Neuropilin 1 mediates epicardial activation and revascularization in the regenerating zebrafish heart

Abstract

Unlike adult mammals, zebrafish are able to naturally regenerate their heart. A key mechanism in zebrafish heart regeneration is the activation of the epicardium, leading to the establishment of a supporting scaffold for newly formed cardiomyocytes, angiogenesis and cytokine secretion. Neuropilins (NRPs) are cell surface co-receptors mediating functional signaling of kinase receptors for cytokines known to play critical roles in zebrafish heart regeneration, including Platelet-Derived growth factor (PDGF), Vascular Endothelial growth factor (VEGF), and Fibroblast growth factor (FGF). Herein, we investigated the role of neuropilins in the response of the zebrafish heart to injury and its subsequent regeneration. All four zebrafish neuropilin isoforms, nrp 1a, 1b, 2a, and 2b, were upregulated following cardiac cryoinjury and were strongly expressed by the activated epicardium. A nrp1a mutant, coding for a truncated, non-functional protein, showed a significant delay in heart regeneration in comparison to Wild-Type fish and displayed persistent collagen deposition. The regenerating hearts of nrp1a mutants were less vascularized and epicardial-derived cell migration and re-expression of the developmental gene Wilms tumor 1 was severely impaired in nrp1a mutants. Moreover, cryoinjury-induced activation and migration of epicardial cells in heart explants was strongly reduced in nrp1a mutant zebrafish. These results identify a key role for Nrp1 in zebrafish heart regeneration, mediated through epicardial activation, migration and revascularization.