Trans-10, Cis-12 Conjugated Linoleic Acid Antagonizes Ligand-Dependent PPARγ Activity in Primary Cultures of Human Adipocytes

We previously demonstrated that trans -10, cis -12 ( 10 , 12 ) conjugated linoleic acid (CLA) causes human adipocyte delipidation, insulin resistance, and inflammation in part by attenuating PPAR γ target gene expression. We hypothesized that CLA antagonizes the activity of PPAR γ in an isomer-specific manner. 10,12 CLA, but not cis -9, trans -11 ( 9 , 11 ) CLA, suppressed ligand-stimulated activation of a peroxisome proliferator response element-luciferase reporter. This decreased activation of PPAR γ by 10,12 CLA was accompanied by an increase in PPAR γ and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPAR γ protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPAR γ ligand (BRL), cultures were treated for 1 wk with 10,12 CLA or 10,12 CLA + BRL and adipogenic gene and protein expression, glucose uptake, and triglyceride (TG) were measured. BRL cosupplementation completely prevented 10,12 CLA suppression of adipocyte fatty acid-binding protein, lipoprotein lipase, and perilipin mRNA levels without preventing reductions in PPAR γ or insulin-dependent glucose transporter 4 (GLUT4) expression, glucose uptake, or TG. Lastly, we investigated the impact of CLA withdrawal in the absence or presence of BRL for 2 wk. CLA withdrawal did not rescue CLA-mediated reductions in adipogenic gene and protein expression. In contrast, BRL supplementation for 2 wk following CLA withdrawal rescued mRNA levels of PPAR γ target genes. However, the levels of PPAR γ and GLUT4 protein and TG were only partially rescued by BRL. Collectively, we demonstrate for the first time, to our knowledge, that 10,12 CLA antagonizes ligand-dependent PPAR γ activity, possibly via PPAR γ phosphorylation by ERK.