Suppression of Lipopolysaccharide-stimulated Tumor Necrosis Factor-α Production by Adiponectin Is Mediated by Transcriptional and Post-transcriptional Mechanisms*

Abstract

Adiponectin is an adipokine with potent anti-inflammatory properties. Treatment of macrophages with adiponectin results in a suppression of lipopolysaccharide (LPS)-stimulated cytokine production. Here we investigated the transcriptional and post-transcriptional mechanisms by which adiponectin suppresses LPS-stimulated tumor necrosis factor (TNF)-α production. Treatment of RAW 264.7 macrophages with LPS increased TNF-α promoter-driven luciferase activity (TNF-α promoter/Luc activity) by 20-fold over basal. After culture with 1 μg/ml globular adiponectin (gAcrp) for 18 h, TNF-α promoter/Luc activity was increased even in the absence of LPS; further challenge with LPS only increased TNF-α promoter/Luc activity by 1.4-fold. Treatment with gAcrp decreased LPS-stimulated ERK1/2 phosphorylation and IκB degradation and suppressed the ability of LPS to increase the DNA binding activity of Egr-1 and p65. gAcrp also suppressed LPS-mediated stabilization of TNF-α mRNA. In controls cells, the half-life of TNF-α mRNA was increased from ∼30 min at base line to ∼80 min in response to LPS. After treatment with gAcrp for 18 h, LPS failed to increase TNF-α mRNA stability. This gAcrp-mediated loss of stimulus-induced stabilization of TNF-α mRNA required the presence of the TNF-α 3′-untranslated region and was associated with an increase in expression and RNA binding activity of tristetraprolin, an mRNA-binding protein that destabilizes TNF-α mRNA. In summary, these data characterize the complex transcriptional and post-transcriptional effects of gAcrp on LPS-stimulated TNF-α expression in macrophages. gAcrp treatment profoundly suppressed the ability of LPS to increase TNF-α transcription and reduced the stimulus-induced stabilization of TNF-α mRNA in response to LPS.