RESUMO
beta-Amyloid (Aß) 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 Aß in AD is unclear. We and others have observed that Aß 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 Aß40 with the cell surface and the α6 integrin receptor sub-unit. We probed the importance of the RHD sequence in Aß40 and found that removal of the residues or their mutation using the Aß8-40 or the D7N early onset AD sequence, respectively, led to a greater interaction between Aß40 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 Aß40 does not mediate Aß-α6 integrin interactions. However, the cyclic RGD mimicking peptide, Cilengitide, reduced the measured interaction between Aß40 fibrils without the RHD sequence and an antibody bound to the α6-integrin sub-unit. We further probed the role of electrostatic forces on Aß40-cell interactions and observed that the Aß 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 Aß-cell surface interactions and may provide insight into development of novel strategies to block Aß-cell interactions that contribute to pathology in Alzheimer's disease.