Response of immortalized murine cementoblasts/periodontal ligament cells to parathyroid hormone and parathyroid hormone-related protein in vitro

Mutations in RABL3 alter KRAS prenylation and are associated with hereditary pancreatic cancer

Pancreatic ductal adenocarcinoma is an aggressive cancer with limited treatment options¹. Approximately 10% of cases exhibit familial predisposition, but causative genes are not known in most families². We perform whole-genome sequence analysis in a family with multiple cases of pancreatic ductal adenocarcinoma and identify a germline truncating mutation in the member of the RAS oncogene family-like 3 (RABL3) gene. Heterozygous rabl3 mutant zebrafish show increased susceptibility to cancer formation. Transcriptomic and mass spectrometry approaches implicate RABL3 in RAS pathway regulation and identify an interaction with RAP1GDS1 (SmgGDS), a chaperone regulating prenylation of RAS GTPases³. Indeed, the truncated mutant RABL3 protein accelerates KRAS prenylation and requires RAS proteins to promote cell proliferation. Finally, evidence in patient cohorts with developmental disorders implicates germline RABL3 mutations in RASopathy syndromes. Our studies identify RABL3 mutations as a target for genetic testing in cancer families and uncover a mechanism for dysregulated RAS activity in development and cancer.

Intermittent parathyroid hormone (PTH) promotes cementogenesis and alleviates the catabolic effects of mechanical strain in cementoblasts

Background

External root resorption, commonly starting from cementum, is a severe side effect of orthodontic treatment. In this pathological process and repairing course followed, cementoblasts play a significant role. Previous studies implicated that parathyroid hormone (PTH) could act on committed osteoblast precursors to promote differentiation, and inhibit apoptosis. But little was known about the role of PTH in cementoblasts. The purpose of this study was to investigate the effects of intermittent PTH on cementoblasts and its influence after mechanical strain treatment.

Results

Higher levels of cementogenesis- and differentiation-related biomarkers (bone sialoprotein (BSP), osteocalcin (OCN), Collagen type I (COL1) and Osterix (Osx)) were shown in 1–3 cycles of intermittent PTH treated groups than the control group. Additionally, intermittent PTH increased alkaline phosphatase (ALP) activity and mineralized nodules formation, as measured by ALP staining, quantitative ALP assay, Alizarin red S staining and quantitative calcium assay. The morphology of OCCM-30 cells changed after mechanical strain exertion. Expression of BSP, ALP, OCN, osteopontin (OPN) and Osx was restrained after 18 h mechanical strain. Furthermore, intermittent PTH significantly increased the expression of cementogenesis- and differentiation-related biomarkers in mechanical strain treated OCCM-30 cells.

Conclusions

Taken together, these data suggested that intermittent PTH promoted cementum formation through activating cementogenesis- and differentiation-related biomarkers, and attenuated the catabolic effects of mechanical strain in immortalized cementoblasts OCCM-30.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0133-0) contains supplementary material, which is available to authorized users.

Comparing Viability of Periodontal Ligament Stem Cells Isolated From Erupted and Impacted Tooth Root

PURPOSE

The aim of the study was to compare the viability of periodontal ligament-derived stem/progenitor cells (PDLSCs) from 2 different sources.

MATERIALS AND METHODS

Periodontal ligament (PDL) tissue was obtained from 20 surgically extracted human third molars and 20 healthy premolars extracted for orthodontic reasons. Periodontal ligament-derived stem/progenitor cells were isolated from 2 different PDL tissue sources and characterized by colony forming unit assay, cell surface marker characterizations, and their osteogenic differentiation potential. To determine cell viability within 2 groups, the colorimetric 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) metabolic activity assay was used. Data were statistically analyzed using independent t-test by SPSS 16 software (SPSS Inc, Chicago, IL).

RESULTS

According to the MTT assay, the mean viability rate ± standard deviation of PDLSCs in the impacted third molar sample cells was 0.355 ± 0.411 and for erupted premolar sample cells was 0.331 ± 0.556. Based on One-Sample Kolmogorov-Smirnov test, P value for impacted and erupted teeth was 0.954 and 0.863, respectively. No statistical difference was seen between 2 groups. (P value > 0.05) CONCLUSIONS: Our results demonstrated that if surgical aseptic technique is a method employed to maintain asepsis, PDLSCs obtained from impacted and erupted tooth root would have the same viability rate.

Evolution of parathyroid hormone receptor family and their ligands in vertebrate

The presence of the parathyroid hormones in vertebrates, including PTH, PTH-related peptide (PTHrP), and tuberoinfundibular peptide of 39 residues (TIP39), has been proposed to be the result of two rounds of whole genome duplication in the beginning of vertebrate diversification. Bioinformatics analyses, in particular chromosomal synteny study and the characterization of the PTH ligands and their receptors from various vertebrate species, provide evidence that strongly supports this hypothesis. In this mini-review, we summarize recent advances in studies regarding the molecular evolution and physiology of the PTH ligands and their receptors, with particular focus on non-mammalian vertebrates. In summary, the PTH family of peptides probably predates early vertebrate evolution, indicating a more ancient existence as well as a function of these peptides in invertebrates.

IL-17 regulates the expressions of RANKL and OPG in human periodontal ligament cells via TRAF6/TBK1-JNK/NF-κB pathways

Interleukin-17 (IL-17 or IL-17A), a pleiotropic cytokine produced by T helper (Th) 17 cells, is involved in the pathogenesis of various autoimmune and inflammatory disorders, including periodontitis. Although the ability of pro-inflammation in periodontitis have been widely investigated, the other biological functions of IL-17, including its role in bone remodeling and the underlying molecular mechanism, have not been well clarified. In the present study, IL-17 could significantly enhance the expression of receptor activator for nuclear factor-κB ligand (RANKL) and inhibit the expression of osteoprotegerin (OPG) in human periodontal ligament cells (hPDLCs), the two critical indicators for osteoclastogenesis, suggesting IL-17 may play a destructive role in the pathogenesis of periodontal bone remodeling. Pharmaceutical signal inhibitors targeted at MAPKs, Akt or NF-κB signals, inhibited IL-17-induced RANKL and OPG regulation. Notably, the enhancement of RANKL was significantly blocked by the inhibitors of JNK and NF-κB signals. The upstream signals were further investigated with the small interfering RNA (siRNA). Both TRAF6 and TBK1 were found to be the critically signal molecules for IL-17-dependent RANKL regulation in hPDLCs. These findings may provide comprehensive understanding of the role of IL-17 in the pathogenesis of periodontitis and might also provide a reasonable way for periodontitis therapy. This article is protected by copyright. All rights reserved.

