Hgs/ESCRT调节体内间充质干细胞自我更新和分化的机制研究

Mesenchymal stem cells (MSCs) are multipotent tissue stem cells required for the development and homeostasis of skeleton system. Due to the lack of in-depth studies on the cell markers and tissue localization of in vivo MSCs, little is known about the fate-determination mechanisms by which MSCs originate, self-renew and differentiate. Functions of endosomal sorting complex required for transport (ESCRT) machinery are involved in multiple cytological processes via controlling the biogenesis of multivesicular bodies as well as the membrane remodeling events in eukaryocytes, however, their roles in MSCs are yet far beyond elucidation. Our preliminary work has established multiple Cre-Loxp-based gene ablation plus lineage tracing mouse models in which the key component of ESCRT complexes, Hgs, was deleted specifically in periosteum MSCs and bone marrow MSCs. Interestingly, we found that Hgs/ESCRT is essential for the self-renewal and osteogenic/chondrogenic differentiation of both periosteum and bone marrow MSCs. In this study, we will clarify the cellular and molecular mechanisms underlying the fate determination of in vivo MSCs as well as their roles in development and diseases, which may conceptually revise our understanding of MSCs and improve the utilization of them.

间充质干细胞（mesenchymal stem cell，MSC）是骨骼发育和稳态维持的组织干细胞。由于长期缺乏体内MSC分子标志物及组织定位的研究，人们对于MSC的来源、自我更新、分化等命运决定机制知之甚少。内体转运分选复合体（endosomal sorting complex required for transport, ESCRT）是近年来发现的真核细胞多囊泡体形成及运输、生物膜重塑的分子机器，参与众多重要的细胞生物学过程，但其对于MSC的生理功能及作用机制一无所知。我们通过基于Cre-LoxP介导的体内细胞谱系示踪和基因功能验证体系，靶向骨膜MSC及骨髓MSC，发现Hgs依赖的ESCRT对于促进MSC自我更新、决定成骨/软骨分化选择具有重要作用。我们的研究将深入研究并阐明体内MSC命运决定的细胞和分子机制及其在发育和疾病中的功能，为精准应用MSC提供理论基础。

骨骼干细胞（skeletal stem cell，SSC）是骨骼发育和稳态维持的组织干细胞。由于长期缺乏体内SSC分子标志物及组织定位的研究，人们对于SSC的来源、自我更新、分化等命运决定机制知之甚少。本课题利用多种特异性标记SSC/骨骼间充质细胞（mesenchymal stromal cell，MSC）的Cre/Dre重组酶工具小鼠、细胞遗传谱系示踪小鼠以及条件基因敲除小鼠，综合骨骼组织单细胞转录组测序数据及其生物信息学分析，提供了直接的体外和体内实验证据证实了Hgs/ESCRT通过下调GSK-3β维持骨膜SSC中的Wnt/β-catenin信号通路，从而决定骨膜SSC的成骨/成软骨分化命运选择的新机制；发现了新的骨膜和骨小梁干骺端SSC类群及特异的分子标记；发现了Tgfbr2依赖的TGF-β信号通路通过协同Wnt/β-catenin信号通路调控牙髓间充质干细胞成牙本质/成骨分化命运选择的功能和机制。这些研究结果揭示了Hgs/ESCRT调节的重要信号通路调控SSC/MSC自我更新和分化命运的新机制，为全面理解骨骼发育和稳态维持以及相关骨骼疾病发生机制提供了新的理论基础。