Nitric Oxide-Induced Activation of the AMP-Activated Protein Kinase α2 Subunit Attenuates IκB Kinase Activity and Inflammatory Responses in Endothelial Cells

BACKGROUND: In endothelial cells, activation of the AMP-activated protein kinase (AMPK) has been linked with anti-inflammatory actions but the events downstream of kinase activation are not well understood. Here, we addressed the effects of AMPK activation/deletion on the activation of NFκB and determined whether the AMPK could contribute to the anti-inflammatory actions of nitric oxide (NO). METHODOLOGY/PRINCIPAL FINDINGS: Overexpression of a dominant negative AMPKα2 mutant in tumor necrosis factor-α-stimulated human endothelial cells resulted in increased NFκB activity, E-selectin expression and monocyte adhesion. In endothelial cells from AMPKα2(-/-) mice the interleukin (IL)-1β induced expression of E-selectin was significantly increased. DETA-NO activated the AMPK and attenuated NFκB activation/E-selectin expression, effects not observed in human endothelial cells in the presence of the dominant negative AMPK, or in endothelial cells from AMPKα2(-/-) mice. Mechanistically, overexpression of constitutively active AMPK decreased the phosphorylation of IκB and p65, indicating a link between AMPK and the IκB kinase (IKK). Indeed, IKK (more specifically residues Ser177 and Ser181) was found to be a direct substrate of AMPKα2 in vitro. The hyper-phosphorylation of the IKK, which is known to result in its inhibition, was also apparent in endothelial cells from AMPKα2(+/+) versus AMPKα2(-/-) mice. CONCLUSIONS: These results demonstrate that the IKK is a direct substrate of AMPKα2 and that its phosphorylation on Ser177 and Ser181 results in the inhibition of the kinase and decreased NFκB activation. Moreover, as NO potently activates AMPK in endothelial cells, a portion of the anti-inflammatory effects of NO are mediated by AMPK.