Abstract

The myocardium possesses one of the highest vascular densities in the body. The outermost wall layer of large and medium-sized vessels, the adventitia, forms a critical interface between the vasculature and the myocardium and serves as a reservoir for stem and progenitor cells capable of differentiating into all vascular wall lineages as well as innate immune cells, including macrophages. Current cardiac organoid models intrinsically develop networks of endothelial cords and small capillary-like structures that resemble cardiac microvessels. However, these microvessels mostly lack an adventitial compartment in vivo. Here, we present a potential alternative assembloid strategy that combines vascular segments from mouse and human origin with either cardiomyocytes or cardiac spheroids derived from human induced pluripotent stem cells, thereby incorporating large diameter vessels and the vascular adventitia into a cardiac tissue model. Within the assembloids, the myocardial component remained contractile and connected to the vascular adventitia, which displayed cellular sprouting toward the hiPSC-derived cardiac tissue. Immunostaining for vascular and immune markers revealed that the adventitia gave rise to endothelial sprouts and macrophage-like cells which integrated into the myocardial tissue. In summary, we present proof of concept for complex assembloids composed of vessel segments and human iPSC-derived cardiomyocytes which contain and maintain an in vivo-like adventitial compartment. We suggest this model may serve as a platform for investigating myocardial–stromal interactions, cardiac tissue repair, and functional remodeling under both physiological and pathological conditions. Furthermore, the incorporation of large-lumen vessel segments may enable future experimental perfusion, rendering the model particularly suitable for drug testing via intravascular delivery.

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