Abstract 3460: Molecular Characterization, Safety and Feasibility of Induced Pluripotent Stem (iPS) Cell Derived Cardiomyocytes for Heart Regenerative Therapy

Abstract

[Background] We recently reported that mouse and human iPS cells could be generated from somatic cells by gene transfer of Oct3/4, Sox2, c-Myc and Klf4. Although the morphology, growth characteristics and pluripotency of iPS cells are believed to be similar to those of ES cells, there are several versions such as Fbx-iPS, Nanog-iPS cells, and it remains unknown whether what type of iPS cell could be appropriate for the cardiovascular regeneration therapy. This study investigated the cardiomyocyte differentiation potential of mouse iPS cells, molecular characterization of iPS-induced cardiomyocytes, and the safety and feasibility of their transplantation into the heart. [Methods and Results] We used several lines of Fbx-iPS and Nanog-iPS cells and induced cardiomyocyte differentiation using the hanging drop culture method. Mouse ES cells were used as control. Both Fbx-iPS and Nanog-iPS cells could differentiate into cardiomyocytes, and the incidence of beating embryoid bodies was similar to that of ES cells. RT-PCR analyses and immunohistochemistry revealed that both iPS cells expressed all the cardiomyocyte marker genes including Nkx2.5, GATA4, MEF2C, myosin light chain-2v, α-myosin heavy chain, atrial natriuretic peptide, and α-sarcomeric actinin, and they showed normal structures. Electron microscopic study revealed that iPS cell derived cardiomyocytes had the typical morphological cardiomyocyte structure, which is difficult to distinguish from that of ES cell derived cells. Electrical physiological study showed that iPS cell derived cardiomyocytes had sinus node-like or fetal ventricular type action potentials. Purified iPS cell derived cardiomyocytes could be successfully transplanted into murine hearts and the engrafted cells survived and were integrated into host myocardium. Nanog-iPS cell derived cells showed no severe complication after transplantation, however Fbx-iPS cell derived cells showed teratoma in the host tissue. Fbx-iPS cells expressed extrinsic c-myc after differentiation. [Conclusions] The iPS cells proved to be an attractive cell source for the regeneration of cardiomyocytes, however safety and careful characterization is necessary before clinical application.