Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Toxicology

Department or School/College

Department of Biomedical and Pharmaceutical Sciences

Committee Chair

Andrij Holian

Commitee Members

Christopher Migliaccio, Zeina Jaffar, Travis Hughes, J.B. Alexander (Sandy) Ross

Keywords

Cholesterol, Lysosomal, Macrophage, Potassium Channel Activity, Silica-Induced Inflammation

Abstract

Chronic inflammation contributes to a number of diseases, driven by NLRP3 inflammasome activity and the lack of resolution. Silicosis is one such disease, brought on by the unresolved inflammation caused by inhaled crystalline silica particles of sufficiently small size. These particles are taken up by alveolar macrophages to protect the fragile alveolar spaces. Silica particles interact with phagolysosomal membranes through nearly free silanol moieties and disrupt the lipid order of the lysosomal membrane thereby causing permeabilization. This permeabilization (LMP) leads to the release of proteases including Cathepsin B that promote the assembly and activation of the NLRP3 inflammasome. The inflammasome is responsible for activating Caspase 1 and initiating the release of inflammatory cytokines such as IL-1β and IL-18. LMP also leads to cell death, releasing the silica particle back into the lung microenvironment to me taken up by other alveolar macrophages, thus perpetuating a cycle of cell death and inflammation that contributes to the fibrotic remodeling of the alveolar spaces and drives silicosis. In order to develop effective therapeutics for the treatment of silicosis and other particle induced NLRP3 mediated respiratory diseases, it is necessary to understand the cellular mechanisms that perpetuate silica-induced inflammation. The lysosome itself presents an attractive target for potential therapeutics as it interacts directly with silica particles. In order to prevent LMP it is necessary to understand how the silica particle interaction with the lysosomal membrane can be disrupted. This research establishes the protective nature of accumulating lysosomal cholesterol in reducing LMP. The commonality of increased lysosomal pH and lysosomal cholesterol accumulation is demonstrated in the efficacy of anti-depressant cationic amphiphilic drugs fluvoxamine and fluoxetine and lysosomal big conductance K+ channel inhibitor paxilline in preventing silica-induced LMP, cell death, and IL-1β release; while, in contrast, preventing lysosomal cholesterol accumulation enhances silica-induced LMP, cell death, and IL-1β release in macrophages.

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© Copyright 2023 Rebekah Louise Kendall