Inhibition of β-amyloid1-42 internalization attenuates neuronal death by stabilizing the endosomal-lysosomal system in rat cortical cultured neurons.

A number of recent studies have indicated that accumulation of β amyloid (Aβ) peptides within neurons is an early event which may trigger degeneration of neurons and subsequent development of Alzheimer's disease (AD) pathology. However, very little is known about the internalization and/or subcellular sites involved in trafficking of Aβ peptides into the neurons that are vulnerable in AD pathology. To address this issue we evaluated internalization of fluoroscein conjugated Aβ1-42 (FAβ1-42) and subsequent alteration of endosomal-lysosomal (EL) markers such as cathepsin D, Rab5 and Rab7 in rat cortical cultured neurons. It is evident from our results that internalization of FAβ1-42, which occurred in a dose- and time-dependent manner, triggered degeneration of neurons along with increased levels and/or altered distribution of cathepsin D, Rab5 and Rab7. Our results further revealed that FAβ1-42 internalization was attenuated by phenylarsine oxide (a general inhibitor of endocytosis) and sucrose (an inhibitor of clathrin-mediated endocytosis) but not by antagonists of N-methyl-d-aspartate (NMDA) glutamate receptors. Additionally, inhibition of FAβ1-42 endocytosis not only protected neurons against toxicity but also reversed the altered levels/distributions of EL markers. These results, taken together, suggest that internalization of exogenous Aβ1-42, which is partly mediated via a clathrin-dependent process, can lead to degeneration of neurons, possibly by activating the EL system. Inhibition of FAβ endocytosis attenuated toxicity, thus suggesting a potential strategy for preventing loss of neurons in AD pathology.