Reduced nitric oxide bioavailability mediates cerebroarterial dysfunction independent of cerebral amyloid angiopathy in a mouse model of Alzheimer’s disease

In Alzheimer's disease (AD), cerebral arteries, in contrast to cerebral microvessels, show both cerebral amyloid angiopathy- (CAA) dependent and -independent vessel wall pathology. However, it remains unclear whether CAA-independent vessel wall pathology affects arterial function thereby chronically reducing cerebral perfusion, and if so which mechanisms mediate this effect. To this end, we assessed the ex vivo vascular function of the basilar artery and a similar-sized peripheral artery (femoral artery) in the Swedish-Arctic (SweArc) transgenic AD mouse model at different disease stages. Further, we used quantitative immunohistochemistry to analyze CAA, endothelial morphology, and molecular pathways pertinent to vascular relaxation. We found that endothelium-dependent, but not smooth muscle-dependent vasorelaxation was significantly impaired in basilar and femoral arteries of 15-month-old SweArc mice compared to that of age-matched wildtype (WT) and 6-month-old SweArc mice. This impairment was accompanied by significantly reduced levels of cyclic GMP (cGMP), indicating a reduced nitric oxide (NO) bioavailability. However, no age- and genotype-related differences in oxidative stress as measured by lipid peroxidation were observed. Although parenchymal capillaries, arterioles, and arteries showed abundant CAA in the 15-month-old SweArc mice, no CAA or changes in endothelial morphology were detected histologically in the basilar and femoral artery. Thus, our results suggest that in this AD mouse model dysfunction of large intracranial, extracerebral arteries important for brain perfusion is mediated by reduced NO bioavailability rather than by CAA. This finding supports the growing body of evidence highlighting the therapeutic importance of targeting the cerebrovasculature in AD.