肿瘤及肿瘤干细胞发生与成体干细胞衰老、分化异常导致的恶性转化密切相关。DNA损伤应答系统通过维持基因组稳定性在干细胞自稳中发挥多层面作用。XPC 作为重要的DNA修复与细胞周期调控分子，其异常可导致多种肿瘤发生，但XPC在干细胞自稳中的角色尚未探及。骨髓间充质干细胞（mesenchymal stem cell,MSC）具有多向分化能力，但MSC体外长期培养可导致衰老或恶转，结合我们首次初步发现XPC缺失则可导致小鼠骨髓MSC分化下降，促进衰老及恶转等重要研究线索，本研究将采用XPC基因敲除鼠模型，结合细胞学与整体动物，通过揭示XPC调控端粒结合蛋白维持端粒稳定性及调控GADD45A参与分化关键基因去甲基化调控等新功能，深入解析MSC衰老、分化异常与恶性转化的内在联系。本研究不仅将突破DNA损伤应答系统经典作用，拓展XPC分子的新功能，同时将有助于揭示干细胞衰老及恶性转化的普遍分子机制。

Mesenchymal stem cells（MSC）are widely used in clinical treatment, however, aging and the potential malignant transformation of MSCs in the long-term culture in vitro seriously affect their application security. The stability of MSCs is relied on the functional DNA damage response. The XPC protein play an important role in the repair of DNA damage and genome stability, the absence of the XPC will increase tumor risk. Our previous work found that aging human MSCs habor defective DNA repair ability. It is also preliminary observed that the XPC knockout promote mesenchymal stem cell aging ，differentiation defection and malignant transformation, and its may be related to genomic instability induced by telomere shortening and epigenetic dysregulation of differention related genes. The project will be in-depth study the mechanism of XPC knockout in mesenchymal stem cell aging, differentiation and malignant transformation. In this project, firstly, we will make an effort to provide the fact that the defection of XPC will promote the aging and malignant transformation of MSCs companied with attenuated differentiation. Secondly, we will try to explore that the defection of XPC contribute to the telomere fusion or shortening via promoting the degragation of temolere-binding protein . Thirdly, we will focus on exploring the role of XPC in the repair-related DNA demethylation .We raised the notion that XPC can promote the differentiation of MSC, via activating DNA demethylation of differentiation related gene through GADD45A. This work will reveal the mechanism of the stability of mesenchymal stem cells and provide a new sight on the origin of cancer stem cells.