Date of Award

Summer 2022

Document Type

Open Access Dissertation

Department

Biomedical Science

First Advisor

Mitzi Nagarkatti

Second Advisor

Prakash Nagarkatti

Abstract

Autoimmune Hepatitis (AIH) is a chronic inflammatory disease of the liver mediated by immune cells and characterized by a variety of parameters including circulating autoantigens, elevated immunoglobulin G (IgG) and aminotransferases, and interface hepatitis. Unfortunately, despite treatment with broadly immunosuppressive drugs, the disease progresses to cirrhosis and end-stage liver disease in several cases. In order to develop a more specific treatment, the mechanisms governing the liver injury resulting from inflammation and autoimmunity need to be elucidated.

For decades, activation of Aryl Hydrocarbon Receptor (AhR) was excluded from consideration as a therapeutic approach due to the potential toxic effects of AhR ligands. However, it is now understood that AhR serves as a key immunomodulator where ligands induce a variety of cellular and epigenetic mechanisms to attenuate inflammation. AhR ligands have been demonstrated to be heavily involved in processes of gene expression, activation, and differentiation. However, despite extensive studies with both endogenous and exogenous ligands, the scope of their involvement is still being revealed. In the first study, we investigated the phenotypic changes induced upon AhR activation via 2,3,7,8- tetrachlorodibenzo dioxin (TCDD) in Concanavalin (Con-A)-induced T cell-mediated liver injury. Our main findings showed that TCDD treatment led to attenuation of ConA-mediated AIH. This was associated with a decrease in infiltrating immune cells, a decrease in the release of the liver injury enzyme alanine transaminase (ALT), and suppression of pro-inflammatory cytokine secretion. Interestingly, though ConA is a well-known polyclonal T cell mitogen, single-cell RNA-sequencing (scRNA-seq) revealed that this compound also induces activation and differentiation of B cells. Upon exploring the genetic profile of cell clusters obtained via this approach, we discovered that phenotypic changes at the transcriptional level occur in immune cells, specifically T cells, upon AhR ligand exposure.

In study two, we explored the phenotypic changes induced upon AhR activation by another AhR ligand, 6-formylindolo[3,2-b]carbazole (FICZ). While FICZ has generally been recognized for its capacity to enhance inflammation, we found that this compound reduced the liver injury in ConA-induced AIH by modulating Kupffer cell responses. Specifically, FICZ reduced the infiltration of pro-inflammatory CD11b+ Kupffer cells. Single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) also revealed changes in chromatin accessibility between treatment groups at the promoters of genes targeting immune cells, such as Cd3e, Cd68, and Itgam.

In the third study, we tried to determine if TCDD or FICZ attenuate AIH through regulation of microRNA (miRNA) profile. Of interest, miR-100-5p was identified as a regulator of mammalian target of rapamycin (mTOR) and was significantly upregulated following treatment with TCDD or FICZ. Further, we suggest a role for hydroxymethylation as a regulatory mechanism in this model as well, specifically in the mTOR gene body.

Collectively, our studies show that AhR agonism reduces inflammation in a murine model of AIH. These data also contribute to the epigenetic regulatory mechanisms that affect the behavior of immune cells in inflammatory states. Thus, targeting such mechanisms may lead to the development of novel therapeutics to treat autoimmune and inflammatory diseases.

Rights

© 2022, Alkeiver Cannon

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