Functional analysis of the cells embedded in bone and cartilage matrices

首席研究员发现，骨细胞（嵌入骨基质中的细胞类型）在骨组织承受机械应力时大量产生骨桥蛋白。特别是，骨桥蛋白表达细胞位于压力侧。这一结果提示骨细胞可能通过产生骨桥蛋白在骨吸收中起重要作用。为了验证这种可能性，采用室内实验法测定了骨桥蛋白的化学引诱活性。结果表明，骨桥蛋白通过与整合素α_vβ_5相互作用，对破骨细胞具有趋化作用。此外，我们测试了骨桥蛋白缺乏小鼠在机械应力负荷下的骨重塑活性。在骨桥蛋白缺失小鼠中观察到骨吸收对压力载荷的缺失，这也表明骨桥蛋白是骨重塑的关键分子。此外，我们通过生产转基因小鼠，鉴定了对机械应力敏感的启动子区域。将骨桥蛋白启动子区与报告基因连接，将DNA片段注射到小鼠受精卵中。当机械应力加载到骨时，我们检测到骨细胞中的GFP信号。结果显示骨细胞具有机械感应细胞的功能。此外，我们还确定了在肥大软骨细胞中表达所需的骨桥蛋白启动子区域。总的来说，基因敲除小鼠和转基因小鼠的产生为我们对骨和软骨基质中嵌入细胞的功能分析提供了新的见解。

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.