Sepsis associated with acute lung injury (ALI) is a common cause of death in hospitalized patients. ALI is in large part the result of lung vascular leakage and protein rich edema and there is a lack of effective therapy. Here, we have proposed a novel strategy to reverse ALI by stimulating an endogenous recovery process that is usually activated after lung injury. Thrombin, an edema-genic factor generated during sepsis, mediates pulmonary vascular leakage by activating protease-activated receptor-1 (PAR-1) on the endothelial cell surface. PAR-1-induced Ca2+ entry via store-operated Ca2+-entry channels (SOCs), disassembles endothelial adherens junctions (AJs) to cause increased lung vascular leak. An endoplasmic reticulum (ER) localized Ca2+ sensor protein stromal interacting molecule-1 (STIM1), is crucial for activating SOC to induce store- operated Ca2+-entry (SOCE) in endothelial cells (ECs). Now, we have identified in a murine model of tamoxifen-inducible endothelial cell (EC)-restricted TAK1 (Map3k7) deletion (Map3k7i?EC), a key role for TAK1 in resolving PAR-1-mediated pulmonary edema formation through regulation of the functions of STIM1, glycogen synthase kinase-3? (GSK-3?) and ?-catenin in ECs. We made the following observations (Supporting Data): i) TAK1 null ECs exhibited augmented SOCE and permeability in response to PAR-1 activation; ii) PAR-1-induced lung vascular permeability in vivo was not reversible in Map3k7i?EC mice; iii) ?- catenin expression was markedly reduced in ECs of Map3k7i?EC mice; iv) glycogen synthase kinase-3? (GSK- 3?) was persistently active in ECs of Map3k7i?EC mice, which may account for the markedly reduced expression of ?-catenin in ECs of Map3k7i?EC mice; v) PAR-1-medatied TAK1 activation was prevented in ECs of EC-restricted STIM1 knockout (Stim1?EC) mice; vi) surprisingly, we observed that SOCE signals the inactivation of GSK-3? via TAK1 activation in ECs; vii) importantly, PAR-1-mediated lung vascular leak was markedly reduced in tamoxifen-inducible EC-restricted GSK-3? knockout (GSK-3?i?EC) mice. Based on these novel observations, in Aim 1, we will test the hypothesis that TAK1 activation secondary to STIM1-mediated SOCE induces STIM1 phosphorylation which in turn inhibits SOCE and dampens lung vascular permeability.
In Aim 2, we will test the hypothesis that TAK1 activation secondary to STIM1-mediated SOCE phosphorylates GSK-3? to inactivate GSK-3?, which in turn promotes increased ?-catenin expression at endothelial AJs to restore endothelial barrier integrity and thereby resolves pulmonary edema. A better understanding of the signaling mechanisms of TAK1 functions downstream of SOCE will lead to novel therapeutic approaches that will resolve pulmonary edema in sepsis.
Sepsis causes death by making lung blood vessel leaky, resulting in pulmonary edema formation. Currently there is no specific treatment for this disease. Lung vascular leakage may be due to defects in the endothelial cells lining the inner blood vessel wall. Coagulation protease thrombin generated during sepsis plays an important role in altering the calcium level in endothelial cells. The present investigation will investigate how increased calcium concentration activates TAK1 kinase in endothelial cells and how the activated TAK1 kinase repair the leaky lung vessels to normalize lung vascular function. Understanding this process will lead to the identification of therapeutic agents for prevention of pulmonary edema formation in sepsis.
