Abstract WP425: Effects of Angiotensin II on Expression and Processing of Amyloid Precursor Protein in Human Cerebral Microvascular Endothelial Cells

Abstract

Background and Purpose: Molecular mechanisms underlying increased risk of Alzheimer’s disease in hypertensive patients are poorly defined. Conflicting results have been reported regarding the effects of angiotensin II (Ang II) on expression of amyloid precursor protein (APP) and enzymes responsible for proteolytic cleavage of APP in the brain. However, no previous studies have directly assessed the effects of Ang II on metabolisms of APP in human endothelial cells. Current study was designed to determine the effects of Ang II on the expression and processing of APP in cultured human brain microvascular endothelial cells (hBMECs). Methods: Human BMECs were treated with increasing concentrations of Ang II (0.1nM to 100nM; incubation time = 24h). The protein expression of APP, α-secretase [a disintegrin and metalloprotease 10, (ADAM10), ADAM9, and ADAM17], β-secretase (β-site APP-cleaving enzyme, BACE1), NADPH oxidase subunits and endothelial nitric oxide synthase (eNOS) were measured by western blot. Production and release of amyloid β-peptides (Aβ) from endothelium were detected by ELISA. Results: In hBMECs, Ang II had no effect on the expression of APP (n=7-9, P>0.05) and α-secretase (ADAM10, n=7-9, P>0.05; ADAM9, n=4-7, P>0.05; ADAM17, n=4-7, P>0.05). Treatment with Ang II at 1nM concentration induced significant increase in BACE1 expression (n=13, P<0.05), however, we did not observe significant changes in production of Aβ40 (n=11, P>0.05) or Aβ42 (n=11, undetectable). The higher concentration of Ang II (100nM) increased expression of NOX4 (n=6, P<0.05). In addition, Ang II (1nM and 10nM) significantly up-regulated eNOS protein levels (n=8-10, P<0.05). Conclusion: Our findings suggest that in hBMECs: a) Ang II does not affect expression of APP and α-secretase-mediated cleavage of APP, and b) Ang II increases expression of BACE1 but does not elevate production and release of Aβ peptides. We also confirm previously reported ability of Ang II to increase expression of NOX4 and eNOS. We speculate that under pathological conditions, increased expression of BACE1 induced by Ang II may predispose cerebrovascular endothelium to elevated amyloidogenic processing of APP.