Fast revascularization of the injured area is essential to support zebrafish heart regeneration
Significance A heart attack occurs when blood flow to part of the heart is blocked, and oxygen and nutrients are unable to reach that tissue, irreversibly damaging cardiac muscle cells. Dead muscle cells are replaced by a noncontractile scar that affects cardiac function. Unlike humans, zebrafish can regenerate their heart after injury, replacing the scarred tissue with new cardiomyocytes. Understanding the mechanisms zebrafish deploy to regenerate their heart may help us design more efficient therapies for human heart disease. In this study, we show that to regenerate their heart, zebrafish quickly revascularize the damaged area, and that this ability to revascularize is temporally restricted. Zebrafish have a remarkable capacity to regenerate their heart. Efficient replenishment of lost tissues requires the activation of different cell types including the epicardium and endocardium. A complex set of processes is subsequently needed to support cardiomyocyte repopulation. Previous studies have identified important determinants of heart regeneration; however, to date, how revascularization of the damaged area happens remains unknown. Here, we show that angiogenic sprouting into the injured area starts as early as 15 h after injury. To analyze the role of vegfaa in heart regeneration, we used vegfaa mutants rescued to adulthood by vegfaa mRNA injections at the one cell stage. Surprisingly, vegfaa mutants develop coronaries and revascularize after injury. As a possible explanation for these observations, we find that vegfaa mutant hearts up regulate the expression of potentially compensating genes. Therefore, to overcome the lack of a revascularization phenotype in vegfaa mutants, we generated fish expressing inducible dominant negative Vegfaa. These fish displayed minimal revascularization of the damaged area. In the absence of fast angiogenic revascularization, cardiomyocyte proliferation did not occur, and the heart failed to regenerate, retaining a fibrotic scar. Hence, our data show that a fast endothelial invasion allows efficient revascularization of the injured area, which is necessary to support replenishment of new tissue and achieve efficient heart regeneration. These findings revisit the model where neovascularization is considered to happen concomitant with the formation of new muscle. Our work also paves the way for future studies designed to understand the molecular mechanisms that regulate fast revascularization.
Proceedings of the National Academy of Sciences