Role of N-terminal residues in Aβ interactions with integrin receptor and cell surface

Abstract

beta-Amyloid (Aβ) is the primary protein component of senile plaques in Alzheimer's disease (AD) and is believed to play a role in its pathology. To date, the mechanism of action of Aβ in AD is unclear. We and others have observed that Aβ interacts either with or in the vicinity of the α6 sub-unit of integrin, and believe this may be important in its interaction with neuronal cells. In this study, we used confocal microscopy and flow cytometry to explore the residue specific interactions of Aβ40 with the cell surface and the α6 integrin receptor sub-unit. We probed the importance of the RHD sequence in Aβ40 and found that removal of the residues or their mutation using the Aβ8-40 or the D7N early onset AD sequence, respectively, led to a greater interaction between Aβ40 and an antibody bound to the α6-integrin sub-unit, as measured by fluorescence resonance energy transfer (FRET). These results suggest that the RHD sequence of Aβ40 does not mediate Aβ–α6 integrin interactions. However, the cyclic RGD mimicking peptide, Cilengitide, reduced the measured interaction between Aβ40 fibrils without the RHD sequence and an antibody bound to the α6-integrin sub-unit. We further probed the role of electrostatic forces on Aβ40–cell interactions and observed that the Aβ sequence that included the N-terminal segment of the peptide had reduced cellular binding at low salt concentrations, suggesting that its first 7 residues contribute to an electrostatic repulsion for the cell surface. These findings contribute to our understanding of Aβ–cell surface interactions and may provide insight into development of novel strategies to block Aβ–cell interactions that contribute to pathology in Alzheimer's disease.