Endothelial β‐arrestins regulate mechanotransduction by the type II bone morphogenetic protein receptor in primary cilia

Modulation of endothelial cell behavior and phenotype by hemodynamic forces involves many signaling components, including cell surface receptors, intracellular signaling intermediaries, transcription factors, and epigenetic elements. Many of the signaling mechanisms that underlie mechanotransduction by endothelial cells are inadequately defined. Here we sought to better understand how β‐arrestins, intracellular proteins that regulate agonist‐mediated desensitization and integration of signaling by transmembrane receptors, may be involved in the endothelial cell response to shear stress. We performed both in vitro studies with primary endothelial cells subjected to β‐arrestin knockdown, and in vivo studies using mice with endothelial specific deletion of β‐arrestin 1 and β‐arrestin 2. We found that β‐arrestins are localized to primary cilia in endothelial cells, which are present in subpopulations of endothelial cells in relatively low shear states. Recruitment of β‐arrestins to cilia involved its interaction with IFT81, a component of the flagellar transport protein complex in the cilia. β‐arrestin knockdown led to marked reduction in shear stress response, including induction of NOS3 expression. Within the cilia, β‐arrestins were found to associate with the type II bone morphogenetic protein receptor (BMPR‐II), whose disruption similarly led to an impaired endothelial shear response. β‐arrestins also regulated Smad transcription factor phosphorylation by BMPR‐II. Mice with endothelial specific deletion of β‐arrestin 1 and β‐arrestin 2 were found to have impaired retinal angiogenesis. In conclusion, we have identified a novel role for endothelial β‐arrestins as key transducers of ciliary mechanotransduction that play a central role in shear signaling by BMPR‐II and contribute to vascular development.