Marvin, A. | Search bioRxiv

bioRxiv2023

A defined clathrin-mediated trafficking pathway regulates sFLT1/VEGFR1 secretion from endothelial cells

FLT1/VEGFR1 negatively regulates VEGF-A signaling and is required for proper vessel morphogenesis during vascular development and vessel homeostasis. Although a soluble isoform, sFLT1, is often mis-regulated in disease and aging, how sFLT1 is trafficked and secreted from endothelial cells is not well understood. Here we define requirements for constitutive sFLT1 trafficking and secretion in endothelial cells from the Golgi to the plasma membrane, and we show that sFLT1 secretion requires clathrin at or near the Golgi. Perturbations that affect sFLT1 trafficking blunted endothelial cell secretion and promoted intracellular mis-localization in cells and zebrafish embryos. siRNA-mediated depletion of specific trafficking components revealed requirements for RAB27A, VAMP3, and STX3 for post-Golgi vesicle trafficking and sFLT1 secretion, while STX6, ARF1, and AP1 were required at the Golgi. Depletion of STX6 altered vessel sprouting in a 3D angiogenesis model, indicating that endothelial cell sFLT1 secretion is important for proper vessel sprouting. Thus, specific trafficking components provide a secretory path from the Golgi to the plasma membrane for sFLT1 in endothelial cells that utilizes a specialized clathrin-dependent intermediate, suggesting novel therapeutic targets.

cell biology↗

bioRxiv2020

SMAD6 Integrates Endothelial Cell Homeostatic Flow Responses Downstream of Notch

ABSTRACTLaminar shear stress regulates blood vessel morphogenesis and subsequent quiescence, leading to vascular homeostasis. Although important for vessel function, how vascular homeostasis is set up and maintained is poorly understood. SMAD6, a scaffold for several signaling pathways, is expressed in developing arteries and its expression is flow-regulated. We found that SMAD6 is essential for endothelial cell flow-mediated responses downstream of the mechanosensor Notch1. Endothelial cells with reduced SMAD6 levels failed to align under homeostatic laminar shear flow, while forced SMAD6 expression rescued misalignment induced by reduced Notch1 signaling. SMAD6-dependent homeostatic laminar flow responses required the Notch ligand Dll4 and Notch transcriptional activity. Mechanistically, neither the N-terminal nor the C-terminal domain of SMAD6 alone rescued flow alignment upon loss of Notch signaling. Endothelial cells with reduced Smad6 levels had compromised barrier function, and RNA profiling revealed upregulation of proliferation-associated genes and down regulation of junction-associated genes. Among junction-related genes affected by SMAD6 levels, the proto-cadherin PCDH12 was upregulated by homeostatic flow and required for proper flow-mediated endothelial cell alignment. Thus, SMAD6 is a critical integrator of flow-mediated signaling inputs downstream of Notch1, as vessels transition from an angiogenic to a homeostatic phenotype.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