Dentin sialoprotein (DSP) transcripts: developmentally-sustained expression in odontoblasts and transient expression in pre-ameloblasts

Enamel biomineralization under the effects of indomethacin and celecoxib non-steroidal anti-inflammatory drugs

The aim of this study was to explore the effects of nonsteroidal anti-inflammatory drugs on biomineralization of enamel. Sixty C57Bl6 male mice were used, which were assigned into three groups: celecoxib (n = 20) or indomethacin (n = 20) treatment for a period of 28 days or received no medication (control group, n = 20). Visual inspection and microcomputed tomography were used to analyze enamel morphology. Scanning electron microscopy–Energy dispersive X-ray and Knoop microhardness test were used to quantify chemical element content (Ca, P, C, O) and enamel microhardness, respectively. Tissues were collected to investigate the synthesis, activity or nuclear translocation of metalloproteinase-20, transcription factor Runx2, dentin sialoprotein and cyclooxygenase-2 enzyme by means of immunohistochemistry, in situ zymography and indirect immunofluorescence. Treatment with indomethacin and celecoxib reduced the Ca and P content, microhardness and mineral density in enamel. Treatment with nonsteroidal anti-inflammatory drugs caused an accumulation of metalloproteinase-20 and overall increased enzymatic activity in enamel matrix, while the synthesis of the transcription factor Runx2 was inhibited by these drugs. Interestingly, indomethacin inhibited Runx2 translocation to the nucleus whereas celecoxib did not. Those findings show that non-steroidal anti-inflammatory drugs impact the enamel biomineralization and could be involved in the etiology tooth enamel defects if used during the period of tooth formation and mineralization.

Dentin Sialoprotein/Phosphophoryn (DSP/PP) as Bio-Inductive Materials for Direct Pulp Capping

Conventional direct pulp capping, such as calcium hydroxide (Ca(OH)₂) or silicate products, usually induces an inflammatory reaction to provoke pulp regeneration. Phosphophoryn (PP) and dentin sialoprotein (DSP), the two most abundant non-collagenous proteins in the dentin matrix, are responsible for dentin mineralization, pulp cell migration, and differentiation. Here we examined the PP and combined DSP/PP as bio-inductive pulp capping materials by in vitro and in vivo tests. Firstly, the effects of the PP dose on pulp cell migration and matrix protein expression were examined by an agarose bead test. Secondly, the role of recombinant DSP (recDSP) and recDSP/PP on stimulating DSP-PP transcript expression was examined by RT-PCR. DSPP mRNA was also knocked down by RNA interference (RNAi) to examine their functions on dentin matrix mineralization. Finally, we used ferret animal models to test PP and recDSP/PP acting as capping agents on in vivo pulp responses and reparative dentin formation. The result showed that intermediate-dose PP was the most effective to enhance cell migration and differentiation. RecDSP/PP strongly enhanced the DSP-PP transcript expression, while inhibition of DSPP mRNA expression by siRNAs partially or completely affected dental pulp cell mineralization. The in vivo results showed that intermediate-dose PP and recDSP/PP proteins induced less pulp inflammation and promoted reparative dentin formation. Contrarily, conventional calcium hydroxide induced severe pulp inflammation. With these findings, DSP and PP could serve as capping agents for pulp capping therapy.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Enamel Defects Associated With Dentin Sialophosphoprotein Mutation in Mice

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is highly expressed in odontoblasts, but only transiently expressed in presecretory ameloblasts during tooth development. We previously generated a knockin mouse model expressing a mouse equivalent (DSPP, p.P19L) of human mutant DSPP (p.P17L; referred to as “Dspp^P19L/+”), and reported that Dspp^P19L/+ and Dspp^P19L/P19L mice manifested a dentin phenotype resembling human dentinogenesis imperfecta (DGI). In this study, we analyzed pathogenic effects of mutant P19L-DSPP on enamel development in Dspp^P19L/+ and Dspp^P19L/P19L mice. Micro-Computed Tomography (μCT) analyses of 7-week-old mouse mandibular incisors showed that Dspp^P19L/P19L mice had significantly decreased enamel volume and/or enamel density at different stages of amelogenesis examined. Acid-etched scanning electron microscopy (SEM) analyses of mouse incisors demonstrated that, at the mid-late maturation stage of amelogenesis, the enamel of wild-type mice already had apparent decussating pattern of enamel rods, whereas only minute particulates were found in Dspp^P19L/+ mice, and no discernible structures in Dspp^P19L/P19L mouse enamel. However, by the time that incisor enamel was about to erupt into oral cavity, distinct decussating enamel rods were evident in Dspp^P19L/+ mice, but only poorly-defined enamel rods were revealed in Dspp^P19L/P19L mice. Moreover, μCT analyses of the mandibular first molars showed that Dspp^P19L/+ and Dspp^P19L/P19L mice had a significant reduction in enamel volume and enamel density at the ages of 2, 3, and 24weeks after birth. Backscattered and acid-etched SEM analyses revealed that while 3-week-old Dspp^P19L/+ mice had similar pattern of enamel rods in the mandibular first molars as age-matched wild-type mice, no distinct enamel rods were observed in Dspp^P19L/P19L mice. Yet neither Dspp^P19L/+ nor Dspp^P19L/P19L mice showed well-defined enamel rods in the mandibular first molars by the age of 24weeks, as judged by backscattered and acid-etched SEM. In situ hybridization showed that DSPP mRNA level was markedly reduced in the presecretory ameloblasts, but immunohistochemistry revealed that DSP/DSPP immunostaining signals were much stronger within the presecretory ameloblasts in Dspp mutant mice than in wild-type mice. These results suggest that mutant P19L-DSPP protein caused developmental enamel defects in mice, which may be associated with intracellular retention of mutant DSPP in the presecretory ameloblasts.

DSPP dosage affects tooth development and dentin mineralization

Dentin Sialoprotein (DSP) and phosphophoryn (PP) are two most dominant non-collagenous proteins in dentin, which are the cleavage products of the DSPP (dentin sialophosphoprotein) precursor protein. The absence of the DSPP gene in DSPP knock-out (KO) mice results in characteristics that are consistent with dentinogenesis imperfecta type III in humans. Symptoms include thin dentin, bigger pulp chamber with frequent pulp exposure as well as abnormal epithelial-mesenchymal interactions, and the appearance of chondrocyte-like cells in dental pulp. To better understand how DSPP influences tooth development and dentin formation, we used a bacterial artificial chromosome transgene construct (BAC-DSPP) that contained the complete DSPP gene and promoter to generate BAC-DSPP transgenic mice directly in a mouse DSPP KO background. Two BAC-DSPP transgenic mouse strains were generated and characterized. DSPP mRNA expression in BAC-DSPP Strain A incisors was similar to that from wild-type (wt) mice. DSPP mRNA expression in BAC-DSPP Strain B animals was only 10% that of wt mice. PP protein content in Strain A incisors was 25% of that found in wt mice, which was sufficient to completely rescue the DSPP KO defect in mineral density, since microCT dentin mineral density analysis in 21-day postnatal animal molars showed essentially identical mineral density in both strain A and wt mice. Strain B mouse incisors, with 5% PP expression, only partially rescued the DSPP KO defect in mineral density, as microCT scans of 21-day postnatal animal molars indicated a reduced dentin mineral density compared to wt mice, though the mineral density was still increased over that of DSPP KO. Furthermore, our findings showed that DSPP dosage in Strain A was sufficient to rescue the DSPP KO defect in terms of epithelial-mesenchymal interactions, odontoblast lineage maintenance, along with normal dentin thickness and normal mineral density while DSPP gene dosage in Strain B only partially rescued the aforementioned DSPP KO defect.

