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Mutations of the endothelial BMP9/10 receptors Alk1 and endoglin are associated with vascular malformations in hereditary hemorrhagic telangiectasia (HHT). Baeyens et al. report that fluid flow potentiates BMP activation of Alk1 signaling to stabilize blood vessels. HHT lesions thus result from a defect in a synergistic mechanical/biochemical signaling pathway.

VE-cadherin plays a critical role in endothelial shear stress mechanotransduction by interacting with VEGFRs through their transmembrane domains.

SummaryForces acting on cells govern many important regulatory events during development, normal physiology, and disease processes. Integrin-mediated adhesions, which transmit forces between the extracellular matrix and the actin cytoskeleton, play a central role in transducing effects of forces to regulate cell functions. Recent work has led to major insights into the molecular mechanisms by which these adhesions respond to forces to control cellular signaling pathways. We briefly summarize effects of forces on organs, tissues, and cells; and then discuss recent advances toward understanding molecular mechanisms.

Endothelial cell (EC) sensing of wall fluid shear stress (FSS) from blood flow governs vessel remodeling to maintain FSS at a specific magnitude or set point in healthy vessels. Low FSS triggers inward remodeling to restore normal FSS but the regulatory mechanisms are unknown. In this paper, we describe the signaling network that governs inward artery remodeling. FSS induces Smad2/3 phosphorylation through the type I transforming growth factor (TGF)-β family receptor Alk5 and the transmembrane protein Neuropilin-1, which together increase sensitivity to circulating bone morphogenetic protein (BMP)-9. Smad2/3 nuclear translocation and target gene expression but not phosphorylation are maximal at low FSS and suppressed at physiological high shear. Reducing flow by carotid ligation in rodents increases Smad2/3 nuclear localization, while the resultant inward remodeling is blocked by the EC-specific deletion of Alk5. The flow-activated MEKK3/Klf2 pathway mediates the suppression of Smad2/3 nuclear translocation at high FSS, mainly through the cyclin-dependent kinase (CDK)-2-dependent phosphosphorylation of the Smad linker region. Thus, low FSS activates Smad2/3, while higher FSS blocks nuclear translocation to induce inward artery remodeling, specifically at low FSS. These results are likely relevant to inward remodeling in atherosclerotic vessels, in which Smad2/3 is activated through TGF-β signaling.