent maxillary cheek-teeth is completed. Dentinogenesis, amelogenesis and cementogenesis were observed in all of them.