Determining and Characterizing Substrates of Protein Degradation Impairments in Models of Alzheimer's Disease

Northwestern University At Chicago, Evanston IL

Investigators

Linked publications, trials & patents

Abstract

Project Summary / Abstract Alzheimer's disease (AD) is a debilitating disorder first recognized over a century ago. Since then, AD has been extensively investigated; however, many questions remain concerning how molecular hallmarks translate to clinical symptoms. Pathologically, AD is characterized by the misfolding and aggregation of proteins, particularly amyloid beta 1-42 peptides (A?42) and hyperphosphorylated tau. Although A?42 accumulation is one of the earliest pathological events, how increased levels of A?42 induce toxicity in neurons and contribute to synaptic loss remains poorly understood. One hypothesis, as evidenced by the plaques and tangles found in AD patients' brains, is that A?42 impairs protein degradation either by directly interacting with proteins or by sequestering or hampering protein degradation machinery causing vulnerable proteins to persist in the brain. This project aims to determine the specific proteins that have decreased degradation dynamics in models of AD-like pathology. Proteins that persist for longer periods due to stunted degradation may potentially contribute to AD etiology through loss-of-function mechanisms or by disrupting protein homeostasis balance, both of which may lead to neuronal dysfunction. To investigate protein degradation dynamics in AD-like pathology, I am using pulse-chase metabolic labeling in an in vivo paradigm with the recently developed APP knock-in mice. I will then analyze the degradation rates of thousands of proteins using proteomic-based quantitative mass spectrometry. In these experiments, proteins are labeled with ?heavy? isotopes, then chased with ?light? isotopes. I subsequently measure degradation rates by monitoring the remaining ?heavy? proteins. Proteins with decreased degradation dynamics in the presence of A?42 may represent substrates of impaired protein degradation and may reveal critical components in early AD pathology. Based on preliminary data, proteins with the most severe degradation impairments were significantly enriched for proteins associated with the presynaptic active zone, especially synaptic vesicle proteins. These proteins had impaired degradation in the cortex and hippocampus, but not the cerebellum, a brain region where A?42 pathology is absent until late stages of the disease, further supporting an A?42 dependent effect. These findings indicate that synaptic vesicle proteins may represent pioneering protein networks that contribute to synaptic dysfunction in AD-like pathology. This project also aims to determine the molecular mechanisms underlying the degradation impairment in synaptic vesicle proteins by investigating the involvement of non-A?42 fragments of APP processing, as well as by investigating the role of tau. This proposal represents a unique approach that has the potential to identify novel proteins or protein pathways that contribute to AD etiology or early pathology, as well as determine potential mechanisms for how some proteins, which may play a critical role in early AD pathology, persist in the brain.