Differentiation of embryonic stem cells into cardiomyocytes: Role of ouabain

Abstract

Embryonic stem cells (ESCs) are able to differentiate into cardiac lineages and thus representing a promising source for cardiac regenerative therapy because of the self-renewal capacity. However, the therapeutic application of ESCderived cardiomyocytes (ESC-CMCs) is limited by the low effi cacy of the current protocols for cardiac differentiation and their immature phenotypes. With the clues of ouabain involving in physiological cardiac hypertrophic signalling pathway, our studies investigated the effects of such cardiotonic steroid on murine (m) ESCs cardiac differentiation. Differentiating mESCs in presence of ouabain yielded a signifi cantly higher percentage of cardiomyocytes. Ouabain was also reported to inhibit Na+ /K+ -ATPase and followed with altered activity of the functionally coupled sodium-calcium exchanger (NCX-1). In our previous studies, the α 1 and 2- isoforms of Na+ / K+ -ATPase, on which the cardiac predominant ouabain acts, were also increased in differentiated mESCs. Furthermore, among the three major MAPK cascades involved in hypertrophic response pathways, it was found that ouabain rescued the blockage of cardiac differentiation by the ERK1/2 pathway inhibitor, U0126. Interestingly, cardiomyocytes isolated from ouabain-treated mESCs exhibited more mature calcium handling kinetics. The higher amplitudes of caffeine-induced Ca 2+ transient suggested a more mature sarcoplasmic recticulum (SR). Ouabain induced cardiac differentiation of mESC and maturation of mESC-CMCs probably via activation of ERK1/2. Further studies are necessary to investigate if ERK1/2 pathway plays a direct role in SR function that governing effi cient calcium homeostasis of ESC-CMCs.