Snakebite victims often present with sepsis-like symptoms, such as edema and respiratory distress syndrome. Analyses of snake venoms have identified a family of proteases characteristic of disintegrin metalloproteases (ADAMs) with the capability to cleave transmembrane molecules. Our previous work supported by this grant has focused on a unique member of this family, ADAM15, with respect to its molecular structure and function in regulating endothelial barrier property. We reported ADAM15 upregulation in the lungs and vascular tissues during inflammation, where it increases endothelial permeability and promotes leukocyte migration via Src- dependent signaling transduced by its cytoplasmic domain. In this renewal application, we plan to bring our investigation on ADAM15 to the next level by examining its novel molecular targets with high translational values and therapeutic potential. The studies will focus on endothelial glycocalyx, a barrier protective structure composed of glycosaminoglycan chains linked to transmembrane proteoglycans and glycoproteins, which are shed into the circulation following injury or major surgery. The central pathway to be tested is that during septic injury, ADAM15 cleaves these transmembrane molecules leading to glycocalyx degradation. The exposure of endothelium to circulating cells and agents, along with shedding products acting as hyperpermeability factors, promotes plasma leakage and leukocyte diapedesis.
Three specific aims are proposed: 1) to characterize ADAM-induced glycocalyx injury during sepsis; 2) to elucidate the molecular mechanisms by which ADAM causes glycocalyx degradation; and 3) to test the therapeutic potential of targeting the ADAM-glycocalyx pathway for treating sepsis. We will employ complementary approaches that integrate physiological responses and molecular reactions at organ, tissue, and cell levels. Innovative experimental models and therapies will be tested. A unique design is the characterization of lung pathophysiology under clinically relevant conditions, taking advantage of the available intact viable human organs provided by a federally certified organ procurement organization. Data derived from the proposed work will provide new mechanistic insights into the molecular pathogenesis of sepsis. The study will also assist in the identification and development of novel therapeutic targets for treating vascular inflammatory injury associated with infection, trauma or major surgery.
The CDC has declared sepsis a medical emergency. Recently redefined as a condition of ?life threatening organ dysfunction caused by a dysregulated host response to infection?, sepsis contributed to more than 2.4 millions deaths in the US during 1999- 2014. Currently, there are no approved drugs that specifically treat this devastating disease. While numerous clinical trials with therapies aimed at altering the general host defense against infection have failed to demonstrate mortality benefits, researchers are facing a great deal of challenges arising from an incomplete understanding of the cellular or molecular processes underlying organ malfunction in response to septic insults. We recently discovered that an enzyme, called a disintegrin metalloprotease (ADAM), plays a critical role in mediating tissue injury associated with sepsis. Here, we propose further in-depth analyses of this molecule, focusing on how dysregulation of ADAM leads to structural and functional damage of the vascular endothelium, a cell barrier lining the surface of blood vessel lumen that prevents leakage of blood contents to surrounding tissues. We will also test new drugs and biological interventions targeting ADAM in the vascular endothelium as potential therapies for sepsis.
