Abstract P339: Endothelium-specific Deletion of Amyloid Precursor Protein Causes Endothelial Dysfunction of Cerebral Arteries

Abstract

Amyloid-β precursor protein (APP) is an integral membrane protein expressed abundantly in the endothelium of cerebral arteries. However, the exact physiological function of APP in endothelial cells is unknown. Mice with vascular endothelium-specific deletion of APP gene (eAPP-KO) were generated using loxP/Cre technology to test the hypothesis that APP plays a key role in the control of vascular endothelial nitric oxide (NO) function. Vasoreactivity of isolated basilar arteries were studied in vitro under pressurized conditions and compared to control littermates. eAPP-KO mice were normotensive (118±2 mmHg vs. control mice: 113±2 mmHg; n=5) and plasma cholesterol and blood glucose levels were not affected by endothelium-specific genetic inactivation of APP. Endothelium-dependent relaxations to acetylcholine were significantly impaired in eAPP-KO mice (maximal relaxation: 30±4% vs. 45±5% for control littermates; P<0.05; n=7-8) while endothelium-independent relaxations to NO-donor diethylamine-NONOate were unchanged (n=5-6). Western blot analysis revealed that protein expression of endothelial nitric oxide synthase (eNOS) was significantly downregulated by 31% in cerebral arteries of eAPP-KO mice (P<0.05 vs. littermates; n=6). Furthermore, basal levels of cyclic guanosine monophosphate were also significantly reduced in cerebral arteries of eAPP-KO mice (0.64±0.09 pmol/mg; P<0.05 vs. littermates: 0.97±0.11 pmol/mg; n=11). In contrast, protein expression of prostacyclin synthase as well as levels of cyclic adenosine monophosphate were not affected by genetic inactivation of APP in endothelial cells (n=5-7). Moreover, superoxide anion levels as determined by HPLC analysis of 2-hydroxyethidium were unaltered in eAPP-KO mice cerebral arteries (1.4±0.2 nmol/mg vs. littermates: 1.2±0.1 nmol/mg; P=n.s.; n=7). Our results demonstrate that impaired endothelium-dependent relaxations to acetylcholine in eAPP-KO mice are caused by the reduced expression and function of eNOS. These findings indicate that under physiological conditions APP expression in cerebral vascular endothelium plays an important role in control of endothelial function.