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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

Izabela Maciejewska, Cameron Cowan, Kathy Svoboda, William T. Butler, Rena D'Souza and Chunlin Qin

Department of Biomedical Sciences, Texas A&M Health Science Center, Baylor College of Dentistry, Dallas, Texas

Correspondence to: Izabela Maciejewska, DDS, PhD, Department of Biomedical Sciences, Texas A&M Health Science Center, Baylor College of Dentistry, 2121 Holcombe Boulevard, Room 818, Houston, TX 77054. E-mail: imaciejewska{at}bcd.tamhsc.edu

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 NH₂-terminal fragment, a COOH-terminal fragment, and the proteoglycan form of the NH₂-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 NH₂-terminal and COOH-terminal regions of DMP1 and confocal microscopy. In rat first molar organs, the NH₂-terminal fragment localized to predentin, whereas the COOH-terminal fragment was mainly restricted to mineralized dentin. In the growth plate of bone, the NH₂-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 NH₂-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)

Key Words: dentin matrix protein 1 • immunolocalization • dentinogenesis • osteogenesis • Forster resonance energy transfer

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