The objective was to determine if endogenous levels of Intersectin1 protein differ between cases and controls in DS and AD, and to characterize the role of Intersectin1 and Intersectin1-regulated pathways in DS, AD, and related pathologies.

Intersectin1 is a versatile scaffold protein that functions in diverse facets of membrane trafficking and cell signaling, in the brain. As a result, Intersectin1 has been implicated in a striking number of diseases that span neurodevelopmental, neuropsychiatric, and neurodegenerative disease categories; however, much remains to be elucidated about the precise cellular and molecular mechanisms underlying these diseases.

Western Blot and densitometry were used to analyze proteins of interest in human samples, transgenic mice, and cell models. Molecular interaction studies were conducted in cell models using Bimolecular Fluorescence Complementation, captured with confocal microscopy, and quantified using ImageJ. In other cases, co-localization studies were achieved by expression of fluorescently tagged proteins in various cell models +/- immunohistochemistry.

Levels of Intersectin1 are increased in trisomic IPS cells relative to euploid cells harvested from DS patients. Whereas, Intersectin1 levels are decreased in the Superior Temporal Cortex of female AD patients, compared to controls, offering the first evidence that Intersectin1 protein levels differ significantly between cases and controls in AD. In transgenic mice, loss Intersectin1 expression was sufficient to alter the levels of key pathogenic proteins including APP, BACE1, and GSK3. For the first time, we demonstrate that (1) Intersectin1 co-localizes with APP and BACE1, (2) Intersectin1/Arf6/BACE1 and Intersectin1/Arfaptin2/BACE1 form complexes at distinct vesicle compartments, (3) and identify PI3KC2β as a novel Arf6 effector.