Dentin Matrix Protein 1 Compensates for Lack of Osteopontin in Regulating Odontoblastlike Cell Differentiation after Tooth Injury in Mice

INTRODUCTION

Although dentin matrix protein 1 (DMP1) and osteopontin (OPN) act as substrates and signaling molecules for odontoblastlike cell differentiation after tooth injury, the mutual interaction between these proteins in the mechanism of odontoblastlike cell differentiation remains to be clarified. This study aimed to elucidate the role of DMP1 and OPN in regulating odontoblastlike cell differentiation after tooth injury.

METHODS

A groove-shaped cavity was prepared on the mesial surface of the upper first molars in wild-type and Opn knockout (KO) mice. The demineralized paraffin sections were processed for immunohistochemistry for nestin and DMP1 and in situ hybridization for Dmp1. For the in vitro assay, the experiments of organ culture for evaluating dentin-pulp complex regeneration using small interfering RNA treatment were performed.

RESULTS

Once preexisting odontoblasts died, nestin-positive newly differentiated odontoblastlike cells were arranged along the pulp-dentin border and began to express DMP1/Dmp1. In Opn KO mice, the expression of DMP1/Dmp1 was up-regulated compared with that of wild-type mice. The in vitro assay showed that the gene suppression of Dmp1 by small interfering RNA showed a tendency to decrease the differentiation rate of odontoblastlike cells from 70.1% to 52.2% in wild-type teeth. In addition, the suppression of Dmp1 in Opn KO teeth tended to lead to the inhibition of odontoblastlike cell differentiation.

CONCLUSIONS

These results suggest that the expression of Dmp1 is up-regulated in Opn KO mice both in vivo and in vitro, and DMP1 compensates for the lack of OPN in regulating odontoblastlike cell differentiation after tooth injury.

Spontaneous Development of Dental Dysplasia in Aged Parp-1 Knockout Mice

Poly(ADP-ribose) polymerase (Parp)-1 catalyzes polyADP-ribosylation using NAD⁺ and is involved in the DNA damage response, genome stability, and transcription. In this study, we demonstrated that aged Parp-1^-/- mouse incisors showed more frequent dental dysplasia in both ICR/129Sv mixed background and C57BL/6 strain compared to aged Parp-1^+/+ incisors, suggesting that Parp-1 deficiency could be involved in development of dental dysplasia at an advanced age. Computed tomography images confirmed that dental dysplasia was observed at significantly higher incidences in Parp-1^-/- mice. The relative calcification levels of Parp-1^-/- incisors were higher in both enamel and dentin (p < 0.05). Immunohistochemical analysis revealed (1) Parp-1 positivity in ameloblasts and odontoblasts in Parp-1^+/+ incisor, (2) weaker dentin sialoprotein positivity in dentin of Parp-1^-/- incisor, and (3) bone sialoprotein positivity in dentin of Parp-1^-/- incisor, suggesting ectopic osteogenic formation in dentin of Parp-1^-/- incisor. These results indicate that Parp-1 deficiency promotes odontogenic failure in incisors at an advanced age. Parp-1 deficiency did not affect dentinogenesis during the development of mice, suggesting that Parp-1 is not essential in dentinogenesis during development but is possibly involved in the regulation of continuous dentinogenesis in the incisors at an advanced age.

Phosphophoryn and Dentin Sialoprotein Effects on Dental Pulp Cell Migration, Proliferation, and Differentiation

Phosphophoryn (PP) and dentin sialoprotein (DSP) are two of the most abundant dentin matrix non-collagenous proteins, and are derived from dentin sialoprotein-phosphophoryn (DSP-PP) mRNA. Mutations in the DSP-PP gene are linked to dentinogenesis imperfecta II and III. Previously, we reported transient DSP-PP expression in preameloblast cells first, followed by co-expression in preameloblasts and young odontoblasts, and finally sustained expression in odontoblasts. This phenomenon raised the possibility that DSP/PP proteins secreted by preameloblasts might promote dental pulp cell migration toward the dental pulp border and promote dental pulp cell differentiation. To examine the effects of DSP/PP proteins on dental pulp cell development, we investigated:(1) native PP effects on dental pulpcell migration and matrix protein expression; and (2) recombinant DSP/PP protein effects on cell proliferation and differentiation. We found that PP promoted cell migration and the expression of high levels of Col type I and PP in dental pulp cells. The addition of recombinant DSP/PP proteins affected cell proliferation and differentiation in a dental pulp cell line. These findings strongly suggest that DSP/PP may modulate cell migration, cell proliferation and differentiation, thus leading to dentin formation. DSP/PP protein may be useful clinically for pulp tissue regeneration.

The functional significance of dentin sialoprotein-phosphophoryn and dentin sialoprotein

Phosphophoryn (PP) and dentin sialoprotein (DSP) are the most dominant non-collagenous proteins in dentin. PP is an extremely acidic protein that can function as a mineral nucleator for dentin mineralization. DSP was first identified in 1981, yet its functional significance is still controversial. Historically, these two proteins were considered to be independently synthesized and secreted by dental pulp cells into the developing dentin matrix. However, with the identification of the DSP coding sequence in 1994, followed 2 years later by the finding that the PP coding sequence was located immediately downstream from the DSP sequence, it became immediately clear that DSP and PP proteins were derived from a single DSP-PP (i.e., dentin sialophosphoprotein, DSPP) transcript. Since DSPP cDNA became available, tremendous progress has been made in studying DSP-PP mRNA distribution and DSP generation from the DSP-PP precursor protein at specific cleavage sites by protease tolloid-related-1 (TLR1) or bone morphogenetic protein 1 (BMP1). The functions of DSP-PP and DSP were investigated via DSP-PP knockout (KO) and DSP knockin in DSP-PP KO mice. In addition, a number of in vitro studies aimed to elucidate DSPP and DSP function in dental pulp cells.

Along with phosphophoryn (PP), dental sialoprotein (DSP) is the dominant non-collagen protein in dentin, and in vitro studies have demonstrated that DSP is involved in inducing the differentiation of dental pulp cells into odontoblast-like cells, which form dentin. PP is known to be involved in the mineralization of dentin, but the functional significance of DSP had been controversial. Helena Ritchie of the University of Michigan School of Dentistry conducted a review of studies investigating the derivation, function and distribution of PP and DSP. It was originally thought that PP and DSP were synthesized independently; later, it became evident that they derive from a single DSP-PP gene. Wider DSP-PP distribution in various tissues, including kidney and salivary glands, and DSP or PP expression in non-mineralized tissues suggest that the proteins may have functions other than mineralization.

Dentin sialophosphoprotein expression in enamel is regulated by Copine-7, a preameloblast-derived factor

OBJECTIVE

Dentin sialophosphoprotein (Dspp) is expressed in odontoblasts and transiently expressed in early ameloblasts. However, the origin of Dspp in ameloblasts remains unclear. Our previous studies demonstrated that copine-7 (CPNE7), a molecule that is secreted by the dental epithelium, is expressed in early ameloblasts and is then translocated to differentiating odontoblasts; its expression levels correlate with odontoblast differentiation under the control of Dspp expression. The objective of this study is to figure out the relationship between CPNE7 and Dspp during amelogenesis.

DESIGN

The gene expression patterns of CPNE7 and dentin sialoprotein (DSP) were examined by immunohistochemistry, western blot analysis, and real-time polymerase chain reaction. The effects of CPNE7 on Dspp regulation were investigated using luciferase and chromatin immunoprecipitation assays in ameloblastic HAT-7 cells.

RESULTS

The gene expression pattern of Cpne7 was similar to that of Dspp during ameloblast differentiation. Moreover, Gene expression omnibus profiles indicated that there is a close correlation between Cpne7 and Dspp expression in various normal human tissues. We also confirmed the effects of CPNE7 on the induction of Dspp in ameloblastic HAT-7 cells. Cpne7 overexpression promoted Dspp expression, whereas Dspp expression was down-regulated by Cpne7 inactivation.

CONCLUSIONS

These results suggest that the expression of Dspp in early amelogenesis is linked to CPNE7, a preameloblast-derived factor.

