Bone Morphogenetic Protein 2 Mediates Dentin Sialophosphoprotein Expression and Odontoblast Differentiation via NF-Y Signaling

Abstract

Dentin sialophosphoprotein (DSPP), an important odontoblast differentiation marker, is necessary for tooth development and mineralization. Bone morphogenetic protein 2 (BMP2) plays a vital role in odontoblast function via diverse signal transduction systems. We hypothesize that BMP2 regulates DSPP gene transcription and thus odontoblast differentiation. Here we report that expression of BMP2 and DSPP is detected during mouse odontogenesis by in situ hybridization assay, and BMP2 up-regulates DSPP mRNA and protein expression as well as DSPP-luciferase promoter activity in mouse preodontoblasts. By sequentially deleting fragments of the mouse DSPP promoter, we show that a BMP2-response element is located between nucleotides ؊97 and ؊72. Tooth development involves sequential and reciprocal interaction between dental epithelial and mesenchymal cells. The formation of dentin or dentinogenesis originates from the neural crest-derived mesenchymal cells and proceeds in a series of cytodifferentiation stages to form odontoblasts in a specific spatial and temporal pattern originating at the principal cusp tip and advancing toward the base of the tooth (1-3). A consequence of odontoblast cytodifferentiation is the expression of specific gene products that form the dentin extracellular matrix. Dentin extracellular matrix is composed of the inorganic components with mostly hydroxyapatite (about 70%) and the organic matrix that consists of collagenous and noncollagenous proteins (NCPs).2 Among the NCPs, dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) are expressed at high levels in tooth, especially in dentin (4, 5). DSP accounts for 5-8% of the NCPs with high carbohydrate and sialic acid levels, whereas DPP is the principal dentin matrix protein with about 50% of the NCPs. DPP, with high levels of aspartic acid and phosphoserine, is believed to be a nucleator or modulator of function related to dentin mineralization and hydroxyapatite crystal formation (6 -8).

The Canonical BMP Signaling Pathway Plays a Crucial Part in Stimulation of Dentin Sialophosphoprotein Expression by BMP-2

“…One possible pathway is that of NF-Y, which interacts with the inverted CCAAT box binding site and is controlled by BMP-2 (19). NF-Y binds to a BMP-2 response element in the mouse Dspp promoter, especially between nucleotides Ϫ97 and Ϫ72 (19). Therefore, we could suppose NF-Y to be another factor that stimulates Dspp expression in response to BMP-2 treatment, but is independent of the canonical BMP signaling pathway.…”

“…Previously, Chen et al (19) showed that BMP-2 treatment of the MD10-F2 mouse pre-odontoblast cell line increased Dspp mRNA expression. They reported that BMP-2 induces Dspp expression through NF-Y, but they did not address the relationship between canonical BMP-2 signaling and Dspp expression.…”

“…One possible pathway is that of NF-Y, which interacts with the inverted CCAAT box binding site and is controlled by BMP-2 (19). NF-Y binds to a BMP-2 response element in the mouse Dspp promoter, especially between nucleotides Ϫ97 and Ϫ72 (19).…”

“…In tooth development, DSPP is a marker of odontoblast differentiation and is associated with dentin mineralization. transcriptional activators (19,28), and Twist1 is a novel transcriptional repressor (29). Here, we have added the components of the canonical BMP-2 signaling pathway to the transcriptional regulation of Dspp gene expression in MDPC-23 mouse preodontoblast cells.…”

Expression of thymosin β4 in odontoblasts during mouse tooth development

“…Further, Tβ4 increases the exocytosis of cytolytic granules from natural killer cells (34). BMP-2 induces the expression of DSPP in odontoblasts during tooth development as well as the expression of heme oxygenase-1 (HO-1), a factor related to pulp cell differentiation, the expression of alkaline phosphatase (ALP), osteopontin (OPN), BSP, DMP-1, and DSPP mRNA (35,36). Overexpression of Bcl-2 also decreases the expression of DMP-1, OC, DSPP, and Col type I mRNA (37).…”