近年研究提示组蛋白去甲基化酶调控骨代谢，但鲜有体内实验证据。本课题组前期研究发现组蛋白去甲基化酶KDM7A抑制骨髓基质细胞成骨分化而促进其成脂分化，此作用依赖于其脱甲基活性。机制研究提示KDM7A通过移除组蛋白甲基化标记促进Wnt通路抑制因子SFRP1及脂肪分化转录因子C/EBPα表达。因此提出KDM7A可能通过抑制经典Wnt通路及促进C/EBPα表达而调控骨髓微环境成骨-成脂分化平衡，影响骨稳态。本项目将完善KDM7A通过调节Wnt通路活性及C/EBPα而调控骨髓基质干细胞和前体细胞定向分化的机制研究；构建成骨前体细胞条件性Kdm7a基因敲除鼠，采用影像学、生物力学、组织形态学结合细胞分子生物学等实验，观察Kdm7a敲除对小鼠骨形成/骨吸收和骨稳态的影响；探索Sfrp1和C/EBPα过表达能否逆转Kdm7a敲除鼠生物表型。本研究将深化对骨发育和骨稳态机制的认识，为骨质疏松防治提供新线索。

A few histone demethylases have recently been reported to play key roles in osteogenic differentiation from marrow stromal stem cells (MSCs), however their in vivo roles remain to be validated. Our preliminary data showed that histone demethylase KDM7A negatively regulated osteogenic differentiation and positively regulated adipogenic differentiation from murine ST2 stromal cell and primary marrow stromal cells. Further mechanism investigations demonstrated that KDM7A increased the expression of canonical Wnt inhibitor secreted frizzled-related protein 1 (SFRP1) by removing histone methylation marks from the promoter of Sfrp1. KDM7A also promoted CCAAT/enhancer binding protein α (C/EBPα) expression by removing histone methylation marks. These suggest that KDM7A might regulate reciprocal commitment of MSCs to osteoblasts and adipocytes, and bone homeostasis through interacting with canonical Wnt signaling and C/EBPα. In the present study we will further investigate the involvement of SFRP1/Wnt signaling and C/EBPα in detail in the reciprocal regulation of osteogenic and adipogenic differentiation by KDM7A using primary marrow stromal cells. Then we will develop Kdm7a-floxed mice and make osteogenic progenitor-specific knockout mice by crossing the Kdm7a-floxed mice with Osx-Cre mice. The phenotypes of the conditional knockout (cKO) mice will be analyzed to demonstrate if the Kdm7a deletion in osteoblast progenitor cells results in altered differentiation of osteoblasts and adipocytes and activity of Wnt/β-Catenin signaling in vivo and then lead to changes in bone homestasis and bone mass. If the above mentioned studies give us positive results, we will further investigate if overexpression of Sfrp1 and/or C/EBPα in mice will rescue the phenotypes observed in the Kdm7a cKO mice. Our proposed studies will provide novel insights into the mechanisms of osteoblast development and bone homeostasis, and implicate potential novel approach for bone loss recovery.