DMP1 C-terminal mutant mice recapture the human ARHR tooth phenotype

Institute of Medical Genetics, Shandong University School of Medicine, Jinan, People's Republic of China.
Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research (Impact Factor: 6.83). 10/2010; 25(10):2155-64. DOI: 10.1002/jbmr.117
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DMP1 mutations in autosomal recessive hypophosphatemic rickets (ARHR) patients and mice lacking Dmp1 display an overlapping pathophysiology, such as hypophosphatemia. However, subtle differences exist between the mouse model and human ARHR patients. These differences could be due to a species specificity of human versus mouse, or it may be that the mutant DMP1 in humans maintains partial function of DMP1. In this study we report a deformed tooth phenotype in a human DMP1 deletion mutation case. Unexpectedly, the deletion of nucleotides 1484 to 1490 (c.1484_1490delCTATCAC, delMut, resulting in replacement of the last 18 residues with 33 random amino acids) showed a severe dentin and enamel defect similar to a dentinogenesis imperfecta (DI) III-like phenotype. To address the molecular mechanism behind this phenotype, we generated delMut transgenic mice with the endogenous Dmp1 gene removed. These mutant mice did not recapture the abnormal phenotype observed in the human patient but displayed a mild rachitic tooth phenotype in comparison with that in the Dmp1-null mice, suggesting that the DI III-like phenotype may be due to an as-yet-undetermined acquired gene modifier. The mechanism studies showed that the mutant fragment maintains partial function of DMP1 such as stimulating MAP kinase signaling in vitro. Last, the in vitro and in vivo data support a role of odontoblasts in the control of fibroblast growth factor 23 (FGF-23) regulation during early postnatal development, although this regulation on Pi homeostasis is likely limited.

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    • "Mesial root length and thickness of the first molar were determined based on the radiographs using ImageJ (National Institutes of Health, Bethesda, MD, USA). Microcomputed tomography (µCT) analysis was performed with the Scanco µCT35 (Scanco Medical, Bassersdorf, Switzerland) as described previously.3 For scanning electron microscopy analysis, the samples were embedded in methyl methacrylate and cut to expose the dental pulps and root canals; the surface was then polished using alumina alpha micropolish II solution (Buehler, Lake Bluff, IL, USA). "
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    ABSTRACT: Dentin matrix protein 1 (DMP1) is essential to odontogenesis. Its mutations in human subjects lead to dental problems such as dental deformities, hypomineralization and periodontal impairment. Primarily, DMP1 is considered as an extracellular matrix protein that promotes hydroxyapatite formation and activates intracellular signaling pathway via interacting with αvβ3 integrin. Recent in vitro studies suggested that DMP1 might also act as a transcription factor. In this study, we examined whether full-length DMP1 could function as a transcription factor in the nucleus and regulate odontogenesis in vivo. We first demonstrated that a patient with the DMP1 M1V mutation, which presumably causes a loss of the secretory DMP1 but does not affect the nuclear translocation of DMP1, shows a typical rachitic tooth defect. Furthermore, we generated transgenic mice expressing (NLS)DMP1, in which the endoplasmic reticulum (ER) entry signal sequence of DMP1 was replaced by a nuclear localization signal (NLS) sequence, under the control of a 3.6 kb rat type I collagen promoter plus a 1.6 kb intron 1. We then crossbred the (NLS)DMP1 transgenic mice with Dmp1 null mice to express the (NLS)DMP1 in Dmp1-deficient genetic background. Although immunohistochemistry demonstrated that (NLS)DMP1 was localized in the nuclei of the preodontoblasts and odontoblasts, the histological, morphological and biochemical analyses showed that it failed to rescue the dental and periodontal defects as well as the delayed tooth eruption in Dmp1 null mice. These data suggest that the full-length DMP1 plays no apparent role in the nucleus during odontogenesis.International Journal of Oral Science advance online publication, 8 August 2014; doi:10.1038/ijos.2014.44.