Parathyroid hormone (1-34) modulates odontoblast proliferation and apoptosis via PKA and PKC-dependent pathways

Parathyroid hormone (PTH) plays a key role in the development and homeostasis of mineralized tissues such as bone and dentine. We have reported that PTH (1-34) administration can increase dentine formation in mice and that this hormone modulates in vitro mineralization of odontoblast-like cells. The purpose of the present study was to investigate whether PTH (1-34) participates in the proliferative and apoptotic signaling of odontoblast-like cells (MDPC23). MDPC23 cells were exposed to 50 ng/ml hPTH (1-34) or vehicle for 1 (P1), 24 (P24), or 48 (P48) hours, and the cell proliferation, apoptosis, and cell number were evaluated. To examine whether changes in the proliferative and apoptotic signaling in response to PTH involve protein kinases A (PKA) and/or C (PKC), MDPC23 cells were exposed to PTH with or without PKC or PKA signaling pathway inhibitors. Overall, the results showed that the PKA pathway acts in response to PTH exposure maintaining levels of cell proliferation, while the PKC pathway is mainly involved for longer exposure to PTH (24 or 48 h), leading to the reduction of cell proliferation and increase of apoptosis. The exposure to PTH reduced the cell number in relation to the control group in a time-dependent manner. In conclusion, PTH modulates odontoblast-like cell proliferative and apoptotic response in a time-dependent manner. Both PKC and PKA pathways participate in PTH-induced modulation in an antagonist mode.

HMGB1 localization during experimental periodontitis

AIM

This study sought to investigate the in vitro expression profile of high mobility group box 1 (HMGB1) in murine periodontal ligament fibroblasts (mPDL) stimulated with LPS or IL-1β and in vivo during ligature- or LPS-induced periodontitis in rats.

MATERIAL AND METHODS

For the in vivo study, 36 rats were divided into experimental and control groups, and biopsies were harvested at 7-30 d following disease induction. Bone loss and inflammation were evaluated. HMGB1 expression was assessed by immunohistochemistry, qPCR, and Western blot.

RESULTS

Significant increases in mPDL HMGB1 mRNA occurred at 4, 8, and 12 h with protein expression elevated by 24 h. HMGB1 mRNA expression in gingival tissues was significantly increased at 15 d in the LPS-PD model and at 7 and 15 d in the ligature model. Immunohistochemical staining revealed a significant increase in the number of HMGB1-positive cells during the experimental periods.

CONCLUSION

The results show that PDL cells produce HMGB1, which is increased and secreted extracellularly after inflammatory stimuli. In conclusion, this study demonstrates that HMGB1 may be associated with the onset and progression of periodontitis, suggesting that further studies should investigate the potential role of HMGB1 on periodontal tissue destruction.

Functional characterization of the parathyroid hormone 1 receptor in human periodontal ligament cells

OBJECTIVES

Intermittent parathyroid hormone (PTH) exerts anabolic effects on bone and has been approved for osteoporosis therapy. The dual actions of PTH are mediated primarily through the parathyroid hormone 1 receptor (PTH1R). Upon ligand binding, PTH1R activates diverse signaling pathways, including cAMP/protein kinase A (PKA)- and phospholipase C/protein kinase C (PLC/PKC)-dependent pathways. PTH1R has been abundantly studied in bone cells. Knowledge on PTH1R characteristics and physiology in periodontal ligament (PDL) cells is still in its infancy.

MATERIALS AND METHODS

We characterized PTH1R in PDL cells in terms of its cellular localization, binding affinity, and signal transduction and compared these characteristics to those of MG63 osteoblast-like cells.

RESULTS

PTH1R mRNA/protein was identified in PDL and MG63 cells. PTH1R was mainly localized on the plasma membrane, in vesicular structures inside the cell, and, to some extent, in the nucleus of both cell types. Binding characteristics of PTH1R were cell type specific, with PDL cells demonstrating a lower binding affinity. The response of cAMP and active PKC production in MG63 cells was dose dependent with increasing PTH(1-34) concentration, whereas in PDL cells, it was regulated biphasically. However, we observed a cross talk between the cAMP/PKA and PLC/PKC signaling pathways, which were regulated diametrically opposed at a given concentration of PTH(1-34).

CONCLUSION

These data indicate that, albeit the similarity in its subcellular distribution, PTH1R in PDL cells exhibits characteristics different from those in MG63 cells, pointing to the cell type specificity of this receptor.

CLINICAL RELEVANCE

The findings further elucidate the characteristics of PTH action in dental tissues and widen the theoretical basis for the development of anabolic treatment strategies.

Combining human periodontal ligament cell membrane chromatography with online HPLC/MS for screening osteoplastic active compounds from Coptidis Rhizoma

We have developed an online analytical method that combines human periodontal ligament cell membrane chromatography (hPDLC/CMC) with high-performance liquid chromatography and mass spectrometry (LC/MS) for recognizing and identifying osteoplastic active components from Coptidis Rhizoma. Retention fractions on hPDLC/CMC were enriched onto an enrichment column and the components were directly analyzed by combining a 10-port column switcher with an LC/MS system for separation and preliminary identification. Using simvastatin (SIM) as a positive control, berberine from Coptidis Rhizoma was identified as the active component which could act on the hPDLC. The MTT colorimetric assay, alkaline phosphatase (ALP) activity, and staining tests revealed that berberine could promote hPDLC growth, increase the secretion of ALP in the culture medium, and enhance the formation of mineralized nodule, thus it is a potential osteoplastic ingredient. This hPDLC/CMC-online-LC/MS method can be applied for screening active components acting on hPDLC from traditional Chinese medicines exemplified by Coptidis Rhizoma and will be of great utility in drug discovery using natural medicinal herbs as a source of leading compounds.

Potential role of high mobility group box protein 1 and intermittent PTH (1-34) in periodontal tissue repair following orthodontic tooth movement in rats

OBJECTIVES

Recent studies indicate that high mobility group box protein 1 (HMGB1) can be released by necrotic and damaged cells and functions as an alarmin that is recognized by the innate immune system. Little is known about the role of HMGB1 within the periodontal ligament (PDL). Therefore, we examined HMGB1 expression by PDL cells in vitro and compared the findings to an in vivo model of orthodontically induced tooth root resorption. In addition, we addressed the question of whether a potentially anabolic intermittent administration of parathyroid hormone (iPTH) would modulate the expression of HMGB1.

MATERIALS AND METHODS

In confluent PDL cell cultures, HMGB1 messenger RNA (mRNA) expression was quantified by real-time polymerase chain reaction. In a rat model comprising 25 animals, mechanical loading for 5 days was followed by administration of either iPTH (1-34) systemically or sham injections for up to 56 days. HMGB1 expression was determined by means of immunohistochemistry and histomorphometry.

