Aβ(1–42) reduces P-glycoprotein in the blood–brain barrier through RAGE–NF-κB signaling

The reduced clearance of amyloid-β peptide (Aβ) from the brain partly accounts for the neurotoxic accumulation of Aβ in Alzheimer's disease (AD). Recently, it has been suggested that P-glycoprotein (P-gp), which is an efflux transporter expressed on the luminal membrane of the brain capillary endothelium, is capable of transporting Aβ out of the brain. Although evidence has shown that restoring P-gp reduces brain Aβ in a mouse model of AD, the molecular mechanisms underlying the decrease in P-gp expression in AD is largely unknown. We found that Aβ(1–42) reduced P-gp expression in the murine brain endothelial cell line bEnd.3, which was consistent with our in vivo data that P-gp expression was significantly reduced, especially near amyloid plaques in the brains of five familial AD mutations (5XFAD) mice that are used as an animal model for AD. A neutralizing antibody against the receptor for advanced glycation end products (RAGE) and an inhibitor of nuclear factor-kappa B (NF-κB) signaling prevented the decrease in Aβ(1–42)-induced P-gp expression, suggesting that Aβ reduced P-gp expression through NF-κB signaling by interacting with RAGE. In addition, we observed that the P-gp reduction by Aβ was rescued in bEnd.3 cells receiving inductive signals or factors from astrocytes making contacts with endothelial cells (ECs). These results support that alterations of astrocyte–EC contacts were closely associated with P-gp expression. This suggestion was further supported by the observation of a loss of astrocyte polarity in the brains of 5XFAD mice. Taken together, we found that P-gp downregulation by Aβ was mediated through RAGE–NF-κB signaling pathway in ECs and that the contact between astrocytes and ECs was an important factor in the regulation of P-gp expression.