Acylation of lysophosphatidylcholine plays a key role in the response of monocytes to lipopolysaccharide

Abstract

Mononuclear phagocytes play a pivotal role in the progression of septic shock by producing tumor necrosis factor-α (TNF-α) and other inflammatory mediators in response to lipopolysaccharide (LPS) from Gram-negative bacteria. Our previous studies have shown monocyte and macrophage activation correlate with changes in membrane phospholipid composition, mediated by acyltransferases. Interferon-γ (IFN-γ), which activates and primes these cells for enhanced inflammatory responses to LPS, was found to selectively activate lysophosphatidylcholine acyltransferase (LPCAT) (P < 0.05) but not lysophosphatidic acid acyltransferase (LPAAT) activity. When used to prime the human monocytic cell line MonoMac 6, the production of TNF-α and interleukin-6 (IL-6) was approximately five times greater in cells primed with IFN-γ than unprimed cells. Two LPCAT inhibitors SK&F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo2,3-dihydro-imidazole-l-yl)heptane phosphonate) and YM 50201 (3-hydroxyethyl 5,3′-thiophenyl pyridine) strongly inhibited (up to 90%) TNF-α and IL-6 production in response to LPS in both unprimed MonoMac-6 cells and in cells primed with IFN-γ. In similar experiments, these inhibitors also substantially decreased the response of both primed and unprimed peripheral blood mononuclear cells to LPS. Sequence-based amplification methods showed that SK&F 98625 inhibited TNT-α production by decreasing TNF-α mRNA levels in MonoMac-6 cells. Taken together, the data from these studies suggest that LPCAT is a key enzyme in both the pathways of activation (priming) and the inflammatory response to LPS in monocytes.