Co-Stimulation of PAFR and CD36 Is Required for oxLDL-Induced Human Macrophages Activation

Francisco J O Rios,Matheus Ferracini,Sonia Jancar,Mariana M Koga,Maurizio Pesce

doi:10.1371/journal.pone.0036632

Francisco J O Rios, Matheus Ferracini + Show 3 more

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https://doi.org/10.1371/journal.pone.0036632

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Journal: PLoS ONE	Publication Date: May 3, 2012
Citations: 76	License type: CC BY 4.0

Affiliation: Universidade de São Paulo

Abstract

The oxidative process of LDL particles generates molecules which are structurally similar to platelet-activating factor (PAF), and some effects of oxidized LDL (oxLDL) have been shown to be dependent on PAF receptor (PAFR) activation. In a previous study, we showed that PAFR is required for upregulation of CD36 and oxLDL uptake. In the present study we analyzed the molecular mechanisms activated by oxLDL in human macrophages and the contribution of PAFR to this response. Human adherent monocytes/macrophages were stimulated with oxLDL. Uptake of oxLDL and CD36 expression were determined by flow cytometry; MAP kinases and Akt phosphorylation by Western blot; IL-8 and MCP-1 concentration by ELISA and mRNA expression by real-time PCR. To investigate the participation of the PI3K/Akt pathway, Gαi-coupled protein or PAFR, macrophages were treated with LY294002, pertussis toxin or with the PAFR antagonists WEB2170 and CV3988, respectively before addition of oxLDL. It was found that the addition of oxLDL to human monocytes/macrophages activates the PI3K/Akt pathway which in turn activates the MAPK (p38 and JNK). Phosphorylation of Akt requires the engagement of PAFR and a Gαi-coupled protein. The upregulation of CD36 protein and the uptake of oxLDL as well as the IL-8 production are dependent on PI3K/Akt pathway activation. The increased CD36 protein expression is dependent on PAFR and Gαi-coupled protein. Transfection studies using HEK 293t cells showed that oxLDL uptake occurs with either PAFR or CD36, but IL-8 production requires the co-transfection of both PAFR and CD36. These findings show that PAFR has a pivotal role in macrophages response to oxLDL and suggest that pharmacological intervention at the level of PAFR activation might be beneficial in atherosclerosis.

Highlights

Accumulation of modified low-density lipoprotein (LDL), such as oxidized LDL, in the arterial wall, and the recruitment of monocytes to the subendothelial space are known to be the main early events in the development of atherosclerosis [1]
These data clearly demonstrate that, oxidized LDL (oxLDL) induced the phosphorylation of ERK1/2, p38 and JNK, only the phosphorylation of p38 and JNK was mediated by PI3K activation
In a previous study we showed that PAF receptor (PAFR) is required for upregulation of CD36 expression and oxLDL uptake by MAPK pathway activation [11]

Summary

Introduction

Accumulation of modified low-density lipoprotein (LDL), such as oxidized LDL (oxLDL), in the arterial wall, and the recruitment of monocytes to the subendothelial space are known to be the main early events in the development of atherosclerosis [1]. It is known that CD36 receptor expression is not regulated by intracellular levels of cholesterol, and is increased in atherosclerotic lesions because of auto-regulation by components of the oxLDL particles [2]. This uncontrolled uptake leads to differentiation of the macrophage into foam cells that play a critical role in development and progression of the atherosclerotic plaque [3]. A number of laboratory studies have provided compelling evidence that CD36 is one of the main scavenger receptors involved in the uptake of oxLDL by monocytes/macrophages. Monocytes from individuals lacking CD36, or experiments using functional blockage with antibodies, decreased oxLDL uptake by about 50% [4]

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