The effect of intracellular Aβ uptake via RAGE on tight junction in retinal pigment epithelium

Abstract

Purpose: Intracellular amyloid beta (Aβ) has been implicated in neuronal cell death in Alzheimer’s disease (AD) and tight junction breakdown of retinal pigment epithelium (RPE) in age-related macular degeneration (AMD). Although Aβ is predominantly secreted from the neuronal cells, the mechanism of Aβ transport into the RPE remain to be fully elucidated. This study is aimed to demonstrate the role of receptor for advanced glycation end products (RAGE) in intracellular Aβ transport and the role of intracellular Aβ in RPE tight junction.

Methods: To evaluate cellular uptake of Aβ in RPE, subretinal injection of Aβ₄₂ or PBS (control) was performed in C57BL/6J mice (N=6). Seven days after subretinal Aβ₄₂ injection, RPE/choroid/scleral complex was flat-mounted. Then, Aβ and ZO-1 were immunostained and observed under confocal microscope. To determine the mechanism how extracellular Aβ translocate into intracellular space in RPE, we immunostained plasma membrane using biotinylation or RAGE after exogenous OAβ₄₂ treatment. Western blot analysis for Aβ and p38 MAPK was performed to investigate the role of RAGE on Aβ uptake in RPE cells using RAGE siRNA or p38 inhibitor (SB 203580). To determine the role of RAGE on barrier function of RPE after Aβ treatment, we measured transepithelial resistance in RPE.

Results: Intracellular Aβ was found concomitantly with breakdown of tight junction in the RPE after subretinal injection of Aβ into the mouse eye. We also presented evidence that RAGE contributed to endocytosis of Aβ in the RPE. siRNA mediated RAGE knockdown prevented RAGE mediated endocytosis of Aβ and subsequent tight junction breakdown in RPE. RAGE-mediated P38 MAPK signaling contributed to endocytosis of Aβ. Blockade of RAGE inhibited Aβ endocytosis, thereby preventing tight junction breakdown in RPE.

Conclusions: Intracellular Aβ via the RAGE/p38 MAPK-mediated endocytosis contributes to breakdown of tight junction in RPE. Thus, we suggest that RAGE could be a potential therapeutic target for intracellular Aβ induced outer BRB breakdown in AMD.