Pilots

Abstract: Alzheimer’s Disease (AD) is the most common cause of age-related dementia, yet its underlying pathology is poorly understood. Large human genetics studies have implicated genes involved in macrophage immune responses as contributing to the disease in humans. Under homeostatic conditions, the only macrophages within the brain are tissue resident microglia, whose origins in the embryonic yolk sac make them unique among macrophages in adulthood. With brain injury or disease, however, circulating macrophages can infiltrate the brain, where they upregulate many microglial genes and masquerade as “microglia-like cells”. These infiltrating macrophages fail to completely differentiate into microglia, however, and intrinsically express high levels of genes associated with neurodegeneration and disease. These findings make determining the extent of macrophage infiltration into the brain of fundamental importance in understanding the pathogenesis of AD in humans, but a lack of specific markers to positively identify infiltrating macrophages from microglia has led to difficulty in determining the distinct responses of these two macrophage populations. We hypothesize that circulating macrophages infiltrate the brain during AD in humans, where they contribute to disease progression. We have validated a panel of several markers specific to either microglia or infiltrating macrophages in human brain tissues. Using these highly specific markers of macrophage origin, we will to quantify the extent of macrophage infiltration in human AD brain tissue samples. Additionally, we will compare the reactivity state of infiltrating macrophages to bona fide microglia in human neurodegeneration, while defining the spatial localization of infiltrating macrophages in relation to amyloid pathology. These studies represent an important step forward in understanding whether and how infiltrating macrophages contribute to AD in humans, that will inform new treatment approaches targeting macrophages for the treatment of neurodegenerative disease.  

Abstract: Protein aggregation is a pathological hallmark of several neurodegenerative diseases, yet, the mechanisms that initiate protein aggregation and how different stages of aggregation impact neuronal health are poorly understood. Tau is a microtubule associated protein that helps stabilize and bundle microtubules in neuronal axons and undergoes pathological aggregation in many neurodegenerative diseases collectively known as tauopathies. Current paradigm suggests that tau pathology is caused by hyper-phosphorylation of tau, which interferes with its microtubule binding, initiating its aggregation in the cytosol. Tau aggregation involves several stages starting with soluble tau oligomers followed by insoluble aggregates consisting of paired helical fibrils (PHFs) and neurofibrillary tangles (NFTs). Histological analysis has focused on characterization of PHFs and NFTs since they are easy to detect due to their large size. However, soluble tau oligomers have been shown to lead to neurotoxicity. Yet, visualizing the progression of tau aggregation in intact cells from early stages of oligomeric tau formation to later stages of NFT formation has been challenging due to limitations of microscopy. Hence, there is a cirtical need to apply new methods to visualize the kinetics of tau aggregation in cells. This current knowledge gap prevents us from studying the mechanisms that initiate aggregation and the impact of various aggregate species, including tau oligomers, on neuronal health. 

My long term goal is to study the mechanisms that initiate protein aggregation in neurodegenerative diseases and understand the impact of early aggregates on neuronal health. Towards this goal, my lab has developed quantitative super-resolution microscopy methods that distinguish the spatial distribution of monomeric from oligomeric proteins in cells. We will employ these cutting edge methods to study tau aggregation in cell models of tauopathies. Our central hypothesis is that tau self-associates to form non-toxic and non-pathological oligomers on microtubules under physiological conditions, tau hyperphosphorylation leads to growth of these oligomeric species and initiates neurodegeneration. The basis of this hypothesis is our preliminary data in which we have imaged P301L tau under non-aggregated and aggregated conditions using super-resolution microscopy. These images revealed tau patches along the microtubule under non-aggregated conditions and a wide range of tau aggregates in pathological conditions, including small amorphous aggregates, fibrils and plague-like structures. The rationale for this project is that the ability to visualize the spatiotemporal evolution of tau aggregation from oligomers to insoluble aggregates in intact cells will allow us to test current paradigms regarding the mechanisms of tau aggregation and develop better therapeutic approaches that help target the most toxic tau aggregates. To achieve our objectives we designed two specific aims:

Aim 1: Test the hypothesis that under physiological conditions tau forms non-toxic molecular complexes and that these complexes are distinct from pathological tau oligomers. 

Aim 2: Determine the impact of pathological tau oligomers on neuronal health. 

Impact: We expect that these studies will lead to a paradigm shift in the way protein aggregation is visualized and studied in neurodegenerative diseases. Using tau as a starting point, we will develop a novel approach that will be broadly applicable to studying protein aggregation in several neurodegenerative diseases including AD, Parkinson’s and Huntington’s. This approach will help unravel the molecular mechanisms that lead to protein aggregation, the impact of early, soluble oligomeric aggregates and their clearance on neuronal health. Our approach can potentially help screen new therapeutic strategies that target early oligomeric protein aggregates.