Differential expression between "DSP-only" and DSP-PP523 transcripts in rat molar teeth

OBJECTIVE

To compare the expression patterns of two multiple transcripts derived from DSP-PP gene during tooth development. One is DSP-only transcript (i.e. does not encode PP) and the other is DSP-PP₅₂₃ transcript, a main DSP-PP transcript.

DESIGN

Unique antisense and sense riboprobes were generated from DSP-only and DSPPP₅₂₃ cDNAs for in situ studies to examine DSP-only and DSP-PP₅₂₃ transcript expression in developing molars. Paraffin-embedded sections (5-7μ m) from embryonic 20day, postnatal 2, 3 and 6days were deparaffined and hydrated. Tissues were prehybridized, then hybridized with DSP-only and DSP-PP₅₂₃ anti-sense (AS) or sense (S) Digoxigenin labeled-riboprobes overnight, and washed. Anti-Digoxigenin antibodies conjugated to alkaline phosphatase were used to detect the presence of bound riboprobes by color reaction with NBT/BCIP. Stro-1 antibody was used for immunohistochemical analysis of Stro-1 protein expression in rat molars.

RESULTS

We found that unlike the DSP-PP₅₂₃ transcript, the DSP-only transcript does not express in the entire polarized mature odontoblasts but is expressed in the areas subjacent to the mature odontoblast layer. In addition, DSP-only transcript is expressed in the dental pulp. Interestingly, Stro-1 protein, a stem cell marker, was also identified in the areas subjacentto odontoblasts and in dental pulp.

CONCLUSION

Differential expression of DSP-only and DSP-PP₅₂₃ transcripts suggest that these two kinds of transcripts may play different roles during dentinogenesis. DSP-PP₅₂₃ transcript is expressed in mature odontoblasts, which actively participates in dentin formation. DSP-only transcript might have a different function.

Dentin sialoprotein facilitates dental mesenchymal cell differentiation and dentin formation

Dentin sialoprotein (DSP) is a dentin extracellular matrix protein. It is involved in dental mesenchymal cell lineages and dentin formation through regulation of its target gene expression. DSP mutations cause dentin genetic diseases. However, mechanisms of DSP in controlling dental mesenchymal cell differentiation are unknown. Using DSP as bait, we screened a protein library from mouse odontoblastic cells and found that DSP is a ligand and binds to cell surface receptor, occludin. Further study identified that the C-terminal DSP domain^{aa 363–458} interacts with the occludin extracellular loop 2^{aa 194–241}. The C-terminal DSP domain induced phosphorylation of occludin Ser⁴⁹⁰ and focal adhesion kinase (FAK) Ser⁷²² and Tyr⁵⁷⁶. Coexpression of DSP, occludin and FAK was detected in dental mesenchymal cells during tooth development. Occludin physically interacts with FAK, and occludin and FAK phosphorylation can be blocked by DSP and occludin antibodies. This DSP domain facilitates dental mesenchymal cell differentiation and mineralization. Furthermore, transplantation and pulp-capping procedures revealed that this DSP domain induces endogenous dental pulp mesenchymal cell proliferation, differentiation and migration, while stimulating blood vessel proliferation. This study elucidates the mechanism of DSP in dental mesenchymal lineages and implies that DSP may serve as a therapeutic agent for dentin-pulp complex regeneration in dental caries.

The Dentin Sialoprotein (DSP) Domain Regulates Dental Mesenchymal Cell Differentiation through a Novel Surface Receptor

Dentin sialophosphoprotein (DSPP) is a dentin extracellular matrix protein that is processed into dentin sialoprotein (DSP), dentin glycoprotein (DGP) and dentin phosphoprotein (DPP). DSP is mainly expressed in odontoblasts. We hypothesized that DSP interacts with cell surface receptors and subsequently activates intracellular signaling. Using DSP as bait for screening a protein library, we demonstrate that DSP acts as a ligand and binds to integrin β6. The 36 amino acid residues of DSP are sufficient to bind to integrin β6. This peptide promoted cell attachment, migration, differentiation and mineralization of dental mesenchymal cells. In addition, DSP (aa183-219) stimulated phosphorylation of ERK1/2 and P38 kinases. This activation was inhibited by an anti-integrin β6 antibody and siRNA. Furthermore, we demonstrate that this DSP fragment induces SMAD1/5/8 phosphorylation and nuclear translocation via ERK1/2 and P38 signaling. SMAD1/5/8 binds to SMAD binding elements (SBEs) in the DSPP gene promoter. SBE mutations result in a decrease in DSPP transcriptional activity. Endogenous DSPP expression was up-regulated by DSP (aa183-219) in dental mesenchymal cells. The data in the current study demonstrate for the first time that this DSP domain acts as a ligand in a RGD-independent manner and is involved in intracellular signaling via interacting with integrin β6. The DSP domain regulates DSPP expression and odontoblast homeostasis via a positive feedback loop.

Osteopontin Is Essential for Type I Collagen Secretion in Reparative Dentin

Osteopontin (OPN) is a highly phosphorylated glycoprotein that is a prominent component of the mineralized extracellular matrix of bone. The secretion of OPN by immunocompetent cells plays a role in the differentiation of odontoblast-like cells during pulpal healing following tooth transplantation. This study aimed to clarify the role of OPN during reparative dentinogenesis. A groove-shaped cavity was prepared on the mesial surface of the upper first molars of wild-type (WT) and Opn knockout (KO) mice, and the samples were collected at intervals of 1 to 14 d. The demineralized sections were processed for immunohistochemistry for Ki67, nestin, OPN, dentin sialoprotein (DSP), integrin αvβ3, and type I collagen; in situ hybridization for Opn, col1a1, and dentin sialophosphoprotein (Dspp); and apoptosis assay. For the loss and gain of function experiments, an in vitro culture assay for evaluating dentin-pulp complex regeneration was performed. On day 1 in WT mice, odontoblasts beneath the affected dentin lost nestin immunoreactivity. On day 3, the expression of Opn was recognized at the mesial dental pulp, and OPN was deposited along the predentin-dentin border. Nestin-positive newly differentiated odontoblast-like cells expressed both Dspp and col1a1 and showed positive immunoreactivity for integrin αvβ3, DSP, and type I collagen. Until day 14, reparative dentin formation continued next to the preexisting dentin at the mesial coronal pulp. In contrast, there was no reparative dentin in the Opn KO mice where nestin- and DSP-positive newly differentiated odontoblast-like cells lacked immunoreaction for type I collagen. The in vitro organ culture demonstrated that the administration of recombinant OPN rescued the type I collagen secretion by odontoblast-like cells in the Opn KO mice. The results suggested that the deposition of OPN at the calcification front is essential for the type I collagen secretion by newly differentiated odontoblast-like cells to form reparative dentin during pulpal healing following cavity preparation.

Detection of a Novel DSPP Mutation by NGS in a Population Isolate in Madagascar

A large family from a small village in Madagascar, Antanetilava, is known to present with colored teeth. Through previous collaboration and 4 successive visits in 1994, 2004, 2005, and 2012, we provided dental care to the inhabitants and diagnosed dentinogenesis imperfecta. Recently, using whole exome sequencing we confirmed the clinical diagnosis by identifying a novel single nucleotide deletion in exon 5 of DSPP. This paper underlines the necessity of long run research, the importance of international and interpersonal collaborations as well as the major contribution of next generation sequencing tools in the genetic diagnosis of rare oro-dental anomalies. This study is registered in ClinicalTrials (https://clinicaltrials.gov) under the number NCT02397824.

