| 研究実績の概要 |
We investigated the initial stages of endochondral ossification during secondary ossification of mouse femur epiphysis. We found that the very initial starting point of mineral formation in the epiphysis occurs at post-natal day 6 (P6), by using microCT and histological analysis. Initial minerals were found in the surroundings of hypertrophic chondrocytes in the medial side of the epiphysis. Interestingly, histological and immunohistochemical analyses showed that initial mineralization until P6 was based on chondrocyte activity only, i.e., it occurred in the absence of osteoblasts. Osteoblasts and endothelial cells were observed inside the epiphysis onward P7.
Electron microscopy-based ultrastructural analysis showed that cell-secreted matrix vesicles were absent in the early steps of osteoblast-independent endochondral ossification. Instead, chondrocyte membrane fragments were found in the fibrous matrix surrounding the hypertrophic chondrocytes. EDS analysis and electron diffraction study indicated that cell membrane fragments acted as nuclei for newly formed calcospherites which initially showed an amorphous calcium phosphate phase, and then transformed into apatite crystal phase. These findings would be valuable to develop novel organic-inorganic hybrid materials for manipulation of biomineralization.
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