Ouabain facilitates cardiac differentiation of mouse embryonic stem cells through ERK1/2 pathway.

AIM

To investigate the effects of the cardiotonic steroid, ouabain, on cardiac differentiation of murine embyronic stem cells (mESCs).

METHODS

Cardiac differentiation of murine ESCs was enhanced by standard hanging drop method in the presence of ouabain (20 μmol/L) for 7 d. The dissociated ES derived cardiomyocytes were examined by flow cytometry, RT-PCR and confocal calcium imaging.

RESULTS

Compared with control, mESCs treated with ouabain (20 μmol/L) yielded a significantly higher percentage of cardiomyocytes, and significantly increased expression of a panel of cardiac markers including Nkx 2.5, α-MHC, and β-MHC. The α1 and 2- isoforms Na(+)/K(+)-ATPase, on which ouabain acted, were also increased in mESCs during differentiation. Among the three MAPKs involved in the cardiac hypertrophy pathway, ouabain enhanced ERK1/2 activation. Blockage of the Erk1/2 pathway by U0126 (10 μmol/L) inhibited cardiac differentiation while ouabain (20 μmol/L) rescued the effect. Interestingly, the expression of calcium handling proteins, including ryanodine receptor (RyR2) and sacroplasmic recticulum Ca(2+) ATPase (SERCA2a) was also upregulated in ouabain-treated mESCs. ESC-derived cardiomyocyes (CM) treated with ouabain appeared to have more mature calcium handling. As demonstrated by confocal Ca(2+) imaging, cardiomyocytes isolated from ouabain-treated mESCs exhibited higher maximum upstroke velocity (P<0.01) and maximum decay velocity (P<0.05), as well as a higher amplitude of caffeine induced Ca(2+) transient (P<0.05), suggesting more mature sarcoplasmic reticulum (SR).

CONCLUSION

Ouabain induces cardiac differentiation and maturation of mESC-derived cardiomyocytes via activation of Erk1/2 and more mature SR for calcium handling.