The vascular barrier that separates blood from tissues is actively regulated by the endothelium and is essential for transport, inflammation, and haemostasis1. Haemodynamic shear stress plays a critical role in maintaining endothelial barrier function2, but how this occurs remains unknown. Here we use an engineered organotypic model of perfused microvessels to show that activation of the transmembrane receptor NOTCH1 directly regulates vascular barrier function through a non-canonical, transcription-independent signalling mechanism that drives assembly of adherens junctions, and confirm these findings in mouse models. Shear stress triggers DLL4-dependent proteolytic activation of NOTCH1 to expose the transmembrane domain of NOTCH1. This domain mediates establishment of the endothelial barrier; expression of the transmembrane domain of NOTCH1 is sufficient to rescue defects in barrier function induced by knockout of NOTCH1. The transmembrane domain restores barrier function by catalysing the formation of a receptor complex in the plasma membrane consisting of vascular endothelial cadherin, the transmembrane protein tyrosine phosphatase LAR, and the RAC1 guanidine-exchange factor TRIO. This complex activates RAC1 to drive assembly of adherens junctions and establish barrier function. Canonical transcriptional signalling via Notch is highly conserved in metazoans and is required for many processes in vascular development, including arterial–venous differentiation3, angiogenesis4 and remodelling5. We establish the existence of a non-canonical cortical NOTCH1 signalling pathway that regulates vascular barrier function, and thus provide a mechanism by which a single receptor might link transcriptional programs with adhesive and cytoskeletal remodelling.
This work was supported in part by grants from the National Institutes of Health (EB00262, EB08396, UH3EB017103 and HL115553) and the National Science Foundation Center for Engineering MechanoBiology (CMMI15-48571). W.J.P. acknowledges support from a Ruth L. Kirchstein National Research Service Award (F32 HL129733) and from the NIH through the Organ Design and Engineering Training program (T32 EB16652), and M.L.K. acknowledges support from the Hartwell Foundation and the NIH through the Translational Research in Regenerative Medicine Training program (T32 EB005583). We thank P. A. Murphy and R. Wang for discussions of preliminary data and M. Schwartz for materials and discussions.