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Thyroid. 2018 Jun;28(6):780-798. doi: 10.1089/thy.2018.0018.

NFE2-Related Transcription Factor 2 Coordinates Antioxidant Defense with Thyroglobulin Production and Iodination in the Thyroid Gland.

Author information

1
1 Service of Endocrinology, Diabetology and Metabolism, Lausanne University Hospital , Lausanne, Switzerland .
2
2 Department of Physiology, Faculty of Biology and Medicine, University of Lausanne , Lausanne, Switzerland .
3
3 Department of Internal Medicine, Division of Endocrinology, School of Medicine, University of Patras , Patras, Greece .
4
4 Department of Pharmacology and Chemical Biology, University of Pittsburgh , Pittsburgh, Pennsylvania.
5
5 Service of Clinical Pathology, Institute of Pathology, Lausanne University Hospital , Lausanne, Switzerland .
6
6 Department of Cell Biology and Biophysics, Faculty of Biology, National and Kapodistrian University of Athens , Athens, Greece .
7
7 Department of Medical Biochemistry, Tohoku University Graduate School of Medicine , Sendai, Japan .
8
8 Instituto de Investigaciones Biomédicas Alberto Sols , Consejo Superior de Investigaciones Científicas y Universidad Autónoma de Madrid, CIBERONC (ISCIII), Madrid, Spain .
9
9 Department of Cellular and Molecular Physiology, Yale School of Medicine , New Haven, Connecticut.
10
10 Women's and Children's Clinic, Department of Obstetrics and Gynaecology, Academic Medical Center, University of Amsterdam , Amsterdam, The Netherlands .
11
11 Dipartimento di Medicina Molecolare e Biotecnologie Mediche, Università degli Studi di Napoli , Federico II, Naples, Italy .
12
12 Department of Medicine, The University of Chicago , Chicago, Illinois.
13
13 Nuclear Biochemistry Division, Argentine National Atomic Energy Commission , Buenos Aires, Argentina .
14
14 CONICET , Buenos Aires, Argentina .
15
15 Department of Pediatrics, The University of Chicago , Chicago, Illinois.
16
16 Department of Committee on Genetics, The University of Chicago , Chicago, Illinois.

Abstract

BACKGROUND:

The thyroid gland has a special relationship with oxidative stress. While generation of oxidative substances is part of normal iodide metabolism during thyroid hormone synthesis, the gland must also defend itself against excessive oxidation in order to maintain normal function. Antioxidant and detoxification enzymes aid thyroid cells to maintain homeostasis by ameliorating oxidative insults, including during exposure to excess iodide, but the factors that coordinate their expression with the cellular redox status are not known. The antioxidant response system comprising the ubiquitously expressed NFE2-related transcription factor 2 (Nrf2) and its redox-sensitive cytoplasmic inhibitor Kelch-like ECH-associated protein 1 (Keap1) defends tissues against oxidative stress, thereby protecting against pathologies that relate to DNA, protein, and/or lipid oxidative damage. Thus, it was hypothesized that Nrf2 should also have important roles in maintaining thyroid homeostasis.

METHODS:

Ubiquitous and thyroid-specific male C57BL6J Nrf2 knockout (Nrf2-KO) mice were studied. Plasma and thyroids were harvested for evaluation of thyroid function tests by radioimmunoassays and of gene and protein expression by real-time polymerase chain reaction and immunoblotting, respectively. Nrf2-KO and Keap1-KO clones of the PCCL3 rat thyroid follicular cell line were generated using CRISPR/Cas9 technology and were used for gene and protein expression studies. Software-predicted Nrf2 binding sites on the thyroglobulin enhancer were validated by site-directed in vitro mutagenesis and chromatin immunoprecipitation.

RESULTS:

The study shows that Nrf2 mediates antioxidant transcriptional responses in thyroid cells and protects the thyroid from oxidation induced by iodide overload. Surprisingly, it was also found that Nrf2 has a dramatic impact on both the basal abundance and the thyrotropin-inducible intrathyroidal abundance of thyroglobulin (Tg), the precursor protein of thyroid hormones. This effect is mediated by cell-autonomous regulation of Tg gene expression by Nrf2 via its direct binding to two evolutionarily conserved antioxidant response elements in an upstream enhancer. Yet, despite upregulating Tg levels, Nrf2 limits Tg iodination both under basal conditions and in response to excess iodide.

CONCLUSIONS:

Nrf2 exerts pleiotropic roles in the thyroid gland to couple cell stress defense mechanisms to iodide metabolism and the thyroid hormone synthesis machinery, both under basal conditions and in response to excess iodide.

KEYWORDS:

Nrf2; animal testing alternatives; iodide; oxidative stress; thyroglobulin; thyroid

PMID:
29742982
PMCID:
PMC5994681
DOI:
10.1089/thy.2018.0018
[Indexed for MEDLINE]
Free PMC Article

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