Role of hippo pathway in developmental and pathologic lymphangiogenesis

Abstract

The Hippo pathway governs cellular differentiation, morphogenesis, and homeostasis but how it regulates these processes in lymphatic vessels is unknown. Therefore, I aimed to reveal the role of the final effectors of the Hippo pathway, YAP and TAZ (YAP/TAZ), in lymphatic endothelial cell (LEC) differentiation, morphogenesis, and homeostasis in vivo and in vitro. During mouse embryonic development, LEC-specific depletion of Yap/Taz disturbed both plexus patterning and valve initiation with upregulated Prox1. Conversely, LEC-specific YAP/TAZ hyperactivation impaired lymphatic specification and restricted lymphatic sprouting with profoundly downregulated Prox1. Notably, lymphatic YAP/TAZ depletion or hyperactivation aggravated or attenuated pathologic lymphangiogenesis in mouse cornea. Mechanistically, VEGF-C activated canonical Hippo signaling pathway in LECs. Indeed, repression of PROX1 transcription by YAP/TAZ hyperactivation was mediated by recruitment of nucleosome remodeling and histone deacetylase (NuRD) complex and endogenous binding activity of TEAD to the PROX1 promoter. Furthermore, YAP/TAZ hyperactivation enhanced MYC signaling and inhibited CDKN1C, leading to cell cycle dysregulation and aberrant proliferation. I find that YAP/TAZ play promoting roles in remodelling lymphatic plexus patterning and postnatal lymphatic valve maintenance by negatively regulating Prox1 expression. I further show that YAP/TAZ act as plastic regulators of lymphatic identity and define the Hippo signaling-mediated PROX1 transcriptional programming as a novel dynamic checkpoint underlying lymphatic endothelial cell plasticity and pathophysiology.