Vascularized Human Cardiac Organoids Reveal Endothelial–Cardiomyocyte Crosstalk and Mechanisms of Carfilzomib-Induced Cardiotoxicity

ABSTRACT Human cardiac organoids (hCOs) provide a powerful platform for modeling heart development and disease, yet their lack of vasculature limits physiological relevance. Here, we generate vascularized human cardiac organoids (vhCOs) by assembling hCOs with blood vessel organoids, enabling the self-organized formation of unified tissues with extensive vascular networks and substantially enhanced cardiomyocyte (CM) maturation. Single-nucleus multiomic profiling reveals CM state resembling the 17-week human fetal heart, while endothelial cells (ECs) acquire cardiac-specific and arterial-like identities. Integrative cell–cell communication analyses and experimental validation identify CM-derived Laminin-α2 as a driver of arterial EC specification, while reciprocal EFNB2 signaling from arterial ECs promotes CM maturation, uncovering bidirectional cardiac–vascular crosstalk. Modeling carfilzomib-induced cardiotoxicity in vhCOs reveals ATF4-dependent endoplasmic reticulum (ER) stress and IL8-mediated inflammatory responses that are blunted in non-vascularized hCOs. Pharmacological attenuation of ER stress alleviates carfilzomib-induced cardiotoxicity. Altogether, vhCOs provide a developmentally advanced and physiologically faithful human cardiac model. Competing Interest Statement The authors have declared no competing interest. Footnotes ↵11 Lead contact