CONTRIBUTION OF HUMAN STEM CELL-DERIVED CARDIOMYOCYTE SUBTYPES TO BIOARTIFICAL CARDIAC TISSUE FORMATION AND FUNCTION

The transplantation of human induced pluripotent stem cell (hiPSC)-derived grafts represents an alternative treatment option for post-myocardial infarction patients. So far, myocardial tissue engineering mainly focused on the generation of ventricular-like tissues providing sufficient contractile function. Atrial- and pacemaker-like cardiomyocytes (CMs) are hypothesized to have a negative effect on tissue function, as they could lead to a lower force development and to arrhythmias after transplantation, respectively. Therefore, we aim to characterize subtype composition in the differentiated CM cultures, as well as in generated tissues thereof and analyze tissue functionality. The hiPSC-CMs are then mixed with human fibroblasts and a matrix to generate bioartifical cardiac tissues (BCTs) using our established bioreactor technology. In order to assess the ratio of individual iPSC-derived CM subtypes, flow cytometry and immunofluorescence (IF) stainings with antibodies targeting subtype-specific markers (MLC2v, COUPTF-2, and MLC2a) were performed. First results revealed a high percentage (~80-90%) of MLC2v positive cells in differentiated CM populations. The remaining cells stained positive for atrial markers (COUPTF-2, MLC2a). Functional measurements mainly focused on BCT contractility and showed forces similar to the native myocardium (~6.5 mN/mm2). In addition, we observed that a higher proportion of ventricular-like CMs leads to higher contractile BCT function. Taken together, these molecular and functional results reveal that our differentiation protocol led to the formation of mainly ventricular-like CMs and that BCTs generated thereof show typical characteristics of myocardial tissues. For future ventricular-like tissue replacement therapy, we aim to perform a risk assessment for "contaminating" cardiac cell types with respect to both BCT function and arrhythmias.