https://doi.org/10.1007/s00392-025-02625-4
1Universitätsklinikum Heidelberg Pharmakologisches Institut Heidelberg, Deutschland; 2Universitätsklinikum Heidelberg Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie Heidelberg, Deutschland; 3Klinikum rechts der Isar Regenerative Medizin kardiovaskulärer Erkrankungen München, Deutschland
Ca²⁺ homeostasis is essential for cardiac function, and its dysregulation is implicated in life-threatening conditions such as arrhythmias, pathological remodeling and heart failure. Despite significant advances in understanding cardiac calcium signaling through animal models, extrapolating these findings to humans remains a challenge. Here, we address this translational gap by leveraging advanced 3D human heart models to study the role of the calcium regulator protein OCaR2 (encoded by Tmem63b) in human cardiac health and disease. OCaR2 plays a pivotal role in regulating calcium release from acidic organelles via NAADP and endo-lysosomal two-pore channels (TPCs). Its loss in mouse models results in fatal ventricular arrhythmias, severe cardiac hypertrophy, and fibrosis under chronic β-adrenergic stimulation (Berlin et al., 2022).
To translate these findings to human physiology, we generated OCaR2-/- human-induced pluripotent stem cell (hiPSC) lines using advanced base editing technologies. These hiPSCs were differentiated into functional 3D heart epicardioids following a previously published protocol by Meier et al. (2023). In this project, we compare wild-type (WT) and OCaR2-/- human heart epicardioids under β-adrenergic stress, focusing on hypertrophy, fibrosis, and arrhythmogenesis. Functional analyses include live calcium imaging, RT-qPCR, and immunohistopathological methods. After 15 days of differentiation, RT-qPCR analysis of WT and OCaR2-/- epicardioids confirmed the expression of markers for cardiac tissue (TNNT2, MYH6, MYL2, MYL3) and the epicardium (BNC1, WT1, TBX18, TCF21). Histological validation through cryosectioning and immunostaining further supported the presence of epicardial and cardiac tissue. We are currently analyzing WT and OCaR2-/- epicardioids treated with phenylephrine (PE) and isoproterenol (ISO) to induce pathological remodeling.
Our preliminary results highlight the importance of 3D human heart organoids as a translational model at the intersection of animal research and extrapolation to the human system. By uncovering the role of OCaR2 in calcium signaling and its implications for cardiac disease, this study contributes to the development of precision therapies targeting calcium dysregulation. Such strategies hold promise for improving outcomes in patients with heart failure and arrhythmias, marking a critical advancement in both preclinical and clinical research.
References
Berlin, M. et al. An endo-lysosomal Ca2+ store in cardiomyocytes controlled by OCaR proteins determines fatal tachyarrhythmias. J Mol Cell Cardiol 173, S28 (2022).
Meier, A. B. et al. Epicardioid single-cell genomics uncovers principles of human epicardium biology in heart development and disease. Nat Biotechnol (2023) doi:10.1038/s41587-023-01718-7.