RESULTS

The in vitro experiments revealed an inhibitory effect of iPTH on basal HMGB1 mRNA expression in confluent PDL cells. In vivo, the mechanical force-induced enhanced HMGB1 protein expression declined time dependently. Intermittent PTH further inhibited HMGB1 expression. The significantly higher basal HMGB1 protein expression in the former compression side was followed by a more pronounced time- and iPTH-dependent decline in the same area.

CONCLUSIONS

These data indicate a major role for HMGB1 in the regulation of PDL wound healing following mechanical load-induced tissue injury.

CLINICAL RELEVANCE

The findings point to the potential benefit of iPTH in the attempt to support these immune-associated reparative processes.

Twenty-five years of PTHrP progress: from cancer hormone to multifunctional cytokine

Twenty-five years ago a "new" protein was identified from cancers that caused hypercalcemia. It was credited for its ability to mimic parathyroid hormone (PTH), and hence was termed parathyroid hormone-related protein (PTHrP). Today it is recognized for its widespread distribution, its endocrine, paracrine, and intracrine modes of action driving numerous physiologic and pathologic conditions, and its central role in organogenesis. The multiple biological activities within a complex molecule with paracrine modulation of adjacent target cells present boundless possibilities. The protein structure of PTHrP has been traced, dissected, and deleted comprehensively and conditionally, yet numerous questions lurk in its past that will carry into the future. Issues of the variable segments of the protein, including the enigmatic nuclear localization sequence, are only recently being clarified. Aspects of PTHrP production and action in the menacing condition of cancer are emerging as dichotomies that may represent intended temporal actions of PTHrP. Relative to PTH, the hormone regulating calcium homeostasis, PTHrP "controls the show" locally at the PTH/PTHrP receptor throughout the body. Great strides have been made in our understanding of PTHrP actions, yet years of exciting investigation and discovery are imminent. © 2012 American Society for Bone and Mineral Research.

Effect of platelet-rich plasma on dental stem cells derived from human impacted third molars

AIM

Platelet-rich plasma (PRP) is fabricated from autologous blood and extensively used to promote soft and hard tissue healing. In the dental field, autologous PRP is widely used combined with dental implant installation and bone graft. This study will evaluate the biologic effect of PRP on the proliferation and the differentiation of human dental stem cells, and find the key cytokines inducing these effects to estimate the clinical feasibility of PRP for dental tissue engineering.

MATERIALS & METHODS

Venous blood was obtained from four individuals and each PRP was fabricated. The human dental stem cells were obtained from the periodontal ligament (PDL) and dental pulp of the surgically extracted human third molars and expanded in vitro. Immunocytochemical staining and flow cytometry with STRO-1 and CD146 confirmed existence of mesenchymal stem cells in the PDL and dental pulp. The effect of PRP on the proliferation of PDL stem cells (PDLSCs) and dental pulp stem cells (DPSCs) was assessed by colony-forming ability measurement, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and bromodeoxyuridine incorporation assay. Alkaline phosphatase activity and calcium deposit were measured to evaluate the mineralization effect of PRP PDLSCs and DPSCs. Alizarin red S staining was used to detect mineral nodules. Odontogenic and osteogenic gene expressions were evaluated in the PRP-treated PDLSCs and DPSCs by real-time quantitative PCR. A protein array was performed to detect the key cytokines that have an important role in the tissue regenerative effect of PRP.

RESULTS

Flow cytometry cell sorting showed that the cells from human PDL and dental pulp contained mesenchymal stem cell populations. Colony-forming ability and cellular proliferation of the dental stem cells were increased at 0.5 and 1% PRP concentration but decreased at 5% concentration. Long-term treatment with 1% PRP enhanced proliferation of the human dental stem cells PDLSCs and DPSCs by 120 h and showed the most significant enhancement at 96 h. PRP also promoted mineralization differentiation of the two kinds of dental stem cells as shown by measurement of alkaline phosphatase activity and calcium deposit under mineralization conditioned media. Increased formation of mineral nodules stained with alizarin red was observed in both PDLSCs and DPSCs after treatment with 1% PRP. Real-time quantitative PCR showed higher odontogenic and osteogenic gene expressions in PRP-treated PDLSCs and DPSCs. RANTES/CCL5 and ICAM-1 were the two key cytokines that were detected in human cytokine array with PRP.

CONCLUSION

The appropriate concentration of the PRP treatment enhanced proliferation and mineralization differentiation of human dental stem cells. RANTES/CCL5 and ICAM-1 might play an important role in PRP-induced tissue regeneration but further study is needed to investigate the whole mechanism.

Implications of cultured periodontal ligament cells for the clinical and experimental setting: a review

The periodontal ligament (PDL) is a key contributor to the process of regeneration of the periodontium. The heterogeneous nature of the PDL tissue, its development during early adulthood, and the different conditions to which the PDL tissue is exposed to in vivo impart on the PDL unique characteristics that may be of consequence during its cultivation in vitro. Several factors affecting the in vivo setting influence the behaviour of PDL fibroblasts in culture. The purpose of this review is to address distinct factors that influence the behaviour of PDL fibroblasts in culture -in vivo-in vitro transitions, cell identification/isolation markers, primary PDL cultures and cell lines, tooth-specific factors, and donor-specific factors. Based on the reviewed studies, the authors recommendations include the use of several identification markers to confirm cell identity, use of primary cultures at early passage to maintain unique PDL heterogeneic characteristics, and noting donor conditions such as age, systemic health status, and tooth health status. Continued efforts will expand our understanding of the in vitro and in vivo behaviour of cells, with the goal of orchestrating optimal periodontal regeneration. This understanding will lead to improved evidence-based rationales for more individualized and predictable periodontal regenerative therapies.

Platelet-rich fibrin is a Bioscaffold and reservoir of growth factors for tissue regeneration

The platelet-rich fibrin (PRF) is known as a rich source of autologous cytokines and growth factors and universally used for tissue regeneration in current clinical medicine. However, the microstructure of PRF has not been fully investigated nor have been studied the key molecules that differ PRF from platelet-rich plasma. We fabricated PRF under Choukroun's protocol and produced its extract (PRFe) by freezing at -80°C. The conventional histological, immunohistological staining, and scanning electron microscopy images showed the microstructure of PRF, appearing as two zones, the zone of platelets and the zone of fibrin, which resembled a mesh containing blood cells. The PRFe increased proliferation, migration, and promoted differentiation of the human alveolar bone marrow stem cells (hABMSCs) at 0.5% concentration in vitro. From the results of proteome array, matrix metalloproteinase 9 (MMP9) and Serpin E1 were detected especially in PRFe but not in concentrated platelet-rich plasma. Simultaneous elevation of MMP9, CD44, and transforming growth factor β-1 receptor was shown at 0.5% PRFe treatment to the hABMSC in immunoblot. Mineralization assay showed that MMP9 directly regulated mineralization differentiation of hABMSC. Transplantation of the fresh PRF into the mouse calvarias enhanced regeneration of the critical-sized defect. Our results strongly support the new characteristics of PRF as a bioscaffold and reservoir of growth factors for tissue regeneration.

