Lipopolysaccharide-induced gene expression in murine macrophages is enhanced by prior exposure to oxLDL

Mathijs Groeneweg,Edwin Kanters,Monique N Vergouwe,Hilde Duerink,Georg Kraal,Marten H Hofker,Menno P.J De Winther

doi:10.1194/jlr.m600181-jlr200

Mathijs Groeneweg, Edwin Kanters + Show 5 more

Open Access

https://doi.org/10.1194/jlr.m600181-jlr200

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Abstract

Uptake of modified lipoproteins by macrophages results in the formation of foam cells. We investigated how foam cell formation affects the inflammatory response of macrophages. Murine bone marrow-derived macrophages were treated with oxidized LDL (oxLDL) to induce foam cell formation. Subsequently, the foam cells were activated with lipopolysaccharide (LPS), and the expression of lipid metabolism and inflammatory genes was analyzed. Furthermore, gene expression profiles of foam cells were analyzed using a microarray. We found that prior exposure to oxLDL resulted in enhanced LPS-induced tumor necrosis factor (TNF) and interleukin-6 (IL-6) gene expression, whereas the expression of the anti-inflammatory cytokine IL-10 and interferon-beta was decreased in foam cells. Also, LPS-induced cytokine secretion of TNF, IL-6, and IL-12 was enhanced, whereas secretion of IL-10 was strongly reduced after oxLDL preincubation. Microarray experiments showed that the overall inflammatory response induced by LPS was enhanced by oxLDL loading of the macrophages. Moreover, oxLDL loading was shown to result in increased nuclear factor-kappaB activation. In conclusion, our experiments show that the inflammatory response to LPS is enhanced by loading of macrophages with oxLDL. These data demonstrate that foam cell formation may augment the inflammatory response of macrophages during atherogenesis, possibly in an IL-10-dependent manner.

Highlights

Uptake of modified lipoproteins by macrophages results in the formation of foam cells
Analysis of foam cell formation bone marrow-derived macrophage (BMM) were incubated with oxidized LDL (oxLDL) for 1, 12, 24, and 48 h to induce different stages of foam cell formation, the cells were activated by LPS for an additional 3 h
Free cholesterol concentration remained at the same level, whereas the amount of intracellular cholesteryl ester (CE) strongly increased over a period of 24 h (Fig. 1A), indicating accumulation and processing of cholesterol in the BMMs

Summary

Introduction

Uptake of modified lipoproteins by macrophages results in the formation of foam cells. We were interested in the effects of oxLDL loading on lipopolysaccharide (LPS)-induced gene ex- Because we did not observe significant differences in gene expression patterns between 24 and 48 h of macrophage exposure to oxLDL, the 48 h incubation time point was omitted in the following experiments (data not shown).

Results

Conclusion