Abstract
Background: Isolation of a pure population of cardiomyogenic cardiac stem cells (CPCs) has been the Holy-Grail in cardiac regeneration. C-kit, a cell surface receptor, has been proposed as a marker of CPCs and the result of multiple preclinical studies and a phase I clinical trial has been encouraging. Nonetheless, optimization of isolation methods is desirable given the heterogeneity of c-kit positive CPCs. We hypothesize that isolation of c-kit positive CPCs based on differential adhesion identifies a superior population of cells. Methods: Non-adherent cells from digested murine hearts were transferred to successive flasks at 2, 4, 24, 48 and 72 hours. Hence, 5 fractions of cells were isolated based on their adhesion profile and labeled rapidly-adherent (1 and 2) and slowly-adherent (3 to 5). Cells were then expanded and sorted based on c-kit expression and expanded to seven passages. Cells were analyzed for surface markers and cardiomyogenic and pluripotent expression profile by flow-cytometry and real-time polymerase chain reaction. Differentiation potential of the two fractions was examined and their paracrine profile compared using human umbilical vein endothelial cells and neonatal rat cardiomyocytes. Results: C-kit expression was maintained in the slowly-adherent fraction while precipitously dropping in the rapidly-adherent one. In addition, the former expressed lower levels of mesenchymal/fibroblast (CD90.2) and macrophage (CD11b/CD45) markers and higher levels of pluripotent (Oct-4, Nanog, Dppa-3, Rif) and cardiac markers (Nkx2.5, Gata4, Mybpc3 and cTnI) comparing to the latter. Finally, slowly-adherent CPCs had superior paracrine profile compared to rapidly-adherent one. Conclusion: C-kit positive CPCs cells isolated from murine myocardium are heterogeneous and better isolation methods are required to enrich a purer population of cardiomyogenic stem cells. In that vein, isolation of c-kit positive CPCs based on their adhesion profile identifies a subpopulation of cells capable of maintaining c-kit positivity and superior in terms of cariomyogenic and pro-angiogenic potential.
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