Endocytosis and Transcytosis of Amyloid-beta Peptides by Astrocytes: A Possible Mechanism for Amyloid-beta Clearance in Alzheimer's Disease

摘要

Amyloid-beta (A beta) peptides, A beta(40), A beta(42), and recently A beta(25)-(35), have been directly implicated in the pathogenesis of Alzheimer's disease (AD). We have previously shown that all three peptides decrease neuronal viability, but A beta(40 )also promotes synaptic disassembling. In this work, we have studied the effects of these peptides on astrocytes in primary culture and found that the three A beta peptides were internalized by astrocytes and significantly decreased astrocyte viability, while increasing ROS production. A beta peptide internalization is temperature-dependent, a fact that supports the idea that A beta peptides are actively endocytosed by astrocytes. However, inhibiting caveolae formation by methyl-beta-cyclodextrin or by silencing caveolin-1 with RNA interference did not prevent A beta endocytosis, which suggests that A beta peptides do not use caveolae to enter astrocytes. Conversely, inhibition of clathrin-coated vesicle formation by chlorpromazine or by silencing clathrin with RNA interference significantly decreased A beta internalization and partially reverted the decrease of astrocyte viability caused by the presence of A beta. These results suggest that A beta is endocytosed by clathrin-coated vesicles in astrocytes. A beta-loaded astrocytes, when co-incubated with non-treated astrocytes in separate wells but with the same incubation medium, promoted cell death in non-treated astrocytes; a fact that was associated with the presence of A beta inside previously unloaded astrocytes. This phenomenon was inhibited by the presence of chlorpromazine in the co-incubation medium. These results suggest that astrocyte may perform A beta transcytosis, a process that could play a role in the clearance of A beta peptides from the brain to cerebrospinal fluid.