Immunostaining and transcriptional enhancement of interleukin-1 receptor type I in the rat dental follicle

Function of Dental Follicle Progenitor/Stem Cells and Their Potential in Regenerative Medicine: From Mechanisms to Applications

Dental follicle progenitor/stem cells (DFPCs) are a group of dental mesenchyme stem cells that lie in the dental follicle and play a critical role in tooth development and maintaining function. Originating from neural crest, DFPCs harbor a multipotential differentiation capacity. More importantly, they have superiorities, including the easy accessibility and abundant sources, active self-renewal ability and noncontroversial sources compared with other stem cells, making them an attractive candidate in the field of tissue engineering. Recent advances highlight the excellent properties of DFPCs in regeneration of orofacial tissues, including alveolar bone repair, periodontium regeneration and bio-root complex formation. Furthermore, they play a unique role in maintaining a favorable microenvironment for stem cells, immunomodulation and nervous related tissue regeneration. This review is intended to summarize the current knowledge of DFPCs, including their stem cell properties, physiological functions and clinical application potential. A deep understanding of DFPCs can thus inspire novel perspectives in regenerative medicine in the future.

IL-1α Regulates Osteogenesis and Osteoclastic Activity of Dental Follicle Cells Through JNK and p38 MAPK Pathways

Inflammatory cytokines such as interleukin-1α (IL-1α) are increased in teeth with periapical lesions. Primary teeth with periapical lesions have a propensity for accelerated eruption of the successors. In this study, we asked whether increased levels of IL-1α in the dental follicle (DF) occurring as the result of periapical lesions promote tooth eruption, possibly due to enhanced osteoclastic remodeling of DF cells (DFCs). To this end, we studied the effect and possible mechanism of IL-1α on osteogenic differentiation, osteoclastogenic activity, and matrix remodeling of DFCs. Results demonstrated that DFCs cultured with IL-1α exhibited reduced osteogenic capacity, higher osteoclastogenic activity, and stronger invasive ability. Phosphorylation of JNK and p38 was upregulated, and pretreatment with SB203580 and SP600125 reversed the effect of IL-1α on DFCs. Neonatal rats subjected to subcutaneous injection of an IL-1 receptor antagonist exhibited a reduced number in activated osteoclasts, increased expression of alkaline phosphatase and osteopontin, and delayed tooth eruption. These data support our hypothesis that increased IL-1α cytokine levels as they occur during periodontal and periapical inflammation cause osteoclastic remodeling of the alveolar socket as a requirement for tooth eruption and thus may indirectly promote the vertical eruption of teeth toward the occlusal plane.

Does Timing of Eruption in First Primary Tooth Correlate with that of First Permanent Tooth? A 9-years Cohort Study

Background and aims. Predicting the teeth eruption time is a valuable tool in pediatric dentistry since it can affects scheduling dental and orthodontic treatments. This study investigated the relationship between the eruption time of first primary and permanent teeth and the variation in the eruption time considering socioeconomic status (SES) in a 9-year population- based cohort study.

Materials and methods. 307 subjects were examined at bimonthly intervals during the first and second years of life and then at six-month intervals until the eruption of first permanent tooth. Eruption times of primary and permanent tooth were recorded for each child. A modified form of Kuppuswamy’s scale was used to assess the SES.

Results. Among 267 subjects completed all follow-ups, the eruption time for first primary and permanent teeth indicated a direct strong correlation; in that one month delayed or early eruption of firstprimary tooth resulted in 4.21 months delayed or early eruption of first appearing permanent tooth (r = 0.91, n = 267, P <0.001). No significant correlation was observed between the eruption time of first primary and first permanent teeth and SES (P = 0.67, P = 0.75, respectively).

Conclusion. The eruption timing for the first primary tooth had a correlation with the first permanent tooth eruption tim-ing, while SES did not have any influence on eruption times.

