Unlike lymphatics elsewhere, the lymphatic system in the GI tract transports absorbed lipids and enables immune surveillance of the billions of bacteria in the gut microbiome. Such specialized functions are thought to require unique genetic and molecular characteristics, but few such specialized features have been identified. Our preliminary studies use a new line of PAR1-Tango transgenic mice to demonstrate high thrombin activity specifically in the lymphatic vessels of the gut, a finding consistent with high expression of the endothelial anti- thrombotic proteins thrombomodulin (THBD) and endothelial protein C receptor (EPCR) specifically in gut lymphatic endothelial cells (LECs). Following inducible, global LEC deletion of THBD or EPCR, we observe fibrin thrombus formation specifically in GI lymphatics that is associated with reduced lymph flow from the gut, phenotypes reversed by antibiotic treatment to reduce gut bacteria. We also detect fibrin thrombus formation in the gut lymphatics of wild-type animals following infection by the enteric bacterial pathogens Salmonella or Yersinia. These studies identify a new in vivo clotting mechanism, lymphothrombosis, that is highly specific for gut lymphatic vessels and that must be regulated by gut LECs to maintain normal gut lymphatic function.
The aims of this proposal will use novel molecular and genetic tools to (i) fully define the process of lymphothrombosis in the gut lymphatic vasculature, (ii) test whether and how GI lymphothrombosis is linked to gut microbiota, and (iii) determine the role of gut lymphothrombosis during GI infection. We predict that these studies will reveal a novel mechanism of thrombosis outside of the blood vascular system that plays a unique and functionally important role in gut lymphatics in both health and disease.
Lymphatic vessels in the GI tract are thought to be specifically adapted for functions related to the gut, but molecular identification of such adaptations is lacking. Our studies reveal that gut lymphatics are exposed to high levels of thrombin and, unlike lymphatic vessels elsewhere, require endothelial expression of the anti- thrombotic proteins THBD and EPCR to prevent the formation of occlusive fibrin thrombi (termed ?lymphothrombosis?). The gut is home to trillions of bacteria, and our preliminary data indicate that gut lymphatics must regulate thrombotic responses to bacteria in both the healthy and pathologic states to maintain normal function. This proposal will use mouse genetic models and established models of GI infection to define the role of lymphothrombosis in the gut during homeostasis and bacterial infection.
