Abstract 33: Role of Epsins in Regulating LPS-Induced Sepsis

Abstract

Background: Sepsis is caused by a deleterious host response to infection, which is primarily responsible for further injury of host tissue and cause of organ dysfunction. However, the underlying regulatory mechanisms are still not fully understood. Our goal is to define the novel role of epsins in regulating sepsis. Methods and Results: We engineered global (iDKO) and endothelial cell-specific (EC-iDKO) epsin deficient mice. When treated with lethal dose of LPS, epsin deficient mice were completely protected from LPS-induced septic death. These mice also exhibited decreased expression of tissue damage biomarkers and recruitment of neutrophils and macrophages to lungs compared to wild type (WT) suggesting that epsin deficiency mitigates sepsis induced tissue injury. Epsin deficiency further reduced expression of proinflammatory cytokines and adhesion molecules in the lungs suggesting that loss of epsin attenuates LPS-induced inflammatory responses. TAT complex production was also decreased in iDKO mice compared to WT indicating diminished coagulation and thrombin production. Knocking down of epsins in HUVECs resulted in reduced cell surface Tissue Factor (TF) expression. Loss of epsin in mice protected against loss of Thrombomodulin (TM), which is downregulated by sepsis. Mechanistically, loss of epsin inhibited LPS-induced TM internalization, while LPS treatment induced the ubiquitination of TM. Furthermore, co-IP of full length epsin 1 or epsin 1 without the UIM domain and TM demonstrated that UIM is required for the interaction between epsin 1 and TM. Collectively, we show that epsin-deficiency upregulates TM surface protein expression by preventing its internalization and subsequent degradation and inhibits heightened TF expression and activation under chronic inflammatory conditions such as that induced by LPS exposure. Conclusions: Our findings demonstrate that epsins play a key role in regulating coagulation and provide fundamental information on the modulation of the ratio of TM/TF in various thrombotic diseases including sepsis. Furthermore, we demonstrate loss of epsin protects mice against LPS-induced sepsis, suggesting a crucial role for epsins in promoting the development of LPS-induced sepsis.