The NH₂-terminal and COOH-terminal Fragments of Dentin Matrix Protein 1 (DMP1) Localize Differently in the Compartments of Dentin and Growth Plate of Bone

Abstract

S U M M A R Y Multiple studies have shown that dentin matrix protein 1 (DMP1) is essential for bone and dentin mineralization. After post-translational proteolytic cleavage, DMP1 exists within the extracellular matrix of bone and dentin as an NH 2 -terminal fragment, a COOHterminal fragment, and the proteoglycan form of the NH 2 -terminal fragment (DMP1-PG). To begin to assess the biological function of each fragment, we evaluated the distribution of both fragments in the rat tooth and bone using antibodies specific to the NH 2 -terminal and COOH-terminal regions of DMP1 and confocal microscopy. In rat first molar organs, the NH 2 -terminal fragment localized to predentin, whereas the COOH-terminal fragment was mainly restricted to mineralized dentin. In the growth plate of bone, the NH 2 -terminal fragment appeared in the proliferation and hypertrophic zones, whereas the COOH-terminal fragment occupied the ossification zone. Forster resonance energy transfer analysis showed colocalization of both fragments of DMP1 in odontoblasts and predentin, as well as hypertrophic chondrocytes within the growth plates of bone. The biochemical analysis of bovine teeth showed that predentin is rich in DMP1-PG, whereas mineralized dentin primarily contains the COOH-terminal fragment. We conclude that the differential patterns of expression of NH 2 -terminal and COOH-terminal fragments of DMP1 reflect their potentially distinct roles in the biomineralization of dentin and bone matrices. (J Histochem Cytochem 57:155-166, 2009) K E Y W O R D S dentin matrix protein 1 immunolocalization dentinogenesis osteogenesis Forster resonance energy transfer WHEN DENTIN is formed, the odontoblasts secrete an unmineralized matrix enriched with collagen and noncollagenous proteins (NCPs), termed predentin. The extracellular matrix of the newly formed predentin begins to mineralize in the matrix vesicles, which show a relation to proteoglycans and bind calcium ions (AranaChavez and Massa 2004). Later, after the controlled deposition of apatite crystals, predentin is transformed into mineralized tissues termed dentin. The endochondral bone formation, however, proceeds in a diverse way and begins with the previously formed cartilage mineralization and latter deposition of the bone matrix termed osteoid, which undergoes calcification and eventually become a bone. A large body of evidence points to

Mineral abnormalities and long-term graft function in pediatric renal transplant recipients: a role for FGF-23?

“…Since protocol biopsies were not performed in the current study, it is not possible to distinguish between these possibilities. However, FGF-23 binds to the FGFR1, the same receptor that is upregulated by anti-HLA class I antibodies and which may lead to vascular endothelial cell proliferation, atherosclerosis and renal fibrosis [26]. Alternatively, FGF-23 levels may be another marker of decreased GFR.…”

The importance of the SIBLING family of proteins on skeletal mineralisation and bone remodelling

“…In DMP1, it is the COOH-terminal fragment that contains the ASARM peptide (Martin et al 2008). The full-length DMP1 is expressed at much lower levels than its fragments, which themselves have different localisation patterns in bone (Huang et al 2008, Maciejewska et al 2008. In the growth plate, while the NH 2 -terminal fragment is localised to the resting, proliferation and pre-hypertrophic zones, the COOH-terminal fragment is found in the calcification front and ossification zone (Maciejewska et al 2008).…”

Failure to Process Dentin Matrix Protein 1 (DMP1) into Fragments Leads to Its Loss of Function in Osteogenesis

“…For Western immunoblotting, we used the polyclonal anti-DMP1-C-857 antibody, which was purified by passing it through an affinity column made of synthetic peptide injected into the rabbits to generate the antisera (18). This affinity-purified anti-DMP1 antibody was used at a concentration of 0.2 g IgG/ml.…”

“…Immunohistochemistry and protein chemistry studies showed that the localization of DMP1-N is different from that of DMP1-C in the tooth and cartilage of the long bone (17,18). These observations in both bone and tooth suggest that the NH 2 -terminal fragment and the COOH-terminal fragment of DMP1, which vary dramatically in chemical structure, may play different roles in osteogenesis and dentinogenesis.…”