BACKGROUND AND PURPOSE We develop a method of imaging exosomes in vivo according to the vital role of exosomes in intercellular communication. This study aims to design a new label method that allows the visualization of labeled exosomes with magnetic resonance imaging (MRI). METHODS We designed a fusion protein consisting of two parts, namely, ferritin heavy chain (FTH1) and a truncated lactadherin. FTH1 is used as an MRI reporter. Lactadherin is a trans-membrane protein. The lactadherin protein are mostly located on the outer surface of exosomes. We replaced the outer membrane part of lactadherin with FTH1, infected mesenchymal stem cells with lentivirus carrying the fusion protein, and isolated exosomes from the labeled cells by ultracentrifugation. Labeled exosomes were validated by transmission electron microscopy images, Western blot, nanosight particle tracking, and visualized in vitro and in vivo by MRI. RESULTS FTH1 expression would suppress mesenchymal stem cell proliferation, whereas the characterization of labeled exosomes remains comparable with unlabeled exosomes. MR imaging shows that exosomes labeled with FTH1 can be visualized in vitro and in vivo. CONCLUSION This innovative reporter-imaging approach to track and visualize exosomes with MRI can be utilized as a tool for the study of the role of exosomes under different conditions.

中文翻译：

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通过磁共振成像在体内可视化来自间充质干细胞的外来体。

背景和目的我们根据外泌体在细胞间通讯中的重要作用，开发了一种体内外泌体成像方法。这项研究旨在设计一种新的标记方法，该方法允许使用磁共振成像（MRI）可视化标记的囊泡。方法我们设计了一个由两部分组成的融合蛋白，即铁蛋白重链（FTH1）和截短的乳黏附素。FTH1用作MRI报告基因。乳粘附素是跨膜蛋白。乳粘附素蛋白大部分位于外泌体的外表面。我们用FTH1代替了乳粘附素的外膜部分，用携带融合蛋白的慢病毒感染了间充质干细胞，并通过超速离心从标记的细胞中分离了外泌体。标记的外泌体通过透射电子显微镜图像，Western印迹，nanosight粒子跟踪，并通过MRI在体内和体外可视化。结果FTH1表达将抑制间充质干细胞增殖，而标记外泌体的表征与未标记外泌体仍相当。MR成像显示可以在体外和体内可视化标记有FTH1的外泌体。结论这种创新的记者-成像方法可利用MRI跟踪和可视化外泌体，可作为研究不同条件下外泌体作用的工具。