Finding fluorescent needles in the cardiac haystack: Tracking the location and fate of hMSCs with quantum dots for electrical and mechanical repair of damaged myocardium.

摘要

Adult myocardium has long been considered an amitotic tissue, incapable of self-repair after injury. Stem cells now show promise for restoring mechanical and electrical function to damaged heart tissue. One major limitation to studying the mechanism of stem cell action in vivo, however, has been the difficulty of labeling and then tracking the cells delivered in animal models. Traditional fluorescent proteins and dyes fail to illuminate exogenous cells amidst the high levels of autofluorescence in the heart. Non-invasive cell tracking methods have been developed but suffer from poor resolution. In order to fully understand the spatiotemporal distribution of stem cell clusters in the heart, as well as determine the fate of these delivered cells, the ideal cell tracking method must overcome these challenges. We have developed a novel technique using quantum dot (QD) fluorescent nanoparticles to track stem cells delivered in vivo. Our approach uniformly loads QDs into human mesenchymal stem cells (hMSCs) with no observed effect on cell proliferation or gene expression. Labeled cells maintain the ability to differentiate in vitro along adipogenic and osteogenic lineages, and terminally differentiated cells retain the QDs. QD-hMSCs can be delivered to myocardium in vivo and easily identified in histologic sections without immunostaining or effects from autofluorescence. After injecting QD-hMSCs into the rat ventricle in vivo, we have generated 3-D reconstructions of their complete distribution with single-cell resolution. Furthermore, we have tracked the fate of QD-hMSCs eight weeks after delivery to the canine heart on an extracellular matrix patch. QD-hMSCs were found to differentiate along an endothelial lineage, suggesting participation by these cells in vasculogenesis. We also identified expression of cardiacspecific markers in cells containing the QD label; in some cases, QD-hMSC-derived cells were found with morphologic hallmarks of mature cardiac myocytes, suggesting they can terminally differentiate into this cell type. In summary, this novel technique of stem cell labeling with QDs provides a robust method for tracking the location and fate of stem cells both in vitro and after delivery in vivo.