Role of Epicardial Microenvironments in Synchronizing Cardiac Growth and Vascular Supply

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Summary of  Proceedings of the National Academy of Sciences https://doi.org/10.1073/pnas.2536457123 
Dr. Ku-Chi Tsao  et al.

Points

Weill Cornell Medicine researchers discovered that localized epicardial hypoxia acts as a primary signal coordinating heart muscle growth and coronary vessel development.
Regional oxygen dips trigger epicardial cells to activate key developmental genes, including vegfaa, loxl2a, and col12a1b, driving parallel myocardial and vascular expansion.
Oxygenated blood delivered by newly formed coronary vessels creates a self-limiting negative feedback loop that suppresses epicardial hypoxia signals.
Mutant zebrafish lacking functional coronary vasculature developed excessively thick and stiff myocardial walls due to dysregulated extracellular matrix crosslinking.
Targeting hypoxia-responsive epicardial signaling pathways offers potential strategies to prevent pathological muscle stiffening and vascular disruption in human heart failure.

Summary

This study evaluated the regulatory mechanisms governing synchronized myocardial expansion and coronary angiogenesis during ventricular maturation in juvenile zebrafish models. Coordinated tissue expansion and vascularization are essential for establishing normal cardiac morphology, contractility, and metabolic homeostasis. Led by Michael Harrison and colleagues at Weill Cornell Medicine, the research investigated whether direct cellular crosstalk or third-party signaling orchestrates the parallel growth of cardiomyocytes and coronary endothelial cells during early heart development.

Live-cell and fixed tissue imaging demonstrated that epicardial cells sense localized tissue hypoxia caused by regional myocardial thickening. In response to regional oxygen deprivation, epicardial cells trigger spatial expression of key morphogenetic genes, including vegfaa, loxl2a, and col12a1b. These epicardial signals act as a central regulatory node, driving synchronized coronary vessel sprouting and cardiomyocyte proliferation. The influx of oxygenated blood via new vessels provides a negative feedback loop that quenches epicardial hypoxia and balances muscular growth.

To assess the physiological consequences of disrupting this feedback mechanism, researchers evaluated cxcr4a mutant zebrafish (cxcr4aum20) lacking functional coronary vessels. In these mutants, persistent epicardial hypoxia and uncoupled myocardial expansion caused excessive ventricular wall thickening, aberrant extracellular matrix crosslinking, and increased myocardial stiffness. The authors conclude that epicardial hypoxia serves as a fundamental self-limiting feedback regulator, offering novel biological targets for mitigating vascular disruption and myocardial fibrosis in heart failure.

Link to the article: https://www.pnas.org/doi/10.1073/pnas.2536457123

References

Tsao, K.-C., Bakis, I., Sun, S., Nakayama, M., Kalmanson, Z., Abd Elmagid, L., Shuster, J. S., Xia, Y., Eichenbaum, J. V., Yu, F. Z., McCain, M. L., Evans, T., Pearson, C. A., Butcher, J. T., Cao, J., & Harrison, M. R. M. (2026). Hypoxia-mediated epicardial signaling coordinates coronary angiogenesis and myocardial expansion during zebrafish ventricle maturation. Proceedings of the National Academy of Sciences, 123(26), e2536457123. https://doi.org/10.1073/pnas.2536457123