Environmental factors are associated with the recent rise in type 1 diabetes (T1D), an autoimmune disease characterized by the destruction of insulin-producing beta cells. In order to develop effective T1D prevention strategies, identification of these environmental risk factors and the mechanisms by which they influence T1D immunopathogenesis is needed. Two environmental factors that have been associated with T1D susceptibility are the diet and the microbiome. One potential mechanistic link between the diet, gut microbiome and T1D is the aryl hydrocarbon receptor (AhR), a transcription factor that is activated by many environmental signals. The objective of this proposal is to determine how the interaction between the diet, microbiome, and AhR can either promote or prevent T1D development. In the first aim of this proposal (K99), Dr. Ehrlich will test the hypothesis that AhR activation by environmental ligands will induce the differentiation of CD4+ cells into either T1D- promoting Th17 cells or T1D-suppresive regulatory T cells depending upon the strength and duration of AhR activation. She will utilize non-obese diabetic (NOD) mice, a model for T1D that is sensitive to environmental perturbations, to determine how the extent of AhR activation influences CD4+ T cell function, gene expression, and T1D development under (1) physiologic conditions comparing wild type to AhR knockout mice and (2) following supplementation with increasing concentrations of the dietary AhR ligand, indole-3-carbinol. In the second aim of this proposal, Dr. Ehrlich will test two hypotheses related to the interplay between AhR, diet, microbiome, and T1D development: (1) Dietary AhR ligands modulate the abundance of intestinal bacteria that are associated with T1D development, and (2) microbiome-derived tryptophan metabolites act through the AhR to influence the autoimmune response and subsequent T1D development. Microbiome sequencing will take place during the K99 phase while the mechanistic studies, which include antibiotic treatments, fecal transfers and tryptophan supplementation, will take place during the R00 phase. In the third aim of this proposal (R00), Dr. Ehrlich will use a humanized mouse model of autoimmune insulitis to evaluate the efficacy of dietary I3C supplementation to prevent T1D immunopathology. The goal is to test the translational immunotherapeutic capabilities of dietary-derived AhR ligands for T1D prevention. The successful completion of the project will provide a missing link into the mechanism by which the diet and microbiome influence T1D. The current project will also provide the experimental basis for future studies that address other environmental AhR ligands (e.g., cigarette smoke, diesel exhaust particles) that could act as risk factors for T1D. In addition, by understanding how AhR signaling influences both proinflammatory and immunosuppressive responses, AhR ligand-based immune-mediated disease prevention strategies can be developed with greater confidence. This proposal builds upon my published and preliminary data and utilizes the strengths of my mentors, my collaborators, and unique facilities at Oregon State University to launch my independent research career in environmental health science.
The aryl hydrocarbon receptor links environmental signals with immune responses. By understanding how aryl hydrocarbon receptor signaling influences T1D susceptibility, new approaches for the prevention of immune- mediated diseases can be developed. This project aligns with the mission of the National Institute of Environments Health Sciences to discover how the environment affects people in order to promote healthier lives.