The peroxisome proliferator-activated receptor β/δ (PPARβ/δ) agonist GW501516 prevents TNF-α-induced NF-κB activation in human HaCaT cells by reducing p65 acetylation through AMPK and SIRT1

Abstract

Nuclear factor (NF)-κB is a ubiquitously expressed transcription factor controlling the expression of numerous genes involved in inflammation. The aim of this study was to evaluate whether activation of the peroxisome proliferator-activated receptor (PPAR) β/δ prevented TNF-α-induced NF-κB activation in human HaCaT keratinocytes and, if so, to determine the mechanism involved. The PPARβ/δ agonist GW501516 inhibited the increase caused by TNF-α in the mRNA levels of the NF-κB target genes interleukin 8 (IL-8), TNF-α and thymic stromal lymphopoietin (TSLP). Likewise, GW501516 prevented the increase in NF-κB DNA-binding activity observed in cells exposed to TNF-α. The reduction in NF-κB activity following GW501516 treatment in cells stimulated with TNF-α did not involve either increased IκBα protein levels or a reduction in the translocation of the p65 subunit of NF-κB. In contrast, GW501516 treatment decreased TNF-α-induced p65 acetylation. Acetylation of p65 is mainly regulated by p300, a transcriptional co-activator that binds to and acetylates p65. Of note, AMP kinase (AMPK) activation phosphorylates p300 and reduces its binding to p65. GW501516 increased AMPK phosphorylation and the subsequent p300 phosphorylation, leading to a marked reduction in the association between p65 and this transcriptional co-activator. In addition, treatment with the PPARβ/δ agonist increased SIRT1 protein levels. Finally, the reduction in IL-8 mRNA levels following GW501516 treatment in TNF-α-stimulated cells was abolished in the presence of the PPARβ/δ antagonist GSK0660, the AMPK inhibitor compound C and the SIRT1 inhibitor sirtinol, indicating that the effects of GW501516 on NF-κB activity were dependent on PPARβ/δ, AMPK and SIRT1, respectively.