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

•NRP1 enables morphological, but not genetic, specialization of endothelial tip cells•NRP1 is essential for matrix-induced CDC42 activation in endothelial cells•NRP1 promotes filopodia extension and actin remodeling via CDC42•Endothelial NRP1 loss and CDC42 inhibition similarly impair angiogenesis

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.

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