Conjugated Linoleic Acid Promotes Human Adipocyte Insulin Resistance through NFκB-dependent Cytokine Production

Soonkyu Chung,J Mark Brown,J Nathan Provo,Robin Hopkins,Michael K Mcintosh

doi:10.1074/jbc.m508159200

Abstract

We previously demonstrated that trans-10, cis-12 conjugated linoleic acid (CLA) reduced the triglyceride content of human adipocytes by activating mitogen-activated protein kinase kinase/extracellular signal-related kinase (MEK/ERK) signaling via interleukins (IL) 6 and 8. However, the upstream mechanism is unknown. Here we show that CLA increased (>or=6 h) the secretion of IL-6 and IL-8 in cultures containing both differentiated adipocytes and stromal vascular (SV) cells, non-differentiated SV cells, and adipose tissue explants. CLA isomer-specific induction of IL-6 and tumor necrosis factor-alpha was associated with the activation of nuclear factor kappaB (NFkappaB) as evidenced by 1) phosphorylation of IkappaBalpha, IkappaBalpha kinase, and NFkappaB p65, 2) IkappaBalpha degradation, and 3) nuclear translocation of NFkappaB. Pretreatment with selective NFkappaB inhibitors and the MEK/ERK inhibitor U0126 blocked CLA-mediated IL-6 gene expression. Trans-10, cis-12 CLA suppression of insulin-stimulated glucose uptake at 24 h was associated with decreased total and plasma membrane glucose transporter 4 proteins. Inhibition of NFkappaB activation or depletion of NFkappaB by RNA interference using small interfering NFkappaB p65 attenuated CLA suppression of glucose transporter 4 and peroxisome proliferator-activated receptor gamma proteins and glucose uptake. Collectively, these data demonstrate for the first time that trans-10, cis-12 CLA promotes NFkappaB activation and subsequent induction of IL-6, which are at least in part responsible for trans-10, cis-12 CLA-mediated suppression of peroxisome proliferator-activated receptor gamma target gene expression and insulin sensitivity in mature human adipocytes.

Highlights

Isomer (e.g. 80% cis-9, trans-11 conjugated linoleic acid (CLA), 10% trans-10, cis-12 CLA)
Trans-10, cis-12 CLA modestly decreased the abundance of total insulin receptor substrate-1 (IRS-1) in the absence and presence of insulin as early as 24 h, but more robustly after 72 h, which is similar to that reported for IL-6-induced insulin resistance in 3T3-L1 adipocytes [16]
The abundance of glucose transporter 4 (Glut4) in the Plasma Membrane (PM) fractions of cultures treated with both insulin and trans-10, cis-12 CLA was lower than in cultures treated with insulin and vehicle

Summary

Introduction

Isomer (e.g. 80% cis-9, trans-11 CLA, 10% trans-10, cis-12 CLA). CLA is available commercially as a dietary supplement for weight loss, with both isomers reported to be present at equal amounts (e.g. ϳ35% each). 19 and 20), phospho-p50/p65 binds to the NF␬B response elements of target genes, thereby inducing their transcriptional activation CLA TG-lowering actions in human adipocytes are consistent with NF␬B activation based on our data [3, 4] showing that trans-10, cis-12 CLA 1) decreases adipogenic gene expression, 2) impairs glucose and fatty acid uptake and conversion to TG, and 3) increases the expression and secretion of several proinflammatory cytokines including IL-6 and IL-8. The aim of the present study was to examine the extent to which NF␬B activation was essential for trans-10, cis-12 CLA-induced cytokine expression and impaired glucose uptake in primary human adipocytes. We demonstrate for the first time that trans-10, cis-12 CLA promotes NF␬B activation before inducing IL-6 expression and insulin resistance in cultures of newly differentiated human adipocytes. Our data suggest that non-adipocytes or stromal vascular (SV) cells secrete a significant amount of cytokines in response to treatment with trans-10, cis-12 CLA

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Conclusion