Mechanisms of U87 astrocytoma cell uptake and trafficking of monomeric versus protofibril Alzheimer's disease amyloid-? proteins.

ABSTRACT: A significant hallmark of Alzheimer's disease is the formation of senile plaques in the brain due to the unbalanced levels of amyloid-beta (A?). However, although how A? is produced from amyloid precursor proteins is well understood, little is known regarding the clearance and metabolism of various A? aggregates from the brain. Similarly, little is known regarding how astrocytes internalize and degrade A?, although astrocytes are known to play an important role in plaque maintenance and A? clearance. The objective of this study is to investigate the cellular mechanisms that mediate the internalization of soluble monomeric versus oligomeric A? by astrocytes. We used a combination of laser confocal microscopy and genetic and pharmacological experiments to dissect the internalization of sA?42 and oA?42 and their postendocytic transport by U87 human brain astrocytoma cell line. Both A?42 species were internalized by U87 cells through fluid phase macropinocytosis, which required dynamin 2. Depleting LDL receptor-related protein 1 (LRP1) decreased sA?42 uptake more significantly than that of oA?42. We finally show that both A?42 species were rapidly transported to lysosomes through an endolytic pathway and subjected to proteolysis after internalization, which had no significant toxic effects to the U87 cells under relatively low concentrations. We propose that macropinocytic sA?42 and oA?42 uptake and their subsequent proteolytic degradation in astroglial cells is a significant mechanism underlying A? clearance from the extracellular milieu. Understanding the molecular events involved in astrocytic A? internalization may identify potential therapeutic targets for Alzheimer's disease.

SUBMITTER: Li Y 

PROVIDER: S-EPMC4062444 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature