Promotion of selective cell attachment by the RGD sequence in dentine matrix protein 1

Advances in antimicrobial hydrogels for dental tissue engineering: regenerative strategies for endodontics and periodontics

Dental tissue infections have been affecting millions of patients globally leading to pain, severe tissue damage, or even tooth loss. Commercial sterilizers may not be adequate to prevent frequent dental infections. Antimicrobial hydrogels have been introduced as an effective therapeutic strategy for endodontics and periodontics since they have the capability of imitating the native extracellular matrix of soft tissues. Hydrogel networks are considered excellent drug delivery platforms due to their high-water retention capacity. In this regard, drugs or nanoparticles can be incorporated into the hydrogels to endow antimicrobial properties as well as to improve their regenerative potential, once biocompatibility criteria are met avoiding high dosages. Herein, novel antimicrobial hydrogel formulations were discussed for the first time in the scope of endodontics and periodontics. Such hydrogels seem outstanding candidates especially when designed not only as simple volume fillers but also as smart biomaterials with condition-specific adaptability within the dynamic microenvironment of the defect site. Multifunctional hydrogels play a pivotal role against infections, inflammation, oxidative stress, etc. along the way of dental regeneration. Modern techniques (e.g., 3D and 4D-printing) hold promise to develop the next generation of antimicrobial hydrogels together with their limitations such as infeasibility of implantation.

Cloning, purification and characterization of human dentine matrix protein 1(DMP1)

Introduction

Human teeth are composed mainly of dentin, formed by the odontoblasts. Dentin matrix protein 1 (DMP1) is one of odontoblast differentiation's most important growth factors. Human DMP1 has yet to be completely identified or studied. This study aimed to clone and characterize human DMP1.

Materials and methods

The DMP1 gene sequence was prepared and cloned by transfection of human 293 cells.

Results

The recombinant DMP1 was purified and characterized.

Conclusion

The results suggested its future use in dental tissue regeneration and tissue engineering.

DMP1 and IFITM5 Regulate Osteogenic Differentiation of MC3T3-E1 on PEO-Treated Ti-6Al-4V-Ca2+/Pi surface

Despite numerous studies on various surface modifications on titanium and its alloys, it remains unclear what kind of titanium-based surface modifications are capable of controlling cell activity. This study aimed to understand the mechanism at the cellular and molecular levels and investigate the in vitro response of osteoblastic MC3T3-E1 cultured on the Ti-6Al-4V surface modified by plasma electrolytic oxidation (PEO) treatment. A Ti-6Al-4V surface was prepared by PEO at 180, 280, and 380 V for 3 or 10 min in an electrolyte containing Ca²⁺/P_i ions. Our results showed that PEO-treated Ti-6Al-4V-Ca²⁺/P_i surfaces enhanced the cell attachment and differentiation of MC3T3-E1 compared to the untreated Ti-6Al-4V control but did not affect cytotoxicity as shown by cell proliferation and cell death. Interestingly, on the Ti-6Al-4V-Ca²⁺/P_i surface treated by PEO at 280 V for 3 or 10 min, MC3T3-E1 showed a higher initial adhesion and mineralization. In addition, the alkaline phosphatase (ALP) activity significantly increased in MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i (280 V for 3 or 10 min). In RNA-seq analysis, the expression of dentin matrix protein 1 (DMP1), sortilin 1 (Sort1), signal-induced proliferation-associated 1 like 2 (SIPA1L2), and interferon-induced transmembrane protein 5 (IFITM5) was induced during the osteogenic differentiation of MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i. DMP1 and IFITM5 silencing decreased the expression of bone differentiation-related mRNAs and proteins and ALP activity in MC3T3-E1. These results suggest that the PEO-treated Ti-6Al-4V-Ca²⁺/P_i surface induces osteoblast differentiation by regulating the expression of DMP1 and IFITM5. Therefore, surface microstructure modification through PEO coatings with Ca²⁺/P_i ions could be used as a valuable method to improve biocompatibility properties of titanium alloys.

Use of phosphorylated PAMAM and carboxyled PAMAM to induce dentin biomimetic remineralization and dentinal tubule occlusion

It is crucial to emphasize the biomineralization therapeutic method to repair etched dentin in clinic. Non-collagenous proteins (NCPs) play critical role in the biomineralization of dentine. In this paper, we synthesized the phosphate-terminated polyamidoamine dendrimer (PAMAM-PO₃H₂) by one-step modification successfully and examined by Fourier-transform infrared spectroscopy (FTIR) and ¹H-nuclear Magnetic Resonance (¹H-NMR) to characterize the structure of PAMAM-PO₃H₂. PAMAM-PO₃H₂ and carboxylterminated dendrimers (PAMAM-COOH) were applied as the dual biomimetic analogs of NCPs. Through the characterization of FT-IR, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), the surfaces of human dentin were covered with regenerated crystals and the dentinal tubules were occluded by PAMAM-PO₃H₂ and PAMAM-COOH. In summary, the combination of PAMAM-PO₃H₂ and PAMAM-COOH may be another feasible therapeutic method for the treatment of dentin caries and dentin hypersensitivity.

A Novel 3D Osteoblast and Osteocyte Model Revealing Changes in Mineralization and Pro-osteoclastogenic Paracrine Signaling During Estrogen Deficiency

Recent in vitro studies have revealed that the mechanobiological responses of osteoblasts and osteocytes are fundamentally impaired during estrogen deficiency. However, these two-dimensional (2D) cell culture studies do not account for in vivo biophysical cues. Thus, the objectives of this study are to (1) develop a three-dimensional (3D) osteoblast and osteocyte model integrated into a bioreactor and (2) apply this model to investigate whether estrogen deficiency leads to changes in osteoblast to osteocyte transition, mechanosensation, mineralization, and paracrine signaling associated with bone resorption by osteoclasts. MC3T3-E1s were expanded in media supplemented with estrogen (17β-estradiol). These cells were encapsulated in gelatin-mtgase before culture in (1) continued estrogen (E) or (2) no further estrogen supplementation. Constructs were placed in gas permeable and water impermeable cell culture bags and maintained at 5% CO2 and 37°C. These bags were either mechanically stimulated in a custom hydrostatic pressure (HP) bioreactor or maintained under static conditions (control). We report that osteocyte differentiation, characterized by the presence of dendrites and staining for osteocyte marker dentin matrix acidic phosphoprotein 1 (DMP1), was significantly greater under estrogen withdrawal (EW) compared to under continuous estrogen treatment (day 21). Mineralization [bone sialoprotein (BSP), osteopontin (OPN), alkaline phosphatase (ALP), calcium] and gene expression associated with paracrine signaling for osteoclastogenesis [receptor activator of nuclear factor kappa-β ligand (RANKL)/osteoprotegerin OPG ratio] were significantly increased in estrogen deficient and mechanically stimulated cells. Interestingly, BSP and DMP-1 were also increased at day 1 and day 21, respectively, which play a role in regulation of biomineralization. Furthermore, the increase in pro-osteoclastogenic signaling may be explained by altered mechanoresponsiveness of osteoblasts or osteocytes during EW. These findings highlight the impact of estrogen deficiency on bone cell function and provide a novel in vitro model to investigate the mechanisms underpinning changes in bone cells after estrogen deficiency.

