Rapamycin efficiently promotes cardiac differentiation of mouse embryonic stem cells

To investigate the effects of rapamycin on cardiac differentiation, murine embryonic stem cells (ESCs) were induced into cardiomyocytes by 10^-4 M ascorbic acid (AA), 20 nM rapamycin alone or 0.01% solvent DMSO. We found that rapamycin alone was insufficient to initiate cardiomyogenesis. Then, the ESCs were treated with AA and rapamycin (20 nM) or AA and DMSO (0.01%) as a control. Compared with control, mouse ESCs (mESCs) treated with rapamycin (20 nM) and AA yielded a significantly higher percentage of cardiomyocytes, as confirmed by the percentage of beating embryonic bodies (EBs), the immunofluorescence and FACS analysis. Rapamycin significantly increased the expression of a panel of cardiac markers including Gata4, α-Mhc, β-Mhc, and Tnnt2. Additionally, rapamycin enhanced the expression of mesodermal and cardiac transcription factors such as Mesp1, Brachyury T, Eomes, Isl1, Gata4, Nkx2.5, Tbx5, and Mef2c. Mechanistic studies showed that rapamycin inhibits Wnt/β-catenin and Notch signaling but promotes the expression of fibroblast growth factor (Fgf8), Fgf10, and Nodal at early stage, and bone morphogenetic protein 2 (Bmp 2) at later stages. Sequential treatment of rapamycin showed that rapamycin promotes cardiac differentiation at the early and later stages. Interestingly, another mammalian target of rapamycin (mTOR) inhibitor Ku0063794 (1 µM) had similar effects on cardiomyogenesis. In conclusion, our results highlight a practical approach to generate cardiomyocytes from mESCs by rapamycin.