Abstract 130: Effects of Genetic Inactivation of Amyloid Precursor Protein in Cerebral Microvasculature

Abstract

Background: Amyloid precursor protein (APP) is expressed in neuronal and non-neuronal tissues in the brain, including cerebrovascular endothelium. However, the physiological role of APP in cerebral vasculature is not completely understood. The present study was designed to determine the effects of inactivation of APP in cerebral microvasculature. Methods: Effect of genetic inactivation of APP was studied both in vitro and in vivo . Cultured human brain microvascular endothelial cells (hBMECs) were incubated with APP-siRNA in vitro , while control-siRNA treated hBMECs served as controls. To study the effect of genetic inactivation of APP in vivo , cerebral microvessels were obtained from APP-deficient (APPKO) mice. Cerebral microvessels from wild-type (C57BL/6) littermates served as controls. Results: Silencing APP expression in hBMECs resulted in selective reduction in endothelial nitric oxide synthase (eNOS) expression (P<0.05, n=6), while expressions of inducible NOS and prostacyclin (PGI2) synthase remained unchanged. Furthermore, loss of APP in hBMECs resulted in significantly increased production (P<0.05, n=5) of superoxide anions, as determined by quantitation of 2-hydroxyethidium from dihydroethidium using HPLC. In line with the results obtained from in vitro studies, cerebral microvessels of APPKO mice also demonstrated increased production of superoxide anions. Furthermore, levels of cGMP, second messenger of endothelial NO, were significantly attenuated in cerebral microvessels of APPKO mice, while levels of cAMP remained unchanged. Conclusions: Our results suggest that genetic inactivation of APP results in oxidative stress and impairment of endothelial NO signaling. We speculate that APP exerts vascular protective effects in the cerebral circulation under physiological conditions.