Structural Immaturity of Human iPSC-Derived Cardiomyocytes: In Silico Investigation of Effects on Function and Disease Modeling

Abstract

Background: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have emerged as a promising experimental tool for translational heart research and drug development. However, their usability as a human adult cardiomyocyte model is limited by their functional immaturity. Our aim is to analyse quantitatively those characteristics and how they differ from adult CMs.Methods and Results: We have developed a novel in silico model with all essential functional electrophysiology and calcium handling features of hiPSC-CMs. Importantly, the virtual cell recapitulates the immature intracellular ion dynamics that are characteristic for hiPSC-CMs, as quantified based our in vitro imaging data. The strong “calcium clock” is a source for a dual function of excitation-contraction coupling in hiPSC-CMs: action potential and calcium transient morphology vary substantially depending on the activation sequence of underlying ionic currents and fluxes that is altered in spontaneous vs. paced mode. Furthermore, parallel simulations with hiPSC-CM and adult cardiomyocyte models demonstrate the central differences. Results indicate that hiPSC-CMs translate poorly the disease specific phenotypes of Brugada syndrome, long QT Syndrome and catecholaminergic polymorphic ventricular tachycardia, showing less robustness and greater tendency for arrhythmic events than adult CMs. Based on a comparative sensitivity analysis, hiPSC-CMs share some features with adult CMs, but are still functionally closer to prenatal CMs than adult CMs. A database analysis of 3000 hiPSC-CM model variants suggests that hiPSC-CMs recapitulate poorly fundamental physiological properties of adult CMs. Single modifications do not appear to solve this problem, which is mostly contributed by the immaturity of intracellular calcium handling.Conclusion: Our data indicates that translation of findings from hiPSC-CMs to human disease should be made with great caution. Furthermore, we established a mathematical platform that can be used to improve the translation from hiPSC-CMs to human, and to quantitatively evaluate hiPSC-CMs development toward more general and valuable model for human cardiac diseases.

All-optical electrophysiology refines populations of in silico human iPS-CMs for drug evaluation

“…Before the upstroke, the new I NCX provides an additional inward contribution (−0.5A/F) that is added to If (−0.25A/F), supporting the membrane depolarization and allowing the opening of the I Na channels. Figure 1 illustrates the contribution of I NCX to the hiPS-CM automaticity, as reported in (16, 33): blocking I NCX reduces its inward component slowing down the rate of spontaneous AP, up to suppression. In particular, an issue in the Paci2018 model was that AP suppression did not happen, in disagreement with in vitro data by Kim et al (33) in response to 2μM SEA0400, an inhibitor of the forward I NCX in a cluster of hiPS-CMs.…”

“…Research on hiPS-CMs is rapidly developing, with new experimental data becoming available, which in turn serve as a driving force for the constantly evolving computational models to offer more accurate in silico tools to the scientific community. Based on in vitro (33) and in silico (16) tests, it was identified that our Paci2018 hiPS-CM model (15) did not properly reflect the role of I NCX in automaticity, i.e. no cessation of spontaneous activity was seen in the model as consequence of a strong I NCX block, as suggested by experiments.…”

“…no cessation of spontaneous activity was seen in the model as consequence of a strong I NCX block, as suggested by experiments. Therefore, we updated this hiPS-CM model to reproduce the specific mechanisms reported in (16, 33). (Figures 1, S1 and Supporting Material).…”

“…A limitation of the Paci2018 hiPS-CM model (15) was noted - namely, failure to reproduce the cessation of the spontaneous electrical activity following strong block of the I NCX , as shown by recent in vitro and in silico experiments (16, 33). A very large window current in Paci2018 for the fast Na + current (I Na ) was identified as the key to sustaining the automaticity upon I NCX block.…”

“…To develop the Paci2019 model (details in the Supporting Material): we updated the formulations for I Na and I f with the ones proposed in (16); we optimized the model parameters to fit the same dataset of in vitro AP and CaTr biomarkers used for (15), which have been recorded at 37°C; we validated the model against the same experimental protocols used for (15). …”