Perivascular Stem Cells at the Tip of Mouse Incisors Regulate Tissue Regeneration

Cells with in vitro properties similar to those of bone marrow stromal stem cells are present in tooth pulp as quiescent cells that are mobilized by damage. These dental pulp stem cells (DPSCs) respond to damage by stimulating proliferation and differentiation into odontoblast-like cells that form dentine to repair the damage. In continuously growing mouse incisors, tissue at the incisor tips is continuously being damaged by the shearing action between the upper and lower teeth acting to self-sharpen the tips. We investigated mouse incisor tips as a model for the role of DPSCs in a continuous natural repair/regeneration process. We show that the pulp at the incisor tip is composed of a disorganized mass of mineralized tissue produced by odontoblast-like cells. These cells become embedded into the mineralized tissue that is rapidly formed and then lost during feeding. Tetracycline labeling not only revealed the expected incorporation into newly synthesized dentine formation of the incisor but also a zone covering the pulp cavity at the tips of the incisors that is mineralized very rapidly. This tissue was dentine-like but had a significantly lower mineral content than dentine as determined by Raman spectroscopy. The mineral was more crystalline than dentine, indicative of small, defect-free mineral particles. To identify the origin of cells responsible for deposition of this mineralized tissue, we genetically labeled perivascular cells by crossing NG2(ERT2) Cre and Nestin Cre mice with reporter mice. A large number of pericyte-derived cells were visible in the pulp of incisor tips with some having elongated, odontoblast-like shapes. These results show that in mouse incisors, rapid, continuous mineralization occurs at the tip to seal off the pulp tissue from the external environment. The mineral is formed by perivascular-derived cells that differentiate into cells expressing dentin sialo-phosphoprotein (DSPP) and produce a dentine-like material in a process that functions as continuous natural tissue regeneration.

Vitamin D Promotes Odontogenic Differentiation of Human Dental Pulp Cells via ERK Activation

The active metabolite of vitamin D such as 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) is a well-known key regulatory factor in bone metabolism. However, little is known about the potential of vitamin D as an odontogenic inducer in human dental pulp cells (HDPCs) in vitro. The purpose of this study was to evaluate the effect of vitamin D3 metabolite, 1α,25(OH)2D3, on odontoblastic differentiation in HDPCs. HDPCs extracted from maxillary supernumerary incisors and third molars were directly cultured with 1α,25(OH)2D3 in the absence of differentiation-inducing factors. Treatment of HDPCs with 1α,25(OH)2D3 at a concentration of 10 nM or 100 nM significantly upregulated the expression of dentin sialophosphoprotein (DSPP) and dentin matrix protein1 (DMP1), the odontogenesis-related genes. Also, 1α,25(OH)2D3 enhanced the alkaline phosphatase (ALP) activity and mineralization in HDPCs. In addition, 1α,25(OH)2D3 induced activation of extracellular signal-regulated kinases (ERKs), whereas the ERK inhibitor U0126 ameliorated the upregulation of DSPP and DMP1 and reduced the mineralization enhanced by 1α,25(OH)2D3. These results demonstrated that 1α,25(OH)2D3 promoted odontoblastic differentiation of HDPCs via modulating ERK activation.

Isolated dentinogenesis imperfecta and dentin dysplasia: revision of the classification

Dentinogenesis imperfecta is an autosomal dominant disease characterized by severe hypomineralization of dentin and altered dentin structure. Dentin extra cellular matrix is composed of 90% of collagen type I and 10% of non-collagenous proteins among which dentin sialoprotein (DSP), dentin glycoprotein (DGP) and dentin phosphoprotein (DPP) are crucial in dentinogenesis. These proteins are encoded by a single gene: dentin sialophosphoprotein (DSPP) and undergo several post-translational modifications such as glycosylation and phosphorylation to contribute and to control mineralization. Human mutations of this DSPP gene are responsible for three isolated dentinal diseases classified by Shield in 1973: type II and III dentinogenesis imperfecta and type II dentin dysplasia. Shield classification was based on clinical phenotypes observed in patient. Genetics results show now that these three diseases are a severity variation of the same pathology. So this review aims to revise and to propose a new classification of the isolated forms of DI to simplify diagnosis for practitioners.

Odontogenic differentiation of vascular endothelial growth factor-transfected human dental pulp stem cells in vitro

Dental pulp stem cells (DPSCs) can be induced towards odontogenic differentiation. Previous studies have shown that vascular endothelial growth factor (VEGF) is able to induce the osteogenic differentiation of cells, but the effectiveness of VEGF in the odontogenic differentiation of DPSCs remains unclear. This study aimed to investigate the effects of lentivirus‑mediated human VEGF gene transfection on the proliferation and odontogenic differentiation of human DPSCs in vitro. DPSCs were transfected with either lentiviral pCDH‑CMV‑MCS‑EFI‑copGFP (pCDH) vector or recombinant pCDH‑VEGF vector, and the growth characteristics of the resulting DPSCs/Vector and DPSCs/VEGF were subsequently assessed. The odontogenic differentiation genes of the two groups of cells, including alkaline phosphatase, osteocalcin, dentin sialophosphoprotein and dentin matrix protein 1 (DMP1), were evaluated by quantitative polymerase chain reaction (qPCR). The specific proteins of odontogenic differentiation, including dentin sialoprotein and DMP1, were analyzed by western blotting. DPSCs/VEGF showed similar proliferation characteristics to DPSCs/Vector during the observation period. qPCR results showed that the relative VEGF gene expression was significantly higher in DPSCs/VEGF than that in DPSCs/Vector two days after transfection (P<0.01). Similarly, western blot analysis showed that the protein expression levels of VEGF were higher in DPSCs/VEGF than those in DPSCs/Vector. On the first, fourth, eighth and 16th days after lentivirus-mediated transfection, the expression of odontogenic differentiation-specific genes and proteins was higher in DPSCs/VEGF than that in DPSCs/Vector. These results indicated that lentivirus-mediated VEGF gene transfection promoted the odontogenic differentiation of human DPSCs in vitro.

Functionalized scaffolds to control dental pulp stem cell fate

Emerging understanding about interactions between stem cells, scaffolds, and morphogenic factors has accelerated translational research in the field of dental pulp tissue engineering. Dental pulp stem cells constitute a subpopulation of cells endowed with self-renewal and multipotency. Dental pulp stem cells seeded in biodegradable scaffolds and exposed to dentin-derived morphogenic factors give rise to a pulplike tissue capable of generating new dentin. Notably, dentin-derived proteins are sufficient to induce dental pulp stem cell differentiation into odontoblasts. Ongoing work is focused on developing ways of mobilizing dentin-derived proteins and disinfecting the root canal of necrotic teeth without compromising the morphogenic potential of these signaling molecules. On the other hand, dentin by itself does not appear to be capable of inducing endothelial differentiation of dental pulp stem cells despite the well-known presence of angiogenic factors in dentin. This is particularly relevant in the context of dental pulp tissue engineering in full root canals in which access to blood supply is limited to the apical foramina. To address this challenge, scientists are looking at ways to use the scaffold as a controlled-release device for angiogenic factors. The aim of this article was to present and discuss current strategies to functionalize injectable scaffolds and customize them for dental pulp tissue engineering. The long-term goal of this work is to develop stem cell-based therapies that enable the engineering of functional dental pulps capable of generating new tubular dentin in humans.

Allogenic tooth transplantation inhibits the maintenance of dental pulp stem/progenitor cells in mice

Our recent study suggested that allogenic tooth transplantation may affect the maintenance of dental pulp stem/progenitor cells. This study aims to elucidate the influence of allograft on the maintenance of dental pulp stem/progenitor cells following tooth replantation and allo- or auto-genic tooth transplantation in mice using BrdU chasing, immunohistochemistry for BrdU, nestin and Ki67, in situ hybridization for Dspp, transmission electron microscopy and TUNEL assay. Following extraction of the maxillary first molar in BrdU-labeled animals, the tooth was immediately repositioned in the original socket, or the roots were resected and immediately allo- or auto-grafted into the sublingual region in non-labeled or the same animals. In the control group, two types of BrdU label-retaining cells (LRCs) were distributed throughout the dental pulp: those with dense or those with granular reaction for BrdU. In the replants and autogenic transplants, dense LRCs remained in the center of dental pulp associating with the perivascular environment throughout the experimental period and possessed a proliferative capacity and maintained the differentiation capacity into the odontoblast-like cells or fibroblasts. In contrast, LRCs disappeared in the center of the pulp tissue by postoperative week 4 in the allografts. The disappearance of LRCs was attributed to the extensive apoptosis occurring significantly in LRCs except for the newly-differentiated odontoblast-like cells even in cases without immunological rejection. The results suggest that the host and recipient interaction in the allografts disturbs the maintenance of dense LRCs, presumably stem/progenitor cells, resulting in the disappearance of these cell types.