    International Journal of Oral Science 08/2014; 6(3). DOI:10.1038/ijos.2014.44 · 2.53 Impact Factor
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    • "One of the major disturbances observed in Dmp1-null animals is the defective dentin formation and mineralization, including a reduced dentin apposition rate, increased predentin width, and a disorganized dentinal tubule arrangement,3,4 as well as changes of phosphate (Pi) homeostasis caused by abnormal increases of fibroblast growth factor (FGF) 23.5 Mutations in human DMP1 cause autosomal recessive hypophosphatemic rickets.5,6 One human Dmp1 deletion mutation case had a deletion of nucleotides 1484 to 1490 (c.1484_1490delCTATCAC) resulting in replacement of the last 18 residues with 33 random amino acids, displayed severe dentin and enamel defects similar to a dentinogenesis imperfecta III-like phenotype.7 Our previous studies suggest that the C-terminal of DMP1 is likely a key functional domain of this matrix protein.7,8 "
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    ABSTRACT: Deletion or mutation of dentin matrix protein 1 (DMP1) leads to hypophosphatemic rickets and defects within the dentin. However, it is largely unknown if this pathological change is a direct role of DMP1 or an indirect role of phosphate (Pi) or both. It has also been previously shown that Klotho-deficient mice, which displayed a high Pi level due to a failure of Pi excretion, causes mild defects in the dentinal structure. This study was to address the distinct roles of DMP1 and Pi homeostasis in cell differentiation, apoptosis and mineralization of dentin and enamel. Our working hypothesis was that a stable Pi homeostasis is critical for postnatal tooth formation, and that DMP1 has an antiapoptotic role in both amelogenesis and dentinogenesis. To test this hypothesis, Dmp1-null (Dmp1−/−), Klotho-deficient (kl/kl), Dmp1/Klotho-double-deficient (Dmp1−/−/kl/kl) and wild-type (WT) mice were killed at the age of 6 weeks. Combinations of X-ray, microcomputed tomography (μCT), scanning electron microscopy (SEM), histology, apoptosis and immunohistochemical methods were used for characterization of dentin, enamel and pulp structures in these mutant mice. Our results showed that Dmp1−/− (a low Pi level) or kl/kl (a high Pi level) mice displayed mild dentin defects such as thin dentin and a reduction of dentin tubules. Neither deficient mouse line exhibited any apparent changes in enamel or pulp structure. However, the double-deficient mice (a high Pi level) displayed severe defects in dentin and enamel structures, including loss of dentinal tubules and enamel prisms, as well as unexpected ectopic ossification within the pulp root canal. TUNEL assay showed a sharp increase in apoptotic cells in ameloblasts and odontoblasts. Based on the above findings, we conclude that DMP1 has a protective role for odontoblasts and ameloblasts in a pro-apoptotic environment (a high Pi level).
    International Journal of Oral Science 12/2012; 4(4). DOI:10.1038/ijos.2012.69 · 2.53 Impact Factor
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    • "The GEP knockdown dentin phenotype prompted us to determine whether recombinant GEP was able to change odontoblasts proliferation and differentiation. We previously created a GEP stable cell line using 293 EBNA cells and generated recombinant GEP 7. In this study, we tested the effect of GEP on a preodontoblast cell line 31, 33. Our data showed that recombinant GEP stimulated proliferation of the preodontoblast cell line at all tested concentrations, although the significant difference was only observed at the 200 ng/ml concentration (Fig. 4A). "
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    ABSTRACT: Granulin epithelin precursor (GEP) is a new growth factor that functions in brain development, chondrogenesis, tissue regeneration, tumorigenesis, and inflammation. The goal of this study was to study whether GEP was critical for odontogenesis and amelogenesis both in vivo and in vitro. The in situ hybridization and immunohistochemistry data showed that GEP was expressed in both odontoblast and ameloblast cells postnatally. Knockdown of GEP by crossing U6-ploxPneo-GEP and Sox2-Cre transgenic mice led to a reduction of dentin thickness, an increase in predentin thickness, and a reduction in mineral content in enamel. The in vitro application of recombinant GEP up-regulated molecular markers important for odontogenesis (DMP1, DSPP, and ALP) and amelogenesis (ameloblastin, amelogenin and enamelin). In conclusion, both the in vivo and the in vivo data support an important role of GEP in tooth formation during postnatal development.
    International journal of biological sciences 11/2010; 6(7):719-29. · 4.51 Impact Factor
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