PAFR activation of NF-κB p65 or p105 precursor dictates pro- and anti-inflammatory responses during TLR activation in murine macrophages.

Edson K Ishizuka,Luciano Ribeiro Filgueiras,Sonia Jancar,Francisco J Rios,Carlos H Serezani

doi:10.1038/srep32092

Abstract

Platelet-activating factor receptor (PAFR) is a G protein-coupled receptor (GPCR) implicated in many diseases. Toll-like receptors (TLRs) play a critical role in shaping innate and adaptive immune responses. In this study, we investigated whether PAFR signaling changes the macrophages responsiveness to agonists of TLR2 (Pam3Cys), TLR4 (LPS), and TLR3 agonist Poly(I:C). Exogenous PAF inhibited the production of pro-inflammatory cytokines (IL-12p40, IL-6, and TNF-α) and increased anti-inflammatory IL-10 in macrophages challenged with Pam3Cys and LPS, but not with Poly (I:C). PAF did not affect mRNA expression of MyD88, suggesting that PAF acts downstream the adaptor. PAF inhibited LPS-induced phosphorylation of NF-κB p65 and increased NF-κB p105 phosphorylation, which is processed in the proteasome to generate p50 subunit. The PAF potentiation of IL-10 production was dependent on proteasome processing but independent of NF-κB transactivation domain. Inhibition of p50 abolished the PAF-induced IL-10 production. These findings indicate that the impaired transcriptional activity of the p65 subunit and the enhanced p105 phosphorylation induced by PAF are responsible for down regulation of pro-inflammatory cytokines and up regulation of IL-10, respectively, in LPS-challenged macrophages. Together, our data unveil a heretofore unrecognized role for PAFR in modulating activation of NF-κB in macrophages.

Highlights

It was shown that both receptors are required for downstream activation, gene transcription, and cytokine production
PAF modulates the production of inflammatory cytokines induced by TLR2 and TLR4 in macrophages
In addition to changes in gene transcription, PAF could influence the activity of enzymes involved in macrophage activation, such as cyclooxygenase 2 (COX2), which generates different prostanoids, including prostaglandin E2 (PGE2)

Summary

Introduction

It was shown that both receptors are required for downstream activation, gene transcription, and cytokine production. The presence of PAFR is associated with an anti-inflammatory profile characterized by high production of interleukin-10 (IL-10) and low levels of IL-12 by macrophages[7,8]. These macrophages are identified as regulatory macrophages, as proposed by Fleming & Mosser[9] and have an important function in the clearance of apoptotic cells and a “damping” effect on the inflammatory process[8]. Given the fact that PAFR drives anti-inflammatory programs in macrophages when associated with the scavenger receptor CD367, we asked what effect PAFR would have on the pro-inflammatory program elicited by TLRs. We speculated that PAFR affect different subunits of NF-κB to induce pro- and anti-inflammatory cytokines. We show that PAF interferes with the NF-κB pathway induced by TLRs in macrophages, driving them towards a regulatory phenotype

Methods

Results

Conclusion