SDF-1/CXCR7轴在3D培养的间充质干细胞向缺血心肌迁徙中的作用

The majority of monolayer culture expanded mesenchymal stem cells (MSC) are entrapped in lungs after intravenous administration, leading to low levels of circulating MSC and engraftment to the ischemic myocardium. Our recent studies show that 3D culture of MSC substantially decreases their entrapment in the lungs, thus allowing more MSC trafficking in the circulation and homing to the ischemic myocardium. Stromal derived factor (SDF)-1, which is upregulated by ischemia and considered a key mediator of hematopoietic stem cell homing along with its receptor CXCR4. However, CXCR4 is expressed only in a small fraction of MSC. In contrast, CXCR7, the newly identified receptor of SDF1, is expressed in most freshly isolated MSC, although its surface expression quickly disappears after culture expansion in monolayer, implying the CXCR7 is more likely a homing receptor for MSC. In this study, we will examine whether 3D culture restores the expression of CXCR7 in MSC; and determine the role of the receptor in MSC migration, trafficking and homing to the ischemic myocardium by overexpressing the gene in monolayer MSC and 3D MSC with low endogenous CXCR7 expression.

传统贴壁培养使间充质干细胞（MSC）静脉注射后大多数阻塞在肺，导致循环MSC水平极低，到达的缺血心肌的数量极少。我们的前期研究显示，3D培养使MSC肺阻塞大幅度降低，为研究MSC向缺血心肌迁徙奠定了基础。缺血损伤使基质衍生因子(SDF-1)的表达增加，但其传统受体CXCR4仅在极少数MSC表达，而新发现的受体CXCR7在多数新分离的MSC中有表达，提示CXCR7更有可能是MSC向缺血组织迁徙的受体。然而，CXCR7的表达在MSC贴壁培养后快速下降。本项目拟研究1）3D培养是否恢复MSC对CXCR7的表达；2）通过过表达CXCR7，研究CXCR7对MSC移行和向缺血心肌迁徙的作用。

MSCs 的归巢能力是MSCs 的一个重要特性，是MSCs 在静脉注射后能够自动向损伤组织移行的基础，也是静脉注射MSCs 治疗心肌梗塞等内脏损伤和系统性疾病的理论依据。该项目重点研究了1）3D培养是否恢复MSCs对CXCR7的表达；2）趋化因子受体CXCR7在MSCs迁徙中的作用及其可能的机制。我们的结果显示，CXCR7提高了2D培养的MSCs的迁徙能力；3D培养的MSCs的迁徙能力，相对于2D培养的MSCs来说，有显著提高；我们进一步发现3D培养本身能够提高CXCR4/CXCR7的mRNA表达和膜表面的表达。所以，高表达CXCR7的MSCs进行3D培养之后，此时，CXCR7并没有进一步提高3D培养的MSCs的迁徙能力。接下来，我们研究了3D培养MSCs 对梗塞心肌的迁徙能力和功能修复能力。同时，我们的研究还发现CXCR7调控MSCs的命运决定，并进一步发现，CXCR7/CXCR4激活的整合素信号分子Kindlin2在调控MSCs的命运决定中起关键作用。该项目对MSCs的再生移植提供了理论基础。