Abstract 1567: The Cardiac Stem Cell: The Adult Mammalian Heart Harbours Oct-4pos Cardiac Stem Cells With Very Broad Developmental Potential
c-kitpos cardiac stem/progenitor cells (CSCs) have been isolated from the adult mammalian heart. Other cells identified by different membrane epitopes have also been described. No markers are available to distinguish between true CSCs and amplifying cells. Oct-4 is a transcription factor whose expression is confined to pluripotent cells. Our objective was to evaluate whether the adult heart contains Oct-4pos cells in the cardiac stem cell pool, representing the true ‘early’ stem cells. We first evaluated Oct-4 expression by immunohistochemistry in the hearts of 4 wk old Oct-4/EGFP transgenic mice, in which EGFP expression is under the Oct-4 promoter. Serial analysis of heart cross-sections showed the presence of Oct-4pos/EGFPpos cells. When FACS-isolated, Oct-4pos/EGFPpos cells stained positive for SSEA-1, Nanog and Bmi-1 and a fraction of the Oct-4pos cells expressed c-kit. When several c-kitpos CSCs where close together in what appeared to be an activated “niche”, only one of them was Oct-4pos. Very few were Isl-1pos and no Oct-4pos/EGFPpos cells were positive for the stem cell antigen, Sca-1. When c-kitpos and Sca-1pos cardiac cells from wild type C57BL/6 mice were FACS-isolated, more than half of the c-kitpos CSCs were also Sca-1pos. None of the Sca-1pos cells were Oct-4pos. A small number of c-kitpos/Sca-1neg CSCs were Oct-4pos. These data were confirmed by rt-PCR and western blot. In culture the Oct-4pos cells were self-renewing and gave origin to c-kitpos and Sca-1pos cells at the periphery of clonal cardiosphere cultures. When grown in “cardiogenic” differentiation media, Oct-4pos/EGFPpos cardiac cells differentiate into myocytes, vascular smooth muscle and endothelial cells. When placed in osteogenic or adipogenic differentiation media, they gave rise to osteocytes and adypocytes, respectively. Importantly, Oct-4pos/EGFPpos cardiac cells also adopted pancreatic endocrine and neuroglial phenotypes. In conclusion, the adult mouse heart harbours a population of pluripotent CSCs expressing Oct-4 with a developmental potential significantly broader than myocardial cells. We propose that these Oct-4pos/c-kitneg/Sca1neg are the most pluripotent cells in the myocardium and likely to be the true adult CSCs.