Mesenchymal stem cell properties of periodontal ligament cells from deciduous and permanent teeth

BACKGROUND

Human postnatal stem cells have been identified in periodontal ligaments (PDLs). In this study, the in vitro biologic properties of CD105(+) enriched cell subsets from PDLs harvested from deciduous (DePDL) and permanent (PePDL) teeth are comparatively assessed.

METHODS

PDL tissue was obtained from 12 teeth (six primary and six permanent) from which CD105(+) CD34(-) CD45(-) cells were isolated by magnetic cell sorting. To identify and quantitatively compare the stem cell markers, DePDL and PePDL cells were assessed for CD166 surface antigen expression by flow cytometry, real-time polymerase chain reaction, and immunostaining for Stro-1 and Oct-4, osteogenic and adipogenic differentiation, and proliferation rate by trypan blue method.

RESULTS

Magnetic cell sorting isolated cell populations containing 23.87% (+/- 11.98%) and 11.68% (+/- 6.27%) of CD105(+) expressing cells from PePDL and DePDL, respectively. Flow cytometric analysis demonstrated a higher proportion of CD105(+) cells coexpressing CD166 surface antigen in PePDL, whereas immunostaining and real-time polymerase chain reaction analysis demonstrated that both cell subsets expressed Stro-1 and Oct-4. DePDL-CD105(+) subsets were more proliferative compared to PePDL subsets, and both cell populations showed multipotential capabilities to differentiate in vitro to osteoblast/cementoblast- and adipocyte-like cells. However, a higher expression of adipogenic-related genes was observed in DePDL cells, whereas PePDL-CD105(+) cell subset presented a more homogeneous osteoblast/cementoblast response.

CONCLUSION

These findings demonstrate that highly purified mesenchymal progenitor cell subsets can be obtained from the PDLs of both deciduous and permanent teeth, and further indicate phenotype dissimilarities that may have an impact on their clinical applications.

PTH increases jaw mineral density in a rabbit model of osteoporosis

Intermittent parathyroid hormone (PTH) administration has been shown to be a promising therapy for systemic bone loss. Accordingly, we hypothesized that PTH could have positive results in treating oral complications of osteoporosis. Hence, we evaluated both mandibular bone loss and its response to PTH in a rabbit model of osteoporosis induced by ovariectomy and glucocorticoid administration. There was a significant and marked decrease in bone mineral density (BMD), bone mineral content (BMC), and calcium content in ash from the osteoporotic peri-alveolar region, which influenced global jaw loss. Remarkably, PTH (1-34) administration to osteoporotic rabbits almost completely reversed BMD, BMC, and calcium content fall in the peri-alveolar region, subsequently reducing global mandibular bone loss. Thus, although the peri-alveolar region is particularly susceptible to osteoporosis, it also responds well to intermittent PTH. Therefore, these results suggest that PTH might represent a valid therapy for improving the osseointegration of dental implants in persons with osteoporosis.

Dental-derived Stem Cells and whole Tooth Regeneration: an Overview

The need for new dental tissue-replacement therapies is evident in recent reports which reveal startling statistics regarding the high incidence of tooth decay and tooth loss. Recent advances in the identification and characterization of dental stem cells, and in dental tissue-engineering strategies, suggest that bioengineering approaches may successfully be used to regenerate dental tissues and whole teeth. Interest in dental tissue-regeneration applications continues to increase as clinically relevant methods for the generation of bioengineered dental tissues, and whole teeth, continue to improve. This paper is concerned about dental-derived stem cells and their characterization. Additionally, since conventional dental treatments partially serve the purpose for replacing missing teeth and always include possible failure rates, the potential of dental-derived stem cells in promoting whole tooth regeneration is also discussed.

KEYWORDS

Dental stem cells; Tissue engineering; Tooth regeneration.

Anabolic effect of intermittent PTH(1-34) on the local microenvironment during the late phase of periodontal repair in a rat model of tooth root resorption

This study examined the histological changes and possible effects of intermittent parathyroid hormone (PTH) (1-34) treatment during the early and late phase of periodontal repair in a rat model of tooth root resorption. In a total of 70 animals, which either received intermittent PTH(1-34) systemically or sham injections for up to 70 days after discontinuation of an orthodontic force, histological characteristics were correlated to time-dependent distinct expression patterns of osteoprotegerin and receptor activator of nuclear factor kappaB ligand by PDL cells in the former compression and tension side of tooth movement by means of immunohistochemistry and histomorphometrical analysis. The balance of these key regulators of bone remodeling was demonstrated to be shifted in favor of hard tissue repair by intermittent PTH administration, which was demonstrated to exert anabolic effects in several cell culture and animal experiments as well as in humans, in the late phase of repair. These data indicate a role for PDL cells as potent regulators of periodontal repair by modifying the local microenvironment and point to the anabolic potential of an intermittent PTH administration to support these reparative processes.

Phosphate: known and potential roles during development and regeneration of teeth and supporting structures

Inorganic phosphate (P(i)) is abundant in cells and tissues as an important component of nucleic acids and phospholipids, a source of high-energy bonds in nucleoside triphosphates, a substrate for kinases and phosphatases, and a regulator of intracellular signaling. The majority of the body's P(i) exists in the mineralized matrix of bones and teeth. Systemic P(i) metabolism is regulated by a cast of hormones, phosphatonins, and other factors via the bone-kidney-intestine axis. Mineralization in bones and teeth is in turn affected by homeostasis of P(i) and inorganic pyrophosphate (PPi), with further regulation of the P(i)/PP(i) ratio by cellular enzymes and transporters. Much has been learned by analyzing the molecular basis for changes in mineralized tissue development in mutant and knock-out mice with altered P(i) metabolism. This review focuses on factors regulating systemic and local P(i) homeostasis and their known and putative effects on the hard tissues of the oral cavity. By understanding the role of P(i) metabolism in the development and maintenance of the oral mineralized tissues, it will be possible to develop improved regenerative approaches.

Parathyroid hormone modifies human periodontal ligament cell proliferation and survival in vitro

BACKGROUND AND OBJECTIVE

Periodontal ligament (PDL) cells show traits that are typical of osteoblasts, such as osteoblastic marker gene expression and the ability to respond to parathyroid hormone (PTH) stimulation in an osteoblast-like manner with respect to differentiation and local factor production. In the present study, we hypothesized that human PDL cells might respond to PTH stimulation with changes in proliferation and cell survival and thereby provide another mechanism by which PTH might affect the reparative potential of PDL cells. We speculated that the maturation state of the cells and the mode of PTH(1-34) administration would have an impact on the cellular response.

