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

TLDR

DMP1 is essential for bone and dentin mineralization, and after proteolytic cleavage it exists as NH₂‑terminal, COOH‑terminal, and proteoglycan fragments within the extracellular matrix. The study aimed to determine the biological roles of each fragment by mapping their distribution in rat tooth and bone. The authors used antibodies specific to the NH₂‑ and COOH‑terminal regions of DMP1 and confocal microscopy to assess fragment localization. NH₂‑terminal DMP1 localizes to predentin and proliferative/hypertrophic bone zones, while COOH‑terminal DMP1 is confined to mineralized dentin and ossification zones; both fragments colocalize in odontoblasts and hypertrophic chondrocytes, and biochemical analysis shows predentin enriched in DMP1‑PG and mineralized dentin dominated by the COOH fragment, indicating distinct roles in dentin and bone biomineralization.

Abstract

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 COOH-terminal 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.