"In sickness and in health": The regulation of junctional integrity in inflamed and healthy endothelial cells

Endothelial cells form a single layer of cells on the luminal side of all blood vessels. This layer of cells represents a dynamic physical barrier that restricts and regulates the movement of blood cells, solutes and fluids from the blood to the tissues surrounding blood vessels. Within this thesis we address several important aspects of endothelial junction regulation.
We then investigated plasminogen activator inhibitor 1 (PAI-1) as a novel regulator of endothelial junction stability. We show that PAI-1, which is expressed by endothelial cells, protects endothelial junctions in the steady state by ensuring efficient vascular endothelial cadherin (VE-cadherin) trafficking to and from the plasma membrane. Moreover, we demonstrated the importance of the phosphorylation of two adjacent serine residues in the RhoGEF Trio for the reformation of endothelial cell-cell junctions after stimulation with thrombin. Further to previous work from our lab we demonstrated here that serine phosphorylation primes Trio for rapid reformation of endothelial junctions. Finally, we returned to endothelial junction regulation in inflammation by demonstrating a role for the ubiquitin ligase cellular inhibitor of apoptosis 1 (c-IAP-1), the ubiquitin-editing enzyme tumor necrosis factor α (TNFα) -induced protein 3 (TNFAIP3) and the deubiquitinase ubiquitin-specific peptidase 8 (USP8) in limiting the extent of TNFα-induced changes to endothelial morphology, permeability and adhesion receptor expression.
Overall we have shown that the serine protease inhibitor PAI-1, serine phosphorylation of the RhoGEF Trio and ubiquitination of proteins involved in TNFα-mediated signaling are important regulators of endothelial junction permeability.