Self-organizing human heart assembloids with autologous and developmentally relevant cardiac neural crest-derived tissues

This study reports the development of a novel human neural crest-heart assembloid (hNCHA) platform, providing a human-relevant, 3D experimental model of early heart development. By successfully integrating induced pluripotent stem cell (iPSC)-derived neural crest cells (NCCs) into human heart organoids (hHOs), the researchers were able to observe and map the developmental trajectories of NCCs as they migrate into the heart, differentiate into specialized cholinergic neurons and glial cells, and form functional synaptic connections with cardiomyocytes. The findings offer significant insights into the role of NCCs in cardiac conduction system maturation, showing that NCC-derived parasympathetic neurons play a crucial role in regulating cardiac rhythm through the neurotransmitter acetylcholine. The study further identifies that migrating NCCs contribute to the mesenchymal populations of the outflow tract, a structure critical to congenital heart health, highlighting the model's high level of similarity to human embryonic heart development. Critically, the research utilizes this model to address the impact of prenatal exposure to Selective Serotonin Reuptake Inhibitors (SSRIs). By exposing NCCs to clinically relevant concentrations of common antidepressants like Paroxetine and Sertraline, the authors provide the first experimental human-based evidence that such exposure can disrupt key transcriptional regulators of autonomic development (specifically PHOX2B), leading to impaired parasympathetic innervation and significant functional cardiac defects. This research provides a valuable tool for future high-throughput drug screening and for gaining a better understanding of the molecular mechanisms underlying congenital heart malformations.

Neural crest cells (NCCs) are a multipotent embryonic cell population of ectodermal origin that extensively migrate during early development and contribute to the formation of multiple tissues. Cardiac NCCs play a critical role in heart development by orchestrating outflow tract septation, valve formation, aortic arch artery patterning, parasympathetic innervation, and maturation of the cardiac conduction system. Abnormal migration, proliferation, or differentiation of cardiac NCCs can lead to severe congenital cardiovascular malformations. However, the complexity and timing of early embryonic heart development pose significant challenges to studying the molecular mechanisms underlying NCC-related cardiac pathologies. Here, we present a sophisticated functional model of human heart assembloids derived from induced pluripotent stem cells, which, for the first time, recapitulates cardiac NCC integration into the human embryonic heart in vitro. NCCs successfully integrated at developmentally relevant stages into heart organoids, and followed developmental trajectories known to occur in the human heart. They demonstrated extensive migration, differentiated into cholinergic neurons capable of generating nerve impulses, and formed mature glial cells. Additionally, they contributed to the mesenchymal populations of the developing outflow tract. Through transcriptomic analysis, we revealed that NCCs acquire molecular features of their cardiac derivatives as heart assembloids develop. NCC-derived parasympathetic neurons formed functional connections with cardiomyocytes, promoting the maturation of the cardiac conduction system. Leveraging this model's cellular complexity and functional maturity, we uncovered that early exposure of NCCs to antidepressants harms the development of NCC derivatives in the context of the developing heart. The commonly prescribed antidepressant Paroxetine disrupted the expression of a critical early neuronal transcription factor, resulting in impaired parasympathetic innervation and functional deficits in cardiac tissue. This advanced heart assembloid model holds great promise for high-throughput drug screening and unraveling the molecular mechanisms underlying NCC-related cardiac formation and congenital heart defects.

The discussion emphasizes the model's success in recapitulating the early stages of human heart development and NCC integration in a controlled 3D environment. The authors highlight the importance of their model in studying the intrinsic cardiac nervous system and the interaction between NCC-derived neurons and cardiomyocytes, which are key for cardiac rhythm and conduction. The researchers address the clinical implications of their findings, specifically regarding the potential risks of antidepressant exposure during early pregnancy. They acknowledge limitations, including the lack of mechanical forces and the absence of certain cell populations, and suggest future directions for incorporating immune cells and endodermal progenitors to increase the model's complexity.