Cardiac reprogramming under defined conditions

FGF2, FGF10, and VEGF greatly promote cardiac reprogramming under defined serum-free conditions by enhancing the conversion of partially reprogrammed cells into fully reprogrammed functional iCMs. Fibroblasts can be directly reprogrammed into cardiomyocyte-like cells (iCMs) by overexpression of cardiac transcription factors, including Gata4, Mef2c, and Tbx5; however, this process is inefficient under serum-based culture conditions, in which the conversion of partially reprogrammed cells into fully reprogrammed functional iCMs has been a major hurdle. Here, we report that a combination of fibroblast growth factor (FGF) 2, FGF10, and vascular endothelial growth factor (VEGF), termed FFV, promoted cardiac reprogramming under defined serum-free conditions, increasing spontaneously beating iCMs by 100-fold compared with those under conventional serum-based conditions. Mechanistically, FFV activated multiple cardiac transcriptional regulators and converted partially reprogrammed cells into functional iCMs through the p38 mitogen-activated protein kinase and phosphoinositol 3-kinase/AKT pathways. Moreover, FFV enabled cardiac reprogramming with only Mef2c and Tbx5 through the induction of cardiac reprogramming factors, including Gata4. Thus, defined culture conditions promoted the quality of cardiac reprogramming, and this finding provides new insights into the mechanism of cardiac reprogramming. In this study, we compared the global gene expression patterns of MEFs, iCMs cultured under the indicated conditions (FBS, SF, FFV), and the hearts. The iCMs were sorted as aMHC-GFP+ cells at 2W and 4W weeks after GMT transduction. We also analyzed the iCMs induced by MT transduction, and iCMs induced from TTFs by GMTMM.