Yap Promotes Noncanonical Wnt Signals From Cardiomyocytes for Heart Regeneration

Rationale: During neonatal heart regeneration, the fibrotic response, which is required to prevent cardiac rupture, resolves via poorly understood mechanisms. Deletion of the Hippo pathway gene Sav in adult cardiomyocytes increases Yap activity and promotes cardiac regeneration, partly by inducing fibrosis resolution. Deletion of Yap in neonatal cardiomyocytes leads to increased fibrosis and loss of neonatal heart regeneration, suggesting that Yap inhibits fibrosis by regulating intercellular signaling from cardiomyocytes to cardiac fibroblasts (CFs). Objective: We investigated the role of Wntless ( Wls ), which is a direct target gene of Yap, in communication between cardiomyocytes and CFs during neonatal heart regeneration. Methods and Results: We generated 2 mouse models to delete Wls specifically in cardiomyocytes ( Myh6-Cas9 combined with AAV9-Wls-g RNAs, and Myh6 cre-ERT2/+ ; Wls flox/flox ). Reanalysis of single-cell RNA sequencing data revealed that Wnt ligands are expressed in cardiomyocytes, whereas Wnt receptors are expressed in CFs, suggesting that Wnt signaling is directional from cardiomyocytes to CFs during neonatal heart regeneration. Wls deletion in neonatal cardiomyocytes disrupted Wnt signaling, revealed by reduced noncanonical Wnt signaling in non-cardiomyocytes. Four weeks after neonatal heart myocardial infarction, heart function was measured by echocardiography. Wls deletion in neonatal cardiomyocytes after myocardial infarction impairs neonatal heart regeneration, marked by decreased contractile function and increased fibrosis. Wls mutant hearts display CF activation, characterized by increased extracellular matrix secretion, inflammation, and CF proliferation. Conclusions: These data indicate that during neonatal heart regeneration, intercellular signaling from cardiomyocytes to CFs occurs via noncanonical Wnt signaling to rebuild cardiac architecture after myocardial infarction.