Apolipoprotein A-I Attenuates Palmitate-Mediated NF-κB Activation by Reducing Toll-Like Receptor-4 Recruitment into Lipid Rafts

Andrew M Cheng,Priya Handa,Francis Kim,Alan Chait,Sanshiro Tateya,Jay Schwartz,Poulami Mitra,John F Oram,Chongren Tang,Partha Mukhopadhyay

doi:10.1371/journal.pone.0033917

Abstract

While high-density lipoprotein (HDL) is known to protect against a wide range of inflammatory stimuli, its anti-inflammatory mechanisms are not well understood. Furthermore, HDL's protective effects against saturated dietary fats have not been previously described. In this study, we used endothelial cells to demonstrate that while palmitic acid activates NF-κB signaling, apolipoprotein A–I, (apoA-I), the major protein component of HDL, attenuates palmitate-induced NF-κB activation. Further, vascular NF-κB signaling (IL-6, MCP-1, TNF-α) and macrophage markers (CD68, CD11c) induced by 24 weeks of a diabetogenic diet containing cholesterol (DDC) is reduced in human apoA-I overexpressing transgenic C57BL/6 mice compared to age-matched WT controls. Moreover, WT mice on DDC compared to a chow diet display increased gene expression of lipid raft markers such as Caveolin-1 and Flotillin-1, and inflammatory Toll-like receptors (TLRs) (TLR2, TLR4) in the vasculature. However apoA-I transgenic mice on DDC show markedly reduced expression of these genes. Finally, we show that in endothelial cells TLR4 is recruited into lipid rafts in response to palmitate, and that apoA-I prevents palmitate-induced TLR4 trafficking into lipid rafts, thereby blocking NF-κB activation. Thus, apoA-I overexpression might be a useful therapeutic tool against vascular inflammation.

Highlights

Low levels of high-density lipoprotein (HDL) cholesterol are associated with increased risk of coronary artery disease and major cardiovascular events
WT C57BL/6 and Apolipoprotein A–I (apoA-I) transgenic mice were maintained on a normal chow diet or a diabetogenic diet (DD) plus 0.15% cholesterol containing diet (DDC) for 24 weeks
The diabetogenic diet containing cholesterol (DDC) diet increased lipid raft markers, a response not seen in apoA-I transgenic mice (Figure 1B)

Summary

Introduction

Low levels of high-density lipoprotein (HDL) cholesterol are associated with increased risk of coronary artery disease and major cardiovascular events. Since HDL is known to exert anti-inflammatory effects against a wide range of inflammatory agents such as oxidized low-density lipoproteins (LDL) [9] oxidized phospholipids [10] and 7-ketocholesterol [11], we sought to investigate whether HDL attenuates vascular inflammatory responses mediated by saturated fats such as palmitate. ApoA-I mimetic peptides, D-4F and L-4F, reduced vascular inflammation induced by streptozotocin injection in Sprague-Dawley rat [17] and improved insulin sensitivity in a mouse model of diabetes and obesity [18]. Based on these findings, we sought to study the role of HDL, and its predominant protein component, apoA-I on saturated fatty acid-induced inflammation in endothelial cells. We hypothesized that apoA-I overexpressing transgenic mice would be protected from inflammatory effects of a high-fat, atherogenic diet

Methods

Results

Conclusion