Comparative characterization of single cells and engineered heart tissues from hiPSC-derived cardiomyocyte subtypes

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research council starting grant 714866 and associated proof-of-concept grant 899422

ZonMW and the Dutch Heart foundation MKMD grant 114021512 and Dutch Heart Foundation Dekker fellowship 2020T023

Rationale: Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes represent an excellent in vitro platform to study cardiac development and model patient-specific diseases. However, their widespread application in drug discovery and regenerative approaches has not yet been realized at least in part due to limited comparative characterization of the available cardiomyocyte subtypes and lack of multicellular models that allow assessment of physiologically relevant parameters.

Perform comprehensive characterization of hiPSC-derived sinoatrial nodal cardiomyocytes (SANCM), atrial cardiomyocytes (ACM) and ventricular cardiomyocytes (VCM) from 2D and 3D cultures.

SANCM, ACM and VCM were generated using directed differentiation protocols. Electrophysiological analysis was performed by single cell patch-clamp. Subtype-specific differences were further characterized by response to neurohumoral agents noradrenaline, and carbachol and If blocker ivabradine. Next, we generated EHTs to evaluate the effect of 3D culturing on cardiomyocyte subtypes and performed optical mapping. To establish a model to study impulse initiation and propagation in vitro, we generated binary EHTs (BIN-EHTs) composed of heteropolar ends of SANCM and ACM.

Gene expression analysis and single cell electrophysiology confirmed identities of respective cardiomyocyte subtypes. While response to noradrenaline and carbachol were as expected, ivabradine testing showed the functional presence of pacemaker current If in ACM, besides SANCM. After three weeks in culture as EHTs, cardiac structural genes were markedly upregulated in all groups. Optical mapping demonstrated a three-fold increase in conduction velocities in ACM and VCM while SANCM EHTs retained slower conduction velocities recapitulating in vivo differences. In BIN-EHTs, SANCM end of the EHT consistently paced the tissues under baseline conditions. Upon treatment with ivabradine, cycle length of BIN-EHTs increased and impulse initiation switched to ACM end in the majority of tissues.

We performed comprehensive characterization of hiPSC-cardiomyocyte subtypes, which recapitulated salient features of their in vivo counterparts. BIN-EHT constructs composed of SANCM and ACM are a valuable rudimentary model for investigating impulse formation and propagation in vitro.