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Angiotensin-converting enzyme 2 (ACE2)-angiotensin (1-7) [Ang (1-7)]-Mas constitutes the vasoprotective axis and is demon-strated to antagonize the vascular pathophysiological effects of the classical renin -angiotensin system .We hypothesize that upregulation of ACE2-Ang (1-7) signaling protects endothelial function through reducing oxidative stress , thus resulting in beneficial outcome in di-abetes.Ex vivo treatment with Ang (1-7) augmented endothelium-dependent relaxation (EDR) in renal arteries from diabetic patients . Both Ang (1-7) infusion via osmotic pump (500 ng? kg -1? min-1 ) for 2 weeks and exogenous ACE 2 overexpression mediated by ad-enoviral ACE2 via tail vein injection rescued the impaired EDR and flow-mediated dilatation ( FMD) in db/db mice.Diminazene acetu-rate treatment (15 mg? kg-1? d-1 ) activated ACE2, increased the circulating Ang (1-7) level, and augmented EDR and FMD in db/db mouse arteries.In addition, activation of the ACE2-Ang (1-7) axis reduced reactive oxygen species (ROS) overproduction de-termined by dihydroethidium staining , CM-H2DCFDA fluorescence imaging , and chemiluminescence assay in db/db mouse aortas and also in high-glucose-treated endothelial cells .Pharmacological benefits of ACE 2-Ang ( 1-7 ) upregulation on endothelial function were confirmed in ACE2 knockout mice both ex vivo and in vitro.We elucidate that the ACE2-Ang (1-7)-Mas axis serves as an important signal pathway in endothelial cell protection in diabetic mice , especially in diabetic human arteries .In summary, endogenous ACE2-Ang (1-7) activation or ACE2 overexpression preserves endothelial function in diabetic mice through increasing nitric oxide bioavail -ability and inhibiting oxidative stress , suggesting the therapeutic potential of ACE 2-Ang(1-7) axis activation against diabetic vasculop-athy.