Spleen Tyrosine Kinase phosphorylates VE-cadherin to cause endothelial barrier disruption in acute lung injury.

Increased endothelial cell (EC) permeability is a cardinal feature of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Tyrosine phosphorylation of VE-cadherin is a key determinant of EC barrier disruption. However, the identity and role of tyrosine kinases in this context are incompletely understood. Here we report that Spleen Tyrosine Kinase (Syk) is a key mediator of EC barrier disruption and lung vascular leak in sepsis. Inhibition of Syk by pharmacological or genetic approaches, each reduced thrombin-induced EC permeability. Mechanistically, Syk associates with and phosphorylates VE-cadherin to cause EC permeability. To study the causal role of endothelial Syk in sepsis-induced ALI, we used a remarkably efficient and cost-effective approach based on gene transfer to generate EC-ablated Syk mice. These mice were protected against sepsis-induced loss of VE-cadherin and inflammatory lung injury. Notably, the administration of Syk inhibitor R788 (fostamatinib); currently in phase II clinical trial for the treatment of COVID-19, mitigated lung injury and mortality in mice with sepsis. These data identify Syk as a novel kinase for VE-cadherin and a druggable target against ALI in sepsis.