BMP信号在Lgr5+小肠干细胞命运决定中的作用及其机制

Adult stem cells can undergo self-renewing and retain pluripotency to differentiate to certain cell types in the adult tissue and organ. Their regenerative ability plays an essential role in maintaining homeostasis and repairing tissue damage. The balance between the self-renewal and differentiation of intestinal stem cells, which locate at the bottom of the intestinal crypts, isare critical for the intestinal epithelium homeostasis. Lgr5 was recently identified as the first definitive intestinal stem cell marker. Although genetic studies have revealed the important function of BMP signaling in maintenance of intestine stem cells in the crypt niche, how BMP signaling controls the fate of Lgr5+ in testinal stem cells is unclear. By analysis of the intestine of the mice in which BMPR1a was conditionally inactivated in the Lgr5+ intestinal stem cells, our preliminary data showed suggested that BMP signaling could suppress the stemness of Lgr5+ intestinal stem cells. In this proposal, we plan to use the RNA sequencing approach to identify novel BMP targets and further investigate how these target genes may affects the self-renewal and differentiation of Lgr5+ intestinal stem cells. As Wnt signaling plays an essential role in Lgr5+ intestinal stem cells, we will also study the crosstalk between BMP and Wnt signaling in the Lgr5+ intestinal stem cells. We anticipate that our research will provide new insights into the fate determination of Lgr5+ intestinal stem cells and lay a foundation for its potential applications in the regenerative medicine.

人体组织和器官内具有自我更新、多向分化潜能的成体干细胞是维持组织稳态、修复组织创伤的关键。位于小肠腺窝中的小肠成体干细胞对维持小肠上皮组织稳态有重要意义。虽然研究报道了BMP信号对小肠陷窝微环境的影响，但由于小肠干细胞的标记物Lgr5刚被发现，BMP信号如何通过调控Lgr5+小肠干细胞中靶基因表达影响其命运决定，进而调节小肠上皮组织稳态尚不清楚。在前期工作中，我们分析了BMP受体BMPR1a基因在Lgr5+成体干细胞中特异性敲除小鼠的小肠表型，发现Lgr5+小肠干细胞中的BMP信号可以抑制其干性。在本项目中，我们计划结合表达谱测序手段寻找BMP的靶基因，进而研究其影响Lgr5+小肠干细胞自我更新和分化的分子机制。另外还将在Lgr5+小肠干细胞中探讨BMP和Wnt信号通路在基因表达层面的crosstalk。预期将为全面了解Lgr5+小肠干细胞的命运决定方式，进而为再生医学领域提供重要基础。

肠道是人体消化系统中重要的组织器官，其发挥着食物消化、营养吸收、废物排泄、抵御外来微生物和病原体等重要功能。与这些功能相应，肠道上皮是成体哺乳动物中更新速度最快的。其快速更新是由位于肠底部隐窝处的Lgr5+干细胞所驱动的。虽然已有多篇文章报道，Wnt信号通路、BMP信号通路、Notch信号通路和EGF信号通路等在小肠干细胞的命运决定中发挥重要作用。然而BMP信号是如何调控小肠干细胞的命运决定尚不清晰。. 本项目发现肠上皮的BMP信号在限制Lgr5+肠干细胞过度增殖中发挥着重要作用，且不依赖于Wnt/β-catenin信号通路。机制上，Smad4通过招募HDAC1直接对肠干细胞的干性基因进行抑制从而抑制了肠干细胞的干性。同时，系统研究阐释了在Lgr5+干细胞命运决定中至关重要的Myh9-Rac1-PAK1-Akt通路；揭示了TNKSs通过抑制细胞凋亡调控肠上皮细胞稳态，在哺乳动物个体水平上证明了其上调Wnt信号通路的作用机制。通过小分子及小鼠模型论证了抑制BMP信号和激活Wnt信号在小肠类器官培养中的重要作用，并由此构建了无生长因子2ki小分子培养体系。. 本项目的各项研究可帮助进一步阐述BMP信号在Lgr5+肠干细胞命运决定中的重要作用，深入了解BMP信号和Wnt信号等微环境对肠上皮细胞的影响，并为未来结直肠癌的治疗提供潜在靶点。构建的2ki培养体系可以极大降低体外培养成本，有助于精准医疗的推进。

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