Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Pharmacology

First Advisor

Sessa, William

Abstract

Immunometabolism is a growing field that centers on a core paradigm:perturbations in metabolism alter a cell’s biological response in immunity and, likewise, inflammatory signals, such as cytokines and pathogens, can directly influence cellular metabolism. Although the carbons within cholesterol cannot be used for catabolic energy production, there is a growing appreciation that a similar relationship exists between cholesterol homeostasis and immunity. The majority of this literature is focused on cholesterol dynamics in the context of leukocyte immunobiology. However, the endothelium also plays an important role during the acute inflammatory response. Endothelial cells (ECs) rapidly respond to extrinsic signals, such as tissue damage or microbial infection, by upregulating factors to activate and recruit circulating leukocytes to the site of injury. Dysregulation or aberrant activation of ECs leads to disease, such as atherosclerosis. I studied the role of cholesterol and its master regulator, SREBP2, in the EC response to acute inflammatory stress. ECs treated with cytokines upregulated SREBP2 cleavage and classical cholesterol biosynthesis gene expression within the late phase of the acute inflammatory response. Furthermore, SREBP2 activation was dependent on NF-kB DNA binding and classical SCAP-SREBP2 processing. I used bacterial cytolysin probes to show that inflammatory stress significantly decreased accessible cholesterol, leading to dysfunctional sterol sensing and downstream SREBP2 cleavage. I also explored what role SREBP2 plays in the EC inflammatory response. Loss of SREBP2 in ECs treated with inflammatory cytokine altered EC phenotype, which was defined by decreased chemokine expression and increased type I inflammatory signaling. Interestingly, this effect on the EC inflammatory transcriptome could not be accounted by changes in cholesterol, but rather through SREBP2 binding to promoters of proinflammatory transcription factors. Preliminary results revealed that Srebf2 knockout in the endothelium protected mice from inflammatory damage. This study is the first to provide an in-depth characterization of the relationship between cholesterol homeostasis and the endothelial acute inflammatory response.

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