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

Abstract

OBJECTIVEOxidative 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 METHODSWe 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.RESULTSForkhead 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.CONCLUSIONSThese 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 induced by metabolic stress and could be a therapeutic target in treating cardiovascular diseases in metabolic syndrome.

Activation of AMP-kinase by AICAR induces apoptosis of DU-145 prostate cancer cells through generation of reactive oxygen species and activation of c-Jun N-terminal kinase

“…However, the capacity of AICAR to stimulate ROS generation is still controversial. A decrease in ROS generation upon AICAR treatment has been observed in the aortic wall of ApoE -/-mice fed a high-fat diet (32), in skeletal muscle cells (33), HUVEC endothelial cells (34) and hepatic stellate cells (35). In contrast ROS elevation and induction of apoptosis were observed in several cancer cell lines including E47 hepatoma cells (13) and glioma (14) as well as in pancreatic β-cells (15).…”

Post-translational modifications of FOXO family proteins

“…FOXO3a is also induced via AMPK, and this effect promotes its nuclear and mitochondrial translocation, resulting in significantly reduced ROS levels, enhanced aerobic respiration and maintaining energy homeostasis (60). Furthermore, prolonged activation of AMPK by AICAR enhances the nuclear import of FOXO3a and improves the adaptability of cells to oxidative stress (61). During hypoxia, AMPK is important for in regulating FOXO proteins in cells.…”

Stimulation of Brain AMP-Activated Protein Kinase Attenuates Inflammation and Acute Lung Injury in Sepsis

“…Two isoforms have been identified for both α subunit (α1 and α2) and β subunit (β1 and β2), and three isoforms have been reported for the γ subunit (γ1, γ2 and γ3) (14). Most recently, several reports indicate that the function of AMPK is not only restricted to the maintenance of energy metabolism, but also to coordination of several housekeeping mechanisms and involvement in modulating oxidative stress and inflammatory mediators (15)(16)(17)(18). An adenosine monophosphate analog, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), has been used as a pharmacological activator to upregulate AMPK activity (19).…”