Synergistic generation of cardiac resident-like macrophages and cardiomyocyte maturation in tissue engineered platforms

Cardiovascular disease stands as the leading cause of death globally, claiming approximately 19million lives in 2020. On the contrary, the development of cardiovascular drugs is experiencing a decline, largely due to the bottleneck in understanding the pathophysiology of various heart diseases and assessing the effects of drugs on healthy human hearts. The development of induced pluripotent stem cell (iPSC) technology and the availability of cardiac cell types in vitro, has resulted in a surge in efforts to fabricate human cardiac models for disease modelling and drug discovery applications. Although numerous attempts evidence successful fabrication of 3 dimensional (3D) engineered heart tissues, the innate immune cell population of the myocardium - particularly cardiac macrophages, was until recently, overlooke. With increasing appreciation of the interactions between cardiomyocytes and macrophages in the myocardium, in this work, isogenic populations of cardiac resident-like macrophages and cardiomyocytes were generated using iPSCs, to understand the interactions between the two cell types in both 2D and 3D settings, and subjected to electric stimulation. After characterizing iPSC-derived macrophages (iMacs) and iPSC-derived cardiomyocytes (iCMs) in depth, the conditioning of iMacs to align to a cardiac resident macrophage-like phenotype in the presence of iCMs in 2D culture was explored. In co-culture with iCMs, iMacs upregulated known genes expressed by cardiac resident macrophages. Additionally, in co-culture with iMacs, iCMs displayed an elongated morphology, improved calcium function and an increase in known maturation genes such as the ratio between MYH7 and MYH6 as well as SERCA2. In a 2D setting, iMacs showed the ability to electrically couple with iCMs and facilitate synchronous beating in iCM cultures. The 2D characterisation was translated into an engineered cardiac tissue model, wherein, improvement in tissue characteristics in the presence of iMacs was demonstrated in terms of increased cell alignment, enhanced cardiomyocyte elongation, physiologically relevant beat rates and improved tissue compaction. Taken together, these findings may open new avenues to use iMacs in engineered cardiac tissue models, not only as an innate immune cell source, but also as a support cell type to improve cardiomyocyte function and maturation.