Immunohistochemical analysis of transporters related to clearance of amyloid-β peptides through blood-cerebrospinal fluid barrier in human brain

A large number of previous reports have focused on the transport of amyloid-beta peptides through cerebral endothelial cells via the blood-brain barrier, while fewer reports have mentioned the transport through the choroid plexus epithelium via the blood-cerebrospinal fluid barrier. Concrete roles of these two pathways remain to be clarified. In this study, we immunohistochemically examined the expression of transporters/receptors that are supposed to be related to the clearance of amyloid-beta peptides in the choroid plexus epithelium, the ventricular ependymal cells and the brain microvessels, using seven autopsied human brains. In the choroid plexus epithelium, immunoreactivity for low-density lipoprotein receptor (LDLR), LDLR-related protein 1 (LRP1), LRP2, formylpeptide receptor-like 1 (FPRL1), ATP-binding cassette (ABC) transporter-A1 (ABCA1), ABCC1 and ABCG4 was seen in 7 of 7 brains, while that for ABCB1, ABCG2, RAGE and CD36 was seen in 0-2 brains. In the ventricular ependymal cells, immunoreactivity for CD36, LDLR, LRP1, LRP2, FPRL1, ABCA1, ABCC1 and ABCG4 was seen in 6-7 brains, while that for ABCB1, ABCG2 and RAGE was seen in 0-1 brain. Immunoreactivity for insulin-degrading enzyme (IDE) was seen in three and four brains in the choroid plexus epithelium and the ventricular ependymal cells, respectively. In addition, immunoreactivity for LDLR, ABCB1 and ABCG2 was seen in over 40 % of the microvessels (all seven brains), and that for FPRL1, ABCA1, ABCC1 and RAGE was seen in over 5 % of the microvessels (4-6 brains), while that for CD36, IDE, LRP1, LRP2 and ABCG4 was seen in less than 5 % of the microvessels (0-2 brains). These findings may suggest that these multiple transporters/receptors and IDE expressed on the choroid plexus epithelium, ventricular ependymal cells and brain microvessels complementarily or cooperatively contribute to the clearance of amyloid-beta peptides from the brain.