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CHARACTERIZING THE ROLE OF FECAL BACTERIAL EXTRACELLULAR VESICLES IN GUT DYSBIOSIS RELATED DISORDERS

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title
CHARACTERIZING THE ROLE OF FECAL BACTERIAL EXTRACELLULAR VESICLES IN GUT DYSBIOSIS RELATED DISORDERS
author
Almousa, Sameh Waleed
abstract
The human gut microbiome plays a crucial role in maintaining overall health. Perturbations inthe gut microbiome, known as gut dysbiosis, have been linked to various disease processes. However, the molecular mechanisms underpinning the role of bacteria in systemic and distant pathologies are relatively unknown. Extracellular vesicles (EVs) are secreted by all cells across all kingdoms of life, including bacteria, and are known to play a role in intercellular communication. In this dissertation, we aimed to characterize the role of fecal bacterial extracellular vesicles (bEV) in gut dysbiosis-related disorders. First, we provide extensive background of the current knowledge of fecal bEV, their role in disease processes, and the challenges associated with their isolation. Major limitations in the current field include inability to segregate bacterial and eukaryotic EV populations from the total fecal EV sample. This confounds the current understanding of bEV in different disease processes as most researchers study a heterogeneous mix of samples. Thus, we optimize a novel methodology to enrich for bEV by using a marker-based immunoprecipitation approach to deplete the eukaryotic EV contribution. We then comprehensively characterize bEV from diet-induced obesity mice (bEVDIO) model of gut dysbiosis. We show that gut dysbiotic bEV are directly involved in mediating both systemic inflammation with concomitant pain hypersensitivity as well as Alzheimer’s disease (AD) neurodegenerative progression. We found that bEV promote pain hypersensitivity through activation of monocytes primarily through lipopolysaccharide (LPS) expressed on their surface along with virulent cargo and increased uptake kinetics. Innovative biodistribution studies show that bEV disrupt intestinal and blood brain barriers and show specific organotropism for brain as well as pain-signaling sites in spinal cord. Cargo analysis revealed enrichment of the precursor metabolite L-histidinol in gut dysbiotic bEV compared to controls. Mechanistic studies show that both L-histidinol and gut dysbiotic bEV promote hallmarks of AD progression, including impaired long term potentiation, xvii neuron hyperexcitability and cell death, and microglia activation. We also elucidated the binding targets of L-histidinol in microglia, and found they are enriched in AD patients. Lastly, we exploited the pro-inflammatory effects of bEV as novel cancer vaccines in the setting of prostate cancer (PCa) model, which is an immune-cold tumor with poor responses to immune checkpoint therapy. We found that bEV especially from the lean mice significantly reduced tumor volumes and increased overall survival, performing similarly as monotherapy or in combination with anti-PD-1 therapy. Taken together, this dissertation provides a novel approach to isolate and characterize the fecal bEV from gut and offers a fresh insight into the complex interplay between the gut microbiome and disease processes, especially revealing the key role of bEV in gut dysbiosisrelated disorders such as pain hypersensitivity and AD. Our work also offers a potential new avenue for the development of novel anti-cancer vaccines for a range of tumors traditionally nonresponsive to immune checkpoint inhibition.
subject
Alzheimer's disease
Bacterial extracellular vesicles
Gut microbiome
Inflammation
Obesity
Pain
contributor
Deep, Gagan (advisor)
Peters, Christopher (committee member)
Whitlow, Christopher (committee member)
Kucera, Gregory (committee member)
Jin, Guangxu (committee member)
date
2023-09-08T08:35:22Z (accessioned)
2023 (issued)
degree
Cancer Biology (discipline)
embargo
2025-09-07 (terms)
2025-09-07 (liftdate)
identifier
http://hdl.handle.net/10339/102606 (uri)
language
en (iso)
publisher
Wake Forest University
type
Dissertation

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