Adma and Ackr3a regulate cardiac lymphatic vessel formation and function during heart development and regeneration

Cardiac lymphatics regulate fluid homeostasis and immune cell clearance. The mechanisms underlying cardiac lymphatic vessel formation remain unclear. We perform spatial transcriptomics on the zebrafish heart at the single-cell level and investigate gene expression patterns in cardiac lymphatic endothelial cells (LECs). adrenomedullin a (adma) is mainly expressed in the epicardium adjacent to cardiac lymphatics. adma mutants develop edema and dilated outflow tracts with mis-patterned and reduced lymphatics, while their ventricular lymphatics are dilated with fewer sprouts, increased lyve1b expression, and altered lymphatic subpopulation composition. Loss of ackr3a, which encodes an Adm decoy receptor, increases lymphatic sprouts. During heart regeneration, adma and ackr3a are expressed in epicardium-derived cells within the wound. Neutrophil clearance is reduced in adma mutants but increased in ackr3a mutants. Our findings uncover the heterogeneity of cardiac LECs and show that Adm and Ackr3 regulate cardiac lymphatic vessel formation in the zebrafish heart.