MATERIAL AND METHODS

PDL cells were challenged with PTH(1-34) intermittently or continuously at different maturation states. Cell number, 5-bromo-2-deoxyuridine (BrdU) incorporation, DNA fragmentation, nitric oxide production and the duration of the PTH(1-34) effect were determined.

RESULTS

Intermittent PTH(1-34) treatment of preconfluent cells caused a significant increase in proliferation and DNA fragmentation, whereas in more mature cells, proliferation was less enhanced while apoptosis was more pronounced than in immature cells. Continuous PTH(1-34) exposure did not alter proliferation in any maturation state but increased DNA fragmentation in preconfluent cells. PTH(1-34) prevented etoposide-induced apoptosis after 6 h but no longer after 24 h. Nitric oxide production was unaffected.

CONCLUSION

These results indicate that human PDL cells respond to PTH(1-34) with changes in proliferative and apoptotic signaling in a maturation-state-dependent manner. Besides changes in local factor production, these findings provide a further possible mechanism to support the idea that PDL cells possess the potential to be involved in the regulation of dental hard tissue repair.

Use of microarrays to find novel regulators of periodontal ligament fibroblast differentiation

Periodontal regeneration requires the coordinated movement and differentiation of several cell types in order to re-establish the cementum, periodontal ligament (PDL), and alveolar bone. Cells in culture are often used as model systems for mature tissues, although they may represent expanded progenitor cell populations. Comparison of transcript expression between fresh PDL tissue and PDL cell isolates by MicroArray analysis has revealed numerous molecular differences. Several transcripts (including alkaline phosphatase, bone sialoprotein, periostin, and fibromodulin) are expressed at higher levels in fresh PDL than in cultured PDL cells. In contrast, PDL cells in culture selectively express a variety of growth factors. Several of these growth factors alter PDL fibroblast behavior. Two members of the transforming growth factor beta family of growth factors, namely, bone morphogenic protein-7 (BMP7) and growth differentiation factor-5 (GDF5), reduce cell proliferation and Stro-1 expression (a bone marrow stromal stem cell marker), whereas only BMP7 induces alkaline phosphatase activity. In contrast, fibroblast growth factor-5 induces enhanced cell proliferation and Stro-1 expression, while repressing alkaline phosphatase activity. The stimulation of PDL cells to differentiate (either by BMP7 or GDF5) inhibits cell motility. Thus, PDL cells in culture are regulated by several factors that differentially stimulate a mineralized (cementoblast-like) fate, a non-mineralized fate (mature fibroblasts), or the propagation of a more naive phenotype (potential progenitors).

Parathyroid hormone induces mitogen-activated kinase phosphatase 1 in murine osteoblasts primarily through cAMP-protein kinase A signaling

BACKGROUND

Parathyroid hormone (PTH) regulates osteoblast function by binding to the PTH receptor 1 (PTHR1) to activate downstream signaling to induce expression of primary response genes (PRGs), which affect various aspects of the osteoblast phenotype. We previously identified PTH-induced PRGs in MC3T3-E1 cells, including mitogen-activated protein kinase (MAPK) phosphatase 1 (mkp1), which dephosphorylates members of the MAPK family. The aim of this study was to explore the molecular mechanisms of PTH's induction of mkp1 in primary mouse osteoblasts.

METHODS

Northern and Western analyses were used to determine mkp1 mRNA and protein expression. In vivo experiments were also performed to determine PTH's effect on mkp1 in mouse calvariae and long bones.

RESULTS

A total of 10 nM PTH and PTH-related protein (PTHrP) maximally induced mkp1 mRNA levels after 1 hour in osteoblasts. PTH also increased mkp1 protein expression, and induced mkp1 mRNA independent of new protein synthesis. PTHR1 triggers protein kinase A (PKA), PKC, and calcium pathways. Although PKA and PKC agonists induced mkp1 mRNA levels, only cyclic adenosine 3':5'-monophosphate (cAMP)-PKA inhibition blocked PTH-induced mkp1 mRNA levels. These data suggest that PTH-induced mkp1 mRNA levels are primarily mediated through the cAMP-PKA pathway. Further, prostaglandin E2 (PGE2), which activates cAMP-PKA and PKC, induced mkp1 mRNA to a greater extent than PGF2alpha and fluprostenol, which activate PKC signaling only. Finally, PTH maximally induced mkp1 mRNA levels in mouse calvariae and long bones in vivo at 0.5 hours.

CONCLUSIONS

mkp1's in vitro and in vivo induction in PTH-target tissues suggests its involvement in some of the effects of PTH on osteoblast function. mkp1 may be an important target gene in the anabolic effect of PTH on osteoblasts.

Parathyroid hormone(1-34) mediates proliferative and apoptotic signaling in human periodontal ligament cells in vitro via protein kinase C-dependent and protein kinase A-dependent pathways

Periodontal ligament (PDL) cells exhibit several osteoblastic traits and are parathyroid hormone (PTH)-responsive providing evidence for a role of these cells in dental hard-tissue repair. To examine the hypothesis that PDL cells respond to PTH stimulation with changes in proliferation and apoptotic signaling through independent but convergent signaling pathways, PDL cells were cultured from human bicuspids obtained from six patients. PDL cells at different states of maturation were challenged with PTH(1-34) intermittently for 0, 1, or 24 h/cycle or exposed continuously. Specific inhibitors to protein kinases A and C (PKA, PKC) and the mitogen-activated protein kinase cascade (MAPK) were employed. At harvest, the cell number, BrdU incorporation, and DNA fragmentation were determined by means of cell counting and immunoassays. Intermittent PTH(1-34) caused a significant increase in cell number in confluent cells as opposed to a reduction in pre-confluent cells. In confluent cells, the effect resulted from a significant increase in proliferation, whereas DNA fragmentation was reduced when PTH(1-34) was administered for 1 h/cycle but increased after PTH(1-34) for 24 h/cycle. Inhibition of PKC inhibited PTH(1-34)-induced proliferation but enhanced apoptosis. Inhibition of PKA enhanced proliferation and DNA fragmentation. Similar results were obtained in less mature cells, although, in the presence of the PKA inhibitor, the PTH(1-34)-induced changes were more pronounced than in confluent cells. In the presence of the MAPK inhibitor, all of the parameters examined were reduced significantly in both maturation states. Thus, PTH(1-34) mediates proliferative and apoptotic signaling in human PDL cells in a maturation-state-dependent manner via PKC-dependent and PKA-dependent pathways.

