Labeling and tracking of mesenchymal stromal cells with EdU.

BACKGROUND AIMS: The thymidine analog bromodeoxyuridine (5-bromo-2-deoxyuridine; BrdU) has been used widely to label cells in culture and in tissue. The labeled cells can also be tracked when transplanted into a suitable host. In the present study we tested a new thymidine analog, 5-ethynyl-2-deoxyuridine (EdU), for labeling and tracking of mesenchymal stromal cells (MSC), specifically adipose tissue-derived stem cells (ADSC).

METHODS: Labeling of ADSC was examined for the dosage effect of EdU and stability of label by Alexa-594 staining followed by fluorescence microscopy. Labeling of various organs/tissues was done by intraperitoneal injection of EdU and examined by histology and fluorescence microscopy. Tracking of ADSC was done by intratissue or intravenous transplantation of EdU-labeled ADSC into various tissues and examined by histology and fluorescence microscopy.

RESULTS: EdU was incorporated specifically into the nucleus in approximately 50% of ADSC and the percentage of cells that remained fully labeled declined with time. Peritoneal injection of EdU resulted in the appearance of EdU-positive cells in most organs and tissues. In the intestine, EdU-positive cells were found in both the epithelium and connective tissues 7 h after injection. Long-term (2-6 week) follow-ups found EdU-positive cells only in the connective tissue. Tracking of ADSC was successful in tissues 10 weeks after intratissue or intravenous transplantation.

CONCLUSIONS: Cell labeling with EdU in culture or living animals can be performed easily. The detection of EdU label requires no harsh treatment or immunologic reaction, as detection of BrdU label does. EdU can be used for long-term tracking of ADSC.