Recombinant Human Dentin Matrix Protein 1 (hDMP1) Expressed in Nicotiana benthamiana Potentially Induces Osteogenic Differentiation

Inductive molecules are critical components for successful bone tissue engineering. Dentin matrix protein-1 (DMP1), a non-collagenous protein in the bone matrix, has been shown to play roles in osteogenic differentiation and phosphate homeostasis. This study aimed to produce recombinant human dentin matrix protein-1 (hDMP1) in Nicotiana benthamiana and investigated the ability of this plant-produced DMP1 to induce osteogenesis in human periodontal ligament stem cells (hPDLSCs). The hDMP1 gene was cloned into the geminiviral vector for transient expression in N. benthamiana. We found that hDMP1 was transiently expressed in N. benthamiana leaves and could be purified by ammonium sulphate precipitation followed by nickel affinity chromatography. The effects of hDMP1 on the induction of cell proliferation and osteogenic differentiation were investigated. The results indicated that plant-produced hDMP1 could induce the cell proliferation of hPDLSCs and increase the expression levels of osteogenic genes, including osterix (OSX), type I collagen (COL1), bone morphogenetic protein-2 (BMP2), and Wnt3a. Moreover, the plant-produced hDMP1 promoted calcium deposition in hPDLSCs as determined by alizarin red S staining. In conclusion, our results indicated that plant-produced hDMP1 could induce osteogenic differentiation in hPDLSCs and could potentially be used as a bone inducer in bone tissue engineering.

Recombinant human dentin matrix protein 1 (DMP1) induces the osteogenic differentiation of human periodontal ligament cells

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Recombinant human dentin matrix protein 1 (DMP1) can be produced in Escherichia coli.

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E. coli produced DMP1 could induce the expression of osteogenic-related genes and calcium deposition in human PDL cells.

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This protein has potential to use for improving tooth repair and regeneration in the future.

The study aimed to produce recombinant human dentin matrix protein 1 (DMP1) and to test, whether the recombinant DMP1 produced in Escherichia coli possesses functional activity. A gene construction comprising a gene encoding for DMP1 protein with polyhistidine sequence at its C-terminus was created using the pET22b plasmid and expressed in E. coli. The optimization of cultivation conditions has enabled the induction of the gene expression with 0.5 mM isopropyl β-D-1-thiogalactopyranoside (IPTG) and DMP1 recombinant protein production at 37 °C for 6 h. The recombinant protein was purified using Ni affinity chromatography. DMP1 influence on the viability, osteogenic differentiation and calcification of human periodontal ligament (PDL) cells was examined. The purified DMP1 could induce the expression of osteogenesis related genes and calcium deposition in PDL cells. These findings indicate that DMP1 produced in E. coli can induce the osteogenic differentiation of human PDL cells, leading to improved tooth repair and regeneration.

The Role of Nephronectin on Proliferation and Differentiation in Human Dental Pulp Stem Cells

Aim

The purpose of the current study was to investigate the effects of nephronectin (Npnt) in human dental pulp stem cells (hDPSCs).

Methodology

Npnt was coated to nontissue culture-treated polystyrene (non-PS) plates. The presence of immobilized protein on the surface was detected by polyclonal rabbit primary anti-Npnt antibody. Then the cell number was counted and compared with PBS-, bovine serum albumin- (BSA-), fish scale type I collagen- (FCOL1-), and human fibronectin- (Fn-) coated wells. Cell proliferation was assessed using CCK-8 assay. Cell morphology was observed under light microscopy and fluorescence microscopy. Lastly, the mRNA expression profiles of integrins, dentin sialophosphoprotein (DSPP), bone sialoprotein (BSP), and mineralization capacity of hDPSCs were investigated by real time RT-PCR and alizarin red staining, respectively.

Results

Npnt mediates hDPSC adhesion and spreading partially via the Arg-Gly-Asp (RGD) motif. Npnt enhanced the mRNA expression of ITGA1, ITGA4, ITGA7, and ITGB1 on day five. Npnt downregulated DSPP but significantly upregulated BSP mRNA expression at day 28. Further, Npnt and FCOL1 accelerated the matrix mineralization in hDPSCs.

Conclusions

The current findings implicate that Npnt would be favorable to recruit hDPSCs and conducive to mineralization in hDPSCs. The combination of Npnt with hDPSCs may offer a promising approach for hard tissue regeneration.

Tailored biomimetic hydrogel based on a photopolymerised DMP1/MCF/gelatin hybrid system for calvarial bone regeneration

Searching for effective osteoinduction factors with higher specificity and biosafety for the preparation of biomimetic materials, which mimic the natural bone extracellular matrix (ECM), seems to be an optimum strategy for achieving ideal bone regeneration.

Dentin Matrix Protein 1 (DMP1): New and Important Roles for Biomineralization and Phosphate Homeostasis

Previously, non-collagenous matrix proteins, such as DMP1, were viewed with little biological interest. The last decade of research has increased our understanding of DMP1, as it is now widely recognized that this protein is expressed in non-mineralized tissues, as well as in cancerous lesions. Protein chemistry studies have shown that the full length of DMP1, as a precursor, is cleaved into two distinct forms: the C-terminal and N-terminal fragments. Functional studies have demonstrated that DMP1 is essential in the maturation of odontoblasts and osteoblasts, as well as in mineralization via local and systemic mechanisms. The identification of DMP1 mutations in humans has led to the discovery of a novel disease: autosomal-recessive hypophosphatemic rickets. Furthermore, the regulation of phosphate homeostasis by DMP1 through FGF23, a newly identified hormone that is released from bone and targeted in the kidneys, sets a new direction for research that associates biomineralization with phosphate regulation.

GaAlAs laser-induced pulp mineralization involves dentin matrix protein 1 and osteopontin expression

OBJECTIVES

GaAlAs lasers induce pulp mineralization by promoting reparative dentinogenesis. This study analyzed the expression of dentin matrix protein 1 (DMP1) and osteopontin in GaAlAs laser-irradiated rat molars, to examine the hypothesis that these proteins play a role in the laser-induced reparative dentinogenic process.

MATERIALS AND METHODS

The mesial surfaces of the upper first molars of 8-week-old Wistar rats were irradiated with a pulsed GaAlAs laser. After 1-14 days, mRNA expression of DMP1 and osteopontin in the coronal pulp was analyzed using real-time PCR. DMP1, osteopontin, and heat shock protein 25 (HSP25) were immunolocalized at 1-21 days.

RESULTS

The pulp exhibited a degenerative zone in its mesial portion on days 1-3, and progressive formation of reparative dentin lined with HSP25-immunoreactive odontoblast-like cells, from day 7 onwards. DMP1 and osteopontin mRNA expression were significantly upregulated on days 1-7 and 3-7, respectively. From day 7 onwards, DMP1 and osteopontin immunoreactivity colocalized along the boundary between the primary and reparative dentin.

CONCLUSION

GaAlAs laser irradiation of rat molars induced upregulated DMP1 and osteopontin mRNA expression in the coronal pulp, followed by the formation of reparative dentin and the colocalization of DMP1 and osteopontin immunoreactivity at the site at which this tissue first appeared.

Effect of dentine phosphophoryn-derived RGD peptides on odontoblast-like cells

AIM

To investigate the effect of RGD peptides derived from dentine phosphophoryn (DPP) on odontoblast-like cell in terms of differentiation and mineralization.

METHODOLOGY

Mouse dental papilla cell line (MDPC-23), a rat odontoblast-like cell line, was used. Briefly, RGD peptides (RGD-1: SESDNNSSSRGDASYNSDES, RGD-2: ANSESDNNSSSRGDA, RGD-3: SRGDASYNSDESKD) were immobilized onto tissue culture polystyrene dishes (TCPS) assisted by carbodiimide chemistry. Surface characterization including carboxyl group quantification and amino acid analysis was carried out to ensure the existence of peptides on plates. Cells were inoculated to those peptides-modified and control dishes. Next, cell morphology was observed under phase contrast microscopy; cell numbers were counted manually using a hemocytometer. Furthermore, differentiation was examined by alkaline phosphatase (ALP) activity quantification, conventional and real-time RT-PCR. Finally, calcific deposition was observed by alizarin red staining and quantified using the cetylpyridinium chloride extraction method. Differences between the experimental groups and the control group were analysed statistically using one-way anova and Tukey's multiple comparison tests.

