Effects of LPS and dietary free fatty acids on MCP-1 in 3T3-L1 adipocytes and macrophages in vitro

K B Cullberg,S B Pedersen,B Richelsen,J Ø Larsen

doi:10.1038/nutd.2014.10

K B Cullberg, S B Pedersen + Show 2 more

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https://doi.org/10.1038/nutd.2014.10

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Journal: Nutrition & diabetes	Publication Date: Mar 1, 2014
Citations: 75	License type: cc-by

Affiliation: Aarhus University Hospital

Abstract

Background:High levels of free fatty acids (FFA) have been suggested to be one of the underlying mechanisms for adipose tissue (AT) inflammation and dysfunction in obesity. Human AT produces several adipokines including monocyte chemoattractant protein-1 (MCP-1), which are involved in the pathogenesis of obesity-mediated inflammation.Objective:In this study, we investigated the effects of lipopolysaccharide (LPS) and a panel of dietary FFA on MCP-1 gene and protein expression in adipocytes and macrophages. Furthermore, we investigated whether the effect of LPS and FFA were mediated through the toll-like receptor 4 (TLR4).Methods:3T3-L1 adipocytes and THP-1 macrophages were incubated for 24 h with the following FFA: monounsaturated fatty acid (oleic acid), saturated fatty acid (palmitic acid) and trans fatty acid (elaidic acid; 500 μM) with and without LPS (2 ng ml−1), and MCP-1 and TLR4 mRNA expression and MCP-1 protein secretion was determined.Results:The results showed that LPS significantly increased MCP-1 and TLR4 expression and MCP-1 secretion in 3T3-L1 adipocytes, and that the MCP-1 expression was blocked by a TLR4 inhibitor (CLI095). The effects of the various FFA on MCP-1 mRNA expression and protein secretion in the adipocytes showed no significant changes either alone or in combination with LPS. In macrophages, palmitic acid increased MCP-1 mRNA expression by 1.8-fold (P<0.05), but oleic acid and elaidic acid had no effects.Conclusions:In conclusion, in 3T3-L1 adipocyte, the TLR4-agonist, LPS, stimulates the proinflammatory chemokine MCP-1. The different classes of FFA did not induce MCP-1 mRNA expression or protein secretion in the adipocytes, but the saturated FFA, palmitic acid, induced MCP-1 mRNA expression in macrophages, possibly because of the higher expression level of TLR4 in the macrophages than the adipocytes. Our results indicate that FFA may induce AT inflammation through proinflammatory stimulation of macrophages.

Highlights

Inflammation in adipose tissue is increasingly considered to be of importance for the development of diseases associated with obesity such as type 2 diabetes and the metabolic syndrome.[1]The mechanistic basis for the inflammatory response in the expanding adipose tissue is still unknown but suggestions include: dysregulation in free fatty acid (FFA) fluxes, oxidative stress, endoplasmatic reticulum stress, adipocyte cell death, inhibition of adipogenesis, fibrosis and hypoxia.[1,2,3] It has long been recognized that plasma free fatty acids (FFA) concentrations are commonly elevated in obese individuals, mainly due to increased FFA release associated with the expansion in fat mass.[4]
Effect of bovine serum albumin (BSA) on monocyte chemoattractant protein-1 (MCP-1) mRNA expression in 3T3-L1 adipocytes In initial studies, we found that the ordinary BSA used elicited a 14.7-fold increase in MCP-1 expression compared with media without BSA
toll-like receptor 4 (TLR4)-deficient knockout mice fed with a diet rich in saturated fatty acid had a lower grade of macrophage infiltration and MCP-1 expression in their visceral adipose tissue compared with wild-type mice.[24]

Summary

Introduction

The mechanistic basis for the inflammatory response in the expanding adipose tissue is still unknown but suggestions include: dysregulation in free fatty acid (FFA) fluxes, oxidative stress, endoplasmatic reticulum stress, adipocyte cell death, inhibition of adipogenesis, fibrosis and hypoxia.[1,2,3] It has long been recognized that plasma FFA concentrations are commonly elevated in obese individuals, mainly due to increased FFA release associated with the expansion in fat mass.[4] It has been found that FFA can serve as an agonist of the toll-like receptor 4 (TLR4) complex.[5] Stimulation of TLR4 activates proinflammatory pathways and induces cytokine expression in a variety of cell types, which drives macrophage accumulation and thereby inflammation.[6,7,8,9,10]. Our results indicate that FFA may induce AT inflammation through proinflammatory stimulation of macrophages

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