Amyloid-β disrupts unitary calcium entry through endothelial NMDA receptors in mouse cerebral arteries

Transient increases in intracellular Ca²⁺ activate endothelium-dependent vasodilatory pathways. This process is impaired in cerebral amyloid angiopathy, where amyloid-β_(1-40) accumulates around blood vessels. In neurons, amyloid-β impairs the Ca²⁺-permeable N-methyl-D-aspartate receptor (NMDAR), a mediator of endothelium-dependent dilation in arteries. We hypothesized that amyloid-β_(1-40) reduces NMDAR-elicited Ca²⁺ signals in mouse cerebral artery endothelial cells, blunting dilation. Cerebral arteries isolated from 4-5 months-old, male and female cdh5:Gcamp8 mice were used for imaging of unitary Ca²⁺ influx through NMDAR (NMDAR sparklets) and intracellular Ca²⁺ transients. The NMDAR agonist NMDA (10 µmol/L) increased frequency of NMDAR sparklets and intracellular Ca²⁺ transients in endothelial cells; these effects were prevented by NMDAR antagonists D-AP5 and MK-801. Next, we tested if amyloid-β_(1-40) impairs NMDAR-elicited Ca²⁺ transients. Cerebral arteries incubated with amyloid-β_(1-40) (5 µmol/L) exhibited reduced NMDAR sparklets and intracellular Ca²⁺ transients. Lastly, we observed that NMDA-induced dilation of pial arteries is reduced by acute intraluminal amyloid-β_(1-40), as well as in a mouse model of Alzheimer's disease, the 5x-FAD, linked to downregulation of Grin1 mRNA compared to wild-type littermates. These data suggest that endothelial NMDAR mediate dilation via Ca²⁺-dependent pathways, a process disrupted by amyloid-β_(1-40) and impaired in 5x-FAD mice.