P4‐071: Involvement of X11/X11L in Alzheimer's‐related beta‐amyloid generation and epileptogenesis

Abstract

Background: Amyloid beta (Ab), originating from cleavage of APP (amyloid precursor protein), is a hallmark of Alzheimer’s disease. P75NTR is known to regulate Abeta deposition in the brain but its role in APP trafficking and processing is not known. Methods: We use FRET (fluorescence resonance energy transfer) analysis to characterize the nature of the APPp75NTR interaction in HEK293 cells which were transfected with p75NTR-CFP and APP-YFP plasmids and controls. These cells were subjected to a range of neurotrophins, and Ab, at differing concentrations. Co-immunoprecipitation and fractionation were used to examine the interaction between p75NTR and APP. Results: The FRET efficiency of APP-p75NTR was significantly higher than the negative control. All neurotrophins triggered an increase in the FRETefficiency between p75NTR and APP. Interestingly, Ab at all concentrations triggered a dramatic increase in FRET efficiency.The interaction increased dramatically within the first 1-3 minutes of the addition of Ab to the cells. Co-IP data support that Abeta enhanced the interaction between APP and p75NTR. When a phosphorylation inhibitor KT5720 was added to transfected cells with added Ab, FRET efficiency dropped. Reciprocally, when a phosphorylation activator 8-BrcAMP was added, FRET efficiency increased significantly. This data seems to support the idea that p75NTR-APP interaction is under the influence of a phosphorylation event. Furthermore FRET efficiency dropped further by blocking endogenous Ab with an antibody 6E10, indicating endogenous Ab may increase the interaction of APP and p75NTR. These results could suggest that Ab may have a positive feed forward mechanism that increases an output of Ab via the interaction among Abeta, p75NTR and APP. Conclusions: We conclude that p75NTR ligands Ab and neurotrophins enhance the interaction of p75NTR-APP in a phosphorylation dependent manner, and the increased interaction of p75NTR-APPmay participate in the pathogenesis of AD.