Regulation of Toll-like Receptor 4 in Acute Inflammatory Disease

DESCRIPTION (provided by applicant): Our laboratory's long-term goal is to discover how inflammation is triggered by microbial and non-microbial stimuli and to control that process therapeutically. Since Toll-like receptor (TLR) function appears central to inflammation and TLR4 function is regulated by extracellular matrix (ECM), the overall objective of this project is to determine how local environment controls inflammation and how this control may be breached to initiate the systemic inflammatory response syndrome (SIRS). Our central hypothesis is that inflammatory stimuli are suppressed in healthy tissue by intact ECM while ECM degradation in disease facilitates or triggers local inflammation and, potentially, SIRS. We plan to test this central hypothesis through two specific aims: 1) Identify TLR4 inhibiting component(s) of intact ECM in vitro; 2) Establish the in vivo role of intact ECM and its degradation in 3 murine models of SIRS (endotoxemia, cerulein-induced acute pancreatitis, acetaminophen-induced acijte hepatitis). We hypothesize that heparan sulfate proteoglycans in intact ECM directly tether TLR4 monomers and thus prevent receptor dimerization and activation by TLR4 agonists. Moreover, we hypothesize that early SIRS events in vivo (e.g., elevation of serum cytokines) are mediated by circulating cells that have little ECM contact. These cells activate enzymes that degrade tissue ECM. This ECM breakdown releases TLR4 expressed on parenchymal cells whose activation then leads to late SIRS events (e.g., distal organ dysfunction). We plan to achieve the first aim by using TLR4 positive and TLR4 negative HEK293 cells, ECM plates, and matrix-degrading agents generated in our laboratory or obtained commercially. We plan to achieve the second specific aim by generating several different chimeric TLR4 mice from TLR4 positive and TLR4 negative C57 NF-kB EGFP reporter mice obtained from University of North Carolina or generated in our laboratory respectively. These chimeric mice will undergo infectious and non-infectious models of SIRS and both early and late SIRS events will be measured. These studies will provide a mechanistic explanation for previous in vitro TLR4 observations and a generalizable model for systemic inflammation in several clinically relevant disease models. These results will also provide potential new therapeutic and diagnostic targets for SIRS. PUBLIC HEALTH RELEVANCE: These studies will describe how inflammation spreads from the liver and pancreas. This data could apply to many different diseases and give a general model for inflammation. This model would give new drug targets to treat inflammation.