Mechanisms Controlling Sensitivity and Resistance to Dioxin-like Compounds: Role of AIP

The aryl hydrocarbon receptor (AHR) plays an essential role in the mechanisms of toxicity of numerous chemical contaminants, including chlorinated dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), some polychlorinated biphenyls (PCBs), and polynuclear aromatic hydrocarbons (PAHs). There is inter- individual variation in sensitivity to effects of these compounds, but the mechanisms are poorly understood. Variation in the human AHR sequence does not fully explain individual differences in response to AHR ligands, suggesting that other components of the AHR pathway are involved in controlling sensitivity. Recent genome- level research in fish populations with evolved resistance to PCBs, TCDD, and PAHs has identified the AHR- interacting protein (AIP) as a candidate resistance gene. AIP is an AHR chaperone that influences the stability and nuclear translocation of AHR, but its exact role is poorly defined. In humans, mutations in AIP predispose patients to familial isolated pituitary adenomas (FIPA), evidence that AIP sequence variation has functional consequences. Whether AIP variation alters the susceptibility to effects of AHR agonists in vivo is not known.

The goal of this basic research is to elucidate the role of AIP and its sequence variants in controlling sensitivity to diverse AHR agonists, including environmental contaminants as well as natural AHR ligands. The central hypothesis is that variation at the AIP locus affects the interaction between AIP and AHR, leading to altered sensitivity to chemicals that cause toxicity and altered gene expression through the AHR. This hypothesis will be tested using complementary studies involving zebrafish (Danio rerio) in vivo and human cells in vitro.

In Aim 1, AIP-null zebrafish generated using CRISPR-Cas9 genome-editing will be used to determine the role of AIP in controlling the sensitivity to developmental toxicity and altered gene expression caused by diverse AHR agonists in vivo. In Aim 2, the human liver cell line HepaRG will be used to investigate the molecular mechanisms by which AIP and its variants, including mutations associated with FIPA, affect AHR function. In Aim 3, targeted knock-in of AIP SNPs into zebrafish will be used to determine how variation in the AIP protein affects the sensitivity to diverse AHR ligands in vivo. This research represents a unique opportunity to use insights from environmental exposures in wild fish populations along with mechanistic studies in human cells and engineered zebrafish embryos to understand fundamental mechanisms underlying individual differences in susceptibility to chemicals that act through the AHR. The studies address goals of the NIEHS 2018-2023 Strategic Plan, including basic research on molecular pathways involved in mediating effects of environmental exposures, research on developmental processes, and understanding mechanisms underlying individual susceptibility.

This research will contribute to fundamental knowledge about the roles of the aryl hydrocarbon receptor (AHR) and AHR-interacting protein (AIP) in controlling individual differences in susceptibility to effects of chlorinated dioxins, polynuclear aromatic hydrocarbons, and other environmental contaminants. Understanding how AIP contributes to altered chemical sensitivity may help to illuminate the overall role of AIP in vertebrate systems, including in the human disease familial isolated pituitary adenoma (FIPA).

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Recent papers:

Independently evolved pollution resistance in four killifish populations is largely explained by few variants of large effect.
Miller JT, Clark BW, Reid NM, Karchner SI, Roach JL, Hahn ME, Nacci D, Whitehead A (2024)
Evolutionary Applications 17: e13648.

The genomic landscape of rapid repeated evolutionary adaptation to toxic pollution in wild fish.
Reid NM, Proestou DA, Clark BW, Warren WC, Colbourne JK, Shaw JR, Karchner SI, Hahn ME, Nacci D, Oleksiak MF, Crawford DL, Whitehead A (2016)
Science 354: 1305-1308.