Amyloid β Interaction with Receptor for Advanced Glycation End Products Up-Regulates Brain Endothelial CCR5 Expression and Promotes T Cells Crossing the Blood-Brain Barrier

Abstract

How circulating T cells infiltrate into the brain in Alzheimer disease (AD) remains unclear. We previously reported that amyloid beta (Abeta)-dependent CCR5 expression in brain endothelial cells is involved in T cell transendothelial migration. In this study, we explored the signaling pathway of CCR5 up-regulation by Abeta. We showed that inhibitors of JNK, ERK, and PI3K significantly decreased Abeta-induced CCR5 expression in human brain microvascular endothelial cells (HBMECs). Chromatin immunoprecipitation assay revealed that Abeta-activated JNK, ERK, and PI3K promoted brain endothelial CCR5 expression via transcription factor Egr-1. Furthermore, neutralization Ab of receptor for advanced glycation end products (RAGE; an Abeta receptor) effectively blocked Abeta-induced JNK, ERK, and PI3K activation, contributing to CCR5 expression in HBMECs. Abeta fails to induce CCR5 expression when truncated RAGE was overexpressed in HBMECs. Transendothelial migration assay showed that the migration of MIP-1alpha (a CCR5 ligand)-expressing AD patients' T cells through in vitro blood-brain barrier model was effectively blocked by anti-RAGE Ab, overexpression of truncated RAGE, and dominant-negative PI3K, JNK/ERK, or Egr-1 RNA interference in HBMECs, respectively. Importantly, blockage of intracerebral RAGE abolished the up-regulation of CCR5 on brain endothelial cells and the increased T cell infiltration in the brain induced by Abeta injection in rat hippocampus. Our results suggest that intracerebral Abeta interaction with RAGE at BBB up-regulates endothelial CCR5 expression and causes circulating T cell infiltration in the brain in AD. This study may provide a new insight into the understanding of inflammation in the progress of AD.