Lysophosphatidylcholine Triggers TLR2- and TLR4-Mediated Signaling Pathways but Counteracts LPS-Induced NO Synthesis in Peritoneal Macrophages by Inhibiting NF-κB Translocation and MAPK/ERK Phosphorylation

Alan Brito Carneiro,Igor Correia Almeida,Vania Sammartino Mariano,Patricia Torres Bozza,Ulisses Gazos Lopes,Esteban Mauricio Cordero Veas,Lilian Lie Nohara,Bruna Maria Ferreira Iaciura,Carla Duque Lopes,Mário Alberto Cardoso Silva-Neto,Georgia Correa Atella,Claudio Romero Farias Marinho

doi:10.1371/journal.pone.0076233

Abstract

BackgroundLysophosphatidylcholine (LPC) is the main phospholipid component of oxidized low-density lipoprotein (oxLDL) and is usually noted as a marker of several human diseases, such as atherosclerosis, cancer and diabetes. Some studies suggest that oxLDL modulates Toll-like receptor (TLR) signaling. However, effector molecules that are present in oxLDL particles and can trigger TLR signaling are not yet clear. LPC was previously described as an attenuator of sepsis and as an immune suppressor. In the present study, we have evaluated the role of LPC as a dual modulator of the TLR-mediated signaling pathway.Methodology/Principal FindingsHEK 293A cells were transfected with TLR expression constructs and stimulated with LPC molecules with different fatty acid chain lengths and saturation levels. All LPC molecules activated both TLR4 and TLR2-1 signaling, as evaluated by NF-қB activation and IL-8 production. These data were confirmed by Western blot analysis of NF-қB translocation in isolated nuclei of peritoneal murine macrophages. However, LPC counteracted the TLR4 signaling induced by LPS. In this case, NF-қB translocation, nitric oxide (NO) synthesis and the expression of inducible nitric oxide synthase (iNOS) were blocked. Moreover, LPC activated the MAP Kinases p38 and JNK, but not ERK, in murine macrophages. Interestingly, LPC blocked LPS-induced ERK activation in peritoneal macrophages but not in TLR-transfected cells.Conclusions/SignificanceThe above results indicate that LPC is a dual-activity ligand molecule. It is able to trigger a classical proinflammatory phenotype by activating TLR4- and TLR2-1-mediated signaling. However, in the presence of classical TLR ligands, LPC counteracts some of the TLR-mediated intracellular responses, ultimately inducing an anti-inflammatory phenotype; LPC may thus play a role in the regulation of cell immune responses and disease progression.

Highlights

Pathogen infection relies on the ability to avoid Toll-like receptor (TLR)-mediated signaling and the triggering of innate immunity
Cells transfected with the empty vector did not display NF-κB translocation (Figure 1C) or detectable levels of secreted IL-8 (Figure 2C), indicating that such events were dependent on the TLR expression constructs and not mediated by other receptors in HEK 293A cells
Different receptors have been proposed for LPC, including G2A and GPR4 [19,20], which are both coupled to G proteins

Summary

Introduction

Pathogen infection relies on the ability to avoid Toll-like receptor (TLR)-mediated signaling and the triggering of innate immunity. 11 human TLRs and 13 murine TLRs have been identified, and each TLR appears to recognize a distinct surface molecule derived from a different microorganism, including bacteria, viruses, protozoa and fungi [5]. These receptors are expressed in different cellular compartments. LPC blocked LPS-induced ERK activation in peritoneal macrophages but not in TLR-transfected cells. In the presence of classical TLR ligands, LPC counteracts some of the TLR-mediated intracellular responses, inducing an anti-inflammatory phenotype; LPC may play a role in the regulation of cell immune responses and disease progression

Methods

Results

Conclusion