NRP1 Regulates CDC42 Activation to Promote Filopodia Formation in Endothelial Tip Cells

Abstract

SummarySprouting blood vessels are led by filopodia-studded endothelial tip cells that respond to angiogenic signals. Mosaic lineage tracing previously revealed that NRP1 is essential for tip cell function, although its mechanistic role in tip cells remains poorly defined. Here, we show that NRP1 is dispensable for genetic tip cell identity. Instead, we find that NRP1 is essential to form the filopodial bursts that distinguish tip cells morphologically from neighboring stalk cells, because it enables the extracellular matrix (ECM)-induced activation of CDC42, a key regulator of filopodia formation. Accordingly, NRP1 knockdown and pharmacological CDC42 inhibition similarly impaired filopodia formation in vitro and in developing zebrafish in vivo. During mouse retinal angiogenesis, CDC42 inhibition impaired tip cell and vascular network formation, causing defects that resembled those due to loss of ECM-induced, but not VEGF-induced, NRP1 signaling. We conclude that NRP1 enables ECM-induced filopodia formation for tip cell function during sprouting angiogenesis.

YAP/TAZ-CDC42 signaling regulates vascular tip cell migration

“…Cell proliferation and migration are essential for angiogenesis and these cell responses are regulated by many different signaling pathways, including the VEGF, Notch, Wnt, FGF, BMP, and integrin signaling responses (9, 12-16). VEGFA and CDC42 are known to regulate extension of the angiogenic front and filopodia formation in angiogenic tip cells (2,17,18).The Hippo signaling pathway is an evolutionarily conserved, pivotal regulator of cell proliferation and organogenesis. YAP and TAZ are key components of the Hippo signaling pathway and function as transcription cofactors that regulate downstream gene expression via association with DNA binding proteins such as 20).…”

Regulation of embryonic neurogenesis by germinal zone vasculature

“…Nrp1-null CD1 mice and endothelial-or NPC-specific NRP1-null C57/Bl6 mice have been described previously (15,20). Sox1-iCreER T2 mice were developed by N.K.…”

“…NRP1 promotes CNS vascularization in response to VEGF-A and ECM signals (14,15) and functions as a VEGF-A and class 3 semaphorin (SEMA3) receptor to regulate neuronal migration and axon guidance (16). Moreover, SEMA3B signals through NRP1 and NRP2 in spinal cord NPCs to orientate their mitotic spindle and regulate the onset of motor neuron differentiation (13).…”

Cross-talk between blood vessels and neural progenitors in the developing brain

“…Nevertheless, embryo-wide or endothelial Nrp1 deletion impairs CNS vascularisation [5,6,44], suggesting that NRP1 acts in ECs to promote brain vascularisation through a VEGF-independent signalling mechanism. This mechanism may involve the modulation of TGF-β signalling [45,46] and the promotion of tip cell filopodia extension and actin cytoskeletal reorganisation via integrin-associated signalling pathways [47].…”