Abstract 15782: The Embryonic Heart Contains Resident C-Kit-Positive Cardiac Stem Cells
C-kit-positive cardiac stem cells (CSCs) are present in the adult heart, but whether these cells are nested within the embryonic organ and contribute to myocardial development remains unclear. Here, we tested whether CSCs are nested in the maturing embryo, participating in the formation of the adult cardiac phenotype. For this purpose, we studied mice in which EGFP is driven by the c-kit promoter. C-kit positive cells were identified in the cardiogenic mesoderm at E6.5, cardiac crescent at E7.5 and at later stages of the fetal heart. Time-lapse two-photon microscopy was employed to document that EGFP-positive CSCs undergo morphogenetic movements within the developing heart and do not translocate to the myocardium from extracardiac regions. EGFP-positive CSCs were negative for markers of hematopoietic cell lineages, excluding their origin from primitive sites of hematopoiesis. The number of CSCs increased linearly from E7.5 to E19, resulting in a 5.6-fold expansion of the stem cell compartment in the heart; 21 CSCs were found at E7.5 and 120 at E19. The growth of the cardiac mass was paralleled by an increase in CSCs; CSCs divided symmetrically and asymmetrically. In the latter case, the commitment to the myocyte lineage in vivo was shown by the non-uniform localization of the cell fate determinant, α-adaptin, in the dividing cell, together with the expression of Nkx2.5, MEF2C, α-sarcomeric actin, troponin I and α-cardiac actinin in one of the two daughter cells. In vitro, EGFP-positive c-kit positive CSCs at E12-E19 were self-renewing, clonogenic and multipotent, all critical determinants of stem cell function. C-kit positive cells differentiated into myocytes and vascular smooth muscle cells (SMCs) and endothelial cells (ECs). The inherent ability of embryonic CSCs to form myocytes was confirmed by fate mapping in vivo. CSCs were obtained at E18 from mice in which EGFP is under the control of the α-MHC promoter. Single cell CSC clones were generated and these cells were delivered to the infarcted LV of wild-type mice. This protocol rescued the infarcted heart resulting in the formation of EGFP-positive myocytes and EGFP-negative vascular SMCs and ECs. In conclusion, lineage negative c-kit-positive cells in the embryonic-fetal heart correspond to bona fide CSCs.
- © 2011 by American Heart Association, Inc.