RESULTS

Peptides were immobilized onto TCPS successfully as evidenced by carboxyl group density and amino acid analysis. Cell morphology remained unchanged between peptides-immobilized groups and control, but adhered cell numbers were higher on those peptides-immobilized dishes (significant differences existed between RGD-1-0.5 with control, RGD-2-0.1 with control, and RGD-3-0.5 with control, respectively). RGD-3-0.5 exhibited the highest ALP activity on day 7 (P < 0.05) and promoted a twofold greater DMP-1 mRNA expression compared to the control on day 10 (P < 0.05). RGD peptides grafted dishes accelerated the mineralization of cells, amongst the experimental groups tested, RGD-3 groups (comprising RGD-3-0.1 and RGD-3-0.5) had significantly higher amounts of calcific deposition as compared to the control (P < 0.05).

CONCLUSIONS

RGD peptides originated from DPP especially RGD-3 promoted MDPC-23 differentiation and mineralization.

Dentin Matrix Proteins in Bone Tissue Engineering

Dentin and bone are mineralized tissue matrices comprised of collagen fibrils and reinforced with oriented crystalline hydroxyapatite. Although both tissues perform different functionalities, they are assembled and orchestrated by mesenchymal cells that synthesize both collagenous and noncollagenous proteins albeit in different proportions. The dentin matrix proteins (DMPs) have been studied in great detail in recent years due to its inherent calcium binding properties in the extracellular matrix resulting in tissue calcification. Recent studies have shown that these proteins can serve both as intracellular signaling proteins leading to induction of stem cell differentiation and also function as nucleating proteins in the extracellular matrix. These properties make the DMPs attractive candidates for bone and dentin tissue regeneration. This chapter will provide an overview of the DMPs, their functionality and their proven and possible applications with respect to bone tissue engineering.

Temporospatial localization of dentine matrix protein 1 following direct pulp capping with calcium hydroxide in rat molars

AIM

To examine the temporospatial expression of dentine matrix protein 1 (DMP1; a noncollagenous protein involved in mineralized tissue formation), osteopontin (another noncollagenous protein detected during reparative dentinogenesis) and nestin (a marker of differentiating/differentiated odontoblasts), following direct pulp capping with calcium hydroxide in rat molars.

METHODOLOGY

The maxillary first molars of 8-week-old Wistar rats had their pulps exposed and capped with calcium hydroxide. The pulp-capped teeth were collected from 6 h to 14 days postoperatively and processed for immunohistochemistry for DMP1, osteopontin and nestin. Cell proliferation was monitored using 5-bromo-2'-deoxyuridine (BrdU) labelling.

RESULTS

The capped pulps initially exhibited superficial necrotic changes followed by the formation of new matrix and its mineralization. DMP1 immunoreactivity was observed in the matrix beneath the necrotic layer from 6 h onwards and present in the outer portion of the newly formed mineralized matrix from 7 days onwards. Osteopontin displayed a similar expression pattern, although it occupied a narrower area than DMP1 at 6 and 12 h. Nestin-immunoreactive cells appeared beneath the DMP1-immunoreactive area at 1 day, were distributed beneath the newly formed matrix at 5 days and exhibited odontoblast-like morphology by 14 days. BrdU-positive cells significantly increased at 2 and 3 days (P < 0.05) and then decreased.

CONCLUSIONS

The deposition of DMP1 at exposed pulp sites preceded the appearance of nestin-immunoreactive cells, active cell proliferation and new matrix formation after pulp capping with calcium hydroxide in rat molars, suggesting that DMP1 acts as a trigger of pulp repair. The colocalization of DMP1 and osteopontin suggests that these two proteins play complementary roles.

Expression of Small Integrin-Binding LIgand N-linked Glycoproteins (SIBLINGs) in the reparative dentin of rat molars

AIM

To analyze the expression and distribution of Small Integrin-Binding LIgand N-linked Glycoproteins (SIBLINGs) in reparative dentin (RepD).

METHODOLOGY

Cavities on the mesial surfaces of rat molars were prepared to expose the pulp, and a calcium hydroxide agent was applied to cap the exposed pulp. The molars with pulp capping were extracted at postoperative 1, 2, and 4 weeks. The immunolocalization of four SIBLINGs, dentin matrix protein 1 (DMP1), dentin sialoprotein (DSP), bone sialoprotein (BSP), and osteopontin (OPN) in RepD, was analyzed in comparison with reactionary dentin (ReaD) and primary dentin (PD).

RESULTS

At two weeks after operation, the region of the exposed pulp formed a layer of reparative dentin bridge sealing the communication between the cavity and pulp chamber. Dentinal tubules in RepD were more irregular in shape and fewer in number than PD. At postoperative 2 and 4 weeks, RepD had lower levels of DMP1 and DSP than PD. BSP and OPN were present in RepD, but not in PD. RepD showed certain similarities to ReaD in the expression of SIBLINGs.

CONCLUSIONS

The reduced levels of DMP1 and DSP may be associated with the decreased number of dentinal tubules in RepD. The expression of BSP and OPN in RepD indicates that the odontoblast-like cells were attempting to produce a hard tissue at a very rapid pace. These findings suggest that in response to the surgical injury, the newly differentiated odontoblast-like cells altered their synthesis of the dentinogenesis-related proteins and produced a hard tissue that is an intermediate between dentin and bone.

The role of acidic phosphoproteins in biomineralization

Biomineralization is the process by which living organisms deposit mineral in the extracellular matrix. In nature, almost 50% of biominerals are calcium-bearing minerals. In addition to calcium, we find biominerals formed from silica and magnetite. Calcium-containing biominerals could be either calcium phosphate as in apatite found in vertebrates or calcium carbonate as in calcite and aragonite found in many invertebrates. Since all biomineralization is matrix mediated, an understanding of the nature of the proteins involved is essential in elucidating its mechanism. This review will discuss some of the proteins involved in the process of biomineralization involving calcium. Two proteins, dentin matrix protein 1 and dentin phosphoprotein (Phosphophoryn) will serve as models for the vertebrate system, and two others - P16 and phosphodontin will serve as models for the invertebrate system.

Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia

As broadly demonstrated for the formation of a functional skeleton, proper mineralization of periodontal alveolar bone and teeth - where calcium phosphate crystals are deposited and grow within an extracellular matrix - is essential for dental function. Mineralization defects in tooth dentin and cementum of the periodontium invariably lead to a weak (soft or brittle) dentition in which teeth become loose and prone to infection and are lost prematurely. Mineralization of the extremities of periodontal ligament fibers (Sharpey's fibers) where they insert into tooth cementum and alveolar bone is also essential for the function of the tooth-suspensory apparatus in occlusion and mastication. Molecular determinants of mineralization in these tissues include mineral ion concentrations (phosphate and calcium), pyrophosphate, small integrin-binding ligand N-linked glycoproteins and matrix vesicles. Amongst the enzymes important in regulating these mineralization determinants, two are discussed at length here, with clinical examples given, namely tissue-nonspecific alkaline phosphatase and phosphate-regulating gene with homologies to endopeptidases on the X chromosome. Inactivating mutations in these enzymes in humans and in mouse models lead to the soft bones and teeth characteristic of hypophosphatasia and X-linked hypophosphatemia, respectively, where the levels of local and systemic circulating mineralization determinants are perturbed. In X-linked hypophosphatemia, in addition to renal phosphate wasting causing low circulating phosphate levels, phosphorylated mineralization-regulating small integrin-binding ligand N-linked glycoproteins, such as matrix extracellular phosphoglycoprotein and osteopontin, and the phosphorylated peptides proteolytically released from them, such as the acidic serine- and aspartate-rich-motif peptide, may accumulate locally to impair mineralization in this disease.

