Bradykinin stimulated activation of AMPK in endothelial cells: a new pathway to reverse endothelial dysfunction?
Chronic renal failure is an independent risk factor for cardiovascular disease. Endothelial dysfunction, the precursor of atherosclerosis, is associated with lipid accumulation within endothelial cells. The energy-sensor AMP-activated protein kinase (AMPK) regulates endothelial cell lipid metabolism by phosphorylating and inhibiting both HMGCoA reductase and acetyl-CoA carboxylase (ACC); rate limiting enzymes of cholesterol and fatty acid synthesis respectively. Bradykinin, the effector molecule of the kinin-kallikrein system, has multiple beneficial effects on endothelial cell function. To determine whether bradykinin regulates AMPK in endothelium, stimulations of bovine aortic endothelial cells (BAECs) with bradykinin were performed. Bradykinin (10-6M) caused a marked and rapid increase in AMPK activity, which occurred within 1 minute and persisted for 30 mins (p<0.05). Activation of AMPK by bradykinin was observed with low bradykinin concentrations (10-9M, p<0.05), consistent with this being in the physiological range. Bradykinin stimulated activation of AMPK caused phosphorylation of ACC-Ser79, consistent with AMPK reducing intracellular fatty acid accumulation. The activation of AMPK by bradykinin was blocked by the specific bradykinin type-2 receptor antagonist HOE-140 (p<0.05). Furthermore, the bradykinin-mediated activation of AMPK and inhibition of ACC were inhibited by STO-609, which is an inhibitor of Ca2+/calmodulin-dependant protein kinase kinase (CaMKK). This suggests that bradykinin activates AMPK independently of changes in cellular AMP/ATP ratio. Overall, these data reveal that therapies that increase the availability of bradykinin, for example angiotensin converting enzyme inhibitors, can activate endothelial cell AMPK and reduce endothelial cell lipid accumulation, thus potentially correcting conditions of endothelial dysfunction.