Electro-metabolic coupling in multi-chambered vascularized human cardiac organoids

The study of cardiac physiology and disease is hindered by physiological differences between humans and small-animal models. Here, we report the generation of multi-chambered vascularized human cardiac organoids under anisotropic stress, and their applicability to study electro-metabolic coupling in cardiac tissue. The organoids are derived from human induced pluripotent stem cells, and integrate sensors for the simultaneous measurement of oxygen uptake, extracellular field potentials and cardiac contraction at resolutions higher than 10 Hz. The microphysiological system allowed us to find that 1-Hz cardiac respiratory cycles are coupled with electrical activity rather than with mechanical activity, that calcium oscillations drive a mitochondrial respiration cycle, that the pharmaceutical or genetic inhibition of electro-mitochondrial coupling results in arrhythmogenic behaviour, and that the induction of arrythmia by the chemotherapeutic mitoxantrone can be partially reversed by the co-administration of metformin. Microphysiological cardiac systems may further facilitate the study of the mitochondrial dynamics of cardiac rhythms and advance the understanding of cardiac physiology. Recent work demonstrated that geometric confinement induces a central cavity to form in cardiac organoids . Other developmental studies showed that complex partitioning only occurs following the development of the cardiac vasculature. To mimic this developmental step, we seeded a mixture of hiPSC-derived cardiomyocytes (hiPSC-CMs) and rat primary cardiac microvascular endothelial cells (CECs) in geometrically-confining microwells. The tissue contracted into a single mass in 4 days and started beating after 10 days. Cardiac organoids were cultured over the next weeks, acquiring smooth exterior and synchronized behaviour following 25 days of culture. GFP-expressing endothelial cells reveal that vascular networks begin forming on day 10, developing into complex circumferentially-aligned networks by day 25. To validate these structural findings we carried out RNA sequencing of the cardiac organoids, comparing their expression to multiple human cardiac tissues, and hiPSC-CMs from two-dimensional cultures. Cardiac organoids showed expression signatures associated with pacemaker (sinoatrial and atrioventricular nodes), endocardium, and epicardium cells, as well as cardiac fibroblasts.