心脏细胞间远距离通讯结构—膜纳米管的形成机制及其对心脏损伤的修复作用

Membrane nanotube (MNT) is a novel structure that connects the mammalian cells over long distance. The classical view that paracrine and gap junction are the only forms of the "communication" between cardiomyocytes (MCs) and cardiofibroblasts (FCs). However, our group first reported that MNTs also can be observed between MCs and FBs, and quantum dots (QDs), Ca2+and mitochondria can be transferred along them between cells over long distance. Although the structure titillates the great interest of us, the molecular basis for MNTs formation, the physiopathological significance and whether it facilitates the repair of the injured CMs remain to be elucidated. In order to clarify these questions, we try to further study the ultrastructure and the composition of MNTs between mouse's CMs and FBs ; examine whether the cytoskeleton related proteins are involved in the regulation of MNTs formation; investigate when myocardial ischemia and hypoxia, whether MNTs can enhance the MCs contract and promote the repair of the mitochondrial injury by transferring Ca2+ and mitochondria. We also plan to study the significance of MNTs in organization level by using myocardial infarction model. This study posts a challenge to the classical "cardiac communication" theory, makes a suggestion that MNT is the important structure for long distance "communication" between cardiac cells, and uncovered the biologic significance of it.

膜纳米管是新近发现的一种细胞间远距离连接结构。传统理论认为心肌细胞和心肌成纤维细胞间"通讯"只有旁分泌和缝隙连接途径。我们课题组首次报道在心肌细胞和心肌成纤维细胞间存在膜纳米管结构，它能介导量子点、线粒体和钙离子等在心脏细胞间的运输。尽管人们对膜纳米管的结构和功能产生了兴趣，但尚不清楚膜纳米管形成的调控机制，膜纳米管在心脏细胞间传递信号的功能意义，甚至心肌受损时膜纳米管能否帮助修复？为此，本项目拟在前期工作基础上，分析小鼠心脏细胞间膜纳米管超微结构和组成成分，探讨细胞骨架相关蛋白对心脏细胞膜纳米管形成的调节作用；探讨在心肌缺血缺氧/线粒体损伤时，膜纳米管能否传输钙信号和线粒体帮助心肌细胞恢复收缩功能和修复线粒体损伤；通过心肌梗死模型，在组织水平进一步探讨膜纳米管的功能意义。研究结果是对心脏细胞间通讯理论的补充，明确膜纳米管是心脏细胞间远距离通讯的结构基础，可帮助心肌的损伤修复。

膜纳米管是新发现的一种细胞间远距离连接解剖结构。传统理论认为心肌细胞和心肌成纤维细胞间“通讯”只有旁分泌和缝隙连接途径。在我们课题组前期研究发现在心肌细胞和心肌成纤维细胞间存在膜纳米管结构，且可传递量子点和钙离子的基础上，在项目执行中，（1）进一步观察了心脏膜纳米管的形成和结构特点，发现微丝是膜纳米管必需的结构蛋白，微管是膜纳米管运输线粒体所必需的，KIF5B是在心脏活细胞间运输线粒体的马达蛋白。（2）线粒体进行跳跃式的变速运动，平均运动速度为17.5±2.1 nm/s，最快的速度可以达到256.0 nm/s。（3）利用心肌细胞的缺氧-复氧病理模型，发现成纤维细胞可通过膜纳米管将线粒体传输到受损心肌细胞中，从而减少线粒体ROS产生和心肌细胞凋亡。研究结果提出了心脏细胞间通讯的新概念，膜纳米管是心脏细胞间远距离通讯的结构基础，可帮助心肌损伤修复。此外, 利用活细胞荧光成像技术，我们实时观察到细胞膜上的TGF-β受体在两种内吞途径clathrin和caveolae介导下的内吞，研究了微丝结合蛋白HIP-55在clathrin介导TGF-β受体内吞中的作用及其机制。这些研究即为研究膜纳米管在方法上奠定了基础，也是本课题对细胞微结构研究的补充和深入。