糖皮质激素性骨质疏松骨髓脂肪化的表观遗传学基础：β-catenin调控骨髓基质细胞PPARγ2基因表观遗传修饰的分子机制

GIucocorticoid-induced osteoporosis (GIO) is the most common secondary osteoporosis. The research on GIO pathophysiological mechanisms is currently an area of intense research interest. Bone marrow adipogenesis, which was undervalued to some extent in the previous studies, is an important pathological phenotype of GIO. There is a negative correlation between osteoblasts and adipocytes, both of which are differentiated from bone marrow stromal cells (BMSCs). Attenuating adipogenic differentiation potential of BMSCs and inhibiting bone marrow adipogenesis is an important strategy to treat GIO. The data from our pilot studies indicated that there were DNA hypo-methylation, histone hyper-acetylation and H3K9 hypo-di-methylation at PPARγ2 promoter in GIO BMSCs. These epigenetic modifications were involved not only in PPARγ2 expression but also in osteoporotic BMSCs adipogenic differentiation potential. We also found that β-catenin/TCF3 protein complex played an important role in the establishment and maintenance of epigenetic modifications at PPARγ2 promoter in osteoporotic BMSCs. Therefore, the current project aims to investigate how β-catenin/TCF3 protein complex modulates the epigenetic modifications at PPARγ2 promoter in GIO BMSCs through interactions with epigenetic-modifying enzymes, including the members of protein complexes, the protein interaction domains and the dynamic patterns of protein complex during bone marrow adipogenesis of GIO. In addition, we will make attempts to employ transgenic technologies to inhibit bone marrow adipogenesis and rescue skeletal pathological phenotypes of GIO mouse through regulating epigenetic modifications. The current project will provide deeper insights into the GIO molecular mechanisms and facilitate the research and development of new strategies to treat GIO.

糖皮质激素性骨质疏松（GIO）是最常见的继发性骨质疏松，发病机制是研究热点。骨髓脂肪化是未足够重视的重要病理表现。成骨与脂肪细胞均来自骨髓基质细胞，存在负相关平衡关系。减弱骨髓基质细胞成脂潜能，进而抑制骨髓脂肪化是治疗GIO的重要策略。前期我们发现GIO小鼠骨髓基质细胞成脂开关PPARγ2启动子DNA低甲基化、组蛋白高乙酰化和H3K9低（双）甲基化上调PPARγ2表达活性，增强骨髓基质细胞成脂潜能；β-catenin与上述表观遗传修饰的建立有关。因此，本项目拟揭示GIO小鼠骨髓基质细胞β-catenin如何通过与表观遗传修饰酶相互作用调控PPARγ2启动子表观遗传修饰，包括蛋白复合体组成、相互作用位点和骨髓脂肪化过程中蛋白复合体动态规律。同时，我们拟利用转基因动物、以表观遗传修饰为靶点抑制GIO骨髓脂肪化、纠正骨病理表型。本项目将为GIO发病机制阐明和新治疗手段建立提供理论基础和实验依据。

糖皮质激素性骨质疏松（GIO）是最常见的继发性骨质疏松，发病机制是研究热点。骨髓脂肪化是未足够重视的重要病理表现。成骨与脂肪细胞均来自骨髓基质细胞，存在负相关平衡关系。减弱骨髓基质细胞成脂潜能，进而抑制骨髓脂肪化是治疗GIO的重要策略。前期我们发现GIO小鼠骨髓基质细胞成脂开关PPARγ2启动子DNA低甲基化、组蛋白高乙酰化和H3K9低（双）甲基化上调PPARγ2表达活性，增强骨髓基质细胞成脂潜能；β-catenin与上述表观遗传修饰的建立有关。因此，本项目拟揭示GIO小鼠骨髓基质细胞β-catenin如何通过与表观遗传修饰酶相互作用调控PPARγ2启动子表观遗传修饰，包括蛋白复合体组成、相互作用位点和骨髓脂肪化过程中蛋白复合体动态规律。同时，我们拟利用转基因动物、以表观遗传修饰为靶点抑制GIO骨髓脂肪化、纠正骨病理表型。而且，围绕老年骨质疏松骨质流失和骨髓脂肪化的分子生物学机制，本项目亦进行了更深层次的研究。从骨髓基质细胞所处骨髓微环境这个角度，我们发现：老年小鼠发生骨质流失和骨髓脂肪化、老年小鼠骨髓基质细胞体外成骨/成脂定向分化潜能失衡、衰老小鼠骨髓微环境中CCL3表达水平升高、骨髓微环境中CCL3可抑制骨髓基质细胞成骨分化潜能促进成脂分化潜能和应用CCL3中和抗体可纠正老年骨质疏松小鼠骨质流失和骨髓脂肪化。本项目的研究为老年骨质疏松分子机制的阐明和新治疗靶点/方法的建立提供实验依据。