2018 — 2019 |
Liu, Chia-Chen |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
Pathogenic Effects of Plasma Apoe On Cns Function and Alzheimer's Disease @ Mayo Clinic Jacksonville
PROJECT SUMMARY/ABSTRACT MAYO CLINIC JACKSONVILLE Alzheimer's disease (AD) is the leading cause of dementia in the elderly with currently no disease-altering therapy. The accumulation, aggregation and deposition of amyloid-? (A?) peptides in the brain are central events in the pathogenesis of AD. Increasing evidence has shown that the ?4 allele of the apolipoprotein E (APOE) gene is the strongest genetic risk factor for AD among its three polymorphic alleles (?2, ?3 and ?4). ApoE regulates A? clearance, A? aggregation, and amyloid deposition in an isoform-dependent manner. ApoE4 also impairs cerebrovascular functions in the brain and has a reduced ability to regulate neuroinflammation. In addition to AD, apoE4 is associated with a greater risk for hypercholesterolemia and atherosclerosis. In periphery, apoE is highly expressed by the liver and plays critical roles in plasma lipoprotein metabolism. ApoE in the central nervous system (CNS) is synthesized de novo by astrocytes. It is known that blood-brain-barrier (BBB) restricts the transport of apoE into and out of the brain. However, because of the existence of apoE in both periphery and the brain, it has been difficult to address the specific contribution of apoE4 from these two domains to cerebrovascular dysfunction and AD-related pathologies. We hypothesize that peripheral apoE4 impairs CNS functions by modulating vascular integrity, inflammatory responses and amyloid pathogenesis, thus accelerating AD-related pathways. To address this, we have generated novel animal models to allow apoE isoform expression in either periphery or the brain, enabling us to address how peripheral apoE impacts the brain functions and AD-related pathways. In addition, we have established several innovative approaches, including in vivo two-photon microscopic imaging to examine BBB integrity, vasomotion and plaque formation, laser speckle contrast analysis to assess the cerebral blood flow, and in vivo microdialysis to measure brain A? and inflammatory cytokines in the brain interstitial fluid for this proposal. We will determine the effects of peripherally-expressed apoE3 or apoE4 on inflammatory responses, cerebrovascular functions, synapses and cognitive behaviors (Aim 1) and brain A? metabolism and amyloid pathology (Aim 2). Our studies will for the first time investigate how peripherally-expressed apoE isoforms affect CNS functions and AD-related pathways and pathologies. As apoE-directed therapy for AD will likely involve regulating apoE in both brain and periphery, our findings will provide mechanistic guidelines as to how apoE isoforms should be individually targeted for AD therapy.
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0.903 |
2019 |
Fryer, John David Liu, Chia-Chen |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Microglial Apoe in Neuroinflammation and Alzheimer's Disease
ABSTRACT Alzheimer disease (AD) is the most common cause of dementia and is characterized by extracellular plaques formed by the deposition of amyloid-? (A?) peptide in brain parenchyma and intracellular tangles formed by the aggregation of tau protein. Genetic variations play a large role in AD risk, with the APOE4 allele strongly increasing risk by >3 fold. ApoE4 has been known to promote amyloid development. Importantly, a recent study from Dr. Holtzman's lab showed that apoE4 accelerates tau-mediated neurodegeneration by influencing microglial responses. Microglia are the innate immune cells of the brain, and apoE as well as several other AD risk genes such as TREM2, CLU, and ABCA7 influence their functions. In our efforts addressing AD-related genes on microglial functions, we discovered that TREM2 is a microglial receptor for apoE; linking two critical genetic risk factors for AD in the microglial pathway. However, whether apoE could act in an autocrine fashion on microglia which regulates brain functions, neuroinflammation and AD pathologies in an isoform-dependent manner has not been examined in vivo. Towards addressing this, we have generated conditional mouse models expressing apoE isoforms exclusively in microglia. Our preliminary studies using these mice have shown that apoE4-microglia exhibit impaired responses to injury compared to apoE3-microglia. In addition, our recent microglial translational profiling (RiboTag) or single-cell RNA- sequencing (scRNAseq) studies also identified microglial apoE as a central hub in networks of both amyloid and tau pathology. We hypothesize that apoE expressed in microglia plays critical roles in modulating microglial reactivity and inflammation in an isoform dependent manner with apoE4-microglia contributing to cognitive deficits and increased amyloid and tau pathology. To test our hypothesis, we will use conditional apoE mouse models deleting or expressing apoE isoforms in microglia in the background of wild-type, amyloid, or tau pathology. To address human relevance, we will assess microglial activation states and AD-related pathologies in human postmortem brains from pathologically-confirmed normal, pathological aging and AD cohorts with different APOE genotypes. To uncover cell type-specific pathways modulated by microglial apoE, innovative technologies will be included, such as in vivo microdialysis to measure the brain inflammatory responses at steady-state or in real time upon injury, in vivo 2-photon (2P) imaging to examine the kinetics of microglial mobilization, and scRNAseq to define apoE-regulated, disease-associated gene profiles in microglia and other brain cell types. Together, our study will employ complementary, integrative and systems-based approaches to evaluate the specific roles of microglial apoE isoforms during aging and AD development which should significantly advance our understanding of apoE, microglia, and AD pathogenesis.
