Tracking the distribution of stem cells is crucial to their therapeutic use. However, the usage of current vectors in cellular labeling is restricted by their low internalizing efficiency. Here, we reported a cellular labeling approach with a novel vector composed of mesoporous silica nanoparticles (MSNs) conjugated with fluorescein isothiocyanate in human bone marrow mesenchymal stem cells and 3T3-L1 cells, and the mechanism about fluorescein isothiocyanate-conjugated MSNs (FITC-MSNs) internalization was studied. FITC-MSNs were efficiently internalized into mesenchymal stem cells and 3T3-L1 cells even in short-term incubation. The process displayed a time- and concentration-dependent manner and was dependent on clathrin-mediated endocytosis. In addition, clathrin-dependent endocytosis seemed to play a decisive role on more internalization and longer stay of FITC-MSNs in mesenchymal stem cells than in 3T3-L1 cells. The internalization of FITC-MSNs did not affect the cell viability, proliferation, immunophenotype, and differentiation potential of mesenchymal stem cells, and 3T3-L1 cells. Finally, FITC-MSNs could escape from endolysosomal vesicles and were retained the architectonic integrity after internalization. We conclude that the advantages of biocompatibility, durability, and higher efficiency in internalization suit MSNs to be a better vector for stem cell tracking than others currently used.

Key words: intracellular internalization • endocytosis • bone marrow • differentiation