Expression of mineralized tissue associated proteins: dentin sialoprotein and phosphophoryn in rodent hair follicles

BACKGROUND

Mammalian hair development and tooth development are controlled by a series of reciprocal epithelial-mesenchymal interactions. Similar growth factors and transcription factors, such as fibroblast growth factor (FGF), sonic hedgehog homolog (SHH), bone morphogenetic proteins (BMPs) and Wnt10a, were reported to be involved in both of these interactions. Dentin sialoprotein (DSP) and phosphophoryn (PP) are the two major non-collagenous proteins secreted by odontoblasts that participate in dentin mineralization during tooth development. Because of striking similarities between tooth development and hair follicle development, we investigated whether DSP and/or PP proteins may also play a role in hair follicle development.

OBJECTIVE

In this study, we examined the presence and location of DSP/PP proteins during hair follicle development.

METHODS

Rat PP proteins were detected using immunohistochemical/immunofluorescent staining. DSP-PP mRNAs were detected by in situ hybridization with riboprobes. LacZ expression was detected in mouse tissues using a DSP-PP promoter-driven LUC in transgenic mice.

RESULTS

We found that PP proteins and DSP-PP mRNAs are present in rat hair follicles. We also demonstrate that an 8 kb DSP-PP promoter is able to drive lacZ expression in hair follicles.

CONCLUSION

We have firmly established the presence of DSP/PP in mouse and rat hair follicles by immunohistochemical/immunofluorescent staining, in situ hybridization with riboprobes and transgenic mice studies. The expression of DSP/PP in hair follicles is the first demonstration that major mineralization proteins likely may also contribute to soft tissue development. This finding opens a new avenue for future investigations into the molecular-genetic management of soft tissue development.

Possible involvement of maspin in tooth development

Maspin is a 42 kDa serine protease inhibitor that possesses tumor suppressive and anti-angiogenic activities. Despite of a huge amount of data concerning the expression pattern of maspin in various tissues and its relevance to the biological properties of a variety of human cancer cells, little is known on the maspin expression in skeletal and tooth tissues. Recently, we reported that maspin may play an important role in extracellular matrix formation in bone by enhancing the accumulation of latent TGF-β in the extracellular matrix. This study was performed to elucidate the possible role of maspin in tooth development. First, an immunohistochemical analysis for human tooth germs at the late bell stage showed the expression of maspin by active ameloblasts and odontoblasts that were forming enamel and dentin, respectively. During rat tooth development, maspin expression was observed for the first time in inner and outer enamel epithelial cells and dental papilla cells at early bell stage. The neutralizing anti-maspin antibody inhibited the proper dental tissue formation in organ cultures of mandibular first molars obtained from 21-day-old rat embryos. In addition, the proliferation of HAT-7 cells, a rat odontogenic epithelial cell line, and human dental papilla cells were suppressed in a dose-dependent manner with anti-maspin antibody. Moreover, RT-PCR analysis showed that the expression of mRNA for tooth-related genes including dentin matrix protein 1, dentin sialophosphoprotein and osteopontin in human dental papilla cells was inhibited when treated with anti-maspin antibody. These findings suggest that maspin expressed in ameloblasts and odontoblasts plays an important physiological role in tooth development through the regulation of matrix formation in dental tissues.

Tissue-specific expression of dentin sialophosphoprotein (DSPP) and its polymorphisms in mouse tissues

Dentin sialophosphoprotein (DSPP) consists of dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). DSPP is highly expressed in mineralized tissues. However, recent studies have shown that DSPP is also expressed in several active metabolic ductal epithelial tissues and exists in a variety of sequences. We have investigated DSPP expression in various mouse tissues using RT-PCR, in situ hybridization and immunohistochemical analyses. To identify DSPP gene polymorphisms, we screened a mouse tooth cDNA library as well as isolated and characterized DSPP variations. Our results show that DSPP is predominantly expressed in teeth and moderately in bone tissues. We also have characterized a full-length DSPP cDNA clone with an open-reading frame of 940 codons and this polyadenylation signal. Compared to previously reported mouse DSPP cDNAs, 13 sequence variations were identified, including 8 non-synonymous single nucleotide polymorphisms and an in-frame indel (8 amino acids) at DPP domain of the mouse DSPP. These 8 amino acids are rich in aspartic acid and serine residues. Northern blot assay showed a prominent band at 4.4kb. RT-PCR demonstrated that this mouse DSPP gene was dominantly expressed in teeth. The predicted secondary structure of DPP domain of this DSPP showed differences from the previously published mouse DPPs, implying that they play different roles during tooth development and formation.

Dynamic processing of recombinant dentin sialoprotein-phosphophoryn protein

Dentin sialoprotein (DSP) and phosphophoryn (PP) are the two noncollagenous proteins classically linked to dentin but more recently found in bone, kidney, and salivary glands. These two proteins are derived from a single copy DSP-PP gene. Although this suggests that the DSP-PP gene is first transcribed into DSP-PP mRNAs, which later undergo processing to yield the DSP and PP proteins, this mechanism has not yet been demonstrated because of the inability to identify a DSP-PP precursor protein from any cell or tissue sample. To study this problem, we utilized a baculovirus expression system to produce recombinant DSP-PP precursor proteins from a DSP-PP(240) cDNA, which represents one of several endogenous DSP-PP transcripts that influence various tooth mineralization phases. Our in vitro results demonstrate that DSP-PP(240) precursor proteins are produced by this system and are capable of self-processing to yield both DSP and PP proteins. We further demonstrated that purified recombinant DSP-PP(240), purified recombinant PP(240), and the native highly phosphorylated protein (equivalent to the PP(523) isoform) have proteolytic activity. These newly identified tissue proteases may play key roles in tissue modeling during organogenesis.

Characterization of excess hard tissue occurring in the mesio-buccal surface of the mandibular first molar in microphthalmic mouse

OBJECTIVE

The aim of the present study was to characterize the excess hard tissue on the mandible of the microphthalmic mouse having a mutation at the mitf locus.

DESIGN

Homozygous mutant (mi/mi) and wild-type (+/+) mice were obtained by mating a breeding pair (strain name, B6C3Fe a/a-Mitf(mi)/J). We used mi/mi and +/+ mice at ages 6, 7, 8, 9, 28, and 49 days for micro-computed tomographic and histologic analyses.

RESULTS

Excess hard tissue was found on the mesio-buccal surface of the mandibular first molar in all 11mi/mi mice, but none was found in the 8mi/+ or 14 +/+ mice. The excess hard tissue was located in the mental foramen connected to the mandibular canal. The mandibular canal passed near the basal part of the incisor and the root of the mandibular first molar due to aberrant development of the teeth and mandible. The excess hard tissue contained predentine immunostained for dentine sialoprotein, a marker for early stages of dentinogenesis, which was first observed at about 7 days of age. Dentine, predentine, pulp, and root-like structures were observed in the excess hard tissue, but neither enamel nor enamel organ was observed.

CONCLUSION

Odontogenic cells in the basal part of the incisor and/or the mandibular first molar with the ability to develop into odontoblasts and pulp cells appeared to migrate through the mandibular canal to the mental foramen, where they developed into odontoblasts and pulp-like cells, and then formed dentine and predentine-like structures.

