SMYD1介导骨髓微环境表观遗传调控间充质干细胞衰老的作用机制研究

The epigenetic regulation of senescent microenvironment on bone marrow mesenchymal stem cells (BMSCs) senescence remains unclear. Here, we found that senescent bone marrow microenvironment promoted BMSCs senescence and identified a key epigenetic factor: histone H3 lysine 4 (H3K4) methylase SMYD1. Therefore, we hypothesize that “bone marrow senescent microenvironment upregulates SMYD1 expression in BMSCs, which activates senescent related genes by methylation of H3K4 and thus induces BMSCs senescence, causing senile osteoporosis”. To test this hypotheses, first, we will measure the role of senile bone marrow supernatant on the BMSCs senescence and SMYD1 gene expression; Second, BMSCs specific SMYD1 knockout mice and transgenic mice will be constructed to measure the effects of SMYD1 on BMSCs senescence and bone mass; then, the downstream pathways network of SMYD1/H3K4 will be identified and constructed; at last, we will test whether BMSCs aptamer-siRNA-SMYD1 could inhibit the senescence of BMSCs and promote bone formation in aged mice. The completion of this project will illustrate the pathogenesis and supply new ideas for prevention and treatment strategies of senile osteoporosis.

衰老微环境调控骨髓间充质干细胞（BMSCs）衰老的表观遗传机制尚不清楚。我们前期研究发现衰老骨髓微环境促进BMSCs衰老，并筛选出关键表观遗传因子：组蛋白H3第4位赖氨酸（H3K4）甲基化酶SMYD1。本课题拟从此着手，提出“骨髓衰老微环境上调BMSCs表观遗传因子SMYD1，其通过甲基化H3K4激活衰老靶基因，促进BMSCs衰老，引起老年性骨质疏松”的假说。为了验证此假说，首先我们检测骨髓微环境对BMSCs衰老及SMYD1的作用；其次构建BMSCs特异性SMYD1基因敲除/转基因小鼠，观察BMSCs衰老及骨量的变化；识别SMYD1下游H3K4靶基因，构建SMYD1/H3K4调控BMSCs衰老的信号通路网络；最后，探究BMSCs适配体-siRNA-SMYD1复合物能否减缓BMSCs衰老，促进骨形成。本项目的顺利开展将为探索老年性骨质疏松发病机理与防治策略提供新思路。

根据全国流行病学调查估算，我国有2亿以上的人群存在低骨量问题，其中60岁以上人群中老年性骨质疏松在老年人群中发病率高达56%。老年性骨质疏松症存在发病率高、易致骨折、骨折致死率高等特点，对我国人民生命健康的危害日益严重，造成了沉重的经济压力和社会的负担。衰老是增龄性骨丢失与老年性骨质疏松发生的决定性因素。细胞在衰老过程中产生衰老相关分泌表型（senescence-associated secretory phenotype, SASP），释放促炎因子、生长因子及趋化因子等一系列细胞因子，改变骨髓微环境，导致骨髓间充质干细胞（BMSCs）衰老、成骨分化减退及成脂分化增强等一系列生物学功能改变，引起骨骼衰老性变化导致老年性骨质疏松。通过高通量测序筛选、细胞分子实验、构建转基因小鼠模型、衰老小鼠模型、骨质疏松症模型以及骨折模型等方法，我们发现在衰老过程中，衰老的免疫细胞在骨髓腔中累积，释放相关因子调控BMSCs上的Plexin-B2受体，使骨髓腔内成骨细胞减少，脂肪细胞堆积增加，出现衰老相关的BMSCs 命运分化偏移，导致骨骼衰老以及骨质疏松症。