DDR2,a Discoidin Domain Receptor,is A Marker Of Periosteal Osteoblast And Osteoblast Progenitors

ObjectiveThe bilayered structure of the periosteum includes the inner bone layer consists of osteoblasts and osteoblast progenitors and the outer layer consists of periosteum fibroblasts.The purpose of this study was to investigate the relationship between discoidin domain tyrosine kinase receptor 2(DDR2),a common surface marker of myocardial fibroblasts,and periosteal osteoblast and osteoblast progenitors.The identification of cell-specific surface markers of the bilayered structure of the periosteum is important for the purpose of tissue regeneration.Methods(1)We investigated the expression of the discoidin domain tyrosine kinase receptor 2(DDR2),fibroblast specific protein-1(FSP-1)and alkaline phosphatase(ALP)in the periosteum of the C57BL/6J mice rib and femur by immunohistochemistry and immunofluorescence.(2)Osteogenic differentiation was compared between DDR2-and FSP-1-expressing cells flow-sorted from the periosteum.Results(1)We showed that DDR2 predominantly labeled osteogenic cells residing in the inner layer of the periosteum and that Pearson's coefficient of colocalization indicated a significant correlation with the expression of ALP.The mineralization of DDR2-expressing osteogenic cells isolated from the periosteum was significantly induced.(2)In contrast,FSP-1 predominantly labeled the outer layer of periosteal fibroblasts,and Pearson's coefficient of colocalization indicated that FSP-1 was poorly correlated with the expression of ALP.FSP-1-expressing periosteal fibroblasts did not exhibit osteogenic differentiation for the induction of bone mineralization,which indicates that they lack osteogenic regeneration ability.ConclusionDDR2 may be a new potential cell surface marker,which can be used for the identification and isolation of osteoblasts and osteoblast progenitors in the inner periosteum.It is of great significance for the regeneration treatment of bone tissue.