TGFBR3介导TRAF6/TAK1信号轴参与MSCs向软骨细胞终末分化进程

Mesenchymal stem cells (MSCs) are well known as viable cell source for tissue-engineered cartilage. However, a yet-unsolved problem is terminal chondrocyte differentiation at later stage of chondrogenesis, instead of stable articular cartilage-like tissue. Previous evidence have shown that the imbalace of Smad1/5/8 signal pathway and Smad2/3 signal pathway was associated with terminal differentiation and mineralization. Previously, we have found that there was constitutively activation of p38 MAP kinase pathways at later stage. Moverover, TGF-β receptor Ⅲ (TGFBR3) had the highest expression and a positive correlation expression with RUNX2, a critical transcription factor with terminal chondrocytic differentiation. On this basis, we here propose the hypothesis that the cross-talk of Smad pathway with no-Smad pathway was involved the terminal differentiation. Further, “TGFBR3” is acted as the “switch ”duing this proscess. This project is intended to study the effects of TGFBR3 regulates terminal chondrocytic differentiation of MSCs by activation of TRAF6/TAK1 signal axis to shift Smad2/3 axis to Smad1/5/8 axis. This will help us better understand the regulatory mechanism of MSCs terminal differentiation process, and find the inhibitor of terminal chondrocytic differentiation, aiming to provide theoretical foundation for the future use of MSCs to construct tissue engineered cartilage.

已知利用MSCs体外诱导成软骨分化过程中易发生软骨细胞终末分化，从而不能构建表型稳定的组织工程化透明软骨。而有关机制尚不完全清楚。课题组前期以TGF-β3诱导BMSCs成软骨分化发现：分化后期Smad2/3信号轴和Smad1/5/8信号轴失衡可能导致了终末分化的发生。其调节机制需进一步阐明。前期预实验结果显示：分化后期，TGF-β受体Ⅲ (TGFBR3)表达明显增加且与终末分化关键转录因子RUNX2的表达呈正相关关系，同时非经典Smad途径（p38MAPK）持续过度激活。由此提出假说：分化后期非经典Smad通路与经典Smad通路“串话”诱导了Smad信号轴转换，TGFBR3可能成为其转换的“开关”? 为此，本项目探索TGFBR3是否介导TRAF6/TAK1信号轴参与Smad信号轴转换。为揭示MSCs发生软骨终末分化有关机制，寻找防止终末分化的调控靶点，构建表型稳定的组织工程化软骨提供依据。

已知利用间充质干细胞（MSCs）体外诱导成软骨分化过程中易发生软骨细胞终末分化，从而不能构建表型稳定的组织工程化透明软骨，但有关机制尚不完全清楚。本项目利用TGF-β3诱导MSCs成软骨分化过程中，研究发现分化后期Smad2/3信号轴和Smad1/5/8信号轴失衡可能是导致了终末分化的发生的重要因素。进一步研究发现，微小RNA（miRNA）在调控MSCs向软骨分化以及终末分化中起到重要的作用。体内外研究结果显示: miR199b-5p，miR-221/222-3p及miR-23a可以参与MSCs向软骨分化与终末分化进程。抑制miR-221/222-3p和过表达miR-23a可以抑制MSCs向软骨细胞终末分化。进一步阐明其有关机制，发现此微小RNA可介导MAPK信号通路以及自噬参与MSCs向软骨细胞终末分化进程。并且TGF-β受体Ⅲ (tgfr3)可作为介导Smad信号轴转换的关键因子。基于本研究结果，微小RNA以及相关信号通路中关键因子可以作为抑制MSCs向软骨细胞终末分化的靶点。因此，本项目的研究成果，为揭示MSCs发生软骨终末分化有关机制，寻找防止终末分化的调控靶点，为构建表型稳定的组织工程化软骨提供依据，进而为推进应用间充质干细胞在临床上治疗软骨相关疾病奠定基础。