骨细胞Kindlin-2调节骨稳态的作用及分子机制研究

大量证据表明骨细胞在骨稳态维持中起关键作用，但是分子机制尚未明确。Kindlin-2是一种局部粘附分子。特异删除小鼠骨细胞Kindlin-2的表达，我们发现不同性别、年龄KO小鼠均有明显骨质疏松样表型，成骨细胞分化、数量及骨形成能力均下降，破骨细胞分化、数量及骨吸收增加。KO小鼠骨细胞表达骨硬化素增多，成骨细胞表达β-catenin减少，骨髓微环境被改变，更有利于MSC向脂肪细胞分化，不利于其向成骨细胞分化。KO小鼠骨细胞表达Rankl增多。应用CRISPR/Cas9技术敲除MLO-Y4细胞中的Kindlin-2，也能上调骨硬化素和Rankl的表达。上述结果首次证明骨细胞Kindlin-2在骨稳态维持中的重要作用。本课题将进一步利用分子、细胞、模式动物等手段，继续深入探讨骨细胞Kindlin-2调节骨稳态的作用及分子机制，研究结果将有助于发现防治骨质疏松症的新靶点，为临床治疗提供理论指导。

Cumulative evidence suggests that osteocytes, embedded in a mineralized bone matrix, play key roles in regulation of bone homeostasis by currently unknown mechanisms. Kindlin-2 is a focal adhesion molecule. To investigate the role of Kindlin-2 in regulation of bone homeostasis, we specifically deleted Kindlin-2 expression in osteocytes in mice. We found that deleting Kindlin-2 in osteocytes causes severe osteopenia throughout life. Kindlin-2 loss in osteocytes not only drastically decreases osteoblast number and function, leading to reductions in osteoid production, mineralization and bone formation, but also promotes osteoclast formation and bone resorption. Our in vitro and in vivo studies demonstrate that Kindlin-2 deletion increases Sclerostin expression in osteocytes and decreases the level of β-catenin protein in osteoblasts, and decreases bone formation. Kindlin-2 loss in osteocytes alters the bone microenvironment that inhibits osteoblastic but favors adipogenic differentiation of mesenchymal stem cells. Kindlin-2 deletion additionally promotes Rankl expression in osteocytes and osteoclast formation and differentiation from the bone marrow monocytes. Kindlin-2 deletion in osteocyte-like cell line MLO-Y4 by CRISPR/Cas9 technology also showed increased expressions of Sclerostin and Rankl. These results uncover a previously unknown key function of Kindlin-2 in osteocytes in regulation of bone homeostasis. In this study, we will continue this extremely exciting project by using a combination of sophisticated molecular and cellular approaches along with multiple novel mouse models and further determine the role and mechanisms whereby osteocytic Kindlin-2 regulates bone homeostasis, which will help on design of novel therapeutic strategies for treatment of skeletal diseases such as osteoporosis.