Chronology and regulation of gene expression of RANKL in the rat dental follicle

Tooth eruption in the rat requires bone resorption resulting from a major burst of osteoclastogenesis on postnatal day 3 and a minor burst of osteoclastogenesis on postnatal day 10 in the alveolar bone of the first mandibular molar. The dental follicle regulates the major burst on postnatal day 3 by down-regulating its osteoprotegerin (OPG) gene expression to enable osteoclastogenesis to occur. To determine the role of receptor activator of nuclear factor-kappa B ligand (RANKL) in tooth eruption, its gene expression was measured on postnatal days 1-11 in the dental follicle. The results show that RANKL expression was significantly elevated on postnatal days 9-11 in comparison to low expression levels at earlier time-points. As OPG expression is high at this latter time-point, this increase in RANKL expression would be needed for stimulating the minor burst of osteoclastogenesis. Tumor necrosis factor-alpha enhances RANKL gene expression in vitro and it may be responsible for up-regulating RANKL in vivo. Transforming growth factor-beta1 and interleukin-1alpha also enhance RANKL gene expression in vitro but probably have no effect in vivo because they are maximally expressed early. Bone morphogenetic protein-2 acts to down-regulate RANKL expression in vitro and, in vivo, may promote alveolar bone growth in the basal region of the tooth.

Influence of aging on tooth eruption: experimental canine mandibular allograft

PURPOSE

Aging is clinically related to tooth eruption; however, there are no known studies that have elucidated the relationship. We examined whether tooth eruption would occur normally in a mature subject.

MATERIALS AND METHODS

Using vascularized composite tissue mandibular transplantation, we extracted portions of immature mandibles including the tooth germs from young beagle dogs and placed them into unrelated immature and mature beagle dogs. We then examined eruption of the lower first molar in the grafted mandibular bone and compared the results clinically, radiographically, and histologically.

RESULTS

Normal tooth eruption was observed in the transplanted mandibles in the young dogs. In the mature dogs, eruption from the gingiva was delayed, whereas that from alveolar bone occurred normally in the transplanted mandibles. Further, the whole crown was covered with a cap of gingival tissue in the mature dogs, although this cap was not gingival overgrowth.

CONCLUSIONS

Tooth eruption is influenced by some unknown factors related to aging. Apparently, apoptosis did not occur in the connective tissues between the reduced enamel epithelia and oral epithelia that overlay the teeth in the mature subjects.

Exposure to oral uranyl nitrate delays tooth eruption and development

The risk of oral exposure to uranium potentially involves the population at large. Tooth eruption and development are ongoing processes that begin during fetal development and continue until the age of 18 y. Since one of the mechanisms involved in tooth eruption is bone formation and it is well documented that uranium inhibits bone formation, the aim of the present work was to study the effect of oral administration of uranyl nitrate (UN) on tooth eruption and development. Wistar rats aged 1 and 7 d were orally administered a single dose of 90 mg kg(-1) body weight of uranyl nitrate. Two age matched groups received an equal volume of saline and served as controls. The animals were killed at 7 and 14 d of age, respectively. Mandibles were resected and processed to obtain bucco-lingual sections oriented at the level of the mesial root of the first mandibular molar, and histomorphometric studies were performed. Results showed that an acute high dose of uranyl nitrate delays both tooth eruption and development, probably due to its effect on target cells.

Cellular, molecular, and genetic determinants of tooth eruption

Tooth eruption is a complex and tightly regulated process that involves cells of the tooth organ and the surrounding alveolus. Mononuclear cells (osteoclast precursors) must be recruited into the dental follicle prior to the onset of eruption. These cells, in turn, fuse to form osteoclasts that resorb alveolar bone, forming an eruption pathway for the tooth to exit its bony crypt. Some of the molecules possibly involved in the signaling cascades of eruption have been proposed in studies from null mice, osteopetrotic rodents, injections of putative eruption molecules, and cultured dental follicle cells. In particular, recruitment of the mononuclear cells to the follicle may require colony-stimulating factor-one (CSF-1) and/or monocyte chemotactic protein-1 (MCP-1). Osteoclastogenesis is needed for the bone resorption and may involve inhibition of osteoprotegerin transcription and synthesis in the follicle, as well as enhancement of receptor activator of NF kappa B ligand (RANKL), in the adjacent alveolar bone and/or in the follicle. Paracrine signaling by parathyroid-hormone-related protein and interleukin -1 alpha, produced in the stellate reticulum adjacent to the follicle, may also play a role in regulating eruption. Osteoblasts might also influence the process of eruption, the most important physiologic role likely being at the eruptive site, in the formation of osteoclasts through signaling via the RANKL/OPG pathway. Evidence thus far supports a role for an osteoblast-specific transcription factor, Cbfa1 (Runx2), in molecular events that regulate tooth eruption. Cbfa1 is also expressed at high levels by the dental follicle cells. This review concludes with a discussion of the several human conditions that result in a failure of or delay in tooth eruption.

