Inflamed endothelial cells express S1PR1 inhibitor CD69 to induce vascular leak

Inflammation disrupts endothelial barrier function and causes vascular leak into the tissue parenchyma. Sphingosine 1-phosphate receptor-1 (S1PR1) in endothelial cells (ECs) is a key inducer of endothelial junctions and barrier function. We report here that ECs activation by the cytokine TNFα and TLR3 agonist polyinosine/polycytosine (pI:C) induces the lymphocyte activation molecule CD69 via the canonical NFκB pathway. EC CD69 stimulates endocytosis of S1PR1, inhibits its downstream intracellular signaling events and barrier function. Administration of TLR4 or TLR3 agonists or intranasal infection of mouse-adapted influenza virus (H1N1) or coronavirus (MHV-A59) induced CD69 in lung ECs. Adeno-associated virus-mediated overexpression of CD69 in lung EC leads to decreased cell-surface expression of S1PR1 and tight junction protein claudin-5, concomitantly with increased vascular permeability in the lungs. Furthermore, lung vascular leak at the peak of H1N1 infection is attenuated in a genetic mouse model which lacks CD69 in the endothelium. These data suggest that endothelial activation during inflammation and viral host-defense induces CD69 which downregulates S1PR1 to induce vascular leakage. CD69 induction during endothelial dysfunction may drive exaggerated inflammation by antagonizing the endothelial protective S1PR1 pathway.