Researchers from the Southern Medical University 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. The researchers 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.
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.
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.