Toll-like receptor 4 signaling regulates cytosolic phospholipase A2 activation and lipid generation in lipopolysaccharide-stimulated macrophages.
Inflammatory lipid mediators such as prostaglandins and leukotrienes play crucial roles in the pathogenesis of bacterial lipopolysaccharide (LPS)-induced inflammation. Cytosolic phospholipase A(2) (cPLA(2)) is a key enzyme in the generation of pro-inflammatory lipid mediators. Here, we found that Toll-like receptor 4 (TLR4) is essential for LPS-induced cPLA(2) activation and lipid release. Inhibition of TLR4 protein expression by TLR4 small interfering RNA or neutralization of TLR4 by the specific antibody against TLR4/MD2 blocked cPLA(2) phosphorylation and cPLA(2)-hydrolyzed arachidonic acid release. Furthermore, activation of the TLR4 signaling pathway by LPS regulated cPLA(2) activation and lipid release. cPLA(2) phosphorylation and cPLA(2)-hydrolyzed lipid release were significantly impaired when TLR4 adaptor protein, either MyD88 or TRIF, was knocked down in LPS-stimulated macrophages. Similarly, LPS-induced arachidonate release was inhibited in cells transfected with a dominant-negative MyD88 or TRIF construct. Subsequently, cPLA(2) activation could be suppressed by inhibition of the TLR4 adaptor protein-directed p38 and ERK MAPK pathways. These findings suggest that, in LPS-induced inflammation, the TLR4-mediated MyD88- and TRIF-dependent MAPK pathways result in cPLA(2) activation and production of pro-inflammatory lipid mediators.
Qi
Hai-Yan
HY
Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA.
Shelhamer
James H
JH
D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000378:metabolism; D033942:Adaptor Proteins, Vesicular Transport / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D018836:Inflammation Mediators / Q000378:metabolism; D008055:Lipids / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism*; D051379:Mice; D053594:Myeloid Differentiation Factor 88; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000943:Antigens, Differentiation; D018836:Inflammation Mediators; D008055:Lipids; D008070:Lipopolysaccharides; D053594:Myeloid Differentiation Factor 88; D019869:Phosphatidylinositol 3-Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D051057:Proto-Oncogene Proteins c-akt; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D051197:Toll-Like Receptor 4; C507780:Myd88 protein, mouse; C476286:Ticam1 protein, mouse; C493487:Tlr4 protein, mouse