ABSTRACT
Myeloid differentiation protein-2 (MD-2), a secreted glycoprotein that binds to both lipopolysaccharide (LPS) and toll like receptor 4 (TLR4), contributes to the fine ligand recognition and signaling activation on LPS-induced inflammation. Here we synthesized a novel MD-2 mimetic peptide (MDMP), derived from the putative LPS-binding domain and TLR4-binding domain of MD-2, and found that MDMP dose-dependently bound to LPS and inhibited LPS-activated Limulus amebocyte lysate (LAL). Pretreatment with MDMP dampened LPS-induced inflammatory responses in RAW264.7 cells, including down-regulation of TLR4-MD-2 complex on the cell surface, suppression of LPS binding to the cells, inhibition of mitogen-activated protein kinase (MAPKs) and nuclear factor kappa B (NF-kappaB) activation, reduction of tumor necrosis factor-alpha (TNF-alpha) production. Further, in vivo pretreatment with MDMP markedly protected against LPS-induced acute lung injury and liver injury, as indicated by the notable reduction of lethality, inflammatory responses and TNF-alpha production. These results demonstrate that MDMP attenuates LPS-induced inflammatory responses in vivo and in vitro, and suggests that MDMP may be useful in the treatment of inflammation associated with LPS.
Subject(s)
Inflammation/drug therapy , Lymphocyte Antigen 96/therapeutic use , Macrophages/drug effects , Acute Lung Injury/prevention & control , Animals , Chemical and Drug Induced Liver Injury/prevention & control , Down-Regulation/drug effects , Horseshoe Crabs , Lipopolysaccharide Receptors/metabolism , Lipopolysaccharides/immunology , Lymphocyte Antigen 96/chemical synthesis , Male , Mice , Mice, Inbred BALB C , Mitogen-Activated Protein Kinases/antagonists & inhibitors , NF-kappa B/antagonists & inhibitors , NF-kappa B/metabolism , Peptides/chemical synthesis , Peptides/therapeutic use , Toll-Like Receptor 4/metabolism , Tumor Necrosis Factor-alpha/antagonists & inhibitors , Tumor Necrosis Factor-alpha/metabolismABSTRACT
Activated hepatic stellate cells (HSCs) play a key role in hepatic fibrogenesis. In injured liver they are the main extracellular matrix protein producing cell type and further perpetuate hepatic injury by secretion of pro-inflammatory mediators. Since LPS-mediated signaling through toll-like receptor 4 (TLR4) has been identified as key fibrogenic signal in HSCs we aimed to test TLR4 as potential target of therapy via ligand-binding soluble receptors. Incubation of human HSCs with a fusion protein between the extracellular domain of TLR4 and MD2 which binds LPS inhibited LPS-induced NFkappaB and JNK activation. TLR4/MD2 abolished LPS-induced secretion of IL-6, IL-8, MCP1, and RANTES in HSCs. In addition, TLR4/MD2 fused to human IgG-Fc neutralized LPS activity. Since TLR4 mutant mice are resistant to liver fibrosis, the TLR4/MD2 soluble receptor might represent a new therapeutic molecule for liver fibrogenesis in vivo.