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0.903 |
2021 |
Liu, Chia-Chen |
U19Activity Code Description: To support a research program of multiple projects directed toward a specific major objective, basic theme or program goal, requiring a broadly based, multidisciplinary and often long-term approach. A cooperative agreement research program generally involves the organized efforts of large groups, members of which are conducting research projects designed to elucidate the various aspects of a specific objective. Substantial Federal programmatic staff involvement is intended to assist investigators during performance of the research activities, as defined in the terms and conditions of award. The investigators have primary authorities and responsibilities to define research objectives and approaches, and to plan, conduct, analyze, and publish results, interpretations and conclusions of their studies. Each research project is usually under the leadership of an established investigator in an area representing his/her special interest and competencies. Each project supported through this mechanism should contribute to or be directly related to the common theme of the total research effort. The award can provide support for certain basic shared resources, including clinical components, which facilitate the total research effort. These scientifically meritorious projects should demonstrate an essential element of unity and interdependence. |
Astrocytic and Microglial Apoe in Aging and Ad @ Mayo Clinic Jacksonville
PROJECT SUMMARY (APOE U19: Project 3) Apolipoprotein E (apoE) is a major genetic determinant of late-onset Alzheimer?s disease (AD) with APOE4 increases the risk and APOE2 being protective compared with common APOE3 allele. Our team-based work will investigate a novel ApoE Cascade Hypothesis (ACH) which will shed light on the disease mechanisms and inform future therapeutic strategies for AD. Here, Project 3 seeks to elucidate whether different isoforms of astrocytic and microglial apoE exhibit different biochemical properties that impact its function, aggregation, and the metabolism of amyloid-? (A?) during aging and AD development. In addition to astrocytes, microglia secrete abundant lipidated apoE with aging and in the context of AD pathogenesis. The disease-associated microglia (DAM) exhibit a conserved transcriptional signature across different AD mouse models with APOE being one of the central hub genes. Interestingly, activated microglia have been shown to induce neurotoxic (A1-like) reactive astrocytes in AD. However, little is known about whether apoE isoform-mediated microglia- astrocyte interaction affects brain functions and amyloid pathologies. To address these questions, we have generated novel inducible mouse models in which human APOE2, APOE3, or APOE4 gene is specifically expressed in astrocytes or microglia. In Aim 1, we will analyze the effects of astrocytic or microglial apoE isoforms on cognitive function, lipid metabolism, neuroinflammation, and vascular integrity during aging. In Aim 2, we will define the impacts of astrocytic or microglial apoE isoforms on brain function, neuroinflammation, and the development of amyloid pathology. In Aim 3, we will determine the role of apoE isoforms in astrocyte- microglia interaction and their association with cerebrovasculature during aging and in the context of amyloid pathology. Using unique mouse models and innovative technologies (ie., in vivo 2-photon imaging and in vivo microdialysis), we will comprehensively investigate how apoE isoforms in glia cells contribute to brain cognition and amyloid pathology. More importantly, multi-disciplinary approaches will be employed by interacting with other projects/cores: 1) The properties of apoE particles from our mouse models will be analyzed by Project 1 and Core B; 2) ApoE amounts and AD-related fluid biomarkers will be measured through Core D; 3) The amyloid pathologies and neuroninflammation will be examined by Core C; 4) The molecular phenotypes of our inducible apoE mouse models will be examined using multi-omics approaches (ie., proteomics, metabolomics, lipidomics and single cell RNA sequencing), with results correlating with human studies through Cores F, G; 5) Our data can be compared with studies from Projects 2 and 4 to further elucidate the cell type-specific effects; and 6) Findings from mouse models can be further validated using human iPSC-derived microglia/astrocyte models in Core E. Through multidisciplinary team with synergized expertise and resources, we will collaboratively understand the apoE-associated disease mechanisms in aging-related conditions and AD.
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0.903 |