TLR4 signaling in endothelial cells (ECs) induces vascular injury by disrupting the endothelial junctional barrier. However, it is not known whether TLR4 signaling can also promote endothelial barrier repair after vascular injury. Here we addressed the role of TAK1 activation downstream of TLR4 in the mechanism of vascular integrity. In inducible EC-restricted TAK1 knockout (TAK1iΔEC) mice, the endothelial barrier was compromised. Blocking TAK1 activity caused spontaneous loss of the endothelial barrier. Importantly, TAK1 inactivated GSK3β via AKT to prevent β-catenin downregulation. We observed in ECs of GSK3βiΔEC mice an increase in β-catenin transfer to the nucleus to form a complex with transcriptio... More
TLR4 signaling in endothelial cells (ECs) induces vascular injury by disrupting the endothelial junctional barrier. However, it is not known whether TLR4 signaling can also promote endothelial barrier repair after vascular injury. Here we addressed the role of TAK1 activation downstream of TLR4 in the mechanism of vascular integrity. In inducible EC-restricted TAK1 knockout (TAK1iΔEC) mice, the endothelial barrier was compromised. Blocking TAK1 activity caused spontaneous loss of the endothelial barrier. Importantly, TAK1 inactivated GSK3β via AKT to prevent β-catenin downregulation. We observed in ECs of GSK3βiΔEC mice an increase in β-catenin transfer to the nucleus to form a complex with transcription factor FoxO1, thus repressing the expression of the tight junction protein claudin-5 and causing vascular leak. Strikingly, in TAK1iΔEC mice, FoxO1 expression was dramatically increased while expression of AKT was suppressed, and in vivo inhibition of FoxO1 prevented sepsis-induced lung vascular leak in GSK3βiΔEC and TAK1iΔEC mice. Further, EC-restricted deletion of FoxO1 in mice suppressed sepsis-induced lung vascular leak and mortality. Our findings point to the potential of targeting the TAK1-AKT-GSK3β-FoxO1 axis as a therapeutic approach to treat uncontrolled lung vascular leak in sepsis.
