Human heart-like models – a new dimension in basic science
29 Aug 2021
Animal model-based approaches are associated with issues relating to ethics and species differences as well as the technical problems of working with small animals. At ESC Congress 2021, three studies have looked at alternative human cell-based models.
An e-Poster by Doctor Yun Liu (Okayama University, China) and colleagues describes the development of a human ‘heart-on-a-chip’ model, which may help to circumvent these challenges. Their model consists of two microfluidic channels separated by a membrane. The bottom channel is seeded with human umbilical vein endothelial cells to mimic the vasculature, while the top channel is seeded with human-induced pluripotent stem cells (hiPSCs) and human gingival fibroblasts, which facilitate cardiac differentiation of hiPSCs.
Using their model, they were able to show spontaneous contraction of hiPSC-derived cardiomyocytes in the 2–3 weeks after differentiation. Live intracellular imaging using a fluorogenic calcium-sensitive dye demonstrated a periodic, coordinated pattern of calcium influx synchronised with contraction. Furthermore, noradrenaline elevated the heart rate of the hiPSC-derived cardiomyocytes in a dose-dependent manner, demonstrating that the model exhibits a functional response.
Anti-cardiac troponin T antibody staining indicated a typical striated pattern providing histological evidence of sarcomere structure. Moreover, anti-CD31 antibody staining for vascular endothelial cells in the bottom channel demonstrated a boundary between cells that would be expected at the cell–cell junction.
The authors concluded that this model may be valuable not only for examining normal physiological heart function and response to treatment, but also for studying the specific pathophysiology of individual patient-derived hiPSCs.
Doctor Matteo Ghiringhelli (Technion - Israel Institute of Technology, Haifa, Israel) and colleagues are using tissue engineering-based strategies to build 3D chamber-specific structures. In their e-Poster, they describe how either atrial or ventricular patches of adult rats can be decellularised to act as scaffolds and then recellularised with hiPSC-derived cardiomyocytes (atrial or ventricular cells). The cardiomyocytes can also be transduced to express the light-sensitive cationic channel, channel-rhodopsin-2 (ChR2).
In their model, the authors demonstrated spontaneous contraction and, depending on the chamber-specific cells seeded, were able to show immunostaining for atrial (MLC-2A) or ventricular (MLC2V) markers, gene expression, action potential morphology and chamberspecific pharmacological responses.
Optical mapping was used to characterise the conduction and repolarisation properties of the generated tissues. The tissue models could be paced, and their electrical activity controlled by either electrical or optogenetic stimulation. Finally, arrhythmogenic re-entrant arrhythmias could be induced and terminated by ‘opto-genetic-defibrillation’.
The authors concluded that these tissue models could be used for a range of applications, including disease modelling, drug testing and regenerative medicine.
A very timely and important use for human-based experimental models is the study of the effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of the coronavirus disease 2019 (COVID-19).
In a session on COVID-19 and basic science, Doctor Julian Wagner (Goethe University Hospital, Frankfurt, Germany) describes a study designed to investigate whether the vascular complications of SARS-CoV-2 variants are due to a systemic inflammatory response or are a direct consequence of viral infection.
hiPSC-derived cardiomyocytes and human endothelial cells from different vascular beds (umbilical vein endothelial cells, coronary artery endothelial cells [HCAEC], cardiac and lung microvascular endothelial cells and pulmonary arterial cells) were inoculated in vitro with SARS-CoV-2 (G614 original strain, B.1.1.7 alpha variant, B.1.351 beta variant and P.1 zeta variant).
Cardiomyocytes and endothelial cells showed a distinct response to SARSCoV2. Cardiomyocytes were permissively infected, yet of all the endothelial cells tested, only HCAECs took up the virus. All endothelial cells were resistant to viral replication. The latter finding suggests that SARS-CoV-2 might indirectly induce endothelial cell dysfunction via a systemic inflammatory response. However, both cardiomyocytes and endothelial cells showed signs of increased toxicity induced by the B.1.1.7 alpha variant, indicating there may be some direct effects. More severe cytotoxicity of novel variants indicate that patients infected with the new variants should be closely monitored.
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Liu Y, et al
Ghiringhelli M, et al
Wagner J, et al