Maturation-state dependent response of human periodontal ligament cells to an intermittent parathyroid hormone exposure in vitro

BACKGROUND AND OBJECTIVES

Parathyroid hormone (parathyroid hormone) has been shown to be capable of exerting anabolic effects on bone when administered intermittently. We hypothesized that parathyroid hormone will modulate the response of periodontal ligament cells in terms of anabolic effects with respect to proliferation, differentiation and the production of key regulatory factors of bone remodeling such as osteoprotegerin and receptor activator of nuclear factor kappaB ligand (RANKL) in a maturation-state dependent manner.

METHODS

Periodontal ligament cells were cultured from human bicuspids obtained from six patients. Following characterization, confluent and preconfluent periodontal ligament cells were challenged with parathyroid hormone (1-34) for 0, 1, 3, 6 or 24 h within three incubation cycles of 48 h each. At harvest, the cell number, alkaline phosphatase specific activity and osteocalcin, osteoprotegerin and RANKL production were determined by means of semiquantitative polymerase chain reaction (PCR) and immunoassays. Dermal fibroblasts and MG63 osteoblast-like cells served as a reference.

RESULTS

Intermittent parathyroid hormone treatment of confluent periodontal ligament cells caused a significant increase in proliferation (+32% maximum) whereas alkaline phosphatase activity, osteocalcin and osteoprotegerin decreased at the transcriptional and translational level (-59.7% maximum). In preconfluent periodontal ligament cells, parathyroid hormone induced a decrease in proliferation (-66.3% maximum) but an increase in differentiation and osteoprotegerin production (+49.2% maximum). RANKL was hardly detectable and unaffected by parathyroid hormone treatment. Similar results were obtained in MG63 cells, whereas parathyroid hormone stimulation did not alter any of the parameters examined in dermal fibroblasts.

CONCLUSION

These results indicate that human periodontal ligament cells respond to an intermittent parathyroid hormone exposure with changes in proliferation, differentiation and osteoprotegerin production in a maturation-state dependent manner and therefore might be regulatorily involved in periodontal regeneration.

Establishment of cementoblast cell lines from rat cementum lining cells by transfection with temperature-sensitive simian virus-40 T-antigen gene

Defining the regulatory mechanisms promoting differentiation and proliferation of cementoblasts has not been well understood, because of the lack of cell models in vitro. To establish an in vitro cell model for the cementoblasts, extracted rat molars obtained from 8-week-old rats were used. Cells lining the root surface (cemetoblasts) were obtained by an enzymatic digestion method, and immediately immortalized by transfection of thermolabile SV40 T-antigen gene. The transfected cementum lining cell clones, RCM-C3 and -C4, were maintained for more than 200 population doublings (PD), while the original cells stopped their growth at 60 PD. Thus, immortalized cell lines decreased expression of SV40 T-antigen and subsequently cell proliferation at non-permissive temperature (39 degrees C). Reverse-transcribed-polymerase chain reaction indicated expression of gene for type I collagen, alkaline phosphatase (ALP), osteopontin, and osteocalcin mRNA at both permissive (33 degrees C) and non-permissive (39 degrees C) temperatures. RCM-C4 expressed higher bone siaploprotein (BSP) mRNA than RCM-C3, and further RCM-C4 showed higher BSP mRNA at 39 degrees C than 33 degrees C. High ALP activity and mineralized nodule formation were observed at 39 degrees C in both cell lines. These findings suggested that the cell lines, RCM-C3 and -C4, are useful model for studying the regulatory mechanisms of differentiation and proliferation of cementoblasts.

Prostaglandins E(2) and F(2alpha) enhance differentiation of cementoblastic cells

BACKGROUND

The prostaglandins (PG) E(2) and PGF(2alpha) are important cytokines in periodontal physiology and pathology. PGE(2) and PGF(2alpha) alter cell function by binding and activating the plasmamembrane G-protein-coupled PG receptors. In this study, we examined the PGE(2) and PGF(2alpha) effects on the immortalized cementoblastic OCCM cells.

METHODS

Confluent OCCM cells were treated with PGE(2), PGF(2alpha), specific activators/inhibitors of the EP prostanoid receptors, a specific activator of the FP prostanoid receptor, and direct activators/inhibitors of the protein kinase C (PKC) signaling pathway. Mineral nodule formation was assessed by the von Kossa stain.

RESULTS

PGE(2) and PGF(2alpha) significantly increased mineralization of OCCM cells. The EP1 and EP3 PG receptor activators 16,16-dimethyl-prostaglandin E(2) and sulprostone, also increased mineralization. In contrast, specific activators of the EP2 or the EP2/EP3/EP4 receptors did not have any effect. Fluprostenol, a specific activator of the FP receptor, significantly increased mineralization of OCCM cells. FP and EP (1 or 3) receptors signal through activation of the protein kinase C (PKC) pathway. Indeed, phorbol 12-myristate 13-acetate (PMA), a direct activator of the PKC pathway, significantly increase OCCM mineralization, while pre-treatment of OCCM cells with the PKC inhibitor GF109203x (bisindolylmaleimide) significantly decreased mineralization.

CONCLUSION

We conclude that PGE(2) and PGF(2alpha) exert an anabolic effect on OCCM mineralization through activation of PKC signaling.

The Role of Parathyroid Hormone-Related Protein in the Regulation of Osteoclastogenesis by Cementoblasts

BACKGROUND

Parathyroid hormone-related protein (PTHrP) promotes osteoclastogenesis by inhibiting expression of osteoprotegerin (OPG), a decoy receptor for the receptor activator of nuclear factor kappa B (RANK), and by enhancing production of RANK ligand (RANKL) by osteoblasts. However, little is known regarding the role of PTHrP in regulating cementoblast-mediated osteoclastogenesis.

METHODS

This study determined the impact of PTHrP on osteoclastogenesis using: 1) OCCM-30 (immortalized murine cementoblasts), 2) RAW 264.7 cells (murine myeloid cells), or 3) OCCM-30 plus RAW 264.7 cells. Cells were treated with PTHrP (1-34), RANKL, or PTHrP and RANKL combined. Enzyme-linked immunosorbent assays (ELISAs) for OPG and RANKL were performed on media and cell lysates, and tartrate-resistant acid phosphatase (TRAP) and mRNA detection for the osteoclast associated receptor (OSCAR) were performed.

RESULTS

The highest numbers of TRAP-positive cells and cells expressing OSCAR were found in the RAW cell group treated with either RANKL alone or RANKL and PTHrP. TRAP-positive cells were fewer when OCCM cells were co-cultured with RAW, but the greatest numbers were still with both PTHrP and RANKL. OPG levels were highest from OCCM cells and PTHrP decreased these levels. In contrast, RANKL levels were low in OCCM cell lysates and PTHrP increased RANKL. In vivo studies also revealed high osteoclastic activity surrounding developing teeth in mice administered PTH.