Enhancement of gene expression in rat dental follicle cells by parathyroid hormone-related protein

Recent studies indicate that parathyroid hormone-related protein (PTHrP) is required for tooth eruption in mice. Localized in the stellate reticulum, PTHrP might exert a paracrine effect on cells of the adjacent dental follicle to initiate eruption. The presence of a follicle is needed for eruption and, at the cellular level, there is an influx of mononuclear cells in the follicle early postnatally in the first mandibular molar of the rat. In turn, these mononuclear cells fuse to form osteoclasts, which erode the alveolar bone to form an eruption pathway. At the molecular level, the dental follicle cells of the rat molar maximally express the genes for monocyte chemotactic protein-1 (MCP-1) and colony-stimulating factor-1 (CSF-1) at day 3 postnatally. Because day 3 also is the time of maximal influx of the mononuclear cells into the follicle, MCP-1 and CSF-1 could be involved in the recruitment/maturation of these cells. To determine if PTHrP can modulate gene expression in the dental follicle, cultured follicle cells were immunostained to show the receptor for PTHrP. The gene expression of this receptor was enhanced by incubating the cells with interleukin-1alpha (IL-1alpha). Next, the ability of PTHrP itself to enhance gene expression of either MCP-1 or CSF-1 in the dental follicle cells was determined by incubating the cells with PTHrP in either a time- or concentration-course manner (1-15 h or 1-100 ng/ml). By reverse transcription-polymerase chain reaction, it was demonstrated that PTHrP enhanced MCP-1 expression in a concentration-dependent fashion, with 50 ng PTHrP/ml inducing maximal expression of either MCP-1 or CSF-1. In the time-dependent studies, PTHrP caused maximal expression within 30 min for either MCP-1 or CSF-1. Immunoblotting revealed that PTHrP also enhanced secretion of MCP-1 by the follicle cells. Thus, one of the actions of PTHrP in tooth eruption may be that it enhances MCP-1 and CSF-1 gene expression and secretion in the dental follicle. Moreover, IL-1alpha may accentuate its action by enhancing the expression for the PTHrP receptor in the follicle cells.

Implications for tooth eruption of the effect of interleukin-1alpha on nuclear factor-kappaB gene expression in the rat dental follicle

Tooth eruption is a localized event and a cascade of molecular signals generated in the dental follicle and stellate reticulum appears to initiate its onset. Consequently, mononuclear cells are recruited into the follicle and, in turn, fuse to become osteoclasts needed to resorb the alveolar bone to form an eruption pathway. One of the transcription factors involved in the sequence of molecular signalling may be nuclear factor (NF)kappaB. This study shows that NFkappaB is expressed and synthesized by cultured dental follicle cells. Moreover, its transcription, activation and translocation were enhanced by interleukin (IL)-1alpha, a potential eruption molecule. The enhancement of transcription of the NFkappaB gene by IL-1alpha was blocked by a tyrosine-specific kinase inhibitor, suggesting that the enhancement may require the phosphorylation of the NFkappaB complex. In vivo, NFkappaB is maximally expressed in the dental follicle of the rat first mandibular molar at day 3 postnatally, the age at which there is a peak influx of mononuclear cells into the follicle. Thus, a transcription factor apparently required for eruption (NFkappaB) is present in the tissue required for eruption, the dental follicle, and its gene expression is maximal at a critical time in eruption.

