Role of Poldip2 in endothelial barrier function and inflammation in the lung

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PROJECT SUMMARY Endothelial cells line the lumen of all blood vessels and play a critical role in maintaining the barrier function of the vasculature. Diminished barrier function and the consequent increase in vascular permeability to plasma proteins and leukocytes has been described in pathological conditions such as acute respiratory distress syndrome and acute lung injury. The resulting tissue edema is associated with loss of aerated lung tissue and high mortality and morbidity. We have discovered that Polymerase delta interacting protein- 2 (Poldip2), a protein with multiple binding partners, is an important modulator of lung endothelial barrier function. Remarkably, using a lipopolysaccharide (LPS)-induced lung injury model, we observed that heterozygous deletion of Poldip2 nearly abolishes LPS-induced barrier dysfunction and extravasation of leukocytes into the lung, markedly improving survival. The effect of Poldip2 depletion on permeability is phenocopied in mice with endothelial-specific deletion of Poldip2. The phenotype of these animals is striking, suggesting that we have identified a novel and previously unappreciated major target for diseases related to EC barrier dysfunction. In this project, we will probe the molecular and cellular mechanisms responsible for this impressive protection to gain insight into potential new therapies. In the first aim, we will examine the specific role of endothelial Poldip2 in barrier function and inflammation in vivo and in vitro, using the LPS-induced injury model. Aim 2 is designed to define the mechanisms by which endothelial Poldip2 regulates barrier function and inflammation, focusing on the role of VE-cadherin signaling and its interplay with angiopoietin-2, as well as the Poldip2-interacting partner Nox4. Finally, in Aim 3, we plan to determine how Poldip2 function is regulated at the molecular and cellular levels. Together, these three aims will allow us to gain new insight into a novel therapeutic target for prevention of protein-rich edema and leukocyte extravasation following lung injury and will delineate the underlying molecular mechanisms. Our work will provide insight into a fundamental mechanism regulating permeability and inflammation that has potential broad applicability to other inflammatory diseases.