A novel splice acceptor mutation in the DSPP gene causing dentinogenesis imperfecta type II.

Dentin sialophosphoprotein (DSPP), a typical dentin-specific protein, is mainly expressed in the dentin extracellular matrix and plays a role in dentin mineralization. BMP-2 provides a strong signal for differentiation and mineralization of odontoblasts and osteoblasts. Previously, BMP-2 treatment is reported to stimulate Dspp expression in the MD10-F2 pre-odontoblast cells through activation of the heterotrimeric transcription factor Y (NF-Y). The canonical BMP signaling pathway is known to contribute greatly to biomineralization, however, it is not known whether it is involved in Dspp expression. Here, we investigated this question. Activation of the canonical BMP-2 signaling pathway in MDPC-23, preodontoblast cell, by overexpression of constitutively active Smad1/5 or downstream transcription factors Dlx5 and Runx2 stimulated Dspp expression. Conversely, knockdown of each element with siRNA significantly blocked the BMP-2-induced Dspp expression. To test whether these transcription factors downstream of BMP-2 are directly involved in regulating Dspp, we analyzed the mouse Dspp promoter. There are 5 well conserved homeodomain binding elements, H1 to H5, in Dspp proximal promoter regions (-791 to +54). A serial deletion of H1 and H2 greatly changed basal promoter activity and responsiveness to Dlx5 or Msx2. However, further deletions did not change the responsiveness to Dlx5 or Msx2. H1 and H2 sites can be suggested as specific response elements of Dlx5 and Msx2, respectively, based on their promoter activity modulation. Thus, the canonical BMP-2 signaling pathway plays a crucial part in the regulation of Dspp expression through the action of Smads, Dlx5, Runx2, and Msx2.

Dentin sialoprotein and dentin phosphoprotein have distinct roles in dentin mineralization

A rare compound mutation involving a 36 bp deletion and 18 bp insertion within exon 5 of the dentin sialophosphoprotein (DSPP) gene has been identified in a family with dentinogenesis imperfecta type III (DGI-III). The DSPP gene encodes two major tooth matrix proteins dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). DSPP mutations associated with DGI-III results in an in frame truncation of the serine aspartic acid triplet repeat found in DPP near the highly conserved carboxyl terminal region shortening the protein by six amino acids. Clinically this family presents with discolored amber opalescent teeth and severe attrition of the tooth structure. This study is the first report of a mutation within DPP associated with a genetic dentin disease. Our study indicates that DGI-III is allelic with some forms of DGI-II with and without progressive hearing loss and dentin dysplasia type II that have been shown to be caused by mutations within the DSP coding or signal peptide regions.

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.

Dentinogenesis and Dentin Sialophosphoprotein (DSPP)

By the Shields classification, articulated over 30 years ago, inherited dentin defects are divided into 5 types: 3 types of dentinogenesis imperfecta (DGI), and 2 types of dentin dysplasia (DD). DGI type I is osteogenesis imperfecta (OI) with DGI. OI with DGI is caused, in most cases, by mutations in the 2 genes encoding type I collagen. Many genes are required to generate the enzymes that catalyze collagen's diverse post-translational modifications and its assembly into fibers, fibrils, bundles, and networks. Rare inherited diseases of bone are caused by defects in these genes, and some are occasionally found to include DGI as a feature. Appreciation of the complicated genetic etiology of DGI associated with bony defects splintered the DGI type I description into a multitude of more precisely defined entities, all with their own designations. In contrast, DD-II, DGI-II, and DGI-III, each with its own pattern of inherited defects limited to the dentition, have been found to be caused by various defects in DSPP (dentin sialophosphoprotein), a gene encoding the major non-collagenous proteins of dentin. Only DD-I, an exceedingly rare condition featuring short, blunt roots with obliterated pulp chambers, remains untouched by the revolution in genetics, and its etiology is still a mystery. A major surprise in the characterization of genes underlying inherited dentin defects is the apparent lack of roles played by the genes encoding the less-abundant non-collagenous proteins in dentin, such as dentin matrix protein 1 (DMP1), integrin-binding sialoprotein (IBSP), matrix extracellular phosphoglycoprotein (MEPE), and secreted phosphoprotein-1, or osteopontin (SPP1, OPN). This review discusses the development of the dentin extracellular matrix in the context of its evolution, and discusses the phenotypes and clinical classifications of isolated hereditary defects of tooth dentin in the context of recent genetic data respecting their genetic etiologies.

