Leptin-Stimulated Endothelial Nitric-Oxide Synthase via an Adenosine 5'-Monophosphate-Activated Protein Kinase/Akt Signaling Pathway Is Attenuated by Interaction with C-Reactive Protein

The AMP-activated protein kinase (AMPK) lies upstream of Akt in the pathway leading to endothelial NO synthase (eNOS) activation. Whether leptin promotes eNOS activation via AMPK-dependent activation of Akt, and which of the two AMPKα catalytic subunits is involved, remains unknown. Leptin resistance may be partly attributed to interaction between leptin and C-reactive protein (CRP). We hypothesized that leptin effect on eNOS activation in human aortic endothelial cells might be blunted by direct interaction with human recombinant CRP. Small interfering RNAs (siRNAs) were used to knock down expression of α1- or α2-AMPK in transient transfection assay to evaluate which is involved in this pathway and whether leptin effect on eNOS activation in human aortic endothelial cells might be blunted by direct interaction with human CRP. siRNA-mediated down-regulation of AMPKα1, but not AMPKα2, abolished leptin-induced Akt-Ser473 phosphorylation, eNOS-Ser1177 phosphorylation, eNOS activation, and cGMP accumulation. ...