Cross Regulation of Sirtuin 1, AMPK, and PPARy inConjugated Linoleic Acid Treated Adipocytes

Trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) reduces triglyceride (TG) levels in adipocytes through multiple pathways, with AMP-activated protein kinase (AMPK) generally facilitating, and peroxisome proliferator-activated receptor c (PPARc) generally opposing these reductions. Sirtuin 1 (SIRT1), a histone/protein deacetylase that affects energy homeostasis, often functions coordinately with AMPK, and is capable of binding to PPARc, thereby inhibiting its activity. This study investigated the role of SIRT1 in the response of 3T3-L1 adipocytes to t10c12 CLA by testing the following hypotheses: 1) SIRT1 is functionally required for robust TG reduction; and 2) SIRT1, AMPK, and PPARc cross regulate each other. These experiments were performed by using activators, inhibitors, or siRNA knockdowns that affected these pathways in t10c12 CLA-treated 3T3-L1 adipocytes. Inhibition of SIRT1 amounts or activity using siRNA, sirtinol, nicotinamide, or etomoxir attenuated the amount of TG loss, while SIRT1 activator SRT1720 increased the TG loss. SRT1720 increased AMPK activity while sirtuin-specific inhibitors decreased AMPK activity. Reciprocally, an AMPK inhibitor reduced SIRT1 activity. Treatment with t10c12 CLA increased PPARc phosphorylation in an AMPK-dependent manner and increased the amount of PPARc bound to SIRT1. Reciprocally, a PPARc agonist attenuated AMPK and SIRT1 activity levels. These results indicated SIRT1 increased TG loss and that cross regulation between SIRT1, AMPK, and PPARc occurred in 3T3-L1 adipocytes treated with t10c12 CLA. Citation: Jiang S, Wang W, Miner J, Fromm M (2012) Cross Regulation of Sirtuin 1, AMPK, and PPARc in Conjugated Linoleic Acid Treated Adipocytes. PLoS ONE 7(11): e48874. doi:10.1371/journal.pone.0048874 Editor: Mengwei Zang, Boston University School of Medicine, United States of America Received May 24, 2012; Accepted October 2, 2012; Published November 14, 2012 Copyright: 2012 Jiang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the University of Nebraska Agricultural Research Division. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected]