Fkbp5ノックアウトマウスを用いた不動性・ステロイド性骨粗鬆症発症機構の解明

2017 Fiscal Year Annual Research Report

• Project/Area Number: 17J04196
• Research Institution: Nagasaki University
• Principal Investigator: 秦 昕 長崎大学, 医歯薬学総合研究科(歯学系), 特別研究員(DC2)
• Project Period (FY): 2017-04-26 – 2019-03-31
• Keywords: 骨代謝学

Outline of Annual Research Achievements

To investigate the molecular mechanism of bone regulation by osteocyte network, Prof. Komori’s group searched unloading induced genes by tail suspension using wild-type and osteoblast-specific Bcl2 transgenic mice, in which osteocyte network is completely disrupted. They identified Fkbp5 (FK 506-binding protein of 51-KDa) as an unloading-induced gene in osteoblasts and osteocytes. Further, as Fkbp5 was previously reported to bind to glucocorticoid receptor (GR) and inhibit the nuclear translocation of GR, Fkbp5-/- mice were expected to suffer severe osteoporosis by glucocorticoid treatment. Therefore, they generated Fkbp5-/- mice to reveal the function of Fkbp5 in disuse osteoporosis and as a mouse model for glucocorticoid-induced osteoporosis.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

I first confirmed that Fkbp5 is upregulated by tail suspension in osteoblasts and osteocytes. In physiological condition, the bone volume of Fkbp5-/- mice was similar to that of wild-type mice. I performed tail suspension experiment and compared Fkbp5-/- mice with wild-type mice. After tail suspension, bone loss was more severe in Fkbp5-/- mice than wild-type mice by micro-CT analyses.
To examine the glucocorticoid-induced osteoporosis, the slow-releasing pellets of prednisolone implanted or daily dexamethasone injected for 4 weeks. In micro-CT analyses, trabecular bone was increased and cortical bone was reduced in prednisolone implanted or dexamethasone injected wild-type mice. In Fkbp5-/- mice trabecular bone was not increased and cortical bone was more severe reduced than wild-type.

Strategy for Future Research Activity

Using the osteoblast and osteocyte fractions from tail-suspended wild-type and Fkbp5-/- mice and their ground control mice, I also perform microarray analysis to identify the differentially expressed genes among wild-type and Fkbp5-/- mice with or without tail suspension. After gene annotation and pathway analyses, the functions of the selected genes will be analyzed by introducing the genes into primary osteoblasts and examining osteoblast differentiation. By co-culturing the primary osteoblasts with bone marrow cells, the function of the selected gene in osteoclastogenesis is also examined.
By combining the results obtained above, molecular mechanism of Fkbp5 in unloading-induced bone loss and the mechanism how osteoblast function is impaired by glucocorticoid will be clarified.