Ectopic expression of dentin sialoprotein during amelogenesis hardens bulk enamel

Dentin sialophosphpoprotein (Dspp) is transiently expressed in the early stage of secretory ameloblasts. The secretion of ameloblast-derived Dspp is short-lived, correlates to the establishment of the dentinoenamel junction (DEJ), and is consistent with Dspp having a role in producing the specialized first-formed harder enamel adjacent to the DEJ. Crack diffusion by branching and dissipation within this specialized first-formed enamel close to the DEJ prevents catastrophic interfacial damage and tooth failure. Once Dspp is secreted, it is subjected to proteolytic cleavage that results in two distinct proteins referred to as dentin sialoprotein (Dsp) and dentin phosphoprotein (Dpp). The purpose of this study was to investigate the biological and mechanical contribution of Dsp and Dpp to enamel formation. Transgenic mice were engineered to overexpress either Dsp or Dpp in their enamel organs. The mechanical properties (hardness and toughness) of the mature enamel of transgenic mice were compared with genetically matched and age-matched nontransgenic animals. Dsp and Dpp contributions to enamel formation greatly differed. The inclusion of Dsp in bulk enamel significantly and uniformly increased enamel hardness (20%), whereas the inclusion of Dpp weakened the bulk enamel. Thus, Dsp appears to make a unique contribution to the physical properties of the DEJ. Dsp transgenic animals have been engineered with superior enamel mechanical properties.

Biological markers for evaluation of root resorption

BACKGROUND

External apical root resorption is a pathologic consequence of orthodontic tooth movement. Cementum and dentin are removed from the root surface while active force is present.

OBJECTIVE

The aim of this study was to identify and quantify extracellular matrix proteins, dentin matrix protein 1 (DMP1), dentin phosphophoryn (PP), and dentin sialoprotein (DSP) in the gingival crevicular fluid (GCF) of subjects undergoing orthodontic treatment.

METHODS

Subjects with mild (less than 2mm) and severe (more than 2mm) root resorption during orthodontic treatment were identified by radiographs. A control group of subjects with neither signs of root loss nor undergoing orthodontic treatment was also identified. GCF was collected from the upper incisors by using filter paper strips (Periopaper). The absorbed GCF was eluted and the proteins were separated by SDS-PAGE analysis and stained. Western blot and ELISA were also performed. One-way ANOVA and Scheffé test were used for statistical analysis.

RESULTS

SDS-PAGE analysis identified proteins at 77, 66, 55, 50 and 26kDa. Immunoblotting did not show any differential expression pattern between control and study groups. ELISA results revealed a significant difference in the concentrations of DMP1, PP and DSP between control and root resorption groups. Concentration of PP and DSP in severe root resorption group was also statistically higher than in mild root resorption group.

CONCLUSION

DSP and PP could be suitable biological markers for monitoring root resorption during orthodontic treatment, since a significant difference in the level of these dentin specific proteins is detected in all groups.

Shear stress facilitates tissue-engineered odontogenesis

Numerous studies have demonstrated the effect of shear stress on osteoblasts, but its effect on odontogenic cells has never been reported. In this study, we focused on the effect of shear stress on facilitating tissue-engineered odontogenesis by dissociated single cells. Cells were harvested from the porcine third molar tooth at the early stage of crown formation, and the isolated heterogeneous cells were seeded on a biodegradable polyglycolic acid fiber mesh. Then, cell-polymer constructs with and without exposure to shear stress were evaluated by in vitro and in vivo studies. In in vitro studies, the expression of both epithelial and mesenchymal odontogenic-related mRNAs was significantly enhanced by shear stress for 2 h. At 12 h after exposure to shear stress, the expression of amelogenin, bone sialoprotein and vimentin protein was significantly enhanced compared with that of control. Moreover, after 7 days, alkaline phosphatase activity exhibited a significant increase without any significant effect on cell proliferation in vitro. In vivo, enamel and dentin tissues formed after 15 weeks of in vivo implantation in constructs exposure to in vitro shear stress for 12 h. Such was not the case in controls. We concluded that shear stress facilitates odontogenic cell differentiation in vitro as well as the process of tooth tissue engineering in vivo.

Dentin-pulp complex responses to carious lesions

To understand the molecular events underlying the dentin-pulp complex responses to carious progression, we systematically analyzed tissue morphology and dentin matrix protein distribution in non-carious teeth and in teeth with enamel and dentin caries. Dentin matrix proteins analyzed included collagen type I, phosphophoryn (PP) and dentin sialoprotein (DSP), all of which play decisive roles in the dentin mineralization process. Human non-carious and carious third molar teeth were freshly collected, demineralized, and processed for hematoxylin and eosin staining. The ABC-peroxidase method was used for immunohistochemical staining of collagen type I, PP and DSP proteins using specific antibodies. In situ hybridization was also performed. In contrast to elongated odontoblasts in non-carious teeth, odontoblasts subjacent to dentin caries were cuboidal and fewer in number. The predentin zone was also dramatically reduced in teeth with dentin caries. The staining intensity for collagen type I, PP and DSP in the dentin-pulp complex increased progressively from non-carious teeth, to teeth with enamel and dentin caries. In situ hybridization studies showed DSP-PP mRNA expression in odontoblasts and dental pulp that was consistent with our immunohistochemical results. These results suggest that carious lesions stimulate the dentin-pulp complex to actively synthesize collagen type I, PP and DSP proteins. This response to carious lesions is likely to provide a basis for reparative and/or reactionary dentin formation.

Ultrastructural and immunocytochemical characterization of immortalized odontoblast MO6-G3

AIM

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

METHODOLOGY

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

RESULTS

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

CONCLUSION

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

The dentin sialoprotein (DSP) expression in rat tooth germs following fluoride treatment: An immunohistochemical study

Fluoride is known to alter expression of dentin matrix proteins and affect their posttranslational modifications.

OBJECTIVE

The objective of our study was to examine dentin sialoprotein (DSP) expression in the early and late bell stages of development of the first molar tooth germs in rats treated with fluoride.

DESIGN AND METHODS

Pregnant dumps were divided into three groups. They were fed a standard diet and from the fifth day of pregnancy, each group received either tap water (with trace amounts of fluoride), tap water with a low concentration of fluoride, or tap water with a high concentration of fluoride. Changes in DSP expression and distribution were visualized by immunohistochemistry.

RESULTS

Immunoreactivity for DSP was detected in the cervical regions of the early bell stage in tooth germs of the 1-day-old animals. The earliest reaction was visible in the control group and the group supplemented with the low fluoride concentration (F(L)) but not in the group supplemented with the high fluoride concentration (F(H)). In early bell stages across all experimental groups, the immunoreactivity to DSP was observed in the cusp tip regions and was localized to preameloblasts, young and mature odontoblasts, dental pulp cells, predentin, and dentin. Generally, more intense positive staining for DSP was detected in animals supplemented with the high fluoride concentration. In the late bell stage found in the 4-day-old control group and the group supplemented with the low fluoride concentration, immunoreactivity for DSP was less intense compared with younger animals. However, immunoreactivity was greater in the group treated with the high dose of fluoride. In this group, the positive immunostaining for DSP, especially in young ameloblasts, was prolonged and relatively strong.

CONCLUSIONS

Fluoride supplementation causes changes in the developmental pattern of DSP expression and its distribution in rat tooth germs.

Synthesis of a potentially bioactive, hydroxyapatite-nucleating molecule

A human phosphophoryn (PP) cDNA was previously cloned from immature root apex total RNA in our laboratory. This cDNA comprises 2,364 bp, encoding 788 amino acids. More than 80% of the sequences are arranged as (DSS)(n) (n = 1-16), DS, and NSS motifs. We hypothesize that the capability of PP to bind Ca(2+) and nucleate hydroxyapatite may depend on these repeated sequences. Two polypeptides were synthesized based on the human PP cDNA sequence to test the hypothesis. One polypeptide has the amino acid sequence DDPNSSDESNGNDD (synthetic polypeptide 1, SP1), which is from the N-terminal end of PP; the other polypeptide, DSKSDSSKSESDSS (synthetic polypeptide 2, SP2), is the PP repeated sequence motif. Phosphorylation of the polypeptides was accomplished by reacting them with adenosine triphosphate and casein kinases I and II. The ability of these molecules to cause mineralization was tested in a steady-state agarose gel system. The results show that phosphorylated SP2 (P-SP2) precipitated approximately 60% of the total Ca + PO(4) precipitated by PP. P-SP1 precipitated about 23% of that precipitated by PP and was similar to the amount precipitated in the control gel, that is, without added peptides. Transmission electron microscopy and X-ray diffraction analysis showed that the precipitate formed in the P-SP2-containing gel was hydroxyapatite. The capability of P-SP2 to nucleate Ca + PO(4) and precipitate hydroxyapatite is a result of the repeated sequence motif, which contains a high percentage of phosphorylated serine. This molecule could be used in the repair and regeneration of dental tissue.

