Lee, Jannifer H.

Abstract Lewy pathology can form over decades in patients with Lewy body diseases, but the causal cellular mechanisms associated with this process remain unclear. This project aims to discover proteins that associate with monomeric and/or oligomeric alpha-synuclein during early stages of the aggregation process. To mimic the aggregation processes, cells expressing a synuclein-biotin ligase fusion protein were treated human recombinant pre-formed fibrils and subjected to BioSITe and mass spectrometry. Using a novel split biotin ligase fused to alpha-synuclein facilitated the identification of proteins specifically associated with multimeric alpha-synuclein. A total of 581 proteins were differentiated into potential interactors of monomeric versus multimeric alpha-synuclein in physiological versus aggregated conditions. The data reveal important phosphorylation mechanisms, connections to insulin processing, and a potential interaction with ALS-associated FUS. Interestingly, we identified that loss of specific interactions may contribute to pathology in patients with sporadic onset of Lewy body diseases. Future studies will validate both true interaction of highlighted proteins with alpha-synuclein, and the impact of such proteins on alpha-synuclein aggregation.

AbstractBackgroundNeuropathologic inclusions formed by hyperphosphorylated protein tau in the brain are a hallmark of Alzheimer’s disease and other human neurodegenerative disorders commonly referred to as tauopathies. Tau lesions differ in their disease‐specific morphological presentations, affected cell type, subcellular compartments and tau isoforms present in the inclusions. In addition, tau filaments isolated from different tauopathies have distinct fibrillar structures that potentially underlie the morphological diversity of tau lesions. The factors that govern the formation of disease‐specific tau lesions and distinct patterns of neurodegeneration and clinical presentations are unknown. To address this gap of knowledge, we performed profiling of proteomes associated with phospho‐tau aggregates in 4 major tauopathies.MethodWe utilized the in‐house developed Probe‐dependent Proximity Profiling (ProPPr) method combined with data‐independent acquisition mass spectrometry to profile phospho‐tau associate proteomes in formalin‐fixed paraffin‐embedded (FFPE) frontal cortex tissue sections from the Mayo Clinic Florida Brain Bank. Selected candidates were validated by fluorescent co‐immunostaining of patient brains with corresponding antibodies.ResultIn situ proximity proteomic profiling revealed over 1300 protein associated with phospho‐tau pathology, including 229 proteins that were identified in all tauopathies. The most significantly enriched GO terms in this protein set common to all the tauopathies were related to chaperone activity, guanyl nucleotide binding, cadherin binding, cytoskeleton, and ion transporter activity, highlighting biological processes and pathways affected by tau aggregation regardless of the type of tau lesion. In addition, we identified 32 proteins with significantly different association with phospho‐tau between tauopathies. Immunostaining of post‐mortem patient frontal cortices confirmed some of the findings from proteomics and revealed differences in abundance and localization patterns of several tau‐associated proteins between tauopathies, uncovering a potential of using these proteins as biomarkers for antemortem diagnosis.ConclusionTau lesions in different tauopathies have differences in their associated proteomes that can be assessed by the ProPPr assay.

AbstractBackgroundAlzheimer’s disease (AD) is characterized by the accumulation of neurofibrillary tangles (NFTs), comprised primarily of microtubule‐associated protein tau. NFTs are defining hallmarks of AD and its accumulation into pathological oligomers and fibrils has been associated with cognitive decline in AD and other tauopathies. Despite its pivotal role in the disease process, we still have a poor understanding of how their formation, toxicity, and spread across brain regions is regulated via tau‐associated proteins that regulate the oligomerization, pathological accumulation, and seeding of tau in affected cell types and vulnerable brain regions.MethodWe have established two proximity‐dependent biotin‐identification (BioID) models as novel approaches to identify the composition and proximal molecular environment of tau aggregates. Using an in vitro and ex vivo model approach coupled with mass spectrometry, we have identified proteins that were primarily associated with mutant tau aggregates vs. soluble wildtype tau and stratified them based on significance, molecular pathway and druggability. Immunoblotting and immunofluorescence were performed to assess the interaction of endogenous and overexpressed top candidates with tau, along with visualization with NFTs in the context of human AD pathology to assess their impact on tau‐aggregate formation and toxicity.ResultTo determine the physiological and aggregate specific interacting partners of tau, we are comparing wild type tau (TauWT) with mutant tau (Tau3xMUT) carrying three tauopathy‐associated mutations (A152T/P301L/S320F). The proteomic analysis from our combined proteomic datasets revealed that significantly changed proteins included candidates involved in RNA processing, as well as protein ubiquitination and proteasome degradation. We have begun validating proteins that are enriched in mutant tau in human tissue of AD, as well as primary tauopathies, that may be druggable targets for tauopathies.ConclusionThis study provides novel insights into cellular pathways and molecular mechanisms of neurodegeneration, by identifying in the context of living neurons and brain tissue different functional classes of tau‐associated proteins with relevance for AD pathophysiology. These are expected to include proteins that may mediate the toxic effect of NFTs, facilitate the formation or degradation of pathological tau aggregates, and catalyze posttranslational modifications of tau oligomers and associated proteins.

