Mini-course (a.2): MECHANISM OF BONE REMODELING IN NORMAL AND DMP-1 DEFICIENT MICE

Summary: Differences in apparent and actual density have been noted in the mineralized tissue of postnatal dentin matrix protein-1 (DMP1) mice. In order to investigate this difference at the lowest hierarchical level, a XANES (X-ray Absorption Near Edge Structure) spectroscopy investigation of DMP1 null mice was performed. Female wild type (WT) and DMP1 null mice (KO) were sacrificed (21 d), stored, and the femurs (n=5) were collected, sectioned, and dehydrated. The K- and L-edges of Ca and P and the L-edge of O were obtained at the Canadian Light Source synchrotron facility.  The P L-edge data (50x50µm spot size, ~10-20 nm penetration depth) showed evidence of soluble phosphate species in the KO samples, but the higher energy P K-edge data (200x50µm, ~500 nm penetration depth) showed no significant difference in the phosphate bonding structures of the WT and KO mice. The low energy Ca L-edge data showed evidence of a local depletion of Ca in the KO mice while the O L-edge data showed increased carbonate content of the KO bone. Taken together this data creates a picture of a unique local coordination of phosphorus in the mineralized tissue of the DMP1-null bone at an earlier stage in the lifecycle than the phenotype is generally observed. These changes observed in the crystal structure of the mineral matrix help explain DMP1 role in the mineralization of tissue.