Trans-10,cis-12-Conjugated Linoleic Acid Instigates Inflammation in Human Adipocytes Compared with Preadipocytes

Kristina Martinez,Arion Kennedy,Tiffany West,Dejan Milatovic,Michael Aschner,Michael Mcintosh

doi:10.1074/jbc.m109.043976

Abstract

We showed previously in cultures of primary human adipocytes and preadipocytes that lipopolysaccharide and trans-10,cis-12-conjugated linoleic acid (10,12-CLA) activate the inflammatory signaling that promotes insulin resistance. Because our published data demonstrated that preadipocytes are the primary instigators of inflammatory signaling in lipopolysaccharide-treated cultures, we hypothesized that they played the same role in 10,12-CLA-mediated inflammation. To test this hypothesis, we employed four distinct models. In model 1, a differentiation model, CLA activation of MAPK and induction of interleukin-8 (IL-8), IL-6, IL-1beta, and cyclo-oxygenase-2 (COX-2) were greatest in differentiated compared with undifferentiated cultures. In model 2, a cell separation model, the mRNA levels of these inflammatory proteins were increased by 10,12-CLA compared with bovine serum albumin vehicle in the adipocyte fraction and the preadipocyte fraction. In model 3, a co-culture insert model, inserts containing approximately 50% adipocytes (AD50) or approximately 100% preadipocytes (AD0) were suspended over wells containing AD50 or AD0 cultures. 10,12-CLA-induced IL-8, IL-6, IL-1beta, and COX-2 mRNA levels were highest in AD50 cultures when co-cultured with AD0 inserts. In model 4, a conditioned medium (CM) model, CM collected from CLA-treated AD50 but not AD0 cultures induced IL-8 and IL-6 mRNA levels and activated phosphorylation of MAPK in naive AD0 and AD50 cultures. Consistent with these data, 10,12-CLA-mediated secretions of IL-8 and IL-6 from AD50 cultures were higher than from AD0 cultures. Notably, blocking adipocytokine secretion prevented the inflammatory capacity of CM from 10,12-CLA-treated cultures. These data suggest that CLA instigates the release of inflammatory signals from adipocytes that subsequently activate adjacent preadipocytes.

Highlights

There is, concern about potential adverse side effects of CLA supplementation, including lipodystrophy [28], steatosis [29], macrophage infiltration to white adipose tissue (WAT [5]), and insulin resistance (9, 30 –32)
Interpretation of Data from the Four Cell Models—We have demonstrated, using four experimental models, that adipocytes are the instigators of 10,12-CLA-induced inflammation in primary cultures of newly differentiated human adipocytes
Results from the cell separation model suggest that adipocytes signal to preadipocytes during treatment with 10,12-CLA in mixed cultures (AD30), as there was an increase in inflammatory gene expression in the PDF, yet no induction of inflammatory genes in cultures containing only preadipocytes (AD0), as shown in the differentiation model and the co-culture insert model

Summary

Introduction

There is, concern about potential adverse side effects of CLA supplementation, including lipodystrophy [28], steatosis [29], macrophage infiltration to white adipose tissue (WAT [5]), and insulin resistance (9, 30 –32). The 10,12-isomer of CLA increases insulin resistance [33] and markers of oxidative stress (e.g. isoprostaglandin (iso-PG) F2␣) and atherosclerosis (e.g. C-reactive protein [34]) in obese men with metabolic syndrome Consistent with these data, CLA supplementation (i.e. equal levels of 9,11- and 10,12-isomers) adversely affects insulin and glucose metabolism in patients with type 2 diabetes [35]. Chronic inflammation driven by NF-␬B and specific mitogen-activated protein kinases (MAPK) antagonize peroxisome proliferator-activated receptor-␥ (PPAR␥) activity, thereby suppressing the transcriptional activation of genes needed for glucose and fatty acid uptake and conversion to lipids Consistent with these data, we have demonstrated that 10,12-CLA suppression of PPAR␥ activity and target gene expression is linked to the activation of extracellular signal-related kinase (ERK)1/2 [23, 37] and NF-␬B [36]. The objective of this research was to identify the role that preadipocytes versus adipocytes play in mediating 10,12-CLA-mediated inflammation in primary cultures of newly differentiated human adipocytes

Objectives

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Results

Conclusion