Amyloid‐β(1‐42) Inhibits Ca2+ Transients Induced by N‐Methyl‐D‐Aspartate Receptor in The Cerebral Vasculature

Abstract

Endothelium‐dependent dilation of cerebral arteries, a process dependent on transient increases in intracellular calcium, contributes to neurovascular coupling (NVC), which is altered in cerebral amyloid angiopathy (CAA).The N‐methyl‐D‐aspartate receptor (NMDAR), a nonselective cation channel with high Ca2+ permeability, has been shown to mediate endothelium‐dependent dilation in cerebral arteries. NMDAR activity is reduced by amyloid‐β, which accumulates around the cerebral vasculature during CAA. We hypothesized that amyloid‐β impairs NMDAR‐induced Ca2+ transients in endothelial cells of cerebral arteries, which impairs endothelium‐mediated dilation in mice. All animal experiments were approved by the University of Arizona IACUC. Data are means ± SEM, both in male and female mice (no sex differences were observed). Cerebral arteries isolated from mice expressing the genetically‐encoded calcium indicator GCaMP8 in endothelial cells (cdh5:Gcamp8) were prepared en face for time‐lapse imaging of endothelial Ca2+ transients induced by NMDAR activation. In fields of view that displayed Ca2+ transients, we found that the NMDAR agonist NMDA (1 μM) increased the frequency of endothelial Ca2+ transients compared to baseline (0.22 ± 0.06 vs 0.58 ± 0.15 Hz, baseline vs NMDA, n = 10 and 13 fields of view from at least 3 mice, p < 0.05, one way ANOVA). Pre‐incubation (5 minutes) of preparations with the NMDAR antagonist D‐AP5 (10 μM) prevented NMDA induction of endothelial cell Ca2+ transients (frequency: 0.14 ± 0.05, n = 10 fields of view, p < 0.05 vs NMDA, one‐way ANOVA). These data suggest that endothelial NMDAR Ca2+ transients can be stimulated in cerebral arteries via NMDA. We then tested whether the peptide amyloid‐β(1‐42), commonly found in CAA, blunted NMDAR‐elicited Ca2+ transients. Cerebral artery preparations were incubated for 30 minutes with 5 μM amyloid‐β(1‐42), then exposed to NMDA. Our preliminary data suggests that pre‐incubation of preparations with amyloid‐β blunts NMDA‐dependent induction of endothelial cell Ca2+ transients (0.21 ± 0.04, n = 10 fields of view, p < 0.05 vs NMDA, one‐way ANOVA). In order to evaluate the effects of amyloid‐β on dilation of cerebral arterioles, we then performed ex vivo pressure myography experiments with cerebral parenchymal arterioles from a mouse model of familial Alzheimer’s disease without aging (5x‐FAD) or wildtype littermates. Our preliminary results suggest that NMDA‐elicited dilation of parenchymal arterioles may be impaired in 5x‐FAD mice (30 μM NMDA, vasodilation (%): 11.06 ± 0.78 vs 6.21 ± 2.09, wildtype vs 5x‐FAD, n = 3 arterioles from 3 mice, p = 0.067, two‐tailed Student’s t‐test). These preliminary data suggest that NMDA receptors in the cerebrovascular endothelium of wildtype mice mediate arteriolar dilation via an increase in Ca2+ transients. Further, amyloid‐β may impair the activity of endothelial NMDA receptors and thus contribute to neurovascular dysfunction via impaired arteriolar dilation in individuals with CAA.Support or Funding InformationNational Heart, Lung and Blood Institute (R00HL140106 to PWP). Supported in part by the Undergraduate Biology Research Program with funds from the University of Arizona Office of the Provost and the College of Medicine.