メカニカルストレス応答遺伝子オステオポンチンの発現調節と機能に関する研究

Mechanical loading and endocrine system change bone architecture through the stimulation of bone remodeling by the action of a numbers of molecules. Recent investigations revealed that osteopontin (OPN) responds to mechanical loading in rats with an experimental system for tooth movement. However, the molecular mechanism of OPN expression in response to mechanical stress is unknown. Therefore, the purpose of this study was to understand the regulation and function of osteopontin in response to mechanical stress loading. Mechanical stress by the experimental tooth movement used orthodontic coil spring was loaded on wild-type mice, OPN knockout mice and transgenic mice lines carrying green fluorescence protein (GFP) under the control of 5.5 kbp length of OPN promoter (GFP-OPN5.5 mice). Furthermore, mechanical force by the motor-driven computer-controlled uniaxial cycle stretch system was loaded to the cultured osteoblasts obtained from calvariae of newborn GFP-OPN5.5 mice. For histological examination, the sections were routinely stained with haematoxylin and eosin (HE). To identify osteoclasts, sections were stained for tartrate resistant acid phosphatase (TRAP). Expressions of endogenous OPN and GFP were examined by in situ hybridization and fluorescence examination. Morphological feature of osteoclasts in OPN knockout mice was compared with wild-type mice. A number of mono-nucleated TRAP positive cells were seen in OPN knockout mice, but multinucleated TRAP positive cells were much fewer. In addition, the size of resorbed area in bone matrix of OPN knockout mice was smaller than the ones of wildtype mice. In GFP-OPN5.5 mice, OPN and GFP mRNA expressing cells were detected in osteocytes, osteoblasts and osteoclasts after 72 hours of treatment, and the localization of GFP was consistent with that of endogenous OPN. Furthermore, similar increase of OPN mRNA and GFP expressing cells was recognized after 72 hours of stress loading on calvarial osteoblasts derived from GFP-OPN5.5 mice. These results indicate the impairment of bone remodeling due to the dysfunction of cell fusion in osteoclasts in OPN knockout mice. It is also suggested that OPN is required for the differentiation of osteoclast. Finally, it is revealed that the promoter region of OPN in response to mechanical stress lies in 5.5 kbp OPN promoter in the upstream region

公開日:2010年1月24日で登録したコンテンツは、国立情報学研究所において電子化したものです。