, Volume 55, Issue 3, pp 743-751
Date: 17 Dec 2011

The peroxisome proliferator-activated receptor (PPAR) β/δ agonist GW501516 inhibits IL-6-induced signal transducer and activator of transcription 3 (STAT3) activation and insulin resistance in human liver cells

Abstract

Aim/hypothesis

IL-6 induces insulin resistance by activating signal transducer and activator of transcription 3 (STAT3) and upregulating the transcription of its target gene SOCS3. Here we examined whether the peroxisome proliferator-activated receptor (PPAR)β/δ agonist GW501516 prevented activation of the IL-6–STAT3–suppressor of cytokine signalling 3 (SOCS3) pathway and insulin resistance in human hepatic HepG2 cells.

Methods

Studies were conducted with human HepG2 cells and livers from mice null for Pparβ/δ (also known as Ppard) and wild-type mice.

Results

GW501516 prevented IL-6-dependent reduction in insulin-stimulated v-akt murine thymoma viral oncogene homologue 1 (AKT) phosphorylation and in IRS-1 and IRS-2 protein levels. In addition, treatment with this drug abolished IL-6-induced STAT3 phosphorylation of Tyr705 and Ser727 and prevented the increase in SOCS3 caused by this cytokine. Moreover, GW501516 prevented IL-6-dependent induction of extracellular-related kinase 1/2 (ERK1/2), a serine–threonine protein kinase involved in serine STAT3 phosphorylation; the livers of Pparβ/δ-null mice showed increased Tyr705- and Ser727-STAT3 as well as phospho-ERK1/2 levels. Furthermore, drug treatment prevented the IL-6-dependent reduction in phosphorylated AMP-activated protein kinase (AMPK), a kinase reported to inhibit STAT3 phosphorylation on Tyr705. In agreement with the recovery in phospho-AMPK levels observed following GW501516 treatment, this drug increased the AMP/ATP ratio and decreased the ATP/ADP ratio.

Conclusions/interpretation

Overall, our findings show that the PPARβ/δ activator GW501516 prevents IL-6-induced STAT3 activation by inhibiting ERK1/2 phosphorylation and preventing the reduction in phospho-AMPK levels. These effects of GW501516 may contribute to the prevention of cytokine-induced insulin resistance in hepatic cells.