Adiponectin, an Adipocyte-Derived Plasma Protein, Inhibits Endothelial NF-κB Signaling Through a cAMP-Dependent Pathway

Abstract

Background —Among the many adipocyte-derived endocrine factors, we found an adipocyte-derived plasma protein, adiponectin, that was decreased in obesity. We recently demonstrated that adiponectin inhibited tumor necrosis factor-α (TNF-α)–induced expression of endothelial adhesion molecules and that plasma adiponectin level was reduced in patients with coronary artery disease ( Circulation . 1999;100:2473–2476). However, the intracellular signal by which adiponectin suppressed adhesion molecule expression was not elucidated. The present study investigated the mechanism of modulation for endothelial function by adiponectin. Methods and Results —The interaction between adiponectin and human aortic endothelial cells (HAECs) was estimated by cell ELISA using biotinylated adiponectin. HAECs were preincubated for 18 hours with 50 μg/mL of adiponectin, then exposed to TNF-α (10 U/mL) or vehicle for the times indicated. NF-κB–DNA binding activity was determined by electrophoretic mobility shift assays. TNF-α–inducible phosphorylation signals were detected by immunoblotting. Adiponectin specifically bound to HAECs in a saturable manner and inhibited TNF-α–induced mRNA expression of monocyte adhesion molecules without affecting the interaction between TNF-α and its receptors. Adiponectin suppressed TNF-α–induced IκB-α phosphorylation and subsequent NF-κB activation without affecting other TNF-α–mediated phosphorylation signals, including Jun N-terminal kinase, p38 kinase, and Akt kinase. This inhibitory effect of adiponectin is accompanied by cAMP accumulation and is blocked by either adenylate cyclase inhibitor or protein kinase A (PKA) inhibitor. Conclusions —These observations raise the possibility that adiponectin, which is naturally present in the blood stream, modulates the inflammatory response of endothelial cells through cross talk between cAMP-PKA and NF-κB signaling pathways.