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

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

A rat 8 kb dentin sialoprotein-phosphophoryn (DSP-PP) promoter directs spatial and temporal LacZ activity in mouse tissues

Dentin sialoprotein (DSP) and phosphophoryn (PP) are two major dentin noncollagenous proteins that are encoded on a single DSP-PP transcript whose expression is tightly regulated during tooth dentinogenesis. The recent identification of this gene transcript in other tissues, including inner ear and jaw tissue, suggests that DSP and PP may have pleiotropic effects on other organs besides teeth. To identify candidate regulatory elements that control DSP-PP temporal and spatial expression, we constructed a -5 kb upstream region rat DSP-PP promoter into the beta-galactosidase expression vector pnLacF plasmid and used this construct to prepare DSP-PP-LacZ transgenic mice. Multiple mouse tissues including teeth, bone, and kidney obtained from the six resulting transgenic mouse lines displayed strong LacZ activity. This spatial distribution was confirmed in several of these tissues by in situ hybridization studies. LacZ activity was transiently expressed in preameloblasts and continuously expressed in odontoblasts demonstrating that this -5 kb rat promoter-dependent LacZ expression mimics reported DSP-PP mRNA expression patterns. Interestingly, this -5 kb rat promoter construct drives LacZ expression according to the rat developmental clock. Based on identified transcription factors present in this -5 kb promoter region, we have identified several probable cis-regulatory modules whose interaction with one another could account for the spatial and temporal distribution of DSP-PP transcripts in developing tissues.

TGF-beta3 induces ectopic mineralization in fetal mouse dental pulp during tooth germ development

Several members of the transforming growth factor (TGF)-beta superfamily are expressed in developing teeth from the initiation stage through adulthood. Of those, TGF-beta1 regulates odontoblast differentiation and dentin extracellular matrix synthesis. However, the molecular mechanism of TGF-beta3 in dental pulp cells is not clearly understood. In the present study, beads soaked with human recombinant TGF-beta3 induced ectopic mineralization in dental pulp from fetal mouse tooth germ samples, which increased in a dose-dependent manner. Further, TGF-beta3 promoted mRNA expression, and increased protein levels of osteocalcin (OCN) and type I collagen (COL I) in dental pulp cells. We also observed that the expression of dentin sialophosphoprotein and dentin matrix protein 1 was induced by TGF-beta3 in primary cultured dental pulp cells, however, not in calvaria osteoblasts, whereas OCN, osteopontin and osteonectin expression was increased after treatment with TGF-beta3 in both dental pulp cells and calvaria osteoblasts. Dentin sialoprotein was also partially detected in the vicinity of TGF-beta3 soaked beads in vivo. These results indicate for the first time that TGF-beta3 induces ectopic mineralization through upregulation of OCN and COL I expression in dental pulp cells, and may regulate the differentiation of dental pulp stem cells to odontoblasts.

Dentin sialoprotein and dentin phosphoprotein overexpression during amelogenesis

The gene for dentin sialophosphoprotein produces a single protein that is post-translationally modified to generate two distinct extracellular proteins: dentin sialoprotein and dentin phosphoprotein. In teeth, dentin sialophosphoprotein is expressed primarily by odontoblast cells, but is also transiently expressed by presecretory ameloblasts. Because of this expression profile it appears that dentin sialophosphoprotein contributes to the early events of amelogenesis, and in particular to those events that result in the formation of the dentino-enamel junction and the adjacent "aprismatic" enamel. Using a transgenic animal approach we have extended dentin sialoprotein or dentin phosphoprotein expression throughout the developmental stages of amelogenesis. Overexpression of dentin sialoprotein results in an increased rate of enamel mineralization, however, the enamel morphology is not significantly altered. In wild-type animals, the inclusion of dentin sialoprotein in the forming aprismatic enamel may account for its increased hardness properties, when compared with bulk enamel. In contrast, the overexpression of dentin phosphoprotein creates "pitted" and "chalky" enamel of non-uniform thickness that is more prone to wear. Disruptions to the prismatic enamel structure are also a characteristic of the dentin phosphoprotein overexpressing animals. These data support the previous suggestion that dentin sialoprotein and dentin phosphoprotein have distinct functions related to tooth formation, and that the dentino-enamel junction should be viewed as a unique transition zone between enamel and the underlying dentin. These results support the notion that the dentin proteins expressed by presecretory ameloblasts contribute to the unique properties of the dentino-enamel junction.

Colocalization of dentin matrix protein 1 and dentin sialoprotein at late stages of rat molar development

Dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP) are acidic proteins found in the extracellular matrices of bones and teeth. Recent data from gene knockouts, along with those of gene mutations, indicate that these two phosphoproteins are critical for bone and tooth development and/or maintenance. However, the precise functions of the two proteins have not been elucidated. In order to gain insights into their functions in tooth formation, we performed systematic, comparative investigations on the immunolocalization of DMP1 and dentin sialoprotein (DSP, a cleaved fragment of DSPP), using the rat first molar at different developmental stages as a model. Immunohistochemistry (IHC) was performed with specific, monoclonal antibodies against the COOH-terminal fragments of DMP1 and against DSP. In 1-day- and 1-week-old rats, weak immunoreactions for DMP1 were observed in dentinal tubules while stronger reactions for DSP were seen in the tubules and predentin. In rats older than 2 weeks, immunoreactions for DMP1 were found in dentinal tubules, predentin and odontoblasts. In 5-week- and 8-week-old rats, strong immunoreactions for DMP1 were widely distributed in odontoblasts and predentin. The distribution pattern of DSP was strikingly similar to that of DMP1 after 2 weeks and the localization of each was distinctly different from that of bone sialoprotein (BSP). The unique colocalization of DMP1 and DSPP in tooth development suggests that the two proteins play complementary and/or synergistic roles in formation and maintenance of healthy teeth.

Effects of dexamethasone, vitamin A and vitamin D3 on DSP-PP mRNA expression in rat tooth organ culture

Vitamin A, 1,25-dihydroxyvitamin D3 and dexamethasone are well-characterized hydrophobic molecules whose biological actions are mediated via different members of the nuclear hormone receptor family. We report here their actions on tooth formation at the molecular level. We have tested the effects of these compounds on osteopontin (OPN), dentin sialoprotein (DSP-PP), and collagen type I expression in pre-mineralization and mineralization stage rat tooth organ cultures which mirror in vivo developmental patterns. These proteins are all believed to participate in the mineralization of dentin. 1,25-Dihydroxyvitamin D3 up-regulated OPN, but had no effect on DSP-PP mRNA expression. Vitamin A up-regulated DSP-PP expression as did dexamethasone. Dexamethasone also up-regulated collagen type I expression. Our results suggest that 1,25-dihydroxyvitamin D3 does not modulate dentin mineralization by directly affecting DSP-PP expression. Vitamin A likely contributes to dentin mineralization by up-regulating DSP-PP expression. Finally, the up-regulation of DSP-PP expression in tooth germ cultures treated with dexamethasone suggests that its application to patient's dental pulp might promote increased extracellular matrix synthesis and mineralization in the pulp and may explain the narrowing of the dental pulp cavity in patients undergoing long-term dexamethasone administration.

