Cationic Lipid and Bacterial Lipopolysaccharides Both Activate Toll-Like Receptor 4 Pathways via Different Binding Regions

Abstract

DiC14-amidine is a cationic lipid which induces pro-inflammatory cytokine secretion in immune cells upon interaction with the Toll-like receptor 4 (TLR4)/Myeloid Differentiation factor-2 (MD-2) membrane bound-complex, the natural sensor of bacterial lipopolysaccharides (LPS) [1-3].The aim of the present work is to characterize the interaction between diC14-amidine and the TLR4/MD2 receptor complex. Taking advantage of the species-dependent activity of TLR4 agonists [4], we compared the TLR4 agonist activity of diC14-amidine in four different species in order to map domains in TLR4 and MD2 that are important for diC14-amidine TLR4-agonist activity. We demonstrate that, while LPS is an agonist in all species, diC14-amidine is a full agonist for human, mouse and cat receptors, but a poor agonist for horse. Using chimeric constructs made from human and horse TLR4 and single mutants, we identify two regions in the human TLR4 that modulates the agonist activity of diC14-amidine. Interestingly, these regions in TLR4 are different from the previously identified bacterial lipopolysaccharides binding domains [5]. How ligand binding to two different regions of the same receptor affects the cellular pathways is currently under investigation.[1] Tanaka, T. et al. (2008) Eur.J.Immunol. 38: 1351-1357.[2] Lonez, C. Et al. (2008) Prog Lipid Res. 47:340-7.[3] Lonez, C; et al. (2012) Adv Drug Deliv Rev. 64:1749-58.[4] Walsh, C. et al. (2008) J.Immunol. 181: 1245-1254.[5] Park, B. S. et al. (2009) Nature 458: 1191-1195.