Nature of the neurotoxic membrane actions of amyloid-β on hippocampal neurons in Alzheimer's disease

The mechanism by which amyloid-beta (A beta b) produces brain dysfunction in patients with Alzheimer's disease is largely unknown. According to previous studies, A beta might share perforating properties with gramicidin, a well-accepted membrane-disrupting peptide. Therefore, we hypothesize that the key steps leading to synaptotoxicity by A beta and gramicidin involve peptide aggregation, pore formation, and calcium dysregulation. Here, we show that A beta and gramicidin form aggregates enriched in beta-sheet structures using electron microscopy, and Thioflavin and Congo Red staining techniques. Also, we found that A beta and gramicidin display fairly similar actions in hippocampal cell membranes, i.e. inducing Ca2+ entry and synaptoxicity characterized by the loss of synaptic proteins and a decrease in neuronal viability. These effects were not observed in a Ca2+ free solution, indicating that both A beta and gramicidin induce neurotoxicity by a Ca2+-dependent mechanism. Using combined perforated patch clamp and imaging recordings, we found that only A beta produced a perforation that progressed from a small (Cl--selective pore) to a larger perforation that allowed the entry of fluorescent molecules. Therefore, based on these results, we propose that the perforation at the plasma membrane by A beta is a dynamic process that is critical in producing neurotoxicity similar to that found in the brains of AD patients. (C) 2014 Elsevier Inc. All rights reserved.