Abstract 3455: Derivation and Functional Characterization of Nkx2.5+ Cardiac Progenitor Cells from Mouse Induced Pluripotent Stem Cells
The induction of pluripotency in adult somatic cells by defined factors raises new possibilities for the diagnosis and treatment of heart diseases. To accomplish this, induced pluripotent stem (iPS) cells must differentiate into functional cardiac cells and maintain long-term phenotypic stability. In this study we examined the ability of iPS cells to differentiate into cardiomyocytes (CMCs) and performed a detailed comparison with CMCs derived from embryonic stem (ES) cells. iPS cells were derived by retroviral-mediated expression of Oct4, Sox2, Klf4, and c-Myc in adult tail fibroblasts from Nkx2.5 cardiac enhancer-eGFP transgenic mice. ES cells were derived from the same mice by conventional methods. Six cell lines each of iPS and ES were allowed to undergo differentiation in vitro and assessed for their expression of eGFP and ability to differentiate into cross-striated CMCs at day 8 and 18 of culture. Electrophysiological studies were performed to assess their chamber-specific differentiation. In addition, iPS and ES cell-derived eGFP+ cardiac progenitor cells (CPCs) were transplanted into mouse hindlimbs to study their engraftment and cardiac differentiation potential in vivo. Both iPS and ES cells formed beating eGFP+ embryoid bodies upon 8 days of differentiation, with comparable levels of cardiac gene expression and numbers of alpha-actinin+, cross-striated cells. In addition, iPS and ES cell-derived cardiac cells showed atrial, ventricular, or conduction system cell-specific action potentials. However, analysis of iPS cells at day 18 of culture revealed a decrease in beating embryoid bodies (55% of day 8), deterioration of sarcomeric structures (30% of day 8), and increased apoptosis when compared to ES cell-derived CMCs. Consistently, transplantation of iPS cell-derived CPCs into mouse hindlimbs resulted in robust cell engraftment at 4 weeks after transplantation, but lack of cardiac troponin-T+ cells. iPS cells derived from adult mouse fibroblasts can give rise to Nkx2.5-expressing CPCs, which functionally differentiate into CMCs. However, these iPS cell-derived CMCs failed to maintain long-term stability in vitro or in vivo after transplantation, in contrast to ES cell-derived CMCs.