CONCLUSIONS

These results demonstrate that PTHrP influences the balance of OPG and RANKL production by cementoblasts, and further indicate that this effect, in the context of surrounding cells, might have a significant impact on osteoclastogenesis, root resorption, and tooth eruption.

Investigation of multipotent postnatal stem cells from human periodontal ligament

BACKGROUND

Periodontal diseases that lead to the destruction of periodontal tissues--including periodontal ligament (PDL), cementum, and bone--are a major cause of tooth loss in adults and are a substantial public-health burden worldwide. PDL is a specialised connective tissue that connects cementum and alveolar bone to maintain and support teeth in situ and preserve tissue homoeostasis. We investigated the notion that human PDL contains stem cells that could be used to regenerate periodontal tissue.

METHODS

PDL tissue was obtained from 25 surgically extracted human third molars and used to isolate PDL stem cells (PDLSCs) by single-colony selection and magnetic activated cell sorting. Immunohistochemical staining, RT-PCR, and northern and western blot analyses were used to identify putative stem-cell markers. Human PDLSCs were transplanted into immunocompromised mice (n=12) and rats (n=6) to assess capacity for tissue regeneration and periodontal repair. Findings PDLSCs expressed the mesenchymal stem-cell markers STRO-1 and CD146/MUC18. Under defined culture conditions, PDLSCs differentiated into cementoblast-like cells, adipocytes, and collagen-forming cells. When transplanted into immunocompromised rodents, PDLSCs showed the capacity to generate a cementum/PDL-like structure and contribute to periodontal tissue repair.

INTERPRETATION

Our findings suggest that PDL contains stem cells that have the potential to generate cementum/PDL-like tissue in vivo. Transplantation of these cells, which can be obtained from an easily accessible tissue resource and expanded ex vivo, might hold promise as a therapeutic approach for reconstruction of tissues destroyed by periodontal diseases.

Cementoblast delivery for periodontal tissue engineering

BACKGROUND

Predictable periodontal regeneration following periodontal disease is a major goal of therapy. The objective of this proof of concept investigation was to evaluate the ability of cementoblasts and dental follicle cells to promote periodontal regeneration in a rodent periodontal fenestration model.

METHODS

The buccal aspect of the distal root of the first mandibular molar was denuded of its periodontal ligament (PDL), cementum, and superficial dentin through a bony window created bilaterally in 12 athymic rats. Treated defects were divided into three groups: 1) carrier alone (PLGA polymer sponges), 2) carrier + follicle cells, and 3) carrier + cementoblasts. Cultured murine primary follicle cells and immortalized cementoblasts were delivered to the defects via biodegradable PLGA polymer sponges, and mandibulae were retrieved 3 weeks and 6 weeks post-surgery for histological evaluation. In situ hybridization, for gene expression of bone sialoprotein (BSP) and osteocalcin (OCN), and histomorphometric analysis were further done on 3-week specimens.

RESULTS

Three weeks after surgery, histology of defects treated with carrier alone indicated PLGA particles, fibrous tissue, and newly formed bone scattered within the defect area. Defects treated with carrier + follicle cells had a similar appearance, but with less formation of bone. In contrast, in defects treated with carrier + cementoblasts, mineralized tissues were noted at the healing site with extension toward the root surface, PDL region, and laterally beyond the buccal plate envelope of bone. No PDL-bone fibrous attachment was observed in any of the groups at this point. In situ hybridization showed that the mineralized tissue formed by cementoblasts gave strong signals for both BSP and OCN genes, confirming its nature as cementum or bone. The changes noted at 3 weeks were also observed at 6 weeks. Cementoblast-treated and carrier alone-treated defects exhibited complete bone bridging and PDL formation, whereas follicle cell-treated defects showed minimal evidence of osteogenesis. No new cementum was formed along the root surface in the above two groups. Cementoblast-treated defects were filled with trabeculated mineralized tissue similar to, but more mature, than that seen at 3 weeks. Furthermore, the PDL region was maintained with well-organized collagen fibers connecting the adjacent bone to a thin layer of cementum-like tissue observed on the root surface. Neoplastic changes were observed at the superficial portions of the implants in two of the 6-week cementoblast-treated specimens, possibly due in part to the SV40-transformed nature of the implanted cell line.

CONCLUSIONS

This pilot study demonstrates that cementoblasts have a marked ability to induce mineralization in periodontal wounds when delivered via polymer sponges, while implanted dental follicle cells seem to inhibit periodontal healing. These results confirm the selective behaviors of different cell types in vivo and support the role of cementoblasts as a tool to better understand periodontal regeneration and cementogen-

Neuroendocrine alterations impair enamel mineralization, tooth eruption and saliva in rats

Neonatal administration of monosodium glutamate (MSG) in rats causes definite neuroendocrine disturbances which lead to alterations in many organ systems. The possibility that MSG could affect tooth and salivary gland physiology was examined in this paper. Male and female pups were injected subcutaneously with MSG (4 mg/g BW) once a day at the 2nd, 4th, 6th, 8th and 10th day after birth. Control animals were injected with saline, following the same schedule. Lower incisor eruption was determined between the 4th and the 10th postnatal days, and the eruption rate was measured between the 43rd and the 67th days of age. Pilocarpine-stimulated salivary flow was measured at 3 months of age; protein and amylase contents were thereby determined. The animals treated with MSG showed significant reductions in the salivary flow (males, -27%; females, -40%) and in the weight of submandibular glands (about -12%). Body weight reduction was only about 7% for males, and did not vary in females. Saliva of MSG-treated rats had increased concentrations of total proteins and amylase activity. The eruption of lower incisors occurred earlier in MSG-treated rats than in the control group, but on the other hand the eruption rate was significantly slowed down. The incisor microhardness was found to be lower than that of control rats. Our results show that neonatal MSG treatment causes well-defined oral disturbances in adulthood in rats, including salivary flow reduction, which coexisted with unaltered protein synthesis, and disturbances of dental mineralization and eruption. These data support the view that some MSG-sensitive hypothalamic nuclei have an important modulatory effect on the factors which determine caries susceptibility.

