Overexpression of Interleukin-4 in the Thyroid of Transgenic Mice Upregulates the Expression ofDuox1and the Anion Transporter Pendrin

Abstract

Background:The dual oxidases (Duox) are involved in hydrogen peroxide generation, which is essential for thyroid hormone synthesis, and therefore they are markers of thyroid function. During inflammation, cytokines upregulate DUOX gene expression in the airway and the intestine, suggesting a role for these proteins in innate immunity. It was previously demonstrated that interleukin-4 (IL-4) upregulates DUOX gene expression in thyrocytes. Although the role of IL-4 in autoimmune thyroid diseases has been studied extensively, the effects of IL-4 on thyroid physiology remain largely unknown. Therefore, a new animal model was generated to study the impact of IL-4 on thyroid function. Methods: Transgenic (Thyr-IL-4) mice with thyroid-targeted expression of murine IL-4 were generated. Transgene expression was verified at the mRNA and protein level in thyroid tissues and primary cultures. The phenotype of the Thyr-IL-4 animals was characterized by measuring serum thyroxine (T4) and thyrotropin levels and performing thyroid morphometric analysis, immunohistochemistry, whole transcriptome sequencing, quantitative reverse transcription polymerase chain reaction, and ex vivo thyroid function assays. Results: Thyrocytes from two Thyr-IL-4 mouse lines (#30 and #52) expressed IL-4, which was secreted into the extracellular space. Although 10-month-old transgenic animals had T4 and thyrotropin serum levels in the normal range, they had altered thyroid follicular structure with enlarged follicles composed of elongated thyrocytes containing numerous endocytic vesicles. These follicles were positive for T4 staining the colloid, indicating their capacity to produce thyroid hormones. RNA profiling of Thyr-IL-4 thyroid samples revealed modulation of multiple genes involved in inflammation, while no major leukocyte infiltration could be detected. Upregulated expression of Duox1, Duoxa1, and the pendrin anion exchanger gene (Slc26a4) was detected. In contrast, the iodide symporter gene Slc5a5 was markedly downregulated resulting in impaired iodide uptake and reduced thyroid hormone levels in transgenic thyroid tissue. Hydrogen peroxide production was increased in Thyr-IL-4 thyroid tissue compared with wild-type animals, but no significant oxidative stress could be detected. Conclusions: This is the first study to show that ectopic expression of IL-4 in thyroid tissue upregulates Duox1/ Duoxa1 and Slc26a4 expression in the thyroid. The present data demonstrate that IL-4 could affect thyroid morphology and function, mainly by downregulating Slc5a5 expression, while maintaining a normal euthyroid phenotype.

Sexual Dimorphism of NADPH Oxidase/H2O2 System in Rat Thyroid Cells; Effect of Exogenous 17β-Estradiol

“…Overexpression of DUOX1 and DUOX2 in thyroid cancers was also reported, however, the results are inconsistent [45,46]. Upregulation of DUOX1 expression can also underlie or contribute to autoimmune thyroid diseases [47].…”

DUOX Defects and Their Roles in Congenital Hypothyroidism

“…Their critical role for DUOX function has been clearly demonstrated in DUOXA1/ DUOXA2 double knockout mice [57] showing a hypothyroid phenotype characterized by the impairment of T4 production in thyroid follicles caused by the absence of DUOX cell surface expression and loss of H 2 O 2 generation ( Fig. 3; personal communication and [58]). Initially, DUOXA proteins were characterized as ER-resident proteins allowing ER-to-Golgi transition of mature DUOX enzymes [10].…”

Mini review: immunologic functions of dual oxidases in mucosal systems of vertebrates

“…DUOX1 mRNA levels are moderately upregulated by Th2 cytokines such as IL-4 and IL-13. DUOX1 expression is promoted by IL-4 in the thyroid of transgenic mice (Eskalli et al, 2016). However, DUOX2 mRNA levels are enhanced by cytokine interferon-γ in primary respiratory tract epithelial cells (Harper et al, 2005).…”