组蛋白去甲基化酶KDM3A和KMD4C在MSC衰老和老年性疾病中的作用和应用研究

Adult mesenchymal stem cells (MSCs) are extremely important for tissue homeostasis, regeneration and repair. MSCs are sensitive to age-related conditions, and their regenerative capability is decreased in aged person. Conversely, MSC senescence contributes to aging-related diseases, such as osteoporosis and osteoarthritis. Nevertheless, the mechanism underlying MSC senescence is largely unknown. Previous work has shown that cellular senescence is accompanied by extensive spatial rearrangement of heterochromatin. However, it is unclear whether heterochromatin reorganization is responsible for MSC aging and what are the mechanisms involved in the heterochromatin reorganization..We have found that MSC senescence is accompanied by a process of dynamic heterochromatin reorganization. We have also found that the KDM3A and KDM4C H3K9 demethylases are highly expressed in the senescent MSCs. Overexpression of KDM3A or KDM4C recapitulates accelerated cellular senescence. Furthermore, KDM3A and KDM4C interact with and regulate chromatin component proteins. Based on these results, we hypothesize that KDM3A and KDM4C play critical roles in heterochromatin reorganization, which is essential for MSC senescence. The goals of this project are to gain novel insights into the role of demethylases in cellular senescence and provide potential epigenetic targets for senescence intervention. ..The proposed study will reveal previously undefined roles of histone demethylases in controlling MSC senescence. The findings from our studies will provide novel insights into the chromatin reorganization that governs stem cell senescence and aging process, which may provide novel therapeutic targets for intervention of geriatric diseases and improvement of stem-cell based therapy.

间充质干细胞(MSC)的衰老和机体总体水平的衰老紧密相关。组蛋白修饰是一种非常重要的表观遗传修饰,参与多种生命过程。然而，我们对MSC衰老过程中涉及到的组蛋白修饰以及相关调控机制却知之甚少。课题组的前期工作发现MSC 的生理性衰老过程伴随着异染色质结构和H3K9去甲基化酶KDM3A和KDM4C的动态改变。过表达和敲降KDM3A或KDM4C都会导致MSC的衰老。KDM3A和KDM4C调控多个异染色质结构基因的表达。为此，本课题拟采用胚胎干细胞定向分化、干细胞生物学、分子生物学、生物信息学和动物疾病模型等生物医学技术,从组蛋白修饰这一全新的角度阐释KDM3A和KDM4C在异染色质重塑和MSC衰老进程中的作用。其最终目标是揭示调控异染色质结构重塑及MSC衰老的全新表观遗传机制，从而帮助MSC越过细胞衰老屏障，增强修复功能并为延缓与MSC衰老密切相关的老年性疾病提供最新的分子靶标。

间充质干细胞,尤其是来源于骨髓的MSC，不仅是造血干细胞的支持细胞，提供了血细胞赖以不断更新的微环境，而且还积极参与机体的骨骼重建和其他组织的损伤修复，在机体的生理和病理性衰老进程中均扮演了至关重要的角色。大量研究表明，细胞在衰老过程中往往伴随着广泛的染色质重塑过程。组蛋白甲基化修饰是一种非常重要的表观遗传修饰,参与调节异染色质形成、X染色体失活、基因印记及DNA的损伤修复等多种生命过程。虽然组蛋白修饰和异染色质结构的改变是衰老进程中的重要事件，我们对MSC衰老过程中涉及到的组蛋白修饰的改变以及相关调控因子知之甚少，该领域的研究工作国内外均处于起步阶段。.本研究瞄准衰老和成体干细胞研究领域所面对的核心问题，从组蛋白修饰这一全新的角度阐释组蛋白去甲基化酶KDM3A和KDM4C在异染色质重塑和MSC衰老进程中的作用。我们首先通过胚胎干细胞MSC定向分化和有条件诱导敲降的细胞模型明确KMD3A和KDM4C在异染色质重塑和MSC衰老的不同阶段扮演了重要的角色。其次通过系统的干细胞生物学和分子生物学，逐步阐明KDM3A和KDM4C通过组蛋白去甲基化酶的活性在转录水平上调控染色质凝集素组成蛋白NCAPD2和NCAPG2的表达，同时与这些蛋白形成复合物参与异染色质重塑的调控。异染色质的重塑和DNA损伤保护密切相关，缺乏由KDM3A 和KDM4C主导的异染色质重塑，令间充质干细胞更快地进入衰老状态。最后我们在Kdm3a敲除小鼠中发现，Kdm3a的缺失造成骨质疏松和骨髓间充质干细胞的老化。过表达NCAPD2可以逆转干细胞老化的表型。最后，我们发现槲皮素具有上调KDM3A的作用，可以逆转敲除鼠中的骨质疏松。本研究首次发现KDM3A和KDM4C不仅可以通过它们的去甲化酶活性调控H3K9的修饰而控制靶基因的转录，而且可以充当骨架蛋白招募其它异染色质组装蛋白共同参与异染色质的重塑过程。本课题的完成将有望为成体干细胞体内移植治疗各种疾病中普遍存在的细胞老化问题提供新的解决办法，也为干细胞介导的再生医学和骨骼系统疾病治疗方法的研究开辟了新的方向，具广阔的临床应用前景。