Clin Res Cardiol (2023). https://doi.org/10.1007/s00392-023-02180-w

Modeling the human heart in 3D: Establishing multicellular cardiac organoids as versatile tool to investigate cardiac pathophysiology in vitro

E. Mohr1, H. Hunkler1, I. Riedel1, T. Thum1, C. Bär1

1Institute of Molecular and Translational Therapeutic Strategies, Hannover Medical School, Hannover;

In the Western world, cardiovascular diseases remain one of the leading causes of death. The prevalence of these diseases will continue to rise in the coming decades, influenced by factors such as increasing life expectancy, western lifestyle and the number of infectious diseases with cardiovascular consequences. Therefore, there is an urgent need for sustainable and complex in vitro models to sufficiently recapitulate the physiology and pathophysiology of the human heart. This is especially important regarding drug discovery and development, leading towards more reliable in vitro testing identifying safe and potent drug candidates for further translational in vivo studies. Conventional in vitro systems are based on adherent, two-dimensional cultivation of cardiac specific cell types such as cardiac fibroblasts (FBs), endothelial cells (ECs) or most important cardiomyocytes (CMs). Besides these standardized models, three-dimensional cultivation has emerged as a broad and versatile field utilizing multiple cell types within a three-dimensional (3D) environment that led inter alia to nutrient and oxygen gradients, cell-cell interfaces promoting paracrine signaling and contact to extracellular matrix similar surroundings. Human cardiac organoids (hCO) resemble a self-organized and -assembled 3D culture system that displays heart-like characteristics. In this context, we established a multicellular cardiac organoid-approach based on previous published protocols [1, 2]. hiPSC-derived CMs, FBs, ECs and adipose tissue derived stem cells form a functional and contracting structure, spontaneous or controlled by electrosimulation. By immunostaining we demonstrate that the organoids self-assemble into a specific architecture where the hiPSC-CMs organize into an outer layer whereas the non-CMs mainly assemble within the organoid’s core. In first disease modeling approaches we show that treatment of healthy hCOs with the specific myosin-7 inhibitor Mavacamten reduces organoid contractility, whereas the hCOs respond to Phenylephrin-Isoprenaline with increased contractility. In addition to contractility assessment in healthy hCOs, these hCOs can be used to model cardiovascular diseases such as a myocardial infarction. By cultivating human cardiac organoids under hypoxic conditions and norepinephrine stimulation, we showed that this leads to impaired calcium handling as well as altered fibrosis related gene expression. Additionally, hypoxic hCOs displayed a larger population of dead cells due to reduced oxygen supply in the organoid core. In summary, we have adapted a multicellular organoid system. Our initial data suggests that this is a valuable platform for cardiac disease modeling. Therefore, in future studies we aim to combine this 3D platform with our hypertrophic cardiomyopathy patient-derived iPSC-CMs. The organoids can then be used for molecular characterization of the disease and serve as a drug discovery platform. [1] Richards DJ, Coyle RC, Tan Y, Jia J, Wong K, Toomer K, et al. Inspiration from heart development:    biomimetic development of functional human cardiac organoids. Biomaterials. 2017; 142:112–23. [2] Richards DJ, Li Y, Kerr CM, Yao J, Beeson GC, Coyle RC, et al. Human cardiac organoids for the modelling of myocardial infarction and drug cardiotoxicity. Nat Biomed Eng. 2020; 4:446–62.

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