Features so far documented in reliably isolated and manipulated cardiac stem cell (CSCs) resident within the cardiac tissue suggest that innovative treatments to repair damaged myocardium could have promising clinical applications. However, the capability of resident cardiac stem cell (CSCs) to differentiated into newly formed cardiomyocyte is still controversial. In this study, the cardiomyogenic potential of c-kit+ CSCs isolated from normal adult mouse hearts was evaluated in an in vitro co-culture system.
Methods Magnetic activated cell sorting (MACS) was used to prepare c-kit+ cells from the hearts of ACT-EGFP/MHC-nLAC double transgenic mice. These animals exhibit widespread enhanced green fluorescent protein (EGFP) expression and cardiomyocyte-restricted nuclear b-galactosidase activity, thus permitting simultaneous tracking of cell survival and differentiation. The c-kit+ cells were cocultured with feeder layer neonatal rat cardiomyocytes (NRCMs) for 7 days. Confocal and fluorescence microscopes were used to quantify the differentiation rate of c-kit+ cells in the immunostained cocultures.
Results A subset of the c-kit+ cells underwent cardiomyogenic differentiation when cocultured with NRCMs (0.15% out of all 70, 747 EGFP+ cells screened), but not when cultured alone or when cocultured with mouse fibroblasts (0.00% of the EGFP+ cells screened). The newly formed cardiomyocytes were EGFP+, nuclear b-galactosidase+ and a-actinin+ with clear sarcomere structure, indicating mature functional properties.
Conclusion Normal adult c-kit+ CSCs are able to differentiate into functional cardiomyocytes, but it is a rear event at least in the in vitro coculture system.