The recombinant human dentin matrix protein 1-coated titanium and its effect on the attachment, proliferation and ALP activity of MG63 cells

The aim of the present work was to design a bio-interactive implant surface by coating recombinant human dentin matrix protein 1 (hDMP1) onto titanium and to investigate the biological function of this material. Firstly, the plasmid containing the hDMP1 cDNA was constructed and hDMP1 was expressed, purified and characterized. Then, hDMP1 was coated onto the surface of Ti substrates via a biochemical technique and the procedure was divided into three steps: in the beginning, titanium was treated by regular polishing and denoted as Cp-Ti; then, Cp-Ti received alkaline and water treatment and was nominated as AW-Ti; finally, AW-Ti was coated with hDMP1 and referred to as hDMP1-Ti. The inserts of hDMP1 genes were detected by enzyme digestion as well as gel electrophoresis, and the complete nucleotide sequence of hDMP1 was tested. The purified recombinant hDMP1 was electrophoresed on a 10 % SDS-PAGE gel. Cp-Ti, AW-Ti and hDMP1-Ti were characterized by X-ray photoelectron spectroscope and water contact angles tests. The biological activity of MG63 cells cultured in the three groups was investigated by the cell attachment, proliferation and alkaline phosphatase activity assays. The results show that hDMP1 was successfully constructed and coated onto the titanium surface, and hDMP1-Ti had higher hydrophilicity than Cp-Ti. Compared with Cp-Ti and AW-Ti, hDMP1-Ti showed better in vitro bioactivity.

Structural disorder in proteins brings order to crystal growth in biomineralization

Biomineralization, the generation of hard tissues of living organisms, is a process strictly regulated by hormones, enzymes and a range of regulatory proteins of which several resisted structural characterization thus far. Without actual generalizations, there have been scattered observations in the literature for the structural disorder of these proteins. To address this issue in general, we have collected SwissProt proteins involved in the formation of bone and teeth in vertebrates, annotated for biomineralization. All these proteins show an extremely high level of predicted disorder (with a mean of 53%), making them the most disordered functional class of the protein world. Exactly the same feature was established for evolutionarily more distant proteins involved in the formation of the silica wall of marine diatoms and the shell of oysters and other mollusks. Because these proteins also show an extremely biased amino acid composition, such as high negative charge, high frequency of Ser and Asp or Pro residues and repetitiveness, we also carried out a database search with these sequence features for further proteins. This search uncovered several further disordered proteins with clearly related functions, although their annotations made no mention of biomineralization. This general and very strong correlation between biomineralization, structural disorder of proteins and particular sequence features indicates that regulated growth of mineral phase in biology can only be achieved by the assistance of highly disordered proteins.

Nuclear localization of DMP1 proteins suggests a role in intracellular signaling

Dentin matrix protein 1 (DMP1) is highly expressed in odontoblasts and osteoblasts/osteocytes and plays an essential role in tooth and bone mineralization and phosphate homeostasis. It is debatable whether DMP1, in addition to its function in the extracellular matrix, can enter the nucleus and function as a transcription factor. To better understand its function, we examined the nuclear localization of endogenous and exogenous DMP1 in C3H10T1/2 mesenchymal cells, MC3T3-E1 preosteoblast cells and 17IIA11 odontoblast-like cells. RT-PCR analyses showed the expression of endogenous Dmp1 in all three cell lines, while Western-blot analysis detected a major DMP1 protein band corresponding to the 57 kDa C-terminal fragment generated by proteolytic processing of the secreted full-length DMP1. Immunofluorescent staining demonstrated that non-synchronized cells presented two subpopulations with either nuclear or cytoplasmic localization of endogenous DMP1. In addition, cells transfected with a construct expressing HA-tagged full-length DMP1 also showed either nuclear or cytoplasmic localization of the exogenous DMP1 when examined with an antibody against the HA tag. Furthermore, nuclear DMP1 was restricted to the nucleoplasm but was absent in the nucleolus. In conclusion, these findings suggest that, apart from its role as a constituent of dentin and bone matrix, DMP1 might play a regulatory role in the nucleus.

Dentin matrix protein 1 (DMP1) signals via cell surface integrin

Dentin matrix phosphoprotein 1 (DMP1) is a non-collagenous, acidic extracellular matrix protein expressed chiefly in bone and dentin. We examined the DMP1 ability to engage cell-surface receptors and subsequently activate intracellular signaling pathways. Our data indeed show that the presence of extracellular DMP1 triggers focal adhesion point formation in human mesenchymal stem cells and osteoblast-like cells. We determine that DMP1 acts via interaction with αvβ3 integrin and stimulates phosphorylation of focal adhesion kinase. Further biochemical characterization confirms the activation of downstream effectors of the MAPK pathways, namely ERK and JNK, after DMP1 treatment. This activation is specifically inhibitable and can also be blocked by the addition of anti-αvβ3 integrin antibody. Furthermore, we show that extracellular treatment with DMP1 stimulates the translocation of phosphorylated JNK to the nucleus and a concomitant up-regulation of transcriptional activation by phosphorylated c-Jun. The evidence presented here indicates that DMP1 is specifically involved in signaling via extracellular matrix-cell surface interaction. Combined with the published DMP1-null data (Feng, J. Q., Ward, L. M., Liu, S., Lu, Y., Xie, Y., Yuan, B., Yu, X., Rauch, F., Davis, S. I., Zhang, S., Rios, H., Drezner, M. K., Quarles, L. D., Bonewald, L. F., and White, K. E. (2006) Nat. Genet. 38, 1310-1315) it can be hypothesized that DMP1 could be a key effector of ECM-osteocyte signaling.

Identification of a novel dentin matrix protein-1 (DMP-1) mutation and dental anomalies in a kindred with autosomal recessive hypophosphatemia

An autosomal recessive form of hypophosphatemia (ARHP) was recently shown to be caused by homozygous mutations in DMP1, the gene encoding dentin matrix protein-1 (DMP-1), a non-collagenous bone matrix protein with an important role in the development and mineralization of bone and teeth. Here, we describe a previously not reported consanguineous ARHP kindred in which the three affected individuals carry a novel homozygous DMP-1 mutation. The index case presented at the age of 3 years with bowing of his legs and showed hypophosphatemia due to insufficient renal phosphate retention. Serum alkaline phosphatase activity was elevated, with initially normal PTH. FGF23 was inappropriately normal at an older age while being treated with oral phosphate and 1,25(OH)(2)D. Similar clinical and biochemical findings, except for elevated FGF23 levels, were present in his 16-month-old brother and his 12.5-year-old female cousin; the parents of the three affected children are first-degree cousins. Nucleotide sequence analysis was performed on PCR-amplified exons encoding DMP-1 and flanking intronic regions. A novel homozygous frame-shift mutation (c.485Tdel; p.Glu163ArgfsX53) in exon 6 resulting in a premature stop codon was identified in all effected individuals. The parents and available unaffected siblings were heterozygous for c.485Tdel. Tooth growth and shape were normal for the index case, his affected brother and cousin, but their permanent and deciduous teeth displayed enlarged pulp chambers. The identified genetic mutation underscores the importance of DMP-1 mutations in the pathogenesis of ARHP. Furthermore, DMP-1 mutations appear to contribute, through yet unknown mechanisms, to tooth development.

