Cardiomyogenic Potential of C-Kit + –Expressing Cells Derived From Neonatal and Adult Mouse Hearts

Abstract

Background— C-kit is a receptor tyrosine kinase family member expressed in hematopoietic stem cells. C-kit is also transiently expressed in cardiomyocyte precursors during development and in a rare cell population in the normal adult heart. In the present study, the cardiomyogenic potential of c-kit + cells isolated from normal neonatal, normal adult, and infarcted adult mouse hearts was evaluated. Methods and Results— Magnetic activated cell sorting 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 β-galactosidase activity, thus permitting simultaneous tracking of cell survival and differentiation. A subset of the c-kit + cells from double transgenic neonatal hearts acquired a cardiomyogenic phenotype when cocultured with fetal cardiomyocytes (2.4% of all EGFP + cells screened) but rarely when cultured alone or when cocultured with mouse fibroblasts (0.03% and 0.05% of the EGFP + cells screened, respectively). In contrast, c-kit + cells from normal adult double transgenic hearts failed to undergo cardiomyogenic differentiation when cocultured with nontransgenic fetal cardiomyocytes (>18 000 EGFP + cells screened) or when transplanted into normal or infarcted adult mouse hearts (14 EGFP + grafts examined). A single c-kit + cell from an infarcted double transgenic adult heart was observed to acquire a cardiomyogenic phenotype in coculture (>37 000 EGFP + cells screened). Conclusions— These data suggest that the ability of cardiac-resident c-kit + cells to acquire a cardiomyogenic phenotype is subject to temporal limitations or, alternatively, that the cardiomyogenic population is lost. Elucidation of the underlying molecular basis may permit robust cardiomyogenic induction in adult-derived cardiac c-kit + cells.