间充质干细胞维持低免疫原性的机制研究

Most current studies regarding the low immunogenicity of mesenchymal stem cells (MSC) focus on the induction possibility of immune response and the influence of proinflammatory factors on MHC expression. The mechanism of MHC expression onto MSC surface is unknown. Reports from the project applicant and other researchers showed that the immunogenicity of MSC and the surface expression of MHC could be induced by proinflammatory factors. There was difference of MHC expression among MSCs at different biological status. In spite of low or no expression of MHC on MSC surface, abundant MHC was detected in cytoplasm. It suggests that the surface expression of MHC is regulated at post-translation stage. Therefore, the purpose of this project is to investigate the effect of translocation-related molecules on surface expression of MHC by MSC, which are at different biological status. To achieve the purpose, this project will establish a MHC knock-down in vitro model for MHC translocation study via RNAi. A general expression profile of MHC and other translocation related molecules in MSC will be firstly analyzed. Then 1-2 important translocation related molecules will be further investigated by using the MHC knock-down model and functional assays. In summary, this project tries to explore the importance of MHC translocation in low immunogenicity of MSC at different biological status. It facilitates to find the critical regulatory molecules in MHC expression pathway so as to prolong the low immunogenicity of MSC.

目前MSC移植免疫原性研究大多针对MSC能否引起免疫应答，以及促炎症因子对表面MHC表达的影响，而对MHC表达的调控机理尚未明确。课题组前期研究（J Cell Sci. 2012）及文献报道MSC的免疫原性可被诱导，在炎症因子作用下不同发育阶段的MSC被诱导后MHC表达程度有差异。未刺激状态MSC表面低表达或不表达MHC，但胞浆内可检测到大量MHC，意味着MHC的表面表达主要在翻译后受调控。因此本项目主要探索转运途径中关键因子对不同发育阶段MSC表面MHC表达的调控。该实验首先对不同发育阶段MSC的表面和胞浆内MHC以及重要转运相关因子表达初步分析，用RNAi技术建立体外MHC转运模型，探寻MHC转运的关键调控因子。该项目发现将揭示MHC的转运途径对MSC维持低免疫原性的重要作用，为促进MSC的移植存活、用于疾病治疗提供了实验基础和新思路。

间充质干细胞（MSCs）作为再生医学中一种重要的细胞治疗工具，其低免疫原性和免疫调控功能对治疗和预防多种疾病发挥重要作用。然而其免疫原性在不同的炎性微环境中会发生不同程度的强化，目前大多数报道尚停留在观察这种现象，对产生这种强化现象的调控机制缺乏进一步研究。本课题以组织缺损治疗中纠正炎性微环境促进再生修复为引，以主要促炎症因子γ干扰素对不同生理状态下的MSCs不同处理时长诱导I型主要组织相容性抗原（MHC-I）的表达为主线，探讨其对产生移植排斥的影响，并进一步调查其产生的机制。结果显示MSCs随着体外扩增时间增加而逐渐老化，且表面表达HLA-I水平升高，在促炎症因子γ干扰素处理后，尽管无论年轻还是衰老的MSCs细胞内HLA-I合成升高，但传代次数少的MSCs可以自我下调表面HLA-I表达，传代次数多的细胞则这种调控能力显著减弱。然而尽管如此，在体内炎性环境里，传代次数少的MSCs仍能够引起免疫应答，产生免疫记忆。经过基因芯片分析，发现经γ干扰素处理后，细胞内大量基因发生变化，经部分数据分析，PPARγ可能参与这一过程。这些证据为进一步操纵调控MSCs免疫原性提供了重要的生物学信息和可能的途径。PPARγ是否为关键调控点还需要进一步探索，找到MSCs免疫原性的关键调控点对治疗方案设计、疗效维持和治疗预后都有深远的科学和实用价值。