Bone formation regulates circulating concentrations of fibroblast growth factor 23

We examined the role of bone remodeling in the regulation of circulating concentrations of FGF23 using mouse models manifesting differing degrees of coupled and uncoupled bone turnover. Administration of the antiresorptive agent osteoprotegerin produced a profound reduction in bone resorption and formation in male and oophorectomized female mice, accompanied by an increase in serum levels of fibroblast growth factor 23 (FGF23) and a reduction in circulating 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. In contrast, exogenous PTH(1-34) administration increased bone turnover and reduced circulating FGF23. In 1,25(OH)(2)D-deficient, 25-hydroxyvitamin D 1alpha-hydroxylase null mice on a high-calcium diet, endogenous PTH was elevated, bone formation but not resorption was increased, and serum FGF23 was virtually undetectable; on a rescue diet, serum calcium was normalized, PTH levels were reduced, bone formation was reduced, and serum FGF23 levels increased. After PTH treatment of wild-type mice, gene expression of dentin matrix protein 1 (DMP1) in bone was increased, whereas gene expression of FGF23 was reduced. In vitro studies in the osteoblastic cell line UMR-106 showed that externally added DMP1 could inhibit FGF23 gene expression and production stimulated by 1,25(OH)(2)D(3). The results show that osteoblastic bone formation is a potent modulator of FGF23 production and release into the circulation, suggest that the biological consequences on mineral homeostasis of circulating FGF23 may also be dependent on the prevailing rate of bone turnover, and provide evidence that DMP1 may be a direct negative regulator of FGF23 production in osteoblastic cells.

Patterned and switchable surfaces for biomolecular manipulation

The interactions of biomolecules and cells with solid interfaces play a pivotal role in a range of biomedical applications and have therefore been studied in great detail. An improved understanding of these interactions results in the ability to manipulate DNA, proteins and other biomolecules, as well as cells, spatially and temporally at surfaces with high precision. This in turn engenders the development of advanced devices, such as biosensors, bioelectronic components, smart biomaterials and microarrays. Spatial control can be achieved by the production of patterned surface chemistries using modern high-resolution patterning technologies based on lithography, microprinting or microfluidics, whilst temporal control is accessible through the application of switchable surface architectures. The combination of these two surface properties offers unprecedented control over the behaviour of biomolecules and cells at the solid-liquid interface. This review discusses the behaviour of biomolecules and cells at solid interfaces and highlights fundamental and applied research exploring patterned and switchable surfaces.

Tissue engineering: state of the art in oral rehabilitation

More than 85% of the global population requires repair or replacement of a craniofacial structure. These defects range from simple tooth decay to radical oncologic craniofacial resection. Regeneration of oral and craniofacial tissues presents a formidable challenge that requires synthesis of basic science, clinical science and engineering technology. Identification of appropriate scaffolds, cell sources and spatial and temporal signals (the tissue engineering triad) is necessary to optimize development of a single tissue, hybrid organ or interface. Furthermore, combining the understanding of the interactions between molecules of the extracellular matrix and attached cells with an understanding of the gene expression needed to induce differentiation and tissue growth will provide the design basis for translating basic science into rationally developed components of this tissue engineering triad. Dental tissue engineers are interested in regeneration of teeth, oral mucosa, salivary glands, bone and periodontium. Many of these oral structures are hybrid tissues. For example, engineering the periodontium requires growth of alveolar bone, cementum and the periodontal ligament. Recapitulation of biological development of hybrid tissues and interfaces presents a challenge that exceeds that of engineering just a single tissue. Advances made in dental interface engineering will allow these tissues to serve as model systems for engineering other tissues or organs of the body. This review will begin by covering basic tissue engineering principles and strategic design of functional biomaterials. We will then explore the impact of biomaterials design on the status of craniofacial tissue engineering and current challenges and opportunities in dental tissue engineering.

Dentin matrix protein-1 isoforms promote differential cell attachment and migration

Dentin matrix protein-1 (DMP1), bone sialoprotein (BSP), and osteopontin (OPN) are three SIBLINGs (small integrin-binding ligand, N-linked glycoproteins) co-expressed/secreted by skeletal and active ductal epithelial cells. Although etiological mechanisms remain unclear, DMP1 is the only one of these three genes currently known to have mutations resulting in human disease, and yet it remains the least studied. All three contain the highly conserved integrin-binding tripeptide, RGD, and experiments comparing the cell attachment and haptotactic migration-enhancing properties of DMP1 to BSP and OPN were performed using human skeletal (MG63 and primary dental pulp cells) and salivary gland (HSG) cells. Mutation of any SIBLING's RGD destroyed all attachment and migration activity. Using its alphaVbeta5 integrin, HSG cells attached to BSP but not to DMP1 or OPN. However, HSG cells could not migrate onto BSP in a modified Boyden chamber assay. Expression of alphaVbeta3 integrin enhanced HSG attachment to DMP1 and OPN and promoted haptotactic migration onto all three proteins. Interchanging the first four coding exons or the conserved amino acids adjacent to the RGD of DMP1 with corresponding sequences of BSP did not enhance the ability of DMP1 to bind alphaVbeta5. For alphaVbeta3-expressing cells, intact DMP1, its BMP1-cleaved C-terminal fragment, and exon six lacking all post-translational modifications worked equally well but the proteoglycan isoform of DMP1 had greatly reduced ability for cell attachment and migration. The sequence specificity of the proposed BMP1-cleavage site of DMP1 was verified by mutation analysis. Direct comparison of the three proteins showed that cells discriminate among these SIBLINGs and among DMP1 isoforms.

Studies of the DMP1 57-kDa functional domain both in vivo and in vitro

Dmp1-null mice and patients with mutations in dentin matrix protein 1 (DMP1) resulting in autosomal recessive hypophosphatemic rickets display similar skeletal defects. As mutations were observed in the last 18 amino acids of DMP1 in 1 subset of patients and as fragments of intact DMP1, a 37-kDa N-terminal and a 57-kDa C-terminal fragment, have been purified from bone and dentin, we hypothesized that the cleaved 57-kDa C-terminal fragment is the essential functional domain of DMP1. To test this hypothesis, different forms of recombinant DMP1 were expressed in 293EBNA, CHO and 2T3 cells. The results showed that DMP1 was processed into a 37-kDa N-terminal and a 57-kDa C-terminal fragment in vitro in all cell lines examined. DMP1 processing in CHO cells was blocked by a furin protease inhibitor, decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone, in a dose-dependent manner. Coexpression of PHEX, a potential upstream protease, had no apparent effect on DMP1 cleavage in 293EBNA cells, suggesting that PHEX may not be required for DMP1 processing. To test the in vivo role of the C-terminal fragment, transgenic mice overexpressing full-length DMP1 or the 57-kDa fragment controlled by the 3.6-kb Col1 promoter were generated. Overexpression of these transgenes had no effect on the wild-type skeleton, but on the Dmp1-null background showed expression in the osteoblast layer and throughout the bone matrix leading to the rescue of the null bone phenotype. This suggests that the 57-kDa C-terminal fragment may be able to recapitulate the function of intact DMP1 in vivo.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Establishment of porcine pulp-derived cell lines and expression of recombinant dentin sialoprotein and recombinant dentin matrix protein-1

The major non-collagenous proteins in dentin have extensive post-translational modifications (PTMs) that appear to be odontoblast-specific, so expression of recombinant dentin proteins in other cell types does not achieve the in vivo pattern of PTMs. We established cell lines from developing porcine dental papillae and used them to express recombinant dentin sialoprotein (DSP) and dentin matrix protein-1 (DMP1). Pulp cells were immortalized with pSV3-neo and clonally selected. Cell lines were characterized by reverse transcruption-polymerase chain reaction (RT-PCR) and assayed for alkaline phosphatase activity and mineralized nodule formation. One of the five cell lines (P4-2) exhibited an odontoblastic phenotype, as determined by expression of tooth-specific markers, response to cytokines, and ability to form mineralized nodules. DSP and DMP1 expression constructs were transiently transfected into various cell lines. DSP, expressed by P4-2 cells, contained chondroitin 6-sulfate, which is a defining modification of the DSP proteoglycan. DMP1 was secreted and cleaved by proteases, even in human kidney 293 cells, which normally do not express DMP1, demonstrating susceptibility to non-specific proteolysis. Both recombinant proteins enhanced P4-2 cell attachment in a dose-dependent manner. We conclude that we have immortalized porcine odontoblast-like cells which express recombinant dentin extracellular matrix components with post-translational modifications that closely resemble those produced in vivo.

