Functional analysis of the cells embedded in bone and cartilage matrices

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Head Investigator found that osteocytes, the cell types that embedded in bone matrix, produce osteopontin abundantly when mechanical stress is loaded to bone tissue. Particularly, osteopontin expressing cells located in the pressure side. This result suggest the possibility that osteocyte play important role for bone resorption by producing osteopontin. To test this possibility, chemoattractant activity of osteopontin was determined by chamber experiment. The result obtained clearly demonstrated that osteopontin act as chemoattractant to osteoclast by interaction with integrin α_vβ_5. Furthermore, we tested the bone remodeling activity of osteopontin-deficient mice with the loading of mechanical stress. The absence of bone resorption to the loading of pressure force was observed in osteopontin nockout mice also demonstrate that osteopontin is a key molecule of bone remodeling. In addition, we identified the promoter region which sensitize mechanical stress by producing transgenic mice. Promoter region of osteopontin was joined with reporter gene and injected the DNA fragment into mouse fertilized egg. We detected GFP signal in osteocytes when mechanical stress loaded to bone. The result revealed the function of osteocytes as mechanosensor cells. In addition, we identified the promoter region of osteopontin which required for the expression in hypertrophic chondrocytes. Taken together, knockout mice and transgenic mice generated provide us a new insight for the functional analysis of the cells embedded in bone and cartilage matrix.