Year of Award

2018

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Cellular, Molecular and Microbial Biology

Department or School/College

Division of Biological Sciences

Committee Chair

David M. Shepherd

Commitee Members

Scott Wetzel, Celine Beamer, Jesse Hay, Mike Minnick

Keywords

Aryl hydrocarbon Receptor, Dendritic cells, drug delivery, nanoparticles, Thymus

Abstract

The Aryl hydrocarbon Receptor (AhR) is a ligand-activated transcription factor best known for its role in xenobiotic metabolism of environmental pollutants. Activation of the AhR by its prototypical ligand 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD) leads to pronounced thymic atrophy and severe immunosuppression. Studies of AhR activation can have dual applications: to better understand AhR-mediated immunotoxicity and to harness its immunomodulatory effects for therapeutic use. Here, we first aimed to determine whether AhR-mediated thymic atrophy was ligand-dependent through the use of dietary and endogenously sourced ligands, indole-3-carbinol (I3C) and 2-(19 H-indole-39 -carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) respectively. We also aimed to identify key mediators of TCDD-induced thymic atrophy through the use of lineage-specific Cre-lox conditional knockout mice. We hypothesized that AhR activation induces thymic atrophy in a ligand-dependent manner and AhR expression within CD11c+ DCs is necessary for thymic atrophy by TCDD. In vivo exposure of ITE and I3C yielded dramatically different thymic outcomes with ITE resulting in severe thymic atrophy similar to TCDD while I3C did not induce atrophy. Through the use of Cre-Lox conditional knockout mice under lineage-specific promoters, we identified a requisite role for AhR activation in CD11c+ cells for TCDD-induced thymic atrophy. We next aimed to apply current understanding of AhR-mediated immune suppression in the development of a liposomal nanoparticle (LNP) delivery system for concentrated delivery of AhR-agonist, ITE, to dendritic cells. Dendritic cells are exquisitely sensitive to AhR activation and promote the generation of regulatory T cells. ITE is a potent inducer of AhR activation; however, it is rapidly metabolized and systemic exposure to high doses can have undesirable effects. Therefore, we hypothesized that the generation and delivery of AhR agonist-loaded liposomal nanoparticles would activate the AhR in dendritic cells leading to a phenotype similar to TCDD, and result in cell-specific uptake when administered in vivo. LNP maintained high ITE entrapment, were of optimal size for dendritic cell uptake, induced AhR-responsive genes in vitro, and were preferentially taken up by splenic APCs. Together, this work furthers our understanding of AhR-mediated thymic atrophy, and presents a novel AhR agonist delivery system for therapeutic application of the AhR.

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© Copyright 2018 Joanna Michelle Kreitinger