Activation of the AMPK-FOXO3 Pathway Reduces Fatty Acid–Induced Increase in Intracellular Reactive Oxygen Species by Upregulating Thioredoxin

Activation of the AMPK-FOXO3 Pathway Reduces Fatty Acid–Induced Increase in Intracellular Reactive Oxygen Species by Upregulating Thioredoxin Xiao-Nan Li 1 , 2 , 3 , Jun Song 1 , 2 , 3 , Lin Zhang 1 , 2 , Scott A. LeMaire 1 , 2 , Xiaoyang Hou 1 , 2 , 3 , Cheng Zhang 1 , 2 , 3 , Joseph S. Coselli 1 , 2 , Li Chen 3 , Xing Li Wang 1 , 2 , Yun Zhang 3 and Ying H. Shen 1 , 2 1 Division of Cardiothoracic Surgery, Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, Texas; 2 Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, Texas; 3 Qilu Hospital, Shandong University, Jinan, Shandong, China. Corresponding authors: Yun Zhang, zhangyun{at}sdu.edu.cn , and Ying H. Shen, hyshen{at}bcm.edu . X.-N.L. and J.S. contributed equally to this study. Abstract OBJECTIVE Oxidative stress induced by free fatty acids contributes to the development of cardiovascular diseases in patients with metabolic syndrome. Reducing oxidative stress may attenuate these pathogenic processes. Activation of AMP-activated protein kinase (AMPK) has been reported to reduce intracellular reactive oxygen species (ROS) levels. The thioredoxin (Trx) system is a major antioxidant system. In this study, we investigated the mechanisms involved in the AMPK-mediated regulation of Trx expression and the reduction of intracellular ROS levels. RESEARCH DESIGN AND METHODS We observed that activation of AMPK by 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) significantly reduced ROS levels induced by palmitic acid in human aortic endothelial cells. Activation of AMPK increased expression of the antioxidant Trx, which mediated the ROS reduction. RT-PCR showed that AMPK regulated Trx at the transcriptional level. RESULTS Forkhead transcription factor 3 (FOXO3) was identified as the target transcription factor involved in the upregulation of Trx expression. FOXO3 bound to the Trx promoter, recruited the histone acetylase p300 to the Trx promoter, and formed a transcription activator complex, which was enhanced by AICAR treatment. AMPK activated FOXO3 by promoting its nuclear translocation. We further showed that AICAR injection increased the expression of Trx and decreased ROS production in the aortic wall of ApoE−/− mice fed a high-fat diet. CONCLUSIONS These results suggest that activation of the AMPK-FOXO3 pathway reduces ROS levels by inducing Trx expression. Thus, the AMPK-FOXO3-Trx axis may be an important defense mechanism against excessive ROS production induce