Surface manipulation of biomolecules for cell microarray applications

Many biological events, such as cellular communication, antigen recognition, tissue repair and DNA linear transfer, are intimately associated with biomolecule interactions at the solid-liquid interface. To facilitate the study and use of these biological events for biodevice and biomaterial applications, a sound understanding of how biomolecules behave at interfaces and a concomitant ability to manipulate biomolecules spatially and temporally at surfaces is required. This is particularly true for cell microarray applications, where a range of biological processes must be duly controlled to maximize the efficiency and throughput of these devices. Of particular interest are transfected-cell microarrays (TCMs), which significantly widen the scope of microarray genomic analysis by enabling the high-throughput analysis of gene function within living cells. This article reviews this current research focus, discussing fundamental and applied research into the spatial and temporal surface manipulation of DNA, proteins and other biomolecules and the implications of this work for TCMs.

Effect of antisense oligonucleotide against mouse dentine matrix protein 1 on mineralization ability and calcium ions metabolism in odontoblast-like cell line MDPC-23

AIM

To study the mineralization ability and the dynamic changes of intracellular and extracellular concentrations of calcium ions in the odontoblast-like cell line MDPC-23 affected by antisense oligonucleotide (AS-ODN) against mouse dentine matrix protein 1 (DMP1).

METHODOLOGY

The expression of DMP1 in MDPC-23 cells was detected by an immunohistochemical method and its blocking outcome by the Western blot method. The alkaline phosphatase (ALP) activity, size and number of mineralized nodules, and the intracellular free ([Ca2+]if), total ([Ca2+]it) and the extracellular ([Ca2+]e) calcium ion concentrations in MDPC-23 cells in the experimental group affected with AS-ODN were compared with those in the control group (paired-samples t-test).

RESULTS

Dentine matrix protein 1 was stably expressed in a stable way in MDPC-23 cells; the expression was only just detectable at 12 h and became negative after 24 h affected by AS-ODN. Compared with the control groups, ALP activity of MDPC-23 cells in the AS-ODN group was decreased (P < 0.05), and both the number and size of mineralized nodules were smaller than those in the control group. [Ca2+]if in the AS-ODN group increased and then decreased after 24 h. [Ca2+]it dropped substantially to the lowest point at 24 h (P < 0.01). [Ca2+]e increased before treatment for 24 h and then dropped, however, it was still higher than that of the control group.

CONCLUSIONS

Antisense oligonucleotide against DMP1 could decrease mineralization ability and affect the intracellular and extracellular concentrations of calcium ions in MDPC-23 cells. This would indicate that DMP1 regulates the metabolism and transportation of calcium ions in odontoblasts, and thus boosts dentine mineralization.

A Chondroitin Sulfate Chain Attached to the Bone Dentin Matrix Protein 1 NH2-Terminal Fragment

Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein shown by gene ablations to be critical for the proper mineralization of bone and dentin. In the extracellular matrix of these tissues DMP1 is present as fragments representing the NH2-terminal (37 kDa) and COOH-terminal (57 kDa) portions of the cDNA-deduced amino acid sequence. During our separation of bone noncollagenous proteins, we observed a high molecular weight, DMP1-related component (designated DMP1-PG). We purified DMP1-PG with a monoclonal anti-DMP1 antibody affinity column. Amino acid analysis and Edman degradation of tryptic peptides proved that the core protein for DMP1-PG is the 37-kDa fragment of DMP1. Chondroitinase treatments demonstrated that the slower migration rate of DMP1-PG is due to the presence of glycosaminoglycan. Quantitative disaccharide analysis indicated that the glycosaminoglycan is made predominantly of chondroitin 4-sulfate. Further analysis on tryptic peptides led us to conclude that a single glycosaminoglycan chain is linked to the core protein via Ser74, located in the Ser74-Gly75 dipeptide, an amino acid sequence specific for the attachment of glycosaminoglycans. Our findings show that in addition to its existence as a phosphoprotein, the NH2-terminal fragment from DMP1 occurs as a proteoglycan. Amino acid sequence alignment analysis showed that the Ser74-Gly75 dipeptide and its flanking regions are highly conserved among a wide range of species from caiman to the Homo sapiens, indicating that this glycosaminoglycan attachment domain has survived an extremely long period of evolution pressure, suggesting that the glycosaminoglycan may be critical for the basic biological functions of DMP1.

Molecular basis of human dentin diseases

In recent years, substantial progress has been made regarding the molecular etiology of human structural tooth diseases that alter dentin matrix formation. These diseases have been classified into two major groups with subtypes: dentin dysplasia (DD) types I and II and dentinogenesis imperfecta (DGI) types I-III. Genetic linkage studies have identified the critical loci for DD-II, DGI-II, and DGI-II to human chromosome 4q21. Located within the common disease loci for these diseases is cluster of dentin/bone genes that includes osteopontin (OPN), bone sialoprotein (BSP), matrix extracellular phosphoglycoprotein (MEPE), dentin matrix protein 1 (DMP1), and dentin sialophosphoprotein (DSPP). To date, only mutations within dentin sialophosphoprotein have been associated with the pathogenesis of dentin diseases including DGI types-II and -III and DD-II. In this article, we overview the recent literature related to these dentin genetic diseases, their clinical features, and molecular pathogenesis.

DMP1 depletion decreases bone mineralization in vivo: an FTIR imaging analysis

The role of DMP1 in mineralization was analyzed by comparing bone mineral and matrix properties in dmp1-null female mice to heterozygous and wildtype controls by FTIR imaging spectroscopy. The observed decreased mineral content in dmp1 null mice indicates a key role for dmp1 in bone mineralization. Indirect effects of DMP1 on other systems also determine the KO phenotype.

INTRODUCTION

Dentin matrix protein 1 (DMP1), an acidic phosphorylated extracellular matrix protein, is highly expressed in mineralized tissues. In vitro, DMP1 peptides can promote or inhibit mineralization depending on the extent of phosphorylation, the peptide size, and concentration. To clarify the biological function of DMP1 protein on in vivo mineralization, this study analyzed bone properties of dmp1 knockout (KO) mice compared with heterozygous (HET) and wildtype (WT) controls.

MATERIALS AND METHODS

Tibias from dmp1 KO and age-, sex-, and background-matched HET and WT mice at 4 and 16 weeks (N(total) = 60) were examined by Fourier transform infrared imaging (FTIRI), histology (n = 6 per genotype and age; N = 36), and geometry by muCT (n = 4 per genotype and age; N = 24). Serum ionic calcium and phosphate concentrations were also determined.

RESULTS

The mineral-to-matrix ratios (spectroscopic parameter of relative mineral content) were significantly lower in dmp1 KO mice tibias compared with WT and HET at 4 and 16 weeks. The mineral crystallinity (crystal size/perfection) was significantly increased in dmp1 KO and HET mice relative to WT. Collagen cross-link ratios (a spectroscopic parameter related to the relative amounts of nonreducible/reducible collagen cross-links) in dmp1 KO were not significantly different from WT and HET. Based on muCT, cortical bone cross-sectional areas at 16 but not 4 weeks were significantly reduced in the KO compared with controls. Maximum, minimum, and polar cross-sectional moments of inertia were significantly lower in dmp1 KO than in HET at 16 weeks but not at 4 weeks. Histological analysis and muCT 3-D images suggested that dmp1 KO mice had osteomalacia. Dmp1 KO mice had significantly lower ionic calcium and phosphate concentrations relative to WT, whereas in the HET, values for phosphate were equivalent, and calcium values were decreased relative to WT values.

CONCLUSIONS

The findings of decreased mineral-to-matrix ratio and increased crystal size in bones of dmp1 KO mice suggest that DMP1 has multiple roles (both direct and indirect) in the regulation of postnatal mineralization. We suggest that direct effects on mineral formation, crystal growth, and indirect effects on regulation of Ca x P concentrations and matrix turnover all contribute to the dominant phenotype in the dmp1 KO mouse.

Binding of two nuclear factors to a novel silencer element in human dentin matrix protein 1 (DMP1) promoter regulates the cell type-specific DMP1 gene expression

DMP1 is an acidic phosphorylated protein with the spatial and temporal expression that is largely restricted to bone and tooth tissues. The biological function of DMP1 is associated with biomineralization of bone, cartilage and tooth development. To study the cell-specific expression of DMP1, a 2,512 bp upstream segment of the human gene was isolated and characterized. A series of progressive deletions of the human DMP1 5' flanking sequence were ligated to the luciferase reporter gene, and their promoter activities examined in transfected human osteoblast-like (MG-63) and dental pulp (HDP-D) cells that express DMP1 and hepatic (HepG2) and uterine (HeLa) cells lacking DMP1 expression. A critical cis-regulatory element located between nt -150 and -63 was found to act as a specific silencer responsible for the negative regulation of DMP1 in HepG2 and HeLa cells. The transcriptional activity of this element in MG-63 and HDP-D cells had a 5-7-fold increase than that observed in HepG2 and HeLa cells. Electrophoretic mobility shift assays (EMSAs) showed that a 6-bp DNA sequence in this element was bound by two nuclear factors that are expressed at high levels in HepG2 and HeLa versus MG-63 and HDP-D cells. Competitive assays by EMSAs suggest that the 6-bp core DNA sequence, AG(T/C)C(A/G)C, is a novel DNA-protein binding site and conserved with high identity in reported DMP1 promoters for all species. Furthermore, point mutations of the core sequence caused a marked increase of DMP1 promoter activity in HepG2 and HeLa cells. We speculate that this silencing cis-element may play a critical role in the regulation of DMP1 cell-specific expression.

Evidence for the proteolytic processing of dentin matrix protein 1. Identification and characterization of processed fragments and cleavage sites

Full-length cDNA coding for dentin matrix protein 1 (DMP1) has been cloned and sequenced, but the corresponding complete protein has not been isolated. In searching for naturally occurring DMP1, we recently discovered that the extracellular matrix of bone contains fragments originating from DMP1. Shortened forms of DMP1, termed 37K and 57K fragments, were treated with alkaline phosphatase and then digested with trypsin. The resultant peptides were purified by a two-dimensional method: size exclusion followed by reversed-phase high performance liquid chromatography. Purified peptides were sequenced by Edman degradation and mass spectrometry, and the sequences compared with the DMP1 sequence predicted from cDNA. Extensive sequencing of tryptic peptides revealed that the 37K fragments originated from the NH2-terminal region, and the 57K fragments were from the COOH-terminal part of DMP1. Phosphate analysis indicated that the 37K fragments contained 12 phosphates, and the 57K fragments had 41. From 37K fragments, two peptides lacked a COOH-terminal lysine or arginine; instead they ended at Phe173 and Ser180 and were thus COOH termini of 37K fragments. Two peptides were from the NH2 termini of 57K fragments, starting at Asp218 and Asp222. These findings indicated that DMP1 is proteolytically cleaved at four bonds, Phe173-Asp174, Ser180-Asp181, Ser217-Asp218, and Gln221-Asp222, forming eight fragments. The uniformity of cleavages at the NH2-terminal peptide bonds of aspartyl residues suggests that a single proteinase is involved. Based on its reported specificity, we hypothesize that these scissions are catalyzed by PHEX protein. We envision that the proteolytic processing of DMP1 plays a crucial role during osteogenesis and dentinogenesis.

Dentin matrix protein 1 is expressed in human lung cancer

We have previously shown that breast and prostate cancers express bone matrix proteins. DMP1 expression was evaluated in 59 human lung cancer samples at the protein and mRNA levels. It was detectable in 80% of the cases, suggesting a potential role for DMP1 in tumor progression and bone metastasis.

INTRODUCTION

Previously, we and others have shown that bone extracellular matrix proteins such as bone sialoprotein (BSP) and osteopontin (OPN) are expressed in various types of cancer that are characterized by a high affinity for bone including breast, prostate, and lung adenocarcinoma. Based on biochemical and genetic features, BSP, OPN, dentin matrix protein 1 (DMP1), and dentin sialophosphoprotein (DSPP) have been recently classified in a unique family named SIBLING (small integrin-binding ligand, N-linked glycoprotein). Therefore, we investigated whether DMP1 could also be detected in osteotropic cancers.

MATERIALS AND METHODS

We first used a cancer array for evaluating the relative abundance of DMP1 transcript in a broad spectrum of human cancer tissues. This screening showed that DMP1 was strongly detectable in lung tumors compared with normal corresponding tissue. In a second step, we used an immunophosphatase technique and a specific polyclonal antibody directed against DMP1 to examine the expression of DMP1 in 59 human non-small cell lung cancer samples, including 29 squamous carcinoma, 20 adenocarcinoma, and 10 bronchioloalveolar carcinoma. Student's t-test was used to determine the statistical significance of immunostaining scores between the lung cancer histological groups studied and between cancer and normal lung tissues.

RESULTS

Our results show that DMP1 is detectable in 90% of the adenocarcinoma and squamous carcinoma analyzed while 8 of 10 bronchioloalveolar specimens were negative. DMP1 immunostaining intensity and extent scores were significantly higher in adenocarcinoma (p = 0.0004) and squamous carcinoma (p < 0.0001) samples compared with adjacent normal lung tissue. In situ hybridization experiments confirmed that DMP1 mRNA is localized in lung cancer cells.

CONCLUSION

In this study, we show that a third SIBLING protein is ectopically expressed in lung cancer. The role of DMP1 in lung cancer is largely unknown. Further studies are required to determine the implication of this protein, next to its sisters SIBLING proteins, in tumor progression and bone metastasis development.

Mechanical loading stimulates dentin matrix protein 1 (DMP1) expression in osteocytes in vivo

Dentin matrix protein 1 (DMP1) was originally postulated to be dentin specific. Further analysis showed that DMP1 is also expressed in mature cartilage and bone. In bone tissue, DMP1 is expressed predominantly in late osteoblasts and osteocytes. DMP1 belongs to the SIBLING (Small Integrin Binding Ligand N-linked Glycoprotein) family of cellular matrix proteins that also includes osteopontin, bone sialoprotein, dentin sialophosphoprotein, and others. In this study, we examined the effect of mechanical loading on expression of DMP1 mRNA and DMP1 protein in alveolar bone in the mouse tooth movement model by in situ hybridization and immunocytochemistry. The expression of DMP1 mRNA was determined quantitatively in mechanically loaded and control sites of dento-alveolar tissue at several time points from 6 h to 7 days after loading. The tooth movement model allows simultaneous evaluation of bone resorption and bone formation sites. Expression of DMP1 mRNA in osteocytes increased 2-fold as early as 6 h after treatment in both the bone formation and bone resorption sites. After 4 days, DMP1 expression in osteocytes increased to a maximum of 3.7-fold in the bone formation sites and 3.5-fold in the resorption sites. Osteoblasts responded in the opposite manner and showed a transient 45% decrease of DMP1 mRNA in bone formation sites and a constant decrease of DMP1 mRNA during the entire course of treatment in the bone resorption sites, with a peak inhibition of 67% at day 2. By immunocytochemistry using a C-terminal region peptide antibody to DMP1, we found that there was a transient decrease in immunoreactivity at 3 days after treatment on both the formation side and the resorption side compared with the matched contralateral control tissue. However by 7 days of loading, there was a dramatic increase in DMP1 protein immunoreactivity on both the formation side and the resorption side. These results represent changes in epitope availability using this antibody or true changes in protein levels. The observations imply that the DMP1 protein is undergoing dynamic changes in either synthesis or other protein/matrix interaction after mechanical loading of alveolar bone. The findings indicate that DMP1 is involved in the responses of osteocytes and osteoblasts to mechanical loading of bone. These results support the hypothesis that osteocytes alter their matrix microenvironment in response to mechanical loading.

