SRF-N调控TGF-β1表达对心肌梗死后心脏干细胞分化的作用研究

Cardiac stem cell (CSC) plays an important role in repairing the injured myocardium and improving the cardiac function. How to effectively improve the differentiation ability of CSC and enhance its function is one of the key and difficult part for the regenerative medicine after myocardial infarction(MI). Serum Response Factor (SRF) is a heart-enriched transcription factor and regulates the cardiac-specific gene expression. Our teammembers have discovered that full-length SRF can be cleaved by Caspase 3 and generate the dominant-negative transcription factor SRF-N that blocks the cardiac specific gene expression. Our Recent studies further demonstrated that transforming growth factor（TGF-β1）was a new target gene of SRF. It is well known that TGF-β1 is a potent factor mediating stem cell differentiation. Therefore, we hypothesis that generation of dominant-negative SRF-N by activated Caspase 3 post MI may be responsible for the suppression of TGF-β1,and then disturb the CSC differentiation and limit the improvement of cardiac function.In this project, we would study the role of SRF-N in CSC differentiation in vitro, as well as repairing the injured myocardium and improving the cardiac function in vivo. Most importantly, the underlying molecular mechanisms regarding the SRF-N-mediated CSC differentiation will be investigated. We expect that the results of this proposal would provide a potential intervention target for improving the efficiency of CSC transplantation. The outcomes of this project may help pushing forward the CSC-based regenerative medicine from the experimental evidences to the clinical applications.

心脏干细胞（CSC）在修复心肌损伤、改善心功能中扮演重要作用。如何有效提高心肌梗死（MI）后CSC的分化能力并增强其功能是MI后再生医学研究的关键和难点之一。血清反应因子（SRF）是在心脏富集的转录因子并调控心肌特异基因的表达。课题组前期研究发现激活的Caspase 3能将完整的SRF分子剪切成SRF-N片段从而竞争性抑制下游靶基因表达，近期又证实转化生长因子-β1（TGF-β1）是SRF新的下游靶基因，而TGF-β1是诱导干细胞分化的关键因子。鉴于此，我们假设MI后产生的剪切片段SRF-N能够竞争性抑制TGF-β1表达，从而干扰CSC的有效分化并限制其功能发挥。本项目拟从体内、体外两个层面研究SRF-N影响CSC分化及其在修复心肌损伤、改善心功能中的作用并探讨其分子机制，以期适当干预以提高CSC移植的有效性。该研究的成功将推动基于CSC的再生医学由实验向临床应用迈进。

近年来关于成体心脏干细胞（CSCs）的理论受到极大的挑战。本研究团队在实际围绕CSCs工作开展的过程中发现分离成年鼠心脏c-Kit+的细胞相对困难且增殖缓慢，严重影响实验的进程。由于新生鼠的心脏修复能力与成年个体截然不同，在项目具体开展过程中我们分离了乳鼠心脏c-Kit+细胞，结果发现在TGF-β1诱导分化下，乳鼠心脏c-Kit+细胞可出现多向分化的潜能。而过表达SRF的N端片段（SRF-N）则可抑制心脏谱系的分化，其机制可能是SRF-N降低NKX2.5的启动子活性。进一步实验显示低氧刺激（2%O2）可诱导乳鼠心脏c-Kit+细胞中SRF-N片段的产生。因而，上述结果提示缺氧能够刺激乳鼠心脏c-kit+细胞产生SRF-N片段而对细胞分化产生负面影响，研究结果为心脏再生医学提供了新策略。