Expression and function of β-site amyloid precursor protein cleaving enzyme 2 in vascular endothelium.

The physiological function of β-site amyloid precursor protein-cleaving enzyme 2 (BACE2) in vascular endothelium of systemic arteries is unknown. In the present study we generated conditional tamoxifen-inducible endothelial BACE2 deficient mice (eBACE2^-/- mice). Electron-microscopic and western blot analyses revealed that BACE2 protein is mainly present in endothelial cells of aorta. Genetic deletion of BACE2 in endothelial cells significantly impaired endothelium-dependent relaxations to Ca²⁺-ionophore A23187 in eBACE2^-/- aortas as compared to tamoxifen treated control mice irrespective of sex. Blockade of nitric oxide synthase (NOS) with N^ω-nitro-L-arginine methyl ester abolished relaxations to A23187. In contrast, endothelium-independent relaxations to nitric oxide donor diethylamine-NONOate were unchanged. Expression of endothelial NOS protein and levels of cyclic nucleotides were also unaffected in eBACE2^-/- mice. Further analysis of the mechanisms underlying impaired endothelial function demonstrated that treatment with thromboxane A₂ receptor antagonist SQ29548 ameliorated relaxations to A23187 in the aorta of male and female eBACE2^-/- mice. Furthermore, mRNA and protein expressions of cyclooxygenase-2 as well as production of thromboxane A₂ and prostaglandin F_2α were significantly increased in the aorta of eBACE2^-/- mice. In contrast, production of 6-keto prostaglandin F_1α and prostaglandin E₂ were not affected. In addition, ex-vivo treatment of wild-type aortas with proinflammatory cytokines decreased protein expression of BACE2. The results of our study suggest that increased production of vasoconstrictor prostanoids are responsible for impairment of endothelium-dependent relaxations to A23187 in the aorta of eBACE2^-/- mice. We report previously unrecognized role of BACE2 in control of endothelial arachidonic acid metabolism and vasomotor function.