Dentin sialophosphoprotein (DSPP) is critical for proper mineralization of tooth dentin, and mutations in DSPP cause inherited dentin defects. Dentin phosphoprotein (DPP) is the C-terminal cleavage product of DSPP that binds collagen and induces intrafibrillar mineralization. We isolated DPP from individual pigs and determined that its N-terminal and C-terminal domains are glycosylated and that DPP averages 155 phosphates per molecule. Porcine DPP is unstable at low pH and high temperatures, and complexing with collagen improves its stability. Surprisingly, we observed DPP size variations on SDS-PAGE for DPP isolated from individual pigs. These variations are not caused by differences in proteolytic processing or degrees of phosphorylation or glycosylation, but rather to allelic variations in Dspp. Characterization of the DPP coding region identified 4 allelic variants. Among the 4 alleles, 27 sequence variations were identified, including 16 length polymorphisms ranging from 3 to 63 nucleotides. None of the length variations shifted the reading frame, and all localized to the highly redundant region of the DPP code. The 4 alleles encode DPP domains having 551, 575, 589, or 594 amino acids and completely explain the DPP size variations. DPP length variations are polymorphic and are not associated with dentin defects.

Dentin sialophosphoprotein (DSPP) plays an important role in the mineralization of both dentin and bones. The Dspp null mice developed periodontal diseases. Patients with DSPP mutations have dentinogenesis imperfecta (DGI), but very little is known about their bone characteristics. This study aims to characterize alveolar bone cells of a DGI patient with DSPP mutation. Pathogenic variants were identified by whole exome and sanger sequencing. Cells isolated from the alveolar bones of a DSPP patient were investigated for their characteristics including cell morphology, attachment, spreading, proliferation, colony formation, mineralization, and osteogenic differentiation. We identified a Thai family with three members affected with autosomal dominant DGI harboring a heterozygous pathogenic missense mutation, c.50C > T, p.P17L, in exon 2 of the DSPP gene. The patients' phenotypes presented deteriorated opalescent teeth with periapical lesions, thickening of lamina dura, furcation involvement, alveolar bone loss, and bone exostoses. The alveolar bone cells isolated from DSPP patient exhibited compromised proliferation and colony formation. Scanning electron microscope revealed altered cellular morphology and spreading. The DSPP cells showed deviated mRNA levels of OCN, ALP, and COL1 but maintained in vitro mineralization ability compared to the control. We demonstrate that the DSPP p.P17L mutant alveolar bone cells had compromised cell spreading, proliferation, colony formation, and osteogenic induction, suggesting abnormal bone characteristics in the patient with DGI caused by DSPP mutation. DSPP mutation can induce the behavior alterations of alveolar bone cells.

A Dentin Sialophosphoprotein Mutation That Partially Disrupts a Splice Acceptor Site Causes Type II Dentin Dysplasia

The present study is aimed at investigating the effects of the exogenous estrogen 17β-estradiol (E2) on odontoblastic differentiation in human dental pulp cells (HDPCs) immotalized with hTERT gene and their molecular mechanism. Proliferation was detected by BrdU assay, and odontoblast differentiation induction was evaluated by the expression of dentin sialophosphoprotein (DSPP), dentin sialoprotein (DSP) and dentin matrix protein1 (DMP1), and alkaline phosphatase (ALP) activity and mineralization. Estrogen receptor-α (ER-α), c-Src, and mitogen-activated protein kinases (MAPKs) were examined and their inhibitors were used to determine the roles on odontogenic induction. E2 significantly promoted the HDPC proliferation, which was mediated by extracellular signal-related kinase 1/2. E2 upregulated DSPP, DSP, and DMP1 as the odontogenic differentiation markers and enhanced ALP activity and mineralization. E2 increased phosphorylation of ER-α and fulvestrant, an ER downregulator, significantly downregulated DSPP, DMP1, and DSP induced by E2. Moreover, E2 treatment activated c-Src and MAPKs upon odontogenic induction, whereas chemical inhibition of c-Src and MAPKs decreased expression of DSPP, DMP1, and DSP and mineralization augmented by E2. Moreover, fulvestrant reduced E2-induced phosphorylation of c-Src and MAPK and inhibition of c-Src by PP2 attenuated activation of MAPKs during E2-induced odontoblastic differentiation. Taken together, these results indicated that E2 stimulates odontoblastic differentiation of HDPCs via coordinated regulation of ER-α, c-Src, and MAPK signaling pathways, which may play a key role in the regeneration of dentin.

Dentin sialophosphoprotein (DSPP) gene mutations cause autosomal dominantly inherited diseases.DSPPgene mutations lead to abnormal expression of DSPP, resulting in a series of histological, morphological, and clinical abnormalities. A large number of previous studies demonstrated that DSPP is a dentinal-specific protein, andDSPPgene mutations lead to dentin dysplasia and dentinogenesis imperfecta. Recent studies have found that DSPP is also expressed in bone, periodontal tissues, and salivary glands. DSPP is involved in the formation of the periodontium as well as tooth structures. DSPP deficient mice present furcation involvement, cementum, and alveolar bone defect. We speculate that similar periodontal damage may occur in patients withDSPPmutations. This article reviewed the effects ofDSPPgene mutations on periodontal status. However, almost all of the research is about animal study, there is no evidence thatDSPPmutations cause periodontium defects in patients yet. We need to conduct systematic clinical studies onDSPPmutation families in the future to elucidate the effect ofDSPPgene on human periodontium.

