Defining how the exocyst regulates insulin-sensitive neuronal amyloid trafficking in Alzheimer's disease

Abstract

An estimated 7.2 million Americans aged 65 and older are currently living with Alzheimer’s Disease (AD), a number projected to rise substantially as the population ages. While AD is characterized by progressive cognitive decline and memory loss, individuals with type 2 diabetes mellitus (T2DM) face a significantly increased risk of developing the disease. A defining pathological feature of AD is the extracellular accumulation of amyloid-β (Aβ) plaques, generated through sequential proteolytic cleavage of the amyloid precursor protein (APP). Despite clinical and epidemiological links between metabolic dysfunction to AD, the mechanistic connection between insulin signaling and Aβ production remains poorly understood. Our preliminary data revealed a novel relationship between the insulin-sensitive exocyst protein complex and APP in neurons. To investigate this, we generated an SH-SY5Y neuronal cell line expressing a pH-sensitive fluorescent glucose transporter 4 (GLUT4) to determine whether the exocyst complex is necessary for insulin-stimulated GLUT4 exocytosis in neurons, as in peripheral tissues. To further define how insulin regulates exocyst function, we analyzed changes in its interactome under varying insulin conditions using two proteomic approaches: cell-surface protein capture in insulin-starved neurons before and after insulin addback, and a novel transgenic neuronal model incorporating proximity-dependent biotin labeling (BioID) enzyme fused to the exocyst. Combined, our data suggest that the exocyst complex functions as an insulin-sensitive regulator of APP trafficking and processing in neurons. These findings collectively support the idea that decreased insulin signaling, in addition to chronic insulin resistant states, may contribute to AD by increasing APP trafficking and processing in neurons, while also potentially identifying potential targets for future therapeutic strategies.