Establishment of human cementifying fibroma cell lines by transfection with temperature-sensitive simian virus-40 T-antigen gene and hTERT gene

Human cementifying fibroma (HCF) is a benign fibro-osseous neoplasm of periodontal ligament (PDL) origin containing varying amounts of mineralized material resembling cementum. In the present study, we established cell lines from HCF, which were detected in the mandible of a 54-year-old Japanese man. To obtain immortalized cell clones, we undertook transfection with temperature-sensitive simian virus-40 (SV40) T-antigen and hTERT into HCF cells. Cells transfected with SV40 T-antigen entered "crisis" state between passages 22 and 35, but activation of telomerase by transfection with hTERT in the SV40-transformed HCF cells resulted in bypass of the crisis and maintenance over passage 200. HCF cell lines decreased the expression of SV40 T-antigen and the activity of cell proliferation at a nonpermissive temperature (39 degrees C) in comparison with that at a permissive temperature (33 degrees C). High activities of alkaline phosphatase and mineralization and the expression of type I collagen, osteocalcin, osteopontin, and bone sialoprotein by reverse transcription-polymerase chain reaction (RT-PCR) were observed in HCF cells at 39 degrees C. Overall, these findings suggest that: (i) HCF cell lines may represent a novel in vitro human cell model for the study of the regulatory mechanism of differentiation and proliferation of the human PDL; and (ii) transfection of plasmids encoding the temperature-sensitive SV40 T-antigen gene and hTERT gene may be useful for obtaining immortalized cell lines from benign human tumor and, probably, nonneoplastic human tissues.

Platelet-derived growth factor (PDGF) gene delivery for application in periodontal tissue engineering

BACKGROUND

A challenge in the reconstruction of periodontal structures is the targeted delivery of growth-promoting molecules to the tooth root surface. Polypeptide growth factors such as platelet-derived growth factor (PDGF) stimulate both cementogenesis and osteogenesis. Recent advances in gene therapy offer the advantage of delivering recombinant proteins to tissues for extended periods of time in vivo.

METHODS

Recombinant adenoviral vectors encoding for the PDGF-A gene were constructed to allow delivery of PDGF transgenes to cells. The recombinant adenoviruses were assembled using the viral backbone of Ad2/CMV/EGFP and replacing GFP (reporter gene encoding green fluorescent protein driven by the cytomegalovirus promoter [CMV] within adenovirus type 2) with the PDGF-A gene. Root lining cells (cloned cementoblasts) were transduced with Ad2/PDGF-A and evaluated for gene expression, DNA synthesis, and cell proliferation. PDGF-inducible genes, c-myc and osteopontin, were also evaluated following gene delivery of Ad2/PDGF-A.

RESULTS

The results revealed high level transduction of cementoblasts by gene transfer for 7 days as evidenced by flow cytometry and Northern blotting. Cementoblast DNA synthesis and subsequent proliferation were stimulated by Ad2/PDGF-A at levels equal to or greater than continuous rhPDGF-AA application. Strong message for the PDGF-A gene and protein as evidenced by Northern blotting and immunocytochemistry was noted. Furthermore, the potent induction of c-myc and osteopontin mRNA was found after PDGF gene delivery to cementoblasts.

CONCLUSIONS

These findings demonstrate that gene delivery of platelet-derived growth factor stimulates cementoblast activity that is sustained above that of rhPDGF-AA application. The use of gene therapy as a mode of growth factor delivery offers a novel approach to periodontal tissue engineering.

Parathyroid hormone-related protein down-regulates bone sialoprotein gene expression in cementoblasts: role of the protein kinase A pathway

PTH-related protein (PTHrP) acts as a paracrine and/or autocrine regulator of cell proliferation, apoptosis, and differentiation and is implicated in tooth development. The current studies employed cementoblasts to determine the role(s) and mechanisms of PTHrP in regulating cementum formation. Results demonstrated that PTHrP repressed gene expression and protein synthesis of bone sialoprotein (BSP) and abolished cementoblast-mediated biomineralization in vitro. The BSP gene inhibition required protein synthesis. The PTHrP analog (1-31) and other activators of the PKA pathway (3-isobutyl-1-methylxathine (IBMX), forskolin (FSK) and Sp-Adenosine-3', 5'-cyclic monophosphorothioate (Sp-cAMPss) also down-regulated BSP gene expression and blocked cementoblast-mediated biomineralization. In contrast, the PTHrP analog (7-34), a PTHrP antagonist, and the activators of the PKC pathway [phorbol 12-myristate 13-acetate (PMA) and phorbol 12, 13-dibutyrate (PDBu)] promoted BSP gene expression. In addition, the PKA pathway inhibitor (9-(2-tetrahydrofuryl) adenine (THFA) partially, but significantly reversed the PTHrP-mediated down-regulation of BSP gene expression. Furthermore, THFA alone significantly increased BSP messenger RNA (mRNA) expression in cementoblasts. In contrast, the inhibitor of the PKC pathway (GF109203X) did not reverse the PTHrP inhibitory effect on BSP gene expression. Furthermore, GF109203X alone dramatically reduced the BSP transcript levels. These data indicate that the cAMP/PKA pathway mediates the PTHrP-mediated down-regulation of BSP mRNA expression in cementoblasts; and furthermore, this pathway may, through an intrinsic inhibition mechanism, regulate the basal level of BSP mRNA expression. In contrast, the activation of PKC promotes BSP gene expression. These data provide new insights into the molecular mechanisms involved in PTHrP regulation of cementogenesis.

Parathyroid hormone-related protein regulates extracellular matrix gene expression in cementoblasts and inhibits cementoblast-mediated mineralization in vitro

Parathyroid hormone-related protein (PTHrP) has been implicated in regulating tooth eruption and/or development. Formation of cementum, a mineralized tissue covering the tooth root surface, is a critical biological event for tooth root development. To test the hypothesis that PTHrP targets cementoblasts (CMs) and acts to regulate cementogenesis, CM cell lines were established and their responsiveness to PTHrP stimulation was determined, in vitro. First, subclones were derived from two immortalized murine cell populations that contained CMs; SV-CM/periodontal ligament (PDL) cells were obtained from the root surface of first mandibular molars of CD-1 mice and immortalized with SV40 T-antigen (TAg), and OC-CM cell population was established from OC-TAg transgenic mice in which their cells harbor an osteocalcin (OC and/or OCN) promoter-driving immortal gene SV40 TAg. Based on our previous in situ studies, CM subclones were identified as cells expressing bone sialoprotein (BSP) and OCN transcripts, while PDL cell lines were designated as cells lacking BSP and OCN messenger RNA (mRNA). CMs exhibited a cuboidal appearance and promoted biomineralization, both in vitro and in vivo. In contrast, PDL cells (PDL subclones) displayed a spindle-shaped morphology and lacked the ability to promote mineralized nodule formation, both in vitro and in vivo. Next, using these subclones, the effect of PTHrP on cementogenesis was studied. CMs, not PDL cells, expressed PTH/PTHrP receptor mRNA and exhibited PTHrP-mediated elevation in cyclic adenosine monophosphate (cAMP) levels and c-fos gene induction. PTHrP stimulation repressed mRNA expression of BSP and OCN in CMs and blocked CM-mediated mineralization, in vitro. Collectively, these data suggest that CMs possess PTH/PTHrP receptors and, thus, are direct targets for PTHrP action during cementogenesis and that PTHrP may serve as an important regulator of cementogenesis.