ACE is a key regulatory enzyme of the renin angiotensin system and has been allocated a central role in cardiovascular disease development. Even though ACE function has been extensively studied, relatively little is known about the molecular mechanisms regulating its expression. Since especially the effect of hemodynamic stimuli on ACE expression has proven controversial, we set out to delineate the effect of fluid shear stress on ACE level. Human umbilical vein endothelial cells exposed to shear stress (12 dyn/cm²) demonstrated a time-dependent decrease in ACE mRNA and protein expression. Although eNOS expression increased in response to shear stress and nitric oxide has previously been reported to negatively regulate ACE expression, we demonstrated that eNOS inhibition was without any consequence on shear stress regulated ACE expression. However, silencing of the shear stress-activated AMP-activated protein kinase (AMPK) using siRNA specific for the catalytic subunit AMPKa2 increased ACE expression under static conditions and attenuated the decrease in ACE protein and mRNA induced by shear stress. Interestingly, suppression of the AMPKa1 subunit also slightly increased static ACE expression, but failed to affect the response to shear stress. The suppressive effect of AMPK on ACE expression was confirmed by activation of AMPK using its activator AICAR or overexpression of a constitutive active AMPK as both treatments decrease endothelial ACE expression. Overexpression of the dominant negative AMPK increased ACE level. Since AMPK activation elicit the phosphorylation and degradation of FOXO transcription factors, we determined whether degradation of FOXO using siRNA mimics this effect. Indeed, suppression of FOXO dramatically decreased endothelial ACE expression. To verify in vitro findings, we assessed the expression of ACE in different arteries from AMPKa1^-/- or AMPKa2^-/- mice and their wild-type littermates. While ACE expression was similar in AMPKa1^+/+ and AMPKa1^-/- mice, the genetic deletion of AMPKa2 significantly increased ACE expression in native endothelial cells of the aorta, aortic arch, small mesenteric arteries and kidney. These data demonstrate that ACE expression is suppressed by AMPK activation in endothelial cells and that shear stress downregulate endothelial ACE expression via AMPKa2 and the consequent downregulation of FOXO. This observation might explain the development of diabetes associated cardiovascular disorders, as AMPK activity has been found to be reduced in diabetic individuals.