Age and APOE genotype impact endothelin-1 response and neuroinflammation

Introduction: Old age and the apolipoprotein (APOE)ε4 (E4) genotype are two of the greatest risk factors for late-onset Alzheimer’s disease (LOAD). LOAD is associated with endothelin (ET)-1-mediated vasoconstriction, neuroinflammation, and cognitive impairment. However, our understanding of LOAD is limited because previous studies have primarily used young mice. In the present study, we hypothesized that age and APOE genotype interact to cause greater ET-1-mediated vasoconstriction, neuroinflammation, markers of oxidative stress, and cognitive impairment. Methods: We studied male and female, young (~6 months, n=23) or old (~24 months, n=31) mice that were homozygous for E4 or the disease-neutral E3 genotype. After six training sessions for the Morris Water Maze, we tested the mice on a probe trial to assess spatial memory. We assessed vasoconstriction to ET-1 in isolated, pressurized posterior cerebral arteries (PCAs), and measured ETB receptor protein in the hippocampus via Western blot. Using qPCR, we measured cerebral artery gene expression for ET converting enzyme (ECE)-1 and ECE-2, and cerebral cortex gene expression for NADPH oxidase (NOX)2, interleukin (IL)-1β, and superoxide dismutase (SOD)2. We quantified immunohistochemical staining for ionized calcium-binding adaptor molecule 1 (IBA1) and glial fibrillary acidic protein (GFAP) in the cerebral cortex. Data are mean ± SEM. Results: PCA vasoconstriction to ET-1 was lower in old E3 mice compared to young E3 mice (23±6.2% vs 54±3.7%, p=0.0005) but was similar between old and young E4 mice (47±5.2% vs 48±3.0%, p=0.9). ETB receptor expression was higher in old mice compared with young mice (1.7±0.6 vs 0.9±0.2, p=0.008), but did not differ by genotype (p=0.5). There was an interaction between age and genotype on cerebral artery ECE-2 expression (p=0.02), with higher expression in young vs. old E3 (1.0±0.2 vs 0.6±0.2) and lower in young vs. old E4 (0.3±0.1 vs. 0.9±0.2). Cerebral artery ECE-1 gene expression was not affected by age or genotype (p >0.05). In the Morris Water Maze probe trial, the old mice spent less time in the target quadrant than young mice (p0.05). In contrast, old E4 mice had a higher microglia content (Iba1, 0.2±0.06% vs 0.1±0.02%, p=0.05) and lower SOD2 expression (p< 0.01) compared with old E3 mice. Conclusion: In E3 mice, cerebral artery ET-1 responsiveness declines with age, and this is associated with greater ETB receptor expression. In contrast, in E4 mice, there were no age-related differences in ET-1 response. While we found no effect of genotype on age-related declines in memory, old E4 mice had greater microglial content and lower antioxidant expression compared with old E3 mice. Thus, the interaction between old age and the E4 genotype leads to altered ET-1 response and greater neuroinflammation, which may contribute to the increased LOAD risk. Funded by the Alzheimer’s Association ALZDISCOVERY-1049110 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.