Human embryonic stem cell-derived cardiomyocytes as a novel in vitro cardiac model system

Objectives: Human embryonic stem cell-derived cardiomyocytes (hESC-CM) are investigated as a source of cardiac cells for cell therapy and as a novel model for drug screening. In this thesis, we asked whether hESC-CM can serve as a valuable system for testing compounds in toxicological screens and we undertook a characterization of their contraction properties with regards to their phenotypic variability. Methods: Contraction was measured using edge detection microscopy (Ionoptix) on clusters of hESC-CM and in paced isolated hESC-CM or other isolated ventricular cardiomyocytes. Cell death assay was performed in adherent isolated cardiomyocytes. hESC-CM were stained with fluorescent markers of apoptosis and necrosis and scanned using automated fluorescence microscopy (Cellomics). Results: Clusters of hESC-CM underwent maturation as seen by the change in their basal beating rate with time of culture and the negative chronotropic effect of adenosine. The development of the chronotropic response to adenosine was heterogenous during the intermediate stage and correlated with the effect of Carbarchol, suggesting the emergence of distinct cardiomyocyte subtypes. Adenosine mediated its effect through the activation of A1 Adenosine receptor and positive inotropic effect in isolated hESC-CM possibly through A2a, as in human failing cardiomyocytes. Apoptosis and necrosis could be detected and quantified specifically in hESC-CM as well as in neonates, allowing further direct inter-species comparison in high content screening approach. hESC-CM and neonates differed in term of sensitivity to apoptosis in response to Chelerythrine and to β-adrenergic stimulation. The pro and anti-apoptotic effects of different immuno-suppressive drugs were evaluated in hESC-CM as a prerequisite for future transplantation. Conclusion: hESC-CM can serve as an alternative cardiomyocyte model for investigating the effect of compounds on contraction and toxicity. Our study points out the developmental stage and possibly the differentiation method as a source of phenotypic heterogeneity. Consequently, the differentiation protocols needs to be standardized and in vitro maturation need to be improved. Also, we showed that the modulation of cell death in hESC-CM might greatly differ from current cardiomyocytes models used for toxicity screens