Tracking of CFSE-labeled endothelial progenitor cells in laser-injured mouse retina

Background Endothelial progenitor cells (EPCs) transplantation is a promising therapeutic strategy for ischemic retinopathy. The current study aimed to establish a simple, reliable and fluorescent labeling method for tracking EPCs with 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFSE) in laser-injured mouse retina.Methods EPCs were isolated from human umbilical cord blood mononuclear cells, cultivated, and labeled with various concentrations of CFSE. Based on fluorescence intensity and cell morphology, a 15 minutes incubation with 5 μmol/L CFSE at 37℃ was selected as the optimal labeling condition. The survival capability and the apoptosis rate of CFSE-labeled EPCs were measured by Trypan blue staining and Annexin V/PI staining assay respectively. Fluorescence microscopy was used to observe the label stability during the extended culture period. Labeled EPCs were transplanted into the vitreous cavity of pigmented mice injured by retinal laser photocoagulation. Evans Blue angiography and flat mounted retinas were examined to track the labeled cells.Results EPCs labeled with 5 μmol/L CFSE presented an intense green fluorescence and maintained normal morphology, with no significant changes in the survival capability or apoptosis rate after being labeled for 2 days, 1 and 4 weeks. The fluorescence intensity gradually decreased in the cells at the end of 4 weeks. Evans Blue angiography of the retina displayed the retinal capillarity network clearly and fluorescence leakage was observed around photocoagulated spots in the laser-injured mouse model. One week after transplantation of labeled EPCs, the fluorescent cells were identified around the photocoagulated lesions. Four weeks after transplantation, fluorescent tube-like structures were observed in the retinal vascular networks.Conclusion EPCs could be labeled by CFSE in vitro and monitored in vivo for at least 4 weeks, and participate in the repair of injured retinal vessels.