Department of Pharmaceutics and the Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota (N.S., K.K.K.); Department of Pharmaceutical Sciences, Rosalind Franklin University of Medicine and Science, College of Pharmacy, North Chicago, Illinois (K.M.A.); and Departments of Radiology (G.L.C., V.J.L.) and Neurology (G.L.C., K.K.K.), Mayo Clinic College of Medicine, Rochester, Minnesota.
Department of Pharmaceutics and the Brain Barriers Research Center, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota (N.S., K.K.K.); Department of Pharmaceutical Sciences, Rosalind Franklin University of Medicine and Science, College of Pharmacy, North Chicago, Illinois (K.M.A.); and Departments of Radiology (G.L.C., V.J.L.) and Neurology (G.L.C., K.K.K.), Mayo Clinic College of Medicine, Rochester, Minnesota
J Pharmacol Exp Ther. 2021 Mar;376(3):482-490. doi: 10.1124/jpet.120.000086. Epub 2020 Dec 10.
Blood-brain barrier (BBB) endothelial cells lining the cerebral microvasculature maintain dynamic equilibrium between soluble amyloid- (A) levels in the brain and plasma. The BBB dysfunction prevalent in Alzheimer disease contributes to the dysregulation of plasma and brain A and leads to the perturbation of the ratio between A42 and A40, the two most prevalent A isoforms in patients with Alzheimer disease. We hypothesize that BBB endothelium distinguishes between A40 and A42, distinctly modulates their trafficking kinetics between plasma and brain, and thereby contributes to the maintenance of healthy A42/A40 ratios. To test this hypothesis, we investigated A40 and A42 trafficking kinetics in hCMEC/D3 monolayers (human BBB cell culture model) in vitro as well as in mice in vivo. Although the rates of uptake of fluorescein-labeled A40 and A42 (F-A40 and F-A42) were not significantly different on the abluminal side, the luminal uptake rate of F-A42 was substantially higher than F-A40. Since higher plasma A levels were shown to aggravate BBB dysfunction and trigger cerebrovascular disease, we systematically investigated the dynamic interactions of luminal [I]A peptides and their trafficking kinetics at BBB using single-photon emission computed tomography/computed tomography imaging in mice. Quantitative modeling of the dynamic imaging data thus obtained showed that the rate of uptake of toxic [I]A42 and its subsequent BBB transcytosis is significantly higher than [I]A40. It is likely that the molecular mechanisms underlying these kinetic differences are differentially affected in Alzheimer and cerebrovascular diseases, impact plasma and brain levels of A40 and A42, engender shifts in the A42/A40 ratio, and unleash downstream toxic effects. SIGNIFICANCE STATEMENT: Dissecting the binding and uptake kinetics of A40 and A42 at the BBB endothelium will facilitate the estimation of A40 versus A42 exposure to the BBB endothelium and allow assessment of the risk of BBB dysfunction by monitoring A42 and A40 levels in plasma. This knowledge, in turn, will aid in elucidating the role of these predominant A isoforms in aggravating BBB dysfunction and cerebrovascular disease.
血脑屏障（BBB）内皮细胞排列在脑微血管中，维持脑内可溶性淀粉样蛋白（A）水平与血浆之间的动态平衡。阿尔茨海默病中普遍存在的 BBB 功能障碍导致血浆和脑内 A 的失调，并导致 A42 和 A40 的比例失调，A40 和 A42 是阿尔茨海默病患者中最常见的两种 A 同工型。我们假设 BBB 内皮细胞能够区分 A40 和 A42，明显调节它们在血浆和脑之间的转运动力学，从而有助于维持健康的 A42/A40 比值。为了验证这一假设，我们在体外的 hCMEC/D3 单层（人 BBB 细胞培养模型）以及体内的小鼠中研究了 A40 和 A42 的转运动力学。尽管在基底外侧，荧光素标记的 A40 和 A42（F-A40 和 F-A42）的摄取率没有显著差异，但 F-A42 的顶端摄取率明显高于 F-A40。由于较高的血浆 A 水平被证明会加重 BBB 功能障碍并引发脑血管疾病，因此我们系统地研究了在 BBB 中使用单光子发射计算机断层扫描/计算机断层扫描成像在小鼠体内的顶端[A]肽的动态相互作用及其转运动力学。对由此获得的动态成像数据的定量建模表明，有毒[A]A42 的摄取率及其随后的 BBB 转胞吞作用明显高于[A]A40。很可能是这些动力学差异的分子机制在阿尔茨海默病和脑血管疾病中受到不同的影响，影响了 A40 和 A42 在血浆和脑中的水平，导致 A42/A40 比值的变化，并引发下游的毒性作用。意义：剖析 A40 和 A42 在 BBB 内皮细胞上的结合和摄取动力学，将有助于估计 A40 与 A42 对 BBB 内皮细胞的暴露，并通过监测血浆中 A42 和 A40 的水平来评估 BBB 功能障碍的风险。这一知识反过来将有助于阐明这些主要 A 同工型在加重 BBB 功能障碍和脑血管疾病中的作用。
