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

Funding Acknowledgements

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.

Objective

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

Methods

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.

Results

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.

Conclusions

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.

Membrin/GOSR2 is a novel NaV1.5-interacting protein modulating cardiac conduction

Background

Genome-wide association studies have associated a locus spanning GOSR2 with QRS- and QT-interval. GOSR2 encodes Membrin, a protein located at the cis-Golgi, which plays a role in protein trafficking. Altered trafficking of the cardiac sodium channel (NaV1.5), encoded by SCN5A, has been shown to reduce cardiac conduction.

Purpose

To explore the modulatory role of Membrin on cardiac conduction and sodium channel availability.

Methods and results

Tandem Affinity Purification in H10 cells (derived from neonatal rat cardiomyocytes) overexpressing the NaV1.5 C-terminus identified Membrin as a putative interactor of NaV1.5. We subsequently confirmed the interaction between NaV1.5 and Membrin by means of a co-immunoprecipitation assay in HEK293A cells that overexpress NaV1.5 and Membrin.

To investigate whether Membrin affects cardiac conduction we recorded optical action potentials from the left ventricle (LV) of Langendorff-perfused hearts from Gosr2+/− mice and wild type (WT) littermate controls. Conduction velocity was measured at steady state pacing (cycle length 120ms) and at the minimal possible cycle length (S2min), during S1S2 pacing. Longitudinal conduction velocity was increased in Gosr2+/− mice compared to WT at steady state- (76.44 vs. 67.00 cm/s) as well as at S2min (62.00 vs. 51.86 cm/s, p=0.039, n=10 and 9, resp.). Single cell patch-clamp studies revealed a shortened action potential duration at 90% repolarization at all pacing frequencies (390 vs 342 V/s at 2Hz, p=0.036) in isolated mid-LV cardiomyocytes of Gosr2+/− mice compared to WT. In addition, the maximal upstroke velocity was increased in Gosr2+/− mid-LV cardiomyocytes at frequencies of 6Hz and higher (390 vs 342 V/s at 6Hz, p=0.044).

Conclusion

Our findings identify Membrin as a novel interacting protein of NaV1.5 and a modulator of cardiac conduction. We propose that Membrin acts through ion channel trafficking or by modulating the posttranslational maturation of ion channels.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Leducq foundation