Type I collagen regulated dentin matrix protein-1 (Dmp-1) and osteocalcin (OCN) gene expression of rat dental pulp cells

In this study, we investigated the effect of type I collagen on dentin matrix protein-1 (Dmp-1) and osteocalcin (OCN) gene expression of dental pulp cells. The mRNA level of Dmp-1 gene was down-regulated; however, OCN gene expression was up-regulated by the culture of dental pulp cells with type I collagen. These findings imply that type I collagen regulates mRNA level of Dmp-1 and OCN gene that are predominantly expressed in active odontoblasts. The change of gene expression by type I collagen was suppressed by the blocking of collagen-integrin interaction. We could conclude that the effect of type I collagen was mediated via binding of collagen to integrin receptors.

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.

Three SIBLINGs (small integrin-binding ligand, N-linked glycoproteins) enhance factor H's cofactor activity enabling MCP-like cellular evasion of complement-mediated attack

Previously we have shown that two members of the newly named SIBLING (small integrin-binding ligand, N-linked glycoproteins) family of proteins, bone sialoprotein, and osteopontin, bound first to a cell surface receptor and then to complement Factor H thereby blocking the lytic activity of the alternative pathway of complement. Another member of this family, dentin matrix protein 1, is shown in this paper to be very similar to osteopontin in that it can bind strongly to Factor H (K(a) approximately 1 nm) and block the lytic activity through either the vitronectin receptor (alpha(V)beta(3) integrin) or CD44. Binding of Factor H to SIBLING localized to the cells surface was demonstrated by fluorescence-activated cell sorting. Extensive overlapping fragment analyses suggests that both dentin matrix protein 1 and osteopontin interact with cell surface CD44 through their amino termini. Similar fragments of bone sialoprotein, like the intact protein, did not functionally interact with CD44. All three proteins are shown to act in conjunction with Factor I, a serum protease that, when complexed to appropriate cofactors, stops the lytic pathway by digesting the bound C3b in a series of proteolytic steps. These results show that at least three members of this family confer membrane cofactor protein-like activity (MCP or CD46) upon cells expressing RGD-binding integrins or CD44. The required order of the assembly of the complex suggests that this cofactor activity is limited to short diffusional distances.

A comparative study of sialic acid-rich proteins in rat bone and dentin

Four sialic acid-rich (SA-rich) proteins found in bone and dentin, osteopontin (OPN), bone sialoprotein (BSP), bone acidic glycoprotein-75 (BAG-75), and dentin matrix protein 1 (DMP1), share some common features. We used SDS-PAGE and Western immunoblots to analyze and compare SA-rich proteins in bone and dentin extracts from rats with a single chromatographic procedure. OPN was detected in dentin extracts, with a relative level less than one-seventieth of that in bone. Both bone and dentin BSP demonstrated an extremely broad distribution pattern, probably due to a high degree of heterogeneity in post-translational modifications. BAG-75 in both bone and dentin was detected as an 83 kDa band, dramatically distinct from that of DMPI. Using a polyclonal antibody raised against a purified bone 57 kDa protein (a portion of DMPI), we detected 150 kDa protein bands in bone fraction; the same bands were recognized by antirecombinant rat DMPI antibody. Bands from dentin migrating at about 150 kDa in earlier fractions and progressing to 200 kDa in later fractions showed a clear immunoreactivity to the anti-57 kDa antibody. We conclude that the majority of DMPI in rat bone is processed into fragments, whereas that in dentin remains intact.

Differential expression of dentin matrix protein 1, type I collagen and osteocalcin genes in rat developing mandibular bone

The expression of dentin matrix protein 1 (Dmp1) mRNA has been compared with that of type I collagen and osteocalcin mRNAs during bone formation in the rat mandible, using in situ hybridization. At embryonic day 15 (E15), type I collagen and osteocalcin mRNAs were expressed by the majority of newly-differentiated osteoblasts attached to unmineralized bone matrices, whereas Dmp1 mRNA expression was confined to only a few osteoblasts. Expression of these genes increased as the number of osteoblasts increased in specimens from E16 to E18. At E20, expression of Dmp1, type I collagen and osteocalcin was also observed in osteocytes. Dmp1 expression continued in osteocytes as they matured up to the 90-day-old specimens, whereas type I collagen and osteocalcin expression in osteocytes almost disappeared at 30 days of postnatal life. In contrast, osteoblasts continued to express type I collagen and osteocalcin in 90-day-old rats, but transiently expressed Dmp1 mRNA, which was seen in the minority of osteoblasts at 14 days of postnatal life. These data show that the developmental expression patterns of Dmp1 in osteogenic differentiation differ from those of type I collagen and osteocalcin, and Dmp1 appears to be expressed by osteocytes throughout ossification in the skeleton. These observations indicate that Dmp1 may serve unique biological functions in osteocyte and bone metabolism.

Differentiation of embryonic mesenchymal cells to odontoblast-like cells by overexpression of dentin matrix protein 1

Cells of the craniofacial skeleton are derived from a common mesenchymal progenitor. The regulatory factors that control their differentiation into various cell lineages are unknown. To investigate the biological function of dentin matrix protein 1 (DMP1), an extracellular matrix gene involved in calcified tissue formation, stable transgenic cell lines and adenovirally infected cells overexpressing DMP1 were generated. The findings in this paper demonstrate that overexpression of DMP1 in pluripotent and mesenchyme-derived cells such as C3H10T1/2, MC3T3-E1, and RPC-C2A can induce these cells to differentiate and form functional odontoblast-like cells. Functional differentiation of odontoblasts requires unique sets of genes being turned on and off in a growth- and differentiation-specific manner. The genes studied include transcription factors like core binding factor 1 (Cbfa1), bone morphogenetic protein 2 (BMP2), and BMP4; early markers for extracellular matrix deposition like alkaline phosphatase (ALP), osteopontin, osteonectin, and osteocalcin; and late markers like DMP2 and dentin sialoprotein (DSP) that are expressed by terminally differentiated odontoblasts and are responsible for the formation of tissue-specific dentin matrix. However, this differentiation pathway was limited to mesenchyme-derived cells only. Other cell lines tested by the adenoviral expression system failed to express odontoblast-phenotypic specific genes. An in vitro mineralized nodule formation assay demonstrated that overexpressed cells could differentiate and form a mineralized matrix. Furthermore, we also demonstrate that phosphorylation of Cbfa1 (osteoblast-specific transcription factor) was not required for the expression of odontoblast-specific genes, indicating the involvement of other unidentified odontoblast-specific transcription factors or coactivators. Cell lines that differentiate into odontoblast-like cells are useful tools for studying the mechanism involved in the terminal differentiation process of these postmitotic cells.