Effects of Secreted Amyloid Precursor Protein-Alpha Peptide Fragments on Glutamate Receptor Subunit Trafficking in the Rat Hippocampus

Abstract

Glutamate receptors play a key role in synaptic plasticity mechanisms and are critical for learning and memory function. Deficits in synaptic plasticity and glutamate receptor functioning are observed in disease states like Alzheimer’s disease, and finding potential therapies for such disease states remains a major global endeavour. Previous research has found that secreted amyloid precursor protein-alpha (sAPPα) has multiple plasticity promoting effects. The aims of the current project were to identify the potential glutamate receptor trafficking promoting effects of functional regions of sAPPα, specifically the peptide CTα16, located at the C-terminal, and RER, located in the E2 domain. Rat hippocampal slices and primary hippocampal cultures were treated with sAPPα and peptides in acetylated form, Ac-CTα16 and Ac-RER for 30 minutes. Analyses of total and cell-surface expression of glutamate receptor subunits GluA1, GluN1, and GluN2A, within hippocampal slices were completed via western blot. Immunofluorescence (mean intensity and puncta density) corresponding to surface and internal GluA1 was analysed using confocal imaging of hippocampal cultures. It was hypothesized that Ac-CTα16 and Ac-RER treatments would upregulate trafficking of GluA1 and GluN1 to the cell surface. Paired t-tests revealed no increases in membrane or total glutamate subunit levels in hippocampal slices. One-way ANOVA revealed a significant increase in cell-surface and intracellular intensities, as well as the density of cell-surface puncta in hippocampal cultures, following Ac-RER treatment. These results failed to replicate the previous finding that sAPPα increases glutamate receptor trafficking, and also indicated that Ac-CTα16 does not increase glutamate trafficking under these conditions, unlike Ac-RER. Additional investigation into the specific changes associated with the RER peptide in slices, including potential effects on other receptor subunits and the localization of detected GluA1-containing receptor increases, may support the development of RER-based peptide therapy.