AbstractBackgroundAlzheimer's disease (AD) and related neurodegenerative diseases are characterized by the accumulation of abnormal protein aggregates. A defining hallmark of AD is the formation of neurofibrillary tangles (NFTs) by aggregation of the microtubule‐associated protein tau into pathological oligomers and fibrils. Although NFTs are believed to play a pivotal role in the disease process, we have a poor understanding of how their formation, toxicity, and spread across brain regions is regulated. Recent data suggest that the seeding behavior of tau is governed by patterns of posttranslational modifications and varying filament structures. Understanding how tau‐associated proteins regulate the oligomerization, pathological accumulation, and seeding of tau in affected neurons and glia is of critical importance for therapy development.MethodTo profile the interactome of tau aggregates, we have established proximity‐dependent biotin‐identification (BioID) as a novel method to identify the composition and proximal molecular environment of insoluble protein aggregates in the context of living brain cells and tissue. Using an in vitro and ex vivo model approach coupled with mass spectrometry, we are generating datasets containing top identified proteins, stratified based on significance and molecular pathway. Once we validate their co‐localization with NFTs in the context of human AD pathology, functional characterization of putative modifiers will be performed to assess their impact on tau‐aggregate and toxicity.ResultTo determine the physiological and aggregate specific interacting partners of tau, we are comparing wild type tau (TauWT) with mutant tau (Tau3xMUT) carrying three tauopathy‐associated mutations (A152T/P301L/S320F) that form hyper‐phosphorylated and thioflavin S‐positive aggregates even in the absence of seeding. The proteomic analysis from our pilot study revealed that significantly changed proteins included candidates involved in RNA processing, as well as protein ubiquitination and proteasome degradation.ConclusionThis study provides novel insights into cellular pathways and molecular mechanisms of neurodegeneration, by identifying in the context of living neurons and brain tissue different functional classes of tau‐associated proteins with relevance for AD pathophysiology. These are expected to include proteins that may mediate the toxic effect of NFTs, facilitate the formation or degradation of pathological tau aggregates, and catalyze posttranslational modifications of tau oligomers and associated proteins.

Traumatic brain injury (TBI) is traditionally characterized by primary and secondary injury phases, both contributing to pathological and morphological changes. The mechanisms of damage and chronic consequences of TBI remain to be fully elucidated, but synaptic homeostasis disturbances and impaired energy metabolism are proposed to be a major contributor. It has been proposed that an increase of extracellular (eATP) adenosine triphosphate (ATP) in the area immediately surrounding impact may play a pivotal role in this sequence of events. After tissue injury, rupture of cell membranes allows release of intracellular ATP into the extracellular space, triggering a cascade of toxic events and inflammation. ATP is a ubiquitous messenger; however, simple and reliable techniques to measure its concentration have proven elusive. Here, we integrate a sensitive bioluminescent eATP sensor known as pmeLUC, with a controlled cortical impact mouse model to monitor eATP changes in a living animal after injury. Using the pmeLUC probe, a rapid increase of eATP is observed proximal to the point of impact within minutes of the injury. This event is significantly attenuated when animals are pretreated with an ATP hydrolyzing agent (apyrase) before surgery, confirming the contribution of eATP. This new eATP reporter could be useful for understanding the role of eATP in the pathogenesis in TBI and may identify a window of opportunity for therapeutic intervention.

Abstract Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, a novel electrode that begins as an uncured, flowable prepolymer that can be injected around a neuroanatomical target to minimize surgical manipulation is developed. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, detailed electrochemical and microscopy characterization of its material properties is performed and the feasibility of using it to stimulate the nervous system electrically in rats and swine is validated. The silicone‐metal‐particle composite performs very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSC C ) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of its simplicity, the Injectrode has the potential to be less invasive, more robust, and more cost‐effective than traditional electrode designs, which could increase the adoption of neuromodulation therapies for existing and new indications.