Bradykinin stimulates endothelial cell fatty acid oxidation by CaMKK-dependent activation of AMPK

Endothelial cell lipotoxicity mediated by accumulation of free fatty acids is an early event in the pathogenesis of atherosclerosis. The energy-sensor AMP-activated protein kinase (AMPK) is a key regulator of endothelial cell lipid metabolism. To test the hypothesis that bradykinin (BK) regulates AMPK and fatty acid oxidation in endothelium, stimulations of bovine aortic endothelial cells (BAECs) with bradykinin were performed. BK stimulation caused a 2.3-fold increase in AMPK activity (p<0.05). Activation of AMPK by BK in BAECs was inhibited by STO-609, an inhibitor of calmodulin-dependent kinase kinase (CaMKK), which is a known kinase upstream of AMPK. BK stimulation of BAECs also increased phosphorylation of acetyl-CoA carboxylase and this was inhibited by both STO-609 and over expression of an adenovirus encoded AMPK dominant negative (Ad-AMPK-DN). Furthermore, BK caused a 1.7-fold increase in palmitate oxidation in BAECs (p<0.05) and this increase was completely inhibited by the Ad-AMPK-DN (p<0.005). Inhibition of AMPK activation in response to BK by STO-609 had no effect on activating phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser(1177), consistent with CaMKK and AMPK not being required for phosphorylation of eNOS in response to BK. In conclusion, BK stimulates endothelial cell fatty acid oxidation by CaMKK-dependent activation of AMPK. The effect of BK on endothelial lipid metabolism represents a novel pathway for targeting fatty acid mediated endothelial cell dysfunction.