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Congenital heart defects (CHDs) are the most common type of congenital defect in humans and affect approximately 1% of all live births1,2,3. Under most circumstances, the reasons for CHDs remain unknown. The ability to create human heart models in the lab that closely resemble the developing human heart constitutes a significant step forward to directly study the underlying causes of CHDs in humans rather than in surrogate animal models.
The epitome of laboratory-grown tissue models are organoids, 3D cell constructs that resemble an organ of interest in cell composition and physiological function. Organoids are often derived from stem cells or progenitor cells and have been successfully used to model many organs such as the brain4,5, kidney6,7, intestine8,9, lung10,11, liver12,13, and pancreas14,15, just to name a few. Recent studies have emerged demonstrating the feasibility of creating self-assembling heart organoids to study heart development in vitro. These models include using mouse embryonic stem cells (mESCs) to model early heart development16,17 up to atrioventricular specification18 and human pluripotent stem cells (hPSCs) to generate multi-germ layer cardiac-endoderm organoids19 and chambered cardioids20 with highly complex cellular composition.
This paper presents a novel 3-step WNT modulation protocol to generate highly complex hHOs in an efficient and cost-effective manner. Organoids are generated in 96-well plates, resulting in a scalable, high-throughput system that can be easily automated. This method relies on creating hPSC aggregates and triggering developmental steps of cardiogenesis, including mesoderm and cardiac mesoderm formation, first and second heart field specification, proepicardial organ formation, and atrioventricular specification. After 15 days of differentiation, hHOs contain all major cell lineages found in the heart, well-defined internal chambers, atrial and ventricular chambers, and a vascular network throughout the organoid. This highly sophisticated and reproducible heart organoid system is amenable to investigating structural, functional, molecular, and transcriptomic analyses in the study of heart development, and diseases, and pharmacological screening.