Investigating Timothy Syndrome in a new innervated heart muscle model – Zafeiriou Lab

Maria Patapia Zafeiriou, Group leader of 3D human excitable cell networks, University Medical Center Goettingen, Germany

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Our research focuses on understanding how the brain and the heart communicate with each other through networks of cells that carry electrical signals. These networks are essential for life: they allow the brain to send instructions to the heart so it can beat at the right rate and strength. When this communication system breaks down, it can cause serious health problems such as seizures, heart rhythm disturbances, heart failure, or even sudden death.

We are especially interested in conditions called channelopathies. These are disorders caused by changes in the proteins that form electrical “channels” in nerve and heart cells. When these channels do not work properly, the balance of signals in the brain and heart is disturbed, which can lead to dangerous outcomes. To investigate these problems, we use human stem cells to create miniature versions of tissues, called organoids, that mimic the brain¹, spinal cord², and heart². These models allow us to study how nerve cells connect to each other and how they communicate with heart cells in ways that are not possible in patients. By doing so, we can better understand the cellular and molecular processes behind diseases like epilepsy and sudden cardiac death.

Under this notion, we created a new type of lab-grown model that links nerve cells with heart muscle. We generate a cluster of nerve cells called a sympathetic neural organoid, made from human induced pluripotent stem cells and programmed to behave like the nerves that control the heart. We then combine it with engineered human heart muscle, also grown from stem cells. When fused together, the two tissues form what we call innervated engineered human myocardium ² (iEHM, Figure 1).

In the iEHM, the nerve cells grow into the heart tissue and form close, working connections with the heart cells—just like in a real human heart. The model also develops vessel-like networks that support its growth. Using light-sensitive stimulation, we can activate the nerve cells and observe how the heart tissue responds. For example, when the nerves are activated, the heart muscle beats faster, showing that the two tissues are functionally connected.

This model gives us a unique way to study diseases where communication between nerves and the heart goes wrong. One such disease is Timothy Syndrome, caused by changes in the calcium channel gene CACNA1C. Children with Timothy Syndrome often experience heart rhythm problems, autism, seizures, and a high risk of sudden death. The faulty calcium channels disrupt the normal flow of calcium in both nerve and heart cells, leading to miscommunication between the brain and the heart.

With our iEHM model, we can now recreate CACNA1C-Related Disorders including Timothy Syndrome, in the lab by using induced pluripotent stem cells from affected patients or by introducing the known CACNA1C mutation into healthy stem cells. This allows us to directly observe how the defective calcium channels affect both the nerve cells and the heart muscle cells, and how this leads to abnormal communication between the two. By studying these interactions in a human-based system, we gain insights into why patients develop life-threatening arrhythmias and neurological symptoms. Importantly, the model also gives us the chance to test new drugs or gene therapies in a controlled setting to see whether they can restore healthy communication between the brain and the heart. By creating this bridge between nerve and heart tissues in a dish, we move closer to understanding—and one day treating—serious conditions like Timothy Syndrome, sudden cardiac death, and heart rhythm disorders linked to brain diseases. In the collaborative spirit of the Timothy Syndrome Alliance, we hope that our work will contribute to finding effective therapies that improve the lives of children and families affected by this devastating condition.

Figure 1. Left, induced pluripotent stem cells (iPSC) generated by patient skin cells are transformed into heart and neuronal organoids in the lab. Fusion of these tissues gives rise to innervated heart muscle in which neurons and heart muscle functionally connect. Right, low and high magnification image depicting neurons (green) and heart muscle cells (red) co-developing in the novel innervated heart muscle model grown from human iPSC.

Credits: Graphic (left) generated by ChatGPT. Immunofluorescence image (right) adapted from Schneider et al 2023 ² .

Literature

1. Zafeiriou, M.-P. et al. Developmental GABA polarity switch and neuronal plasticity in Bioengineered Neuronal Organoids. Nat. Commun. 11, 3791 (2020).
2. Schneider, L. V. et al. Bioengineering of a human innervated cardiac muscle model. 2023.08.18.552653 Preprint at https://doi.org/10.1101/2023.08.18.552653 (2023).