Dentin defects represent a cluster of relatively rare heritable disorders affecting the formation and mineralization of dentin. Major clinical features include loss of enamel with extreme wear of exposed dentin, opalescent tooth discoloration, short roots with pulpal calcification and increased tooth mobility, and frequent periapical radiolucencies. Historically, these inherited conditions have been classified by Shields et al. (1) as either dentinogenesis imperfecta (DGI) types I, II and III, or dentin dysplasia (DD) types I and II. DGI type I is now universally designated as osteogenesis imperfecta with dentinogenesis imperfecta (OI/DGI) and is caused by type I collagen mutations. Among the genes expressing the non‐collagenous proteins in dentin, only the DSPP gene has been implicated in the etiology of DD type II and all DGI types, suggesting that heritable dentin defects can be viewed as a continuum rather than as distinct disease entities. Dental treatment strategies should aim to preserve the affected dentitions by protecting teeth from wear, restoring them to compliance with the specific structural characteristics of the defective dentin, and anticipating early tooth loss. Endodontic treatment of the affected teeth is very challenging because of the peculiar pulp morphology and most often has poor prognosis. If conventional therapy is not an option, periapical curettage and retrograde filling is a possible alternative, except in the case of teeth with short roots.

The present study aims to investigate the mutation in a Chinese family with dentin dysplasia type II (DD-II) and to summarize mutation hotspots, clinical manifestations, and disease management strategies. Phenotype analysis, clinical intervention, mutation screening, and cosegregation analysis within the enrolled family were performed. A summary of the reported mutations in the dentin phosphoprotein (DPP) region of dentin sialophosphoprotein (DSPP) was analyzed. Pathogenicity prediction analysis of the physical properties and function of DSPP variants was performed by bioinformatic processing. Clinical management strategies are discussed. A novel pathogenic mutation (c.2035delA) in the DPP region of DSPP was identified, which was cosegregated in the family. The immature permanent teeth of patients with DD-II presented with X-shaped root canal phenotypes. Most of the identified mutations for DD-II were clustered in the DPP region between nucleotides 1686-2134. Points of differential diagnosis, clinical interventions, and management strategies are proposed. This study revealed a novel DSPP frameshift mutation and presented new clinical features of DD-II. The locus involving nucleotides 1686-2134 of DSPP may represent a mutational hotspot for the disease. Appropriate management of DD-II at different stages is important to avoid the development of secondary dental lesions.

Premature loss (early loss) of primary teeth will disrupt the eruption of permanent teeth due to reduced space for eruption of the permanent teeth. Lack of space causes permanent teeth to erupt outside the correct dental arch, or push against neighboring teeth causing malocclusion in children. Dental caries is one of the main factors causing premature loss of primary teeth, especially in children with low levels of oral hygiene. Children with disabilities tend to have higher rates of dental caries and premature loss of teeth than children without disabilities. The role of parents is much greater in maintaining dental and oral health, considering the limitations of children to carry out dental and oral care independently. The low awareness and attitude of parents in an effort to maintain primary teeth is influenced by the wrong stigma that primary teeth will be replaced by permanent teeth so that there is no need for optimal care or maintenance. This study aims to describe the level of knowledge, attitudes, and behavior of parents of children with special needs regarding the importance of the role of children's primary teeth in the Special Elementary School (SDLB) Surabaya. This type of research is observational analytic with a cross-sectional approach. The results obtained in this study are 44.6% of respondents have a fairly good knowledge, 58.4% of respondents have a fairly good attitude, and 37.6% of respondents in the category of behavior are quite good.

The study of cell-to-cell interaction in experimental co-culture systems is very important and relevant to the context of biomaterial scaffolds used for tissue regeneration. In this study, scaffolds, which allow direct and indirect cell-to-cell contact and separation of each cell type, were developed using one of the most utilized biopolymer, poly-D, L-lactide (PDLLA). The assembled scaffold had enough mechanical strength to withstand experiments and maintain its shape. It is separated easily into core and outer portion for further experiments, which could be conducted to examine the effects of co-culture. Co-culture with dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) increased proliferation of both cell types and dentin sialophosphoprotein (DSPP) mRNA expression in co-cultured PDLSCs. In immunohistochemical examination, dentin sialoprotein (DSP) expression in both cell types was up-regulated in co-culture compared to that of mono-culture. The longer the culture period, the more DSP expressions were up-regulated. Osteopontin (OPN) expression in both cell types was also up-regulated in co-culture. Co-culture of dental stem cells improved cell proliferation and osteogenic differentiation. This study demonstrates that biomimetic co-culture method for tooth tissue engineering may be potentially applied to study dental stem cell behavior in tooth regenerative medicine.