Physiology of stem cell-derived cardiomyocytes

Abstract

All chapters in this thesis revolve around the general theme, stem cells and their electrophysiological characteristics and capacity to induce pro-arrhythmia. The first part of this thesis focusses on key aspects that are relevant to possible pro-arrhythmic effects of stem cell transplantation. An important factor in this context is intercellular coupling through gap junctions. Connexin43, the main cardiac gap junction protein, is poorly expressed in stem cells differentiating into mesodermal cells. We found that the transcription factor Snail1 represses functional connexin43 expression in differentiating stem cells. Furthermore, spontaneous activity as observed in stem cell-derived cardiomyocytes is a clear indication of pro-arrhythmic potential. Studies by our group and others have demonstrated poor expression of the potassium inward rectifier current in stem cell-derived cardiomyocytes. In this thesis, we demonstrate a proof of concept that spontaneous activity can be suppressed through electrotonic interaction by co-culture with Kir2.1 expressing cells. The exposure to increasing levels of catecholamines during development exerts an important influence on maturing cardiomyocytes in vivo. It may be possible that adrenergic stimulation is also beneficial to differentiation of immature cardiomyocytes in vitro. We found that beta-adrenergic stimulation increased conduction velocity, probably via increased expression of cardiac sodium and calcium channels. Evaluation of spontaneous activity and gap junctional communication between grafted cardiomyocytes and host myocardium is not feasible in vivo, therefore we devised an in vitro model that allowed us to integrate the key pro-arrhythmic aspects in an accessible model. In the second part, we describe a new human source for stem cell-derived cardiomyocytes, the human fetal cardiac progenitor cells. Given the fact that these cells originate from the heart, it is likely that they are committed to the mesodermal or cardiac lineage. We found that they can differentiate into cardiomyocytes with efficiencies up to 90% and have an electrical phenotype that is more mature than that observed in other stem cell-derived cardiomyocytes. These findings bring clinical use of autologous stem cells for cardiac regeneration a step closer but also provide us with a valuable in vitro model that may be useful in pharmacological studies.