Year 3

Cardiovascular diseases remain the major cause of death in the western world. Stem and progenitor cell-derived cardiomyocytes (SPC-CMs) hold great promise for myocardial repairs. Recent advances in reprogramming somatic cells to induced pluripotent stem cells (iPSCs) open the door for future patient-specific, cell-based therapies. However, most SPC-CMs displayed immature electrophysiological (EP) phenotypes with variable automaticity. Implanting these electrically immature cardiomyocytes (CMs) into hearts might carry arrhythmogenic risks. Human embryonic stem cell (hESC)- or human iPSC-derived cardiomyocytes (hESC-CMs or iPSC-CMs) provide a model system to study the development of CMs, in part because they are an immature population of cardiomyocytes that could continue to mature in the embryoid body (EB) environment. Elucidating cellular factors and molecular pathways governing electrical maturation of early hESC-CMs would enable engineered microenvironment to create electrophysiologically compatible hESC-CMs for a safe cell-based therapy of cardiovascular diseases.
Using hESC-CMs and an antibiotic-selection system to isolate hESC-CMs (>95% purity), we found that non-myocardial cells in EBs induced electrical maturation and ion channel expression of primitive hESC-CMs during differentiation. A novel add-back (co-culture) method was established to enable an engineered microenvironment for controlled EP maturation of primitive hESC-CMs. With these established methods, we further studied the role of endothelial cells (ECs) and their molecular pathways in inducing EP maturation of primitive hESC-CMs. In the Year 3, our data confirmed that Endothelin-1 (ET-1), secreted from endothelial cells, influenced the EP maturation of primitive hESC-CMs through mainly a subtype of the ET-1 receptors. In particular, we confirmed with patch-clamp recordings that ET-1 significant influenced the expression of two specific types of ion channels of early hESC-CMs. We also found that neuregulin affects ion channel development of primitive hESC-CMs in a different fashion from ET-1. In addition, we have generated new iPSC lines from various fibroblast sources and found that fibroblast sources influence the cardiogenic potentials of iPSC lines. We have performed microRNA profiling and found that a certain set of miRNAs might underlie the cardiogenic potentials of cardiomyocytes derived from iPSCs generated from various fibroblast sources. Our findings might provide significant insights in directed ion channel maturation of primitive SPC-CMs and in improving the safety of current cell-based therapies in hearts.