Binding of the Alzheimer amyloid β-peptide to neuronal cell membranes by fluorescence correlation spectroscopy

The deposition of the Alzheimer amyloid beta-peptide (A beta) fibrils in brain is a key step in Alzheimer's disease. The aggregated A beta is found to be toxic to neurons since cells die when the aggregated A beta is added to the cell culture medium. However, target of action of A beta to cells is unknown. We have applied the fluorescence correlation spectroscopy (FCS) technique to study the existence of a receptor or target molecule for the Alzheimer amyloid beta-peptide (A beta) in cultured human cerebral cortical neurons. FCS measurement of the fluorophore rhodamine-labeled A beta (Rh-A beta) shows diffusion times: 0.1 ms, 1.1 ms and 5.9 ms. Thus, 0.1 ms corresponds to the unbound Rh-A beta, and 1.1 ms and 5.9 ms correspond to slowly diffusing complexes of Rh-A beta bound to a kind of receptor or target molecule for A beta. Addition of excess non-labeled A beta is accompanied by a competitive displacement, showing that the A beta binding is specific. Full saturation of the A beta binding is obtained at nanomolar concentrations, indicating that the A beta binding is of high affinity. The notion that using FCS we have found a kind of receptor or target molecule for A beta makes an important point that A beta kills cells possibly by affecting cell membranes via a receptor or target molecule. This study is of highly significance since it suggests that A beta possibly affects neuronal cell membranes of Alzheimer patients via a receptor or target molecule. (C) 2007 Elsevier Inc. All rights reserved.