Human blood-brain barrier receptors for Alzheimer's amyloid-β 1-40. Asymmetrical binding, endocytosis, and transcytosis at the apical side of brain microvascular endothelial cell monolayer

A soluble monomeric form of Alzheimer's amyloid-β (1-40) peptides (SAβ_1-40) is present in the circulation and could contribute to neurotoxicity if it crosses the brain capillary endothelium, which comprises the blood-brain barrier (BBB) in vivo. This study characterizes endothelial binding and transcytosis of a synthetic peptide homologous to human sAβ_{1- 40} using an in vitro model of human BBB. ¹²⁵I-sAβ_1-40 binding to the brain microvascular endothelial cell monolayer was time dependent, polarized to the apical side, and saturable wi'th high- and low-affinity dissociation constants of 7.8±1.2 and 52.8±6.2 nM, respectively. Binding of ¹²⁵I-sAβ_1-40 was inhibited by anti-RAGE (receptor for advanced glycation end products) antibody (63%) and by acetylated low density lipoproteins (33%). Consistent with these data, transfected cultured cells overexpressing RAGE or macrophage scavenger receptor (SR), type A, displayed binding and internalization of ¹²⁵I-sAβ_1-40. The internalized peptide remains intact > 94%. Transcytosis of ¹²⁵I-sAβ_1-40 was time and temperature dependent, asymmetrical from the apical to basolateral side, saturable with a Michaelis constant of 45±9 nM, and partially sensitive to RAGE blockade (36%) but not to SR blockade. We conclude that RAGE and SR mediate binding of sAB_1-40 at the apical side of human BBB, and that RAGE is also involved in sAβ_1-40 transcystosis.