Studying Aggregation in Neurodegenerative Disease using Synthetic Proteins

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Summary/Abstract Protein misfolding and aggregation to form fibrils are common features of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and related diseases such as PD with dementia (PDD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA). Drugs that reverse or block protein aggregation, combined with early diagnosis, provide the prospect for a cure that preserves the patient's memories, personality, and control of bodily function. To design such drugs and diagnostic agents, one must understand the process of aggregation within neurons and propagation to “infect” new neurons in order to identify the most relevant targets for imaging and intervention. Our study will focus on the accumulation of fibrillar aggregates of α-synuclein (αS), commonly associated with PD, and tau, commonly associated with AD. In many cases, copathology of αS and tau is observed, blurring the classical boundaries between these diseases and demanding a more detailed understanding of aggregation mechanisms. Tau and αS are both meta-stable proteins that can form toxic oligomers and fibrillar aggregates under pathological conditions, including states of aberrant oxidative stress or post-translational modification (PTM). However, in spite of much study, the causes of tau coaggregation under pathological conditions remain unclear. We will investigate the molecular basis for tau fibril seeding by select αS fibril strains. Specifically, we will test two hypotheses: 1) Direct physical interactions between αS fibrils and tau monomers lead to tau aggregation; and 2) αS fibrils cause changes in cell signaling and/or mitochondrial function that indirectly trigger tau aggregation. In order to probe these hypotheses and determine their relative impact, we will perform cell-based studies in which tau aggregation is seeded with in vitro pre-formed fibrils (PFFs) or amplified, seeded fibrils (ASFs) templated from AD, PDD, DLB, or MSA patient material. Probes attached to αS, tau, and other key proteins will be used to track localization in fluorescence microscopy studies and identify physical proximity using photocatalytic labeling. This will allow us to determine how αS fibril interactions in cells lead to tau aggregation by first identifying the relevant proteins as well as their PTMs, and then observing their colocalization with live cell imaging using non-perturbing fluorescent amino acid tags. Our studies will draw important connections between AD related diseases (ADRDs), which typically feature tau pathology, and the synucleinopathies, PDD, DLB, and MSA. These findings will provide key mechanistic insight into ADRD/PD comorbidities and have the potential to identify new therapeutic targets that can prevent the triggering of tau pathology in response to αS aggregation.