The immunohistochemical localization of the interferon-gamma and granulocyte colony-stimulating factor receptors during early amelogenesis in rat molars

Previous studies, in which the known janus kinase and signal transducer and activator of transcription (STAT) isoforms were immunohistochemically mapped in developing rat molars, implicated a sizeable list of cytokine superfamily receptor (CSR)/signal-transduction pathway (STP) linkages in the cells of the enamel organ involved in the events leading directly to early amelogenesis. Various combinations of upregulated janus kinases and STATs are known to be linked to single or small groups of CSRs. On the basis of the previous observations it was hypothesized that the interferon-gamma receptor (IFNgamma r) and the granulocyte colony-stimulating factor receptor (G-CSF receptor) would be localized in specific sites in the cells of the enamel organ during early amelogenesis. To verify this, whole-head, freeze-dried sections were here obtained at the level of the mandibular first and second molar from newborn and 5-day-old rats. These sections were not demineralized or fixed, reducing the possibility of false-negative results. Antibodies to the IFNgamma r and the G-CSF receptor were localized using a modification of the avidin-biotin complex method. In the newborn rats, IFNgamma r was localized in the preameloblasts in the cervical loop, the proximal and distal ends of presecretory ameloblasts, the outer enamel epithelium, the dental lamina, and in bone. In 5-day-old rats, it was confined to the proximal ends of the presecretory and secretory ameloblasts. The G-CSF receptor was observed in the molars of newborn rats in the preameloblasts, the proximal and distal ends of the presecretory ameloblasts, outer enamel epithelium, and in bone. In 5-day-old rats, G-CSF receptor was localized in the preameloblasts, the proximal ends of presecretory and secretory ameloblasts, the stellate reticulum, the outer enamel epithelium, and in bone. These findings indicate that the IFNgamma r and the G-CSF receptor, and their downstream STP linkages, are upregulated in the cells of the enamel organ and may be involved in the events leading directly to early enamel formation.

Confocal laser scanning microscopic study [corrected] of tartrate-resistant acid phosphatase-positive cells in the dental follicle during early morphogenesis of mouse embryonic molar teeth

Tartrate-resistant acid phosphatase (TRAPase)-positive cells were examined during the early morphogenesis of mouse mandibular first molar teeth, using a simultaneous azo dye-coupling technique and confocal laser scanning microscopy (CLSM). CLSM of paraffin-embedded sections revealed that cells exhibiting TRAPase fluorescence appeared along the marginal region of the condensed dental mesenchyme, not yet the dental follicle, at embryonic day 12 (E12). The follicle was recognized histologically as a population of fibroblastic cells in tooth organs at E14, and TRAPase-positive cells were localized among the follicular cells. Light-microscopic observations of microsliced thick sections showed the overall morphology of the TRAPase-positive cells. A few positive cells of E13 tooth organs were oval, and the intense reaction products of TRAPase revealed complex processes on positive cells in E14 tooth organs. Three-dimensional fluorescent images of TRAPase-positive cells using microsliced sections and CLSM showed their unique morphology of long processes with small spine-like projections at E14. Thus, TRAPase-positive cells appeared in the region of the prospective follicle at the bud stage (E12 and 13) before the formation of the follicle proper. In addition, the formation of the follicle and the appearance of TRAPase-positive cells with unique morphology were correlated in their developmental stage (E14). The findings suggest that the TRAPase-positive cells may be involved in the formation of the dental follicle in early tooth morphogenesis.

In vivo effect of interleukin-1 alpha on colony-stimulating factor-1 gene expression in the dental follicle of the rat molar

Interleukin-1 alpha (IL-1 alpha) acts in vitro to enhance the gene expression of colony-stimulating factor-1 (CSF-1) of dental follicle cells. Because the dental follicle is required for tooth eruption and because CSF-1 appears to be a key molecule in initiating eruption, it was the aim of this study to determine if IL-1 alpha could enhance the expression of the CSF-1 gene in the dental follicle in vivo. To determine this, rats were injected with IL-1 alpha at different ages postnatally and the total RNA was isolated from the dental follicles of the first mandibular molars. Reverse transcription-polymerase chain reaction showed that IL-1 alpha enhanced the expression of CSF-1 in the follicle. Thus, IL-1 alpha may play a part in the cascade of molecular signals that initiate eruption by its effect upon the CSF-1 gene.