Immunohistochemical characterization of rapid dentin formation induced by enamel matrix derivative

The purpose of this study was to examine the pulpal expression of dentin-related proteins during enamel matrix derivative (EMD)-induced reparative dentin formation in a pulpotomy model in pig incisors. Pulpotomies were performed on 72 lower incisors in 24 adult miniature swine. The exposed pulp tissue was treated with EMD or covered with a calcium hydroxide paste (Dycal). At predefined time-points, ranging from 4 days to 12 weeks, experimental teeth were extracted and examined by use of light microscopy, and expression of dentin-related proteins in the pulps was investigated by immunohistochemistry, using antibodies against type I collagen, dentin sialoprotein (DSP), sheathlin, and EMD. In all EMD-treated teeth a substantial amount of reparative dentin formation was observed. The amount of reparative dentin in calcium hydroxide-treated teeth was significantly smaller than in EMD-treated teeth (P < 0.005) and was less effective in bridging the pulpal wounds. Immunohistochemistry demonstrated that enamel matrix proteins were present in detectable amounts at the application site for about 4 weeks. Moreover, the expression of proteins related to dentin formation in the wounded pulp tissue was about 2 weeks advanced in EMD-treated teeth. These findings demonstrate that enamel matrix molecules have the capacity to induce rapid pulpal wound healing in pulpotomized teeth, and suggest that the longevity and continued presence of enamel matrix macromolecules at the application site can be utilized to stimulate growth and repair of dentin over a period consistent with a favorable clinical outcome.

Regulation of the Cell Type-specific dentin sialophosphoprotein gene expression in mouse odontoblasts by a novel transcription repressor and an activator CCAAT-binding factor

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) with a highly restricted expression pattern in tooth and bone. Mutations of the DSPP gene are associated with dentin genetic diseases. Regulation of tissue-specific DSPP expression has not been described. To define the molecular basis of this cell-specific expression, we characterized the promoter responsible for the cell-specific expression of the DSPP gene in odontoblasts. Within this region, DNase I footprinting and electrophoretic mobility shift assays delineated one element that contains an inverted CCAAT-binding factor site and a protein-DNA binding site using nuclear extracts from odontoblasts. A series of competitive electrophoretic mobility shift assay analyses showed that the protein-DNA binding core sequence, ACCCCCA, is a novel site sufficient for protein binding. These two protein-DNA binding sequences are conserved at the same proximal position in the mouse, rat, and human DSPP gene promoters and are ubiquitously present in the promoters of other tooth/bone genes. Mutations of the CCAAT-binding factor binding site resulted in a 5-fold decrease in promoter activity, whereas abolishment of the novel protein-DNA binding site increased promoter activity by about 4.6-fold. In contrast to DSPP, expression levels of the novel protein were significantly reduced during odontoblastic differentiation and dentin mineralization. The novel protein was shown to have a molecular mass of 72 kDa. This study shows that expression of the cell type-specific DSPP gene is mediated by the combination of inhibitory and activating mechanisms.

Detection of dentin sialoprotein in rat periodontium

Cloning and sequencing of the cDNA indicates that dentin sialophosphoprotein (DSPP) is a precursor of both dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Dentin sialophosphoprotein must be proteolytically processed to form these two extracellular matrix (ECM) proteins. Numerous studies led us to conclude that DSP (and DSPP) are exclusively expressed by odontoblasts and preameloblasts. However, recent observations suggest a wider distribution. To test this hypothesis, we conducted systematic studies on rat first molar during root formation with immunohistochemical techniques using specific anti-DSP polyclonal and monoclonal antibodies. We also performed in situ hybridization, using high-stringency RNA probes to detect DSP transcripts. Immunohistochemical studies demonstrated that DSP is not only localized in odontoblasts, dentin ECM and preameloblasts, but also in alveolar bone, cellular cementum, osteocytes, cementocytes, and their matrices. The results of in situ hybridization were consistent with those from immunohistochemistry, showing the expression of DSP transcripts in osteoblasts of alveolar bone, fibroblasts in periodontal ligament and cementoblasts in cellular cementum. Together, these observations suggest that DSP is involved in formation of the periodontium as well as tooth structures.

Development of an odontoblast in vitro model to study dentin mineralization

The aim of the present work was to characterize the odontoblastic proliferation, differentiation, and matrix mineralization in culture of the recently established M2H4 rat cell line. Proliferation was assessed by cell counts, differentiation by RT-PCR analysis, and mineralization by alizarin red staining, atomic absorption spectrometry, and FTIR microspectroscopy. The results showed that M2H4 cell behavior closely mimics in vivo odontoblast differentiation, with, in particular, temporally regulated expression of DMP-1 and DSPP. Moreover, the mineral phase formed by M2H4 cells was similar to that in dentin from rat incisors. Finally, because in mice, transforming growth factor (TGF)-beta1 over-expression in vivo leads to an hypomineralization similar to that observed in dentinogenesis imperfecta type II, effects of TGF-beta1 on mineralization in M2H4 cell culture were studied. Treatment with TGF-beta1 dramatically reduced mineralization, whereas positive control treatment with bone morphogenetic protein-4 enhanced it, suggesting that M2H4 cell line is a promising tool to explore the mineralization mechanisms in physiopathologic conditions.

mRNA expression and protein localization of dentin matrix protein 1 during dental root formation

Dentin matrix protein 1 (DMP1) is an acidic phosphoprotein. DMP1 was initially detected in dentin and later in other mineralized tissues including cementum and bone, but the DMP1 expression pattern in tooth is still controversial. To determine the precise localization of DMP1 messenger RNA (mRNA) and the protein in the tooth, we performed in situ hybridization and immunohistochemical analyses using rat molars and incisors during various stages of root formation. During root dentin formation of molars, DMP1 mRNA was detected in root odontoblasts in parallel with mineralization of the dentin. However, the level of DMP1 mRNA expression in root odontoblasts decreased near the coronal part and was absent in coronal odontoblasts. DMP1 protein was localized along dentinal tubules and their branches in mineralized root dentin, and the distribution of DMP1 shifted from the end of dentinal tubules to the base of the tubules as dentin formation progressed. During the formation of the acellular cementum, DMP1 mRNA was detected in cementoblasts lining the acellular cementum where its protein was localized. During the formation of the cellular cementum, DMP1 mRNA was detected in cementocytes embedded in the cellular cementum but not in cementoblasts, and its protein was localized in the pericellular cementum of cementocytes including their processes. During dentin formation of incisors, DMP1 mRNA was detected in odontoblasts on the cementum-related dentin, where its protein was localized along dentinal tubules near the mineralization front. The localization of DMP1 mRNA and protein in dentin and cementum was related to their mineralization, suggesting that one of the functions of DMP1 may be involved in the mineralization of dentin and cementum during root formation.

Extracellular matrix proteins and the dynamics of dentin formation

Dentinogenesis involves controlled reactions that result in conversion of unmineralized predentin to dentin when apatite crystals are formed. This process is dynamic: Maturation events occur within predentin beginning at the proximal layer and progressing to the predentin-dentin (PD) border. One type of controlled reaction is the proteolytic processing of dentin sialophosphoprotein (DSPP) to dentin sialoprotein (DSP) and dentin phosphoprotein (DPP), by cleavage of at least three highly conserved peptide bonds. We postulate that this processing event represents an activation step, resulting in release of DPP, which is active in its effects on formation and growth of apatite crystals. Dentin matrix protein 1 (DPM1), present as a processed fragment (57-kD protein) in bone, is seen in dentin on sodium dodecyl sulfate polyacrylamide gel electrophoresis as one intact protein of 150-200 kD. Anti-57-kD antibodies elicit immunoreactivity in bone, dentin, and cellular cementum. In bone, the reactivity is associated with osteocytes and their cell processes. Similarly, dentin shows reactivity in odontoblasts, predentin, and the odontoblast processes. In summary, the processing of large sialic acid-rich proteins into smaller fragments may be an important part of the controlled conversion of predentin to dentin and osteoid to bone.