\u3ci\u3eTrans\u3c/i\u3e-10, \u3ci\u3eCis\u3c/i\u3e-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 PPARγ target gene expression. We hypothesized that CLA antagonizes the activity of PPARγ in an isomerspecific 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 PPARγ by 10,12 CLA was accompanied by an increase in PPARγ and extracellular signal-related kinase (ERK)1/2 phosphorylation, followed by decreased PPARγ protein levels. To investigate if 10,12 CLA-mediated delipidation was preventable with a PPARγ 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 PPARγ 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 PPARγ target genes. However, the levels of PPARγ 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 liganddependent PPARγ activity, possibly via PPARγ phosphorylation by ERK

Conjugated linoleic acid-mediated inflammation and insulin resistance in human adipocytes are attenuated by resveratrol*

Inflammation plays a role in trans-10, cis-12 (10,12)-conjugated linoleic acid (CLA)-mediated delipidation and insulin resistance in adipocytes. Given the anti-inflammatory role of resveratrol (RSV), we hypothesized that RSV would attenuate inflammation and insulin resistance caused by 10,12 CLA in human adipocytes. RSV blocked 10,12 CLA induction of the inflammatory response by preventing activation of extracellular signal-related kinase and induction of inflammatory gene expression (i.e., IL-6, IL-8, IL-1β) within 12 h. Similarly, RSV suppressed 10,12 CLA-mediated activation of the inflammatory prostaglandin pathway involving phospholipase A2, cyclooxygenase-2, and PGF2α. In addition, RSV attenuated 10,12 CLA increase of intracellular calcium and reactive oxygen species associated with cellular stress, and activation of stress-related proteins (i.e., activating transcription factor 3, JNK) within 12 h. 10,12 CLA-mediated insulin resistance and suppression of fatty acid uptake and triglyceride content were attenuated by RSV. Finally, 10,12 CLA-mediated decrease of peroxisome proliferator-activated receptor γ (PPARγ) protein levels and activation of a peroxisome proliferator response element (PPRE) reporter were prevented by RSV. RSV increased the basal activity of PPRE, suggesting that RSV increases PPARγ activity. Collectively, these data demonstrate for the first time that RSV prevents 10,12 CLA-mediated insulin resistance and delipidation in human adipocytes by attenuating inflammation and cellular stress and increasing PPARγ activity